S6G Dr. B. D. Steele on an 



connexion between A and the valve a, at v. The bottom of 

 the reservoir D is situated 16 centimetres above the highest 

 point of the tube //. 



The shorter limb of the U-tube h is 25 centimetres long, 

 and the enlargement i is 75 cm. above the level of the side- 

 delivery tube on F. 



Twenty pounds of mercury are required to work a pump, 

 of the foregoing dimensions. 



Filling the Pump. 



Before starting to fill the pump, the stopcock c and the 

 pinchcock on I are closed, and mercury is poured into the 

 vessels a and F, and into the traps z and k. The trap k is 

 provided with a side-tube at the point y, to enable this to be 

 done, and when sufficient mercury has been inserted this tube 

 is sealed off. The water-pump is now connected at the trap 

 z, and the mercury required to fill the pump is poured into 

 E. Under the action of the water-pump, which must be 

 sufficiently powerful to reduce the pressure in the apparatus 

 to 10 or 15 cm. (whilst the side-tube is open to the atmo- 

 sphere), the mercury rises in the tube m. Air is, however, 

 slowly leaking in through the constricted branch of q, and 

 this air breaks the mercury in m into columns which are 

 carried over into B. In this way the whole of the mercury 

 required is pumped rapidly from E into B. 



Working the Pump. 



It has been already stated that the pump was designed 

 (1) to discharge the extracted gas into the water-pump, (2) 

 to collect samples of the gas for examination, and (3) to 

 collect the whole of the gas from any piece of apparatus. 

 The manner of working of the pump will be best shown by 

 describing in detail the course of one complete stroke when 

 it is working as required for case (1). 



Starting irom the time when a small quantity of the 

 mercury required for filling the pump remains in E, and 

 when the pressure in A, B, 0, and 1) has been reduced to 10 

 or 15 centimetres, it will be seen that with the removal of the 

 last globule of mercury from E into B, air can freely enter 

 the latter vessel through the tube w. The water-pump is 

 not capable of removing the air as quickly as it enters, and 

 the consequent rise in pressure causes the mercury to rise in 



