This is a subject that can only be decided by each engineer in reference to the special conditions and requirements at each colliery, after careful inquiry into the differences in first cost, fuel, repairs, attendance, the duty performed, and the money value of the advantages gained by the abolition of steam underground.

This applies equally well to the proposed plan of running pumps by power transmitted from the surface by means of wire ropes.

The accompanying table from the Report of the Inspectors of Mines for 1876, compiled by Mr. T. D. Jones, shows the performance of 25 rod pumps and 72 steam pumps in the Lehigh district. While it apparently contains some erroneous figures, it is nevertheless valuable in showing the large amount of water pumped in this district, and the large reserve pumping capacity provided.

CHAPTER XIX.

Ventilation and Ventilators.

It is beyond the province of this report to enter upon a discussion of the principles and theories upon which all ventilating systems are dependent. The current mining-engineering literature of the day is filled with articles treating not only of the principles but also of the details of mine ventilation, and several pamphlets and books-mostly English, but that are for sale by booksellers in this countrylately published, thoroughly and clearly define these laws;

"Friction of Air in Mines," by J. J. Atkinson, published by Van Nostrand, "Coal, Mine Gases, and Ventilation,' by J. W. Thomas, London, Mr. Hermon's "Prize Essays on the Prevention of Accidents in Mines," London, 1874, are standard reference works.

The correspondents' column of the Shenandoah Mining Herald furnishes a medium through which the miners and mine bosses of anthracite collieries are constantly interchanging their opinions and recording their experience,—a large number of the communications bear directly upon this subject, and contain information valuable to every miner. The chief objection to open columns in which all communications are published, is that many are unable to separate the chaff from the grain, and frequently accept the opinions of others as demonstrated facts.

In the Wyoming district, especially in the neighborhood of Wilkes-Barre, the best means of securing proper ventilation is the most important mining problem to be solved. Great trouble is also experienced in dealing with explosive mine gases in the deeper portions of the Schuylkill basin.

In the Wilkes-Barre district, workings on the lowest level are sometimes opened with two airways and a gangway, each driven twelve feet wide by six or eight feet high, to (307 AC.)

drain off the gas, and it is often necessary to let the gangway and airways stand for several months before workings can be opened out.

When two airways are driven, the gangway is located between them, with eight or ten yard pillars between, and the intake air is divided into two splits, one passing through the new workings and the other out through the airway next the solid.

Throughout this district the airways are usually from seventy to over one hundred feet of cross-sectional area.

In the Lehigh region they are frequently made just large enough to satisfy the requirements (20 and 25 sq. ft.) of the Mines Ventilation Act.

The plan usually pursued in opening new workings is to drive an airway and gangway together, with a pillar of six to twelve yards between. When the bed is thick and dips steeply, the airway is driven in the coal over the gangway, and the airway coal is then loaded in cars standing on the gangway. Cross-headings are holed through between the two passages at intervals of ten to twenty yards.

The working face of the gangway and the airway are ventilated either by means of a brattice or brattice cloth hung near the cross-heading to throw the air-current into the face, or by means of a small blower (fan) and wooden air pipes (See Figs. 55 and 56.)

Cross-headings.-These are generally driven as small as possible; three to five feet wide and four to six feet high are the common limits. As they are for temporary use only, and must be closed by doors, brattice, or masonry stopping, they are made only large enough to pass the required amount of air.

Doors.-Wooden doors, so hung (on a post, or in a frame sill) that they are self-closing, are in use throughout the anthracite region. The space around the door-sill is planked or boarded up, or closed with masonry to prevent leakage, and a piece of brattice cloth or some similar material is often tacked to the bottom of the door to lessen the leakage. They are hung to open against the air-current.

The number of doors necessary depends principally upon the method by which the breasts are ventilated.

All of the main doors are opened and closed by a doortender ("trapper boys") whose sole duty is to open the door for the passage of a trip of cars, and to see that it is promptly closed after the passage of the cars.

At some collieries the number of doors is very large, and several devices have been invented to either open and shut the door automatically, or to enable the driver of the trip to open and close it by means of ropes, levers, etc. None of these have been adopted in the anthracite region. The law requires a door-tender for every main door, and also provides that the doors shall be so hung that they will be self-closing, therefore these appliances could not be legally used, but there are other objections that would effectually exclude them from nearly all anthracite collieries, viz: 1. The door may not open promptly and the mules and cars may suffer; 2. The door may be closed by the driver before the cars have all passed through; 3. A lump of coal on the roadway may keep the door from closing, or prevent it from being opened; 4. The automatic devices are complicated, expensive, and apt to get out of order or to get clogged up with coal and dirt.

Stoppings.-Masonry is generally used for stoppings in fiery mines, but temporary stoppings, and stoppings in nongaseous mines, are often built of boards or plank. In flat workings in thick seams massive masonry walls are often necessary to close up old workings. These walls are built of slate and rock picked out of the gob, and are not infrequently from four to six feet thick at the base.

Stoppings closing airways of ordinary size are made from one to three feet thick.

Many engineers believe that all stoppings should be made very heavy in order to resist the shock from an explosion of gas and confine the effects of the explosion to the district or split in which the accident occurs: others hold that this practice only confines the gas so that the effect of the explosion is concentrated on the passageways (airways, etc.) remaining open, and that the damage done and the danger

to life are greatly decreased when the stoppings blow out, as these new openings act as vents or safty valves, and may allow the force of an explosion, which if confined would do great damage, to distribute itself almost harmlessly throughout the mine.

Brattices.-The customary method of building brattices is shown by Page Plate No. 9. A series of posts are placed along the gangway or passage, and a board partition built, care being taken to cut the top boards to fit inequalities in the roof; waste is thrown against the bottom board to close any openings caused by irregularities in the floor.

It is impossible to make an ordinary brattice even approximately air-tight. Long brattices always leak a large quantity of air. Better results can be obtained by using grooved-and-tongued lumber, than with ordinary boards.

Fig. 51 shows the method of ventilating new workings opened by tunnel on the Wharton bed at Hazleton. The air is carried in through an airway bratticed off on one side of