To find out if tap water and sea water contain dissolved solids Class practical and Demonstration Tap water and sea water are evaporated . They are also boiled to release their dissolved gases . Lesson organisation This is a class practical and teacher demonstration. If there is sufficient apparatus, students could do the three evaporations in parallel. Alternatively, the three types of water could be distributed round the class and the results compared at the end. It takes quite a long time for the water in a beaker to boil, so this should be built into the planning. The teacher demonstration could be set up while the students are waiting for their water to evaporate. If several of the shortcuts suggested above are used, these experiments could be done in 45 minutes. Health & Safety and Technical notes 1 If the real thing is not available, 'sea water' can be made up by dissolving about 35 g of sodium chloride in 1000 cm 3 of tap water. This will provide enough for both parts of the experiment. (Note: sea water contains a complex mixture of salts, but this gives a suitable solution for this experiment, resembling sea water in having 3.5% salinity). Procedure Students' experiment a Set up a Bunsen burner on a heat resistant mat. Over it, place a tripod and gauze. b Half fill a beaker with water and place it on the gauze. c Take a watch-glass and place enough tap water on it to cover half