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 pistons
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 seventeenth 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.