ur mill is so combustible as to
be explosive and dangerous, and Mr. Galloway has shown that many colliery
explosions are due not to the presence of gas so much as the presence of
fine coal-dust suspended in the air. If only fine enough, then such dust is
eminently combustible, and a blast containing it might become a veritable
sheet of flame. (Blow lycopodium through a flame.) Feed the coal into a
sort of coffee-mill, there let it be ground and carried forward by a blast
to the furnace where it is to be burned. If the thing would work at all,
almost any kind of refuse fuel could be burned--sawdust, tan, cinder heaps,
organic rubbish of all kinds. The only condition is that it be fine enough.

Attempts in this direction have been made by Mr. T.R. Crampton, by Messrs.
Whelpley and Storer, and by Mr. G.K. Stephenson; but a difficulty has
presented itself which seems at present to be insuperable, that the slag
fluxes the walls of the furnace, and at that high temperature destroys
them. If it be feasible to keep the flame out of contact with solid
surfaces, however, perhaps even this difficulty can be overcome.

Some success in blast burning of dust fuel has been attained in the more
commonplace method of the blacksmith's forge, and a boiler furnace is
arranged at Messrs. Donkin's works at Bermondsey on this principle. A
pressure of about half an inch of water is produced by a fan and used to
drive air through the bars into a chimney draw of another half-inch. The
fire bars are protected from the high temperatures by having blades which
dip into water, and so keep fairly cool. A totally different method of
burning dust fuel by smouldering is attained in M. Ferret's low temperature
furnace by exposing the fuel in a series of broad, shallow trays to a
gentle draught of air. The fuel is fed into the top of such a furnace, and
either by raking or by shaking it descends occasionally, stage by stage,
till it arrives at the bottom, where it is utterly inorganic and mere
refuse. A beautiful earthworm economy of the last dregs of combustible
matter in any kind of refuse can thus be attained. Such methods of
combustion as this, though valuable, are plainly of limited application;
but for the great bulk of fuel consumption some gas-making process must be
looked to. No crude combustion of solid fuel can give ultimate perfection.

Coal tar products, though not so expensive as they were some time back, are
still too valuable entirely to w