In the lower part of the smoking furnace, which is made of boiler plate
and can be put in communication with the tube, e, there are large
apertures that may be wholly or partially closed by means of registers
so as to carry to the hot gas derived from combustion any quantity
whatever of cold and dry air, and thus cause a variation at will of the
temperature of the gases which are disengaged from the tube, e.

The use of these smoking apparatus heated by gas does away also with the
inconveniences of the ordinary system, in which the products are soiled
by cinders or dust, and which render the gradual heating of objects to
be baked difficult. At the beginning, there is allowed to enter the
lower part of the small furnace, S, through the apertures, a very
considerable quantity of cold air, so as to lower the temperature of the
smoke gas that escapes from the tube, e, to 30 or 50 degrees. Afterward,
these secondary air entrances are gradually closed so as to increase the
temperature of the gases at will.

* * * * *




THE EFFICIENCY OF FANS.


Air, like every other gas or combination of gases, possesses weight;
some persons who have been taught that the air exerts a pressure of 14.7
lb. per square inch, cannot, however, be got to realize the fact that a
cubit foot of air at the same pressure and at a temperature of 62 deg.
weighs the thirteenth part of a pound, or over one ounce; 13.141 cubic