After addition, some of the solid molecules will be replaced by the non volatile cellulose, and so less will evaporate, and therefore the vapor pressure will be less. Now, adding volatile cells or molecules that do evaporate increases vapor pressure according to a modified version of Rolls Law. And that's simply because now we have the solid molecules evaporating and the volatile solid molecules evaporating. So the final pressure is the sum of the two pressures. The second collage of property is called the boiling point. The boiling point is the temperature at which the liquid molecules have enough kinetic energy to escape into the gas state.