26 



issued at a cheap price by the Cambridge University Press, so that 

 farmers could readily obtain it. In addition, each month a series 

 of Notes was issued in the Ministry's Journal showing- how ihe 

 available supplies might best be utilised. 



It was more diflicull, iiowever, to give useful information 

 about tile substitutes that would be needed when the fertiliser 

 supplies became too much reduced. Ordinarily, fertiliser trials 

 iiave to be continued for two or three successive seasons before a 

 definite opinion can be expressed on their merits : during the War, 

 however, some sort of opinion had to be given in three or four 

 weeks. Rapid methods of laboratory testing- were therefore de- 

 veloped : growing seedlings were used to indicate whether (as not 

 infrequently happened) toxic substances were present : rates cf 

 nitrification in soil were determined to find out how far the sub- 

 stance would yield nutrient material to the plant : farm crops were 

 kept growing in pots to afford opportunities of testing any 

 material that seemed promising. A considerable number of possi- 

 ble fertilisers were sent in for examination by the Food Production 

 Department, the Board of Agriculture, the Ministry of Munitions, 

 the National Salvage Council, and other bodies. 



Mucli of the information was wanted for the purpose of 

 economising sulphuric acid, so that the maximum quantity might 

 be handed over to the Ministry of Munitions for the manufacture of 

 explosives. In Peace time, the farmer had been the chief consumer 

 of sulphuric acid ; in 1917, however, the Ministry of Munitions were 

 requiring- all the acid they could find and were leaving- much less 

 than usual for the fertiliser manufacturers. The situation was 

 serious : in pre-war days the farmer had required 870,000 

 tons of chamber acid per annum (equivalent to 580,000 tons of 

 pure acid) , and the extra food production programme was calling 

 for even more than this. But the Ministry of Munitions was 

 obdurate, and supplies were cut down at a rate which seemed to 

 some of the more nervous to threaten a very serious situation : the 

 production of sulphate of ammonia fell from 350,000 tons per 

 annum to little over 250,000 tons, while that of superphosphate 

 fell from 800,000 tons to 500,000 tons per annum. 



Fortunately, a partial substitute for sulphuric acid was avail- 

 able in the form of nitre-cake, and although no fertiliser manufac- 

 turer liked it or had a good word for it, it seemed as if it might 

 have to be used extensively in the manufacture of superphosphate 

 and of sulphate of ammonia. Important and difficult technical 

 problems were involved both at the factory and on the farm, 

 necessitating a considerable amount of experimental work. 

 Thanks to the co-operation of the manufacturers, working- solutions 

 of the difficulties were found, and there is little doubt that both 

 sulphate of ammonia and superphosphate could have been made 

 from nitre-cake had the necessity arisen. Fortunately it did not, 

 and the situation was eased before it became too serious. 



A considerable amount of work was also done in the examina- 

 tion of new sources of potassium compounds to take the place of 

 the Stassfurt salts which had previously been our sole source of 

 supply. A certain number of residues from manufacturing 

 processes were available, but in the main they suffered 



