to bend or buckle up under the load, showing that stiffness is an important element in the condition of strength.
Specimens were also tested measuring 4″ × 4″ (Table CXXVII.), but the results obtained were scarcely so satisfactory as before, in consequence of the sudden falling off in strength in the 21-inch piece; still there is, perhaps, sufficient to indicate that the maximum of strength would be in a length of about 20″, in which case the proportion of base to length would still be as 16:20 or 4: 5.
Table CXXVIII. shows the result of some vertical tests on pieces 6″ × 6″ and even larger, but the lengths are not in the same proportion to the scantlings given in former tables, there not being any means at my disposal for holding pieces of greater length than 30 inches. Whether the result would have been the same if this had been possible, cannot therefore be determined by the experiments herein referred to.
| Number of the specimen. |
Deflections. | Total weight required to break each piece. |
Specific gravity. |
Weight reduced to specific gravity 600. |
Weight required to break 1 square inch. | ||
| With the apparatus weighing 390 lbs. |
After the weight was removed. |
At the crisis of breaking. | |||||
| Inches. | Inch. | Inches. | lbs. | lbs. | |||
| 1 | 2.25 | .10 | 5.15 | 845 | 534 | 949 | 211.25 |
| 2 | 2.00 | .05 | 4.50 | 700 | 478 | 878 | 175.00 |
| 3 | 1.25 | .10 | 4.65 | 970 | 673 | 866 | 242.50 |
| 4 | 1.25 | .05 | 5.25 | 856 | 512 | 1003 | 214.00 |
| 5 | 1.75 | .10 | 6.15 | 944 | 639 | 886 | 236.00 |
| 6 | 1.25 | .10 | 5.15 | 945 | 656 | 864 | 236.25 |
| Total | 9.75 | .40 | 30.85 | 5,260 | 3492 | 5446 | 1315.00 |
| Average | 1.625 | .066 | 5.142 | 876.66 | 582 | 908 | 219.16 |
Nos. 1, 2, and 3 broke with a scarph-like fracture, 10 inches in length; 4 and 5 a little longer and more splintery: 6 about 15 inches, and also splintery.
