of obtaining pure Silver. 285 
potash, or even a concentrated solution, if cold, has no appa- 
rent action on chloride of silver; and this, I presume, explains 
how the reaction about to be described has not been noticed. 
But a solution of potash, spec. grav. 1:25 to 1:30, with the 
aid of heat, decomposes almost instantaneously the moist 
chloride of silver, converting it into a heavy, fine jet-black 
powder, which is pure oxide of silver. This oxide dissolves 
without the smallest residue, and without effervescence in 
diluted nitric acid, and yields a colourless and pure nitrate. 
The heat of the spirit-lamp reduces the oxide to a coherent 
spongy mass of absolutely pure silver. 
The following method appears to me the most advantageous. 
The cupreous solution of silver is precipitated by common 
salt, while hot, and the chloride of silver well washed by decan- 
tation with hot water. It should also be broken down with 
a spatula of platinum or a glass rod, during the washing, but 
not ground in a mortar, which causes it to cake, and impedes 
the action of the potash. The chloride, while still moist, is 
covered to about half an inch with a solution of caustic potash, 
spec. grav. 1°25 at least, and then boiled. During the boil- 
ing, which is best performed in a capsule of clean iron, silver 
or platinum, the chloride is to be well stirred, in order to 
bruise all curdy or lumpy particles. In five or ten minutes 
the powder has become black. If a small portion, taken out 
and washed, do not dissolve without residue in dilute nitric 
acid, the potash is to be decanted off, and the powder, still 
moist, is to be well rubbed down in a mortar, which may 20w 
be done with advantage. It is then returned into the capsule, 
and again boiled for five minutes with the same, or with fresh 
potash. It will now dissolve entirely in nitric acid; but if 
not, a second grinding will infallibly succeed. It is now only 
necessary to wash the oxide, which is completed by decanta- 
tion in a few minutes, as the powder, from its great density, 
sinks at once to the bottom. The first two or three washings 
are made with hot water, the remainder with cold water; for 
when the oxide is nearly washed, it rises partially to the sur- 
face, with hot water, and thus a loss is occasioned in decant- 
ing. Of course, the whole washings (except the first, owing 
to the strength of the potash) may be conducted on a filter. 
But the powder is so fine, that probably a good deal would 
adhere to the paper when dry. 
This oxide of silver appears in a form quite distinct from 
that of the oxide precipitated by potash from the nitrates, and 
is hitherto undescribed. It is very dense, homogeneous, and 
has a pure black colour, which has, if anything, a tint of blue; 
whereas the common oxide is bulky, far less dense, and of a 
grayish brown colour. ‘They appear, however, to be chemi- 
