PROFESSOR J. W. MALLET ON THE ATOMIC WEIGHT OF GOLD. 
423 
Altogether but five experiments made in this way yielded results which seemed 
worthy of being used to determine the atomic weight of gold, and it is of course 
unsatisfactory to know that these were selected out of a much larger number, mainly 
because, while not known to be in any way vitiated by apparent defects, they lead to 
values for the atomic weight in question close to those obtained by other methods and 
other experimenters. It is possible that this near approach to agreement may merely 
result from a balance of errors in opposite directions, which taken separately would 
have caused the experiments to be rejected. Some other experiments, under 
apparently similar conditions, gave figures for the atomic w^eight differing from those 
reported by one or two whole units. 
These only admissible results are the following :— 
Experiment. 
Character of gold 
in solution. 
Character of gold 
in plates. 
Gold deposited. 
Silver deposited. 
I. 
A, h. 
B 
grm. 
5-2721 
grm. 
2-8849 
II. 
6-3088 
3-4487 
HI. 
4-2770 
2-3393 
IV. 
3-5123 
1-9223 
Y. 
3-6804 
2-0132 
Aside from other difficulties liable to be encountered in carrying out this electrolytic 
method, the two most important sources of possible inherent error which suggest 
themselves are the occlusion of hydrogen by the metallic deposit and the instability of 
the atomicity of gold in the solution electrolysed. 
The separation of. hydrogen on the cathode plate, whether in bubbles (which 
may be avoided by proper regulation of the current) or occluded by the inetal (which 
does not seem to be completely avoidable with any current, although the amount of 
occluded gas was extremely small in a number of my experiments), must be ascribed to 
decomposition, simultaneous with that of the cyanide of gold, either of w^ater or, more 
probably, of cyanide of potassium, with secondary action of the potassium on the 
water. In either case, it is by no means clear that the proportion of current giving 
rise to this liberation of hydrogen can be counted upon as the same in the gold solution 
and in that of silver; and hence, even though it be fairly assumed that Faraday’s 
principle of equivalent electrolysis by the same current is strictly correct for the 
ensemble of chemical actions in the two cells, the portion of current actually concerned 
in depositing gold or silver only in each of the respective cells may conceivably not be 
silver solutions, the gold as potassium auri-cliloride, obtained results which showed that this metal was 
deposited at the rate of 1 atom for 3 of silver. Calculating on this basis from his two experiments, 
the atomic weight of gold comes out = 196‘311 and 194'197 ; for silver = 107'66. 
In one experiment of my own, using sodium ai;ri-chloride, the result showed that the gold was thiown 
down for the most part as a triad, but partly as a monad, element. 
