144 ELECTROLYSIS. 



Japing, a solution of silver chloride dissolved in potassic 

 cyanide ; Urquhart, a mixture of silver chloride and sodic 

 chloride ; Brandely, a precipitate of argentic nitrate by potassic 

 carbonate mixed with calcined potassium ferricyanide, &c. 



Potassium ferricyanide pretty freely liberates silver, silver 

 chloride dissolved in sodic chloride gives a chalky deposit ; all 

 solutions containing oxide, carbonate, or silver chloride give 

 irregular results ; the solution of argentic cyanide dissolved in 

 potassic cyanide is alone exempt from inconvenience ; it is 

 therefore the only one which it is interesting to study. 



This is the formula indicated by Koseleur : 



Potassic cyanide of first quality 500 grammes. 



Silver cyanide obtained from virgin silver .. 250 

 Distilled water 10 litres. 



This solution is prepared in the following manner : 

 1. In a porcelain cup of one litre capacity put 



Virgin silver in shots 250 grammes. 



Pure nitric acid at 40 degrees 500 



Heat the mixture on a charcoal or gas fire, placing the cup 

 on an iron tripod in order to prevent its immediate contact with 

 the flame. 



The acid rapidly attacks and dissolves the silver, and 

 abundantly liberates yellow fumes, the inhalation of which 

 must be carefully avoided. 



When the yellow fumes have subsided, there only remains 

 in the cup a more or less greenish, bluish, or colourless liquid 

 according to the proportions of copper which are contained in 

 the silver to be obtained in the trade. 



The fire is then increased in order to evaporate the excess 

 of acid which disappears in the shape of white fumes. The 

 matter dries and swells. A more active fire smelts it like 

 sealing-wax. It is then taken off the fire, holding the cup with 

 a rag, and the liquid is spread on the wall of the cup where it 

 soon gets congealed. Silver nitrate is thus obtained. 



When the whole is perfectly cold the cup is turned upside 

 down on a piece of paper, and a slight tapping detaches the silver 

 nitrate. 



