mount of heat be generated by the combustion of
1 g. of each of the allotropic modifications of sulphur? (b) Would the
same amount of sulphur dioxide be formed in each case?

2. Is the equation for the preparation of hydrosulphuric acid a
reversible one? As ordinarily carried out, does the reaction complete
itself?

3. Suppose that hydrosulphuric acid were a liquid, would it be necessary
to modify the method of preparation?

4. Can sulphuric acid be used to dry hydrosulphuric acid? Give reason
for answer.

5. Does dry hydrosulphuric acid react with litmus paper? State reason
for answer.

6. How many grams of iron sulphide are necessary to prepare 100 l. of
hydrosulphuric acid when the laboratory conditions are 17 deg. and 740 mm.
pressure?

7. Suppose that the hydrogen in 1 l. of hydrosulphuric acid were
liberated; what volume would it occupy, the gases being measured under
the same conditions?

8. Write the equations representing the reaction between hydrosulphuric
acid and sodium hydroxide and ammonium hydroxide respectively.

9. Show that the preparation of sulphur dioxide from a sulphite is
similar in principle to the preparation of hydrogen sulphide.

10. (a) Does dry sulphur dioxide react with litmus paper? (b) How
can it be shown that a solution of sulphur dioxide in water acts like an
acid?

11. (a) Calculate the percentage composition of sulphurous anhydride
and sulphuric anhydride. (b) Show how these two substances are in
harmony with the law of multiple proportion.

12. How many pounds of sulphur would be necessary in the preparation of
100 lb. of 98% sulphuric acid?

13. What weight of sulphur dioxide is necessary in the preparation of 1
kg. of sodium sulphite?

14. What weight of copper sulphate crystals can be obtained by
dissolving 1 kg. of copper in sulphuric acid and crystallizing the
product from water?

15. Write the names and formulas of the oxides and oxygen acids of
selenium and tellurium.

16. In the commercial preparation of carbon disulphide, what is the
function of the electric current?

17. If the Gay-Lussac tower were omitted from the sulphuric acid
factory, what effect would this have on the cost of production of
sulphuric acid?

CHAPTER XV

PERIODIC LAW

A number of the elements have now been studied somewhat closely. The
first three of these, oxygen, hydrogen, and nitrogen, while having some
physical properties in common with each other, have almost no p