M.—AGRICULTURE 253 
two later J. J. Dobbie carried out the first experiments with the slag in 
North Wales. 
The now classic experiments laid down by Prof. Somerville in 1896 
and carried on and developed by his successors, Sir Thomas Middleton 
and Prof. Gilchrist, have demonstrated the value of this addition to phos- 
phatic fertilisers and show as the result of twenty-five years’ experiments 
that basic slag is, for certain types of soil, even more valuable than 
superphosphate. Changes in the modern methods of steel making and 
the effect of the large amount of scrap iron and steel available in the years 
succeeding the war brought about a considerable alteration in the com- 
position of the slags produced in this country. About ten years ago, 
therefore, the Ministry of Agriculture and Fisheries set up a permanent 
committee on basic slag ‘ to consider the development and improvement 
of the manufacture of basic slag and the extension of its use.’ This 
* committee has produced a valuable series of reports, the last (tenth) report 
being published in September 1932. The work of the committee has been, 
in general, ‘to make a detailed study of the agricultural values of the slags 
now available to farmers and the chemical means by which these values 
can be expressed.’ By means of the old but empirical citric acid test, the 
slags produced in this country can be divided into two groups—a high- 
soluble group in which 80 per cent. or more of the phosphoric acid is 
soluble in 2 per cent. citric acid and a low-soluble group in which less than 
40 per cent. is soluble. The experiments in recent years have been 
carried out with hay, and while no final conclusion can be drawn at this 
stage, the results indicate that with this crop the high-soluble slag showed, 
in the first year, a slight superiority over superphosphate and a marked 
superiority over mineral phosphate and low-soluble basic slag, and there 
was in addition a considerable improvement in the quality as well as the 
quantity of the hay obtained from the more active phosphatic fertilisers. 
The figures obtained for the recovery of phosphoric acid were interesting. 
For two years, the recovery of phosphoric acid added were superphosphate 
12 per cent., high-soluble slag 9 per cent., mineral phosphate 4 per cent. 
and low-soluble slag 2 per cent. 
Pot experiments with barley carried out from 1927 to 1931 gave similar 
results, the high-soluble slags giving better results even than superphos- 
phate on certain types of soil (e.g. Millstone Grit) and markedly better 
than the low-soluble slags. 
It must always be borne in mind that basic slag is a by-product and that 
its composition may be altered by changes in the methods of steel manu- 
facture. The need for the work of such a committee is, therefore, 
obvious and the committee should be continued. 
The beneficial effects of mineral phosphates as fertilisers was noticed 
as far back as 1845. New sources of material and improvements in the 
methods of grinding have led to a great extension of their use in recent 
years, 
Superphosphate—Improved methods of manufacture and better 
sources of raw material have led to a progressive improvement in the 
quality of this fertiliser. In 1907 the total world production was 7,813,570 
metric tons and in 1930 this had been almost exactly doubled (15,582,162 
