﻿Copper and Brass by means of Electric Force. 43 



after many experiments, he has adopted the plan of adding to 

 any brass electrolytic solution (but preferably to that containing 

 potassic cyanide and amnionic tartrate, mentioned above) the 

 oxides of the constituent metals as well as their cyanides, and, if 

 this does not perfectly stop gaseous evolution, some cupric am- 

 monide*. The resulting solution has been found to produce 

 brass of a uniform character ; and it gives a deposit which, when 

 microscopically examined, is in texture very much like that pro- 

 duced by the acid copper solution containing zinc, recommended 

 by Napier ; the solution is capable of depositing the alloy to any 

 thickness. If combined oxygen is carried to the cathode by the 

 cupric ammonide, the action may be expressed by the equation 



At the cathode before chemical reaction. At the Cat %£ t j£"' chemical 



{Cu 2 0,4NH 3 + 4H 2 0} +H 2 = Cu 2 +4NH 3 + 5H 2 0. 



Cupric ammonide. Hydrogen. Copper. Ammonia. Water. 



The formula for cupric ammonide is that of Malaguti and 

 Sarzeau. The cupric ammonide and the eliminated hydrogen 

 go to the cathode, chemical reaction then takes place, copper is 

 deposited, ammonia is in solution, and water is formed. 



The imperfect results afforded by ordinary brass solutions are : 



1st. The porous character of the deposit, arising from the se- 

 paration between the parts of the needle-shaped structure. 



2nd. The constant and brisk evolution of hydrogen, being 

 favoured by the pointed character of the deposit from its com- 

 mencement, augments as the coating grows in thickness, and 

 gives in a short time, and at the attainment of an insignificant 

 thickness, a tree-like formation, which still further degenerates 

 as the coating proceeds, so as to render the accomplishment of 

 any thickness more than a mere film impracticable. In practice, 

 the article being coated is taken out every few minutes, scratch- 

 brushed, and then replaced. With two hours of this treatment, 

 the coating is still porous and is very little better than that given 

 by a skilful application of bronze-powder, and then it has to be 

 varnished (when used for coating iron) to prevent rust-spots 

 forming on its surface by the action of the air. 



3rd. The evolution of hydrogen consumes electric power, and 

 renders a high intensity requisite to make up for the loss ; so 

 that, with ordinary solutions, twoBunsen's cells, of considerable 

 effective positive surface, are barely sufficient to bring out the 

 article in a serviceable condition. 



4th. It is very difficult, and in some cases impossible, to pre- 

 vent the exudation of some of the solution occluded within the 

 pores. This exudation causes unsightly spots, which are only 

 apparent after the work has been completed some hours. 

 * Walenn's Patent- Specification, No. 3930, a.d. 1868. 



