"Another very curious thing," proceeded Harry, "in regard to boiling, has been discovered lately. A kettle might be too hot to boil water in. Take a little bar of silver, heated very highly; dip it into water. At first, you have no boiling, and you don't have any at all till the silver has cooled some degrees. Put a drop of water into a platinum dish, heated in the same way, and it will run about without boiling till the heat diminishes; and then it bursts into steam. M. Boutigny, the French chemist, made this discovery. Vapor forms between the drop of water and the red-hot metal, and, being a bad conductor of heat, keeps the heat of the metal for some time from flowing into the water. Owing to this, water, and mercury even, may be frozen in a red-hot vessel if the experiment is managed cleverly. A little more than a couple of centuries ago, this would have been thought witchcraft." "And the philosopher," added Mr. Bagges, "would have been fried instead of his water-drop. Let me see--eh? what do they call this singular state of water?" "The spheroidal state," answered Harry. "However, that is a state that water does not get into in a kettle, because kettles are not allowed to become red hot, except when they are put carelessly on the fire with no water in them, or suffered to remain there after the water has boiled quite away!" "Which is ruination to kettles," Mrs. Wilkinson observed. "Of course it is, mamma, because at a red heat iron begins to unite with oxygen, or to rust. Another thing that injures kettles is the fur that collects in them. All water in common use contains more or less of earthy and other salts. In boiling, these things separate from the water, and gradually form a fur or crust inside the kettle or boiler." "And a nice job it is to get rid of it," said his mamma.