PHOSPHORUS 193 



slag exists in the form of tetracalcium phosphate. However, an 

 excess of calcium oxid is present, and the phosphorus in slag under 

 suitable conditions can be made available. No doubt, the lime 

 produces some benefit for its own sake on certain classes of soil. 

 In value, the phosphorus is rated at 10 cents a pound, the same as 

 in bone meal. 



The iron ores from the Lake Superior region, which are used in 

 the Illinois Steel Works, contain too small an amount of phosphorus 

 to give value to the slag produced, but some phosphorus-bearing 

 ores are used in Pennsylvania, and slag phosphate has been pro- 

 duced and used in that state to a limited extent for several years. 



In Europe very large quantities of slag phosphate are produced 

 and sold under the name of Thomas slag, although Jacob Reese, 

 who for many years controlled the production in Pennsylvania, 

 claimed priority over the European discovery. 



The conditions under which the different forms of phosphorus 

 should be used are discussed in the following pages. 



