314 TINNING, PLATING, &C. 



both these substances consist of copper covered with a thin coat of 

 real silver, yet they are not made in the same way. In making 

 French plate, copper, or more commonly brass, is heated to a cer- 

 tain degree, and silver leaf is applied upon the heated metal, to 

 which it adheres by being rubbed with a proper burnisher. It is 

 evident, that the durability of the plating must depend on the num. 

 ber of leaves which are applied on the same quantity of surface. 

 For ornaments which are not much used, ten leaves may be suffici- 

 ent ; but an hundred will not last long, without betraying the me. 

 tal they are designed to cover, if they be exposed to much hand, 

 ling, or frequently washed. After the same manner may gold leaf 

 be fixed, either on iron or copper. Gold is applied on silver, by 

 coating a silver rod with gold leaf; and the rod being afterwards 

 drawn into wire, the gold adheres to it ; the smallest proportion 

 of gold, allowed by act of parliament, is 100 grains to 576O 

 grains of silver j and the best double-gilt wire is said to have about 

 twenty grains more of gold to the same quantity of silver*. It 

 has been calculated, that when common gilt wire is flatted, one 

 grain of gold is stretched on the flatted wire to the length of above 

 401 feet, to a surface of above 100 square inches, and to the 

 thinness of the 492090th part of an inch : and M. de Reaumur 

 says, that a grain of gold may be extended to 2900 feet, and co- 

 ver a surface of more than 1400 square inches ; and that the thick, 

 ness of the gold, in the thinnest parts of some gilt wire, did not 

 exceed the fourteen millionth part of an incht. The gold, when 

 thus applied, is thinner than when silver is gilt in the following 

 manner, which is yet reckoned one of the cheapest ways, and is 

 used in making various toys. Gold is dissolved in aqua regia y 

 and linen rags being dipped into the solution, they take up some 

 particles of gold ; the rags being burned to ashes, and the ashes 

 being rubbed on the silver, the gold adheres to it, and is rendered 

 visible by being well burnished. 



Lewis Com. Phil. p. 53. i Id. 60. 



