Chemical Affinity in terms of Electromotive Force. 15 
n 
Values o1 —, 
m 
Determination of the Numerical Values of the Voltaic Constants 
and Lhermovoltaic Constants applicable to various kinds of 
Two-fluid Cells. 
170. In all the cells examined, wherever possible, the plates 
used were coated over by an electro-deposited coat of metal, 
thrown down by a moderately weak current from a strong 
solution of a pure salt of the metal. The plates employed 
usually exposed a total surface of 3 or 4 square centimetres, 
and the electro-coating was effected by passing the current 
from three to five Leclanché quart-cells in series through a 
decomposing cell, in which the plate to be coated formed the 
negative electrode, the positive one being a plate of the same 
metal in as great a state of purity as practicable ; the elec- 
trodes were usually some 3 or 4 centimetres apart. Under 
these circumstances the coating of metal formed was fairly 
tough and coherent, although in certain cases somewhat 
erystalline on the surface. Copper thus deposited from a 
strong solution of copper sulphate formed a coating of great 
regularity and toughness. In some cases, however, bright 
plates of fused metal were necessarily employed, e. g. with 
iron and aluminium. With zinc the -plates always consisted 
