Marsh test

Sensitive 1836 method for arsenic in which the acidified sample is added to zinc and dilute sulphuric acid. The evolved arsine gas (AsH3) is decomposed in a heated glass tube and deposits a mirror of elemental arsenic on a cool zone of the tube. Sensitivity down to a few micrograms. Superseded by GFAAS and HG-AAS but still taught and still examined.