in the ratio of about 1% of the former to 99% of the latter.
Compounds of thorium, like those of radium, are found to
possess radio-activity, but in a less degree.

EXERCISES

1. How could you detect lead if present in tin foil?

2. Stannous chloride reduces gold chloride (AuCl_{3}) to gold. Give
equation.

3. What are the products of hydrolysis when stannic chloride is used as
a mordant?

4. How could you detect arsenic, antimony, or copper in lead?

5. Why is lead so extensively used for making water pipes?

6. What sulphates other than lead are insoluble?

7. Could lead nitrate be used in place of barium chloride in testing for
sulphates?

8. How much lead peroxide could be obtained from 1 kg. of minium?

9. The purity of white lead is usually determined by observing the
volume of carbon dioxide given off when it is treated with an acid. What
acid should be used? On the supposition that it has the formula
2PbCO_{3}.Pb(OH)_{2}, how nearly pure was a sample if 1 g. gave 30 cc.
of carbon dioxide at 20 deg. and 750 mm.?

10. Silicon belongs in the same family with tin and lead. In what
respects are these elements similar?

11. What weight of tin could be obtained by the reduction of 1 ton of
cassiterite?

12. What reaction would you expect to take place when lead peroxide is
treated with hydrochloric acid?

13. White lead is often adulterated with barytes. Suggest a method for
detecting it, if present, in a given example of white lead.

CHAPTER XXX

MANGANESE AND CHROMIUM

====================================================================
| | | | |
| SYMBOL | ATOMIC | DENSITY | MELTING | FORMULAS OF ACIDS
| | WEIGHT | | POINT |
__________|________|________|_________|_________|___________________
| | | | |
Manganese | Mn | 55.0 | 8.01 | 1900 deg. | H_{2}MnO_{4} and
| | | | | HMnO_{4}
Chromium | Cr | 52.1 | 7.3 | 3000 deg. | H_{2}CrO_{4} and
| | | | | H_{2}Cr_{2}O_{7}
====================================================================

~General.~ Manganese and chromium, while belonging to different families,
have so many features in common in their chemical conduct that they may
be studied together with advantage. They differ from most of the
elements so