A NON-ABSORBING ATMOMETER 9 



is about 1.2 cm. in diameter, and forms a shallow, inverted funnel 

 with the lower surface of the paraffined cork stopper. This 

 serves to conduct air bubbles, which may catch on the under 

 surface of the stopper in filling the reservoir, to the exterior. 

 The tube extends 5 cm. above the cork stopper, and is graduated 

 to tenths of cubic centimeters. The zero point on the tube 

 serves as a zero point in filling the reservoir. 



To install the instrument the paraffined cork stopper, into 

 which the tubes A A', B and E, have been properly fitted, is 

 tightly appressed into the mouth of the reservoir F. A suffi- 

 cient amount of clean mercury is allowed to fall from a pipette 

 into the openings in the upper end of each of the tubes A' and B, 

 to form a column 5 cm. to 6 cm. high in tube A', and slightly 

 more than this in tube B. After the porous cup has been placed 

 in position and the reservoir filled with distilled water, a rubber 

 tube is attached to the free end of the filling tube A' , and gentle 

 suction is applied. Water rises from the reservoir into the tube 

 B' ', at the same time that the mercury in this tube is drawn into 

 the bulb C, where water passes freely and rises in the tube B, 

 filling the porous cup. When the cup is filled water passes into the 

 tube A A' , the mercury in this tube having been drawn into 

 the bulb D, where the water is allowed to pass freely and escape 

 into the rubber tube, which is then removed. The mercury in 

 the bulbs C and D, drops back into the tubes below. To prevent 

 water loss from the reservoir by evaporation through the tube E, 

 and to prevent the entrance of water through this tube from 

 without in times of rain, a vial is placed over the end of this tube. 

 A suitable vial is also placed over the end of the tube A', to ex- 

 clude dirt. The instrument is now ready for operation. 



To replace the cup with a new one it is only necessary to re- 

 move the old cup from its support and to place the new cup into 

 position, after which suction is applied to the tube A ' , as in in- 

 stalling. 



A- water evaporates from the surface of the cup, the mercury 

 rises in tube A, and falls in tube A', coming to rest with the 

 mercury level in A, slightly higher than in A', the difference in 

 the height of the two columns depending upon the height of the 



V 



