“Why, heat,” said his father.
“Then why don’t you say heat?” said Rollo.
His father laughed.
“What are you laughing at, father?” said Rollo.
“Why, that’s the same question that you asked me at first, and I promised to wait till mother came before I explained it. So we will wait until she comes.”
They did not have to wait long, for Rollo’s mother soon returned; and she put out her lamp by means of a little extinguisher which was attached to the stem of the lamp itself. Then she sat down at the table, by the light of a great lamp which was burning upon it, and took out her work.
Rollo’s father then repeated to her what he had just been telling Rollo, namely, that different substances took fire at different degrees of heat; and he said that it would be a very interesting experiment to take a long iron bar, and put a small quantity of several different substances upon it, in a row, and then heat the bar gradually, from end to end all alike, until it was very hot, and so see in what order the various substances would take fire.
“I would have,” said he, “phosphorus, sulphur, sawdust, charcoal, saltpetre, oil,—we should have to make a little hollow in the iron for the oil,—alcohol, spirits of turpentine, and perhaps other things. The phosphorus would take fire first, I suppose, and then perhaps the sulphur, and others in succession.”
“Well, father,” said Rollo, “I wish you would. I should like to see the experiment very much.”
“No,” said his father, “I cannot actually try such an experiment as that. I could not get such a bar very conveniently; and, if I had the bar and all the substances, I could not heat the bar exactly equally. It could not be done very well, except in a chemical laboratory. But it would be a very pretty experiment, if it could be performed.”