Chemistry of Essential Oils

410 THE CHEMISTRY OF ESSENTIAL OILS

tion described on p. 389 are as follows, and certain of the samples were
checked by means of a Carius determination :—

No.

i—i

Q 3 4 5 6 7 8

Lime Method

Chlorine, per Cent.

•19

Not weighable

•20

•19

nil

•17

•28

•17

Sulphuric Acid

Method, per Cent.

1-83

0'13

1-8

1-7

trace

—

Nitro-sulphuric

AriH MfitlinH

per Cent.

2-14

0-13

1

*

9

1-7

trace

1-63

2-66

1-42

Carius Method,

per Cent.

2'2

0-15

2-0

1-9

trace

The United States Pharmacopoeia have adopted the method devised
by Sadtler, but this is not very satisfactory. It is based upon the forma-
tion of the phenylhydrazone. The benzaldehyde is added to an excess
of phenylhydrazine in alcoholic solution, and the phenylhydrazone is
filtered off. The uncombined phenylhydrazine is then neutralised with
semi-normal hydrochloric acid, and the amount of acid required is de-
ducted from the quantity required to neutralise the same quantity of
phenylhydrazine in a blank experiment. Unfortunately, the end point
with methyl orange is not sharp, and the method cannot be considered a
satisfactory one. The low minimum of benzaldehyde required for ben-
zaldehyde and bitter almond oil (85 per cent.) is practically an admission
that low results are obtained by this process. The method devised by
Ripper gave better values, although these, too, are only approximately
accurate. Eipper shakes up the aldehyde with a bisulphite solution of
known strength and titrates back the excess of bisulphite with iodine
solution at a low temperature. According to Dodge, the most suitable
manner of carrying out this method is as follows: 0

• 15 gram aldehyde
  or bitter almond oil is weighed in a flask containing exactly 25 c.c. of a,
  say, i n. bisulphite solution, and brought to solution by gentle shaking.
  The flask is then closed, left standing in ice water for one and a half to-
  two hours, after which the ice-cold solution is titrated with deci-normal
  iodine solution, starch being used as an indicator. A blank test is carried
  out in the same way, the benzaldehyde-content being calculated from
  the difference (1 c.c. deci-normal iodine solution = 0


• 
  

  0053 gram benzal-
  dehyde). The reaction is completed as soon as the blue colour persists
  for a few seconds. By this method Dodge, in the case of pure benzalde-
  hydes, found from 94*8 to 99'0 per cent.
  Determination with hydroxylamine (Walther's method as modified by
  A. H. Bennett) offered no advantages as compared with the iodometric
  process, inasmuch as in the case of pure benzaldehydes only 93

  
  

• 5 and
  95'1 per cent, were found. On the other hand, the estimation with
  phenylhydrazine recommended by Denis and Dunbar gives useful,
  although at times rather too high, values (95-1 to 100'9 per cent.), but
  in this method the unstable character of the reagent is a disadvantage.
  In this process 10 c.c. of a solution of the oil of 5 per cent, strength are
  mixed with 10 to 15 c.c. of a fresh 10 per cent, solution of phenylhy-
  drazine, the liquid shaken, the flask tightly closed, and allowed to stand