72 ELECTROTYPE PROCESSES. 



terminates with a medal attached to the wire of the battery. The 

 electricity from the battery passes through all these cells, and 

 reduces its equivalent in each cell. Thus the reduction of 32 grains 

 of zinc in the battery would deposit 32 grains of copper multiplied 

 by 6 times, or as many times as there are cells. 



This is correct in principle, and at first sight seems to be exceed- 

 ingly economical ; but it is not so, for every cell adds so much to 

 the resistance of the current, that intensity batteries must be used : 

 so that, supposing we have a compound cell of 6 divisions, in 

 which are placed 6 separate medals, it would require a battery of 6 

 pairs of plates to give intensity sufficient to overcome the resistance, 

 and the same number of medals could be made of the same weight 

 by 6 separate zincs, and in less than half the time they could be 

 made by this arrangement, and with a less destruction of zinc. For 

 large operations, where the article receiving the deposit and the 

 electrode are necessarily a good way apart, the process is altogether 

 impracticable in a commercial point of view. This is one of the 

 remarkable instances where theoretical possibility and commercial 

 economy are at variance. 



Effects of Resistance. At page 60 we mentioned, that if a single 

 cell deposit 100 grains in a given time, and it be converted into a 

 battery having the two electrodes in a solution of sulphate of copper, 

 there will only be deposited in the same time 30 grains. This is 

 caused by the extra resistance which the solution between the two 

 electrodes, in the decomposition cell, offers to the passage of the 

 electricity, the amount of which corresponds to the amount deposited 

 the latter depending upon the former. 



If we take two small plates of copper and zinc amalgamated, and 

 place them in dilute sulphuric acid, in contact, but not so close as to 

 prevent the gas evolved from the copper plate to escape, and allow 

 them to remain until there have been dissolved from the zinc 100 

 grains, and we call this the measure of the maximum amount of 

 electricity which that surface of zinc and copper can give out in the 

 time taken to dissolve the 100 grains ; then, if the two metals in the 

 acid be separated one inch, being connected by a wire or slip of 

 copper above the liquid, and kept in action the same length of time 

 as the former, there will be dissolved from the zinc, only about 56 

 grains. If the wire in connection with the zinc and copper be 

 extended and cut in the middle, and have a piece of copper attached 

 to each of the same size as the zinc plate in acid, and these be 

 placed in another vessel containing a solution of sulphate of copper 

 (as fig. 4), and put an inch apart, and the whole kept in action 

 the same length of time as before, it will be found in this case that 

 only 10 grains of zinc are dissolved. From these experiments we 

 see, that the resistance of the one inch of acid between the zinc and 



