text: V. G. Khlopin developed a method of mechanical enrichment to improve the quality of raw barium-radium sulfates rich in silica (together with engineer S. P. Alexandrov). Later, the scientist transformed the Curie-Debierne method of conversion of sulfates into carbonates under the condition of saturation of sulfates with silica - through the combination of soda with caustic soda (together with P. A. Volkov).
  On the basis of theoretical assumptions, V. G. Khlopin proposed several methods of fractional crystallization of barium-radium salts, excluding evaporation of solutions - by increasing the concentration of the same ion in the cold: fractional precipitation of chlorides with hydrochloric acid (1921), fractional precipitation of bromides (together with M. A. Pasvik, 1923), fractional precipitation of nitrates (with P. I. Tolmachev, with A. P. Ratner, 1924-1930). A. Pasvik, 1923), fractional precipitation of nitrates (with P. I. Tolmachev, with A. P. Ratner, 1924-1930), fractional precipitation of chromates (M. S. Merkulova), fractional precipitation of chlorides with zinc chloride (I. Y. Bashilov and Y. S. Vilnyansky, 1926).
  In 1924, V. G. Khlopin created a general theory of the fractional crystallization process, which greatly facilitated the calculation of the technological process in general and the development of the required apparatus for its implementation in particular. A number of versions of the conventional crystallization scheme were hereby based on calculations used in plant practice. Later this theory was applied and developed in the All-Russian Research Institute of Chemical Reagents and Particularly Pure Chemicals for obtaining chemically pure substances by recrystallization.