§ 351. General Method for the Detection of Opium.—It is usually laid down in forensic works that, where poisoning by opium is suspected, it is sufficient to detect the presence of meconic acid in order to establish that of opium. In a case of adult poisoning there is generally substance enough available to obtain one or more alkaloids, and the presence of opium may, without a reasonable doubt, be proved, if meconic acid (as well as either morphine, narcotine, thebaine, or other opium alkaloid) has been detected. Pills containing either solid opium or the tincture usually betray the presence of the drug by the odour, and in such a case there can be no possible difficulty in isolating morphine and meconic acid, with probably one or two other alkaloids. The method of extraction from organic fluids is the same as before described, but it may, of course, be modified for any special purpose. If opium, or a preparation of opium, be submitted to Dragendorff’s process (see [p. 242]), the following is a sketch of the chief points to be noticed.
If the solution is acid—
(1.) Benzene mainly extracts meconin, which dissolves in sulphuric acid very gradually (in twenty-four to forty-eight hours), with a green colour passing into red. Meconin has no alkaloidal reaction.
(2.) Amyl alcohol dissolves small quantities of meconic acid, identified by striking a blood-red colour with ferric chloride.
If now the amyl alcohol is removed with the aid of petroleum ether, and the fluid made alkaline by ammonia—
(1.) Benzene extracts narcotine, codeine, and thebaine. On evaporation of the benzene the alkaloidal residue may be dissolved in water, acidified with sulphuric acid, and after filtration, on adding ammonia in excess, thebaine and narcotine are precipitated, codeine remaining in solution. The dried precipitate, if it contain thebaine, becomes blood-red when treated with cold concentrated sulphuric acid, while narcotine is shown by a violet colour developing gradually when the substance is dissolved in dilute sulphuric acid 1 : 5, and gently warmed. The codeine in the ammoniacal solution can be recovered by shaking up with benzene, and recognised by the red colour which the solid substance gives when treated with a little sugar and sulphuric acid.
(2.) Chloroform especially dissolves the narceine, which, on evaporation of the chloroform, may be identified by its general characters, and by its solution in Fröhde’s reagent becoming a beautiful blue colour. Small quantities of morphine may be extracted with codeine.
(3.) Amyl alcohol extracts from the alkaline solution morphine, identified by its physical characters, by its forming a crystalline precipitate with iodine and hydriodic acid, and the reaction with iodic acid to be described.
§ 352. Morphine (C17H17NO(OH)2 + H2O).—Morphine occurs in commerce as a white powder, sp. gr. 1·205, usually in the form of more or less perfect six-sided prisms, but sometimes in that of white silky needles. When heated in the subliming cell (described at [pp. 257-8]), faint nebulæ, resolved by high microscopic powers into minute dots, appear on the upper disc at 150°. As the temperature is raised the spots become coarser, and at 188° distinct crystals may be obtained, the best being formed at nearly 200°, at which temperature morphine begins distinctly to brown, melt, and carbonise. At temperatures below 188°, instead of minute dots, the sublimate may consist of white circular spots or foliated patterns. One part of morphine, according to P. Chastaing, is soluble at a temperature of 3° in 33,333 parts of water; at 22°, in 4545 parts; at 42°, 4280; and at 100°, 4562. It is scarcely soluble in ether or benzene. Absolute alcohol, according to Pettenkofer, dissolves in the cold one-fortieth of its weight; boiling, one-thirtieth. Amyl alcohol, in the cold, dissolves one-fourth per cent., and still more if the alkaloid be thrown out of an aqueous acid solution by ammonia in the presence of amyl alcohol; for under such circumstances the morphine has no time to become crystalline. According to Schlimpert, 1 part of morphine requires 60 of chloroform for solution; according to Pettenkofer, 175.
Morphine is easily soluble in dilute acids, as well as in solutions of the caustic alkalies and alkaline earths; carbonated alkalies and chloride of ammonium also dissolve small quantities. The acid watery, and the alcoholic solutions, turn the plane of polarisation to the left; for sulphuric, nitric, and hydrochloric acids [α]r = 89·8°; in alkaline solution the polarisation is less, [α]r = 45·22°. It is alkaline in reaction, neutralising acids fully; and, in fact, a convenient method of titrating morphine is by the use of a centinormal sulphuric acid—each c.c. equals 2·85 mgrms. of anhydrous morphine.