The furnace superintendent is just explaining to the other party that No. 2 furnace has been “hanging” for a couple of days and is still dangerous. “If you realize,” said he, “the great weight of coke, ore, and limestone in that furnace, you can see what a splash it would make if the clogged, bridged part with all above it should fall suddenly into the molten pool in the ‘hearth’ of the furnace. Two years ago No. 1 broke out and the molten metal caught and burned to death one of our men and injured several others. ‘Hanging’ does not occur when the furnace is working right, but failure of the charge to come down evenly is very serious sometimes. A blast furnace is like a coquette; she has to be handled just so, and even then you cannot always be sure what she is going to do next. “Oh yes,—where does the iron come from? Well, we often read nowadays of a man and his ‘affinity.’ Now the chemist has used that word ‘affinity’ for years to describe the liking or attraction of one chemical ‘element’ for another; in fact, that is where this recent colloquial use of the word originated. Iron ore is nothing more nor less than metallic iron, the element, chemically combined with oxygen, another element which constitutes one-fifth of the air we breathe. Under conditions produced in the blast furnace, though for centuries wedded to iron, oxygen deserts him for her ‘affinity’ carbon, which is best known to you as coke, coal, or charcoal. The iron, now free, becomes molten at the high temperature encountered (about 2800° to 3000° F.) and descends into the ‘hearth’ or bottom of the furnace, while oxygen and her new partner escape out of the top of the furnace in gaseous form. When molten iron has accumulated in the hearth to the extent desired it is tapped out as you will soon see. [Illustration: DIAGRAMMATIC SKETCH OF BLAST FURNACE ] “The limestone charged has ‘affinity’ for dirt and certain other impurities of the ore which it removes in molten form as the ‘cinder’ or ‘slag’ which is there running into the ladle. When cold, this cinder is a dark greenish-black, glassy substance, which of recent years has come to be used to a certain extent in the manufacture of Portland cement but is mainly used for filling-in purposes. Some is crushed and utilized in concrete mixtures and for road building. In Chicago considerable land has been ‘made’ by dumping slag into the lake, and South Chicago is reported as standing on a swamp which has been filled in with slag from the steel works there. [Illustration: OLD-FASHIONED PIG BED ] “This immense furnace is simply a strong steel shell lined two or three feet thick with fire bricks. At the ‘bosh,’ which is the region where the greatest heat is produced, hollow bronze plates are inserted among the bricks of the lining through which circulating cold water keeps the bricks from being fused.