1874.! Economy of Fuel. 71 
temperature, heating-stoves are employed, consisting most 
generally of a series of iron pipes within a furnace, through 
which the heat for the blast is drawn. The highest tempe- 
rature and the best results have, however, been obtained 
with Whitwell’s hot-blast fire-brick stoves, by the use of 
which, at Consett, iron has been made with 17 cwts. 2 qrs. 
of coke per ton, the blast being at a pressure of 3 lbs. per 
inch, and the temperature about 1400°. With an increased 
pressure of blast to 4 lbs., and a decrease in temperature to 
I200, an increased production of pig-iron was the result, 
but the consumption of coke rose to 19 cwts. 2 qrs. per ton. 
Under the most economical system of working, with open- 
topped furnaces, an enormous amount of fuel is wasted by 
the escape of the vapours of combustion, many of them 
only half consumed at a high temperature. So early as the 
beginning of the present century (1811), the important 
practical problem of the utilisation of the waste gas of iron- 
smelting furnaces was solved in a satisfactory manner in 
France; but upwards of five and twenty years elapsed 
before it began to attract the serious attention of iron- 
masters in Great Britain or on the Continent of Europe. 
The first attempts made in this country were exceedingly 
crude, and much of the carbonic oxide was allowed to 
escape unburnt into the air, by which an enormous amount 
_of heat, capable of being developed by the combustion of 
that gas, was lost. The calorific effect of the waste gas is 
due partly to its sensible heat, and partly to the heat 
developed by its combustion in contact with atmospheric 
air. In some furnaces, the gas is taken off through several 
circular openings ata short distance below the level of the 
solid contents of the furnace, their exhaustion being effected 
by means of a high stack. In others, there is an annular 
passage or flue near the mouth, extending all round, and 
communicating with the interior by several short passages, 
and in this case, also, the aid of a stack is required for ex- 
haustion. The most general method is, however, to close 
the top of the furnace with a ‘‘ cup and cone.” 
We must not close our account of economy of fuel in the 
blast-furnace without some reference to Ferrie’s self-coking 
blast-furnace. In considering the problem of utilising the 
gases escaping from blast-furnaces worked with raw coal, it 
occurred to Mr. Ferrie that much of the difficulty would be 
overcome if the coal could be coked in the furnace in some- 
what the same way as it is coked in gas retorts. In the 
application of these ideas to a large furnace at the Monkland 
Works, the mouth of the furnace is closed by a bell and 
