CYANAMID — manufacture:, CHE:MISTRY AND USES 53 



Of the greatest activity is manganese hydroxide; second, 

 iron hydroxide containing manganese hydroxide; and third, 

 iron hydroxide free of manganese. The activity of the next 

 most active materials can properly be ascribed to their con- 

 tents of iron oxide. The difference in the activity of red and 

 white bauxite is very likely due to the difference in iron con- 

 tent. The greater activity of sandy kaolin as compared with 

 kaolin is probably due to the presence in the former of zeolitic 

 substances, which, as Ulpiani found, have a high activity. 



The low activity of the kaolin, considering the large specific 

 surface it possesses, suggested that the properties of the vari- 

 ous substances are not merely surface phenomena, but that 

 their specific chemical nature is of importance. Manganese 

 hydroxide and the two iron ores were mixed with glass sand 

 in the proportion of i gram to lOO grams sand, and a sample 

 of 0.1 gram manganese hydroxide with lOO grams glass sand. 

 These mixtures moistened as before with cyanamide solution 

 containing 33 mg. nitrogen, gave the following results, as com- 

 pared with the kaolin of the preceding experiment : 



