viii PREFACE 



be produced in the future and in 1915 laid out field experiments in 

 Essex to compare these newer types with the old familiar Thomas or 

 Bessemer slag. These experiments were continued for five years and 

 they gave a mass of data so important in character as to deserve wide- 

 spread circulation among farmers and agricultural experts. Separate 

 publication was therefore advised and the Syndics agreed to its in- 

 clusion in the Cambridge Agricultural Monographs. 



Fortunately Dr Scott Robertson had included also some typical 

 mineral phosphates in the trials so that valuable information has been 

 obtained in regard to a second problem which, while not pressing in 

 1915, has grown in importance since and is likely to be serious in the 

 future. 



This second problem arises as a direct consequence of the circum- 

 stance that basic slag is a by-product only, and not a primary object 

 of manufacture. From the steel-makers' point of view it is relatively 

 unimportant. Some 4 cwts. only are obtained for each ton of basic 

 steel produced, and while the ton of steel has been worth anything 

 from 27 in 1920 to 10 in 1921, the 4 cwts. of slag is worth less than 

 5s. to the steel-makers and only about 15s. even after the slag grinder 

 has graded, ground and bagged it. The steel-maker cannot afford to 

 alter his processes in any way that would lengthen them or make them 

 more costly or hazardous. The agriculturist must therefore take the 

 slag as he finds it and cannot expect the consideration that would be 

 shown him by the makers, say, of superphosphate, which is a primary 

 object of manufacture and not a by-product. The practical result is 

 that the composition of basic slag is determined by the conditions 

 under which the steel-maker is working, and the total amount pro- 

 ducible is regulated by the demand for steel ; neither of which factors 

 is in any way within the control of the agriculturist or influenced to 

 any appreciable extent by his demands. 



It is important that this distinction between basic slag and other 

 fertilisers should be recognised. If the farmers of this country demanded 

 double their present supplies of superphosphate, of nitrates, of sul- 

 phate of ammonia or of potassic fertilisers, the manufacturers could 

 provide the additional material : if, however, basic slag were desired 

 over and above the quantity determined by the demand for steel it 

 could not be supplied except perhaps by importation. 



The position thus created is being explored by the Permanent Com- 

 mittee set up by the Ministry of Agriculture to advise on basic slag. 

 On the agricultural side there is evidence that the farmers of the 

 United Kingdom might with advantage to themselves and the com- 



