COMPARATIVE ECONOMY OF LIME AND MARL. 387 



3°. Where it is to be spread over grass lands without destroying the 

 herbage, it is in most cases safer to allow the lime to slake spontaneous- 

 ly, and in the open air rather than in a covered pit. It is thus obtained 

 in an exceedingly fine powder, which can be easily spread, and, while 

 it is sufficiently mild to leave the tender grasses unharmed, it contains 

 a sufficient quantity of caustic lime (p. 368) to produce those chemical 

 changes in the soil on which the efficacy of quick-lime depends. 



4°. Where lime is applied to the fallow, is ploughed in, well har- 

 rowed or otherwise mixed with the soil, it is generally of little conse- 

 quence in which of the above states it is laid on. The chief condition 

 is, that it be in the state of a fine powder, and that it be well spread 

 and intimately mixed with the soil. Before these operations are con- 

 cluded the lime will be very nearly in the state of combination in 

 which it exists in spontaneously slaked lime — whatever may have 

 been the state of causticity in which it has been applied. 



You will understand that the above remarks apply only to localities 

 where burned lime is usually or alone used for agricultural purposes. 

 There may be localities where marl also exists, or shell or lime-stone 

 sand, in greater or less abundance, and in such places it may be a ques- 

 tion of some importance to determine which it would be better or more 

 economical to apply. In such a case you may safely proceed upon 

 the principle that the lime in the marls, &c., will ultimately produce 

 precisely the same efTects, upon your land as the lime from the kiln, 

 provided you lay on an equal quantity, and in an equally minute state 

 of division. The effect will only be a little more slow, and the full 

 fertility of the land a year or two longer in being brought out. You 

 would therefore consider, 



1°. How niuch of the marl or sand must I add to be equal to a ton 

 of lime-shells? This will depend on the per-centage of lime which 

 the marl contains. Suppose it to contain 20 per cent., or one-fifth of its 

 weight of lime, (not carbonate of lime, but of lime in the state in which 

 it comes from the kiln, 100 lbs. of carbonate containing 56 lbs. quick 

 lime, p. 364,) then five tons of the marl will be equal to one ton of lime 

 shells. But as the lime in the marls and sands is never in so minute 

 a stale of division as in the slaked lime, the same quantity of lime in 

 the former cannot be so equally diffused through the soil as in the lat- 

 ter state. An allowance must therefore be made on this account, and 

 an additional quantity equal to one-fourth or one-fifth of the whole add- 

 ed, for the purpose of equalizing the effect. 



2°. Which of the two, the quick-lime or its equivalent of marl, can 

 I obtain and apply at the less cost ? This will not be difficult to calcu- 

 late, the proportion of Hme contained in the marl being once ascertained. 



3°. This question of economy being decided, it is necessary to con- 

 sider the kind and quantity of the earthy matter with which the lime 

 in the marl is mixed. If it be a lime-sand or sandy marl, it may be un- 

 fit to apply to light and sandy soils ; if it be a stiff unctuous clay marl, it 

 may only render stiffer and more difficult to work the clay lands on 

 which you may propose to spread it. In such cases as these, however 

 economical the use of marls or lime-stone sands may be, the intelligent 

 farmer will prefer the addition of quick-lime wherever it is readily ac- 

 cessible. 



17 



