One of the best ways of roughly determining whether a given food belongs in the Coal, the Kindling, or the Paper class, is to take a handful or spoonful of it, dry it thoroughly by some means,--evaporating, or driving off the water,--and then throw what is left into a fire and see how it will burn.

A piece of beef, for instance, would shrink a good deal in drying; but about one-third of it would be left, and this dried beef would burn quite briskly and would last for some time in the fire.

A piece of bread of the same size would not shrink so much, but would lose about the same proportion of its weight; and it also would burn with a clear, hot flame, though not quite so long as the beef.

A piece of fat of the same size would shrink very little in drying and would burn with a bright, hot flame, nearly twice as long as either the beef or the bread.

These would all be classed as Coal foods.
Then if we were to dry a slice of apple, it would shrink down into a little leathery shaving; and this, when thrown into the fire, would burn with a smudgy kind of flame, give off very little heat, and soon smoulder away.