66o Experiments with Calcium Cyanamide. [feb., 



(2) The water soluble phosphoric acid in the superphosphate 

 is rendered insoluble in proportion to the amount of cyanamide 

 introduced. As would be expected, the free lime of the 

 cyanamide combines with the soluble calcium phosphate 

 in^the superphosphate to form a calcium phosphate insoluble 

 in water. A mixture of 1 part cyanamide to 10 parts super- 

 phosphate precipitates most of the soluble phosphate, when 

 the mixture is raised to 1 to 5 all the soluble phosphate has been 

 converted into di-calcium phosphate. 



(3) The amount of citric acid soluble phosphate (determined 

 by the official method of shaking for half an hour with 2 per 

 cent, citric acid solution*) undergoes little change from the 

 mixing. Evidently the reaction between the slaked lime 

 from the cyanamide and the soluble phosphate gives rise to 

 di-calcium phosphate, the usual precipitated or " reverted " 

 phosphate which is completely soluble in citric acid solution. 

 Yery little change to tri-calcium phosphate is brought about 

 either by the lime or the heating. 



From the fertiliser point of view, then, the mixture of cyana- 

 mide with superphosphate occasions no loss of nitrogen, but 

 more or less of the phosphoric acid ceases to be water soluble, 

 remaining, however, as the readily available di-calcium phos- 

 phate. While the precipitated phosphate cannot be regarded 

 as of quite the same value as water soluble phosphate, the 

 falling-off in fertilising value is slight. 



Various attempts were made to ascertain how much of the 

 nitrogen of the original cyanamide had been converted into 

 ammonium salts in the mixed manures ; the results were, 

 however, unsatisfactory owing to the fact that the unchanged 

 cyanamide is itself continuously decomposed when distilled 

 with magnesia. They indicated, however, that little formation 

 of ammonium salts had taken place. 



Some experiments were also made to see if any quantity of 

 the dicyanodiamide, which is said to be poisonous to plants, had 

 been produced in the mixture. Six pots were made up, each 

 containing about 3 kilos, of sand, and, in addition to potassium 



* The citric acid solution is used to discriminate between phosphates which are 

 readily soluble in soil water, such phosphates as are found in basic slag or basic 

 superphosphate or are produced in the soil by the application of superphosphate, and 

 on the other hand, the unchanged phosphate of lime which is practically insoluble in 

 the citric acid. 



