We study experimentally friction in ceramic mixture. Two schemes of tests were realized. These schemes differ from each other by the design of friction units. It is shown that parameters of friction depend mainly on stress-strain state of specimens and on peculiarity of frictional contact. Irrespective of test procedures, the force of friction depends on a normal load nonlinearly and this relationship is the same for the both methods. As the normal pressure increases, the constant of friction decreases and zero is its limiting value. We demonstrate a relationship between properties of surface of a material and its volumetric properties. We propose an equation describing the process of friction in disperse systems considering their equations of state.