Book III. SPECIES OF MINERAL MANURES. 345 



ciples altogether different. Quicklime, in being applied to land, tends to bring any hard 

 vegetable matter that it contains into a state of more rapid decomposition and solution, 

 so as to render it a proper food for plants. Chalk, marl, or carbonate of lime, will 

 only improve the texture of the soil, or its relation to absorption ; it acts merely as one 

 of its earthy ingredients. Chalk has been recommended as a substance calculated 

 to correct the sourness of land. It would surely have been a wise practice to have 

 previously ascertained the certainty of this existence of acid, and to have determined its 

 nature, in order that it might be effectually removed. The fact really is, that no soil was 

 ever yet found to contain any notable quantity of uncombined acid. The acetic and 

 carbonic acids are the only two that are likely to be generated by any spontaneous 

 decomposition of animal or vegetable bodies, and neither of these has any fixity when 

 exposed to the air. Chalk having no power of acting on animal and vegetable sub- 

 stances, can be no otherwise serviceable to land than as it alters its texture. Quicklime, 

 when it becomes mild, operates in the same manner as chalk; but in the act of becoming 

 mild, it prepares soluble out of insoluble matter. Bouillon la Grange says that gelatine 

 oxygenised becomes insoluble, and vegetable extract we know becomes so from the same 

 cause ; now lime has the property of attracting oxygen, and, consequently, of restoring 

 the property of solubility to those substances which have been deprived of it, from a com- 

 bination with oxygen. Hence the uses of lime on peat lands, and on all soils containing 

 an excess of vegetable insoluble matter. ( Grisenthwaite. ) 



2288. Marl, and even shell sand, have been known to act chemically on peat bogs, and 

 to produce astonishing benefits. True and genuine peat bogs contain a considerable 

 quantity of an acid which has some aflSnity to gallic acid, and often yield phosphoric acid 

 to analysis. It appears to be thesg acids which confer on peat earth its highly antiseptic 

 qualities, and prevent the complete decay of woody fibre in such situations. When either 

 true marl or shell sand is laid as a manure in such soils, a rapid decomposition of the vege- 

 table matter takes place, owing to the calcareous matter uniting with the acid which 

 before impregnated the woody fibre ; and such land soon becomes very productive, pro- 

 bably also because the carbonic acid of the marl and shell sand is applied to the growth 

 of living vegetables as it is gradually disengaged by the union of these acids with 

 the lime. {T. S. T.) 



2289. Effect of lime on wheat crops. When lime is employed upon land where 

 any quantity of animal matter is present, it occasions the evolution of a quantity of 

 ammonia, which may, perhaps, be imbibed by the leaves of plants, and afterwards undergo 

 some change so as to form gluten. It is upon this circumstance that the operation of 

 lime in the preparation for wheat crops depends ; and its eflicacy in fertilising peat, and 

 in. bringing into a state of cultivation all soils abounding in hard roots, dry fibres, or inert 

 vegetable matter. 



2290. General principles for applying lime. The solution of the question whether 

 quicklime ought to be applied to a soil, depends upon the quantity of inert vegetable 

 matter that it contains. The solution of the question, whether marl, mild lime, or 

 powdered limestone ought to be applied, depends upon the quantity of calcareous matter 

 already in the soil. All soils which do not effervesce with acids are improved by mild 

 lime, and ultimately by quicklime ; and sands more than clays. When a soil, deficient 

 in calcareous matter, contains much soluble vegetable manure, the application of quick- 

 lime should always be avoided, as it either tends to decompose the soluble matters by 

 uniting to their carbon and oxygen so as to become mild lime, or it combines with the 

 soluble matters, and forms compounds having less attraction for water than the pure 

 vegetable substance. The case is the same with respect to most animal manures ; but 

 the operation of the lime is different in different cases, and depends upon the nature of 

 the animal matter. Lime forms a kind of insoluble soap vrith oily matters, and then 

 gradually decomposes them by separating from them oxygen and carbon. It combines 

 likewise with the animal acids, and probably assists their decomposition by abstracting 

 carbonaceous matter from them combined with oxygen ; and consequently it must render 

 them less nutritive. It tends to diminish, likewise, the nutritive powers of albumen from 

 the same causes ; and always destroys, to a certain extent, the efficacy of animal manures, 

 either by combining with certain of their elements, or by giving to them new arrange- 

 ments. Lime should never be applied with animal manures, unless they are too rich, or 

 for the purpose of preventing noxious effluvia. It is injurious when mixed with any 

 common dung, and tends to render the extractive matter insoluble. According to- 

 Chaptal {Chimie apjdiquee, ^c. i. 153.), lime forms insoluble composts with almost all 

 animal and vegetable substances that are soft, and thus destroys their fermentative pro- 

 perties. Such compounds, however, exposed to the continued action of the air, alter in 

 course of time ; the lime becomes carbonate ; the animal or vegetable matters decompose 

 by degrees, and furnish new products as vegetable nourishment. In this view, lime 

 presents two great advantages for the nutrition of plants ; the first, that of disposing 

 certain insoluble bodies to form soluble compounds ; the second, that of prolonging the 



