P. Granville put into practice between Alum Bay in the Isle of Wight and the Needles lighthouse a method which depends upon conduction through sea water.
He also showed that crystals of alum cannot be obtained by dissolving alumina in sulphuric acid and evaporating the solutions, but when a solution of potash or ammonia is dropped into this liquid, it immediately deposits perfect crystals of alum (Sur la regeneration de l'alun, Marggraf's Opusc. ii.
A., 1884, p. 93); several copper mines in Khorasan, Samnan, Azerbaijan and Kerman; some of lead, two considerably argentiferous, in Khorasan, Tudarvar (near Samnan), Anguran, Afshar (both west of Zenjan), and Kerman; two of iron at Mesula in Gilan and Nur in Mazandaran; two of orpiment in Afshar and near Urmia; one of cobalt at Kamsar (near Kashan); one of alum in Tarom (near Kazvin); and a number of coal in the Lar district, north-east of Teheran, and at Hiv and Abyek, north-west of Teheran.
Various minerals are employed in the manufacture of alum, the most important being alunite or alum-stone, alum schist, bauxite and cryolite.
In the writings of the alchemists we find the words misy, sory, chalcanthum applied to alum as well as to iron sulphate; and the name atramentum sutorium, which ought to belong, one would suppose, exclusively to green vitriol, applied indifferently to both.
Early in 1898 permanent stations were established between Alum Bay and Bournemouth, a distance of 142 m., where successful results were obtained.
Pliny says that there is another kind of alum which the Greeks call schistos.
The western promontory is flanked on the north by the picturesque Alum Bay, and the lofty detached rocks known as the Needles lie off it..
Salts of ammonium were also known; while alum was used as a mordant in dyeing.
The presence of sulphuric acid in potash alum was known to the alchemists.