332 Dr. Stenhouse's Examination 



which collect on the sides and neck of the retort, while the 

 empyreumatic liquor which passes into the receiver gives 

 pretty distinct indications of containing pyrogallic acid. 



The Tannin of Tea. — In order to separate the tannin of tea 

 from the other proximate principles of the plant, its aqueous 

 infusion was precipitated with acetate of lead, and the preci- 

 pitate carefully washed with hot water. Green tea gave a 

 bright yellow precipitate, but that of black tea had a brownish- 

 yellow colour. The lead salts were decomposed by sulphu- 

 retted hydrogen : the solution of the tannin of green tea had 

 only a slight yellow colour, while that of black tea had a much 

 darker colour, but in other respects the properties of both 

 appeared to be the same. The following are the effects upon 

 them of different reagents : — with solution of gelatine they gave 

 white bulky precipitates, and they also gave copious white 

 precipitates with tartar-emetic. Protosulphate of iron throws 

 down bright bluish-black precipitates, nitrate and chloride 

 of iron, olive black, and acetate of iron purple black preci- 

 pitates. The solution of the tannin when evaporated to dry- 

 ness on the water-bath, became of a reddish-brown colour, and 

 was partially decomposed. 



When this tannin was subjected to distillation, it invariably 

 yielded a quantity of pyrogallic acid, which sometimes ap- 

 peared in crystals upon the sides of the retort, but which 

 more frequently remained dissolved in the empyreumatic li- 

 quor which passed into the receiver. In this it was easily de- 

 tected by the usual reagents. It gave a fine reddish-purple 

 colour when dropped on milk of lime, with protosulphate and 

 protonitrate of iron, a fine indigo-blue colour, and with proto- 

 chloride, a blue resembling ammoniuret of copper. As the 

 quantity of pyrogallic acid obtained was always much less 

 than that which the same quantity of the tannin of either galls 

 or shumac would have yielded, I was led to suspect that it 

 did not arise from the decomposition of the tannin in the tea, 

 but resulted from some gallic acid with which the tannin was 

 mixed. Of the accuracy of this opinion I was speedily con- 

 vinced by the following experiment : — On treating a strong 

 solution of the tannin with nearly half its bulk of sulphuric acid 

 added by little and little at a time, a dark brown precipi- 

 tate fell consisting of the tannin combined with the acid. It 

 was however much more soluble than the corresponding com- 

 pound of the tannin of galls. It was collected on a cloth filter, 

 strongly compressed, and washed with a little cold water to 

 free it as much as possible from adhering acid. When sub- 

 jected to distillation it did not afford the slightest trace of 

 pyrogallic acid, showing evidently that the pyrogallic acid 



