6 THOMAS MACFAELANE: 



consequences of this invention. Chemical manufacturers began to face the question as to 

 how the phosphoric acid thus separated from the iron could be made use of Large quan- 

 tities of Thomas-Gilchrist slag were accumulating at Bessemer steel works in England 

 and elsewhere, and it was found to contain from 16 to 20 per cent, phosphoric acid and 

 from 46 to 54 per cent, lime and magnesia. Compared with our Canadian apatite, it 

 seemed indeed to be a meagre raw material for fertilisers. Nevertheless, the manufacture 

 of superphosphates from it was attempted, and an article called " Thomas precipitate " 

 put upon the market by German manufacturers. But before this business had time 

 to develop, it was found that by applying the slag itself as a manure, without any pre- 

 paration beyond grinding to a very fine powder, the most satisfactory results could be 

 obtained. Tlie problem of utilising it has, therefore, been attacked and solved, and the 

 phosphorus which for fifty years was the dread of our iron masters, has now no terrors 

 for them, and has reached at last a sphere of widely extended usefulness in agriculture. 



It would be rather an undesirable result, if this saving of waste should have the 

 effect of reducing the value of our apatite deposits ; yet the most recent investigations 

 point in this direction. In the Chemiker Zeitung, of March 2nd last, the following ultimate 

 analysis of Thomas slag is given : — 



Phosphoric acid 19-02 



Silica 8-20 



Manganoiis oxide 5 -24 



Ferrous oxide 8'06 



Ferric oxide 5 • 14 



Lime 49-90 



Sulphur 0-60 



Maprnesia 3-40 



Alumina 1 ' 10 



100-66 



Small crystals having been discovered in the slag possessing the composition of 

 quadrobasic phosphate of lime, the proximate composition of the slag has been computed 

 from the above analysis with the following result : — 



Quadrobasic phosphate of lime 49-02 



Silicate of lime 15-85 



Lime (uncoiiibined) 11-00 



Sulphide of calcium 1-35 



Manganous oxide 5-24 



Ferrous oxide ^ 8-06 



Ferric oxide ' 5-14 



Magnesia 3 40 



Alumina 1-10 



100-16 



This view of its composition is supported by the fact that the slag is decomposed 

 with facility by dilute acids ; and further, SV'S p. c. of its phosphoric acid is soluble in a 

 solution of citrate of ammonia, a circumstance that would indicate its agricultural value 

 to be equal to that of the precipitated or reverted phosphoric acid of artificial fertilisers. 

 This is just what field experiments with it, in an extremely fine condition, have proved. 



