Abstract: The automatic analyzer for the assay of liquid samples comprises an exchangeable mixing chamber whose mixing chamber is tapered toward the bottom and is provided with an outlet which is followed by a bore which connects the mixing chamber to an outlet opening. An abrupt transition is formed between said bore and the outlet opening for the analyzed liquid. The abrupt transition is a restriction which serves as a collecting trap for disturbing particles, e.g. coaguli, which might lead to undesirable obstructions elsewhere. Those particles which cannot be flushed away laterally by another outlet opening are eliminated by removing the mixing chamber from the base and blowing it through. A sealing ring serves for a tight seal between the plane bottom of the mixing chamber and the connection. A fluid sensor is provided in order to detect the sample liquid flowing through this connection.