Table 26.—Analysis of coal from Dunmore No. 1 bed

Figure 23.—Map Of No. 2 slope section of No. 1 Dunmore hed, at Northwest colliery. Temple Coal Co. Hatched areas are second mined

Mining methods.—A slope was driven down the pitch from the surface, and at intervals of approximately 600 to 700 feet gangways were turned to the right and to the left and were driven on the contour of the coal to permit drainage. A pillar about 100 feet wide was left to protect the gangway, and the room necks were turned up the pitch on 50-foot centers. These necks were connected by thinness of the coal made it necessary to take up rock in the roadways in the rooms.

When three rooms have been connected, an undercutting machine makes a cut across the face of the three, a distance of 150 feet. The coal is shot down by a miner and is loaded into the mine cars by laborers. As soon as a working place has progressed a short distance the three adjoining rooms are started, making another longwall face that is connected to the first but is approximately 50 feet behind it. As soon as a new face has progressed a short distance a third 150-foot face is started, making a total longwall face of 450 feet in steps. This is shown fairly well on road 16 off 2 slope in Figure 23. When three of these places have been started, a pillar is left about 100 feet thick and another set of longwall faces is begun, which is likewise shown in Figure 23.

When the room necks have been connected, the face cut by the undercutters, and the coal loaded out, the rock that is taken up from the bottom of the roadways and the refuse in the coal is hand packed into the space between the roadways, making a solid, rock-packed pillar. Enough space is always left between the ends of this rockpacked pillar to permit the undercutters to make their cuts. As the work progresses up the pitch some coal is left along one of the roadways to give further support to the roof.

These longwall faces are advanced until they meet the gangways above them. While the roadways are being cleaned up, the small pillars of coal that were left to protect the roof are recovered. Thus the recovery of coal in the territory approximates 100 per cent.

All the work is done on one shift. The mining machine undercuts one of the 150-foot faces each day. A miner then drills holes approximately every 8 feet, loads and fires them, and sets whatever timber may be necessary. After the coal is shot down a laborer for each roadway loads the 2-ton mine cars. As there are three roadways for 150 feet the laborer must carry the coal a maximum distance of 25 feet before loading it into the cars. Because of this extra handling and the necessary separation and gobbing of the refuse, a laborer can load an average of only two of the 2-ton mine cars in a day. If a laborer has time to clean up his place before the next undercut is made, he very often assists the miner in placing props and in drilling. In addition to the laborers, machine runners, and miners there is a section boss who has charge of a longwall face. This man is supposed to be an all-round workman and assists the machine runners and miners when necessary.

Operating data.—Laborers can load out the coal in about three days after a round has been fired, and machine runners take the same of moving the mining machine under its own power from place to place, the company finds it is a little more convenient to load the machine on a special car built for the purpose. After the machine has cut a longwall face it loads itself on this car and is hauled by a mule to the adjoining longwall face. Time is thus saved under the conditions that exist in this colliery.

The greatest dead expense involved in this piece of mining is the taking up of the bottom rock, which is estimated to cost more than $1.25 per ton of coal produced. In order that all of the men will not be taking up bottom in the roadways at the same time the work is so planned that not more than 2 out of 10 places will be on rock work on each day. This means that the production of coal will be regular.

For each 150-foot longwall face there are 10 laborers to load coal and rock, one miner, a machine runner and his helper, and one boss. These men will ordinarily produce about 16 cars of coal a day. All of the work is done by company men, and no contract is let.

EXPERIMENTAL LONGWALL MINING

Bed mined.—For some time a certain company has been experimenting with longwall mining at one of its collieries in the Western Middle field in order to determine, if possible, a feasible method for its other mines. The experiments were performed in the No. 8 slope section, 1 east gangway, of the No. 5 bed. The coal, which is very hard, has the following analysis:

At the point of sampling, the cover is about 80 feet thick; it is a hard sandstone that seems to have a decided parting 9 feet above the top of the coal. The floor of the bed is soft sandstone, and the bed itself is 20 to 36 inches thick; 4 to 6 inches of this is a clod which comes down when the coal is shot.

Mining methods.—This company attempted to work a 200-foot longwall face, and undercut the coal with a low-vein machine, which made a 5i/£>-foot cut. To support the roof, props were stood on 6-foot centers (both ways), and cogs were placed parallel to the face (six coal to the gangway, the bottom of which was taken up to give clearance for the mine cars. Work progressed for about 100 to 125 feet. (See fig. 24) There was considerable settling during the 125-foot advance, but little, if any, break until the 125-foot advance was made. This break occurred after some warning. Too heavy timbering was thought to be the reason for the loss of the face.

After this attempt the company started another longwall face, mining in the same way as before, but instead of cogs and props to

Fiodrb 24.-Map showing two experimental long- second time. The company

Operating data.—In the course of this work the machines undercut the coal during one shift, the coal was loaded out a second shift, and the timbering was done on a third shift. By this method approximately 10 to 12 cars of coal (capacity of car, 120 cubic feet) were obtained. The small output is also due to faults in the vein and to the lack of experience of the men who were accustomed to work on the pitch. Some trouble was caused by necessary pop-hole drilling and blasting of bottom coal frozen to the bottom and left there by the

support the roof it used three rows of 6-inch-diameter props, 8, 16, and 24 feet from the face and 6 feet apart. When an undercut was made and a new row of props placed, the last row of props was shot and the roof allowed to fall. Two rows of cogs were placed along the main gangway, and one row of cogs along the upper gangway to provide an escape way. The roof broke when the props were shot, but again, instead of breaking to the surface, the roof only broke for 9 feet and fell as before. When the longwall face had progressed 100 feet the main roof broke to the face, causing loss of the face for the

One miner and a helper were employed. Two men to load the scraper at the face, a machine runner and his helper, two hoisting engineers, a timber gang of three laborers, and four additional laborers were employed, a total of 15 men; production was therefore less than one car a day for each man.

Two hoisting engineers were necessary, as one was used on the timber shift to run the hoist when timber was taken up the working place.

SCRAPER MINING

One form of mechanical mining has been developed in the anthracite region—scraper mining. It originated at the mines of the Lehigh Valley Coal Co., but has reached its highest development at the mines of the Hudson Coal Co. and the Raven Run Coal Co.

A description of a number of methods that have been worked out and the results that have been obtained appear below.

The use of scrapers in longwall faces has been mentioned in the preceding section, under " Experimental longwall mining." Although this type of mining was not successful at the colliery described, the method of using the scrapers is the same as that for mines where longwall mining was successfid.

The best results with scrapers have been obtained at the mines of the Hudson Coal Co.

SCRAPER MINING ON MEDIUM PITCHES

In the anthracite region the mechanical handling of coal underground is becoming more and more important from year to year, and the different conditions under which mechanical appliances are used have considerable interest to an engineer when he is considering introducing the appliances in his mine.

Scraper mining will be discussed in this bulletin from several angles, and in the brief description that follows it will be considered for use on pitches that may be too heavy to allow use of a mine car, yet too light for the coal to run on the floor itself or on sheet iron. , Scraper mining will also be discussed in relation to the angle of the room face and in connection with longwall mining.

The Colonial Collieries Co., at its Madeira colliery, Parsons, Pa., is using scrapers on pitches of 5 to 15° in beds where the coal is 24 to 36 inches thick.

Bed mined.—The work the writer examined or inspected was in the B bed, which is the top split of the Bottom Red Ash bed and has a cover at this point of between 250 and 300 feet. The map (fig. 25) shows that the rooms are driven on 50-foot centers and are 30 feet