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 (AsH3), while under hyperalkaline solution, the degassing of the reduced ammonia (NH3) is greatly facilitated (the ammonium ion being soluble in aqueous solution under acidic conditions). See also Atomic hydrogen welding References Further reading Hydrogen Electrolysis Hydrogen Obsolete scientific theories