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The alloys of the As-Se system from pure selenium to 60 at% A s are typical glassy semiconductors. They are converted into the liquid state without structural order-disorder transitions. Energy spectrum transformation and conductivity mechanism investigations are possible in the c a s e when the short-range o r d e r is continuously chahged during the melting process and fGrther melt heating .In our paper the optical (in glass) and electric (in melt) properties of the 40, 46.3, and 51.3 at% A s compounds were investigated. spectra were obtained with the spectrophotometer "Specord", the electric conductivity and thermal e. m. f . were investigated in a high-pressure argon

and Bi doped (1 and 1.5 wto/) Bi, Te, and Se is investigated over a large temperature range using solid as well as liquid samples (for Se the amorphous state is also included). The dopants Zn, Ga, In, and Sn strongly affect the thermo e.m.f. of solid but not of liquid Bi. Liquid Te and Se are found to show semiconductor properties determined strongly by impurities, especially for se. The change in the sign of the thermo e.m.f. of liquid Se is explained by the existence of oxygen atoms acting as acceptors.