The species responsible for silica dissolution is the hydroxide anion (OH–). The high pH conditions are said to be alkaline and one also speaks of the alkalinity of the basic solutions. For the sake of electroneutrality, (OH–) anions need to be accompanied by positively charged cations, Na+ or K+ in NaOH or KOH solutions respectively. Na and K both belong to the alkali metals column in the Mendeleev table. When speaking of alkali's, one systematically refers to NaOH and KOH basic hydroxides, or their corresponding oxides Na2O and K2O in cement. Therefore, it is the hydroxide, or the oxide, component of the salt which is the only relevant chemical species for silica dissolution, not the alkali metal in itself. However, to determine the alkali equivalent content (Na2Oeq) in cement, because the need to maintain electroneutrality in solids or in solution, one directly measures the contents of cement in Na and K elements and one conservatively considers that their counter ions are the hydroxide ions. As Na+ and K+ cations are hydrated species, they also contribute to retain water in alkali-silica reaction products.