it would not have proved the value to have been extracted from the
coal, for it was not the complete test to apply.

The condition of things in the furnace may be illustrated thus: If we
should mingle a quart of molasses and a gallon of water, it would
require considerable manipulation and some time to cause them to
unite. Why? Because one element is so much denser than the other; but
if we should mix a quart of the gallon of water with the quart of
molasses, and render their densities somewhere near the density of the
remaining water, and then pour the masses together, there would be a
more speedy commingling of the two. And so with the furnace. I have
always maintained that every furnace should be lined with fire-brick,
in order that it shall be so intensely hot when the air enters that
the air shall instantly be heated to the same degree of tenuity as the
hot gases themselves, and the two will then unite like a flash--and
that is heat. And here is the solution of the Wye Williams mystery of
failure when cold air was introduced upon the top of a fire to aid
combustion. The proof of the necessity for heat to aid the chemical
assimilation of the volatilized coal elements is seen in starting a
fire in a common stove. At first there is only a blue flame, in which
the hand may be held; but wait until the lining becomes white hot, and
then throw on a little coal, and you will find a totally different
result. It is also seen in the Siemens gas furnace, with which you are
doubtless familiar. There is the introduction of gas with its
necessary complement of air. Until the furnace and retorts become
heated, the air and gas flutter through only partially united, and do
little good; but as soon as the retorts and furnace become thoroughly
hot, the same gas and air will melt a fire-brick.

These are common phenomena, which are familiar, but apt to be