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44 APPLICATION OF THE LAWS OF HYDRAULICS
(Fig. 27) that the flame follows the hearth of the furnace, if the
furnace does not hold any ingots, and this is very nearly what may
be actually seen in this furnace.
In the furnace at the Lyswa works (Fig. 28) there has been
found to be a complete identity between the actual and calculated
heights of the strangulating ridges in the roof above the hearth of
the furnace (calculated value 539 mm; actual dimension 525 mm),
but the dimension computed for the height at waste gas ports was
considerably less than that in the furnace. When these conclu-
sion had been reached, A. J. Onoufrowitch, managing director of
the works in the Lyswa district, was asked the following questions
regarding the details of the work of this furnace :
1. Have the strangulations in the roof any effect in forcing the
hot gases down on the hearth of the furnace?
2. Do the gases seem to remain at a short distance above the
hearth of the furnace at the waste gas end?
A reply was received giving the following facts concerning the
record of this furnace:
The furnace had been originally constructed without strangula-
tions and worked very badly. The managing director had then
dropped portions of the roof a sufficient distance to bring the hot
gases down to the hearth. He stated that he had been led by
trial to give this lowered section a height of 525 mm (Fig. 28),
the thickness of the layer of hot gases in the furnace chamber.
To the second question he replied that the furnace had not
worked well at the end connected with the chimney (the rear end
of the furnace), the hot gases seeking the roof. He proposed to
correct this condition later by the removal of the present roof,
replacing it by a horizontal roof 150 mm lower; Ayoo would then
be equal to 500 mm.
This shows that Yesmann's formula has received a complete
confirmation in the computations verifying these two furnaces.
It is accordingly permissible to make some other comparisons.
The "N" furnace heated £=1.31 times the weight of
ingots, but it consumed per second
times the volume
of fuel burned at Lyswa; that is to say, per unit weight of ingots,
the consumption of fuel was -^-^=2.11 times greater in the