480 stimson: mercury vapor pump 



G, 3 mm. long with a throat 1.8 mm. in diameter, which sends the 

 mercury vapor through a tube 0, 3.5 mm. diameter, across which 

 is supported the pressure from a water aspirator used as a fore 

 pump. Care must be taken to leave sufficient clearance around 

 the end of the nozzle G, and the tube has been slightly tapered 

 leaving a clearance of 0.7 mm., which seems to be sufficient to 

 prevent condensed mercury vapor from collecting to make a 

 seal. It appears that the size of this unit cannot be reduced 

 below a certain limit determined by the surface tension of mer- 

 cury. The pressure of the vapor in the boiler and feed tubes, E, 

 has been raised to as high as 20 to 25 cm. of mercury, as is indi- 

 cated while the pump is in action by the height of the mercury 

 columns in tubes K. In the high vacuum stage a DeLaval 

 nozzle, F, with a throat 0.7 mm. in diameter has been used ex- 

 panding by about a ten to one taper to a diameter of 5 mm. dis- 

 charging into a tube nearly a centimeter in diameter. 



The operation of the pump is as follows. Cooling water 

 entering at tube A flows up through the water jacket B above 

 the lower end of nozzle F, up through the water jacket C above 

 nozzle G, and out tube D. Mercury vapor from the boiler 

 entering through tubes E flows through the nozzles F and G, 

 is liquefied in the condensation chambers H and /, falls into the 

 tubes K, and returns to the boiler through tube L. Gas from a 

 vessel to be exhausted enters at M, flows past nozzle F, is com- 

 pressed by the jet of mercury vapor in the condensation chamber 

 H, and flows up through tube N to the intermediate pump. 

 From here it flows past the nozzle G and is compressed through 

 in the chamber / to a pressure measured by the attached 

 manometer, then out by tube P to the water aspirator. 



Tests of the pump described above indicate a speed, when 

 working against a primary pressure of 4 cm., of about 250 cm. 3 

 per sec. when speed is defined 2 as 



S = V/t\ogpx/p 2 



where S is speed, V is volume, t is time, pi and p 2 are initial and 

 final pressures. The pump gives a limit of pressure of non- 



2 Gaede. Ann. d. Physik, (5) 41: 365. 1913. 



