PART II. 



CALIBRATION TESTS. 



The calorimeter used for the later calibration tests of the two bicycle 

 ergometers was the so-called chair calorimeter, which has been described 

 in detail by Benedict and Carpenter. 1 Since this description was pub- 

 lished, it has been found desirable to change the location of the entrance 

 from the top to the front of the apparatus. This permits the easy in- 

 troduction of the ergometer and the carrying of the driving-shaft straight 

 out from the front of the calorimeter. 



The apparatus consists, in brief, of a series of chambers surrounded by 

 alternate layers of air and insulating materials. The inner copper cham- 

 ber is surrounded by a layer of air, in which is located the structural-steel 

 framework of the calorimeter. A zinc wall incloses this air-space, and is 

 in turn surrounded by a second air-space of approximately 8 cm., which 

 is inclosed by an insulating outer layer of hair-felt, with a final covering 

 of asbestos. Between the zinc and copper walls there is a series of thermo- 

 electric junctions which indicate the temperature differences between the 

 two. By arbitrarily heating or cooling the air between the hair-felt and 

 the zinc wall, the temperature of the latter can be controlled at will and 

 adjusted so that it will be equal to that of the copper wall, thus preventing 

 any heat radiation and holding the calorimeter adiabatic. The heat given 

 off by the subject is absorbed by a current of cold water passing through 

 a system of brass pipes inside the chamber, the heat-absorbing surface of 

 these pipes being greatly increased by a large number of copper disks, 

 approximately 5 cm. in diameter, which are soldered to them. The rate 

 of flow and the temperature of the water entering the chamber are ar- 

 bitrarily adjusted so as to bring away the heat as rapidly as it is produced. 

 The mean temperature of the air in the calorimeter is thus held constant, 

 this being the criterion of the thermal equilibrium. As the current of 

 water enters and leaves the chamber its temperature is accurately meas- 

 ured with mercurial thermometers; from the mass and rise in temperature 

 of the water the amount of heat brought away can be readily computed. 

 When the apparatus is used for calibrating the ergometer, in the final 

 calculation of the total intake of heat, it is necessary to deduct the heat 

 of magnetization, i. e., the heat produced in the coils of the magnet. As 

 previously stated, this is with the first ergometer 10.9 calories per hour 

 when the magnetizing current is 1.25 amperes, and with the new ergom- 

 eter 17.8 calories per hour when the magnetizing current is 1.5 amperes. 



1 Benedict and Carpenter, Carnegie Institution of Washington Publication No. 123, 

 1910, p. 10. 



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