a device for the determination of at least one substance in a liquid which comprises a reaction compartment containing a reagent for the substance , a measuring compartment for collection of a predetermined volume of a liquid sample and a facility for transport of the liquid sample , collected in the measuring compartment , to the reaction compartment . the measuring compartment and the reaction compartment are connected with each other by a canal so that when the measuring compartment , with the liquid sample therein , is elevated above the reaction compartment , the liquid flows downwardly into the reaction compartment .