acid. The whole mixture is then agitated by means of air pumps, which
bring as much as possible every particle of oil in contact with the
acid. The acid has no affinity for the oil, but it has for the tarry
substance in it which discolors it, and, after the agitation, the acid
with the tar settles to the bottom of the agitator, and the mixture is
drawn off into a lead-lined tank. After the removal of the acid and tar,
the clear oil is agitated with either caustic soda or ammonia and water.
The alkali neutralizes the acid remaining in the oil, and the water
removes the alkali, when the process of refining is finished. A few
refiners improve the quality of their refined oil by redistilling it
after treating it with acid and alkali. All distillates of petroleum
have to be treated with acid and alkali to refine them. There is one
thing peculiar about the distillates of petroleum, and that is that the
run which follows naphtha, which is called "the middle run oil," is the
highest test oil that is made, running as high as 150 and 160 degrees
flash, while the common oil which follows, viz., from 45 down to 33
degrees Baume, will range at only about 100 flash, or 115 and 120
degrees burning lest.

An oil that will stand 100 flash will stand 110 burning test every time.
Kerosene oil, at ordinary temperature, should extinguish a match as
readily as water. When heated it should not evolve an inflammable vapor
below 110 degrees, or, better, 120 degrees Fahrenheit, and should not
take fire below 125 to 140 degrees Fahrenheit. As the temperature in a
burning lamp rarely exceeds 100 degrees Fahrenheit, such an oil would
be safe. It would produce no vapors to mix with the air in the lamp and
make an explosive mixture; and, if the lamp should be overturned, or
broken, the oil would not be liable to take fire. The crude naphtha
sells at from three to five cents per gallon, while the refined
petroleum or kerosene sells at from fifteen to twenty cents. As great