PROFESSOR J. W. MALLET ON THE ATOMIC WEIGHT OF GOLD. 
417 
While taking’ due note of the recent literature on the subject of the quantitative 
electro-deposition of metals from their solutions, especially the reports of work hy 
A. Classen,'" Lord Rayleigh and Mrs. Sidgwick,! Dr. Gore,| Thos. Gray,§ and 
W. N. SHAW,i| the author of the present paper made for himself a somewhat extended 
preliminary examination of the effect of varying conditions on such depositions, so far 
at least as seemed to be required for his immediate purpose. 
The general arrangement of apparatus adopted consisted of a horizontal strip, 
4 mm. thick, of vulcanite, or hard vulcanized india-rubber, about 26 cm. long hy 3 cm. 
wide, near each end of which and in the middle of the width were two small holes, 
through which passed short bits of brass rod, each having attached to it above a 
binding screw, and below a forceps-like clip, which could be opened by pressure on 
two little outside studs, but closed firmly, on release of this pressure, by the elasticity 
of the metal. In these clips were supported the plates of metal to be immersed in 
the electrolysed solutions, and to serve as anode and cathode terminals respectively, 
there being two pairs of such plates, one pair near each end of the vulcanite strip, 
with four corresponding binding screws. The electric current passed from the first 
binding screw through one of two metallic solutions—as, for instance, that containing 
gold—between the first pair of plates, consisting of the same metal as that in this 
solution, then from the second binding screw to the third (at the other end of the 
vulcanite strip) by a stout copper wire above, and then through the second of the two 
solutions—as, for instance, that of silver—between the second pair of plates, consisting 
again of the same metal as that in the solution in which they were immersed, thus 
reaching the fourth and last binding screw, the first and last binding screws being, of 
course, connected hy wires with the terminals of the galvanic cells used to develop 
the current. Fig. 3 shows the disposition in question. The source of the electric 
current was for the most part galvanic cells of the Meidinger pattern, hut in some of 
the experiments small Daniell cells, and also a Clamond thermo-electric battery, were 
used. The lower parts of the clips were heavily electroplated with the same metal as 
that in the solution to which they respectively belonged, in order to avoid any risk of 
contamination of the solution, in case there should be spattering or accidental 
immersion, even for a moment, of any part of the clip. 
It was decided to place the plates vertically in the liquids, but to make the vertical 
height small in proportion to width, so as to preserve as far as possible a uniform 
condition of the solution in depth. The form adopted for the plates was that of fig. 4, 
the shaded part of the surface being coated with hard paraffine, with a view to 
* A. Classen, ‘ Quantitative Cliemische Analyse durch Electrolyse,’ 2* * * § ^® aufl., Berlin, 188G. 
t ‘ Phil. Trans.,’ 1884, p. 411. 
I ‘ Nature,’ March 16, 1882 ; Feb. 1 and Feb. 15, 1883. 
§ ‘ Phil. Mag.,’ Nov., 1886, p. 389; and March, 1888, p. 179. 
II ‘ Phil. Mag.,’ Feb., 1887, p. 138. 
MDCCCLXXXIX.-A. 3 H 
