The temperature necessary for the complete carbonization of the organic
substances of animal charcoal is from 430° to 500° C. In order to
transmit this temperature from the cylinder to the charcoal it is
indispensable that the air surrounding the cylinder be heated to 480°
to 550°. If the heating of the animal black exceeds 500° the product
hardens, diminishes in volume, and loses its porosity. There are two
methods of ascertaining the temperature of the red-hot bone black by
means of the pyrometer: First, by inserting the tube of the instrument
into the black. (Fig. 6, a.) Second, by finding the temperature of the
hot gases in the furnaces (Fig. 6, b.). In the first case, the plunge
tube should be of sufficient length to allow its extremity to penetrate
to the very bottom layer of the red-hot black. This mode of direct
control of the temperature of the black is only employed for
ascertaining the work accomplished by the furnace, that is to say, the
ratio existing between the temperature of the hot air surrounding the
cylinder and the black itself. This calculation being effected, it is
useless to note the differences of temperature which arise in the spaces
between the cylinders of which the furnace is composed.
The position that the pyrometer should occupy is subordinate to the
construction of the furnace. Fig. 6 shows the type which is most
employed.
[Illustration: Fig. 6.--The Pyrometer mounted on a bone-black furnace.]
In a furnace with lateral fire-place, cc are the heating cylinders,
and dd the cooling cylinders. C D is the plate on which are mounted
vertically the former, and from which are suspended the latter, b shows
the pyrometer, the length of which must be such that the manometric
apparatus shall stand out one or two inches from the external surface of
the wall, while its tube, traversing the wall, shall reach the very last
row of heating cylinders.
That the apparatus may form a permanent regulator for the stoker it is
well to adapt to it an arrangement permitting of a graphic control of
the work accomplished and signaling by means of an electric bell when
the temperature of the gases in the furnace descends below 480° C. or
rises above 550° C.
APPLICATION OF THE APPARATUS TO BRICK FURNACES AND IN THE MANUFACTURE OF
CHEMICAL PRODUCTS.
The operation of heating brick furnaces is generally performed according
to empirical methods, the temperature having to vary much according to
the products that it is desired to obtain. It is necessary, however, for
a like product to maintain as uniform a temperature as possible. These
observations are particularly applicable to continuous furnaces such as
annular brick furnaces, etc., in which a uniformity of temperature in
the different chambers is of vital importance to perfect the baking. In
these furnaces the tube of the pyrometer is inserted through one of the
apertures at the top, as shown in Fig. 7. The dial is graduated up to
750°, which is more than sufficient, since the temperature of the upper
part of a compartment fully exposed to the heat rarely exceeds 670° to
680° C.
[Illustration: Fig. 7.--The Pyrometer mounted on a brick furnace.]
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