|
Main
- books.jibble.org
My Books
- IRC Hacks
Misc. Articles
- Meaning of Jibble
- M4 Su Doku
- Computer Scrapbooking
- Setting up Java
- Bootable Java
- Cookies in Java
- Dynamic Graphs
- Social Shakespeare
External Links
- Paul Mutton
- Jibble Photo Gallery
- Jibble Forums
- Google Landmarks
- Jibble Shop
- Free Books
- Intershot Ltd
|
books.jibble.org
Previous Page
| Next Page
Page 5
Composition of air--
by volume 0.788 N + 0.197 O + 0.001 CO2 + 0.014 H2O
----------------------------------------------------
by weight 0.771 N + 0.218 O + 0.009 CO2 + 0.017 H2O
This law is, however, subject to some apparent exceptions. Carbon
burned in protoxide of nitrogen, or laughing gas, N_{2}O, produces
about 38 per cent. more heat than the same substance burned in pure
oxygen, notwithstanding that the work of decomposing the protoxide of
nitrogen has to be performed. In marsh gas, or methane, CH_{4}, again,
the energy of combustion is considerably less than that due to the
burning of its carbon and hydrogen separately. These exceptions
probably arise from the circumstance that the energy of chemical
action is absorbed to a greater or less degree in effecting molecular
changes, as, for example, the combustion of 1 pound of nitrogen to
form protoxide of nitrogen results in the absorption of 1,157 units of
heat. Berthelot states, as one of the fundamental principles of
thermochemistry, "that the quantity of heat evolved is the measure of
the sum of the chemical and physical work accomplished in the
reaction"; and such a law will no doubt account for the phenomena
above noted. The equivalent heat of combustion of the compounds we
have practically to deal with has been experimentally determined, and
therefore constitutes a secure basis on which to establish
calculations of the caloric value of fuel; and in doing so, with
respect to substances composed of carbon, hydrogen, and oxygen, it is
convenient to reduce the hydrogen to its heat-producing equivalent of
carbon. The heat of combustion of hydrogen being 62,032 units, that of
carbon 14,544 units, it follows that 4.265 times the weight of
hydrogen will represent an equivalent amount of carbon. With respect
to the oxygen, it is found that it exists in combination with the
hydrogen in the form of water, and, being combined already, abstracts
its combining equivalent of hydrogen from the efficient ingredients of
the fuel; and hence hydrogen, to the extent of 1/8 of the weight of
the oxygen, must be deducted. The general formula then becomes:
Heat of combustion = 14,544 {C + 4.265 (H-(O/8))},
and water evaporated from and at 212�, taking 966 units as the heat
necessary to evaporate 1 pound of water,
lb. evaporated = 15.06 {C + 4.265 (H-(O/8))},
carbon, hydrogen, and oxygen being taken at their weight per cent. in
the fuel. Strictly speaking, marsh gas should be separately
determined. It often happens that available energy is not in a form in
which it can be applied directly to our needs. The water flowing down
from the mountains in the neighborhood of the Alpine tunnels was
competent to provide the power necessary for boring through them, but
it was not in a form in which it could be directly applied. The
kinetic energy of the water had first to be changed into the potential
energy of air under pressure, then, in that form, by suitable
mechanism, it was used with signal success to disintegrate and
excavate the hard rock of the tunnels. The energy resulting from
combustion is also incapable of being directly transformed into useful
motive power; it must first be converted into potential force of steam
or air at high temperature and pressure, and then applied by means of
suitable heat engines to produce the motions we require. It is
probably to this circumstance that we must attribute the slowness of
the human race to take advantage of the energy of combustion. The
history of the steam engine hardly dates back 200 years, a very small
fraction of the centuries during which man has existed, even since
historic times.
The apparatus by means of which the potential energy of fuel with
respect to oxygen is converted into the potential energy of steam, we
call a steam boiler; and although it has neither cylinder nor piston,
crank nor fly wheel, I claim for it that it is a veritable heat
engine, because it transmits the undulations and vibrations caused by
the energy of chemical combination in the fuel to the water in the
boiler; these motions expend themselves in overcoming the liquid
cohesion of the water and imparting to its molecules that vigor of
motion which converts them into the molecules of a gas which,
impinging on the surfaces which confine it and form the steam space,
declare their presence and energy in the shape of pressure and
temperature. A steam pumping engine, which furnishes water under high
pressure to raise loads by means of hydraulic cranes, is not more
truly a heat engine than a simple boiler, for the latter converts the
latent energy of fuel into the latent energy of steam, just as the
pumping engine converts the latent energy of steam into the latent
energy of the pumped-up accumulator or the hoisted weight.
Previous Page
| Next Page
|
|