at Ver'i Low Rates of Shear. 68$ 



Results of First Experiments. 



Two liquids were tried, a heavy kerosene and distilled 

 water. As regards the earlier experiments, it will be sufficient 

 to state the results without entering into the details of the 

 measurements. The maximum rate of shear in these experi- 

 ments was about 5 radians per second for water and 0*2 for 

 kerosene. The following results were obtained for kerosene, 

 the first fignre being in each case the viscosity at the low 

 rate of shear, while the figure following it in brackets is 

 the viscosity at the same temperature as obtained by the 

 ordinary capillary-tube method at a maximum rate of shear 

 of about 20.000 radians per second :— 0'0232 (0*0235), 0-0243 

 (00246), 0*0239 (0-0239). 0*0244 (0*0244). In these expe- 

 riments the method of a siphon for raising the level in one 

 of the vessels together with the use of two optical levers was 

 employed. The constants of the levers were obtained by 

 supporting the movable leg on a micrometer screw-gauge. 

 Using exactly the same method and instrumental constants, 

 the results for distilled water were*: — 0*0114 (0*0105), 

 0*0116 (0*0105), 0*0115 (0*0104). In each case the water 

 had been left at rest in both tube and vessels from 20 to 24 

 hours after it was introduced in order to insure the level 

 being the same in both vessels. 



As these re.-ults seemed to indicate that the viscosity of 

 water is 9 or 10 per cent, greater at the lower rates of shear, 

 ir was considered advisable to vary the experiment somewhat. 

 For tlii- purpose, the method of initially raising the level of 

 the liquid in one of the vessels by placing in it a body of 

 known volume (a steel cylinder) was used, and the constant 

 of the optical lever was determined by running a known 

 volume of liquid from a pipette into the vessel on which the 

 optical lever was mounted, the capillary tube being mean- 

 while closed by a rubber cap ; also the surface of the water 

 in cadi vessel was stirred up before readings were begun in 

 order to destroy any surface-rigidity. On each occasion 

 several determinations of the viscosity were made, the first after 

 the liquid bad been at rest in the tube about 24 hours, and the 

 succeeding ones in each set a- quickly as the water could be 

 brought back to the same level in the two vessels. The 

 following are the percentages by which the viscosity of water 

 at slow shear exceeded the ordinary value at high shear, the 

 successive sets of determinations being separated by dashes : — 

 (1)12, 11. in. lo. L0— (2)10,9,5,4— (3)13,9,8,7,6. The 

 same method was applied to kerosene, and as before its 

 viscosity was found thesameai high and at low rates of shear. 



* The numbers in bracket- were found by graphical interpolation from 

 Thorpe and Rodger's results, Phil. Trans, vol. clxxvii. (1886). 



