TIN 



1003 



it is let down through the opening, when it is considered to be ready for calcining. 

 Beneath the oven and connected with it by an opening through which the ore when 

 sufficiently roasted is made to pass, is an arched opening about 4 feet wide, termed 

 the ' wrinkle.' Here the ore is collected, whilst another charge is being placed in 

 the furnace. About 7 cwts. or 8 cwts. of ore is the quantity usually roasted at one 

 time. Whilst undergoing this operation, dense fumes of arsenic and sulphur escape 

 with the smoke from the fire, and pass through large flues, divided into several 

 chambers (figs. 1985 to 1987) where the former is collected. The flue is often 70 

 yards long, and the greatest deposit of arsenic takes place at about 15 yards from the 

 oven or furnace. Instead of being at once completely roasted, the ' whits ' from the 

 stamps are sometimes first ' rag ' (or partially) burnt, for about six or eight hours. 

 The object of this partial burning is to save time and expense, nearly three-fourths of 

 it being thrown away after dressing it from the first burning. 



1985 



1986 



The machine called originally 'Brunton's Patent Calciner' (fig. 1988), for cal- 

 cining tin ore, is gradually coming into use in Cornwall, and is adopted in many of 

 the larger mines. Its operation may be thus briefly described : A revolving circular 

 table, usually 8 feet or 10 feet in diameter, turned by a water-wheel, receives 

 through the hopper the tin-stuff to be roasted or calcined. The frame of the table is 

 made of cast iron, with bands, or rings, of wrought iron, on which rests tho fire-bricks 

 composing the surface of the table. The flames from each of the two fireplaces pass 

 over the ore as it lies on the table, which slowly revolves at the rate of about once in 

 every quarter of an hour. In the top of the dome, over the table, are fixed three 

 cast-iron frames, called the ' spider,' from which depend numerous iron coulters, or 

 teeth, which stir up the tin-stuff, as it is carried round under them. The coulters on 

 one of the arms of the ' spider ' are fixed obliquely, so as to turn the ore downwards 

 from one to the other the last one at the circumference of the table, projecting the 

 ore (by this time fully calcined) over the edge, into one of the two ' wrinkles' 

 beneath. A simple apparatus called the ' butterfly,' moved by a handle outside tho 

 building, diverts the stream of roasted tin-stuff, as it falls from the table, either into 

 one or the other as may be required. Unlike the operation of roasting in the oven 

 previously described, the calciner requires little or no attention ; the only care requisite 

 being to see that the hopper is fully supplied, and the roasted ore removed when 

 necessary from the wrinkles. 



For this description of the burning-house and of the calciner, we are indebted to 

 Mr. James Henderson's communication to the Institution of Civil Engineers. 



We have been favoured with the following notes on the action of Brunton's calciners. 

 employed at Fabrica la Constanto, Spain, which are of great value, as are also the 

 additional suggestions. 



Diameter of revolving bed, 14 feet. 



Revolution of bod per hour from 3 to 4, or about 1 foot of the circumference per 

 minute. 



