Abstract: A process for mixing a liquid sample to be analyzed with periodic air movements includes the steps of placing the sample in a sample container and alternately directing air jets onto different regions of the surface of the sample, wherein the air jets displace the surface regions and produce turbulence in the sample. An apparatus is provided for practicing the process.

Abstract: A cell for mixing operations and for optical examinations of liquids has a measuring region which has a small cubic capacity and a relatively large height. In a horizontal cross-section that measuring region has curved transitional wall portions between parallel end wall portions for receiving incident radiation and side walls. In the measuring region, the side walls have inwardly curved portions, which protrude inwardly to such an extent that in a transverse sectional view a tangent to the apex of each inwardly curved portion intersects the parallel end wall portions at an edge thereof or at a point which is inwardly spaced from said edge so that a double-tapered beam of measuring radiation will be closely approached by the inwardly curved side wall portion. At least one side wall portion may constitute a positive lens.