"What? Why, you'd scald your hand off!" cried Mr. Bagges.
"No, you wouldn't. The steam rushes out tremendously hot, but it expands instantly so very much, that the heat in it directly becomes latent in a great measure; which cools it down sufficiently to allow you to hold your hand in it without its hurting you. But then you would have to mind where you held your hand; because where the steam began to condense again, it would be boiling hot."
"I had rather take your word for the experiment than try it, young gentleman," Mr. Bagges observed.
"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.
"Well, chemistry has lessened that difficulty," replied Harry. "The fur is mostly carbonate of lime. In that case, all you have to do is to boil some sal-ammoniac—otherwise muriate, or more properly hydrochlorate of ammonia—in the furred vessel. The hydrochloric acid unites with the lime, and the carbonic acid goes to the ammonia. Both the compounds formed in this way dissolve and wash away; and so you may clean the foulest boiler or kettle. This is a rather important discovery; for the effect of fur in a kettle is to oppose the passage of heat, and therefore to occasion the more fuel to be required to boil water in it, which is a serious waste and expense when you have a large steam-boiler to deal with. Dr. Faraday mentions the case of a Government steamer that went to Trieste, and during the voyage had so much fur formed in her boiler as to oblige all her coal to be consumed, and then the engineers were forced to burn spars, rigging, bulkheads, and even chopped cables, and to use up every shaving of spare timber in the ship. Soot underneath the kettle, as well as fur inside it, is a hindrance to boiling, as it is a bad conductor; and that is the reason why one can bear to hold a kettle of hot water, which is very sooty on its under surface, on the flat of the hand. So a black kettle doesn't give out its heat readily to what touches it, and so far it is good to keep water hot; but it gets rid of heat in another way; as I dare say you know, uncle."