194 REPORT—1890. 
that electrolytes still conduct when the rapidity of alternation is two 
hundred millions per second. 
If there should be evidence to show that there is no rapidity of alter- 
nation for which electrolytes behave as diclectrics and no waves so long 
that electrolytes are opaque, we might take up Lodge’s ! third suggestion, 
that the number of molecules actually taking part in the conduction is 
too small to affect the properties of the substance in bulk, but this would 
have important bearings on the theory of conduction. 
(d.) The only immediate effect of the passage of the current upon the body 
of a homogeneous electrolyte is to alter its temperature, and the alteration 
of temperature takes place in accordance with Joule’s law. 
There are two statements involved in this proposition. First, the 
chemical effects take place entirely at the electrodes: although the 
electricity is conveyed convectively through the electrolyte there is no 
change in the physical or chemical properties of the fluid in the inter- 
mediate vessel of the cell described in Part I. The electrolyte between 
the anode and cathode vessel produces the electro-magnetic effect corre- 
sponding to the current, but it gives no other evidence that a current is 
passing ; it is the same fluid in the same condition as if no current were 
passing. This amounts to asserting a negative,and by it I do not intend 
to deny the possibility of some evidence of changed condition being 
ultimately discovered. Reinold and Riicker found no evidence of change 
of state in their films. Lord Rayleigh ? has looked for an effect upon the 
power of transmitting light, but the result of his experiments is to show 
that in dilute sulphuric acid a current of one ampére per square centi- 
metre does not alter the velocity of light by one part in thirteen millions, 
or fifteen metres per second. Ihave thought it possible that there might. 
be a change in the absorption spectrum of the liquid during the passage 
of the current; but the spectrum is a complicated phenomenon, and no 
difference is visible in the cases I have tried. It is much to be desired 
that the change, if any, in the condition of the conducting fluid should 
be speedily brought to light, as the question has an important bearing on 
the dissociation theory. Secondly, Joule’s law applies equally to electro- ° 
lytes and metallic conductors. With the acceptance of Ohm’s law, this 
does not seem really to imply more than is included in the first statement 
above. For if there is no change in the condition of the electrolyte, the 
only expenditure of energy upon it is that required to maintain the 
current, and the resistance is the amount of work required to maintain 
unit current; so Joule’s law follows if the resistance is constant. If there 
were any chemical cling, as Lodge calls it, of the atoms in the molecules, 
the law could not be true; so if it be trne we must give up the idea of 
polarisation in the interior of an electrolyte, and the idea of a finite 
electric force being required to separate a molecule into ions. A number 
of direct experimental verifications of Joule’s law for electrolytes have 
been attempted by Joule,? by E. Becquerel,t by Jahn * for CuSO,+200 
H,0 and CuSO,+150H,0 (current between ‘106 and ‘162 ampére) and 
for ZnSO,+200H,0 and ZnSO,+300H,O (current strength between 
°037 and ‘05 ampére), and by Kopp® for ZnSO,. In no case has any 
deviation from the law been detected. 
1 B.A. Rep. 1885, p. 768. 2 Thid. 1888, p. 341. 
% Phil. Mag. 19, 1841, p. 274, 
* Ann. de Chim. [3] 9, 1843, p. 54; see Wied. Hlec. 2, § 482-486. 
5 Wied. Ann. 25, 1885, p. 49 5 Beibl. 10, 1886, p. 714. 
