e three rather rare elements belonging in the same family
with chromium, and form many compounds which are similar in
formulas to the corresponding compounds of chromium. They can
play the part of metals and also form acids resembling chromic
acid in formula. Thus we have molybdic acid (H_{2}MoO_{4}), the
ammonium salt of which is (NH_{4})_{2}MoO_{4}. This salt has
the property of combining with phosphoric acid to form a very
complex substance which is insoluble in nitric acid. On this
account molybdic acid is often used in the estimation of the
phosphoric acid present in a substance. Like chromium, the
metals are difficult to prepare in pure condition. Alloys with
iron can be prepared by reducing the mixed oxides with carbon
in an electric furnace; these alloys are used to some extent in
preparing special kinds of steel.

EXERCISES

1. How does pyrolusite effect the decolorizing of glass containing iron?

2. Write the equations for the preparation of manganous chloride,
carbonate, and hydroxide.

3. Write the equations representing the reactions which take place when
ferrous sulphate is oxidized to ferric sulphate by potassium
permanganate in the presence of sulphuric acid.

4. In the presence of sulphuric acid, oxalic acid is oxidized by
potassium permanganate according to the equation

C_{2}H_{2}O_{4} + O = 2CO_{2} + H_{2}O.

Write the complete equation.

5. 10 g. of iron were dissolved in sulphuric acid and oxidized to ferric
sulphate by potassium permanganate. What weight of the permanganate was
required?

6. What weight of ferrochromium containing 40% chromium must be added to
a ton of steel to produce an alloy containing 1% of chromium?

7. Write the equation representing the action of ammonium sulphide upon
chromium sulphate.

8. Potassium chromate oxidizes hydrochloric acid, forming chlorine.
Write the complete equation.

9. Give the action of sulphuric acid on potassium dichromate (a) in
the presence of a large amount of water; (b) in the presence of a
small amount of water.

CHAPTER XXXI

GOLD AND THE PLATINUM FAMILY

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| | ATOMIC | | HIGHEST | HIGHEST | MELTING
| SYMBOL | WEIGHT | DENSITY | OXIDE | CHLORIDE | POINT
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