The air
entering through the brick arch is heated to from 200 to 300 degrees
by contact with the layer of poor stuff, the cinnabar is ignited, and
its sulphur oxidized, and the quicksilver vaporized and, condensing in
the aludels, flows toward the depression in the central portion of the
line. The temperature goes on increasing, until, twelve hours after
the beginning of this period, the thermometer shows 212 degrees C. at
the first aludels. This lasts for 18 hours, and then the third or
"cooling period" begins, which takes from 24 to 26 hours, and during
the beginning of which the temperature in the furnaces still rises. It
is then opened and cooled down. A very elaborate series of
observations made on the temperatures of various parts of the
condensing apparatus of the Almaden furnaces has shown that at the
aludels nearest to them the heat increases steadily until it reaches
249 degrees C., 44 hours after the beginning of the operation; that in
the middle of the line, at the depression, the maximum is 50 degrees
50 hours after starting the fires; and that at the end it does not
surpass 39 degrees. In the final condensing chamber, the temperature
varied, running downward from 40 degrees during the heating period to
14 degrees, rising again to 29 degrees toward the close.
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