DRESSING OF ORES 



159 



treatment of ores, Mr. King has designed a suitable retort and magnetic machine, and 

 separates blende from carbonate of iron, copper pyrites from blende, and any mixture 

 of ores in which one portion can be rendered magnetic, first getting rid of the lighter 

 gangues by water dressing. 



Calcining Ores. In Taylor's ' Kecords of Mining ' published in 1829, a description 

 and drawing of Brunton's continuous calciner is given. This apparatus has long 

 'been used at various mines in Cornwall for getting rid of arsenic, sulphur and other 

 impurities with which tin-stuff is sometimes associated. The table is about 12 feet 

 'diameter, and makes from six to eight revolutions per hour, the stuff being introduced 

 at the centre, and discharged at a point on the periphery of the table. Oxland and 

 Blocking's calciner is now adopted at several mines, and consists of a trommel 

 mounted on carrier wheels, about three feet inside diameter and 32 feet long, with a 

 fall of 1 in 16 or 1 in 24, according to the size and nature of the stuff to be treated. 

 The inside of this trommel is lined with fire-brick, the fire-place being at one end, and 

 a feed-screw at the other. The calcination is performed by the heat generated in the 

 fire-place passing through the cylinder. The cylinder makes from six to eight 

 revolutions per hour. Inside of the cylinder, for about two-thirds of its length from 

 the fire-place, are four longitudinal ledges, as in a mortar mill, for the purpose of 

 turning over the stuff. 



The time necessary for passing a charge from the entrance to the exit point in the 

 trommel varies from three to six hours. 



From the calciners the stuff is taken to various dressing machines, and sufficiently 

 concentrated for the smelting furnace. 



Other continuous calciners are in use, some for the purpose of producing sulphurous 

 vapours to form sulphuric acid, such as Grerstenhofer and Hasenclever, and which 

 doubtless admit of ready application to the treatment of tin ores. 



The machinery requisite for the enrichment of distinct classes of ore cannot well be 

 grouped within the limits of a specification. The quantity of stuff to be disposed of 

 within a given period, the value of the ore, the character of the vein-stone, the difference 

 of density between one substance and another, the price of labour, together with any 

 other direct or collateral feature, must carefully be considered. But in most cases, 

 the machines enumerated in the following list may be successfully applied for the 

 purposes stated : 



t KEDTJCING MACHINERY. 



1. Stone-breakers . . For reducing to fragments all hard and non-elastic stuff, 



for the cobbing process, crusher, stamps, and disinte- 

 grator. 



2. Crushing mill . . For reducing to grains stuff for the hand-pickers, jiggers, 



and buddies. 



3. Disintegrators . . For producing sand for jiggers or buddies. 



izers. 

 5. Stamps 



1. Kilns . 



2. Wash Trommels . 



For reducing stuff for treatment in fine sand jiggers, 

 buddies, or tables. 



WASHING APPARATUS. 



For disintegrating and freeing vein-stone, in order to 

 render it suitable for hand picking, cobbing, stone- 

 breaker and crusher, also partly for the sizing trommels 

 and jiggers. 



Ditto. 



SIZING AND CLASSIFYING APPARATUS. 



1. Trommels 



. . For sizing stuff, sometimes for hand picking, but chiefly 



for coarse and fine sand jiggers. 

 2. Single and divisional^ 



column's?' Priding L Eor classif y in g stuff for fine sand jiggers, buddies and 

 cones, and pyramidal I ^les. 

 boxes . . .J 



CONCENTRATORS. 



1. Eotatory separator 



For freeing sand from slime, and partly classifying the 

 sand for jiggers or buddies. 



