Page:First course in biology (IA firstcourseinbio00bailrich).pdf/19

 some hours, examine the saucers and bottles and compare and record the results. Explain. State three conditions that are favorable to evaporation. State three ways in which evaporation may be prevented or decreased.

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