it had
been charged with the coke dust and crushed zinc ore.

"Why is it necessary first to crush the ore and roast it, and then
afterwards put it in the crucible with the crushed coke?"

"Zinc is not found in a native state. This ore is in the form of an
oxide, as it is called. In roasting, certain of the impurities are
driven off in gases, and mixing it with charcoal or coke and then
applying heat to the confined mass, causes the zinc to melt and finally
go off into a gas, as we shall presently see."

After the heat had been applied for some time a white smoke began to
appear at the mouth of the clay tube, and a little later a blue vapor
appeared.

"Now bring that pan here, so we can catch it."

Soon the dripping commenced, and as it ran out and came into contact
with the air, it turned into a solid, greyish color.

"This is what is called spelter, or the pig of zinc, and this is what is
sold to refiners, who take out all the dross or impurities so it can be
rolled or used for galvanizing iron, or for other purposes."

"I do not see how we can use this metal, now that we have it."

"You said the other night that you wished we had a better light."

"That was the reason I was so anxious to see whether we couldn't get
some kerosene at the 'hole.'"

"As we didn't succeed in finding petroleum we shall have to depend on
our zinc, I suppose."

"What, light out of zinc?"

"No; but by the zinc route."

That was another new development to the boys.

"Harry made a sage remark some months ago. It was to the effect that in
order to start to make anything we had to make something that made
something to make something with. In order to make electricity by means
of a battery, we had to go through all this process of turning out the
zinc, which we have just completed; then, if you have not forgotten it,
we had quite a time in converting our copper ore into a copper which we
could use. We were compelled to make charcoal, and then coke, with the
aid of the charcoal; and now that we have coke, we must again grind it
up and make a mortar, so we can form it into little plates or slabs.
From the copper we got a liquid, which I asked you to save, and that is
vitriol, or sulphate of copper. You see, all these things are necessary
before we could possibly attempt to set up a primary battery, and start
the first lighting plant."

Not an hour was lost at the Cataract home and factory. All took the
keenest delight in forwarding