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THE POPULAR SCIENCE MONTHLY 



of the rod attached to the piston g, which rises and falls as the 

 volume of air beneath it varies in accordance with the demands 

 of the furnace or the slight irregularities of supply. The air 

 was conveyed to the furnace through a metal pipe, c, connected 

 with the wooden bottom of the wind-chest by a flanged elbow. 

 Blowing-tubs of a square cross-section with corresponding pis- 



Fig. 2. A Pair of Blowing-Tubs. 



tons have been used with success, and as late as 1873 three such 

 machines were in use in Detroit for furnishing blast to a large 

 cupola ; and, notwithstanding the primitive construction of this 

 blowing apparatus, the melting was quite as satisfactory and 

 economical as the best of the present day.* 



Having now described the various forms of apparatus for 

 blowing furnaces and forges in use at the beginning of the seven- 

 be mi ill century, we will again turn our attention to the progress 

 of the manufacture of iron in America. The first iron-works 

 built in this country that are entitled to be called successful 



* The average record of the. cupola blown by these square wooden "blowing-tubs"' was 

 eleven pounds of metal melted by one pound of fuel. Very few cupolas now in use do as 

 well, and by far the greater number are not more than half as economical. W. F. D. 



