SUPERPHOSPHATE OF LIME. 263 



200 lbs. of raw bones burned, give 100 lbs. 



bone-ash, $0,600 



Burning and grinding, 250 



87J lbs. of oil of vitriol, at 3 cts. per lb., . 2.625 



$3,475 



or, per pound, SO.1.896 



If there is added for labor besides that for 



burning, <fec., ...... .104 



$0.2.000 

 the cost is 2 cts. per lb. 



This is for a superphosphate which contains all the phos- 

 phoric acid of bone in a soluble state. 



It is this soluble state of phosphoric acid which is most to 

 be desired by the farmer. Every care should be taken by 

 him that his phosphoric acid falls not back into its insolu- 

 ble state of phosphate of lime, magnesia, alumina or iron, 

 when it comes in contact with these elements in soil, or in 

 the compost heap. Lime, or leached ashes, would immedi- 

 ately reduce the phosphoric acid to insoluble bone earth. 



308. In the crude mass formed from bone ash and oil of 

 vitriol, as above described, there is no longer any superphos- 

 phate of lime, or at most, only a very small quantity. It 

 has been shown how very small a portion of lime is com- 

 bined with phosphoric acid in the superphosphate, when that 

 is made from pure bone earth. If to such a superphosphate 

 of lime, an alkaline sulphate is added, as, for instance, sul- 

 phate of soda, or Glauber's salt, decomposition ensues, sul 

 phate of lime, insoluble, is formed, and phosphate of soda, 

 soluble, takes the place of phosphate of lime. Now, in oper- 

 ating on bone ash with oil of vitriol, alkaline sulphates are 

 formed, which with those already existing in the ash, precip- 



