§ 383. Meconin (Opianyl) (C10H10O4) is in the form of white glittering needles, which melt under water at 77° and in air at 90°, again coagulating at 75°. It may be sublimed in beautiful crystals. It is soluble in 22 parts of boiling, and 700 of cold water; dissolves easily in alcohol, ether, acetic acid, and ethereal oil, and is not precipitated by acetate of lead. Its solution in concentrated sulphuric acid becomes, on warming, purple, and gives, on the addition of water, a brown precipitate. Meconin may be prepared by treating narcotine with nitric acid. Meconin, in large doses, is a feeble narcotic; 1·25 grm. (20 grains) has been given to man without result.
§ 384. Meconic Acid (C7H4O7) crystallises in white shining scales or small rhombic prisms, with three atoms of water (C7H4O7 + 3H2O), but at 100° this is lost, and it becomes an opaque white mass. It reddens litmus, and has a sourish taste. It is soluble in 115 parts of cold, but dissolves in 4 parts of boiling water; it dissolves easily in alcohol, less so in ether. It forms well-marked salts; the barium and calcium salt crystallise with one atom of water, the former having the composition BaH4(C7HO7)2; the latter, if ammonium meconate is precipitated by calcium chloride, CaH4(C7HO7)2; but if calcium chloride is added to the acid itself, the salt has the composition C7H2CaO7 + H2O. If meconic acid is gently heated, it decomposes into carbon dioxide and comenic acid (C6H4O5). If the heat is stronger, pyromeconic acid (C5H4O3)—carbon dioxide, water, acetic acid, and benzole are formed. Pyromeconic acid is readily sublimed in large transparent tables. Chloride of iron, and soluble iron salts generally, give with meconic acid (even in great dilution) a lively red colour, which is not altered by heat, nor by the addition of HCl nor by that of gold chloride. Sugar of lead and nitrate of silver each give a white precipitate; and mercurous and mercuric nitrates white and yellow precipitates. In any case where the analyst has found only meconic acid, the question may be raised in court as to whether it is a poison or not. The early experiments of Sertürner,[418] Langer, Vogel, Sömmering, and Grape[419] showed that, in comparatively speaking large doses, it had but little, if any, action on dogs or men. Albers[420] has, however, experimented on frogs, and found that in doses of ·1 to ·2 grm. there is, first, a narcotic action, and later, convulsions and death. According to Schroff,[421] there is a slight narcotic action on man.
[418] Ann. Phys., xxv. 56; xxvii. 183.
[419] De opio et de illis quibus constat partibus, Berol., 1822.
[420] Arch. Path. Anat., xxvi. 248.
[421] Med. Jahresb., 1869.
The most generally accepted view at the present time is that the physiological action of meconic acid is similar to that of lactic acid—viz., large doses cause some depression and feeble narcosis.
In a special research amongst organic fluids for meconic acid, the substances are extracted by alcohol feebly acidulated with nitric acid; on filtration the alcohol, after the addition of a little water, is distilled off, and to the remaining fluid a solution of acetate of lead is added, and the whole filtered. The filtrate will contain any alkaloids, whilst meconic acid, if present, is bound up with the lead on the filter. The meconate of lead may be either washed or digested in strong acetic acid to purify it, suspended in water, and freed from lead by SH2; the filtrate from the lead sulphide may be tested by ferric chloride, or preferably, at once evaporated to dryness, and weighed. After this operation it is identified. If the quantity is so small that it cannot be conveniently weighed, it may be estimated colorimetrically, by having a standard solution of meconic acid, containing 1 mgrm. in every c.c. A few drops of neutral ferric chloride are added in a Nessler cylinder to the liquid under examination; and the tint thus obtained is imitated in the usual way, in another cylinder, by means of ferric chloride, the standard solution, and water. It is also obvious that the weight of the meconic acid may be increased by converting it into the barium salt—100 parts of anhydrous baric meconate, (Ba2C7H2O7), being equivalent to 42·3 of meconic acid (C7H4O7).