COLLODION-NITROUS DERIVATIVES FROM SUGAR, ETC. 139

Mixed acids of the strength HNO3+H2SO4+2H2, produce the compound C, which is largely soluble both in ether and in glacial acetic acid; it is highly combustible, but scarcely explosive. The compound D is formed when acids of the strength 2HNO+ 2H2SO1+5H2O are used; it is but sparingly soluble in alcohol and ether, and not soluble in boiling glacial acetic acid.

Collodion. The solution of pyroxylin in a mixture of ether and alcohol is known under the name of collodion, from kóλλa, glue, in allusion to its glutinous character. Pure methylic alcohol may be used as a solvent without the addition of ether. When this solution is exposed to the air for a few moments in the form of a thin layer, the solvent evaporates, leaving the pyroxylin as a transparent membranous pellicle. Collodion has been applied to excoriated surfaces, for the purpose of forming an artificial skin in order to protect them from the action of the air; but its most important application is in the preparation of a sensitive transparent surface for the reception of photographic images (1018), by diffusion over plates of glass, after it has been duly impregnated with a soluble iodide. On immersing the film in a solution of nitrate of silver, the whole surface becomes impregnated with iodide of silver in the most favourable condition for the reception of photographic impressions. According to Hadow, the compound B is that which is best fitted for the preparation of photographic collodion. The temperature at which the compound is formed has also a very material influence upon the mechanical qualities of the collodion. If the temperature be not raised to 122° (50° C.) or upwards, the solution is viscid and glairy, and does not diffuse itself readily over the glass. The successful preparation of a good photographic collodion requires attention to a number of minute precautions, which are detailed in Hardwich's Manual of Photography.

(1105) Nitrous Derivatives from Sugar, &c., allied to Pyroxylin. Other substances besides cellulin may be converted into bodies more or less analogous to pyroxylin, by the action of a mixture of nitric and sulphuric acids. Powdered cane sugar is con

verted by the same mixture of acids into a bitter yellowish mass of resinous appearance; it is very slightly soluble in water, and according to Sobrero contains €12H18(NO2)4011. A somewhat similar compound may be formed from gum arabic, and also from milk sugar. If starch be treated with concentrated nitric acid it is rapidly dissolved, and if the viscid solution thus obtained be immediately diluted with water, a white tasteless insoluble preci

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pitate is occasioned, termed xyloidin, which appears to be a substitution product of starch and peroxide of nitrogen, E12H16(NO2)4→10' analogous to the foregoing; this substance, by digestion in hydropotassic sulphide (KHS), is reconverted into the soluble modification of starch, which becomes blue when mixed with iodine, whilst xyloidin does not yield a blue with iodine. But the most remarkable body belonging to this class is one which is produced when mannite is acted upon by the mixture of nitric and sulphuric acids. It is insoluble in water, but is readily dissolved by boiling alcohol; the nitromannite [ЄH.(NO2)6] crystallizes in fine needles as the solution cools. This compound explodes powerfully by a blow from a hammer. If gently heated it may be melted, but at a higher temperature than that required for its fusion it explodes, and produces red vapours.

8

2

2

In all these cases it will be observed that the derivative nitrous compounds are produced from the saccharine or amylaceous substance by the substitution of a variable number of atoms of hydrogen by an equal number of atoms of peroxide of nitrogen; each atom of nitric acid, when acted upon by an atom of hydrogen derived from the organic body, yielding one atom of water and one of peroxide of nitrogen; HNO3 + H becoming NO, +H,→. The water is absorbed by the sulphuric acid contained in the mixture, which, after its action upon the organic compound, is found in all cases to have become diluted by the water thus removed from the body submitted to its influence. The addition of the sulphuric acid in these cases has two advantages, one being the removal of the water produced by the reaction; the other, the prevention of the solution of the new compound, and its further alteration by the nitric acid. A mixture of nitric and sulphuric acids is now frequently employed for the purpose of obtaining compounds in which NO, is substituted for hydrogen: nitroglycerin (¤ ̧H¿(N→1⁄2) ̧Ð ̧, and various other compounds may be obtained in this manner with facility; the reaction however requires careful watching, as it is apt to become tumultuously violent, and sometimes, as in the case of nitroglycerin, the compounds which are formed are liable to explode during their preparation.

5

3

(1106) Tunicin x (H) is the name given to a substance closely allied to cellulin, which is formed in the outer envelopes of the Tunicata, or Ascidia (cynthia or phallusia), from which it is prepared by treating them successively with concentrated hydrochloric acid, and with aqueous potash of sp. gr. 128, and then washing with water. It is coloured yellow by an alcoholic tincture

TUNICIN-LIGNIN-PAPER-MAKING.

141

of iodine, dissolves slowly without blackening in concentrated sulphuric acid, and on boiling the solution with water it yields a fermentable sugar, which reduces the alkaline cupric tartrate. It is chiefly remarkable as being an animal product which has the same composition as vegetable fibre.

(1107) LIGNIN.-The incrusting matter contained within the cellular tissue, which gives hardness to wood, is most abundant in the heart-wood of trees, and in the hard shells of many varieties of nuts. This substance appears to be a mixture of several proximate principles; it contains a larger proportion of hydrogen than cellulin, the proportion of oxygen being insufficient to convert the whole of the hydrogen into water. This incrusting matter does not appear to have a uniform composition in all woods. It is, however, always characterized by being soluble in alkaline liquids, though it is insoluble in water. Sulphuric acid chars it, and an aqueous solution of chlorine attacks and dissolves it. When submitted to distillation in closed vessels, it evolves acetic acid; and it is found that the harder the wood, and the larger the proportion of this incrusting substance which it contains, the greater is the proportion of acetic acid which is furnished when equal weights of different woods are subjected to destructive distillation. When ligneous fibre is moderately heated with solid caustic potash potassic oxalate and acetate are formed.

The ligneous matter is generally deposited in a state of mixture with a variable quantity of resinous matters, which colour the wood and increase its inflammability. The deposited fibre also contains a certain proportion of saline matter, as well as small quantities of compounds containing nitrogen.

The applications of cellulin and of ligneous fibre in the arts are numerous and of great importance. Besides its every-day use in the form of wood, the fibre constitutes the basis of all linen, cotton, and hempen goods; and after these substances have ceased to be serviceable as textile fabrics, they are still, in the hands of the paper-maker, converted into a material scarcely less valuable.

(1108) Paper-making. The rags which are employed in the manufacture of paper are sorted, according to the material of which they consist, into linen, cotton, hempen, and woollen; and are afterwards further separated into white, coloured, and black. The seams and knots are cut out, and the rags are then well beaten to get rid of dust and dirt. Coloured rags can be employed in the preparation of writing-paper if they be first bleached

by the action of chlorine, which is sometimes applied to them in the gaseous form. For this purpose the rags are moistened, and placed on perforated shelves in wooden or stone chambers, into which the gas is transmitted. An excess of chlorine must be carefully avoided, because it is liable to enter into chemical combination with the fibre, and, by displacing a portion of the hydrogen, to form a substitution compound, which, being destitute of tenacity, furnishes a brittle paper. More frequently, however, the rags, after having been reduced to the form of pulp, are bleached by means of chloride of lime. In all cases it is necessary to ensure the removal of the last traces of chlorine, which would not only cause the paper to become brittle, but when the paper is used for manuscript purposes would gradually discharge the ink. The removal of the chlorine is effected by the addition of a small quantity of sodic sulphite or hyposulphite; if the sulphite be used the chlorine is converted into chloride of sodium, and the sulphite into sodic sulphate, whilst sulphurous anhydride is set free:

2 Na2SO ̧+Cl2=2 NaCl + Na2SO ̧+SO2·

The rags having been partially cleansed, either in their bleached or unbleached condition, are reduced by mechanical means into a fibrous paste, or smooth uniform pulp, with water. This pulp is then extended over wire strainers in a layer of uniform thickness, which when drained forms a film of paper. If this be simply dried and pressed it forms blotting, or filtering paper, and is too porous to be used as writing-paper. In order to fit it for the ink, it is sized, or coated with a mixture of weak fine glue and alum, by which means it is rendered less permeable to water. Many manufacturers mix the size with the pulp before it is made into sheets, but in this case it is necessary to employ a size of a description different from that which is applied to the finished sheets. The size which is to be mixed with the pulp usually consists of a mixture of three parts of a resinous soap and two parts of starch, to which a small quantity of alum is added.

Of all the numerous materials which have been tried as the basis of paper, none has been found so well adapted for the purpose as linen rags. Straw has been used to some extent as a material for paper, and it was at one time thought, owing to the abundance and cheapness of this substance, that it might be made a valuable substitute for rags, the supply of which is becoming inadequate to meet the demand; but the loss of material, from its

GENERAL REMARKS ON STARCH AND WOODY FIBRE. 143

brittle nature, during the process of manufacture, and other unforeseen circumstances, more than counterbalanced the advantage gained from the abundance of the supply. Within the last few years a species of grass (Stipa tenacissima), known as Esparto grass, has been very largely imported from Spain to supply a portion of the necessary fibre. It requires boiling for several hours with one-tenth or more of its weight of caustic soda in solution to remove the resinous material in which it abounds; the yellow fibre is afterwards bleached with chloride of lime, and may be employed, when mixed with half its weight of pulp from rags, in the making of an inferior paper now largely consumed.

(1109) General Remarks on Starch and Woody Fibre.-The facts already mentioned show the ready convertibility of the organized bodies, starch and lignin, into others which, though of organic origin, are yet devoid of structure, and therefore of a less complicated nature. In most cases great similarity exists in the ultimate composition of these bodies, many having identically the same composition as those from which they are derived: others, if not identical, differ among each other only in the presence or absence of the elements of water. It is, therefore, not surprising that a gradual transition should occur from the elaborate arrangement of the dense and compact tissue of the wood into the comparatively loose texture and low organization of starch; the ligneous tissue undergoing modifications of density, which gradually diminish from the compact structure of the lignum vitæ to the spongy cells of the fungus or lichen. The tissue of the Iceland moss, for example, presents a close analogy with starch; it is gradually disintegrated by boiling, it swells up into a gelatinous mass, and yields a magma colourable by iodine: thence we arrive at true starch, and gradually, as the organization of this body is broken up by the successive action of chemical agents, the addition of iodine produces a coloration less and less intense, until in the perfect formation of dextrin it disappears altogether; and at length sugar, in place of the cellular structure, crystalline form becomes apparent.

in

(1110) On the Decay of Woody Fibre and the Means of preventing it. When wood in a moist state is exposed to the air, it gradually undergoes decomposition; a species of fermentation is occasioned by the nitrogenized constituents, in consequence of which oxygen is absorbed, carbonic anhydride and water are exhaled, and the wood crumbles down into a blackish brown vegetable mould called humus, ulmin, or gein. This decay occurs