120 



OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



Another improvement in manometers which was made before 

 beginning Series II was the introduction of the "safety bulb," which 

 is blown in the tube just below the calibrated portion, and which 

 prevents an escape of the gas when it is under diminished pressure. 



The methods of calibration 

 were also improved, and more 

 attention — although by no 

 means so much as at a later 

 period — was given to the ir- 

 regularities of capillary depres- 

 sion. 



2. The greatest improvement 

 in apparatus, however, was in the 

 devices for maintaining temperature, 

 though gas and electric stoves, regu- 

 lated by thermostats, were not intro- 

 duced for the control of bath and 

 room temperatures until later. The 

 first bath so furnished was the crude 

 forerunner of that seen in Figures 35, 

 36, and 37, pages 69 and 70. It was 

 a large rectangular affair (Figure 47) 

 consisting of two superimposed com- 

 partments. The lower one contained 

 water, which was kept in circulation 

 by means of a pump (Figure 48). 

 The air in the upper, or manometer, 

 compartment was drawn continu- 

 ously through pipes (Figures 48 and 

 49) lying in the water below by means 

 of a second pump. The temperature 

 of the water in which the cells were 

 suspended was regulated, as best it 

 could be at that time, by means of 

 immersed electric stoves, which were 

 controlled by a thermostat ; while that 

 of the air in the manometer space was 

 kept approximately the same by pass- 

 ing it uninterruptedly through the pipes in the water, 

 all double and were packed with hair. 



It will be shown later that a system of bath regulation such as that 

 described is exceedingly imperfect. Nevertheless, it was a great 

 improvement on that employed in Series I. 



3. The improvement in the cathetometer (Figure 25, page 44) which 

 enabled us to dispense with the micrometer eye-piece of the telescope, 



Fig. 48, 



•Pumping arrangements on larger 

 scale than in Figure 47. 



The walls were 



