40 CYANAMID — MANUFACTURE:, CHEJMISTRY AND USJ^S 



ever, that the cyanamide is not removed solely by a process 

 of absorption, since it is characteristic of absorption processes 

 that a state of equilibrium is usually reached between the sub- 

 stance in solution and in the absorbing surfaces within a day. 

 The substance that is being absorbed never disappears entirely 

 from the solution. In the present experiment, the reaction 

 proceeds to complete disappearance of the cyanamide. The 

 rate of removal of cyanamide is practically constant after the 

 first 9 days, and shows no tendency to become zero thereafter, 

 as it would if an equilibrium were being approached. Such 

 rapid removal of the cyanamide to the very end of the experi- 

 ment can be due only to chemical conversion of the cyanamide 

 to other forms. 



INFLUENCE OF CONCENTRATION. 



The following experiment was made by Ulpiani to deter- 

 mine the effect of varying the concentration of cyanamide. 

 In each of a series of glass tubes was placed lOO grams of 

 soil, which was covered with 25 cc. of a solution of cyanamide 

 at various concentrations. At the end of 3 days and at the 

 end of 10 and 30 days, certain tubes, as shown in the table, 

 were taken out, thoroughly mixed with 75 cc. water and after 

 standing one hour were filtered with suction, and cyanamide 

 was determined. The following results were obtained: 



