GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 71 



filling the bag to a definite point, as shown by the pointer, a delicate man- 

 ometer is attached to the can by means of a pet-cock and the oxygen is 

 admitted by operating the switch B imtil the desired tension is reached. 



In order to provide for the maximum sensitiveness for weighing D and 

 its appurtenances, the electric connection is broken at the cylinder by means 

 of the plug N" and the rubber tube is connected by a glass connector which 

 can be disconnected during the process of weighing. Obviously, provision 

 is also made that there be no leakage of air out of the system during the 

 weighing. The current at F is obtained by means of a storage battery 0. 

 The apparatus has been in use for some time in the laboratory and has 

 proved successful in the highest degree. 



TENSION-EQUALIZER. 



The rigid walls of the calorimeter and piping necessitate some provision 

 for minor fluctuations in the absolute volume of air in the confined system. 

 The apparatus was not constructed to withstand great fluctuations in pres- 

 sure, and thin walls were used, but it is deemed inadvisable to submit it 

 even to minor pressures, as thus there would be danger of leakage of air 

 through any possible small opening. Furthermore, as the carbon dioxide 

 and water-vapor are absorbed out of the air-current, there is a constant 

 decrease in volume, which is ordinarily compensated by the admission of 

 oxygen. It would be very difficult to adjust the admission of oxygen so as 

 to exactly compensate for the contraction in volume caused by the absorp- 

 tion of water-vapor and carbon dioxide. Consequently it is necessary to 

 adjust some portion of the circulating air-current so that there may be a 

 contraction and expansion in the volume without producing a pressure on 

 the system. This was done in a manner similar to that described in the 

 earlier apparatus, but on a much simpler plan. 



To the air-pipe just before it entered the calorimeter was attached a 

 copper can with a rubber diaphragm top. This diaphragm, which is, as a 

 matter of fact, a ladies' pure rubber bathing-cap, allows for an expansion or 

 contraction of air in the system of 2 to 3 liters. The apparatus shown 

 in position is to be seen in fig. 25, in which the tin can I is covered with the 

 rubber diaphragm J. If there is any change in volume, therefore, the rub- 

 ber diaphragm rises or falls with it and under ordinary conditions of an 

 experiment this arrangement results in a pressure in the chamber approxi- 

 mately that of the atmosphere. It was found, however, that even the slight 

 resistance of the piping from the tension-equalizer to the chamber, a pipe 

 some 26 millimeters in diameter and 60 centimeters long, was sufficient to 

 cause a slightly diminished pressure inside the calorimeter, inasmuch as the 

 air was sucked out by the blower with a little greater speed than it was 

 forced in by the pressure at the diaphragm. Accordingly the apparatus 

 has been modified so that at present the tension-equalizer is attached di- 

 rectly to the wall of the calorimeter independent of the air-pipe. 



