Popular Science Monthly/Volume 82/June 1913/Alcohol from a Scientific Point of View I
|ALCOLOL FROM A SCIENTIFIC POINT OF VIEW|
UNIVERSITY OF CALIFORNIA
SOME problems permit of a ready and satisfactory solution with but little difficulty, while in fullness others remain obscure for generation upon generation, being resolved slowly and at great pains. In the latter class stand the problems involved in the study of alcohol. Some of these, although investigated for centuries, have been but recently solved or are still in the process of solution. Other associated problems remain which are but little better understood to-day than they were in the time of Aristotle.
Of this group of problems, solved or in the process of solution, I should like to consider in order the following parts:
|Alcohol:||I.||Its Discovery and Nature.|
|II.||The Relative Toxicity of the Various Alcohols.|
|III.||The Destiny of Alcohol in the Body.|
|IV.||The Action of Ethyl Alcohol on the Body-and on its Output of Physical and Mental Work.|
I. The Discovery and Nature of Alcohol
Through many ages nature has been elaborating a substance which has come to affect human progress most profoundly. This substance we to-day call alcohol. Although the existence of alcohol was surmised almost four centuries before the Christian era, yet practically twelve centuries intervened before its extraction, and ten centuries more elapsed before its nature and the biological significance of its origin were fully made out.
To appreciate the conditions confronting men who attacked problems of the sort in the infancy of science, we should look back to those ages in which natural phenomena called forth extravagant explanations, a day when apparatus and laboratories were unknown and, above all, a time when the scientific momentum, which is ours because they labored, was yet unborn. Under such conditions the work on alcohol was begun.
Alcohol Early Detected in Wine
Two important observations were early made concerning wine. The first of these was that wine, unlike water, if thrown into the fire emits a flame. When questioned as to the cause of the phenomenon Aristotle answered that the flame was due to an exhalation contained in the wine. Later, Pliny related that the wine from Falernus Ager blazed up at the contact of a flame—a wine, as Berthelot remarks, evidently rich in inflammable exhalation.
Since men of that period knew that sea water vaporized and condensed was drinkable, we might expect that it was but a step to the extraction of the inflammable exhalation. But a long step it proved to be! An attempt at condensation was in fact made at that time with the result that wine upon evaporation became water.
It was not until the fourth century of the Christian era that an adequate distilling apparatus was perfected; and this, although used in the distilling of various substances, seems not to have been employed for the production of alcohol. Not until the writings of Marcus Græcus, in fact (twelfth or thirteenth century), do we get unmistakable evidence of the distillation of alcohol—the distillate obtained being called "aqua ardens."
An explicit account of the process of distillation and a description of the characteristics of the alcohol thus obtained occur in a Latin manuscript published about 1438—but which according to Berthelot contained older excerpts. In this the preparation of alcohol is described as follows:
Thus from the time of Aristotle to the period immediately following that of Marcus Græcus there elapsed an interval of considerably more than a thousand years in which through extended effort, the exhalation of wine was eventually obtained. As time passed methods were devised by which aqua ardens was procured in greater concentration. It should be stated, however, that the word "alcohol" as applying to present-day alcohol was not used until the sixteenth century and further that alcohol in the purity in which it is now obtained is a product of the century just passed.
The second of the early discoveries made in the study of wine was that of its stimulating effect on man. An interpretation of this effect in later years greatly influenced the use of alcohol. Prominent in this interpretation stands the name of Arnaldo de Villaneuva. In his work entitled "The Conservation of Youth" (1309) after speaking of the delicacy of the nature of the spirit of wine, and enumerating the various maladies cured by it, he adds that the spirit of wine should be called "eau de vie," for it prolongs life.
From the time of Arnaldo de Villaneuva to the present there has been growing a counter belief in the minds of many that the prolongation of life is not one of the characteristics to be associated with "eau de vie." Indeed, some believe that "eau de vie" curtails rather than prolongs life, and some there are who go so far as to maintain that "eau de vie" should be called "eau de mort." But this is aside from the subject! It is of interest, however, to note that out of the opinion expressed by Arnaldo de Villaneuva probably grew the prevailing belief in Europe in the efficacy of the daily use of brandy, and to the latter may be attributed the custom of the mint julep or so-called old-age drink prevalent in parts of our own south.
Alcohol Discovered in Substances other than Wine
Man, seeking ways of producing alcohol from substances other than wine, early made the important observation that fermentation and the production of alcoholic liquids go hand in hand. This discovery, as time passed, became common knowledge, with the result that fermented liquids from different sources came to be looked upon as characteristic national drinks—thus in France wine from grapes, in Jamaica rum from cane, in Russia vodka from rye, in Japan saki from rice, in Germany beer from barley and in America whiskey from Indian corn.
But some substances long used in the formation of alcohol, unlike the juice of grapes, are themselves unfermentable. Some of these we shall consider more in detail.
Common or cane sugar, although of itself incapable of undergoing alcoholic fermentation, by the action of a ferment invertase, takes up a molecule of water, splitting into glucose and fructose, both of which are fermentable. Thus cane sugar, , becomes (glucose) and (fructose). From the fermentation of glucose and fructose alcohol results.
The starch of cereal grains when converted into fermentable sugar likewise becomes an effective source for alcoholic fermentation. It has long been known that a starch paste, to which malt or malt extract (containing diastase) has been added, becomes transformed into a sugar maltose. Now maltose itself is not subject to alcoholic fermentation, and so it must be acted upon by another ferment, maltase. This converts the maltose into dextrose and glucose, the latter of which we have seen to be produced in the case of cane sugar.
In 1837 Cahours employed potatoes as a source for alcoholic fermentation. The starch of potatoes is insoluble in cold water, but upon heating it in the presence of dilute sulphuric acid the starch is converted into fermentable sugar. In this process in addition to the ethyl alcohol produced a considerable amount of one of the higher alcohols, amyl alcohol, was discovered.
Two years earlier than the discovery of amyl alcohol another alcohol was obtained. This was produced not by fermentation, but by the destructive distillation of wood, and was therefore called wood or methyl alcohol.
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 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 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|
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 living in a liquid medium in order to secure sufficient oxygen procured it from the sugar, thus, as we have said, producing from the latter and alcohol. The production of alcohol hence resulted as a product of metabolism in the body of a living organism.
It has been more recently shown, however, that the active cause of fermentation is to be found not in the yeast itself, but in a ferment (or enzyme) produced by the yeast cell. This ferment Buchner has succeeded in freeing from the cell, so that it is now possible to produce alcoholic fermentation without the presence of the living yeast.
But this discovery does not detract from the work of Pasteur, to whom is due the great credit of definitely showing the importance of living organisms, the yeasts, in the production of alcohol, since without the yeast cell the ferment or enzyme would not be produced.
The nature of the experiments by which Pasteur demonstrated the importance of the yeast is of interest. In the first place he showed that grape juice filtered and kept from contact with the air is not subject to alcoholic fermentation. In the second case he demonstrated that grape juice sterilized by heat is, if similarly protected, unfermentable. In the third case he showed that if the yeasts caught on the filter used in the first series of experiments be added to the sterile juice of the second series, fermentation ensued.
Pasteur was asked the origin of the yeasts which make the alcohol in wine. The question was answered by an experiment. Taking the grapes and completely removing from them the fuzz or "bloom," he extracted the juice free from contact with the air. No fermentation followed, consequently no alcohol resulted. From this it was learned that the yeasts necessary for the production of the alcohol of wine live in nature in the air and are found in abundance on the outside of the grape. If the grapes be crushed the sweet juices serve as food for the yeast plants. These when well fed grow rapidly and, by a simple process of budding, produce myriads of yeast plants. These, like their parents, give rise to ferments which break down the sugar into and alcohol.
It was later found that although these yeasts may increase greatly in numbers, a strong percentage of alcohol is impossible in nature. This is due to the singular fact that when the strength of alcohol increases perceptibly the organisms forming it are unable to thrive in their own product. Hence they increase more slowly. When a strength of 12 per cent, of alcohol is reached reproduction is manifestly checked, and at 14 per cent, all cell activity ceases.
To increase the strength and purity of the alcohol thus formed in nature, man, as we have seen, has resorted to the processes of distillation and rectification by which alcohols practically free from impurities may be obtained in concentration.
- Some give the date of Marcus Græcus in the eighth century.
- Eau de vie—The elixir of life.
- To be seen on the walls of one of the well-known sanatoria of France.