COMMERCIAL FERTILIZERS 59 



tracted bone, bone ashes, and bone-black, which are used to 

 a small extent as fertilizers. 



The phosphoric acid obtained from chemical sources is 

 generally in the form called phosphate. There are two kinds 

 of phosphates, the natural mineral phosphates and the 

 manufactured phosphates. 1. Rock phosphate is a natural 

 form. It is thought to be the fossilized excrement and re- 

 mains of fish-eating animals which lived ages ago. These 

 fossil deposits are found in South Carolina, Florida, and 

 Tennessee. The rock is dug out and ground very fine and 

 then it is ready to apply to the land. Rock phosphate is quite 

 variable in its content. The South Carolina rock contains 

 about 26 per cent., the best grades of Florida rock about 40 

 per cent., and the Tennessee rock from 30 to 32 per cent, of 

 phosphoric acid. The rock phosphate is very slowly avail- 

 able. 2. Basic or phosphoric slag, also called Thomas slag, 

 is a by-product in the making of certain kinds of steel. It 

 comes in the form of a fine powder and contains 15 to 20 per 

 cent, of phosphoric acid. There is also a good deal of lime and 

 oxide of iron mixed with it. 3. The manufactured phosphate 

 is frequently called a super-phosphate. A super-phosphate is 

 a phosphoric acid fertilizer in which the phosphoric acid is 

 quickly available. Super-phosphates are made by treating 

 ground bone or ground rock phosphate with sulphuric acid. 

 Such treatment dissolves the original material and makes 

 new combinations which are more easily dissolved in the soil. 

 (1) Dissolved bone is ground bone treated with sulphuric 

 acid and contains about 2 per cent, nitrogen and 13 per cent, 

 of phosphoric acid. (2) Acid phosphate, or dissolved rock, 

 is made by treating ground rock phosphate with sulphuric 

 acid. The amount of phosphoric acid in the acid phosphate 



