4:4:2 E. W. Morley — Self- Acting Mercurial Air pump. 



therefore placed so as not to differ much in level when b is 

 up and c is down. The tube,/' is also made rather small, and 

 may be pinched. It is thus easy to make the ingress of air 

 last two seconds, or ten. or a hundred. 



Most of the work of my pumps is done during the night 

 and without attention : it is accordingly necessary to restore 

 any air lost from the gas bag by leakage through connections. 

 The tube k therefore conveys the air pressure to a small bottle 

 containing mercury. When the air in the system is compressed, 

 this mercury rises in n ; when the pressure is relieved, this 

 mercury again descends ; if air has escaped, the negative pres- 

 sure on the gas bag caused by the outflow of water draws in 

 air through n, and thus keeps up the supply for compression. 



It is desirable that no considerable sparking should take 

 place within the Toepler pump. A small current may be sent 

 through a relay, so that the spark in the pump is very small ; 

 or the circuit may be broken outside of the pump before it is 

 broken within it. The latter method is used in the air com- 

 pressor from which the drawing was made. Fig. 2 shows the 

 device used. In the position seen, the circuit is completed 

 from a, through the springs c c to d, by means of the contact 

 piece b. If now the circuit is also completed through the 

 pump, the magnet will lift its armature. The pulley will 

 then turn ; but before the release of air pressure has begun, 

 the contact piece b will have moved away from c, and the 

 spark on opening the circuit will therefore occur between b 

 and c and not within the Toepler pump. 



An air trap for Toepler pumps. 



In some of the work in my laboratory, a mercurial air pump 

 is required to transfer gas from one vessel to another without 

 admixture with air. To do this with a Toepler pump of the 

 ordinary pattern is practically impossible. Air intrudes be- 

 tween the rubber tube and the mercury which it contains. As 

 soon as the glass tube is slightly fouled, this air insinuates itself 

 between the mercury and the glass and soon rises into the 

 pump body. But a not very complicated addition to the 

 Toepler pump avoids this source of leakage. 



The pump from which fig. 3 was drawn avoids contact of 

 rubber and mercury ; and it is possible that this source of 

 leakage may not exist. But it nevertheless contains the modi- 

 fication just mentioned. This consists of a second small 

 Toepler pump designed to free from air the mercury which 

 enters the major pump. 



The mercury holder^ is connected to the pump body g by a 

 glass tube bent as shown. When the atmospheric pressure 



