CYANAMID — MANUFACTURE, CHEMISTRY AND USES 21 



An aliquot part of the filtrate, now free from cyanamide, 

 is treated with potassium hydroxide solution in excess, and is 

 boiled until no more ammonia comes off. The precipitate con- 

 tains all the dicyandiamide and some silver oxide. Dilute the 

 solution with an equal volume of water, filter on a nitrogen- 

 free filter, wash with some water, and determine nitrogen in 

 the precipitate by the Kjeldahl method. 



Brioux^ claims that the boiling of the strongly alkaline 

 cyanamide-free solution containing the precipitate of silver 

 dicyandiamide and silver oxide causes a conversion of about 

 1.5 per cent, of the total nitrogen of the dicyandiamide, and he 

 has modified the method so as to obviate this error. His 

 method is briefly as follows : 



Brioux's Modified Caro Method. — Extract the soluble nitro- 

 gen from I or 2 grams of finely ground sample by frequent 

 shaking for three or four hours in a flask with 250 cc. cold 

 water, and filter through a dry filter without washing. In 

 one aliquot portion of 100 cc. of the filtrate determine cyana- 

 mide and dicyandiamide, and in the other determine cyanamide 

 alone. 



For combined cyanamide and dicyandiamide nitrogen : For 

 each 0.1 gram nitrogen (approx.) in the solution add 20 cc. 

 of 5 per cent, silver nitrate solution. Then add 20 cc. of 

 10 per cent, potassium hydroxide solution. A brown precipi- 

 tate of mixed cyanamide and dicyandiamide salts forms. 

 Filter and wash with cold distiled water. Determine total 

 nitrogen in the residue by the Kjeldahl process, substituting 

 I gram copper sulphate in place of the mercury. 



For cyanamide nitrogen : In the other portion of the extract 

 from the sample add for each o.i gram nitrogen, 20 cc. of 

 5 per cent, silver nitrate solution. Add an excess of ammonia. 

 A yellowish-brown precipitate forms. Filter and wash with 

 water slightly ammoniacal, finishing with cold distilled water 

 until the washings are free from soluble silver salts. Dissolve 

 the residue in dilute nitric acid (1:2) and determine silver 

 ^ Annales de la Science agron. francaise et etrangere, April 1910. 



