Barium Cyanide, Ba(CN)₂

Barium Cyanide, Ba(CN)₂, is formed by passing anhydrous hydrocyanic acid over cooled barium hydroxide crystals, and dissolves in the water of crystallisation of the hydrated baryta. With anhydrous barium oxide or hydroxide too vigorous a reaction takes place and the cyanide is decomposed. Prismatic crystals of the dihydrate, Ba(CN)₂.2H₂O, may be obtained by adding a slight excess of hydrocyanic acid and evaporating in vacuo in presence of sulphuric acid and a small quantity of caustic potash. They are deliquescent and readily decomposed by the carbon dioxide of the air. Over sulphuric acid in vacuo the more stable monohydrate is obtained, and this may be completely dehydrated by a slow current of dry air, first at 75° C., and then at 100° C. The anhydrous salt is white and very hygroscopic. It is also very soluble in water, eight parts dissolving in ten of water, and fairly soluble in alcohol. The heat of hydration to the monohydrate is 1.94 Cal., and to the dihydrate 3.17 Cal.

Barium cyanide is also formed by the action of carbon monoxide on barium nitride, by the calcination of barium ferrocyanide and extraction with water, and by the action of cyanogen gas on barium amalgam. Pure barium cyanide may be prepared by suspending finely powdered barium hydroxide in light petroleum and adding an emulsion of anhydrous hydrocyanic acid in light petroleum. It fuses at about 600° C. and is rather volatile.

By passing nitrogen over barium carbide heated to redness in iron retorts, about 30 per cent, of the carbide is converted into cyanide, the rest forming barium cyanamide. By fusing with sodium carbonate the remainder of the carbon is taken up and cyanide formed.

When the cyanide is heated to 300° C. in the presence of steam the whole of the nitrogen is evolved in the form of ammonia, leaving barium formate,

Ba(CN)₂ + 4H₂O = Ba(HCOO)₂ + 2NH₃.

The compound Ba(CN)(OCH₃).CH₃OH is obtained when hydrocyanic acid is passed into a methyl alcohol solution of barium oxide. It loses alcohol at 100° C., and at still higher temperatures forms the basic cyanide, BaO.Ba(CN)₂.

Aqueous solutions of barium cyanide dissolve insoluble cyanides of some of the heavy metals forming crystalline double salts - for example, BaHg(CN)₄.3H₂O in needles, 2Ba(CN)₂.3Hg(CN)₂.23H₂O in transparent octahedra, and Ba(CN)₂.Hg(CN)₂.HgI₂.6H₂O; barium manganocyanide, Ba₂Mn(CN)₆, barium manganicyanide, Ba₃[Mn(CN)₆]₂, barium manganese manganocyanide, BaMn[Mn(CN)₆], and also a double manganocyanide of barium and potassium; barium cobaltocyanide, Ba₂Co(CN)₆, and an unstable barium chromocyanide, and also a barium ruthenocyanide, Ba₂Ru(CN)₆.6H₂O.