Joseph Black describes his discovery of carbon dioxide ("fixed air") and magnesium in a paper to the Philosophical Society of Edinburgh in 1755.

The Scottish chemist has observed that magnesia, now known to be a compound of magnesium, gives rise to a soluble sulfate, whereas that derived from lime (which is now known to be calcium oxide) is known to be insoluble.

Magnesia is thus shown to be an alkaline earth different from lime.