CHAPTER I.. Section I.

SECTION I.

How many elementary substances are known?

In what combinations is oxygen found? What proportion of the earth's crust consists of it?

In what combinations does hydrogen occur? Nitrogen? Carbon? Sulphur? Chlorine? Fluorine? Iron? Manganese?

How does silicium occur? Aluminium? Potassium? Sodium? Calcium? Magnesium?

How are these elementary substances classified? (Silicium, or silicon, has but a doubtful claim to be regarded as metallic.)