The property which this salt possesses of deflagrating with combustible bodies, affords a ready indication of its presence. The process also, which we have described under the history of nitric acid, (p. [312]) as the one suggested by Dr. Wollaston, and adopted by Dr. Marcet in his examination of sea water, furnishes an elegant mode of ascertaining the presence of a nitric salt.
Cl. IV. NARCOTIC POISONS.
These constitute a class of vegetable poisons, less extensive, perhaps, but of far greater importance and interest, than the one we have already considered. It would not be easy to enumerate the various purposes to which the active imagination of man has applied the tribe of narcotic plants. Medicines, poisons, intoxication, and madness, lie concealed beneath their juices. They have, in their turn, arrested the pangs of disease, and inflicted death upon the unsuspecting object of hatred and revenge; they have animated the courage of the warrior, inspired the enthusiasm of the poet, soothed the sorrows of the wretched, and furnished the debauchee with a daily source of sensual gratification; effects which, although apparently incompatible with each other, may be commanded by the same substance, in a different dose. It would be foreign to the plan of this work to enter into a physiological inquiry into the modus operandi of these extraordinary agents; and the author relinquishes the labour with less regret, as he has already, in another work,[[415]] very fully considered the several theories which have been advanced for its explanation.
Opium, and its Preparations.
This well known drug is the inspissated juice of the Papaver Somniferum (Polyandria Monogynia. Nat. Ord. Rhoedææ, Linn. Papaveraceæ Juss.) obtained by making incisions in the half ripe capsules, at sun-set, when the night dews favour the exudation of the juice, which is collected in the morning by old women and children, who scrape it from off the wounds with a small iron scoop, and deposit the whole in an earthen pot, where it is worked by wooden spatulas in the sun-shine, until it attain a considerable degree of spissitude. It is then formed by the hand into cakes, which are laid in earthen basins to be further exsiccated.[[416]] Two kinds are found in commerce, distinguished by the names of Turkey, and East Indian opium. The latter kind is regarded as being inferior to the former.
Turkey opium occurs in flat pieces, of a solid compact texture, possessing considerable tenacity; its specific gravity is 1·336, so that, when compared with concrete juices of other plants, it is heavy, being exceeded only in this respect by opoponax and gum arabic. It is of a reddish-brown, or fawn-colour, and has a peculiar, heavy, and narcotic odour; its taste is acrid, bitter, and hot. By long exposure to the air, it becomes hard, and breaks with a glimmering fracture, owing to the presence of a few saline particles. It is plastic, and when worked with the fingers is adherent to them. When brought near a lighted candle it inflames, and burns with a brilliant light, but its odour at that time is not narcotic. It is partially soluble in water, alcohol, æther, wine, vinegar, and lemon-juice. When triturated with hot water, five parts in twelve are dissolved, six suspended, and one part remains perfectly insoluble, and resembles the gluten of wheat, but is of a dark colour. The alcoholic is more highly charged with its narcotic principle than the aqueous solution; but spirit, rather below proof, is its best menstruum.
Few vegetable substances have been more frequently, or more ably submitted to analysis; and the history of the successive steps by which our knowledge respecting its composition has advanced, must encourage us in hoping that we shall shortly be enabled to identify, by chemical tests, the presence of opium, with as little difficulty and as great precision as we are already capable of recognising a metallic poison.
According to the latest chemical views respecting the composition of this body, it may be stated to consist of the following principles, viz. resin, gum, bitter extractive, sulphate of lime, gluten, and the three lately discovered bodies, narcotine, morphia, and meconic acid.
In the year 1803, Derosne first obtained from opium a crystalline substance, which he found to dissolve in acids, but he does not appear to have instituted many experiments, for the elucidation of its nature and properties. In 1804 Seguin discovered another crystalline body, and although he described many of its properties, what appears very extraordinary, he never even hinted at its alkaline nature. Sertuerner, at Eimbeck in Hanover, had at the same time as Derosne and Seguin, obtained these crystalline bodies, but it was not until the year 1817, that he first proclaimed the existence of a vegetable alkali, and attributed to it the narcotic powers which distinguish the operation of opium; to this body, he gave the name of Morphia, and it would appear to be the same as the essential salt of Seguin. The salt of Derosne was also at first mistaken for the same principle, but the experiments of Robiquet have pointed out its distinctive properties, and it has received the name of Narcotine.
Morphia, upon which the soporific powers of opium depend, appears to exist in native combination with a peculiar acid, to which the name of meconic acid has been bestowed. The following are the essential characters of this alkaline body, when procured in a state of purity.[[417]]