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KKKi-X'T OK Ft'Kl,, Kl.l-XKS, TK.M I'KU ATI'l< K, K.'I'f. 307
when the temperature is (••.» decrees F., and the percentage of moisture in the atmosphere about <>. 511 pur cent., which is about the1 average in Chicago.
It lias been found by experieiiee tliat about 33,000 etibie feet of air are required to melt -j.ooo pounds of iron in ordinary eupohi practice. This air will weij^h about 2,500 pounds, and is heated originally to a hij^h temperature by the ignited coke before it becomes active in supporting; further combustion. Also any niois ture eontained in this air must be brought to the temperature of til.' j^'ascs which escape from the top of the cupola. This latter t .'mperature varies greatly, but will IK* in the vicinity of 500 degrees F. for i^ood practice.
If the temperature of thr atmosphere should drop to 32 de-e,;ves F., this means that the air delivered to the cupola must be heated 30 decrees, so as to brini;' it to the normal. The specific h'-at of air beinjj;' taken at o.-j^S, we obtain 2,">oo X ;V» X u- «3;^ == i 7, ^o B. T. 1T. as tin.' amount of heat required to do this work, or theoretically about \-\$ pounds coke would be consumed if we obtained perfect combustion. The fact bein^' that the actual amount of heat obtained from the combustion of coke in a cupola is only about '4 of the theoretical, it follows that the actual coke consumed for tins extra lu-atin;,-; is about =;'., pounds, which should be added to the usual amount «>f i,>r,o pounds per ton of iron, mak-niy»; '.i-"^1.. pounds, or a ratio of about 7.* iron fo i coke.
If, at the same time, the air is rharv.ed with particle:; of moisture, as when a heavy snow-st«»nn is in pro^irss, if will contain, suv, about j-io per c.-nt. of fro/.en water. In the ;v>":> pound « total tiii*; will amount to u» pound:;, which must be transformed into vapor at 500 derives F., involving 1.^,7.|o B. T, H. of beat, < )n the other hand, this amount is reduced by the heat expended in raising the average vapor of n.^, per cent, in <>;» <lcj,»rt***s air to Sou decrees I1*., which amounts to 2,714 B. T. I-,, leaving an extra. amount «»f r«;,o;^> B, T. I*. coii:»umed by the snow, which will aj;ain rcfpure about 3.ft pound;-; coke,
The* total «'oke consumption in the above ease will therefore be •.!ni|. i pounds pe!' (on of iron, or a ratio of 7.7 iron to i coke, in onler to deliver the melted iron in the same condition as on an ordinary day. In other words, an additional fuel consumption <>!' a little over 3,h per cent, is needed under the above conditions...................... 3,658 units £