GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 55 



The interior of the chamber and all appliances are constructed of metal 

 except the chair in which the subject sits. This is of hard wood, well shel- 

 lacked, and consequently non-porous. With this calorimeter it is desired 

 to make studies regarding the moisture elimination, and consequently it is 

 necessary to avoid the use of all material of a hygroscopic nature. Although 

 the chair can be weighed from time to time with great accuracy and its 

 changes in weight obtained, it is obviously impossible, in any type of 

 experiment thus far made, to differentiate between the water vaporized 

 from the lungs and skin of the man and that from his clothes. Subsequent 

 experiments with a metal chair, with minimum clothing, with cloth of 

 different textures, without clothing, with an oiled skin, and various other 

 modifications affecting the vaporization of water from the body of the man 

 will doubtless throw more definite light upon the question of the water 

 elimination through the skin. At present, however, we resort to the use of 

 a wooden chair, relying upon its changes in weight as noted by the balance 

 to aid us in apportioning the water vaporized between the man and his 

 clothing and the chair. 



The walls of the chamber are semi-rigid. Owing to the calorimetric fea- 

 tures of this apparatus, it is impracticable to use heavy boiler-plate or heavy 

 metal walls, as the sluggishness of the changes in temperature, the mass of 

 metal, and its relatively large hydrothermal equivalent would interfere 

 seriously with the sensitiveness of the apparatus as a calorimeter. Hence 

 we use copper walls, with a fair degree of rigidity, attached to a substan- 

 tial structural-steel support; and for all practical purposes the apparatus 

 can be considered as of constant volume. Particularly is this the case 

 when it is considered that the pressure inside of the chamber during an 

 experiment never varies from the atmospheric pressure by more than a few 

 millimeters of water. It is possible, therefore, from the measurements of 

 this chamber, to compute with considerable accuracy the absolute volume. 

 The apparent volume has been calculated to be 1,347 liters. 



OPENINGS IN THE CHAMBER. 



In order to communicate with the interior of the chamber, maintain a 

 ventilating air-current, and provide for the passage of the current of water 

 for the heat-absorber system and the large number of electrical connections, 

 a number of openings through the walls of the chamber were necessary. 

 The great importance of maintaining this chamber absolutely air-tight 

 renders it necessary to minimize the number of these openings, to reduce 

 their size as much as possible, and to take extra precaution in securing 

 their closure during an experiment. The largest opening is obviously the 

 trap-door at the top through which the subject enters, shown in dotted out- 

 line in fig. 7. While somewhat inconvenient to enter the chamber in this 

 way, the entrance from above possesses many advantages. It is readily 



