NITROGEN 135 



nitrogen, If per cent phosphoric acid, and 1 per cent 

 potash. 



(e) Calcium cyanamide is a manufactured organic source 

 of nitrogen. It is a dark crystalline powder which, when 

 exposed to the air, increases in weight, due to the slaking 

 of the lime. This results in a lessening of the per cent of. 

 nitrogen that it contains, not by losing its nitrogen, but 

 because of the increased weight of the product. 



Calcium cyanamide is manufactured by heating a mix- 

 ture of limestone and coke in an electric furnace to a tem- 

 perature of 1100 C. At this temperature calcium and 

 carbon unite to form carbide (CaC2). The finely powdered 

 calcium carbide has purified nitrogen gas passed over it 

 when it is at a white heat and under these conditions it 

 will take up two atoms of nitrogen according to the fol- 

 lowing formula: 



CaC 2 +N 2 = CaCN 2 +C. 



The nitrogen of the air is purified either by passing it 

 over red-hot metallic copper or by the fractional distilla- 

 tion of liquid air. The manufactured product contains as 

 impurities carbon, quicklime, silica, iron oxide, and cal- 

 cium sulphide, phosphide and carbonate. It contains about 

 20 per cent nitrogen, which is equivalent to 57 per cent of 

 calcium cyanamide. 



The impurities in cyanamide, consisting of small quan- 

 tities of sulphides, carbides, and phosphides, are decom- 

 posed by the soil moisture when applied, and, unless suf- 

 ficient time elapses for the escape of these products of 

 decomposition that are harmful, the germination of seed 

 is affected. The American Cyanamide Company claims 

 that they have an improved process whereby the injurious 

 impurities are removed. Their product is known as " Im- 

 proved Cyanamide," and the nitrogen is present partly as 

 the cyanamides of calcium and sodium, and partly as 

 nitrate of soda. The American Fertilizer Handbook of 



