Respecting the colouring matter and an extremely small quantity of a volatile body with pepper-like odour, we know but little. After the colouring matter has been precipitated from an aqueous solution of opium by lead acetate, the liquid becomes again coloured by exposure to the air. As to the volatile body, it may be removed by acetone or benzol, but has not yet been isolated.
The salts of inorganic bases, chiefly of calcium, magnesium and potassium, contain partly the ordinary acids such as phosphoric and sulphuric, and partly an acid peculiar to the poppy.
Good opium of Asia Minor dried at 100° C. yields 4 to 8 per cent. of ash.
Poppy-juice contains neither starch nor tannic acid, the absence of which easily detected substances affords one criterion for judging of the purity of the drug.
The proportion of water in opium is very variable. In drying Turkey opium previous to pulverization and for other pharmaceutical purposes, the average loss is about 12½ per cent.[252] Bengal opium, which resembles a soft black extract, is manufactured so as to contain 30 per cent. of water.
As the active constituents of opium, or at all events the morphine, can be completely extracted by cold water, the proportion of soluble matter is of practical importance. In good opium of Asia Minor previously dried, the extract (dried at 100° C.) always amounts to between 55 and 66 per cent.,—generally to more than 60, thus affording in many instances a test of the pureness of the drug. Dried Indian opium yields from 60 to 68 per cent. of matter soluble in cold water.[253]
The peculiar constituents of opium are of basic, acid, or neutral nature. Some of these substances were observed in opium as early as the 17th and 18th century, and designated Magisterium Opii. Bucholz in 1802 vainly endeavoured to obtain a salt from the extract by crystallization. In 1803, however, Charles Derosne, an apothecary of Paris, in diluting a syrupy aqueous extract of opium, observed crystals of the substance now called Narcotine, which he prepared pure. He believed that the same body was obtained by precipitating the mother liquor with an alkali, but what he so got was morphine. It is needless to pursue the further researches of Derosne. Ingenious as they were, it was reserved for Friedrich Wilhelm Adam Sertürner, apothecary of Einbeck in Hanover (nat. 1783, ob. 1841) to discover their true interpretation.
Sertürner had been engaged since 1805 with the chemical investigation of opium, and in 1816 he summarized his results in the statement that he had enriched science (we now translate his own words[254])—“not only with the knowledge of a remarkable new vegetable acid [Mekonsäure (meconic acid) which he had made known as Opiumsäure in 1806], but also with the discovery of a new alkaline salifiable base, Morphium, one of the most remarkable substances, and apparently related to ammonia.” Sertürner in fact distinctly recognised the basic nature and the organic constitution of morphium (now called Morphine, Morphia, or Morphinum), and prepared a number of its crystalline salts. He likewise demonstrated the poisonous nature of these substances by experiments on himself and others. Lastly, he pointed out, though very incorrectly, the difference between morphine and the so-called Opium-salt (Narcotine) of Derosne. It is possible that this latter chemist may have had morphine in his hands at the same time as Sertürner, or even earlier. This honour is also due to Séguin, whose paper “Sur l’Opium” read at the Institute, December 24, 1804, was, strange to say, not published till 1814.[255] To Sertürner, however, undoubtedly belongs the merit of first making known the existence of organic alkalis in the vegetable kingdom,[256]—a series of bodies practically interminable. As to opium, it still remains after nearly seventy years a nidus of new substances.
Solutions of morphine in acids or in alkalis rotate the plane of polarization to the left.
The morphine in opium is combined with meconic acid, and is therefore easily soluble in water.[257] The Narcotine is present in the free state, and can be extracted by chloroform, boiling alcohol, benzol, ether, or volatile oils,[258] but not by water. It dissolves in 3 parts of chloroform, in 20 of boiling alcohol, in 21 of benzol, in 40 of boiling ether. Its alkaline properties are very weak, and it does not affect vegetable colours. If we examine opium by the microscope we cannot at once detect the presence of narcotine, but if first moistened with glycerin, numerous large crystals may generally be found after the lapse of some days. If the opium has been previously exhausted with benzol or ether, in order to remove the narcotine, no such crystals will be formed. Hence it follows that narcotine pre-exists in an amorphous state.