Chemical Affinity in terms of Ldlectromotive Force. 7 
the true value of the B.A. unit is about 1:3 per cent. lower 
than that thus assumed; next, Lord Rayleigh’s recent valua- 
tions of the H.M.F. of Clark’s cell indicate 1:434 instead of 
1-457, or 1°6 per cent. lower (this correction including the 
previous one). Still smaller values, 1:427 to 1°483 volt, or 
from 1°7 to 2:1 per cent. lower than Clark’s value, have 
recently been obtained by Von Httingshausen (Zeitsch. fir 
Fllectrotechnik, 1884, Heft xvi.); whilst, lastly, the value of 
Jf, the factor for converting heat units into volts, as deduced 
from the most recent experiments of Mascart, Kohlrausch, 
and Lord Rayleigh, is nearly as much below 4410; these three 
observers finding for the C.G.S. electrochemical equivalent of 
silver respectively the values ‘01124, -011183, and between 
°01118 and °01119, from which a mean value of close to ‘0112 
results ; so that F= = ='0001038 ; whence, taking 
J =41°55 x 10°, it follows that JF=4313, or 2:2 per cent. 
below 4410. So that, on the whole, both EK and Ey are uni- 
formly overvalued below by amounts probably amounting to 
between 1°6 and 2-2 per cent.; whence their differences will 
evidently be overvalued to sensibly the same extent. The 
errors thus introduced into the values assigned to the various 
thermovoltaic constants calculated are in no case of such 
magnitude as to interfere with the general character of the 
inferences drawn from the numbers thus deduced. 
167. A number of cells have been examined, in which a 
sparingly soluble electrolyte was employed in the form of the 
solid salt suspended in a solution of some other salt (usually 
the one surrounding the other plate), e.g. zine-silver-chloride 
cells, where the silver plate was surrounded by a magma of 
silver chloride suspended in zinc-chloride solution; or cad- 
mium-lead-sulphate cells, where lead sulphate suspended in 
eadmium-sulphate solution surrounded the lead plate. Some 
noteworthy peculiarities have been observed with such cells 
as regards the fluctuations in the values of a and 6 in the 
formula H=e+a—b with variations in solution-strength. 
Thus, with zinc-lead-sulphate cells (set up with a magma of 
lead-sulphate and zinc-sulphate solution round the lead plate) 
the effect of variation in the strength of the zinc-sulphate 
solution surrounding the lead plate is not the same, either in 
magnitude or sign, as the effect of the sane variation in the 
strength of the zinc-sulphate solution surrounding the zinc 
plate. In the latter case (as already shown, Part VIII.) the 
effect is of this kind, that as the solution-strength increases 
the numerical value of ) continually increases, its sign being 
always the same, viz. positive; but in the former case this is 
not so, the numerical value of a increasing with the strength 
