Nor has Huntsman’s form of furnace been greatly changed, as the illustrations prove. Though gas and oil as well as coal are, in many cases, used as the fuel, the general design of the furnace has remained the same. For a century crucibles were made from clay molded to form, slowly dried and very carefully burned. Usually each steel maker made his own crucibles. They could be used but three times, becoming so thin and tender after use for three batches of steel that they were not safe for a fourth. Graphite crucibles are now very largely used. They withstand the severe heat much better and can be used five or six times. The expense item for either clay or graphite crucibles is a large one. [Illustration: THE STALWART MELTERS ] After filling with small pieces of blister or shear steel the crucibles are entirely surrounded by coal or coke in the furnace pit. The fire is so regulated that the steel is not too quickly melted. Fresh coal or coke must be put in around the crucibles two or even three times. When he thinks the steel should be molten, the expert attendant known as the “melter” quickly removes the tight fitting cover of the crucible and with an iron rod determines whether any unmelted pieces remain. After complete melting the steel must be “killed,” else it will boil up in the mold upon pouring and leave a spongy or insufficiently solid “ingot” or block of steel. This “killing” of steel is a rather peculiar phenomenon. It is accomplished by allowing the steel to remain quiet in the furnace for another half hour or so. Undoubtedly the quieting is the result of the escape of the gases or impurities which are contained in the charge, and absorption of the chemical element, silicon, from the walls of the crucible. We have met this element, silicon, before in our metallurgical journey and we will likely meet it several times again. To the metallurgist it is secondary in importance only to carbon. [Illustration: PULLING THE CRUCIBLE ] When the steel has been properly melted and killed it is ready to pour. An assistant lifts the cover from the melting hole, the “puller-out” seizes the crucible just below the bulge with circular tongs and pulls it from the coke which surrounds it. The slag is skimmed off the top and the steel poured into iron molds forming small “ingots,” usually from 2 to 4 inches square and two feet or more long. Every part of the process, even the pouring, must be done with extreme skill and care or the product suffers. After liberation from their molds, the ingots are heated and either rolled or hammered down to the sizes desired for tools, etc. As stated before, crucible steel necessarily is an expensive material both on account of high labor and crucible costs. For this reason, many have resorted to the process used in the very small way mentioned for the manufacture of Wootz steel—the melting of wrought iron bar or soft steel in a crucible with carbon.