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 iraotional distillations which may hare to 

 be pel-formed in the analysis of plants, small flasks provided with 

 the dephlegiuators recommended by Linneman may be used. 

 <Cf. § U3.) 



§ 31. Stearoptmes, «fc.— The following are the more important 

 constituents of ethereal oils that have up to the present time 

 been observed : Terpenes of the composition Ou)H,s often boiling 

 at 155° to 157°,- polymers of the samet of the formula CijHj^ 

 and CjjHjjj, boilbg frequently at about 190° or about 250°; 

 oxygenated compounds of the formula C^jHjpO, CiDH^gO, C^gHjgO, 

 CioH,p, CioHigO, CioHijOg, hydrocarbons of the formula C„Hi4 

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

 C^Hjn aeries. Qf these constituents of oils, it is noticeable that 

 those containing oxygen crystallize in the cold more readily than 

 hydrocarbons of the formula CjjHjg, and to the former, therefore, 

 our attention must be specially directed in the examination pf 

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

 the exception of otto of roses = C„H2„). 



If such a stearoptene has been isolated, its purification should 

 be attempted by repeatedly crystallizing from alcohol or ether, 

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

 efBcient 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 whetiier 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 contaiining oxygen, as well 

 as those containing hydrocarbons, of the f6rmula CuHj^ and 

 CjoHgj, yield very characteristic colour reactions with the re- 

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

 terpenes of the formula C,(,Hjg show less inclination to give 

 marked reactions. These latter oils may often, be purified for 

 ultimate analysis by distillation over metallic sodium. 



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

 tioned — which indeed, although frequently agreeing in their 



