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XL An Air-mercury Pump, for raising Mercury in dif- 

 ferent kinds of Mercurial Pumps. By Frederick J. 

 Smith, M.A., Millard Lecturer on Mechanics and Physics, 

 Trinity College, Oxford *. 



MANY people who constantly use the mercury-pump of 

 Sprengel, or other forms of pumps iu which a vacuum 

 is produced by the fall of mercury, must have felt that it 

 would be a considerable help in their work if the mercury 

 which falls in working the pump could be returned at once 

 to the cistern at the top of the instrument without any 

 personal attention, so that the process of exhaustion might 

 go on without interruption for days together if nece : sary. 

 The instrument which I now describe, when added to the 

 ordinary mercurial pump, renders it perfectly self-acting. I 

 propose to call the device the Mercury Elevator. 



In the Philosophical Magazine for 1888, vol. xxv. p. 313, 

 I described a water-engine, whereby mercury was raised for 

 driving a pump used for exhausting glow-lamps. This 

 arrangement was satisfactory but costly, and required careful 

 adjustment. The instrument about to be described produces 

 the same results, while it can be easily made up from appa- 

 ratus in daily use in every laboratory. The idea of a 

 Sprengel pump completely reversed both in position and 

 action, first suggested to me the possibility of making this 

 instrument. 



The mercury elevator is nothing more than a Sprengel 

 pump, inverted, and worked backwards. Where a vacuum 

 is formed under ordinary circumstances, air is forced in, 

 and instead of little cylinders of mercury falling they are 

 raised. 



The construction is shown in the appended diagram, 

 where A is the cistern of the Sprengel or other mercurial 

 pump ; B C D, a tube furnished with a side tube at C, and 

 attached at D to the catcher of the Sprengel pump E. By 

 means of the pinch-cock F, the supply of compressed air is 

 controlled. The air may be compressed either by an ordinary 

 condensing pump driven by any prime mover, or by the 

 following arrangement, which may be used where there is a 

 supply of water at a sufficient pressure. 



G is an ordinary water-pump. When water under pres- 

 sure enters at L, air is drawn in at G, and is discharged at 

 K into a copper cylinder H ; here the air and water separate ; 



* Communicated by the Author. 



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