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COMMUNICATIONS RECEIVED SINCE THE END OF THE SESSION. 



I. " On some Varieties of Tannin." By JOHN STENHOUSE, 

 LL.D., F.R.S., F.C.S. Received June 28, 1861. 



In two communications "On some Astringent Substances as 

 sources of Pyrogallic Acid," read before the London Chemical 

 Society in the years 1842, 1843, I showed that the usual division of 

 the varieties of tannin into two genera to wit, those which give black, 

 and those which give green precipitates with salts of iron, though 

 called in question by Berzelius, is still well-founded : and likewise, that 

 these twp genera consist of a great variety of species, which, though 

 closely resembling each other in properties, are still dissimilar in 

 nature ; the only instances in which the same species of tannin had 

 been procured from two different plants, being those of nut-galls and 

 sumach. Professor Strecker's important observation made some 

 seven years ago, that grape-sugar is produced when the tannin of 

 gall-nuts is boiled with dilute sulphuric acid, seemed to render a 

 further examination of the varieties of tannin desirable. 



Sumach. 



As the tannin of Sumach cannot be obtained in such a high state 

 of purity as that of nut-galls by Pelouze's ethep process, I was 

 obliged to employ other methods by no means so satisfactory, but 

 which still yield a tolerably pure tannin. A strong decoction of 

 sumach was therefore treated with acetate of lead, which threw down 

 a pale yellow precipitate. This was washed by decantation, and then 

 decomposed by sulphuretted hydrogen and filtered : the filtrate ha- 

 ving been boiled with dilute sulphuric acid, on standing for some 

 time, deposited crystals of impure gallic acid. These were collected 

 on a filter, and the mother-liquor, when neutralized with chalk, gave 

 abundant indications of sugar, both by Trommer's test and when sub- 

 jected to fermentation. A second decoction of sumach, when cold, 

 was treated with sulphuric acid, which threw down a copious preci- 

 pitate ; this when boiled was also resolved into gallic acid aud grape- 



