When two chemical substances come in contact with each other, through what is called a phase, they will interact with each other in that phase. They may also have an interface. If a substance accumulates within a phase this is called absorption, if the same process happens on the interface, it is called adsorption. In the year 1909, James William McBain introduced the word Sorption to describe such a process, in the case where it is not easy or meaningful to make a difference between absorption and adsorption.