22 
ORIGINAL COMMUNICATIONS. 
which had remained untouched for twenty years, was found 
when examined, to have deposited one-sixteenth of its weight 
of a yellow crystalline matter, while the supernatant oil was 
highly charged with the same, and had a density of 1.0935; 
that of the recent oil being from 1.03 to 1.04. Oil of juniper, 
which had stood nearly the same length of time, deposited a 
thick viscous resinous matter, of a dark claret color. Oil of 
copaiba is particularly disposed to deposite a resin by absorb- 
ing oxygen. From the above statement, it would appear that 
the camphors hold an intermediate place between carburets of 
hydrogen and resins. 
Proust has advanced the idea that camphor is a character- 
istic ingredient of those volatile oils derived from the natural 
order of plants Labiatese, and from the number of individuals 
already discovered to contain it, there is much probability in 
the assertion. 
From the foregoing observations, it would appear that cam- 
phor bears the same relation to the oil of camphor, that other 
crystalline deposites bear to the oils from which they are 
deposited; also, that volatile oils contain less oxygen when re- 
cent, than when old; that the absorption of oxygen produces, in 
some instances, crystalline compounds, and in others true 
resins ; and that the color and density of the oils vary in 
proportion to the quantity of these substances generated from 
and held in solution by them. 
Hence the specific of oils, if taken properly, is a good test 
for their purity and age. A course of experiments on this 
subject, might result in the discovery of a standard by which 
to judge of the purity of volatile oils. If all those plants 
which yield essential oils, were tested as to the time most proper 
to obtain these substances from them, and that period of their 
age recorded, we have every reason to believe that the density 
of the oils obtained from different individuals of the same age 
and species, would be nearly alike; therefore, all specimens 
which would not come up to the standard, should either be 
rejected as adulterated, or as having been distilled before the 
proper period. Should, however, the oils be of greater specific 
