On the Desulphafation of Metals, 63 



sufficient to mention, that at Pezey there have been seen 

 roasted ores of lead, containing a great deal of sulphate of 

 lead, the flux of which, in the Scotch furnace, gave no 

 fhattes, and yet they produce a great quantity when they are 

 passed to the common furnace. 



If heat alone decomposes easily and completely the me- 

 tallic sulphurets, the upper part of the high furnaces will 

 be very proper for operating the roasting of ores ; tor besides 

 the temperature being a little elevated, the air which ascends 

 to that height, being deprived of a part of its oxygen, forms 

 very little more of these, sulphates which are opposed to the 

 separation of the sulphur : but it is quite different, and in 

 my eyes it is a new proof of the little effect of the action of 

 caloric alone upon substances. The sulphur is separated 

 from the sulphurets, as we have seen, in the state of sul- 

 phurous acid, and oxygen is indispensable to its formation. 

 In furnaces not much raised, the air which touches the ore 

 recently thrown in, still contains a great deal of oxygen y 

 the sulphurous acid formed is soon subjected to the deox- 

 idating action of the coals; if there be. a small portion of it 

 decomposed, a new sulphuret is formed, which is afterwards 

 roasted like the mineral. In the Scotch furnace, for example, 

 when mattes are melted, they are thrown successively into 

 the furnace, and what has escaped one operation is decom- 

 posed by a second. In high furnaces, on the contrary, the 

 ores placed in the upper part undergo but a very imperfect 

 desulphuration, because the air which comes in contact with 

 it contains but very little free oxygen, the. sulphurous acid 

 formed in the interior is in a great measure decomposed by 

 traversing the whole height of the furnace filled with coals, 

 and the sulphuret is recomposed; the latter tends by its 

 gravity to gain the basin, where it does not arrive until 

 after a series of decompositions, which cannot take place, 

 as we have in fact observed, without there resulting a con-, 

 s'fderable loss in metal. 



All these facts seem to leave no doubt as to the following 

 proposition : The decomposition of the meta'lic sulphurets 

 by roasting is produced by the oxygenation of its compounds,. 



Fs an4 



