330 Journal of Agricultural Research voi.xviii,no.6 



phosphate rock, would be oxidized to sulphuric acid when mixed with 

 soil and render the phosphate soluble. 



Lipman, McLean, and Lint (9, 10), in 191 6, probably first demonstrated 

 the practical value of rendering inert phosphates soluble by the oxida- 

 tion of sulphur in soils. Since then Lipman and McLean (7, 8, 11) have 

 continued their experiments and have shown that mixtures of soil, rock 

 phosphate, and sulphur, both with and without manure, would furnish 

 amounts of soluble phosphate that could be substituted for commercial 

 acid phosphate. Furthermore, pot experiments conducted by them 

 have shown that this product compares very favorably in value with 

 the commercial article. 



Brown and coworkers {4, 5, 6) obtained some favorable results on 

 sulphofication in Iowa soils and its effect on the availability of phos- 

 phates. Ames and Richmond, in Ohio (j, 2, 5), have made some inter- 

 esting experiments of this kind, although part of their work has included 

 other phases of sulphur oxidation. Others might be mentioned, but 

 a fairly complete bibliography of the whole sulphur problem in its rela- 

 tion to soils and plant growth is given by McLean (11). 



The earlier work demonstrated, as was to be expected, that various 

 types of soils have different sulphofying powers and consequently dif- 

 ferent capacities to render phosphate soluble. For this reason Dr. 

 Lipman, of the New Jersey Agricultural Experiment Station, suggested 

 that it would be desirable to carry on compost experiments with sul- 

 phur, rock phosphate, and soils from various localities. Only in this way 

 would it be possible to find whether or not the process would prove of 

 general application. 



With this idea in view, and following his suggestion as to the amounts 

 of material to use, the first compost experiments were started here in May, 

 1917. In the meantime, however, the war had come on; and the increased 

 cost of acid phosphate, due to the acute shortage of sulphuric acid re- 

 quired in the manufacture of munitions, brought this subject to the atten- 

 tion of the National Research Council, Council of National Defense. 



Since it appeared at the time that the supply of sulphuric acid allowed 

 to the fertilizer industry would have to be greatly curtailed, if not en- 

 tirely stopped, this process would, if proved satisfactory, have offered a 

 desirable substitute for commercial acid phosphate. For this reason, in 

 November, 1917, the work was taken in charge by the Agricultural Com- 

 mittee of the National Research Council mentioned and carried on as a 

 war emergency measure. The cooperators in the work were designated 

 as experts in the above council and asked to continue the work as out- 

 lined by their committee. As a result, part of the experiments described 

 here were carried on according to the directions sent out by this commit- 

 tee, and others which will be described later were carried on at the same 

 time. 



