Down through the little hole the thermit, that a minute before had been only a coarse dark gray powder like metal filings, seemingly the last thing on earth that would catch fire, flows into the pouring gate of the mould in a steady stream of white-hot liquid steel. The white glow from the metal is brighter than any electric light. It is so intense that although the workmen wear heavy dark goggles, they shade their eyes and turn their heads away. Now you will be wondering, if you know anything about steel and its wonderful properties, how it is that this can be good steel when it is all mixed up with the aluminum oxide or slag. The reason it is of best quality is that as soon as the reaction reduces the whole mass to a molten liquid the heavier steel, set free, as the scientists say, but as we have chosen to think of it, robbed of the aluminum, sinks to the bottom, while the lighter aluminum oxide rises to the top. Consequently the steel goes into the mould to make the weld while the slag, having risen to the top, will be found at the top of the pouring gate, and only around the outer edges of the weld. When the pour is completed the workmen go away and leave it to cool. It is usually left over night, sometimes as long as forty hours, when the weld is a very large one. Finally the mould is broken down and the weld is found complete, with big extensions of the steel extending from the weld, in just the shape of the pouring gate "riser" and heating aperture. The molten thermit steel rushing in at the bottom of the mould has risen between the heated broken ends, and all around them, in just the shape left by the wax pattern. As the scientists say, the thermit steel has united the broken sternframe and formed a homogeneous mass with it. In other words the terrific heat of the thermit rushing on the heated ends has resulted in the two parts becoming one with the added thermit steel. After the mould is broken down the oxygen-gas torch comes into use again to cut away the ends of steel sticking up where they had cooled in the pouring gate, "riser" and heating aperture. After this the weld looks like a great swelling upon the sternframe, and if the swelling is where it will not interfere with the working of the rudder or steamer propellers, nothing more need be done. On the other hand, if the swelling is in the way, it can be reduced to the size of the frame, and squared off with machines built for the purpose. Thus the ship is repaired and is ready to be taken out of drydock for her next trip, as good as new.