Dr. W. Gregory on a method of obtaining pure Silver. 283 
lime were exactly the same as those of ordinary pyrogallic 
acid. It is evident, therefore, that pyrogallic acid does not 
combine with ammonia, but is slightly oxidized when brought 
in contact with it. 
The addition of a little potash also rendered solutions of 
pyrogallic acid alkaline and even darker coloured than am- 
monia does. The coloration takes place first at the surface 
of the liquid, and is evidently the effect of oxidation. When 
evaporated zm vacuo it became a black gummy nfass, which 
showed no disposition to crystallize. When this black mass 
was dissolved in water, in which it is very soluble, and treated 
with sulphuric acid, it effervesced, apparently from the escape 
of carbonic acid. It also gave off the vapours ofsacetic acid 
in abundance. These were easily recognisable by their smell, 
and by their immediately reddening litmus paper when held 
over them, When the solution was very concentrated, a little 
of a dark brown matter precipitated; but if the solution was 
at all dilute no precipitate appeared. I made an unsuccessful 
attempt to collect this precipitate on a filter, and to free it 
from adhering sulphuric acid by washing it with cold water. 
The whole of the black matter was speedily dissolved and 
passed through the filter. Soda produced similar effects on 
pyrogallic acid. It is plain, therefore, that pyrogallic acid is 
decomposed by the alkalies, but does not combine with them, 
and that its acid properties, if indeed it possesses any, are very 
feeble. In this and some other respects it closely resembles 
pyromeconic acid. 
When pyrogallic acid is dropped into acetate of copper, it 
causes a dark brown precipitate, which however quickly be- 
comes black, and is very soluble. When we attempt to col- 
lect it on a filter and to wash it, the greater portion of the salt 
is dissolved by thewater. The liquid when it first passes through 
the filter is colourless, but on standing a few minutes it becomes 
dark brown and slowly deposits a new precipitate. The com- 
pound first formed appears to be decomposed by the water. 
When pyrogallic acid is added to a solution of bichromate of 
potash, it immediately turns it yellowish brown, and then dark 
brown till the liquid is almost opake, but no precipitate falls. 
LI. On a new Method of obtaining pure Silver, either in the 
Metallic State or in the form of Oxide. By Wit11am Gre- 
cory, M.D., F.R.S.L., Member of the Chemical Society, &c.* 
HE chemist, as well as the metallurgist, has frequent oc- » 
casion to purify silver, especially from copper, which is 
dissolved along with it by nitric acid, the proper solvent of 
* Communicated by the Chemical Society; having been read Fe- 
bruary 7, 1843. 
