gasoline proper the boiling point ranges from 90° to 200° F. Naphtha is a name broadly applied to all light distillates, but more especially to those boiling at 80° to 120° F., and whose gravity varies from as low as 62° B. up to 76° B. Benzine (q.v.) represents the least volatile product of the naphthas and has a specific gravity of about 0.73 (57° to 62° B.), and a boiling point of 120° to 150° F. Ligroine forms a special grade of solvent naphtha of a specific gravity of 0.715, and a boiling point of 194° to 248° F. Following the lighter naphthas come the illuminating oils, divided into heavy and extra heavy naphthas; in the process of distillation these may either be carried off separately or together. In the former case, the heavy naphthas may be redistilled and separated into benzine and light distillate. The latter may then be mixed with the extra heavy naphthas in varying proportions to form white oil or export oil. There are many grades of domestic illuminating oil or kerosene, which differ chiefly in fire test.
After the naphthas have passed off, the residuum is forced through steam-jacketed filters filled with bone black or fuller's earth; the first portions of the filtrate represent light oils, and are followed by successively heavier ones. When the petroleum belongs to the paraffin group, the residuum is sometimes placed in the tar still for further distillation, and there the heavy vapors are carried over by the aid of superheated steam, the presence of the latter also preventing dissociation of the oil, which if it occurred would be followed by a lowering of viscosity of the lubricating oil and a decrease in the amount of paraffin obtained. The distillates containing the paraffin are freed from the latter by chilling, the effect of this being to cause a separation of the waxy paraffin scales. The oils thus freed from the paraffin are important lubricants, and under this class a number of grades are known as spindle oil, engine oil, summer dark oil, winter dark oil, cylinder oil, valve oil, etc. The residue now left in the tar still is a porous mass of separated carbon, solid decomposition products termed coke. The tar is sometimes used without further distillation for the manufacture of vaseline.
Many of the distillates obtained in the treatment of crude petroleum contain acid constituents as well as compounds which in time impart a dark color and unpleasant odor to the distillate. Raw distillates, when used for illuminating purposes, also rapidly char the wick and lose their power of being drawn upward by capillarity. It is therefore customary to purify the various fractions obtained by treatment with sulphuric acid and caustic soda, before they are marketable. The distillate, which has been first cooled to 60° F., is agitated with sulphuric acid in tall cylindrical tanks of wrought iron lined with sheet lead, and known as agitators; about 1½ to 2 per cent. of acid is required. The acid is then washed out with water, and a 1 per cent. solution of caustic soda added, after which a second agitation takes place, followed by washing.
The percentage of the various fractions yielded by different oils varies. Many Pennsylvania oils yield 8 to 10 per cent. naphtha, 70 to 80 per cent. refined oils, 5 to 9 per cent. residuum and 5 per cent. loss. In the distillation of 100 gallons of crude petroleum there are obtained on the average about 76 gallons of illuminating oil, 11 gallons of gasoline, benzine, and naphtha, and 3 gallons of lubricating oil, while the residuum and loss amount to 10 gallons.
Testing of Refined Oils. Refined oils are
usually tested for their color, gravity, flashing
and burning points, and sometimes for their
behavior when cooled (cold test). The color is
determinable by inspection. The gravity is a
measure of the purity of the distillate. Too large
a proportion of the lighter oils renders the product
unsafe for illuminating purposes, while too great
a percentage of the heavier oils interferes with
its free burning qualities. The gravity test is
commonly made by placing the oil in a tall jar
and inserting a hydrometer marked preferably
with the Baumé scale (water has a value of 10
on this scale). The temperature of oil when this
test is made should be 60° F. The fire test
inincludes the determination of the flashing point,
i.e. the temperature to which the oil must be
heated in order to produce a momentary explosion
of the mixture of inflammable vapor, and of
the burning point, i.e. the temperature to which
the oil must be heated in contact with the air to
take fire and burn on the surface. The burning
point is commonly from 6° to 20° C. higher than
the flashing point. Kerosene for lighting
purposes should have a flashing point of not less
than 110° F., and a burning point of not less
than 125°. Both the flashing point and burning
point are carefully regulated by law in most
civilized countries so as to run the minimum risk
from explosion. The cold test is of importance
for lubricating oils, and is made in order to
determine the temperature at which the oil thickens
or becomes cloudy. It can be made by cooling the
oil in a small tube and noting the temperature
at which the oil ceases to flow when the tube is
inclined.
Uses. The two chief uses of the distillates from crude petroleum are for illumination and lubrication, but the various fractions in many cases have special applications. Rhigolene is used as a local anaesthetic; petroleum ether is employed as a solvent for caoutchouc, fatty oils, and plant principles, and for carbureting air in gas machines; gasoline is employed in the extraction of oil from oil seeds, in carbureting coal gas, in gasoline lamps, stoves, and plumbers' lamps. Naphthas in general are employed as solvents for resins in varnish-making, and in the manufacture of oilcloth. Boulevard gas fluid is a product of 0.68 specific gravity used in street lamps, while benzoline is a deodorized naphtha of 0.70 specific gravity. Benzine is employed for dry cleaning, as a substitute for and adulterant of turpentine for cleaning printer's type, and for dyers' and painters' use. The benzine of the U. S. Pharmacopœia has a specific gravity of 0.67 to 0.77, and a boiling point of 122° to 144°, and therefore represents a higher distillate. Astral oil and mineral sperm oil are special illuminating oils of high flashing points. Crude petroleum is much used for fuel purposes in engines. Along the Pacific Coast, especially in southern California, where good coal is scarce, the locomotives consume large quantities of crude oil. Paraffin residue is placed on the market for medicinal purposes under the name of vaseline, petroleum ointment, and cosmoline. It is also used in the manufacture of chewing gum, and for insulating purposes in electric work.
Production. The growth of the petroleum industry in the United States is shown in the fol-
