iVb 



actually employed. All connect ions are by glass tubes. 

 The U-tube "a" contains a column of mercury the function 

 of which will be described below. The tube "v" communi- 

 cates with a vacuum line by means of which the cups 

 can be drawn full of water or washed out, when necessary. 

 When not in use this tube is closed by a pinchcock on 

 the rubber tube connecting it with the vacuum line, 

 as described below. The enlargement in the U-tube 

 above the mercury column is for the purpose of preventing 

 the accidental drawing of the mercury into the cups 

 when water is being drawn through under vacuum. The 

 nearly horizontal arm above and to the right of the en- 

 larged portion is slightly inclined upward toward the 

 right for the same reason. The dimensions given in 

 figure 3 have been found satisfactory but are not es- 

 sential. ".7ater taken is measured by means of the scale 

 on the water-reservoir "b", which reservoir is refilled 

 through the tube at the left. A number of pots can be 

 arranged conveniently as shown in figure 4, the connect- 

 ions from the vacuum end of the porous cup system 

 and from the water-supply tube of the water reservoir, 

 being brought by rubber tubes to main vacuum and water 

 lines which lie on the board in front of the pots. Both 

 connections are closed by pinch-cocks on the rubber 

 tubes. The U-tube s containing the mercury columns pass 

 under this board and connect the water reservoirs in 

 front with the pots behind. 



