200 c.c. of an ordinary commercial oil of E. dives were subjected to distillation under reduced pressure, and after the removal of the lower boiling terpenes, two fractions were obtained boiling at 11 millimetres pressure: -

These two fractions were repeatedly distilled at 11 millimetres until a portion, boiling at 108° C. and containing 98 per cent. ketone, was obtained. This had specific gravity at 150 C. = 0.9392; rotation aD - 50.02°, and refractive index at 200 = 1.4850.

Another commercial sample of oil of E. dives was first distilled under reduced pressure and the ketone fraction separated; the piperitone was then prepared in the pure condition by the aid of sodium bisulphite. This had specific gravity at 20° C. = 0.9348; rotation aD - 40.05°; refractive index at 20° = 1.4837, and boiled at 106-107° under 10 millimetres pressure, and at 229-230° (uncorr.) at 760 millimetres.

There appears to be no uniformity in optical rotation with the several samples of piperitone which have so far been separated, and it is thus evident that the left rotation is only the predominant form.

Analysis of piperitone showed the formula to be' CIOHl6O. 0.1064 gram, gave 0.3067 CO2 and 01030 H2O.

C. = 78.62, and H. = 10.75 per cent. C10H16O requires C. = 78.94, and H. = 10.53 per cent.

The molecular refraction calculated for a C10Hl6O ketone with one double bond, is 45.82; found 46.49. It has been shown by Auwers and Hessenland [Ber. 41 (1908) 1812] that menthenones of this character, with a conjugated double bond, require an addition of 0.83 to the aggregate, and if this addition be made for piperitone the result is closely theoretical.

The reaction with bromine in chloroform solution showed the molecule to be unsaturated. The bromine was absorbed in quantity, but eventually gave off hydrobromic acid.

The bromide was a heavy mobile oil, and on analysis gave a return of 58.9 per cent. bromine.

C10Hl6Br2O contains 51.2 per cent. Br., and C10HI5Br3O, 61.3 per cent. Br.

With hydroxylamine, piperitone gave a normal oxime and an oxamino-oxime, the former melting at 110-111° C. and the latter at 169-170° C, the oxamino-oxime readily decomposed Fehling's solution, and when boiled with mercuric oxide in alcoholic solution, the mixture assumed a blue colour due to the formation of a nitroso-compound from the NHOH group.

The semicarbazone, prepared with piperitone which had been regenerated from the bisulphite compound, melted at 219-220° C. If it had been prepared with the ketone obtained directly by repeated distillation under reduced pressure, two semicarbazones were formed, the least soluble of these melting at 175-176° C. and the more soluble at 182-183°. The latter was always tinted yellow. The semicarbazones can thus be prepared in three modifications.