[satterly] viscosity EXPERIMENT 119 



In the apparatus used for some years in my elementary laboratory 

 in Toronto to find the coefficient of viscosity of air a uniform 

 capillary tube AB (Fig. 1) about 30 cms. long and 1^ mm. in bore is 

 selected and two short tubes of about the same bore are carefully sealed 

 on at right angles at two points C, D, about 6 cms. from the ends, and 

 to these are sealed a length UT of three-eighths inch glass tubing 

 bent as shown in the diagram. This tube serves as a pressure gauge 

 and the arms just enclose a wooden millimetre scale 55 graduated 

 alike on the two edges. The tube is mounted by brass clips on a 

 wooden stand L, a strip of white paper being placed as a backing to 

 the tube. In some forms a tube runs from the bottom of the U-tube 

 back under the upturned V notch in the stand and communicates 

 by a rubber tube to a funnel supported in a bracket at the back. 

 ,This tube may be clipped tight with a screw clamp. 



By means of the funnel and tube water is supplied to the mano- 

 meter. Sometimes by accident a large current of air is sent through 

 the viscosity tube and the water in the gauge is blown out. It is not 

 an easy matter to replace the water without some device as mentioned 

 above. 



The complete apparatus for the experiment is arranged as shown 

 in Fig. 1, which is self-explanatory. 



For a given position of the screw clamp X the water flow soon 

 gets steady and consequently the position of the water in the gauge 

 UT. When this stage has been reached the water from N is collected 

 in a 500 c.c. graduated cylinder. The time of collection of 500 c.c. 

 is noted and the gauge readings. The volume per second is obtained 

 by dividing 500 c.c. by this time. If two students work at this 

 experiment the times are noted by an ordinary watch, and the experi- 

 ment repeated until constant results are obtained. If only one student 

 works at it a stopwatch is supplied. 



By tightening up the screw clamp to various degrees a set of 

 corresponding values of pressures and volumes is obtained. When 

 the bottle has run out a piece of tubing R connected to a cold water 

 tap serves to fill the bottle again and meanwhile it is safer to dis- 

 connect the tube F from the viscosity tube. The experiments can 

 then be repeated. 



To get the radius of the bore of the tube an accurate travelling 

 microscope may be used. In Toronto we use instruments with 

 verniers reading to one-hundredths of a millimetre. The microscopes 

 are sighted straight at the end of the tube and the cross wire carried 

 from one tangential position to the bore to the opposite position. 

 This is done for horizontal and vertical diameters at both ends of 



