SUPERPHOSPHATE OF LIME. 225 



the cause of the favorable action of ground bone upon cer- 

 tain crops. It was long supposed that this action was due 

 to the organic matter of the bones, and it was not then sus- 

 pected that the mineral part of the bones, which was known 

 to consist in large part of phosphoric acid, had anything to 

 do with the luxuriant growth of grass and root crops to 

 which bones were applied. The experiments of Liebig 

 proved that the phosphoric acid was really the most impor- 

 tant element of the bones, and this was further shown by 

 the fact that burned bones, bone ash, or "earth of bones," 

 as it was called, exerted a very marked effect upon crops* 

 to which it was applied. But it was found that the phos- 

 phate of lime, both as it existed in fresh bones and in the 

 remains of extinct animals, was too slow in its effects and a- 

 la rue quantity w r as required to show any profitable results'. 

 Hence further experiments were made and it was found 

 that when the ground bones were digested with a certain 

 quantity of sulphuric acid, mixed with water, they became 

 changed in character; that a portion of the lime in them 

 was dissolved and united with the sulphuric acid forming sul- 

 phate of lime or gypsum, leaving a double portion of the 

 phosphoric acid combined with the remainder of the lime. 

 In this state, the phosphate of lime or the phosphoric acid 

 in it, was partly soluble in water and still more so in acid- 

 ulated water; hence this double phosphate or bi-phosphate 

 of lime exerted a very much more active effect upon the 

 crops than the bones did. It was further found that it was. 

 possible to take still more of the lime from the bones, leaving 

 but one- third of it in combination with the phosphoric acid, 

 and proportionately increasing the ratio of the acid; the re- 

 sulting single lime, or mono-calcic or treble phosphate being 

 called superphosphate of lime. This compound is soluble 

 in water, and hence its effects are still more active than the 

 former one upon crops to which it is applied. 



But in effect, this form of phosphate of lime is unstable, 

 and easily reverts to its former condition by combining 

 again with lime which it finds in the soil, or with iron or 

 other bases, and thus becomes less soluble. 



