ARTIFICIAL SLATES. 205 



Another Method. — Wash well the surface of the copper or brass, 

 with water acidulated with muriatic acid, and liaving a little com- 

 mon salt and cream of tartar dissolved in it. Then wash it with 

 pure water, and rub the surface briiiht with leather. 



Dissolve some silver in aquafortis ; dilute it whCn dissolved with 

 an equal quantity of pure water : add to it a small plate or rod of 

 copper, which will precipitate the silver in a metallic state and in 

 a fine powder. Pour otf the solution of copper : wash the pre- 

 cipitate with water. Take of the washed precipitate 20 grains 5 

 grind it with two drachms of cream tartar, two drachms of common 

 salt, and half a drachm of alum. With a clean ra^, rub the sur- 

 face of i!ie polished copper or brass with this moistened mixtuie, 

 and when the white color appears, wash it, and polish it with the 

 fleshy part of the thumb. 



This process is analogous to ti.e method of whitening brass-wire 

 to make brass pins ; the wire is boiled in a solution of tartar with 

 a little common salt, in which solution you put tiiin^iis of pure tin. 



All these methods of silvering may be protected by varnish of 

 mastic or sandarach. 



Another Way. — Clean the surface of your copper or brass with 

 crocus martis, tin putty, or finely silled rotten-stone. Heat the 

 metal (juickly, and while hot. cover the surface with silver-leaf; 

 press it hard to the surface of the copper or brass, and when cold 

 enough, burnish it. You may repeat this. 



To Plate Cupper zoilh Silver, 

 Upon one side of a flat polished ingot of copper, sift thinly some 

 finely powdered glass of borax through line muslin. Place on it a 

 plate of silver of nearly equal surface ; bind it down tight with iron 

 wire : hammer it so that the surfaces shall be in Contact. Expose 

 it to a low red heat which will melt tbe borax. Then pass the 

 plated ingot while warm, through a roller. It will now be joined 

 to the copper, and can be rolled out with it. Good plating should 

 have a twentieth of its weight of silver on it. 



[Cooper'' s Chemical .Amusement. 



ARTIFICIAL SLATES. 



A species of artificial slates have been used in Russia, which are 

 said to be very valuable, as being lighter than common slates, im- 

 pervious to water, incombustible, and made of any required form 

 or size. They have been analyzed by M. Giorgi, who finds lliem 

 to consist of bolar earth, chalk, or carbonate of lime, strong glue, 

 paper pulp, and linseed-oil. 'J'he earthy materials are to be 

 pounded and sifted, and the glue dissolved in water; the paper is 

 the common paper pulp, which, after being steeped in water, has 

 been pressed, or it may be bookbinders' or stationers' shavings 

 boiled in water and pressed. The linseed-oil is to be raw. The 

 paper pulp is to be mixed in a mortar, with the dissolving glue, the 

 earthy materials then added and beaten up, and the oil added duv- 



