. How crops grow. A treatise on the chemical composition, structure, and life of the plant, for all students of agriculture ... Agricultural chemistry; Growth (Plants). 358 HOW CEOPS GEOW. acid or alkali is carried beyond a point peculiar to each substance, contraction of the colloid takes place. The colloids just named acquire the power of combiniag with an increased proportion of water and of forming higher gelatinous hydrates in consequence of contact with dilute acid or alkaline reagents. Even parchment-paper is more elongated in an alkaline solution than in pure water. When thus hydrated
. How crops grow. A treatise on the chemical composition, structure, and life of the plant, for all students of agriculture ... Agricultural chemistry; Growth (Plants). 358 HOW CEOPS GEOW. acid or alkali is carried beyond a point peculiar to each substance, contraction of the colloid takes place. The colloids just named acquire the power of combiniag with an increased proportion of water and of forming higher gelatinous hydrates in consequence of contact with dilute acid or alkaline reagents. Even parchment-paper is more elongated in an alkaline solution than in pure water. When thus hydrated and dilated, the colloids present an extreme osmotic ; An illustration of membrane-diffusion which is highly instructive and easy to iwoduce, is the following: A cavity is scooped out in a carrot, as in fig. 68, so that I the sides remain ^ inch or so thick, and a quantity of dry, crushed sugar is introduced; after some time, the previously dry sugar wUl be converted into a syrup by withdrawing water from the flesh of the carrot. At the same time the latter will visibly shrink from the loss of a portion of its liquid contents. In this case the small portions of juice moistening the cavity form a strong solution with the sugar in contact with them, into which water diffuses from the adjoining cells. Doubtless, also, sugar penetrates the parenchyma of the carrot. In the same manner, sugar, when sprinkled over thin- skinned fruits, shortly forms a syrup with the water which it thus withdraws from them, and salt packed with fresh meat runs to brine by the exosmose of the juices of the flesh. In these cases the fruit and the meat shrink as a result of the loss of water. Graham observed gum tragacanth, which is insoluble in water, to cause a rapid passage of water through a mem- brane in the same manner from its power of imbibition, although here there could be no exosmose or outward movement. The application of these facts and principles to explain- Digitized by Mic
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectagricul, bookyear1868
