'090 



Prof. Wilmer DufF on Poiseuille's Lax 



These results seemed to show that the difference between 

 the viscosity of water at low rates of shear and that at high 

 rates was greater the longer the liquid had been at rest. In 

 each determination, the total amount of flow was so small that 

 only a small part of the water was expelled from the tube. 

 The only possible explanation seemed to be that the water 

 dissolved from the tube a very small amount of some consti- 

 tuent that had an extraordinarily large effect on the viscosity 

 at low rates of shear. The following experiments were decisive. 



Final Results. 

 The first of the following sets of experiments was made 

 with a view to measuring the viscosity of water as soon as 

 possible after the water had been allowed to enter the tube, 

 and then at increasing intervals of time afterwards. Every- 

 thing having been made ready for reading, a bubble of air 

 was first blown through the tube to completely remove the 

 water in it. As soon as the reading of the level became 

 stationary, the body of known volume was quickly lowered 

 beneath the surface of the water in one vessel, and readings 

 of the level of the water in the other vessel were made every 

 minute for five minutes. After the intervals noted in the 

 first column of the Table the process was repeated without 

 the water being blown out of the tube. 



Section of first vessel at level of water = 317-6 cm. 2 = A,. 

 Section of second vessel at level of water = 321*7 cm. 2 = A 2 . 



Volume of steel cylinder = 28*84 c.c. 



Rise of level produced by steel cylinder = "09081 cm. = /* . 



Length of tube = 139*5 cm. = /. 



Radius of tube = '1675 cm.=r. 



Time of flow = 300 sec. = t\ — 1 . 



Volume of calibrating pipette = 8*547 c.c. 



Time 



liquid was 



in tube. 



Temp. 



Cali- 

 bration 

 reading. 



Cbange 

 of scale 

 in 5 min. 



Value of 



scale - 

 division. 



hi. 



Viscosity j Viscosity 



(low (high 



shear). . shear). 



Per cent. 



dif- 

 ference. 



22 m 

 37 m 



o 



6-47 

 6-49 



15-84 



6-51 

 651 



•001677 



" 



•068S1 

 •06881 



•01 469 -01450 

 •01469 -01449 



1*3 



1-4 



2 h 48 m 

 3h 3 m 

 3h 21m 



6-75 

 6-76 

 6-82 



" 



6-48 

 6-47 

 647 





•06892 

 •06895 

 •06895 



•01477 -01437 

 •01480 -01437 

 •01480 -01435 



2-8 

 30 

 3-1 



20 b 



670 

 672 

 6-76 



15-72 



55 



6-38 

 6-37 

 6-40 



•01691 



" 



•06909 

 •06913 

 •06902 



•01491 

 •01494 

 •01486 



•01440 

 •01439 

 •01437 



3-5 

 3-8 

 3 4 



3-7 

 4-0 



401 1 



6-42 

 6-45 



" 



633 

 6-32 



•06926 

 •06930 



•01504 

 •01508 



01451 

 •01450 



