tle, water will collect on it. This is distilled
water, and is purer than that in the kettle. Petroleum was at first
distilled in a rough way; but now it is done with the utmost care and
exactness. The crude oil is pumped into boilers holding six hundred
barrels or more. The fires are started, and the oil soon begins to
turn into vapor. This vapor passes through coils of pipe or long,
straight, parallel pipes. Cold water is pumped over these pipes, the
vapor turns into a liquid again, and we have kerosene oil.

This is the outline of the process, but it is a small part of the
actual work in all its details. Kerosene oil is only one of the many
substances found in petroleum. Fortunately, some of these substances
are light, like gasoline and benzine; some, like kerosene, are
heavier; and paraffin and tar are heaviest of all. There are also
gases, which pass off first and are saved to help keep the furnace
going. Then come the others, one by one, according to their weight.
The stillman keeps close watch, and when the color and appearance of
the distillate changes, he turns it off into another tank. This
process is called "fractional distillation," and the various products
are called "fractions." No two kinds of petroleum and no two oil wells
are just alike, and it needs a skillful man to manage either.

Even after all this distillation, the kerosene still chars the wick
somewhat--which prevents the wick from drawing up the oil
properly--and it still has a disagreeable smell. To fit it for burning
in lamps, it must be treated with sulphuric acid, which carries away
some of the impurities, and then with caustic soda, which carries away
others. Before it can be put on the market, it is examined to see
whether it is of the proper color. Then come three important tests.
The first is to see that it is of the proper weight. If it is too
heavy, it will not burn freely enough; if it is too light, then there
is too much of the lighter oils in it for safety. The second test is
the "flash test." The object of this is to see how hot the oil must be
before it gives off a vapor which will burn. The third, the "burning
test," is to discover how hot the oil must be before it will take fire
and burn on the surface. Most civilized countries make definite laws
forbidding the sale of kerosene oil that is not up to a standard of
safety. Oil for use in lamps should have an open flash test of at
least 100 deg. F. and a burning point of not less