THE ODOUR OF BITTER ALMOND. 18] 
Jacobsen * recommends a process in which benzidene chloride 
is heated with glacial acetic acid and zine chloride, benzaldehyde 
and acetyl chloride being formed ; the necessary amount of water 
is then allowed to flow in, and the acetic acid which is formed 
recovered. 
The artificial benzaldehyde of commerce, which is used in the 
colour industry and prepared from benzyl chloride, is always more 
or less impure, retaining traces of chlorinated compounds of 
pungent repulsive odour which render it unfit for perfumery 
purposes f. 
The artificially prepared benzaldehyde comes into the market 
nearly always free from prussic acid; but yet, it is occasionally 
met with containing that acid—which has of course been added 
by the manufacturer to supply an order. The usual method of 
testing bitter-almond oil for prussic acid is as follows :—From 
10 to 15 drops of the oil are shaken up with 2 or 3 drops of 
30-per-cent. soda solution. To this is added a few drops of a 
solution of slightly oxidized sulphate of iron. After another 
vigorous shaking, the liquid is slightly acidified with dilute 
hydrochloric acid. When the precipitate is dissolved, the presence 
of prussic acid is manifest by the appearance of the characteristic 
blue deposit. The least trace of prussic acid may be detected in 
this way. Or, the oil may be dissolved im alcohol and a solution 
of potash and sulphate of iron added ; then, on the addition of a 
dilute acid, Prussian blue is formed. 
A sure and delicate test-paper for indicating the presence of 
* Ber. Deutsch. chem. Ges. xiii. p. 2013; xiv. p. 1425. 
+ Benzyl chloride, C,H.CH,Cl, is prepared on the large scale by the action of 
chlorine on boiling toluene (Ann. Chem. Pharm. ccxxi. p. 365), the toluene 
being contained in large glass balloons heated by a bath of calcium chloride, and 
the chlorine passed through in such a manner that it chiefly comes in contact 
with the vapour of the toluene. This is effected by only allowing the leaden 
conducting tube, which terminates in a short piece of glass tubing, to dip a 
small distance below the surface of the boiling liquid. The vapours of toluene 
are condensed by a cooling arrangement and the hydrochloric acid evolved is 
led into water. The product is washed with water containing a little caustic 
soda, and the benzyl chloride freed from unaltered toluene and higher substi- 
tution-products by distillation. Benzyl chloride is a colourless liquid, the 
vapour of which has a penetrating aromatic smell, rapidly produces a flow of 
tears, and attacks the mucous membrane most violently. It boils at 176° and 
has a sp. gr. of 1:107 at 14°. 
