ON THE TURPENTINES. 131 
of the balsam of Mecca is allowed to fall upon a glass of water, 
the balsam extends itself instantaneously and completely over 
the whole surface of the liquid, in a thin and nebulous layer. 
By waiting a few moments to allow the volatile oil to evapo- 
rate, the resin becomes so solid that by touching it with a pin, 
it can be removed in a consistent mass. When a drop 
of the turpentine of the fir is allowed to fall upon a glass of 
water, it precipitates to the bottom at once, then returns to 
the surface, retaining the form of a well defined globule. Yet 
if the surface of the liquid be carefully examined, it will be 
found covered with a thin pellicle, presenting all the colors of 
the rainbow ; so that the contraction of the drop of resin ap- 
pears to be owing to the layer of volatile oil which is produced 
immediately upon the surface of the water, but by little and little 
the drop spreads itself unequally, and pushes the irridescent 
layer to different points of the surface. Both parts are then 
equally resplendent by reflection. Lastly, inspected after a few 
minutes, the resin, as in the Balsam of Mecca, is sufficient- 
ly solid to be removed in an entire piece with a pin. 
This mode of treatment indicates great volatility in the vo- 
latile oil of the turpentine of fir ; and, in fact, when kept in a 
vessel not hermetrically sealed, it is not long in forming a so- 
lid pellicle upon its surface, which is not the case with the 
turpentine of the larch ; and when exposed to the air, in a thin 
layer upon a leaf of paper, it drys completely in eight and for- 
ty hours. If at another period I have expressed a contrary 
opinion, it was because I then took for the turpentine of the 
fir, an article which was that of the larch. Finally, the larch 
turpentine is entirely soluble in alcohol, whilst that of the fir 
contains a resin entirely insoluble in that menstruum. Thus, 
take a nebulous turpentine of the larch, and it will form a trans- 
parent solution with alcohol, while, on the contrary, the most 
transparent turpentine of the fir will form a lactescent and 
turbid solution, and, in clarifying itself by time, will deposit 
upon the side of the vessel, a granulated insoluble resin. 
These characters are moreover entirely conformable to the 
analyses of the two turpentines made by Berzelius, as regards 
