"And then, if we break the plaster of Paris, and take out what is left of the coal, we shall have some coke," said Alec.
"Yes," replied Johnny.
Sue now appeared, bringing a small cold chisel. Johnny took a file from the closet, and, placing the chisel over the flame of the lamp, began to file it briskly: beautiful little points of light at once commenced to play about the file and chisel at the point of contact.
"Why don't the filings fall down into the flame?" inquired Alec.
"I suppose the current in the flame blows them up, they are so small," replied Johnny, "or perhaps the motion of the file does."
Alec, Belle, and Sue then took turns at making the "fireworks," as Sue called them.
"I think I understand now about fire being a chemical union between oxygen and other substances," said Alec; "but I don't understand about the heat. What makes heat? or why does a chemical union of that kind produce heat?"
"Why, friction makes heat," replied Johnny; "particles of matter coming against each other violently. You know the Indians used to get the oxygen to combining with the carbon and hydrogen in two pieces of dry wood, by rubbing them together briskly; and before matches were invented, they kindled a fire by striking flint and steel over tinder; and a steel peg in your shoe-heel sometimes strikes fire on the pavement by the heat produced by friction; and I think I have seen it stated, that, when oxygen is uniting with other substances, it is the very quick motion of the little particles of matter among themselves that produces the heat."
"I shouldn't think such little invisible particles as those of oxygen and hydrogen could make friction enough by their motion as to produce heat," said Alec.
"Why, Alec," replied Belle, "don't you remember what terrible force the air has in hurricanes, and even in a common gale?"