402 



sugar. This reaction, therefore, in addition to former experiments, 

 serves to confirm the identity of tannin in oak-galls and sumach. 



When sumach is long kept, the tannin it contains appears to be 

 resolved in a great measure into gallic acid and grape-sugar, owing 

 to its undergoing a species of natural fermentation. Accordingly 

 under these circumstances when simply boiled with water, sumach 

 emits an odour resembling that of tea, and yields a large quantity of 

 sugar and gallic acid, but mixed with much impurity. Sumach 

 therefore, though it contains much gallic acid, owing to the impuri- 

 ties present in it, is not a good source of that acid. 



I may also remark that the amount of tannin in sumach varies 

 considerably, some specimens being very rich and others very poor. 

 This probably arises from the circumstance that the sumach of com- 

 merce is the product of various kinds of Ehus, such as Rhus cotinus, 

 Rhus coriaria, &c. 



Chinese Galls. 



These singularly-shaped galls, which are angular and slightly 

 translucent, have been imported into this country in small quantities 

 for the last fourteen or fifteen years. They are said to be found on 

 the branches of a plant which grows in Japan. From the small 

 amount of the colouring matter they contain, Chinese galls are 

 greatly preferred for the manufacture of gallic acid. Oak-galls, on 

 the other hand, are the best source of pyrogallic acid. The decoc- 

 tion of Chinese galls gave a copious white precipitate with acetate 

 of lead. This was decomposed by sulphuretted hydrogen, and filtered ; 

 the clear liquid, when boiled with sulphuric .acid, was resolved into 

 gallic acid and grape-sugar, as in the two preceding instances. Another 

 portion of the filtered liquid was evaporated to dry ness, and destruc- 

 tively distilled. It yielded a very large quantity of pyrogallic acid. 

 It is clear, therefore, that gall-nuts, Chinese galls, and the various 

 kinds of sumach, contain the same species of tannin. 



The Tannin in Tea. 



The tannin both of green and black tea is invariably accompanied 

 by a small quantity of gallic acid, which does not arise from the de- 

 composition of the tannin in the tea, as is the case with nut-galls, 

 sumach, or Chinese galls. On treating a strong decoction of tea, when 

 cold, with nearly half its bulk of sulphuric acid, the tannin falls as a 



