THE- TRANSPIRATION OF AIR THROUGH A PARTI- 

 TION OF WATER. 



By C. BARUS. 

 (Read April 21, 1911.) 



1. Molecular Transpiration of a Gas. — Ever since 1895 I have 

 observed that the Cartesian diver, used in my lectures, grew regularly 

 heavier from year to year. The possibility of such an occurrence 

 is at hand ; for the imprisoned air is under a slight pressure-excess 

 as compared with the external atmospheric air. But this pressure 

 gradient is apparently so insignificant as compared with the long 

 column of water through which the flow must take place, that oppor- 

 tunities of obtaining quantitative evidence in favor of such trans- 

 piration seem remote. If, however, this evidence is here actually 

 forthcoming, then the experiment is of unusual interest, as it will 

 probably indicate the nature of the passage of a gas, molecularly, 

 through the intermolecular pores of a liquid. It should be possible 

 for instance to obtain comparisons between the dimensions of the 

 molecules transferred and the channels of transfer involved. 



2. Apparatus. — Hence on February 27. 1890, I made a series of 

 definite experiments^ sufficiently sensitive that in the lapse of years 

 one might expect to obtain an issue. The swimmer was a small 

 light balloon-shaped glass vessel, vd, Fig. i, unfortunately with a 

 very narrow mouth, 2 mm. in diameter, at d, in the long column of 

 water A. The small opening however gave assurance that the air 

 would not be accidentally spilled in the intervening years. For this 

 reason it was temporarily retained, the purpose being that of getting 

 a safe estimate of the conditions under which flow takes place. 



In Fig. I ab is a rubber hose filled with water, terminating in the 

 receiver R. Here the lower level of w^ater may be read ofif. More- 

 over R is provided with an open hose C, through which pressure or 

 suction may be applied by the mouth, for the purpose of raising or 



^ Am. Joiini. of Sci.. IX., 1900, pp. 397-400. 



117 



