Cyanides of the Metals. 61 



terms double-cyanides, bicyanides, &c., which are usually 

 given to such compounds, we consider neither necessary nor 

 sufficiently expressive. 



9. The equivalent numbers employed are those given in 

 Dr. Turner's * System,' namely, — Cyanogen 26*39, potassium 

 39'15, cyanide of potassium 65' B% gold 199*20, cyanide of 

 gold 225-59. 



10. Cyanide of Gold. — Little is said in any systematic trea- 

 tise of the cyanide of gold. Berzelius, almost the only chemist 

 who mentions this compound, says, " That this salt presents 

 itself under the form of a pale yellow substance, insoluble in 

 water, which is obtained by precipitating the chloride of gold 

 with cyanide of potassium, and gives as its composition the 

 formula Au, Cyg." Kane also mentions this pale yellow com- 

 pound, and gives it the same composition. It may readily be 

 obtained by decomposing the chloride of gold with cyanide of 

 potassium, but both solutions must be saturated, and care 

 must be taken not to add an excess of cyanide of potassium ; 

 the product however by this process is very small compared 

 to the quantity of gold employed, and it is necessary to pro- 

 ceed as follows to obtain the whole of the gold as cyanide : — 

 Saturated solutions are to be used, and a slight excess of cya- 

 nide of potassium added, so as to redissolve the cyanide of 

 gold; the whole is to be evaporated to perfect dryness, treated 

 with nitric or muriatic acids to decompose the cyanide of po- 

 tassium, again evaporated to dryness, and gently heated so as 

 to expel the excess of acid, when cold water is to be added, 

 and the whole thrown upon a filter and thoroughly washed. 

 Obtained in this way however it generally contains a portion 

 of silica, particularly if the cyanide of potassium has been 

 prepared in earthenware crucibles; and to obtain the cyanide 

 pure we have recourse to other methods. The best process 

 is to decompose the cyanide of gold and potassium. The salt 

 is to be dissolved in a small portion of distilled water, nitric 

 or muriatic acid added, and the liquid brought to a boiling 

 heat, the cyanide of gold then precipitates ; but it is necessary 

 to expel the excess of acid by evaporation before the whole 

 of the cyanide is obtained; the dry mass is then treated with 

 water, thrown upon a filter and well washed. 



The cyanide of gold obtained by the last method is of a 

 beautiful canary yellow colour, which is not affected by expo- 

 sure to light, or by the action of acids : it is an exceedingly 

 tine powder, and readily passes through a single filter; it 

 is insoluble in caustic potash and water ; is slightly solu- 

 ble in nitric, muriatic, and sulphuric acids when recently 

 precipitated ; is soluble in ammonia, hyposulphite of soda, 

 and readily so in cyanide of potassium ; when fused at a red 



