BOOK II. SPECIES OF MINERAL MANURES. 245 



1 1 70. Quick-lime, in its pure state, whether in powder, or dissolved in water, is injurious 

 to plants. In several instances grass has been killed by watering it with lime-water. 

 But lime, in its state of combination with carbonic acid, is a useful ingredient in soils. 

 Calcareous earth is found in the ashes of the greater number of plants ; and exposed 

 to the air, lime cannot long continue caustic, for the reasons that were just now 

 assigned, but soon becomes united to carbonic acid. When newly-burnt lime is exposed 

 to air, it soon falls into powder ; in this case it is called slacked lime ; and the same effect 

 is immediately produced by throwing water upon it, when it heats violently, and the 

 water disappears. Slacked lime is merely a combination of lime, with about one third 

 of its weight of water ; i. e. fifty-five parts of lime absorb seventeen parts of water ; and 

 in this case it is composed of a definite proportion of water, and is called by chemists 

 hydrate of lime ; and when hydrate of lime becomes carbonate of lime by long exposure 

 to air, the water is expelled, and the carbonic acid gas takes its place. When lime, 

 whether freshly burnt or slacked, is mixed with any moist fibrous vegetable matter, there 

 is a strong action between the lime and the vegetable matter, and they form a kind of 

 compost together, of which a part is usually soluble in water. By this kind of operation, 

 lime renders matter which was before comparatively inert, nutritive ; and as charcoal 

 and oxygen abound in all vegetable matters, it becomes at the same time converted into 

 carbonate of lime. 



1171. Mild lime, powdered limestone, marls, or chalks have no action of this kind 

 upon vegetable matter; they prevent the too rapid decomposition of substances 

 already dissolved ; but they have no tendency to form soluble matters. It is obvious 

 from these circumstances, that the operation of quick-lime, and marl, or chalk, depends 

 upon principles altogether different. Quick-lime, 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 and 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 de- 

 composition of animal or vegetable bodies, and neither of these has any fixity when ex- 

 posed to the air. Chalk having no power of acting on animal and vegetable substances, 

 can be no otherwise serviceable to land than as it alters its texture. Quick-lime, 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. Boullion 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 

 combination with oxygen. Hence the uses of lime on peat lands, and on all soils con- 

 taining an excess of vegetable insoluble matter. ( Grisenthwaite. ) 



1 172. Effect of lime on wheat crops. When lime is employed upon land where there is 

 present any quantity of animal matter, 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 efficacy in fertilising peat, and in bring- 

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

 vegetable matter. 



1173. General principles for applying lime. The solution of the question whether quick- 

 lime 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 are improved by mild lime, and ultimately by quick-lime, which do not 

 effervesce v/ith acids ; 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 with 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 



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