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The behaviour of the primary cosmic ray composition near the knee may be considered as being of fundamental importance in studies of the knee nature. In this paper experimental data obtained with the KASCADE array are considered and patterns of the knees in electron and muon size spectra are compared. Such a comparision provides valuable information to check the consistency of the existing experimental data and model predictions. Improvements in the existing simulation methods are essential to ultimately establish the results of the KASCADE mass composition studies. Evidently some revision of hadronic interaction models is needed to eliminate the discrepancy between mass compositions derived with and without KASCADE hadronic calorimeter data.

A binary uncharged isotopic mixture at liquid density is described by the state variables M , and M,, the component masses, volume V and temperature T. To these, in an extended irreversible thermodynamic treatment, is added the diffusion flow Jd. In the framework ofthis approach, a kinetic equation relates j,, to the driving force, -V T ( p ,p 2 ) , where the p 2 are chemical potentials and T is kept constant in computing the gradient. To calculate the coefficient y of this force, a microscopic model is adduced which expresses y in terms of PTT, the pressure tensor. Evaluation of y and application of reciprocity permits the calculation of @, the thermodynamic force associated with Jd. Once @ is known, integrability conditions for the Helmholtz function yield the O ( J i ) terms in the pressure P and the p 8 . From these results and an estimate from computer simulations of the relaxation time for Jd, we obtain D, in the diffusion coefficient, D = D , + D , J i . Estimates for a hard-sphere model representing a mixture of 36Ar and 40Ar predict that all the J : terms in D, P, p , are negligible unless iJd/ 3 IO4 kg m-' s-' at liquid density.

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