A law stating that if the mass and pressure of a gas are held constant, then gas volume increases linearly as the temperature rises. When gases react, they do so in volumes that bear a simple ratio to one another and to the volume of the product, if it is a gas, temperature and pressure remaining constant. This is sometimes written as where k is a constant dependent on the type, mass, and pressure of the gas, and T is the absolute temperature. For an ideal gas . It is named after Gay-Lussac (1778–1850) who proposed the law in 1808, which led to Avogadro’s law.