162 MANUKES. VII. 



% 



Lime ... ... ... 45-04 



Magnesia ... ... 6-42 



Alumina ... ... ... 1-50 



Ferrous oxide ... ... 2*10 



Ferric oxide ... ... 15-42 



Manganous oxide ... ... 3'50 



Vanadious oxide ... ... 1-35 



Silica ... ... ... 5-80 



Sulphur ... ... ... 0-32 



Calcium ... ... ... 0-40 



Phosphorus pentoxide ... 18-10 



99-95 



The sulphur present seems to exist as a sulphide, probably 

 of calcium. The phosphoric acid is present as tetracalcium 

 phosphate, Ca 4 P 2 9 , a substance which sometimes occurs 

 nearly pure as crystals imbedded in the slag. 



According to Hoyermann and Wagner" the citrate-solubility 

 of the phosphoric acid in basic slag is greatly increased if the 

 slag be fused with sand. Wagner states that the citrate-solu- 

 bility (by which he judges of the availability) of the basic slag 

 of commerce varies from 100 to 40 %, and that a high solubility 

 depends upon the presence of at least a certain percentage of 

 silica. Kidsdalet denies this and states that the only function 

 of the silica is the neutralising of a certain proportion of the 

 free lime of the slag and thus preventing the action of this 

 upon the citrate solution employed. 



Many attempts to improve basic slag as a manure have been 

 made, some directed to the removal of the iron, others the 

 sulphur, while others have attempted to render the phosphoric 

 acid more soluble, by treatment with sulphuric acid. Practi- 

 cally all these attempts have been abandoned, and the only 

 process through which the slag is passed is 'that of grinding. 

 This must be thoroughly done, for it is found that the availa- 

 bility of the phosphoric acid depends very largely upon the 

 fineness of subdivision. A sample should contain at least 80 

 or 90 % of powder which passes through a sieve of 100 meshes 



* Chem. Zeitung 1895, 1511. t Jour. Soc. Chem. Ind. 1895, 170. 



