"Law of corresponding states" says that

• , two different gases behave similarly, if their reduced properties (i.e. P, V and T) are same.
• the surface of separation (i. e. the meniscus) between liquid and vapour phase disappears at the critical temperature.
• no gas can be liquified above the critical temperature, howsoever high the pressure may be.
• the molar heat of energy of gas at constant volume should be nearly constant (about 3 calories).