Absorption is the process by which things are absorbed.
Adsorption, on the other hand, describes the act of gas or liquid molecules adhering to a surface.
Both words are commonly misspelled as absorbtion and adsorbtion. This spelling error is usually corrected automatically by a computer’s spell check.
The spelling change comes from pronunciation over time. The voiced consonant of /b/ is grouped with the voiceless /tion/. Another example are the words describe and description.
Examples
A new Cushman & Wakefield office market report released on Thursday estimates that total net office space absorption recorded a 16% increase across the top eight cities between January and June, 2014 compared to the same period last year. [Times of India]
The absorption is ultraweak, and the photo-induced effect in the focusing region is therefore comparable to that obtained by a nonfocused laser beam with a high absorption effect. [SPIE]
CytoSorbents’ purification technologies are based on biocompatible, highly porous polymer beads that can actively remove toxic substances from blood and other bodily fluids by pore capture and surface adsorption. [Wall Street Journal]
AdvantaPure said its TPE material, AdvantaFlex, provides an alternative to silicone because it offers lower absorption and adsorption characteristics than silicone and does not contain silicone oils, substances that are undesirable in some biological processes. [Rubber News]