No. 6. DEPARTMENT OF AGRICULTURE. 833 



product ul' the process is a substance coutaining 15 to 20 per cent, 

 of phosphoric acid. It is metallic in appearance, but may be ground, 

 forming a dark brown meal. The phosphoric acid is in combina- 

 tion chiefly with lime, us tetra-calcium phosphate; it is insoluble 

 in water, slightly soluble in ammonium citrate, and is, by ordinary 

 methods of analysis, classified largely as insoluble. Yet its condi- 

 tion is such that soil water, when charged with carbonic acid, will 

 dissolve it to a considerable degree. Thomas slag is largely used 

 and highly valued in Germany, and is the cheapest form in which 

 phosphoric acid can be obtained by the farmers of that country. 

 \Yaguer states that two compounds of this material, ground fine 

 (but no acid treatment), containing 18 per cent, phosphoric acid 

 and no other valuable plant food, and costing four and one-half 

 cents, produces the first year after its use, the same increase in 

 yield as one pound of soluble phosphoric acid from bone meal cost- 

 ing six and one-half cents. And in the second year the effect of 

 the Thomas slag was twice that of the other. These are important 

 facts, but the place of this slag phosphate among the commercial 

 fertilizers of this country has yet to be determined. 



This material gets the name, by which it is best known in Europe, 

 from S. G. Thomas, of England, who claimed to be the prior in- 

 ventor of the basic process of making pure steel. This claim was 

 disputed by Jacob Keese, of Pennsylvania, and the courts of this 

 country have confirmed the claim of Rieese. The slag is now manu- 

 factured by the latter in large quantities at Pottstown, Pa., and is 

 sold under the name of Odorless Phosphate. This is the slag very 

 finely pulverized, but not treated with acid. An idea of the growth 

 of the consumption of slag phosphate may be gotten from the fol- 

 lowing report, showing its production : 



5S_a_1902 



