VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 485 



it became much less soluble ; so that on adding water to it not much dissolved, 

 and by repeating this process once or twice, it seemed to become not more solu- 

 ble than selenite made in the common manner. This solubility of the selenite 

 caused some trouble in trying the experiment ; for while it continued much 

 soluble it would have been impossible to have distinguished a small mixture of 

 nitrous salt ; but by the above-mentioned process I was able to distinguish as 

 small a proportion as if the selenite had been originally no more soluble than 

 usual. 



The nature of the neutral salts made with the phlogisticated vitriolic and 

 nitrous acids has not been much examined by the chemists, though it seems well 

 worth their attention ; and it is likely that many, besides the foregoing, may 

 differ remarkably from those made with the same acids in their common state. 

 Nitre formed with the phlogisticated nitrous acid has been found to differ con- 

 siderably from common nitre, as well as sal polychrest from vitriolated tartar. 



In order to try whether any vitriolic acid was produced by the phlogistication 

 of air, I impregnated 50 oz. of distilled water with the fumes produced on mix- 

 ing 52 oz. measures of nitrous air with a quantity of common air sufficient to 

 decompound it. This was done by filling a bottle with some of this water, and 

 inverting it into a basin of the same, and then, by a syphon, letting in as much 

 nitrous air as filled it half-full ; after which common air was added slowly by the 

 same syphon, till all the nitrous air was decompounded. When this was done, 

 the distilled water was further impregnated in the same manner, till the whole of 

 the above-mentioned quantity of nitrous air was employed. This impregnated 

 water, which was very sensibly acid to the taste, was distilled in a glass retort. 

 The first runnings were very acid, and smelt pungent, being nitrous acid much 

 phlogisticated ; what came next had no sensible taste or smell ; but the last run- 

 nings were very acid, and consisted of nitrous acid not phlogisticated. Scarcely 

 any sediment was left behind. These different parcels of distilled liquor were 

 then exactly saturated with salt of tartar, and evaporated ; they yielded 87-i- grs. 

 of nitre, which, as far as I could perceive, was unmixed with vitriolated tartar or 

 any other substance, and consequently no sensible quantity of the common air 

 with which the nitrous air was mixed was turned into vitriolic acid. It appears, 

 from this experiment, that nitrous air contains as much acid as 2-f- times its weight 

 of saltpetre ; for 52 oz. measures of nitrous air weigh 32 grains, and, as was be- 

 fore said, yield as much acid as is contained in 87v grains of saltpetre ; so that 

 the acid in nitrous air is in a remarkably concentrated state, and I believe more 

 than li times as much so as the strongest spirit of nitre ever prepared. 



Having now mentioned the unsuccessful attempts I made to find out what be- 

 comes of the air lost by phlogistication, I proceed to some experiments, which 

 serve really to explain the matter. In Dr. Priestley's last vol. of experiments is 



