When a solute is added to a solvent the freezing point of the solution is lower than that of the pure solvent. The lowering of freezing point is very small. A chemist called Beckmann invented a thermometer capable of measuring these small temperature changes accurately. The Beckmann thermometer must be calibrated at the start of the experiment. An incomplete diagram of the Beckmann apparatus is shown containing pure liquid cyclohexane, an organic solvent with a freezing point of about 6.5°C. The diagram does not show how the cyclohexane could be frozen. [Figure 1.1: Diagram with Beckmann thermometer, stirring wire, stopper, boiling tube, pure liquid cyclohexane] The method for determining the lowering of freezing point is as follows. step 1 Add 20.00 g of pure liquid cyclohexane to a clean dry boiling tube. step 2 Place the stopper containing the Beckmann thermometer and stirring wire into the boiling tube. step 3 Cool the pure cyclohexane. When it starts to freeze, set the Beckmann thermometer to 0.00 to calibrate it. step 4 Allow the pure cyclohexane to melt. Remove the stopper from the boiling tube. Add 0.250g of an organic solid X to the pure cyclohexane and replace the stopper. Stir the solution to dissolve X and refreeze the solution. Record the new freezing point. step 5 Allow the solution to melt. Remove the stopper from the boiling tube. Add a further known mass of X to the solution and replace the stopper. Stir the solution to dissolve X and refreeze the solution. Record the new freezing point. step 6 Repeat step 5 until sufficient readings are obtained.