314 



THE HUMAN MOTOR 



will run into the latter through the syphon balancing the apparent 

 increase in weight of the bell. Also the vessel K receives a flow 

 of water through E, which assures a constant level, the excess 

 passing off by the overflow T. 



The capacity of the bell is, as a rule, from 50 to 250 litres. The 

 volumes of gas expired are read on a graduated scale, H, over 

 which moves an aluminium pointer. An apparatus of 200 litres 

 capacity is sufficient, but if necessary two may be coupled 

 together (fig. 221). Another advantage of the counterweight 

 spirometer is that the gases are preserved in it and samples for 

 analysis can be taken from the top of the bell by unscrewing the 

 cap R. Fig 221 indicates the manner in which this can be done.. 



242. With the ordinary meter samples of the gas are taken 

 during the experiment in the following manner : Before entering 

 the spirometer, the gases pass through a small vessel, F, which 

 holds about 1 litre (fig. 222). Into this vessel penetrates a 

 capillary tube, A A', which is prolonged externally to form a bend 

 terminated by an elbow immersed in mercury. A three-way 



Fie 222. 



Apparatus for sampling expired gases. 



cock, R, is fitted, as shown, which can connect A and B A and A' 

 or B and A' (fig. 223). With the cock in the first position, the 

 mercury reservoir, B', is raised to fill B up to the line a and the 

 opening is regulated so that by hooking the reservoir B' to a low 

 support, the mercury runs slowly from B to B'. When the ex- 

 periment is terminated, the cock is turned to position No. 2, 

 which isolates the gas. 



ft* 223. 



Positions of the 

 three-way cock. 



