256 OXALIC ACID ; CITRIC ACID. 



answered by the cream of tartar. Its chief use is in many 

 processes of dyeing and calico-printing. 



401. Another vegetable acid much used in the arts is the 

 Oxalic, which is well known as a violent poison. From the 

 resemblance of its crystals, in size and general form, to those of 

 Epsom salts, it has not unfrequently been administered by 

 mistake, with the most dreadful consequences. This acid is 

 found united with potash, in the leaves of the "Wood-sorrel and 

 common Sorrel ; and the oxalate of potash is prepared from their 

 leaves in large quantities, in Switzerland and the neighbouring 

 countries, where these plants grow abundantly. Its long needle- 

 like crystals may be seen lying amongst their tissues, if a thin 

 section of the stem or leaf-stalks be placed under the microscope. 

 This salt is known as Salt of Sorrel ; but it is sometimes sold 

 under the name of Salt of Lemons, to which title it has no right 

 whatever. The acid may be separated from it, as in the former 

 instance ; and it is employed for many purposes by the dyer and 

 calico-printer ; as well as for removing the stains of ink, iron- 

 moulds, &c., which it does without injuring the texture of the 

 stuff. 



402. The acid which gives sharpness to the juices of lemons, 

 oranges, limes, and a variety of other fruits, and is known under 

 the name of Citric acid, is likewise one which has many im- 

 portant uses, besides that of imparting a peculiarly refreshing 

 character to these juices. It is largely employed by calico- 

 printers, who now usually import their own lemon-juice, and 

 concentrate it for themselves. At one time, the citric acid, which 

 is not combined in the juice with any earth or alkali, was 

 obtained by chemical processes in separate crystals ; but it is now 

 found, that the impurities of the juice do not interfere with its 

 use in calico-printing ; and it is employed for this purpose, 

 almost in its original state. For other purposes, however, pure 

 citric acid is required ; and this is partly made in Sicily, where 

 Lemons are abundantly produced, and from which island, with 

 the neighbouring continent of Italy, the greater part of the juice 

 consumed in Britain is imported. Pure citric acid is used in the 

 preparation of the best morocco Leather ; for improving a beau- 



