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MECHANICAL LOADING UNDERGROUND
The application of the power shovel to strip mining and that of the undercutting machine to the work of the underground miner are milestones in the gradual substitution of machine for hand labor in the mines. The year 1923 witnessed the first widespread attention to another machine, which promises even greater results—the underground loader. The report of the United States Coal Commission on underground management in bituminous-coal mines,17 issued in September, 1923, brought into public notice the development of machines to replace the laborious and solitary task of shoveling coal by hand into the mine cars.
An inquiry by the Geological Survey, the results of which are probably not complete, showed that up to the end of 1923 a total of 105 machines were in use in 52 mines and that the quantity loaded by machine in 1923 was at least 2,000,000 tons. Arrangements are being made to collect regular statistics of machine loading hereafter. In the meantime the curve showing the rate of introduction of the undercutting machine (fig. 40) is of interest because it throws some light on the rate at which the loader can be introduced.
The practice of washing bituminous coal has not increased in recent years. The quantity of washed coal obtained in 1923 was 20,140,000 tons (Tables 46 and 47). Though larger than in 1920 or 1921 this was much below the record of 25,483,000 tons, established in 1917.
The statistical record of coal washed begins in 1906. From 2.7 per cent of the total output in that year the washed coal rose to a maximum of 4.8 per cent in 1914, and remained at about that level until 1917; since then it has declined (fig. 41).
Washing is carried on extensively in but few districts. In Alabama it is the dominant method of preparation, and 60.1 per cent of the output of that State in 1923 was washed coal. In Georgia, Washington, and Michigan also washing is frequently applied to the product, but in all other States the proportion washed is small. In point of quantity washed, Alabama easily held first place in 1923, with 12,285,000 tons; Pennsylvania, with 2,497,000 tons, was second; and Illinois, with 1,521,000 tons, was third.
The proportion of cleaned coal to material washed in 1923 was 90 per cent, the refuse being 10 per cent.
17 U.S. Coal Commission Ropt., vol. 3, pp. 1893–1969, 1925.
FIGURE 41.-Tonnage of washed coal and percentage of bituminous-coal output washed, 1906–1923
TABLE 46.—Bituminous coal washed at mines, 1906-1923
• The returns for 1911 were apparently incomplete, but the error can not now be corrected. As published, they showed 12,355,716 tons washed and 10,830,823 tons of cleaned coal, equivalent to 2.7 per cent of the total output.
Canvass not made.
Table 47.—Bituminous coal washed at mines in 1923, by States
CLASSES OF MINES, BY OUTPUT In discussing the number of mines distinction must be made between commercial mines and the small workings known as "wagon mines," "snowbirds,” and “country banks.” The line
“ between the commercial mine and the small working, however, is difficult to draw. Mere size of output is not a criterion, for some wagon mines ship rather large quantities of coal. Absence of a railroad switch is not a criterion, for this would exclude from the commercial class some large mines that ship by river or truck or that deliver their product to associated industries at the mouth of the mine.
In practice the Geological Survey has found a safer criterion to be size in conjunction with steady operation. All mines that produce 10,000 tons or more a year are classed by the Survey as "commercial mines,” but the commercial class also includes much smaller mines, some of which have an annual output of 1,000 tons or less but produce year after year and show a fairly continuous existence.
Workings still smaller or less continuous in operation have been classed by the Survey as “small mines.” The term is not satisfactory, however, because it is not sufficiently definite, and in the
present report these workings are generally called “wagon mines," the term that in common usage most nearly describes them. A mine may be shifted from the list of commercial mines to the list of wagon mines or vice versa, as the course of the work at the mine may make such a shift advisable.
For convenience in studying production by size of mines, the Survey divides the mines into five classes. Class 1 includes mines that produce each year more than 200,000 tons; class 2, those that produce less than 200,000 and more than 100,000 tons; class 3, those that produce less than 100,000 and more than 50,000 tons; class 4, those that produce less than 50,000 and more than 10,000 tons; and
class 5, those that produce less than 10,000 tons. As this classification is made according to performance, not according to capacity, the number of mines in a given class is not constant from year
to year. In 1918, for example, 821 mines were listed in class 1; in 1919, 550; in 1920, 701; in 1921, 482; in 1922, 416; and in 1923, 748. These fluctuations do not indicate a corresponding change from year to year in the number of mines having the acreage and the development that would enable them to produce annually 200,000 tons or more, but they do indicate that in a given year only the number of mines listed in class 1 were able to produce more than 200,000 tons.
MINES IN 1923
The number of mines active in each producing class varies with the condition of the coal market. A year of very high prices calls into operation thousands of small producers. Thus in 1920 the Geological Survey obtained information concerning 14,766 mines, of which
5,845 were wagon mines and country banks. In the depression of 1921 most of these small workings were closed. With the high prices that followed the strike of 1922, thousands of them reopened, and the total number of mines of all sizes of which the Survey could obtain records in that year was 14,150. By the end of 1922, however, the spot price was rapidly declining and the small operations were already beginning to close. Thus although the spot price stood at $4.38 in January, 1923, it soon fell to a level so low that many commercial mines found it difficult to operate, and by midsummer wagon-mine coal had again disappeared from the market. The lower prices of 1923 are revealed by the total number of mines recorded as in operation–11,715, as against 14,150 in 1922.
How these 11,715 mines were distributed among the five size classes recognized by the Geological Survey is shown in Table 49. Illinois continued to lead in the proportion of total output mined by class 1 operations. In that State 134 mines produced more than 200,000 tons in 1923; and they constituted 21.4 per cent of the total number of mines and contributed 74.8 per cent of the entire output of the State. West Virginia and Pennsylvania, though producing more coal, have relatively fewer mines of the largest size. In West Virginia class 1 mines constituted 6.8 per cent of the State total and produced 34.5 per cent of the output. The conditions of the Appalachian region, where in many places the beds now worked crop out above the water level and are readily accessible by slope and drift, favor small-scale development, whereas on the plains of the Middle West the necessity of sinking shafts puts a premium upon larger operations. Other States in which class 1 mines contributed the major portion of the output were Indiana, Montana, Pennsylvania, Utah, and Virginia. The average production of class 1 mines throughout the United States was 355,440 tons in 1923.
The immense number of small mines has given rise to an exaggerated idea of their importance as suppliers of coal. In comparison with most other years 1923 was favorable to their operation, yet as will be seen from Figure 42, although mines of class 5 constituted about 52 per cent of the total number, they produced but 2 or 3 per cent of the total output. In other words, even if all the 6,114 mines in class 5 were closed or permanently abandoned the potential output of the country would be reduced by less than 3 per cent. Moreover, if all mines of class 4 (producing from 10,000 to 50,000 tons) should also be abandoned, only 15 per cent of the 1923 output would be withdrawn from the market. The closing of every operation in class 4 and class 5, though leaving only 24 per cent of the number of mines active in 1923, would leave 85 per cent of the production and presumably at least 85 per cent of the potential capacity of the country. It is therefore clear that elimination of the wagon mines would have practically no effect on the potential capacity and that the closing of even all mines producing less than 50,000 tons annually would fail to provide full-time operation for those remaining.
FIGURE 42-Relative numbers and production of large and small bituminous-coal mines. Although the class 1 mines, with an individual output of 200,000 tons or over, constituted only 6.4 per cent of the total number,
they produced 47.1 per cent of the total output in 1923. The very large number of small mines-52 per cent of the total number-furnished only 3 per cent of the output