Chemistry of Essential Oils

444 THE CHEMISTEY OF ESSENTIAL OILS

Citric acid can also be detected by precipitating as calcium citrate.

This test is carried out by saponifying about 2 grams of the oil, or the

residue of evaporation of 5 grams of oil, with alcoholic potash, diluting

the solution with water, neutralising with hydrochloric acid, removing the

alcohol on the water-bath, and then extracting the solution with ether, and

filtering. For the calcium test the solutions are rendered faintly alkaline

with a trace of caustic soda, after which a few drops of concentrated

chloride of calcium solution are added and the whole boiled. Any citric

acid which is present is shown by a precipitate, which is often formed

only after some time.

Oxalic acid, resulting from the use of ethyl oxalate as an adulterant,

is^ similarly detected, the calcium precipitate then 'having the usual char-

acters of calcium oxalate.

With the exception, however, of triethyl citrate, nearly all the non-

volatile esters are to a great extent removed mechanically during the

evaporation in the oil vapour. To detect, for example, glyceryl acetate,

ethyl oxalate, ethyl tartrate, and ethyl succinate, the evaporation should

only be proceeded with until about 10 to 15 per cent, of the oil is left in

the dish, and this residue tested for the various acids.

Terpinyl acetate is indicated by a difference to be observed in the

apparent ester value by different times of saponification. This ester is

far more resistant to the action of caustic alkali than is linalyl acetate,

and requires two hours at least for complete saponification. Hence, if

the oil shows a difference in the saponification value in thirty minutes

and in two hours, which amounts to more than from 1 to 2, terpinyl

acetate is almost certainly present. The following tablel shows the

effect of this partial-saponification on the two esters and on adulterated

oils :—

Time of Saponification.

Linalyl Acetate
Terpinyl „
Bergamot Oil

E. No.

+ 5 °/0 Terpinyl Acetate

+ 10 °/0

+ 25% „

191*5

108-2

80-3

82-5

79-9

78-8

15 mins.

217-5

166-8

94-5

94-8

96-4

100-6

30 mins.

223*2

209*7

97'3

101'2

102*8

1081

45 mins.

223-7

233-4

97-5

102-1

105-2

116-4

1 hr.

223*1

245*8

97*8

104-7

108*3

119*0

2hrs.

224-7

262-7

98-5

107-2

112-5

126-8

Fractional saponification, with the use of varying amounts of caustic

alkali, will also reveal the presence of terpinyl acetate.

The following table will indicate the differences observed when about

N

2'5 grams of the oil are saponified (1) with 20 c.c. of -^ alkali for two

N

hours, and (2) with 10 c.c. of -^ alkali, diluted with 25 c.c. of alcohol for

A

one hour :—

(^1) Schimmel's Report, October, 1910, 60.