Experiments carried out by french chemists jacques alexandre césar charles and joseph-louis gay-lussac and british physicist lord kelvin determined a quantitative relationship between the volume and temperature of a gas. their data showed that for a container of gas held at constant pressure, the volume and temperature are directly proportional. for example, if you inflate a balloon outdoors with cold air on a cold day and then take it inside, it will expand, and it might even burst. this happens because as the temperature of the air inside the balloon increases, the volume of the balloon increases as well. what is less obvious is the quantitative relation: if the pressure is held constant, then when the temperature is doubled, the volume is doubled as well.