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PROFESSOR J. W. MALLET OR THE ATOMIC WEIGHT OF GOLD. 
the stopper in place. Air, purified by passing through a red-hot tube, then through 
a solution of potassium permanganate and sulphmic acid, and dried by passing 
through concentrated sulphuric acid and over solid potash, was introduced by the 
tube a, which went clown to near the level of the hcjuid to be evaporated, while this 
air, charged with vapour of water from the liquid, was withdrawn through the tube 
h by means of a water-jet pump ; the bottle was moderately heated by immersion to 
the greater part of its height in a water bath. 
In filtering the gold solutions no paper or other organic material was used, but fine 
white siliceous sand, previously boiled in nitric and hydrochloric acids, washed wdth 
water, and well ignited to burn off any organic matter, was substituted, supporting it 
on coarser sand and larger fragments of quartz, similarly purified, and the whole 
arranged so as to prevent the possibility of any sand grains being mechanically carried 
into the filtered liquid. Vessels of hard glass and Berlin porcelain were employed. 
Care was taken to work in a clean laboratory atmosphere, free from gases or vapours 
which might affect the materials dealt with. 
First Series of Experiments. 
A neutral solution of auric chloride was prepared by cautiously heating auric 
chloride, made, as suggested by Julius Thomsen, by the direct action of pure 
chlorine upon finely divided metallic gold, until such an amount of chlorine 
had been given off that on treating the residual material vfth modei’ately 
