212 



ELECTRO-METALLURGY 



is present, the hydrogen, instead of being freed in the fjprm of gas, combines uiih 

 oxygen of the oxide of copper, and liberates the metal, which in its nascent state 

 is deposited on the mould, and produces the electrotype copy of the same. Ono 

 battery cell is sufficient for -working in this way in copper ; it is increased in size in 

 proportion to the size of the object operated upon. And, although for small subjects, 

 such as medals, a vertical arrangement will act very well ; for large objects, it has 

 been often found of great advantage to adopt a horizontal arrangement, placing tho 

 mould beneath the copper-plate. The varying density of a still solution in the 

 vertical arrangement is not without its effect upon tho nature of the deposit, both on 

 its character and its relative thickness. This has been in some instances obviated, 

 and tho advantage of tho vertical method retained by keeping tho solution in motion, 

 either by stirring or by a continuous flow of liquid. 



Wo have described principally Danioll's battery as tho generating cell in electro- 

 metallurgical operations; but Mr. Smee's more simple arrangement of platinised 

 silver and zinc, excited with diluted sulphuric acid, has been found in practice more 

 economical and convenient. 



Fig, 796 is a Smee's cell ; a vessel of wood, glass, or earthenware, contains diluted 

 sulphuric acid, one p;irt of acid in eight or ten of water ; a platinised silver plate s, 

 sustained by a piece of wood w, is furnished with a plate of zinc, z z, on each side, so 

 as to turn to useful account both sides of tho silver plate. The zinc 

 plates are connected by the binding screw b. Platinisation consists in 

 applying platinum in fine powder to tho metallic surface. "When 

 hydrogen is liberated by ordinary electric action upon a surface so 

 prepared, it has no tendency to adhere or cling to it ; but it at once 

 rises, and in fact gets out of the way, so that it never, by its presence 

 or lingering, interferes with the prompt and ready continuance of the 

 electric action ; and in this way the amount of supply is well kept up. 

 Platinisation is itself another illustration of working in metal by 

 electricity. A few crystals of chloride of platinum are dissolved 

 in diluted sulphuric acid. A voltaic current is made to enter this 

 solution by a plate of platinum and to come out by a silver plate. 

 Two or three Daniell's or Smee's cells are necessary for the opera- 

 tion. The chloride of platinum is decomposed, and tho metal is 

 deposited upon the silver plate ; not, however, in the reguline compact 

 form, as in the rase of copper, but in a state of black powder in no 

 way coherent. This affords also an illustration of the different 

 behaviour of metals under analogous circumstances. Copper is of all metals the most 

 manageable ; platinum is among the more unmanageable. 



Mr. C. V. Walker has, with great advantage, substituted graphite for silver. Tho 

 material is obtained from gas retorts, and is cut into plates a quarter of an inch thick, 

 or thicker, when plates of a larger size are cut. He platinises these plates in the 

 usual way as above described, and deposits copper on their upper parts, also by elec- 

 trotype process, and solders a copper slip to tho electrotype copper, in order to make 

 tho necessary connection. 



Utilisation of Copper Scraps in Electro-Plating. The following description of M. C. 

 Guerin's method of utilising scraps of copper, in lieu of plates, as a soluble anode in 

 electro-plating, has been published by tho ' Scientific American.' By this process the 

 inventor utilises cuttings and other scraps, previously-deposited films, and, in a word, 

 all tho metal which would bo otherwise thrown aside as useless for such a purpose. 

 Fig. 797 is a representation of the receptacle used fo holding tho copper scraps. Jt. 



797 



is simply a prismatic box about l in. broad, sustained in the bath by tin- two longi- 

 tudinal rods shown at the top. Tho ucting sides aro pierced each with about 100 



