TARTARIC ACID. 201 



497. Pure citric acid is obtained from the juice of 

 limes or lemons, by a process resembling that used in 

 the preparation of pure acetic acid (490). The sour 

 juice is saturated with powdered chalk, which forms 

 with its acid an insoluble citrate of lime ; this is 

 well washed with pure water, to remove the mucilage 

 and other foreign matters present in the juice of the 

 fruit. The pure citrate of lime is subsequently de- 

 composed by dilute sulphuric acid, sulphate of lime 

 is formed, and, as the clear solution cools, the citric 

 acid is deposited in crystals. 



498. Tartaric acid is obtained from the juice of 

 grapes, pine-apples, and several other fruits; its 

 principal source is wine, from which it is deposited as 

 a super-salt of potash. The hi- or super-tartrate of 

 potash is slightly soluble in water, but almost insolu- 

 ble in a mixture of spirit and water ; hence, after 

 the fermentation of grape juice and consequent form- 

 ation of spirit, the bitartrate of potash previously 

 dissolved, is thrown down as a crystalline precipitate, 

 constituting argol, or cream of tartar (309). 



499. Tartaric acid is manufactured from tartar, by 

 the use of lime and sulphuric acid. When tartar is 

 boiled with chalk, the excess of wine in the tartar 

 combines with lime, and forms an insoluble tartrate 

 of lime. This salt, decomposed by sulphuric acid, 

 yields pure tartaric acid. 



500. The tartar deposited by red wine, has always 

 a pink or red color, and contains some of the coloring 

 matter of the grape. By boiling it with a portion 



