576 THE POPULAR SCIENCE MONTHLY. 



At this time, Van Helmont made a first step, by pointing out that the 

 peculiar hissing and bubbling of a fermented liquid are due, not to the 

 evolution of common air (which he, as the inventor of the term " gas," 

 calls " gas ventosum"), but to that of a peculiar kind of air such as is 

 occasionally met with in caves, mines, and wells, and which he calls 

 " gas sylvestre." 



But a century elapsed before the nature of this " gas sylvestre," or, 

 as it was afterward called, " fixed air," was clearly determined, and it 

 was found to be identical with that deadly "choke-damp" by which 

 the lives of those who descend into old wells, or mines, or brewers' 

 vats, are sometimes suddenly ended ; and with the poisonous aeriform 

 fluid which is produced by the combustion of charcoal, and now goes 

 by the name of carbonic-acid gas. 



During the same time it gradually became clear that the presence 

 of sugar was essential to the production of alcohol and the evolution 

 of carbonic-acid gas, which are the two great and conspicuous products 

 of fermentation. And finally, in 1*787, the Italian chemist, Fabroni, 

 made the capital discovery that the yeast-ferment, the presence of which 

 is necessary to fermentation, is what he termed a " vegeto-animal " sub- 

 stance or is a body which gives off ammoniacal salts when it is burned, 

 and is, in other ways, similar to the gluten of plants and the albumen 

 and casein of animals. 



These discoveries prepared the way for the illustrious Frenchman, 

 Lavoisier, who first approached the problem of fermentation with a 

 complete conception of the nature of the work to be done. The words 

 in which he expresses this conception, in the treatise on elementary 

 chemistry, to which reference has already been made, mark the year 

 1789 as the commencement of a revolution of not less moment in the 

 world of science than that which simultaneously burst over the politi- 

 cal world, and soon engulfed Lavoisier himself in one of its mad eddies : 



e may lay it down as an incontestable axiom that, in all the operations 

 of art and nature, nothing is created ; an equal quantity of matter exists both 

 before and after the experiment: the quality and quantity of the elements re- 

 main precisely the same, and nothing takes place beyond changes and modifica- 

 tions in the combinations of these elements. Upon this principle, the whole art 

 of performing chemical experiments depends ; wo must always suppose an exact 

 equality between the elements of the body examined and those of the product 

 of its analyses. 



Hence, since from must of grapes we procure alcohol and carbonic acid, I 

 have an undoubted right to suppose that must consists of carbonic acid and 

 alcohol. From these premises we have two modes of ascertaining what passes 

 during vinous fermentation : either by determining the nature of, and the ele- 

 ments which compose, the fermentable substances ; or by accurately examining 

 the products resulting from fermentation ; and it is evident that the knowledge 

 of either of these must lead to accurate conclusions concerning the nature and 

 composition of the other. From these considerations, it became necessary accu- 

 rately to determine the constituent elements of the fermentable substances; 



