Boyle's law of the gas, and "k" is a constant. The equation states that the product of pressure and volume is a constant for a given mass of confined gas and this holds as long as the temperature is constant. For comparing the same substance under two different sets of conditions, the law can be usefully expressed as The equation shows that, as volume increases, the pressure of the gas decreases in proportion. Similarly, as volume decreases, the pressure of the gas increases. The law was named after chemist and physicist Robert Boyle, who published the original law in 1662. This relationship
Lifting gas of the lifting capability of hydrogen to that of helium will remain the same. This calculation does not include the mass of the envelope need to hold the lifting gas. At higher altitudes, the air pressure is lower and therefore the pressure inside the balloon is also lower. This means that while the mass of lifting gas and mass of displaced air for a given lift are the same as at lower altitude, the volume of the balloon is much greater at higher altitudes. A balloon that is designed to lift to extreme heights (stratosphere), must be able to expand