PKOFESSOR J. W. WALLET ON THE ATOMIC WEIGHT OF GOLD. 
425 
fifth series of experiments, and having immersed in it a pair of plates of “ proof” gold, 
as already described, was employed for the deposition of the gold. The same current 
which traversed this cell was passed through a hydrogen voltameter of special con¬ 
struction,"^' made of glass, in a single piece, the general character of which will be 
seen from fig. 5. 
Fig. 5. 
When this instrument was to be ]3repared for use, it was cautiously heated pretty 
strongly in an air-bath to remove the film of moisture and air from the internal surface, 
drawing dry air through by means of an aspirator. Clean mercury, previously heated, 
was then poured in through the funnel a, going down to nearly the bottom of the 
cylindrical vessel h, until this vessel—about 30 mm. in diameter and 60 mm. in height— 
was completely filled, and also the tubes and stop-cocks c, d, e, and /, each of these in suc¬ 
cession being opened to allow escape of air, and afterwards closed; /’was a three-waystop- 
cock, which could either be made to open communication between the parts of the tube 
on either side of it, or to simply close this tube, or to close this tube and establish 
communication between the vessel b and the outside air through the base of the stop¬ 
cock ; it was in this last-named way that air and surplus mercury were allowed to 
escape, filling the tube between h and f with mercury, but not allowing of any of the 
* This piece of apparatus—an excellent specimen of skilful glass-blowing—was made, from drawings 
furnished by me, by Mr. Emil Greiner, of 63, Maiden Lane, New York. 
MDCCCLXXXIX.-A. 3 I 
