1903.] MABERY—THE COMPOSITION OF PETROLEUM. 53 
It is well known that paraffine breaks down very readily into 
hydrocarbons with lower molecular weights, but it is not possible 
to polymerize the lower hydrocarbons into the solid paraffine hydro- 
carbons. The tendency in cracking of any constituents of petro- 
leum is toward the formation of the lower series and finally carbon 
in the form of coke. So far as experimental evidence and observa- 
tion have shown the nature and relations of the hydrocarbons 
which compose the different series in petroleum, the conclusion is 
convincing that the lower members of the series were formed from 
the higher. A single break in the ring of a methylene is sufficient 
to form by the addition of hydrogen a paraffine hydrocarbon. 
In answer to the third question, as to the formation of the sul- 
phur, nitrogen and oxygen compounds in petroleum, these bodies 
have evidently not been built up synthetically, but are the products 
of decomposition of more highly organized constituents of organic 
bodies. It would seem that the small proportions of these bodies 
in Pennsylvania oil, as compared with the larger proportions in the 
limestone oils and California oil, should be strong evidence in 
favor of a different origin, that Pennsylvania oil came from organic 
vegetable remains, which should permit of the small amounts of 
sulphur and nitrogen compounds found in this class of oils. 
But I think it can be asserted as a fact that the very large pro- 
portion of nitrogen compounds in California petroleum, amounting 
to one-fifth or more of the total weight of the oil, can only be 
accounted for by accepting animal remains as the source of their 
formation. As a summation of what is at present known of the 
origin of petroleum, the following answers may be given to the 
questions propounded above: 
1. Petroleum containing large proportions of the volatile hydro- 
carbons, especially of the series C,H.,4., such as Pennsylvania 
petroleum, was formed from vegetable organic matter. The lime- 
stone petroleum and California petroleum was formed from organic 
matter of animal origin. 
2. Cellulose, starch and other similar bodies in plants, and the 
fats and nitrogen compounds in animal bodies, by gradual decom- 
position with exclusion of air, gave first the heavier bodies found 
in petroleum, and by natural agencies during long periods of time, 
with no considerable rise in temperature, further decomposition 
included as products the hydrocarbons with smaller molecular 
weights. 
