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When Joseph Black was studying the properties of carbon dioxide, he found that a candle would not burn in it. When a candle was burned in a closed container of air, the candle would go out eventually, and the remaining air would not support a flame. This was normal, but when the carbon dioxide (caused by the candle) was absorbed by chemicals, some air was not absorbed. The air that remained did not support a flame.
He turned this problem over to his student at the time, Daniel Rutherford. Rutherford kept a mouse in a space with a confined quality of air until it died. Then, he burned a candle in the remaining air until it went out. Afterwards, he burned phosphorus in that, until it would not burn. Then the air was passed through a carbon dioxide absorbing solution. The remaining air did not support combustion, and a mouse could not live in it.
Rutherford called the gas (which we now know would have consisted primarily of nitrogen