AS INDICATED BY OSMOMETERS. 



59 



through an angle of 90 degrees. The instrument was erected hori- 

 zontally with the collodion membrane vertical. In such a position the 

 thistle-tube osmometers, operating against water, showed consistently- 

 uniform rates of water entrance, at least after the lapse of an initial 

 time period. It appears that there is an initial dilution of the layer 

 of solution abutting against the vertical membrane. This dilution 

 does not proceed far, however, before it inaugurates a rising convection 

 current along the membrane's inner surface, a current which of course 

 brings new and practically undiluted solution into the 

 osmotically active region of the instrument. There seems soon 

 to be established a dynamic equilibrium, and for long periods 

 of time this convection appears ; to remain nearly continuous 

 and practically uniform, as. is clearly indicated by ^ the long- 

 continued maintenance of nearly uniform rates of water intake. 

 It seems probable that there is established and held a rather 

 definite gradient in solution concentration, from the nearly undi- 

 luted concentration at the lower margin of the membrane to the 

 perhaps considerable dilution at the upper margin. The bulge of 

 the thistle bulb is adapted to keep the diluted solution above 

 from a rapid mixing with the main mass, so that it is not surprising 

 that uniform rates of water entrance may be long maintained. 

 Eventually, of course, the diluted solution above will extend 

 downward far enough to decrease seriously the intake rate. 



Fig. 1. — Diagram showing osmometer as arranged to operate 

 against water. The membrane closes the large opening 

 of the thistle tube, the small opening is joined to a gradu- 

 ated pipette by rubber tubing. 



In setting up the osmometers to operate against 

 water they were arranged as is indicated in figure 1. 

 The stem of the thistle tube was passed through a 

 flat cork stopper closing the opening of a horizontal 

 jar, the bulb of the instrument lying within the jar. 

 nearly filled with water, the atmosphere being allowed access to the 

 upper surface of the water through a small opening near the upper edge 

 of the stopper. The small, external end of the osmometer was con- 

 nected, by a loop of heavy-walled rubber tubing, to the lower extremity 



The latter was 



