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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 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-stnn 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