CAPILLARY RESPIROMETRY 317 



exception that the biological material is placed only in one of them. 

 The index droplet is placed on the capillary by introducing a little 

 kerosene into one of the drilled holes, and removing the excess by 

 absorbing it into the end of a hardwood toothpick. Then the droplet 

 is forced to the proper position and the capillary is clamped in place. 



The assembled apparatus is tested for leaks by warming one end 

 with the hand. When the hand is removed, the index droplet will re- 

 turn to its original position if no leaks are present. 



Calibration. The volumes of the chambers are determined, after 

 greasing the metal to prevent amalgamation, by filling with mercury, 

 squeezing out the excess by pressing a glass plate over the chamber, 

 and weighing the mercury left. The volumes of the Lucite discs are 

 also determined by weighing them and dividing by the specific grav- 

 ity of the Lucite. The volumes of the capillary posts and the capillary 

 tubes are calculated from measurements of the dimensions of the 

 holes. 



Corrections for the volume of kerosene adhering to the capillary 

 walls were found to be 0.45 ± 0.10% for a 0.57 mm. diameter capil- 

 lary, and 0.42 ± 0.07 for a 0.22 mm. capillary, in experiments by 

 Cunningham and Kirk (1940). The corrections were determined by 

 measuring the length of a kerosene droplet before and after it was 

 made to move along the capillary for a known distance. The volume 

 of liquid on the walls, calculated from this measurement, divided by 

 the total volume of the capillary traversed by the droplet times 100 

 gives the percentage error. 



Calculations. Cunningham and Kirk (1940) gave the deriva- 

 tions of the formulae which may be used to calculate changes in the 

 amount of gas in the apparatus. The change in the gas volume 

 (AFp„) at the initial pressure (Po), which equals the barometric 

 pressure at the time the apparatus is sealed, is given by the following 

 expression for the case of a reaction liberating carbon dioxide, as in 

 the interaction of acid and bicarbonate in the reaction chamber: 



/ Vr. \ 



AVp, = nAd 



-Yc - Ad/ 



where n is the ratio of the total volume of the two chambers to the 

 volume of the compensation chamber, A the effective cross-sectional 

 area of the capillary (actual area minus 0.4% to correct for the film 

 of kerosene which coats the wall), d the displacement of the index 



