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Alcohol, or pure spirit of wine, is met with in commerce practically free from all impurities save water. Proof spirit, rectified spirits of wine, and methylated spirit, though of service in cleaning oil-pictures and for many other purposes, ought not to be used in the preparation of varnishes. For this purpose pure alcohol, often called absolute alcohol, is required; but provided that it contains no water the presence of wood-spirit is no drawback to its use. in commerce, nearly absolute alcohol, made both from spirits of wine and from methylated spirit, is obtainable; but it may be prepared by operating upon the strongest available spirits of wine in the following manner: The spirit is distilled in a water-bath until no further strengthening of the alcoholic distillate is secured by repetition of the process; then a dry retort is half-filled with small, clean, hard fragments of quicklime, the strong spirit is poured upon these so as to somewhat more than cover them, and then the whole is left overnight; distillation from a water-bath is then commenced, when it will be found that a spirit comes over which contains no more than one part of water in two hundred. Eeven this small proportion may be removed by redistilling the alcohol from a very little metallic sodium.

The last distillate, when a small portion of it is shaken up with its own bulk of benzene, should mix perfectly with the latter, causing no turbidity. But it should be borne in mind that absolute alcohol is a very hygroscopic liquid, greedily absorbing water from the air; it must, therefore, be kept in well-stoppered bottles, filled almost completely. In absolute alcohol some of the more intractable resins, even some kinds of copal, readily dissolve. The specific gravity of absolute alcohol at 15° C. is .794, while, if it contains but 1 percent of water, its specific gravity is distinctly higher, namely, .797.

Last Update: 2011-01-23