The presence of piperitone can be determined somewhat readily in Eucalyptus oils, as the crystalline compound formed when treated with sodium-amalgam in ether-alcohol solution is quite characteristic. The crude oils of some species, particularly that of E. dives, may be employed directly, but those in which piperitone is only present in small amount should first be fractionated. 10 c.c. of the oil are added to twice the volume of a mixture of ether and alcohol, or even 90 per cent. alcohol alone, and the necessary amount of sodium amalgam added. After some time an insoluble crystalline product will have formed if piperitone be present; this can be filtered off, purified from boiling alcohol, and the melting point determined.

For quantitative determination the method of Burgess (Analyst, March, 1904) can be applied, as the reaction with piperitone goes quite smoothly, using a 35 per cent. solution of neutral sodium sulphite. 5 c.c. of the oil are introduced into a 200 c.c. flask, with the neck graduated in 1/10 of a c.c. The sodium sulphite solution is then added, together with two or three drops of ordinary phenolphthalein solution; the flask is then placed in a boiling water bath and thoroughly shaken. The red colour formed is neutralised with a 10 per cent. solution of acetic acid, and the process repeated until the formation of the red colour does not take place on further heating. The unabsorbed oil is then lifted into the neck and read off when cold; the difference between that amount and the 5 c.c. taken gives the quantity absorbed, and this, multiplied by 20, the percentage of piperitone.

It is hardly likely that Eucalyptus oils other than that of E. dives will be employed for the commercial production of piperitone, and as the fractionation can be readily carried out, the commercial article should not contain less than 90 per cent. of that ketone.