148 ELECTROLYSIS. 



a silver bath is improved by the presence of a moderate pro- 

 portion of organic matter, a too sudden introduction of the 

 same, or its introduction in too large quantities at a time, 

 must be guarded against. For instance, when candlesticks, 

 which generally contain a mixture of rosin and pitch, are put 

 into the bath without having been first emptied, a large pro- 

 portion of the organic substances will be dissolved by the 

 cyanide, and the conductivity of the bath will be reduced in a 

 certain proportion ; the deposit will be irregular and spotty. 



But when an old bath has gradually become charged with 

 a- small quantity of organic matter, the deposits obtained 

 are brighter and more adhering than those obtained from a 

 new bath. 



OXIDISED OR ANTIQUE SILVER. The colour known as 

 oxidised silver is obtained as follows : 



1. The silver-plated object is brushed with a camel's-hair 

 brush and a solution of platinum chloride in sulphuric ether, 

 alcohol, or cold water. 



2. The following solution is then applied on it in the same 

 manner : 



Sulphate of copper 2 parts in weight. 



Potassic nitrate * j dissolve in acetic acid. 



Ammonic hydrocnlorate .. .. 2j 



3. The ammonic hydrosulphate, concentrated or dilute, 

 gives a more or less deep shade. 



4. Sulphurous vapours give a steel-blue shade. The parts 

 which must not be touched should be protected by a coating. 



5. Nitric acid alone produces the superficial oxidisation of 

 silver. 



WEAKENED SOLUTIONS. The gradual accumulation of 

 potassic salts which results from the action of the air upon 

 the free potassic cyanide comparatively rapidly alters the 

 silver solutions ; these do not then deposit the metal with the 

 fine colour or the solidity with which they did it at first ; it then 

 becomes necessary to extract the silver from the bath and 

 prepare a new solution. 



This operation is carried out in one of the two following 

 manners : The first is effected by adding acid until the metal 



