Q. Where is all this quantity of air stowed in the apple?
A. The inside of an apple is made up of little cells (like a honey-comb), each of which contains a portion of the air.
Q. When an apple is roasted, why is one part made soft, while all the rest remains hard?
A. When an apple is roasted, the air in the cells next to the fire is expanded and flies out; the cells are broken, and their juices mixed together; so the apple collapses (from loss of air and juice), and feels soft in those parts.
Q. What is meant by the “apple collapsing?”
A. The plumpness gives way, and the apple becomes flabby and shrivelled.
Q. Why do sparks of fire start (with a crackling noise) from pieces of wood laid upon a fire?
A. The air in the wood (expanded by the heat), forces its way through the pores of the log; and carries along with it the covering of the pore, which resisted its passage.
Q. What is meant by the “pores of the wood?”
A. Very small holes in the wood, through which the sap circulates.