SUPERPHOSPHATE OF LIME. 257 



Result is, phosphoric acid, lime, lime, plaster. 

 Add to this, . . . O.V, 



Result is, phosphoric acid, lime, plaster, plaster. 



The neutral phosphate of lime is thus, by 2 equivalents of 

 oil of vitriol, changed to two portions of plaster and one of 

 super or acid phosphate of lime. Leaving out the plaster, if 

 to the superphosphate is added enough O. V. to unite with 

 all the lime, -^ of the superphosphate will remain unacted 

 on ; while f of the lime of the remaining J of the superphos- 

 phate unite to the oil of vitriol, and form plaster, the other 

 fourth of the lime combines with "a// the phosphoric acid, and 

 forms superphosphate containing 1 acid to \ lime, or 4 acid 

 to 1 lime. This may be considered as almost free phospho- 

 ric acid. It is a compound known to chemists as quadri- 

 phosphate of lime ; that is, quadruple phosphate. Phos- 

 phoric acid dissolves its own weight exactly, and no more, 

 of phosphate of lime ; of course this compound of 4 acid to 

 1 lime, being almost free acid, dissolves that ^ of the super- 

 phosphate of lime which had been unacted on by the O. V., 

 and thus forms a true biphosphate or double superphosphate 

 of lime, a compound of 2 acid to 1 lime. 



This may appear somewhat complicated to those unac- 

 quainted with chemical changes. Perhaps the subject may 

 be illustrated and elucidated by representing by words the 

 substances, and by figures their weights, or equivalent num- 

 bers. Supposing the operations to be performed on pure 

 bone earth, the mass remaining after the addition of the best 

 commercial O. V. will be represented as follows : 



156 lbs. of ) contain Phosphoric acid. Lime. Lime. Lime. 



bone earth ) lbs. 72 28 28 28 

 add 

 lOOlbs. O.V. = 50 50 



