Joseph Black discovered carbon dioxide, which he called fixed air
or just air.
He wrote, “It is therefore probable, that, had we also a method
of separating the fixed alkali from an acid, without, at the same time,
saturating it with air, we should then obtain it in a caustic form;
but I am not acquainted with an instance of this separation in chemistry.”
It took another 53 years and the invention of the electric battery
for Davy to use electrolysis to separate the metal from magnesium oxide.
The invention of magnesium flash powder in 1887 let Jacob Riis
photograph the dark side of New York City.
See also in The book of science:
Readings on wikipedia: