410 



GASOMETRIC-POLAROGRAPHIC METHODS 



tissue to be studied, the calibration curves in Figure 149 arc actually 

 unchanged within the experimental error between 28° and 37°. The 

 negligible effect of the temperature change results from counter- 

 balancing the associated changes in D and the solubility of oxygen. 

 However, the temperature must be known in order to convert 

 partial pressures into concentrations of oxygen. 



0.2 04 06 0.8 1.0 1.2 1.4 1.6 1,8 

 DISTANCE FROM PLATINUM SURFACE, mm. 



Fig. 148. Concentration-distance 

 curve at various times after beginning 

 linear diffusion. Assumed value of D, 

 4.0 X 10~^ cm.^/sec. From Davies and 

 Brink (194£) 



20 40 50 80 100 120 140 160 

 OXYGEN TENSION, mm Hg 



Fig. 149. Current vs. oxygen ten- 

 sion from current-time curves. Elec- 

 trode No. 11. Same solution, tempera- 

 ture, 28 °C. Potential, —0.60 v. vs. 

 0.15 M calomel. From Davies and 

 Brink (1942) 



Control experiments have revealed no evidence that substances 

 other than oxygen are electrolyzed under the conditions employed. 

 The recessed electrode offers the distinct advantage that the meas- 

 urements may be made independent of the diffusion coefficient in 

 the medium beyond the orifice. To maintain constancy of the diffu- 

 sion coefficient within larger recesses, they are filled with agar gel 

 containing 0.15 M sodium chloride. The smaller recesses exclude 

 particulate matter by virtue of the narrow bore; the diffusion of 

 solutes into the recess has no appreciable effect on the value of D 

 Another advantage of the recessed electrode is its freedom from 

 the effects of convection in the external solution. 



