868 On an Automatic Toepler Pump. 



is very small, the gas is displaced from G at every stroke of 

 the pump, and the overflowing mercury finds its way from s, 

 through F, into p and E. 



If the pressure is more than 1 or 2 centimetres, it is neces- 

 sary to manipulate the pinchcock on I. 



In the great majority of instances it is onlv during the 

 first five or six strokes of the pump that this will be necessary, 

 and in this case it is most convenient to open I at the end of 

 each stroke, exactly as described in case (2). 



Should the vessel to be exhausted be very large, the pinch- 

 cock I must be regulated so that the mercury contained in 

 the bulb u flows into D at such a rate that the last drop, 

 followed by air, enters D at the moment when the latter has 

 become about half full of mercury. If I is properly regulated, 

 it is found that mercury flows through it only when the tube m 

 is open to the atmosphere, and not when the reservoir B is 

 exhausted by the water-pump. 



In obtaining high exhaustion it is advisable to leave the 

 stroke-cylinder A in open communication with the apparatus 

 to be exhausted for a longer time than 40 seconds. This 

 object is obtained by attaching a side-tube to p, the capacity 

 of which increases the volume of mercury which must siphon 

 through q at every stroke. 



The quantity of mercury, and hence the time of flow, can 

 be regulated by sliding a well- fitting glass piston in this 

 subsidiary tube. 



The time occupied by a complete stroke of the pump that 

 is described here is 160 seconds, during 40 of which the 

 communication at v is open. By the use of the subsidiary 

 tube on p (not shown in the diagram) the total time is 

 increased to four minutes, that during which v is open is 

 increased to two minutes. 



In order to stop the pump, all that is necessary is to close 

 the pinchcock iv when the tube m contains mercury, and then 

 to disconnect the water-pump at z when the vessel A is 

 empty of mercury. To start the pump afresh, the pump is 

 attached to z and the pinchcock w is opened. 



Chemical Laboratories, 

 The University of Melbourne. 



