CHEMICAL RELATIONS BETWEEN WATER AND HYDROCARBONS. 101 
disseminated sulphur are not uncommon along the western edges 
of the Coalinga and Midway-Sunset fields, and it seems probable that 
these accumulations have been derived from sulphate by the reducing 
action of hydrocarbons. 
The other important gaseous product of the reaction between 
sulphate and the hydrocarbons is carbon dioxide. As already 
stated, there is almost invariably sufficient carbonic acid to form 
bicarbonate exclusively in the waters in the zone of alteration, and 
in addition many of these waters contain a dissolved excess of free 
carbon dioxide. Unfortunately, the few determinations that have 
been made of the quantity of free carbon dioxide give no idea of the 
amount present in the water underground. The writer has seen 
several waters so heavily charged that they effervesced when they 
were brought to the surface, and the dissolved gas may cause some 
waters to rise or flow. Free carbon dioxide is present also in many of 
the modified waters above the zone of alteration, but it has not been 
observed in the normal waters, in many of which a deficiency of 
carbon dioxide and the consequent presence of some normal carbonate 
are observable. 
The hydrocarbon gas of many of the California fields contains a 
considerable proportion of carbon dioxide, much of which, in the 
writer’s opinion, has probably been formed in the same manner as 
the free, half-bound, and combined carbonic acid associated with 
the oil-field waters. In general, the gas in the shallower western 
portions of the Coalinga and Midway-Sunset fields contains more 
carbon dioxide than that in the deeper eastern portions. In other 
words, the natural gas near the outcrop generally contains more 
carbon dioxide than that several miles away. This is to be expected 
if the carbon dioxide is formed by the interaction of the sulphate 
water and the hydrocarbons, for most of the sulphate water enters 
the strata at their outcrops and it is therefore in this locality that the 
reaction should be most vigorous. The percentage of carbon dioxide 
in the gas generally ranges between 3 and 25, but the gas from a 
well about 600 feet deep in sec. 22, T. 19 S., R. 15 E., in the Eastside 
Coalinga field,'contains 49 per cent of carbon dioxide. As carbon 
dioxide is inert it acts as a diluent in natural gas and lowers its 
heating value. The following table shows analyses of gas from wells 
in the Coalinga, Midway, and Sunset fields. 1 Analysis 7 represents 
gas from the deep eastern part of the Midway field; it will be noted 
that the carbon dioxide is low in this gas, and a number of other 
analyses of gas from the same locality show still smaller amounts. 
1 A few other analyses are given by I. C. Allen and W. A. Jacobs (Physical and chemical properties of the 
petroleums of the San Joaquin Valley of California: U. S. Bur. Mines Bull. 19, p. 56,1912) 
