﻿Investigating Transpiration of Gases through Tubes. 251 



Considerable simplification is introduced, however, if the 

 transpired gases be allowed to escape into the atmosphere ; 

 pressures slightly in excess o£ that of the atmosphere may 

 then be used, and short, uniform capillaries employed. 



The pressure requires to be automatically kept constant by 

 a device which does not interfere with the accurate mea- 

 surement of the volume transpired. For this purpose it is 

 desirable to allow the transpiration of a constant volume of 

 gas, and to measure the volume between points at which the 

 cross-sectional area of the vessel is small. These improve- 

 ments are embodied in the apparatus to be described, which 

 will be found very convenient in practice and has the advantage 

 of being readily constructed. 



The apparatus consists of a mercury reservoir. A. provided 

 with the usual constant-pressure device; the stem of the 



S 2 



