736 GEOLUGY A^D MINING ES'DUSTEY OF LEADVILLl.. 



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 that so muck chloro-bromo 

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



REACTIONS OF IKOX COMPOUNDS. 



No. 44. Reactions of carbona'e of iion., — Carbonate of iron IS reduced at red heat to 

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

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

 toside of irou (Percy).- The writer has found a similar magnetic oxide of iron in slags 

 and mattes. 



No. 45. ReacL:on3 of peroxide of iron — Under the iiitineuce ofcarbonic oxide, peroxide 

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

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

 perature until it readies 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 carbouic oxide, 

 ])eroxide of iron losing more than 50 per cent, of its oxygen, some metallic irou is 

 ])ioduced. This is an important fact, but one which is ijiotbuudly moditied in the lur- 

 uace, wheie ca:bouic oxide is diluted with nitrogeu and carbouic acid. 



No. 46 Atthetemperatuieof41^°C. — that is, at the temperature at which metal- 

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

 oxide of iron and oxide of carbon (Bell). 



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

 bouic acid aud 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 carbonic 

 oxide (Bell). 



No. 48 Mixtures ofcarbonic acid aud oxide reduce peroxide of iron, but 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 carbon (CO. 9 



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

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

 composition Fe='J1.4.', C=0.33, = S.25 (Bell), lu pure oxide of carbon spongy 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 aud silver smelting take place jointly 



> All quotiitious from I. L. liell are from li:.s Clifmieal Pbeuomeua ol' Irou Smeltiug. Lou- 

 don, 1872. 



2 Percy's Metallurg.v of Iron ;m<l Steel. Loudou, 1S6-1. 



