CALCULATION OF RESULTS. 79 



CALCULATION OF THE VOLUME OF AIR RESIDUAL IN THE CHAMBER. 



The ventilating air-circuit may be said to consist of several portions of 

 air. The largest portion is that in the respiration chamber itself and con- 

 sists of air containing oxygen, nitrogen, carbon dioxide, and water-vapor. 

 This air is assumed to have the same composition up to the moment when 

 it begins to bubble through the sulphuric acid in the first acid-absorber. 

 The air in this absorber above the acid, amounting to about 14 liters, has a 

 different composition in that the water-vapor has been completely removed. 

 The same 14 liters of air may then be said to contain carbon dioxide, nitro- 

 gen, and oxygen. This composition is immediately disturbed the moment 

 the air enters the potash-lime can, when the carbon dioxide is absorbed 

 and the volume of air in the last sulphuric-acid absorber, in the sodium- 

 bicarbonate can, and in the piping back to the calorimeter may be said to 

 consist only of nitrogen and oxygen. The air then between the surface of 

 the sulphuric acid in the last porcelain absorber and the point where the 

 ingoing air is delivered to the calorimeter consists of air free from carbon 

 dioxide and free from water. Formerly this section also included the 

 tension-equalizer, but very recently we have in both of the calorimeters 

 attached the tension-equalizer directly to the respiration chamber. 



In the Middletown apparatus, these portions of air of varying compo- 

 sition were likewise subject to considerable variations in temperature, in 

 that the temperature of the laboratory often differed materially from that 

 of the calorimeter chamber itself, especially as regards the apparatus in 

 the upper part of the laboratory room. It is important, however, to know 

 the total volume of the air inclosed in the whole system. This is obtained 

 by direct measurement. The cubic contents of the calorimeter has been 

 carefully measured and computed ; the volumes of air in the pipes, valve 

 systems, absorbing vessels, and tension-equalizer have been computed from 

 dimensions, and it has been found that the total volume in the apparatus 

 is, deducting the volume of the permanent fixtures in the calorimeter, 1,347 

 liters. The corresponding volume for the bed calorimeter is 875. These 

 values are altered by the subject and extra articles taken into the chamber. 



From a series of careful measurements and special tests the following 

 apparent volumes for different parts of the system have been calculated: 



Liters. 



Volume of the chair calorimeter chamber (without fixtures) 1360.0 



Permanent fixtures (5) ; chair and supports (8) 13.0 



Apparent volume of air inside chamber 1347.0 



Air in pipes, blower, and valves to surface of acid in first acid vessel 4.5 



Apparent volume of air containing water-vapor 1351.5 



Air above surface of acid in first sulphuric-acid vessel and potash-lime can. 16.0 



Apparent volume of air containing carbon dioxide 1367.5 



Air in potash-lime can, second sulphuric-acid vessel and connections, 



sodium-bicarbonate cans, and pipes to calorimeter chamber 23.5 



Apparent volume of air containing carbon dioxide, water, oxygen, 



and nitrogen 1391.0 



