74 GARDENING FOB THE SOUTH. 



the insoluble phosphate must be converted into some 

 form which is soluble — that is, which dissolves in water. 

 This can be done by treating it with sulphuric acid (oil 

 of vitriol). 



2.— SOLUBLE PHOSPHATE OF LIME. 



"This is known under several other names, as acid phos- 

 phate of lime, acid calcium phosphate, acid phosphate, 

 superphosphate of lime, superphosphate, mono calcium 

 phosphate, etc. It is not found actually occurring. 



"As indicated above, the soluble calcium phosphate is 

 made by treating the insoluble calcium phosphate with 

 sulphuric acid. By this treatment a portion of the cal- 

 cium is removed from the phosphate and unites with the 

 sulphuric acid, forming calcium sulphate or sulphate of 

 lime, in addition to the soluble phosphate. This mixture 

 of the soluble phosphate and sulphate of calcium is 

 known as superphosphate of lime. The phosphate in this 

 form, being easily soluble in water, can be readily taken 

 up by plants, and is, therefore, of great value as a fer- 

 tilizer. The sulphate of lime is also known to have value 

 as a fertilizer. In plain superphosphate of lime there are 

 generally formed about 116 pounds of sulphate of lime 

 for each 100 pounds of soluble phosphate of lime. The 

 value of superphosphates depends upon the amount of 

 soluble phosphate contained in them. 



3.— REVERTED PHOSPHATE OF LIME. 



"Reverted phosphate of lime is known also as reverted 

 calcium phosphate, precipitated phosphate of lime, di- 

 calcium phosphate, citrate-soluble phosphate, etc. 



"When soluble phosphate of lime is allowed to stand 

 for some time it will happen under certain conditions 

 that some of the soluble phosphate is changed into a less 

 soluble form of phosphate. This is not the same form 

 as ordinary insoluble calcium phosphate above described; 



