20 CYANAMID — MANUFACTURE, CHEMISTRY AND USES 



cent, nitrogen. To determine ammonia weigh out 0.85 gram 

 of finely ground sample. Each cc. of half-normal acid is 

 equivalent to i per cent, ammonia. 



Procedure. — Place the carefully weighed sample in a Kjeldahl 

 flask of about 300 cc. capacity. Add 10 grams of ground 

 potassium sulphate. Shake until well mixed with the sample. 

 Add 25 to 30 cc. of concentrated sulphuric acid and shake 

 until well mixed. Heat slowly for 30 minutes, then heat with 

 a full flame for one and one-half hours. Cool, dilute, and 

 transfer to a distillation flask. (Distillation can be made from 

 the digestion flask if desired.) Add an excess of sodium 

 hydroxide, and distil 200 cc. into a measured quantity of the 

 standard half-normal acid, containing some cochineal indi- 

 cator. Titrate the excess of acid with tenth-normal alkali. 



DETERMINATION OF CYANAMIDE AND 

 DICYANDIAMIDE. 



Caro Method. — Of the various methods for determining 

 cyanamide and dicyandiamide, that of Caro^ seems to be the 

 best. The reagents used are as follows : 



(a) Silver acetate solution. 100 grams of silver acetate are 

 placed in a liter flask, covered with 400 cc. of 10 per cent, 

 ammonium hydroxide, and the flask is filled to the mark with 

 water. 



(b) 10 per cent, solution of potassium hydroxide. 



The procedure is as follows: 5 g. of Cyanamid or lime- 

 nitrogen is agitated by hand or in a shaking machine with 

 450 cc. of water for about 2j4 hours, and the flask filled to 

 500 cc. An aliquot part (250 cc.) is treated with ammonia 

 until it smells strongly thereof and then with silver acetate 

 solution in excess. The precipitate of silver cyanamide salts 

 (p. 12), after shaking and standing a little while, is gathered 

 on a nitrogen-free filter, washed with water until no ammo- 

 nium salts run through, and the nitrogen in it is determined 

 by the Kjeldahl method. 



^ Caro, Schiick, Jacoby— loc cit. 



