= the bar already loaded with 7000 lbs., we have by col. 9, ⚫00000009403 × 532 x 1000 05, orth of an inch. If this bar had been loaded with a ton only, then 532 lbs. would have produced an extension of 00000007433 × 532 × 1000 = 0395, or inch; but if loaded with 7 tons, then the extension would have been 0000001662 × 532 × 1000·0884, or inch. The effect of a given tensile strain is therefore not uniform, but varies with the load which the bar bears beforehand, in the ratio of 2.236 to 1 by col. 9 with initial strains of 7 tons and ton. 1 11.3 (607.) "Compression of Cast Iron."-Mr. Hodgkinson made experiments on the compression of bars of cast iron about 1 inch square and 10 feet long, which were inclosed in a frame of cast iron, which prevented lateral flexure. They were an easy fit, and the bar was oiled and was struck occasionally in different parts with a hammer to eliminate as much as possible the effects of friction. There were four kinds of iron, being in fact the same as those whose extension under tensile strains had been previously determined (601), namely, Lowmoor No. 2, Blaenavon No. 2, Gartsherrie No. 3, and a mixture of Leeswood No. 3 and Glengarnock No. 3 in equal proportions. There were two experiments on each kind, therefore 8 experiments altogether, and the mean results are given by Table 89, the observed compressions being reduced to parts of the length for convenience of application. It will be observed that, as with the extensions so with the compressions,-they are not simply proportional to the strains, but increase in a higher ratio throughout, this result being due to defect of elasticity. Mr. Hodgkinson has given rules for the compression of cast iron under crushing strains which agree fairly with the experimental results; the following is a modification of those Rules:: (608.) C = .0123634 — {·000152853 (609.) In which We C: (·000004283 x W). Wc = (5773 × C) – (233473 × C2). C the compressive strain in tons per square inch. = the compression in parts of the length. TABLE 89.—Of the COMPRESSION of CAST IRON by CRUSHING STRAINS, being the Mean Results of Experiments Strain per Square Inch, on four kinds of Iron. By each Mean, per Ton. Mean, Per Lb., when Mean 0001744 00000007786·00000007844 12,844.000 12,749,000 0001812 00000008088 00000008477 12,363,100 11,796,500 0001827 00000008154 00000008626, 12, 263,400 11,592, 150 ⚫0001842 00000008223 00000008781, 12, 160,700 11,388,750 33,600 29,120 13 ⚫0024774 ⚫0025058 ⚫0002149 31,360 14 ⚫0027547 ⚫0027310 ⚫0002252 ⚫0029451 15 .0030118 ⚫0029765 ⚫0002455 35,840 16 ⚫0032746 ⚫0032493 ⚫0002728 ⚫0034291 ⚫0057788 ⚫0057024 ⚫0005096 17 ⚫0035760 ⚫0035574 ⚫0003081 18 ⚫0039333 ⚫0039058 ⚫0003484 ⚫0043039 ⚫0042945 ⚫0003887 ⚫0043600 ⚫0047242 ⚫0047235 ⚫0004290 ⚫0051762 ⚫0051928 ⚫0004693 ⚫0052160 0001858 00000008294 00000008941 12,057,400 11, 184, 200 00000008367 00000009117 11,951,900 10,968,050 000192800000008605 00000009818 11,621,000 10,185,115 00023670000001056·0000002001 9,463,300 4,997,220 9,058,700 4,558,178 8,641,800 4,232,010 € (5) (6) ⚫0063960 ⚫0062523 ⚫0005499 ⚫0068425 ⚫0005902 0000002722 ⚫0074730 .0006305 00029890000001334 0000002902 ⚫0081438 ⚫0006708 000313200000013980000003082 ⚫0088519 ⚫0007111 ·0003279 0000001464 0000003262 (7) ·0002718 00000012140000002542 8,240,200 3,934,400 00028510000001273 7,858,800 3,674,030 7,493,600 3,446,020 7,151,400 3,244,650 6,830,100 3,065,550 (8) (9) (10) (11) TABLE 89.—Of the COMPRESSION of CAST IRON by CRUSHING STRAINS, &c.-continued. ⚫0112300 ⚫0008320 ⚫0121023 ⚫0008723 ⚫0130149 ⚫0009126 ⚫0139678 ⚫0009529 ⚫0149610 ⚫0009932 ⚫0159945 ⚫0010335 Per Lb., when 00047410000002117 0000004882 0000001964 0000004522 000457000000020400000004702 ⚫0096063 ⚫0007514 ⚫0103980 ⚫0007915 0003743 00000016710000003802 (2) (3) ⚫0170683 ⚫0010738 .0181824 ⚫0011141 0004914 00000021940000005062 ⚫0193368 ⚫0011544 0005089 00000022720000005242 ⚫0205315 ⚫0011947 0005264 00000023500000005422 4,724,500 2,048,320 4,558,200 1,975,495 4,401,200 1,907,670 4,254,900 1,844,350 (5) (6) (7) (8) (9) (10) (11) ⚫0243574 ⚫0013156 Thus, to find the compression by 12 tons, we have first ·000004283 × 12 = 000051396; then (·000152853 Again, to find the strain due to a compression of ⚫00187422 in a bar whose length ⚫000003513, then = 1.0; we have first 001874222 = 5733 × 00187422 = 10.82 233473 000003513 = .82 10.00 tons compressive strain. The col. 5 in Table 89 has been calculated by this rule up to 13 tons, beyond which the experimental results, as plotted in a diagram, seem to show that the rule gives the compressions too small. In the experiments the maximum strain was 51,480 lbs., or nearly 23 tons per square inch; continuing the curve by judgment, we have obtained the compressions up to 42 tons per square inch, which is nearly the mean ultimate crushing strain for British Cast iron, as determined by numerous experiments on 23 different kinds of iron; see Table 31 and (132). Beyond the experimental strain of 23 tons, therefore, the compressions given are of doubtful accuracy. (610.) In order to determine the compressions with heavier strains up to the crushing load, Mr. Hodgkinson made another series of experiments on short cylinders of various kinds of cast iron inch diameter, and 11⁄2 inch high, except one specimen, which was 1 inch diameter and 2 inches high, the results of which are given by Table 90. For comparison we have given in the first line the mean compressions of long bars in a guideframe, as found by the former experiments, and given in Table 89. (611.) It will be observed that the experiments on short cylinders gave very anomalous results, exceeding greatly those obtained from the long bars. Confining ourselves to 20 tons per square inch, which is well within the limits of the observed Y |