In modern Chinese, this radical is used to form characters representing gaseous chemical elements and compounds.
Literature
Fazzioli, Edoardo (1987). Chinese calligraphy : from pictograph to ideogram : the history of 214 essential Chinese/Japanese characters. calligraphy by Rebecca Hon Ko. New York: Abbeville Press. ISBN0-89659-774-1.
GF 0011-2009 Table of Indexing Chinese Character Components prescribes 201 principle indexing components and 100 associated indexing components (in brackets) used in Simplified Chinese. Not all associated indexing components are listed above.