the "points" by which the miner is usually influenced in selecting a drill, viz: The cost, weight, bulk, the facility with which it may be set and a hole started, efficiency of the clamping device, wearing quality of the bits, power required to run it, the facility with which it may be used in different positions, and the wearing qualities of the machine as a whole. The efficiency of the machine, in other words, the speed of boring, depends principally upon the quality and tempering of the bit and the shape in which the cutting edges are dressed, and not upon any peculiarity in the design of the machine.

For tough slate and rock work, drills in which the power is geared (1 to 3, to 6) are successful where other drills are useless, but in drills of this class the power applied may often produce too great a tortional strain on the auger, and the advantages of having the power increased by gearing is handicapped by the necessity of limiting the power applied, to the strength of the auger.

*

The method of lengthening the auger by inserting a segment between the bit and the feed screw is clearly shown by the illustrations. As these machines are designed to replace the method of drilling by hand, but not to effect any change in the method of locating, changing, or firing the holes, the bits are made to bore a hole of about the same size as by the ordinary method.

Powder.

Black Powder has been shown by long experience to give the best results in anthracite mining, both in its efficiency as compared with other explosives, and especially in producing a minimum quantity of fine coal.

Higher explosives of the dynamite family, which produce no flame, are not infrequently used in gaseous workings, and also in driving gangways and air-courses when the coal is very hard or gaseous.

* I have used this term "auger" because it properly describes this part of the tool; and as the "drilling" is performed by a rotary motion and moreover by a true auger, the process is properly described as a boring and not a drilling operation. For this reason I have referred to these machines as boring tools.

I am not aware that any comparative experiments have been made to determine the excess of fine coal produced by explosives of this class, and as such experiments would furnish results holding good only for coal of the same physical character, thickness, and hardness, lying at the same angle of dip, no general conclusions of value could be deduced from them. It has already been abundantly demonstrated by experience that the loss from the percentage of fine coal produced by the higher explosives is so large that it more than counterbalances the saving from increased efficiency.

We therefore find the use of explosives of this class restricted to sinking or driving, and to mining in workings where, from the presence of gas, the use of explosives proproducing a flame is extremely dangerous.

The details of charging and firing the shots are similar in almost every respect to the practice in other mining and quarrying districts. The charge is made up in the form of a paper cartridge, slightly smaller than the diameter of the hole, the hole is cleaned with the scraper, the cartridge is inserted, the blasting needle inserted, the hole is tamped, the needle withdrawn, the fuse (squib) adjusted and the shot fired.

Before firing a shot, the miners or laborers working in close proximity to the working in which the blast is located, are (or should be) warned by the miner, so that they may retreat to a place of safety.

From the Inspectors of Mines reports, it appears that over 15,000,000 pounds of powder were required to mine 27,000,000 tons of coal, or more than 600,000 kegs of 25 lbs. each, or about 7,000 tons,-an average of about 91 ounces of powder for each ton of coal. The amount actually used varies from three or four ounces or less to one pound per ton.

Proper deductions must be made for coal mined by the men without powder, and for powder used in driving tunnels, gangways, and airways, in sinking slopes and other rock work.

In addition to the coal actually blown down, a considerable quantity is often left so shattered by the shot that it

may be loosened and pulled down with a pick, crowbar, or or drill.

Picks are also used in cleaning the coal for loading, to split off layers of slate or bony coal which are found adhering to the larger lumps.

The common straight pick, one of the many forms of which is shown by Fig. 42, used for under-cutting in bituminous mines, also has many friends in the anthracite regions. Curved picks are also used, and are much preferred by some miners.

AC.

Fig. 42.

AC.

Fig. 43.

In cleaning the coal in the mine, generally on the breaker platform, picks with a single-curved point and a hammerhead, are often used. Picks of this type may be considered as a combined pick and sledge, and must be classed with combination tools, towards which few good mechanics are favorably disposed; but in work of this class this tool is very serviceable.

CHAPTER XI.

Underground Railways and Slopes.

It is sometimes assumed that the construction of a mine railway is similar in every respect to that of a road located on the surface, and, therefore, that a mine road may be constructed and kept in as good condition as a surface railway, but it can easily be shown that this view is entirely untenable.

As the grade of the road is necessarily governed by that of the gangway, it is not always possible to adopt the grade best adapted for haulage of both loaded and empty cars; but as the gangway grade is commonly just sufficient for free drainage, the fall of the mine roads is nearly always with the direction taken by the loaded cars.

This fall averages from four to six inches per one hundred feet; the grade most likely to give the best haulage results, is from seven to ten inches per one hundred feet, or nearly double the grade commonly adopted.

As the haulage cost is small as compared to other items, this difference is so slight that it may be entirely ignored, and the gangway grades necessitated by drainage requirements may be considered to represent also a grade that may be properly adopted on all main-haulage roads.

The rough uneven floor of the gangway is the surface on which the sills are laid, and the top line of sills resting on knolls or ridges in the floor, determines the level of the road. The sills lying in depressions are blocked up to the proper level by placing beneath them a few pieces of slate, but it is not uncommon to see such sills suspended by the rails.

(179 AC.)

It is evident that a road built in this way, with the sills resting partly on rock or coal, and partly on loose slate, cannot be kept in good condition. Such a road-bed has none of the characteristics of a surface road in which the sills rest on earth, or rock ballast, which gradually yields until the sills have settled to a firm, uniform bearing.

The shocks to which the road is subjected from the cars, and the thrusts from the mules' hoofs (to which the sills act like cleats on a steamboat gangway plank) keep the track in a very uneven condition, so that there are few roads with either good alignment or even grade, and the shifting, unstable character of such roads inevitably leads to bad joints and irregular curves.

In addition to these, several other conditions unfavorable to the maintainance of good roads exist in greater or less degree at all colleries, the principal one being the rapid decay of the sills.

Broken slate or other mine refuse is used for ballast to fill in between the sills, and the whole track soon fills up with small fragments of coal and dirt; but as this is of a loose, shifting nature, and is constantly shaken up by the mules, it is of little service as ballast, and hardly deserves the name.

Branch gangways (in flat workings) are sometimes turned off at a very sharp curvature to the main haulage road, and the same may be said of branches running into underground tunnels, but as a rule the curves on main haulage roads are not excessively sharp.

Guage.

The same variance of opinion found among mine superintendents and engineers in every other mining district of the civilized world in regard to the best guage for haulage roads, exists to-day in the Anthracite coal fields.

It is generally admitted that a guage of more than four feet cannot be economically adopted, and that guages less than two feet and six inches are inadmissible. The guages most commonly in use are two feet six inches, two feet nine inches, three feet, three feet six inches, three feet nine