112 A RESPIRATION CALORIMETER. 



FACILITIES FOR REMOVING METAL CHAMBER. 



In case of accident to any part of the outside of the calorimeter 

 chamber it is necessary to have easy access to that part. The partic- 

 ular form of construction above described was adopted to secure ready 

 accessibility to all parts of the apparatus, as already explained. 



The calorimeter chamber, exclusive of any fittings, weighs 605 

 pounds. To facilitate withdrawing the chamber from the wooden 

 casing, six large castors, three on each side, are fastened to the bot- 

 tom. These castors move in iron tracks laid on the floor of the inner 

 wooden structure, the tracks being of the grooved iron commonly used 

 in bridge construction. The raised edges serve as guides to the wheels. 

 Beyond the inner wooden floor each track is continued along a stiff 

 joist, the end of which is cut so as to fit over the wooden casing of the 

 calorimeter and thus allow the ends of the track to come together and 

 form a continuous passage for the wheels of the calorimeter. The 

 joists are laid on the floor of the laboratory and when not in use are 

 removed. When supporting the calorimeter they are held rigidly up- 

 right by a cross-piece at the outside ends. Figure 25 shows the tracks 

 extending from the wooden casing, and figure 29 shows the calorimeter 

 rolled out upon them. 



METHODS OF PREVENTING GAIN OR LOSS OF HEAT TO CHAMBER. 

 It has been stated that the heat generated within the chamber can 

 not escape from it except by the means provided for carrying it away 

 and measuring it. In order that this shall be the case and also that the 

 amount thus measured shall include only that produced within the 

 chamber and shall not be augmented by heat from external sources, 

 there must be no gain or loss of heat through the metal walls, the 

 openings in the walls, or the air current. The arrangements for pre- 

 venting gain or loss of heat by these channels are here described. 



PREVENTION OF GAIN OR Loss THROUGH THE METAL WALLS. 



If the zinc wall were colder than the copper there would be an out- 

 ward flow of heat, i. e., a loss, and if it were warmer there would be an 

 inward flow or gain. To prevent the passage of heat in either direc- 

 tion, or, more strictly, to provide that the small quantity that may pass 

 one way shall be exactly counterbalanced by an equal quantity in the 

 other direction, the temperature of the zinc is regulated in accordance 

 with that of the copper. This is accomplished by heating or cooling 

 the air-space surrounding the zinc walls as necessary, according to 

 whether the zinc is colder or warmer than the copper. 



First of all, then, it is necessary to detect differences between the 

 temperature of the copper and that of the zinc wall. 



