H. L. Wells — Self-feeding Sprengel Pump. 393 



The tube N* is about 50 mm long, and 12 mm in diameter, and 

 is surrounded by a larger tube, not shown in the figure, which 

 is closed at both ends with rubber stoppers and filled with con- 

 centrated glycerine. f This glycerine may be replaced by 

 mercury where moisture in the exhausted space is to be care- 

 fully guarded against. 



The tube G, with which the vessel to be exhausted is con- 

 nected, is of rather heavy glass with a small bore. The high- 

 est point of its curve at the top should be above any possible 

 level of mercury in the reservoir C. The tube O has a bore 

 of 8-10 ram so that it may readily fill with mercury, while its 

 prolongation, to which the valve is attached, has a bore of about 

 6 mm . The height of B above A determines the amount of 

 mercury raised by a given stream of water. In the present 

 apparatus this height is 500 mm , and it is sufficient to work the 

 pump rapidly, but where a sufficient water-pressure was availa- 

 ble, it would perhaps be better to increase this to 600 mm or 

 more, with a corresponding addition to the height of the 

 whole apparatus. It is evident that the height of this reser- 

 voir above the valve-bottle should be considerably less than 

 the column of mercury which the head of water at disposal 

 will raise by direct pressure. This water-pressure, in the case 

 of an apparatus of the dimensions just described, is less than 

 necessary to run an ordinary water-jet pump at its best effi- 

 ciency ; in fact, this apparatus was devised in order to over- 

 come the difficulties, due to varying water-pressure in this 

 laboratory, which were experienced with the water-pump in 

 distilling under diminished pressure, and it may be mentioned 

 that the apparatus has been very successful for this purpose. 

 The bottle A should be as small in diameter as convenient for 

 making the attachments, and its stopper should be securely 

 wired down before putting on the pressure. 



The support to which the apparatus is attached is an upright 

 board 300 mm wide with a base about 600 mm square. The reser- 

 voirs B, C and D are securely set into the board in such posi- 

 tions that the various tubes rest against its surface. 



To start the action of the apparatus a slow stream of water 

 is first started through it, then mercury is poured in at B. A 

 trial will determine approximately the best speed at which to 

 run the water. 



When the use of the pump is to be discontinued the clamp 

 L is first closed and the excess of mercury, which need be only 

 a small quantity, is allowed to be carried up into C before 



* A connection of this kind for a Sprengel pump is described by Johnson and 

 Jenkins, Am. Chem. Jour., vol. ii., p. 29. 



f A joint surrounded by glycerine for this purpose is described by Frankland 

 and Armstrong, Jour. Chem. Soc, 1868, p. 91. 



