392 



SMITH'S INTERMEDIATE CHEMISTRY 



Calcium Chloride, CaCl 2 . Chloride of calcium is obtained 

 as a by-product in the Solvay process (p. 366) and in other indus- 

 tries. It crystallizes from water as the white hexahydrate, 

 CaCl2,6H 2 O, and is very soluble. The porous, granular variety, 

 used for drying gases, is made by driving most of the water out of 

 the hexahydrate by heat. The granular form is used in large 

 amounts for sprinkling on dusty roads. The salt, being deliques- 

 cent (p. 118), attracts water from the air and moistens the dust 

 with calcium chloride solution. The saturated solution does not 

 freeze until 48 is reached, so that chilled calcium chloride 

 brine is used in refrigerating appliances (p. 306). 



* Calcium Cyanamide CaCN2. Calcium carbide, when 

 strongly heated, absorbs nitrogen, giving a mixture of calcium 

 cyanamide and carbon (nitro-lime) : 



N 2 - CaCN 2 + C. 



n 



FIG. 97 



The carbide is pulverized and placed in a cylin- 

 drical furnace (Fig. 97), holding 300 to 450 kg. The 

 heat (800 to 1000) is furnished by the passage of 

 a current of electricity through a thin carbon rod, 

 which passes through the axis. The tube sur- 

 rounding the rod and the other partitions are of 

 cardboard, which burns up and leaves openings 

 for the circulation of the nitrogen. The latter is 

 made by the fractionation of liquid air and is in- 

 troduced under pressure. In thirty-five hours 



nitrogen ceases to be absorbed, and the product is pulverized 

 when cold. 



Calcium cyanamide is now manufactured in large quantities 

 at Niagara Falls (Ontario) and Odda (Norway) for use as a 

 fertilizer. It is also a valuable source of ammonia, and was utilized 

 very extensively as such for the manufacture of explosives during 





