RESIN. 
they absorb a quantity of oxygen from the air. West 
rum put 30 grains of oil of turpentine into 40 cubic 
inches of oxy-muriatie acid gas. Heat was evolved, the 
oil gradually evaporated, and assumed the form of yel 
low resin *. Mr Proust observed, that when volatile oil 
is exposed to the air, it is partly converted into a resin, 
and partly-into a crystallized acid ; usually the benzoic 
or the camphoric. Hence we see that the oil is con 
verted into two distinct substances. During this change 
oxygen is absorbed; and Fourcroy has observed that a 
portion of water is also formed t. It is probable, from 
these facts, that resin is volatile oil deprived of a por 
tion of its hydrogen, and combined with oxygen. Re 
sin, therefore, is to volatile oil what wax is to fixed oil; 
and doubtless owes its formation to the changes which 
the volatile oils of vegetables undergo. 
To know whether any vegetable substance contains 
resin, we have only to pour some sulphuric ether upon 
it in powder, and expose the infusion to the light.. If 
any resin be present the ether will assume a brown co 
lour f. 
Resin is contained in a great variety of plants. Some 
times it exudes and concretes upon the surface of the 
plant ; sometimes it flows out in considerable quantity 
when the plant is wounded; but very often it remains 
mixed with the vegetable fibres, from which it may be 
extracted by alcohol, and afterwards purified from ex 
tract by water. 
The number of resins is immense, as there is scarce 
a single plant which is destitute of them. They differ 
from each other chiefly in colour, taste, smell, and con 
* Crell's Annals, i. 1790. 
Fourcroy, vi. 16. 
t Hermstadt. 
207 
Chap. 1. 
Plants con 
taining it.