Mr. Henry on Ferments and Fermentation. 27 c 



Sir Torbern Bergman, aerial acid, was that 

 which firft attraded their notice. This gas which 

 had been remarked, even by Van Helmont, to 

 be difcharged, in great quantities, from liquors, 

 in the vinous fermentation, was found by Dr. 

 Prieftley, to be again mifcible, with them j and 

 he proved that, on the prefence of this gas, the 

 brifknefs and pleafantnefs of thefe liquors de- 

 pended, and that, when deprived of it, they 

 became vapid and flat. 



But though the Hon. Mr. Cavendifh had 

 proved the feparation, and afcertained the quan- 

 tity of this gas, difcharged in fermentation, and 

 though Dr. Prieftley had early made the above- 

 mentioned obfervations, it does not appear to 

 have occurred to thefe philofophers, that this 

 gas was the exciting caufe, as well as the produd, 

 of fermentation. 



It is a faft well known to brewers of malt 

 liquors, that wort, contrary to what takes place 

 in liquors more purely faccharine, as the juice 

 of the grape, cannot be brought into the vinous 

 fermentation, without the addition of a ferment i 

 for which purpofe yeaft or barm, which is a vif- 

 cid frothy fubftance, taken from the furface of 

 other mafles of fermenting liquor, has been, 

 commonly, ufed. 



But the nature of this fubftance, much lefs its 

 mode of aftion, has not been confidered, with 



T 2 that 



