286 ILLINOIS ACADEMY OF SCIENCE 
AN IMPROVED FORM OF HIGH VACUUM HIGH 
SPEED MERCURY VAPOR AIR PUMP 
ABSTRACT 
CuHas. T. Knipp, UNIVERSITY OF ILLINOIS 
Dr. Gaede’ of Berlin, in a recent number of the Annalen, 
described an air pump based partially upon the principle of 
the aspirator, in which the air to be evacuated diffuses through 
a narrow slit into a stream of mercury vapor and is carried 
away with it. Langmuir’, of the General Electric Company, 
pointed out that even greater speeds in evacuation may be 
obtained by replacing the slit by a large nozzle opening into a 
condensing chamber surrounded by a water jacket. The un- 
derlying principle is that the gas is trapped mechanically by 
the condensing mercury vapor and forced onward along the 
walls of the condensing vessel to a side opening through which 
the accumulated gas is drawn by the supporting pump. 
The writer has improved the design and efficiency of this 
pump by making it more compact and at the same time se- 
curing better heat insulation at certain points and more effec- 
tive cooling at others. An idea of the speed of evacuation 
may be obtained from the following test. A 6 litre flask was 
attached to the mercury vapor pump which in turn was sup- 
ported by a Gaede rotary mercury pump. With the Gaede 
pump operating alone (it should be remarked that this pump is 
the type now generally used in the production of very high 
vacua) it required 52 minutes to produce an X-ray vacuum; 
while with the mercury vapor pump operative it required but 
2% minutes to produce the same vacuum. 
1, Ann. Phys., 46, 357, 1915. 
2. Phys. Rev., 8, 48, July 1916; Gen. Elect. Rev., 19, 1060, Dec. 1916. 
