The Last Fight for Phlogiston and the Death of Priestley
Samuel Soloveichik Yeshiva University N e w York, New York
Phlogiston was the leading idea in chemistry for almost a century. Formulated first by Becher and developed later by Stahl, it captivated the minds of the chemists of the 18th century. Not only chemists but also great men in other disciplines were spellbound by the phlogiston idea. Kant wrote in his "Critique of Pure Reason," as late as 1787, "Stahl's phlogiston theory was like a light to natural scientists (I)." The chief merit of the phlogiston theory lay in coordinating and showing the basic similarity among seeminelv - " diversified ~henomena in chemistry and physiology. Phlogiston was considered to be an element that was contained in all combustible substances and in metals and escaned on burnine: or rustina. The residues of substances remaining after phlogiston had escaped could be converted to their original form by adding phlogiston. Thus, charcoal, considered rich in phlogiston, could convert calcinated metals into their respective metallic forms. When Cavendish obtained hydrogen by the action of metals on acids, he believed it to he pure phlogiston, since the gas burned without leaving a residue, and calces treated with the gas regenerated the respective metals. Cavendish was hailed for having obtained phlogiston from the metal, but the question remained about other materials, such as charcoal: Would they yield phlogiston as metals do? The search for an answer to this question became the task of Joseph Priestley.
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Priestley Isolates "Phlogiston" from Charcoal
In 1796, after years of experimentation, Priestley obtained a gas by the action of charcoal on iron scales (Fea04),the chemical behavior of which was similar to that exhibited by the gas that Cavendish "obtained from metals." The gas also burned with a blue flame without leaving a residue and reduced calces to their respective metals. Priestley believed that he succeeded in isolating nhloaiston from charcoal just as Caveudish isolated it from metals. There was one difficulty however: the inflammable gas obtained from charcoal was 14 times heavier than the one obtained from metals. But so unimportant, yet, was the question of weight that chemists, while recognizing that this was a heavy form of inflammable air, did not suspect that it was a different gas. The followers of Lavoisier who explained chemical phenomena in terms of the union with oxygen theory, could not explain the production of an "inflammable
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Presented before the Division of History of Chemistry a t the 140th Meeting of the ACS, Chicago, Illinois, September, 1961.
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gas" from charcoal for it did not occur to them that it could be an oxide of carbon. Priestley's Weapon Against Lovoisier's Theory
Priestley seized upon the inability of the followers of Lavoisier to "explain away" the production of inflammable gas from charcoal (3) and used i t as an argument in all his discussions with the opponents of phlogiston. He was sure that he had found the ultimate weapon by means of which he would overturn the "despicable" French doctrine. In a letter to Dr. Benjamin Rush (3) dated August 8, 1799, Priestley wrote: Raving much leisure and no disposition to idleness, I have been busy, and I think pretty successfully in my experiments, one object of which has been the overturning of the French system of chemistry.
Priestley continued his experiments until the year 1800, and summarized the results of his experiments in the treatise entitled "Doctrine of Phlogiston Established (4)." He felt that with this publication he had put an end to the French system of chemistry. At that time chemists had recognized the following inflammable airs: (1) The light "inflemmable air" obtained bp the action of metals on acids; (2) The heavy "inflammable air" obtained by heating charcoal ; (3) The heavy "inflammable air" obtained by the action of finery cinder on charcoal; (4) The "inflarnma,ble air" (our water gas) produced by passing steam over red hot charcoal.
Priestley believed all these inflammable airs to be the same phlogiston united with different quantities of water (5). Cruickshank's Articles
Priestley's joy in disproving Lavoisier's theory did not last long, for in the year 1801, the Nicholson Journal published two reports by William Cruickshank which proved beyond any doubt that heavy "inflammable air" hitherto thought to be hydrogen, was an oxide of carbon (6). The reports of Cruickshank were, in effect, detailed accounts of experimental data on the oxides of carbon. In these, he related that he repeated the experiments of Priestley with finery cinder and charcoal, and obtained both "fixed air" (COz) and "inflammable air." He also subjected various metallic oxides to the action of charcoal and obtained both %xed air" and "inflammable air." Those oxides which parted easily with their oxygen yield chiefly "fixed air," vhile the others yield chiefly heavy "inflammable air." Finally, he was able to reduce "fixed air" to the "inflammable gas." He, therefore, concluded that there are two oxides of
carbon, and heavy inflammable gas is an oxide of carhon, containing less oxygen than fixed air for given weight of carbon. Because of the fact that the whole problem of the various inflammable gases with their different weights was up to that time shrouded in mystery, the elucidation of the entire matter was hailed in London and Paris as a momentous scientific event (7). The import of the reports on the controversy between the remaining obstinate followers of Stahl's theory and Lavoisier's disciples, was emphasized in the title of the report1 as well as in the report itself. which ends vith the following ( 8 ) : "We likewise conceive that the- obje:tions to the new system of chemistry advanced on this head by Dr. Priestley are sufficiently answered. We find that these gaseous oxides are very different from what the Doctor conceived them to he and the presencenf water doesnot appear to henecessary to their production."
Priestley's Reaction
Priestley realized that Cruickshank's reports constituted a mortal blow to the phlogiston theory, and devoted all his energy and resourcefulness to prove Cruickshank wrong. In the same year in which Cruickshank's report appeared in Nicholson's Jouma!, there also appeared a long paper on the same subject in Annales de Chimie by Desormes and Clement (9). The two French chemists arrived a t the same conclusions as Cruickshank, on the basis of extensive experiments with charcoal. They obtained heavy inflammable air by passing carbon dioxide over red hot charcoal. Priestley ignored this report entirely, either because a report by French chemists in support of a French doctrine was not as bad as a report by a distinguished English chemist, or simply because the article in the French journal did not come to his attention. I n letters published in Nieholsm's Jounzal (lo), Priestley attacked Cruickshank: "If heavv "inflammable air" is an oxide of carbon, one should he able to cite another oxide which is inflammable. Can Cruickshank paint to such an oxide? Furthermore, Cmickshank's assertion that heavy inflammable gas is an oxide of rasbon not only repudiates Priestley's theory, but also those of Berthollet, Woodhouse and Lavoisier."
I n one of his letters, Priestley wrote (11): "Having just received a letter from a friend in Paris in which I find that great account is made of the observations of Mr. Cruickshmk so that it is now taken for granted that I must accede to the new thwry, I beg you would add to my former letter that Mr. Cruickshank himself abandons the most fundamental principle of that theory which is that the only source of inflammable air is water. Mr. Lavoisier, speaking about the inflammable air from charcoal and water, which is similar t o that from charcoal and finery cinder, says ("Elements of Chymistry," p. 87 of the English translation): 'It cannot possibly be disengaged from the charcoal and must consequently be produced from water.""
This letter illustrates how Priestley's obdurate clinging to phlogiston obscured his capacity for sound analysis. Actually, Lavoisier, who did not suspect the existence of an oxide of carbon other than carbon dioxide, could 'The title reeds: "Some Observations on Different Hydrocarbons and Combinations of Carbon with Oxygen, etc., in Reply to Dr. Priestley's Late Objections to the New System of Chemistry."
only ascribe the inflammable properties of water gas to the hydrogen derived from the water; and Cruickshank, who found out about the existence of carhon monoxide and identified heavy "inflammable air" as carhon monoxide, did not in any way betray Lavoisier. In chemical circles in Europe, Priestley's personal attacks on Cruickshank (he even called him a bigot) (19), as well as his blind devotion to phlogiston, in spite of the accumulated evidence, made a very had impression. I t was quite all right to be a phlogistonist in 1774, but to be one in 1803%was an outrage. In 1774, he had found himself in company of illustrious names such as Cavendish, Scheele, Kirwan, etc., but in 1803 he was fighting alone against the trend. I t is true that there were some phlogistonists left in Germany, hut in France and in England there were practically none left among the great. Even Priestley's old comrade in arms for phlogiston, Kirwan, the man who first suggested that inflammable air was phlogiston was now a convert of the new system of chemistry ( I S ) , and so were many other former phlogistonists. It is, therefore, quite pathetic to hear of the old Priestley spending time in his laboratory, trying to prove that carbon monoxide was not carbon monoxide but hydrogen. Rumors About Priestley's Death
At the time Priestley was experimenting feverishly with charcoal and finery cinder, he took sick; and rumors started to spread among his friends in France that an attempt had been made to poison him. In 1804, when Priestley died, the same circles ascribed his death to poisoning. Even in the eulogy oration that Cuvier pronounced before the French Academy of Science he mentioned that Priestley's death was the result of poisoning (14). Evidently, Priestley's enemies were suspected of making such an attempt. However, this is quite incredible, since no mention was made of it in the United States; and Priestley's son, who gave a detailed account of his father's life in the United States, never referred to it. Did Carbon Monoxide Poison Priestley?
The assertion that an attempt was made on Priestley's life has not been substantiated. However. the possibility of his being poisoned by his "prerious phlogiston" cannot be excluded. In order to uphold the phlogiston theory Priestley kept himself busy experimenting with finery cinder and charcoal, which produced carbon monoxide. Priestley's son, in describing his father's activities during this period, mentions that he used to do experiments in his laboratory preliminary to writing replies to Mr. Cr~ickshank.~ In the description of what his son calls "the last scene of Priestley's life," we read as follows (16): "A few days before his death, he went to the laboratory and found his weakness very great, that he got back with difficulty, that just afterwards, his granddaughter, a. child of about six or In 1803, Priestley published a second edition of his "Doctrine of Phlogiston Estilblished." J., "Memoirs of Dr. Joseph Priestley" to the ~PRIESTLEY, year 1795, with a continuation to the time of his decease, by his son, Joseph Priestley, printed for J. Johnson, London, 1806, p. 207. Volume 39, Number 12, December 1962
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seven years came to him to claim the fulfillment of a promise he made her the evening before to give her 5 pennies. He gave her the money and was going to speak t o her, but found himself unable. H e informed me of this, speaking very slowly, and added that. he never felt more pleasantly in his whole life than he did during the time h~ was unable to speak."
Priestley's statement that he was unable to speak and yet felt very pleasantly is significant in terms of what we now know about carbon monoxide asphyxia. Cecil K. Drinker, professor of physiology and Dean of School of Public Health, Harvard University, in his book entitled Carbon Afonoxtde Asphyxia (16) quotes J . S. Haldane's description of the effects of advancing asphyxia based chiefly on experiments upon himself, and says:
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". . In many respects the symptoms of anoxaemis, resemble those of drunkenness, and a man suffering from anoxaemia cannot he held responsible for his acts. Without reason he may begin to laugh, shout, sing. . He is, however, a l m p quite confident that he himself is perfectly sane nnd reasonable, though he may notice, for instance, that he cannot walk r w write properly, cannot remember what has just happened, and cannot properly interpret his visual impressions. When unable to stand, owing t o experimental CO poisoning, Haldane has always been quite confident of his own sanity, and i t was only afterwards that he realized that he could not have been in s ratimal stnteof mind. The subtlety of these mental effects cannot be too much emphasized. The person affected may be brought to the very verge of unconsciousnees without appreciating in the least degree that anything is wrong. This is particularly true when relatively high concentrations of carbon monoxide are encountered. We have seen a man gassed as part of an experiment, scoff at the idea. that anything wns amiss only to fall unconscious on attempting to leave the room."
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Of course, the evidence that Priestley's collapse in the laboratory a few days before his death was the result of carbon monoxide poisoning is merely circumstantial. I assume that he did take some precautions when he worked with the hot charcoal inasmuch as he believed that "inflammable air" is phlogiston, and that air saturated with phlogiston was not fit for life was one of the early postulates of Stahl's theory. However, the precautions taken may not have been adequate, and most probably were not those that one would take today when working with the same materials. Indeed, while in a general way it was known that combustion of coal produces poisonous vapors (IT), it was not known that this is due to the presence of "inflammable gas." As late as 1812, the Dictionnaire des Science Medicales of Paris stated, "It has not yet been definitely determined to which of these gases (carbon monoxide or hydrogen sulfide) are due the 'These Nmocl have been popping up in European histories "The for more than a century. See also: G. LOCKEMANN'~, Story of Chemistry," Philosophical Library, New York, 1959, p. 101.
pernicious effects of vapors from charcoal(18)." Priestley, who was firmly convinced that the "inflammable air" from charcoal was the same as the "inflammable air" obtained by the action of metals on acids (only containing a little water), would certainly not have ascribed the toxic effect of burning charcoal to "inflammable air." Priestley's son, when telling of his father's last visit to the laboratory and his near-collapse there, did not know about the symptoms of carbon monoxide poisoning; but he did know that his father was wrong in his dispute with Cruickshank. This may be the reason why the son touches lightly upon Priestley's work with charcoal and finery cinder instead of elaborating upon it. I t is clear, however, that Priestley kept on returning to his laboratory with the hope of finding proof that heavy inflammable gas was not an oxide of carbon, but the same stuff as the inflammable gas derived from the action of metals on acid. Without such proof, he knew the battle was lost. Priestley's laboratory work in connection with his stubborn fight for phlogiston sheds light on the circumstances of his death and offers an explanation to the symptoms of poisoning, which gave rise to fantastic rumors that Priestley was killed by his enemies.' Literature Cited ( 1 ) LOCKEMAXN, G., "The Story of Chemistry," Philoaophicsl Library, New York, 1959, p. 83. (2) WHITE, J. H., "The History of the Phlogiston Theory," Edward Arnold and Co., London, 1932, p. 115. ( 3 ) BOLTOX,H. C., editor, "Scientific Correspondence of Priestley," Privately Printed, New York, 1892, p. 136. ( 4 ) PRIESTLBY,J., "Doctrine of Phlogiston Estzhlished." Northumberland, Pennsylvania, 1800. ( 5 ) PRIESTLEY.J., J . Nal. Phil. Chem. d A r k , pp. 181-1, London, February 1802. ( 6 ) CRUICXSHAXK, W., J. flat. Phil. Chem. & Arts, pp. 1-9, London, April 1801, and pp. 201-11, September 1801. (7) SMITH,E. F., "Priestley in America," P. Blakistan's Son and Co., Philadelphia, 1920, p. 152. (8) CRUICK~FIANK, W., ibid., April 1801, pp. 8-9. D. C., A N D CLEMENT, D. F., Ann. Chim., Paris, (9) DESORUES, 1801,pp. 26-64. (10) PRIESTLEY,J., J. Nal. Phil. Chem. and Ada, Vol. 1, pp. 1 8 1 4 . London. March 1802: Vol. 2. DD. 69-70, June
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(12) SMITH,E. F.,ibid.,p. 152. (13) WHITE,J. H.,ibid., p. 123. (14) CUVIER, M., "Eloge Historique de Joseph Priestley," Memoirs de la Classe dea S e i a c e ~ Mnlhematiques el P h ~ i p u e de s l'lnstilul de Fmnee, Vol. 6,1805, p. 57. 115) J.. "M~moirs of Dr. Joseuh Priestley," J. . . PRIESTLET. .. ~ o h n s o n ; ~ o n d o n1806, , p. 14. (16) DRINKER,C. K., "Carbon Monoxide Asphyxia," Oxford University Press, New York, 1938, p. 63. H., "Element& Cherniae," Leiden, 1732, p. 25i. (17) BOERHAVVE, (18) Aaphyxie par le Gaz Oxide de Carbone et par le Gax Hydrogene Carbon&, "Dictionnaire dcs Sciences Medicales," Vol. 2, Paris, 1812, pp.390-1.
"Teaching Machines and Programed Learning" The U. S. Department of Health, Education, and Welfare, Officeof Education, has prepared a Dsmnhlet with the above title which survevs the 1962 status of the industrv. Dirretories of maihines.. ,Droerams. .. . mmufaetl~rers.and nuhiishers should Drove osrticularlv h f u l to those investi~ ~ t i 11w n g uw of this instnrcric,nnl r w i h d Fur m l lw'thv ~ S ~ p ~ r i n r e n ~ loi & tl h untwts, 1'. S. Olliw, \t':tshinfluu 25, I). C., prie e Sll.yG ~ ; u v o r n n w ~Prinring ~r ~
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