Viscometry. 157 



apparatus of Eedwood. I have found the following results 

 using a cylinder oil : — 



Temp. No. of Tests. Max. Min. Mean. 



250° F. 11 34.0 sec. 33.0 sec. 33.5 sec. 



200° F. 16 45-3 " 44.5 " 44.8 " 



In order to determine the change in the rate of flow due 

 to lowering of the level, I made series of tests taking, in 

 each case, three successive portions of 50 cc. The inilial 

 level is always 2J inches above the upper surface of the 

 nozzle : 

 1. Temp. 250° F. (means)— 



1st, 50 cc. 2nd, 50 cc. 3rd, 50 cc. 



33.5 sec. 34.7 sec. 36.0 sec. 



At 200° F.— 



44.8 sec. 47.2 sec. 50.6 sec, 



The withdrawal of 150 cc. causes the level to fall about 

 three-eighths of an inch, corresponding to an increase in 

 time of about 2J- seconds at 250° F., and about 5J- seconds 

 at 200° F., a guarantee that any slight error in the adjust- 

 ment of original level can have but a very trifling effect on 

 the rate of flow. The following experiments were made 

 with a sample of glycerine diluted to the density of Eed- 

 wood's standard rape oil, viz. : — 1.226 at 15.5° C. 



Redwood's Viscometer. — The temperature of the laboratory 

 during these experiments was 68° F. I attempted to keep 

 that of the dilute glycerine at 60°, but found this to be 

 impossible. The following series of seven tests were made 

 at 59.5° to 61.5°:— 



Max., 483 sec. Min., 460 sec. Mean., 469. 5 sec. 



With the form of instrument which I have described above, 

 I found it quite easy to keep the temperature constant to 

 within 0.5 degree during the time of the experiment : — 



Max. 



313.5 



308.4 



305.0 



209.0 



166.0 



The above represent consecutive series of tests, and illus- 

 trate the extremes of experimental error. (See note p. 168.) 



k Expts. 



Temp. 



5 



60.0° F. 



5 



60.5° F. 



7 



61.0° F. 



6 



70.0° F. 



4 



75.0° F. 



Min. 



Mean. 



310 



311.7 sec, 



306 



307.0 " 



300 



302.1 " 



205 



207.0 " 



164 



165.0 " 



