Simplify the following text for a Grade 7 native English-speaking person.
Original: Chromium alum is used in the tanning of leather as chromium ( III ) stabilizes the leather by cross linking the collagen fibers within the leather . However , this application is obsolete because the simpler chromium ( III ) sulfate is preferred .
Simplified: It was used in making leather ; now chromium ( III ) sulfate is used instead .