Should the shipping weight of any entire order exceed by more than one (1) per cent the weight computed from the approved shop drawings, the amount in excess of the said one (1) per cent will not be paid for, unless in the entire order the weight of plates exceeding thirty-six (36) inches wide be greater than thirty (30) per cent of the whole, in which case the allowable variation shall be increased to two (2) per cent.

WROUGHT IRON.

All wrought iron, if any be used, must be of the best quality obtainable, tough, ductile, fibrous, and of a uniform quality; also straight, smooth, and free from cinder-pockets or injurious flaws, buckles, blisters, or cracks. No steel scrap shall be used in its manufacture.

The tensile strength, determined from test-pieces in the same manner as specified for steel, shall not fall below fifty thousand (50,000) pounds per square inch; and the elastic limit shall not be less than twenty-six thousand (26,000) pounds per square inch. The elongation, determined in the same manner as specified for steel, shall not be less than twenty (20) per cent.

All wrought iron must bend cold one hundred and eighty (180) degrees, without sign of fracture, to a curve the inner radius of which equals the thickness of the piece tested. Soft steel is to be used instead of wrought iron wherever practicable.

CAST IRON.

Except where chilled iron is specified, all castings shall be of tough, gray iron, free from injurious cold-shuts or blowholes, true to pattern, and of a workmanlike finish. Sample-pieces one (1) inch square, cast from the same heat of metal in sand-moulds, shall be capable of maintaining on a clear span of four (4) feet six (6) inches a central load of five hundred (500) pounds when tested in the rough bar. All castings shall be straight and out of wind, with proper and approved  uniform  thickness  of  metal, and shall have perfect, sharp,