Such a treatise, however, could not attain the highest degree
of usefulness without a consideration of the theory of calcina-
tion sufficient to enable and encourage all who make use of the
more practical part to follow with ease the chemical reactions
on which the process is based. These reactions can be more
easily appreciated and remembered after first becoming famil-
ial* with the apparatus and means by which the exposure of
the substances under treatment to the influence of heat and
air is effected. The theoretical discussion will be postponed
until this familiarity is attained.
This roasting apparatus must vary according to the me-



THE ROASTING OF COPPER ORES IN LUMP FORM. 39

chanical condition of the ore under treatment — that is, whether
fine or coarse. (See article by the author, " The Boasting of
Copper Ores and Furnace Products." United States Geologi-
cal Survey , Mineral Resources of ike United States, Albert
Williams, Jr., 1883.) It is assumed that the process of calci-
nation, as executed in the dry metallurgy of copper, has to
deal with the oxidizing of only two classes of material, ores
and mattes. The appliances for the roasting of these sub-
stances in lump form may be divided into three classes :

1. Heap roasting. Suited to both ore and matte.
2. Stall roasting —

a. Open stalls. Suited only to ore.
b. Covered stalls. Suited to both ore and matte.
3. Kilns. Suited only to ore.
