154 Selections from Foreign Science. 



ret with the common hydrosulphocyanic acid. — 23. Sulphate of zinc 

 added to the salt in excess caused the gradual formation of a white 

 precipitate, and after some days, of pyramidal crystals of an olive- 

 green colour. Treated with potash these crystals gave oxide of 

 zinc and hydrosulpuretted hydrosulphocyanate of potash. 



24. The ammoniacal salt decomposed by potash, lime, and 

 baryta, gave compounds of these bases, with the peculiar acid. 

 Some difficulty attends the conversion in preventing decomposi- 

 tion. Some of the ammoniacal salt in solution was mixed with a 

 portion of solution of potash, insufficient to decompose the whole 

 of it; the mixture, slightly heated, was put with sulphuric acid 

 under the air-pump to remove the free ammonia. After some 

 time, the liquor, no longer alkaline, was mixed with a fresh quan- 

 tity of potash, and treated as before ; and this was repeated until 

 it became permanently alkaline, when a little more of the ammo- 

 niacal salt was added, and the operation finished by the air-pump. 

 This solution, by evaporation in the air-pump, gave a saline crystal- 

 line mass, readily soluble in water and alcohol, it being a true hy- 

 drosulphuretted hydrosulphocyanate of potash. The aqueous so- 

 lution, heated, deposited sulphur, and became common hydrosul- 

 phocyanate of potash. The alcoholic solution, left in a vessel im- 

 perfectly closed, underwent the same change. 



26. Similar preparations of lime and baryta were made; the ex- 

 cess of lime was removed by alcohol, the excess of baryta by car- 

 bonic acid ; the alcoholic solution of the calcareous compound, 

 evaporated in the air-pump, gave a substance in appearance like 

 gum. 



Crystallized Hydrosulphuret of Cyanogen, 



27. The phenomena appearing by the use of salts of iron, (14 

 and 17,) were then particularly referred to. The white substance 

 there mentioned is best obtained by dissolving one part of the am- 

 moniacal salt in 180 parts of water, and adding a mixture of one 

 sulphuric or muriatic acid to sixteen of water, until the whole is 

 strongly acid. Immediately a solution of persulphate or mu- 

 riate of iron is to be added in small portions ; the liquor darkening 

 at first, soon becomes colourless, and a large quantity of white 

 crystalline scales form, and are deposited. If too much salt of 

 iron be added, so as to cause a permanent red colour, the preci- 

 pitate is of a yellow tint. 



29. This substance contains no iron, but is a particular com- 

 pound of sulphur, carbon, nitrogen, and hydrogen, containing pro- 

 bably more sulphur and less hydrogen than the acid of the salt 

 which furnished it. When perfectly pure it is white as snow, and 

 in the form of shining scales ; it has scarcely any odour, and does 

 not change remarkably by contact with air. Hot water decom- 

 poses it, producing common hydrosulphocyanic acid. It dissolves 



