45^ Mr, John Taylor on the Smelting of [June, 



valuable metal, it is of course treated with every precaution to 

 guard against waste. 



. Some metallic substances will be found, however, which, from 

 their specific gravity approaching nearly to that of tin ore, or 

 rather exceeding it, cannot be removed by any process of wash- 

 ing ; these are mostly decomposable by a red heat, which the 

 oxide of tin will bear without alteration. Therefore, after as 

 ijmch has been done as possible to render the ores clean on the 

 dressing-floors, they are taken to the burning-house, which is 

 furnished with small reverberatory furnaces, on the floor of which 

 the ores are spread and submitted to the action of a moderate, 

 atid regular fire : they are frequently turned over by an iron rake 

 to expose fresh surfaces, and a considerable volatilization o^ sul- 

 phur and arsenic takes place ; the former seems principally to be 

 consumed, and the latter is condensed by long horizontal flues 

 constructed for this purpose. After the ores come from the 

 burning-house, the process of dressing is completed by further 

 washing, which is rendered easy by the alteration which has 

 been produced in the relative w^eight of the substances. 



Copper ore is not unfrequently present in these cases, and, as 

 it is in part converted into sulphate of copper, the water which is 

 first used is preserved, and a portion of copper obtained from it 

 by means of iron. 



The great specific gravity of the tin ore, as I have before 

 remarked, renders it possible with care to subject it to many 

 operations in dressing without much waste ; and they are, there- 

 fore, applied until the whole is generally so clean, as to yield a 

 produce of metal equal to from 50 to 75 per cent. In this state 

 they are sold by the miner to the smelter, who determines their 

 value by assaying a sample, carefully taken from the whole 

 quantity. 



The furnaces for smelting Mine Tin are all of the common 

 reverberating kind, and are of sufficient size to hold twelve to 

 sixteen hundred weight of ore. 



The charge is prepared by mixing it with a proportion of stone 

 coal, or Welch culm, to which is added a moderate quantity of 

 slaked lime ; these are turned over together and moistened with 

 water, which prevents the too rapid action of the heated furnace, 

 and which would otherwise volatihze some of the metal before 

 fusion commenced. 



The heat employed is a very strong one, and such as to bring 

 the whole into perfect fusion ; it is continued seven or eight 

 hours, when the charge is ready to draw. For this purpose, the 

 furnace is furnished with a tap-hole leading from the lowest part 

 of the bottom, which, during the processes stopped with clay or 

 mortar, and under which is placed an iron kettle to receive the 

 ■ metal. The furnace has also a door at the end opposite the fire- 

 -place, through which the slag or scoria may be raked out from 



