740 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



culated for 100 pounds of ore. This figure is calculated from the capacity of the 

 furnace, aud I'epreseuts very uearly a semi charge of smelter C, but as a great mauy 

 furuaces run charges of this weight it ^vill be adopted in this discussion. The fur- 

 nace is capable of smelting this charge in about seven minutes, giving a cake of slag 

 weighing 281.052 pounds, aud it is as.sumed that at the time of the experiment the 

 furnace is properly filled with eleven similar charges, each charge being divided into 

 two layers, a layer of fuel and old slag aud a layer of flux and ore, all these supposi- 

 tious and all the figures adopted being in ]ierfect accordance with the practical work- 

 ing of the furnace. 



The composition in pounds of the charge in zone 150°, the zone in which it is 

 thrown into the furnace, will be as follows : 



Carbon 79.599 



Gases from fuel 2. 955 



Carbouicacid (C'-s. 747) 32.073 



Oxygen 33.793 



Moisture 22.023 



Lead (total CO. combined with PbO = 14.6e7; PbO=6-.774: = 4.934) .. 63.840 



Silver 0.930 



Metallic iron (Fe30i-^9 1. 036 ; FeO=86.620; Fe;03=96.244) 67.371 



Oxide of lead in slag 5.580 



Alumina 12.093 



Peroxide of iron 2. 595 



Peroxide of manganese (JIuO= 9. 9.j2: 0=2.24.3) 12.195 



Silica 78.606 



Lime ), , ^,,, . , ■ ■ ,- ^,h_-n ^ 17.682 



. > (total CO- in combinatiou=l/. 40b) < ,. ^.^ 



Magnesia ) < lo. /17 



Alkalies 3.153 



Old slag 52.323 



Total 50:>.527 



Weight of blast — It will be Seen in the discussion of losses in each zone of the 

 furnace that of the 79.599 pounds of carbon thrown in the furnace with each charge 

 only 32.1257 pounds reach the zone of combustion. It is this quantity of carbon which 

 will enable us to calculate the quantity of air necessary to convert it into carbonic 

 acid in seven minutes, an excess of air being injurious and calculated to cool the 

 furnace. As 32.1257 pounds of carbon require 85.0085 pounds of oxygen for their com- 

 bustion into carbonic acid, it is deduced from the composition of air given previously 

 that the air blown in the furnace in seven minutes will be composed of — 



Oxygen 85.6685 



Moisture 4.2023 



Carbonic acid .- 0. 1600 



Kitrogen 310.1031 



Total 400.1339 



In other words, the weight of air strictly necessary to burn the carbon left in the 

 smelting charge at the tuyeres is about four-fifths of the weight of the charge thrown 

 in at the feed-hole. At sea-level the volume of air corresponding to the weight of 

 400.1339 would be 5,350 cubic feet (1 cubic foot:=53S.5G9 grains). In Leadville, at the 

 normal pressure of 21 inches of mercury, the volume of the same weight of air is rep- 

 resented by 7,900.2 cubic feet. 



