The Sun.
London, England, 1854-04-19 00:00:00

INSTITUTION OF CIVIL ENGINEERS.

At the last meeting of this society, Mr. James Simp-
son, president, in the chair, the evening was entirely
devoted to the discussion of the papers by Mr. J. Simp-
son, jun., and Mr. C. Wye Williams, "On the Manage-
ment of the Engine and other Furnaces, and the
Prevention of Smoke." An explanation was given, by
means of a diagram, of several divisions of the process,
leading to the combustion of gas in furnaces. The first
division gave the mere relative gross bulk of gas and air
required for combustion. In the second the mechanical
mixture of the gas and air was described, such mixture,
or contact of atoms, being essential to the subsequent
chemical union. The third exhibited the several consti-
tuents of gas and air—the former being hydrogen -and car-
bon ; the latter, oxygen and nitrogen; the relative volumes
of each were given, and it was shown that ten volumes of
air were absolutely essential to the combustion of one
volume of gas. The fourth division showed the propor-
tions in which those constituents combined. The nature
of flame and smoke was examined ; showing that the
intense heat, caused by the combustion of the hydrogen,
was the direct cause by which the temperature of the
carbon was raised to that of white heat, which produced
the luminosity of flame. This process was illustrated by
reference to the mode of producing the intense heat and
luminosity required for the oxy-hydrogen miscroscope.
In the latter the piece of lime or carbon, on which the
heat was projected, was instantly raised to the tempera-
ture of extreme luminosity, neither the lime nor carbon,
however, suffering rapid combustion. In the former, the
carbon of the gas was raised, by the same means (the
combustion of the hydrogen) to the high temperature,
but could not suffer combustion until it was brought into
contact, in its turn, with its equivalent of the oxygen of
the air. If, however, that supply of air was not pro-
vided before the carbon lost'its high temperature, it re-
turned to its previous and natural state of a black sub-
stance, and gave the black character to the products,
called smoke. The first important condition was then
shown to be, the providing the required quantity of air.
Reference was then made to the area, recommended by
some authorities, as lieing sufficient to allow the quan-
tity to enter a furnace. It had been considered, that
! even half a square inch of aperture for each square foot
of furnace grate was, sufficient for the combustion of the
fuel. This was, however, stated to be insufficient for
practical purposes. The proper area for admission being
from 4 to 6 square inches for each foot of grate, accord-
ing to the extent of draught and the nature of the coal.
This serious difference was supposed to have been caused
by an erroneous calculation of the rate of the current
of air entering. For, if half a square inch of area was
all that was allowed, the air must have a velocity ten
times greaten than could be shown to have ever been
attained. Thus, supposing a furnace to be 4 feet by 2
feet 6 inches, equal to 10 square feet of bar surface, this
would effect a combusion of 2 cwt. of coal per hour,
and require, for the gas alone, a supply of 10,000 cubic
feet per hour, or for 20 cwt. of the coal, 100,000 cubic
feet. The following comparison of velocity of the en-
tering air for the supply of the gas gave some idea of the
cause of underrating the required area of admission :--

Air aperture per Velocity of Quantity of air Quantity for
square foot of draught per per each ton of
grate. second. hour.. coal.

6 square inches at 5 ft. persec. 7,500 cubic ft. 75,000
6 „ „ at 10 „ . 15,000 „ 150,000