136 



Analyses of Ashes of Plants. 



dieted that a time will come when, in the cultivation of land 

 already brought into a state of high fertility, the application of 

 artificial manures^, except in rare cases, will be looked upon as an 

 unnecessary and unjustifiable waste of money. At the present 

 stage of agricultural practice, the only necessary loss of its mineral 

 ingredients which the land sustains, is comprised in that portion 

 which is sent into our large towns in the different grains and in 

 the bones of animals, and that other small (but unfortunately 

 often too considerable) portion which is lost l3y the drainage of 

 liquid from the stables and manure heap. The purchase of 

 bones to restore the phosphate of lime removed by the growing 

 by sheep and the milk of the cows, should hardly perhaps be 

 looked upon in the light of the application of artificial manures, 

 because nothing can be more reasonable than to give back what 

 we have taken from the soil ; and the measures now in progress 

 for rescuing the sew^age of our large towns, and an improved 

 system in the manufacture and preservation of natural manures at 

 the homestead, will leave but little on the credit side of the land. 

 But allowing a certain and considerable yearly diminution of the 

 mineral elements of fertility in land, we have yet, so to speak, an 

 almost infinite supply of these bodies in the soil itself, provided 

 we knew how we might economically avail ourselves of it. This 

 (the item of expense) is after all, the turning point — most soils, if 

 sufficiently exposed by repeated stirrings and cultivation to the 

 action of the natural agents, water and air, would yield up abun- 

 dant materials for the growth of luxuriant crops of roots, and 

 through their means of corn. 



We know from the constitution of the rocks from which they 

 have been produced, that all soils containing any clay, must con- 

 tain also considerable quantities of potash; and there is every 

 reason to believe that no sandy or chalk soil is absolutely deficient 

 in this alkali. Again, the experiments of Dr. Daubeny and 

 Professor Fownes have Jed us to believe that phosphoric acid is 

 a constituent of the chalk and limestone strata, as well as of 

 the older rocks; and the recent investigations of Dr. R. D. 

 Thompson * and of Mr. Sullivan, f go a great w-ay to prove that 

 this acid, so important to agriculture, is present in all the great 

 mineral masses of the globe, whether of ancient and igneous 

 origin, such as granite, gneiss, and all volcanic rocks, or the more 

 modern aqueous deposits of which so large a portion of the soil 

 of England consists. The presence of phosphoric acid in the 

 older rocks is however the important point, because its existence 

 (as insoluble phosphate of lime) in the sedimentary deposits 



' Philosophical Magazine,' xxvii. p. 310. 



t Ibid., p. 161. 



