DISPERSION OF PHOSPHATE OF LIME IN SOIL. 137 



are dispersed, and that in one spot of the ground one of 

 these granules weighing 22 milligrammes (J of a grain) 

 during the course of a certain time becomes soluble in 

 carbonic acid water, and spreads in the surrounding soil ; 

 first of all the earth immediately around this granule will 

 be saturated with phosphate of lime, then as the carbonic 

 acid remains in the water and its solvent power con- 

 tinues, a fi'esh solution will be formed, which will again 

 offer phosphate of hme for absorption to a wider extent 

 of earth ; at length, when the 22 milhgrammes of phos- 

 phate of Hme are thoroughly diffused in the surrounding 

 earth, they -will supply 20 cubic decimetres of earth with 

 the maximum of this nutritive substance in the form best 

 suited for absorption. The rapidity with which the phos- 

 phate of Hme wiU dissolve and spread depends upon its 

 extent of surface ; accordingly, if we suppose the granule 

 to be converted into a fine powder, a solution wiU be 

 formed richer in phosphate of Hme just in proportion to 

 the greater number of particles exposed within the same 

 time to the solvent action of the carbonic acid. There- 

 fore, assuming that in a certain state of greater division 

 twice or three times as much is dissolved in a given time, 

 we infer that distribution under favourable circumstances 

 wlU take place in one-half or one-third of the time it 

 would take without the division. 



If, therefore, in a given case the restoration of the 

 productive power in a soil by fallowing or manurmg 

 depends upon the earth when drained of phosphoric acid 

 by the roots of plants receiving the needful phosphoric 

 acid back again from the surrounding earthy particles, 

 it follows that with an equal amount of earthy phos- 

 phates the time required to accomplisli this end will be 

 shortened in proportion to the division of the earthy 

 phosphates. 



