ON THE PURITY. OF THE OTTO OP ROSES. 319 
ployed for comparison is called oil of Geranium, and came 
from Nice. I also examined some oil of rose-wood, which 
w;ts distilled at Paris some years ago, and some of that 
found in commerce. Three re-agents will serve to distin- 
guish the pure otto — iodine, nitrous acid vapor, and sul- 
phuric acid. 
Test with Iodine. — A small quantity of iodine is placed 
in a small glass vessel with a wide mouth ; around it watch- 
glasses are arranged, each containing one or two drops of 
the oils under examination, and the whole is covered with 
a bell-glass. At the end of a few hours the vapor of the 
iodine is found to have condensed upon every part of the 
interior of the bell-glass, and upon the glasses containing 
the oils ; but the margin of the watch-glasses containing the 
substituted oils is much more colored than that of the glass 
containing the otto ; and when the former oils become 
brown, the latter retains its natural color. After some hours 
the vessel containing the iodine may be removed ; and then, 
the effect still continuing, the otto remains white, whilst the 
other oils become perfectly black. On exposing the watch- 
glasses to the air, the iodine which has condensed upon the 
margin of those containing the otto is volatilized, and the 
glass becomes almost colorless, whilst the others retain 
their black color. I am satisfied that this test will serve, 
not only to determine the nature of the otto of roses, but 
also whether any oil of geranium or rose-wood is present 
in it or not. 
Nitrous Jicid Test. — For this I use a small glass vessel, 
placed upon a plate. 10 or 15 grms. of concentrated nitric 
acid are placed in it ; and some copper turnings added. 
Around this, watch-glasses are placed, containing one, or 
at the most, two drops of the oils, and the whole is covered 
with a flat bell-glass. In a few minutes the oil of rose- 
wood acquires a dark-yellow color ; the otto acquires nearly 
