The mixture of filings used in this process is called thermit. A technical definition of the product is as follows: "Thermit is a mixture of finely divided aluminum and iron oxide. When ignited in one spot, the combustion so started continues throughout the entire mass without supply of heat or power from outside and produces superheated liquid steel and superheated liquid slag (aluminum oxide)." Thus the makers of thermit call the pure metal that results from the combustion, thermit steel. For the boy who has studied chemistry the simple equation by which the scientist described the process to his young friend will mean as much as his long explanation. The equation is: Fe_{2}O_{3} + 2Al = Al_{2}O_{3} + 2Fe. The scientist simply went on to say that Fe_{2}, iron, and O_{3}, oxygen, in the equation means iron oxide, while 2Al means aluminum. Thus we have iron oxide plus aluminum, heated to 5,400 degrees Fahrenheit, equals aluminum oxide, Al_{2}O_{3}, plus pure iron, 2Fe. These signs are simply the abbreviations scientists use for expressing processes in the terms of mathematical equations. With this general outline of the principle of the thermit process in mind its actual application will seem a simple matter. Suppose that a great steel ship ploughing her way through a storm breaks her sternframe. This is the steel framework upon which the rudder post is mounted, and naturally a fracture puts the rudder out of commission. Repairs must be made before the ship can make another trip. Quick repairs are desired by the owners. Perhaps the ship is a passenger steamer due to leave port in a few days with passengers and mail, so to put the liner in drydock, wait for the steel mills to cast a new sternframe, wait for it to come by freight, and then wait for the steelworkers to fit the piece in the place of the broken one is a matter of weeks, perhaps more. With the thermit process at hand this is not necessary. The company that manufactures and sells thermit has big plants in several cities in various parts of the world, but if there is steel repairing to be done elsewhere the company will send its materials and expert workmen on a minute's notice. So if the crippled ship limps into the port where there is a thermit plant the repairs can begin at once, but there need be only a little delay otherwise, because the captain of the ship can notify his owners of the damage by wireless while still out at sea, and long before he reaches the port he is making for they can have a complete thermit outfit on the way. One of the biggest advantages of the thermit process of repairing machinery or structural steel is that the welding in a great many cases can be made without taking the complicated parts to pieces. Consequently after the ship is in drydock the workmen build a wooden scaffolding about the broken sternframe, so that they can work the better.