Devarda's alloy, is an alloy of aluminium, copper and zinc. Devarda's alloy is used as reducing agent in analytical chemistry for the determination of nitrates after their reduction to ammonia under alkaline conditions. 

Devarda's alloy is a reducing agent that was commonly used in wet analytical chemistry to produce so-called nascent hydrogen under alkaline conditions in situ. 

When a solution of nitrate ions is mixed with aqueous sodium hydroxide, adding Devarda's alloy and heating the mixture gently, liberates ammonia gas. After conversion under the form of ammonia, the total nitrogen is then determined by Kjeldahl method.

In the Marsh test, used for arsenic determination, 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. 

DEVARDAS ALLOY