MECONIC ACID A substance found in opium, in which it exists in combination with the alkali illegible. It was first noticed by Seguin in 1804, and a few years after, more particularly described by Sertuerner, who named it mecon (piver), poppy. Meconate of lime is one of the results of a peculiar process for obtaining morphia from opium [Omit, ALKALOIDS or]; this is put into ten times its weight of water at 200', and hydrochloric acid is added until it is dissolved ; the solution is to be filtered, and on cooling it deposits bi-meconate of lime in the state of light, scaly, or acicular crystals ; these are again to be dissolved In hot and very dilute hydrochloric acid, which separates the remainder of the lime, and on cooling, the meconic acid crystallises in scales containing six equivalents of water of crystal lisation. They are to be freed from colouring matter by subsequent treatment with purified animal charcoal, and recrystallisation. Isleconie acid has then the following properties: it acts on litmus paper, and bas a sour taste ; it is soluble in four times its weight of water, and also in alcohol. The crystals do not alter by exposure to the air, but when heated to 212° they lose 21.5 per cent. of water, and become opaque. Although when heated even to near 250° the acid is not totally decom posed, yet the boiling solution gives out carbonic acid gas, and a brown substance is formed, which is comeuic acid. When strongly heated, it is totally vaporised. When mixed with a solution of chloride of gold, and heated, it is decomposed, and metallic gold is precipitated. This acid possesses the characteristic property of forming a purplish-red coloured solution with the persalts of iron, and this is regarded as one of the best tests of its presence in the opium from which it is derived. It has been asserted that meconic acid is an antidote in eases of poisoning by corrosive sublimate, but this is not the case. It has no effect whatever.
Meconic acid is tribasic; one, two, or three atoms of the water in the above formula being replaceable by an equal number of equivalents of a base with formation of mono., bi-, or tri-metallic salts, called meconates. Their properties are as follow :—Meconate of Ammonia crystallises in quadrilateral prisms, dissolves in one and a half times its weight of water, yields water when heated, and afterwards sublimes without decomposing. of Potash crystallises in tables and leaves, contains water of crystallisation, and is soluble in twice its weight of cold water. Meconate of Soda crystallises in fine needles, which contain much water of crystallisation, and are soluble in five times their weight of water. Meconate of Lime forms acicular crystals, which contain water of crystallisation, and are soluble in eight times their weight of water. When the acid is in excess the salt crystallises in prisms, and is difficultly soluble in water. Meconate of Magnesia when neutral is only slightly soluble, but the supersalt dissolves readily ; it crystallises in flattened needles, which are brilliant and transparent, and have an acid and bitter taste. Meconate of Baryta is slightly
soluble in water. Meconate of Iron is a colourless and very soluble salt, which becomes red by exposure to the air, and more rapidly by the addition of nitric acid. The Pcrmeconate of Iron is also a soluble salt, and is of a fine red colour, destroyed by heat, by sulphurous acid, and protoxide of tin. Med:mate of Silver explodes when heated. Meconate of Oxide of Ethyt, or econic Ether, or Ethyl-meconic acid 2110, C„HO„), separates out in acicular crystals on evaporating the liquid formed on paaaing dry hydrochloric acid gas through a solution of meconic acid in absolute alcohol. lt forms very stable salts, called Ethylmeronatcs. The mother-liquor from the preparation of ethylmeconic acid contains crystalline Dicthylmeconic acid HO, Mcconamic acid is precipitated when hydrochloric acid is added to Meconamate of Ammonia. The latter salt is produced by the reaction of ammonia and ethylinceonic acid.
Comenic acid, Metameconic acid, Parameconic acid (C„II,0„2H0). It has been mentioned above that when a solution of meconic acil is heated to ebullition, carbonic acid is evolved, and a brownish solution results; this consists of colouring matter and comenic acid. When a meconate, as of potash or lime, is boiled with hydrochloric acid, no colouring matter results, and yet comenic acid is formed.
This acid is soluble in sixteen times its weight of boiling water, and separates on cooling in hard anhydrous grains, which, like the meconie acid, redden the persalts of iron, but they differ from it in every other respect.
It is formed by the mere separation of carbonic acid, by subtracting two equivalents of which from meconic acid we obtain the acid in question :— Commie acid is biba.sic, forming neutral and acid comenates. Ethyl comenic acid is formed in a similar way to ethylmeconic acid. adore, comet:iv acid 3 Aq.) is obtained by the action of chlorine I on comenic acid. t, crystallisti in short prisms.
Cornenamic add Prepared by the action of heat upon a solution of comenate of ammonia. On adding a little hydrochloric acid, and cooling, It crystallises out in plates The comenamates are monobasio.
Pyromeconic acid is obtained by heating meconic acid, which yields about one-fifth of its weight. It is purified by pressure between folds of blotting paper, and crystallisation from solution in water. It is fusible between and 257°, and then flows like oil ; it is entirely soluble at a moderate temperature, and is more soluble in alcohol than in water. It turns the persalts of iron red, and its salts are generally soluble in water. It is formed by the separation of four equivalents of carbonic acid and one equivalent of water, from two equivalents of meconie acid. It is colourless, very sour, and mono-basie.
Bromine and iodine displace hydrogen, and form Brom- and Iodo pyromeconic acids.