First she placed two thermometers in each cylinder, then by using the air pump, she evacuated the air from one cylinder and compressed it in the other. Allowing both cylinders to reach the same temperature, she placed the cylinders in the sunlight to measure temperature variance once heated and under different moisture conditions. She performed this experiment on CO 2, common air, and hydrogen.[10] Of the gases she tested, Foote concluded that carbonic acid (CO 2) trapped the most heat, reaching a temperature of 125 °F (52 °C).[11] From this experiment, she stated "“The receiver containing this gas became itself much heated—very sensibly more so than the other—and on being removed [from the Sun], it was many times as long in cooling.”[12] Looking to the history of the Earth, Foote theorized that "An atmosphere of that gas would give to our earth a high temperature; and if, as some suppose, at one period of its history, the air had mixed with it a larger proportion than at present, an increased temperature from its own action, as well as from increased weight, must have necessarily resulted."[4][14]