— 42 — 



solidifying point i8° to 19 ; d 27 o 1,040; «d 2 5° — °°4 o/ ; acid 

 number 42,50; ester number 114 = 3O,9°/ methyl ester of sali- 

 cylic acid 1 ). 



Fennel Oil. A question which was submitted to us some con- 

 siderable time ago, as to the cause of the occurrence that fennel oil 

 is sometimes heavier than water, induces us to return to this subject 

 in this place. When fennel oil 2 ) is kept in an unsuitable manner, 

 that is to say when light and air are admitted, a gradual increase in 

 the specific gravity is observed which may finally bring the latter 

 above 1. 



This increase in the weight is due to oxidation -processes, or occur- 

 rences of polymerisation, as the anethol present in the fennel oil in 

 the presence of light and air partly oxidises into anisic aldehyde and 

 anisic acid, and partly becomes polymerised. The products in question 

 now not only cause an increase in the specific gravity, but also at the 

 same time a greater solubility of the oil. Moreover, the solidifying 

 point is naturally greatly influenced, and finally such oils no longer 

 solidify at all. 



Whereas normal fennel oil has the following properties: d 15 o 0,965 

 to 0,975; solidifying point -f-3 to -j-6°, sometimes over -f-8°; soluble 

 in 6 to 8 vol. and more 80 per cent, alcohol, possibly with cloudiness, 

 we found for an oil which had changed in the manner described above, 

 d 15 o 1,0053; solidifying point — 8°; soluble in 3 vol. and more 80 per 

 cent, alcohol. 



These differences become still more pronounced in the case of pure 

 anethol. An anethol which had been exposed for two years to the 

 influence of light and air, had undergone a remarkable change, as will 

 be seen from the following comparison: 



I. Original anethol: d 25 o 0,9846; «r> ±o°; n D25° 1*56079; solidify- 

 ing point ~j-2i°3 / ; soluble in 2 and more vol. 90 per cent, alcohol. 



II. The same anethol after having been kept for two years, light 

 and air being admitted: d 25 o 1,1245: «d ±o°; n D25° i>549o6; does 

 not yet solidify at — 20 ; soluble in 1,5 to 2 and more vol. jo per 

 cent, alcohol. 



The changed oil had a yellow colour and was less mobile than 

 normal anethol; the taste was no longer like anise, but disagreeable 

 and bitter. By treatment with bisulphite, anisic aldehyde could be 

 isolated, but only traces of anisic acid could be detected. The bulk 

 of the anethol had become polymerised. 



1 ) Comp. our work on the essential oil of acacia blossoms, Report October 1903, 

 18. Journ. f. prakt. Chem. II. 68 (1903), 749. 



2 ) The same applies also to anise oil. Comp. Gildemeister and Hoffmann, 

 "The Volatile Oils", page 561. 



