July 31,1916 Respiration Calorimeter 715 



CHANGE IN TEMPERATURE) OF OBJECTS IN THE CHAMBER 



Any change in the temperature of the walls of the chamber, or of the 

 material confined within them, involves a quantity of heat for which 

 allowance should be made in computing that produced in the chamber. 

 For example, if the walls of the chamber are warmer at the end than at 

 the beginning of the experiment, they have absorbed some of the heat 

 that was produced in the chamber; while if they are cooler at the end 

 of the experiment, some of their heat has been added to that in the 

 chamber. The quantity of heat for which allowance must be made is 

 computed from the change in the temperature of the walls and their 

 hydrothermal equivalent — that is, the amount of heat involved per degree 

 of temperature change in the walls. 



The change in temperature is determined by electric-resistance ther- 

 mometers devised for this apparatus. The resistance wire is wound in a 

 flat coil about 5 cm. in diameter, which is firmly attached to one surface 

 of a disk of stiff brass 55 mm. in diameter and 1.5 mm. thick. Through 

 a hole in its center the disk is slipped over a short brass bolt projecting 

 from the surface of the copper wall, so that by screwing a nut down on 

 the bolt the disk may be clamped tightly against the wall, with the re- 

 sistance wire between them. Between the wall and the wire are two or 

 three layers of tinfoil to provide thermal contact in case of irregularity in 

 the copper. The whole thermometer comprises 10 such coils, one for the 

 top, one for the bottom, and one for the upper half and one for the lower 

 half of each side. Each coil has a resistance of 45 ohms, but the 10 coils 

 are connected in a series parallel arrangement to form a unit having a 

 resistance of about 18 ohms at 20 C. The leads from this unit connect 

 with the special switch and the Wheatstone bridge mentioned on page 

 709. The galvanometer will indicate a lack of balance due to a change 

 of 0.05 in the temperature of the walls. 



The most satisfactory data obtained in determining this factor indicate 

 that for a change of i° in the temperature of the walls the correction in 

 the quantity of heat measured by the calorimeter would not exceed 1.5 

 Calories. 



The correction involved in the change in temperature of the active 

 material in the chamber is computed from the weight and specific heat 

 of the material, and the temperature change as measured by an electric- 

 resistance thermometer. One or the other of the two thermometers men- 

 tioned on page 709 is put into the mass of active material in such manner 

 as to be in intimate contact with it. Tests with ripening fruit have shown 

 that thermometers used in this manner indicate temperature change at 

 least as accurately as a thermometer thrust into the flesh of one of the 

 fruits. 



