DESCRIPTION OF APPARATUS. 33 



The algebraic increase in weight of the soda-lime bottles and the 

 following Williams bottle in the carbon-dioxide absorbing system gives 

 the weight of the carbon dioxide absorbed during the experimental 

 period. The volume of oxygen introduced may be determined from 

 the loss in weight of a small cylinder or, as indicated in figure 1 , meas- 

 ured by conducting it from a large cylinder through a carefully calibrated 

 gas-meter which is immersed in water to prevent sudden fluctuations in 

 temperature. To prove the efficacy of the soda lime as an absorbent, 

 a part of the air current may be deflected through two petcocks and 

 passed through a solution of barium hydroxide in a small Erlenmeyer 

 flask. The slightest trace of carbon dioxide will produce a turbidity 

 in the solution. 



To eliminate the effect of the long dead space between the mouth- 

 piece, P, and the main ventilating air-pipe, a supplementary pipe E is 

 connected from a point near the mouthpiece to the main air-pipe. By 

 this means the air-current may be deflected so that it will pass directly 

 by the mouthpiece and within a few centimeters of the lips of the sub- 

 ject. The rubber tubes connecting the subject with the ventilating 

 system are of sufficient length and flexibility to permit considerable 

 lateral and vertical head-motion by the subject while walking, this 

 being essential to his comfort. 



In actual experimenting, before the experimental period is begun, 

 the 3-way valve N is so turned that the subject breathes room air. 

 Then, at the end of a normal expiration, the 3-way valve is again turned, 

 connecting the subject with the main ventilating air-current as seen in 

 the diagram. Immediately afterwards the valve M (which has previ- 

 ously been open, giving free passage of the air into the metal tee leading 

 to the tension equalizer) is also turned, thus deflecting the air-current 

 through the supplementary pipe E, so that it passes near the mouth of 

 the subject. 



Before connecting the subject with the ventilating system, the motor 

 is started to equalize pressure throughout the system and then stopped. 

 Sufficient oxygen is next admitted to distend the rubber bathing-cap 

 until a slight positive pressure is observed on the manometer. On 

 starting the blower again, the rubber bathing-cap sinks somewhat, due 

 to the compression of the air in forcing its way through the sulphuric 

 acid and the various absorbing-vessels. At the first inspiration the 

 rubber cap sinks down into the can, rising again with each expiration. 

 As the oxygen is consumed, the height to which the rubber cap fills 

 decreases and oxygen is admitted to keep the fluctuations of the 

 bathing-cap to approximately the same range. At the conclusion of 

 the experiment, the valve M is first turned and shortly afterwards the 

 valve N is also turned, always at the end of a normal expiration. At 

 this point the experimental period is concluded so far as the subject is 

 concerned. The motor is next allowed to run for a minute or two to 



