118 ETIIEUEAL OILS. 



evaiDoration is less than O'OOl. 10' cc. Avould, therefore, contain 

 0"163 gram instead of 0-1 G6 gram. 



^137. Estimation u-ith Bisulphide of Carbon.— Instesid of petro- 

 lenm spirit, Osse also tried bisulphide of carbon, as recommended 

 by Hager ^ for the quantitative estimation of camphor, as well as 

 mixtures of both liquids, without attaining better results. He 

 has therefore decided in favour of petroleum spirit alone, which, 

 however, should not contain any oils boihng at a temperature 

 higher than 40° C. 



In analyzing vegetable substances such a petroleum spirit is 

 preferable to mixtures of the same with bisulphide of carbon, as 

 it has a lesser solvent power for resins, etc. Ethereal oils may 

 be extracted from their aqueous solutions by petroleum spirit,^ 

 and may therefore be estimated in the aqueous portion of the 

 distillate (§ 24) by shaking with that solvent and evaporating a 

 measured quantity of the solution after separation from the 

 aqueous liquid. I have also employed this method for estimating 

 the essential oil in the official ((romatic uxiters. 



§ 138. Influence of Fixed Oil. — Osse also made experiments with 

 the view of ascertaining Avhether the presence of fixed oil could 

 affect the determination of ethereal oil, either by itself increasing 

 in weight during the exposure to the air or by preventing the eva- 

 poration of the ethereal oil at 110" C, He found that a prettj^ 

 close approximation to the truth might generally be arrived at by 

 deducting 0-09 to O'l per cent, from the weight of the fat after 

 heating to 110°. No ajipreciable error would be caused by the 

 oxidation of the fixed oil during the evaporation of the petroleum 

 spirit, as the presence of the latter, even in small quantities, pie- 

 vents or delays such change. 



0-875 gram olive oil Avas mixed with O-Ool gram oil of turpen- 

 tine and heated for an hour to 110^ C. The weight of the 

 residue was 0'87;") gram, which did not alter if the heating were 

 •continued two hours longer. 



1'426.') gram olive oil and 0'0r)75 gram oil of cinnamon weighed 

 after 



' Pharm. Centralblatt, xiii. 449. 



- Drageiidorff, paper read at a meeting of the German ' Apothekerverein ' 

 in Cologne, 1873 ; ' Ermittehing der (Jifte,' 2nd ed., 46, 187<J. 



