238 SYSTEMS OF PERMANENT AGRICULTURE 



compound, tricalcium phosphate, Ca 3 (PO 4 ) 2 , the difference be- 

 tween these two groups being the presence of more or less organic 

 matter within the pores of the bone, while the products in group 2 

 contain little or no organic matter. In group 3 the phosphorus 

 is contained in a basic or alkaline compound or mixture, and in 

 group 4 the phosphorus exists chiefly in monocalcium phosphate, 

 an acid salt. This form of phosphorus is soluble in water, and even 

 the dicalcium, or "reverted," phosphate is soluble in very weak 

 solvents (as in neutral ammonium citrate solution) ; while all prod- 

 ucts in groups i, 2, and 3, are known as insoluble forms of phos- 

 phorus. 



About seventy years ago Sir John Lawes, independent of a 

 suggestion previously made by Liebig, treated bone meal with 

 sulfuric acid and formed an acid phosphate that proved of greater 

 benefit to the turnip crop grown on the Rothamsted soils than 

 the crushed bone or coarse bone meal then in use; and in 1842 

 a patent was taken out by him for treating mineral phosphates 

 with sulfuric acid in order to increase their availability in crop 

 production. 



Acidulated bone meal has been much used as a fertilizer, but 

 gradually its use has given way, largely because the most success- 

 ful and influential farmers in our Eastern states have insisted that 

 in the long run fine-ground pure raw bone meal was more profit- 

 able than acidulated bone. It is always recognized that the acidu- 

 lated bone gave the best results the first year, but, on the basis of 

 equal cost, the raw bone proved much more durable, and hence, 

 more profitable in the end, especially where good rotations were 

 practiced and some effort made to keep the soil supplied with 

 organic matter. 



In more recent years steamed bone meal is replacing the raw 

 bone, because, as a rule, it gives better results, due in part to its 

 larger phosphorus content and in part to the fact that it is usually 

 more finely ground than the raw bone. There are still to be found 

 those who argue that " if one wishes to benefit himself, he should 

 use acidulated phosphates, but if he wishes to benefit his grand- 

 children, he should use bone." However, the farmers' demand 

 for " pure raw bone " and for " steamed bone meal " continues to 

 increase, and this steady demand is based upon long-continued 



