of it in a tumbler of water. We shall speedily find that the water will rise in the tube higher than the surface of the water in the tumbler. Another explanation has been given of this curious phenomenon. If we take a long glass tube, 4 feet long, and inch bore, and tie over its lower extremity with a piece of bladder; fill it half full of a saturated solution of common salt, coloured by infusion of litmus, and then introduce it into a jar of pure water, so that the water in the tube and jar shall stand at the same level. In the course of 24 hours the fluid in the tube will be found to be much higher than that of the exterior vessel. The result of this experiment is similar to that of placing two gases of different densities on opposite sides of a porous membrane; the lighter gas passes through most rapidly, while the heavier gas is slower in its progress. The complicated stem of a plant is conceived to afford a series of similar experiments. When an ingoing current increases the volume, it is said to rise by endosmose, or accumulation from without; when it decreases by an outgoing current, it is said to descend by exosmose, or accumulation from within. The ascent of the sap very much depends on the presence of leaves; so that if we cut off a branch from a tree, and dip the lower extremity in a solution of acetate of iron, leaving the upper leaves, the wood will be impregnated with the colour, but not so distinctly if they are removed.

92

93

Ascent of Vegetable Sap and Animal Fluids. Some light has been thrown on the ascent of the sap and animal fluids, not only by the phenomena of endosmose, but also by the experiments of Hales and Liebig. Fig. 92. represents a barometer tube filled with water, the wide end being covered with ox-bladder, and the small end open and inverted in mercury. In the course of a few hours we observe that the mercury ascends, and continues gradually to rise, in consequence of the evaporation through the bladder. Hence there is a constant tendency to the formation of a vacuum, which is prevented from actually being produced by the ascent of the mercury. If we view the bladder as representing the leaves of trees, or as the animal skin, we have a close parallel, and may form some notion of the enormous force occasioned by the evaporation on these surfaces. If the bladder be covered with oil, the evaporation ceases; or if it be allowed to become dry, neither air nor water will pass through it. The contact of water is essential to this action. If the ascent of the sap, then, be dependent upon some such principle, we can easily understand how any obstruction to the ascent would be attended by such a disease as the potato blight, which is observed always to commence in the stem. In fig.93. the two extremities of the tube are tied with bladder, the siphon being filled with water. Evaporation goes on at both ends, and a vacuum occurs at the upper bend, into which, however, air makes its way. If we immerse the lower part of the long limb in a blue solution of salt, the coloured fluid soon becomes visible above the bladder, and it gradually rises, displacing the water which evaporates through the bladder of the short limb; the same observation applies to other fluids, so that as a general expression it appears that all liquids

move towards the membrane from which evaporation takes place, the amount of motion being proportional to the rapidity of evaporation and to the temperature and state of moisture of the atmosphere. As the vacuum tends to form in the inside of the bladder, we observe that the atmospheric pressure renders the exterior surface of that membrane hollow or concave.

Hence

any fluid placed on it externally will be pressed inwards, and be absorbed as the expression is in medicine; and during this action evaporation must be impeded.

The structure of a plant supplies us with an useful arrangement in the study of vegetable chemistry. Plants consist essenSection of Taxus baccata (Kieser.)

:- 1. The nature

tially of cells. We have, therefore, to consider :of the matter of which they are composed. 2. The substances secreted in the cells, as starch, woody matter. 3. The composition of the solid matters existing in the sap, as sugar, gum, &c. 4. Other secretions of plants comprising the alkaloids and colouring matters. 5. The excretions or resins. Such a classification cannot be strictly maintained in the present state of the science; but it affords a connection between physiology and chemistry.

Manures. As plants extract a certain amount of salts from the soil, which are entirely removed at harvest, it is obvious that the soil will become gradually impoverished, unless steps are taken to replace the matter which is carried away. This process

is termed manuring, and hence a true theory of manures is to restore to the soil what is removed by the crops grown upon it. In the present state of our knowledge it is inferred, that the analyses of the ashes of plants supply us with the proper ingredients to constitute manures.

I. SUBSTANCES FORMING THE CELLS.

Cellulin, Cellulose (Lignin of Prout), C12 H10 10° Properties. A white, solid diaphanous body insoluble in cold water, alcohol, ether, and oils. Specific gravity 1.525. Strong sulphuric acid and phosphoric acid attack it without heat, and

In

render it soluble in water, and capable of being precipitated by alcohol. Caustic soda swells it up and acts on its surface. this way it softens it for bleaching. It is not affected by iodine, except in some mushrooms, where a violet colour is produced.

Preparation. Obtained in its purest form from cotton or linen. These substances are to be torn into shreds; washed with cold, then with hot water; digested in boiling caustic soda for 2 or 3 hours; diffused through water, and a current of chlorine gas passed; after which it is digested in caustic soda. It is then washed successively with water, acetic acid, boiling water, digested in ether and alcohol, and lastly dried in a vacuum at 2120. By a similar process, but with more difficulty, it may be extracted from wood. The sporules of some mushrooms produce a violet colour with iodine, and hence they appear to contain cellulin. NO, in a concentrated state, dissolves cellulin, and converts it into xyloidine or nitramidine (C12 H, O, NO,), which is precipitated by the addition of water. This substance may be formed by dipping paper into strong acid, and washing with water. It constitutes an excellent match-paper; cellulin is also the basis of gun cotton, or ternitramidine, (C12 H, O, 3NO,), already described under nitric acid (p. 69.) To obtain Dextrin a soluble form of cellulin, we triturate in a mortar 100 parts of fine surgeon's lint with 140 parts HOSO,, added drop by drop, and stir until a gummy mass is formed; dilute with water, and saturate with chalk or barytes. By the addition of alcohol dextrin is precipitated, which possesses the same composition as cellulin, and by the addition of SO, and heat, is capable of being changed into sugar. In every respect it resembles a similar product from

starch.

Woody Matter. The interior of the walls of the cells is lined as trees grow, by a hard woody matter, which is deposited after the formation of the cell, as a kind of encrustation. It may be separated from the cellular matter, by cutting the wood lengthways, and then pounding it in a mortar into a pulp with water. This paste is treated successively with soda, hydrochloric acid, alcohol, and ether. Caustic soda then dissolves the lignin, which is again precipitated by an acid. The precipitate consists of 3 bodies, one of which is brownish yellow and is soluble in alcohol, ether, and water, containing 68 per cent. of carbon; the second brown, soluble in alcohol, insoluble in ether, containing 51 per cent. of carbon; and the third a gray body insoluble in alcohol, ether, and water, and containing 48 carbon. The terms fungin and suberin, have been applied to the woody matter of mushrooms and cork. Decay of Wood. Wood is apt to decay if not properly seasoned; that is, the sap which contains albumen must be washed out; otherwise a species of fermentation takes place, the albumen acting like yeast. The cellulin and ligneous

matter disappear in part, in the form of carbonic acid and water while humus or mould remains. Oak wood (C36 H22 O22), for example, is converted by exposure to the air into humus (C34 H18 018), by the loss of 2 carbonic acid and 4 hydrogen oxidised by the air to form water (2CO2, 4HO). To prevent the fermenting action of the albumen, wood is seasoned by exposing it to the weather; or it is put into a running stream of water to wash away its sap; or it is steeped in solutions of salts, which unite with the albumen and coagulate it. Upon this principle the corrosive sublimate (Kyan's patent) and chloride of zinc (Burnett's patent) act. Wood coal (C33 H21 O16), and even pit coal, are supposed to be produced by a similar action. Probably the latter has also been subjected to the influence of heat. If we subtract 9 atoms CO2 3 water and 3CH, from the above formula for wood, we obtain the expression for splint coal, C24 H13 O. The coals are divided into 4 species for practical purposes:-1. Splint and cherry coal, for producing heat, contain about 82 per cent. of carbon; 2. Caking coal, for the same purpose, of similar composition; 3. Anthracite, containing above 90 per cent. of carbon; 4. Cannel, parrot, or gas coal, with from 65 to 75 per cent. of carbon, adapted for lighting purposes. These coals when distilled yield heavy and light oils, containing carbonic acid, leucol, aniline, &c., and naphthaline, a crystalline body, which is of interest in consequence of the facility with which its hydrogen can be replaced by other substitutional bodies.

Bleaching or blanching is the process for whitening cellulin, or depriving it of a yellow tinge which it naturally possesses. This is effected by 1. Washing the goods with water; 2. Boiling them in soda to remove grease, and also to soften the surface of the cellulin; 3. Steeping them in a weak solution of bleaching powder, or chemio, as it is technically called (hypochlorite of lime); 4. Steeping in weak sulphuric acid, or souring, as this is termed.

Paper making. Paper being made from waste linen and cotton rags, and even from waste cotton wool, straw, and ropes, it is obvious that it consists entirely of cellulin, its quality depending upon the purity of that substance present. The rags are subjected to the same bleaching processes as in the manufacture of cloth. 1. They are sorted and cleaned according to their quality; 2. They are shaken in a revolving cylinder; 3. Boiled in caustic soda; 4. Reduced to pulp by means of a beating engine; 5. The pulp is bleached; 6. It is combed out into fibres, and allowed to flow into a chest, where it is ready for being converted into paper: 7. Paper is made from the pulp either by the hand or the machine; by the hand, it is formed into sheets by a mould of wire; it is then dried, and is in the condition of blotting paper; 8. To convert it into writing paper it is soaked in a

solution of glue and alum; 9. It is then subjected to the action of hot iron plates and rollers. When thus pressed, three or four times, it is termed rolled or hot pressed, and when more frequently glazed The blue colour of some kinds of paper is given by cobalt mixed with the size.

paper.

Dyeing consists in the application of colouring matter, so as to cause it to adhere to cloth. If we take a piece of cotton or calico, and place it in a solution of madder, and then wash it, the colour is entirely removed. To fix the colour, therefore, a chemical application is required, which, being first attached to the cloth, then unites with the colour. This substance is termed a mordant or biter (from mordeo, I bite). It may be easily illustrated by dipping cloth in a solution of acetate of lead, and

95

Cotton. (Bauer.) ammonia; throw it on a a spatula in a solution

96

Wool.
(Girardin.)

then in a solution of bichromate of potash. The lead is the mordant, and fixes the chromic acid, thus depositing chrome yellow on the cloth. The most satisfactory explanation of the process is that the acetate of lead enters into the tube (fig. 95.) of which the cotton and linen consists, fills it like a bag, and remains there to receive the chromic acid. (Crum.) If we dissolve alum, which is a valuable mordant in water; precipitate the alumina by filter and wash it; mix it by means of of madder or Brazil wood, and throw

Linen.

the whole on a filter; the liquid will pass through clear, while the colouring matter and alumina remain combined on the filter, and

may be dried. This experiment demonstrates the affinity between the colour and the mordant.

Calico printing consists in the application of colours to the cloth, by means of blocks and cylinders (as in book printing), after the use of a mordant. Wool differs (fig. 96.) from cotton and linen, in being a minutely jointed tube.

M