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Kansas:

TABLE 45.-Summary of stripping operations that produced bituminous coal in 1923—Continued

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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," 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.

COAL-WASHING OPERATIONS

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 Rept., vol. 3, pp. 1893–1969, 1925.

1906. 1907

1908.

1909

1910.

1911.

1912.

1913.

1914.

1915.

1916.

1917.

1918.

1919.

1920.

1921.

1922.

1923.

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FIGURE 41.-Tonnage of washed coal and percentage of bituminous-coal output washed, 1906-1923

TABLE 46.-Bituminous coal washed at mines, 1906–1923

Canvass not made.

Year

Coal
washed
(net tons)

Cleaned coal (net tons)

Refuse
(net tons)

5

6

PER CENT OF TOTAL OUTPUT

3

Percent

age of cleaned coal to total output

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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.

TABLE 47.-Bituminous coal washed at mines in 1923, by States

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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

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