stoichiometry (n.)
"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. Related: Stoichiometric.