10 



Scientific Proceedings, Royal Dublin Society. 



Through the kindness of Mr. A. McMullea of the Guinness Research 

 Laboratory, we were supplied with both pressed yeast and that skimmed from 

 the vats with adhering beer. The beer was removed by centrifuging or by 

 pressing through a linen cloth by hand. 



In Table I are recorded the results thus obtained, A being the depression 

 of freezing-point, P the osmotic pressure in atmospheres calculated from A, 

 and c the specific electrical conductivity at 0°. 



Table I. 



From the above figures it may be seen that, both in osmotic pressure and 

 electrical conductivity, pressed yeast gives values which are much higher than 

 those of wort. Baker's yeast, however, gives a low osmotic pressure, but a 

 high conductivity even after washing. 



The figures afforded by the sap of yeast and by the surrounding nutritive 

 fluid may be seen in Table II, p. 11. 



On comparing the results given by beer with those of wort it is at once 

 apparent that while the electrical conductivity remains much the same, the 

 osmotic pressure becomes approximately three times as great during fermenta- 

 tion, when interrupted at the usual stage in the commercial process. Very 

 complete fermentation, however, judging from the single experiment we 

 performed, occasions a fall in osmotic pressure after the initial rise, and is 

 accompanied by a marked increase in the conductivity (see Table I, No. 

 597). It is, however, possible that the conditions of this fermentation were 

 abnormal, and there was probably considerable loss of liquid by evaporation. 

 The above-mentioned experiment is substantiated by No. 609, which is the 

 beer of No. 606 allowed to stand at air-temperature in a closed vessel with 

 ;x little yeast. It will be noted that there is a fall in pressure, but a sliglit 

 rise in conductivity. 



