Scientific American Supplement, No. 795, March 28, 1891

Chapter 7

Chapter 74,066 wordsPublic domain

At first sight it seems a dangerous experiment to mix a heavy hydrocarbon gas with oxygen, but it must be remembered that although hydrogen and carbon monoxide only need to be mixed with half their own volume of oxygen to give a most explosive mixture, yet as the number of carbon and hydrogen atoms in the combustible gas increase, so does the amount of oxygen needed to give explosion. Thus coal gas needs rather more than its own volume, and ethylene three times its volume, to give the maximum explosive results, while these mixtures begin to be explosive when 10 per cent. of oxygen is mixed with hydrogen or water gas, 30 per cent. with coal gas, and over 50 per cent. of oil gas of the character used. It is claimed that if this gas was used as an enricher of coal gas, 5 per cent. of it would increase the luminosity of 16-candle gas by about 40 per cent.

Oxygen has been obtained for some time past from the air on a commercial scale by the Brin process, and at the present time there seems every prospect of our being able to obtain oxygen at a rate of about 3s. 6d. per 1,000 cubic feet. Another process by which this important result can also be obtained was first introduced by Tessie du Mothay, and has now just been revived. It consists of passing alternate currents of steam and air over sodic manganate heated to dull redness in an iron tube; the process has never been commercially successful, for the reason that the contents of the tube fused, and flowing over the surface of the iron rapidly destroyed the tubes or retorts, and also as soon as fusion took place, the mass became so dense that it had little or no action on the air passing over it. Now, however, this difficulty has been partly overcome by so preparing the manganate as to prevent fusion, and to keep it in a spongy state, which gives very high results, and the substance being practically everlasting, the cost of production is extremely low.

It is proposed to feed this by a separate system of pipes to small gas jets, and by converting them into practically oxyhydrogen blow pipes, to raise solid masses of refractory material to incandescence, and also by supplying oxygen in the same way to oil lamps of particular construction, to obtain a very great increase in illuminating power.

Whether these methods of employing cheap oxygen would be successful or not, I do not wish to discuss at the present time, but there is no doubt but that cheap oxygen would be an enormous boon to the gas manager, as by mixing 0.8 per cent. of oxygen with his coal gas before purification, he could not only utilize the method so successfully introduced by Mr. Valon at Ramsgate, but could also increase the illuminating value of his gas.

In speaking of the structure of flame, I pointed out that close to the burner from which the gas giving the flame is issuing, a space exists in which no combustion is going on--in other words, a flame is never in contact with the rim of the burner. This is best seen when the gas is turned low--with a batswing burner, for instance--turned so low that only a small non-luminous flame is left, the space between burner and flame will appear as great as the flame itself, while, if the gas is mixed with an inert diluent like carbon dioxide, the space can be very much increased.

Several theories have been brought forward to explain this phenomenon, but the true one is that the burner abstracts so much heat from the flame at that point that it is unable to burn there, and this can be proved by the fact that where a cold object touches the flame, a dividing space, similar to that noticed between flame and burner, will always be observed, and the colder the object and the more diluted the gas the greater is the observed space. If a cold metal wire or rod is held in a non-luminous flame, it causes an extinction of the gas for some considerable space around itself; but as the temperature of the rod rises, this space becomes smaller and smaller until the rod is heated to redness, and then the flame comes in contact with the rod.

In the same way, if the burner from which the gas is issuing be heated to redness, the space between burner and flame disappears. It has already been shown that cooling the flame by an inert diluent reduces the illuminating value, and finally renders it more luminous; and we are now in a position to discuss the points which should be aimed at in the construction of a good gas burner.

In the first place, a sensible diminution in light takes place when a metal burner is employed, and the larger the surface and thickness of the metal the worse will be its action on the illuminating power of the flame; but this cooling action is only influencing the bottom of the flame, so that with a small flame the total effect is very great, and with a very large flame almost _nil_.

The first point, therefore, to attend to is that the burner shall be made of a good non-conductor. In the next place, the flow of the gas must be regulated to the burner, as, if you have a pressure higher than that for which the burner is constructed, you at once obtain a roaring flame and a loss of illuminating power, as the too rapid rush of gas from the burner causes a mingling of gas and air and a consequent cooling of the flame. The tap also which regulates the flame is better at a distance from the burner than close to it, as any constriction near the burner causes eddies, which give an unsteady flame.

These general principles govern all burners, and we will now take the ordinary forms in detail. In the ordinary flat flame burner, given a good non-conducting material, and a well regulated gas supply, little more can be done, while burning it in the ordinary way, to increase its luminosity; and it is the large surface of flame exposed to the cooling action of the air which causes this form of burner to give the lowest service of any per cubic foot of gas consumed. Much is done, moreover, by faulty fittings and shades, to reduce the already poor light given out, because the light-yielding power of the flame largely depends upon its having a well rounded base and broad, luminous zone; and when a globe with a narrow opening is used with such a flame--as is done in 99 out of 100 cases--the updraught drags the flame out of shape, and seriously impairs its light-giving powers, a trouble which can be got over by having the globe with an opening at the bottom not less than 4 inches in diameter, and having small shoulders fixed to the burner, which draw out the flame and protect the base from the disturbing influence of draughts.

The Argand burner differs from the flat flame burners in that a circular flame is employed. The air supply is regulated by a cylindrical glass, and this form of burner gives a better service than the flat flame burner, as not only can the supply of gas and air be better adjusted, but the air being slightly warmed by the hot glass adds to the temperature of the flame, which is also increased by radiation from the opposite side of the flame itself.

The chief loss of light in such a burner depends upon the fact that, being circular, the light from the inner surface has to pass through the wall of flame, and careful photometric experiments show that the solid particles present in the flame so reduce its transparency that a loss amounting to about 25 per cent. of light takes place during its transmission.

The height of the flame also must be carefully adjusted to the size of the flame, as too long a chimney, by increasing the air supply unduly, cools, and so lowers the illuminating power of the flame. Experiments with carbureted water gas gave the following results, with a consumption of 5 cubic feet per hour:

Size of Chimney. | Height of Flame. | Candle Power. | ------------------+------------------+---------------| 6 X 1-7/8 | 2-1/2 | 21 | 7 X 1-7/8 | 2-1/4 | 21.3 | 8 X 1-7/8 | 2-1/8 | 20.8 | 9 X 1-7/8 | 1-7/8 | 18.2 | ------------------+------------------+---------------+

For many years no advance was made upon these forms of burner, but when, ten years ago, it was recognized that anything which cools the flame reduces its value, while anything which increases its temperature raises its illuminating power, then a change took place in the forms of burner in use, and the regenerative burners, introduced by such men as Siemens, Grimston, and Bower, commenced what was really a revolution in gas lighting.

By utilizing the heat contained in the escaping products of combustion to raise the temperature of the gas and air which are to enter into combination in the flame, an enormous increase in the temperature of the solid particles of carbon in the flame is obtained, and a far greater and whiter light is the result.

The Bower lamp, in which (at any rate in the later forms) the flame burns between a downward and an upward current of air, was one of the first produced, and so well has it been kept up to date that it still holds its own; while as types of the "inverted cone" regenerative burner, we may also take the Cromarty and Wenham lights, which have been followed by a host of imitators, and so closely are the original types adhered to that one begins seriously to wonder what the use of the Patent Office really is.

The Schulke, and the last form of Siemens regenerative burner, however, stand apart from all the others by dealing with flat and not conical flames, and in both regeneration is carried on to a high degree. The only drawback to the regenerative burner is that it is by far the best form of gas stove as well as burner, and that the amount of heat thrown out by the radiant solid matter in the flame is, under some circumstances, an annoyance. But, on the other hand, we must not forget that this is the form best adapted for overhead burners, and that nearly every form of regenerative lamp can be adapted as a ventilating agent, and that with the withdrawal of the products of combustion from the air of the room, the great and only serious objection to gas as an illuminant disappears.

When coal gas is burned, the hydrogen is supposed to be entirely converted into water vapor, and the carbon to finally escape into the air as carbon dioxide; and if this were so, every cubic foot of gas consumed would produce approximately 0.52 cubic foot of carbon dioxide and 1.34 cubic feet of water vapor, while the illuminating power yielded by the cubic foot of gas will, of course, vary with the kind of burner used.

Roughly speaking, the ordinary types of burner give the following results:

So that the regenerative forms of burner, by giving the greatest illuminating power per cubic foot of gas consumed, yield a smaller amount of vitiation to the air per candle of light emitted.

An ordinary room, say 16' X 12' X 10', would not be considered properly illuminated unless the light were at least equal to 32 candle power; and in the table below the amount of the oxygen used up and the products of combustion formed by each class of illuminant and burner in attaining this result are given, the number of adults who would exhale the same amount during respiration being also stated.

From these data it appears, according to rules by which the degree of vitiation of the air in any confined space is measured by the amount of oxygen used up and carbon dioxide formed, that candles are the worst offenders against health and comfort. Oil lamps come next, and gas least. This, however, is an assumption which practical experience does not bear out. Discomfort and oppression in a room lighted by candles or oil are less felt than in one lighted by any of the older forms of gas burner; and the partial explanation of this is to be found in the fact that, when a room is illuminated with candles or oil, people are contented with a feebler and more local light than when using gas. In a room of the size described, the inmates would be more likely to use two candles placed near their books, or on a table, than thirty-two scattered about the room.

Moreover, the amount of water vapor given off during the combustion of gas is greater than in the case of the other illuminants. Water vapor having a great power of absorbing radiant heat from the burning gas becomes heated, and diffusing itself about the room, causes great feeling of oppression; the air also being highly charged with moisture, is unable to take up so rapidly the water vapor which is always evaporating from the surface of our skin, whereby the functions of the body receive a slight check, resulting in a feeling of _malaise_.

Added to these, however, is a far more serious factor which has, up to the present, been overlooked, and that is that an ordinary gas flame, in burning, yields distinct quantities of carbon monoxide and acetylene, the prolonged breathing of which in the smallest traces produces headache and general physical discomfort, while its effect upon plant life is equally marked.

AMOUNT OF OXYGEN REMOVED FROM THE AIR, AND CARBON DIOXIDE AND WATER VAPOR GENERATED TO GIVE AN ILLUMINATION EQUAL TO 32 CANDLE POWER.

(The amount of light required in a room 16' X 12' x 10'.)

|Quantity of | | Products of Combustion| | | Materials | Oxygen | | Carbon | | Illuminant | Used | Removed |Water Vapor| Dioxide |Adults| --------------+------------+----------+-----------+-----------+------+ Sperm Candles |3,840 grains|19.27 c.f.|13.12 c.f. |13.12 c.f. | 21.8 | Paraffin Oil |1,984 " |12.48 c.f.| 7.04 c.f. | 8.96 c.f. | 14.9 | Gas (London)--| | | | | | Burners: | | | | | | Batswing | 11 c.f. |13.06 c.f.|14.72 c.f. | 5.76 c.f. | 9.6 | Argand | 9.7 c.f. |11.52 c.f.|12.80 c.f. | 5.12 c.f. | 8.5 | Regenerative| 3.2 c.f. | 3.68 c.f.| 4.16 c.f. | 1.60 c.f. | 2.6 |

Ever since the structure of flame has been noted and discussed, it has been accepted as a fact beyond dispute that the outer almost invisible zone which is interposed between the air and the luminous zone of the flame is the area of complete combustion, and that here the unburnt remnants of the flame gases, meeting the air, freely take up oxygen and are converted into the comparatively harmless products of combustion, carbon dioxide and water vapor, which only need partial removal by any haphazard process of ventilation to keep the air of the room fit to support animal life. I have, however, long doubted this fact, and at length, by a delicate process of analysis have been able to confirm my suspicions. The outer zone of a luminous flame is not the zone of complete combustion; it is a zone in which luminosity is destroyed in exactly the same way that it is destroyed in the Bunsen burner; that is the air penetrating the flame so dilutes and cools down the outer layer of incandescent gas that it is rendered non-luminous, while some of the gas sinks below the point at which it is capable of burning, with the result that considerable quantities of the products of incomplete combustion carbon monoxide and acetylene escape into the air, and render it actively injurious.

I have proved this by taking a small platinum pipe, with a circular loop on the end, the interior of the loop being pierced with minute holes, and by making a circular flame burn within the loop so that the non-luminous zone of the flame just touched the inside of the loop, and then by aspiration so gentle as not to distort the shape of the flame, withdrawing the gases escaping from the outer zone. On analyzing these by a delicate process, which will be described elsewhere, I arrived at the following results:

GASES ESCAPING FROM THE OUTER ZONE OF FLAME.

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.