126 CHEMICAL FERTILIZERS 



2 grammes of a highly citric soluble basic slag and calcined 

 it with fluorspar, and then submitted the resulting material 

 to an extraction with 2 % citric acid. The results of subse- 

 quent analysis was that, in the first citric acid extraction, 

 there was rather less than 30 % of soluble phosphates ; in the 

 second extract, 35 % more was obtained ; and in the third 

 extraction 24 % more, thus showing that fluorspar hinders 

 the solution of slag in citric acid. It may be argued that the 

 presence of fluorine hinders the solubility of phosphate in 

 the soil as well as in the Wagner test, and this may reasonably 

 be assumed until the contrary is proved. 



A very large proportion of the basic slag which is now 

 produced in Great Britain is of a low citric solubility. Many 

 thousands of tons of fluorspar slag are produced annually as 

 a waste product, and some firms even pay a few pence per 

 ton to have this taken out to sea and sunk. It is a curious 

 point to note that, in the United States, some of the rock 

 phosphates which give a very low figure to Wagner's citric 

 test are actually preferred to slags with a high citric solu- 

 bility. By submitting slags and rock phosphates to con- 

 tinuous extraction, Robertson has shown that the rate of 

 extraction by citric acid is more rapid in the case of the 

 fluorspar slags than it is with the rock phosphates. The 

 long discussions which have taken place on details about 

 the solubility of basic slag now need revision as the result of 

 altered conditions in manufacture. 



Whatever the future may hold as to the relative importance 

 of arable versus grazing farming, the amount of phosphatic 

 manures that will be required for use in this country is certain 

 to increase, and the supply of basic slag may be insufficient 

 for application to grazing land and permanent hay. Under 

 such conditions the only practical policy will be to use for 

 grass land all the slags that can be ground economically 

 and carried by rail and farm cart, and to make up the defici- 

 ency with the more expensive but quicker acting superphos- 

 phate or the cheap but slow rock phosphate. As basic 

 slag is particularly suitable for grazing land on heavy clay 

 soils, the right thing to do is to reserve the stocks of basic 



