SILVER AND GOLD PLATING. 147 



The pieces must be passed rapidly through this bath and 

 be rinsed again in a few pure waters. 



4. Amalgamation. The final preparation consists in im- 

 mersing the scoured pieces for a few seconds in an amalgama- 

 ting liquor composed of 10 litres of water and 100 grammes of 

 binoxide of mercury ; the pieces are stirred, and a quantity of 

 pure sulphuric acid free of arsenic sufficient for dissolving the 

 peroxide of mercury is poured into the solution. The mixture 

 must have a limpidity equalling that of water. After being 

 rinsed once more in pure water the pieces are taken to the 

 silver bath. 



CONDUCT OP THE OPERATION. The deposition is begun 

 with a current the electromotive force of which does not ex- 

 ceed 2 to 3 volts, and the intensity 50 amperes per square 

 metre ; after fifteen minutes' immersion, the objects are taken 

 out and inspected in order to ascertain if they are regularly 

 coated with silver and if no spot or other defect is noticed ; 

 they are brushed with tartar, rinsed, and dipped into a hot solu- 

 tion of potassic cyanide ; they are rinsed again in pure water 

 and placed back either into the first bath or into another silver 

 bath where they are left until the coating has acquired the re- 

 quired thickness. In first-class firms of platers, the deposit 

 of silver on articles for the table (table-spoons, forks) readies 

 from 80 to 100 grammes per dozen. The coating operation 

 lasts three or four hours with the dynamo machine, and from 

 eight to twelve hours with a battery. 



Before taking the objects out of the bath it is necessary to 

 interrupt the current, otherwise they would receive a slight 

 yellow coloration. 



POLISHING OF THE PIECES. After being coated, the pieces 

 must be dipped into a water containing some free potassic 

 cyanide, then rinsed in boiling water and dried in sawdust 

 (boxwood or mahogany, but not pine). The scraping of the 

 parts which are to be bright is done by hand or in the lathe 

 with hard hair brushes sprinkled with pulverised brick. The 

 surface is then polished with tripoli and red, and afterwards 

 burnished with special steel or agate tools and soaped water. 



OBSERVATIONS RELATING TO ORGANIC MATTERS. Although 



L 2 



