18 
PJNUS SYLVESTRIS. 
that wax does to the fixed oils ; wax being a fixed oil, and resin a 
volatile oil saturated with oxygen. Although the term liquid resirt 
has been applied to the fluid turpentine, it is more properly to be 
understood to mean the hard substance ; in which sense we now 
speak of if, observing by the way, that all terebinthinous exudations, 
wl^ether fluid or solid, may be considered as resins prior to the sepa- 
ration of the essential oil. When volatile oils are exposed for a 
sufiicient time to the action of the atmosphere they absorb oxygen, 
acquire consistency, and are converted into resins. These resins for 
the most part have a sub-acid taste, resembling that of the essential 
oils; they are devoid of smell, are non-conductors of electricity, 
specific gravity varying, but all of them heavier than water, in which 
fluid they are insoluble under any temperature ; ihey are soluble in 
alcohol, and some of them in the fixed oils ; they are also for the most 
part soluble in the volatile oils, and in many of the acids ; the 
sulphuric and nitric acids convert them into a kind of tannin. 
According to Mr. Hatchett they are readily dissolved by alkaline 
leys, and the solution has the properties of soap. When exposed 
to a gentle heat they soften, and finally melt, and if the heat be 
increased they take fire, burning with a strong yellow flame, and 
emitting a considerable volume of smoke. When volatile oil is 
exposed to the air it is converted, partly into a resin, and partly 
into an acid which crystallizes; this acid is geuer&Uy the camphoric 
or the benzoic, sometimes the succinic. 
Medical Properties and Uses of Common Turpentine. 
As the medical properties of the turpentines are all nearly similar,, 
differing only in degree, we shall notice this part of our subject 
when we come to treat of the purer kinds which are administered 
internally. 
Thus. In warm seasons or climates the Pinus Sylveslris yields a 
resinous juice, which exudes spontaneously, and to which the name 
of Thus, or common frankincense, was formerly given; but as this 
substance is more properly the produce of the Pinus Abies, we shall 
treat of it under that head. 
Resina Flava. Yellow Resin. Baked Turpentine^ 
We have already said that turpentine is composed of an essential 
oil, a resin, and a small quantity of succinic or other acid. The 
residuum of the process for obtaining the essential oil gets different 
names, according to the manner in which it is treated : if the 
distillation be performed without addition, and continued until the 
whole of the essential oil is driven oft^ there will appear some traces 
of empyreuma in the residuum, which then obtains the name of rosin^ 
