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ATMOMETRY AND THE POROUS CUP ATMOMETER 



BURTON EDWARD LIVINGSTON 



The Johns Hopkins University, Baltimore, Md. 



Ill 



Installation 



The Absorbing Mounting. For laboratory work, in rooms, 

 green-houses, and in any exposures where rain and heavy dew 

 will not be encountered, the simple absorbing mounting (see fig. 

 5) is to be recommended. This consists merely in a rubber 

 stopper closing the open (lower) end of the cup and bearing, 

 through a perforation, a rigid, insoluble tube (glass, hard rubber, 

 block tin, copper, possibly brass), of about 6 mm. bore, which 

 connects with the water reservoir below. The tube should 

 project a few centimeters into the cup. On the longer free 

 part of the tube is placed a perforated cork stopper, its larger end 

 toward the center of the tube, as is the larger end of the rubber 

 stopper. This cork should fit the tube tightly so as not to slide 

 readily up and down. It has a small oblique groove (2-3 mm. 

 wide and of the same depth) on one side; a reservoir bottle is 

 provided to take the cork stopper, and when the latter is in 

 place air can enter or leave the bottle through the open groove. 

 The groove in the cork may be replaced by inserting through the 

 cork a short tube of small bore, its projecting upper end reflexed 

 in the form of an inverted J and loosely plugged with cotton. 

 The bottle used is an ordinary one of narrow mouth, holding 

 from 250 to 1000 cc. according to the requirements. The cork 

 stopper is so placed upon the tube that the latter reaches nearly 

 to the bottom of the bottle when the stopper is firmly in place. 

 The cork should extend above the neck of the bottle far enough 

 to give safe fingerhold, to avoid danger of moving the stopper 

 upon the tube. A file mark upon the lower part of the bottle 

 neck serves as a zero mark when filling the bottle. 



95 



THE PLANT WORLD, VOL. 18, XO. 4, 1015. 



