WITH REFERENCE TO HORTICULTURE. 19 



second. According to some writers, inorganic manures also act spe- 

 cifically ; alkaline matters being found in all, and some sorts in many 

 plants. 



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 quick- 

 lime ; and in this state, when laid on the soil, having a powerful 

 attraction for water, it assists in the conversion of woody fibre and 

 other organic matters into the substance called humus, forming humate 

 of liine, 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. 



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 which 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 mild 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, which would cause crops to become too rank, to lessen the 

 putrescence of organic matter by the formation with it of humate of 

 lime. In short, quicklime 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. 



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. A 

 small 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 previously exist. 



Carbonate of lime, or chalk, in its native state, differs from un- 

 burnt 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 pulverize 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 beneficial 

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

 perty of retaining water without at the same time becoming adhe- 

 sive. Hence it may be used both on sands and clays, to render the 

 latter more friable without diminishing 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 



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