178 FEATHER-ALUM — GILPIN, 
ef Iron and Alumina, such as the mineral forming the subject of 
this paper. As the alkalies are frequently present in appreciable 
quantities in clays, true Potash or Soda Alums are often formed. 
When clay slates are impregnated with these sulphates they 
are termed Aluminous, and are sometimes rich enough to yield 
Alum on the commercial scale. The following outline of the 
process is from Dana’s Mineralogy, p. 128. The rock is first 
slowly heated, after piling it in heaps, in order to decompose 
fully the pyrites, and transfer the Sulphuric Acid of any Sul- 
phate of Iron to the Alumina, and thus produce the largest 
amount possible of Sulphate of Alumina. It is next lixiviated in 
stone cisterns.. The lye containing this sulphate is afterwards 
concentrated by evaporation, and then the requisite proportion 
of Potash (sulphate or chloride, alum containing potash as 
well as alumina) is added to the liquid. A precipitate of Alum 
falls which is afterwards washed and crystalised. In France 
Ammoniacal Salts are used instead of Potash, and an Ammoniacal 
Alum is formed. 
At Whitby, in Yorkshire, the business of Alum making is a 
very old one, having been commenced by Sir Thomas Challoner 
in 1460, who brought workmen from France where the process 
had long been kept secret as a privilege of the ecclesiastical 
powers. The Alum shale occurs in strata of Liassic age, and is 
overlaid by a hard compact stone, known locally as “dogger.” 
The Shale bed is about 200 feet thick, and is a hard bluish gray 
shaly clay which rapidly crumbles on exposure. The whole 
depvsit abounds in iron pyrites, but only the richer portions are 
excavated for treatment: About 65 tons of the Shale yield a 
ton of Alum. It would unduly extend the limits of this paper 
to give the full details of the manufacture, which is based on 
that already outlined. 
In the United States there are no deposits of Alum Shale of 
any commercial value, but the salt is manufactured to the extent 
of 20,000 tons annually, valued at about $800,000. It is nearly 
all made from alum clays imported from France and England, 
The process of manufacture is very simple and consists in mixing 
the Alum Shale with Sulphuric Acid, dissolving out the resulting 
