"There are various ways by which the ocean gets rid of some of its salt, the most important of which is the making of salt, by men, out of salt water; and the natural manufacture, by the salt water lodging in the rocks, and then evaporating, and leaving the salt, which is collected in large quantities. There may be some way of its escaping, too, that has not been found out. I am pretty sure there is some natural provision by which the ocean can never become too salt, as long as the earth is intended for the home of man."
"I thought the reason why the ocean is salt, is because there is a great deal of salt in the bottom, which washes up into the water," remarked Ruth.
"That may be one reason," replied Johnny; "though the books don't say so. Don't you think, Pierre, that a good deal of the salt may have come from salt deposits under the oceans?"
"I don't see why not. There is a great amount of surface under the oceans, and it would be a wonder if there were not great deposits of salt there, as well as on the land; although they must be pretty well covered up by this time, by ocean deposits."
"But how about those retorts?" asked Felix, who had seen Johnny's experiment of making a little retort out of a clay pipe.
"I don't know what a retort is," remarked Julia.
"Nor I," said Ruth.
"A retort is a place where you heat any combustible very hot, without letting the air get to it. Of course, if there is no oxygen at hand, it can't burn; and so the heat merely causes the hydrogen to separate from the carbon, in the form of gas. They have large retorts at the gas-works, in which they heat soft coal excluded from the air; and, you know, the gas that is driven out is carried through pipes into the houses and stores, and then, when the gas is allowed to escape from one of the jets, they light it, and, because there is oxygen around, it burns steadily until you shut it off; that is, until you exclude the air."
"But how about your retorts in your big laboratory?" asked Felix.
"The largest that I have heard of," continued Johnny, "is around Pittsburg. That is in the soft-coal region. The heat in the earth has driven off the gas, or hydrogen, from the coal in the mines. Once, when they were boring a well, some of this pent-up gas, which was where they happened to be boring, burst out in a kind of explosion, tearing their boring apparatus all to pieces, and frightening the workmen pretty thoroughly. Afterwards the gas at this hole got on fire, and burned in a great big jet. But it was some time before the Pittsburg folks got it through their heads that nature had some monstrous big gas-works under them, so that they had only to pipe the gas, and bring it into their houses and manufactories, to get rid of using the coal that made Pittsburg such a black, smoky city. But they found it out after a while; and now they have not only natural-gas lights, but gas-fires in their manufactories, so that the atmosphere is as pure in Pittsburg as in any other manufacturing city."