362 
Messrs Purvis and Wilks, The influence 
glass and copper vessels. The effects of the influences were 
traced in determinations of the optical activity, the copper oxide 
reducing power, the nitrogen content, the acidity, and the specific 
gravity of the distilled fermented solution (and therefore the 
amount of alcohol produced). The temperature of the fermenting 
wort was noted from time to time. 
Description of the Apparatus. 
In the first series of experiments there were four copper vessels, 
and one side of three of these was replaced (1) by ordinary glass, 
(2) by red glass, (3) by an ammoniacal solution of copper sulphate; 
whilst, for the experiments in the dark, a copper vessel of the same 
size and volume as the first three was used. As regards the first 
three vessels they were arranged with the glass sides facing a 
fairly large incandescent light, the red glass copper vessel a little 
further away than the other three, and they were covered with 
loosely fitting lids. The four vessels, and the central light, were 
covered with thick black cloth so as to exclude any external light. 
The time during which the fermentation was allowed to proceed 
varied from 4 to 7 days. 
The nitrogen determinations were by Kjeldahl’s method; the 
specific gravities by a specific gravity bottle ; the optical activity 
by a three shadow polariscope ; the copper oxide by reduction 
of the oxide by hydrogen in small glass tubes and weighing the 
copper produced. In determinations of the acidity, 50 c.c. of one of 
the fermented solutions were made up to a definite volume, 4 c.c. 
N 
of litmus solution added, and — alkali until, as far as could be 
roughly judged, neutralisation was complete; 50 c.c. of this 
solution were then placed in a Nessler cylinder. Fifty c.c. of the 
other solutions made up to the same volume as before were then 
neutralised until on taking out 50 c.c., the same tint was observed 
as the original 50 c.c. The method was also used in the nitrogen 
determinations, and it gave most satisfactory results. 
As regards the temperature observations, we only give the 
details in the second series of experiments, and merely note 
the average temperatures in the others. In the determination 
of the other constituents we give the mean of two separate 
experiments. 
Sterilised hopped wort was used in the series of experiments 
A. and C. : whilst a specially prepared fermentable solution was 
used in the series of experiments B. (p. 369). 
