€>D £RUSSIC ACID. 279 



came necefTary, therefore, for me to direct my enquiries ac- 

 cording to the indications afforded by my own experiments, 

 and to continue them till I (liould become acquainted with the 

 caufe of fixity in afubftance which immediately on its forma- 

 tion, poflefled properties quite oppofite to thole which it 

 feemed to poflefs during the action of calcination, 



Perfeverance in varying my enquiries on this object, gave The calcination 

 / °. . J ^ . . V affords only car- 



me an opportunity of making many important oblervations,| )oaared azote 



and to afcertain, by decifive experiments, that the Pruffic cal of potato. The 

 cination gives nothing more than the carbonated azote of P nt - g; V en S tni water 

 afh, and that the hydrogen which enters into the compofitior. is applied: 

 of the pruffire, is always the refult of a combination which 

 takes place fubfequent to the calcination. Hence I faw that 

 it was this circumftance which fo long produced the chemical 

 illufion, and from which we flill confound this production with 

 that contained in the crucible. But it is a phaenomenon wor- 

 thy of remark, and of which the explanation is very proper 

 to throw light on the nature and formation of pruffire, that the 



carbonated azote of potafh pofTeffes the property of inftanily — which fluid is 

 , r i*i , ■ . inftmty decom- 



decomponng water ; and at the moment the water is decom- po f e <j # 



pofed, the pruffire is formed, together with ammonia and car- 

 bonic acid. Though this immediate production of three new 

 compounds is the refult of very complicated affinities which 

 are difficult to be well made out; we may neverthelefs fufpect 

 that the potafli, which is always found in excels in pruffic cal- 

 cinations, is the fubftance which in this cafe preponderates in 



the affinities, and that this fubftance, by a predifpofjng a<trac- Ex P la " a £°Vu 

 . , , , the effect of the 



tion, promotes the oxigenation of the carbon at the expence affinities. 

 of the oxigen of the water ; the hidrogen, which being fet at 

 liberty by this fubtraction of oxigen, unites at the fame time 

 with the carbonated azote of potafh. One part of the hidro- 

 gen is thus employed in forming ammonia, while the other 

 ferves to form the pruffire, which was not pruffire for want of 

 the hydrogen, its third element. It is (till farther in favour of 

 this theory that fhe potafh in its progrefs to faturation with 

 carbonic acid may, by long ebullition, fucceffively convert 

 the greater part of the pruffire, into ammonia and carbonic 

 acid ; this decompofition ufually continues til! the potafh is 



completely faturated with the carbonic acid. Hence it is th a t Tne P rufl * lc 



, _ .. . . , , , yit lixivium may be 



a very good pruffic lixivium may be partly decompoled by decompofed by 



fimple ebullition, and that in all- pruffic calcinations, thofe water and loft 



• • , incurred* 

 which 



