PAPERS ON PHYSICS 313 



pressures that are lower than those claimed by the company. 

 Furthermore, it appears that pump A112 has improved 

 with use. 



The relative speed of exhaustion of the two pumps is also 

 shown by the curves. In general the speed is a complex 

 function of the volume exhausted, the time, and the pressure 

 at the beginning and at the end. and need not be considered 

 here. It should be noted, however, that it required about 

 27 minutes to reach the limit (.00051 mm. of mercury) in 

 exhausting the 1.3 liter volume, while approximately 85 

 minutes were required to reach the same limit in the case 

 of the 6 hter volume, and 120 minutes to reach the above 

 limit when the 13 liter volume was exhausted. This rela- 

 tion is best shown by the curve in Fig. 3, where volume in 

 liters is plotted against time in minutes required to reach 

 the limit .00051 mm. This curve is for pump No. A186. 



The foregoing data show that this t>T)e of oil vacuum 

 pump is quite rapid, and reaches a surprisingly high vacuum. 

 It is therefore well suited to be used as a fore pump to any 

 large throated rapid acting mercury vapor pump, since 

 there is ample overlapping — a necessary condition in any 

 system of exhaustion where fore or supporting pumps are 

 used. 



Laboratory' of Physics 

 University of Illinois 

 April, 1921. 



