Imágenes de páginas
PDF
EPUB

plant reaches maturity, but every part contains some trace of this alkaloid. The percentage of nicotine is greater just as the leaf reaches maturity, than in either the green or overripe leaves. Apparently the formation and accumulation of nicotine in the leaf continue as long as there is growth. The effect of nicotine, after plant growth ceases, is not understood, nor is the office of nicotine in the economy of the plant definitely stated. The amount of nicotine in the whole leaf (exclusive of the stems or midribs), of American-grown tobacco, ranges from less than one per cent to nearly six per cent of the chemically dry substance.

"This variation in the percentage of nicotine," says Carpenter, "is due, in some measure, to different varieties, but whatever variety is grown, or what other conditions prevail, it is almost always noticed that those influences which tend to produce a coarse, rank growth, containing a large percentage of albuminoids, also produce a comparatively large amount of nicotine. The climate, nature of soil and fertilizers, treatment of crop, etc., all have their influence. Of all these conditions, that of soil and fertilizers seems to be the most important. A rich, heavy soil, fertilized with a strong nitrogenous manure, is apparently favorable to the production of a high percentage of nicotine, while the reverse is true of a light, sandy soil containing little organic matter. Havana-grown tobacco, which contains a low percentage, has, in addition to soil, the benefit of a very moist atmosphere.

"For this reason, some have attributed the reverse conditions as favorable to the production of nicotine. From the results of the investigation of tobaccos grown in the United States, we can find no ground for this assertion. Tobacco of the seedleaf variety grown in Connecticut, on a rich loam, gave over four per cent of nicotine, while that grown on a sandy loam soil contained only about one per cent. There we have different conditions of soil in the same climate; and other instances of a similar character might be cited.

"As nicotine is the active principle of tobacco, upon which the stimulating effect largely depends, it would naturally appear that its development to a high degree would be desirable, but such is not the case. What are considered the best qualities almost always contain a snail percentage, while a large percentage usually indicates coarseness. While, as stated, certain conditions are conducive to the development of nicotine, it is undoubtedly true that the subsequent treatment has some influence on the amount present in the finished product. The different fermentative processes required to develop proper flavor and color necessarily decompose, to a greater or less extent, the different compounds present in the leaf. It may be true, therefore, that in some cases the nicotine content may be appreciably less in the fermented product than was present in the green plant. For this reason, the analyses of the different varieties which have been subjected to different processes of curing and fermenting, cannot safely be relied upon as giving the exact amount developed by certain conditions in the field, but the results, in a general way, confirm what has been previously noted."

Davidson finds that changes in the amount of nicotine in leaf at the time of topping, curing, and after being properly cured, are very slight, but in the cured state it seems to be much greater. He questions this latter point.

Other Substances in Tobacco.Tobacco, like other plants, contains small proportions of starch, sugar and woody fiber, or cellulose, the amount and nature of which governs, to some extent, the burn of tobacco. These elements, together with the fatty and resinous substances present, also have much influence on the flavor of the leaf. The nitrogen-containing substances or albuminoids, also form an important constituent, the effect of which is but little understood, and the same is true of the acids in tobacco—nitric, citric, acetic and pectic. There are other organic or carbonaceous substances, of which still less is known.

Ash or Mineral Ingredients make up a large part of the tobacco plant. The ash constitutes from 15 to 25 per cent of the chemically dry leaf, 5 to 15 per cent of the stalk, and from 5 to 15 per cent of the root. The quantity and character of the mineral ingredients have a profound influence on the quality of leaf, especially for smoking. These mineral ingredients vary widely in different varieties, and also in the same variety under different conditions (see Table IV, Pages 112 and 113). Potash and lime each constitute about one-third of the ash, the other third being composed of phosphoric acid, magnesia, soda, sulphuric acid, carbonic acid, chlorine, sil;.ca (sand), alumina (clay) and iron (ferric oxide).

Effect of Constituents.—The principal ingredients that are supposed to most affect quality are, nicotine, nitrogen, potash, lime, magnesia and chlorine. The quantity of nicotine in the leaf is governed, to some extent, by the amount and character of the nitrogenous substances the plant feeds upon. The other elements also vary in amount with variety, soil, climate and fertilizer. One cannot speak positively of their effect upon the curing or chewing quality of the leaf.

Why certain crops of leaves of tobacco burn well and others burn badly, is not fully understood.. Nessler demonstrated that tobacco which contains large quantities of chlorides does not burn well, especially when the quantity of potash present is small. Nessler found, from examination of forty-six samples of tobacco grown in different parts of Baden, on soils of diverse character, that the more potash and the less chlorine a leaf contains, the longer it will continue to glow when lighted. The higher the per cent of potash, the more chlorine may be present without seriously affecting the burn of the leaf. A Sumatra leaf with 0.64 to 0.78 per cent of chlorine and 5 per cent of potash, burned very well, while a Baden tobacco with 0.4 per cent chlorine and only 3 per cent of potash burned badly. On the other hand, the less chlorine there is in the leaf, the less potash is necessary to secure a good burning quality. He concludes that no tobacco burns well which has less than 2.5 per cent potash, if there is with it more than 0.4 per ?ent chlorine.

Schloesing made some experiments on poor, sandy soil that was somewhat calcareous, and yet clayey enough to be rather tenacious. The soil contained very little chlorine, sulphuric acid or potash. Plots to which no potash was applied gave bad-burning tobacco; those fertilized with chlorides gave tobacco which contained about four times as much chlorine as the others, showing that chlorine is readily assimilated by the plant; and the tobacco containing this large proportion of chlorine burned badly.

Both Schloesing and Nessler, from independent experiments and investigations, agree that the burning quality of tobacco is governed by the presence of the soluble carbonate of potash, and that when the potash is combined with chlorine, the combustibility is poor. This is not fully confirmed by the Poquonock experiments, which seem to indicate that a small amount of chlorine is not objectionable, while it is essential to normal plant growth. But an excess of chlorine is unfavorable to a good burn. This is true both before and after fermentation. Plots K and L received much more chlorine than the others, it being supplied in the double manure salt; the leaf from these plots had less capacity to hold fire than most of the others.

Other investigations in this country also do not sustain the idea that the burning quality is entirely controlled by the composition of the ash, and it is now believed that combustibility is the result of several conditions, of which the ash is but one. These conditions are, the abundance of organic potash salts (i. e., those yielding carbonate of potash), the abundance but not excessive quantity of woody tissue, and the abundance of sulphates. Mineral salts which fuse at the burning temperature, such as the chlorides and phosphates of potash and soda, hinder free burning; and sugar, gum and albuminous matters are difficult of combustion, and therefore impede burning.

Composition at Different Stages of Growth also varies widely in both organic and mineral substances. Original analyses of three Virginia tobaccos, set forth in the Appendix, show that at time of cutting, the leaf contains about twice as much ash as the stalk, and the same quantity of nitrogen, more lime, and twice as much insoluble matter; but the stalk contains over twice as much phosphoric acid as the leaf, one-third more potash and four times the chlorine. The composition of the leaf alone undergoes but little change from time of topping until cured. The stalk, when cured, has gained slightly in nitrogen and phosphoric acid, much in lime, but has lost nearly one-fourth of its potash.

How to Supply the Principal Ingredients is the vital problem, in growing fine tobaccos. But a sharp distinction must be drawn between what the tobacco plant contains, and how large a supply of the elements of the plant food are essential for a successful crop. Chemical analyses are valuable in determining absolutely the percentage of the food elements contained in the plant, and they give an excellent basis for intelligently framing a manurial supply, but afford little indication of the quantity required. Under the old English system of

« AnteriorContinuar »