38 APPLICATION OF THE LAWS OF HYDRAULICS
erators, and its passage through the flues and reversing valves
to the base of the chimney, commences at the heating chamber
where the hydrostatic pressure is equal to that of the atmosphere.
In order to draw the light gases downward to the bottom of the
regenerator chamber, it is necessary to establish a negative
hydrostatic pressure or draft depression at that level.
This is the function of the chimney, which, therefore, has a
1. To draw the hot gases down to the bottom of the regenerator.
2. To impress upon them the necessary velocity and to over-
come the losses of head due to changes in the direction of flow,
changes in velocity and the friction against the walls of the flues,
etc., in this portion of the furnace.
The computations for reverberatory furnaces, based upon the
laws of hydraulics, were included, some time ago, among the
obligatory exercises.for the students in the metallurgical section
of the Polytechnic Institute of Petrograd; as a result of this, a
very large number of these furnaces in the workshops of Russia
have been recalculated. Ordinarily the problem, as given,
involved the computation for furnaces actually in use within the
different plants, based upon the daily consumption of fuel. The
volume of producer gas being determined, the volume of the
products of combustion was calculated. This was usually based
upon a secondary air supply one and one-half times as great as the
theoretical air supply. The analysis of these furnaces actually
in service has shown the following:
1. That open-hearth furnaces of defective construction were
subject to a rapid filling up of the regenerators, and for this reason
served only during comparatively short campaigns; the velocities
were too great, and the hydrostatic pressure of the hot air and
gases was barely sufficient to produce the necessary velocity.
Sometimes these computations showed negative results, that is to
say, the calculations showed that forced draft was necessary for
operation of the furnace. But, nevertheless, the furnace worked
without forced draft, though in a defective manner which caused
trouble. It follows, therefore, that these methods of computation
have in themselves a certain factor of safety.
2. The gas regenerators and the air regenerators should receive
different volumes of the waste gases. In computing these two
quantities of gas, it was found that the draft depressions necessary