Emile and Jules, while eating their little lunch of apples and bread, looked on at this curious work without saying a word. They promised themselves to ask their uncle the reason for whitening the inside of the copper saucepans with tin. In the evening, accordingly, they spoke of the tinning and plating. “Highly cleaned and polished iron is very brilliant,” explained their uncle. “The blade of a new knife, Claire’s scissors, carefully kept in their case, are examples. But, if exposed to damp air, iron tarnishes quickly and covers itself with an earthy and red crust called—” “Rust,” interposed Claire. “Yes, it is called rust.” “The big nails that hold the iron wires where the bell-flowers climb up the garden wall are covered with that red crust,” remarked Jules; and Emile added: “The old knife I found in the ground is covered with it too.” “Those large nails and the old knife are encrusted with rust because they have remained for a long time exposed to the air and dampness. Damp air corrodes iron; it becomes incorporated with the metal and makes it unrecognizable. When rusty, iron no longer has the properties that make it so useful to us; it is a kind of red or yellow earth, in which, without looking attentively, it would be impossible to suspect a metal.” “I can well believe it,” said Jules. “For my part, I should never have taken rust for iron with which air and moisture had become incorporated.” “Many other metals rust like iron; that is to say, they are converted into earthy matter by contact with damp air. The color of rust varies according to the metal. Iron rust is yellow or red, that of copper is green, lead and zinc white.” “Then the green rust of old pennies is copper rust,” said Jules. “The white matter that covers the nozzle of the pump must be lead rust?” queried Claire. “Exactly. The prime difficulty with rust is that it makes metals ugly: they lose their brilliance and polish; but it works still greater injury. There are harmless rusts which might get mixed with our food without danger: such is iron rust. On the contrary, copper and lead rusts are deadly poisons. If, by mischance, these rusts should get into our food, we might die, or at least we should experience cruel suffering. We will speak only of copper, for lead, on account of its quick melting, cannot go on the fire and is not used for kitchen utensils. Copper rust, I say, is a mortal poison; and yet they prepare food in copper vessels. Ask Mother Ambroisine.” “Very true,” said she, “but I always have my eye on my saucepans: I keep them very clean and from time to time have them replated.” “I don’t understand,” put in Jules, “how the work that the tinsmith did this morning could prevent the copper rust being a poison.”