Fail by crushing with length under.......................... 5 diameters Principally by crushing from........................... 5 to 15 " Partly by crushing, partly by bending, from - - - 15 to 25 " Altogether by bending above.............................. - - 25 "
 Cast iron of average quality is crushed with - - 49 tons per square inch. Wrought iron of average quality is crushed with 16 " " " Wrought iron is permanently injured with - - - 12 " " " Oak wrought is crushed with........................ 4 " " " Deal wrought is crushed with ------- 2 " " "

The comparative strength of different columns, of different lengths, will be seen very clearly from the following table derived from experiments by Mr. Hodgkinson:-

 Wrought Iron Bars. Proportion of Length to Thickness. Gave way with Square. Length. ins. ft. ins. 1 X 1 7½ 7½ to 1 21.7 tons per sq. inch " 1 3 15 to 1 15.4 " " 2 6 30 to 1 11.3 " " 5 0 60 to 1 7.5 " " 7 6 90 to 1 4.3 " ½ x½ 5 0 120 to 1 2.5 " "" 7 6 180 to 1 1. "

To find the strength of any wrought iron column with square ends.

Area of column sq. inches X tons per inch corresponding to proportion of length, as per table above = Breaking weight, tons.

If the ends are rounded, divide the final result by 3 to find the breaking weight.

In columns of oblong section, the narrowest side must always be taken in calculating the proportion of height to width.

To find the strength of round columns exceeding 25 diameters in length. Mr. Hodgkinson's rule.

(Diameter, ins.)3.6 / (Length, tt.)1.7 X Tabular No. = Breaking weight, tons.

 Square Ends. Rounded or Moveable Ends. Wrought Iron..... 77 26 Cast Iron....... 44 15 Dantzic oak................. 4.5 1 7 Red deal.................. 33 1.2

A column should not be loaded with more than 1-3 of the breaking weight in any case, and as a general rule, not with more than 1-4; for purposes o machinery not with more than 1-6 to 1-10, according to circumstances.

Tables of Powers/or the Diameters and Lengths of Columns.

 Diameter. 3.6 Power. Diameter. 3.6 Power. 1 in. 1. 7 in. 1102.4 ¼ 2.23 ¼ 1251. ½ 4.3 ½ 1413.3 ¾ 75 ¾ 1590.3 2 121 8 1782.9 ¼ 18.5 ¼ 1991.7 ½ 27. ½ 2217.7 ¾ 3816 ¾ 2461.7 3 52 2 9 2724.4 ¼ 69.63 ¼ 3006.85 ½ 90.9 ½ 3309.8 ¾ 116.55 ¾ 3634.3 4 147. 10 398107 ¼ 182.9 ¼ 4354.2 ½ 224.68 ½ 4745.5 ¾ 272.96 ¾ 5165. 5 328.3 11 5640.7 ¼ 391.36 ¼ 6083-4 ½ 462.71 ½ 6584.8 ¾ 543.1 ¾ 7114.4 6 632.91 12 7674.5 ¼ 733.41 1/2½ 8 44.28 ¾ 967.15
 Length. 1.7 Power. 1 1. 2 3 25 3 6.47 4 10.556 5 15.426 6 21.031 7 27:332 8 34.297 9 41.9 10 50119 11 58.934 12 68.829 13 78.289 14 88.8 15 9985 16 111.43 17 123.53 I8 136.13 19 149.24 20 162.84 21 176.92 22 191.48 23 206.51 24 222