378 GASOMETRIC-MANOMETRIC METHODS 



(12) CALCULATIONS 



The Diver Constant. A constant must be determined for each 

 diver which represents the total gas volmne (V) in the diver when 

 the latter is at its equilibrium position at a given pressure (P) and 

 temperature (t). V may be measured in two ways: 



(1) By subtracting the total volume of the liquids in the diver 

 from the total volume of the diver itself, and then correcting the 

 gas volume obtained at barometric pressure and room temperature 

 to P and t. The total volume of the diver is determined by weighing 

 or filling from a burette. 



(2) By calculating V according to the formula: 



y _ gp + Voil((}oil + Vw4>w — Voil<i>M — Vw4>M — igD4>Af/<t>gl) 



where g, v, and 4> represent weight, volume, and density, respectively, 

 and subscripts D, oil, w, M, and gl refer to diver, oil, aqueous 

 phase, medium, and glass, respectively. This formula is derived from 

 the expression which is based on the fact that, at equilibrium, the 

 density of the diver unit equals that of the flotation medium : 



'W 



_ gp + Voil(t>oil + Vw(l>i, 



y + Voii + v,r + gp/<i>ei 



In practice, the first method is less exact than the second for 

 divers of the type described, because of the difficulty of measuring 

 exactly the volume of mouth seals and the total volume of small 

 divers by filling with a liquid. The chief reason for this is the poorly 

 defined surface of the liquid at the mouth. 



According to Lindestr0m-Lang (1943), the errors of the values 

 in the formula for V which would result in a 1% error in V are: 



Voii 33% 



Vu, 50% 



<t>,i 1% 



<t>^f 0.5% 



<i>oii, <t>w 12% 



For divers having a total volume of <5 [A., an accuracy of 0.02 

 mg. in igr,) may be desirable, while for larger divers, an accuracy 

 of 0.1 mg. is sufficient as a rule. 



