DADD. — To dash out a small fire of gas, or a small accumulation of gas with a jacket.

DAM. — (See Frame Dam.)

DANT. — Soft sooty coal found at backs, and at the leaders of hitches and troubles.

DARG. — A fixed quantity of coal to be worked for a certain price. This word is seldom used in the Newcastle collieries, but is the general term in use about Scremerston. It is equivalent to the hewing or score price of the Newcastle collieries.

DASHING-AIR. — Mixing air and gas together, until by being completely incorporated the mixture ceases to be inflammable. This is done by giving the air after its first union with the firedamp a considerable length of run or course. The quantity of air must be ample for sufficient dilution.

DAVY-LAMP. — A safety-lamp invented by Sir Humphrey Davy in 1815. It consists of an oil cistern of copper, brass, or other material, containing the wick and oil, and covered by a tight-fitting and close topped cylinder of wire-gauze containing 784 apertures to the square inch, within which firedamp may explode and burn, but without communicating flame to the gas outside of the cylinder. The cylinder should not exceed 1½ inch in diameter and may be 8 inches in height. (Sir Humphrey Davy on the Safetylamp and on flame, &c.) The only case in which the Davy lamp is stated to be unsafe, is when exposed to a rapid current of explosive atmosphere, from which it may be up to a certain point protected by a shield.

The first safety lamp was invented by Dr. William Reid Clanny, of Sunderland, in May, 1813, in which the flame of the lamp was insulated, and supplied with air by means of a small pair of bellows. This lamp was first tried in the Harrington Mill Pit, November 20th, 1815. Safety lamps were also contrived by Mr. Brandling, of Newcastle, and Dr. J. Murray, of Edinburgh, but being dependent upon a regular arrangement of the position of gases in the order of their specific gravities, they were not of any practical utility. At about the same time with Sir Humphrey Davy, Mr. George Stephenson, then an engineer at Killingworth Colliery, invented a safety lamp, of which the principle is essentially the same as the Davy. The application was slightly different, the flame of the lamp being surrounded by a cylinder of glass (since surrounded by one of wiregauze) and the air admitted into the lamp by means of apertures in the ring at the bottom of the cylinder, the burnt air passing through a perforated copper cap covering the top of the glass. The principle upon which both lamps depend, viz., the impassibility of flame through small tubes, was probably discovered simultaneously by both Sir Humphrey Davy and Mr. Stephenson, but the application of wire-gauze must belong exclusively to the former.

Other lamps have also been contrived, viz., Messrs. Upton and Roberts', Martin's, Mueseler's, Clanny's, &c. ; but as the whole of these are to be referred for their safety to the use of small tubes, or wire-gauze, they are, though in some cases possessing great merit, nothing more than modifications of Davy's or Stephenson's lamp (1849).

Many improvements in safety lamps have been made in recent years, greatly increasing their security under difficult and dangerous conditions. It has been found that whereas at a velocity of current of 6 feet per second, the Davy exploded the surrounding gas ; that at 7 feet, 12 feet and 17 feet, the Clanny, Stephenson, and Mueseler lamps as referred to above, did the same. Lamps of modern construction will not explode until they are exposed to a current of from 30 to 40 feet per second. The fullest information on this subject is given in the Report of the Royal Commission on Mines, issued 15th March, 1886.

DAY-HOLE. — An adit or level, driven in at the side of a hill, for the purpose of working the minerals lying within it. Also called a Day-drift, or a Grove; or a drift driven down in the seam from the out-crop.

DAY-SHIFT. — When a pit is worked both night and day it is said to be worked double-shift, the set of men employed during the day being called the day-shift, and that employed at night, the night-shift.

DEAD. — Unventilated

DECK. — The platform of a cage upon which the tubs stand when being drawn up or lowered down the pit.

DELIVERY-DRIFT. — Water pumped up a shaft is not usually lifted higher than is necessary ; it is delivered into a drift or adit driven from low ground into the shaft. This is called a delivery or off-take drift.

DEPUTIES. — A set of men employed in setting timber for the safety of the workmen; also in putting in brattice and brattice stoppings. They also draw the props in the workings from places where they are no longer required for further use. Their wages were about 20s. per week in 1849, at present from 25s. to 30s. There cannot be any fixed rule for the number of deputies to be employed in a pit, this depending altogether upon the nature of the roof and consequent quantity of timber required to be set for its support, also upon the greater or less quantity of firedamp produced by the coal. Upon an average the number of deputies may be stated at 1 for every 7 or 8 scores of 6 tons each.

DIAGONAL-STAPLE. — A staple sunk diagonally in the line of the back end of the main beam of a pumping engine and a point in the pumping shaft from 10 to 20 fathoms from the surface. Its use is to divide the work of a double-acting engine between the two ends of the beam, by means of a lever beam in the shaft, placed in a hole or chamber made for the purpose, at the bottom of the diagonal staple. The spears working the low set or sets are hung from the lever end, and are also connected by the diagonal spears passing through the diagonal staple from the same point to the inner end of the beam. The upper sets are attached to the outer end of the beam. The result of this arrangement is that when the inner end of the beam ascends it draws up the diagonal spear, lever or V-bob (as it is called), and low set of spears, the outer end of the beam and high set of spears descending, and vice-versa. (See V-bob.)

DILLY. — An inclined plane underground, worked by a balance weight placed upon a tram upon a separate tramway, heavy enough to draw up an empty tub, but lighter than, and drawn up by, a full tub. It is controlled by a brake, so that the ascending empty tub can be stopped and exchanged for a full one at any p]ace upon the plane where required.

DIP. — Declivity of the strata or coal seams; to the dip, below the level.

DIPPER. — A hitch which throws down the coal in front of the drift approaching it. The same hitch approached from the opposite direction would be called a riser.

DIRT. — A term to express foulness or fire damp.

DOGS. — (See Keps.)

DOOR. — Doors are used underground, where unless a passage were required from time to time, stoppings would be necessary. They are usually placed in pairs sufficiently distant to allow the set of tubs to stand or pass through them without both doors being open at once. Several different descriptions of doors are employed, of which are the following

Frame Doors. — A frame door is set in a proper frame made for the purpose. It only opens in one direction, viz. against the current of air, and should always be hung so as to fall to, should anyone passing through it neglect to draw it close. Frame doors are always placed in rolleyways. They should be 6 feet in height and 5 feet in width. The stanchions or frames should be built up with bricks. Frame doors, placed in the barrow way, should be similarly set, and of sufficient size to allow of the passage of the tubs. The trapper is provided with a place to sit or stand in on the windward side of the door, which he pulls open by means of a cord when required. Man doors, which are placed for convenience of communication between different currents of air, are small frame doors which need not be more than 20 inches square, and are secured by screw locks, the keys to which should only be in the possession of the underviewer, overman, or master-wasteman.

Fly or Swing Doors. — These are set in proper frames, and are so constructed as to open both ways, but so, also, as always to fall close when left alone, with sufficient weight to resist the pressure of the air. They are usually protected by a spring on each side to prevent them from being damaged by the tubs when pushed through them. By having a piece of upright board, 8 or 10 inches broad, nailed on the face of the falling stanchion, and by having a piece of brattice-cloth nailed along the bottom, these doors can be made very effective and are very suitable in the workings, but not in the rolley-ways. Hanging sheets made of bratticecloth are often substituted for fly-doors.

A Bearing-in or Main Door is a door which forces the air through an entire district. This should be a frame door and doubled. A Sheth Door is placed in a going headway's course, where otherwise a sheth stopping would be necessary. (See Coursing.) This may be either a frame or a fly-door as thought proper.

DOUBLE WORKING. — Two hewers working together in a board or wall. An addition of 2d. per yard to the yard price, or 3d. or 4d. per score to the score price in wide boards is frequently made for the inconvenience supposed to be attached to this manner of working. (1849.)

DOWELL. — An iron bolt, sometimes used in putting main brattice together, a portion of the bolt being let into the tinder-plank, the remainder passing into a hole in the upper. (See Brattice.)

DOWNCAST. — The shaft or drift from the surface by which the fresh air passes into the workings. Also a hitch or slip which casts down the seam below the level at which time hitch is found; it is also called a down-throw or dip hitch.

DOWN-THROW. — (See Downcast.)

DRAG. — A piece of iron or wood put between the spokes of a tub or waggon-wheel to check its progress where the dip of the way is considerable. When applied to waggons at bank it is always of wood, and of much larger dimensions. Also the resistance which the air meets with in its passage through the workings.

DRAW. — To remove props which are no longer required in the whole by means of a maul, and in the broken by a pout or punch. (See Maul, and Pout or Punch.)

DREDGE SUMP. — A reservoir through which a current of water is made to flow before passing to a pump, in order that any small stones or sludge may be retained by settlement, so as not to fill up or obstruct the water passage into the pump, or wear away the clack or bucket, or gag the same by sticking between the falls and the shell.

DRIFT. — In coal, an exploring place. Usually a pair of companion drifts are driven simultaneously for ventilation, one being called the fore and the other the back drift. Drifts in stone (called stone drifts) are mostly single. They are driven sometimes for the purpose of exploration, but more frequently because rendered necessary by the occurrence of dislocations in the strata. Stone drifts are often driven for the purpose of cutting other seams of coal, or the same seam at a different level.

DRILL. — A rod of iron, with a chisel end, used in boring a hole in coal or stone in which powder or other explosive is to be placed for blasting. The hammer used in drilling a hole is called a drilling hammer.

DRIVER. — A boy employed in driving the horses on the main roads underground. He is usually 14 or 15 years of age, and his wages are from 13d. to 15d. per day of 12 hours (1849). At present they are from 14d. to 18d. per day of 8 hours.

DROP. — (See Staith.)

DROP-STAPLE. — An interior pit, sunk upwards, by which coals from an upper seam, or from the same seam thrown up by a hitch, are lowered in a cage, lifting the cage with an empty tub as it descends. The drum or sheave is governed by a brake.

DRY-SPEARS. — (See Spears.)

DUFF. — Small coals, from which, by means of the apparatus, the nuts have been separated. (See Apparatus.)

DUMB-DRIFT. — "A drift by which the return air is carried into the upcast shaft without passing over the furnace." (Nicholson.)

DYKE. — A fissure in the strata, filled with basalt and detritus from other rocks; sometimes accompanied by a dislocation. Large slips, or hitches, are also called dykes, as the Ninety-fathom dyke, the Tantobie dyke, &c.