VOL. LXXX.] PHILOSOPHICAL TRANSACTIONS. 723 



duced by the explosion to ^ of their original bulk. The residue was then trans- 

 ferred over mercury into a slender graduated tube, and distilled water being ad- 

 mitted, -j^g. were absorbed. To a portion of this water, when filtered, vitriolated 

 silver was added, which instantly occasioned a copious precipitate. To a 2d 

 portion was added muriated barytes, which occasioned a slight white precipitate 

 not re-dissolvable in a large quantity of water ; lime-water being added to a 3d 

 portion, did not produce any sensible precipitation. From the last fact it does 

 not follow, that no fixed air existed in the residue, because the marine acid, 

 which it evidently contained, would dissolve the calcareous earth of the lime- 

 water. As a great diminution however resulted from the combustion ; and as it 

 appeared from chemical tests, that the residue was mostly composed of marine 

 and vitriolic acid airs, it is manifest that if any fixed air was produced, its 

 quantity must have been very inconsiderable. 



It has been already observed, that a slight precipitation took place on the 

 addition of the muriated barytes. The precipitate was much more considerable 

 when, on repeating the experiment, the residue after the explosion was not 

 transferred into a graduated tube before the admission of the distilled water ; but 

 the latter was immediately introduced into the vessel in which the airs were 

 fired. The reason of this difference is evident. The slight precipitate by the 

 muriated barytes, in the first instance, depended on the existence of a small 

 quantity of vitriolic acid in an aerial form, or in the state of volatile vitriolic 

 acidy which was transferred together with the phlogisticated and marine acid air 

 into the 2d tube ; but the greater part of the vitriolic acid produced by the com- 

 bustion adhered, in a fixed state, to the surface of the tube in which the airs 

 were fired ; and therefore, when the distilled water was immediately introduced 

 into this tube, a copious precipitate was deposited on the addition of muriated 

 barytes. Hence it appears, that when pure air and sulphureous hepatic air, ob- 

 tained from artificial pyrites by the marine acid, are fired together in the above 

 proportions, the products are fixed vitriolic acid, together with a small quantity 

 of the volatile vitriolic and marine acids, in an aerial form. The residue, which 

 the distilled water did not absorb, was the phlogisticated air that existed in the 

 pure air before the combustion. 



From subsequent trials it appeared, that when hepatic and pure air were fired 

 in equal bulks, the residue had a strong odour of volatile vitriolic acid, and also 

 contained a small proportion of undecomposed hepatic air. These facts seem to 

 prove, that the conversion of sulphur into volatile or fixed vitriolic acid depends 

 on the quantity of pure air with which it is supplied. The marine acid air, 

 found in this experiment, did not appear to form one of the constituent princi- 

 ples of the hepatic air, but to be merely diffused through it ; for it was almost 

 wholly separated, by means of distilled water, from a different portion of the 



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