THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 107 

 THE CALORIMETER CHAMBER. 



The dimensions of the chamber and its construction of metal have 

 been given in the discussion of the respiration apparatus (p. 12). The 

 walls, ceiling, and floor of the chamber are of sheet copper, polished 

 on the inner surface. Copper offers many advantages as a metal surface 

 for the interior of the calorimeter chamber, because it will take a high 

 polish, thus aiding in the distribution of heat by reflection, and it con- 

 ducts heat rapidly, thereby tending to equalize local differences in 

 temperature. As a further aid in the reflection and distribution of heat 

 and equalization of temperature, the four upright corners of the chamber 

 are rounded. These features are of particular importance in the matter 

 of determining changes in temperature of the walls, which is funda- 

 mental to the prevention of the gain or loss of heat through the walls, 

 as explained beyond. 



Outside the copper walls of the chamber and concentric with them, 

 but separated by an air-space of 7.6 cm., corresponding to the width 

 of the wooden framework by which the copper walls are supported, is 

 another metal covering, the purpose of which will be described later. 

 For this covering the cheaper metal, zinc, is very satisfactory. Sheets 

 of zinc (Brown & Sharpe gage 25), each 3 by 7 feet and weighing 14 

 pounds, were used in this construction. Since this covering need not 

 be airtight, the joints were soldered only at convenient places, and 

 the zinc is nailed to the wooden framework between the two layers of 

 metal. There are, however, no apertures large enough to disturb the 

 ' ' dead air ' ' in the space between the zinc and the copper. 



WOODEN WALLS SURROUNDING THE CHAMBER. 



To protect the calorimeter chamber against fluctuations in the tem- 

 perature of the calorimeter laboratory, and especially to provide op- 

 portunity for controlling the temperature of the metal walls in the 

 manner described beyond, there are two concentric coverings of wood 

 completely surrounding it, with an air-space of 7 cm. between the zinc 

 wall and the inner wooden partition and a corresponding space between 

 this and the outer wooden covering. This construction is equivalent 

 to a double- walled wooden house, into which the calorimeter chamber 

 is inserted. The details of the construction follow, reference being 

 made to the horizontal cross-section in figure 8 and the end and side 

 vertical cross-sections in figures 23 and 24. 



At each corner of the house, between the two wooden walls, an up- 

 right (b, b, and c, c, in fig. 8) extends from floor to ceiling of the labo- 

 ratory, thus providing rigid supports. As seen in figure 8, the two 



