Of course, an iron ship must be made long enough and broad enough so that when it is completed there will be sufficient air contained within the hull to make the combination lighter than water. Always, therefore, when a ship is to be built, competent engineers must go over the plans of the vessel and calculate the air capacity, so as to make sure she will float. Nowadays it would be difficult to sink a modern vessel by boring one small hole in the bottom, because the bottom and sides are lined with enclosed steel air-chambers, and a ship will keep afloat even if one or a number of holes are made. The reason is, of course, that when you bore a hole into one of these air-chambers the water rushing in will fill that air-chamber with water, but as there is no connection from the inside with the rest of the ship, the water can get no further. Why Does a Poker Get Hot at Both Ends if Left in the Fire? Both ends of the poker become heated because the poker is made of iron, and iron is a particularly good conductor of heat. To understand this we must look into the question of what a good conductor of heat is. In this case the particles of iron, which combined form the poker, are so close together that when those at the end of the poker which is in the fire get hot, the particles at that end hand the heat on to the particles next to them, and so on until the whole poker is hot. The difference between a thing which is a good conductor of heat and a thing which is not a good conductor, lies in the ability of the different particles which compose it to hand the heat on to the others. Did you ever notice that the handle of a solid silver spoon will become hot if the spoon is left in hot coffee? Solid silver is a good conductor of heat. A plated spoon is not a good conductor, however, and will not become hot if left in the cup of hot coffee as a solid silver spoon will. Would a Wooden Spoon Get Hot? A wooden spoon would not get hot, because wood is not a good conductor of heat. The atoms which compose the wood have not the power to transmit the heat to each other. This is strange, too, when we think that a poker is a good conductor of heat, but will not burn, while wood is not a good conductor, but will burn readily. Perhaps you have already discovered this in connection with a wood fire. One end of a stick of wood may be burning fiercely, and yet you can pick it up by the other end and find it is not even warm. This proves to you that wood is not a good conductor of heat, and explains why the handle of a wooden spoon in a bowl of hot soup will not get hot while the handle of a silver spoon will. Why Does Iron Turn Red When Red Hot?