224 Prof, von Kohell upon Galvanography. 



thus the interior of the copper vessel receives a fresh coating of 

 copper, while the zinc plate is gradually dissolved in the form of 

 sulphate of zinc. The two metals therefore, the zinc and the 

 copper, assume opposite characters, the zinc attracting the acid 

 of the sulphate of copper and the oxygen of the water, the cop- 

 per of the vessel attracting the copper of the sulphate of copper, 

 (due to the reduction of the oxide of copper contained in it by 

 the hydrogen of the water,) and thereby having the thickness of 

 its mass increased. If this process is allowed to continue for a 

 sufficient time, the blue solution of the sulphate of copper is at 

 last deprived altogether of its color and does not contain any 

 more copper at all, after which no further change is observed. 



Such an arrangement of the galvanic apparatus is termed a 

 simple circuit, and it is said to be completed, when the zinc is 

 brought into connection with the copper by a strip of metal as 

 described above. 



If upon the bottom of the copper vessel another piece of metal 

 be laid, for instance a plate of lead, platina, silver, gold, &c., it 

 will be found that when the circuit is closed, this plate becomes 

 coated with copper derived from the solution of the sulphate, 

 which is a proof that it assumes the same condition as the copper 

 itself with which it is in contact. Such substances therefore con- 

 duct the galvanic influence through their mass, and are therefore 

 called conductors. Whereas if a piece of glass, quartz, porcelain, 

 wax, stearine, &c. be laid upon the bottom of the vessel, it will 

 be found when such substances are present of a considerable size, 

 at least, that no deposit of copper takes place upon them, and 

 hence they are termed non-conductors of the galvanic influence. 

 All metals are more or less good conductors ; of the non-metallic 

 bodies, plumbago and charcoal — the latter especially in the form 

 of coke — are good conductors. 



When the surface of a non-conducting body is coated with a 

 conductor, copper will of course be deposited also thereon, so that 

 it is only necessary to invest the surface of wax, stearine or other 

 non-conductors, with a good coat of plumbago, of silver powder, 

 bronze powder, or some such substance, in order to precipitate 

 copper upon them. 



If a strip of copper is made fast to the zinc plate of the above 

 described apparatus, and another strip in like manner to the cop- 

 per vessel, and if these strips instead of being united in the way 



