146 LIME. 



the carbonic acid is driven off and the lime remains. This is called 

 quick lime, which, when exposed to the air, ultimately falls into 

 powder, by absorbing carbonic acid from the air and forming thereby 

 carbonate of lime again ; or, when water is thrown upon it, swells and 

 becomes one-third heavier by the combination with it of the oxygen of 

 the water, and giving off the hydrogen with the latent heat of the 

 water which before kept it in a fluid state. Lime is used in a mild 

 state, as a carbonate, in marls, chalk, powdered shells, etc. ; or in a 

 caustic or quick state, as it comes from the burning or after being 

 slacked. Marl contains from 5 to 20 per cent, of carbonate of lime in 

 the state of a fine powder. Shell-sand, found on the shores, contains 

 also from 20 to 50 per cent, of silicious sand. Some lime-stones also 

 contain considerable magnesia, and hence are called magnesian lime- 

 stones. Most lime-stones contain some magnesia which is useful for 

 plants, but if above 10 per cent, it is thought to be deleterious. The 

 quantity of lime used in dressing and the frequency of its use should 

 depend on the depth of the soil and the mode of culture. A large or 

 more frequent application is necessary if the soil be wet, but when it 

 is thin and dry a moderate coat will penetrate to the depth of 8 or 10 

 inches, or the ordinary extent of ploughing. A thinner dressing still 

 is requisite on old pasture lands, the grasses living in 2 or 3 inches of 

 soil. But in reclaiming lands, or laying them down to grass, a heavy 

 dressing is often necessary ; and in ordinary arable culture considera- 

 ble quantities are used because the soil is deeper on stiff clay soils 

 after draining, and where there is much vegetable matter much lime 

 may be profitably added. 



The chemical constitution of soils is not materially affected by the 

 use of lime. All soils contain naturally more or less. 300 bushels 

 applied to the acre seldom amounts to 1 per cent, by weight, of a soil 

 12 inches deep, when well mixed. If thinner, the per cent, will be 

 in proportion. The effects of lime are seen gradually to diminish, so 

 that in a few years, on analyzing the soil, it has entirely disappeared ; 

 hence the importance of occasional lime at least. Rains, charged 

 with carbonic acid by the air, dissolve the carbonate of lime, and re- 

 move much of the lime. Other portions of it are dissolved by the 

 formation of acids in the soil, and it is therefore readily removed by 

 rains. The first action of quick lime on the soil is to combine with 

 all the acid matter, by which the soil may be said to be sweetened ; 

 and some of the liquid compounds it thus forms, enter the roots as the 

 food of the plant. Portions also decompose saline compounds of iron, 

 alumina, manganese, pot-ash or soda, found in the soil, part of which 

 are the food of plants. The organic matter of the soil likewise un 

 dergoes a more ready decomposition by which many compounds are 

 formed highly important in vegetation. By being soluble in cold water, 

 this matter is readily diffused through the soil, and when reconverted 



