10 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



THE CALORIMETER. 



In describing this apparatus, for the sake of clearness, the calorimetric 

 features will be considered before the appliances for the determination of 

 the respiratory products. 



FUNDAMENTAL PRINCIPLES OF THE APPARATUS. 



The measurements of heat eliminated by man, as made by this apparatus, 

 are based upon the fact that the subject is inclosed in a heat-proof chamber 

 through which a current of cold water is constantly passing. The amount 

 of water, the flow of which, for the sake of accuracy, is kept at a constant 

 rate, is carefully weighed. The temperatures of the water entering and 

 leaving the chamber are accurately recorded at frequent intervals. The 

 walls of the chamber are held adiabatic, thus preventing a gain or loss of 

 heat by arbitrarily heating or cooling the outer metal walls, and the with- 

 drawal of heat by the water-current is so controlled, by varying the tem- 

 perature of the ingoing water, that the heat brought away from the calo- 

 rimeter is exactly equal in amount to the heat eliminated by radiation and 

 conduction by the subject, thus maintaining a constant temperature inside 

 of the chamber. The latent heat of the water vaporized is determined by 

 measuring directly the water vapor in the ventilating air-current. 



In the construction of the new calorimeters a further and fundamental 

 change in construction has been made in that all the thermal junctions, 

 heating wires, and cooling pipes have been attached directly to the zinc wall 

 of the calorimeter, leaving the outer insulating panels free from incum- 

 brances, so that they can be removed readily and practically all parts in- 

 spected whenever desired without necessitating complete dismantling of the 

 apparatus. This arrangement is possible except in those instances where 

 connections pass clear through from the interior of the chamber to the 

 outside, namely, the food-aperture, air-pipes, water-pipes, electrical connec- 

 tions, and tubes for connections with pneumograph and stethoscope ; but 

 the apparatus is so arranged as to have all of these openings in one part of 

 the calorimeter. It is possible, therefore, to remove all of the outer sections 

 of the calorimeter with the exception of panels on the east side. 



This fundamental change in construction has proven highly advan- 

 tageous. It does away with the necessity of rolling the calorimeter out of 

 its protecting insulating house and minimizes the delay and expense inci- 

 dental to repairs or modifications. As the calorimeter is now constructed, 

 it is possible to get at all parts of it from the outside, with the exception of 

 one small fixed panel through which the above connections are passed. 

 This panel, however, is made as narrow as possible, so that practically all 

 changes can be made by taking out the adjacent panels. 



