deal about the concrete made out of slag. And there was a neat little point made when it was discovered that about two cents a pound could be saved in the manufacture of iron by freezing all the moisture out of the atmospheric air before it was heated for the blast. But the best is yet to come. Quite a little bit of money has been made in this country from the manufacture of iron. What do you say to the proposition to make the iron itself a mere by-product to something even more valuable?

Valuable Gas Ran to Waste.

From the top of the furnace in which iron ore is liquefying in the fervent heat there rushes out a gas, largely carbon monoxide, whose hunger for oxygen has been only half satisfied. If it could get that other atom of oxygen it would be a gas that would only smother us when it didn't make the soda-fountain fizz. As it is, carbon monoxide is deadly poison.

It has to be put to some use. It doesn't burn under a boiler very well. It is necessary to keep a bed of coals going so that the furnace-gas may stay lighted. But it has been found that even when it is too poor to keep alight it will explode in the combustion chamber of a gas-engine.

It has also been found that a furnace smelting seven tons of pig-iron an hour will make enough furnace-gas to supply nine thousand horse-power per hour.

Deducting gas and power that can be economically used on the premises, it is estimated that there will be a surplus of power to sell of five thousand horse-power per hour. Now that we are able to transmit power cheaply by high-tension currents, it is easy to see what this means. In New York they sell electromotive force for from four cents per horse-power per hour up to twelve cents. Call it two cents, and five thousand horse-power per hour means a hundred dollars, which is more money than seven tons of pig-iron will bring.

A lot has been done with cog-wheels; a lot is being done with wires; but when it comes to recovering wealth from waste, it is the test-tube that will do it. And so, study chemistry, young man.