Scientific Agriculture. 



338 



[April 1908. 



unaltered carbide in their product, so 

 that the evolution of acetylene from the 

 cyanamide which was noticed with some 

 of the earlier products no longer takes 

 place. 



To test the point a current of air satur- 

 ated with moisture by bubbling through 

 water was led over 20 grams of cyanamide 

 in a flat-bottomed flask and then through 

 a washing bottle containing a solution 

 of ammonical silver nitrate of known 

 strength. Blackening of the silver solution 

 slowly took place, and after the air cur- 

 rent had been continued for seven days 

 the solution was examined. A very small 

 amount of black precipitate was recover- 

 ed, and this on testing proved to contain 

 silver acetylide, silver sulphide and a 

 trace of phosphide; the amount recovered 

 was, however, too small for analysis. As- 

 suming that it had been precipitated by 

 acetylene and calculating from its weight 

 back to calcium carbide the original crude 

 cyanamide contained :— 



Experiment 1.— 0*048 percent, calcium 



carbide. 



2.-0-062 



quantities which are negligible. 



In another experiment 20 grams of cya- 

 namide were shaken into a large bottle 

 with a little water, and the bottle stop- 

 pered and put aside for a day in a warm 

 place. The bottle was then carefully 

 opened and a light introduced; the taper 

 burnt quietly because not enough inflam- 

 mable gas had been generated to pro- 

 duce an explosive mixture. Since the 

 exposure in both the above experiments 

 was much more severe than could obtain 

 in practice, it may safely be concluded 

 that the traces of acetylene, sulphuret- 

 ted hydrogen and phosphine that will be 

 obtained from the crude cyanamide can 

 be neglected, for they will never become 

 a source of danger or even inconveni- 

 ence. The sulphate and phosphide de- 

 tected doubtless arise from traces of 

 sulphate present in the limestone origin- 

 ally employed in the manufacture of 

 the carbide. 



(3) In testing the effect of mixing cya- 

 namide with other manures superphos- 

 phate alone need be considered ; it is 

 the only manure containing free acid in 

 quantity (dissolved bones being merely 

 a form of superphosphate), so that with 

 it the maximum of chemical action would 

 take place. Only the water contained in 

 other manures would react with the free 

 lime of the cyanamide ; further, it is with 

 superphosphate that mixtures would 

 most usually be wanted in practice. 



An ordinary commercial grade of 

 superphosphate was used, and three 

 separate lots, each of 2 cwts. were mixed 



with 11, 22 and 44 lb. of cyanamide res- 

 pectively. The mixing was done on the 

 stone floor of a manure shed ; the 

 manures were weighed out, a layer of 

 superphosphate was spread on the floor 

 and a shovelful of the cyanamide sprin- 

 kled over it, then another layer of super- 

 phosphate and another shovelful of 

 cyanamide until the whole was mixed. 

 The heap was then broken down, passed 

 through a sieve, the lumps reduced, and 

 the mixing and formation of the heap 

 were repeated four times to secure com- 

 plete incorporation of the two manures. 

 The heap was then made up, thermome- 

 ters were put up into it and read from 

 time to time ; finally, on the next day, 

 the mixture was weighed and put up 

 into bags, which were left in the 

 manure shed and examined at intervals. 

 The mixing was a disagreeable operation 

 because of the light powdery nature of 

 the cyanamide, which filled the air and 

 hung about as a cloud for a long time ; 

 it was, however, during the weighing out 

 and the first adding of the cyanamide 

 that this occurred, for as soon as it came 

 in contact with the superphosphate no 

 further dust arose during the rest of the 

 process. 



During mixing the heap began to get 

 warm, and with the larger proportions 

 of cyanamide began to steam a little ; 

 no offensive gases were, however, given 

 off, so that it was only the first dustiness 

 caused by moving the original cyana- 

 mide that caused inconvenience or un- 

 pleasantness. 



As will be seen from the temperature 

 records a considerable development of 

 heat followed the mixing, due in the 

 main to the slaking of the free lime in 

 the cyanamide and its reaction with the 

 acid calcium phosphate; the temper- 

 ature was, however, kept down by the 

 evaporation of the surplus water in the 

 superphosphate and might have been 

 still further reduced, had it been 

 thought desirable, by sprinkling a little 

 water over the mass while the mixing 

 was going on. 



To test this point a further experi- 

 ment was tried in which two separate 

 hundredweights of superphosphate were 

 spread on the floor and 56 lb-of cyanamide 

 was carefully poured on each, covered 

 with the superphosphate and mixed as 

 before. In one case, No. 4, nothing was 

 added to the mixture of two parts super- 

 phosphate and one cyanamide, but in the 

 other, No. 5, two gallons of water were 

 sprinkled on from a water pot as the 

 mixing went on. This kept the dust 

 down entirely, so that it was possible to 

 complete the mixing without any trouble 

 from the fineness of the cyanamide. 

 The highest temperature reached was 



