THE ODOUR OF BITTER ALMOND. 179 
nitric acid sp. gr. 15 the smallest quantity of alcohol may be 
detected. Chromate of potash does not affect it. 
For the detection of the adulteration of nitrobenzene in oil of 
bitter almonds, it has been recommended to shake the suspected 
sample in a test-tube, with one-half its weight of solid caustic 
potash. The yellow colour of the oil is not changed if it is pure ; 
but if nitrobenzene be present, the colour will soon change to a 
characteristic red. If a considerable quantity of nitrobenzene be 
present, the red colour is changed to a more or less fine green 
colour, which, on the followmg day, again becomes red. The 
quantity of nitrobenzene is determined by agitating the adulterated 
oil violently and repeatedly with four volumes of a concentrated 
solution of bisulphite of sodium ; after some time rectified ether 
is added, which dissolves the nitrobenzene, and by evaporation 
permits its estimation. To prove the residue of the evaporation 
to be nitrobenzene, it can be converted into aniline. 
To distinguish the natural oil from the artificial oil which is 
frequently substituted for it, and to detect the presence of the 
latter, a simple process has been recommended, based on a reaction 
produced by the organic chlorinated compounds always contained 
as impurities in the artificial oil. It consists in saturating a piece 
of folded filter-paper with the oil to be examined, and after 
placing it m a porcelain dish standing in a larger one, igniting it, 
and covering it over with a large inverted beaker, the sides of 
which have been wetted with water. The combustion-gases be- 
come absorbed on the moist sides of the beaker, from which they 
are washed on to a filter with a little distilled water. The filtrate, 
when treated with solution of silver nitrate, should give no turbidity, 
much less a precipitate of silver chloride. Genuine essential oil 
of bitter almonds, distilled in the ordinary way from almonds or 
peach-kernels, never gives a chlorine reaction. (Schimmel.) 
Some manufacturers free the oil from hydrocyanic acid ; the 
purified oil, however, oxidizes much more readily than when in 
the crude state, so that others add hydrocyanic acid and warm 
gently in order to make it keep better, the nitril being formed *. 
When, however, it is desirable to store the oil freed from hydro- 
cyanic acid, the oil should be very carefully dried from all traces 
of water by agitation with fused calcium chloride. 
* Bull. Soc. Chem. [2] viii. p, 459. 
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