MICROLITER DI\^R TECHNIQUE 379 



Holier (1943, page 464) has explained that the calculation may 

 be simplified as follows: "Assuming that we are always using the 

 same medium (which is generally true) and that it has the density 

 (f)M, then the quantity go — {Qd 4>M/<i>ai) is a constant charac- 

 teristic for each diver and may be calculated once for all and 

 recorded in the diver inventory. Since, moreover, the same stock of 

 paraffin oil will be used in all experiments it is likewise possible 

 once for all to calculate the values of Vou 4>ou— ou <f>M and to plot 

 them as a function of Vou- The same applies to the volume of the 

 aqueous solutions, the densities of which in most cases deviate so 

 little from 1 that they may be ignored. With these two curves 

 drawn the whole calculation of V becomes a matter of reading the 

 values of V^ — Vw(J)m and Vou (pou — Vou (t>M from the curves, adding 

 them to Qd — (gD4>M/(t>oi) and dividing b}- the value of c^a/ which 

 is also known once for all." 



Change in Gas Volume. The pressure change (Ap) is read 

 directly on the manometer. The equilibrium pressure (P) is actually 

 the manometric pressure (p), plus the barometric pressure at the 

 moment the air bottle was sealed, plus the hydrostatic pressure of 

 the medium over the diver, plus capillary pressure at the bound- 

 ary between the mouth seal and the gas in the diver neck. When 

 calculating the change in equilibrium pressure (aP), this quantity 

 may be made equal to (Ap) since all the other factors are essentially 

 constant. The surface tension factor is eliminated by using sodium 

 taurocholate in the medium. The relation Ap = aP requires the 

 correction : 



P = p (1 + 1000 A/y/) 



where A is the cross-sectional area of the bore of the manometer 

 tube, F/ the vol. of the air bottle, and 1000 the barometric pressure 

 in cm. of Brodie soln. For the dimensions of the manometer tube 

 and air bottle given previously (pages 348-350) the correction 

 amounts to about 1%. 



When no correction is required for the solubility of the gas in the 

 liquids in the diver, the following relationship holds: 



AV = FAP/Po 



where Po is the normal pressure (1000 cm. Brodie soln.). However, 

 the effect of the gas solubility is appreciable in many instances, and 



