CHEMICAL RELATIONS BETWEEN WATER AND HYDROCARBONS. 103 
produced in the Buena \ ista Hills is used it also becomes heavier and 
more viscous and passes to a substance resembling solid asphalt. 
The chemical reactions involved in this change are probably of two 
kinds. A part of the sulphur may combine with certain oil con¬ 
stituents to form simple sulphur compounds or complex sulphur 
derivatives, another portion may unite with some of the hydrogen 
of the oil and pass off as hydrogen sulphide. By the loss of hydrogen 
a condensation or polymerization of the hydrocarbon molecules is 
effected, and this change is reflected in the increase in the gravity of 
the oil itself as it approaches solid asphalt. Oxygen acts in a similar 
way; some of it may be taken into combination to form complex 
acids or phenols and part of it may unite with the hydrogen of the 
oil to form water. 1 Oxygen has been determined in so few analyses 
of oil from the San Joaquin Valley fields that its relation to the 
gravity of the oil, except in a very broad way, is not known; but 
the percentage of sulphur has been determined in a great many 
samples and appears to bear a fairly constant relation to the gravity 
of the oil. If more than 0.75 per cent of sulphur is present the specific 
gravity of the oil is generally greater than 0.945 (18° Baume). The 
sulphur content of oils of 0.985 to 1.000 specific gravity (12° to 10° 
Baume) is usually 1 per cent or more, whereas that of oils of 0.875 
to 0.905 gravity (30° to 25° Baume) is generally less than 0.50 per 
cent. 2 
That oxygen and sulphur may be important agents in determining 
the character of petroleum is evident from the likelihood that the oil 
in its migration will encounter one or both of these common elements 
in some available form. Oxygen is probably the less important under 
ordinary conditions, but in some places the oil doubtless derives oxy¬ 
gen from oxygenated waters, and in others it may possibly be con¬ 
tributed locally by oxidizing agents such as manganese dioxide. The 
action of sulphur is probably more widespread, and sulphur is believed 
to be afforded abundantly by the reduction of the sulphate waters. 
There are other possible sources of sulphur, but they need not be con¬ 
sidered here. 
It is evident that in any one field the action of both oxygen and 
sulphur on the oil will be more or less localized, since ordinarily the 
quantity of these substances available is insignificant as compared 
with that of the petroleum. Most of the oil in the San Joaquin 
1 Mabery, C. F., and Byerly, J. H., The artificial production of asphalt from petroleum: Am. Chem. 
Jour., vol. 18, p. 141, 1896. See also Hausmann, J., and Pilat, S., Studien fiber die Oxydation der Petrol- 
kohlenwasserstoffe: Cong, internat. p^trole Compt. rend. sess. 3, p. 378,1907. 
2 Analyses of oil from the oil fields of San Joaquin Valley are given in the following publications: Arnold, 
Ralph, and Anderson, Robert, Geology and oil resources of the Coalinga district, Cal., with a report on the 
chemical and physical properties of the oils, by I. C. Allen: U. S. Geol. Survey Bull. 398, pp. 264-272, 1910. 
Allen,I. C.,and Jacobs, W. A., Physical and chemical properties of petroleums of the San Joaquin Valley 
of California: Bur. Mines Bull. 19,1912. Allen, I. C., Jacobs, W. A., Crossfield, A. S., and Matthews, R. R., 
Chemical and physical properties of the petroleums of California: Bur. Mines Tech. Paper 74,1914. 
