Mr. J. Taylors LccUtres on Mtialliirgi/. 153 



verberatory furnaces at a moderate red heat. In the copper 

 works in South Wales, each furnace contahis full three tons of 

 raw ores, which are frequently turned, to expose fresh surfaces, 

 for twelve hours. 



Lead ores are treated in the same manner, in the same fur- 

 nace often, which with a higher heat is used to melt them, and 

 the charge seldom exceeds a ton. 



Tin ores being, as has been explained, simple oxides, and 

 not decomposable in this way, are roasted or calcined princi- 

 pally to alter the specific gravity of the pyrites with which they 

 are mixed, which thus may be separated by subsequent dressing 

 or washing. The furnaces for this purpose in Cornwall are 

 called burning -houses. 



Iron ores, though commonly oxides, are often mixed with 

 sulphurets or iron pyrites, and are roasted to free them from 

 the sulphur ; this however is not done in furnaces, but the ore 

 is stratified with refuse coal and burnt in large heaps in the 

 open air. 



At the Paris and Mona copper mines in the island of 

 Anglesea, where the ores are poor in metal, but contain a 

 large proportion of sulphur, they are treated in the same way, 

 except that they do not find it necessary to use coal, as a small 

 quantity of wood is sufficient to set the ore on fire, and com- 

 bustion goes slowly on, owing to the sulphur ; a heap of 300 

 or 400 tons is eight months in burning, and some of the sul- 

 ])hur is sublimed and is condensed in chambers or vaults to 

 which the flues are conducted. 



In the process of calcination sulphur is generally inflamed, 

 and uniting with the oxygen of the atmosphere is converted 

 into sulphurous acid gas, which mixed as it is with the vapour 

 of certain volatile metals, such as arsenic, zinc, antimony or 

 lead, forms a dense and suffocating smoke destructive of ve- 

 getation, but it does not apj}ear so prejudicial to animal life, 

 except vv here lead is prevalent. Whoever h.as seen the coun- 

 try roantl the cojiper works at Swansea, will have observed 

 the desolating effect of the smoke; and yet it is proved on the 

 best evidence that the men are not subject to any peculiar dis- 

 ease. One set of works there belonging to Messrs. Vivians, 

 who purchase the ores li-om the mines in Cornv.alI, sometimes 

 work at the rate of GOO tons j)er week. These gentlemen 

 have lately constructed, at a great expense, erections to con- 

 dense the noxious vaj)ours, and upon which they have con- 

 sulted Mr. Phillips and other eminent chemists. They have 

 ak()gi!thcr 81 reverberatory furnaces, of which 25 are used 



ibr calcining. 



Tht 



