OXYGEN AND THE NATURE OF ACIDS. u; 



to this volume. But having afterwards procured a lens of twelve inches 

 diameter and twenty inches focal distance, I proceeded with great 

 alacrity to examine, by the help of it, what kind of air a great variety of 

 substances, natural and factitious, would yield, putting them into the 

 vessels represented in Fig. a, which T filled with quicksilver, and kept in- 

 verted in a bason of the same. Mr. Warltire, a good chymist and lec- 

 turer in natural philosophy, happening to be at that time in Calne, I 

 explained my views to him. and was furnished by him with many 

 substances, which I could not otherwise have procured. 



With this apparatus, after a variety of other experiments, an account 

 of which will be found in its proper place, on the 1st of August, 1774, 

 I endeavored to extract air from mercurius calcinatus per se; and I 

 presently found that, by means of this lens, air was expelled from it very 

 readily. Having got about three or four times as much as the bulk of 

 my materials, I admitted water to it, and found that it was not imbibed 

 by it. But what surprized me more than I can well express was that a 

 candle burned in this air with a remarkably vigorous flame, very much 

 like that enlarged flame with which a candle burns in nitrous air ex- 

 posed to iron or liver of sulphur; but as I had got nothing like this re- 

 markable appearance from any kind of air besides this particular modi- 

 fication of nitrous air, and I knew no nitrous acid was used in the prepa- 

 ration of mercurius calcinatus, I was utterly at a loss how to account 

 for it. 



In this case, also, though I did not give sufficient attention to the 

 circumstance at that time, the flame of the candle, besides being larger, 

 burned with more splendor and heat than in that species of nitrous air; 

 and a piece of red-hot wood sparkled in it, exactly like paper dipped in a 

 solution of nitre, and it consumed very fast; an experiment which I had 

 never thought of trying with nitrous air. 



At the same time that I made the above mentioned experiment, I 

 extracted a quantity of air, with the very same property, from the com- 

 mon red precipitate, which being produced by a solution of mercury in 

 spirit of nitre, made me conclude that this peculiar property, being simi- 

 lar to that of the modification of nitrous air above mentioned, depended 

 upon something being communicated to it by the nitrous acid; and since 

 the mercurius calcinatus is produced by exposing mercury to a certain 

 degree of heat, where common air has access to it, I likewise concluded 

 that this substance had collected something of nitre in that state of heat 

 from the atmosphere. 



This, however, appearing to me much more extraordinary than it 

 ought to have done, I entertained some suspicion that the mercurius 

 calcinatus, on which I had made my experiments, being bought at a 

 common apothecary's, might, in fact, be nothing more than red pre- 

 cipitate; though, had I been anything of a practical chymist, I could not 



