Models of Blast Furnaces 7 



makes the iron stronger, less brittle, and more diffi- 

 cult to melt. When practically all the carbon is re- 

 moved the product is wrought iron or mild steel 

 according to the method of refining employed. When 

 the refined product contains certain definite amounts 

 of carbon it is tool steel or other high grade steel. 

 The output of a blast furnace is large. Some furnaces 

 have yielded over 900 tons of iron per day. The fur- 

 nace represented by the model yields 300 tons daily. 



Earlier Types of Furnace 



Two models in the left half of the case represent 

 two obsolete types of iron smelting furnaces. One 

 was in use one hundred and fifty years ago, the other 

 sixty years ago and even later. They illustrate the 

 immense advance in the art of iron smelting during 

 the past two hundred years and call attention to the 

 relatively recent introduction of the modern furnace 

 with its large capacity and moderate cost of operation. 

 Before the time of the Catalian forge, the earliest of 

 those shown, more primitive devices were employed 

 and the progress from this forge to the modern furnace 

 was marked by a number of furnace types other than 

 those represented by these models. 



II. THE COLD BLAST IRON SMELTING 



FURNACE 



The central model of the three represents a cold 

 blast iron smelting furnace modelled on the same scale 

 as the hot blast furnace to the right. It is called a cold 

 blast furnace because the blast of air which keeps it in 

 operation is not heated. This furnace was the im- 

 mediate predecessor of the hot blast furnace of today 

 which has completely superseded it. It was in general 

 use in this country at the time of the civil war and for 



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