392 GASOMETRIC— MANOMETRIC METHODS 



(7) CHOICE OF DIVERS FOR DIFFERENT 

 RESPIRATION RATES 



The choice of divers for measurements of respirations of approxi- 

 mately known intensities should follow the general considerations 

 given by Zeuthen (1943, page 509) : 



1. The changes in equilibrium pressure should fall in the range 

 of 3-10 cm. water per hour (2-20 if necessary) . 



2. The respiration rate must not be great enough to move (PO2) 

 toward W. This can be checked by observation through the micro- 

 scope. 



3. Total changes in equilibrium pressure over 50 cm. water 

 (corresponding to a drop in oxygen in the diver from 21 to 16%) 

 should be avoided. 



4. It is well to calculate, for the diver dimensions used, the 

 magnitude of the respiration rate which would result in the danger 

 of oxygen deficiency (perhaps even the carbon dioxide absorption 

 should be calculated according to the formulae of Zeuthen, 1943, 

 pages 492-494) . The following formula is used to relate the dimen- 

 sions to the respiration rate: 



_ OAlAao, . <^o. 



R o'lOj 



where I (in mm.) is the greatest length of TT^ permissible for the 

 respiration intensity R (in /tl./hr.), A is the cross-sectional area of 

 the diver capillary, in mm.^ 0-02 is the "standard rate of passage" 

 for oxygen through water at 20° ; its value is 0.204. o-q is the 

 "standard rate of passage" for oxygen through paraffin oil to which 

 the value, 0.10, has been ascribed; and L^, in mm., is the average 

 length of the diffusion path through PO2, which is defined as Ld = 

 L -{- (2r/3), where L is the shortest distance between the oil menisci 

 and r is the radius of the diver capillary. Thus: 



A I 2r\ 0.204 



When there is a tendency to condensation of moisture on the 

 walls of L2, when W consists of fresh water, a film of oil about 0.05 

 mm. thick is placed on W . Then: 



