abour than an ordinary
reverberatory furnace.

_The Thwaite-Denny Revolving Furnace._--This new type of furnace, which
is fired with gaseous fuel, is stated to combine the advantages of the
Stetefeldt, the Howell-White, and the Bruckner.

It is constructed as follows:--Three short cylinders, conical in shape
and of graduated dimensions, are superimposed one over the other, their
ends terminating in two vertical shafts of brickwork, by which the three
cylinders are connected. The powdered ore is fed into the uppermost
cylinder and gravitates through the series. The highest cylinder is the
largest in diameter, the lowest the smallest.

The gas flame, burnt in a Bunsen arrangement, enters the smallest end
of the lowest cylinder and passes through it; then returns through the
series and the ore is reduced by the expulsion of its sulphur, arsenic,
etc., as it descends from the top to the bottom. The top cylinder is
made larger than the one below it and the middle cylinder is made larger
than the lowest one in proportion to the increased bulk of gases and
ore.

The powdered ore in descending through the cylinders is lifted up and
showers through the flame, falling in its descent a distance of over
1000 feet. By the time it reaches the bottom the ore is thoroughly
roasted.

Provision is made for the introduction of separate supplies of air
and gas into each cylinder; this enables the oxidising treatment to be
controlled exactly as desired so as to effect the best results with all
kinds of ore. Each cylinder is driven from its own independent gearing,
and the speed of each cylinder can be varied at will.

The output of this type of furnace, the operations of which appear to be
more controllable than those of similar appliances, depends, of course,
upon the nature of the ore, but may be considered to range within the
limits of twelve to fifty tons in twenty-four hours, and the cost of
roasting will vary from 2s. 6d. to 4s. per ton, depending upon the
quality of ore and of fuel.

The gaseous fuel generating system permits not only the absolute control
over the temperature in the furnace, but the use of the commonest kinds
of coal, and even charcoal is available.

The power required to drive the Thwaite-Denny furnace is four indicated
horse-power.

_The Molesworth Furnace_ also is a revolving cylindrical appliance,
which, to say the least of it, is in many respects novel and ingenious.
It consists of a slightly cone-sh