Chemical Composition—The active principle of tobacco, first isolated in 1828 by Posselt and Reimann, is a volatile, highly poisonous alkaloid termed Nicotine, C₁₀H₁₄N₂. It is easily extracted from tobacco by means of alcohol or water, as a malate, from which the alkaloid can be separated by shaking it with caustic lye and ether. The ether is then expelled by warming the liquid, which finally has to be mixed with slaked lime and distilled in a stream of hydrogen, when the nicotine begins to come over at about 200° C.
Nicotine is a colourless oily liquid, of sp. gr. 1·027 at 15° C., deviating the plane of polarization to the left; it boils at 247° and does not concrete even at -10° C. It has a strongly alkaline reaction, an unpleasant odour, and a burning taste. It quickly assumes a brown colour on exposure to air and light; and appears even to undergo an alteration by repeated distillation in an atmosphere deprived of oxygen. Nicotine dissolves in water, but separates on addition of caustic potash; it occurs in the dried leaves to the extent of about 6 per cent., but is subject to great variation. The seeds of tobacco are stated by Kosutany[1715] as grown in Hungary to contain from 0·28 to 0·67 per cent. of the alkaloid.
It has not been met with in tobacco-smoke by Vohl and Eulenberg (1871), though other chemists assert its occurrence. The vapours were found by the former to contain numerous basic substances of the picolinic series, and ceded to caustic potash, hydrocyanic acid,[1716] sulphuretted hydrogen, several volatile fatty acids, phenol and creasote. There was further observed in the imperfect combustion of tobacco the formation of laminæ fusible at 94° C., and having a composition C₁₉H₁₈. Oxide of carbon is also largely met with.
Tobacco leaves, whether fresh or dried, yield when distilled with water a turbid distillate in which, as observed by Hermbstädt in 1823, there are formed, after some days, crystals of Nicotianin or Tobacco Camphor. According to J. A. Barral, nicotianin contains 7·12 per cent. of nitrogen (?). By submitting 4 kilogrammes of good tobacco of the previous year to distillation with much water, we obtained nicotianin, floating on the surface of the distillate, in the form of minute acicular crystals, which we found to be devoid of action on polarized light. The crystals have no peculiar taste, at least in the small quantity we tried; they have a tobacco-like smell, perhaps simply due to the water adhering to them. When an attempt was made to separate them by a filter, they entirely disappeared, being probably dissolved by an accompanying trace of essential oil. The clear water showed an alkaline reaction partly due to nicotine; this was proved by adding a solution of tannic acid, which caused a well-marked turbidity. Nicotianine is in our opinion a fatty acid contaminated with a little volatile oil as in the case of Capsicum ([see page 454]), or Iris ([see article Rhizome Iridis]).
Among the ordinary constituents of leaves, tobacco contains albumin, resin and gum. In smoking, these substances, as well as the cellulose of the thick midrib, would yield products not agreeable to the consumer. The manufacturer therefore discards the midrib, and endeavours by further preparation to ensure at least the partial destruction of these unwelcome constituents, as well as the formation of certain products of fermentation (ferment-oils), which may perhaps contribute to the aroma of tobacco, especially when saccharine substances, liquorice, or alcohol, are added in the maceration to which tobacco is subjected.
Tobacco leaves are remarkably rich in inorganic constituents, the proportion varying from 16 to 27 per cent. According to Boussingault, they contain when dry about 1 per cent. of phosphoric acid, and from 3 to 5 per cent. of potash, together with 2½ to 4½ per cent. of nitrogen partly in the form of nitrate, so that to enable the tobacco plant to flourish, it must have a rich soil or continual manuring.[1717]
The lime, amounting to between a quarter and a half of the entire quantity of ash, is in the leaf combined with organic acids, especially malic, perhaps also citric. The proportion of potash varies greatly, but may amount to about 30 per cent. of the ash.
Commerce—There were imported into the United Kingdom in the year 1872, 45,549,700 lb. of unmanufactured tobacco, rather more than half of which was derived from the United States of America. The total value of the commodity thus imported was £1,563,382; and the duty levied upon the quantity retained for home consumption amounted to £6,694,037. In 1876 the consumption of tobacco had increased to 47,000,000 lb., i.e. 1½ lb. per head of the population.
In the United States 559,049 acres of land being in 1875 under cultivation with tobacco yielded a crop of 367,000,000 lb.
Uses—Tobacco has some reputation in the removal of alvine obstructions, but it is a medicine of great potency and is very rarely used.