354 GASOMETRIC-MANOMETRIC METHODS 



a micro flame. The flame should acquire a faint sodium tinge. 



This process can be replaced by heating for about 20 min. at 

 400° in a furnace. It is necessary to heat the diver neck to insure 

 proper moistening of the neck by the seals. 



8. Handle the clean divers only with clean forceps (cork- 

 tipped forceps are recommended). Clean divers should never be 

 touched with the fingers. Store the divers in stoppered glass tubes. 



Afljusting the Weight of the Diver. The weight of the diver 

 must be adjusted so that when it is finally charged for an experi- 

 ment the equilibrium pressure will approximate the barometric 

 pressure. The desired weight of the diver may be calculated from 

 the formula: 



9d = 



1 — {<t>m/<t>gl) 



where Qd is the desired weight of the diver, Fu- the aqueous volume 

 in the bottom and neck of the charged diver, V,. the total diver 

 volume, Voii the vol. of the paraffin oil seal, Vm the vol. of the 

 mouth seal, </>„„ </>(„7, 0„, 4)gi the densities of the medium, paraffin 

 oil, aqueous charge, and glass, respectively. The total volume [Vt) 

 is measured by weighing the diver to 0.1 mg., first empty, and then 

 filled with water. The densities of the liquids may be determined 

 with a Mohr-Westphal balance, and the glass density by weighing 

 2-5 g. of the glass in air and in water to 1 mg. If air bubbles are 

 present in the glass of the diver, the density can be obtained by the 

 flotation method. Holter has given the following proportions of 

 ethylene dibromide and bromoform to make flotation liquids of the 

 densities indicated: 



Ethylene dibromide, Bromoform, j22.50 



ml. ml. °40 



20 5 2.314 



15 10 2.460 



15 15 2.529 



10 20 2.643 



Of course it is possible that different grades of the two compounds 

 will give mixtures with different densities. The following example of 

 the calculation of the desired weight of a diver has been taken from 

 Holter (1943, page 427) : "A diver made from Jena glass of specific 

 gravity 2.40 weighs 12.9 mg. empty and 23.6 mg. filled with water. 



