6 VEGETABLE GROWING. 



analysis of it before one can know its value. The 

 natural rock gives up the element slowly, so it is 

 necessary to grind and treat it chemically to make the 

 phosphoric acid available. In this condition, it is 

 known as "acid phosphate," or u superphosphate." 



BONES AS A SOURCE OF PHOSPHORIC ACID. 



A second source of considerable commercial impor 

 tance is the reduced hones from various animals. Be- 

 fore the discovery of the phosphate rock, this was a 

 very important source ; while the price of ground 

 bone for fertilizer has not declined very much as a re 

 suit of the discovery of rock phosphate, it has not in- 

 creased as it otherwise would have. In their natural 

 state, bones yield phosphoric acid but slowly, but, 

 being crushed and treated with chemicals, they can be 

 made to yield it up rapidly and become available in a 

 short time. A vegetable grower having several tons 

 of bones could make it profitable to change the insol- 

 uble phosphate of lime to a soluble form, which is 

 usually called phosphoric acid. The best way to 

 proceed is to grind the bones to meal ; place about 

 forty pounds of this meal" in a wooden tub, con- 

 taining thirty pounds of water ; then add thirty 

 pounds of sulphuric acid of a specific gravity of 1.7. 

 Much less water could be used, but this quantity will 

 enable one to mix the acid and bones more evenly. 

 The essential part of the bones is the phosphate of 

 lime, and, as before mentioned, this is insoluble, or, at 

 best, only a small portion of it will go into solution. 

 Now, when the sulphuric acid is supplied, it becomes 

 a superphosphate, or acid phosphate; some people call 

 it phosphoric acid, but the chemists object to this term 

 because it is incorrectly used. This superphosphate is 

 readily dissolved by water, and in such a state can be 

 taken up and used by plants. After the sulphuric acid 



