82 
When tannin is distilled in close vessels, the 
principal products are charcoal, carbonic acid, and 
inflammable gasses, with a minute quantity of vola- 
tile alkali. Hence its elements seem the same as 
those of extract, but probably in different propor- 
tions. The characteristic 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 chemical qualities. 
There are many varieties of tannin, which pro- 
bably owe the difference of their properties to 
combinations with other principles, especially ex- 
tract, 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 precipi- 
tate, 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 Hematine, differs 
from other species of tannin, in affording a pre- 
cipitate 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 perhaps be regarded as a substance inter-* 
mediate between tannin and extract. 
Tannin is not a nutrtive 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 
