Page:Popular Science Monthly Volume 82.djvu/574

570 This alcohol is obtained by distilling the wood in iron retorts at a high temperature (about five hundred degrees C). The vapors thus driven off when condensed are found to contain, in addition to a large percentage of methyl or wood spirit, acetone, acetic acid, etc. Upon being freed from these foreign substances methyl alcohol is obtained in purity.

The alcohol obtained at the time of Marcus Græcus contained a relatively large amount of water and in addition numerous foreign substances. To remove these was the task set for succeeding workers. It was found that the percentage of aqua ardens could be perceptibly raised if the alcohol collected be redistilled. If the process of redistillation be repeated a number of times, a concentration approximating 90 to 95 per cent, was possible.

In the present-day commercial manufacture of alcohol the apparatus has been so perfected that by a single distillation an equally high percentage is obtainable.

By neither of these methods, however, is it possible to render alcohol anhydrous, or free from water. But alcohol of a relatively high percentage placed in contact with a chemical, such as caustic lime or baryta having a strong affinity for water, and then redistilled may be rendered practically free from water.

The foreign substances present in the alcohol were found to be principally glycerin, succinic acid and higher alcohols, traces of several of the latter, such, for example, as propyl, butyl and amyl alcohol, being found in ethyl alcohol.

To separate amyl alcohol from ethyl it is necessary to employ a physical property which in the different alcohols is perceptibly different—that is, the boiling points. While ethyl boils at 78.4° C, propyl at 97° and butyl at 117°, amyl does not reach its point of ebullition until it is elevated to a temperature of 132° C.

It would therefore appear that the separation of amyl alcohol from ethyl would be easily effected by raising the temperature of the mixture to 78.4° C. and thus driving off the ethyl alcohol. This is in fact the method used, but it is found that while the first part of the distillate is largely ethyl, later amyl is also given off at a temperature far below its boiling point. In a word a single distillation is by no means sufficient to separate the two. By a process known as fractional distillation, it has been found (Roscoe and Schorlemmer) that when a temperature of 80 to 90° C. is employed 88.1 per cent, of ethyl alcohol is distilled off and that 11.9 per cent, of amyl also passes over. In the case when the temperature is raised from 131 to 132° C. 0.2 per cent, of ethyl is still obtained and 99.8 per cent, of amyl.

Since the boiling points of propyl and butyl alcohol approximate