338 SCIENCE OF AGRICULTURE. Part II. 



2220. Quick-lime, in its pure state, whether in powder, or dissolved in water, is injuri- 

 ous 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 im- 

 mediately 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 com- 

 post 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 car- 

 bonate of lime. 



2221. Mild lime, jwwdered 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 prin- 

 ciples altogether diflferent. Quick-lime, in being applied to land, tends to bring any 

 hard vegetable matter tliat it contains into a state of more rapid decomposition and solu- 

 tion, 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 pre- 

 viously 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 car- 

 bonic acids are the only two that are likely to be generated by any spontaneous decom- 

 position of animal or vegetable bodies, and neither of these have any fixity when exposed 

 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. ) 



2222. 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 am- 

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

 inert vegetable matter. 



2223. 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 eflervesce with 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 diflferent 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 



