520 GEOLOGY OF OHIO. 
of iron represents 0.402 tons oxygen. This would, by the above com- 
bustion, furnish 1,688 heat units’; adding to this the 2,964 produced by 
burning at tuyeres, we get, under this assumption, 4,652 units, an excess 
of 652 heat units over what is required to make the iron. 
Too many figures are lacking to draw exact conclusion from the 
above discussion, but certainly this much appears, the high temperature 
at which the gas escapes from the top of the furnace is one great source 
of heat loss, and is accompanied, as the last figure shows, by a failure 
to even closely realize the true working of the furnace, in which the car- 
bonic acid formed by the reduction of the ore escapes from the furnace 
without reduction. The 600 units of heat excess above calculated would 
mean, that this amount of heat was absorbed by the reduction of carbonic 
acid by carbon. The exact amount could only be properly calculated by 
working from analyses of the gas. The heat requirement above given 
is excessive, as all amounts were made large to cover doubtful knowl- 
edge; probably a closer computation would show more striking differ- 
ences and a larger waste of fuel still. 
But while the amount used is in excess of what ought to be needed, 
it is also evident that the actual requirement is very large. This is due 
to the lean mixture, which necessitates a very large amount of slag and 
a consequent increase of fuel, which means more blast, and thus more 
air and gas to heat. 
Raw Coal and Coke Furnaces. 
The best iron smelters are beginning to recognize that there is but 
little reason in adopting different outlines for coke and for raw coal 
furnaces, especially in the lower part of the furnace; hexce, these fur- 
naces will be described at the same time. 
The furnaces using these materials are distributed through the dif- 
ferent districts, as indicated by the special description of each district 
and by the table of furnaces. They present much greater variety in 
equipment and construction than the charcoal furnaces ; they show pro- 
gressive changes in outline, which are of interest in showing the growth 
of the knowledge of the true principle on which furnace construction 
should be based. An endeavor has been made to obtain the outlines 
and results of the working of the more typical furnaces throughout 
the State. 
