OF PLANTS BY MANURING. DO 



ing with bone-dust must be principally attributed 

 to this ingredient of bone. Phosphoric acid, in its 

 free state, is soluble in water, but when brought 

 into contact with lime combines with it to form 

 a white, insoluble powder, called phosphate of lime. 

 In this combination we find it as the chief con- 

 stituent element of bones ; in this combination it 

 occurs also in the solid excrements of cows, horses, 

 and sheep ; and we discover the same combination 

 in the seeds of plants. It enters into the same rela- 

 tions with magnesia, which always occurs in plants 

 in association with lime, as with lime or lime-earth. 

 Mixtures of phosphate of lime and magnesia are 

 therefore called, in familiar language, for the sake 

 of brevity, " phosphoric acid earths." Since these 

 are insoluble, they only work more slowly in the 

 mass than when they are made soluble by other sub- 

 stances. This is effected gradually by the matters 

 engendered in the decay of manure, and rapidly by 

 the action of strong acids ; for instance, by sulphuric 

 or muriatic acid. The latter method is now very 

 generally adopted by English farmers, in order to 

 obtain a more prompt and energetic action from 

 bones. Their experience has shown that phosphoric 

 acid more especially calls forth an exceedingly vigor- 

 ous growth of the roots of plants, and for this reason 

 vitriolized bones are considered the best manure for 

 turnips, carrots, beet-root, etc. According to the re- 

 sults of numerous experiments, phosphoric acid pro- 

 duces its full effect only when azotized substances 

 are present at the same time in sufficient quantity. 



