Whilst drying and fermenting, the tobacco undergoes great changes. Some substances are decomposed, others are newly formed. The highly complicated compounds, the albuminoids, undergo first decomposition, and in doing so give rise to more simple combinations. Nitric acid, ammonia, and other substances less known are chiefly, if not entirely, derived from the products of the decomposition of albuminoids. The substances that cause the objectionable pungent smell in tobacco are formed from the broken-up constituents of these high combinations. The conditions under which these bad-smelling combinations originate are not properly known; but it is probable that they are developed with, and under the same conditions that cause the formation of, ammonia, as the disagreeable pungent flavour is found generally in tobacco that has undergone fermentation to a great extent. It is believed that the conditions that favour the development of nicotine are also conducive to the formation of albuminous substances in the leaf, viz. fresh nitrogenous manure, bad physical state of the soil, &c.
According to Nessler, the quality of tobacco depends to a great degree on the amount of cellulose it contains. He found that a good tobacco invariably contained more than a bad one, Havana yielding as much as 46 per cent. The fact that tobacco burns better after being stored for a time may be partly due to an increase of cellulose in it.
Every tobacco contains more or less fat, gum, ethereal oil, &c. It is not properly known in what way fatty matters affect the quality of tobacco. Many other organic matters exist in tobacco in combination with substances from which it is most difficult to separate them; they have not as yet been quantitatively ascertained, and are therefore little known. Most of them are only developed during the drying and fermenting of the leaf; their presence, however, considerably affects the quality of the tobacco.
The amount of ash constituents in the tobacco is considerable, varying between 16 and 28 per cent. There cannot be said to exist a definite relation between the total amount of ash in the tobacco and its quality, as tobaccos yielding much ash are sometimes of good, and at other times of bad, quality; a good tobacco may yield much or little ash. The relative proportion in which the ash constituents exist is, however, of the greatest importance. It has been ascertained that the presence of some special mineral elements modify to a great extent the quality of the tobacco. Of all ash constituents, potash (K₂O), more correctly speaking potassium carbonate (K₂CO₃), affects the quality of tobacco in the highest degree. Schlösing has pointed out that the good burning qualities of a tobacco depend on the presence in it of potash in combination with a vegetable acid; that a soil deficient in potash is unfit to produce tobacco of good quality. Numerous analyses have tended not only to corroborate the assertion made by Schlösing, but to demonstrate also, that it is not the total amount of potash, but the potash found as a carbonate, which existed in the plant in combination with a vegetable acid, that is the constituent chiefly affecting the combustibility of a tobacco. The complete analyses of Nessler have shown that, although a tobacco may contain a great amount of potash, it does not necessarily follow that the tobacco burns well. He found that some German tobaccos contained more potash than Havana, although the latter burned much better than the former; and that a great amount of potash did not always indicate a great amount of carbonate of potash. Although tobaccos yielding a great amount of carbonate of potash in their ash generally burn well, there may be conditions which neutralize the good effect of this combination, as a large proportion of albuminoids. It may therefore be said that the combustibility of a tobacco is improved in proportion as its ash yields more carbonate of potash, other conditions being equal.
Among the minor salts, the chlorides deserve most attention. It has been found that they generally retard the burning of tobacco, and, that as they increase, carbonate of potash decreases. Lime is invariably found more or less in the ash, but it has not been ascertained to what extent its presence affects the quality of the tobacco; good tobacco may contain much or little, so that its presence is probably not of great importance. The same may be said of soda, magnesia, and phosphoric acid. According to Nessler, their proportions may vary thus:—Potash, 1·95–5 per cent.; lime, 6·5–9·2; soda, 0–1·63; magnesia, 0·12–0·99; phosphoric acid, 0·57–1·39.
In connection with the chemistry of tobacco, and the rational manuring of the crop, the name of Prof. S. W. Johnson, Chemist to the Connecticut State Board of Agriculture, must be placed in the foremost rank. Indebtedness is acknowledged to Prof. Johnson for a copy of his valuable report, quoted in the Bibliography at the end of this work.
In November, 1884, a paper was read by Dr. John Clark, on the composition of tobacco, before the Society of Chemical Industry, which is sufficiently interesting to be quoted at length.
Dr. Clark remarks that the “tobacco plant is very extensively cultivated in various parts of the world, and after it has reached its maturity it is cut and dried on poles. When the plant is in proper condition, the leaves are stripped from the stalk, sorted and cured, by which means they are converted into the tobacco of commerce. The good leaves are called ‘wrappers,’ and the infirm or defective ones, which are separated from the others, are called ‘mediums and fillers.’ The term ‘strips’ is applied to tobacco leaves, from which 20 to 25 per cent. of the stem or midrib has been removed to suit the requirements of manufacturers in this country more especially. Tobacco is largely imported into the United Kingdom, partly in the manufactured state, but principally in the unmanufactured or leaf form.
“Through the kindness of a well-known firm of tobacco manufacturers, I have been furnished with authentic samples of the principal varieties of leaf tobacco, imported into this country, and the accompanying table gives the proportions of mineral matter or ash, alkaline salts, and sand, which these contain. For the sake of comparison the results are all stated in the dry tobacco, and in order to ensure greater accuracy, the analysis was, in each case, made with several leaves, which were separated into laminæ and stem, and the whole of each incinerated. The difference in the composition of the laminæ and the stem is very marked, especially as regards alkaline salts, and is of importance more especially to the snuff manufacturer.
| Composition of Various Kinds of Leaf Tobacco. | |||||||||
| Whole Leaf. | Laminæ. | Stem. | |||||||
| Dried at 212° F., | Dried at 212° F., | Dried at 212° F., | |||||||
| per cent. | per cent. | per cent. | |||||||
| Ash. | Alk. | Sand. | Ash. | Alk. | Sand. | Ash. | Alk. | Sand. | |
| Salt. | Salt. | Salt. | |||||||
| U. S. Kentucky | 19·11 | 6·84 | 2·57 | 18·93 | 5·43 | 3·06 | 21·69 | 13·51 | ·68 |
| do. | 18·50 | 6·68 | 1·82 | 15·50 | 2·77 | 2·39 | 26·07 | 16·68 | ·38 |
| do. | 25·99 | 9·69 | 3·51 | 24·88 | 6·70 | 4·17 | 29·36 | 20·01 | 1·10 |
| do. Strips | 15·73 | 4·31 | 2·61 | 15·57 | 4·07 | 2·71 | 16·95 | 6·35 | 1·37 |
| U. S. Missouri | 20·96 | 5·07 | 4·63 | 20·46 | 2·62 | 5·27 | 22·61 | 12·72 | 1·90 |
| do. | 22·01 | 6·32 | 3·51 | 21·36 | 4·96 | 3·88 | 23·62 | 12·37 | 1·53 |
| do. | 18·88 | 4·81 | 2·61 | 17·18 | 2·88 | 3·21 | 22·17 | 10·68 | ·92 |
| do. | 18·36 | 4·60 | 3·44 | 17·05 | 2·50 | 4·07 | 22·39 | 11·10 | 1·49 |
| U. S. N. Carolina | 14·50 | 5·99 | ·63 | 12·98 | 3·92 | ·74 | 18·64 | 11·72 | ·23 |
| Paraguay | 30·80 | 8·15 | 12·32 | 31·07 | 6·37 | 14·41 | 30·37 | 14·78 | 4·91 |
| Brazil—Carmen | 20·54 | 7·81 | ·42 | 20·42 | 7·24 | ·46 | 20·86 | 9·37 | ·31 |
| Holland | 21·83 | 11·37 | ·13 | 20·16 | 8·99 | ·55 | 25·15 | 17·20 | ·12 |
| Turkey—Cavallo | 13·79 | 5·05 | 3·06 | 21·86 | 8·28 | ·72 | 15·44 | 7·73 | ·24 |
| do. Latakia | 19·50 | 7·19 | ·55 | 21·86 | 8·28 | ·72 | 15·44 | 7·73 | ·24 |
| do. Samsoun | 18·39 | 6·98 | ·49 | 17·59 | 5·32 | ·44 | 21·72 | 13·42 | ·60 |
| Japan | 15·67 | 6·86 | ·50 | 14·60 | 5·59 | ·54 | 19·84 | 11·55 | ·35 |
| China | 18·58 | 2·40 | 6·30 | 17·94 | 1·66 | 6·94 | 20·57 | 5·27 | 3·61 |
| Havana | 20·99 | 8·19 | 1·02 | 20·91 | 7·51 | 1·04 | 21·02 | 10·33 | ·92 |
| Manilla | 21·80 | 6·54 | ·14 | 21·25 | 5·49 | ·13 | 22·50 | 9·09 | ·14 |
| German | 22·27 | 3·76 | 1·79 | 22·12 | 2·78 | 1·87 | 23·13 | 4·63 | 1·39 |
| Sumatra | 18·61 | 7·20 | ·13 | 18·71 | 6·59 | ·09 | 18·14 | 9·11 | ·28 |