 Another memorable series of researches commenced about 1872, in conjunction with his assistant Alfred Tribe, resulted in the discovery of the zinc-copper couple, and its application to the production of the organozinc compounds and to other purposes.The couple has long since found its way into every laboratory in the world, and as a reducing agent has met with applications not only in connection with carbon compounds but for many purposes in analysis.In 1874 and 1876 Gladstone was invited to deliver the Royal Institution Christmas Lecture on "The Voltaic Battery" and "The Chemistry of Fire" respectively.