In present work we studied dependencies of transitional contact rê of extruded samples Bi₈₅Sb₁₅ solid solution with the alloy mass. %, 57Bi + 43Sn with melting temperature Tm » 412 K on the intensity of magnetic field and temperature. This contact alloy is broadly use at commutation of thermoelements on the base Bi—Sb system solid solution. At the fixing of contact on torahs of extruded samples Bi₈₅Sb₁₅ occurs a mutual diffusion of components of solid solution and contact alloy each to other. So as result of diffusions of atoms Sn from the contact alloy in Bi₈₅Sb₁₅ solid solution near the contact appears near-contact layer of given solid solution, doped by atoms of tin. By doping near contact layer of branches of thermoelements on the base of Bi₈₅Sb₁₅ solid solution with donor impurities, compensating action of acceptor atoms, diffusing from the contact alloy in this layer, possible vastly lower rê and raise efficiency of thermoelements.