THE CITRINE ODOURS. 71 
to nine tenths of the whole distillate, had a sp. gr. of 0°899, and in 
respect to its formula and molecular weight was identical with 
limonen, but the rhomboid crystals of the tetrabromide melted 
first at 102° to 103°. The principal constituent of the third 
fraction was the sesquiterpene, C,;H.,, which is present in old oils 
in far larger proportion than in new oils ; it has a sp. gr. of 0°9847, 
and does not form a crystalline tetrabromide or dihydrochloride. 
The first two fractions are optically active, but the third is inactive. 
According to Oliveri* the rotatory power of oil of lemon in a 
column 20 centimetres long varies with age between +117° and 
+ 123°, and it is suggested that this character might be utilized 
to detect an adulteration with oil of turpentine. Investigations 
made by Schimmel and Co. indicate the sp. gr. of expressed oil of 
lemon to be 0°857 to 0°863 at 15° C., and the rotatory power in a 
100-millim. tube + 40° 10’ to +62°; the sp. gr. of the distilled 
oil being found 0°856, and the rotation of same +66° 20’. It 
would appear that slight variations in the conditions under which 
oil of lemon is prepared are apt to cause considerable differences 
in the physical properties of the oil, and that a reliable commercial 
oil of uniform strength and free solubility in rectified spirit would 
be of great advantage. 
A so-called ‘‘Terpene-free” oil of lemon has been prepared during 
the last ten years at Pirna-on-the-Elbe. Experiments recently made 
on this oil show that it more readily becomes altered in flavour by 
keeping and by exposure than when mixed in its natural state with 
its own terpene f. 
In various essential oils of the Citrine series Messrs. Schimmel 
and Co. have discovered an aldehyde called citral, C,)H,,O, to 
which is ascribed the aroma. According to their researches, 
normal oil of lemon contains 7} per cent. of citral; but it is 
admitted that, “as it lacks some part of the freshness which cha- 
racterizes good oil of lemon, it should be used mixed with the 
natural product. A mixture of 1 kilo of oil of lemon and 
75 grammes of citral will be equal in strength and aroma to 
2 kilos of oil of lemon (7.e. 75 grammes of citral possess the 
strength of aroma of 1 kilo of oil of lemon).” { In a partial 
* Apot. Zeit. 1891, p. 341. + Ph. J. [8] xxii. p. 876. 
} One ounce of citral in 15 ozs. of 95 per cent. alcohol is considered equivalent 
to 16 ozs. of lemon-oil. Even in liquids containing only 30 per cent. alcohol 
citral forms a clear solution. 
