106 A RESPIRATION CALORIMETER. 



THE CALORIMETER SYSTEM AND MEASUREMENT OF HEAT. 



This section deals with that portion of the respiration calorimeter 

 which is involved in the calorimetric measurements. It has been ex- 

 plained (p. 4) that the arrangements for measuring respiratory products 

 aud those for measuring heat are intimately combined in the same 

 apparatus. In this description, however, the calorimeter will be con- 

 sidered for the most part as if it were independent of the respiration 

 apparatus, though in a few instances it will be convenient to refer, for 

 more detail, to what has already been described. 



GENERAL PRINCIPLE OF THE CALORIMETER. 



As a device for measuring heat, the apparatus here described may be 

 designated a constant temperature, continuous-flow water calorimeter. 

 It is so devised and manipulated that gain or loss of heat through the 

 walls of the chamber is prevented, and the heat generated within the 

 chamber can not escape in any other way than that provided for carry- 

 ing it away and measuring it. A small part of the total quantity leaves 

 the chamber as latent heat of water vapor in the air current of the 

 respiration apparatus, but the larger part is sensible heat absorbed by a 

 current of cold water passing through a coil of pipe within the chamber. 

 By regulating the temperature and rate of flow of this current of water, 

 the rate at which the heat is absorbed may be controlled in accordance 

 with that at which it is generated within the chamber, and thus the 

 temperature of the chamber may be kept constant. 



The quantity of heat carried out of the chamber as latent heat of water 

 vapor is determined from the quantity of water vapor removed from the 

 air current and the latent heat of vaporization of water. The quantity 

 of heat absorbed and removed by the water current is determined from 

 the quantity of water passing through the coil, its increase in tempera- 

 ture, and the specific heat of water at different temperatures. Theo- 

 retically the sum of these two quantities of heat thus determined should 

 equal the total generated within the chamber, but in actual experiments 

 with man various corrections, such as heat gained or lost by articles sent 

 into or brought out of the chambers, etc., must also be taken into 

 account. 



The things to be especially considered in this discussion, then, are 

 the arrangements for preventing gain or loss of heat through the walls 

 of the chamber and the arrangements for bringing heat away from the 

 chamber and measuring it. In the description of these many subordinate 

 related topics must also be discussed. 



