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RESPIRATION CALORIMETER AND EXPERIMENTS. 219 
which the two metal walls are securely attached. This metal chamber is the 
calorimeter proper. In order to protect it from the fluctuations of temperature 
of the room in which it stands, it is enclosed within three concentric walls of 
wood. Between the zinc and the innermost wooden wall is an air space (B) of 
5 cm. (2 in.), between this wall and the next is a third air space (C) of 5 cm., 
and finally between this and the outer wall is a fourth air space (D), likewise of 
5 cm. The wooden walls are made of matched pine covered with sheathing 
paper. The outer one is double with sheathing paper between. The air in the 
spaces A and C is “‘dead air,” while that in the spaces B and D can be kept in 
constant circulation by means of rotary fans in boxes outside. Each of the 
spaces B and D is continuous around the sides and over the top and bottom of 
the talorimeter, and each communicates with its fan box by means of one 
passage extending from the top of the air space to the top of its fan box, and 
another from the bottom of the air space to the bottom of the fan box. We 
may thus look upon these air spaces as shields guarding the interior space 
occupied by the calorimeter from changes in temperature without. They thus 
render necessary aid in accomplishing a fundamental object, namely, the keeping 
of the temperature of the air in the space B the same as that of the interior of 
the chamber. When these temperatures are the same there will be no passage 
of heat through the walls, either into or out of the chamber. 
The outer air current (D) is used for the coarser regulations of temperature. 
In the middle of the dead air space (C) is a wall of sheathing paper intended to 
more effectually prevent the external temperature from affecting that of the 
calorimeter. 
The walls are provided at the right with glass doors or windows. At E in 
figure 10 is a cylinder of copper which passes through the walls of the chamber 
and also through the encasing walls of wood. This cylinder, which is I5 cm. 
(6 in.) in diameter, serves for passing food and other materials into and out of 
the calorimeter chamber, and is here called the ‘‘ food aperture.” It is closed at 
the ends by caps a and 4. The outer cap (4) is screwed tightly to the cylinder 
so as to make an air-tight closure. Outside of this is a box or cover (c), made 
of wood and filled with cotton or other non-conducting material, the purpose 
being to prevent the passage of heat through E. 
Measurements of temperature.—The measurements of temperature are made 
in part by mercury thermometers, but mainly by electrical methods. The 
electrical measurements of temperature are made by use of either the German 
silver-iron thermal junctions or by resistance coils of fine copper wire. Pro- 
vision is made for connecting these with a D’Arsonval galvanometer especially 
constructed for the purpose by Mr. O. S. Blakeslee, Mechanician of Wesleyan 
University. The electrical thermometers permit measurements of one-hundredth 
of a degree Centigrade or less. 
Temperature of air inside the chamber.—Inasmuch as the temperature of the 
air is not the same in different parts of the chamber, and it is desirable to know 
the average or resultant temperature of the whole, the attempt is made to learn 
a ~ the latter by the use of a series of five electrical thermometers at places near the 

sides, top, and bottom. These consist of resistance coils of copper wire con- 
nected with a slide-wire Wheatstone bridge and the galvanometer outside. ‘The 
