ON THE NITROGEN INDUSTRY AND OUR FOOD SUPPLY. 435 



of the air to form nitric acid was launched unsuccessfully in Canada. Two years 

 later, in 1907, the arc process was established in Norway, and calcium nitrate was 

 put on the market as a fertiliser. Thus Crookes' dream of the commercial production 

 of nitrogenous fertilisers from the nitrogen of the air was realised in less than ten 

 years. But it was the Haber-Bosch process for the fixation of nitrogen which was 

 to supersede all others, and make it possible for us to produce all the nitrogen 

 fertilisers we require now, and as far in the future as we can see. 



In 1906 to 1909 Prof. Haber investigated the chemical equilibrium between 

 nitrogen, hydrogen and ammonia when heated under a pressure over a catalyst. 

 Then Dr. Bosch, of the Badisch Analin u. Soda Fabrik, successfully manufactured 

 ammonia on a large scale by this process in 1913 to 1914. 



The fixation of nitrogen in the form of ammonia is so much cheaper than by any 

 other process that this process has very largely replaced the cyanamide and arc 

 processes, and it has shaken the Chili nitrate industry to its foundation, so that the 

 Chilean Government and the nitrate manufacturers have had to revise their methods 

 and their processes. 



[Dr. Slade then showed diagrammatically how the nitrogen industry had 

 already achieved considerable importance in 1898, and it was not until 1920 that the 

 synthetic nitrogen production became greater than the Chilean nitrate production.] 



Nitrogen Feetilisees. 



After this short summary of the position of the nitrogen industry to-day, let us 

 consider what becomes of this nitrogen. 



The world's consumption in 1928 of nitrogen in the form of ammonium sulphate 

 from synthetic ammonia and bye-product coke-ovens, cyanamide, nitrate of lime, 

 nitro-chalk and ammonia liquor was 1,442,000 tons, aJId"tti the form of Chili nitrate 

 401,000 tons, making a total of 1,843,000 tons, of which 185,000 are used in industry 

 and 1,658,000 tons are consumed as fertilisers. If fixed nitrogen is worth £50 a ton — 

 which is about its price in sulphate of ammonia to-day — then the value of the nitrogen 

 used in fertilising was £83,000,000. 



Now in an acre of typical English arable soil we have in the top nine inches a 

 quantity of humus containing about 2,500 lbs. of nitrogen, and at certain times of 

 the year changes take place in the soil making some of this nitrogen into nitrates, 

 in which form it is available for absorption by the plant. The result of this is that 

 in the spring about 1 per cent, of the nitrogen in the humus is present in the form of 

 nitrate ; thus we have present about 25 lbs. of nitrogen available for the plant. As 

 this available nitrogen is used up by the plant it is partly replaced by more nitrate 

 being formed from the humus, but during the time of greatest growth there is a 

 considerable depletion of available nitrogen in the soil. Owing to the continuous 

 breaking down of the humus the nitrogen absorbed by the plant is often more than 

 25 lbs., besides what is washed away by rain. The supply of available nitrogen may 

 be increased by the addition of nitrates or ammonium salts, for the latter are rapidly 

 oxidised to nitrates in the soil. 



If we spread 1 cwt. of sulphate of ammonia over an acre of ground this adds 

 23 lbs. of nitrogen to this area, or, if we consider the top nine inches of the soil over 

 this area of an acre, we add 1 lb. of nitrogen to each 120,000 lbs. of soil. Such a 

 small amount that we might be doubtful whether it would be suflficient to make any 

 appreciable difference to plants grown on this area. But we have seen that this 

 quantity is of the same order as the quantity of available nitrogen already in the soil. 



I cannot demonstrate to you in the course of a lecture the effect of nitrogen on the 

 growth of an actual plant, but I can show you a cinematograph film which has been 

 used for propaganda purposes in Germany. This film was produced bj' taking a 

 photograph of the plants every twenty minutes — day and night — by means of a 

 clock. Thus one second corresponds to about five hours' growth and one minute to 

 twelve days. 



We will now enquire into the magnitude of the increased yields of crops which 

 can be obtained by the use of nitrogen fertilisers. The figures given in Table I are 

 average increased yields of various crops obtained on good soil for the addition of 

 each pound of nitrogen in a fertiliser. They are the averages over many years and 

 many different soils, so that they are the increased jdelds that may be expected for 

 the addition of each pound of nitrogen — if there is not a deficiency of potash or 

 phosphoric acid in the soil. 



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