The subject of “dephlogisticated air” naturally continued to interest him, and he again returns to it in this volume, for he says:—He then experiments with manganese, which Scheele, who independently discovered oxygen, had already employed, and finds that it yields the new air both when heated alone or with oil of vitriol. The production of oxygen from manganese was contrary to his expectations as the substances he had hitherto used, the precipitate per se and the red lead and the nitre, had all been subjected to “the influence of the atmosphere,” whereas “here was pure air from a substance which for anything that appeared had always been in the bowels of the earth, and never had had any communication with the external air.” This led to the surmise that possibly the expulsion of dephlogisticated air from such mineral substances

人民日报海外版关注宜游城市:宜游城市蓄势待发 Modern eudiometry, making use of methods of far greater precision than were possible to Priestley, has confirmed his supposition that atmospheric air is remarkably constant in composition, and that its wholesomeness depends upon other causes than the relative amount of the dephlogisticated air contained in it.203.

“Having acquired a fondness for experiments, even slighter inducements than I have had would have been sufficient to determine my conduct.”Perhaps the most important of the many papers contained in this volume are those which relate to the “Melioration of Air by the Growth of Plants,” a subject to which Priestley gave attention, even whilst at Leeds, in 1771. In these papers he clearly proves that this “melioration” is connected with the green matter of leaves and that it is dependent upon sunlight. This observation is of fundamental importance and attracted much attention..

“Upon this, as upon other occasions, I can only repeat that it is not my opinions on which I would be understood to lay any stress. Let the new facts, from which I deduce them, be considered as my discoveries, and let other persons draw better inferences from them if they can. This is a new and a wide field of experiment and speculation, and a premature attachment to hypothesis is the greatest obstruction we are likely to meet with in our progress through it; and as I think I have been pretty much upon my guard myself, I would caution others to be upon their guard too.”“When,” he says, “I first discovered the property of nitrous air as a test of the wholesomeness of common air, I flattered myself that it might be of considerable practical use, and particularly that the air of distant places and countries might be brought and examined together with great ease and satisfaction; but I own that hitherto I have rather been disappointed in my expectations from it.... I gave several of my friends the trouble to send me air from distant places, especially from manufacturing towns, and the worst they could find to be actually breathed by the manufacturers, such as is known to be exceedingly offensive to those who visit them; but when I examined those specimens of air in Wiltshire, the difference between them and the very best air in this county, which is esteemed to be very good, as also the difference between them and specimens of the best air in the counties in which these manufacturing towns are situated, was very trifling.... I have frequently taken the open air in the most exposed places in this country at different times of the year, and in different states of the weather, etc., but never found the difference so great as the 208 inaccuracy arising from the method of making the trial might easily amount to or exceed.”Another suggestive paper is on “Respiration and the Use of the Blood,” which was read to the Royal Society on January 25, 1776, and appears in the Phil. Trans., vol. lxvi. Priestley, of course, regarded respiration as a phlogistic process, and “that the use of the lungs is to carry off a putrid effluvium, or to discharge that phlogiston, which had been taken into the system with the aliment, and has become, as it were, effete, the air that is respired serving as a menstruum for that purpose.” This he thinks he has “proved to be effected by means of the blood, in consequence of its coming so nearly into contact with the air in the lungs, the blood appearing to be a fluid wonderfully formed to imbibe and part with that principle which the chemists call phlogiston, and changing its colour in consequence of being charged with it or being freed from it.” The facts in this paper are for the most part correctly stated, but the discoverer of oxygen led the world woefully astray as to the part played by that gas in the phenomena of respiration..

“When,” he says, “I first discovered the property of nitrous air as a test of the wholesomeness of common air, I flattered myself that it might be of considerable practical use, and particularly that the air of distant places and countries might be brought and examined together with great ease and satisfaction; but I own that hitherto I have rather been disappointed in my expectations from it.... I gave several of my friends the trouble to send me air from distant places, especially from manufacturing towns, and the worst they could find to be actually breathed by the manufacturers, such as is known to be exceedingly offensive to those who visit them; but when I examined those specimens of air in Wiltshire, the difference between them and the very best air in this county, which is esteemed to be very good, as also the difference between them and specimens of the best air in the counties in which these manufacturing towns are situated, was very trifling.... I have frequently taken the open air in the most exposed places in this country at different times of the year, and in different states of the weather, etc., but never found the difference so great as the 208 inaccuracy arising from the method of making the trial might easily amount to or exceed.”Of all the quantitative exercises performed by Priestley, by far the most numerous depended upon his application of nitric oxide to measure the “goodness” of air.the eye of the general scholar” as in either of the two former volumes, although he trusts they will “be thought no less valuable by philosophers and chemists.” Priestley, it would seem, was conscious that he was beginning, as the phrase goes, “to write himself out.”.

“Lest my readers should be alarmed at this addition of one volume after another on the same subject, I do assure them that I shall now certainly give them and myself some respite, and deliver the torch to anyone who may be disposed to carry it, foreseeing that my attention will be sufficiently engaged by speculations of a very different nature.... It will be a great satisfaction to me, after the part that I have taken in this business, to be a spectator of its future progress, when I see the work in so many and so good hands, and everything in so rapid and so promising a way.“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”Perhaps the most important of the many papers contained in this volume are those which relate to the “Melioration of Air by the Growth of Plants,” a subject to which Priestley gave attention, even whilst at Leeds, in 1771. In these papers he clearly proves that this “melioration” is connected with the green matter of leaves and that it is dependent upon sunlight. This observation is of fundamental importance and attracted much attention.. read more

Perhaps the most important of the many papers contained in this volume are those which relate to the “Melioration of Air by the Growth of Plants,” a subject to which Priestley gave attention, even whilst at Leeds, in 1771. In these papers he clearly proves that this “melioration” is connected with the green matter of leaves and that it is dependent upon sunlight. This observation is of fundamental importance and attracted much attention.“There are few experiments the rationale of which I less pretend to understand than the production of genuine and permanent inflammable air from alkaline air by means of the electric spark.... One query on this subject is, whence comes the phlogiston, which is certainly a principal ingredient in the constitution of inflammable air. Alkaline air, indeed, contains phlogiston, because in the manner in which I have generally produced it, it is itself partially inflammable; but it is not nearly so much so as the inflammable air which is produced by means of it. Besides, it will appear by the following experiments that the quantity of the inflammable air far exceeds that of the alkaline.”“On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them.....

Modern eudiometry, making use of methods of far greater precision than were possible to Priestley, has confirmed his supposition that atmospheric air is remarkably constant in composition, and that its wholesomeness depends upon other causes than the relative amount of the dephlogisticated air contained in it..

“As it sometimes amuses myself it may perhaps amuse others to look back with me to the several steps in the actual progress of this investigation, some of which I overlooked in my last account of it.”As regards the subject of “air” in general, although a large number of isolated observations are recorded in somewhat tedious detail, no new fact of first-rate importance is apparent. The experiments are largely supplementary to those in the preceding volumes and are for the most explanatory or corroborative of them. Perhaps the most important are those dealing with “the production of nitrous air in which a candle will burn,” by which is signified the gas we now know as nitrous oxide, but which Priestley eventually termed dephlogisticated nitrous air. The process he employed is no longer used in the production of this gas, but it sufficed in his hands to determine its individuality without doubt.

Modern eudiometry, making use of methods of far greater precision than were possible to Priestley, has confirmed his supposition that atmospheric air is remarkably constant in composition, and that its wholesomeness depends upon other causes than the relative amount of the dephlogisticated air contained in it.As regards the subject of “air” in general, although a large number of isolated observations are recorded in somewhat tedious detail, no new fact of first-rate importance is apparent. The experiments are largely supplementary to those in the preceding volumes and are for the most explanatory or corroborative of them. Perhaps the most important are those dealing with “the production of nitrous air in which a candle will burn,” by which is signified the gas we now know as nitrous oxide, but which Priestley eventually termed dephlogisticated nitrous air. The process he employed is no longer used in the production of this gas, but it sufficed in his hands to determine its individuality without doubt.As regards the subject of “air” in general, although a large number of isolated observations are recorded in somewhat tedious detail, no new fact of first-rate importance is apparent. The experiments are largely supplementary to those in the preceding volumes and are for the most explanatory or corroborative of them. Perhaps the most important are those dealing with “the production of nitrous air in which a candle will burn,” by which is signified the gas we now know as nitrous oxide, but which Priestley eventually termed dephlogisticated nitrous air. The process he employed is no longer used in the production of this gas, but it sufficed in his hands to determine its individuality without doubt..

In the fifth volume, which was published in the 209 spring of 1781, with a dedication to Dr Heberden, when Priestley had moved to Birmingham, he again returns to this subject. Practically all the experimental work to which it relates was done whilst he was with Lord Shelburne, and mainly at Calne. During the former parts of the summer of 1780 he suffered from an illness which greatly interfered with his work, although he thinks that during his incapacity for making experiments his “hints for the farther prosecution of them are greatly accumulated.” It cannot be said that the five papers on the relations of vegetation to air, with which the volume opens, added very materially to the fundamental fact which Priestley had discovered. They furnished, however, additional evidence of it and no doubt stimulated further inquiry. If his facts could not be controverted, his explanations and surmises were at least open to attack, and a number of observers, both here and abroad, busied themselves with the problems of physiological botany thereby suggested..

“There are few experiments the rationale of which I less pretend to understand than the production of genuine and permanent inflammable air from alkaline air by means of the electric spark.... One query on this subject is, whence comes the phlogiston, which is certainly a principal ingredient in the constitution of inflammable air. Alkaline air, indeed, contains phlogiston, because in the manner in which I have generally produced it, it is itself partially inflammable; but it is not nearly so much so as the inflammable air which is produced by means of it. Besides, it will appear by the following experiments that the quantity of the inflammable air far exceeds that of the alkaline.”. read more

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“that the air of all those places, which from the long experience of the inhabitants has been reputed unwholesome, is found to be so to a very great degree of exactness by the eudiometer.... The air of the Pontine lakes, that of the Sciroccho at Rome (so very unwholesome), that of the Campagna Romana, of the Grotto del Cane, of the Zolfatara at Naples, of the baths of Nero at Baja, of the seacoast of Tuscany, were all examined by me and found to be in such a state as daily experience led me to expect.”.

He then experiments with manganese, which Scheele, who independently discovered oxygen, had already employed, and finds that it yields the new air both when heated alone or with oil of vitriol. The production of oxygen from manganese was contrary to his expectations as the substances he had hitherto used, the precipitate per se and the red lead and the nitre, had all been subjected to “the influence of the atmosphere,” whereas “here was pure air from a substance which for anything that appeared had always been in the bowels of the earth, and never had had any communication with the external air.” This led to the surmise that possibly the expulsion of dephlogisticated air from such mineral substancesPriestley’s methods of experiment with his various “airs” were very uniform. He tried their solubility in water, their power of supporting or extinguishing flame, whether they were respirable, how they behaved with acid and alkaline air, and with nitric oxide and inflammable air, and lastly how they were affected by the electric spark. He occasionally made attempts to weigh them, but his determinations of their relative density were altogether untrustworthy. Indeed, it is evident from the terms in which he speaks of these efforts that he was conscious of their inadequacy. The result of submitting alkaline air (ammonia) to the electric spark, whereby it is resolved into nitrogen and hydrogen, surprised him not a little..

He several times noticed the deep blue liquid which nitrogen peroxide forms with cold water. He made many attempts to use nitric oxide as an antiseptic, especially for culinary purposes. But the gastronomic results with fowls and pigeons were not to his liking, although he says, “my friend Mr Magellan ... had not so bad an opinion of this piece of cookery as I had.” One cannot read Priestley’s description of his multifarious experiments without being struck with the number of occasions in which he just missed making discoveries of first-rate importance. It is obvious that he had obtained chlorine without recognising it, even before the news of Scheele’s discovery reached this country. He had also prepared, without knowing it, phosphoretted hydrogen and phosphorous acid. At times, however, he can follow a clue with remarkable perspicacity; as in his observation of the cause of the “flouring” of mercury, and in his discovery of a method of removing lead and tin from that metal.“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”He then experiments with manganese, which Scheele, who independently discovered oxygen, had already employed, and finds that it yields the new air both when heated alone or with oil of vitriol. The production of oxygen from manganese was contrary to his expectations as the substances he had hitherto used, the precipitate per se and the red lead and the nitre, had all been subjected to “the influence of the atmosphere,” whereas “here was pure air from a substance which for anything that appeared had always been in the bowels of the earth, and never had had any communication with the external air.” This led to the surmise that possibly the expulsion of dephlogisticated air from such mineral substancesAs regards the subject of “air” in general, although a large number of isolated observations are recorded in somewhat tedious detail, no new fact of first-rate importance is apparent. The experiments are largely supplementary to those in the preceding volumes and are for the most explanatory or corroborative of them. Perhaps the most important are those dealing with “the production of nitrous air in which a candle will burn,” by which is signified the gas we now know as nitrous oxide, but which Priestley eventually termed dephlogisticated nitrous air. The process he employed is no longer used in the production of this gas, but it sufficed in his hands to determine its individuality without doubt.The preface is noteworthy for its plea for the position of experimental science in the scheme of general education.the eye of the general scholar” as in either of the two former volumes, although he trusts they will “be thought no less valuable by philosophers and chemists.” Priestley, it would seem, was conscious that he was beginning, as the phrase goes, “to write himself out.”.

2014. read more

I“Having acquired a fondness for experiments, even slighter inducements than I have had would have been sufficient to determine my conduct.”In the fifth volume, which was published in the 209 spring of 1781, with a dedication to Dr Heberden, when Priestley had moved to Birmingham, he again returns to this subject. Practically all the experimental work to which it relates was done whilst he was with Lord Shelburne, and mainly at Calne. During the former parts of the summer of 1780 he suffered from an illness which greatly interfered with his work, although he thinks that during his incapacity for making experiments his “hints for the farther prosecution of them are greatly accumulated.” It cannot be said that the five papers on the relations of vegetation to air, with which the volume opens, added very materially to the fundamental fact which Priestley had discovered. They furnished, however, additional evidence of it and no doubt stimulated further inquiry. If his facts could not be controverted, his explanations and surmises were at least open to attack, and a number of observers, both here and abroad, busied themselves with the problems of physiological botany thereby suggested.“To determine whether the phenomena attending the impregnation of the solution of green vitriol with nitrous air depended in any measure upon the seeming astringency of that solution ... I impregnated a quantity of green tea, which is also 205 said to be astringent, with nitrous air, but no sensible change of colour was produced in it.”At the instigation of Mr Woulfe, whose name mainly lives in connection with a useful piece of chemical apparatus, Priestley was encouraged to hope that he would.

“On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them.....

“To determine whether the phenomena attending the impregnation of the solution of green vitriol with nitrous air depended in any measure upon the seeming astringency of that solution ... I impregnated a quantity of green tea, which is also 205 said to be astringent, with nitrous air, but no sensible change of colour was produced in it.”“When,” he says, “I first discovered the property of nitrous air as a test of the wholesomeness of common air, I flattered myself that it might be of considerable practical use, and particularly that the air of distant places and countries might be brought and examined together with great ease and satisfaction; but I own that hitherto I have rather been disappointed in my expectations from it.... I gave several of my friends the trouble to send me air from distant places, especially from manufacturing towns, and the worst they could find to be actually breathed by the manufacturers, such as is known to be exceedingly offensive to those who visit them; but when I examined those specimens of air in Wiltshire, the difference between them and the very best air in this county, which is esteemed to be very good, as also the difference between them and specimens of the best air in the counties in which these manufacturing towns are situated, was very trifling.... I have frequently taken the open air in the most exposed places in this country at different times of the year, and in different states of the weather, etc., but never found the difference so great as the 208 inaccuracy arising from the method of making the trial might easily amount to or exceed.”He several times noticed the deep blue liquid which nitrogen peroxide forms with cold water. He made many attempts to use nitric oxide as an antiseptic, especially for culinary purposes. But the gastronomic results with fowls and pigeons were not to his liking, although he says, “my friend Mr Magellan ... had not so bad an opinion of this piece of cookery as I had.” One cannot read Priestley’s description of his multifarious experiments without being struck with the number of occasions in which he just missed making discoveries of first-rate importance. It is obvious that he had obtained chlorine without recognising it, even before the news of Scheele’s discovery reached this country. He had also prepared, without knowing it, phosphoretted hydrogen and phosphorous acid. At times, however, he can follow a clue with remarkable perspicacity; as in his observation of the cause of the “flouring” of mercury, and in his discovery of a method of removing lead and tin from that metal..

211“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”“Lest my readers should be alarmed at this addition of one volume after another on the same subject, I do assure them that I shall now certainly give them and myself some respite, and deliver the torch to anyone who may be disposed to carry it, foreseeing that my attention will be sufficiently engaged by speculations of a very different nature.... It will be a great satisfaction to me, after the part that I have taken in this business, to be a spectator of its future progress, when I see the work in so many and so good hands, and everything in so rapid and so promising a way.“But that kind of writing,” he says, “is a thing of a very different nature from this. I can truly say ... that single sections in this work have cost me more than whole volumes of the 204 other; so great is the difference between writing from the head only and writing, as it may be called, from the hands.”Other observers, less careful or more sanguine than Priestley, were, however, successful in detecting the differences which prejudice led them to anticipate. Thus Signor Marsilio Landriani of Milan, whose name has already been mentioned in connection with the theory of subterraneous fires, in the course of a tour through Italy had the satisfaction of convincing himself.

“To determine whether the phenomena attending the impregnation of the solution of green vitriol with nitrous air depended in any measure upon the seeming astringency of that solution ... I impregnated a quantity of green tea, which is also 205 said to be astringent, with nitrous air, but no sensible change of colour was produced in it.”Although Priestley clearly recognised the production of the inflammable air, “in no respect to be distinguished from that which is extracted from metals by acids,” and inferred it must come from the alkaline air (“the production having its limits”), he failed to detect the other constituent of ammonia. His determination of the actual increase in volume was inaccurate, and his attempt to explain the phenomenon wholly fallacious..

the eye of the general scholar” as in either of the two former volumes, although he trusts they will “be thought no less valuable by philosophers and chemists.” Priestley, it would seem, was conscious that he was beginning, as the phrase goes, “to write himself out.”“the doctrine of dephlogisticated air supplies the easiest solution imaginable of this very difficult phenomenon. Let any person but attend to the phenomena of the detonation of charcoal in nitre, and that of dipping a piece of hot charcoal into a jar of dephlogisticated air, and I think it will be impossible for him not to conclude that the appearances are the very same and must have the same cause.”“But,” he adds, “I have since seen reason to suspect that hypothesis, plausible as it appears. Indeed, some of my late experiments would lead me to conclude that there is no acid at all in pure air.”Although Priestley clearly recognised the production of the inflammable air, “in no respect to be distinguished from that which is extracted from metals by acids,” and inferred it must come from the alkaline air (“the production having its limits”), he failed to detect the other constituent of ammonia. His determination of the actual increase in volume was inaccurate, and his attempt to explain the phenomenon wholly fallacious.Although Priestley clearly recognised the production of the inflammable air, “in no respect to be distinguished from that which is extracted from metals by acids,” and inferred it must come from the alkaline air (“the production having its limits”), he failed to detect the other constituent of ammonia. His determination of the actual increase in volume was inaccurate, and his attempt to explain the phenomenon wholly fallacious.“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”. read more

Another suggestive paper is on “Respiration and the Use of the Blood,” which was read to the Royal Society on January 25, 1776, and appears in the Phil. Trans., vol. lxvi. Priestley, of course, regarded respiration as a phlogistic process, and “that the use of the lungs is to carry off a putrid effluvium, or to discharge that phlogiston, which had been taken into the system with the aliment, and has become, as it were, effete, the air that is respired serving as a menstruum for that purpose.” This he thinks he has “proved to be effected by means of the blood, in consequence of its coming so nearly into contact with the air in the lungs, the blood appearing to be a fluid wonderfully formed to imbibe and part with that principle which the chemists call phlogiston, and changing its colour in consequence of being charged with it or being freed from it.” The facts in this paper are for the most part correctly stated, but the discoverer of oxygen led the world woefully astray as to the part played by that gas in the phenomena of respiration.“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”the eye of the general scholar” as in either of the two former volumes, although he trusts they will “be thought no less valuable by philosophers and chemists.” Priestley, it would seem, was conscious that he was beginning, as the phrase goes, “to write himself out.”The preface is noteworthy for its plea for the position of experimental science in the scheme of general education.He explains how he was led to his speculation that “this kind of air, and consequently of atmospherical air, which is the same thing but in a state of inferior purity,” consists “of earth and spirit of nitre.”.

He several times noticed the deep blue liquid which nitrogen peroxide forms with cold water. He made many attempts to use nitric oxide as an antiseptic, especially for culinary purposes. But the gastronomic results with fowls and pigeons were not to his liking, although he says, “my friend Mr Magellan ... had not so bad an opinion of this piece of cookery as I had.” One cannot read Priestley’s description of his multifarious experiments without being struck with the number of occasions in which he just missed making discoveries of first-rate importance. It is obvious that he had obtained chlorine without recognising it, even before the news of Scheele’s discovery reached this country. He had also prepared, without knowing it, phosphoretted hydrogen and phosphorous acid. At times, however, he can follow a clue with remarkable perspicacity; as in his observation of the cause of the “flouring” of mercury, and in his discovery of a method of removing lead and tin from that metal.“As it sometimes amuses myself it may perhaps amuse others to look back with me to the several steps in the actual progress of this investigation, some of which I overlooked in my last account of it.”The preface is noteworthy for its plea for the position of experimental science in the scheme of general education.203“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”.

He explains how he was led to his speculation that “this kind of air, and consequently of atmospherical air, which is the same thing but in a state of inferior purity,” consists “of earth and spirit of nitre.”Other observers, less careful or more sanguine than Priestley, were, however, successful in detecting the differences which prejudice led them to anticipate. Thus Signor Marsilio Landriani of Milan, whose name has already been mentioned in connection with the theory of subterraneous fires, in the course of a tour through Italy had the satisfaction of convincing himself“Lest my readers should be alarmed at this addition of one volume after another on the same subject, I do assure them that I shall now certainly give them and myself some respite, and deliver the torch to anyone who may be disposed to carry it, foreseeing that my attention will be sufficiently engaged by speculations of a very different nature.... It will be a great satisfaction to me, after the part that I have taken in this business, to be a spectator of its future progress, when I see the work in so many and so good hands, and everything in so rapid and so promising a way..

Of all the quantitative exercises performed by Priestley, by far the most numerous depended upon his application of nitric oxide to measure the “goodness” of air.At the instigation of Mr Woulfe, whose name mainly lives in connection with a useful piece of chemical apparatus, Priestley was encouraged to hope that he wouldHe several times noticed the deep blue liquid which nitrogen peroxide forms with cold water. He made many attempts to use nitric oxide as an antiseptic, especially for culinary purposes. But the gastronomic results with fowls and pigeons were not to his liking, although he says, “my friend Mr Magellan ... had not so bad an opinion of this piece of cookery as I had.” One cannot read Priestley’s description of his multifarious experiments without being struck with the number of occasions in which he just missed making discoveries of first-rate importance. It is obvious that he had obtained chlorine without recognising it, even before the news of Scheele’s discovery reached this country. He had also prepared, without knowing it, phosphoretted hydrogen and phosphorous acid. At times, however, he can follow a clue with remarkable perspicacity; as in his observation of the cause of the “flouring” of mercury, and in his discovery of a method of removing lead and tin from that metal.“the doctrine of dephlogisticated air supplies the easiest solution imaginable of this very difficult phenomenon. Let any person but attend to the phenomena of the detonation of charcoal in nitre, and that of dipping a piece of hot charcoal into a jar of dephlogisticated air, and I think it will be impossible for him not to conclude that the appearances are the very same and must have the same cause.”.

“When,” he says, “I first discovered the property of nitrous air as a test of the wholesomeness of common air, I flattered myself that it might be of considerable practical use, and particularly that the air of distant places and countries might be brought and examined together with great ease and satisfaction; but I own that hitherto I have rather been disappointed in my expectations from it.... I gave several of my friends the trouble to send me air from distant places, especially from manufacturing towns, and the worst they could find to be actually breathed by the manufacturers, such as is known to be exceedingly offensive to those who visit them; but when I examined those specimens of air in Wiltshire, the difference between them and the very best air in this county, which is esteemed to be very good, as also the difference between them and specimens of the best air in the counties in which these manufacturing towns are situated, was very trifling.... I have frequently taken the open air in the most exposed places in this country at different times of the year, and in different states of the weather, etc., but never found the difference so great as the 208 inaccuracy arising from the method of making the trial might easily amount to or exceed.”“Upon this, as upon other occasions, I can only repeat that it is not my opinions on which I would be understood to lay any stress. Let the new facts, from which I deduce them, be considered as my discoveries, and let other persons draw better inferences from them if they can. This is a new and a wide field of experiment and speculation, and a premature attachment to hypothesis is the greatest obstruction we are likely to meet with in our progress through it; and as I think I have been pretty much upon my guard myself, I would caution others to be upon their guard too.”Priestley’s methods of experiment with his various “airs” were very uniform. He tried their solubility in water, their power of supporting or extinguishing flame, whether they were respirable, how they behaved with acid and alkaline air, and with nitric oxide and inflammable air, and lastly how they were affected by the electric spark. He occasionally made attempts to weigh them, but his determinations of their relative density were altogether untrustworthy. Indeed, it is evident from the terms in which he speaks of these efforts that he was conscious of their inadequacy. The result of submitting alkaline air (ammonia) to the electric spark, whereby it is resolved into nitrogen and hydrogen, surprised him not a little.“When,” he says, “I first discovered the property of nitrous air as a test of the wholesomeness of common air, I flattered myself that it might be of considerable practical use, and particularly that the air of distant places and countries might be brought and examined together with great ease and satisfaction; but I own that hitherto I have rather been disappointed in my expectations from it.... I gave several of my friends the trouble to send me air from distant places, especially from manufacturing towns, and the worst they could find to be actually breathed by the manufacturers, such as is known to be exceedingly offensive to those who visit them; but when I examined those specimens of air in Wiltshire, the difference between them and the very best air in this county, which is esteemed to be very good, as also the difference between them and specimens of the best air in the counties in which these manufacturing towns are situated, was very trifling.... I have frequently taken the open air in the most exposed places in this country at different times of the year, and in different states of the weather, etc., but never found the difference so great as the 208 inaccuracy arising from the method of making the trial might easily amount to or exceed.”Another suggestive paper is on “Respiration and the Use of the Blood,” which was read to the Royal Society on January 25, 1776, and appears in the Phil. Trans., vol. lxvi. Priestley, of course, regarded respiration as a phlogistic process, and “that the use of the lungs is to carry off a putrid effluvium, or to discharge that phlogiston, which had been taken into the system with the aliment, and has become, as it were, effete, the air that is respired serving as a menstruum for that purpose.” This he thinks he has “proved to be effected by means of the blood, in consequence of its coming so nearly into contact with the air in the lungs, the blood appearing to be a fluid wonderfully formed to imbibe and part with that principle which the chemists call phlogiston, and changing its colour in consequence of being charged with it or being freed from it.” The facts in this paper are for the most part correctly stated, but the discoverer of oxygen led the world woefully astray as to the part played by that gas in the phenomena of respiration.He then experiments with manganese, which Scheele, who independently discovered oxygen, had already employed, and finds that it yields the new air both when heated alone or with oil of vitriol. The production of oxygen from manganese was contrary to his expectations as the substances he had hitherto used, the precipitate per se and the red lead and the nitre, had all been subjected to “the influence of the atmosphere,” whereas “here was pure air from a substance which for anything that appeared had always been in the bowels of the earth, and never had had any communication with the external air.” This led to the surmise that possibly the expulsion of dephlogisticated air from such mineral substances.

He points out, as already stated, that he must have had the new gas in his hands as far back as November 1771, having obtained it from nitre. He admits that he had no particular view in making his crucial experiment of August 1, 1774,“There are few experiments the rationale of which I less pretend to understand than the production of genuine and permanent inflammable air from alkaline air by means of the electric spark.... One query on this subject is, whence comes the phlogiston, which is certainly a principal ingredient in the constitution of inflammable air. Alkaline air, indeed, contains phlogiston, because in the manner in which I have generally produced it, it is itself partially inflammable; but it is not nearly so much so as the inflammable air which is produced by means of it. Besides, it will appear by the following experiments that the quantity of the inflammable air far exceeds that of the alkaline.”210At the instigation of Mr Woulfe, whose name mainly lives in connection with a useful piece of chemical apparatus, Priestley was encouraged to hope that he wouldThe ease with which nitre parts with its oxygen on 207 heating furnished Priestley with the true explanation of its so-called “detonation,” “concerning which,” he says, “the most improbable conjectures have been advanced by the most eminent philosophers and chemists.” After a reference to the hypothesis of Macquer, who assumes that what he calls “a nitrous sulphur” is produced, Priestley points out that. read more

2015 4:30 am 203Another suggestive paper is on “Respiration and the Use of the Blood,” which was read to the Royal Society on January 25, 1776, and appears in the Phil. Trans., vol. lxvi. Priestley, of course, regarded respiration as a phlogistic process, and “that the use of the lungs is to carry off a putrid effluvium, or to discharge that phlogiston, which had been taken into the system with the aliment, and has become, as it were, effete, the air that is respired serving as a menstruum for that purpose.” This he thinks he has “proved to be effected by means of the blood, in consequence of its coming so nearly into contact with the air in the lungs, the blood appearing to be a fluid wonderfully formed to imbibe and part with that principle which the chemists call phlogiston, and changing its colour in consequence of being charged with it or being freed from it.” The facts in this paper are for the most part correctly stated, but the discoverer of oxygen led the world woefully astray as to the part played by that gas in the phenomena of respiration..

210“But,” he adds, “I have since seen reason to suspect that hypothesis, plausible as it appears. Indeed, some of my late experiments would lead me to conclude that there is no acid at all in pure air.”“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”“might assist in sustaining subterraneous fires.... The solution of the phenomena of subterraneous fires would certainly be much easier on the supposition of their supplying their own pabulum, by means of dephlogisticated air contained in substances exposed to their heat. I therefore desired Mr Landriani, who being in Italy had a good opportunity of making inquiries on the subject, to inform me whether any of those substances, and particularly manganese be found in their volcanoes; and his answer makes it rather probable that those fires are, in part, sustained by this means.”“that the air of all those places, which from the long experience of the inhabitants has been reputed unwholesome, is found to be so to a very great degree of exactness by the eudiometer.... The air of the Pontine lakes, that of the Sciroccho at Rome (so very unwholesome), that of the Campagna Romana, of the Grotto del Cane, of the Zolfatara at Naples, of the baths of Nero at Baja, of the seacoast of Tuscany, were all examined by me and found to be in such a state as daily experience led me to expect.”Perhaps the most important of the many papers contained in this volume are those which relate to the “Melioration of Air by the Growth of Plants,” a subject to which Priestley gave attention, even whilst at Leeds, in 1771. In these papers he clearly proves that this “melioration” is connected with the green matter of leaves and that it is dependent upon sunlight. This observation is of fundamental importance and attracted much attention.Another portion of the work is concerned with supplementary observations on the gases treated of in the preceding volumes, partly by way of correction and partly additional. Here and there we have a suggestive passage, as in the paper on “Experiments on the Mixture of Different Kinds of Air that have no Mutual Action,” in which he thus clearly indicates the principle of the intra-diffusion of gases.

The subject of “dephlogisticated air” naturally continued to interest him, and he again returns to it in this volume, for he says:—.

“Having acquired a fondness for experiments, even slighter inducements than I have had would have been sufficient to determine my conduct.”There is little in the third volume of permanent value. It is largely an account of a series of disconnected observations on the action of nitric acid upon a variety of substances, which, however, led to no general conclusions. It is, however, certain that if Priestley could have induced himself to follow up certain of his observations he would have arrived at facts of far greater importance than those he actually narrates. “Speculation,” he said, by way of rejoinder to Lavoisier, “is a cheap commodity. New and important facts are most wanted, and therefore of most value,” and the new and important facts were within his grasp if he had only reached out for them.“that the air of all those places, which from the long experience of the inhabitants has been reputed unwholesome, is found to be so to a very great degree of exactness by the eudiometer.... The air of the Pontine lakes, that of the Sciroccho at Rome (so very unwholesome), that of the Campagna Romana, of the Grotto del Cane, of the Zolfatara at Naples, of the baths of Nero at Baja, of the seacoast of Tuscany, were all examined by me and found to be in such a state as daily experience led me to expect.”Priestley’s methods of experiment with his various “airs” were very uniform. He tried their solubility in water, their power of supporting or extinguishing flame, whether they were respirable, how they behaved with acid and alkaline air, and with nitric oxide and inflammable air, and lastly how they were affected by the electric spark. He occasionally made attempts to weigh them, but his determinations of their relative density were altogether untrustworthy. Indeed, it is evident from the terms in which he speaks of these efforts that he was conscious of their inadequacy. The result of submitting alkaline air (ammonia) to the electric spark, whereby it is resolved into nitrogen and hydrogen, surprised him not a little.The preface is noteworthy for its plea for the position of experimental science in the scheme of general education..

The ease with which nitre parts with its oxygen on 207 heating furnished Priestley with the true explanation of its so-called “detonation,” “concerning which,” he says, “the most improbable conjectures have been advanced by the most eminent philosophers and chemists.” After a reference to the hypothesis of Macquer, who assumes that what he calls “a nitrous sulphur” is produced, Priestley points out that“But that kind of writing,” he says, “is a thing of a very different nature from this. I can truly say ... that single sections in this work have cost me more than whole volumes of the 204 other; so great is the difference between writing from the head only and writing, as it may be called, from the hands.”“might assist in sustaining subterraneous fires.... The solution of the phenomena of subterraneous fires would certainly be much easier on the supposition of their supplying their own pabulum, by means of dephlogisticated air contained in substances exposed to their heat. I therefore desired Mr Landriani, who being in Italy had a good opportunity of making inquiries on the subject, to inform me whether any of those substances, and particularly manganese be found in their volcanoes; and his answer makes it rather probable that those fires are, in part, sustained by this means.”“excepting that of extracting air from a variety of substances 206 by means of a burning lens in quicksilver, which was then a new process with me, and which I was very fond of.”As regards the subject of “air” in general, although a large number of isolated observations are recorded in somewhat tedious detail, no new fact of first-rate importance is apparent. The experiments are largely supplementary to those in the preceding volumes and are for the most explanatory or corroborative of them. Perhaps the most important are those dealing with “the production of nitrous air in which a candle will burn,” by which is signified the gas we now know as nitrous oxide, but which Priestley eventually termed dephlogisticated nitrous air. The process he employed is no longer used in the production of this gas, but it sufficed in his hands to determine its individuality without doubt..

2017 5:44 am “Lest my readers should be alarmed at this addition of one volume after another on the same subject, I do assure them that I shall now certainly give them and myself some respite, and deliver the torch to anyone who may be disposed to carry it, foreseeing that my attention will be sufficiently engaged by speculations of a very different nature.... It will be a great satisfaction to me, after the part that I have taken in this business, to be a spectator of its future progress, when I see the work in so many and so good hands, and everything in so rapid and so promising a way.“might assist in sustaining subterraneous fires.... The solution of the phenomena of subterraneous fires would certainly be much easier on the supposition of their supplying their own pabulum, by means of dephlogisticated air contained in substances exposed to their heat. I therefore desired Mr Landriani, who being in Italy had a good opportunity of making inquiries on the subject, to inform me whether any of those substances, and particularly manganese be found in their volcanoes; and his answer makes it rather probable that those fires are, in part, sustained by this means.”“Upon this, as upon other occasions, I can only repeat that it is not my opinions on which I would be understood to lay any stress. Let the new facts, from which I deduce them, be considered as my discoveries, and let other persons draw better inferences from them if they can. This is a new and a wide field of experiment and speculation, and a premature attachment to hypothesis is the greatest obstruction we are likely to meet with in our progress through it; and as I think I have been pretty much upon my guard myself, I would caution others to be upon their guard too.”. read more

Chauhan.

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210“Lest my readers should be alarmed at this addition of one volume after another on the same subject, I do assure them that I shall now certainly give them and myself some respite, and deliver the torch to anyone who may be disposed to carry it, foreseeing that my attention will be sufficiently engaged by speculations of a very different nature.... It will be a great satisfaction to me, after the part that I have taken in this business, to be a spectator of its future progress, when I see the work in so many and so good hands, and everything in so rapid and so promising a way.“On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them....211The ease with which nitre parts with its oxygen on 207 heating furnished Priestley with the true explanation of its so-called “detonation,” “concerning which,” he says, “the most improbable conjectures have been advanced by the most eminent philosophers and chemists.” After a reference to the hypothesis of Macquer, who assumes that what he calls “a nitrous sulphur” is produced, Priestley points out that“On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them....“the doctrine of dephlogisticated air supplies the easiest solution imaginable of this very difficult phenomenon. Let any person but attend to the phenomena of the detonation of charcoal in nitre, and that of dipping a piece of hot charcoal into a jar of dephlogisticated air, and I think it will be impossible for him not to conclude that the appearances are the very same and must have the same cause.”.

“To determine whether the phenomena attending the impregnation of the solution of green vitriol with nitrous air depended in any measure upon the seeming astringency of that solution ... I impregnated a quantity of green tea, which is also 205 said to be astringent, with nitrous air, but no sensible change of colour was produced in it.”Another portion of the work is concerned with supplementary observations on the gases treated of in the preceding volumes, partly by way of correction and partly additional. Here and there we have a suggestive passage, as in the paper on “Experiments on the Mixture of Different Kinds of Air that have no Mutual Action,” in which he thus clearly indicates the principle of the intra-diffusion of gases.As regards the subject of “air” in general, although a large number of isolated observations are recorded in somewhat tedious detail, no new fact of first-rate importance is apparent. The experiments are largely supplementary to those in the preceding volumes and are for the most explanatory or corroborative of them. Perhaps the most important are those dealing with “the production of nitrous air in which a candle will burn,” by which is signified the gas we now know as nitrous oxide, but which Priestley eventually termed dephlogisticated nitrous air. The process he employed is no longer used in the production of this gas, but it sufficed in his hands to determine its individuality without doubt.210.

These passages evidently were written under the influence of the feeling of resentment with which he viewed the criticism to which his speculations were subjected abroad. Fontana, Lavoisier and others were, indeed, zealously engaged in using Priestley’s own facts to destroy the conception by which he explained them. An appeal to the balance was felt to be necessary, and Priestley, as a logician, could not resist it. But he was no quantitative chemist: the habits of a Cavendish were quite foreign to his genius: patient, scrupulous attention to numerical accuracy was not one of his characteristics: he was one of the most industrious of experimenters—delighting, indeed, in manipulation for the mere sake of it, but withal hasty and superficial. It is nowhere evident in his writings that his problems were attacked according to any carefully-thought-out plan. He confesses indeed, on more than one occasion, he tested the inflammability of one of his numerous “airs” because he had a lighted candle near him: had the candle not been lighted it would not have occurred to him to do it. Priestley was, in fact, a pioneer: he showed the existence of a new world for science, and he 202 himself roamed over a portion of it, like a second Joshua; but he had not the experience or the aptitude to accurately map out even that fraction..

As regards the subject of “air” in general, although a large number of isolated observations are recorded in somewhat tedious detail, no new fact of first-rate importance is apparent. The experiments are largely supplementary to those in the preceding volumes and are for the most explanatory or corroborative of them. Perhaps the most important are those dealing with “the production of nitrous air in which a candle will burn,” by which is signified the gas we now know as nitrous oxide, but which Priestley eventually termed dephlogisticated nitrous air. The process he employed is no longer used in the production of this gas, but it sufficed in his hands to determine its individuality without doubt.“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”Priestley’s methods of experiment with his various “airs” were very uniform. He tried their solubility in water, their power of supporting or extinguishing flame, whether they were respirable, how they behaved with acid and alkaline air, and with nitric oxide and inflammable air, and lastly how they were affected by the electric spark. He occasionally made attempts to weigh them, but his determinations of their relative density were altogether untrustworthy. Indeed, it is evident from the terms in which he speaks of these efforts that he was conscious of their inadequacy. The result of submitting alkaline air (ammonia) to the electric spark, whereby it is resolved into nitrogen and hydrogen, surprised him not a little..

the eye of the general scholar” as in either of the two former volumes, although he trusts they will “be thought no less valuable by philosophers and chemists.” Priestley, it would seem, was conscious that he was beginning, as the phrase goes, “to write himself out.”. read more

“excepting that of extracting air from a variety of substances 206 by means of a burning lens in quicksilver, which was then a new process with me, and which I was very fond of.”“But,” he adds, “I have since seen reason to suspect that hypothesis, plausible as it appears. Indeed, some of my late experiments would lead me to conclude that there is no acid at all in pure air.”He explains how he was led to his speculation that “this kind of air, and consequently of atmospherical air, which is the same thing but in a state of inferior purity,” consists “of earth and spirit of nitre.”“There are few experiments the rationale of which I less pretend to understand than the production of genuine and permanent inflammable air from alkaline air by means of the electric spark.... One query on this subject is, whence comes the phlogiston, which is certainly a principal ingredient in the constitution of inflammable air. Alkaline air, indeed, contains phlogiston, because in the manner in which I have generally produced it, it is itself partially inflammable; but it is not nearly so much so as the inflammable air which is produced by means of it. Besides, it will appear by the following experiments that the quantity of the inflammable air far exceeds that of the alkaline.”.

“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”Of all the quantitative exercises performed by Priestley, by far the most numerous depended upon his application of nitric oxide to measure the “goodness” of air.Modern eudiometry, making use of methods of far greater precision than were possible to Priestley, has confirmed his supposition that atmospheric air is remarkably constant in composition, and that its wholesomeness depends upon other causes than the relative amount of the dephlogisticated air contained in it..

He explains how he was led to his speculation that “this kind of air, and consequently of atmospherical air, which is the same thing but in a state of inferior purity,” consists “of earth and spirit of nitre.”.

“On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them....“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”“When,” he says, “I first discovered the property of nitrous air as a test of the wholesomeness of common air, I flattered myself that it might be of considerable practical use, and particularly that the air of distant places and countries might be brought and examined together with great ease and satisfaction; but I own that hitherto I have rather been disappointed in my expectations from it.... I gave several of my friends the trouble to send me air from distant places, especially from manufacturing towns, and the worst they could find to be actually breathed by the manufacturers, such as is known to be exceedingly offensive to those who visit them; but when I examined those specimens of air in Wiltshire, the difference between them and the very best air in this county, which is esteemed to be very good, as also the difference between them and specimens of the best air in the counties in which these manufacturing towns are situated, was very trifling.... I have frequently taken the open air in the most exposed places in this country at different times of the year, and in different states of the weather, etc., but never found the difference so great as the 208 inaccuracy arising from the method of making the trial might easily amount to or exceed.”The preface is noteworthy for its plea for the position of experimental science in the scheme of general education.“But that kind of writing,” he says, “is a thing of a very different nature from this. I can truly say ... that single sections in this work have cost me more than whole volumes of the 204 other; so great is the difference between writing from the head only and writing, as it may be called, from the hands.”“But,” he adds, “I have since seen reason to suspect that hypothesis, plausible as it appears. Indeed, some of my late experiments would lead me to conclude that there is no acid at all in pure air.”. read more

Of all the quantitative exercises performed by Priestley, by far the most numerous depended upon his application of nitric oxide to measure the “goodness” of air..

Although Priestley clearly recognised the production of the inflammable air, “in no respect to be distinguished from that which is extracted from metals by acids,” and inferred it must come from the alkaline air (“the production having its limits”), he failed to detect the other constituent of ammonia. His determination of the actual increase in volume was inaccurate, and his attempt to explain the phenomenon wholly fallacious.The preface is noteworthy for its plea for the position of experimental science in the scheme of general education..

There is little in the third volume of permanent value. It is largely an account of a series of disconnected observations on the action of nitric acid upon a variety of substances, which, however, led to no general conclusions. It is, however, certain that if Priestley could have induced himself to follow up certain of his observations he would have arrived at facts of far greater importance than those he actually narrates. “Speculation,” he said, by way of rejoinder to Lavoisier, “is a cheap commodity. New and important facts are most wanted, and therefore of most value,” and the new and important facts were within his grasp if he had only reached out for them.“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”“Having acquired a fondness for experiments, even slighter inducements than I have had would have been sufficient to determine my conduct.”.

203.

At the instigation of Mr Woulfe, whose name mainly lives in connection with a useful piece of chemical apparatus, Priestley was encouraged to hope that he wouldAnother portion of the work is concerned with supplementary observations on the gases treated of in the preceding volumes, partly by way of correction and partly additional. Here and there we have a suggestive passage, as in the paper on “Experiments on the Mixture of Different Kinds of Air that have no Mutual Action,” in which he thus clearly indicates the principle of the intra-diffusion of gases.210“Upon this, as upon other occasions, I can only repeat that it is not my opinions on which I would be understood to lay any stress. Let the new facts, from which I deduce them, be considered as my discoveries, and let other persons draw better inferences from them if they can. This is a new and a wide field of experiment and speculation, and a premature attachment to hypothesis is the greatest obstruction we are likely to meet with in our progress through it; and as I think I have been pretty much upon my guard myself, I would caution others to be upon their guard too.”Another suggestive paper is on “Respiration and the Use of the Blood,” which was read to the Royal Society on January 25, 1776, and appears in the Phil. Trans., vol. lxvi. Priestley, of course, regarded respiration as a phlogistic process, and “that the use of the lungs is to carry off a putrid effluvium, or to discharge that phlogiston, which had been taken into the system with the aliment, and has become, as it were, effete, the air that is respired serving as a menstruum for that purpose.” This he thinks he has “proved to be effected by means of the blood, in consequence of its coming so nearly into contact with the air in the lungs, the blood appearing to be a fluid wonderfully formed to imbibe and part with that principle which the chemists call phlogiston, and changing its colour in consequence of being charged with it or being freed from it.” The facts in this paper are for the most part correctly stated, but the discoverer of oxygen led the world woefully astray as to the part played by that gas in the phenomena of respiration.. read more

In the course of some observations on the effect “of impregnating oil of vitriol with nitrous acid vapour” he discovered nitrosulphuric acid, the so-called “Leaden Chamber Crystals,” whose properties and behaviour with water he describes with accuracy and even eloquence. Of these crystals he says: “A more beautiful appearance can hardly be imagined, and I am afraid I shall never see the like again.” He also noticed the formation of the dark brown compound which nitric oxide forms with a solution of green vitriol, and adds:—The preface is noteworthy for its plea for the position of experimental science in the scheme of general education.“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”.

He several times noticed the deep blue liquid which nitrogen peroxide forms with cold water. He made many attempts to use nitric oxide as an antiseptic, especially for culinary purposes. But the gastronomic results with fowls and pigeons were not to his liking, although he says, “my friend Mr Magellan ... had not so bad an opinion of this piece of cookery as I had.” One cannot read Priestley’s description of his multifarious experiments without being struck with the number of occasions in which he just missed making discoveries of first-rate importance. It is obvious that he had obtained chlorine without recognising it, even before the news of Scheele’s discovery reached this country. He had also prepared, without knowing it, phosphoretted hydrogen and phosphorous acid. At times, however, he can follow a clue with remarkable perspicacity; as in his observation of the cause of the “flouring” of mercury, and in his discovery of a method of removing lead and tin from that metal.Priestley’s methods of experiment with his various “airs” were very uniform. He tried their solubility in water, their power of supporting or extinguishing flame, whether they were respirable, how they behaved with acid and alkaline air, and with nitric oxide and inflammable air, and lastly how they were affected by the electric spark. He occasionally made attempts to weigh them, but his determinations of their relative density were altogether untrustworthy. Indeed, it is evident from the terms in which he speaks of these efforts that he was conscious of their inadequacy. The result of submitting alkaline air (ammonia) to the electric spark, whereby it is resolved into nitrogen and hydrogen, surprised him not a little.“There are few experiments the rationale of which I less pretend to understand than the production of genuine and permanent inflammable air from alkaline air by means of the electric spark.... One query on this subject is, whence comes the phlogiston, which is certainly a principal ingredient in the constitution of inflammable air. Alkaline air, indeed, contains phlogiston, because in the manner in which I have generally produced it, it is itself partially inflammable; but it is not nearly so much so as the inflammable air which is produced by means of it. Besides, it will appear by the following experiments that the quantity of the inflammable air far exceeds that of the alkaline.”The subject of “dephlogisticated air” naturally continued to interest him, and he again returns to it in this volume, for he says:—.

“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”“Upon this, as upon other occasions, I can only repeat that it is not my opinions on which I would be understood to lay any stress. Let the new facts, from which I deduce them, be considered as my discoveries, and let other persons draw better inferences from them if they can. This is a new and a wide field of experiment and speculation, and a premature attachment to hypothesis is the greatest obstruction we are likely to meet with in our progress through it; and as I think I have been pretty much upon my guard myself, I would caution others to be upon their guard too.”Modern eudiometry, making use of methods of far greater precision than were possible to Priestley, has confirmed his supposition that atmospheric air is remarkably constant in composition, and that its wholesomeness depends upon other causes than the relative amount of the dephlogisticated air contained in it.Priestley’s methods of experiment with his various “airs” were very uniform. He tried their solubility in water, their power of supporting or extinguishing flame, whether they were respirable, how they behaved with acid and alkaline air, and with nitric oxide and inflammable air, and lastly how they were affected by the electric spark. He occasionally made attempts to weigh them, but his determinations of their relative density were altogether untrustworthy. Indeed, it is evident from the terms in which he speaks of these efforts that he was conscious of their inadequacy. The result of submitting alkaline air (ammonia) to the electric spark, whereby it is resolved into nitrogen and hydrogen, surprised him not a little.“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”The fourth volume made its appearance in March 1779, with a dedication to Sir George Savile, who had rendered Priestley the service of introducing him and his invention of soda-water to the notice of the Admiralty. In the preface, which is commendably short, he makes some reference to the respite which he had promised himself and his readers, but trusts, by way of extenuation, “it may be sufficient to allege the instability of human purposes and pursuits.” He had intended to devote himself to metaphysics.“But,” he adds, “I have since seen reason to suspect that hypothesis, plausible as it appears. Indeed, some of my late experiments would lead me to conclude that there is no acid at all in pure air.”.

“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”The subject of “dephlogisticated air” naturally continued to interest him, and he again returns to it in this volume, for he says:—.

Although Priestley clearly recognised the production of the inflammable air, “in no respect to be distinguished from that which is extracted from metals by acids,” and inferred it must come from the alkaline air (“the production having its limits”), he failed to detect the other constituent of ammonia. His determination of the actual increase in volume was inaccurate, and his attempt to explain the phenomenon wholly fallacious.Another suggestive paper is on “Respiration and the Use of the Blood,” which was read to the Royal Society on January 25, 1776, and appears in the Phil. Trans., vol. lxvi. Priestley, of course, regarded respiration as a phlogistic process, and “that the use of the lungs is to carry off a putrid effluvium, or to discharge that phlogiston, which had been taken into the system with the aliment, and has become, as it were, effete, the air that is respired serving as a menstruum for that purpose.” This he thinks he has “proved to be effected by means of the blood, in consequence of its coming so nearly into contact with the air in the lungs, the blood appearing to be a fluid wonderfully formed to imbibe and part with that principle which the chemists call phlogiston, and changing its colour in consequence of being charged with it or being freed from it.” The facts in this paper are for the most part correctly stated, but the discoverer of oxygen led the world woefully astray as to the part played by that gas in the phenomena of respiration.“that the air of all those places, which from the long experience of the inhabitants has been reputed unwholesome, is found to be so to a very great degree of exactness by the eudiometer.... The air of the Pontine lakes, that of the Sciroccho at Rome (so very unwholesome), that of the Campagna Romana, of the Grotto del Cane, of the Zolfatara at Naples, of the baths of Nero at Baja, of the seacoast of Tuscany, were all examined by me and found to be in such a state as daily experience led me to expect.”

“There are few experiments the rationale of which I less pretend to understand than the production of genuine and permanent inflammable air from alkaline air by means of the electric spark.... One query on this subject is, whence comes the phlogiston, which is certainly a principal ingredient in the constitution of inflammable air. Alkaline air, indeed, contains phlogiston, because in the manner in which I have generally produced it, it is itself partially inflammable; but it is not nearly so much so as the inflammable air which is produced by means of it. Besides, it will appear by the following experiments that the quantity of the inflammable air far exceeds that of the alkaline.”the eye of the general scholar” as in either of the two former volumes, although he trusts they will “be thought no less valuable by philosophers and chemists.” Priestley, it would seem, was conscious that he was beginning, as the phrase goes, “to write himself out.”“On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them....“the doctrine of dephlogisticated air supplies the easiest solution imaginable of this very difficult phenomenon. Let any person but attend to the phenomena of the detonation of charcoal in nitre, and that of dipping a piece of hot charcoal into a jar of dephlogisticated air, and I think it will be impossible for him not to conclude that the appearances are the very same and must have the same cause.”These passages evidently were written under the influence of the feeling of resentment with which he viewed the criticism to which his speculations were subjected abroad. Fontana, Lavoisier and others were, indeed, zealously engaged in using Priestley’s own facts to destroy the conception by which he explained them. An appeal to the balance was felt to be necessary, and Priestley, as a logician, could not resist it. But he was no quantitative chemist: the habits of a Cavendish were quite foreign to his genius: patient, scrupulous attention to numerical accuracy was not one of his characteristics: he was one of the most industrious of experimenters—delighting, indeed, in manipulation for the mere sake of it, but withal hasty and superficial. It is nowhere evident in his writings that his problems were attacked according to any carefully-thought-out plan. He confesses indeed, on more than one occasion, he tested the inflammability of one of his numerous “airs” because he had a lighted candle near him: had the candle not been lighted it would not have occurred to him to do it. Priestley was, in fact, a pioneer: he showed the existence of a new world for science, and he 202 himself roamed over a portion of it, like a second Joshua; but he had not the experience or the aptitude to accurately map out even that fraction.“But that kind of writing,” he says, “is a thing of a very different nature from this. I can truly say ... that single sections in this work have cost me more than whole volumes of the 204 other; so great is the difference between writing from the head only and writing, as it may be called, from the hands.”

2016 9:49 am “On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them....203He explains how he was led to his speculation that “this kind of air, and consequently of atmospherical air, which is the same thing but in a state of inferior purity,” consists “of earth and spirit of nitre.”. read more

These passages evidently were written under the influence of the feeling of resentment with which he viewed the criticism to which his speculations were subjected abroad. Fontana, Lavoisier and others were, indeed, zealously engaged in using Priestley’s own facts to destroy the conception by which he explained them. An appeal to the balance was felt to be necessary, and Priestley, as a logician, could not resist it. But he was no quantitative chemist: the habits of a Cavendish were quite foreign to his genius: patient, scrupulous attention to numerical accuracy was not one of his characteristics: he was one of the most industrious of experimenters—delighting, indeed, in manipulation for the mere sake of it, but withal hasty and superficial. It is nowhere evident in his writings that his problems were attacked according to any carefully-thought-out plan. He confesses indeed, on more than one occasion, he tested the inflammability of one of his numerous “airs” because he had a lighted candle near him: had the candle not been lighted it would not have occurred to him to do it. Priestley was, in fact, a pioneer: he showed the existence of a new world for science, and he 202 himself roamed over a portion of it, like a second Joshua; but he had not the experience or the aptitude to accurately map out even that fraction.203He points out, as already stated, that he must have had the new gas in his hands as far back as November 1771, having obtained it from nitre. He admits that he had no particular view in making his crucial experiment of August 1, 1774,.

211As regards the subject of “air” in general, although a large number of isolated observations are recorded in somewhat tedious detail, no new fact of first-rate importance is apparent. The experiments are largely supplementary to those in the preceding volumes and are for the most explanatory or corroborative of them. Perhaps the most important are those dealing with “the production of nitrous air in which a candle will burn,” by which is signified the gas we now know as nitrous oxide, but which Priestley eventually termed dephlogisticated nitrous air. The process he employed is no longer used in the production of this gas, but it sufficed in his hands to determine its individuality without doubt.At the instigation of Mr Woulfe, whose name mainly lives in connection with a useful piece of chemical apparatus, Priestley was encouraged to hope that he would“But that kind of writing,” he says, “is a thing of a very different nature from this. I can truly say ... that single sections in this work have cost me more than whole volumes of the 204 other; so great is the difference between writing from the head only and writing, as it may be called, from the hands.”.

The fact was Priestley could not keep away from his laboratory.“Having acquired a fondness for experiments, even slighter inducements than I have had would have been sufficient to determine my conduct.”

“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”Other observers, less careful or more sanguine than Priestley, were, however, successful in detecting the differences which prejudice led them to anticipate. Thus Signor Marsilio Landriani of Milan, whose name has already been mentioned in connection with the theory of subterraneous fires, in the course of a tour through Italy had the satisfaction of convincing himself“As it sometimes amuses myself it may perhaps amuse others to look back with me to the several steps in the actual progress of this investigation, some of which I overlooked in my last account of it.”“might assist in sustaining subterraneous fires.... The solution of the phenomena of subterraneous fires would certainly be much easier on the supposition of their supplying their own pabulum, by means of dephlogisticated air contained in substances exposed to their heat. I therefore desired Mr Landriani, who being in Italy had a good opportunity of making inquiries on the subject, to inform me whether any of those substances, and particularly manganese be found in their volcanoes; and his answer makes it rather probable that those fires are, in part, sustained by this means.”.

“To determine whether the phenomena attending the impregnation of the solution of green vitriol with nitrous air depended in any measure upon the seeming astringency of that solution ... I impregnated a quantity of green tea, which is also 205 said to be astringent, with nitrous air, but no sensible change of colour was produced in it.”203“might assist in sustaining subterraneous fires.... The solution of the phenomena of subterraneous fires would certainly be much easier on the supposition of their supplying their own pabulum, by means of dephlogisticated air contained in substances exposed to their heat. I therefore desired Mr Landriani, who being in Italy had a good opportunity of making inquiries on the subject, to inform me whether any of those substances, and particularly manganese be found in their volcanoes; and his answer makes it rather probable that those fires are, in part, sustained by this means.”.

The fact was Priestley could not keep away from his laboratory.. read more

Perhaps the most important of the many papers contained in this volume are those which relate to the “Melioration of Air by the Growth of Plants,” a subject to which Priestley gave attention, even whilst at Leeds, in 1771. In these papers he clearly proves that this “melioration” is connected with the green matter of leaves and that it is dependent upon sunlight. This observation is of fundamental importance and attracted much attention.“excepting that of extracting air from a variety of substances 206 by means of a burning lens in quicksilver, which was then a new process with me, and which I was very fond of.”.

“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”“On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them....“the doctrine of dephlogisticated air supplies the easiest solution imaginable of this very difficult phenomenon. Let any person but attend to the phenomena of the detonation of charcoal in nitre, and that of dipping a piece of hot charcoal into a jar of dephlogisticated air, and I think it will be impossible for him not to conclude that the appearances are the very same and must have the same cause.”The fact was Priestley could not keep away from his laboratory..

He explains how he was led to his speculation that “this kind of air, and consequently of atmospherical air, which is the same thing but in a state of inferior purity,” consists “of earth and spirit of nitre.”“If we wish to lay a good foundation for a philosophical taste, and philosophical pursuits, persons should be accustomed to the sight of experiments and processes in early life. They should, more especially, be early initiated in the theory and practice of investigation, by which many of the old discoveries may be made to be really their own; on which account they will be much more valued by them. And, in a great variety of articles, very young persons may be made so far acquainted with everything necessary to be previously known as to engage (which they will do with peculiar alacrity) in pursuits truly original.”The ease with which nitre parts with its oxygen on 207 heating furnished Priestley with the true explanation of its so-called “detonation,” “concerning which,” he says, “the most improbable conjectures have been advanced by the most eminent philosophers and chemists.” After a reference to the hypothesis of Macquer, who assumes that what he calls “a nitrous sulphur” is produced, Priestley points out that.

“When,” he says, “I first discovered the property of nitrous air as a test of the wholesomeness of common air, I flattered myself that it might be of considerable practical use, and particularly that the air of distant places and countries might be brought and examined together with great ease and satisfaction; but I own that hitherto I have rather been disappointed in my expectations from it.... I gave several of my friends the trouble to send me air from distant places, especially from manufacturing towns, and the worst they could find to be actually breathed by the manufacturers, such as is known to be exceedingly offensive to those who visit them; but when I examined those specimens of air in Wiltshire, the difference between them and the very best air in this county, which is esteemed to be very good, as also the difference between them and specimens of the best air in the counties in which these manufacturing towns are situated, was very trifling.... I have frequently taken the open air in the most exposed places in this country at different times of the year, and in different states of the weather, etc., but never found the difference so great as the 208 inaccuracy arising from the method of making the trial might easily amount to or exceed.”The preface is noteworthy for its plea for the position of experimental science in the scheme of general education.211“The result of my trials has been this general conclusion: that when two kinds of air have been mixed it is not possible to separate them again by any method of decanting or pouring them off, though the greatest possible care be taken in doing it. They may not properly incorporate, so as to form a third species of air, possessed of new properties; but they will remain equally diffused through the mass of each other; and whether it be the upper or the lower part of the air that is taken out of the vessel, without disturbing the rest, it will contain an equal mixture of them both.”.

The subject of “dephlogisticated air” naturally continued to interest him, and he again returns to it in this volume, for he says:—“But that kind of writing,” he says, “is a thing of a very different nature from this. I can truly say ... that single sections in this work have cost me more than whole volumes of the 204 other; so great is the difference between writing from the head only and writing, as it may be called, from the hands.”.

211“might assist in sustaining subterraneous fires.... The solution of the phenomena of subterraneous fires would certainly be much easier on the supposition of their supplying their own pabulum, by means of dephlogisticated air contained in substances exposed to their heat. I therefore desired Mr Landriani, who being in Italy had a good opportunity of making inquiries on the subject, to inform me whether any of those substances, and particularly manganese be found in their volcanoes; and his answer makes it rather probable that those fires are, in part, sustained by this means.”“excepting that of extracting air from a variety of substances 206 by means of a burning lens in quicksilver, which was then a new process with me, and which I was very fond of.”In the fifth volume, which was published in the 209 spring of 1781, with a dedication to Dr Heberden, when Priestley had moved to Birmingham, he again returns to this subject. Practically all the experimental work to which it relates was done whilst he was with Lord Shelburne, and mainly at Calne. During the former parts of the summer of 1780 he suffered from an illness which greatly interfered with his work, although he thinks that during his incapacity for making experiments his “hints for the farther prosecution of them are greatly accumulated.” It cannot be said that the five papers on the relations of vegetation to air, with which the volume opens, added very materially to the fundamental fact which Priestley had discovered. They furnished, however, additional evidence of it and no doubt stimulated further inquiry. If his facts could not be controverted, his explanations and surmises were at least open to attack, and a number of observers, both here and abroad, busied themselves with the problems of physiological botany thereby suggested.“On taking leave of this subject I would entreat the candour and indulgence of my readers for any oversights they may discover in me as a philosopher, or imperfections as a writer. I am far from pretending to infallibility; but I have the satisfaction to reflect that, imperfect as my works may be found 201 to be, they are each as perfect as I was able to make them.....

210Other observers, less careful or more sanguine than Priestley, were, however, successful in detecting the differences which prejudice led them to anticipate. Thus Signor Marsilio Landriani of Milan, whose name has already been mentioned in connection with the theory of subterraneous fires, in the course of a tour through Italy had the satisfaction of convincing himself“But,” he adds, “I have since seen reason to suspect that hypothesis, plausible as it appears. Indeed, some of my late experiments would lead me to conclude that there is no acid at all in pure air.”He several times noticed the deep blue liquid which nitrogen peroxide forms with cold water. He made many attempts to use nitric oxide as an antiseptic, especially for culinary purposes. But the gastronomic results with fowls and pigeons were not to his liking, although he says, “my friend Mr Magellan ... had not so bad an opinion of this piece of cookery as I had.” One cannot read Priestley’s description of his multifarious experiments without being struck with the number of occasions in which he just missed making discoveries of first-rate importance. It is obvious that he had obtained chlorine without recognising it, even before the news of Scheele’s discovery reached this country. He had also prepared, without knowing it, phosphoretted hydrogen and phosphorous acid. At times, however, he can follow a clue with remarkable perspicacity; as in his observation of the cause of the “flouring” of mercury, and in his discovery of a method of removing lead and tin from that metal.He points out, as already stated, that he must have had the new gas in his hands as far back as November 1771, having obtained it from nitre. He admits that he had no particular view in making his crucial experiment of August 1, 1774,. read more