One hundred parts, by weight, of pure water are always formed by the union of 11.11 parts of hydrogen, and 88.89 parts of oxygen, and can be separated into these quantities of those substances.

When water is formed by the union of hydrogen and oxygen, in the ratio of 11.11 parts by weight of the former to 88.89 of the latter, the properties of the two substances which coalesce to form it disappear, except their masses.

It is customary to say that water _contains_ hydrogen and oxygen; but this expression is scarcely an accurate description of the facts.

What we call _substances_ are known to us only by their properties, that is, the ways wherein they act on our senses.

Hydrogen has certain definite properties, oxygen has other definite properties, and the properties of water are perfectly distinct from those of either of the substances which it is said to contain.