Measuring reaction rates. Footage of the start of a laboratory experiment to measure reaction rates. This reaction is between sodium thiosulphate (beaker at left) and dilute hydrochloric acid (reagent bottle and beaker at right). A temperature probe is used to measure the temperature of the sodium thiosulphate solution before the acid is added to start the reaction. The starting temperature is needed as part of the calculations of the reaction rate. A stopwatch (lower centre) will be used to time the reaction. For the second stage of the reaction, see clip K004/1465.