more nearly that of ethyl, it is practically impossible, even by repeated fractional distillation, to remove all traces of these.
The alcohols with a higher boiling point are also found to differ from ethyl alcohol in another respect—that is, in their chemical form or molecular weight. The molecular weight of ethyl alcohol taken as a standard is 46; that of propyl, 60; that of butyl, 74; and that of amyl, 88. It is thus seen that in both molecular weight and boiling point, alcohols of fermentation fall into a regular series ascending from ethyl to amyl.
In addition to the above alcohols of fermentation is wood or methyl alcohol which reaches its boiling point at only 66° C. (or 66.5°) and has a molecular weight of 32.
The molecular weights and boiling points found for the primary alcohols named may be briefly summarized as follows:
| Alcohol | Molecular Weight | Boiling Point | |
| Methyl | 32 | 66.0° C. | |
| Ethyl | 46 | 78.4° C. | |
| Propyl | 60 | 97.0° C. | |
| Butyl | 74 | 117.0° C. | |
| Amyl | 88 | 132.0° C. | |
The Biological Significance of Fermentation
While the production of alcohol has long been associated in the minds of all peoples with the process of fermentation, yet the exact nature of the process was unknown until the significant work of Pasteur appeared. Pasteur in his work on fermentation, as in all his work, was unwilling to accept blindly an interpretation of the meaning of the process until he had examined in detail and elucidated step by step the actual occurrences taking place.
By taking the juice of the grape he observed, as had often been observed before, that upon leaving it for a time at a warm temperature, bubbles of gas arose. This gas was evidently the result of a chemical process going on within the mixture. But to Pasteur is due the credit of showing for the first time that within the mass of grape juice the thousands of living organisms (which Latour, Schwann and others had already seen) were busily engaged in the process of digesting a part of the sugar contained in the juice. Pasteur believed that these living organisms, by taking oxygen from the sugar, caused the splitting up of the sugar into two substances. One of these he had seen arising as bubbles of gas—carbon dioxide—the other remained in the mixture, gradually increasing in strength as more and more was produced. The latter substance Aristotle had spoken of as the exhalation of wine. Marcus Græcus denominated it aqua ardens. We call it alcohol. The organisms which thus produce alcohol are the yeasts, many kinds of which are now known.
To Pasteur fermentation was life without air. That is, the yeasts
