Devardas alloy (alloy of aluminium (~45%), copper (~50%) and zinc (~5%)) is a reducing agent that was commonly used in wet analytical chemistry to produce in situ' so-called nascent hydrogen under alkaline conditions for the determination of nitrates () after their reduction into ammonia (). 
In the Marsh test, used for arsenic determination (from the reduction of arsenate () and arsenite () into arsine ()), hydrogen is generated by contacting zinc powder with hydrochloric acid. 
So, hydrogen can be conveniently produced at low or high pH, according to the volatility of the species to be detected. Acid conditions in the Marsh test promote the fast escape of the arsine gas (AsH), while under hyperalkaline solution, the degassing of the reduced ammonia (NH) is greatly facilitated (the ammonium ion  being soluble in aqueous solution under acidic conditions).