ON FRUSS1C ACID-. £>$ \ 



I may obferve, in fupport of what I have here advanced, Berthollet tirft 

 that M. Berthollet, whofe fagacity is well known, has proved, p ru{ f ic gas con _ 

 more than fifteen years ago, by a very accurate analyfis, that ttias no oxigcn. 

 what was called the pruflic acid, does not contain oxigen. It 

 is true indeed, that there are many chemifts no lefs celebrated, 

 who have not coincided in this opinion, and have coniidered 

 what M. Berthollet had advanced as very far from complete 

 proof. I mud, neverthelefs, infill that the labours which that 

 learned chemifi: has made known on this object, are a prelude, 

 in fome fort, to the difcoveries which remained to be made, 

 in order to complete the hiftory of the properties of the pruflic 

 acid. 



It remains then very evidently demonftrated from thefe re- The theory is 

 fults, as well as thofe obtained by M. Berthollet, how far this [he^efukTbe^ 

 theory is fatisfaclory, and how much it enables us to explain neficial. 

 facts, reflecting which we have hitherto had no very correct 

 notions. Laiily, from all thefe new applications, we mav, 

 with a knowledge of the caufes, fabricate in the large way, 

 cryflals of pruffiate of potafh, by oxide of iron. It is now a 

 confiderable time fince I firft prepared fimilar cryftals, but 

 without being able to eftablifh a theory fufficiently clear to be 

 communicated. 



It is to be remarked that Pruffian blue obtained with the The Prufiian 

 pruffiate of potafh by the oxide of iron, gives a blue of the moft blue f eatly im " 

 exquifite beauty. Its interior fracture is fmooth and of a cop- 

 perifh hue, fimilar to that (een in indigo of the beft quality. 

 An obfervalion which equally deferves mention is, that the 

 pruffiate of potafh by oxide of iron has the property of form- 

 ing with a hot folution of fulphate of alumine, a magma ana- 

 logous to that of boiled fecula. If the mixture be diluted with Prirfliate of 

 water to favour the feparation of the precipitate it is then of aIumine * 

 a iky blue colour. This precipitate vvafhed and dried becomes 

 of a deep blue, approaching to black; its fracture is fmooth 

 and has a refinous appearance ; it is the pruffiate of alumine 

 by the oxide of iron. 



Recapitulation. 

 It reful ts from all that has been here faid : Recapitulation 



1 . That the pruffic calcination contains but two of the ele- i. Pruffic cal- 

 ments of pruffire, azote and carbon: and that the third ele- C1 " at ' 0n glve3 



~ i r • r> i ., . n only azote and 



ment neceflary to the composition or the acid, is the refult of carbon along 

 a combination formed after the calcination. with rfie alka1 '* 



2. That 



