However, during the melting down of the charge the steel scrap becomes molten and its constituents merge with those of the other iron materials charged. We get out of the cupola, then, a mixture which, disregarding the losses and gains due to the air of the blast, the fuel, etc., is an average of the materials charged. We, therefore, no longer have any steel, but a cast iron which has a somewhat lower silicon, phosphorus and carbon than the softer cast irons. The greater strength of the alloy is due to its composition and only indirectly to the fact that steel was used in its production. The physical properties of the steel charged have been entirely obliterated in the melting process. [Illustration: SPLIT PATTERN OF WOOD, SURFACE-COATED WITH SHELLAC VARNISH ] This view that semi-steel only indirectly gets its increase in strength from the steel charged is confirmed by its structural appearance under the microscope, as was shown in numbers 74 and 92d which were given on page 79, and the photomicrographs given here, and by its extreme brittleness under hammer blows. Under such shock it is but little more resistant than cast iron. [Illustration: CORE THAT MAKES HOLE IN CASTING ] This weakness under “shock” was shown by tests from which the table which follows was compiled. Bars one inch square and thirteen inches long laid on supports exactly twelve inches apart, were struck at the center by a twenty-five pound weight. It took seven blows to break the cast iron bar, the semi-steel bar required eleven, while cast steel withstood ninety-two blows. Even this does not adequately express the great resistance of the cast steel (another alloy not yet discussed), for the height of the “drop” was being increased one inch with every blow, and the cast steel bar, on account of its bending, had to be regularly turned. The total foot-pounds exerted by the blows are given in the table which follows: [Illustration: DRAG, OR BOTTOM HALF OF MOLD, AFTER PATTERN IS WITHDRAWN ] [Illustration: DRAG WITH CORE IN PLACE AND COPE, OR TOP HALF OF MOLD READY TO CLOSE ] [Illustration: TRANSPARENT MOLD, SHOWING RELATIVE POSITIONS OF CORE, CASTING, SPRUE, ETC. ] ══════════════════════╤════════╤══════╤══════ Alloy │Tensile │Number│Total │Strength│ of │ Foot │ │Blows │Pounds ──────────────────────┼────────┼──────┼────── Cast Iron │ 23,400│ 7│ 102 Semi-Steel │ 35,050│ 11│ 206 Malleable Cast Iron[8]│ 37,140│ 22│ 1,580 Cast Steel[8] │ 72,120│ 92│10,112 ──────────────────────┴────────┴──────┴────── Footnote 8: On account of bending, the malleable iron and the steel bars had to be turned several times.