116 Mr. F. J. Smith on an Air-mercury Pump. 



the air passes through the tube P to a drying-chamber Q, 

 and to the elevator RCB, the water rises in the tube M N, 

 and is discharged at N (the tubes are shown broken to 

 economize space in the diagram); the pressure of the air is 

 controlled by the pressure of the supply at L, and by the 

 vertical height of M N. 



When the elevator is to be used, water is turned on at L, 

 till it flows freely at N, and F is slightly opened ; then the 

 Sprengel pump is started. As soon as sufficient mercury 



has collected to overflow, it is immediately raised by the 

 compressed air into A, the sum of the lengths of the little 

 columns such as S, T, &c. being less than the length of the 

 column R D. 



As the water used in compressing the air is in no way 

 injured by the process, it may fill a tank and be used for 

 any purpose. 



The elevator will of course raise many other liquids besides 

 mercury. If water is used instead of air, the mercury is also 

 raised but wetted in the process. Water may be used when 

 fluids which do not mix with it are to be dealt with. 



In the diagram the supports which carry the tubes, &c, 

 have been left out for the sake of clearness. In the instru- 

 ment, which has been at work for the last two years in the 

 Millard Laboratory, the height of the tube M N is about 

 eight feet, and the pressure of water at L 36 lb. per square 



