A NON-ABSORBING ATMOMETER MOUNTING 259 



then drawn out into a capillary at one end. The piece BB' has 

 its constricted portion from 3 to 4 cm. long, with a total length of 

 about 10 cm. The other piece (CC) has a much longer capillary 

 portion, which is then bent back upon itself to form a J, with the 

 shorter arm about 8 cm. in length, ending about a centimeter 

 above the beginning of the constriction in the longer arm. The 

 J is very narrow, so that it may slide into the tube A A', as shown 

 in the figure. The total length of the unconstricted part of this 

 tube is such that it may reach to within about a centimeter of 

 the bottom of the reservoir. 



The tube AA\ after being inserted in the stopper of the reser- 

 voir, is fitted at each end with a piece of pure-gum rubber tubing 

 3 cm. long, in such a manner that it extends 1.5 cm. over the end. 

 These two pieces of tubing should have a wall thickness of about 

 1 mm. and such a bore as to fit the smaller glass tubes rather 

 tightly. The bent portion of tube CC is then inserted into the 

 opening A' of the tube AA', through the rubber connection at 

 A' so that the non-constricted portion extends about 2 cm. into 

 the larger tube. Mercury is then placed in tube AA', the end 

 of the tube CC being covered (at D) to a depth of from 6 to 7 mm. 

 There should be enough mercury above the open end of the capil- 

 lary tube to fill the latter as high as the bend. The larger end of 

 tube BB' is inserted into the rubber stopper of the atmometer 

 cup. 



To install the instrument, the reservoir is filled and its stopper 

 is inserted, carrying tubes A A' and CC and also an air-inlet tube, 

 E. Suction is next applied at A, so that water passes the 

 mercury at D and rises to the level A. No air bubbles should be 

 included. Unless the atmometer cup is too porous, it is inverted 

 and filled with water and its stopper (bearing tube B^') is pressed 

 into place so that water rises to the end B'. When there is no 

 air in tube BB', the cup and tube are again inverted and the end 

 B' is inserted into the water at A and gradually pressed through 

 the rubber connection into the tube AA', for a distance of from 

 5 to 6 cm. The mercury should not be forced beyond the bend 

 ate. 



