the Mercurial Air-pump, 133 



This apparatus is connected with the air-pump by means of a 

 caoutchouc tube, provided at both ends with a hollow conical 

 metallic plug. 



One of these plugs is put into the hole which the main-cock, 

 h, of every air-pump is already provided with, for the purpose of 

 either shutting off exhausted vessels from the pump, or of filling 

 them again with air ; and the other plug is put alternately into 

 one of the nozzles i and k. 



When the apparatus is to be worked, it is necessary first of 

 all to fill the bottle A with quicksilver nearly up to the tubulus : 

 in my instrument forty pounds are required for this purpose. 

 The main-cock h of the air-pump must then be turned so that 

 the caoutchouc tube connected with it communicates with the 

 barrels. 



The other plug of the caoutchouc tube is next put into the 

 nozzle k, the handle of the cock g is placed vertical with the end 

 p downwards, and the pump is set in motion. 



Two strokes of the pistons of my pump are sufficient to bring 

 the mercury to the required height ; that is, not only to fill the 

 vessel B completely, but also to drive it through the cock g into 

 the small vessel d placed above it, as is needful to ensure the 

 complete displacement of all air. 



When this has been done, the cock g is turned through 45° 

 with p towards the left, so as to close the vessel B. The plug 

 of the caoutchouc tube is then taken out of the upper nozzle k 

 and put into the lower one, and the pumping is continued. 



Four strokes of the pistons of my pump suffice to empty again 

 the vessel B of mercury, notwithstanding its considerable size, 

 and thus to produce therein a vacuum such as cannot be sur- 

 passed without boiling the mercury. 



In order to employ this vacuum for the required purpose, the 

 handle of the upper cock g is placed horizontal with the end p 

 towards the left, whereby the lateral passage l } and the tubes or 

 other pieces connected with it, are put into communication with 

 the exhausted vessel B. 



The bottle A may for the sake of safety be previously closed 

 by the cock/, although this is not necessary so long as the con- 

 nexion with the pump is maintained. When the exhaustion is 

 completed, the vessel B must likewise be closed again by turning 

 the cock g. 



This is in general the course of the exhaustion, which must of 

 course be repeated as often as needful. 



ness, as placed at right angles to the cock g ; it is better, however, to place 

 it in a line with the axis of the cone of the cock, and to give this a double 

 boring like that of the cock h of the air-pump. In this way the quicksilver 

 is prevented from getting into the passage I. 



