106 



RESEARCHES ON THE VOLATILE HYDROCARBONS. 



the addition of C H 



in homologous 



series* 



The data for these considerations may 

 be more conveniently arranged in tabular form, exhibiting at once, in serial order the 

 formulae, boiling-points, elementary difference, and the corresponding difference of 



boiling-point. 



1 . Of the Hydrocarbons obtained from Pennsylvania Petroleum. 



1st Series. 



Formula, 



Boiling-point 



Cg H 10 

 C 12 H 14 

 Ci6 H 18 



C 18 H 



20 



O 



0.0 



30.2 



61.3 



90.4 



119.5 



150.8 



(?) 



Elementary 

 Difference. 





C 2 H 2 

 C 2 H 2 

 C 2 H 2 

 C 9 H 2 



a Ho 



Difference of 



boiling-point 

 found. 



30.2 



31.1 

 29.1 



29.1 



31.3 



Range of Tempera- 

 ture within which the 

 substance would all 

 distil.f 



o 





150.8 



5 



1.5 



0.8 

 1.0 



1.0 



0.8 

 30°.16 



Average increment of boiling-point for the addition of C 8 H 2 = 30M6. 



shall include the boil 



from Pennsylvania petroleum, and the oil distilled from Albert coal ; reserving for a subsequent memoir all 



t 



bodies 



for the purpose of showing the impossibility of there having been any essential error in the determinations of 



boiling-points ; as is evinced 



residue within such narrow limits. With so small a range of temperature, it is evident that it would make no 

 practical difference whether either extreme or the mean of the observations be taken for the boiling-point. 

 The fact that these substances distil without residue within so short a range of temperature, is also of 



[ 



coal 



u 



about equal to those in the other. 



goe 



be formed as to the decree of Duritv of 



-„ «. ww «o lamcepuon may be tormed as to the degree of purity of the substances treated ot in 



this and in the following tables, from a mere inspection of the ranges of temperature here given; and in order 

 that the almost absolute constancy of the boiling-points, in most ca<es, may not be overlooked, I would refer to 

 the preceding memoir for further details concerning the boiling-points of such of these bodies as are therein 

 treated of. For example, it will be found under the head « Determination of boiling-point " of benzole, that in 

 the distillation it required 50 minutes for the temperature to rise 0°.2; while in one of the following tables 

 it will be seen that the range of temperature within which the benzole distilled to dryness was found to be 

 .8. Likewise, by reference to the « Determination of boiling-point " of toluole it will be observed that 

 »t was found to boil absolutely constant 48 minutes; while the range of temperature given in the table 

 re erred to is 0°.7. In such cases as these, the slight rise of temperature which takes place just before going 

 to dryness, is doubtless to be attributed to superheating of the vapor, in consequence of there being so small 



