July 23, 



1 90S] 



NA TV RE 



272, 



THE FIXATION OF ATMOSPHERIC NITHOGE.X 

 AS CYANAMIDE. 



IS Nature of August 30, 1906, an article was pub- 

 lished describing- the Birkeland Eyde process for 

 the fixation of atmospheric nitrogen by electrothermic 

 methods and the conversion of the nitric acid so ob- 



Copp«r Retort Oven 



Fii.. I. — Nitrogen Absorption Retort. 



tained into calcium nitrate, which is used as a fer- 

 tiliser in place of Chili saltpetre. Since thaf date the 

 Birkeland-Eyde works at Notodden, in Norway, have 

 been considerably enlarged, owing to the success 

 which met their initial efforts. The necessity of ob- 

 taining large quantities of nitrogen in a form suit- 

 able for fertilising purposes does not require to be 

 reiterated again, because the fact that the available 

 sources are being depleted, and the demand for nitro- 

 gen for agricultural purposes continually increases, is 

 now universally recognised. This has led many in- 

 vestigators to endeavour to fix atmospheric nitrogen 

 in some other form, which it is hoped will be mo.c 

 economical than that of direct oxidation in the electric 

 arc. 



The amount of Chili saltpetre exported in 1907 was 

 1,740,000 tons, and in order to replace this by the 

 fixation of atmospheric nitrogen, it is necessary to 

 employ 280,000 tons of the gas, and this is the amount 

 which, it is calculated, is contained in the atmosnhere 

 over every nine acres of the globe. .Another method 



menced by Drs. Frank and Caro in 1895, when they 

 were endeavouring to produce cyanides by heating a 

 mixture of calcium carbide and sodium carbonate in 

 presence of nitrogen. The results were not very satis- 

 factory, and therefore barium carbide was substituted, 

 and this substance was found to absorb nitrogen with 

 great avidity at between 700° and 800° C. It was 

 intended to treat the barium cyanide with potassium 

 or sodium carbonate, and thus produce the cyanides. 

 On examination of the products produced, however, 

 it was found that not only did barium carbide produce 

 barium cyanide, but also a more complex compound 

 was formed, which upon examination proved to be 

 barium cyanamide according to the equation : — 



BaC„ + 2N = BaCN2 + C. 

 The product obtained in the reaction usually con- 

 tained 30 per cent, of barium cyanide and 40 per cent, 

 of C3'anamide, the remainder consisting of barium 

 oxide and carbon. It was found, however, that the 

 barium cyanamide and barium cyanide could easily 

 be converted into potassium cyanide by melting with 

 potassium carbonate as follows : — 



Ba(CN)„ + BaCN., + C + 2K2C03 = 4KCN + 2HaC03. 

 Experiments were then taken up with calcium car- 



.\mmoni;i it 



Electric Furnaces at Odda for producing Cyanam 



of fixing nitrogen is known, and that is the form- 

 ation of calcium cyanamide by the heating of cal- 

 cium carbide in a stream of nitrogen obtained from 

 the atmosphere. The researches which led to the 

 discoverv of calcium cyanamide were originally com- 



Fid. 3. — .\mmunia Producing .Apparatus. 



bide, and investigation showed that by altering the- 

 conditions it was possible to convert the whole of the 

 calcium carbide into cyanamide 

 according to equation i. Now 

 when calcium cyanamide is de- 

 composed by means of water, 

 ammonia is produced thus : — 



CaCNo + 3H„0 = CaCOj + 2(NIl3). 



It seemed, then, that it might be 

 possible to obtain the ammonia for 

 purposes of fertilisation, that is to 

 say, employ cyanamide directly as 

 a manure, but as the reaction only 

 takes place with water at high 

 temperatures, agricultural authori- 

 ties were inclined at first to doubt 

 the possibility of employing this 

 product, as it was presumed the 

 ammonia would probably not be 

 liberated by the moisture of the 

 soil. However, experiments showed 

 that the cyanamide actually does 

 decompose in the soil, and that it 

 acts as a source from which plants 

 can obtain the nitrogen which 

 they require for nutriment. The 

 product has therefore been put upon the market under 

 the name of " Nitrolim." Some difiiculties, however, 

 were met with, one being that the finished product 

 often contains some quantities of calcium oxide, there- 

 fore on exposure to moist atmosphere the nitrolim in- 



NO. 2021, VOL. 78] 



