277 
ON THE COLOURING PRINCIPLE OF VOLATILE OILS AND A 
NEW BODY, AZULENE. 
BY SEPTIMUS PIESSE, F.C.S. 
It is generally known that essential oils or ottoes of plants have peculiar and 
characteristic colours, they are either yellow, blue, green, brown, or white, i. c. 
colourless. 
Having made some progress towards the discovery of the nature of the matters 
which impart these several colours, I now record the facts ascertained. 
The principal interest rests with the blue substance which gives colour to the 
otto of chamomile, because this same body is present in other volatile oils and 
imparts to them a green colour, being at the time under disguise by a yellow 
resin, which is also present in volatile oils of a green tint. 
When blue otto of chamomile is subjected to fractional distillation, the white 
hydrocarbon anthemidine is easily separated from the blue colouring, because 
the latter requires a much higher temperature to vaporize it than the former. 
By the fractional distillation of otto of wormwood, Absinthii, I obtain first a 
nearly colourless hydrocarbon, then at the third fractioning an oil having a 
brilliant green colour, which at the fifth fractioning divides into a blue oil and 
a residuary yellow resin. 
Wheb otto of Patchouly, obtained by distilling with water the Indian herb 
Pogostemon Patchouly , is subjected to fractional distillation, I obtain in like 
manner, first a colourless hydrocarbon, then, but not till the eleventh fractioning, 
a beautiful blue oil and a brown-yellow residue ; the great number of fraction¬ 
ings required to separate the blue oil in this case is caused by the closer boiling- 
points between the patchouly hydrocarbon, the blue oil, and the resin, all of 
which are exceedingly high. The otto of bergamot from the rind of the fruit, 
Citrus bergamia , as also otto of Ceylon Lemon-grass, Anclropogon Schoenanthus , 
yield by the same treatment small portions of this blue colouring. By repeated 
rectification of the blue fluid, from whatever source derived, I at length render 
it free from extraneous matter and in a state of purity, it then has a fixed boiling- 
point of 576° Fahr., its sp. gr. 0-910; when boiled, it produces a dense vapour of 
a blue colour, having special optical* characters. I have named this substance 
Azulene, from azure—blue. The analysis of Azulene shows its formula to be :— 
C 16. 82-05 81-21 
II 18. 11-12. 10-95 
O. 6-83. 7-84 
100-00 100-00 
Or, C 10 H 12 -j~IIO, 
The yellow colouring-matter which imparts its tint to the several ottoes, ap¬ 
pears to be an oxidized portion of the otto so stained. In nearly all instances, 
* Sir David Brewester lias optically examined two blue ottoes which owe their colour to the 
presence of azulene, namely Matricaria Chamomilla and Achillea Millefolium. “ Without 
entering,” says Sir David, “into details respecting the general action of these oils upon. the diffe¬ 
rent-coloured portions of the spectrum, I shall confine myself to a slight notice of their specific 
action in which they differ from all the various bodies which I have yet examined. 
“ Between the two lines A and B, of Fraunhofer’s map of the spectrum, there are two groups 
of lines shown in that map. The two oils absorb the light in these portions more powerfully 
than in the portions adjacent to them. No other fluid or solid on which I have made experi¬ 
ments acts in a a similar manner; but what is very remarkable, the earth’s atmosphere exercises 
a similar action when the sunlight passes through its greatest thickness at sunrise and 
sunset.” 
