The paper presents the results of an experimental study of the isobaric heat capacity of solutions of electrolytes of the water and NaCl system in the temperature range 288-373K. To measure the heat capacity of electrolytes, the method of monotonous heating was used (developed by Professor M.M.Safarov). The total relative error of measuring the heat capacity of this place with a confidence probability of 95% is on average equal to 3.8%. It is established that the specific isobaric heat capacity of electrolytes decreases with increasing temperature and concentration of sodium chlorine. The addition of fullerene leads to an increase in the heat capacity of solutions of the water and sodium chlorine system. On the basis of experimental data and the law of thermodynamic similarity, approximation dependences were obtained. Using the expressions obtained, it is possible to calculate the heat capacities of electrolytes at different temperatures and concentrations of fullerene nanoparticles.