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83 <br />• First, the container used for evaporation should have a <br />large surface area so that a thick cake of residue is not <br />formed. It appears that a thick cake retains moisture (13, <br />14). .Also, the weight of the evaporation container should <br />be light and made of inert material so that it can be heated <br />to 180°C (350°F). An aluminum pie plate should work nicely. <br />They come in a 5-inch size that weighs less than 5 g, and <br />this size easily fits on a triple beam balance, and maintains <br />a constant weight. <br />Supplies <br />1. Aluminum pie plate (5-inch size) <br />2. Triple beam balance <br />3. Heat source of less than 100°C (200°F) and then 180°C <br />• (350°F). A regular food oven will be sufficient. <br />4. A filtering setup which uses Whatman No. 50 filter <br />paper may be necessary if the water is turbid. <br />Procedure <br />Collect 1 liter of suspension free water or filter one <br />liter of water to eliminate suspended solids. The water <br />should be unacidified and analysis should be started within <br />24 hours. Evaporate the liter of water in 200 ml amounts <br />into an aluminum pie plate which has been preweighed to a <br />constant weight. Evaporation should take place in the low <br />temperature oven. Upon evaporation of the water, dry the <br />sample in the high temperature oven for 2 hours. Weigh the <br />plate :immediately upon cooling. The weight difference <br />