Elongation, 27.0 per cent, in 8 inches. Crossways, Ultimate strength, 28.8 tons per square inch. Elongation, 24.0 per cent, in 8 inches.

18. Chemical Analysis Of A Sample Representing ⅝" Thick Mild Steel Plate

Tensile tests of the above sample -

Lengthways, 28.9 tons per square inch. Elongation, 26.0 per cent, in 8 inches. Crossways, 28.6 tons per square inch. Elongation, 28.0 per cent, in 8 inches.

19. Chemical Analysis Of A Sample Representing 6½" X ⅞" Flats, Used In The Manufacture Of Links For Hauling Chains

Results of tensile tests of the above sample (Analysis No. 19) -

Breaking strain. Elongation in 8 inches.

Tons per square inch. Per cent.

32.2 26.0

This specimen is from the same class of material represented in Tests Nos. 8 to 23 inclusive (Table No. 17), under the heading of "Steel for Special Purposes." It represents a class of steel slightly higher in ultimate tensile strength, and having a slightly lower percentage of elongation than the bulk of the material represented in the tables. The processes through which the steel went in the manufacture of the finished link (shown in Figs. 410, 422) proved the excellence of the material.

20. Chemical Analysis Of A Sample Representing 3" X 3" X ⅜" Mild Steel Angles

Tensile tests of the above sample -

Ultimate strength, 28.3 tons per square inch.

Elongation, 25.0 per cent, in 8 inches. Bending tests satisfactory.

21. Chemical Analysis Of A Sample Representing 3½" X 3½" X ⅜" Mild Steel Angles

Tensile tests of the above sample -

Ultimate strength, 29.8 tons per square inch.

Elongation, 27.0 per cent, in 8 inches. Bending tests satisfactory.

22. Chemical Analysis Of A Sample Representing ½" Mild Steel Plate

Tensile tests of the above sample -

Lengthways, 27.2 tons per square inch

Crossways, 27.8 tons per square inch.

Elongation, Lengthways, 2.70 per cent, in 8 inches. Crossways, 25.0 per cent, in 8 inches. Bending tests satisfactory.

For comparison with the foregoing mechanical tests and chemical analyses of mild steel, the following table of the results of mechanical tests on wrought-iron bars, rectangular and round, is appended. The material here indicated represents good present-day practice in the manufacture of wrought iron, and is of as high a quality as could be readily obtained under ordinary commercial conditions. As the manufacture of wrought-iron plates is no longer of the importance that once belonged to it, no comparison between the old and the modern material need in this respect be instituted.

Table No. 18. Results Of Physical Tests On Wrought-Iron Bars, Rectangular And Round

se mechanical tests are described by tests Nos. 28 to 36 inclusive (Table No. 18) is of interest, when compared with the analThe following chemical analysis of a mixture of the samples whoyses of mild steel given above.

Chemical Analysis Of A Sample Representing Wrought-Iron Round Bars ¾ Inch To 1½ Inch Diameter

The results of the tensile tests are given in the Table No. 18, tests Nos. 28 to 36 inclusive, the mean ultimate tensile strength being 24.6 tons per square inch, and the mean ultimate elongation 20.1 per cent, in 8 inches, ranging from 13 to 28 per cent.

The student will observe in the above analysis the low percentage of carbon and manganese, the high percentage of phosphorus, and last, but not least, the presence of slag to the extent of nearly 1 per cent.; the material is, however, of good quality.

The foregoing remarks on the mechanical tests and chemical analyses required for the determination of the quality and strength of structural mild steel could hardly be considered complete, even in the elementary form in which they have been presented, without a reference to that important branch of laboratory investigation, the microscopic examination of the structure of metals. More than a reference to this subject is not, however, within the scope of these notes, the subject demanding the discussion of refinements of methods and of results which are beyond the more rough-and-ready determinations of commercial tests and analyses.

The results to be obtained from microscopic investigation give ample promise of high scientific value in the future, in the determination of the general equations subsisting between the mechanical qualities, chemical constituents, and microscopic structure of the specimens examined, but for the everyday requirements of the designer of structural steel-work, this method has not yet superseded the more ordinary process of mechanical testing and chemical analysis above referred to, especially when the comparatively small area of surface of section examined under even moderately high powers is taken into consideration, while the amount of material to be accepted or rejected is measured in tons.