i '8 COMPARATIVE UTILITY OF BURNIJD AND UNBDRNED LIME. 



which result I'rom the union of the organic matter with oxygen, the 

 more abundant in general also the production of those gaseous and 

 t^olatile compounds which they form by uniting with hydrogen, so 

 that, in promoting the formation of the one class of bodies, lime also 

 favors the evolution of the other in greater abundance, and thus in 

 a double measure contributes to the exhaustion of the soil. 



The disposmg action of lime to this twin form of decomposition, few 

 varieties of organic matter can resist, — and hence arises the well 

 known efficacy of lime in resolving and rendering useful the appa- 

 rently inert vegetable substances that not unfrequently exist in the 

 soil. 



§ 28. Of the comparative utility of burned and unburned lime. 



Is there no advantage, then, you may ask, in using caustic or burned 

 rather than carbonated or unburned lime? If the ultimate effects of 

 both upon the land be the same, why be at the expense of burning ? 

 Among other benefits may be enumerated the following : — 



1°. By burning and slaking^ the lime is reduced to the state of an iin- 

 palpable^owder, finer than could be obtained by any available method 

 of crushing. It can in consequence be diffused more uniformly through 

 he soil, and hence a smaller quantity will produce an equal effect. 

 This minute state of division also promotes in a wonderful degree the 

 chemical action of the lime. In all cases chemical action takes place 

 between exceedingly minute particles of matter, and among sohd sub- 

 stances the more rapidly, the finer the powder to which they can be re- 

 duced. Thus a mass of iron or lead slowly rusts or tarnishes in the air, 

 but if the mass of either metal be reduced to the state of an impalpable 

 powder — which can be done by certain chemical means — it will take 

 fire when simply exposed to the air at the ordinary temperature, and 

 will burn till it is entirely converted into oxide. . By mere mechanical 

 division the apparent action of the oxygen of the air upon metals is aug- 

 mented and hastened in this extraordinary degree — and a similar re- 

 sult follows when lime in an impalpable state is brought into contact 

 with the vegetable matter upon which it is intended to act. 



2^. The effect of burned lime is more powerful and more immediate 

 than that of unburned Hme in the form of chalk, marl, or shell sand. 

 Hence it sooner neutralizes the acids which exist in the soil, and 

 sooner causes the decomposition of vegetable matter of every kind to 

 commence, upon which its efficacy, in a greater degree, depends. 

 Hence, when it can easily be procured, it is better fitted for sour grass 

 or arable lands, for such as contain an excess of vegetable matter, and 

 especially for such as abounds in that dead or inert form of organic mat- 

 ter which requires a stronger stimulus — the presence of more power- 

 ful chemical affinities, that is — to bring it into active decomposition. 

 In such cases, the lime has already done much good before it has been 

 brought into the mild state — and remaining afterwards in this state in 

 the soil, it still serves, in a great measure, the same slower after-pur- 

 poses as the original addition of carbonate would have done. 



3°. Besides, if any portion of it, after the lapse of two or three 

 years, still linger in the caustic state, (p. 368,) it will continue to pro- 

 voke more rapid changes among the organic substances in the soi^ 

 than mild lime alone could have done. 



