DRESSING OF ORES 



121 



partraents e, corresponding in number with the degrees of fineness into which it is 

 desired to classify the ores. The vessel having been filled with water, the ore is 

 caused to fall regularly through a spout into the body of water rotating with the ves- 

 sel a b, round the axis c. In order to carry the water round with the vessel a b, a 

 blade is fitted between the two cylinders a and 6, which, if put in a suitable position 

 does not interfere with the sorting. 



The particles of ore having the greatest specific gravity will fall most rapidly 

 through the water, and will consequently pass out at the bottom of the vessel a b, at 

 a point nearest the stationary spout t, whilst the particles next in specific gravity will 

 fall in the next compartment, and so on. The particles of ore to be classified accord- 

 ing to their specific gravity must be as nearly as possible the same size, whilst any 

 material in a granular state, and of the same specific gravity in all its particles, will 

 be classed according to size. The action of the apparatus continues till the compart- 

 ments e are full of ore. When full, the weighted levers r, are lifted up, and the ore 

 allowed to escape with the water. In places where water is plentiful, the apparatus 

 may be made to work continuously by giving to the opening t, such a size that no 

 more water can escape with the ore than is continually supplied. The compart- 

 ments e, may in this case be much smaller. Where water is scarce the quantity re- 

 quired may be reduced considerably by fixing a bottom to the inner cylinder a, and 

 leaving this cylinder empty. The drum will thereby get a tendency to float, which 

 may be overcome as far as necessary by putting ballast in it. By these means a 

 quantity of water equal to the cubic contents of this cylinder will be saved ; at the 

 same time, by giving greater dimensions to the compartments e, the water will be made 

 to do duty a longer time. The number of revolutions of the drum will be found in 

 most cases to range between the limits of two to six per minute ; the diameter of the 

 drum from about four feet and upwards ; the size of the ore grains, or particles, from 

 one thirty-second to half an inch. The power required is extremely small, and one 

 man can attend to a greater number of these machines. 



Edwards and Beacher's Mineral and Coal Washing Machine, consists of two rect- 

 angular cisterns. Within a few inches of the top of these, perforated plates or 

 screens, E fig. 702, are fixed, upon which the material to be washed is fed through 



a hopper, which also connects the two cisterns. On the inner sides of the cisterns 

 are two apertures closed by flexible discs, or diaphragms of leather, c, which, when 

 the machines are filled with water, cause it to rise and fall through a certain space, 

 by means of a horizontal vibratory motion, which they receive from an excentric 

 on a shaft, which is driven either by a steam-engine attached directly to it, or by a 

 driving belt and pulley, A. See WASHING COAL. 



The action of the flexible diaphragms is similar to that of cylinders and pistons, 

 which are sometimes substituted for them. Above the driving shaft is a smaller one, 

 B, which is driven at a slower rate by means of spur-wheels, and gives, by cranks 

 or exeentrics, a horizontal motion backwards and forwards to sets of scrapers F, above 

 the cisterns. These are so arranged as to remove the upper stratum of the substance 

 being acted upon, and discharge it into waggons or other convenient receptacles ; 



