16 Messrs. Wright and Thompson on the Determination of 
of pure metal superficially amalgamated with pure mercury. 
The cells employed were uniformly constructed of two small 
beakers or porcelain vessels containing respectively the metals 
and fluids employed, and united by a siphon-tube, consisting 
of an inverted Y-tube, the lower ends of which were covered 
over with thin animal membrane secured by a silk thread, and 
rendered watertight, when requisite, at the junction of the 
glass and membrane by the application of a little melted gutta- 
percha, so that no leakage into or from the siphon took place, 
saving by osmosis through the membrane. In all cases the 
temperature varied from 18° C. by only + a few degrees. 
Saving in the case of certain experiments quoted from pre- 
vious portions of these researches, and a few others made for 
special reasons with the quadrant-electrometer, all the obser- 
vations were made by means of the galvanometer, currents 
being used of such small density as to produce no sensible 
depreciation in the E.M.F.; in most cases an external resist- 
ance of a megohm (and in many of much more) being 
employed, the valuation being obtained by comparing the 
readings of the cell to be examined with those of an Alder- 
Wright’s normal Daniell cell* through the same resistance, 
using the formula 
B=1-114x ”, 
n 
where m is the average reading of the cell to be valued, and 
n that of the standard Daniell. Usually alternate readings 
of the two cells were taken for 20-30 minutes after first 
setting up, and averaged to obtain the values of m and n. 
A. Voliaic and Thermovoltaic Constants of Metals immersed 
in Solutions of their Sulphates. 
I. Copper. 
171. Hlectro-copper presents the remarkable and almost 
* The term “normal Daniell cell” has been applied by different 
observers to very different forms of cell, varying several per cents. in 
E.M.F. amongst themselves, principally according as sulphuric acid of 
one strength or another, or zinc-sulphate solution saturated or otherwise, 
is used to surround the zinc plate. What is here referred to as an 
“ Alder-Wright’s normal Daniell” is a cell set up after Raoult’s form of 
construction, with amalgamated-pure-zinc and electro-copper plates im- 
_ mersed in pure solutions of their respective sulphates of the same molecular 
strength, preferably of strength mMSO, 100 H,O, where m is near to 
2:0, 2. e. with copper-sulphate solution nearly but not absolutely saturated, 
so as not to deposit crystals by chilling or slight evaporation. The ratio 
of the E.M.F. of such a cell to that of a Clark’s cell at 15°°5 has been 
found to be sensibly ‘765 to unity. 
