specific Gravity , and comparative Wear of Gold. 51 
was internally of a gray colour,* and was extremely brittle ; but 
the plate from which the portion of gold had been separated, 
remained perfectly ductile, and did not retain any of the arsenic ; 
for, although it was superficially discoloured, it was unchanged 
in every other respect, excepting that the sharpness of its edges 
was destroyed, and the thickness was reduced from of an 
inch to that of common writing paper. 
The effects produced by the arsenic, in this experiment, were 
very remarkable ; for the plate was as uniformly and evenly 
reduced in its thickness as if it had been planed ; and, while the 
portion which had dropped from it was combined with a very 
large quantity of arsenic, the remaining part of the plate appeared 
to have preserved the whole of its original ductility and purity. 
These singular effects took place, as I have already observed, 
in so short a time as 12 or 15 minutes; but I wished to ascer- 
tain whether the same would not happen, more or less, within 
a smaller period, and under circumstances not so favourable to 
the union of arsenic with gold. 
11. 
Two six-inch crucibles were fitted, and inverted in the man- 
ner already described, and a plate of the standard gold, similar 
in size and quality to that which had been employed in the first 
experiment, was in like manner suspended within the upper 
crucible or dome. 
A semicircular piece was cut out of the lip of this crucible, 
so that, when inverted and luted upon the lower vessel, there 
was an aperture of about inch in diameter, which was 
* The external colour was like that of fine gold, in consequence of the arsenic 
having been volatilized from the surface of the ingot, by the heat of the lower crucible. 
H 2 
