THE TECHNOLOGIST. [Feb. 1, 1865. 



332 TIN AND ITS USES. 



been liberated, and the mineral consequently transmitted into a metal. 

 After casting the assay into a little iron mould, and scraping the crucible, 

 the scoria or slag, composed of a decarbonised culm, is pounded and 

 washed off on a concave shovel, leaving there the fine particles of tin on 

 account of their greater specific gravity as a residue, which were not in- 

 cluded in the assay on emptying the crucible. By weighing the whole 

 the produce is ascertained, and by re-melting gently the assay, and refin- 

 ing it by separating the dross the quality is determined. 



The produce of mines vary very much, the better quality of ores 

 yielding the best results ; but from stream tin a produce of 13 to 15 per 

 20 or 65 to 75 per cent., and from mine tin of 12 to 14 per 20, or 55 to 

 65 per cent., may give a general idea of the yield. The purchase takes 

 place in the following manner : — It is understood that a reduction from 

 the produce takes place of lj in 20, or 6| per cent., as the cost for 

 smelting defrayed by the miner; but as such a charge is exorbitant, 

 although custom still allows the deduction, it is compensated for by 

 a corresponding increase or decrease in the standard, as the circum- 

 stances of the trade admit. Assuming a produce of 15 per 20, and a 

 deduction of lj for returning charges, with a standard of 110s. per 

 cwt., the following calculation will show the price payable to the 

 miner: — 15 product, less lj deduction, leaves 13 J ; and this, at 110s. 

 per cent, standard, gives 1,512s. 6d., equal to 751. 12s. 6d. per ton, or 

 from the price per ton equal to 75Z. 12s. 6d. ; and a produce of 15, less 

 1 J deduction, the standard may be found thus : — Produce 15, less 1 j, 

 equals 13| ; and 751. 12s. 6d. equals 15125 shillings, which being divided 

 by 13| gives 110s. standard. 



There is always 5 per cent, allowed on the weight, which may be 

 considered as an equivalent for waste ; and allowing 21. per ton for 

 smelting charges, the following will show the actual difference in an 

 assumed case between the cost at the smelting-house and the market of 

 sale : — 



Supposed price in London, 1 30Z. per ton, from which deduct interest 

 and discount equal to 51. ; this leaves net cash for the smelter, 125Z. The 

 gross produce being 15, free from deduction, and 751., the price per ton 

 payable to the miner, will give 100s. standard per cwt., or 1001. per ton, 

 to which add 2Z., the cost for smelting, making 102Z. : this will give a 

 difference of 23J. 



When a sufficient quantity of ore has been collected, the smelting is 

 commenced, and the system is alike in all cases : — A reverberatory fur- 

 nace is used, the general size being about 8X3 feet. This furnace will 

 smelt about lj tons in six hours, consuming as flux about one-fifth of 

 culm ; and for fuel about 1^ tons of Welsh coals. The ore and culm, 

 as flux, are mixed together, well wetted to prevent the escape of the 

 fine particles of tin until conglomerated by the heat, and as already 

 alluded to in the case of the assay, during the smelting there is great 

 ebullition, but on its ceasing, and while the white wave of flame is 



