years ago, in this connection, was with an overhead structure (with the coke-oven charging larry tracks beneath) of rectangular section. Into this box, the coal was sluiced with the wash-water, the water filtering off through the coal-mass by means of suitable conduits made in the bottom and sides. He found that the coal was packed so hard and fast that it could not be got down through any kind of gate or door in the bottom, and he had to arrange the bin so as to have a bottom which was completely removable in small sections, plank by plank, in order that the stored coal could be removed. He had subsequently modified his plans, so that the storage and filtration is in pits in the ground, the reloading being done by clam-shell buckets operated from gantries. This system works very well, and has overcome the difficulty referred to.

He would like to ask what percentage of moisture Mr. Scott found in the drained coal, and how far this could be reduced by longer drainage. In his experience, the moisture was reduced to about 6 per cent in 72 hours. After that time, it remained practically the same, apparently being held by capillarity, and even stirring up or handling did not reduce this moisture to any appreciable amount, except so far as exposure to the air might dry the coal.

The beauty of this system, apart from points of economy, was in the perfect recovery of the sludge. This was disseminated (as it should be) entirely throughout the washed coal-mass, and formed a uniform product for coking. By any other system, this sludge was recovered by itself; the oven or ovens which received it must be treated somewhat differently, and the resulting coke-product would be of a quality unlike the usual product.

Furthermore, a plant washing small coal, suitable for mechanical stoker-use for steam-raising, had the advantage of receiving the sludge along with the rest of the marketable product; but, if recovered separately, it would have to be remixed by a separate operation or thrown away, as by itself it is of no value for steamraising, being too finely divided to permit of its being fired by hand or machinery.

Mr. WILLIAM SCOTT (Leeds) wrote that he first turned his attention to the necessity of recovering the finer portions of coal, which hitherto had been lost in the settlings, in 1895. Then a

brick hopper, 20 feet high and 15 feet square, was erected, having a bottom lined with maltkiln-tiles, which answered admirably so far as drainage was concerned. Three hoppers accommodated the quantity of coal treated, one hopper being charged, one draining, and from the other coal was drawn. He had experienced the trouble complained of by Mr. Claghorn, but the greater part of the coal could be withdrawn by pottering with a long iron rod through the sliding-door at the bottom of the hopper. The Craig system seemed to him to be immeasurably superior to the hoppersystem, as the tank, being circular in form, the process of unloading the hopper is done mechanically by a series of revolving knives taking out a core, about 2 feet in diameter, after which a revolving circular vertical scraper is gradually worked downward and at the same time sweeps the remainder of the contents of the hopper into this central space, whence eventually it falls through the door at the bottom into the coke-oven tub. He agreed with Mr. Claghorn's remarks as to the period of drainage, and he had found that after a certain time no further reductions of moisture occurred. He did not think that it would be desirable to reduce the amount of moisture remaining in the washed coal below 6 per cent.; otherwise owing to the lightness of the product, there would be a loss in exposed positions such as the top of a cokeoven, where it might be scattered from the top of the tub; and there would be greater waste in charging the oven from the tub, where there is often a drop of 4 or 5 feet due to varying gradients of the tram-road.

THE MINING INSTITUTE OF SCOTLAND.

ANNUAL EXCURSION,

HELD AT DOUGLAS COLLIERY, AUGUST 16TH, 1902.

The members were received by Mr. Robert Russell, managing director of the Coltness Iron Company, Limited, Mr. Douglas Jackson, his assistant, and the officials of Douglas colliery, and shewn over the works.

DOUGLAS COLLIERY.

BY DOUGLAS JACKSON.

Douglas colliery is situated in the parish of Douglas and county of Lanark, and about 8 miles from the town of Lanark, on the Muirkirk branch of the Caledonian railway.

Two pits are sunk, 75 feet apart, and there is a day-level mine at Howgill, which cross-cuts the highly-inclined strata to the same coal-seams to which the pits are sunk. The Lord Dunglass pit, 16 feet by 10 feet within the barring, is used for winding and pumping. The Lady Mary pit, 13 feet by 10 feet, is also used for winding and is the upcast shaft for the ventilation of the colliery. The pits are sunk to a depth of 786 feet, and pass through the following seams of the Lower Coal-measures:

See also "The Douglas Coal-field, Lanarkshire," by Mr. Robert Weir,

Trans. Inst. M.E., 1899, vol. xvi., page 436.

The combined thickness of the coal-seams, at the pits, is 37 feet 2 inches, but most of them increase gradually in thickness towards the outcrop, where their combined thickness is 55 feet.

The seams are being worked forward to the boundary by the stoop-and-room method. The rooms are driven 10 feet wide, the stoops are 200 feet square, and the latter will be worked by the longwall method, backwards from the boundary. The workings to the rise have a gradient of 1 in 4, and the loaded hutches are run down by self-acting inclines to the levels, and are drawn by ponies to the pit-bottom.

Howgill Day-mine.-A small area of the coal-field, severed from the pits by the "great dyke," a large downthrow fault to the south-east of about 300 feet, is worked by the Howgill daymine on the stoop-and-room method, the stoops being formed 35 feet long on the level course, by 20 feet to the rise, and the rooms are driven 10 feet wide. The seams are inclined at an angle varying from 40 to 60 degrees from the horizontal. The loaded hutches are lowered to the levels on carriages worked by the backbalance system, and afterwards drawn by ponies in rakes of 20 at a time along the day-level mine a distance of 2,100 feet, the declination outwards being 1 in 144. The hutches are then hauled to the Lord Dunglass and Lady Mary pits, a distance of about 4,600 feet on a tramway having gradients varying from level to 1 in 6, by means of an endless haulage-rope, worked on the bogie system, three hutches being attached to each bogie. The signalling for the haulage is done by a combined telephone arrangement, and can be operated from both ends. The ventilation of the Howgill workings is produced by a high-speed forcingfan, 4 feet in diameter, driven by an electromotor running at 700 revolutions per minute, giving a total quantity of 12,000 cubic feet of air per minute.

Winding-engines, etc.-The winding-engines, at both pits, are of the same dimensions, each consisting of two horizontal cylinders of the trunk type, 20 inches in diameter by 43 feet stroke, with drums, 12 feet in diameter by 3 feet wide. Both windingengines are fitted with Frew equilibrated slide-valves, suitable for a steam-pressure of 120 pounds per square inch, and with Bertram visors for the prevention of over-winding.

The pithead-frames are of pitchpine, and the pulleys are 12 feet in diameter. The cages, made of steel, are single-decked for two steel hutches placed end to end, and carry about 11 cwts. of coal each.

Ventilation. The ventilation of 80,000 cubic feet of air per minute, at inch of water-gauge, is produced by a Waddle fan, 25 feet in diameter, running at 54 revolutions per minute. It is driven by a horizontal engine with a single cylinder, 20 inches in diameter by 30 inches stroke, and has a large margin of power for increasing the ventilation when necessary. No firedamp has been known to exist in the locality, and open lights are used in all the workings.

Pumping Plant.-The compound horizontal differential Hathorn-Davey pumping-engine, placed at the surface, was erected in 1897. The cylinders are respectively 38 inches and 66 inches in diameter, by 10 feet stroke. The exhaust-steam from the engine is conveyed down the shaft to an ejector-condenser, at a depth of 90 feet, where the pump discharges its water into a day-level driven from the Douglas water, and a vacuum is produced of 13 pounds per square inch. The pumps are actuated by a pair of 15 feet bell-cranks, built of steel, attached direct to the engine; and each works a pair of single-acting ram-pumps in two lifts. The top-lift pumps, 20 inches in diameter by 10 feet stroke, are placed in the shaft at a depth of 384 feet from the surface. The rising-main is 19 inches in diameter. The pump-rods are made of pitchpine, 16 inches square, in 40 feet lengths, strapped together by four wrought-iron plates, each 22 feet long, 12 inches wide and 1 inch thick. The lower-lift pumps, 12 inches in diameter by 10 feet stroke, are placed at the pit-bottom, and discharge their water through a column of pipes, 11 inches in diameter, into the 384 feet level. The pump-rods, made of pitchpine, 12 inches square, and strapped together by four wrought-iron plates, are connected to the 16 inches pumprods by forged-iron crossheads: the rods being thus made to balance each other. The pumping-engine generally works about 16 hours per day, at an average rate of speed of 4 strokes per minute, and discharges about 1,200 gallons of water per minute; but it is capable of working at 6 strokes, and would