« PreviousContinue »
of characteristic tests; and in such cases we must consider ourselves very fortunate, if we can show that there is any alkaloid present. To ascertain the poisonous effect of the separated alkaloid, the quantity obtained is usually too small, and with regard to the chemical tests, it must be borne in mind, that the alkaloids show, in this respect, a great similarity.
It is a very fortunate circumstance, that in the majority of cases there is but very little doubt in regard to the nature of the poison employed, and all that remains to be done by the legal chemist, is to show that the poison really existed in the body, etc. For this reason, the chemical examination has, not unfrequently, more a scientific than a practical inter
$ 104. The separation of the alkaloid, in the arest possible condition, is, as mentioned above, to be aimed at before all other things; to ascertain its nature, constitutes the next step. Of the alkaloids which may become the objects of our investigation, some are volatile, as nicotine, conicine, etc., others non-volatile, as morphine, strychnine, veratrine, etc. We shall commence with describing their most characteristic properties and tests.
Nicotine.—It is a colorless, oily liquid, becoming yellow on exposure to air, of acrid taste, and of a faint odor; it is usually said to possess the odor of tobacco, but I should rather call it an ethereal odor, which is most distinctly noticed in the dilute state. It is readily soluble in ether and alcohol; water and alcohol dissolve it in considerable quantity. The alcoholic solution affects tumeric-paper. On distillation with water, it passes over with the watery vapors; when distilled alone, it is partially decomposed.
With acids, it forms non-volatile salts, which are soluble in water and in alcohol, but not in ether. On mixing the solution of a salt of nicotine with caustic soda and ether, the liberated alkaloid dissolves in the latter, and on evaporating the ethereal solution it remains behind as an oily drop. On distilling a salt of nicotine with a solution of caustic soda, there results a distillate containing nicotine. In order to obtain the whole of the alkaloid, it is advisable to add some water to the contents of the retort, as soon as they become too concentrated, and to repeat the distillation.
If a distillate containing nicotine is neutralized with oxalic acid, and afterwards evaporated, oxalate of nicotine remains behind ; if the distillate contained ammonia, as will usually be the case, it is mixed with some oxalate of ammonia. Alcohol dissolves the oxalate of nicotine, but does not affect the oxalate of ammonia; by this means the two may be separated. The alcoholic solution yields, on evaporation, the oxalate of nicotine.
If another acid, ex. gr. tartaric, sulphuric, hydrochloric acid, is chosen to effect the neutralization of a distillate containing nicotine, it is evident that the corresponding nicotine-salt is obtained. In using sulphuric acid, an excess must be avoided, lest the mass might become charred. The removal of fatty substances may be effected by dissolving the salt in water, or by washing with ether.
To reagents, nicotine and its salts behave as follows:
Terchloride of gold produces in a watery solution a reddish yellow precipitate, readily soluble in an excess of nicotine.
Bichloride of platinum causes a yellow precipitate; the solution must be perfectly free from ammonia; this may be effected by continued heating, or by the treatment of a nicotine-salt with alcohol.
A solution of nicotine causes precipitates in solutions of neutral and basic acetate of lead, in acetate of copper, in chloride of cobalt, and in many other metallic salts. [Chlorine-gas decomposes nicotine with evolution of hydrochloric acid gas, and formation of a blood-red liquid, which on exposure to the rays of the sun, becomes colorless.)
On adding a solution of iodine (prepared from iodine, water, and a little iodide of potassium), to a solution of nicotine, a yellow precipitate is thrown down; this precipitate disappears after some time, but on adding more of the iodine-solution, a copious precipitate of a kermes-brown color is produced (ammonia decolorizes a solution of iodine).
A solution of tannine produces a copious white precipitate.
A solution of chloride of nicotine gives, with bichloride of platinum, a yellowish-red, crystalline precipitate, which is a double chloride of platinum and nicotine, and which is with difficulty soluble in water, and insoluble in alcohol and ether. From a dilute solution, the compound separates in pretty large prisms. If the nicotine contained ammonia, the double chloride of platinum and ammonium is formed at the same time; this compound is immediately produced; in order to obtain the nicotine double-salt separate, the liquid is rapidly filtered off from the precipitate; the double chloride of platinum and nicotine is gradually deposited from the filtrate.
[If nicotine is added in small portions to a lukewarm, acid solution of protochloride of platinum, care being taken that the temperature do not rise too high, orange-yellow crystals of a double chloride of platinum and nicotine are obtained. On pouring off the mother liquor and evaporating, red prismatic crystals of another double chloride are formed.]
Terchloride of gold produces in solutions of the salts of nicotine a yellow, flocculent precipitate, which • dissolves with difficulty in hydrochloric acid. A solution of iodine produces a kermes-brown, and a solution of tannine, a whitish precipitate.*
Of a!l the reactions for nicotine, its volatility is the most characteristic; only conicine shows a similar behavior, but this is easily distinguished by its odor, and by being much less soluble in water.
$ 105. Conicine.--This alkaloid is, like nicotine, an oily, colorless liquid, which becomes yellow on exposure to air. Its odor, which is represented as resembling that of young mice, is exceedingly disagreeable and benumbing, and much more distinct, than that of nicotine; its taste. is acrid. It is readily soluble in alcohol and ether. [With the vapors of nitric, hydrocholoric, and acetic acid, it forms thick white fumes. It coagulates albumen.] Water does not take up so much of this alkaloid as of nicotine; hence it is, that by being shaken up with not too large
* Compare: Chemie der organischen Alkalien, von HartungSchwarzkopf. München, 1855.
a quantity of water, it is divided into drops, and on resting, collects again on the surface as an oily layer. On adding some caustic soda to a moderately concentrated solution of a salt of conicine, the liquid becomes milky, owing to the separation of the alkaloid in minute drops, like an essential oil; on resting for some time, these drops unite and form an oily layer on the surface. On spontaneous evaporation of its ethereal solution, it remains behind, as a yellowish, oily drop. Its alcoholic solution colors turmericpaper brown, with a purple tinge.
Mixed with water and an acid, salts are formed, and the peculiar odor of the alkaloid disappears. On evaporating the solution of a salt of conicine, it assumes a brownish color, and the residue contains some ammonia ; this even takes place if the temperature is kept very low. An excess of a strong acid, most especially of sulphuric acid, acts destructively. The salts are readily soluble in water and alcohol; insoluble, or nearly so, in ether.
On addition of caustic soda to the solution of any of its salts, the alkaloid is liberated, and its peculiar odor becomes perceptible; on distilling, the conicine passes over with the watery vapors. By neutralizing the distillate with oxalic acid (an excess of which is not injurious), and evaporating, oxalate of conicine is obtained ; a subsequent treatment with alcohol may be resorted to, for the purpose of purifying it from an admixture of oxalate of ammonia; the latter is insolnble in alcohol, while the former is taken up by this solvent.
Conicine and its salts, behave to reagents in essentially the same manner as nicotine and its salts.