base (ammonia) replaces a weaker one (water) The Lewis and Brønsted–Lowry definitions are consistent with each other since the reaction H+ + OH− H2O is an acid–base reaction in both theories. Solvent system definition One of the limitations of the Arrhenius definition is its reliance on water solutions. Edward Curtis Franklin studied the acid–base reactions in liquid ammonia in 1905 and pointed out the similarities to the water-based Arrhenius theory. Albert F.O. Germann, working with liquid phosgene, , formulated the solvent-based theory in 1925, thereby generalizing the Arrhenius definition to cover aprotic solvents. Germann pointed out that in many solutions, there are ions in equilibrium with the neutral solvent molecules: solvonium ions: a generic name for positive ions. (The term solvonium has replaced the older term lyonium ions: positive ions formed by protonation of solvent molecules.) solvate ions: a generic name for negative ions. (The term solvate has replaced the older term lyate ions: negative ions formed by deprotonation of solvent molecules.) For example, water and ammonia undergo such dissociation into hydronium and hydroxide, and ammonium and amide, respectively: 2 + 2 + Some aprotic systems also undergo such dissociation, such as dinitrogen tetroxide into nitrosonium and nitrate, antimony trichloride into dichloroantimonium and tetrachloroantimonate, and phosgene into chlorocarboxonium and chloride: + 2 + + A solute that causes an increase in the concentration of the solvonium ions and a decrease in the concentration of solvate ions is defined as an acid. A solute that causes an increase in the concentration of the solvate ions and a decrease in the concentration of the solvonium ions is defined as a base. Thus, in liquid ammonia, (supplying ) is a strong base, and (supplying ) is a strong acid. In liquid sulfur dioxide (), thionyl compounds (supplying ) behave as acids, and sulfites (supplying ) behave as bases. The non-aqueous acid–base reactions in liquid ammonia are similar to the reactions in water: + → + → Nitric acid can be a base in liquid sulfuric acid: + 2 → + + 2 The unique strength of this definition shows in describing the reactions in aprotic solvents; for example, in liquid : + → + Because the solvent system definition depends on the solute as well as on the solvent itself, a particular solute can be either an acid or a base depending on the choice of the solvent: is a strong acid in