30 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
uniformly distributed, and all solutions have definite properties, 
which depend on the nature and proportional amounts of the sub¬ 
stances of which they are composed. By chemical analysis of 
water only the proportional amounts of the constituents are deter¬ 
mined. The nature of each constituent, that is, its conduct toward 
other substances whose natures are known, has been learned by other 
methods, and as the properties of a solution are an assemblage of 
the properties of all its constituents, the properties of a water may 
be deduced from the statement of its analysis. 
The amount and character of the mineral substances dissolved in 
different waters vary greatly and depend on many factors. Chief 
among these are the chemical character and physical condition of 
the materials encountered, the heat and pressure, the duration of 
the contact, and the amount and character of the substances pre¬ 
viously dissolved. Water Under a given temperature and pressure 
can dissolve only a definite amount of any substance; and if the 
heat and pressure are lowered, as, for example, when an underground 
water emerges at the surface, the excess of dissolved matter may go 
out of solution as a precipitate. It is through this readjustment to 
changed conditions that mineral matter is deposited around some 
springs or wells. Similarly, if two waters carrying different salts 
in solution come into contact, a chemical reaction may take place 
and some of the dissolved material may be precipitated. Although 
many of the reactions that take place are obscure and can not be 
completely explained, the properties of natural solutions, which are 
the net results of these reactions, furnish a rational basis for general 
classification. 
In addition to dissolved mineral solids or gases, which chiefly deter¬ 
mine the chemical properties of a water, two other classes of sub¬ 
stances are generally present—material in suspension, which can be 
removed by filtering, and material in colloidal solution, a state inter¬ 
mediate between suspension and true solution. In the present 
study consideration has been given chiefly to the commoner dis¬ 
solved mineral substances. Small amounts of several elements, such 
as lithium, barium, phosphorus, and boron, are probably present in 
some of the oil-field waters, but they do not materially affect the 
quality of the water and their determination is not essential to a 
study of the relations of water to petroleum. 
COLLECTION OF SAMPLES. 
In most districts the collection of representative water samples for 
analysis is a simple matter, but in the oil fields, where the universal 
aim is to shut the water out of the wells, it is often very difficult. In 
wells that supply water for industrial uses the depth of the water 
sands is generally known, and samples can, of course, be easily taken, 
