Then they all said good-bye to each other, and Little Mitchell and the lady went on. They crossed the Watauga valley, which is easy enough, it is so narrow; then they crossed the Watauga River, which is hard enough, the bridge is so narrow, and so high up in the air, and wobbles so you are afraid of your life to go over it,—but you have to, or else stay on the wrong side of the river, which, you understand, is quite a river here, very swift and rather deep. But they got safely over the wobbly bridge, and went on through the forest, only stopping a few minutes to look at a birch-still. A birch-still is a place where they distil birch-oil out of birch-bark. Do you know how it is done? Well, you ought to, for you eat so much birch-oil. You don’t think you ever ate any birch-oil in your life? Oh, but I _know_ you have eaten it. I am perfectly sure you sometimes eat wintergreen candy and other things flavored with wintergreen. That is, you call it wintergreen; but it is not that at all, it is birch. You see the flavor is the same, and it is much easier to get it out of the birch. The way they do is to strip the bark from the young black-birch trees,—which of course kills the trees, and that is too bad; but they do it, and chop the bark into little pieces, which they put into a long wooden box with a zinc bottom. When the box is full of bark, they put in some water, and fit on the cover, and plaster all the cracks with clay until the box is air-tight,—all but a little round hole in the cover that has a lead pipe fitted into it. Then they build a fire in the fire-hole under the box, and soon the steam from the boiling water escapes through the pipe that is fitted in the cover. The pipe is coiled up in a barrel of water when it leaves the box, and is kept cool by a little stream of water which runs into the barrel all the time. Of course the steam that escapes through the pipe is turned back to water when it becomes cooled, passing through the coil in the barrel, and finally runs out of the other end of the pipe into a bottle. There is birch-oil in the steam that goes over, and the oil runs into the bottle with the water, but being heavier than water it sinks to the bottom of the bottle. When the bottle is full, the water runs out at the top; but when it gets full of oil, they do not allow that to run over,—they take away the bottle of oil and put an empty bottle in its place. Yes, I know that oil is said to float on water, and some oil does, but birch-oil is heavy, as I have told you, and sinks to the bottom.