186 PAINTING MATERIALS
Springer, 1923], pp. 56-126) corroborates this by concluding that alcohol was not
the discovery of the Alexandrian or Arabian alchemists, but first became known
probably in the XI century and in Italy. He finds the first mention of it in the
Mappae Clavicula, a MS. of the XII century, and a later one in the MSS of
the so-called 'Marcus Graecus' which date from 1250 to 1300. Other Italian
writers of the XIII century speak of its medicinal value. Its use spread rapidly
after the Great Plague of 1340 (see G. Sarton, Introduction to the History of
Science [Baltimore: The Williams and Wilkins Co., 1927], I, 533-534; II, 29,
130, 408, 1038-1039). It is said (see Samuel Couling, The Encyclopaedia Sinica
[London: Oxford University Press, 1917], under ' Wine') that distillation of
alcoholic spirits was first introduced into China in the Yuan Dynasty (XIII
century).
The name has an Arabic origin, the particle #/and the word kohl, a term used
for centuries to designate any fine powder, particularly an eye paint from anti-
mony sulphide. Its application to a volatile liquid, especially the spirit of wine,
seems to have been made by Paracelsus in the early XVI century. Before that
the terms aqua ardens in the Middle Ages and aqua vitae in the Renaissance, were
commonly given to it.
Although much alcohol is made synthetically, most of that used in industry is
still the product of the fermentation of sugar, or of natural carbohydrates which
yield sugar, by enzymic action. Cane sugar and beet sugar molasses are the princi-
pal sources, but cereals like wheat, barley, and corn, and also potatoes, are like-
wise important. The Weizmann process for production of butyl alcohol by fer-
mentation of corn starch yields about 10 per cent of ethyl alcohol as a by-product.
Alcohol from fermentation has to be concentrated and separated from water and
similar impurities by distillation and rectification. This is done in high columnar
stills where the vapors condense on bafHe plates and are redistilled with progressive
enrichment. Industrial alcohol has about 5 per cent of water and can not prac-
tically be purified further by distillation because alcohol and water form a con-
stant boiling mixture when the distilled vapors contain 97.2 per cent alcohol
by volume.
Synthetic ethyl alcohol, marketed as * ethanol,' is now made in quantity from
ethylene gas, obtained from the cracking of petroleum, or is made from acetylene.
This is identical in composition and properties with alcohol derived from fer-
mentation.
Absolute or anhydrous alcohol is ethyl alcohol free from water. This is 200 proof
(loo U. S. proof contains 50 per cent alcohol; proof spirit [U. S.] has 42.52 per
cent by weight of absolute alcohol in distilled water). The 5 per cent of water left
in the alcohol that conies from straight distillation can be removed in order to
make absolute alcohol by a special process (Keyes) of azeotropic distillation with
benzene or by redistillation over quicklime or over a hydrate-forming salt. Now it
is made industrially in large quantities and at a fairly low cost. Absolute alcohol is