Loschmidt diffusion apparatus

In this experiment the mutual diffusion coefficients for the Ar—CO2 and He—CO2 systems are to be measured using a modified Loschmidt apparatus. These transport coefficients are then compared with theoretical values calculated with hard-sphere collision diameters. 

Modified Loschmidt apparatus, to be used according to procedure B. Stopcock A should have a very large bore which is as close as possible to the diameter of the diffusion tube. Stopcocks Bto should be high-vacuum type. As a safety precaution, each gas lecture bottle should be connected to the system via a reducing valve or a pressure-relief valve. 

Loschmidt diffusion apparatus (a) curves showing schematically the quantity A7 = 75, - 7 (h) cell ... 

Our task here is to derive an expression that describes how the composition of a multicomponent mixture changes with time in a Loschmidt diffusion apparatus of the kind described in Section 5.5. The composition profile for a binary system is given by Eqs. 5.5.5 and 5.5.6) the solution to the binarylike multicomponent problem is given by the same expressions on replacing the binary diffusivity in those equations by the effective diffusivity. The average composition in the bottom tube after time Z, for example, is given by... 

FIGURE 2.3-9 (a) Loschmidt diffusion apparatus, and (b) composition profiles... 

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