260 EARL S. JOHNSTON 



If the cup is too porous to be mounted as just described, then 

 its stopper is inserted and the cup is immersed in a vessel of water 

 with the tube BB' projecting upward, suction being appHed at the 

 free end. When cup and tube are filled, the end B' is closed with 

 the finger and the cup is inverted. Then the free end of the tube 

 is opened and quickly inserted into tube AA' sl^ described above. 



This instrument may be slightly modified by inserting end A 

 of tube A A' in the rubber stopper of the atmometer cup and 

 shortening tube BB', so as to make the rubber connection at A 

 come to be within the cup. Such an arrangement adds rigidity, 

 but necessitates a different method of installation. To install 

 the instrument thus modified, insert tube A A' into both stoppers, 

 and attach rubber connections as described above. Attach a 

 piece of thin-walled rubber tubing to end C and insert the tube 

 CC in AA'. Fill both tubes by placing the end A in water and 

 applying suction at the free end of the thin-walled rubber tubing. 

 This tubing is then closed with a tubing clamp and reversed. 

 Mercury is dropped into end A and tube BB' is inserted into its 

 place through the rubber connection, until the glass just pro- 

 jects beyond the latter. If this procedure does not result in 

 completely filling BB' with water additional water may be added 

 at the open end B. The cup is then immersed in water and its 

 rubber stopper is inserted under water. When tight, the mount- 

 ing and cup are removed from the water and erected, the clamp 

 on the thin-walled rubber tubing below C being released and the 

 tubing removed just before the lower end of the mounting is 

 inserted in the reservoir. 



The mounting above described, or its modification, may be 

 attached to any reservoir that can receive the tube AA' ', a 

 large-mouth bottle is not required. It is more compact than the 

 non-absorbing forms thus far described and is less apt to suffer 

 breakage. The rubber-tubing connections require occasional 

 renewal, about once a month. 



