114 



OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



filled the space except over the window (b). The window was covered 

 by a separate pad, which could be introduced or withdrawn through 

 the small outer door (d). The top of the box was removable. 



The cell — with a long thermometer whose bulb was immersed in 

 the water surrounding the cell — was placed in the box and packed 

 with hair, except where it was necessary to leave vacant spaces for the 

 purpose of reading the instruments. The exterior of the box was 

 protected, during an experiment, by coverings of thick hair-felt, by 

 woolen cloths, and even by sheepskins. Care was also taken to mod- 



Fig. 46. — First bath employed for measurement of osmotic pressure. 

 Double-walled, and filled between with hair. 



(a) Inner door; (b) glass window; (c) outer door; (d) door of size of (6). 



erate somewhat the extremes of temperature in the room in which 

 the bath was located. No attempt was made to maintain some 

 precise temperature, e. g., 20°. The cell was filled and placed in the 

 bath, and was protected in the manner described, at the temperature 

 of the room. In a general way, the origin and the modus operandi 

 of thermometer effects were understood, but it was foreseen that their 

 existence depends on the rate at which the solvent can pass in either 

 direction through the membrane to compensate the changes in the 

 volume of the inclosed solution which are due to fluctuations of tem- 

 perature. It was believed, moreover, that, in solutions protected as 



