In liquid chromatographs, one frequently works with liquid mixtures whereof the mixing proportion is varied as a function of time in a definite manner. On account of the very low conveying capacities and the very varied viscosities of the liquids to be analysed, definite mixing proportions cannot be achieved due to the fact that the streams of the liquids to be mixed are supplied together at the same time and the mixing proportion is determined by regulating the force of the stream. Instead of this, small portions of the liquids to be mixed together are supplied continuously in succession to a mixing chamber by means of valves having a time control, in which chamber the individual liquid components are mixed together. In order to provide a notion of the orders or magnitude, which occur in devices of this type, it can be mentioned that typical conveying capacities are in the range of between 0.1 and 10 ml/min. Accordingly, the volume of the mixing chambers used in this case is within the order of several milliliters.
Known mixing chambers for this application were provided with a stirrer, which consisted of a permanent magnetic member located inside the chamber and of a device located outside the mixing chamber for producing a rotary field. The provision of such a stirrer requires considerable technical resources and in particular both as regards the construction and location of the electromagnet for producing the rotary field, as well as with regard to the necessity of providing a special current supply for this purpose. In this case it should be taken into consideration that the liquids to be mixed may have a very high viscosity and on the other hand, the dimensions of the mixing chamber and of the stirrer located therein are relatively small, so that the production of high moments of rotation is difficult, as the latter could be required for mixing highly viscous liquids. Furthermore, it may be necessary to construct the mixing chamber so that it withstands very high pressures, namely pressures of several hundred Bars. However, the use of such a stirrer precludes ferromagnetic materials for the production of such mixing chambers.