1874.] Economy of Fuel. 73 
welding point. In an ordinary re-heating furnace, a ton of 
coal heats only 12 tons of iron, and therefore produces 
only one twenty-third part of the maximum theoretic effect. 
In melting one ton of steel in pots, 24 tons of coke are con- 
sumed; and, taking the melting point of steel at 3600 F., 
the specific heat at o*11g, it takes 428 heat units to melt 
a pound of steel; and, taking the heat-producing power 
of common coke also at 12,000 units, I ton of coke ought 
to be able to melt 28 tons of steel. ‘The Sheffield pot steel 
melting-furnace, therefore, only utilises one-seventieth part 
of the theoretical heat developed in the combustion. 
Several methods are now in use whereby greater economy 
in fuel results, but we shall not now do more than 
give special notice to one of these, as the object of 
fac present article is not so. much to refer to all 
methods of economising fuel, but rather to point out 
to what extent economy has been attained in various 
branches of consumption. We propose here merely to 
specify the Siemens’s regenerative furnace, which is now too 
well known to require any detailed description, and by the 
use of which a ton of steel is melted with 12 cwts. of small 
coal, whereas in the ordinary furnace at Sheffield, about 
3 tons of Durham coke are necessary to accomplish the 
sameend. In this one operation, therefore, in the process 
of steel manufacture, a saving of four-fifths of the fuel 
ordinarily employed is capable of being effected. 
Turning now to Mr. Bessemer’s system of steel manufac- 
ture, we find where 33 tons of coke are ordinarily used per 
ton of steel, 3 cwts. only is required for his process; and we 
find that gentleman stating, in evidence, before the Coal 
Commission of 1871, that ‘“‘if we take the present produc- 
tion of cast steel, in this country, by my process, at 150,000 
tons a year, we should have a saving of a little over half a 
million tons of coke in that time, representing, of course, its 
proportion of coal, the amount being greater or less according 
to the purity of the coal employed.” 
In estimating the waste of fuel under steam boilers, it is 
necessary to remember that in burning 1 1b. of carbon in 
the presence of free oxygen, carbonic acid is produced, and 
14,500 units of heat are liberated. Each unit of heat is 
convertible into 774 units of force or mechanical energy ; 
and hence, 1 lb. of carbon represents really 11,223,000 units 
of potential energy ; that is to say, the mechanical energy 
set free in the combustion of 1 lb. of pure carbon is the same 
that would be required to raise 11,223,000 pounds weight one 
foot high, or as would sustain the work which we call 
VOL. IV. (N.S.) L 
