« PreviousContinue »
left to rest for some time. The formation of a precipitate points to narcotine.
If no precipitate was produced by bicarbonate of soda, a fresh portion of the residue under examination is digested with anhydrous alcohol in a test-tube closed with a cork-stopper. If the substance remains undissolved, it is strychnine (to be corroborated by the reactions given in § 108); if it dissolves, it may be veratrine or brucine. The latter two are distinguished by their behavior towards nitric acid (v. $ 109 and $ 112)]
§ 123. M. Stas, in pursuing the course above described, has succeeded in isolating from mixtures with foreign substances, the following alkaloids : morphine, codeine, strychnine, brucine, veratrine, emetine, colchicine, aconitine, atropine, and hyoscyamine. Thus, he has extracted morphine from opiuin; strychnine and brucine from nux vomica ; veratrine from extract of veratrum; emetine from extract of ipecacuanha; colchicine from tincture of colchicum ; aconitine from the aqueous extract of aconite; hyoscyamine from a very old extract of hyoscyamus. Of the volatile alkaloids, he thinks that conicine, nicotine, aniline, picoline, and petinine, may be detected. In cases where the exact nature of the alkaloid escapes detection, M. Stas considers it very probable that at least the natural family of plants in which it occurs may be ascertained.
$ 124. Numerous experiments, made in my laboratory, have proved the method of Stas to be very exact for the detection of the volatile alkaloids, and also for strychnine and veratrine. But to show the presence of morphine, some precautions must be used, lest it should escape detection.
Mr. Von Poellnitz has proved, experimentally, that, when the solution of a salt of morphine is mixed with carbonate of soda, and agitated with ether immediately afterwards, the ether dissolves the alkaloid, and deposits it in crystals on evaporation. But, when the ether is added after some time only, the morphine separates in a crystalline condition, and on then agitating the mass with ether, this solvent does not take up any appreciable quantity. It is, therefore, absolutely necessary that the ether be added immediately after neutralization of the aqueous solution of the salt of morphine with bicarbonate of soda has been effected (v. $ 117); the ethereal solution should be poured off as soon as possible and then exposed to evaporation. Professor Polstorff states that ether containing some alcohol is a better solvent for morphine than pure ether.
On account of the easy solubility of morphine in alkaline liquids, it is of importance that the alkaline solution (§ 117), after having been repeatedly agitated with ether, should not be thrown away, but subjected to a further treatment. The ether is removed by gentle heat; if the liquid appears turbid from particles of morphine, a little caustic soda is added; the limpid liquid is then mixed with a strong solution of chloride of ammonium, and exposed to the atmosphere in an open vessel. If any morphine is present, it will separate in crystals.
$ 125. M. Stas, in his memoir, expresses himself strongly against the use of the tribasic acetate of lead, and that of charcoal, as purifying and decolorizing agents. He urges against the use of the leadsalt, that it does not completely remove all foreign matter; that the sulphureted hydrogen, which has to be passed through the liquid to precipitate the excess of lead, enters into combination with many organic substances, forming compounds of a very unstable character, which undergo decomposition on exposure to air, or on application of heat, and thereby cause the liquid to assume a more or less dark color, and disagreeable odor, an odor which remains tenaciously adhering to the substances afterwards extracted from these liquids; that a poisonous substance is brought into the matters, and that thus the opportunity is lost of subsequently examining them for mineral poisons. The use of animal charcoal for the purpose of decolorizing is inadmissible, on account of its property of removing alkaloids from solutions; the whole of the poison may thus be lost.
§ 126. This property of animal charcoal has been taken advantage of by Graham and Hofmann,* to detect the presence of strychnine in beer. It is evident that the same method is equally well adapted for other liquids and a great many other alkaloids. These gentlemen proceeded in the following manner:
The suspected beer is left for twelve hours in contact with animal charcoal, with frequent stirring. The liquid is then separated from the charcoal by filtration, and the latter washed once or twice with a little water. The charcoal has taken up all the strychnine, and the filtrate is free from any bitter
* Annalen der Chemie und Pharm. Bd. 83. p. 39, also Pharm. Journal and Transact. Vol. xi. p. 504-506.
taste. In order to obtain the alkaloid from the charcoal, the latter is treated with boiling alcohol for half an hour. From the alcoholic extract, the alcohol is removed by distillation; to the remaining aqueous liquid, some caustic soda is added, until it shows an alkaline reaction; the mixture is agitated with ether, and the ethereal solution exposed to evaporation. The residue is tested with sulphuric acid and bichromate of potassa, or ferrocyanide of potassium.
[MM. Graham and Hofmann satisfied themselves, by a series of experiments, of the exactness of their method. Half a grain of strychnine was dissolved in half a gallon of beer; two ounces of animal charcoal were then added, and left in contact with the liquid for twenty-four hours. The charcoal was then separated from the liquid by filtration, and boiled for half an hour with eight ounces of alcohol, care being taken to replace, by fresh portions of alcohol, the loss caused by vaporization. The alcohol was then removed by distillation, the residue mixed with caustic potassa, agitated with ether, and the ethereal solution exposed to spontaneous evaporation on a watch-crystal. On addition of a drop of sulphuric acid and a particle of bichromate of potassa, the characteristic violet color was produced.]
$ 127. In a case of poisoning with tincture of colchicum, which occurred in Berlin (Pharm. Centralblatt. 1855. p. 139), MM. Schacht and Casper extracted the alkaloid [colchicine ?] in following essentially the method of Stas.
Wittstock treated the contents of the stomach with alcohol, mixed with a few drops of hydrochloric acid; concentrated the liquid by evaporation at 30° C., to the consistency of a thin syrup; treated the residue with water; separated the liquid by filtration from the insoluble fatty matter; and brought the liquid again to the consistency of a syrup. The residue he dissolved in water; added magnesia usta, in order to set the alkaloid free, agitated the mixture with ether, and exposed the ethereal solution to evaporation. The residue from the last operation possessed a bitter taste, and its solution in acidulous water gave a white precipitate with tannine, a yellow precipitate with bichloride of platinum, and a kermes-brown precipitate with tincture of iodine. By a similar process he extracted the alkaloid from the tincture of colchicum.
$ 128. If it is the object of the investigation simply to show the presence of a volatile alkaloid, the method of Stas may be slightly modified. The substances are treated with alcohol and tartaric, or oxalic acid; the extract is concentrated by evaporation; the resulting aqueous solution is separated by filtration from the insoluble matters; the filtrate is mixed with a solution of caustic soda, and distilled. The alkaloid will be found in the distillate. For its separation, two ways may be followed. The distillate is either agitated with ether, and the ethereal solution exposed to evaporation; or it is neutralized with oxalic acid, the liquid concentrated by evaporation, and the residue treated with caustic soda and ether, when also an ethereal solution of the alkaloid is obtained. Operating in this manner, Lehmann (Pharm. Centralblatt. 1853. p. 927) detected nicotine in the stomach of a boy who died of the effects