736 GEOLOGY AND MIXING INDUSTRY OF LEADVILLK. 



No. 42 it is a well-known fact that this compound is volatile; hence its presence 

 in large quantities in the lead dust and even in the lost fumes. 



NO. 43 Chloride of silver is reduced in the dry way by metallic lead and also by 

 metallic iron. It is owing to these important reactions tha-t so much chloro-biomo 

 iodide of lead is formed and that so much silver is reduced in the bullion. 



REACTION'S OK 1ROX COMPOUNDS. 



No. 44. Reactions of carbonate of iron Carbonate of iron is reduced at red heat to 

 the state of magnetic oxide of iron with formation of carbonic oxide (I. Lowthiau 

 Bell), 1 with formation of peculiar magnetic oxide of iron, containing an excess of pro 

 toxide of iron (Percy). 8 The writer has found a similar magnetic oxide of iron in slags 

 and mattes. 



No. 45. Reactions of peroxide of iron Under the influence of carbonic oxide, peroxide 

 of iron begins to lose oxygen at the temperature of 200 C., protoxide of irou being 

 formed as well as carbonic acid. The decomposition increases rapidly with the tem- 

 perature until it reaches 417 C. The loss in oxygen is greater in the same lapse of 

 time in a rapid current of carbonic oxide. At 410 C. peroxide of iron loses 30 per 

 cent, of its oxygen in a slow current of carbonic oxide and 50 per cent, in a rapid cur- 

 rent of the same gas (Bell). In the blast furnaces of Leadville the conditions are 

 those of a rapid current. To form magnetic oxide, peroxide of iron must lose 11.1 per 

 cent, of its oxygen, and to form protoxide of iron 33.3 per cent. Consequently at the 

 temperature of 410 i. e., below red heat and in a rapid current of carbonic oxide, 

 peroxide of iron losing more than 50 per cent, of its oxygen, some metallic irou is 

 produced. This is an important fact, but one which is profoundly moditied in the fur- 

 nace, wheie carbonic oxide is diluted with nitrogen and carbonic acid. 



No. 46 Atthe tetnperatureof41iC. that is, at the teuiperatureat which metal- 

 lic irou makes its appearance it is rapidly attacked by carbonic acid, with formation of 

 oxide of irou and oxide of carbou (Bell). 



No. 47 At the same temperature of 417 C. a mixture of equal volumes of car- 

 bonic acid and carbouic oxide exerts no action upon metallic iron, but at full red heat 

 the carbouic acid of the mixture is rapidly decomposed and converted into carbouic 

 oxide (Bell). 



NO. 48 Mixtures of carbonic acid and oxide reduce peroxide of iron, bu; only to 

 the state of protoxide, at the temperature of 417 C., with formation of carbouic acid 

 (Bell). 



No. 49 A mixture of carbouic acid with an excess of oxide of carbou (CO 2 9 

 volumes, CO 100 volumes) oxidizes spongy iron, and carbon is deposited from reduced 

 oxide of carbon, oxide of irou being formed. Pure spougy irou thus treated has for 

 composition Fe=91.42, C=0.33, O=8.25 (Bell). In pure oxide of carbou spougy irou 

 takes up as much as 23 per cent, of carbou (Bell). 



The above considerations, which are purely theoretical, are interesting as show- 

 ing the mechanism of the formation of cast irou in the blast furnaces, such as those 

 of Leadville, in which the phenomena of lead and silver smelting take place jointly 



1 All quotations from I. L. Bell are from his Chnmical Phenomena ot Iron Smelting. Lon- 

 don, 1872. 



8 Percy's Metallurgy of Irou and Steel. Loudou, 1864. 



