WASHING COAL 1093 



The classifier is formed of a kind of oblong rectangular chest, made of iron 

 plates, in the inside of which are placed stages of perforated plates, the apertures in 

 which decrease in a downward direction. Sufficient space is allowed between each 

 plate for the motion of the materials. At the bottom of the perforated plates are 

 disposed inclined planes for throwing on one side the product of the sifting, which 

 escapes through a slope made on the side of the sifter. A bottom fixed to the 

 classifier itself, and like it moveable, receives the dust in the finest numbers, if the 

 sifting has been effected in the dry way, or else this bottom is immoveable and fixed 

 to longerons which support the classifier, if the sifting take place in water, as we are 

 about to point out. 



The classifier is suspended by two or three pairs of articulated handles turning 

 on axles fixed to longerbns : by that means it enjoys an extreme freedom of motion 

 in a longitudinal direction. A rapid reciprocating motion is communicated by a 

 ' bielle,' which receives the action of a bent axle firmly established on a foundation 

 fixed on the principal wall of the chamber of the machine. The motion of rotation 

 is communicated to the axle by the disposition of an iron pinion d'angle working 

 into a. 



The bac is formed of a rectangular chest in cast iron, i/, one part of the bottom of 

 which is inclined at 45, the other lower parts remaining horizontal. 



Opposite one of the lesser sides of the rectangle is placed a cylinder o, opening 

 into the oblong chest at about half its height. The chest i/ is prolonged under the 

 cylinder, in order to increase the stability of the system and the capacity of the 

 drain-well (puisard). 



A cast-iron box, M M', is firmly fixed in the interior of the bac, on flanges of cast 

 iron with vertical faces. This box has a slight inclination from M towards M'. It is 

 covered with a perforated plate, usually of copper, fastened to the frame by a number 

 of iron pins or bolts easy of replacement. The size of the holes varies according to 

 that of the matters brought into the bac. 



A cast-iron door, N, traverses, opening outward, is fixed at a slight height above the 

 frame, serving as a kind of partition dividing the materials in the bac, and against it 

 a fiood-gate N', by means of which the opening beneath the cast-iron door may be 

 closed at pleasure. 



A counter flood-gate, N', is placed at the lower extremity of the frame ; in raising it 

 a barrier is formed of variable height, by means of which the substances between the 

 flood-gate and counter flood-gate may be arrested. 



A piston, c, receives from the machine a sufficiently rapid reciprocating motion. 



Everything being thus arranged, if the bac is supposed to be filled with water to 

 the level of the front face at N', and that the substances to be washed fill the space in 

 the bac between this level and the perforated plate of the frame, the piston working 

 upwards and downwards will press the water in the body of the cylinder, and will 

 force it by its incompressibility to pass through the holes in the perforated plate ; it 

 will establish above this plate an ascending current, which, if of sufficient power, will 

 raise the substances submerged. 



The resistance to the rise of each body will be in proportion to its specific gravity, 

 and the height it will be carried will follow an inverse law, supposing the fragments 

 to be of nearly equal sizes. 



The slates which fall over the counter flood-gate fall into a pocket or reservoir, N, 

 whence they are discharged on opening a flood-gate, K'. Pressed by the upper column 

 of water, they slide with a slight admixture of water on the inclined plane. K' N', 

 which can be pierced with holes ; the water escapes, and the slate only falls directly 

 into the waggon of discharge. 



The bent axle of transmission, s s, moves in a groove turning on a pivot at its ex- 

 tremity. The rotation of the axle communicates an oscillating motion to it. 



The deposit formed in the drain-well is emptied through an opening of the flood- 

 gate placed at the lower part. An opening serving as a man-hole is reserved for 

 effecting internal repairs without the necessity of raising the frame. 



All coal contains a portion of earthy matters or impurities which, in the form of 

 bands or scales, are generally in some degree apparent to the eye, and constitute the 

 ashes and clinker left by combustion. The small coal which is sent out of mines 

 necessarily contains a still larger proportion, frequently exceeding 10 per cent., con- 

 sisting chiefly of shale and iron pyrites derived from the roof or floor of the seam of 

 coal, or from the bands of impurities interstratified with it. Generally these impurities 

 are so incorporated with the mass of the coal that it must be crushed in order suffi- 

 ciently to detach them. The pyrites, which contain nearly the whole of the sulphur 

 found in coal-seams, is well known to be very injurious either in a heating or smelting 

 furnace, in the manufacture or working of iron, in gas-making, in coking, and other 

 processes. 



