670 



NA TURE 



[November 18, 1922 



The Nitrogen Industry. 

 By Prof. C. H. Desch. 



THE discussion on the nitrogen industry, organised 

 by Section B (Chemistry) of the British Associa- 

 tion at the Hull meeting, proved to be a great success 

 in spite of certain obvious difficulties in the way of 

 such a discussion at the present time. There are many 

 processes in the field for the fixation of nitrogen, and 

 commercial rivalries make it impossible to secure com- 

 pletely frank and unbiassed accounts of the merits of 

 the various systems. Much information of great 

 scientific value has, for commercial reasons, to remain 

 unpublished. The Section was therefore fortunate in 

 obtaining a general survey of the subject from Dr. J. 

 A. Harker, whose experience in this field during and 

 since the war was exceptionally great, his practical 

 acquaintance with most of the competing processes 

 enabling him to take an impartial view of many con- 

 troversial matters. His paper makes it easier for 

 chemical readers to judge of the value of statements 

 appearing in the technical periodicals and in the 

 popular Press. According to Dr. Harker, there is 

 little to be added in the way of statistical material to 

 the Report of the Nitrogen Products Committee pub- 

 lished some eighteen months ago, while the fluctua- 

 tions in the German exchange make it quite unprofitable 

 to discuss German conditions of production or the 

 possibility of dumping, topics which would otherwise 

 have been attractive to the author of such a paper. 

 The nitrogen question has attracted so much public 

 attention that it has even found its way into school 

 examination papers, although profound ignorance on 

 the subject prevailed five or six years ago, not only 

 among the general public, but also in the circle of 

 high officials directly concerned with questions of 

 national importani e. 



The oldest process for the synthesis of nitrogen com- 

 pounds from atmospheric nitrogen is that which 

 employs the electric arc. The great plants in Norway, 

 of immense size and working with the greatest success, 

 are avowedly derived from the laboratory apparatus 

 of the late Lord Rayleigh, and Prof. Birkeland stated 

 that his decision to establish the process as an in- 

 dustrial one was based on the famous presidential 

 address to the British Association by Sir William 

 Crookes. Lord Rayleigh's experiments included the 

 measurement of the relation between the energy 

 consumed and the nitrogen fixed, and it is a striking 

 fact that even now less than two per cent, of the energy 

 of the average arc furnace is absorbed as chemical 

 energy in the initial oxidation of the nitrogen. The 

 modern plants are of enormous size, the two plants at 

 Rjukan, for example, employing a total of 200,000 

 kilowatts, generated at an astonishingly low cost by 

 means of water power. Several modified arc processes 

 have been tried experimentally, including the Kilburn 

 Scott three-electrode furnace. The use of enriched 

 air has been tried on a large scale by a company 

 having works in Switzerland and Germany, a closed 

 circuit being used, and the nitrogen peroxide removed 

 by cooling instead of absorption. This operation is 

 not free from danger, and serious explosions have 

 taken place. The an- furnace plants erected in France 

 during the war have been closed, the power plants 



NO. 2768, VOL. I io] 



being required for their original purpose, the electrifica- 

 tion of railways. 



Of the many processes for the production of syn- 

 thetic ammonia, the original Haber process, the most 

 familiar of all. has been successfully worked by the 

 Badische Co. at Oppau, and at the even larger works 

 recently completed at Merseburg in Saxony. The 

 pressure in this process is 200 atmospheres, which is 

 not now regarded as high, and the gases move slowly 

 through reaction vessels 40 feet long and 3 feet in 

 external diameter, the walls being 6 inches thick. The 

 gases are pre-heated and circulated. The process 

 worked out at University College, London, by the 

 Nitrogen Products Committee uses higher gas velocities, 

 and was planned to yield about 5 kgm. of ammonia per 

 hour for each litre of space filled with catalyst, instead 

 of 400 gm. as in the Haber system. The first American 

 plant at Sheffield, Alabama, used activated sodamide 

 as the catalyst, but it is not surprising, in view of the 

 action of water vapour on this substance, that it proved 

 a failure ; the later modified plant of the Solvay 

 Process Co.. now making liquid ammonia for the 

 refrigerating industry, has avoided the defects. 



The Claude process uses very high pressures of 900- 

 1000 atmospheres, and the issuing stream contains 

 as much as 25 per cent, of ammonia. Circulation is 

 replaced by multiple stage working, and the reaction 

 vessels, made by a Sheffield steel firm from a special 

 heat-resisting material, are surprisingly small. Hydro- 

 gen is to be produced by an improved process from 

 coke oven gas. Electrolytic hydrogen is used on 

 several plants, notably at Terni in Italy, and it seems 

 likely that where water power is cheap, hydrogen can 

 be economically prepared by this means, provided 

 that the form of the cell can be improved. 



Cyanamide, regarded by some as obsolete, remains 

 the cheapest form of combined nitrogen, but in spite 

 of this, many of the war works using this process have 

 been closed. The largest plant is that of the American 

 government at Mussel Shoals, the future of which is 

 still uncertain. The German cyanamide plants are 

 being increased in size. A disadvantage of this com- 

 pound for agricultural purposes is that it is liable to 

 change into dicyandiamide, but attempts are being 

 made to convert it into other more valuable compounds. 

 One American company is converting it into a mixed 

 fertiliser, ammonium phosphate, which is useful but 

 al pit nit too costly. In Switzerland the calcium 

 cyanamide has been converted to free cyanamide by 

 carbonic acid, and then into urea. Mixed with mono- 

 calcium phosphate, a product known as phosphazote 

 is obtained, and this substance is used for vines, the 

 cost not being high. Mixed salts containing ammonium 

 nitrate have suffered in popularity through the Oppau 

 explosion, but the use of powerful blasting cartridges, 

 which caused that explosion, is indefensible. 



The cyanide process, the oldest of all nitrogen fixa- 

 tion processes, is in use in America for making the 

 acid for plant fumigation, and researches are in 

 progress with the object of cheapening the manu- 

 facture. 



In concluding his paper, Dr. Harker directed atten- 



