Abstract: Apparatus and method are described for measuring and recording as a function of time the resultant-weight of a test object immersed in a fluid medium. The apparatus and method are particularly suitable for determining a change in a chemical and/or physical property of a material exposed to a fluid, and for measurements such as of the floating forces produced by buoyant pharmaceutical dosage forms. An electronic toploader balance, with a weight-transmitter device connected to an electromagnetic measuring module of the balance, is positioned above a container so that the lower end of the weight-transmitter device extends into a solvent within the container. The weight transmitter device performs the double function of holding the test object submerged in the solvent and of transmitting to the balance the reacting force, that is the resultant-weight of the test object.