SOLVENTS AND DILUENTS 195
is a common cleaning agent. Its volatility and flammability prevent a wide use of
it as a paint thinner. The gasoline from American sources contains several hydro-
carbons, but chiefly hexane, heptane, and octane. That from Rumanian and
Russian sources may have hydrogenated benzene compounds called naphthenes.
Being a mixture, gasoline has no definite boiling point but, rather, a boiling range
as wide as from 60° to i2o°C.
Glycerol (glycerine [CH2OH-CHOH'CH2OH]), is a trihydric alcohol, clear,
syrupy, and with a sweet taste. It was first prepared in 1779 by Scheele through
the saponification of olive oil with litharge. Now it is obtained chiefly as a by-
product of soap manufacture. It is miscible in all proportions with water, alcohol,
and many organic solvents. In the practice of painting it is chiefly used as a
moistening and plasticizing agent, particularly for aqueous mediums such as egg
white, gelatin, and gum.
Glycol Ethers. This name is given to a series of solvents rather recently de-
veloped and sold under the trade name, cellosolve. Besides cellosolve itself, which
is ethylene glycol monoethyl ether, there are: methyl cellosolve (ethylene glycol
monomethyl ether), butyl cellosolve (ethylene glycol monobutyl ether), and
cellosolve acetate (ethylene glycol monoethyl ether acetate). Because of strong
solvent action, medium and low volatility, stability, mild odor, and tolerance for
aromatic hydrocarbons, the series has had a wide commercial use in the manu-
facture of coatings from synthetic resins. Since they contain no ester group, they
do not develop acidity through hydrolysis. In the treatment of paintings, par-
ticularly the removal of old and discolored films of varnish, they are used alone or
as ingredients to couple mixtures of hydrocarbons with alcohols or ketones.
Gum Spirits of Turpentine (see Turpentine).
Hexane, the colorless, volatile, liquid, aliphatic hydrocarbon (C6Hi4), is a
normal component of most gasolines, but serves also as a special solvent. It is
prepared by careful fractional redistillation of lower petroleum fractions.
Ketones (see Solvents, classification).
Methyl Acetate (CH3COOCH3). This ester is derived from methyl alcohol and
acetic acid, and can be prepared by distilling the former over calcium or sodium
acetate in the presence of sulphuric acid. It is also a by-product of wood distilla-
tion. The odor faintly resembles that of methyl alcohol, the liquid is clear, boils
at 53 to 59°C., and is the most volatile of the ester type of solvents as well as the
most active. In this respect it resembles acetone. It mixes with water but is liable
to decomposition by hydrolysis, with the formation of acetic acid. The vapors are
not strongly toxic but are highly flammable.
Methyl Alcohol (wood alcohol, methanol). This, the simplest member of the
alcohol series, has the formula, CH3OH. Formerly it all came from the dry dis-
tillation of vegetable waste, particularly wood. Repeated distillation or special
treatment is necessary in order to get a pure product, the chief difficulty being
the removal of acetone which is also the product of this dry distillation. That