28 SUBSTANCES SOLUBLE IX PETROLEUM SFIEIT. 



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. Stearojjfencs, etc. — The following are the more important 

 constituents of ethereal oils that have up to the present time 

 been observed : Terpenes of the composition CjoH^q often boiling 

 at 155° to 157°; polymers of the same, of the formula C15H24 

 and C00H32, boiling frequently at about 190° or about 250° ; 

 oxygenated compounds of the formula C^QHgoO, C^oH^gO, C^oHjßO, 

 CiqHj^O, C10H12O, C^QRy2^.2 ; hydrocarbons of the formula C^oHi^ 

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

 CnHg,, series. Of these constituents of oils, it is noticeable that 

 those containing oxygen crystallize in the cold more readily than 

 hj-drocarbons of the formula Cj^Hj^, 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 = CH^,,). 



If su.ch a stearojJtene has been isolated, its purification shovJd 

 be attempted bj' repeatedly crystallizing from alcohol or ether, 

 j)ressing 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, Avith 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^^Hg^ and 

 C^qH-jo, yield very characteristic colour reactions with the re- 

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

 terpenes of the formula CjqHjq show less inclination to give 

 marked reactions. These latter oils may often be purified for 

 lütimate analysis by distillation over metallic sodium. 



§ 32. Other Coiidituents. — Besides the constituents already men- 

 tioned — which indeed, although frequently agreeing in their 



