In order to use a thermometer, we need to have marks along the narrow tube for reading the level of the liquid. But how can we decide where to put the marks and how to number them? In order to mark or calibrate a thermometer, it is helpful to be able to produce and recognize some standard temperatures. Investigation 2 For this experiment, you will need about 75 mL of water. Place the water in a beaker and record the temperature. Heat the beaker over a burner or hot plate and record the temperature of the water every 30 seconds. Do not let the thermometer rest on the bottom of the beaker; instead place the thermometer about halfway into the water and stir gently. Do not let the thermometer touch the sides of the beaker. Record the time when the water starts to boil vigorously. (Note: small bubbles of air come out of solution when water is heated. Do not mistake this for boiling, which involves larger bubbles.) Stop the experiment after the water has been boiling for at least three minutes. Make a graph of the temperature versus time from your data. Indicate on the graph the time when the water began to boil