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and which, at the period of its introduction, constituted one of 
the most remarkable events in the history of the iron trade. 
It is now, however, asserted by some manufacturers, that 
experience has proved that Neilson’s invention mainly served to 
remedy a defect in furnaces of his time, viz :—want of capacity, 
which defect, when removed, was as efficacious in saving fuel as 
the hot blast itself, i.e. a ton of iron, with cold blast, could be made 
in a furnace seventy one feet high, with“s small a consumption 
of fuel as was required when hot blast was applied to a furnace 
fifty-three feet in height,—in each case identically the same materials 
being used. The “fifty-three feet” hot blast furnace has been proved 
to turn out a larger make of iron than that blown with cold air 
(probably two hundred tons per week, against one hundred and 
twenty tons) ; but on the other hand, the larger furnace, without 
any apparatus to maintain, or fuel to expend for heating the air, 
is able to do its work as efficiently in point of fuel consumed in 
the furnace as the other, assisted by the more complicated 
appendage suggested by Neilson. 
This problem of the most economical and effective mode of 
constructing and working blast furnaces, is one on which opinions 
still vary, but the importance of it may be shewn by the following 
figures given by Mr. Lowthian Bell :— 
Furnace of Cubic feet - 6,000 12,000 16,000 26,000 41,000. 
Weekly make, tons - 220° “aG0''* eno '' B4oo |") 550, 
Weekly make per 1,000¢. ft. 37 23 22 16 ra 
The effect of a large furnace of 41,000 cubic feet producing 
less in proportion than one of 16,000 cubic feet, is that the charge 
for interest on outlay is about one hundred to sixty-six in favor of 
the latter, but if including more expensive engines, heating stoves, 
etc., the proportion would be one hundred to ninety-two. 
In addition to what has just been stated, it must also be borne 
in mind that the phenomena connected with the operations of the 
blast furnace are liable to be affected by so many disturbing 
causes, namely, quality of fuel, of limestone, and of iron ore, 
efficiency of the heating apparatus, the size of the tuyeres, and the 
