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II. 



OSMOTIC PEESSURES IN PLANT-ORGANS. 



III. — The OsMOTtc Pressure and Ei.ectrical OoNnuoxiviTV of 

 Yeast, Beer, and Wort. 



By henry H. DIXON, Sc.D., F.R.S., 

 University Professor of Botany, Trinity College, Dublin ; 



AND 



W. E. G. ATKINS, M.A., Sc.B., A.I.C., 

 Assistant to the Professor of Botany, Trinity College, Dublin. 



[Read April 15. Published May 24, 1913.] 



In view of the rapid metabolism of the yeast-cell as regards carbohydrates a 

 study of the osmotic equilibrium between it and the solution which it ferments 

 seemed to be of interest. 



It has recently been demonstrated by Paine (5) that alcohol penetrates 

 the yeast cell readily, a state of equilibrium being soon reached in which the 

 ratio of alcohol in the cell to that outside is a constant, deviating only slightly 

 from 0'85. Salts, on the other hand, penetrate to a small extent, the ratio 

 of the internal and external concentrations being no more than 0'l-0'25, 

 except in the ease of poisonous substances. Indeed, it is an open question 

 how much of this apparent absorption is really due to adsorption on the 

 surface. 



To determine the osmotic pressure the method of thermo-electric 

 cryoscopy (1) was employed. The unaltered yeast-juice was obtained by 

 freezing the dry material in liquid air and eentrifuging the resulting fluid 

 mass as described in detail in our account of zymase extraction (3). 



The electrical conductivity of the juice, beer, and wort was also determined, 

 to give an idea of the relative proportions of electrolytes and non-electrolytes 

 concerned in the production of osmotic pressures. The apparatus was the 

 usual one, which we employed in previous work (2) . All specific conductivity 

 measurements were carried out at 0°, and are recorded as reciprocals of the 

 resistance in ohms, not in Siemens' units. 



SCIENT. PEOC, E.D.S., VOL. XIV., NO. II. C 



