LEARNING THE MANIPULATION OF TESTS.
Practice in making superficial qualitative tests of water, produces skill in reading the meaning of the various chemical re-actions. This skill can be rapidly developed by practice on prepared specimens. Water for experiments on carbonate of lime can be prepared by dissolving calcite crystals or marble dust in hydrochloric acid, or by mixing chalk with clean rain-water, and filtering it till free from turbidity. While the chalk is mixed with the water, and unfiltered, the specimen will be made stronger by blowing air from the lungs through a glass tube into the water. A preparation for testing sulphate of lime may be made by dissolving some gypsum in distilled water. Fluid magnesia, dropped into pure water, will provide carbonate of magnesia specimens; and Epsom salts will give the magnesia re-action, with the addition that it will indicate sulphuric acid under the chloride of barium test. A grain of salt no larger than a pin-head dropped into a pint of distilled water, will give a distinct chlorine test when nitrate of silver solution is added. Stronger, or even weaker, salt solution can be used by the experimenter while he is working into practice. A small piece of sulphate of iron, dissolved in water, will provide a test for iron.