28 SUBSTANCES SOLUBLE IN PETROLEUM SPIRIT. 



about 250. This knowledge forms, of course, a good basis on 

 which a separation may be attempted. 



For these and other fractional distillations which may have to 

 be performed in the analysis of plants, small flasks provided with 

 the dephlegmators recommended by Linneman may be used. 

 (Cf. 143.) 



31. Stearoptenes, etc. The following are the more important 

 constituents of ethereal oils that have up to the present time 

 been observed : Terpenes of the composition C 10 H 16 often boiling 

 at 155 to 157; polymers of the same, of the formula C 15 H 24 

 and C 20 H 32 , boiling frequently at about 190 or about 250 ; 

 oxygenated compounds of the formula C 10 H 20 0, C 10 H 18 0, C 10 H 16 0, 

 C 10 H 14 0, C 10 H 12 O, C 10 H 12 2 ; hydrocarbons of the formula C 10 H M 

 are more rarely to be found ; still less frequently those of the 

 C n H 2I1 series. Of these constituents of oils, it is noticeable that 

 those containing oxygen crystallize in the cold more readily than 

 hydrocarbons of the formula C 10 H 16 , and to the former, therefore, 

 our attention must be specially directed in the examination of 

 the crystalline ' stearoptenes ' obtained by cooling the oils (with 

 the exception of otto of roses = C n H 2n ). 



/" If such a stearoptene has been isolated, its purification should 

 T be attempted by repeatedly crystallizing from alcohol or ether, 

 i pressing the crystals each time between blotting-paper. The co- 

 efficient of refraction may then be ascertained in the alcoholic 

 solution of the pure substance ; the melting-point, boiling-point, 

 and vapour-density determined ; and, finally, an ultimate analysis 

 made. It should also be ascertained whether hydrocarbons can 

 be obtained by distillation over phosphoric anhydride or chloride 

 of zinc. 



The liquid portions of the various fractions should be subjected 

 to similar experiments, with the exception of the last. It will 

 frequently be found that ethereal oils containing oxygen, as well 

 as those containing hydrocarbons, of the formula C 15 H 24 and 

 C 20 H 32 , yield very characteristic colour reactions with the re- 

 agents detailed in 28, 142 ; whilst oils consisting principally of 

 terpenes of the formula C 10 H 1G show less inclination to give 

 marked reactions. These latter oils may often be purified for 

 ultimate analysis by distillation over metallic sodium. 



32. Other Constituents. Besides the constituents already men- 

 tioned which indeed, although frequently agreeing in their 



