1905.] 



The Alcoholic Ferment of Yeast- Juice. 



417 



8. Products of Fermentation in the Presence of Phosphate. 



The carbon dioxide evolved during the initial period after the addition of a 

 phosphate is the product of a true alcoholic fermentation of the glucose, in 

 which alcohol and carbon dioxide are produced in equivalent amounts. This 

 was proved in the following way. Twenty-five cubic centimetres of a solution 

 containing 2'5 grammes of glucose and 5 c.c. of a 0'3 molar solution of 

 potassium phosphate were added to 25 c.c. of yeast-juice ; the mixture was 

 incubated and the carbon dioxide collected and measured. 



As soon as the rate of evolution had become constant, a further addition 

 of 10 c.c. of 0*3 molar phosphate solution was made and the fermentation 

 again continued until the rate had become constant. The gas evolved was 

 tested and found to be carbon dioxide. The total amount evolved during the 

 experiment, which lasted for 2 hours 10 minutes, was 163-4 c.c. at 19°"6 and 

 758 - 6 mm. or 291 gramme, the equivalent of the phosphate added being 

 0*196 gramme. The liquid was then distilled with steam and the alcohol 

 estimated in the distillate, 1*312 grammes being found to be present. 

 Twenty-five cubic centimetres of the original juice were found to contain 

 0*983 gramme of alcohol and therefore 1*312 — 0*983 = 0'329 gramme were 

 formed by the fermentation of the sugar. The ratio of alcohol to carbon 

 dioxide produced is therefore 0*329/0*291 = 1"13, which agrees well with the 

 ratio previously found by similar methods for the fermentation of glucose by 

 yeast-juice.* The theoretical ratio is 1*04. 



Lactic acid and acetic acid were also estimated in the original juice and 

 after fermentation in presence of phosphate, but only a very small variation 

 was observed. Twenty-five cubic centimetres of juice gave before fer- 

 mentation 0122 gramme of zinc lactate and 0*083 gramme of acetic acid, 

 and after fermentation 0*102 gramme of zinc lactate and 0'072 gramme 

 of acetic acid. 



9. Fate of the Phosphoric Acid. 



"When the fermented liquid is boiled and filtered almost the whole of the 

 phosphorus present is found in the filtrate, but it is nearly all in a form 

 which is not precipitated by ammoniacal magnesium citrate mixture. 



In the following experiment three quantities of 25 c.c. of yeast-juice were 

 taken : — 



A. Hot water was added, the solution heated in a boiling water-bath and 

 the coagulate filtered off and well washed. 



B. Ten cubic centimetres of a 30 per cent, glucose solution and 10 c.c. of 



* Harden and Young, 1 Ber.,' 1904, vol. 37, p. 1052. 



2 H 2 



