166 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 
formule, boiling-points, elementary difference, and the corresponding difference of 
boiling-point. 
1. Of the Hydrocarbons obtained from Pennsylvania Petroleum. 
Ist SERIEs. 
« Range of Tempera~- 
Formula. Boiling-point. eae’ parame por bicmoee ee a 
founds distil.t 
fo} Q ° 
Cy Hy 0.0 (?) 
Cy Hie 30.2 C, H, 80.2 15 
C.. His 61.3 C, H, 31.1 0.8 
Cy Ay 90.4 C,H, 29.1 1.0 
Cig Ais 119.5: C, H, 29.1 1.0 
Cis Hoy 150.8 C, H, 31.3 0.8 
150.8 + 5 = 30°.16 
Average increment of boiling-point for the addition of C, H, == 30°.16. 
* Tn considering this question I shall include the boiling-points of the substances which I have separated 
from Pennsylvania petroleum, and the oil distilled from Albert coal; reserving for a subsequent memoir all 
other facts which have been derived from the study of these bodies. 
{ The ranges of temperature given in this and in the corresponding columns of the following tables, are 
for the purpose of showing the impossibility of there: having been any essential error in the determinations of 
the boiling-points ; as is evinced by the facet, in each case, that the whole product was found to distil without 
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 
much value as proof of the existence of the two parallel series in petroleum and in coal-oil, with boiling-points 
so near together; [as shown by comparison of the boiling-points of the first with the second series from petro- 
leum ; and also of the two corresponding series from Albert coal-oil]; especially if this is considered in con- 
nection with the fact, so far as my experience goes, that the quantities of material in one series are generally 
about equal to those in the other. 
That no erroneous conception may be formed as to the degree of purity of the substances treated of 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 cases, 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 
0°.8. Likewise, by reference to the “Determination of boiling-point” of toluole it will be observed that 
it was found to boil absolutely constant 48 minutes; while the range of temperature given in the table 
referred 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 
