A Text-book of Paper-making. C. F. Cross
III. SCHEME FOR THE DIAGNOSIS AND CHEMICAL ANALYSIS OF PLANT SUBSTANCES.
It will be convenient at this point to present to the reader a general scheme for the chemical analysis of fibrous raw material.
We have already discussed (p. 4) the methods for the determination of cellulose in fibrous substances. This is to the paper-maker the most important constituent, and is that upon which his calculations of the value of a raw material are based. Not only, however, is it of the greatest importance for him to be able accurately to determine the amount of cellulose, but it is necessary to be able to form some idea of the nature of the cellulose and also the ease with which it can be obtained from the fibre. This latter point can only be properly established by direct trial of the fibre under the conditions existing in the factory. It should also be borne in mind that these conditions influence to a considerable degree the amount of cellulose, actually obtained in practice, and that therefore the percentage shown by a careful determination in the laboratory should only be taken as an indication of the amount likely to be realized. The student will be able, from what has been said before of the properties of the different celluloses, to apply his knowledge to a determination of any particular specimen. In order to supplement this knowledge, it may be well at this particular point to cite the chief results of an investigation bearing upon this point by Webster (Chem. Soc. Journ., 1883, p. 23).
His method of investigation consisted in (1) estimating {43} the cellulose; (2) determining the loss sustained by the fibre when boiled for 5 minutes, and also for 60 minutes, with an alkaline solution (caustic soda 1 per cent. Na2O), the former being taken to represent the purely solvent action, the difference between the two amounts being an indication of the degrading action of the soda; (3) determining the ultimate composition (C H and O) of the fibre substance. It should be observed that the specimens were carefully averaged and purified by boiling in glacial acetic acid and in alcohol. On carefully considering the following table it will be seen that the chief points brought out by Webster’s investigation are (1) the association of a low carbon percentage with pectous properties and considerable degrading action on long boiling in alkali. The bearing of this will be better understood in connection with a discussion of the properties of pectic acid (p. 28) and the oxycelluloses (p. 13). (2.) The influence of the composition of the original fibre on the isolated cellulose.
The solutions of aniline sulphate and of the aniline colours give valuable aid in a diagnosis of plant substances. Webster observed, as was to be expected, that the yellow colour produced could be taken as an indication of the amount of lignification, those fibres which were of a pectous nature showing little or no colour. On the other hand, when the fibres were treated with a neutral solution of the so-called alkali-blue it was found that the converse took place, highly pectous fibres being dyed much more deeply than those which were lignified. (Compare the action of aniline colours on oxycellulose, p. 11.)
{44}
| FIBRO-VASCULAR BUNDLES OF MONOCOTYLEDONOUS PLANTS. | ||||||
| Agave Americana. | Yucca gloriosa. | Ananassa sativa (Pine Apple.) | Musa paradisiaca (Manilla). | Phormium tenax (New Zealand Flax). | ||
|---|---|---|---|---|---|---|
| 1. Yield of cellulose by chlorine method | 81·2 | 80·8 | 76·3 | 62·8 | 86·3 | |
| 2. Character of isolated cellulose | Fibres free. | Fibres free. | Fibres agglutinated. | Fibres agglutinated. | Fibres partially agglutinated. | |
| 3. Loss in boiling 1 per cent. caustic soda (5 minutes) | 9·9 | 14·5 | 9·6 | 18·6 | 5·8 | |
| 4. Ditto (60 minutes) | 14·6 | 16·5 | 19·0 | 31·7 | 9·9 | |
| 5. Ash | 1·0 | 1·3 | 1·0 | 1·6 | 0·9 | |
| 6. Elementary composition | ||||||
| C. | 45·9 | .. | 42·5 | 42·6 | 44·4 | |
| H. | 6·1 | .. | 5·6 | 5·6 | 5·9 | |
| 7. Lignified or otherwise. Aniline sulphate reaction | Lignified. | Lignified. | Lignified. | Lignified. | Lignified. | |
| BAST FIBRES OF DICOTYLEDONOUS PLANTS. | |||||||
| Boehmeria Puya. | Urtica heterophylla (Nilgherry Nettle). | Crotolaria juncea (Sunn). | Hibiscus strictus. | Linum usitatissimum (Flax). | Corchorus capsularis (Jute). | ||
|---|---|---|---|---|---|---|---|
| 1. Yield of cellulose by chlorine method | 83·8 | 95·0 | 76·9 | 63·0 | 82·0 | 75·0 | |
| 2. Character of isolated cellulose | Fibres partially agglutinated. | Fibres free. | Fibres free. | Fibres partially agglutinated. | Fibres free. | Fibres free. | |
| 3. Loss in boiling 1 per cent. caustic soda (5 minutes) | 15·6 | 2·6 | 5·3 | 13·7 | 7·8 | 17·2 | |
| 4. Ditto (60 minutes) | 24·1 | 7·3 | 10·7 | 25·5 | 16·6 | 18·6 | |
| 5. Ash | 3·7 | 1·0 | 0·9 | 2·0 | 1·7 | 1·1 | |
| 6. Elementary composition | |||||||
| C. | 41·8 | 42·9 | .. | .. | 43·7 | 47·1 | |
| H. | 6·0 | 5·9 | .. | .. | 5·9 | 5·9 | |
| 7. Lignified or otherwise. Aniline sulphate reaction | Not lignified. | Not lignified. | Lignified. | Lignified. | Not lignified. | Lignified. | |
If the student require more precise knowledge of the nature of a fibrous material than that afforded by a determination of the cellulose, the following method of analysis will prove of service.
About two grms. are taken and dried at 110–115° C. until the weight remains constant: the loss represents water. The fibre is then treated with a hot mixture of benzene and alcohol, dried as before and weighed: the loss is fat, wax, {45} &c. The residue from this treatment is then repeatedly exhausted with boiling water and again dried at 110–115° C. and weighed: the loss is put down as aqueous extract. The exhausted fibre is then treated for cellulose by either of the methods given on p. 19. The ash is determined in a separate portion.
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