Sec. 8.8] INDIRECT METHODS FOR MEASURING DEUTERIUM 



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plotting the densities of several mixtures of known density against the 

 reciprocals of their falling times. The deviation from Stokes' law may be 

 calculated from the differences between the reciprocals of the times of fall 

 of the known mixtures and that of pure water [54]. 



Depending upon the range of concentrations being determined, this method 

 gives a precision in density of about 1 to 4 parts 

 in 10 6 , corresponding to 0.001 to 0.004 per cent 

 of deuterium. The errors introduced in the 

 combustion and purification processes are larger 

 and may raise the maximum over-all error to 

 0.02 per cent of deuterium. 



8.8. Diffusion Gradient. This method is 

 similar to the falling-drop method in that the 

 density of a drop of the liquid to be tested is 

 determined by introducing the drop into another 

 liquid with which it is immiscible. It differs 

 chiefly in that the reference liquid is so prepared 

 that it presents a linear gradient of density and 

 the drop falls only to an equilibrium position 

 at which the specific gravity of the surrounding 

 medium is equal to its own. The density of the 

 drop is found by comparing the equilibrium 

 position of the unknown sample with the posi- 

 tions of other drops of known density. This 

 method offers the advantage of avoiding the 

 errors due to convection currents inherent in the 

 falling-drop method [15-17,70]. 



Figure 59 shows the type of tube used in this 

 method [15]. The tube is mounted in a vertical 

 position to the depth indicated by A in a thermo- 

 stated water bath. A gradient suitable for 

 determination of the deuterium in deuterium 

 oxide-water mixtures containing between and 

 10 per cent deuterium oxide may be prepared 

 from two bromobenzene-kerosene mixtures, the 

 lighter one having a density of about 0.99 and the heavier a density of 

 about 1.02 [70]. 



The tube is placed in the thermostat (regulation to +0.01 is sufficient), 

 and the heavier mixture is poured in up to the middle of the tube connecting 

 the two bulbs. Next the lighter mixture is brought to the bath temperature 

 and added cautiously through a funnel with a filter up to the level shown at B 

 in Fig. 59. In order to obtain a uniform distribution of the two mixtures in 



Fig. 59. 

 gradient. 



Tube for diffusion 



