206 PAINTING MATERIALS
oils. It is flammable and, although irritating when breathed, is not particularly
toxic.
Alcohols contain the hydroxyl group, -OH. Because of this group, they are
strongly polar, fairly active chemically, and may be considered as organic bases.
The most common member of the group is ethyl alcohol (ethanol), and its homo-
logues carry names with a similar ending—methanol, propanol, and others. The
latter, synonyms for methyl and propyl alcohol, get their names usually because
they are synthetic products. Lower alcohols are water-miscible in all proportions.
They act as solvents on resins and some synthetic materials but poorly on fats,
waxes, and true gums. Higher alcohols have low miscibility with water. Vapors
of the lower alcohols are flammable and explosive. They irritate the mucous
membrane but, with the exception of methyl alcohol, are not toxic.
Esters are considered to be reaction products of organic bases (alcohols) and
organic acids. An example is Ethyl Acetate derived from ethyl alcohol and acetic
acid. As a group they are noticeable for a sweet and rather fruity odor. They are
weakly polar and only the lower esters are hydrophyllic; these may hydrolyze
back to alcohol and acid. The higher esters, however, are not easily decomposed.
Esters of high molecular weight are much used as plasticizers.
Ketones are distinguished by the presence of the carbonyl group, = CO. The
lower ketones are neutral and highly volatile, and only the lowest are hydrophyllic.
The higher members are solids. The most important of the lower ketones is acetone
or dimethyl ketone, a strong solvent for natural resins, synthetic resins, or cellu-
lose derivatives, and miscible with most other organic solvents and diluents.
Glycol ethers are derived from the dibasic alcohol, glycol, by replacement of a
hydroxyl group with an ether group. The most important of this group, all of
which are of fairly recent development, is the so-called c cellosolve'—ethylene
glycol monoethyl ether.
Polyhydric aliphatic alcohols differ from common alcohols in having more
than one hydroxyl group. Ethylene glycol or glycol is dihydroxy alcohol and lies
between ethyl alcohol and glycerine. This glycerine or glycerol, in turn, is tri-
hydroxy alcohol. These are similar to mono-alcohols in their chemical properties
but have higher viscosity and lower volatility. They become more hygroscopic in
proportion to the number of hydroxyl groups they contain.
Ethers are organic compounds in which two hydrocarbon radicals are joined
by an oxygen atom. Being very slightly polar, they have good solvent action on
waxes and fats.
Amines contain the —NH2 group and form derivatives with many organic
compounds. A few of these have special uses in connection with organic solvents.
The amino derivatives of the polybasic alcohols, particularly triethanolamine, are
useful emulsifying agents. Pyridine and morpholine have special uses as solvents
for linoxyn, dried linseed oil.