300 VEGETABLE SUBSTANCES. 



which the fruit grows. When fresh squeezed all 

 seems equally sharp and good. The hot weather, 

 however, is its test, and there is much of the juice we 

 buy which will not bear it : it often changes very 

 quickly, and^a mawkish acid remains. Though the 

 early juice resists the heat the best, he can positively 

 assert that with the utmost care there is no certainty 

 of preserving its native sharpness in the hot months but 

 by the addition of lime or some other similar agent*/' 



Besides the employment of citric acid in medicine, 

 domestic economy, and calico-printing, there are 

 many other arts in which it proves a valuable aux- 

 iliary. It is used in the preparation of the best Mo- 

 rocco leather ; for improving that peculiar solution of 

 tin applied in producing the most exquisite specimens 

 of the scarlet dye ; and for altering the hue of some 

 colours which are exclusively used in the dyeing of 

 silk. 



Citric acid is extremely easy of solution ; one 

 ounce and a quarter can be perfectly dissolved in one 

 ounce of cold water, while boiling water dissolves 

 double its own weight. It is this solubility which 

 renders it so useful to the manufacturer. 



The juice of many other fruits besides that from 

 limes and lemons, will afford citric acid either alone 

 or mixed with othertcid. ~The cranberry, the red 

 whortleberry, the cherry, the berry of the night-shade, 

 and the hep of the wild briar yield chiefly citric acid ; 

 while in the red gooseberry, the currant, the bilberry, 

 the hawthorn, the black cherry, the wood strawberry, 

 the cloudberry, and the raspberry, it is mixed with 

 nearly an equal proportion of malic acid. 



Gallic acid obtains its name from the gall-nut, the 

 substance which yields it the most readily and in the 

 greatest abundance. 



* Parkes' Chemical Essays. 



