stimson: mercury vapor pump 



479 



thus increasing the 

 dimensional reasonin w 

 the dimensions of the elements of 

 a second or intermediate stage 

 which will support a relatively 

 large pressure. . 



If both stages are to be oper- 

 ated from the same boiler, as is 

 extremely desirable, some change 

 has to be made in the design of 

 the high vacuum unit. On ac- 

 count of the increased boiler pres- 

 sure a constriction will be neces- 

 sary to cut down the flow of 

 mercury vapor to a sufficiently 

 low value. This can be most ef- 

 fectively accomplished by using a 

 long DeLaval nozzle which will 

 simultaneously introduce the ad- 

 vantages of reduction of pressure 

 and increase of velocity. 



These principles have been con- 

 sidered in the construction of 

 pumps indicated in figure 1 . Sam- 

 ple dimensions will be given to 

 indicate working sizes, although 

 the size will in most cases depend 

 on the speed desired. The pump 

 in question, including its boiler, 

 was constructed entirely of Pyrex 

 glass which is well adapted to 

 this use and can be rapidly manip- 

 ulated. The boiler was made of 

 a half liter Erlenmeyer flask with 

 slightly rounded bottom. 



In the intermediate stage is a 

 short slightly expanding nozzle 



density of the discharged vapor. This 

 ; will enable one to proportion properly 



Fig. 1. Two-stage pump. 



