3© Electrolytic Crystallization of Metals. 



arborescent forms characteristic of these metals ; copper in a 

 more compact form. 



In the experiment with cupric chloride, the bright green 

 colour of the saturated solution helps to make apparent the 

 phenomenon known as migration of the ions. The dilution of 

 the solution near the cathode, due to their unequal speed of 

 migration, causes striae of more dilute, and therefore lighter 

 coloured solution to ascend from this neighbourhood. 



I referred above to the observed fact that while the metal is 

 deposited at the negative pole, the chlorine or other anion of 

 the compound is evolved at the positive pole. The question 

 arises as to how the compound is split up so as to evolve its 

 parts at these two distant points without either of those parts 

 appearing in the interval between the poles. This question has 

 been asked ever since Nicholson and Carlisle in the first year of 

 this century discovered the decomposition of chemical compounds 

 by the current. It has not yet received an entirely satisfactory 

 answer. 



One of the earliest explanations assumed that each metal atom 

 had a little positive electric charge on itself, and was therefore 

 attracted like a pith ball to the negatively charged pole, and con- 

 versely each chlorine atom had a little negative charge causing 

 it to be attracted to the positive pole. This hypothesis seems 

 to me to amount simply to an admission that we know little or 

 nothing about electricity or atoms. To take an analogy, we 

 know that an atom of tin in combining undirectedly with two 

 atoms of chlorine evolves a definite amount of heat, but we do 

 not, therefore, assume that this heat was previously charged on 

 those atoms ; yet when the combination takes place in a directed 

 way so that electricity is thereby evolved in place of heat, 

 such electricity is, with no more apparent reason, said to have 

 been previously charged on the atoms. 



Coupled with the supposition that the atoms were charged 

 in opposite ways, it was necessary to introduce some theory that 

 would allow them to be freely attracted to the opposite poles. 

 It was, therefore, assumed that a compound such as tin chloride 

 was separated into independent tin atoms and chlorine atoms by 



