b. Give the formula and properties of the acid of which the carbonates are salts. Try the action of hydrochloric acid on a small amount (about 1 g.) of each of the following carbonates: sodium carbonate, potassium carbonate, magnesium carbonate (R). How can you detect the presence of carbonates? Is limestone a carbonate? Is the action of sulfuric and nitric acids on carbonates similar to that of hydrochloric acid (R)? Why is carbonic acid so readily liberated from carbonates ?

c. Pass a current of carbon dioxide through 10 cc. of the laboratory solution of sodium hydroxide (1 part of sodium hydroxide to 10 parts of water). Does the solution remain clear? When no more of the gas is absorbed, evaporate the solution to dryness and test the residue for carbonates. What is the residue (R)?

d. In what respects does carbon dioxide resemble sulfur dioxide ?

e. Half fill a small beaker with limewater and pass carbon dioxide through the liquid (R). Continue until the precipitate which at first forms is dissolved (R), and then divide the solution into two parts. To the one add a little clear limewater (R); to the other apply heat until it boils rapidly (R). Account for the fact that carbon dioxide will cause a precipitate in a solution of calcium hydroxide but not in a solution of sodium hydroxide.

112. Oxidation of urea. Prepare about 100 cc. of a solution of sodium hypochlorite by passing chlorine into a cold solution of sodium hydroxide (§ 107) until the chlorine is no longer readily absorbed, thus leaving some sodium hydroxide present in solution with the sodium hypochlorite (R). Fill a test tube with the solution and invert it in a small evaporating dish partially filled with the same solution. Now, by means of a medicine dropper, the small end of which is curved slightly, introduce into the solution in the test tube a few drops of a solution of urea (R).

CHAPTER XIX

THE LAW OF GAY-LUSSAC

NOTE. Before performing the experiment, read the directions carefully and report to the instructor for quiz on the methods.

113. Determination of the volume of hydrogen obtained from a known volume of hydrogen chloride. Prepare some sodium amalgam as follows: Pour about 10 cc. of mercury into an evaporating-dish and heat slightly (hood). Add, one at a time, five pieces of sodium, each

as large as a pea. If each bit of the
sodium does not combine with the
mercury on coming in contact with it,
start the combination by pushing the
sodium under the surface of the mer-
cury by means of a long glass rod.
After the sodium has all been added,
the resulting amalgam into a small

pour
bottle and stopper it.

Obtain from the storeroom a tube about 50 cm. in length and 15 mm. in

A

B

C

FIG. 48

diameter (Fig. 48, C), and fill it with dry hydrogen chloride. To do this, arrange an apparatus according to Fig. 48. Generate hydrogen chloride in A, dry it by passing it through the concentrated sulfuric acid in B, and conduct it into C by means of a long delivery tube. When the tube C is completely filled with the gas, slowly withdraw it from the delivery tube, pour in the sodium amalgam prepared above, and at once close the mouth of the tube firmly with the thumb, slightly moistened. Now shake the tube so as to bring the gas into contact with