THE 



AMEEICAN 

 JOURNAL OF SCIENCE, &c. 



Art. I. — On the principles involved in the Reduction of Iron and 

 Silver Ores, ivith a supplementary notice of some of the principal 

 Silver Mines of Mexico and South America ; hy Lt. W. W. 

 Mather, Instructor of Mineralogy and Geology at the U. S. 

 Military Academy, West Point. 



I. Iron. 

 1. Roasting of Iron Ores. 



The roasting of iron ores, is almost constantly found to result in 

 the production of a purer iron than would be obtained by smelting 

 without previous roasting. Another advantage is, that if the roasting 

 be properly performed, less combustible matter is required for both 

 the smelting and roasting, than would be for the smelting alone, with- 

 out the roasting. 



There are three principal objects in roasting iron ores, viz. 



1. To vaporize injurious substances, or change their states of com- 

 bination. 



2. To increase the porosity of the ore. 



3. To diminish the cohesion, and render it more easily broken. 

 The iron ores, during the roasting process, increase in volume, and 



with one or two exceptions, diminish in weight. The increase of 

 volume causes a considerable degree of porosity in the ore, and this 

 is of great advantage during the smelting. It allows the carburetted 

 gases to penetrate every part of the fragments of ore, and thus to 

 deoxidize it, and to carbonize the iron, far more rapidly, than if the 

 action was confined to the surface alone. 



The ores generally contain sulphur, in greater or less proportion, 

 and, during the roasting, they are converted either into oxides, sul- 

 phates, or sulphurets of a lower degree of combination. The latter 

 class of sulphurets, by exposure to the weather, are converted into 



Vol. XXIV,— No. 2. 28 



