336 



[April 1908. 



SCIENTIFIC AGRICULTURE. 



EXPERIMENTS WITH CALCIUM 

 CYANAMIDE. 



By A. D. Hall, m.a. 



The nature of calcium cyanamide, the 

 new nitrogenous fertiliser manufactured 

 by combining the free nitrogen of the 

 atmosphere with calcium carbide, is now 

 well known (see Journal, 1906, Vol. 13, 

 pp. 38, 216, 410) ; and numerous field ex- 

 periments both in this country and 

 abroad, have established the fact that as 

 a manure it is practically as effective, 

 nitrogen for nitrogen, as sulphate of 

 ammonia. Certain practical difficulties 

 in its use have, however, been pointed 

 out ; it is sold in so fine a powder that it 

 is difficult to handle and disagreeable to 

 sow. It was regarded as so liable to 

 change in a damp atmosphere as to be 

 dangerous to store, and when first intro- 

 duced it was recommended that it should 

 never be mixed with other manures but 

 sown separately a week or ten days 

 before the seed. In view of the fact 

 that the manufacture is now being 

 undertaken on a large scale, and that 

 certain improvements have been effected 

 in the process, it seemed necessary to 

 re-examine the manure from these points 

 of view ; its efficiency as a fertiliser 

 being no longer in doubt. 



The questions that seemed to require 

 investigation were as follows :— 



(1) How far is the material hygros- 

 copic, so that it cannot well be stored 

 under ordinary conditions in bags in a 

 manure store or shed ? 



We are not concerned with its storage 

 on a large scale by the manufacturer or 

 the merchant, bnt with the way it would 

 affect a farmer who might have a stock 

 on hand for a month or two before using, 

 but who had no special means of keep- 

 ing it in a dry atmosphere. Assuming 

 further that some moisture will be 

 absorbed, is any loss of fertilising 

 material brought about thereby ? 



(2) Since calcium cyanamide is made 

 from calcium carbide, which by the 

 action of water gives off inflammable 

 acetylene, is ihere any danger of the 

 generation of this or other dangerous 

 gases from unchanged carbide remaining 

 in the manure, wheu it is stored and 

 exposed to damp air ? 



(3) Can the cyanamide be safely mixed 

 with other manures, particularly super- 

 phosphate, or is there a generation of 

 heat or gases to a dangerous or incon- 



venient extent ? At the same time does 

 either the cyanamide or the superphos- 

 phate suffer any loss of fertilising value ? 



At the outset it should be borne in 

 mind that calcium cyanamide is slowly 

 attacked by water or by moist air and is 

 converted into ammonia and calcium 

 carbonate, roughly in accordance with 

 the equation = 



CaCN 2 + 3H2 O^CaCO.? +2NH3. 



There is, however, in the commercial 

 fertiliser a considerable amount of quick- 

 lime, which absorbs water and becomes 

 slaked lime in the usual way ; this 

 slaking of the free lime being the first 

 action that takes place when the crude 

 cyanamide is exposed to moisture. Once 

 the cyanamide has been decomposed 

 there is nothing that will retain the 

 ammonia produced except any excess of 

 moisture that may be present, hence 

 there is always a possibility of loss of 

 the valuable part of the manure, the 

 ammonia, if it is exposed too long to the 

 air ; in the soil the ammonia would, 

 of course, be immediately absorbed by 

 the humus or the clay. 



The action of the acids upon the crude 

 cyanamide is similar ; a compound of 

 the acid with the quicklime is at once 

 produced with considerable evolution of 

 heat, then the cyanamide is attacked to 

 form compounds of lime and ammonia 

 with the acid in question. 



Experimental.— A quantity of calcium 

 cyanamide was supplied to the Rotham- 

 sted Experimental Station by the North- 

 Western Cyanamide Company, who are 

 establishing large works in Norway for 

 the manufacture and supply of the 

 manure to north-western Europe. The 

 sample in question came from the works 

 at Piano d'Orte in Italy, where the 

 process is now being carried out in a 

 large scale. It contained, as a mean of 

 several analyses, 17'24 per cent, of 

 nitrogen and was the usual fine black 

 powder, which had been treated by some 

 special process before export, in order to 

 render it less hygroscopic and easier to 

 handle. 



(1) Absorption of Water, &c., on 

 Exposure.— A series of small quantities 

 (lgram) of cyanamide was weighed out 

 on watch glasses and placed under a 

 large bell jar over water, thus ensuring 

 the maximum exposure of a thin layer 

 of the manure to the action of moist air. 

 At weekly intervals two watch glasses 

 were withdrawn, and one was weighed 

 in the wet condition and the second 

 dried in the steam oven. The nitrogen 



