FEATHER-ALUM — GILPIN. 17¥ 
Melanterite, the first of the minerals mentioned in this paper, 
belongs to the Copperas group, which contains among its more 
noteworthy species, the hydrous sulphates of Iron, Zine, and 
Copper. The first named occurs in nature as a product of the 
decomposition of iron pyrites, and is largely made from the 
waste oil of vitriol from wire and galvanising works, with scrap 
iron, and from alum shale. The production of Copperas in the 
United States in the year 1882 was estimated at 15,000,000 
pounds, valued at three quarters of a cent per pound. It is 
largely used by tanners and dyers on account of its forming a 
black colour with tannic acid. It is also used in paper mills, 
bleacheries, paint and ink manufactories, and as a disinfectant. 
White Vitriol is a similar compound, formed naturally from 
the oxidation of Zine Sulphide, and commercially by the action 
of Sulphuric acid on Zine. As met in the Arts, White Vitriol is 
a form made by melting the Crystallised Sulphate and agitating 
it until it cools in a granular state. 
Blue or Copper Vitriol is used in many dyeing and other 
chemical operations. When it occurs in nature in solution, as in 
the water flowing from copper lodes, large quantities of the 
metal are obtained by exposing it to the action of iron, when it 
is precipitated as a red mud, easily smelted and refined. 
The minerals Feather-Alum and Pickeringite mark further 
steps in this chemical action of air and moisture on Sulphur. 
They may, broadly speaking, be considered as belonging to the 
native Alum group, the members of which contain water and 
sulphate of Alumina and some other sulphate. In Potash Alum, 
the common Alum of the shops, this other sulphate is a sulphate 
of potash. The corresponding sulphate in the other Alums is 
that of Soda, Magnesia, Ammonium, Iron or Manganese, and 
finally we have Alunogen, already referred to, a simple hydrous 
sulphate of Alumina. 
We have already remarked on the formation of Sulphate of 
Tron by the oxidation of iron pyrites. When this action takes 
place in the presence of clays, largely composed of Silicate of 
Alumina, part of the Sulphuric Acid unites with the Alumina, 
and the commonest resulting form is that of a hydrous sulphate 
