THE BEST METHOD OF MAKING SILVER SOLUTION. 105 



cyanide of potassium as the process just described, and brings, 

 moreover, an equivalent of potash into the solution, which is a 

 disadvantage. The following diagram shows the reactions that 

 occur : 



Substances used : Substances produced : 



Oxide of silver = AgO 



Cyanide of potassium = KCy 

 Cyanide of potassium = ECy 

 AgO -f 2 KCy 



Potash = KO 

 Cyanide of silver) 

 and potassium) 

 KO + KC,AgCy. 



Solution made with Chloride of Silver. The nitrate of silver may 

 also be precipitated by adding a solution of common salt to it, and 

 treating it in the same way as described for precipitation by 

 cyanide of potassium : this would form chloride of silver, which 

 may be dissolved in cyanide of potassium, thus forming the silver 

 solution. But the objection urged against the use of oxide of 

 silver is equally applicable in the case of chloride; and much 

 greater care is required in precipitating large quantities and strong 

 solutions of silver by common salt, than by cyanide of potassium, 

 the chloride of silver being more soluble in the salts of the alkalies 

 as the nitrates, chlorides, and sulphates than cyanide of silver 

 is ; and there is therefore great liability to loss by this process, in 

 which we have not the redeeming quality of a saving of materials, 

 as the following diagram will show : 



Substances used : Substances produced : 



Chloride of silver = AgCl 

 Cyanide of potassium = KCy 

 Cyanide of potassium = KCy 



Chloride of potassium = KC1 



Cyanide of silver) 



= = 



and potassium) 



* A p 



= = R Cy, AgCy 



AgCl + 2 KCy = KCl + KCy, AgCy. 



Thus, we observe that the action taking place is not mere solution 

 but decomposition ; which upon one hundred ounces of silver in this 

 preparation produces an impurity of seventy ounces of chloride of 

 potassium, which, although not very injurious to the solution, would 

 be much better away. 



The Best method of Making Silver Solution. The best and 



cheapest method of making up the silver solution is by the battery, 

 which saves all expense of acids and the labour of precipitation. 

 This is effected by taking advantage of the principle of non-transfer 

 of metal in electrolytes (see page 76). To prepare a silver solution 

 which is intended to have an ounce of silver to the gallon (see p. 104), 

 observe the following directions: Dissolve 123 ounces of cyanide of 

 potassium in 100 gallons of water ; get one or two flat porous vessels, 



