o4 
the other ions with which it may be associated. For example, the velocity 
of the chlorine ion is the same when determined from solutions of K Cl, 
Na Cl or H Cl. The important general law has also been found that the 
conductivities of neutral salts are additively made up of two values, one 
dependent on the positive, the other upon the negative ion. If then tlie 
velocities of the ions themselves be known the conductivity of a salt may 
be calculated. The results of: Kohlrausch received strong confirmation 
from some very ingenious experiments by Lodge and Wetham, in which 
the migration of the ions was made to produce a change of color in the 
solution and could thus be directly observed. 
In 1887 the theory was advanced by Arrhenius and Ostwald that disso- 
ciation is directly effected by solution or fusion, and that in very dilute 
solutions the dissociation is practically complete. Arrhenius holds that 
the ions carry charges of electricity, positive or negative, dependent upon 
their nature, but of equal quantity in every ion. The remaining part of 
the theory is similar to that of Clausius and others. According to this 
theory the ratio of conductivities for different densities of solution gives 
a measure of the relative dissociation or ionization. If, the act of solution 
affects the dissociation necessary to admit electrolysis, chemically pure 
substances ought not to be decomposed by the electric current, and this 
is found to be the case. It is curious that two substances like hydro- 
chlorie acid and water, which separately are insulators, should when 
mixed conduct readily, and that practically only one of them should be 
decomposed. This, however, is only one of the many problems still to be 
solved. Another question is, how do the ions obtain their electric charge? 
Still another, what is the nature of the force which causes ionization? 
There are many more. 
When we turn to the commercial applications of electro-chemistry we 
are met with the astonishing evidences of activity. Only twenty years 
ago there was comparatively little evidence of the importance of this 
branch of applied electricity. At the electrical exhibition in 1881 electro- 
chemistry was apparently of comparatively little prominence. A factory 
which could annually produce a few hundred tons of copper electro- 
lytically was considered a wonder. The production of thousands of tons 
a month is beginning to be looked upon as commonplace. There is. 
scarcely a metal which cannot be deposited electrolytically with compar- 
ative ease, and the prices of some of the rarer metals are going down 
