Cyanides of the Metals. 69 



by cooling; they do not deliquesce in the air; their solution 

 does not affect test papers, has a sweet taste when first taken 

 into the mouth, but becomes disagreeably bitter, and the sensa- 

 tion is not easily removed ; it may be boiled for any length of 

 time without decomposition. 



The crystals are easily affected by light, the solution very 

 little so ; but a piece of paper dipped into it and dried is very 

 sensitive to light, and would, in our opinion, be a superior 

 salt for photogenic processes to any at present in use. We 

 may also observe here that the analogous salt of gold is ex- 

 cellently adapted for the same purposes. 



Cyanide of potassium and silver is decomposed by all acids, 

 precipitating the silver as a cyanide ; the hydracids however 

 decompose the cyanide of silver also. 



Sulphuretted hydrogen precipitates the silver from solu- 

 tions of cyanide of potassium and silver as a sulphuret. A so- 

 lution of the salt is not effected by alkaline or earthy chlorides, 

 nor by carbonates. 

 Perchloride of mercury gives a white precipitate. 



Protosalts of iron a brownish-white 



Persalts of iron a brownish-yellow 



Lead, nitrate and acetate ... a white 



Protosalts of tin a yellowish-white 



Copper salts a light green 



Sulphate of zinc a white 



Gold a yellowish-white 



Nitrate and chloride of cobalt . a pink, passing to a light violet. 

 Manganese sulphate no precipitate. 



In the last paper we referred to the superior affinity of 

 cyanogen for silver in the presence of cyanide of potassium, 

 decomposing every salt of silver but the sulphuret, to form 

 cyanide of potassium and silver. As, for example, if cyanide 

 of potassium is added to cyanate of silver, the latter is decom- 

 posed by 2 equivalents of cyanide of potassium, and there 

 is produced one of cyanide of potassium and silver with one 

 of cyanate of potash. The reaction may be expressed thus: 



\ p , ,rCyO ^Cyanate of 



1. Cyanate oil ^ -^^ potash. 



silver. ' - ^ 



2. Cyanide of J ^^ 



potassium. | ^ ^^ ~^^~~->:x. Cyanide of potas- 



sium and silver. 



A similar reaction takes place when cyanide of potassium 

 is added to the oxide of silver, carbonate of silver or chlo- 



