<Dd> Ca (OH) (aq) + Na CO (s) → CaCO ↓ + 2 NaOH (aq) </Dd> <P> This process was superseded by the Solvay process in the late 19th century, which was in turn supplanted by the chloralkali process which we use today . </P> <P> Sodium hydroxide is also produced by combining pure sodium metal with water . The byproducts are hydrogen gas and heat, often resulting in a flame, making this a common demonstration of the reactivity of alkali metals in academic environments; however, it is not commercially viable, as the isolation of sodium metal is typically performed by reduction or electrolysis of sodium compounds including sodium hydroxide . </P> <Dl> <Dd> For further information in historical production, see alkali manufacture . </Dd> </Dl>

Which metal reacts with alkali to produce hydrogen