80 
Bird-lime, a substance which may be procured 
from the holly, is very analogous to gum elastic in 
its properties. Species of gum elastic may be ob- 
tained from the misletoe, from gum-mastic, opium, 
and from the berries of the Smilax caduca, in which 
last plant it has been lately discovered by Dr. 
Barton. 
Gum elastic, when distilled, affords volatile 
alkali, water, hydrogene, and carbon in different 
combinations. It therefore consists principally of 
azote, hydrogene, oxygen e, and carbon ; but the 
proportions in which they are combined have not 
yet been ascertained. Gum elastic is an indiges- 
tible substance, not fitted for the food of animals ; 
its uses in the arts are well known. 
7. Extract, or the extractive principle, exists in 
almost all plants. It may be procured in a state 
of tolerable purity from saffron, by merely infusing 
it in water, and evaporating the solution. It may 
likewise be obtained from catechu, or Terra japo- 
nica, a substance brought from India. This sub- 
stance consists principally of astringent matter, 
and extract ; by the action of water upon it, the 
astringent matter is first dissolved, and may be 
separated from the extract. Extract is always more 
or less coloured : it is soluble in alcohol and water, 
but not soluble in ether. It unites with alumina, 
when that earth is boiled in a solution of extract ; 
and it is precipitated by the salts of alumina, 
and by many metallic solutions, particularly the 
solution of muriate of tin. 
From the products of its distillation, it seems to 
be composed principally of hydrogene, oxygene, 
carbon, and a little azote. 
