juiy 3 i.i9i6 Respiration Calorimeter 705 



As part of the arrangement described on page 716 for preventing the 

 passage of heat through the walls, ceiling, and floor of the chamber, these 

 surfaces are duplicated by sheet-copper top, bottom, and sides screwed 

 to the outer edge of the wooden frame, the inner and the outer metal 

 walls being thus separated by an air space 25 mm. across. There are 

 openings in these walls for the windows and the "outlet " described above. 



Surrounding the entire chamber, about 25 mm. from the outer metal 

 wall, is a heat-insulating cover (PI. XCIII) consisting of two layers of 

 cork board 38 mm. thick, alternating with three layers of museum board 

 6 mm. thick, built up on wooden frames. The top, bottom, and side 

 sections are built separately, and the several sections fit together with 

 double-rabbeted joints, so that any one may be removed without regard 

 to the others, or the entire cover may be instantly taken off. One sec- 

 tion, as shown in Plate XCIII, is divided along the vertical median line, 

 and all pipes and wires passing to the copper walls and to the "outlet" 

 are brought out between the two halves of this section. The sections 

 covering the two sides have openings to correspond with those in the 

 walls of the calorimeter. The bottom section of the cover rests upon 

 a substantial oak platform raised about 18 cm. from the floor of the 

 laboratory. 



DETERMINATION OF THE GASEOUS EXCHANGE 



The respiration chamber in which the active material is confined is part 

 of a closed air circuit through which a stream of air is constantly moving. 

 The air which leaves the chamber is passed through purifying devices 

 and returned again to the chamber. In the purifying devices the gaseous 

 products resulting from the activity of the material in the chamber, which 

 are carried out in the outgoing air, are absorbed. The purifying devices 

 described below are those for the absorption of water vapor and carbon 

 dioxid; but others could be substituted for these or connected with them 

 if desired. 



The quantities of water vapor and carbon dioxid carried from the 

 chamber in a given period are shown by the changes in the weights of 

 the absorbers during the period; and from these data, with due allow- 

 ance for changes in the quantities of gases in the air of the chamber, the 

 production of water vapor and carbon dioxid by the active material 

 during the period is determined. 



With a ventilation system of this type, as fast as any gas is removed 

 from the air, other gas is introduced to maintain atmospheric pressure 

 in the chamber. Usually oxygen is admitted, that being the gas con- 

 sumed in respiration, as the term is commonly employed ; but it is possible 

 to vary the composition of the air at will, and if desired, to maintain an 

 atmosphere of carbon dioxid or nitrogen or any other gas, which may be 

 admitted to the system as oxygen is in the experiment as ordinarily 

 conducted. 



