BLACK DYES. VEGETABLE ACIDS. 255 



demand, in consequence of the introduction of another source, 

 from which gallic acid may be obtained at a much cheaper rate. 

 This is in the cups of the acorns of the Yelani Oak, a species 

 which grows abundantly in Greece, and in the maritime parts of 

 Asia Minor. These cups, which do not contain gallic acid in the 

 same proportion as gall-nuts, are known in commerce by the 

 name of Yalonia ; but in consequence of their cheapness (being 

 only about one-fifth the price of galls) the consumption of them 

 is very great. During the year 1830, the quantity of gall-nuts 

 employed in England was 2,297 cwt. ; whilst that of Yalonia was 

 86,538 cwt. Many other astringent substances may be used as 

 black dyes with iron ; and a good deal of the Sumach imported 

 into Britain is used for this purpose, as are also walnut husks in 

 France ; the shells of chestnuts, too, have been employed, although 

 not profitably. In India, the juice of the fruit of the Myro- 

 balans, which is not unlike a plum, is used for dyeing black with 

 iron ; and when the pulpy portion is freed from the stone, which 

 is useless, it contains more gallic acid than an equal weight of 

 galls, and might be made a profitable article of commerce. 



400. From gallic acid, we may naturally proceed to speak of 

 the other acids, which are produced by Yegetables. These are 

 all, like the foregoing substances, formed by the plant itself, from 

 the elementary bodies it receives as food ; and thus they may be 

 regarded as true products of vegetable secretion, and not as 

 merely separated by the plant from the surrounding soil. In this 

 last light we must regard the earths and alkalies obtained from 

 plants, and not as products of their secreting processes. The 

 acid which is employed in largest quantity, is the Tartaric. 

 This is obtained from the crust that is deposited by wine, when 

 kept a long time ; the amount of which depends, chiefly, upon 

 the degree of acidity in the wine. The crust which goes by the 

 name of Argol, chiefly consists of tartaric acid in combination 

 with potash, forming what is commonly known as Cream of 

 Tartar ; and this requires to be purified from its colouring- 

 matter and other impurities, before it can be employed in the 

 arts. The acid is easily obtained in a separate form by chemical 

 processes ; and it is employed for many purposes, which cannot be 



