1821.] the Composition of Prussiates. 445 



It is evident that the phenomena produced by the metaUic 

 cyanurets and hydrocyanates can be explained only b}^ a theory 

 analogous to that proposed for the muriates by MM. Gay-Lussac 

 and Thenard, and which was afterwards adopted and developed 

 by Sir H. Davy; and this analogy of the phenomena presented 

 by the cyanurets is undoubtedly a circumstance which is very 

 favourable to this theory. 



It seems to follow from the experiments above-mentioned^ 

 that the cyanurets of very electro-positive bases ; that is, of the 

 metals which form alkalies, do not decompose water, and do not 

 form hydrocyanates. The weaker bases, such as glucina,* 

 ammonia, the greater number of metallic oxides, on the contrary^ 

 become hydrocyanates, which, w^hen exposed to a high temper- 

 ature, either do not become cyanurets, or do not form them 

 without having a part of their cyanogen decomposed by the 

 oxygen of the bases, and yielding at the same time carbonic 

 acid, ammonia, and metallic carburets. With the exception of 

 hydrocyanate of iron and ammonia, it appears that when one of 

 the bases occurs in the state of hydrocyanate, the other is so 

 likewise ; so that there is no compound of a cyanuret and a 

 hydrocyanate. When the cyanurets combine with an additional 

 quantity of base, it appears that the cyanuret becomes an hydro- 

 cyanate, and that the whole becomes a subhydrocyanate ; such 

 is probably the state of combination of cyanuret of mercury with 

 oxide of mercury. 



Before I conclude these observations, I shall say a few words 

 upon the acid called ferruginous hydrocyanic acid, and which 

 has been considered as a peculiar acid, of which the iron is an 

 element. This compound is produced when a stronger acid 

 combines with the second base of a ferruginous hydrocyanate ; 

 then the whole quantity of hydrocyanic acid combines wdth the 

 protoxide of iron, and these results are hydrocyanate wi»h excess 

 of acid, in which the protoxide is combined with three times as 

 much acid as in the neutral salt. All that I have already stated 

 upon the nature of the cyanurets and ferruginous hpdrocyanates 

 is evidence in favour of this manner of regarding this acid sub- 

 stance. Porrett has described two methods of obtaining this 

 acid, one of which is to decompose the cyanuret of iron and 

 barium by sulphuric acid ; and the other to decompose the 

 cyanuret of iron and potassium by means of a solution of tartaric 

 acid in alcohol. The fluid being left to spontaneous evaporation, 

 crystals are obtained. Neither of these methods gives the 

 superb ydrocyanate of iron in a pure state. 



* Glucina gives a soluble hydrocyanate, which, reduced by evaporation, becomes a 

 transparent varnish, which is often bluish. It is obtained by the double decomposition 

 of sulphate of glucina and cyanuret of lead and iron. There is also a ferruginous hydro- 

 cyanate of alumina. When neutral, it is but slightly soluble ; but with excess of acid, 

 it may be dissolved. It is prepared with hydrate of alumina and ferruginous prussic 

 acid. 



