Eucalyptus-Oils of Victoria. 207 



This determination of the proportions of tlie two ingredients 

 from the density of the mixture can be controlled by a similar 

 calculation in connection with the specific refractive energy. It 

 is well known, that if r^ and r^ are the specific refractive energies 

 of two substances present in proportions /j and p.^ by weight and 

 r the sp. ref. energy of the mixture 



(/i + p;)r ^ pi r\ + /. r.,. 



and px + /., = 100, then /, = 100 ^ ~ ^^ 



^ ^ - ^ r\ - r^ 



According to this formula the sp. ref. energies ought to vary 

 steadily with the densities, if the oils consisted of two main 

 ingredients, and they do vary steadily on the whole, but with 

 marked exceptions, showing that individual oils cannot be taken 

 as mixtures of only the two main substances. By applying the two 

 formuliB (density and sp. ref. energy) to the measurements for an 

 oil, it can be ascertained by the agreement of their results 

 whether the oil is a mixture of a Terpene and Cineol or not. 



As another physical constant, whose measurement might be 

 expected to give definite indications as to the proportions of the 

 two main ingredients in a Eucalyptus- Oil, the viscosity seemed 

 promising, as the viscosity of Cineol at ordinary temperatures 

 would naturally be expected to be much larger than that of a 

 Terpene, seeing that it is much nearer its solidifying point ; thus, to 

 test the applicability of measurements of viscosity to the analysis 

 of the Eucalyptus-Oils, the following experiments were made. 



A cylindrical glass separator of 170 c.c. with a tap at the 

 bottom had 40 cm. of circular capillary tube connected to it by 

 an india-rubber joint. The whole was so arranged that the 

 capillary hung vertically from the separator, so that its upper end 

 was 30 cm. from the maik on the neck of the separator to which 

 the oil was filled up in every case. The time was noted for 20 

 c.c to run through the capillary ; under these circumstances the 

 viscosity is proportional to the time taken and to the density of 

 the liquid ; to obtain the specific viscosity referred to, water at 

 16-5°C. as 100, all that is necessary is to multiply 100 times the 

 time taken by any oil by its density, and to divide by the time 

 for water. The following are the results for certain oils and 

 mixtures : — 



