of Astringent Substances. 333 



I had previously obtained was not derived from the tannin of 

 the tea. When another portion of the precipitated tannin 

 was boiled with tolerably dilute sulphuric acid, it did not yield 

 any gallic acid, but was changed into a dark brown substance, 

 nearly insoluble in cold, and but very little more so in boiling 

 water. It gave a grayish black precipitate with protosulphate 

 of iron, but was not precipitated either by gelatine or tartar- 

 emetic. It dissolved however pretty easily both in alcohol 

 and alkalies, forming dark brown solutions. It is evident 

 therefore that though in some of its properties the tannin of 

 tea agrees pretty closely with that of nut-galls, still the pro- 

 ducts of its decomposition are essentially different. 



The tea was next examined for the gallic acid which it evi- 

 dently contained, and this I was always able to procure by 

 either of the following methods : — The mixture of tannate 

 and gallate of lead obtained by precipitating a decoction of 

 tea by acetate of lead, was decomposed as before by sulphu- 

 retted hydrogen and evaporated to dryness. It was then ma- 

 cerated with a very little cold water which removed most of 

 the tannin, but dissolved scarcely any of the gallic acid. The 

 residue was again dried, reduced to powder and mixed with 

 some sand, was repeatedly agitated with aether in a stoppered 

 bottle. The aethereal solution was then poured off, and al- 

 most the whole of the aether was recovered by distillation. 

 The residue when left to spontaneous evaporation deposited 

 crystals, which at first had a yellow colour, but which were 

 rendered perfectly white by a second crystallization. The 

 other process was somewhat more tedious, but by it very small 

 quantities indeed of gallic acid can be detected. It consists 

 in putting a number of bits of prepared skin into the mixed 

 solution of tannin and gallic acid already mentioned, and al- 

 lowing them to remain for nearly a fortnight till the whole of 

 the tannin is absorbed by the skin. The gallic acid is then 

 precipitated by acetate of lead, and the precipitate having 

 been well washed, first with hot water and then with spirits of 

 wine, is to be decomposed by sulphuretted hydrogen. 



When evaporated to dryness and treated with aether as 

 before, crystals of gallic acid are readily obtained, which are 

 at first much purer than those got by the former method. 

 I examined several specimens both of black and green tea, 

 and also one of Assam tea, in every instance with similar re- 

 sults. It is evident, therefore, that tea, besides a species of 

 tannin which gives bluish-black precipitates with protosul- 

 phate of iron, invariably contains a small but constant quan- 

 tity of gallic acid, a constituent which has hitherto been over- 

 looked. 



