1836] 



FARMERS' REGISTER, 



137 



Lime wlien exposed to the air, attracts carbonic 

 acid, which is ahvays to be found in the atmos- 

 phere; it thus passes back to the state of carbonate, 

 but in so doing gradually tails to powder, and is 

 then said to be air-slaked. It" slaked with water, 

 it also falls to a powder, which still retains the caus- 

 tic character of the burnt lime; but this powder, 

 when exposed to the air, unites wiih carbonic acid 

 more rapidly than when in mass. 



Lime, in its caustic state, has the property of ra- 

 pidly decomjiosing vegetable and animal sub- 

 stances, thus hastening the )iatural processes by 

 wliich they are finally destroyed; or, to speak- 

 more properly, have their elements resolved into 

 new combinations. The oliensive and unwhole- 

 some gases, which are given out by this composi- 

 tion, are absorbed by the lime, and prevented liom 

 mixing with the air. The same property is pos- 

 sessed in a less degree by the carbonate of lime, 

 and probably by its other compounds; but in order 

 that either this earth or its comjiounds shall man- 

 ilest this property, they must be in small iiag- 

 meats, or, which is better, in fine powder. 



Wet sand and plastic clay, and those soils to 

 which they give their characters, also possess the 

 property of absorbing gases; but they liave this 

 in a very inferior degree to lime and its compounds. 

 As the gases generated by the decomposition of 

 vegetable and animal substances Ibrm a large part 

 of the necessary Ibod of plants, it is obvious that 

 a soil which contains the carbonate of lime, may 

 retain and store them up for use, while they will 

 . be lost ill soils of a different character. 



Carbonate of lime may also be made a most 

 important article in the preservation of the most 

 valuable p?r!s of putrescent manures, until they 

 can be applied to the soil. In this way marl is 

 applied to a great extent in China; the night soil 

 of their numerous population is there Ibrmed into 

 cakes like bricks, with marl, and thus loses its of- 

 fensive smell;- but when these are applied as ma- 

 nure to the land, they give out the gases again, as 

 they are required, for the nourishment of plants. 

 So also in Norfolk, the sjte fordunghills is prepared 

 by a layer of marl, vvhich is incorporated with the 

 manure from time to time, and retains the gases 

 which would be otherwise lost. 



Lime may therefore be applied in its caustic 

 form in some cases in agriculture, for it will has- 

 ten the decomposition of animal and vegetable 

 matters which might otherwise be inert; it will 

 also neutralize acids, which experieneed farmers 

 well know to exist in many soils, which they in 

 con-scquence call sour. But the latter purpose 

 will be answered as well by the carbonate of lime, 

 which may be applied as it exists in marl or shells, 

 or as it may be prepared by grinding limestone. 

 Caustic lime is also dangerous in its aisplication. 

 for it will corrode and destroy living vegetables, and 

 hasten the decomposition of the vegetable matter 

 of the soil to such a degree as to injure its fertility. 

 Except upon turf-bogs, and land loaded with tim- 

 ber not wholly decompqsed, quick or caustic lime 

 ought not to be used; but to burn lime, and then 

 by slaking to reduce it to the form of fine powder, 

 which is speedily carbonated by exposure to the 

 air, is amore ready, and generally a cheaper mode 

 of obtainino- the carbonate in a convenient form, 

 than to grind limestone to powder in mills. Yet 

 for many of the most valuable uses of lime in ag- 

 riculture, the latter method, if as cheap, would 

 answer as well. 



Vol. IV— 18 



I Lime slowly combines with the earth silica, and 

 produces a compound very diOerent in character 

 from either. It is this, to cite a fact in proof of 

 our statement, which gives the hardness and so- 

 lidity to ancient mortar. The carbonate of lime 

 will serve to ibnn this compound; and thus, when 

 it has had time to act upon sand, it renders a sili- 

 cious soil more retentive of moisture; while if ap- 

 |)lied to clay, by combining with its silicious mat- 

 ter, it renders it more friable; and it is to the for- 

 mation of this compound by slow degrees, that 

 we are inclined to ascribe the valuable mechani- 

 cal properties of loamy soilfj, and the gradual ame- 

 lioration produced by the use of lime, marl, and 

 shells as manure. 



Besides silica, alumina, and lime, an earth call- 

 ed magnesia is likewise found in some soils. It is 

 also, in the form of carbonate, a frequent constitu- 

 ent of limestones. This earth has many proper- 

 ties in common with linle; like lime it is capable of 

 neutralizing acids; and when deprived of carbon- - 

 ic acid by heat, corrodes vegetable substances. It 

 probably also hastens putrefaction, and both it and 

 its carbonate are capable of absorbing the gases 

 let loose in that natural process. It is, however, of 

 little interest in agriculture, except as a part of 

 some of the limestones which are used as manure. 

 These, if applied 'in large quantities, are some- 

 times very injurious to vegetation; the reason of 

 this is, that magnesia does not rejiass to the state 

 of carbonate as rapidly as lime, and therefore re- 

 tains its corrosive quality long after the lime has 

 again become mild by its union with carbonic acid. 

 In less quantities, however, the magnesian lime- 

 stones may serve as a manure, but their applica- 

 tion requires great caution, particularly when the 

 quantity of magnesia amounts ro 25 per cent. 



All of the simple substances we have mention- 

 ed, except perhaps the last, either separate or in 

 various states of combination, exist in plan's. 

 The manner and character of the combination is 

 influenced by the vital action of the plant, which 

 causes them to form compounds, ofien in direct 

 opposition to the maimer in Avhich the ordinary 

 laws of chemistry would direct. It thus happens 

 that so soon as the plant ceases to live, these 

 chemical laws, being no longer impeded, begin to 

 exert their influence; and if it be in such a state as 

 will admit of the several elements acting readily 

 upon each other, a decomposition, more or less rca- 

 pid, of the vegetable structure ensues. It is a law 

 of chemistry, that its action is always aided by the 

 bodies being in a fluid state; and the action is often 

 impossible when the bodies are perfectly free from 

 moisture. Hence the direct chemical action, and 

 consequent decomposition, takes place with great- 

 er certainty and more rapidity in green juicy and 

 succulent vegetables, than upon those which have 

 been deprived of moisture either naturally or ar- 

 tificially. Thus grass, if heaped up in a recent 

 state, decomposes, and if but partially dried, is 

 heated, and may even take fire, by the chemical 

 action of its elements; while, if dried by exposure 

 to the sun and air, and then laid up in a dry place 

 in the form of hay, it is almost indestructible. A 

 moderate degree ol' heat and access to lur are also 

 necessary to promote the chemical action by 

 which decomposition is effected. This decompo- 

 sition is often attended with motion among the 

 parts; and always, if the mass has a liquid form, 

 as in the expressed juice of vegetables, or in the 



