=Tests for Acid, Alkaline, and Neutral Substances.=--For _acid tests_, use sour buttermilk (which contains _lactic acid_), or _hydrochloric acid_ diluted in ten parts water, or _strong vinegar_ (which contains _acetic acid_). Has the acid a characteristic (“sour”) _odor_ and _taste_ (test it only when very dilute)? Rub dilute acid between the fingers; how does it feel? Is there any effect on the fingers? Obtain litmus paper at a druggist’s. Dip a strip of red litmus and of blue litmus paper into the acid. What result? For _alkaline tests_, dissolve in a glass of water a spoonful of baking soda or some laundry soap; or dissolve an inch stick of caustic soda in a glass of water. Test odor and “feel” of last solution as with the acid; likewise test effect of alkaline solution on red and blue litmus paper. Record results. Alkalies are strong examples of a more general class of substances called _bases_, which have the opposite effect from acids. Test pure water. Has it odor? A taste? Test it with red and blue litmus paper. Water is a _neutral_ substance: that is, it is neither an acid nor an alkali (or base). After making appropriate tests, write _ac_, _al_, or _neu_ after each name in the following list (or write in three columns): vinegar, soda, saliva, sugar, juice of apple, lemon, and other fruits, milk, baking powder, buttermilk, ammonia, salt water. Pour some of the alkaline solution into a dish, gradually add dilute acid (or sour buttermilk), stirring with glass rod and testing with litmus until the mixture does not turn red litmus blue nor blue litmus red. The acid and alkali are then said to have _neutralized_ each other, and the resulting substance is called a _salt_. The salt may be obtained by evaporating the water of the solution. Most common minerals are salts. If the last experiment is tried with soda and sour buttermilk, the demonstration will show some of the facts involved in bread making with the use of these substances. =Test for Starch.=--Starch turns blue with iodine. The color may be driven away by heat, but will return again as the temperature lowers. Procure a few cents’ worth of tincture of iodine and dilute it. Get a half dozen pieces of paper and cardboard, all different, and test each for starch by placing it over mouth of bottle and tipping the bottle up. If much starch is present the spot will be blue-black or dark blue; if little starch, pale blue; if no starch, brown or yellowish. Make pastes with wheat flour, potato starch, and corn starch. Treat a little of each with a solution of rather dilute tincture of iodine. Try grains from crushed rice with the same solution. Are they the same color? Cut a thin section from a potato, treat with iodine and examine under the microscope.