$2 On the Desulphuration of Metals. 



the formation of the oxide of lead which will cover it J an<£ 

 the sulphate of lead not being capable of being any longer 

 mixed with the galena, there will be no method left of de- 

 sulphuration. 



, The roasting of galena in the reverberating furnace is 

 therefore reduced to the conversion of the sulphur which it 

 contains into sulphurous acid ) and as it is "produced in a 

 great measure by the intermedium of the sulphate of lead 

 which is continually formed, this process admits of a much 

 more complete desulphuration than the others. 



The same decomposition of the sulphuret of lead by the 

 sulphate, in my opinion, takes place also in the treatment 

 of the ores of lead in what are called Scotch furnaces : in 

 Scotland they roast and melt galena by one uninterrupted 

 operation, employing coal and turf. 



This kind of furnace is employed with success in the 

 mine at Pezey, in melting roasted galena containing at least 

 •i. of its weight of sulphate of lead. It gives no mattes as 

 a final result, which proves that it admits of the decompo- 

 sition of the sulphate and the separation of the sulphur 

 contained in it. I am of opinion that the action of the 

 portion reduced to the state of sulphuret by the contact of 

 the coals upon the undecomposed sulphate, is one of the 

 principal causes of the desulphuration produced. 



We have had occasion to speak of several kinds of fur- 

 naces, (the Fahlun and Scotch furnaces among the rest,) in 

 which the metallic sulphurets will undergo a real roasting; 

 but there are others where this effect is scarcely perceptible. 

 I consider the present as a proper opportunity for intro- 

 ducing some reflections upon the differences they exhibit hi 

 this respect. They ought to excite the more interest, be- 

 cause they are intimately connected with the present sub- 

 ject, and explain some phsenomena which cannot be ac- 

 counted for from the way in which the operation of roasting 

 has o-enerallv been regarded. • 



It is a well-known fact, in foundries, that the highest 

 furnaces are those which admit of desulphuration the least, 

 or, in the language of the workmen, they produce the most 

 mattes. If a convincing proof of this is wanted^ it will be 



- sufficient 



