II. 



THEOEIES OF FERMENTATION. 



10. Stahl's Theory of Fermentation. 



WHOEVER was the first to leave the juice of sweet fruit to 

 itself in storage for a few days had the pleasure of observing a 

 phenomenon hitherto unknown the incipient decomposition of 

 the mass which we now-a-days term alcoholic fermentation. 

 This observation was made at so early a date that we have no 

 record of it beyond myth and tradition. The Greeks feted the 

 deity Bacchus as the inventor of wine, and the Egyptians ascribed 

 to Osiris the first introduction of brewing. 



Acquaintance with the nature of this phenomenon was, how- 

 ever, of an extremely superficial character for a very long time. 

 Even in the later Middle Ages the word fermentatio (fermentation) 

 was employed as synonymous with digestio (digestion), the latter 

 word being also currently used to denote any form of chemical 

 reaction; and the word "ferment" was applied to any body 

 capable of producing such reaction. 



At an early date it would necessarily be noticed that the 

 " must " when in a state of fermentation became covered with a 

 froth, and that at the end of this operation a copious deposit, viz., 

 yeast, was left at the bottom of the vessels. Fermentation was 

 therefore looked upon as a process of purification, by which the 

 initially turbid and discoloured liquid was so improved and freed 

 from dirt, that the purified alcohol exhibited its true properties. 

 For this reason the deposit was described as the fceces vini or 

 faeces cerevisice, i.e. the excrement of the wine or beer. This 

 view was held by, e.g. Basilius Valentinus, a German monk and 

 alchemist, who lived at Erfurt early in the fifteenth century. 



It was also noticed that this sediment was a powerful ferment, 

 i.e. it was capable of rapidly exciting a brisk fermentation in still 

 unfermented liquids, such as wine-must or beer-wort. This idea 

 was adopted in other branches of chemistry, so that any reaction 

 was considered as elucidated when the body acting as " ferment " 

 therein could be identified. Moreover, the "philosopher's stone," 

 the goal of the labours and aspirations of the alchemists, was 

 nothing but the much sought for, but never discovered, universal 

 "ferment" for every possible chemical process ! 



Among the disciples of the alchemic school, one other, viz., 



