Acetylene, The Principles Of Its Generation And Use

F >> F. H. Leeds and W. J. Atkinson Butterfield >> Acetylene, The Principles Of Its Generation And Use

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Neuberg gives these figures for different burners (1900) as supplied by
Pintsch:

______________________________________________________________________
| | | | | |
| | Gas | | Candles | |
| Burner. | Pressure, | Consumed, | Light in | per |
| | Inches | Cubic Feet | Candles. | Cubic Foot. |
| | | per Hour. | | |
|____________________|___________|____________|__________|_____________|
| | | | | |
| No. 0, slit burner | 3.9 | 1.59 | 59.2 | 37.3 |
| " 00000 fishtail | 1.6 | 0.81 | 31.2 | 38.5 |
| Twin burner No. 1 | 3.2 | 0.32 | 13.1 | 40.8 |
| " " " 2 | 3.2 | 0.53 | 21.9 | 41.3 |
| " " " 3 | 3.2 | 0.74 | 31.0 | 41.9 |
| " " " 4 | 3.2 | 0.95 | 39.8 | 41.9 |
|____________________|___________|____________|__________|_____________|

The actual candle-power developed by each burner was not quoted by
Neuberg, and has accordingly been calculated from his efficiency values.
It is noteworthy, and in opposition to what has been found by other
investigators as well as to strict theory, that Neuberg represents the
efficiencies to be almost identical in all sizes of the same description
of burner, irrespective of the rate at which it consumes gas.

Writing in 1902, Capelle gave for Stadelmann's twin injector burners the
following figures; but as he examined each burner at several different
pressures, the values recorded in the second, third, and fourth columns
are maxima, showing the highest candle-power which could be procured from
each burner when the pressure was adjusted so as to cause consumption to
proceed at the most economical rate. The efficiency values in the fifth
column, however, are the mean values calculated so as to include all the
data referring to each burner. Capelle's results have been reproduced
from the original on the basis that 1 _bougie decimale_ equals 0.98
standard English candle, which is the value he himself ascribes to it (1
_bougie decimale_ equals 1.02 candles is the value now accepted).

_____________________________________________________________________
| | | | | |
| Nominal | Best | Actual Consumption | Maximum | Average |
| Consumption,| Pressure| at Stated Pressure. | Light in | Candles per|
| Litres. | Inches. | Cubic Feet per Hour.| Candles. | Cubic Foot.|
|_____________|_________|_____________________|__________|____________|
| | | | | |
| 10 | 3.5 | 0.40 | 8.4 | 21.1 |
| 15 | 2.8 | 0.46 | 16.6 | 33.3 |
| 20 | 3.9 | 0.64 | 25.1 | 40.0 |
| 25 | 3.5 | 0.84 | 37.8 | 46.1 |
| 30 | 3.5 | 0.97 | 48.2 | 49.4 |
|_____________|_________|_____________________|__________|____________|

Some testings of various self-luminous burners of which the results were
reported by R. Granjon in 1907, gave the following results for the duty
of each burner, when the pressure was regulated for each burner to that
which afforded the maximum illuminating duty. The duty in the original
paper is given in litres per Carcel-hour. The candle has been taken as
equal to 0.102 Carcel for the conversion to candles per cubic foot.

___________________________________________________________________
| | | | |
| | Nominal | Best | Duty. Candles |
| Burner. | Consumption.| Pressure. | per cubic foot. |
|_______________________|_____________|__________ |_________________|
| | | | |
| | Litres. | Inches. | |
| Twin . . . . | 10 | 2.76 | 21.2 |
| " . . . . | 20 | 2.76 | 23.5 |
| " . . . . | 25 | 3.94 | 30.2 |
| " . . . . | 30 | 3.94-4.33 | 44.8 |
| ", (pair of flames) | 35 | 3.55-3.94 | 45.6 |
| Bray's "Manchester" | 6 | 1.97 | 18.8 |
| " | 20 | 1.97 | 35.6 |
| " | 40 | 2.36 | 42.1 |
| Rat-tail . . . | 5 | 5.5 | 21.9 |
| " . . . | 8 | 4.73 | 25.0 |
| Slit or batswing . | 30 | 1.97-2.36 | 37.0 |
|_______________________|_____________|___________|_________________|

Granjon has concluded from his investigations that the Manchester or
fish-tail burners are economical when they consume 0.7 cubic foot per
hour and when the pressure is between 2 and 2.4 inches. When these
burners are used at the pressure most suitable for twin burners their
consumption is about one-third greater than that of the latter per
candle-hour. The 25 to 35 litres-per-hour twin burners should be used at
a pressure higher by about 1 inch than the 10 to 20 litres-per-hour twin
burners.

At the present time, when the average burner has a smaller hourly
consumption than 1 foot per hour, it is customary in Germany to quote the
mean illuminating value of acetylene in self-luminous burners as being 1
Hefner unit per 0.70 litre, which, taking

1 Hefner unit = 0.913 English candle

1 English candle = 1.095 Hefner units,

works out to an efficiency of 37 candles per foot in burners probably
consuming between 0.5 and 0.7 foot per hour.

Even when allowance is made for the difficulties in determining
illuminating power, especially when different photometers, different
standards of light, and different observers are concerned, it will be
seen that these results are too irregular to be altogether trustworthy,
and that much more work must be done on this subject before the economy
of the acetylene flame can be appraised with exactitude. However, as
certain fixed data are necessary, the authors have studied those and
other determinations, rejecting some extreme figures, and averaging the
remainder; whence it appears that on an average twin-injector burners of
different sizes should yield light somewhat as follows:

_______________________________________________________
| | | |
| Size of Burner in | Candle-power | Candles |
| Cubic Feet per Hour. | Developed. | per Cubic Foot. |
|______________________|______________|_________________|
| | | |
| 0.5 | 18.0 | 35.9 |
| 0.7 | 27.0 | 38.5 |
| 1.0 | 45.6 | 45.6 |
|______________________|______________|_________________|

In the tabular statement in Chapter I. the 0.7-foot burner was taken as
the standard, because, considering all things, it seems the best, to
adopt for domestic purposes. The 1-foot burner is more economical when in
the best condition, but requires a higher gas pressure, and is rather too
powerful a unit light for good illuminating effect; the 0.5 burner
naturally gives a better illuminating effect, but its economy is
surpassed by the 0.7-foot burner, which is not too powerful for the human
eye.

For convenience of comparison, the illuminating powers and duties of the
0.5- and 0.7-foot acetylene burners may be given in different ways:

ILLUMINATING POWER OF SELF-LUMINOUS ACETYLENE.

_0.7-foot Burner._ | _Half-foot Burner._
|
1 litre = 1.36 candles. | 1 litre = 1.27 candles.
1 cubic foot = 38.5 candles. | 1 cubic foot = 35.9 candles.
1 candle = 0.736 litre. | 1 candle = 0.79 litre.
1 candle = 0.026 cubic foot. | 1 candle = 0.028 cubic foot.

If the two streams of gas impinge at an angle of 90 deg., twin-injector
burners for acetylene appear to work best when the gas enters them at a
pressure of 2 to 2.5 inches; for a higher pressure the angle should be
made a little acute. Large burners require to have a wider distance
between the jets, to be supplied with acetylene at a higher pressure, and
to be constructed with a smaller angle of impingement. Every burner, of
whatever construction and size, must always be supplied with gas at its
proper pressure; a pressure varying from time to time is fatal.

It is worth observing that although injector burners are satisfactory in
practice, and are in fact almost the only jets yet found to give
prolonged satisfaction, the method of injecting air below the point of
combustion in a self-luminous burner is in some respects wrong in
principle. If acetylene can be consumed without polymerisation in burners
of the simple fish-tail or bat's-wing type, it should show a higher
illuminating efficiency. In 1902 Javal stated that it was possible to
burn thoroughly purified acetylene in twin non-injector burners, provided
the two jets, made of steatite as usual, were arranged horizontally
instead of obliquely, the two streams of gas then meeting at an angle of
180 deg., so as to yield an almost circular flame. According to Javal,
whereas carbonaceous growths were always produced in non-injector
acetylene burners with either oblique or horizontal jets, in the former
case the growths eventually distorted the gas orifices, but in the latter
the carbon was deposited in the form of a tube, and fell off from the
burner by its own weight directly it had grown to a length of 1.2 or 1.5
millimetres, leaving the jets perfectly clear and smooth. Javal has had
such a burner running for 10 or 12 hours per day for a total of 2071
hours; it did not need cleaning out on any occasion, and its consumption
at the end of the period was the same as at first. He found that it was
necessary that the tips should be of steatite, and not of metal or glass;
that the orifices should be drilled in a flat surface rather than at the
apex of a cone, and that the acetylene should be purified to the utmost
possible extent. Subsequent experience has demonstrated the possibility
of constructing non-injector burners such as that shown in Fig. 13, which
behave satisfactorily even though the jets are oblique. But with such
burners trouble will inevitably ensue unless the gas is always purified
to a high degree and is tolerably dry and well filtered. Non-injector
burners should not be used unless special care is taken to insure that
the installation is consistently operated in an efficient manner in these
respects.

GLOBES, &C.--It does not fall within the province of the present volume
to treat at length of chimneys, globes, or the various glassware which
may be placed round a source of light to modify its appearance. It should
be remarked, however, that obedience to two rules is necessary for
complete satisfaction in all forms of artificial illumination. First, no
light much stronger in intensity than a single candle ought ever to be
placed in such a position in an occupied room that its direct rays can
reach the eye, or the vision will be temporarily, and may be permanently,
injured. Secondly, unless economy is to be wholly ignored, no coloured or
tinted globe or shade should ever be put round a source of artificial
light. The best material for the construction of globes is that which
possesses the maximum of translucency coupled with non-transparency,
_i.e._, a material which passes the highest proportion of the light
falling upon it, and yet disperses that light in such different
directions that the glowing body cannot be seen through the globe. Very
roughly speaking, plain white glass, such as that of which the chimneys
of oil-lamps and incandescent gas-burners are composed, is quite
transparent, and therefore affords no protection to the eyesight; a
protective globe should be rather of ground or opal glass, or of plain
glass to which a dispersive effect has been given by forming small prisms
on its inner or outer surface, or both. Such opal, ground, or dispersive
shades waste much light in terms of illuminating power, but waste
comparatively little in illuminating effect well designed, they may
actually increase the illuminating effect in certain positions; a tinted
globe, even if quite plain in figure, wastes both illuminating power and
effect, and is only to be tolerated for so-believed aesthetic reasons.
Naturally no globe must be of such figure, or so narrow at either
orifice, as to distort the shape of the unshaded acetylene flame--it is
hardly necessary to say this now, but some years ago coal-gas globes were
constructed with an apparent total disregard of this fundamental point.

CHAPTER IX

INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING

MERITS OF LIGHTING BY INCANDESCENT MANTLES.--It has already been shown
that acetylene bases its chief claim for adoption as an illuminant in
country districts upon the fact that, when consumed in simple self-
luminous burners, it gives a light comparable in all respects save that
of cost to the light of incandescent coal-gas. The employment of a mantle
is still accompanied by several objections which appear serious to the
average householder, who is not always disposed either to devote
sufficient attention to his burners to keep them in a high state of
efficiency or to contract for their maintenance by the gas company or
others. Coal-gas cannot be burnt satisfactorily on the incandescent
system unless the glass chimneys and shades are kept clean, unless the
mantles are renewed as soon as they show signs of deterioration, and,
perhaps most important of all, unless the burners are frequently cleared
of the dust which collects round the jets. For this reason luminous
acetylene ranks with luminous coal-gas in convenience and simplicity,
while ranking with incandescent coal-gas in hygienic value. Very similar
remarks apply to paraffin, and, in certain countries, to denatured
alcohol. Since those latter illuminants are also available in rural
places where coal-gas is not laid on, luminous acetylene is a less
advantageous means of procuring artificial light than paraffin (and on
occasion than coal-gas and alcohol when the latter fuels are burnt under
the mantle), if the pecuniary aspect of the question is the only one
considered. Such a comparison, however, is by no means fair; for if coal-
gas, paraffin, and alcohol can be consumed on the incandescent system, so
can acetylene; and if acetylene is hygienically equal to incandescent
coal-gas, it is superior thereto when also burnt under the mantle.
Nevertheless there should be one minor but perfectly irremediable defect
in incandescent acetylene, viz., a sacrifice of that characteristic
property of the luminous gas to emit a light closely resembling that of
the sun in tint, which was mentioned in Chapter 1. Self-luminous
acetylene gives the whitest light hitherto procurable without special
correction of the rays, because its light is derived from glowing
particles of carbon which happen to be heated (because of the high flame
temperature) to the best possible temperature for the emission of pure
white light. The light of any combustible consumed on the "incandescent"
system is derived from glowing particles of ceria, thoria, or similar
metallic oxides; and the character or shade of the light they emit is a
function, apart from the temperature to which they are raised, of their
specific chemical nature. Still, the light of incandescent acetylene is
sufficiently pleasant, and according to Caro is purer white than that of
incandescent coal-gas; but lengthy tests carried out by one of the
authors actually show it to be appreciably inferior to luminous acetylene
for colour-matching, in which the latter is known almost to equal full
daylight, and to excel every form of artificial light except that of the
electric arc specially corrected by means of glass tinted with copper
salts.

CONDITIONS FOR INCANDESCENT ACETYLENE LIGHTING.--For success in the
combustion of acetylene on the incandescent system, however, several
points have to be observed. First, the gas must be delivered at a
strictly constant pressure to the burner, and at one which exceeds a
certain limit, ranging with different types and different sizes of burner
from 2 to 4 or 5 inches of water. (The authors examined, as long ago as
1903, an incandescent burner of German construction claimed to work at a
pressure of 1.5 inches, which it was almost impossible to induce to fire
back to the jets however slowly the cock was manipulated, provided the
pressure of the gas was maintained well above the point specified. But
ordinarily a pressure of about 4 inches is used with incandescent
acetylene burners.) Secondly, it is necessary that the acetylene shall at
all times be free from appreciable admixture with air, even 0.5 per cent,
being highly objectionable according to Caro; so that generators
introducing any noteworthy amount of air into the holder each time their
decomposing chambers are opened for recharging are not suitable for
employment when incandescent burners are contemplated. The reason for
this will be more apparent later on, but it depends on the obvious fact
that if the acetylene already contains an appreciable proportion of air,
when a further quantity is admitted at the burner inlets, the gaseous
mixture contains a higher percentage of oxygen than is suited to the size
and design of the burner, so that flashing back to the injector jets is
imminent at any moment, and may be determined by the slightest
fluctuation in pressure--if, indeed, the flame will remain at the proper
spot for combustion at all. Thirdly, the fact that the acetylene which is
to be consumed under the mantle must be most rigorously purified from
phosphorus compounds has been mentioned in Chapter V. Impure acetylene
will often destroy a mantle in two or three hours; but with highly
purified gas the average life of a mantle may be taken, according to
Giro, at 500 or 600 hours. It is safer, however, to assume a rather
shorter average life, say 300 to 400 burning hours. Fourthly, owing to
the higher pressure at which acetylene must be delivered to an
incandescent burner and to the higher temperature of the acetylene flame
in comparison with coal-gas, a mantle good enough to give satisfactory
results with the latter does not of necessity answer with acetylene; in
fact, the authors have found that English Welsbach coal-gas mantles of
the small sizes required by incandescent acetylene burners are not
competent to last for more than a very few hours, although, in identical
conditions, mantles prepared specially for use with acetylene have proved
durable. The atmospheric acetylene flame, too, differs in shape from an
atmospheric flame of coal-gas, and it does not always happen that a coal-
gas mantle contracts to fit the former; although it usually emits a
better light (because it fits better) after some 20 hours use than at
first. Caro has stated that to derive the best results a mantle needs to
contain a larger proportion of ceria than the 1 per cent. present in
mantles made according to the Welsbach formula, that it should be
somewhat coarser in mesh, and have a large orifice at the head. Other
authorities hold that mantles for acetylene, should contain other rare
earths besides the thoria and ceria of which the coal-gas mantles almost
wholly consist. It seems probable, however, that the composition of the
ordinary impregnating fluid need not be varied for acetylene mantles
provided it is of the proper strength and the mantles are raised to a
higher temperature in manufacture than coal-gas mantles by the use of
either coal-gas at very high pressure or an acetylene flame. The
thickness of the substance of the mantle cannot be greatly increased with
a view to attaining greater stability without causing a reduction in the
light afforded. But the shape should be such that the mantle conforms as
closely as possible to the acetylene Bunsen flame, which differs slightly
with different patterns of incandescent burner heads. According to L.
Cadenel, the acetylene mantle should be cylindrical for the lower two-
thirds of its length, and slightly conical above, with an opening of
moderate size at the top. The head of the mantle should be of slighter
construction than that of coal-gas mantles. Fifthly, generators belonging
to the automatic variety, which in most forms inevitably add more or less
air to the acetylene every time they are cleaned or charged, appear to
have achieved most popularity in Great Britain; and these frequently do
not yield a gas fit for use with the mantle. This state of affairs, added
to what has just been said, makes it difficult to speak in very
favourable terms of the incandescent acetylene light for use in Great
Britain. But as the advantages of an acetylene not contaminated with air
are becoming more generally recognised, and mantles of several different
makes are procurable more cheaply, incandescent acetylene is now more
practicable than hitherto. Carburetted acetylene or "carburylene," which
is discussed later, is especially suitable for use with mantle burners.

ATMOSPHERIC ACETYLENE BURNERS.--The satisfactory employment of acetylene
in incandescent burners, for boiling, warming, and cooking purposes, and
also to some extent as a motive power in small engines, demands the
production of a good atmospheric or non-luminous flame, _i.e._, the
construction of a trustworthy burner of the Bunsen type.
This has been exceedingly difficult to achieve for two reasons: first,
the wide range over which mixtures of acetylene and air are explosive;
secondly, the high speed at which the explosive wave travels through such
a mixture. It has been pointed out in Chapter VIII. that a Bunsen burner
is one in which a certain proportion of air is mixed with the gas before
it arrives at the actual point of ignition; and as that proportion must
be such that the mixture falls between the upper and lower limits of
explosibility, there is a gaseous mixture in the burner tube between the
air inlets and the outlet which, if the conditions are suitable, will
burn with explosive force: that is to say, will fire back to the air jets
when a light is applied to the proper place for combustion. Such an
explosion, of course, is far too small in extent to constitute any danger
to person or property; the objection to it is simply that the shock of
the explosion is liable to fracture the fragile incandescent mantle,
while the gas, continuing to burn within the burner tube (in the case of
a warming or cooking stove), blocks up that tube with carbon, and
exhibits the other well-known troubles of a coal-gas stove which has
"fired back."

It has been shown, however, in Chapter VI. that the range over which
mixtures of acetylene and air are explosive depends on the size of the
vessel, or more particularly on the diameter of the tube, in which they
are stored; so that if the burner tube between the air inlets and the
point of ignition can be made small enough in diameter, a normally
explosive mixture will cease to exhibit explosive properties. Manifestly,
if a tube is made very small in diameter, it will only pass a small
volume of gas, and it may be useless for the supply of an atmospheric
burner; but Le Chatelier's researches have proved that a tube may be
narrowed at one spot only, in such fashion that the explosive wave
refuses to pass the constriction, while the virtual diameter of the tube,
as far as passage of gas is concerned, remains considerably larger than
the size of the constriction itself. Moreover, inasmuch as the speed of
propagation of the explosion is strictly fixed by the conditions
prevailing, if the speed at which the mixture, of acetylene and air
travels from the air inlets to the point of ignition is more rapid than
the speed at which the explosion tends to travel from the point of
ignition to the air inlets, the said mixture of acetylene and air will
burn quietly at the orifice without attempting to fire backwards into the
tube. By combining together these two devices: by delivering the
acetylene to the injector jet at a pressure sufficient to drive the
mixture of gas and air forward rapidly enough, and by narrowing the
leading tube either wholly or at one spot to a diameter small enough, it
is easy to make an atmospheric burner for acetylene which behaves
perfectly as long as it is fairly alight, and the supply of gas is not
checked; but further difficulties still remain, because at the instant of
lighting and extinguishing, i.e., while the tap is being turned on or
off, the pressure of the gas is too small to determine a flow of
acetylene and air within the tube at a speed exceeding that of the
explosive wave; and therefore the act of lighting or extinguishing is
very likely to be accompanied by a smart explosion severe enough to split
the mantle, or at least to cause the burner to fire back. Nevertheless,
after several early attempts, which were comparative failures,
atmospheric acetylene burners have been constructed that work quite
satisfactorily, so that the gas has become readily available for use
under the mantle, or in heating stoves. Sometimes success has been
obtained by the employment of more than one small tube leading to a
common place of ignition, sometimes by the use of two or more fine wire-
gauze screens in the tube, sometimes by the addition of an enlarged head
to the burner in which head alone thorough mixing of the gas and air
occurs, and sometimes by the employment of a travelling sleeve which
serves more or less completely to block the air inlets.

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