PROFESSOR J. W. MALLET ON THE ATOMIC WEIGHT OF GOLD. 
419 
By heating in a Sprengel vacuum I found traces of oxygen in the rolled silver 
plates, and extremely minute traces of gas, apparently also oxygen, were likewise 
obtained from the gold plates, before either had been used. 
The middle of the vulcanite strip was supported at a suitable heiglit, so as to allow 
of equal immersion of tbe two pairs of plates in their respective solutions, which 
were contained in small vessels of good hard glass, free from lead. Care was taken 
to keep the vulcanite strip dry, so that there should be no practical defect of insula¬ 
tion between the two plates of each pair; the necessity for this precaution having 
been shown in some of the very early preliminary experiments with copper plates, 
using a wooden supporting strip ; some puzzling results being traced back to a little 
accidental moistening with sulphate of copper solution of the part of the strip 
between one pair of plates, while those of the other pair were well insulated as to the 
strip from which they hung. 
In all the experiments the two pairs of plates, previously ignited in the Sprengel 
vacuum, cooled, and weighed, were placed in position in the clips, the distance between 
the parallel surfaces of the plates of each pair being the same, and in most of the 
experiments measuring about 2'5 cm., and connection was made with the terminals of 
the galvanic cell or cells used before immersion of the plates in the metallic solutions. 
All four plates were immersed at the same moment, and at the end of the experiment 
were in like manner lifted out of the solutions at the same moment, before the current 
had been broken. They were immediately introduced into one after another of several 
portions of distilled water, before removal from the clips, thorough washing, heating 
in the Sprengel vacuum, and final weighing. 
A preliminary course of experiments was carried out with plates of pure electrotype 
copper (both pairs) in solutions of cupric sulphate, in order to test the effects, if any, 
of the following differences in the conditions of the two electrolysis cells compared. 
1 . Effect of Difference in the Degree of Concentration of the Two Solutions. —The 
solution in one of the two vessels in which the plates were immersed being made to con¬ 
tain but one-tenth the proportion of cupi’ic sulphate existing in the other, acidification 
and all other conditions being tbe same for both, only a very minute difference was 
found between the quantities of copper deposited in the same time on the two cathode 
plates, and the difference was not invariably in the same direction. The tendency 
however, seemed on the whole to be toward a slightly larger amount thrown down 
hydrochloric acid, and the chloride of silver, after a thorough washing with pure water, is dried and 
reduced in the melting pot with pure carbonates of soda and potash and carbon in the shape of wheat 
flour, the melting being done in a clay crucible. The resulting silver bar is then dissolved in dilute 
nitric acid, and after standing some time filtered, precipitated, and reduced as before ; then remelted 
with the addition of pure nitrate of potash and borax. This generally gives a bar somewhat brittle 
(crystalline in fracture). It is then remelted, and stirred with a pine stick, and chloride of ammonium 
added; when the chloride has disappeared the metal is poured. I find this method more satisfactory 
than any other 1 have tried.” 
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