stoichiometry (n.) Look up stoichiometry at Dictionary.com
"science of calculating the quantities of chemical elements involved in chemical reactions," 1807, from German Stöchiometrie (1792), coined by German chemist Jeremias Benjamin Richter (1762-1807) from Greek stoikheion "one of a row; shadow-line of a sundial," in plural "the elements" (from PIE *steigh- "to stride, step, rise") + -metry "a measuring of." Related: Stoichiometric.