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(132.) Admitting the experiments on specimens whose height is double the diameter, col. 1, as the more correct, the mean resistance of cast iron to crushing may be taken at 43 tons, or 96,320 lbs. per square inch, and the mean tensile strength, in col. 2, being 7.142 tons, or 16,000 lbs., the ratio becomes practically 6 to 1.

It will be observed that there is great variation in the crushing strength of cast iron, as shown by col. 1, Devon being 64.92 and Lowmoor 25.198 tons, giving a ratio of 2.57 to 1.0. The mean crushing strength being 100, the maximum = 156, and the minimum 61; the effect of re-melting is shown by col. 3 of Table 2.

With the tensile strength the variation is much less, ranging from 10.477 tons in Clyde iron to 5.667 with Lowmoor, the variation being 1.85 to 1.0: the mean tensile strength being 100, the maximum = 147, and the minimum = 79. Table 147.

(133.) “ Wrought Iron and Steel.”—It is shown in (503) that there is great difficulty in determining the ultimate or absolute crushing strength of all malleable metals such as wrought iron, which in short specimens flow or spread out laterally under the pressure rather than crush or break. Wrought iron practically fails entirely with about 12 tons per square inch, the extensions and compressions with greater strains becoming excessive, as shown by the diagram, Fig. 215. Experiments on the transverse strength (520) seem to show 24 tons as the absolute crushing strain, but with pillars of different kinds 19 tons per square inch agrees the best with the results of experiment (201), from which it appears that the resistance of wrought iron is 24 ; 19 = 1.26, or 26 per cent. greater in beams than in pillars. The wrinkling strain shows similar differences, namely, 104 ; 80 = 1.30, or 30 per cent. greater in beams than in pillars (322).

With steel, the apparent crushing strength under transverse strains seems to be 61.48 tons per square inch (507), but with steel pillars, 52 tons agrees better with experiment (268), the difference being 61:48 - 52 = 1.18, or 18 per cent.

This difference of resistance to crushing in beams and pillars is remarkable, but admits of explanation. In a short pillar every part of the cross-section is equally strained or nearly so, but in a beam the strain is a maximum at the edge of the section, and is supposed to diminish in arithmetical ratio toward the neutral axis, where it becomes nil, as shown in (494) and Fig. 164. But when a wrought-iron bar is deflected by the transverse strain, the malleable nature of the metal causes it to yield so much under the maximum pressure at the remote edge that heavier strains are thrown on the rest of the section. For example, Fig. 30 is the section below the neutral axis of a bar of any material whose maximum resistance to crushing at A = 19 tons per square inch, therefore 9} tons at B, 4 at C, &c., the mean of the whole being = 9} tons. Let Fig. 31 be a similar beam where the maximum = 24 tons, &c., the mean of the whole being 12 tons. Now let Fig. 32 be another beam whose resistance at B = 141 tons: if, therefore, the resistance is proportional to the distance from the neutral axis, it should be 29 tons at A, but if we allow that the metal there compresses excessively, as in diagram, Fig. 215, until it is reduced to 19 tons, we then have a double series of strains as in the figure, the mean of the whole being 12, as in Fig. 32. It will now be observed that Fig. 32 gives the same mean crushing strain with 19 tons maximum, as Fig. 31 gave with 24 maximum: the apparent maximum strain in Fig. 32 is 24 tons, although the real maximum 19 tons only: see (504).

In confirmation of this reasoning it should be observed that with cast iron, which maintains comparative uniformity in its compression under crushing strain, as shown by the diagram, Fig. 215, the crushing strength is the same in pillars as in beams, namely, 43 tons per square inch.

(134.) “ Timber.”—Table 32 gives Mr. Hodgkinson's experiments on the crushing strength of various kinds of timber: the results in col. 2 were a mean of about 3 experiments on cylinders 1 inch diameter and 2 inches high, with flat ends, the woods being moderately dry or in the ordinary state. Col. 1 were specimens turned to the sizes and kept drying in a warm place for two months: the lengths of these specimens were in some cases 1 inch only, being equal to the diameter, which would increase the strength a little (129).

TABLE 32.-Of the STRENGTH of TIMBER to RESIST CRUSHING

STRAINS, in Lbs." and Tons per Square Inch.

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Alder
Ash
Bay-wood
Beech
Birch, English

American
Box
Cedar
Crab-tree
Deal, red

white
Elder
Elm
Fir, Spruce
Hornbeam
Mahogany
Oak, English

Quebec

Dantzic Pine, pitch

yellow .

red Plum Poplar Sycamore Teak Larch Walnut. Willow ..

6,960 6831 6,896
9,363 8683 9,023
7,518 7518 7,518
9,363 7733

8,548
6,402 3297

4,850 11,663 8970* 10,316 9,971 7670* 8,820 5,863 5674 5,768 7,148 6499 6,824 6,586 5748 6,167 7,293 6781

7,037
9,973 7451 8,712
10,331 7950* 9,140
6,819

6499 6,659
7,289 4533 5,911
8,198
8198

8,198
10,058
6184

8,271
5,982
4231

5,106
7,731 5950*

6,840 6,790 6790

6,790 5,445 5375

5,410 7,518

5395 6,457 10,493 8241

9,367 5,124 3107 4,116 9,207* 7082 8,144 12,101 9310* | 10,706 5,568 3201 4,385 7,227 6063 6,645 6,128 2898 4,513 (1) (2) (3)

3.08 4:03 3.36 3.81 2:16 4.60 3.94 2.58 3.05 2.75 3:14 3.89 4:08 2.97 2.64 3.66 3.69 2.28 3:05 3.03 2.41 2.88 4:18 1.84 3.67 4.78 1.96 2.97 2.02 (4)

1.02 1.08 1.00 1.21 1.94 1.30 1.30 1:03 1:10 1:15 1.08 1:34 1.30 1:05 1.60 1:00 1.55 1.41 1.30 1.00 1.01 1.40 1.27 1.65 1.30 1.30 1.74 1.19 2:11 (5)

Calculated from the general ratio of the experiments in columns 1 and 2, which is 1.3 to 1.0.

The effect of the drying process on most kinds of wood is to increase the crushing strength, varying from nothing with bay, mahogany, and pitch-pine to 2:11 with willow, col. 5 : the mean increase for the 29 kinds of timber is 1.30, or 30 per cent. In several cases indicated by a * the experiments were made with the wood in one of the states only: in those cases the strength in the other state was calculated by the general ratio 1 to 1:3, &c.

TABLE 33.-Of the STRENGTH of STONE, &c., to Resist a CRUSHING

Strain in Lbs. and Tons per Square Inch.

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16,240 13,507) 14,873 6.64 2 Bramah,
14,493 10,080 12,275 5.48
11,760 10,080 10,931 4.88
11,267 9,520 10,394 4.64
10,304 9,206 9,766 4.36
8,736 6,356 7,271 3.25

8,283 3.70 Rennie.
6,356 2.84

10,911 4.87 7,661 5,645 6,653 2.97 Bramah. 8,688 5,487 7,000 3.12 3 Rennie. 4,571 3,729 4,150 1.85 2

9,160 4.10

5,713 2.55 9,900 7,773 8,825 3.94 2 Bramah. 5,040 4,189 4,614 2:06 2 2,509 2,240 2,374 1.06 2 10,326 8,960 9,632 4.30 2 10,640 7,840 9,251 4.13

3,216 1.436 Rennie.
9,681 4.322
9,220 4.116

7,433 3.318 3,925 1,085 2,185 9754 E. Clark.

501 .2237 Rennie. 13,375 10,820 12,062 5.385 4 Bramah.

6,059 2.700 Rennie.

7,713 3.443 4,344 3,145 3,744 1.671 38,825 20,775 30,047 13:41 8 Fairbairn 2,453 2,074 2,264 1.01 B. White.

1,244 55

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TABLE 33.–Of the STRENGTH of STONE, &c.—continued.

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Concrete Stone, Portland

Cement 1 part, Sand 2

parts, 270 days old Do., Portland Cement

part, Sand 3 parts, 70

days old Do., Portland Cement i

part, Shingle 10 parts, 30

days old.. Brick Cubes, in Portland

Cement, neat, 30 days

old .. Do., Portland Cement i

part, Sand 2 parts, 52

days old Do., Portland Cement i

part, Sand 3 parts, 30

days old Do., Roman Cement, neat, i

30 days old .. Do., Roman Cement 1 part,

Sand 2 parts, 52 days old)
Ordinary Mortar

Do., 14 years old
Brick, 9-in. Cubes, in Cement

pale red
red
Pavior's ..

Burnt extra
Fire,

Stourbridge

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(135.) “Stone, c.”—Table 33 gives a summary of experiments on the crushing strength of stone: those by Bramah were on cubes from 4 to 6 inches square, and were obtained by means of a 12-inch hydraulic press, with which very accurate results could hardly be expected (83); however, they are perhaps correct enough for practical purposes.

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