Joseph Priestley Noflhumberland,Pennsylvania synthesized by Robert E. Schofield' Case Western Reserve Jnivers ty Cleveland, Ohio 44 106
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A Discourse on the Branches of Natural Philosophy Most Particularly Related to Chemistry Introduction
Joseph Priestley (1733-1804) is remembered by history as a chemist, but by profession he was a Unitarian minister. During the course of researches carried on as a leisure-time activity, he isolated eight gases, including oxygen; he first noted the phenomena of photosynthesis and differential gaseous diffusion; and he is the discoverer of naturally and artificially carbonated water. Most of his researches were done in England between 1771 and 1784. After that much of his scientific effort was directed against the oxidation theory which his great rival Antoine Lavoisier had constructed in part out of Priestley's discoveries. In 1794 he came to the United States. At once he was the most famous scientist in the country, and he brought with him an excitement and a sense of participation in European science which Americans had lacked. Although most American chemists were already adopting the views of Lavoisier, they gave Priestley a sympathetic hearing. The American Philosophical Society considered him for its presidency and invited him to give its annual oration in 1797. By that time, however, he was securely settled in Northumberland, Pennsylvania, and reluctantly declined the invitation; but in the paper which follows we are pretending that he accepted. Although there is no evidence that Priestley ever delivered a general lecture in chemistry-his appearance before scientific societies being confined to descriptions of his experiments and discoveries-it may reasonably beargued that the lecture which follows is consistent with what he might have said. The greater part of the wording has been taken directly from his many writings, while the remainder has been constructed to conform to his style and beliefs. The form of Priestley's arguments against the French chemists is chiefly that of the description of experiments he has performed to counter those cited by the oxidationists. I t soon becomes clear, however, that the substance of his argu-
ment is a different thing, for experiments do not speak for themselves and in their variant interpretations of the same experiments, Priestley and his opponents are talking a t cross purposes. There is no common ground for communication. The chemists who followed Lavoisier are concerned with establishing chemistry as an autonomous science with a firm, quantitatively descriptive base. Priestley, on the other hand, wishes to integrate chemical explanations into natural philosophy and, beyond that, Christian theology. Thus he hoped to explain chemical phenomena in terms of ultimate particles moved by forces of attraction and repulsion which he equated with the will of an omni~resenteod. In the short run, thl~rench-chemistswere right. They bannished ~hilosonhvfrom chemistrv seekine onlv to know operationahy whiih kbstances were"tru1y eLments and in what proportions by weight or volume these elements combined to form compounds. By focusing their attention on analytical chemistry, they laid hare the building blocks of which all things are made. Americans of the late 18th century could see the common sense and practicality of this approach. In the long run, however, Priestley's dream of understanding whv substances of nature combine the way thev do in terms-of dhysical chemistry and underlying natural lawwas to he the more compelling. In a sense he left it for us, retrospectively, to make-his pl&osophical claim for him. The lecture below, synthesized by the author was delivered by him in costume and with experimental demonstrations as a Bicentennial public lecture a t the University of Delaware on January 7,1976. I t has also been produced for television. A color videotape can he rented or bought from the University of Delaware. The illustrations accomnanvine the article are drawn from these re-enactments. 'This introduciion was written by Robert E. SehaReld and edited by John J. Beer.
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Address My Friends and Brethren of the Philosophical Society: Having reached that time of life when I can expect to do no more than close out old pursuits, I am grateful for the opportunity to address you on those general questions which have divided phlogistonists from anti-phlogistonists. My laboratory having been re-established for my fullest use but this summer, I have had nothing materially new of my own to advance against the new chemistry for nearly six years, or since the destruction of my apparatus in those riots in Birmingham which were the initiating occasion of my seeking refuge and asylum among you. No doubt there are others, therefore, who could address this task with greater timeliness, hut as this may well he the last time I shall have opportunity to express my thoughts on these subjects, I beg your indulgences to my efforts and this more particularly as by a resolution reached early on my coming to this country, I relinquished access to a class of sympathetic hearers such as I had but recently left in England.
Hardly had I arrived in America when I was favoured with an invitation to succeed the late Dr. Carson as professor of chemistry at the University in this city. I was truly sensible of the honour done me by the invitation and earnestly considered the acceptance of it, for I know well the respect owing that institution, especially in its concern for the education of persons for the middling, useful ranks of society as well as the learned professions, an education for which the subject of chemistry is peculiarly suitable. Besides I flattered myself I could he seful in the position, a t least as one who could communicate the present state of the subject in the debate which has so lately engaged the energies of philosophers in Europe. But my family, library, and apparatus having been settled in Northumberlandtown, my courage failed me and I was the more disuaded by the consideration that I could by no means supply so many lectures as such a course requires. The only general lectures on such topics I ever gave were those included in a short course of experimental philosophy delivered at the VoIume 53. Number 7, July 1976 / 409
Lack of weight has indeed been a primary criticism made of phlogiston by the new chemists.
New College, Hackney and though I have made some discoveries in some branches of chemistry, I have never given much attention to the common routines of it and know hut little of the common processes. Happily a more suitable candidate for the position was found in the ingenious and candid Dr. Woodhouse, amember of this society and former pupil of my friend, the learned Dr. Rush. Dr. Woodhouse has f i e d the post with great distinction and, with the energetic Dr. Mitchill of New York and Dr. Maclean of the College in New Jersey, in answers to me has made the United States a theater of discussion of the contending systems of chemistry. But though their arguments in support of the anti-phlogiston theory daily swell the numbers, already in the ascendancy in Europe, who have adopted that hypothesis, the evidence is yet inconiiiderable enough tu gain my nisent. As we all a y e e in our wishes for thr pre\.alence of truth iind as the cause of truth is most favoured hy free discussion, not hy thr reign of a Hubespierrc or the methuds of a nhilosouhi~nlSvnod. " , I hee the favour of \,our attention and your answers to my objections. Experimental ohiloso~hv. part, is . .. of which chemistrv. is . conversant of the properties of bodies and of the changes of those . ~ r o. ~ e r t i in e sdifferent circumstances. Amone the cirrumstances which occasion such changes 31P the addition of sub
