MABERY. — THE COMPOSITION OP PETROLEUM. 583 



After establishing a homologous series by analysis, evidently the only 

 means available for Pelouze and Cahours to determine the molecular 

 size of the hydrocarbons was to assume that a hydrocarbon constituted 

 the chief portion of any distillates that collected in unusually large 

 amounts, and to compute the series in unbroken order from the lower 

 members. 



Several attempts were made to ascertain the presence of the hydro- 

 carbon C 2 oH 42 ; but the distillates between the limits 215° and 225° 

 were small, and in none of them did the molecular weight obtained 

 correspond to this formula. 



Heneicosane, C 2 iH 44 , and Liquid Hydrocarbon, C 2 iH 42 . 

 From Distillate 230° -232°, 50 mm. 



Larger quantities of distillates amounting to 200 grams collected at 

 230°-232°, for the most part at 230°-23 1° • The specific gravity of the 

 unpurified distillate was 0.8321 ; after purification it gave 0.8230. A 

 combustion of the purified oil gave the following percentages of carbon 

 and hydrogen : — 



0.1540 grm. of the oil gave 0.4813 grm. CO., and 0.1968 grm. H 2 0. 



Calculated for 

 CnILn C,,H W . 



Found. 



C 85.70 85.14 85.23 



H 14.30 14.86 14.32 



There was evidently some loss in this analysis, but the percentages 

 are more satisfactory for the formula C 21 H 42 . It will be shown that this 

 distillate was a mixture of a solid hydrocarbon with an oil of higher 

 specific gravity. Its molecular weight was determined at the freezing 

 point of benzol. 



I. 1.4807 grm. of the oil and 25.9125 grms. benzol gave a depression 



of 0°.949. 

 II. 0.6845 grm. of the oil and 19.48 grms. benzol gave a depression 

 of 0°.579. 



Calculated for Found. 



C 21 II 4; , C 21 H 44 . I. II. 



294 296 295 297.4 



The index of refraction of this hydrocarbon was found to be 1.4608, 

 corresponding to the molecular refraction : — 



