compounds.

3. In the preparation of phosphine, why is coal gas passed into the
flask? What other gases would serve the same purpose?

4. Give the formula for the salt which phosphine forms with hydriodic
acid. Give the name of the compound.

5. Could phosphoric acid be substituted for sulphuric acid in the
preparation of the common acids?

6. Write the equations for the preparation of the three sodium salts of
orthophosphoric acid.

7. Why does a solution of disodium hydrogen phosphate react alkaline?

8. On the supposition that bone ash is pure calcium phosphate, what
weight of it would be required in the preparation of 1 kg. of
phosphorus?

9. If arsenopyrite is heated in a current of air, what products are
formed?

10. (a) Write equations for the complete combustion of hydrosulphuric
acid, methane, and arsine. (b) In what respects are the reactions
similar?

11. Write the equations for all the reactions involved in Marsh's test
for arsenic.

12. Write the names and formulas for the acids of antimony.

13. Write the equations showing the hydrolysis of antimony trichloride;
of bismuth nitrate.

14. In what respects does nitrogen resemble the members of the
phosphorus family?

CHAPTER XXI

SILICON, TITANIUM, BORON

=================================================================
| | | | |
| SYMBOL | ATOMIC | DENSITY | CHLORIDES | OXIDES
| | WEIGHT | | |
____________|________|________|_________|___________|____________
| | | | |
Silicon | Si | 28.4 | 2.35 | SiCl_{4} | SiO_{2}
Titanium | Ti | 48.1 | 3.5 | TiCl_{4} | TiO_{2}
Boron | B | 11.0 | 2.45 | BCl_{3} | B_{2}O_{3}
=================================================================

~General.~ Each of the three elements, silicon, titanium, and boron,
belongs to a separate periodic family, but they occur near together in
the periodic grouping and are very similar in both physical and chemical
properties. Since the other elements in their families are either so
rare that they cannot be studied in detail, or are best understood in
connection with other elements, it is convenient to consider these three
together at this point.

The three elements are very difficult to obtain in the free state, owing
to their strong attraction for other elements. They can be