28 €YANAMID MANUFACTURE), CHEMISTRY AND USES 



tion is only a small portion of the true correction required. The 

 true increase in weight is best determined by direct weighing 

 of the initial and final sample, or by comparing the calcium 

 content of the initial and final samples. The latter involves 

 very accurate calcium determinations, if the results are to be 

 significant. 



The absorption of "combined water" and of carbon dioxide 

 takes place for the most part in accordance with the follow- 

 ing equations, which probably account for the formation of 

 dicyandiamide, urea, calcium cyanamide carbonate, and cal- 

 cium carbonate: 



2CaCN, + 2H,0 = Ca(CN.NH), + Ca(OH),, 

 Ca(CN.NH), + 2H,0 = (H,CN,), + Ca(OH)„ 

 CaCN, H- 3H,0 =- CO(NH,), + Ca(OH)„ 

 CaCN, 4- CO, + H,0 = CaCN,.CO,.H,0, 

 Ca(OH), + CO, = CaCO^ + H,0. 



After long periods of exposure there are formed slight 

 amounts of secondary derivatives, so that old Cyanamid will 

 contain the following substances : 



Calcium cyanamide CaCN, 



Acid calcium cyanamid Ca(HCN2)2 



Basic calcium cyanamid CaCN2.Ca(OH)2 



Calcium cyanamide carbonate CaCN2C02.H20 



Dicyandiamide (H2CN2)2 



Urea CO(NH2)2 



Amidodicyanic acid H3C2N3O (slight amounts) 



Melamine (H2CNj)3 (slight amounts) 



Ammeline • H5C3N5O (slight amounts) 



Ammonium hydroxide NH^OH (traces) 



The following scheme shows the relation of some of these 

 forms to each other, and a possible mechanism for their deriva- 

 tion from calcium cyanamide: 



