274 



NA TURE 



[July 23, 1908 



creased in bulk, which was objectionable for storage 

 purposes, as the jute sacks in which it was contained 

 burst. By, however, taking precautions to line the 

 sacks first of all with double paper, this difficulty was 

 got over, and also by improved methods of manu- 

 facture the amount of lime produced was lessened. 

 As regards the actual part played by cyanamide in 



I'M.. 1.- Ul-ic \ a lij\", ^l^^^e n.uiiejt-- lirian^on. 



the soil various theories have been put forth ; e.g. it 

 would appear that when brought into contact with 

 the ground the cyanamide is first decomposed through 

 the action of the moisture and also of the carbon 

 dioxide in the soil as follows : — 



CaCN^ + HjO + COo^HjCN., t-CaCOj, 



and the free cyanamide will then, by absorption of 

 water, probably be further decom- 

 posed into urea, 



H„CN„+HoO^CO: 



Also the decomposition is greatly 

 assisted by the myriads of 

 microbes which are in variably 

 found in cultivated soil. 



Experiments have shown that 

 calcium cyanamide is more suit- 

 able in some soils than in others, 

 e.^. if the soil is in an acid state 

 it is necessary previously to lime 

 it. Such soils are found in high 

 moorland and in sandy places 

 because they are very poor in lime, 

 and when applied to such land, 

 cyanamide, unless lime is first 

 added, is distinctly harmful, but 

 with most other soils it is very 

 satisfactory. 



Nitrolim can also be mixed with 

 other fertilisers, such as basic slag, 

 potassium salts or superphosphate, 

 but with this latter particular pre- 

 cautions have to be employed owing to the free phos- 

 phoric acid combining with the free lime in the 

 cyanamide. This difiiculty, it is stated, has now been 

 got over. One advantage which cyanamide has over 

 Chili saltpetre is that it is less soluble in water, and 

 is therefore not so liable to be washed away in the 



NO. 2021, VOL. 78] 



drains and so lost, consequently the unchanged 

 cyanamide which may have been left in the ground 

 after the first harvest is readily available for the 

 succeeding one. 



Cyanamide is manufactured from calcium carbide 

 of_ the same quality as that which is used for illumin- 

 ating purposes. The carbide as it comes from the 

 electric furnace is ground up and 

 charged into retorts, which are 

 made of fire-proof material, and 

 are mounted in a furnace similar 

 to the retorts employed for the 

 manufacture of gas. (Fig. i 

 shows this arrangement diagram- 

 matically.) The nitrogen is then 

 passed over the carbide, the retort 

 being maintained at a temperature 

 of from 800° to 1000° C. The 

 nitrogen is produced either by the 

 1-indc system of fractional distilla- 

 tion of the air or by passing air 

 over heated copper turnings, the 

 resulting copper oxide being re- 

 converted to the metal by passing 

 reducing gases over it. In the 

 r>inde process the oxygen which 

 remains after the separation of the 

 nitrogen is a useful bye-product. 

 .•\s soon as the carbide in the re- 

 torts is saturated with nitrogen — a 

 fact which becomes evident bv the 

 controlling gas meter coming to a 

 standstill — the calcium cyanamide 

 is extracted in the form of a hard 

 cake, and is cooled in vessels from which air is ex- 

 cluded. When cool it is ground into a fine powder, 

 and is ready for use. 



During the last vear a new electric furnace ha; 

 been devised for heating the carbide while it is ab- 

 sorbing the nitrogen, and this has given such satis- 

 faction that now all the older retorts are being re- 

 placed by the electrically heated ones. The process is 



tj. 5. — Ai.iui iiiii.L,iiiL;> at N5tre Dame de Brianijon. 



cheaper, and the operating costs per furnace are 

 lower, also the life of the retort is practicallv un- 

 limited, which was not the case with the older re- 

 torts (Fig. 2 shows a number of these retorts in 

 position.) 

 The yield of carbide at most works is about two 



