They are all hot enough, but compare them with the temperature of 5,400 degrees Fahrenheit or about 3,000 degrees Centigrade, which is attained by the thermit reaction. The range of temperature in which we can live extends from a little over 100 degrees to 70 or 80 degrees below zero, and yet man can so direct the heat of the thermit reaction that it will work for him. The commonest use of the process is in welding steel or iron, such as broken parts of machinery and welding steel rails, and steel or iron pipes. Besides this, the thermit process will reduce many metals to a high degree of purity. After spending a few minutes in seeing how the inventor of this process came to discover it, we will take a little trip in our mind's eye to some of the places where the thermit process is in use, and see what happens. As you know, metals rarely come from the mines in a state of purity. They usually are very much mixed up with rock, slag, and other minerals, so that it takes a complicated process called smelting to separate them. Even then they are not pure, and more complicated processes have to be gone through with. Oxides, or metals that have been oxidized, are common because oxidization merely means that the metal has been burned so that each atom of metal has taken up an atom of oxygen to make what is called a molecule of oxide. Iron ore is usually found in the form of iron oxide, because when this great earth was nothing but a swirling ball of burning gases, probably as hot as the sun, gradually cooling and forming a great cauldron of molten matter, boiling and bubbling more fiercely than the hottest cauldron of molten metal in any steel mill, much of the matter that later became iron ore was burned or oxidized. Other chemical actions too technical for our attention just now were responsible for other forms of ore, such as sulphides, etc. When the earth cooled sufficiently to become solid, these things were completed, and they only had to remain hidden away under the surface for ages and ages until a little man who could live but a hundred years at the utmost solved the deepest secrets of the earth's formation. Thus, to obtain pure metals the oxygen must be removed from the oxide. In other words, it must be reduced. Plainly such reduction was a problem of smelting, but Doctor Goldschmidt in his efforts to obtain purity was working along lines of smelting, in his little German laboratory, very different from the ones in general use.