In studying the properties of carbon dioxide, Joseph Black found that a candle would not burn in it. A candle burning in a closed container of ordinary air would go out eventually, and the air that was left would then no longer support a flame. This behavior certainly seemed reasonable, since the burning candle had formed carbon dioxide. But when the carbon dioxide in the trapped air was absorbed by chemicals, some air remained unabsorbed. This air that was left and that was not carbon dioxide would still not support a flame.

Black turned this problem over to one of his students, the Scottish chemist Daniel Rutherford (1749-1819). Rutherford kept a mouse in a confined quantity of air till it died. He then burned a candle in what was left until the candle went out. He then burned phosphorus in what was left after that, until the phosphorus would no longer burn. Next, the air was passed through a solution that had the ability to absorb carbon dioxide. The air remaining now would not support combustion; a mouse would not live in it and a candle would not burn.

Rutherford reported this experiment in 1772. Since Rutherford and Black were both convinced of the validity of the phlogiston theory, they tried to explain their results in terms of this theory. As mice breathed and as candles and phosphorus burned, phlogiston was given off and entered the air, along with the carbon dioxide that was formed. When the carbon dioxide was later absorbed, the air left behind still contained much phlogiston. In fact, it contained so much phlogiston as to be saturated with it; it would accept no more. That was why objects no longer burned in it.

On this reasoning Rutherford called the gas he had isolated "phlogisticated air". Nowadays, we call it nitrogen, and give Rutherford the credit for its discovery.