ved from a grated furnace to pass completely through
the cylinder.

A characteristic size for this Bruckner furnace is one having a length
of 12 feet and a diameter of 6 feet. A furnace of this capacity will
have an inclusive weight (iron and brickwork) of 15 tons.

The time of operation, with the Bruckner, will vary with the character
of the ore under treatment and the nature of the fuel employed. Four
hours is the minimum and twelve hours should be the maximum time of
operation.

By the addition of common salt with the batch of ore, such of its
constituents as are amenable to the action of chlorine are chlorinated
as well as freed from sulphur.

Where the ore contains any considerable quantity of silver which should
be saved, the addition of the salt is necessary as the silver is very
liable to become so oxidised in the process of roasting as to render
its after treatment almost impossible. I know a case in point where an
average of nearly five ounces of silver to the ton, at that time worth
30s., was lost owing to ignorance on this subject. Had the ore been
calcined with salt, NaCl, the bulk of this silver would have been
amalgamated and thus saved. It was the extraordinary fineness of the
gold saved by amalgamation as against my tests of the ore by fire assay
that put me on the track of a most indefensible loss.

_The Howell-White Furnace._--This furnace consists of a cast iron
revolving cylinder, averaging 25 feet in length and 4 ft. 4 in. in
diameter, which revolves on four friction rollers, resting on truck
wheels, rotated by ordinary gearing.

The power required for effecting the revolution should not exceed four
indicated horse-power.

The cylinder is internally lined with firebrick, projecting pieces
causing the powdered ore to be raised over the flame through which it
showers, and is thereby subjected to the influence of heat and to direct
contact oxidation.

The inclination of the cylinder, which is variable, promotes the gradual
descension of the ore from the higher to the lower end. It is fed into
the upper end, by a special form of feed hopper, and is discharged into
a pit at the lower end, from which the ore can be withdrawn at any time.

The gross weight of the furnace, which is, however, made in segments to
be afterwards bolted together, is some ninety to one hundred tons.

The furnace is fired with coal on a grated hearth, built at the lower
end; it is more economical both in fuel and in l