218 Brown. — Some Studies on Yeast. 
Berthelot’s final result, after making a small correction for the non-volatile 
products of fermentation, indicated that the gramme molecule of dextrose 
liberated on fermentation 32-0 7 kilogram-centigrade heat units, corre- 
sponding to 178-1 calories per gramme of sugar. 
But the possible errors of such indirect methods are very great, and 
are all accumulated on the final result. 
In 1895 Boufifard (Compt. rend., 1895, 121, 357) made the first attempt 
to determine the heat of fermentation by direct means, employing for this 
purpose a Berthelot’s calorimeter containing a litre of grape-juice, to which 
had been added a further quantity of dextrose. When all due corrections 
were applied, Bouffard’s experiments pointed to the heat of fermentation of 
dextrose being K 23*5, or 130 calories per gramme of dextrose. 
A few years later, the problem was attacked by Adrian Brown (Journ. 
Fed. Inst. Brewing, vol. vii, 1901, p. 93). 
The great difficulty which had been experienced by Boufifard was one 
which is incidental to all measurements of thermal effects produced by 
comparatively slow reactions, viz. that of determining the rate of cooling of 
the calorimeter and its contents. Adrian Brown reduced this possible error 
by employing as his calorimeter a fermenting vessel of about 1,300 gallons 
capacity, as used in a brewery under the ‘ high fermentation ’ system. 
The liquid operated upon in this vessel was an ordinary brewer’s wort, 
and observations were made at sufficiently short intervals almost to eliminate 
the cooling correction. 
The amount of sugar (maltose) fermented between any two intervals 
corresponding to a definite rise of temperature was ascertained from the loss 
in specific gravity of the liquid after deprivation of its alcohol, and the 
application of the known ‘divisor’ for maltose. The specific heat of the 
wort being taken at 0-9678, the final conclusion was arrived at that 
the heat liberated by the fermentation of 1 grm. of maltose is 119-2 calories. 
Within the last few years I have made various attempts to determine 
the heat of fermentation of maltose by a method substantially the same as 
that used by Adrian Brown. The principal points of difference were that 
I used larger vessels, varying in content from 1,800 to 14,000 gallons, and 
that the fermented sugar was estimated from the amount of alcohol formed, 
the exact ratio of alcohol to sugar at different stages of the fermentation of 
a malt-wort having been previously determined in the course of a separate 
investigation. 1 
Twelve such experiments were made, and a critical examination of the 
results points to a value of about 125 calories as representing the heat of 
fermentation of 1 grm. of maltose, this value including the heat due to 
hydrolysis of the maltose at the moment of its fermentation. 
1 See Reports on Original Gravities in process of publication in the Tourn. of Fed. Institutes of 
Brewing. 
