"You know," said Frank, as soon as they were seated in their zeriba, "how gas is made for illuminating purposes?"
"Certainly I do," was the reply, "for I learned that when I studied chemistry."
"Just run over the process," Frank suggested.
"Let me see," responded his cousin. "The coal is baked in retorts, which are generally made of clay. They are closed up tight as soon as the coal is put in, and the hot fire beneath them causes the coal to give out its gas, which is carried away by iron pipes."
"All right so far," said Frank.
CHARGING A RETORT IN A GAS FACTORY.
"The retorts are set in a framework of brick, and look like small ovens. The coal is put in with a long shovel, and after the retort is closed it is baked four or five hours, when it is drawn out and replaced by a fresh charge.
"The gas goes from the retorts to the purifier, which consists of a series of pipes surrounded by water. It travels through these pipes till it is thoroughly cooled and gives up the tar and other impurities contained in it; then it passes through water and water-spray, to wash away ammonia, another impurity; next it is forced through powdered lime, to remove the sulphur contained in it; and then it goes to the gasometer, whence it is carried in pipes to the places where it is to be consumed."