VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 4QJ 



retort, it yielded 256(300 gr. measures of dephlogisticated air,* the standard 

 of different parts of which varied from 3 to 3.65, but at a medium was 3.35. 

 The matter remaining in the retort dissolved readily in water, and tasted alkaline 

 and caustic. On adding diluted spirit of nitre to the solution, strong red fumes 

 were produced ; a sign that the acid in it was very much phlogisticated, as no 

 fumes whatever would have been produced on adding the same acid to a solution 

 of common nitre ; that part of the solution also which was supersaturated with 

 acid became blue ; a colour which the diluted nitrous acid is known to assume 

 when much phlogisticated. The solution, when saturated with this acid, lost its 

 alkaline and caustic taste, but yet tasted very different from true nitre, seeming 

 as if it had been mixed with sea-salt, and also required much less water to dis- 

 solve it ; but on exposing it for some days to the air, and adding fresh acid as 

 fast as, by the flying off of the fumes, the alkali predominated, it became true 

 nitre, unmixed, as far as I could perceive, with any other salt.-}- 



It has been remarked, that the dephlogisticated air procured from nitre is less 

 pure than that from red precipitate, and many other substances ; which may 

 perhaps proceed from unglazed earthen retorts having been commonly used for 

 this purpose, and which, conformably to Dr. Priestley's discovery, may possibly 

 absorb some common air from without, and emit it along with the dephlogisti- 

 cated air ; but if it should be found that the dephlogisticated air procured from 

 nitre, in glass or glazed earthen vessels, is also impure, it would seem to show 

 that part of the acid in the nitre is turned into phlogisticated air, by absorbing 

 phlogiston from the watery part. 



From what has been said it appears, that there is a considerable difference in 

 the manner in which the acid acts in the production of dephlogisticated air from 

 red precipitate and from nitre ; in the former case the acid comes over first, leav- 

 ing the remaining substance deprived of part of its phlogiston ; in the latter the 

 dephlogisticated air comes first, leaving the acid loaded with the phlogiston of 

 the water from which it was formed. On distilling a mixture of quicksilver and 

 oil of vitriol to dryness, part of the acid comes over, loaded with phlogiston, in 

 the form of volatile sulphureous acid and vitriolic acid air ; so that the remaining 

 white mass may be considered as consisting of quicksilver deprived of its phlo- 

 giston, and united to a certain proportion of acid and water, or of plain quick- 

 silver united to a certain proportion of acid and dephlogisticated air. Accord- 

 ingly on urging this white mass with a more violent heat, the dephlogisticated air 



* This is, about 8 1 gr. measures from 1 gr. of nitre ; and the weight of the dephlogisticated air, 

 supposing it 800 times lighter than water, is -fa of that of the nitre. In all probability it would 

 have yielded a much greater quantity of air, if a greater heat had been applied — Orig. 



+ This phlogistication of the acid in nitre by heat has been observed by Mr. Scheele ; see his ex- 

 periments on air and fire, p. 45, English translation. — Orig. 

 VOL. XV. 3 S 



