DIFFERENT METALS FOR PLATING. 



119 



Rate of depositing Silver. When articles are taken out of the 

 solution they are swilled in water, and then put into boiling water : 

 they are afterwards put into hot sawdust, which dries them per- 

 fectly. Their colour is chalk-white. They are generally weighed 

 before being scratch-brushed ; that is, brushed with the fine wire- 

 brushes and stale beer as already described. Although this opera- 

 tion does not displace any of the silver, still, in taking off the chalky 

 appearance, there is a slight loss of weight ; the appearance after 

 scratching is that of bright metallic silver. Any thickness of silver 

 may be given to a plate by continuing the operation a proper length 

 of time. One ounce and a quarter, to one ounce and a-half of 

 silver, to the square foot of surface, will give an excellent plate about 

 the thickness of ordinary writing paper. 



Bright Deposit. A little sulphuret of carbon added to the plating 

 solution prevents the chalky appearance, and gives the deposit the 

 appearance of metallic silver : the reaction which takes place in this 

 mixture is not yet understood. The best method of applying the 

 sulphuret of carbon is to put one or two ounces into a large bottle, 

 then fill it with strong silver solution, having an excess of cyanide 

 of potassium, and let it repose for several days, shaking it occasion- 

 ally. A little of this silver solution is added, as required, to this 

 plating solution, which will give the articles plated the same appear- 

 ance as if scratched. 



Different Metals for Plating. Silver may be deposited upon any 

 metal, but not upon all with equal facility. Copper, brass, and 

 German silver, are the best metals to plate : iron, zinc, tin, pewter, 

 and Britannia metal, are much more difficult ; lead is easier, but it 

 is not a good metal, because of the rapidity with which it tarnishes, 

 and from its softness easily yields to the pressure of the burnisher : 



