passing from the smallest sized to the largest sized revolver. Then,
again, we may, reckoning a certain constant amount of heat lost per
each revolver furnace of the small size, consider that if we doubled
the size of such revolver, we should lose by no means double the
amount of heat lost with the small apparatus; but only the same as
that lost in the small furnace _plus_ a certain fraction of that
quantity, which will be smaller the better and more efficient the
arrangements are. Then, again, there is an economy in iron plate for
such a large revolver; there is economy in expense on the engine power
and on fuel consumed, as well as in wear and tear.

Just to mention fuel alone, we saw that with an ordinary large sized
revolver, the coal consumption was 13 cwt. per ton of salt cake
decomposed in the black ash process; but with the giant revolver we
have been describing, that consumption is reduced to 10 cwt. per ton
of cake decomposed.

[Illustration: A NEW MONSTER REVOLVING BLACK ASH FURNACE. (2 Figures.)]

The question will be probably asked, How is it possible to get a flame
from one furnace to carry through such a long revolver and do its work
in fusing the black ash mixture effectively from one end to the other?
The furnace employed viewed in front looks very like an ordinary
revolver fireplace, but at the side thereof, in line with the front of
the revolver, at which the discharge of the "crude soda" takes place,
there are observed to be three "charging holes," rather than doors,
through which fuel is charged from a platform directly into the
furnace through those holes.

The furnace is of course a larger one than furnaces adjusted to