TEE A WAKHNING OF THE SIS ED 



61 



the twine will shorten and make a tight joint. It is 

 well to prepare several tubes, since some are sure to 

 work better than others. 



Place in each tube a strong syrup (a 

 solution of sugar in water) , stand them in 

 a tnmbler of water, mark the height of the 

 liquid in each tube, and leave them over 

 night. In the morning it will be found that 

 the sugar has absorbed water through the 

 membrane and that the liquid has risen in 

 the tube. Choose the one which shows the 

 greatest rise, for future experiments. 



To demonstrate that the absorption of 

 water can produce pressure, it suffices to fill 

 the tube completely full of syrup, invert in 

 a tumbler of syrup and tie on a piece of 

 sheet rubber (such as toy balloons are made 

 of) , holding the end under the syrup all the 

 time so as to exclude air. The rubber 

 should be tied on in the same way as the 

 bladder. The tube may now be rinsed in 

 water and then placed in water as before 

 (see Fig. 51). In a day or so the rubber 

 will become tightly stretched, showing that 

 pressure has been generated. 



In order to estimate how much pressure 

 is produced, we may proceed as follows: 

 Remove the rubber and fill the tube to within 



51. Apparatus 

 for demon- 

 strating that 

 osmosis ex- 

 erts p r e s - 

 sure. 



