OPTICAL— LEVER RESPIRO.M ETR V 



399 



6. Take readings at 5 min. intervals after allowing 5 min. for the 

 initial eqnilibration. 



2. Optical-Lever Respironielry 



Heatle}', Berenblnm, and Chain (1939) developed an apparatus 

 in which a respiration chamber of 40-80 fA. is ground into a glass 

 plate and covered with a mica membrane to which mirrors are 

 attached. A change of gas pressure within the chamber causes the 



I 



I 





miJLp. 



Fig. 137. Component parts of respiration chamber: A, B, C, cups witli 

 cavities for two, three, and four separate droplets, respectively; D, mica mem- 

 brane with mirrors attached; E. "plate"; F. complete assembly ready for plac- 

 ing in brass case. From Hentlcy (1940) 



mica to bulge and a compensating external pressure can be applied 

 to restore the membrane to its original position as indicated by an 

 optical lever. From the volume of the gas space and the change in 

 pressure required to keep it constant, the change in the gas volume 

 may be calculated. The instrument is sufficiently sensitive to measure 

 changes in the gas volume of 1 lA. per hour (about 200 times as 

 sensitive as the usual Barcroft or Warburg apparatus). 



