232 Scientific Proceedings, Royal Dublin Society. 



encouraged me in this attempt. Accordingly a quantity of sap was collected 

 from a branch of Ilex Aquifolhim by means of eentrifuging ; and this after 

 exposure to air and without any special treatment was introduced into several 

 capillary tubes, which had been prepared in a manner similar to those used 

 in the other experiments. 



The first tube closed at a temperature of 78"20° C, and ruptured on 

 cooling to a temperature of 72'00° C. (see Experiment No. 7 in the Table). 

 This rupture occurred simultaneously with a slight shock accidentally dealt 

 it by the stirrer of the vessel of water in which it was immersed. Had it 

 not been for this, probably a lower temperature would have been attained 

 without rupture. Taking these figures and the dimensions of the tube into 

 account, the tension developed must have been about 75 atmosplieres. 



Another tube containing some of the same sample of sap completely 

 filled at a temperature of 91'10°C. On one occasion rupture took place 

 only when a temperature of 76-20° C. was reached ; on another occasion a 

 rupture developed at some temperature below 81"50°C. In the latter case, 

 when the tube hadiallen to 8r50°C., it was witlidrawn from the water for 

 examination, and rupture occurred some seconds after it was lifted from 

 the water. In the first instance the tension must have approximated to 

 207 atmospheres ; while in the second a tension of about 132 atmospheres 

 was attained before rupture occurred. 



Tiie former of these is the higliest yet recorded, I believe, for the 

 cohesion of any liquid. Possibly this very good cohesion possessed by 

 unboiled sap is due to the presence of colloids in it. It seems probable 

 that when the tension is just adequate to start a rupture, if tlie latter 

 remains sufficiently small, its surface tension will be able to withstand 

 the stretching action due to the contraction and cohesion of the liquid. 

 Thus, if the rupture at its first inception can be delayed in spreading, it 

 may be obliterated and cohesion re-established. The presence of the 

 colloid may bring about the necessary delay.' The appearance exhibited 

 occasionally in these sap-containing tubes may be interpreted as favouring 

 this view. The click of rupture is not, in these eases, attended by the develop- 

 ment of a single bubble becoming surrounded by a group of small visible 

 bubbles, but, at the moment of rupture, a milky semi-opaque region develops 

 in the tube. This slowly rises and clears away as it turns into a mass of 

 excessively minute bubbles. Here apparently at the destruction of cohesion 

 countless numbers of minute ruptures have been simultaneously produced. 



No. 8 gives the details of a third observation with this tube. 



' The fact that the presence of colloids leads to a large volume-contraction of the solvent may also 

 increase the cohesion of the sap. 



