176 ELECTROLYSIS. 



importance of the work in hand. We will only make upon this 

 subject a single remark, that is, that their depth should be 

 sufficient for lodging not only the electrodes but also the 

 sediments resulting from a long period of working. The copper 

 solution being denser at the bottom than at the top, it is 

 necessary, in order to obtain a regular thickness of deposit on 

 the mould, to continuously stir the liquid. 



If the wooden vats can be made water-tight without any 

 internal lining, this would be better than any other system. 

 Otherwise we would recommend a lining made of sheet lead 

 soldered together with a red soldering iron in preference to a 

 lining of gutta-percha, marine glue, or any other substance. 



MODUS OPERANDI. When the mould has been coated with 

 plumbago, all the parts which are to remain intact are touched 

 with a brush dipped in hot wax, and it is then immersed in 

 slightly alcoholised water, a jet of water being afterwards 

 directed upon it so as to remove the excess of plumbago and 

 the air bubbles which adhere to the surface. 



The mould is afterwards placed in the bath ; a very small 

 surface of anode must at first be immersed to prevent too rapid 

 a deposition ; this is important, as otherwise the copper might 

 be deposited in a granulated state. The current must be 

 intelligently regulated ; it should be moderated at the beginning 

 or the deposit would have a granulated appearance and a black 

 colour. When the deposit has commenced in good conditions 

 a bright layer starts from the suspending wire and extends 

 itself gradually radiating upon the surface coated with plum- 

 bago. After a short time the anode is gradually lowered down, 

 thereby increasing the surface of action according to the pro- 

 gress of the deposition. When the mould is completely covered 

 the anode can be completely immersed and the strength of the 

 current increased without inconvenience. 



The principal consideration for a manufacturer is to produce 

 well and rapidly. Certain experimenters, guided by a long 

 experience and the exact knowledge of the principles of their 

 art, work twice as quickly as some others, obtaining at the same 

 time copper electros with a very fine and very close grain. 



Many causes may interfere with the rapidity of the deposi- 



