Binary Theory

Binary Theory, in Chemistry, takes cognisance of the mode of construction of salts. It assumes that all salts contain merely two substances, which either are both simple, or of which one is simple and the other a compound playing the part of a simple body. The best and most familiar illustration of the binary theory is common salt or chloride of sodium, NaCl, which is constructed of the metal sodium, Na, and the non-metal chlorine, Cl, and is at a glance seen to be a binary compound (a compound of two). In like manner, fluor-spar, or the fluoride of calcium, CaF₂, consists of the metal calcium, Ca, and the non-metal fluorine, F; and iodide of potassium, KI, largely employed in photography, of potassium, K, and iodine, I. Although this theory attracted much attention from 1837 to 1855, and was adopted by Liebig and other chemists, it never met with general acceptance, and has now been quite superseded. See ACIDS and SALTS.