The caller sat down and asked his friend to tell something more about these two marvelous inventions. The story was several days in the telling, for there were visits to foundries and experiments in the laboratory, besides many long talks.
"First we will see about thermit," said the man, and began to talk as he worked over a crucible.
THERMIT HEAT PROCESS
As a result of his discovery that by starting a terrific battle for oxygen between two metals he could reduce one of them to almost absolute purity, Dr. Hans Goldschmidt has converted to the use of man a process of welding so simple and yet so forceful that it is making world-wide changes in the working of metals. This battle itself is the most interesting feature of the Goldschmidt process because of the terrific heat it generates.
Imagine sticking your finger into boiling water. By so doing you would be exposing your flesh to a temperature of 212 degrees Fahrenheit. Imagine sticking your finger into a pot of molten lead if even for the fraction of a second. You know very well what the effect would be. The temperature is 618 degrees Fahrenheit. Still again, think of a redhot iron. This is about 1,652 degrees Fahrenheit. Steel boils at 3,500 degrees.
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.
His first object was to reduce iron oxides. First, he knew that aluminum has a great affinity for oxygen, or, in other words, when the two are heated will absorb oxygen like a sponge will absorb water, only more forcibly and more violently than any such comparison even faintly suggests. In yet other words, aluminum wants oxygen more than any other metal does. Of course no chemical changes would occur if a piece of iron oxide and a piece of aluminum were set side by side, any more than we would have gunpowder if we set a chunk of saltpetre, a chunk of sulphur, and a chunk of charcoal all in a row. The iron oxide and the aluminum would have to be mixed by cutting or filing them into small pieces and making a coarse powder. Still nothing would happen without heat to start it.