CHAPTER XV

ALKALIES

CONTRASTED with acids in their effects upon litmus are the

Taste each of the above-named materials and note which of

them are sour. Dissolve the solids in water. Squeeze out the juice of the lemon and apple. Test all the liquids thus obtained with red and with blue litmus paper. Record results in tabular form as follows:

Some salts affect litmus in the same way as acids - turning blue to red. These are said to have an acid reaction. Examples are alum, zinc sulphate, and cream of tartar. A considerable number have no action on either red or blue litmus. These are said to have a neutral reaction. Salt, saltpeter, and Epsom salt are neutral. Still others have an effect directly the opposite of that of the acids; that is, they turn red litmus blue. Such are said to have an alkaline re

action. Examples are baking soda (sodium bicarbonate), washing soda (sodium carbonate), and borax (sodium borate).

Experiment 44.

Materials:

Sodium under oil, cut in pieces large enough to yield a test
tube of gas in the experiment. (Cubes of 3 mm. or inch
are suitable for a 30 cc. test tube.)

Lead foil (tea lead) or oiled paper in pieces inch square.
Caustic soda sticks inch long.

Red litmus paper.

Apparatus:
Forceps.
Dish.

Handle the sodium with forceps, being careful not to allow it to touch the hands or clothing. Examine a freshly cut surface of sodium and compare it with the lead and aluminium. To what class do all three of these substances belong? Lay the sodium on filter paper for a few seconds to free it from oil, then wrap it in the lead foil (or oiled paper) leaving a small opening at one end. Fill a test tube with water, cover it with the thumb, and invert it in a dish of water. Seizing the wrapped piece of sodium, open end up, with the forceps, bring it quickly underneath the mouth of the inverted test tube. As the water enters the wrapping and comes in contact with the sodium, gas is evolved and collects in the test tube, displacing the water. When the action ceases, again cover the mouth of the test tube and invert the tube. Remove the thumb and immediately apply a lighted match or splint to the mouth of the test tube. What gas do you infer to have been formed by the reaction of the sodium and water?

Examine the liquid left in the dish, comparing it with the water originally used. Note its feel and its effect on red litmus paper. Dissolve the piece of caustic soda in half a test tube of water. Compare this solution with the liquid in the dish.

To determine what elements caustic soda contains, answer the following questions and make Experiment 45.

Can the gas collected in the present experiment have been produced by decomposition of the sodium? Why? Where must the sodium be at the end of the experiment? What are the elements of water? Which of these two elements must be a constituent of the caustic soda? What two elements does caustic

A Scottish chemist and physicist, noted for his researches upon heat and for his discovery of carbon dioxide, which he called "fixed air." Black explained the difference between the mild and the caustic alkalies, the relation of lime to limestone, and the distinction between lime and magnesia.