VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 4Q3 



when it was procured from plants or from turbith mineral : and it seems not 

 likely that air procured from plants, and still less likely that air procured from a 

 solution of mercury in oil of vitriol, should contain any nitrous acid. Another 

 strong argument in favour of this opinion is, that dephlogisticated air yields no 

 nitrous acid when phlogisticated by liver of sulphur ; for if this air contains 

 nitrous acid, and yields it when phlogisticated by explosion with inflammable air, 

 it is very extraordinary that it should not do so when phlogisticated by other 

 means. 



But what forms a stronger, and I think almost decisive argument, in favour of 

 this explanation is, that when the dephlogisticated air is very pure, the con- 

 densed liquor is made much more strongly acid by mixing the air to be exploded 

 with a little phlogisticated air, as appears by the following experiments. 



A mixture of 18500 grain measures of inflammable air with 9750 of dephlo- 

 gisticated air, procured from red precipitate, were exploded in the usual manner ; 

 after which, a mixture of the same quantities of the same dephlogisticated and 

 inflammable air, with the addition of 2500 of air phlogisticated by iron filings 

 and sulphur, was treated in the same manner. The condensed liquor, in both 

 experiments, was acid, but that in the latter evidently more so, as appeared also 

 by saturating each of them separately with marble powder, and precipitating the 

 earth by fixed alkali ; the precipitate of the 2d experiment, weighing } of a 

 grain, and that of the first being several times less. The standard of the burnt 

 air in the 1st experiment was 1.86, and in the 2d only 0.9. It must be observed, 

 that all circumstances were the same in these two experiments, except that in 

 the latter the air to be exploded was mixed with some phlogisticated air, and that 

 in consequence the burnt air was more phlogisticated than in the former ; and, 

 from what has been before said, it appears that this latter circumstance ought 

 rather to have made the condensed liquor less acid ; and yet it was found to be 

 much more so ; which shows strongly that it was the phlogisticated air which 

 furnished the acid. 



As a further confirmation of this point, these 2 comparative experiments were 

 repeated with a little variation, namely, in the first experiment there was first 

 let into the globe 1 500 of dephlogisticated air, and then the mixture, consisting 

 of 12200 of dephlogisticated air and 25900 of inflammable, was let in at dif- 

 ferent times as usual. In the 2d experiment, besides the 1500 of dephlogisti- 

 cated air first let in, there was also admitted 2500 of phlogisticated air, after 

 which the mixture, consisting of the same quantities of dephlogisticated and 

 inflammable air as before, was let in as usual. The condensed liquor of the 2d 

 experiment was about 3 times as acid as that of the first, as it required 1 1 9 grs. 

 of a diluted solution of salt of tartar to saturate it, and the other only 37. The 

 standard of the burnt air was 0.78 in the 2d experiment, and 1.96 in the first. 



