426 THE CHEMISTRY OF ESSENTIAL OILS
fruits having a rougher rind, covered with oil vessels, and containing;
an acid and very bitter juice.
A tree twenty to thirty years old yields annually from 15 to 20 kilos-
of flowers. In Grasse alone 200,000 to 300,000 kilos are produced
annually. A hundred kilos yield at least 40 kilos of orange flower
water and 100 grms. of oil.
At an age of twenty to twenty-five years the trees produce the
maximum yield of fruits, usually from 600 to 1000 oranges per annum.
In Spain and Algeria trees exist which produce 2000 to 3000 fruits-
annually. The peel is used for liqueurs and for the manufacture of
marmalade, as well as for the production of the essential oil.
There are three distinct types of essential oil obtained from the
orange, namely, the flower oil, known as neroli oil, the oil from the
leaves and young shoots known as petitgrain oil, and the peel oil,,
known simply as " orange " oil.
Sweet orange oil, prepared in a similar manner to lemon oil, has the
following characters :—
Specific gravity 0-848 to 0-853
Optical rotation-f+ 94° „ + 99°
Refractive index 1-4728 „ 1-4745
On distilling the first 10 per cent, in a Ladenburg flask, this fraction
should have an optical rotation, should be equal to or at most about 1°
lower than that of the original oil. The aldehyde-content, calculated as
decylic al iehyde, determined by the phenylhydrazine method described
under lemon oil, varies from 14 to 2'5 per cent.
On evaporation on a water-bath, sweet orange oil yields from 15 to-
4 per cent, of fixed residue, which has an acid value of 11 to 30 and an
ester value of 115 to 170. Spanish orange oil, however, which is ex-
pressed from a dark-skinned orange, yields from 7 to 9 per cent, of fixed
residue.
West Indian orange oil occasionally has .a refractive index as low as
1'4700, but this is an exceptionally low value.
According to Schimmel & Co., Jamaican sweet orange oil contains-
from 23 to 32 per cent, of aldehydes calculated as decylic aldehyde
from a phenylhydrazine determination, whilst the bitter oil contains only
0*75 to 1-5 per cent.
The oil consists principally of dextro-limonene which is present to
the extent of about 90 per cent, or over. Decylic aldehyde is one of the
principal odorous constituents of the oil; linalol, Z-terpineol, d-terpineol,
nonyl alcohol, methyl anthranilate and traces of caprylic acid esters are
also present.
Bitter orange oil only differs very slightly from sweet orange oil, and
the composition of the two oils is practically identical. The physical
characters of the oils vary to a trifling extent, those of bitter orange oil
being as follows :—
Specific gravity 0-850 to 0-856
Optical rotation + 90° „ + 95°
Refractive index 1-4720 „ 1-4748
Non-volatile residue ...... 2-5 to 4
- 5 per cent.
The optical rotation of the first 10 per cent, distilled should be higher
than, or not more than 1° lower than the rotation of the oil itself.
An orange oil prepared in an abnormal method from Manila oranges
has been examined by Gibbs and Agcaoili,
1
according to whom the
1
Philipp. Jour. Sci., vii., A. 6.