62 



OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



THE BATH FOR 0°. 



As previously intimated, the bath which is employed for determina- 

 tions at 0° does not conform to the general 

 principle upon which all baths for higher 

 temperatures are constructed. The essential 

 difference between it and the others is that 

 in the bath for 0° there is no forced circula- 

 tion of water and air. An attempt was made 

 to construct a bath in partial conformity 

 with the general principle in question. In 

 this, a large mass of ice was made the "cooling 

 surface," and the exterior of the bath the 

 11 heating surface." Waterwas passed rapidly 

 over the ice, and then over the compart- 

 ments in which the cells were located. It was 

 found, however, that the lowest temperature 

 which it was practicable to maintain in this 

 manner was always a little above 0° ; and that 

 owing to imperfect control of the heating 

 surface, the temperature was subject to con- 

 siderable fluctuations which produced large 

 thermometer effects. 



The bath which was finally evolved for the 

 determination of osmotic pressure at zero is 

 seen in Figures 31, 31 L, and 31 M . The ap- 

 paratus, which is made of heavy galvanized 

 sheet iron, consists of three principal parts: 



First, a can (A), in which the cells are placed; 



second, a much larger one (B), in which A 



is suspended by means of the arrangement 



seen in Figure 31 L; and third, the cylinder 



(C), which shuts down tightly upon B. 



There is an inclosed chamber (e) running 



through the whole length of C and open at 



both ends, in which are located the upper 



ends of the manometers and the two ther- 

 mometers which are seen in the figure. The 



thermometers and manometers are exposed 



to view, when a reading is to be made, by 



opening the felt-lined door (/). In order 



that the door may be opened and closed 



from the outside, the detachable rod (g) is 



made to pass through the top of the larger 



bath (to be described later) which surrounds 



A, B, and C. The bottoms of both A and B are perforated so that 



no water can collect in the cans. 



Fig. 3 1 . — Interior ice bath for meas- 

 uring osmotic pressure at 0°. 



(A) Galvanized-iron can contain- 

 ing cells; (B) galvanized-iron 

 ice-container surrounding (.4) ; 

 (C) galvanized-iron ice-container 

 which shuts down upon (B) ; (e) 

 protected compartment for ma- 

 nometers and thermometers; (/) 

 padded door to (e) ; (g) arrange- 

 ment for opening and closing the 

 door from above the outer ice bath, 

 which is not shown in the figure ; 

 (L) arrangement for suspending 

 (A) in (B); (M) cover to (A). 



