Memoirs of Dr. Joseph Priestley

by Joseph Priestley

APPENDIX, NO. 1.

Of the discoveries in factitious Airs before the time of Dr. Priestley, and of those made by himself.

Dr. Priestley has given a general though brief account[33] of what had been done by his predecessors in this department of experimental Philosophy, and Sir John Pringle in his discourse before the Royal Society on occasion of presenting Dr. Priestley with the Copley Medal in 1772[34] has entered expressly, and more fully into the history of pneumatic discoveries. The same subject was taken up about three years after by Mr. Lavoisier still more at large, in the introduction to his first Vol. of Physical and Chemical Essays, of which a translation was published by Mr. Henry of Manchester in 1776. It is unnecessary to detail here what they have written on the history of these discoveries. It may be observed that no mention is made by any of these gentlemen of an experiment of Mr. John Maud, in July 1736[35], who procured (and confined) inflammable air from a solution of Iron in the vitriolic acid. Inflammable air had been procured from the White Haven coal mines, and exhibited to the Royal Society by Mr. James Lowther, but I do not recollect any notice of its having been collected from a solution of metals in acids, and its character ascertained before Mr. Maud’s experiment; for Hales, though he procured both inflammable and nitrous air, did not examine their properties. But it is much more extraordinary that neither Sir John Pringle who was a Physician, or Mr. Lavoisier who was so much occupied under government, respecting the Theory of the formation, and the practice of manufacturing Saltpetre from Nitre beds, should not have known, or have noticed the five treatises of Mayow on chemical, phisiological and pathological subjects, published a century preceding. Mayow is quoted by Hales,[36] by Lemery,[37] and by Brownrigg,[38] but though they appear to have read his work, it is evident that they knew not how to appreciate, or to profit by it. Haller[39] also refers to him, and he is respectfully quoted by Blumenbach[40]: but his book nevertheless long remained in comparative obscurity. From their time Mayow has been neglected until his writings were noticed by Dr. Forster, in 1780,[41] and again announced as almost a discovery in the chemical world, by Dr. Beddoes in the year 1790. His doctrines touch so nearly on the subsequent discoveries of Priestley, Scheele, Lavoisier, Crawford, Goodwin, &c. that it seems absolutely necessary to discuss his pretensions, before those of his successors can be accurately admitted. As I am acquainted with Dr. Beddoes’s pamphlet on Mayow, from the analytical review of it only, (V. vi.) and have no opportunity here of consulting it, I shall take up Mayow’s book, and give an account of his tenets, from the work itself.

[33] In the beginning of his first vol. of experiments: it is an abridgment of Sir J. Pringle’s discourse.

[34] Discourses p. 4.

[35] Martyn’s abridgment of the Philosophical transactions v. 9. p. 396. I think Maud’s experiment in 1736 likely to have suggested those of Mr. Cavendish in 1766.

[36] Vegetable Statics v. 2. p. 234.

[37] Mem. de l’Acad. Royale 1717 p. 48. On ne dit pourtant point trop sous quelle forme ce nitre se contient dans l’air, et Mayou, Auteur Anglois et grand defenseur du Nitre-Aèrien voulant èclaircir cette difficultè, suppose l’air impregnè par tout d’une espece de nitre metaphysique, qui ne merite pas trop d’ètre refutè, quoi-qu’il l’àit cependant ètè suffisamment par Barchusen et par Schelhamer. Le fondement de l’opinion du Nitre aèrien, c’est comme le rapporte Mayou lui mème, qu’apres avoir enlevè à une terre tout le Nitre qu’elle contenoit, si on l’expose ensuite à l’air pendant un certain tems elle en reprend de nouveau: il est vrai que si l’observation ètoit parfaitement telle qu’elle vient d’ètre rapportèe, on auroit une plus grande raison qu’on n’en a, de supposer dans l’air une très-grande quantite de nitre, et de mettre sur le compte de ce nitre aèrien un grand nombre d’effets auquels il n’a certainement aucune part.

The experiment of Lemery mentioned in Dr. Watson’s Essay on Nitre, is in p. 54 of the Mem. de l’acad. royale for 1717 not for 1731.

It sometimes happens to men whose genius far transcends the level of their day, to be from that very circumstance neither understood nor believed by their contemporaries. Until the discoveries of modern chemistry, who would have given Sir Isaac Newton credit for his conjecture that the Diamond was an inflammable substance? The fact which Lemery sneers at, the reproduction of nitre in the earth, is established beyond contradiction by the authors quoted by Dr. Watson (Chem. Ess. v. 1. p. 318-321) and in Bowle’s account of the nitre earths in Spain, and in Andreossi’s memoir on the Saltpetre of Egypt. Though it is far from improbable that after lixiviation these earths may again become gradually impregnated with putrefying animal or vegetable matter to serve for the future crops of nitre.

[38] Philosophical transactions v. 55 p. 232.

[39] Dr. Priestley in his preliminary account of the discoveries and theories on respiration (Exp. on air v. 3 p. 356. abridged edit.) quotes Haller’s great work on Physiology. Haller quotes Mayow in three or four places; but it is no wonder the quotations did not strike Dr. Priestley with any curiosity to examine Mayow’s book, for Haller certainly did not understand his theory. For instance Lib. 8. § 13. Nitrum aereum. Si ad verum sensum nitri aerei hypothesis revocata fuisset parum utique ab eà differt quam novissimè proposuimus. Nitrum quidem ipsum incautiosius olim Physiologi in aere obvolitare scripserunt, et ex pluvià et nive colligi; idemque passim ex rupibus efflorescere (Sprat ex Henshaw p. 264 major cal. hum.) exque plantis et stercoribus educi (Fludd Niewentydt, 563-4. Mayow de nitro aereo. Lower de Corde c. 3. Thurston 52. 53. Besse Analyse tom 1 et en lettre en reponse à M. Helvet. 114.) id nitrum aiunt in pulmonibus ad sanguinem venire, et ab eo ruborem illum elegantem, et fermentationem (Mayow, Thurston penult. ess. T. 3 p. 265) et calorem sanguinis accedere aut vicissim sanguinem condensari.

Certainly the id nitrum, is not Mayow’s. M. Rosel seems first to have ascertained the existence of nitre in plants. A late experiment of Dr. Priestley’s, of which he gave an account in a letter to Dr. Wistar, seems to make it probable that there may be nitre in snow.

[40] Blumenbach’s Physiology, Caldwell’s translation, Philadelphia, 1795. § 162. Speaking of the theories of animal heat, “But all these hypotheses are embarrassed with innumerable difficulties; whereas on the other hand the utmost simplicity, and an entire correspondence with the phenomena of nature combine in recommending and confirming that doctrine in which the lungs are considered as the focus or fire place where animal heat is generated, and the deplogisticated part of the air which we breathe as the fuel that supports the vital flame. That justly celebrated character Jo. Mayow sketched out formerly the leading traces and the first great outlines of this doctrine which in our times has been greatly improved, extended and farther elucidated by the labours of the illustrious Crawford.”

Dr. Darwin however is certainly right in supposing that heat is evolved in many other processes of the animal economy, beside inspiration.

[41] See the translation of Scheele by Dr. John Reinhold Forster 1780 p. XIII.

In p. 437 of v. 5 of the analytical review of Hopson’s Chemistry, before Dr. Beddoes’s account of Mayow in 1790 the latter is stated as the author of discoveries that might have given rise to the present system of pneumatic Chemistry.

Two of Mayow’s Essays, viz. de Respiratione and de Rachitide, appear to have been published at Leyden, in 1671, the author who died at the age of 34, being then 26 years old. The propositions which I have thought it necessary to extract from Mayow’s work, (ed. of 1674, Oxford,) and which I shall insert, will give a concise, but faithful view of his discoveries and conjectures in pneumatic Chemistry.[42] The abridgements of Beddoes and Fourcroy, I have no opportunity to consult, and as Mayow’s book is far from being common, I have deemed it by no means an unnecessary labour to give the reader an opportunity of judging for himself, what is the precise extent of the claim, which the patrons of Mayow’s reputation may fairly set up. It is also, of the more importance in a history of this subject, to notice the pretensions of this writer, as it appears that Boyle’s experiments on artificial air, in his physico-mechanical experiments were not made until the year 1767 et seq. Though the first edition of that treatise repeatedly quoted by Mayow was in 1661. Mayow’s experiments therefore ought to have been, and probably were known to Boyle at the publication of his last edition.[43]

[42] I believe Dr. Beddoes gives no more than the heads of each chapter and, a brief analysis of the contents. Dr. Beddoes in his remarks on Fourcroy’s account of Mayow, Ann. de Chimie. No. 85, Nich. Jour. v. 3 quarto p. 108 states Mayow at the time of his death to have been only 27 and 28: but he was born in 1645 and died in 1769. Biog. Dict. 8vo. ed. of 1798.

[43] I do not find that Boyle quotes Mayow, though their labours in the same field were contemporary. But Boyle in his hidden qualities of the air published in 1674 has an observation that looks as if derived from Mayow. “And this undestroyed springiness of the air, with the necessity of fresh air to the life of hot animals, suggests a great suspicion of some vital substance if I may so call it, diffused through the air, whether it be a volatile nitre or rather some anonymous substance, sidereal or subterraneal, though not improperly of kin to that which seems so necessary to the maintenance of other flames.”

The following is an analysis of Mayow’s essays, so far as relates to his chemical Philosophy.

Chap. 1st. Of Nitre. The air is impregnated with a vital, igneous, and highly fermentative spirit of a nitro-saline nature, p. 1.

Nitre is a salt consisting of an acid and an alkaline part, as appears by the Analysis, and by the generation of nitre; for if this salt be deflagrated with sulphur, the acid spirit will fly off, and may be collected by means of a tubulated retort and a receiver: and so if it be deflagrated with tartar, the residuum will be equal in weight to the tartar employed, though much of that, is of a fœtid oily nature. This appears also from the composition of nitre, by the addition of spirit of nitre to an alcali, p. 2-4. The fixed part of nitre is obtained from the earth; pure earth being probably a compound of salt and sulphur. p. 8.

Chap. 2d. On the aereal and fiery spirit of nitre.

The air seems to contain an acid, as appears from the regeneration of vitriolic acid after the calcination of Vitriol, and from the rusting of steel filings in a moist air; p. 10. A component part of the acid of nitre, is derived from the air, which evidently contains something necessary to the support of flame. But this aereal pabulum of flame, is not air itself, for air remains when the confined taper is extinguished: nor is it as vulgarly supposed, the salt called nitre, p. 12. But that these fire-air particles exist also in nitre is evident, since this salt will support the combustion of sulphur in vacuo. Fill a tube with gunpowder slightly moistened, and it will burn out in vacuo, or with its mouth inverted over water. Hence the aereal part of nitre, is the same with the fire-air particles of the atmosphere, and is one component part of the acid spirit of nitre: the other being (like the fixed part) obtained from the earth, p. 17. 18. The fiery particles thus common to nitre and to the air, he denominates nitro-aereal. It is these that give causticity to spirit of nitre, and occasion the red fumes observed in distilling it, p. 18. They do not take fire of themselves in nitre, because they are inveloped with moisture; but when combined with salt of tartar, and thrown on the fire in a dry state they inflame, p. 20.

Chap. 3d. Of the nature of the nitro-aereal and fiery spirit. Fire he conceives to consist of these nitro-aereal particles set in violent motion by means of sulphureous bodies, in the cases of culinary fire: but by some other means, in the cases of the solar rays collected by a burning glass, and of the celestial fires. The corrosive and caustic nature both of fire and nitrous acid, seems to argue that it proceeds in both from the nitro-aereal particles they contain, 22-24. That fire is not of a sulphureous nature is evident, for nitre will not take fire in an ignited crucible; but oil thrown in, takes fire immediately. So if a piece of metal be held over a candle, the fire particles pass through the metal, but the sulphureous smoke adheres to the under side. p. 27.

That the heat occasioned by a burning glass, consists of these nitro-aereal particles is evident, for diaphoretic antimony may be made, either first by calcination with a lens, or secondly, by the repeated affusion of nitrous acid, or thirdly, by the deflagration of nitre on the antimony. Diaphoretic antimony made by calcination, increases on weight,[44] by means of the nitro-aereal particles fixed in it by the process. p. 28, 29.

[44] It was first observed by John Rey in 1630 that metals calcined, gain weight by the absorption of air. See an account of his book by M. Bayen Journ. de Rozier 1775 v. 1 p. 48. There are also some experiments by Boyle that shew the accession of weight on the calcination of metals, but he does not seem aware of the theory. Shaw’s Boyle, Fire and Flame weighed v. 2 p. 394, &c.

Chap. 4th. On the origin of acid liquors, and the earthy part of Spirits of nitre. From p. 34, it appears that he knew nothing of the absorption and combination of his nitro-aereal particles in the vitriolic acid, during the combustion of sulphur, but explains the whole mechanically by the saline portion of the sulphur being broken down into minute pointed particles, by the violent attrition of the nitro-aereal particles, and so becoming fluid and sharpened. He seems too, not to know that the colcothar of martial vitriol is no component part of sulphur, p. 37. The same mechanical explanation he applies to the formation of the ligneous acids, and to the impregnation of the caput mortuum or colcothar of vitriol, with fresh acid by exposure of air. In the succeeding paragraph, p. 39, he supposes that marchasite (martial pyrites) imbibes the nitro-aereal particles from the atmosphere, and thus acid is formed. In like manner he explains the formation of acids produced by fermentation, by the collision between the nitro-aereal, and the sulphureo-saline particles of the mass. p. 41. So also he supposes nitrous acid to be produced by the detention of his nitro-aereal particles by the terrene saline particles found in the earth, p. 43. Hence he concludes generally, p. 43, that acid salts are formed from a saline basis brought into fusion or fluidity by the nitro-aereal part of the air: and sums up his theory of nitre, by stating it to be a triple salt, composed of nitro-aereal particles, united to a terrene basis forming the acid, which then unites to the fixed basis, supplied also by the earth.

Chap. 5th. On Fermentation. He gives in this chapter his theory of fermentation, as arising from the conflict of his nitro-aereal principle which he thinks may be termed mercury, and the sulphureous principle: evidently meaning by the latter, the Phlogiston of Stahl: and he states broadly, p. 60. that pure sulphur can never admit of accension, but by means of the nitro-aereal particles obtained from the atmosphere. The rest of his reasoning in this chapter, does not seem deserving of further notice.

Chap. 6th. On the nitro-aereal spirit as the cause of rigidity and elasticity. These he explains by the fixation and state of his nitro-aereal particles in bodies endowed with these properties. In p. 69 he endeavours to account why boiled water freezes sooner than that which has not been boiled; a fact which Dr. Black has made the subject of a paper in the 45th vol. of the Philosophical transactions. But his reasonings throughout this chapter are not calculated to add to his reputation, or to the mass of knowledge of the present day.

Chap. 7th. The elastic force of the Air depends on its nitro-aereal particles. In what way exhausted air is reimpregnated with them. Of the elements of Heat and Cold. This chapter contains experiments to shew that the elasticity of the air is owing to the nitro-aereal particles contained in it: which may be destroyed by the burning of a candle or other combustible substances, and also by the breathing of animals. When the atmospheric air contained in a glass jar inverted over water, will no longer support flame or animal life, the water rises in the jar, owing to the diminished elasticity of the air, not being able to counteract the pressure of the surrounding atmosphere on the water p. 100. He finds p. 101 that the diminution by burning a taper in a given quantity of the air, is about one thirtieth of the whole, and by the breathing of mice and other animals about one fourteenth. Thence he concludes p. 106 that by means of respiration the elastic part of the air enters into the blood, and that the sole use of the lungs is not as some suppose, to break down the blood in its passage into very minute particles. That combustion and respiration have similar effects on atmospherical air, he concludes, p. 108, from the fact, that a candle and a small animal inclosed together in a glass jar over water, the one will not burn, nor the other remain alive above half the time that they would if alone. Mayow however, did not consider his nitro-igneous and elastic particles to be either pure air, or even a component part of the common air, as air, notwithstanding the ambiguity of the passages in p. 114 and 118; but as particles of a different nature, attached to and fixed in the atmospheric particles; and detached (excussas) by the means above mentioned, p. 118 and 121. His explanation of elasticity generally in this chap. and of the difficulty arising from the obvious resistance to the Atmosphere, and the expansibility of the air in which a taper has been extinguished, or an animal died, seem too obscure and unintelligible to merit transcribing. It is evident however upon the whole from p. 123 compared with p. 100 and 135 that he conceived the diminution of such air to arise from diminished elasticity, but he supposes it to be denser than common air 123. In a subsequent part of this chapter p. 128 et seq. he states his theory of the manner in which deteriorated air recovers its loss, viz. that the nitro-aereal particles being lighter than the atmospherical, float abundantly in the higher regions; and that the part of the atmosphere deprived of them below, being forced upward by the pressure of the atmosphere above, obtains a renewal of these particles by mixture with the strata where they abound.

The element of fire, he supposes to reside in the body of the Sun, which is no other than a mass of nitro-aereal particles driven in perpetual gyration with immense velocity. Cold, which he considers as some thing positive (p. 130) he thinks consists in these particles assuming a pointed form, and moving not in gyration but strait forward. Much of his reasoning indeed throughout the book, savours greatly of the mechanical and corpuscular philosophy prevalent in his day.

Chap. 8th. On the nitro-aereal spirit as inspired by animals. Formerly he thought that in respiration the nitro-aereal particles were rubbed or shaken off (atterere, excutere 146) from the common air by the action of the lungs, at present he thinks the air itself enters the mass of the blood, is there deprived of these particles, and of part of its elasticity. To prove this he produces an experiment of the diminution of air by the vapours from iron dissolved in nitrous acid: but the beautiful deductions of Dr. Priestley from a similar experiment, never occurred to him; on the contrary he expressly states that it is an Aura, but not Air p. 145 and though afterward in chap. 9 p. 163, 164 he inclines to doubt, yet again in p. 168 he denies it that character.

In p. 146 he proceeds to state the uses of these nitro-aereal particles, which (147) he considers as the principle of life and motion both in animals and vegetables. By the mutual action of the nitro-aereal, with the sulphureo-saline particles contained in the blood, a fermentation is excited necessary to animal life, and to the warm fluid circulation of the blood (ad sanguinis æstum.) To these particles imbibed from the air, he attributes the difference in colour between the venous and arterial blood; and he shews this, from the numerous air bubbles arising in an exhausted receiver from warm arterial blood: but his experiment to illustrate the difference, from the colour produced by the nitrous acid with vol. alk. seems very little to the purpose p. 150.

To the fermentation arising from this mixture of nitro-aereal particles with the blood, he ascribes animal heat, and accounts satisfactorily for the increased heat of the body during strong exercise, from the more frequent inspirations occasioned by the exertion (p. 152, 306:) but his replies to the objections of Dr. Willis, drawn from the phenomena of fermenting mixtures, are very inconclusive.

Chap. 9th. Whether air can be generated anew. He repeats the experiment of dissolving iron in dilute nitrous acid, and finds that though some of the vapour be absorbed, a portion still remains uncondensible even by severe cold. On substituting dilute vitr. for nitr. acid he finds an aura which is hardly absorbed or condensed at all. Hence he doubts whether these auræ be not entitled to the appellation of air, especially as by subsequent experiment he shews that they are equally expansible with common air. In making this last experiment he exhibits the method of transferring air from one vessel to another (Tab. 5. Fig. 5.) much in the manner afterwards described by Mr. Cavendish in 1766.[45] From the inability of these auræ to support animal life (Tab. 5. Fig. 6.) he concludes finally that they are not air, though not very dissimilar p. 171. The succeeding five chapters do not seem to contain any facts or conjectures that can add to Mayow’s reputation. His Hypotheses are completely superceded by the more accurate knowledge of the present day. In his tract on quick lime p. 225 he seems to have forestalled the acidum pingue of Dr. Meyer published exactly a century afterward. It may be noted that in his treatise on the Bath waters p. 259, he describes fishes as collecting vital air from the water, and respiring like land animals. (Aereum aliquod vitale ab aquà, veluti aliàs ab aurà secretum et in cruoris massam trajiciatur.) The air bladder he considers rather as a reservoir of air to be inspired, than a receptacle for excreted air; though the latter opinion is made probable by Dr. Priestley.[46]

[45] Boyle had invented an apparatus for transferring air from one receiver of an air-pump to another, but not under water.

[46] See Nich. Journ. v. 3 p. 119 on the probability of fishes separating oxygen from the water they inhabit.

The first part of his Treatises on Respiration is chiefly anatomical. In p. 300 et seq. he states more fully his opinion, that vital air, is of a nitro-saline nature: that it is the principle of life, both in Animals and Vegetables: that combined with the sulphureo-saline particles in the blood, it is the stimulus to the muscular fibre, and of course to the heart as a muscle, p. 305; but that the fermentation occasioned by the introduction of these particles into the blood, is not confined to the left ventricle of the heart, but commences, in the passage of the blood through the lungs, and continues in the Arteries. This evidently approaches the theory, advanced by Dr. Goodwyn in his tract on the Connection of life with respiration about sixteen years ago, viz. that the pure air combined with the blood is the stimulus to the left ventricle of the heart, and produces the alternate contraction, and dilation on which the circulation depends. Dr. Lower, in his treatise de motu sanguinis, and Fracassati, and Dr. Frederick Slare attributed the change of the colour of venous blood into a florid red, to the combination of the air with it. Lower I believe preceded Mayow, who quotes him, p. 148; the date of Fracassati’s and Dr. Slare’s’ observations I have not been able to ascertain, but they must have been near the time of Mayow. Lowth. Ab. v. iii. p. 237.

In his third treatise on respiration, he explains the Animal œconomy of the fœtus in utero, by suggesting that the fœtus is supplied by the placenta, not with venous, but with arterial blood brought by the umbilical Arteries; so that the required stimulus of the nitro-aereal particles being thus conveyed, supercedes the necessity of the lungs for the purpose. This he ingeniously illustrates by the known experiment, that a dog into whom arterial blood is infused, though respiring with great difficulty before, hardly respires at all. A similar theory he applies to the life of the chick in ovo. This treatise seems to have suggested Dr. Beddoes’s illustration of his theory of consumption from the state of pregnancy.

In a subsequent Essay on animal spirits, he conceives them to be, if not the same with the nitro-aereal part of the atmosphere, yet to consist of this, so far as they are necessary to the production of muscular motion, which he attributes entirely as before to nitro-aereal particles, p. 24 and 40, of chap. 4, on the animal spirits.

I do not observe any thing else in Mayow’s book worth noting on the present occasion; or sufficiently connected with pneumatic Chemistry.

From the analysis thus given of[47] what Mayow has advanced, it appears, that he clearly comprehended the atmosphere to consist of a mixture of two parts, the one the efficient cause of life and of combustion, the other not of itself necessary to either.

[47] At the time this was written neither Dr. Bostock’s treatise on respiration or the books therein quoted p. 200 had arrived here. Nor have I had an opportunity of consulting the references there made to Prof. Robinson, Dr. Thompson, Dr. Yeates, or Fourcroy’s account of Mayow.

That the vital part of the air, was also a constituent part of nitre, the effects of both being in essential particulars the same.[48]

That the vital part of the atmosphere entering the blood through the vessels in the lungs, is conveyed to the left ventricle of the heart, and becomes the stimulus to the contractions of that muscle, and is equally essential to the whole system of muscular contraction.

[48] Mr. Ray wrote “A dissertation (in 1696) about respiration,” in which he supposes the air to pass from the bronchia and lungs into the substance of the blood, and there (pabuli instar) it foments and maintains the vital flame which he supposes to be in the sulphureous parts of the blood, as the air foments the common flame of a candle, and that the nitre has nothing to do with it. See Durham’s collection of Ray’s letters.

That the vital part of the atmosphere thus combined with the blood becomes also the source of animal heat.

That this vital part is equally necessary to the fœtus in utero as to the adult, and that the use of the lungs in the former case is superceded by the functions of the umbilical artery and placenta; by means of which, blood already impregnated with the vital air, is conveyed to the fœtus.

That the respiration of fishes, is dependant on the particles of air mixed with watery element they inhabited.

That heat, flame, and combustion, depend on two universal principles, and the gentleness or violence of their mutual conflict: the one being a principle of inflammability universally diffused in combustible bodies, and the other the vital or igneous part of the atmosphere.

These propositions evidently touch upon the most brilliant of the pneumatic discoveries of the authors already quoted; and not a little extraordinary it is, that they should have remained so long unknown, unnoticed, and not understood.

The sulphur of Mayow is decidedly the Phlogiston of Stahl; the fire air of the former is the fire air of Scheele, the dephlogisticated air of Priestley, and the Oxygen of Lavoisier.

The combination of oxygen with the blood by means of respiration, first discovered as was thought by Lavoisier, is clearly stated by Mayow; who has also forestalled the elaborate theories of Crawford on animal heat, of Goodwyn, on muscular stimulus, and of Beddoes on the succedaneum for respiration in the fœtus.

Boyle, though he must certainly have known of Mayow, neither quotes him, nor uses, or improves on his experiments; though as I have already remarked, he seems to have had notions of the atmosphere much like those adopted by Mayow. Whether this neglect arose from the pride of birth, or the pride of knowledge, or the pride of age, (for Boyle was almost twice the age of Mayow) or from jealousy of Mayow’s abilities, cannot now be ascertained. From that time until Hales published his statics in 1726, pneumatic experiments were neglected, and the mathematical philosophy which Newton’s discoveries rendered fashionable, absorbed for many years the attention of men of Science, particularly in England. The way in which Lemery, Hales and Brownrigg speak of Mayow, evidently shews that his theories were not understood, nor his merits appreciated.

That Mayow was unknown to Black and Cavendish until of late years, is highly probable at least, if not absolutely certain. Neither these philosophers, nor Dr. Priestley, could have passed over Mayow’s book, without being struck with his ideas, and publicly referring to them in their chemical works.

That Dr. Priestley was unacquainted with Mayow is certain, from the limited extent of his reading at the early period of his experiments (from 1770 to 1776 or 1777,) in books of chemistry and theoretic physiology: from Mayow, not being quoted by any of the writers whose works Dr. Priestley would be likely to consult except Hales and Brownrigg, and not by them in a manner to induce any farther curiosity: from their being unnoticed by Black, Cavendish, Sir John Pringle, and Lavoisier, in particular: from the custom that Dr. Priestley had of acknowledging the sources of his ideas in all cases where they originated from the discoveries of others, as in his references to Hales, Brownrigg, Cavendish, &c; and from his making no mention of Mayow in his express account of the labours of his predecessors on the subject of animal respiration. That both he and Sir John Pringle before the Royal Society in 1772 and 1776 should expressly treat the history of discoveries in which Mayow bore so distinguished a part, and omit noticing him altogether, had they known of his works, is incredible. It is evident that he was then an obscure writer, and not in repute, or he would have occurred to them; or some of their philosophical friends would have suggested the propriety of referring to his publications.

Neither is it likely that Scheele would have been acquainted with Mayow’s writings, though it is singular that he escaped the notice of Lavoisier who I believe was employed under government in the collection of essays on the theory and manufacture of saltpetre and in the superintendance of the saltpetre works, especially as Mayow was mentioned though disrespectfully by Lemery, in his paper on nitre before referred to. But there certainly is no evidence that Lavoisier obtained his ideas of oxygen and its combination with the blood from Mayow, or his theory of metallic calcination from Jean Rey, though his obligations to Dr. Priestley have not been always acknowledged with the candour and liberality that men of science would expect from Lavoisier.

Mayow had more than ordinary discernment in comparing known facts, and drawing conclusions from them, but he does not appear to have had the talent of imagining decisive experiments, of varying them, of observing and noting all the natural phenomena attendant upon them, or sufficient industry in pursuing them. It is one thing to make a plausible conjecture, and another to verify it. Those alone are entitled to the honour of discoveries who not merely start the theory, but take the pains of pursuing it by experiments and resting it on the basis of well conceived and accurately ascertained facts, sufficiently numerous and varied to obviate the most prominent objections. Mayow has reasoned with great acuteness and conjectured with singular felicity, but he added little to the mass of philosophical KNOWLEDGE in his day. He composed and decomposed nitre and ascertained the existence of vital air in this substance as well as in the atmosphere, but he did not collect, exhibit, and examine it. He knew how to make artificial air from nitrous acid and iron, but all the extraordinary properties of this gas, remained unobserved by him as well as by others until collected and imprisoned by Dr. Priestley, and exposed to the question under his scrutinizing eye. Indeed as an experimentalist Dr. Priestley stands unrivalled. The multiplicity of his experiments, their ingenuity, their bearings upon the point in question, their general importance, and their fidelity, were never equalled upon the whole, before or since. Nor is it any detraction from their merit with those who are accustomed to experiment, that they hold out no pretensions to that suspicious accuracy, which has too often depended more upon arithmetical calculations than upon actual weight and measure. The many kinds of aeriform fluids discovered by Dr. Priestley, the many methods of procuring them, the skilfull investigation of their properties, the foundation he laid for the labours of others, the simplicity, the novelty, the neatness, and the cheapness of his apparatus, and his unequalled industry, have deservedly placed him at the head of pneumatic Chemistry. Nor should it be forgotten that while he thus outstripped his predecessors and contemporaries in the field of experiment, it formed not as with them the business of his life, but (among other branches of literature and philosophy successfully cultivated) the occupation of his leisure hours, the relaxation from what he deemed more important, more laborious, and more obligatory pursuits.

Before his time (excluding Mayow) Boyle had discovered that air might be generated, fatal to animal life. It was known that common air would only serve a certain time for the purposes of combustion and respiration. The mephitic exhalations from natural Grottoes had been remarked. Inflammable air both natural and artificial had been exhibited before the royal society. Hales had ascertained the presence of air in a great number of substances where it was not commonly suspected though he had not the skill to examine the properties of the air produced. Black had ascertained the presence of fixed air in limestone, and Brownrigg, Lane, and Venel had illustrated the theory of mineral waters. But it was the paper of Cavendish in 1766 on fixed and inflammable air produced from various substances by means of acids, fermentation and putrefaction, that first introduced a stile of experimenting in pneumatic chemistry, more neat, more precise, and scientific than had hitherto been known.

The attention of Dr. Priestley, however to these subjects was not originally excited by the works of his predecessors, but by the accident of his proximity to a brew-house at Leeds, where of course fixed air (a subject that had attracted much attention about that time) would be produced in a large way. It was thus that one experiment led to another, until the fruits of his amusements were the discoveries on which his philosophical reputation is principally founded. It is no more than justice to his character to mention in this place, that of all men living he was the freest from literary deception and the vanity of authorship. He never claims the merit of profound investigation or great foresight, for discoveries that might easily have been so stated as if they had been the pure result of those qualifications, but which were in reality the offspring of accident and circumstance. He excites others to patient labour in the field of experiment, from observing that success does not depend so much on great abilities or extensive knowledge, as on patient attention, and perseverance; and that much of his own reputation was owing to the discovery of facts that arose in the course of his pursuits, the result of no previous theory, unlooked for and unexpected. In v. 3 p. 282 of his experiments on air he says “Few persons I believe have met with so much unexpected good success as myself in the course of my philosophical pursuits. My narrative will shew that the first hints at least of almost every thing that I have discovered of much importance have occurred to me in this manner. In looking for one thing I have general found another, and sometimes a thing of much more value than that which I was in quest of. But none of these unexpected discoveries appear to me to have been so extraordinary as that I am about to relate (viz. the spontaneous emission of dephlogisticated air from water containing a green vegetating matter) and it may serve to admonish all persons who are engaged in similar pursuits, not to overlook any circumstance relating to an experiment, but to keep their eyes open to every new appearance and to give due attention to it however inconsiderable it may seem.”[49] To this candour of disposition, and the readiness with which he acknowledged his mistakes and his oversights, even those who opposed his opinions bear honourable testimony. “The celebrated Priestley himself (says M. Berthollet in his reply to Kirwan on Phlogiston p. 124 of the Eng. translation) often sets us the example, by rectifying the results of some of his numerous experiments.”

[49] See also the 1st, vol. of his early edition of experiments on air p. 29.

Numerous indeed those experiments were as well as important: far too numerous to be particularised here; though it may not be improper to call to the recollection of the reader some of the more interesting facts which we owe to Dr. Priestley, and the times of their discovery and communication.

The first of his publications on pneumatic chemistry was in 1772, announcing the method of impregnating water with fixed air, and on the preparation and medicinal uses of artificial mineral waters; a discovery that domesticated much of the knowledge that had heretofore been disclosed only in the works of learned societies; and that beautifully exemplified how much of the health and the pleasure of common life, might depend on the ingenious researches of men of science. Though this was the first publication of Dr. Priestley on the chemistry of the airs, he had certainly commenced his experiments in this branch of Science, soon after his arrival at Leeds, and as early at least, as 1768. In the year 1771 he had already procured good air from saltpetre; he had ascertained the use of agitation, and of vegitation as the means employed by nature in purifying the atmosphere destined to the support of animal life, and that air vitiated by animal respiration was a pabulum to vegetable life; he had procured factitious air in a much greater variety of ways than had been known before, and he had been in the habit of substituting quicksilver in lieu of water, for the purpose of many of his experiments. In his paper before the Royal Society, in the spring of 1772, which deservedly obtained him the honour of the Copley Medal, he gives an account of these discoveries. In the same paper he announces the discovery of that singular fluid nitrous air,[50] and its beautiful application as a test of the purity or fitness for respiration of airs generally. In the same paper he shews the use of a burning lens in pneumatic experiments, he relates the discovery and properties of marine acid air; he adds much to the little of what had been heretofore known of the airs generated by putrefactive processes, and by vegetable fermentations, and he determines many facts relating to the diminution and deterioration of air, by the combustion of Charcoal, and the calcination of metals.

[50] Honestly referring to Dr. Hales and Mr. Cavendish for any idea that might have remotely led to this discovery (See Obs. on air 1st ed. v. 1 p. 108) the discovery however was completely his own.

Dr. Priestley seems always to have thought nitrous air as convenient a substance for eudiometrical experiments as any of the later substitutes, viz. the liquid sulphurets and the combustion of phosphorus. The foundation of Mr. Davy’s substitute, muriat or sulphat of iron saturated with nitrous air, was as Mr. Davy acknowledges first discovered by Dr. Priestley himself. See Nich. Journ. for Jan. 1802 p. 41. The different states of the solutions of iron in vitriolic acid have been ingeniously applied to the analysis of mixed gasses by Humboldt and Vauquelin.

Soon after this, in confirmation of Sir John Pringle’s theory of intermittents and low fevers being generally owing to moist miasma when people are exposed to its influence, he ascertained by means of his nitrous test that the air of marshes was inferior in purity to the common air of the atmosphere.[51]

He had obtained very good air from saltpetre in 1771, but his full discovery of dephlogisticated air, seems not to have been made until June or July, 1774,[52] when he procured it from precipitate per se, and from red lead. This was publicly mentioned by him at the table of Mr. and Madame Lavoisier, at Paris, in October 1774, to whom the phenomena were until then unknown. The experiments on the production of dephlogisticated air, he made before the scientific chemists at Paris about the same time, at Mr. Trudaine’s. This hitherto secret source of animal life and animal heat, of which Mayow had but a faint and conjectural glimpse, was certainly first exhibited by Dr. Priestley, and about the same time, (unknown to each other) by Mr. Scheele of Sweden. For the honour of science, it were much to be wished that the pretensions of Mr. Lavoisier were equally well founded. He has done sufficient and been praised sufficiently for what he has done, to satisfy a mind the most avaricious of fame; he is deservedly placed in the first rank among the philosophers of his day, and he ought not to have thrown a shade over his well earned reputation, by claiming for himself the honour of those discoveries which he had learned from another.

[51] Phil. trans. v. 54 p. 92.

[52] See Doctrine of Phlog. established p. 119.

From this brief account of the first stage of Dr. Priestley’s chemical labours, it appears that during the short period of two years, he announced to the world more facts of real importance, and extensive application, and more enlarged and extensive views of the œconomy of nature, than all his predecessors in pneumatic Chemistry had made known before.

In 1776 his observations on respiration were read before the Royal Society; in which he clearly discovered that the common air inspired, was diminished in quantity, and deteriorated in quality, by the action of the blood on it through the blood vessels of the lungs; and that the florid red colour of arterial blood, was communicated by the contact of air through the containing vessels. His experiments on the change of colour in blood confined in a bladder, took away all doubt of the probability of this mode of action. I cannot help thinking that the circumstance of Dr. Priestley’s mind being so much occupied with the prevailing theory of Phlogiston, was the reason why he did not observe that the diminution of the air, and the florid colour of the arterial blood was owing to the absorption of the pure part of the atmosphere, rather than to any thing emitted from the blood itself. This part of the theory of respiration Mr. Lavoisier has certainly established; though it is by no means ascertained as yet whether the vital part of the atmosphere inspired, is wholly and alone absorbed, or whether in reality something is not contributed in the lungs to the formation of the fixed air found after expiration.[53]

[53] That azote is absorbed during respiration as Dr. Priestley supposed contrary to Mr. Lavoisier’s opinion, is made extremely probable by the experiments of Mr. Davy, whose accuracy is well known. Researches, p. 434. The formation of water in this process, is certainly no more than conjecture as yet. Dr. Bostock has lately published a very useful and laborious history of discoveries relating to respiration, both anatomical and pneumatical.

In 1778 Dr. Priestley pursued his experiments on the property of vegetables growing in the light to correct impure air, and the use of vegetation in this part of the œconomy of nature. A discovery which was announced to several men of science in England previous to the publication of the same ideas by Dr. Ingenhouz.[54] Indeed from its having been communicated to M. Magellan whose pleasure and whose occupation it was, to give information of new facts to his philosophical correspondents, and of this in particular to Dr. Ingenhouz then engaged in similar researches, there is hardly a doubt but the latter knew of the experiments then pending on the subject by Dr. Priestley.

[54] Doctrine of Phlogiston established, p. 107, et. seq. The theory of the amelioration of impure air by the absorption and excretion of vegetables growing in the light, has been doubted by Dr. Darwin in his Phytologia, and opposed by Count Rumford in a paper published in the transactions of the Royal Society, for 1787: also by Dr. Woodhouse of Philadelphia, Nicholson’s Journal, for July 1802, and by Mr. Robert Harrup, Nicholson’s Journal, for July 1803.

It is painful to notice these aberrations from propriety in the conduct of men highly respectable in the philosophical world, arising from an over anxious avarice of literary fame, and an improper jealousy of the reputation of another. Not that it derogates from the character of a philosopher to wish for the applause of those who know how to appreciate his merit, or who are benefited by his exertions; such an anxiety is laudable when it does not lead to encroachments on the literary rights of others; nor is it at all desireable under the present circumstances of human nature, to expect from men of science an attention to their pursuits arising from motives of pure benevolence alone, and excluding all views, hopes, and expectations of the gratifying tribute of public approbation. I believe no man ever laboured with a more single eye to public utility than Dr. Priestley. But consideration in society, and the respectability attendant upon great talents, and great industry, successfully employed for the benefit of mankind, is a motive to useful exertion so universal, so honest, so laudable, and withal so powerful, that it is the common interest, as well as the duty of society, to bestow it liberally where it has been earned faithfully, and to concede it to those only, who have really deserved this honourable reward.

From this period Dr. Priestley seems to have attended to his pneumatic experiments as an occupation; devoting to them a regular portion of his time. To this attention, among a prodigious variety of facts tending to shew the various substances from which the gasses may be procured; the methods of producing them; their influence on each other, and their probable composition, we owe the discovery of vitriolic acid air, of fluor acid air, of vegetable acid air, of alkaline air, and of dephlogisticated nitrous air, or gazeous oxide of azote as it has been called, the subject of so many curious experiments by Mr. Davy. To these we may add the production of the various kinds of inflammable air by numerous processes that had escaped the observation of Mr. Cavendish; in particular the formation of it by the electric spark taken in oils, in spirits of wine and in alkaline air; the method of procuring it by passing steam through hot iron filings, and the phenomena of that hitherto undetermined substance the finery cinder, and its alliance to steel. To Dr. Priestley we owe the very fine experiment of reviving metallic calces in inflammable air and its absorption in toto, apparently at least, undecomposed. He first ascertained the necessity of water to the formation of the gasses, and the endless production of air from water itself.

Dr. Priestley’s experiments on this subject, to wit: the generation of air from water, opened a new field for reflection, and deserves more minute notice. No theory has yet been proposed adequate to the explanation of the facts. He had before remarked that water was necessary to the generation of every species of air, but the unceasing product of air from water had never been before observed.

In his first set of experiments he procured air, by converting the whole of a quantity of water into steam: then, to obviate the objection to the water having imbibed air from the atmosphere he put the water on mercury in long glass tubes immersed in mercury: in a third process he used no heat, but merely took off the pressure of the atmosphere. In all these cases a bubble of air was extricated from the water, which being separated by inclining the tube, another bubble was again produced on each repetition of the experiment. That this could not be air imbibed from the atmosphere appeared from this, that though the first portions were generally purer than atmospheric air, the next became less pure, and at length wholly phlogisticated.

It did not appear that the addition of acids, enabled the water to yield more air, nor did he succeed in attempting to convert the whole of a given quantity of water into air, although exposing the water confined over mercury to heat, and separating the air produced, it still continued to produce more air for twenty or thirty repetitions of the experiments. When a certain proportion of air was thus produced at any one time, no continuance of the experiment would encrease the quantity until it was separated. Hence he concludes that the longest continuance of water in the state of vapour would not convert it into air. The water used was pure distilled water previously boiled to separate any adventitious air that might have been imbibed from the atmosphere. The precautions he used, and the replies to such objections as he foresaw the experiment would be liable to, are detailed in the papers he published on the subject, to wit, a separate pamphlet published in England in 1793, and a communication in the Am. Ph. trans, v. IV. p. 11-20.

In the last mentioned paper, he proceeds also to give an account of some experiments on the property of water to imbibe different kinds of air, and the conversion of sp. of wine, into inflammable air.

This paper inserted in the American transactions, was read before that society in Feb. 1796. In Ap. 1800 another paper was read before the same society on the production of air by the freezing of water Am. Ph. trans. v. V. p. 36. In this paper he recapitulates the general result of his former experiments on the generation of air from water, namely “that after all air had been extracted from any quantity of water by heat or by taking off the pressure of the atmosphere, whenever any portion of it was converted into vapour, a bubble of permanent air was formed, and this was always phlogisticated. The process with the Torricellian vacuum (he says) I continued for some years and found the production of air equable to the last. The necessary inference from this experiment is, that water is convertible into phlogisticated air, or that it contains more of this air intimately combined with it than can be extricated from these processes in any reasonable time.”

He proceeds to state his imperfect attempts to procure air from water by freezing, until he procured cylindrical iron vessels seven or eight inches high and near three inches wide at the bottom, the upper orifice closed with a cork and cement, in the centre of which was a glass tube about one fifteenth of an inch in diameter. In this apparatus the water in the iron vessel was frozen by means of snow and salt, the vessel being immersed in mercury, and the water contained over the mercury. The quantity of water was about three ounces. The experiment was repeated nine times without changing the water, and the last portion of air procured in this manner was as great as any of the preceding; so that there remained no reasonable doubt but that air might be produced from the same water in this manner ad libitum. Having obtained near two inches of air in the glass tube, Dr. Priestley put an end to the experiment, and examining the air found it wholly phlogisticated, not being affected by nitrous air, and having nothing inflammable in it.

The inference drawn by the Doctor from those experiments is, that water when reduced by any means into the state of vapour, is in part converted into phlogisticated air; and this is one of the methods provided by nature for keeping up the equilibrium of the atmosphere, as the influence of light on growing vegetables is the means of recruiting the other part; both of them being subject to absorption and diminution in several natural processes. And he thinks that they strengthen also the opinion, that water is the basis of every kind of air, instead of being itself a compound of hydrogen and oxygen according to the new theory. At all events the experiments themselves must be considered as extremely curious, as well as new.

The water and the salt thus made use of gave rise to another experiment of the most important nature to the present theory of chemistry, if it should on future repetition be ultimately verified. This experiment related by Dr. Priestley in a letter to Dr. Wiston is in substance as follows. Having repeatedly used as above mentioned a freezing mixture of common salt and snow, the experiment being finished, he evaporated the snow water in an iron vessel and recovered the salt. The salt thus recovered contained some calx of iron. He put it by in a bottle and labelled it, according to his usual practice. In October 1803, he wanted to procure some marine acid, and took the salt thus procured by evaporating the snow water, for the purpose. On commencing the distillation, he was surprized to find the receiver full of the characteristic red fumes of the nitrous acid. The vitriolic acid used for the purpose was diluted with about an equal quantity of water. On finishing the process, he took some of the acid in the receiver, and dissolved copper in it, and thus procured good nitrous air. He was himself perfectly persuaded that no nitre had been used in the freezing mixture, nor had any by accident or design been mixed with the salt. He was not unacquainted with the common mode of clearing black oil of vitriol by the addition of nitre. So that no means of accounting for this curious fact remained, but the snow or the iron: he seemed to think that should this experiment be fully verified hereafter, it would confirm the vulgar hypothesis of snow containing nitre, and account for the fertilizing quality usually attributed to snow. He had no opportunity in that winter of repeating the experiment as he died in about three months after, and his previous illness had compelled him to forsake his laboratory.

Of the almost discarded theory of Phlogiston Dr. Priestley to his death remained the strenuous advocate, and almost the sole supporter; ipse Agmen. Beautiful and elegant as the simplicity of the new doctrine appears, many facts yet remain to be explained, to which the old system will apply, and the French theory is inadequate. These are collected with an ingenuity of arrangement, and a force of reasoning in the last pamphlet published by the Doctor on the subject,[55] which no man as yet unprejudiced can peruse, without hesitating on the truth of the fashionable theory of the day.

[55] The doctrine of phlogiston established 1803.

Certainly, it has not yet been sufficiently explained on the new theory, what becomes of the Oxygen from the decomposed water in the solution of metals in acids; nor why inflammable air is produced when one metal in solution is precipitated by another; nor why dephlogisticated air is hardly to be procured from finery cinder, if at all; nor why this substance so abounding in oxygen according to the new theory, will not oxygenate the muriatic acid; nor why it should answer all the purposes of water in the production of inflammable air from charcoal; nor why water in abundance should be produced when finery cinder is heated in inflammable air, and none when red precipitate is exposed to the same process; nor what becomes of the oxygen of the decomposed water when steam is sent over red hot Zinc, and inflammable air is produced without any addition in weight to the Zinc employed; nor why there should be a copious production of inflammable air when hot filings of Zinc are added to hot mercury in a hot retort and exposed to a common furnace heat, which I believe is an unreported experiment of Mr. Kirwan’s; nor why sulphur and phosphorus are formed by heating their acids in inflammable air without our being able to detect the oxygen which on the new theory ought to be separated, nor why water should be produced by the combustion of inflammable air with,47 of oxygen, and nitrous acid when,51 of oxygen is employed, for this experiment can now no more be doubted than explained; nor why on the new doctrine the addition of phlogisticated air, should make no alteration in the quantity of acid thus obtained; nor why red hot charcoal slowly supplied with steam, should furnish inflammable air only and not fixed or carbonic acid air; nor why nothing but pure fixed air should be produced by heating the carbonated Barytes in the same way; nor why fixed air should be formed under circumstances when it cannot be pretended that Carbon is present, as when gold, silver, platina, copper, lead, tin and bismuth are heated by a lens in common air over lime water; or why the grey and yellow calces of lead should furnish carbonic acid and azote, and no oxygen; nor why the residuum of red lead when all its oxygen is driven off by heat should be either massicot or glass of lead according to the degree of heat, and not lead in its metalline state; nor why plumbago with steam should yield inflammable and not fixed air; nor why minium and precipitate per se heated in inflammable air should produce fixed air; nor why on the evaporation of a diamond in oxygen, the fixed air produced should far exceed the weight of the diamond employed, if some of the oxygen had not entered into the composition of the carbonic acid so formed; nor why there should be a constant residuum of phlogisticated air (or azote) after the firing of dephlogisticated and inflammable airs, if it be not formed in the process; nor why phlogisticated air if a simple substance, should be so evidently formed in the various processes enumerated by Dr. Priestley in the 13th section of the pamphlet of which I have made the foregoing abstract? whether the doctrine of phlogiston is still to be used as the key to the gate of chemical theory, or whether it be properly thrown aside for the elegant substitute of the French chemists, can hardly be ascertained, until the preceding difficulties are cleared up on the new doctrine, for on the old theory they are sufficiently explicable. The summary of arguments in favour of Phlogiston, published by Dr. Priestley, in 1803, are evidently too important, and too difficult of reply, to be slighted by those who adopt the opposite opinions. Non nostri est tantas componere lites. Should the old theory ultimately fall, it maybe fairly said of its respectable supporter, si Pergama dextra defendi potuit, etiam hac defensa fuisset.

This was almost the last of Dr. Priestley’s chemical publications,[56] through all which, his characteristic talent as an author has been eminently preserved, that of not only adding greatly to the existing stock of knowledge, but exciting others to exertion and reflection in the same line of pursuit. Nor can I help thinking that much of the labours of the French philosophers in this department of science would never have been undertaken, if they had not been called forth by the previous discoveries, not of Lemery, Margraaf, Bayen, Macquer, and Beaumè, but of Hales, Black, and Macbride; of Cavendish and Priestley and Scheele.[57] Would to God there were no other object of contest between the rival nations of Great Britain and France, but which should add most to the sum of human knowledge, and contribute most to the means of human happiness.

[56] To the end of this Appendix will be subjoined a list of the scattered papers on Philosophical subjects which Dr. Priestley published in periodical collections, besides those which are inserted in the Philosophical transactions.

[57] I do not mean to deny the tribute of praise to Marriotte and Venel, any more than to Brownrigg and Lane, and it is certain that Lavoisier was engaged in pneumatic experiments, previous to 1774.

It is impossible to conclude the preceding account better than by the following extract of a letter to Mr. Lindsey from a man[58] well able to appreciate the labours of Dr. Priestley; and the late testimony in favour of his discernment by Dr. Bostock. “To enumerate Dr. Priestley’s discoveries, would in fact be to enter into a detail of most of those that have been made within the last 15 years. How many invisible fluids whose existence evaded the sagacity of foregoing ages has he made known to us? The very air we breathe, he has taught us to analyze, to examine, to improve: a substance so little known, that even the precise effect of respiration was an enigma until he explained it. He first made known to us the proper food of vegetables, and in what the difference between these and animal substances consisted. To him Pharmacy is indebted for the method of making artificial mineral waters, as well as for a shorter method of preparing other medicines; metallurgy for more powerful and cheap solvents; and chemistry for such a variety of discoveries as it would be tedious to recite: discoveries which have new modelled that science, and drawn to it and to this country, the attention of all Europe. It is certain that since the year 1773, the eye and regards of all the learned bodies in Europe have been directed to this country by his means. In every philosophical treatise, his name is to be found, and in almost every page. They all own that most of their discoveries are due either to the repetition of his discoveries, or to the hints scattered through his works.”[59]

[58] Richard Kirwan, Esqr.

[59] Vindiciæ Priestlianæ, p. 68.

“This is not the only instance” (says Dr. Bostock,[60] speaking of Mr. Jurin’s opinion that azote was generated, instead of being absorbed, in the process of respiration as Dr. Priestley, and after him Mr. Davy had supposed,) “in which, after the conclusions of Dr. Priestley have been controverted by his contemporaries, a more accurate investigation of the question, has ultimately decided in his favour. The complicated apparatus, and imposing air of minuteness which characterize the operations of the French chemists, irresistibly engage the assent of the reader, and scarcely permit him to examine the stability of the foundation upon which the structure is erected. The simplicity of the processes employed by Dr. Priestley, the apparent ease with which his experiments were performed, and the unaffected conversational stile in which they are related have, on the contrary been mistaken for the effects of haste and inaccuracy. Something must also be ascribed to the theoretical language which pervades, and obscures the chemical writings of this Philosopher, in consequence of his unfortunate attachment to the doctrine of Phlogiston.”

[60] Essay on respiration, p. 208.

When the operose experiment of the French chemists on the formation of water, shall have been sufficiently repeated, and verified by other experiments to the same point, less complex, less tedious, less expensive, and easy to be repeated; when the water thus supposed to be formed is sufficiently distinguished from the water absolutely necessary to the generation of all airs, and attendant upon them[61] both in a state of mixture and combination; and when the difficulties enumerated a page or two back, as attendant on the modern theory shall be explained on the new system, as well as on that of Stahl, then, and not until then, will it be time to lament Dr. Priestley’s unfortunate attachment to the doctrine of Phlogiston.

[61] Mr. Kirwan found that common inflammable air from iron, and vitriolic-acid, contained about 2-3 of its weight of water mixed with it; which might be separated from the air by means of concentrated vitriolic-acid in a watch glass over mercury, without diminishing the quantity or altering the characteristic properties of the air thus treated.

Of Dr. Priestley’s other Scientific Works.

The other philosophical labours of Dr. Priestley consist of his history of electricity, his history of the discoveries relating to light and colour, and his popular introductions to perspective, electricity and natural philosophy.

It appears that after the publication of his history of electricity, he intended to have pursued the plan, by composing similar histories of every branch of science: a magnificent idea, and which none but a man conscious of uncommon powers could have contemplated. Few men indeed were so capable of such an undertaking as Dr. Priestley; for independant of his habits of patient and regular industry in his literary pursuits, and the wide field of his attention to scientific objects, he had a facility of perusing, abstracting, and arranging the works of others, not commonly attendant even upon equal abilities in other respects. This great undertaking of Dr. Priestley to embrace the various departments of philosophy, appears a labour sufficient for one life; and had due encouragement been afforded, this projected series of histories would in all probability have been compleated, usefully to the world, and reputably to himself. But he proposed this undertaking laborious as it was, without designing that it should occupy the whole or the principal portion of his time, but his leisure hours only; for at no period did he postpone his professional duties, or his theological studies, to any other object whatever. The life of Dr. Priestley is almost a perpetual illustration of a seeming paradox, respecting mental energy, that men of talents, uncommonly laborious, and who appear to get through more business than one person could be supposed equal to, have usually more leisure time at their disposal, than those who have little to do: so much does the habit encrease the power of exertion. Nor was any man less averse to the innocent pleasures of social enjoyment than Dr. Priestley, or better calculated as well as more inclined to contribute to the common stock of amusing, and instructive conversation. It cannot indeed be truly said of him, as Dr. Johnson[62] once related of himself, that he had never refused an invitation to dinner on account of business but once in his life, yet no man more readily found leisure for social intercourse. This arose from his habit of dividing his time into certain portions appropriated to his respective pursuits, and determining to perform a certain quantity of literary duty, within the assigned period.

[62] On that day, (Dr. Johnson said) as it was an unusual deprivation, he found himself disinclined, and unable to attend steadily to the work that led him to refuse the invitation. He walked about his library occasionally looking over first one book and then another until about four o’clock when weary of staying within he went to a tavern to dine. Dr. Johnson had for a long time a dislike to Dr. Priestley who bore two of the characters most in disrepute with Dr. Johnson, that of a whig and a dissenter. Dr. Priestley’s pursuits also consisting so largely of heterodox theology, which Dr. Johnson abominated, and experimental philosophy which he heartily despised, they had hardly a common point of union. Toward the latter part of Johnson’s life, they met; and upon the friendly terms that ought to obtain between two men, who, each in their way, deserved so well of the republic of letters.

The first edition of his history of Electricity, was in 1767: it went through another edition in 1769, and a third in 1775. It was published at a very happy time, when electricity was a favourite object of attention to many respectable men of science then living, and it contributed in a great degree to turn the public attention toward the study of these phenomena. Very much of what has been done since may be fairly attributed to the popularity given to this branch of experimental philosophy by Dr. Priestley. Nor did he confine himself to a mere narration of the labours of others; the second volume contains many new experiments of his own, and some of them form very curious and important additions to the stock of electrical knowledge.[63] The discoveries of the last thirty years, particularly including those of Galvanic Electricity, are so numerous, and so dispersed in volumes difficult to be procured, that a continuation of this history is a desideratum in the scientific world; at one time there was an expectation of seeing it from the pen of Mr. Nicholson, whose general knowledge, and industry, as well as his attention to this branch of philosophy in particular, render him peculiarly qualified for the task. But the proposals he communicated to Dr. Priestley, on the subject, were not pursued to effect.[64]

[63] Dr. Priestley among his other experiments on electricity first ascertained the conducting power of charcoal and the calcination and vitrification even of the most perfect metals by the electric spark. He seems first to have used large batteries, which M. Van Marum and his associates have carried to such extent.

The solutions of the metals, the gasses produced and the circumstances which accelerate and prevent these effects in Galvanic processes with the pile of Volta, as detailed by Dr. Priestley in his paper on this subject in Nich. Journ. for March 1802 p. 198 form very important additions to the mass of knowledge respecting the Galvanic fluid. Nor are his discoveries in pneumatic electricity, of the conversion of oils, spirit of wine and the alkaline gass into inflammable air or hydrogen of less moment.

[64] Dr. Bostock, who seems to have many requisites to qualify him as the historian of particular branches of science, has published a good attempt toward the history of Galvanism in Nicholson’s Journal.

These histories of detached branches of Science, would not only be highly useful, but they may be considered as in some measure necessary to the accurate pursuit, and advancement of science itself. They are not only useful for the purpose of shewing the discoveries that have been made, and the time of their publication, the ideas that appear to have suggested them, the persons to whom we are indebted for them, and their effect on the spirit of enquiry at the time, but they prevent a man of science from being led into mistakes, from doing what has been already done, from suggesting what has been already published, and from ignorantly claiming to himself the merit due to the labours of a predecessor. Books are now so multiplied, in languages so various, obtained with so much difficulty, and at an expence so far exceeding the usual means of scientific men, that those who like Dr. Priestley fully and faithfully execute a work of this description are real benefactors to mankind.[65]

[65] The transactions of the various academies and philosophical societies in Europe amount at least to 1000 volumes in quarto. The royal society of England in 1665 led the way to similar institutions.

The history of Electricity was composed by Dr. Priestley in one year. The three editions of the work in less than eight or nine years sufficiently shew that, in the opinion of men of science, it was well composed: otherwise the celerity of its composition, would no doubt derogate from, instead of adding to, the well earned reputation of the author; and rather tend to shew that he was too careless or too conceited to take the necessary pains and employ the necessary time to make it fit for public inspection. Every man owes to the public, that if he professes to instruct them, he should dedicate as much labour as the subject demands, or at least as much time as it is in his power to devote to it. I fully accede to the ingenious correction of the nonum prematur in Annum, suggested by the witty Dr. Byrom of Manchester; but something of the Limæ Labor, respect for the tribunal of the public demands of every man who appears before them in the character of an author. Dr. Priestley has in more instances than one, been accused of unnecessary if not of culpable rapidity in his literary compositions: but he never professed to be a fine writer; he never sought after the beauties of stile; and his common language was sufficiently neat and expressive, to communicate the facts and the arguments upon which it was employed. It is also to be remarked, that the facility of composition which he acquired from long practice, made that labour light to him, which would have been too much for a less skilful and a less experienced composer. In many instances indeed of his rapid publications, he had not to seek for arguments, but to express in his unornamented and unaffected manner, the ideas that forced themselves upon him relating to a subject previously considered and upon which he had long made up his mind.

The History of Discoveries respecting LIGHT and COLOURS published in 1772 was a more difficult task, nor did it meet with equal encouragement. Sir Isaac Newton’s important labours in this branch of science, could not be fully comprehended without a portion of mathematical knowledge not even then so common as formerly, among the philosophers of the day. Mathematical studies seem to have in themselves very little to interest, compared with other literary pursuits; although by long attention and habit, that interest may be excited and kept up. It was about this time that the popular phenomena of chemistry and electricity more decidedly took their stand in the field of science, and irresistably seized hold on the attention of the world: phenomena, highly amusing in themselves, strongly attractive from their novelty, of evident and immediate application, and that promised an incalculable harvest of honourable and useful discovery, to such as would become their votaries. Little had been done in this department of philosophy, little previous knowledge was required to comprehend all that was known, and those who were unable to read a page of Sir Isaac Newton with profit, could easily mix an acid and an alkali, or turn the wheel of an electrical apparatus.

By this time too, it had been discovered, that there were other powers in nature that must be called in to explain appearances, which the mechanical and corpuscular philosophy had endeavoured to elucidate in vain. Such were magnetism, electricity and chemistry. It began to be found out, that the science of calculation, was but an aukward handmaid to their sister branches of natural philosophy, while physiology, laughed outright at the clumsy addresses of her mathematical admirers, from Borelli to Keill.

The discoveries therefore relating to light and colours, at the time when Dr. Priestley proposed his history, being intimately associated with the study of the mathematics, and the profound investigations of Sir Isaac Newton, were out of the beat of the less laborious, but more fashionable philosophy of the day; and were not so generally interesting to the Sciolists and Amateurs. Hence the work in question, though treated in a very entertaining and popular manner, and by no means crouded with reference to Diagrams or abstruse discussions, was not popular even among that class of readers, who might reasonably be calculated on, as the purchasers of such a performance. The subscribers indeed were sufficiently numerous, and respectable, but by far the majority were defaulters in respect of payment. It did not pay the bookseller: and of course still less did it recompence Dr. Priestley in a pecuniary point of view, especially as he had gone to considerable expence with a view to the completion of his extended plan. To him indeed, though pecuniary loss was a serious evil, pecuniary profit was a consideration of small importance: his motives to literary labour seem uniformly to have arranged themselves as follows, utility, reputation, profit.

The work in question is certainly too brief, considering the importance of the subject: many parts of it, the theory of Huygens, Euler, and Franklin for instance, seem to have merited more discussion. That all the phenomena of light depend on the Sun, as the reservoir, whence all the emanations of that fluid to the various parts of the system are supplied, the lighting of a candle is alone sufficient to refute. The facts discovered to us by modern Chemistry will suggest a great many other doubts of the doctrines respecting light, which were regarded as well established when Dr. Priestley’s book was written. But it was a faithful account of the knowledge of the day, and an unprejudiced tribute to the reputation of those philosophers who had from time to time extended the boundaries of science on the subjects treated of.

Not a little has been added to the mass of facts then published, by the subsequent experiments of Dr. Priestley himself, and his fellow labourers in the Chemistry of the Gasses: and notwithstanding the experiments of Sir Isaac Newton and his predecessors, the theory of light and colours is not yet rested upon facts sufficiently numerous, and decisive to satisfy the enquiries dictated by the present state of knowledge.

But with all these disadvantages, the work has nevertheless maintained its ground, for we have no where else so systematic, and compleat, though brief an account of what had been made known to the world on this important branch of scientific inquiry. It will always remain a valuable performance; and to the author an honourable one, from the knowledge and ability required in its compilation, from the fairness of the account it gives, and the entertaining statement of facts and suggestions interspersed through the book.

It is greatly indeed to be wished, that these histories should be continued on the plan which Dr. Priestley has adopted. So that all the prominent facts should be collected in the order of their discovery, and a full view be given of the ground already gone over. Abridgments, do not answer this purpose; the theories that dictated the experiments are not detailed, their truth or their fallacy cannot be judged of, and sufficient merit is not attributed to the labours of the discoverer, or the bearings of his facts on his theory, sufficiently explained. To attain gradually to the summit of the temple of science, we must not only build on the foundations of our predecessors, but know somewhat of their intentions at the time of laying them.

The minor treatises of Dr. Priestley on electricity, perspective and natural philosophy, have this discrimination of character, that they are more calculated to allure young people to the study of those subjects than almost any of the introductions which have either preceded or succeeded. Philosophy is made, not an abstruse science, but a delightful amusement. Indeed it was the fort of Dr. Priestley to make knowledge intelligible and popular, and treat it in such a way, as to invite rather than deter, those who were inclined to enter upon these delightful pursuits. The plainness and simplicity of his syllabus, the amusing complexion of the Phenomena, by which he illustrates his doctrines, and the facility with which the one can be made, and the other comprehended, affords a very useful example to those who may have the same object hereafter in view. This was doubtless, owing to his long experience as a teacher: and his success in that capacity among his pupils, with the electrical machine, and the air pump, is full evidence of the practical utility of his plans of instruction.

Catalogue of Dr. Priestley’s smaller pamphlets and uncollected papers on philosophical subjects.

Nicholson’s Journal. new series.
V. 1 p. 181.	Reply to Mr. Cruikshank’s.
Ibid 198.	Experiments on the Pile of Volta.
V. 2 p. 233.	On the conversion of iron into steel.
V. 3 p. 52.	On air from finery cinder and charcoal.
V. 4 p. 65.	Farther reply to Mr. Cruikshank’s.
Amer. Trans.
V. 4 p. 1.	Experiments and observations relating to the analysis of atmospherical air.
V. 4 p. 11.	Farther experiments relating to the generation of air from water.
Ibid p. 382.	Appendix to the above articles.
Republished Ib. Vol. V.	p. 1. Experiments on the transmissionof acids and other liquors in the form of vapours over several substancesin a hot earthen tube.
	p. 14. Experiments on the change ofplace in different kinds of airthrough several interposing substances.
	21. Experiments relating to the absorption of air by water.
	28. Miscellaneous experiments relating to the doctrine of phlogiston.together.
	36. Experiments on the production of air by the freezing of water.
	42. Experiments on air exposed toheat in metallic tubes.
New-York Med. Repos.	Title and Date.
Vol. 1 p. 221.	Considerations on the doctrine of Phlog. and the Decomp. of water. (Pamphlet) 1796.
Ibid p. 541.	Part 2d of do. (Pamphlet 1797.)
Vol. 2 p. 48.	(Pamphlet) to Dr. Mitchell.
Ibid p. 163.	(Pamphlet) on Red Precipitate of Mercury as favourable to the doctrine of Phlogiston, July 20, 1798.
Ibid p. 263.	Experiments relating to the calces of metals communicated in a fifth letter to Dr. Mitchell. October 11, 1798. (Pamphlet.)
Ibid p. 269.	Of some experiments made with ivory black and also with diamonds. (Pamphlet) 11 October, 1798.
Ibid p. 383.	On the phlogistic theory, January 17, 1799. (Pamphlet.)
Ibid p. 388.	On the same subject. February 1, 1799.
Vol. 3 p. 116.	A reply to his antiphlogistian opponents, No. 1.
Vol. 4 p. 17.	Experiments on the production of air by the freezing of water.
Ibid p. 135.	Experiments on heating Manganese in inflammable air.
Ibid p. 247.	Some observations relating to the sense of hearing.
Vol. 5 p. 32.	Remarks on the work entitled “A brief history of epidemic and pestilential diseases,” May 4, 1801.
Ibid p. 125.	Some thoughts concerning dreams.
Ibid p. 264.	Miscellaneous observations relating to the doctrine of air, July 30, 1801.
Ibid p. 390.	A reply to Mr. Cruikshank’s observations in defence of the new system of chemistry, 5 Vol. Nicholson’s Journal p. 1, &c.
Vol. 6 p. 24.	Remarks on Mr. Cruikshank’s experiments upon finery cinder and charcoal.
Ibid p. 158.	Observations on the conversion of iron into steel.
Ibid p. 271.	Additional remarks on Mr. Cruikshank’s experiments on finery cinder and charcoal, November 15 1802.