a little water, boil the water, and conduct the steam into B until 5 or 10 cc. of liquid has been collected. Pour this into a beaker and save it for further experiments. Complete the following equations:

b. Add 3 drops of sulfuric acid to 5 cc. of water in a test tube. To this add a few drops of a solution of barium chloride. Note that

a precipitate forms (R). Now add 3 or 4 drops of hydrochloric acid. Does the precipitate dissolve? The formation with barium chloride of a precipitate which is insoluble in hydrochloric acid consti

A

B

tutes a good test

for sulfuric acid.

FIG. 37

Now apply this test to the liquid taken from the bottle B (Fig. 37). Note the results.

c. Recall the action of dilute sulfuric acid on zinc (R). Try the action of the concentrated acid on zinc, applying a gentle heat, if necessary, to start the reaction. What gas is now evolved? Explain. Write in steps the equations for the reactions which take place when copper is acted on by nitric acid and hot concentrated sulfuric acid respectively, pointing out the similarity in the action of the two acids. Gently heat a small bit of charcoal with 2 or 3 cc. of concentrated sulfuric acid. What gas is evolved (R)?

d. Put a drop of concentrated sulfuric acid on a splint and gently warm it above a flame. Pour a few drops on 0.5 g. of sugar in a test tube. Examine after a few minutes. Account for the results.

e. Why is sulfuric acid used in the preparation of other acids?

92. Salts of sulfuric acid: sulfates. a. Obtain a crystal of each of five or six different sulfates, dissolve them in water, and test each solution with litmus paper. Why do some of the sulfates have an acid reaction? Try to dissolve a crystal of sulfate of antimony, of bismuth, or of mercury in pure water. What do you observe? Explain.

b. Dissolve in a little water a crystal of each of the following sulfates: sodium sulfate, magnesium sulfate, copper sulfate. Apply to each the barium chloride test for sulfuric acid (R). Can sulfates be detected by this method? Dissolve a crystal of sodium sulfite in water and apply the same test. How can you distinguish between sulfates and sulfites? (Sulfites very often contain more or less of the corresponding sulfates, owing to the absorption of oxygen from the atmosphere.)

c. Is sulfuric acid monobasic or dibasic? Explain these terms. With due care pour about 10 cc. of concentrated sulfuric acid into 100 cc. of water, and divide the solution into two equal parts. Carefully neutralize the one part with sodium hydroxide and evaporate the solution to about 25 cc. Set aside for a day to obtain crystals. What are they? Divide the second part into two equal portions. Neutralize the one part as before; then add the second portion. What should be in solution? Evaporate as in the other case and set aside to crystallize. Compare the two kinds of crystals in appearance. Heat a few of each kind in a dry test tube. What difference do you note?

CHAPTER XII

THE CHLORINE FAMILY

93. Hydrogen fluoride; hydrofluoric acid. (The gas is very corrosive and must not be inhaled; its solution must not be brought in contact with the skin.) Warm gently over a small, luminous flame a glass plate on which some pieces of paraffin have been placed. When the paraffin is melted, tilt the plate about so as to cover it with a uniform layer of the wax. When the plate becomes cold, scratch your name through the wax with a pin or other sharp point. Place in a lead dish 3 g. of powdered fluorite and add sufficient sulfuric acid to make a paste of it. Cover the dish tightly with the waxed side of the glass plate and set it in the hood for an hour; then remove the paraffin and examine the glass. Write the equations for all the reactions involved. In what kind of bottles is hydrofluoric acid stored?

94. Preparation of chlorine. (All of the following experiments must be performed in the hood, and great care taken not to inhale the gas.) a. Place about 1 g. of manganese dioxide in a test tube, add 2 or 3 cc. of hydrochloric acid, and heat gently (R).

b. In a similar way test the action of hydrochloric acid upon lead peroxide, potassium permanganate, and potassium dichromate. Will all compounds containing oxygen oxidize hydrochloric acid? Try lead oxide (litharge) and sodium sulfate.

c. Repeat experiment a, replacing the hydrochloric acid with small amounts of common salt and sulfuric acid. The manganese dioxide and salt should first be mixed together and the sulfuric acid added to the mixture. Compare the reactions in a and c (R). Which of the two methods is the cheaper for preparing chlorine? Give reason for your answer.