156 Laboratory Arts 



first formed just redissolves. Note the volume of cyanide 

 solution used, and add to the preparation one-tenth in excess 

 of that already used. Make up the solution to i litre, and 

 shake up well with 5 c.c. of carbon disulphide, allowing the 

 liquid to settle, and filtering before use. 



The brass should be well cleaned, washed in hot dilute 

 caustic potash solution, and then in cold water several times. 

 Finally, it is to be immersed momentarily in a i per cent, 

 solution of mercurous nitrate, and well rinsed before plating. 



The silver should be rather heavily deposited, and cleaned 

 up by polishing first with a brush made by binding about a 

 hundred 6-inch pieces of fine brass wire into a bundle, and 

 wrapping tightly with brass wire to within half an inch of each 

 end ; then polishing with powdered rotten stone and oil, and 

 finally with rouge. Otherwise the silver may be burnished 

 after " scratch-brushing " with the wire brush, in the manner 

 already indicated for burnishing silver. 



A powder composed of one part by weight of silver nitrate, 

 two parts potassium cyanide, and five parts of precipitated 

 chalk, ground finely together, and applied to brass with a 

 moistened rag, will cause a layer of silver to be deposited on 

 the surface of the brass, but the layer is very thin, and wears 

 off readily. In some cases, however, the application of this 

 preparation may save electrolytic deposition, though the 

 electrical method is well worth the extra trouble. 



