In chemistry, the CPK coloring is a popular color convention for distinguishing atoms of different chemical elements in molecular models.
A plastic ball-and-stick model of proline. These models usually comply with CPK coloring.
Hofmann's methane model
A box of ball-and-stick model pieces colored to represent several of the common elements.
August Wilhelm von Hofmann
August Wilhelm von Hofmann was a German chemist who made considerable contributions to organic chemistry. His research on aniline helped lay the basis of the aniline-dye industry, and his research on coal tar laid the groundwork for his student Charles Mansfield's practical methods for extracting benzene and toluene and converting them into nitro compounds and amines. Hofmann's discoveries include formaldehyde, hydrazobenzene, the isonitriles, and allyl alcohol. He prepared three ethylamines and tetraethylammonium compounds and established their structural relationship to ammonia.
August Wilhelm von Hofmann
Hofmann, 1846
Hofmann's methane model
Monument to Hofmann at Berlin, destroyed in 1944 by British air raid