A Text-book of Paper-making. C. F. Cross
a mass of ligno-cellulose (jute) is allowed to lie for a long period in a damp state, it undergoes resolution accompanied by structural disintegration. The soluble products of this change are acid bodies of the pectic class, and astringent substances closely resembling the tannins. In this decomposition also we have evidence of the plastic condition of the ligno-cellulose molecule, of the variety of its modes of resolution, according to the various directions in which it is attacked.
Decomposition by Heat.
—The celluloses burn in the air with {24} a quiet luminous flame. When heated out of contact with the air, they are completely resolved into gaseous and volatile products on the one hand, and a residual black mass, which, although containing a high percentage of carbon, and approximating in its properties to the element itself, nevertheless contains hydrogen and oxygen in essential chemical union with the carbon, in consequence of which it is expedient to apply the term pseudo-carbon to this as to all similar substances. The volatile products of the destructive distillation of pure cellulose have not been studied, but those of certain of the ligno-celluloses (woods) have been exhaustively investigated, and have moreover, a very considerable commercial importance. They divide themselves into two groups (a) soluble in water, and containing, besides water, acetic acid, methyl alcohol, methylic acetate and acetone; (b) insoluble in water, or wood tar, containing tolyene, xylene, cymene, naphthalene, chrysene, anthracene, retene, pittacal, cedriret solid paraffins, &c. The quantity of the pseudo-carbon (charcoal) obtained is, in the case of the hard woods, about 25 per cent. of their weight. The liquid portion of the products amount to some 50 per cent., and contains about one-fifth of the carbon of the original wood; the remainder of the carbon is eliminated in the gaseous form (CO, CO2, &c.). The proportion of acetic acid is 3–4 per cent., the tar amounting to 7–8 per cent.
The coals themselves may be regarded as pseudo-carbon derivatives of celluloses, formed by a process of molecular condensation, the true nature of which remains a matter of speculation. In this view, the whole of our vast series of aromatic or benzene compounds, derived as they are from the products of the destructive distillation of coals, may be traced back to a cellulose origin.
Pseudo-carbons are obtained as products of the action of various reagents upon the celluloses, and other of the so-called carbo-hydrates. These reagents, such as sulphuric acid, act in virtue of their dehydrating power; and the recognition of this fact, together with the supposed “carbonaceous” {25} character of the product, led to the erroneous conclusion that the carbohydrates are in such decompositions simply resolved into carbon and water; a conclusion which seems to derive additional warrant from the peculiar numerical relationship which exists between the C, H, O atoms of all the members of the group. Their relation is expressed in the general formula Cn H2(n−m) O(n−m), and in the somewhat misleading term carbohydrate, which is applied to the whole group. We now know that the removal of water from these bodies by the action of dehydrating agents—including heat—follows the ascertained laws of chemical dehydration, involving molecular condensations and rearrangement, and that the pseudo-carbons are the extreme terms of a series of such condensations or cumulative resolutions. The matter, however, is not as yet sufficiently investigated to enable us to state with any preciseness the mechanism of these changes. Still this general statement will enable us to avoid many of the erroneous views which have existed on the subject, and in a measure to anticipate the results of future investigation.6
6 It is worthy of mention that by the action of chlorine in presence of water, and by the action of concentrated nitric acid upon the cannel coals, substitution derivatives are formed resembling those obtained by the action of these reagents respectively upon the ligno-celluloses.
General conclusions.
—The aldehydic character of the group of ligno-celluloses is typical of the constituents of plant tissues generally, and is, there can be no doubt, extended to the celluloses. Indeed the evidence of biological observation goes to show that the ligno-celluloses are formed, by a process of chemical modification, from some more purely cellulosic tissue, which preceded it, and with this modification there is, nevertheless, a retention of the general features of the original cellulose. In the domain of animal chemistry, recent investigation has also shown that the development of proteid tissues finds its chemical expression in their aldehydic characteristics, or as it has been put, the immediate physical cause of life is to be found in the chemical tension of aldehydes. The meaning of this expression will be readily grasped on {26} reference to the properties of the aldehydes as a group; their power of combining with oxygen; of uniting by their own molecules, to polymerise; of uniting by way of dehydration; of combining with the aromatic alcohols; a consensus of properties which shows them to possess an activity surpassing that of any other group of compounds. The evidence of biology, added to our knowledge of the properties of these substances, would lead us therefore to define cellulose as a condensed aldehyde allied to the sugars, and likewise containing alcoholic OH groups; and ligno-cellulose a compound cellulose, containing a cellulose nucleus or residue so combined with certain groups which may be included in the term non-cellulose, that it yields, under the action of reagents, products belonging either to the aromatic, the furfural, or the fatty group.
Adipo-cellulose.
—Cork or Cuticular Tissue.—From the mode of formation of cork and cuticular tissues, it has been concluded that they are also modified celluloses. The aggregate ultimate composition of cork is represented by the following percentage numbers:
| C | 65·7 |
| H | 8·3 |
| O | 24·5 |
| N | 1·5 |
Cork, however, unlike the jute fibre, is by no means chemically simple, but can be resolved by the action of mere solvents into a number of proximate constituents, such as acids, a variety of fatty bodies, nitrogeneous bodies, &c.
Cuticular tissues, such as constitute the covering of fruits, are more simple in composition; the cuticle of the apple after purification, has the following percentage composition:
| C | 73·66 |
| H | 11·37 |
| O | 14·97 |
The cuticular substance of cotton, straw, esparto, &c., are doubtless similar bodies. These numbers point to a {27} remarkable similarity in composition to the fats, and, indeed, from the results of his study of this tissue, Frémy concluded that it was a fat in everything but its physical properties, of which we may mention insolubility in alcohol and in ether, and infusibility. This tissue, however, as also cork, contains a cellulose residue, which may be isolated by any of the methods of treatment given for ligno-cellulose. Under the action of boiling nitric acid these tissues are resolved into cellulose on the one hand, and a series of fatty acids or products of their decomposition, suberic and adipic acids, &c., on the other; the latter amounting in the case of cork to 40 per cent. of the weight of the substance treated. The cellulose obtained by this treatment is but 2–3 per cent.; this number, however, represents only