268 Prof. Liebig on the Preparation of 



time into it; the oxide of lead is instantaneously reduced to 

 metal, which at first remains as a fine powder mixed with the 

 cyanate formed, but melts with greater heat into a regulus. 

 The fluid mass is poured out, and the salt, which is nothing 

 else than cyanate of potash, being finely pounded, is boiled so 

 long with alcohol as crystals are obtained. The crystalliza- 

 tion of the cyanate of potash salt from alcohol is not requisite 

 in the application of that salt to the preparation of urea. 



Cyanide of Potassium as a reducing agent. — It is difficult 

 to conceive with what extreme facility the cyanide of potassium 

 deprives certain metallic oxides and sulphui*ets of their oxygen 

 and sulphur, for it approaches nearest in that respect to pure 

 potassium. The process of preparation of cyanide of potas- 

 sium and that of the cyanate afford two instances of this re- 

 ducing power ; the iron remains either as powder mixed with 

 the fused cyanate, or its particles aggregate together and form 

 a spongy mass. A process might be founded on this reduc- 

 tion for determining in the dry way the amount of metal in an 

 iron ore. When a weighed quantity of the ore is exposed 

 with a mixture of cyanide of potassium and carbonate of pot- 

 ash in a porcelain crucible to a strong red heat, the alumina 

 and silica go into the slag, from which the reduced iron can 

 then be separated by cold water and weighed. The protoxide 

 of manganese is not reduced by the cyanide of potassium ; 

 this, when contained in the ore, must be determined by a 

 separate operation. When oxide of copper is sprinkled on 

 melting cyanide of potassium, it is immediately reduced with 

 evolution of heat and light; after washing, a regulus of pure 

 metallic copper is obtained. The reduction proceeds most 

 beautifully with the oxides of tin and antimony. At a low red 

 heat the oxide of tin is converted into a bright regulus, which 

 may easily be separated from the slag. The oxide of anti- 

 mony and antiraonious acid may be reduced in the same way 

 to the metallic state. All these reductions ensue at a low red 

 heat scarcely visible in daylight, which consequently has the 

 advantage, that not a trace of the reduced metal is lost by vola- 

 tilization. Sulphuret of tin and sulphuret of antimony are 

 reduced by gently melting them with cyanide of potassium 

 before the blowpipe or in the porcelain vessel, with the same 

 ease as their corresponding oxides ; the slag then contains 

 the sulphocyanide of potassium. The cyanide of potassium 

 does not only possess this reducing power in the dry way, but 

 likewise in a dissolved state : mixed with a solution of alloxan, 

 a heavy crystalline precipitate, scarcely soluble in water, of 

 dialurate of potash, is formed in a few seconds. 



Cyanide of Potassium as an agent of separation in Qtianti' 



