946 ORGANIC ACIDS. 



acid liquid which condenses in oily strise, with carbonic acid 

 gas. These appearances indicate two stages in the distillation, 

 and if the process be interrupted when the disengagement of 

 water and inflammable vapour ceases, the fixed residue in the 

 retort contains no citric acid, but a new acid produced by its 

 decomposition, which proves to be the same with the acid from 

 the Aconitum napellus and Equisetum fluviatile, and which was 

 already known under the names of aconitic and equisetic acid. 

 This acid is soluble in ether, which citric acid is not. It is 

 also readily converted into aconitic ether, by the action of dry 

 hydrochloric acid upon its solution in alcohol, and is preci- 

 pitated by water, while citric acid not being etherified by this 

 process remains in the liquor. Aconitic ether is easily de- 

 composed by caustic potash, and the acid may be derived from 

 the potash salt. Aconitic acid forms only small confused 

 crystals. When briskly distilled it affords the two following 

 isomeric acids, which sublime (see page 712.) 



Itaconic acid, HO -f- C 5 H 2 O 3 ; known also as pyrocitric acid 

 arid citricic acid. It crystallizes in rhomboidal tables, is soluble 

 in 17 parts of water at 50, in 10 at 68; soluble also in alcohol 

 and ether. 



Citraconic acid (hydrated), HO + C 5 H 2 O 3 ; distinguished also 

 as citribic acid by M. Baup. It is obtained anhydrous by dis- 

 tillation as an oily limpid liquid, C 5 H 2 O 3 , which distils at 212 

 without decomposition. 



SECTION V. 



TAHTARIC AND PARATARTARIC ACIDS AND THE PRODUCTS OF 

 THEIR DECOMPOSITION. 



TARTARIC ACID. 



Formula of the crystallized acid, 2HO + C 8 H 4 O 10 ; a bibasic 

 acid. 



This acid, which in common with so many others was first 

 prepared by Scheele, exists in many fruits, and also as tartrate 

 of lime in several roots, but is prepared only from the juice of 

 the grape, which contains tartaric acid in the form of tartar or 

 bitartrate of potash. The last salt precipitates during the fer- 

 mentation of wine, owing to its insolubility in alcohol ; in the 

 crude state, it is known as argol, and is highly coloured, when 



