Automatic Toepler Pump. 867 



A, and, driving the gas before it into the receiver c, it over- 

 flows through the tubes li and t into the vessel F, from this 

 into p, and finally through o into the large bulb E. This 

 overflowing mercury closes first the constricted and then the 

 open end of the branched tube q, and thus cuts off the supply 

 of air to the reservoir B. 



The water-pump now reduces the pressure in the reservoirs 

 B and D, and as a consequence the mercury immediately 

 begins to flow back through the U-tube d, from A into B. 

 and the overflow into F and p ceases. 



About forty seconds after the closing of the tube q the 

 mercury will have fallen to the point v, and in the meantime 

 ihe mercury in p has been slowly siphoning through the 

 branched tube q into the bulb E. 



With the constriction used, the time required to empty p 

 is eighty seconds, and there is therefore an interval of forty 

 seconds between the opening of the communication at v and 

 the emptying of the tube p. During this time the apparatus 

 to be exhausted remains in communication with the stroke- 

 cylinder A. Following the last globule of mercury which 

 siphons from p into E, air enters through the shorter branch 

 oH q, and the mercury in E is pumped back into the reservoir 



B, and finally, when all the mercury has been removed from 

 E, air again enters freelv through the tube m. and another 

 stroke begins. The gas that accumulates in C finds its way 

 through the tube h, the bulb D, and the trap k, to the water- 

 pump. 



Case (2). If it is desired to collect samples of the gas, this 

 can be done as follows : — 



A test-tube of the size required is filled with mercury, and 

 inverted over the turned-up end of the tube </, the pinchcock 

 t is closed, and at the following stroke of the pump mercury 

 flows, by way of /', C, and h t into the bulb D. When a quantity 

 more than sufficient to till the bulb C has accumulated here, 

 the pressure in D is caused to rise by opening the pinchcock 

 on the tube /, when the gas in C is forced into the tube 

 placed to receive it. The excess of mercury flowing into s 

 finds its way as before into p and E. 



Finally, the pinchcock I is closed, that at t opened, and the 

 cycle proceeds as previously described. 



Case (3). Should it be desired to collect the whole of the 

 gas from the apparatus being exhausted, trie pinchcock t 

 must be kept closed, and a vessel to receive the gas must he 

 placed as before over the end of g. If the pressure in the 

 apparatus is low, that is. if the quantity of gas to be collected 



