WITH REFERENCE TO HORTICULTURE. 



61 



principle. This principle may be stated to be the rendering more soluble of 

 the organic matters already in the soil in most instances, and in some cases 

 rendering soluble matters insoluble, so as to diminish excessive fertility, and 

 prepare a reserve of the fertilising principle for future use. Quicklime, for 

 example, effects the first of these objects, and slaked lime the second. 

 According to some writers, inorganic manures also act specifically ; alkaline 

 matters being found in all, and some sorts in many plants. 



194. Lime. This is by far the most important of all the mineral manures. 

 It is applied to soil in the form of quick or hot lime, mild or slaked lime, and 

 chalk or carbonate. Quicklime is procured by burning chalkstone or lime 

 rock till the water and the carbonic acid gas are driven off. Immediately 

 after burning, it forms what is called quicklime ; and in this state, when 

 laid on the soil, having a powerful attraction for water (201), it assists in 

 the conversion of woody fibre and other organic matters into the substance 

 called humus, forming humate of lime, which again is rendered soluble and 

 fit for supplying the food of plants by the action of the carbonic acid gas 

 in the soil, or supplied to it by water or the atmosphere. 

 ' 195. Mild lime. When water is thrown on quicklime, it becomes what 

 is called slaked, falls down into a fine white powder, and, re-absorbing 

 great part of the water wliich had been driven off by burning, it becomes 

 what chemists call hydrate of lime ; and soon after, from the absorption of 

 carbonic acid gas, it becomes what is called mUd lime. The use of lime in 

 this state is partly the same as that of caustic or quicklime ; and partly, 

 also, when there is a superabundance of soluble manure, so as to cause crops 

 to become too rank, to lessen the putrescence of organic matter by the for- 

 mation with it of humate of lime. In short, quicklim.e may be said to 

 increase the solubility of inert organic matter, and mild lime to render less 

 .soluble organic matter already in a state of solubility. 



196. The application of lime to soil may also be useful in cases where 

 there is not already a sufficient portion of that earth ; but, to ascertain this, 

 a chemical analysis of the soil should be previously made. The smallest 

 quantity of quicklime added to a soil in which little or none previously existed, 

 will effect a great permanent improvement ; and the same may be said of a 

 small quantity of clay added to a soil in which that ingredient did not pre- 

 viously exist. (172.) 



197. Carbonate of lime, or chalk, in its native state, differs from unburnt 

 limestone in being of a much softer texture, and more easily acted on either 

 mechanically or by the weather. When burned, it of course becomes lime, 

 and may be used either in a caustic or mild state ; but in chalky countries 

 it is most commonly laid on land in its natural state, and left to pulverise 

 by the influence of the weather. It is supposed to have no effect upon inert 

 vegetable fibre, and to be incapable of generally uniting with humic acid ; so 

 that it appears to be destitute of the two properties of caustic and mild lime, 

 viz., that of rendering insoluble matter soluble, and the contrary. Its bene- 

 ficial effects are attributed to its altering the texture of soil, and to its pro- 

 perty of retaining water without at the same time becoming adhesive. Hence 

 it may be used both on sands and clays, to render the latter more friable 

 without dimmishing its retentive powers, and the former more absorbent 

 without adding to its tenacity. Chalk, also, may be considered as a specific 

 manure, since carbonate of lime is an ingredient in almost all the plants 

 which have hitherto been analysed by chemists. 



