CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 439 



acids having a less affinity than itself towards the bases is owing solely 

 to the small energy of action in the pile ; for if the action were more 

 powerful, all the acids would be indiscriminately transferred to the 

 positive pole. 



The electric current employed by us in order to produce decomposi- 

 tions, may arise from two causes ; the chemical reaction which the two 

 liquids in contact exercise on each other, and the chemical action of 

 the liquid of the small tube on the metal immersed in it. In the first 

 case, if the reaction be sufficiently energetic, the second cause may be 

 dispensed with : in like manner, if the second cause be of sufficient in- 

 tensity, the first becomes superfluous. But when both are feeble and 

 tiie currents resulting from them have the same direction, their sum is 

 then indispensable to the production of the electro-chemical effects. 

 In general, whenever the two currents take the same course, their sum 

 cannot but be favourable to the decompositions and the formation of 

 the products. It often happens that these two currents are so weak 

 that the reduction of the oxide in the great tube cannot take place. In 

 that case there is no effect produced. If, therefore, after an interval of 

 some days, we perceive no precipitation of copper on the plate of cop- 

 per immersed in the solution of the nitrate or the sulphate, it is useless 

 to continue the experiment longer, and the apparatus must be changed. 

 In the experiment in which the great tube contains sulphate of copper, 

 and the small one contains, in its lower part, potter's clay moistened 

 with a solution of nitrate of potash, and alcohol, the chemical re- 

 action of the nitrate on the sulphate has had considerable influence in 

 producing the current which has decomposed the sulphate of copper ; 

 for the action of the alcohol on the lead must have been sufficiently 

 feeble to give rise to a sensible electric current. It would be desirable 

 to operate always on such solutions as would exercise on each other 

 chemical actions sufficiently energetic to give out the requisite currents, 

 when the plate immersed in the liquid is gold or platina, in order that 

 we may be able to study the phsaenomena of decomposition and recom- 

 position with facility, and independently of the reaction of the oxides. 

 This would be the only course to be taken in order to discover what it 

 is that takes place in the liquid organic compounds, when, by means of 

 electricity, we introduce into them such bodies as are capable of carry- 

 ing off some of their constituent parts. This want of sufficient reac- 

 tion in the liquids may be supplied by operating with the following 

 apparatus, which enables us, when we wish, to avoid the action of the 

 metallic oxides formed at the positive pole. As this apparatus enables us 

 to operate in a great variety of cases, we shall more minutely describe 

 its construction and use. 



We take three jars A, A', A", (fig. 3.) placed in a line at a short 

 distance from each other. The first is filled with a solution of suljjhate 

 or nitrate of copper ; the second, with a solution of that substance 



