66 OSMOTIC PRESSURE OF AQUEOUS SOLUTIONS. 



If the temperature of the hydrant water is above that at which the 

 bath is to be maintained, the block-tin spiral pipe (Figure 33) is 

 inserted between the tap and dd (Figure 32 C). To cool the water 

 which enters at a, before it passes through b, dd, and cd into the bath, 

 the large and well-protected box in which the spiral is located is packed 

 with ice. In this manner, it is practicable to maintain a quite low 

 temperature in the warmest weather. 



The bath just described is used principally for bringing solutions to 

 temperature and for maintaining them at temperature, for the com- 

 parison of thermometers and the adjustment of thermostats, and for 

 other similar purposes. The various instruments and vessels are held 

 in their places in the bath by means of adjustable 

 supports or clamps, of which that for bottles is 

 shown in Figure 32 A . ( 



The maintenance of any temperature from a (LL^ \ \ 



little above 0° to that of the room can be readily ( --LL. I LI \ 



accomplished by means of the hydrant water, with ( -~~~ i i— L 



or without ice. If, however, a temperature above 3zE) 



that of the room is to be maintained, the flow of the ( LLT ^ 



hydrant water is cut off. The outer surface of the ( LH \ \Z_ ] 



bath and the exposed surface of the water then ( ■ — . i h~J 



become the "cooling" surface, and the bath works ( — "j p— - ) 



on precisely the same principle as before. If a ClD 



temperature above 50° is to be maintained, the fig. 33.— Coil of block- 

 consumption of electric energy becomes expensive hTathfg wlteTbefore 

 in large baths, and it is well to accomplish a portion it enters the drcuiat- 

 of the heating by means of gas. This is done in i n a g th s . ystem within the 

 various ways, but most simply by removing the (o) Entrance . (6)exit . 

 wooden base and mounting the bath on a large 

 iron tripod over a ring burner of suitable diameter, taking care, of 

 course, so to regulate the quantity of burning gas that the stove alone 

 can not raise the temperature of the bath to the required height. 



Type II. 



Figure 34 represents one of the more recent forms of bath, in which 

 the membranes are deposited and in which the cells and the solutions 

 are maintained at the temperature at which osmotic pressure is to be 

 measured. 



The "cooling 7 ' surface is furnished by the horizontal brass pipes 

 (1 to 8) . The hydrant water, cooled by ice if necessary, enters by pipe 1 

 and, after circulating through all the six intervening pipes in the order 

 in which they are numbered, it leaves the bath by pipe 8. For all tem- 

 peratures below the highest temperature of the room, it is necessary to 

 keep some water in circulation in this system of pipes. The amount to 

 be sent through will, of course, depend on the difference between the 



