USE OF PHOSPHORUS IN DIFFERENT FORMS 239 



experience in the practice of agriculture. These products are 

 everywhere looked upon as safe fertilizers. They .never injure the 

 soil, and where most used they are classed with farm manure in 

 that regard. And this is a correct view, for farm manure and bone 

 are two important products from the same source. In other words, 

 from the fertility standpoint, animals separate crops roughly 

 into manure and bone, and if we return the bone with the manure, 

 we thus return practically all of the fertility removed by the crop, 

 except a part of the nitrogen, which it is not necessary to return 

 directly, because the legumes are able to secure it from the air. 



Basic slag phosphate, a by-product in the manufacture of steel 

 from pig iron containing considerable quantities of phosphorus, 

 has been used as a phosphorus fertilizer since 1882. 



Recent investigations 1 by Director Hall of Rothamsted have con- 

 vinced him that the typical phosphorus compound in basic slag 

 is a double phosphate and silicate of calcium of the composition 

 Ca 3 (CaO) (PO 4 ) 2 CaSiO 3 , but the more common teaching has been 

 that a tetracalcium phosphate, Ca 3 (CaO) (PO 4 ) 2 , exists in the slag. 

 In any case the slag contains very considerable proportions of 

 lime, which undoubtedly greatly assists in the disintegration 

 of the product after being incorporated with the soil, thus bringing 

 the phosphate into an extremely finely divided state. The presence 

 of lime in the slag is of itself of some benefit on certain soils, al- 

 though as a source of lime it is, of course, very expensive and very 

 insignificant, compared to ground limestone. 



The use of slag phosphate is quite likely to give disappointing 

 results for the first year or two, resembling natural bone in this 

 regard; but like bone, also, it gives very satisfactory results with 

 continued use, and no prejudice has developed regarding its use 

 on account of any supposed injury to the soil. 



Herbert Ingle, in his "Manual of Agricultural Chemistry," 

 makes the following significant statements (page 162) : 



"Many attempts to improve basic slag as a manure have been made, some 

 directed to the removal of the iron, others the sulfur, while others have attempted 



1 This statement is based upon the information given by Director Hall in con- 

 nection with his course of lectures before the Graduate School of Agriculture of the 

 Association of American Agricultural Colleges and Experiment Stations, held at 

 Cornell University, July, 1908. His final conclusions should not be assumed in 

 advance of publication by him. 



