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, 

 tlat 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. 



Oxysulplairet 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 

 arc, composed of two plates, the one copper and the other antimony ; 

 the j)late of copper being immersed in the nitrate, and the plate of an- 

 timony in the hyposulphite. The first becomes covered Avith 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. 



SuJphuret of Tin. — Sulphuret of tin may be obtained in ^'ery small 

 crystals, possessing a 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 decimetref in 

 length and five or six millimetres J 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 

 ^lour), which is easily detached, and becomes gradually covered with 

 Ajnall crj-stals, which appear, when seen through a microscope, to be 

 regular octahedrons, presenting the same aspect as those of the "-a- 

 lena. When the tube is opened, a gas escapes, which difiiises the 

 • V? of an inch, f About 3^ inches. I About ^'^ of an inch. § About 1 inch. 



