GALVANISM. 413 



•wTiat is an "^83. For conveniencG in certain experi- 

 Eiectrode? ments, the ends of the copper wires connect- 

 ing the poles of the galvanic battery are frequently 

 terminated with thin strips of platinum, which are called 

 Electrodes. The platinum slip connected with the posi- 

 tive pole forms the positive electrode, and that with the 

 negative pole, the negative electrode. 



Platinum is used for the reason, that in employing the battery for effecting 

 decompositions, it is frequently necessary to immerse the ends of the con- 

 ducting wires in corrosive liquids, and this metal generally is not affected by 

 them. 



What is Eiec- '<^84. Electto-metallurgy, or electrotyping, is 

 tro-metauurgf f ^q ^j.|. qj. procGss of depositing, from a metal- 

 lic solution, through the agency of galvanic electricity, a 

 coating or film of metal upon some other substance.* 

 Upon what is ^he process is based on the fact, that when 

 bated ? ^"^""^^^ a galvanic current is passed through a solu- 

 tion of some metal, as of sulphate of copper 

 (sulphuric acid and oxyd of copper), decomposition takes 

 place ; the metal is separated in a metallic state, and 

 attaches itself to the negative pole, or to any substance 

 that may be attached to the negative pole ; while the 

 oxygen or other substance before in combination with the 

 metal, goes to, and is deposited on the positive pole. 



In this way a medal, a wood-engraving, or a plaster cast, if attached to the 

 negative pole of a battery, and placed in a solution of copper opposite to the 

 positive pole, will be covered with a coating of copper ; if the solution con- 

 tains gold or silver instead of copper, the substance will be covered with a 

 coating of gold or silver in the place of copper. 



The thickness of the deposit, providing the supply of 

 the metallic solution be kept constant, will depend on the 

 length of time the object is exposed to the influence of the 

 battery. 



In this way, a coating of gold thinner than the thinnest gold-leaf can bo 

 laid on, or it may be made several inches or feet in thickness, if desired. 



The usuiU arrangement for conducting the electrotype process is represented 



• The preneral name of electro-metalhirpy includes aU the various processes and results 

 which different inventors and manufacturers have dcsi<niated as fjalvano-plastic, electro- 

 plastic, galvaso-type, electro-typing, and electro-pUting and gilding. 



