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mable gasses, with a minute quantity of volatile alkali. 

 Hence its elements seem the same as those of extract, 

 but probably in different proportions. The charac- 

 teristic property of tannin is its action upon solutions 

 of isinglass or jelly ; this particularly distinguishes it 

 from extract, with which it agrees in most other che- 

 mical qualities. 



There are many varieties of tannin, which pro- 

 bably owe the difference of their properties to com- 

 binations with other principles, especially extract, 

 from which it is not easy to free tannin. The purest 

 species of tannin is that obtained from the seeds of the 

 grape ; this forms a white precipitate, with solution 

 of isinglass. The tannin from gall-nuts resembles it 

 in its properties. That from sumach affords a yellow 

 precipitate ; that from kino a rose coloured ; that 

 from catechu a fawn coloured one. The colouring 

 matter of Brazil wood, which M. Chevreul considers 

 as a peculiar principle, and which he has called Hema- 

 tine, differs from other species of tannin, in affording 

 a precipitate with gelatine, which is soluble in abun- 

 dance of hot water. Its taste is much sweeter than 

 that of the other varieties of tannin, and it may per- 

 haps be regarded as a substance intermediate between 

 tannin and extract. 



Tannin is not a nutritive substance, but is of 

 great importance in its application to the art of tanning. 

 Skin consists almost entirely of jelly or gelatine, in an 

 organized state, and is soluble by the long continued 

 action of boiling water When skin is exposed to so- 

 lutions containing tannin, it slowly combines with 



