e gleams of
fire from the little iron doors made the place look weird and ghostly.
Long iron pipes reached from each of the upper doors up to one very large
horizontal pipe or cylinder near the ceiling overhead. This cylinder ran
the whole length of the room, and, at its farther end, joined another
iron pipe which passed through the wall.

"Those are the furnace-doors down below," said Mr. Carter to the
children. "What you see burning inside of them is coke. Coke is what is
left of the coal after we have taken the gas and tar out of it. The upper
doors open into the retorts, or ovens, that we fill every five hours with
the coal from which we want to get gas. Each retort holds about two
hundred pounds, and from that amount we get a thousand cubic feet of
gas."

"Is it just common coal;" asked Kitty, "like what people burn in stoves?"

"Not exactly. It is a softer kind, containing more of a substance called
hydrogen than the sorts that are generally used for fuel. Several
different varieties are used: 'cherry,' 'cannel,' 'splint,' and so on,
and they come from mines in different parts of England and Scotland,
chiefly. Glasgow, Coventry and Newcastle send us a great deal."

Philip started as if a bright idea had struck him. "Is that what people
mean when you're doing something there's no need of, and they say 'you're
carrying coals to Newcastle?'"

"Yes. You see such an enterprise would be absurd. Just notice the man
yonder with the long iron rod! He is going to open one of the retorts,
take out the old coal--only it is now coke--and put in a fresh supply."

A workman in a grimy, leather apron loosened one of the retort doors, and
held up a little torch. Immediately a great sheet of flame burst out, and
then disappeared.

He took the door quite off, and there was a long, narrow oven with an
arched top, containing a huge bed of red-hot coals.

"What a splendid place to pop corn!" exclaimed Kitty.

Papa laughed. "You would find it warm work," said he, "unless you'd a
very long handle to your corn-popper." And Kitty thought so too, as she
went nearer the fiery furnace.

"You see," said Mr. Carter, "these red-hot coals have been changed a
great deal by the heat. They have given up all their gas and tar, and are
themselves no longer coal, but _coke_. We shovel out this coke and use it
as fuel in the furnaces down below to help heat up the next lot. Then new
coal is put into the retorts, and they are closed up with ir