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of light and of copper on fermentation. 
Details of the Experiments. 
A. 
I. Equal volumes of hopped wort were placed in the four 
vessels and allowed to ferment under the influence of ordinary 
English yeast. The analysis of the unfermented wort gave: copper 
oxide reducing power of 20 c.c. of a 5 % solution = 0T 89 gm Cu. 
The optical activity at 15° C. for 100 % wort = + 17 - 68°. 
N 
The N. content ; 50 c.c. of — H 2 S0 4 were used, and 42‘7 c.c. of 
N 
— NaHO were required to neutralise excess after Kjeldahling 
10 c.c. of the wort. 
The temperature on starting the fermentation was lo^ 0 C., and 
the average temperatures between 24 April at 2 p.m. and 27 April 
at 9.30 a.m., were : 
dark = 22 - 6° C. 
white =23 ‘2 „ 
red =22-9 „ 
blue = 22'4 „ 
After the fermentation the following results were obtained. 
(1) Optical activity for 100% solution at 15° C. : 
dark = + 1440° 
white = + 7-98 
red = + 8-08 
blue = + 7 ‘86 
The number for the dark is high and comparable with that of 
the original wort. It may be the result of the action of acidifying 
organisms growing very rapidly ; and at the rather low starting 
temperature the resultant acid dissolving a little copper of the 
vessel, and thereby influencing detrimentally the growth of the 
yeast. In the remaining experiments the wort was previously 
warmed to a temperature higher than 15° C. 
(2) Copper oxide reducing power — 20 c.c. of a 5 % solution 
gave : 
dark = 04580 gm. Cu. 
white =04345 „ 
red =04930 „ 
blue =04895 
It is noticeable that the copper oxide reducing power is com- 
parable with the optical activity, with the exception of the white 
light. The discrepancy is not quite explicable, for in the 
remaining experiments, the white light ones are quite normal 
and comparable. 
