vi TENSION REQUIRED TO RAISE THE SAP 135 



1-30 



1^20 



1-10 



1-00 



90 



80 



70 



60 





Velocity proportional to the pressure. Through- 

 out this discussion it has been assumed that the 

 velocity is proportional to the pressure. This is usually 

 done. Fig. 21 shows that this is certainly approximately 

 true for pressures up to 16 units head. In this diagram are 

 plotted the results of many experiments, the object of which 

 was to determine if the 

 amount transmitted in 

 a given time is propor- 

 tional to the pressure, as 

 the former assumption 

 would involve. The 

 utmost care was taken 

 to obtain clean water to 

 supply to the wood and 

 to free the latter from 

 clogging material as 

 much as possible. The 

 water used was distilled, 

 the vessels and tubes of 

 supply were repeatedly 

 washed with distilled 

 water before using, and 

 the surface of the wood 

 freshly cut and rinsed 

 with distilled water im- 

 mediately before the ex- 

 periment began. The woody cylinder was 3 cm. long. It 

 was supported horizontally, and a tongue of bibulous paper 

 was applied to the outer surface of the wood and hung 

 down vertically into a little phial which received the drops 

 of transmitted water. The time required for five drops 

 to fall from the tongue was noted by means of a stop- 

 watch, and the weight of these five drops determined by 

 weighing the phial. The mean of three such observations 

 is given in Table 16 for each pressure. 



50 



40 



30 



20 



10 



6 8 10 



Units Head 



Fig. 21. 



12 



14 16 



