Abstract: Apparatus for enabling continuous monitoring of a mixture ratio of two different liquids as well as to limit it to those mixture amounts which are drawn off at a particular time for the purpose of being used which includes a receptacle filled by a liquid or through which the liquid flows. The receptacle comprises two electrodes insulated from each other and located opposite each other at which a capacitance measuring device determining the respectively occurring capacitance is connected. The dielectric constants of the components of the mixture which differ in many mixtures, for instance, in an oil-water mixture, permit, because of the fixed dimension of the constituted condenser, the determination of the composition of the mixture by means of the respectively existing dielectric constant so that, for instance, harmful water penetrating into oil systems provided for lubrication can be determined in small amounts and can trigger appropriate warning signals.