TABLE 40.— Bituminous coal mined by different methods, 1922–23 18, 324, 740 1, 110, 046 60, 636 929, 390 1, 327, 564 2, 802, 511 4,876, 774 2, 581, 165 192, 490 274, 722 3, 156, 615 321, 580 1,951, 316 6,411 107, 364 58, 692 950 20. 7 2. 2 1.7 179, 841 .2 1.3 .6 7 77, 244, 239 18.3 59, 826, 544 14. 2 267, 032, 931 63. 2 10, 225, 142 2.4 7,939, 243 1.9 422, 268, 009 The percentage shot from the solid declined from 17 in 1911 to 12.5 in 1923. The influences that have brought about the change are partly humanitarian and partly economic. The heavy charges of powder weaken the roof and pillars and thus increase the danger of falls of roof and coal, the most prolific source of fatal accidents to coal miners. Another objection to this method, based upon commercial rather than humanitarian considerations, is that the heavy charges of explosives required to blow down coal that has not been undercut or sheared produce a much higher proportion of fine or small coal and make the lump coal so friable that it disintegrates in handling and in transportation. The growing use of mechanical stokers and the developments made in the use of powdered coal have robbed this objection of much of its force, but the danger to the mine and to the workers still continues, and in some States shooting from the solid is forbidden by law. The decline in the percentage mined by hand from 29.7 in 1911 to 17.6 in 1923 is due almost entirely to economic influences. Machine cutting makes possible a much greater output per man and it has tended to replace cutting by hand wherever the natural conditions permit and the differential between the wage rate for pick mining and the combined rate for cutting and loading is sufficient to cover the cost of the machine. In consequence, the proportion mined by machine rose from less than half in 1911 to two-thirds in 1923. In rate of growth the proportion mined by stripping has exceeded even that by machine cutting. In 1915, when the first statistics on the subject were collected, the strip pits produced 0.6 per cent of the total; in 1923 their contribution was 2.1 per cent, or more than three times as much. The use of stripping has been stimulated by high wage rates prevailing in the union fields and by the greater output per man per day which it makes possible. The relative proportions mined by the several methods differ greatly from State to State (Table 40). Solid shooting remains the dominant method in Kansas, Arkansas, Iowa, and Tennessee, where from 77.6 to 49.7 per cent of the product in 1923 was obtained in this way. In the southern Appalachians and Virginia it is still largely used. In the northern and middle Appalachians it is seldom reported. Operators in the fields of the interior and in the Far West, outside of Michigan, Utah, and Colorado, still employ it extensively. The States from which the smallest percentages were reported in 1923 were Ohio (1.6 per cent), Pennsylvania (2.5 per cent), and West Virginia (3.9 per cent). Mining by hand remains the dominant method in Maryland, New Mexico, Texas, and Washington, all States where either natural conditions, the age of the workings, or cheap labor make the substitution of solid shooting or machine cutting less advantageous than elsewhere. In 16 out of the 26 States shown in Table 40 more coal is now mined with cutting machines than by any other method. Michigan and Ohio lead, with 92.7 and 88.5 per cent respectively, followed by Kentucky (84.2), West Virginia (78.7), Virginia (73.5), Illinois (68.3), and Utah (68.3). Kansas, with 2.2 per cent, shows the smallest proportion mined by machine of all the important producing States. Strip mining is confined to the outcrops of flat or gently dipping beds in the interior fields or on the western edge of the northern Appalachians, where considerable areas of coal lie within a few feet of a level surface. COAL-CUTTING MACHINES The number of coal-cutting machines of all types in use in the bituminous-coal mines in 1923 was 21,229, an increase of 793 over the number in 1922. The average output per machine, which depends more on the number of days worked than on-the size of the FIGURE 40.–Bituminous coal produced by undercutting machines and strip pits, 1891–1923 machines, was 17,779 tons in 1923, about the same as in the war years and in 1920. By States the data are given in Table 41. The year 1923 set a new record in total quantity mined by cutting machines—377,435,000 tons, against 339,813,000 tons in 1920, the highest figure previously attained. The growth of machine-mined tonnage since 1891, when the statistics were first collected, is shown in Table 42 and Figure 40. In the anthracite mines of Pennsylvania the physical conditions are ill adapted to the use of cutting machines, and the quantity won by machines is small. In 1923 it was 1,079,055 gross tons (Table 43), considerably more than in 1920 and 1921, but less than in the war years. TABLE 41.-Number of coal-cutting machines in bituminous-coal mines, aretage output per machine, and per cent of total product mined by machines, 1913, 1922, and 1923 23. 3 4.8 .3 73. 2 1.7 70.0 20. O 33. 2 13.4 1, 263 377 355 395 10, 94020, 466 22, 067 9, 300 3, 809 4,767 600 3, 151 17, 686 13, 710 17, 191 81 4, 311 6, 471 14, 584 2, 458 5, 597 4, 452 1, 784 1, 928 / 11, 365 18, 678 19, 559 13 31 47 6,384 9,776 | 12, 398 130 88 80 6, 636 10, 152 13, 579 95 15, 746 28, 600 5,000 9, 258 15, 260 103 207 183 6, 511 6, 756 8, 943 6, 301 6,337 6, 481 14, 678 10, 355 17, 020 5 4, 204 11, 804 8, 904 26 4, 45312, 227 9, 726 3,936 15, 500 | 16, 214 21, 592 15, 645 | 14,689 18, 237 16, 37920, 436 21, 229 14, 801 13, 067 | 17, 779 1,681 2, 342 44. 9 4.2 7. 2 55. 3 41.3 195 208 TABLE 42.-Bituminous coal mined by undercutting machines, 1891-1923 TABLE 43.—Pennsylvania anthracite mined by undercutting machines, 1916–1923 |
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