Cyanamide

Cyanamide, NC·NH2, the amide of normal cyanic acid, obtained by the action of ammonia on cyanogen chloride, bromide or iodide, or by the desulphurization of thio-urea with mercuric oxide; it is generally prepared by the latter process. It forms white crystals, which melt at 40° C., and are readily soluble in water, alcohol and ether. Heated above its melting point it polymerizes to di-cyandiamide (CN2H2)2, which at 150° C. is transformed into the polymer n-tri-cyantriamide or melamine (CN2H2)3, the mass solidifying. Nascent hydrogen reduces cyanamide to ammonia and methylamine. It gives mono-metallic salts of the type NC·NHM when treated with aqueous or alcoholic solutions of alkalis. Di-metallic salts are obtained by heating cyanates alone, e.g. calcium, or cyanides in a current of nitrogen, e.g. barium.

Calcium cyanamide has assumed importance in agriculture since the discovery of its economic production in the electric furnace, wherein calcium carbide takes up nitrogen from the atmosphere to form the cyanamide with the simultaneous liberation of carbon. It may also be produced by heating lime or chalk with charcoal to 2000° in a current of air. The commercial product (which is known in Germany as “Kalkstickstoff”) contains from 14 to 22% of nitrogen, which is liberated as ammonia when the substance is treated with water; to this decomposition it owes its agricultural value. It appears that with soils which are not rich in humus or not deficient in lime, calcium cyanamide is almost as good, nitrogen for nitrogen, as ammonium sulphate or sodium nitrate; but it is of doubtful value with peaty soils or soils containing little lime, nor is it usefully available as a top-dressing or for storing.

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