V 



444 E. W. Morley — Self- Acting Mercurial Air pump. 



rising for the next stroke has parti}' filled the pump body g, 

 let I be lowered ; the mercury which tills the passage from g to k 

 will run into I and so open this passage. The air in g will 

 therefore be freely discharged into k. The simple raising and 

 lowering of I performs the same function as the use of the 

 third stopcock of the Geissler pump ; and it introduces no 

 source of leakage. It very greatly increases the perfection of 

 the vacuum which can be attained with a Toepler pump. 



It was hoped to give here the result of a measurement of 

 the efficiency of the same pump with this device alternately 

 active and inactive ; but a serious accident makes it at present 

 impossible. 



The means by which the motion of I is made automatic is 

 shown at u and o. n contains mercury ; it is connected with o 

 and pivotted near n. The air pressure which works the pump 

 is conveyed to n. When the mercury of the pump rises in g, 

 mercury is also driven from n to o / this becomes heavy, 

 draws I downward, and so opens the passage from g to k. This 

 passage as well as I is filled when the air is discharged into k, 

 and remains full when I is raised, to be opened again at the 

 next stroke. The device will no doubt be thought rather 

 fragile : but out of some twenty-five or thirty breakages of 

 Geissler and Toepler pumps in my laboratory, it is the whim- 

 sical fact that this is the only part which has not yet been 

 broken. 



One less important matter may be mentioned. About 

 twenty Toepler pumps have been broken in my experiments 

 by the impact of ascending mercury against the upper part of 

 the pump body. It was better economy of time to break 

 them than to drive them slowly : but very vexatious. If the 

 attempt is made to avoid breakage from this cause by elongat- 

 ing the upper part of the pump body, so as to give a slow 

 motion to the ascending mercury, a contrary evil is introduced. 

 The descending mercury clings in the tube, and at last falls so 

 heavily as to split the tube j?/ as has happened to me several 

 times. JSTow a contrivance has been in use which it is hoped 

 may prevent breakage without retarding the action of the 

 pump. It consists of a float seen at r, fig. 3. This is so ad- 

 justed as to settle into the neck of f just before the mercury 

 in g rises to the danger point. The flow of mercury is then 

 checked by the loosely fitting float, and, what is more im- 

 portant, oscillation is prevented. It works well so far, al- 

 though it has not been long enough in use to warrant confident 

 recommendation. But of the air compressor here described it 

 is proper to speak confidently. The one which has been in 

 use longest often makes twenty thousand strokes without 

 failure or readjustment. 



