THE CONQUEST OF NATURE 



the top as a long roaring flame, of a red color at first 

 but gradually changing into white, and then faint 

 blue. These changes in color are indicative of the 

 changes that are taking place in the metal, and the 

 appearance of a certain shade of color indicates that 

 the conversion into steel is complete, and that it is 

 time for shutting off the blast of air. Any mistake in 

 this matter even the variation of thirty seconds' time 

 means a loss of thousands of dollars in the quality 

 of steel produced. The man whose duty it is to de- 

 termine this important point, therefore, holds an ex- 

 ceptionally delicate and responsible position, and 

 receives pay accordingly. 



In deciding the exact moment when the blast shall 

 be turned off, this workman is guided entirely by the 

 sense of sight. Mounted on a platform commanding 

 the best possible view of the mouth of the converter 

 and wearing green glass goggles of special construc- 

 tion, this man watches the change of color in the flame 

 until a certain shade is reached a shade that to the 

 ordinary untrained observer does not differ in appear- 

 ance from that of a moment before when he gives 

 the signal to shut off the blast. When this signal is 

 given the contents of the converter is no longer 

 common-place cast iron, but steel, ready to be molded 

 into rails, boilers, or a thousand and one other 

 useful things. 



The contents of the converter may now be drawn 

 off as liquid steel into molds of any desired shape and 

 size, and when cooled will be ready for shipment. 

 But in the great steel factories the metal is not ordi- 



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