THE REGULATION OF TEMPERATURE. 63 



The "larger bath" referred to above is one of those ordinarily used for 

 measurements of pressure at higher temperatures. To prepare it for 

 use at 0°, it is stripped of all its interior accessories, including circulating 

 pipes and pump, leaving the copper-lined rectangular tank entirely 

 empty. On the bottom of this, in the center, is placed a staging about 

 5 centimeters high, on which rests the ice-filled arrangement consisting 

 of A, B, and C. All the space in the tank which is not occupied by A, 

 B, and C is filled with closely packed broken ice, and the water which 

 collects upon the bottom is removed by means of an automatic siphon. 

 All the space in the upper part of the bath — usually designated as the 

 "air space" — which is not occupied by the upper part of C is filled with 

 ice containers of such form that they surround C except directly in 

 front of the door (/). One of these occupies the space between the 

 upper end of C and the top of the outer bath, the upper end of the cham- 

 ber (e) being covered to prevent the entrance of water. 



All of the ice-containers in the air space above are open at the lower 

 end, so that the broken ice moves constantly downwards as it melts 

 away underneath, keeping the tank below and also the can (2?) always 

 full. A little over 150 kilograms of ice are required to fill the bath 

 properly, and the amount of fresh ice which it is necessary to introduce 

 daily is between 25 and 30 kilograms. 



The container above C and C itself, after the ice in them has been 

 picked out, can be lifted through the opened top of the outer bath when- 

 ever cells are to be removed from A. If cells are to be introduced, all 

 parts of the bath except C and the container above it are closely packed 

 with ice, and, after waiting until the temperature in A has fallen to 0°, 

 the cells are placed in position. C is brought down upon B and packed 

 with ice. Finally, the container which belongs directly above C is 

 placed in position and filled with ice. 



The arrangement described above serves its purpose perfectly. The 

 temperature in A does not deviate sensibly from 0°. There are, there- 

 fore, no appreciable thermometer effects. The temperature of the 

 manometer space (e) may be affected somewhat by the lamp used in 

 reading, unless one interposes a screen for the purpose of cutting down 

 the heating effect of the light. We have employed for this purpose a 4 

 per cent solution of nickel sulphate, which — as determined by means of a 

 thermocouple — reduces the heating effect of the lamp nearly 99 per cent. 



BATHS FOR MAINTENANCE OF TEMPERATURE ABOVE ZERO. 



Descriptions of the earlier forms will be omitted. The baths which 

 were first employed in an attempt to measure osmotic pressure were 

 found to be incapable of maintaining sufficiently exact temperatures. 

 In other words, the thermometer effects produced by their fluctuations 

 of temperature were intolerably large. The baths which are now used 

 and which will be described are the products of a persistent attempt to 

 reduce these effects to harmless proportions. They all belong to cer- 



