Luminous. Bunsen.
Nitrogen. 76.612 80.242
Water vapor. 14.702 13.345
Carbon dioxide. 2.201 4.966
Carbon monoxide. 1.189 0.006
Oxygen. 2.300 1.430
Marsh gas. 0.072 0.003
Hydrogen. 2.888 0.008
Acetylene. 0.036 Nil.
------- -------
100.000 100.000
The gases leaving the luminous flame show that the diluting action of
the nitrogen is so great that considerable quantities even of the
highly inflammable and rapidly burning hydrogen escape combustion,
while the products of incomplete combustion are present in sufficient
quantity to account perfectly for the deleterious effects of gas
burners in ill-ventilated rooms. The analyses also bring out very
clearly the fact that, although the dilution of coal gas by air in
atmospheric burners is sufficient to prevent the decomposition of the
heavy hydrocarbons with liberation of carbon, and so destroy
luminosity, yet the presence of the extra supply of oxygen does make
the combustion far more perfect, so that the products of incomplete
combustion are hardly to be found in the escaping gases.
These experiments are of the gravest import, as they show more clearly
than has ever been done before the absolute necessity for special and
perfect ventilation where coal gas is employed for the illumination of
our dwelling rooms.
When coal gas was first employed during the early part of this century
as an illuminating agent, the low pitch of the old fashioned rooms,
and the excess of impurities in the gas, rendered it imperative that
the products of combustion of the sulphur-laden gas should be
conducted from the apartment, and for this purpose arrangements of
tubes with funnel shaped openings were suspended over the burners. The
noxious gases were thus conveyed either to the flue or open air; but
this type of ventilator was unsightly in the extreme, and some few
attempts were made to replace it by a more elegant arrangement, as in
the ventilating lamp invented by Faraday, and in the adaptation of the
same principle by Mr. I.O.N. Rutter, who strove for many years to
direct attention to the necessity of removing the products of
combustion from the room. But with the increase of the gas industry,
the methods for purifying the coal gas became gradually more and more
perfect, while the rooms in the modern houses were made more lofty;
and the products of combustion being mixed with a larger volume of
air, and not containing so many deleterious constituents, became, if
not much less noxious, at all events less perceptible to the nose. As
soon as this point was reached, the ventilating tubes were discarded,
and from that day to this the air of our dwelling rooms has been
contaminated by illuminants, with hardly an effort to alleviate the
effect produced upon health. I say "hardly an effort," for the Messrs.
Boyle tried, by their concentric tube ventilators, to meet the
difficulty, while Mr. De la Garde and Mr. Hammond have each
constructed lamps more or less on the principle of the Rutter lamp;
but either from their being somewhat unsightly, or from their
diminishing the amount of light given out, none of them have met with
any degree of success. In places of public entertainment, where large
quantities of coal gas are consumed for illuminating purposes, the
absolute necessity for special ventilation gave rise to the "sun
burner," with its ventilating shaft. This, however, gives but a very
poor illuminating power per cubic foot of gas consumed, due partly to
the cooling of the flame by the current of air produced, and partly to
its distance from the objects to be illuminated.
The great difficulty which in the whole history of ventilation has
opposed itself to the adoption of proper arrangements for removing the
products of combustion has been the necessity of bringing the tube to
carry off the gases low down into the room, and of incasing the burner
in such a way that none of the products should escape; but with the
present revolution in gas burners this necessity is entirely done away
with, and the regenerative burner offers the means not only of
removing all the products of combustion but also of effecting thorough
ventilation of the room itself, as experiments made some few years ago
showed me that a ventilating regenerative burner, burning 20 cubic
feet of gas per hour and properly fitted, will not only remove all its
own products of combustion, but also over 5,000 cubic feet per hour of
the vitiated air from the upper part of the room. I am quite aware
that many regenerative lamp makers raise various objections to fitting
ventilating lamps, these being chiefly due to the fact that it
requires considerable trouble to fit them properly; but I think I have
said enough to show the absolute necessity of some such system, and
when there is a general demand for ventilating lamps, engineering
skill will soon find means to overcome any slight difficulties which
exist.
Having disposed in a few words of a subject which, if fully treated,
would occupy a long course of lectures by itself, I will pass on to
the consideration of gas as at present used as a fuel.
There is no doubt that gas is the most convenient and in many ways one
of the best forms of fuel for heating and cooking purposes, and the
efforts which all large gas companies are now making to popularize and
increase the use of gas for such purposes will undoubtedly bear fruit
in the future. But before the day can come for gas to be used in this
way on a large scale, there is one fact which the gas manager and gas
stove manufacturer must clearly realize and submit to, and that is
that no gas stove or gas water heater, of any construction, should be
sent out or fitted without just as great care being taken to provide
for the carrying away of the products of combustion as if an ordinary
fuel range was being fitted. Do not for one moment allow yourself to
be persuaded that, because a gas stove or geyser does not send out a
mass of black smoke, the products of combustion can be neglected and
with safety allowed to mingle with the atmosphere we are to breathe.
Scarcely a winter passes but one or more deaths are recorded from the
products of combustion given off from various forms of water heaters
used in bath rooms; scarcely a cookery class is given, with gas
stoves, that one or more ladies do not have to leave suffering from an
intense headache, and often in an almost fainting condition. And the
same cause which brings about these extreme cases, on a smaller scale
causes such physical discomfort to many delicately organized persons
that a large class exist who absolutely and resolutely decline to have
gas as an illuminant or fuel in any of their living rooms; and if the
use of gas, more especially as fuel, is to be extended, and if gas is
to hold its own in the future against such rivals as the electric
light, then those interested in gas and gas stoves must face the
problem, and by improving the methods of burning and using gas do away
with the present serious drawbacks which exist to its use.
The feeling has gradually been gaining ground in the public mind that,
when atmospheric burners and other devices for burning coal gas are
employed for heating purposes, certain deleterious products of
incomplete combustion find their way into the air, and that this takes
place to a considerable extent is shown by the facts brought forward
in a paper read by Mr. William Thomson before the last meeting of the
British Association.
Mr. Thomson attempted to separate and determine the quantity of carbon
monoxide and hydrocarbons present in the flue gases from various forms
of gas stoves and burners, but, like every other observer who has
attempted to solve this most difficult problem, he found it so beset
with difficulties that he had to abandon it, and contented himself
with determining the total amounts of carbon and hydrogen escaping in
an unburned condition, experiments which showed that the combustion of
gas in stoves for heating purposes is much more incomplete than one
had been in the habit of supposing, but his experiments give no clew
as to whether the incompletely burned matter consisted of such
deleterious gases as carbon monoxide and acetylene, or comparatively
harmless gases, such as marsh gas and hydrogen. After considerable
work upon the subject, I have succeeded in doing this by a very
delicate process of analysis, and I now wish to lay some of my results
before you.
If a cold substance, metal or non-metal, be placed in a flame, whether
it be luminous or non-luminous, it will be observed that there is a
clear space, in which no combustion is taking place, formed round the
cool surface, and that as the body gets heated so this space gets less
and less until, when the substance is at the same temperature as the
flame itself, there is contact between the two. Moreover, when a
luminous flame is employed in this experiment the space still exists
between the cool body and the flame, but you also notice that the
luminosity is decreased over a still larger area although the flame
exists.
This meaning that, in immediate contact with the cold body, the
temperature is so reduced that the flame cannot exist, and so is
extinguished over a small area; while over a still larger space the
temperature is so reduced that it is not hot enough to bring about
decomposition of the heavy hydrocarbons with liberation of carbon to
the same extent as in hotter portions of the flame. Now, inasmuch as
when water is heated or boiled in an open vessel, the temperature
cannot rise above 100°C., and as the temperature of an ordinary flame
is over 1,000°C., it is evident that the burning gas can never be in
contact with the bottom of the vessel, or, in other words, the gas is
put out before combustion is completed, and the unburned gas and
products of incomplete combustion find their way into the air and
render it perfectly unfit for respiration.
The portion of the flame which is supposed to be the hottest is about
half an inch above the tip of the inner zone of the flame, and it is
at this point that most vessels containing water to be heated are made
to impinge on the flame; and it is this portion of the flame, also,
which is utilized for raising various solids to a temperature at which
they radiate heat.
In order to gain an insight into the amount of contamination which the
air undergoes when a geyser or cooking stove is at work, I have
determined the composition of the products of combustion, and the
unburned gases escaping when a vessel containing water at the ordinary
temperatures is heated up to the boiling point by a gas flame, the
vessel being placed, in the first case, half an inch above the inner
cone of the flame, and in the second, at the extreme outer tip of the
flame.