198 PAINTING MATERIALS
hydroxide, potassium hydroxide, or ammonia are made up for use in a paste with
sawdust, chalk, starch, or similar bulky materials.
Penetrant is a term used for any one of various sulphated and sulphonated
higher fatty acids, alcohols, and esters. When used even in very small amounts,
these reduce interfacial tension between liquids and solids. Thereby they Increase
ease of wetting and penetration (see Surface-Active Agent; also B. G. Wilkes and
J. N. Wickert, ' Synthetic Aliphatic Penetrants/ Industrial and Engineering
Chemistry, XXIX [1937], pp. 1234-1239).
Petroleum Ether is a petroleum distillate, chiefly hexane, with a boiling range
between 40° and 60°C. Although too volatile for a diluent in paints and lacquers,
it is a good extracting agent for soft resins, oils, and waxes.
Petroleum Spirit, a term that may indicate any Petroleum Thinner, is used
also specifically for a distillate boiling in the range of 60° to i2o°C. This is similar
to Benzine and Gasoline.
Petroleum Thinner (benzine, gasoline, mineral spirits, naphtha, petroleum
spirits). The name is used for those hydrocarbons obtained from the distillation
of crude petroleum and commonly employed with paints and varnishes. They are
produced by most of the large oil companies; Gardner lists many of them (see pp.
570-574) and includes data on evaporation rates, distillation ranges, flash points,
density, and other properties. The solvent properties of the petroleum thinners
vary considerably according to the particular kinds of hydrocarbons they contain,
to th^ir structure, molecular weight, and proportions. They are good thinners
and solvents for mineral and fatty oils, but hard fats (like tristearin) have limited
solubility in them. Resins are poorly dissolved in petroleum thinners containing
high percentages of aliphatics but are more soluble in those containing hydro-
genated aroma tics (naphthenes). Cellulosic compounds and polymerization
products like vinyl acetate are generally insoluble. The higher boiling fractions
are used as thinners for oil paints, varnishes, wax polishes, and emulsions, and
they now displace turpentine for many purposes. They have wide industrial
application because of their cheapness.
Although the Babylonians, the Assyrians, and other peoples of the Near East
were acquainted with crude petroleum and related substances like asphalt and
bitumen obtainable from the regions of the Caspian Sea (Baku), the Dead Sea,
and Mesopotamia, there is no sign that they refined it and put it into any prepara-
tions of paint and varnish. Even though the art of distillation was perfected in
early mediaeval times (see Alcohol), no definite mention of a distillate as a painter's
material occurs until the XVII century in the MS. of De Mayerne (Berger, III,
108, 188, and 190). Petroleum products did not come into commercial use for
paint thinning until the latter part of the XIX century. Heaton says (p. 17) that
in 1885 Samuel Banner first introduced petroleum distillate as a solvent for the
paint industry under the name, Patent Turpentine (English patent 12,249 of that
year). For some time it was regarded as only a cheap substitute, but within the
last twenty-five years it has found a more respectable place in the paint and