Duplex Mercurial Air-Pump. 379 



make their appearance can be easily pumped out. The 

 apparatus is so compact that it can be held in the hands while 

 in operation, not requiring mounting on a board. The pump 

 is very simple, and a glance at the accompanying diagrams 

 will make its construction clear. It will be seen to consist of 



two bulb-pumps joined at the base by a U-tube of glass (fig. 1) . 

 The pumping is done by rocking the apparatus, the mercury 

 filling the exhaust-bulbs A A alternately. This duplex action 

 makes the pumping very rapid, for one bulb exhausts while 

 the other fills, there being no lost time. The traces of gas 

 liberated in the discharge-tube are pumped over into the ex- 

 hausted bulbs B B, where they are stored, being prevented 

 from returning by the mercury which remains in the W traps 

 between A and B. The upper bulbs are joined by a tube E, 

 which has a small lateral tube P blown into it ; this arrange- 

 ment being necessary for the preliminary exhaustion. 



Mercury is first introduced through P until the bulbs A A 

 are half full. A gentle rocking of the apparatus is necessary, 

 as the fluid is held up in the bulbs B by the compression of 

 the air in A. 



When enough mercury has been introduced, the apparatus 

 is placed in the position shown in fig. 3, when the fluid 

 should stand at the level indicated in the diagram. The side 

 tube P is now drawn out into a thick- walled capillary in a 

 blast-lamp, in order to facilitate the subsequent closing of the 

 apparatus. This tube being connected with a good mercury- 

 pump by means of a well-greased, thick-walled rubber hose, 



