Identification of the Alkaloid
The alkaloid having been isolated by one of the preceding methods, it remains to establish its identity. Owing to the small number of reactions characteristic of organic compounds, this is a matter of considerable difficulty. There are two cases possible: the alkaloid may either be volatile or fixed.
The Alkaloid Is Volatile
In this case it may consist of nicotine, conine or aniline: less known alkaloids (piccoline, etc.) may also be present. We will confine ourselves to the consideration of the three first mentioned.
The alkaloid is divided into several portions which are placed on watch-glasses and submitted to the following tests:
a. A drop is treated with nitric acid: this may, or may not, impart a red tint to the alkaloid; if it does, another drop is treated with dry hydrochloric acid gas: if it assumes a deep violet color, it probably consists of conine.
b. In case a red color was not produced by the addition of nitric acid, another drop is treated with chloride of lime. If it acquires a violet tint, and two other drops, when heated, one with arsenic acid, the other with nitrate of mercury, become red, the body present consists of aniline.
or an homologous base.
c. Should the above tests fail to give positive results, and the substance, when treated with chlorine, assumes a blood-red color, and with hydrochloric acid does not change in the cold but turns to a deep violet color upon boiling, it probably consists of nicotine.
The Alkaloid Is Fixed
A very minute quantity is dissolved in the smallest possible amount of hydrochloric acid, and an excess of ammonia added. Three cases are now possible: (a) A precipitate, insoluble in an excess of the precipitant, is immediately formed; (b) a precipitate is formed, which, at first dissolves, but is subsequently deposited from the fluid; (c) no precipitate is produced, or, in case one forms, it dissolves in an excess of the precipitant and fails to separate out upon allowing the fluid to stand.
A. Ammonia Produces a Permanent Precipitate
A small quantity of an aqueous solution of carbonic acid is poured over the alkaloid in the water-glass, and notice taken whether it dissolves or not: in either case the mixture is evaporated on a water-bath to dryness, in order to avoid a loss of substance.
CARBONIC ACID FAILS TO DISSOLVE THE ALKALOID.
After the evaporation is completed, ether is added to the watch-glass: the alkaloid may, or may not, be dissolved. The ether is then evaporated at the ordinary temperature of the air.
Ether fails to dissolve the alkaloid.
It probably consists of berberine.
In this case, it will possess a yellow color, and its hydrochlorate will give a reddish-brown precipitate upon addition of sulphide of ammonia.
Ether dissolves the alkaloid.—A small portion is treated with nitric acid. If an intense green coloration is produced, the remaining portion is dissolved in ether, and an ethereal solution of oxalic acid added. If the precipitate now formed does not dissolve upon the addition of a little water, there is reason to suppose the presence of aricine.
Provided the addition of nitric acid did not produce a coloration, the mixture of the alkaloid and this acid is treated with a small quantity of sulphuric acid: if the fluid now acquires a red color, the substance probably consists of narcotine.
Should both nitric and sulphuric acids fail to cause a reaction, the alkaloid is dissolved in ether, precipitated by an ethereal solution of oxalic acid, and the precipitate treated with a little water. If it dissolves, it probably consists of papaverine.
CARBONIC ACID DISSOLVES THE ALKALOID.
The substance is treated with ether, notice being taken if it dissolves, which is evaporated at the ordinary temperature of the air so as to prevent a loss of minute portions of the alkaloid.
Ether dissolves the alkaloid.—If nitric acid gives first a scarlet, then a yellow color, sulphuric acid a yellow, changing to red and violet, and hydrochloric acid a violet color, the alkaloid present is probably veratrine.
If the above colorations are not produced, chlorine water is added to another portion of the substance, then ammonia; the formation of a green color, changing to violet and turning red upon a renewed addition of chlorine water, denotes the presence of quinine.
In case all of these tests give but negative results, and the alkaloid is soluble in concentrated sulphuric acid, a solution being formed which assumes a reddish-violet tint when stirred with a glass rod previously dipped in bromine water, the presence of delphine.
is indicated.
Ether fails to dissolve the alkaloid.—If the substance is capable of being sublimed,N it consists of cinchonine.
b. Ammonia produces a precipitate, which redissolves in an excess of the precipitant, but separates out after the lapse of an hour.
The substance is treated with cold absolute alcohol and its solubility in this menstruum noted. If it readily dissolves, it probably consists of brucine.
The presence of this alkaloid is confirmed by applying the following tests: (1) Nitric acid imparts a blood-red color to the substance; (2) if treated with sulphuric acid, it acquires a reddish tint which subsequently changes to yellow and green; (3) chlorine at first fails to cause a coloration, but after some time a yellow color which afterwards changes to a red is produced; (4) upon treating the substance with bromine, it immediately assumes a violet tinge.
In case the alkaloid is only slightly soluble in alcohol, there is reason to infer the presence of strychnine.
The following confirmatory tests should be applied: (1) If the substance is treated with a mixture of sulphuric acid and an oxidizing body, such as bichromate of potassa, binoxide of manganese, or peroxide of lead it acquires a violet color, which changes into red and finally passes into a clear yellow; (2) the addition of bichloride of platinum produces a precipitation of the hydrochlorate.
Should, however, the substance be only slightly soluble in alcohol, and the above reactions fail to take place, the presence of solanine.
is indicated. In presence of this alkaloid the following reactions will occur: (1) Upon treating the substance with concentrated sulphuric acid, it assumes a rose tint, which changes after some time has elapsed first to a deep violet, then to a brown color; (2) a solution of a salt of the alkaloid reduces gold and silver salts; (3) the addition of oxalic acid produces a precipitate in the aqueous and even acid solution of its salts.
C. Ammonia Fails to Produce a Precipitate, or Redissolves Permanently the One Formed
The solubility of the alkaloid in ether is ascertained. If it be soluble, it may consist of aconitine, atropine or codeine; if insoluble, of emetine or morphine.
The alkaloid is soluble in ether.—If bichloride of platinum fails to precipitate the hydrochlorate from a neutral solution of the alkaloid, and sulphuric acid causes it to assume a yellow color which subsequently changes to a reddish-violet, it probably consists of aconitine.
In case bichloride of platinum causes a precipitate and sulphuric acid fails to produce the yellow coloration referred to above, the presence of either atropine or codeine is indicated. In order to decide which of these bases is present, the substance is dissolved in pure chloric acid and the solution allowed to spontaneously evaporate. If the alkaloid is deposited during this operation, it probably consists of atropine.
If this is not the case, there is reason to infer the presence of codeine.
The alkaloid is insoluble in ether.—If it dissolves in acetone it probably consists of emetine.
If acetone fails to dissolve it, the presence of morphine.
is indicated.
The following confirmatory tests should be applied: (1) Upon treating the substance with nitric acid, it acquires a blood-red color; (2) the addition of a solution of a persalt of iron produces an evanescent blue coloration; (3) chloride of gold is colored blue, when treated with the alkaloid; (4) the substance reduces iodic acid: this reduction is detected by adding to the acid a little starch-paste, which turns blue upon the liberation of the iodine; (5) permanganate of potassa, if heated with the substance, is reduced and acquires a green color.