MRCONIC ACID. 937 



crystallizes in regular octahedrons, of a honey-yellow colour ; 

 is insoluble in cold water, and decomposed by boiling water. 



SECTION II. 

 MECONIC ACID AND ITS CONGENERS. 



Meconic acid, 3HO,C 14 HO n -i-6HO, is a tribasic acid, which 

 crystallizes with 6 atoms of water of crystallization. It is 

 found only in opium, of which it is the characteristic acid ; it is 

 named from WKUV, the poppy. It is best obtained by decom- 

 posing meconate of potash dissolved in 16 to 20 parts of hot 

 water with 2 or 3 parts of pure hydrochloric acid, and crystal- 

 lizes on cooling. The solutions in this process must neither be 

 boiled, nor filtered through paper, as the latter may contain 

 iron. (Robiquet). It crystallizes in pearly plates, which are 

 soft to the touch, and possess an acid and astringent taste. It 

 is sparingly soluble in cold water, but very soluble in hot water ; 

 it is equally soluble in alcohol. Salts of the peroxide of iron 

 produce a deep red solution with meconic acid, without occa- 

 sioning any precipitate. Chloride of mercury does not destroy 

 the colour of this solution (Parnell), a property by which me- 

 conic acid may be distinguished from the persulphocyanide of 

 iron, which is also red, but becomes yellow when chloride of 

 mercury or gold is added to it. 



A concentrated solution of meconic acid becomes yellow, 

 when boiled, and then deep brown, and there are formed car- 

 bonic acid, oxalic acid, comenic acid, and a dark brown matter. 

 Boiling dilute sulphuric acid, or hydrochloric acid, converts it 

 with effervescence into carbonic acid and comenic acid. 



The meconates contain all 3 atoms of base, one of which is gene- 

 rally water. Meconate of lead contains 2 atoms of oxide of lead; it 

 is an insoluble white powder, which is thrown down from a solu- 

 tion of opium by acetate or subacetate of lead. After being washed, 

 it is diffused through water and decomposed by a stream of 

 sulphuretted hydrogen, to liberate the meconic acid, which may 

 then be indicated by a persalt of iron ; becoming of a wine-red 

 colour. 



Comenic acid, 2HO,C 12 H 2 O g , a bibasic acid, which crystal- 

 lizes in very hard crusts or crystalline grains, with nothing 



