JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VII SEPTEMBER 19, 1917 No. 15 



PHYSICS. — A two-stage mercury vapor pump. H. F. Stimson, 

 Bureau of Standards. (Communicated by E. Buckingham.) 



A "Condensation Pump" was described by Dr. Irving Lang- 

 muir 1 which not only produced the highest vacuum yet obtained 

 with a pump but had a speed of exhaustion (cm. 3 /sec.) greater 

 than any previously existing high vacuum pump. The pump is 

 exceedingly simple. A stream of mercury vapor from a boiler 

 is sent down from a mouth or nozzle into a water jacketed 

 chamber, entrains the gas coming past the nozzle, and condenses 

 when striking the walls of the chamber, thus preventing flow of 

 mercury vapor back to oppose the oncoming gas. This pump 

 requires for its operation a primary vacuum of a few tenths of 

 a millimeter of mercury pressure. 



Conditions sometimes make it necessary or desirable to use 

 as a source of primary vacuum either a water aspirator or some 

 mechanical pump which fails to reach a pressure low enough to 

 accommodate a single stage condensation pump. Two pumps 

 modified by Prof. C. A. Kraus of Clark University to essentially 

 the same form as Dr. Langmuir's later design were seen by the 

 author early in September, 1916, working in series against a 

 primary vacuum of 2 cm. given by a water aspirator. The 

 expediency of using a water aspirator even at times when the 

 vapor pressure of water is high has led to the present further 

 development of the mercury vapor pump. 



• l Jour. Franklin Inst., 182: 719. 1916; Gen. Elec. Rev., 19: 1060. 1916. 



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