318 ON THE PURITY OF THE OTTO OF ROSES. 
ART. LXX VI. — MEANS OF DETERMINING THE PURITY OF 
THE OTTO OF ROSES. 
By M. Guibourt. 
The high price of this article renders it a matter of great 
importance to be enabled to decide upon its purity. The 
following means,, if used in combination, will leave no doubt 
upon this point. 
The physical characters can be but little depended upon ; 
thus, the yellow color with a tinge of green and its point of 
congelation may be readily imitated. Its odor also is so 
powerful, that a certain quantity of any other oil of a some- 
what similar odor might be added without sensibly dimin- 
ishing that of the otto. The manner in which it crystallizes 
is of a certain amount of importance. When, after having 
been liquefied by a gentle heat, it is allowed to cool slowly 
and at rest, it remains as it were transparent, in consequence 
of the thinness and the perfect transparence of its long and 
pointed crystals, which resemble the blades of daggers ; and 
on varying their position as regards the light, these laminse 
reflect all the prismatic colors. When the otto of roses has 
been adulterated with any uncrystallizable oil, which re- 
quires that its property of congealing should be imparted by 
the addition of spermaceti, it presents, when solidified, a 
number of fine needles, which, however, are not transpa- 
rent, but render the mass uniformly semi-opake. But for 
this test to be of any value, the otto must be allowed to 
crystallize slowly and at rest; otherwise it becomes nebu- 
lous and opake, like that which has been adulterated. 
The oil most frequently used for its adulteration is that 
of several species of Pelargonium. The oils derived from 
the different species cannot be all identical, since M. Recluz 
has described one which is solid, whilst that which is met 
within commerce is always liquid. The oil which I em- 
