315, 



ILLINOIS STATE ACADEMY OF SCIENCE 



exactly one-tenth the former volume. Readings at 5-minute 

 intervals were again taken. The data relative to this pump 

 with these two volumes are contained in Table I. 



Just recently (April 11) the department purchased a 

 second Cenco-Hyvac oil pump. This was at once connected 

 up as shown in Fig. 1, first with the 13 liter volume, then 

 with a 6 liter volume, and finally with the 1.3 liter volume. 

 The running conditions, etc., were exactly the same as in the 

 first pump. The data relative to these three volumes are 

 contained in Table II. 



The data in Tables I and II are plotted in Fig. 2, in which 

 the crosses represent pump No. A112, received in December, 

 1920, and the dots pump No. A186, purchased recently. A 

 careful study of the tables and curves makes further com- 



40 







Ti 



me m rwinu'L'ea 



FIG. 3. 



ment seem scarcely necessary; suffice it to say that the 

 hmit of pump A112 appears to be at about .00085 mm. 

 mercury, while that of pump A186 is about .0050 mm. mer- 

 cury. Tags attached to the pumps indicated .001 mm. mer- 

 cury for A112, and .00055 mm. for A186. Thus the data 

 obtained in our laboratory place the respective limits at 



