System for mixing solutions comprising: - a device for mixing solutions, comprising: a first container having: (i) a cylindrical upper part provided with an upper opening configured for filling and emptying an internal volume of the container, (ii) a lower wall which is conical or frustoconical in shape, (iii) a solid, i.e. unperforated, cylindrical and/or conical internal wall, the upper opening being the only fluid passage into and out of the container a stem passing through the opening of the container, said stem being integral with the internal wall of the container, - at least one second container (26a-26e) capable of containing solutions, each second container (26a-26e) being capable of entirely containing the first container; - means for displacing the first container and/or each second container (26a-26e) capable of entirely immersing the first container in each second container; and - rotational drive means for the first container so as to mix the solutions present in the first and second containers when the first container is entirely immersed in the solution present in the second container (26a-26e), characterized in that the internal wall of the first container has a section, defined perpendicular to an axis Z, which is constant from the upper opening towards the lower wall of the first container. - a device for mixing solutions, comprising: a first container having: (i) a cylindrical upper part provided with an upper opening configured for filling and emptying an internal volume of the container, (ii) a lower wall which is conical or frustoconical in shape, (iii) a solid, i.e. unperforated, cylindrical and/or conical internal wall, the upper opening being the only fluid passage into and out of the container a stem passing through the opening of the container, said stem being integral with the internal wall of the container, a first container having: (i) a cylindrical upper part provided with an upper opening configured for filling and emptying an internal volume of the container, (ii) a lower wall which is conical or frustoconical in shape, (iii) a solid, i.e. unperforated, cylindrical and/or conical internal wall, the upper opening being the only fluid passage into and out of the container (i) a cylindrical upper part provided with an upper opening configured for filling and emptying an internal volume of the container, (ii) a lower wall which is conical or frustoconical in shape, (iii) a solid, i.e. unperforated, cylindrical and/or conical internal wall, the upper opening being the only fluid passage into and out of the container a stem passing through the opening of the container, said stem being integral with the internal wall of the container, - at least one second container (26a-26e) capable of containing solutions, each second container (26a-26e) being capable of entirely containing the first container; - means for displacing the first container and/or each second container (26a-26e) capable of entirely immersing the first container in each second container; and - rotational drive means for the first container so as to mix the solutions present in the first and second containers when the first container is entirely immersed in the solution present in the second container (26a-26e),