570 TEE POPULAR SCIENCE MONTHLY 



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. 



Concentration and Purification of Alcohol 



The alcohol obtained at the time of Marcus Grascus 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 redis- 

 tillation be repeated a number of times, a concentration approximating 

 90 to 95 per cent, was possible. 



In the preseijt-day commercial manufacture of alcohol the appa- 

 ratus 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 



