The Paper gives an account of experiments which have been made upon the electrical conductivities, the corrosion products and tensile properties of high purity aluminium and certain light aluminium alloys, which have been exposed to London atmosphere for a period of 24 years. The elements concerned are copper, nickel, manganese and zinc in varying amounts up to a few per cent. The variation of electrical conductivity, the growth of the corrosion product and its composition have been studied, and the tensile properties before and after exposure have been compared. Finally, there is a note on the corrosion products of high conductivity copper.