VOL. LXXIV.J PHILOSOPHICAL TRANSACTIONS. 495 



that the small residuum which remains after its phlogistication proceeds only from 

 the impurities mixed with it. It was just said, that some dephlogisticated air 

 was reduced by liver of sulphur to -^ of its original bulk ; the standard of this 

 air was 4.8, and consequently the standard of perfectly pure dephlogisticated air 

 should be very nearly 5, which is a confirmation of the foregoing opinion ; for 

 if the standard of pure dephlogisticated air is 5, common air must, according 

 to this opinion, contain 4- of it, and therefore ought to lose x of its bulk, by 

 phlogistication, which is what it is actually found to lose. From what has been 

 said, it follows, that instead of saying air is phlogisticated or dephlogisticated by 

 any means, it would be more strictly just to say, it is deprived of, or receives, an 

 addition of dephlogisticated air ; but as the other expression is convenient, and 

 can scarcely be considered as improper, I shall still frequently make use of it in 

 the remainder of this paper. 



There seemed great reason to think, from Dr. Priestley's experiments, that 

 both the nitrous and vitriolic acids were convertible into dephlogisticated air, as 

 that air is procured in the greatest quantity from substances containing those 

 acids, especially the former. The foregoing experiments however seem to show, 

 that no part of the acid is converted into dephlogisticated air, and that their use 

 in preparing it is owing only to the great power which they possess of depriving 

 bodies of their phlogiston. A strong confirmation of this is, that red precipi- 

 tate, which is one of the substances yielding dephlogisticated air in the greatest 

 quantity, and which is prepared by means of the nitrous acid, contains in reality 

 no acid. This I found by grinding 400 grs. of it with spirits of sal ammoniac, 

 and keeping them together for some days in a bottle, taking care to shake them 

 frequently. The red colour of the precipitate was rendered pale, but not entirely 

 destroyed ; being then washed with water and filtered, the clear liquor yielded 

 on evaporation not the least ammoniacal salt. 



It is natural to think, that if any nitrous acid had been contained in the red 

 precipitate, it would have united to the volatile alkali, and have formed ammo- 

 niacal nitre, and would have been perceived on evaporation ; but in order to 

 determine more certainly whether this would be the case, I dried some of the 

 same solution of quicksilver from which the red precipitate was prepared with a 

 less heat, so that it acquired only an orange colour, and treated the same quan- 

 tity of it with volatile alkali in the same manner as before. It immediately 

 caused an effervescence, changed the colour to grey, and yielded 52 grs. of 

 ammoniacal nitre. There is the utmost reason to think therefore, that red pre- 

 cipitate contains no nitrous acid ; and consequently that, in procuring dephlogis- 

 ticated air from it, no acid is converted into air; and it is reasonable to conclude 

 therefore, that no such change is produced in procuring it from any other 

 substance. 



