CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 433° 
crystallizes in very fine silky needles. This double hyposulphite is 
gradually decomposed, and we obtain at last, on the plate of copper, 
flat opake crystals with triangular faces two millimetres* in length. 
These crystals are of a metallic gray colour, and some of them exhibit 
tints of a bluish cast: their powder is blackish. They are soluble in 
ammonia, to which they give a blue colour, and it is easy. to perceive 
that they are composed only of sulphur and copper. Hitherto there 
has not been a sufficient quantity of this sulphuret collected to deter- 
mine the relative proportions of the metal and the sulphur. 
Oxysulphuret of Antimony.—In order to prepare the kermes, the 
same liquids are employed as in the preceding experiment, and the 
communication is established between the two tubes by means of an 
are, composed of two plates, the one copper and the other antimony ; 
the plate of copper being immersed in the nitrate, and the plate of an- 
timony in the hyposulphite. The first becomes covered with copper, pro- 
ceeding from the decomposition of the nitrate, while the other, as well as 
the sides of the tube, becomes covered with a reddish brown precipitate. 
Some time afterwards there are formed, on the antimony, small red 
octahedral crystals, and crystallized plates of the same nature as the 
precipitate. These crystals may be dissolved in neutral hydrosulphate 
of potash, and give out sulphuretted hydrogen by the action of the 
hydrochloric acid in which they are dissolved. They are made yellow 
by the alkalis. All these are characteristic of the oxysulphuret of 
antimony: the theory of its formation being the same as that of the 
sulphuret of silver, it is unnecessary to dwell longer on it. 
Sulphuret of Tin.—Sulphuret of tin may be obtained in very small 
crystals, possessing 2 metallic brightness; but the success of the ex- 
periment depends on the electro-chemical action being very feeble. 
The operation is therefore difficult to be conducted. 
Sulphuret of Lead or Galena.—This compound also is obtained 
in regular tetrahedral crystals, but the method to be pursued is different 
from that adopted in a former case. A tube, about one decimetre} in 
length and five or six millimetres{ in diameter, is closed at one end. 
The lower part is filled, to the height of two or three centimetres §, with 
black sulphuret of mercury. On this we pour a solution of chloride of 
magnesium : a plate of lead is then plunged into the liquid to the very 
bottom of the tube. The apparatus being hermetically sealed, is 
then left to the electro-chemical action. In a month or six weeks 
we begin to perceive on the interior surface of the tube, above the sul- 
phuret, a very thin layer of a brilliant precipitate (of a metallic gray 
colour), which is easily detached, and becomes gradually covered with 
small crystals, which appear, when seen through a microscope, to be 
regular octahedrons, presenting the same aspect as those of the ga- 
lena. When the tube is opened, a gas escapes, which diffuses the 
*-ofaninch. + About 3tinches. + About zy Of an inch. § About 1 inch. 
