| v = (5/2)l for a 7½-lined crater. |
12. There are other good reasons for believing that Lebrun’s value for the vertical radius is too small; but as its use leads to increasing the charges designed to produce crushing effects, the error, if it exists, is in the right direction, and justifies the use of the formula until more exact data are available.
EXPLOSIVES.
13. No military mining operations of note have been carried on since the introduction of dynamite and other high explosives; consequently our knowledge of their value for work of this kind rests entirely upon the results obtained from experimental mines. Unfortunately but few experiments seem to have been made, and the published results of these are very meagre.
14. Two mines fired at Krems in 1873 with L. L. R. of 12 ft. in earth weighing 100 lbs. per cubic foot and charged, one with 173 lbs. gunpowder, the other with 58 lbs. dynamite (kind not stated), gave crater radii, respectively, of 12.75 and 10.25 feet. Lebrun’s formulas applied to these give to gunpowder and dynamite the ratio 1 : 1.688.
Two powder-mines and one dynamite-mine, each of 12 ft. L. L. R., were fired at Willet’s Point in 1878. The powder-mines were each charged with 200 lbs. cannon-powder and the dynamite mine with 82 lbs. dynamite No. 1.
No. 1 powder-mine gave a crater radius of 15½ ft.
No. 2 powder-mine gave a crater radius of 15¼ ft., or a mean of 15⅜ ft.
The dynamite-mine gave a crater radius of 14½ ft.
The relative values of cannon powder and dynamite resulting from the application of the same formulas to these mines is 1 : 1.997.[11]