S. F. Peckham on the Distillation of Hydrocarbons. 15 
large group, the higher members of which have very high boil- 
ing points ; or perhaps there is still another group containing 
a still larger proportion of carbon. As the different members 
of these groups decrease in density, the proportion of hydrogen 
increases, and as they increase in density, the proportion of 
carbon increases. The process of “cracking” Pennsylvania 
oils, therefore, is simply subtraction of carbon ; and it appears 
om the results of experiment and analysis, that each addi- 
tional atom of carbon is held by a feebler affinity than the last, 
consequently the stability of the members increases as the pro- 
portion of carbon decreases. The lower the member is in the 
series, the stronger is the affinity of the hydrogen for the car- 
bon, and consequently, the higher is the temperature required 
for the production of the member next below it. Thus it is 
that over-heating dense paraftine oils produces medium or illu- 
minating oils; over-heating illuminating oils produces still 
lower and more volatile liquids ; at a still higher temperature 
the products become gaseous, and at an excessively high tem- 
perature, light rather than heavy carburetted hydrogen gas is 
produced, 
In the absence of actual demonstration by fractionation, I 
am led to believe from the behavior of California petrole 
that they do not contain either the Naphtha or Beta-naph- 
tha series in appreciable quantity ; nor do they contain the 
members of the Pittoleum group yet isolated im large propor- 
tion, but are doubtless made up of the higher members of that 
group, or a still more highly carbonized and unstable group 
not yet described, with which is mingled one or more nitro- 
hydrocarbons yet more easily decomposed. Be this fact or fancy, 
the appearance and physical properties of the refined pressure 
distillate from these oils, lead to the opinion that it is made up 
of the same members of which refined Pennsylvania petroleum 
is composed. The lightest oils existing in crude California 
petroleum change in a few. weeks, after treatment, to a 
yellow color, even when tightly corked and exposed only to the 
light. A bottle of refined pressure distillate in my possession 
has now been prepared nearly two years, yet its color has 
