REFRACTIVE INDICES WITH OTHER DATA OF EUCALYPTUS OILS. 41 



the oil to a dry test tube, using a narrow pipette, and then 

 to run in 2 cc. of the alcohol from a burette, graduated in 

 tenths, and afterwards by drops until the end was reached, 

 agitating between each addition. The solubilities of the 

 oils in alcohol are given in the previously mentioned work, 

 but only in i volumes. The solubility results being of 

 some value, this was not sufficiently delicate, so the more 

 soluble oils were again determined. In no instance, with 

 the crude oils, was solubility reached with an equal volume 

 of 70°/° alcohol. For the more insoluble oils the previously 

 recorded results were used. Although the specific refrac- 

 tive energy has been calculated for each sample, yet these 

 results do not appear to be sufficiently distinctive, or by 

 themselves of any very great value, but if the solubilities 

 are used in conjunction with the refractive indices, very 

 good results are obtained. The best method appears to be 

 to multiply the refractive index by 10 times the solubility 

 result. As the solubility, diminishes the figures increase 

 considerably. Those Eucalyptus oils richest in eucalyptol 

 have the greatest solubility in 70°/° alcohol, and have also 

 the least refractive indices, consequently they stand at the 

 top of the list. Only in one instance — that of a highly 

 rectified commercial oil of E. polybractea — was a less figure 

 than 15 obtained. This method seems to be a good one by 

 which to determine the quality of a Eucalyptus oil of the 

 eucalyptol class, and would be fatal to sophistication. It 

 might, perhaps, be thought preferable to dispense with the 

 factor, and to use the solubility test simply as an indepen- 

 dent check on the refractive index. A standard partly 

 based on these determinations, together with a qualitative 

 test for eucalyptol, might be arranged, and if desired an 

 ester determination might also be made. That the ester 

 content has some influence may be assumed, because in 

 the first 30 of the list of eucalyptol oils, no less than 11 

 contained esters giving a saponification number between 



