660 



Scientific Proceedings, Royal Dublin Society. 



Comparison of the conductivities shown in the last two columns indicates 

 that the application of the linear viscosity correction to the conductivities of 

 the Island Bridge saps, which is recorded in Table IV, has resulted in a con- 

 siderable over-estimate of the amount of electrolytes present. The decrease 

 shown by electrolytes with increasing concentration of sugar, to which it will 

 be remembered attention was drawn in Table IV, must be therefore greater 

 than the figures in the table indicate. 



It will have been noted that high viscosities in the sap are usually 

 accompanied by low conductivities ; as this suggested that the large viscosities 

 shown by the saps from Island Bridge may to some extent have been 

 associated with the failure of a small concentration of metallic ions to 

 coagulate the gums, it was thought that by freezing these saps the dis- 

 turbance introduced into the viscosity correction by the presence of gums 

 might be partially removed. Freezing the saps of course effects an increase 

 in the concentration of electrolytes. It is not clear why this clumping of 

 colloids should not proceed in the sap of the living cell. 



The results recorded in Table VIII will serve to illustrate the effect 

 obtained by immersing the sap in a freezing mixture of - 10° C. 



Table VIII. 



The results indicate that, instead of a decrease, a marked augmentation in 

 the viscosity of the sap has been effected ; it is doubtful whether this is to be 

 associated with the freezing of the sap, or is merely due to a growth in viscosity 

 such as occurs in emulsoids with age ; it is even possible that pectase, which 

 is normally present in the sap of Syringa vulgaris, may have been responsible. 



As many emulsoids are extremely sensitive to mechanical treatment, it 

 seemed possible that the intense disturbance effected by centrifuging the sap 

 might lead to a great diminution of the viscosity of the gums. 



A preliminary experiment carried out on a gum arabic sol seemed to support 

 this view ; it was found that prolonged centrifuging at high speeds consider- 

 ably decreased the viscosity of this gum, and ultimately brought about some 

 precipitation. On repeating this treatment on the sap, however, no appreciable 

 decrease in the viscosity could be obtained. 



Unless some means can be found of readily eliminating the gums without 



