406 
PROFESSOR J. W. MALLET OR THE ATOMIC WEIGHT OF GOLD. 
free from any metallic contamination, and the reduction is more easily effected than 
with oxeJic acid. 
Starting with United States gold coin, it was first heated to bright redness in a 
mutfie, as a precaution against the presence of any traces of mercury, and to remove 
any grease, &c., from the surface, and then dissolved in a mixture of pure hydro¬ 
chloric and nitric acids in the right proportions. The solution was evaporated with 
excess of hydrochloric acid nearly to dryness, the auric chloride redissolved in a 
considerable quantity of water, and the solution allowed to settle for four or five days. 
The greater part of the clear licpiid, drawn off with a syphon, and filtered through 
very fine siliceous sand,^ was again evaporated nearly to dryness, adding towards the 
end a few drops of pure sulphuric acid, in case of the conceivable, though unlikely, 
presence of such traces of lead as this might reveal; much pure water was added, the 
solution again cleared by subsidence for several days, and the greater part of the clear 
liquid again drawn off and filtered. This solution was now rendered pretty strongly 
acid with hydrochloric acid, and fractionally precipitated by sulphurous acid (SO 3 was 
evolved from sodium sulphite), at as low a temperature as possible, and in the dark, 
putting aside the first and last portions of the metal thrown down, and reserving for 
further treatment the (largest) middle portion. The gold thus obtained was well 
washed with water, boiled with nitric acid alone, again washed, boiled with hvdro- 
chloric acid alone, again washed, dried, and heated strongly with fused acid sulphate 
of potassium in a porcelain crucible, boiled with dilute hydrochloric acid, and then 
with water. The metal was redissolved in aqua regia, the solution evaporated nearly 
to dryness, with addition of pure hydrobromic acid towards the end, very largely diluted 
with water, and' allowed to stand for two days, well protected from dust, before again 
syphoning off as much of the cleai' portion as could be safely removed without risk of 
disturbing the remainder at the bottom, using a conical precipitating jar with greatest 
diameter below, and filtering the liquid through siliceous sand as before. The evapo¬ 
ration with hydrobromic acid was repeated twice more, and the clear solution—allowed 
the last time to stand a month before being syphoned oft' and filtered—was then 
reduced, once witli oxalic acid (neutralizing the liquid with pure sodium hydroxide 
from the metal), once (after re-solution) with sulphurous acid, and once with formic 
acid, washing the reduced metal well each time before redissolving in aqua regia. In 
the first and second of these reductions a little of the metal first and last thrown 
down was rejected, and in the final reduction with formic acid the first portion 
])recipitated, about one-fifth of the whole, was reserved for use, labelled A, a, the 
middle portion, about three-fifths, was labelled A, h, and the last portion, the 
remaining one-fifth, was also preserved for use, marked A, c, so that it might be 
seen whether any difference in the character of the metal could be detected in the 
* The sand was carefully purified beforehand by boiling with nitric and hydi-ochloric acid, thorough 
washing with watei', and heating to redness in the air. 
