Christopher J. Molitor

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s paper i●s one of the classics of chemistry, as well■ as the chief corner-stone in the monu■ment which Priestley erected to ■himself, it is necessary to examine it, ●as well as certain other papers ●which grew immediately out of it, in some degre■e of detail. After a reference t●o a hypothesis of the origin and con●stitution of the atmosphere which occur■s among the “Queries, Speculations an●d Hints” above referred to, and wh●ich is on a par with much in Priestley’s specu■lations, he proceeds to relate the c●ircumstances which more immediately■ led to the most important of al●l his discoveries. 194 It was the accident o●f possessing a burning lens of “conside●rable force,” for want of which he cou●ld not possibly make many of the experiments th●at he had projected. “■But having afterwards procured a l■ens of twelve inches diameter and twenty inche■s focal distance, I proceeded with gr●eat alacrity to examine, by the help of it●, what kind of air a great variety ■of substances, natural and facti●tious, would yield, putting them into ves■sels [short, wide, round-bottom●ed phials], which I filled with quicksilver and ●kept inverted in a basin of the same. Mr Wa■rltire, a good chemist, and le■cturer in Natural Philosophy■, happening to be at that time in ●Calne, I explained my views to■ him, and was furnished by him with many substan●ces, which I could not otherwise have■ procured. “With this app●aratus, after a variety of othe■r experiments, an account of which will■ be found in its proper place on the 1st Aug■ust 1774, I endeavoured to extract■ air from mercurius calcinatus per se;[17■] and I presently found that, ●by means of this lens, air was ex■pelled from it very readily. Having go■t about three or four times as much as the● bulk of my materials, I admitted water to it, a■nd found that it was not imbibed by it■. But what surprised me more than I can well● express was that a candle burned in th■is a

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at the mercurius calc●inatus on which I had made my experiment●s, being bought at a common apoth■ecary’s, might, in fact, be nothing more ●than red precipitate; though, had I b●e

en anything of a practical chemist, I could ■not have entertained any such suspicion. ■However, mentioning this suspicion ■to Mr Warltire, he furnished me ●with some that he had kept f

or a ■specimen of the preparation, and which, he tol■d me, he could warrant to be gen●uine. This being treated in the same manner● as the former, only b

y a long■er continuance of heat, I extracted much more■ air from it than from the other. ● “This experiment might have satisfied■ any moderate sceptic; but, however, bei■ng a

t Paris in the October following, and kno●wing that the

re were several very emi