PHOSPHATIC MANUKES 227 



rollers, sifted to remove pieces of iron, and finally ground 

 in powerful roller-mills to the state of fine powder in which 

 it is ordinarily placed on the market. 



Chemical Composition. The following complete 

 analysis x shows the proportions of the various con- 

 stituents in a typical sample. 2 



Per cent. 

 Calcium oxide . . . . . . . 41*58 



Magnesium oxide . . . . . . .6*14 



Aluminium oxide ........ 2*67 



Ferric oxide 8'54 



Ferrous oxide 13 '62 



Manganous oxide . . . 3'79 



Vanadium oxide ........ 1'29 



Silica 7-38 



Calcium sulphide . . . . . . . . 0'54 



Sulphur trioxide . . . . . . . 0'12 



Phosphorous pentoxide 14'36 



99-93 



The composition, however, is very variable. It depends 

 primarily upon the composition of the crude iron, and 

 to some extent also, upon the composition and quantity 

 of the materials used to purify it. 



The proportion of phosphates in the final product 

 will obviously be greater or less according to the amount 

 of phosphorus in the crude iron, and it may be increased 

 by the presence of phosphates in the materials added to 

 the pig iron in the converter. In some cases phosphatic 

 lime has been purposely employed in order that the resulting 

 slags may show a high percentage of phosphates. This 

 greatly increases their commercial value, but unless the 



1 Journal of the Iron and Steel Institute, 1887. 



2 Owing to the introduction of silica to increase the solubility and 

 other recent improvements in manufacture the composition of he 

 slags now produced differs slightly in some respects from that given 

 above. 



Q 2 



