Part 35 (2/2)

_In the Service of the King_

Very early the next morning the boys, who had caught the Doctor's enthusiasm, began again their task of digging through the ”out crop”

coal, which began now to grow softer and more workable, while the coal itself grew steadily better in quality.

But about noon, when they had pushed their little shaft about a dozen feet into the hill, the Doctor ordered a cessation of the digging.

”We must put in some supports for our roof,” he said, ”or we shall presently be caught in a cave in.”

”How are we to do it?” asked Jack.

”Well, I am not a mining engineer,” answered the Doctor, ”but I've seen enough of the work to know how to protect a little shaft like this, anyhow. The engineers, when they come, will of course tear out all that we do, because they must drive a big shaft into the hill, while all we want to do is to push a little gallery three or four feet wide far enough in to find the best of the coal. But even in doing that we must securely support the roof of our mine. So we'll cut some timber and put it in place. Jack, I wish you would choose the trees to be cut.”

”All right!” said Jack. ”What dimensions are required?”

”First of all,” answered the Doctor, ”we want from six to ten pieces of oak, say four feet six inches long and fully twelve inches in diameter.

They will serve for roof timbers, and will be enough to carry us thirty or forty feet further. Then for perpendicular supports--one at each end of each timber--we shall need just twice as many perfectly straight oaken sticks eight or nine inches in diameter.”

”But why do you want big sticks to go crossways and comparatively little ones for the perpendicular supports?” asked Ed. ”The perpendicular timbers must after all bear the weight.”

”Oh, that's simple enough,” said Tom, whose perceptive faculties were always alert. ”You see a stick set up on end, if it is perfectly straight and set true, will bear vastly more weight than a stick of twice or three times its thickness, if laid crossways. In fact a straight eight-inch stick nine feet long, if set on end will support nearly as much as another stick nine feet thick--if there were any sticks that thick--laid lengthwise.”

”That's it,” said the Doctor. ”We want heavy timbers across the top, supported by stout eight- or nine-inch sticks set endwise under them.

Now, Jack, select the best trees and we'll all get to work as soon as dinner is over. We'll get the dinner ready while you choose the timber to be cut.”

The cutting of the timber was a small task to expert young wood choppers; but it was a very difficult task for the six boys to bring the timbers to the mine and set them in place. True, only two frames had to be set up for the present, but the cross pieces, short as they were, were enormously heavy, and it required all the ingenuity as well as all the strength the boys could command, to get these two frames up, each consisting of one cross piece under the roof and two uprights supporting it.

When night came only one of the two frames was in place, and it was obvious, as Jack said, that ”another half day must be wasted on such work” before they could begin mining again. But that evening the Doctor dug two bushels of coal out of the farthest end of the shaft, built a special fire, placed the coal on it, and carefully covered it with earth.

”What are you doing, Doctor?” asked his crony, Tom.

”I'm making a c.o.ke oven, Tom,” he replied. ”I want to see how our coal will c.o.ke.”

”But I don't understand about c.o.ke,” answered Tom. ”Why is it that when you burn most of the substance out of coal it will make a hotter fire than with all its combustible materials in it?”

”That isn't quite the case, Tom,” answered the Doctor. ”What we do in making c.o.ke is chiefly to expel the gas from the coal and to roast out the sulphur, which seriously interferes with the making of sufficient heat to smelt iron. Some coal gets burnt up in the process; some makes an indifferent and nearly worthless c.o.ke; while some makes a c.o.ke that would melt the heart of a miser. Now, as I told you the other night, I am convinced as a geologist, that a little further in our mine we shall come to coal so free from sulphur that we can smelt iron with it without making c.o.ke of it at all. But it is always preferable to make c.o.ke of it, and so I'm trying to see what sort of c.o.ke our coal will make. Of course we haven't come to the real coal yet, but I can tell a good deal by what we have now. We'll let my little c.o.ke oven roast all night and in the morning I'll know a great deal more than I do now. But if you have any question in your mind as to the gas making capacity of this coal, I'll remove it at once.”

With that he went to the camp fire, seized a blazing brand and applied it to the little mound of earth under which he had buried his coal.

Instantly the whole outside of the mound was aflame.

”That's the gas,” said the Doctor. ”You see there's plenty of it, even in the imperfect coal that we've reached. It will burn out presently and meantime its heat will help roast my coal into c.o.ke.”

After supper the boys again plied the Doctor with questions concerning coal. Tom began it by saying:

”You told us the other evening, Doctor, that the value of a bed of coal depends upon many things besides its location and its accessibility to market. What are those things?”

”Thickness, for one thing,” answered the Doctor, ”and that is a point in which our mine excels. You see coal seams are of every thickness, from that of a knife blade to beds 100 feet through. Those last are very rare, however. In this country the seams vary from knife blade thickness to about nine or ten feet. Now, in working a coal mine the men, of course, must have room to stand up in the shaft, so that wherever the vein is less than six feet thick a good deal of rock or earth must be removed so as to give sufficient height to the mine. It costs as much to remove the rock or earth as to handle a like amount of coal, and the stuff is worthless. So you see it is greatly more profitable to work a thick than a thin vein. Indeed there are very few veins under three or four feet thick that it pays to work at all. Our deposit here appears to be about nine feet thick, and that means much to us.

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