456 Dr. A. Harden and Mr. W. J. Young. [Jan. 17, 
bicarbonate, the amount of the latter present in the arsenate solution used 
was previously estimated by neutralising a known quantity with hydro- 
chloric acid and measuring the carbon dioxide evolved. A solution of 
sodium bicarbonate, also containing 10 grm. of glucose per 100 c.c., was then 
made up which yielded the same amount of carbon dioxide when neutralised 
as the arsenate solution. The liquid in each flask was made up to the same 
volume with this sodium bicarbonate solution. The fermentation flasks 
containing the proper quantities of arsenate solution and bicarbonate were 
then incubated at 25° and the rates of fermentation observed. The effect of 
bicarbonate is to cause a slight increase in the rate of fermentation, owing to 
a diminution of the acidity of the juice (Buchner). 
The following results, all obtained from a single sample of yeast-juice, 
are typical, and show the nature of the relation between concentration of 
arsenate and rate of fermentation. . 
When the concentration of arsenate is very low, the rate falls off very 
rapidly from the maximum, and the numbers obtained in these cases can 
only be regarded as approximate. This is the case in the present set of 
observations for amounts of arsenate less than 0°1 c.c. 
Experiment 6.—20 cc. of yeast-juide+a cc. of 03 molar arsenate 
+ (20—«x)c.c. sodium bicarbonate solution. Glucose, 4 grm. © 
Arsenate solution per ee oe elas Maximum rate of 
40 c.c. mixture. f er ema ar » fermentation. 
ermenting mixture. 
c.c. c.c. per 5 minutes. 
0 (6) 3°5 
0 :005 0 :000037 6:3 
0°01 0 ‘000075 8:0 
0 ‘02 0 ‘00015 14:2 
0 :04 0 :00038 19 °9 
O'l 0 ‘00075 29 °7 
0:2 0 :0015 35 ‘0 
0°5 0 :00375 34 °9 
1 0 ‘0075 29 °5 
2 0-015 23 °2 
5 0 :0375 145 
10 0 °075 8 °7 
15 0 °1125 5°3 
20 0°15 3 °2 
The same results are exhibited graphically in the accompanying curves, 
in which the rate is plotted against the cubic centimetres of arsenate present 
in the mixture. Curve B represents the earlier portion of A, plotted with a 
twenty-fold scale of abscisse. 
