根据理想气体状态方程，R= pVm/T，因此只需在压力较低时测定一组实际气体的p、Vm、T 值，就可以得到普适气体常数R了。

实际上没有一种气体完全符合理想气体状态方程，但在压力足够低，温度足够高，即密度足够小的情况下，例如在常温低压下，CH4分子本身体积小，分子间距大，分子间引力小，因而其pVT特性接近理想气体的规律。In fact, no gas completely conforms to the ideal gas state equation, but when the pressure is low enough, the temperature is high enough, that is, the density is low enough. For example, at room temperature and low pressure, CH4 molecule itself has small volume, large molecular spacing, and small gravitational attraction between molecules, so its pVT characteristics are close to the law of ideal gas.

气体的粘度随压力增高而增高。在低压时，气体粘度随温度升高而增加，随着压力的增加，温度升高对粘度增大的影响越来越小，当压力很高时（100×105Pa以上），气体粘度随温度升高而降低，明显表现出类似于液体的性质。Table 1-13 shows the dynamic viscosity of methane at different pressures and temperatures. It can be seen from the table that the viscosity of gas increases with the increase of pressure. At low pressure, the gas viscosity increases with the increase of temperature. With the increase of pressure, the influence of temperature increase on the increase of viscosity becomes smaller and smaller. When the pressure is very high (100×105Pa and above), the gas viscosity decreases with the increase of temperature, showing obvious properties similar to liquid.

A. 闸阀

B. 减压阀

C. 安全阀

D. 大小头

A. 气体平均分子量

B. 理想气体状态方程

C. 饱和蒸汽压

D. 气化潜热