THE TECHNOLOGIST. [Jan. 1, 1865. 



ELECTRO-PLATING. 



In France, electro-plating is regulated by law, every manufac- 

 turer being required to weigh each article when ready for plating 

 in the presence of a comptroller appointed by the Government, and 

 to report the same article for weighing again when the plating has 

 been done. In this way the comptroller knows to the fraction of a 

 grain the amount of the precious metal that has been added, and puts 

 his mark upon the wares accordingly, so that every purchaser may know 

 at a glance just what he is buying. As to the amount of silver consumed 

 in ordinary plating : An ounce and a half of silver will give to a surface 

 a foot square a coating as thick as common writing-paper. And since 

 silver is worth 5s. per ounce, the value of the silver covering a foot 

 square would be about 7s. 6d. At this rate, a well-plated tea-pot or 

 coffee-pot is plated at a cost in silver of not more than 7s. to 8s. The 

 other expenses, including labour, would hardly be more than half that 

 amount. Electro-gilding is done in like manner. The gold is dissolved 

 in nitric-hydrochloric acid, washed with boiling nitric acid, and then 

 digested with calcined magnesia. The gold is deposited in the form of an 

 oxide, which, after being washed in boiling nitric acid, is dissolved in 

 cyanide of potassium, in which solution the articles to be plated with 

 gold, after due preparation, are placed. Iron, steel, lead, and some other 

 metals that do not readily receive the gold deposit require to be slightly 

 plated with copper. The positive plate of the battery must be of gold, 

 the other plate of iron or copper. The process is the same as that above 

 described. The popular notion is, that genuine-electro gilding must 

 necessarily add a good deal to the cost of the article plated. This is 

 erroneous. A silver thimble may be handsomely plated, so as to have 

 the appearance of being all gold, for 3d., a pencil-case for 10d., and a 

 watch-case for 4s. An estimate of the relative value of electro-gilding, 

 as compared with silver-plating, considering the cost of material alone, 

 is about 15 to 1. The quantity of silver used in plating the ware sent 

 in such large quantities to the colonies is about an ounce to the square 

 mile ; one hard cleaning exposes the base metal, and your bargain of 

 plate from auction or that cheap store may be thrown on the dust- 

 heap. 



