on some of the leading doctrines of caloric , &c. 361 
212®, some small bubbles will be evolved, principally owing 
to the moisture dispersed in the pores of the oil, from the 
water originally mixed with the crude turpentine in its dis- 
tillation. If the heat be very rapidly thrown in, while the 
upper surface of the oil of turpentine has the area only of a 
one or two ounce phial, it is possible to heat it to 360° or 
370°, in apparent contradiction to the theory of latent heat ; 
for when a liquid boils in an open vessel, according to Dr. 
Black, its temperature should remain stationary. The true 
cause of this phenomenon is developed towards the conclusion 
of this memoir. The specific caloric of the vapour of the 
volatile oil is so small, compared to that of water, that the 
heat may readily be quicker introduced than the boiling pro- 
cess can abstract it. Concerning the boiling point of this 
oil, I have since inquired of a manufacturer ; and he states 
its boiling point at 320°. Essential oil of rosemary, when 
kept for some time, boils at 270®; recent oil at 212 0 . To 
assign the cause of this difference, is foreign to our present 
object. 
The vapour of ether follows nearly the same rate of expan- 
sion as water, if we start from their respective boiling points. 
This was observed also in Mr. Dalton’s experiments ; and 
from this single analogy, chiefly, he laid down the general 
law, “ that the variation in the force of vapour from all liquids 
“ is the same for the same variation of temperature, reckon- 
“ ing from vapour of any given force.” 
My experiments on oil of turpentine and petroleum show 
the fallacy of this generalization, if we reckon the common 
thermometric scale a tolerably correct index of temperature ; 
but if, with Mr. Dalton, we consider our thermometric scale. 
