suspected the existence of the numerous totally distinct gaseous
elements which are now known, or dreamed that the air we breathe and
the water we drink are compounds of gaseous elements.

But, in 1754, a young Scotch physician, Dr. Black, made the first
clearing in this tangled backwood of knowledge. And it gives one a
wonderful impression of the juvenility of scientific chemistry to think
that Lord Brougham, whom so many of us recollect, attended Black's
lectures when he was a student in Edinburgh. Black's researches gave
the world the novel and startling conception of a gas that was a
permanently elastic fluid like air, but that differed from common air
in being much heavier, very poisonous, and in having the properties of
an acid, capable of neutralising the strongest alkalies; and it took
the world some time to become accustomed to the notion.

A dozen years later, one of the most sagacious and accurate
investigators who has adorned this, or any other, country, Henry
Cavendish, published a memoir in the "Philosophical Transactions," in
which he deals not only with the "fixed air" (now called carbonic acid
or carbonic anhydride) of Black, but with "inflammable air," or what we
now term hydrogen.

By the rigorous application of weight and measure to all his processes,
Cavendish implied the belief subsequently formulated by Lavoisier,
that, in chemical processes, matter is neither created nor destroyed,
and indicated the path along which all future explorers must travel.
Nor did he himself halt until this path led him, in 1784, to the
brilliant and fundamental discovery that water is composed of two gases
united in fixed and constant proportions.