Measuring reaction rates. Time-lapse footage of a laboratory experiment to measure reaction rates. This reaction is between sodium thiosulphate and dilute hydrochloric acid. The clip starts with the addition of the acid to the sodium thiosulphate solution. A stopwatch (right) is used to time the reaction and the solution is swirled by hand at regular intervals. The progress of the reaction is measured by the formation of sulphur which make the solution go cloudy. The time taken for the cross on the white paper below the reaction beaker to no longer be visible is noted. For the first stage of this experiment (measuring the starting temperature), see clip K004/1466.