+---------------+------------------+------------------+-------------------+
| | | Grains of Oil | |
| | | per candle-power |Total Candle-power.|
| Type. | Name. | per hour. | |
| | +---------+--------+---------+---------+
| | |American.|Russian.|American.| Russian.|
|---------------+------------------+---------+--------+---------+---------+
| /| Veritas, 60-line | 64.5 | 112.5 | 122.5 | 78 |
| | | " 30-line | 42.5 | 50. | 60 | 60 |
| | | " 20-line | 43.75 | 58.5 | 40 | 35 |
|Circular wick| | Ariel, 12-line | | | | |
| | | center draught | 52.8 | 70.9 | 18 | 18 |
| | | Reading, 14-line | 97.9 | 85.4 | 12 | 12 |
| | | Kosmos, 10-line | 63.9 | 97.2 | 9 | 9 |
| \| Wizard, 15-line | 56.9 | 51.3 | 18 | 19 |
| /| Wanzer, no glass | 42.6 | 48.3 | 17 | 17 |
|Flat wick, | | Solid slip, gauze| | | | |
| single | | and cone | 84.4 | 84.4 | 8 | 8 |
| | | Old slip, fixed | | | | |
| \| gauze | 60.9 | 89.3 | 7 | 7 |
|Flat wick, /| Feeder wick | 56.2 | 55.7 | 20 | 22 |
| duplex \| Ordinary | 51.2 | 46.6 | 20 | 22 |
+---------------+------------------+---------+--------+---------+---------+
American oil--Sp. gr. 0.7904; flash-point, 110°F. Russian oil--Sp.
gr. 0.823; flash-point, 83° F.
According to Sir Boverton Redwood, duplex burners which give a flame
of 28 candle-power have an average oil consumption of 50 grains per
candle per hour, while Argand flames of 38 candle-power consume about
45 grains of oil per candle per hour. These figures were obtained from
lamps of the best types, and to obtain information as to the
efficiency of the lamps used in daily practice, a number of the most
popular types were examined, using both American and Russian oil. The
results obtained are embodied in Table 1. The first noteworthy point
in this table is the apparent superiority of the American over Russian
oil in the majority of the lamps employed, and there is no doubt that
the bulk of the lamps on the market are constructed to burn American
or shale oil. A second interesting point is that with the flat-flame
lamps the Russian oil is as good as the American. We have Redwood's
authority, moreover, for the fact that after prolonged burning the
Russian oil, even in lamps least suited to it, gives highly improved
results. Although the average consumption with these lamps is close
upon 60 grains per candle with American oil, yet some of the burners
are so manifestly wasteful that 50 grains per candle-power per hour is
the fairest basis to take for any calculation as to cost.
The dangers of the mineral oil lamp, which were a grave drawback in
the past, have been very much reduced by improvements in construction
and quality, and if it were possible to abolish the cheap and
dangerous rubbish sold in poor neighbourhoods, and to prevent the use
of side-fillers and glass reservoirs in lamps of better quality, a
still larger reduction in the number of accidents would take place. In
the use of the lamp for domestic purposes only soft well-fitting wicks
should be employed, and the lamp should be filled with oil each day so
as never to allow it to burn too low and so leave a large space above
the surface of the oil in the reservoir. The lamp should never be
moved whilst alight, and it should only be put out by means of a
proper extinguisher or by blowing across the top instead of down the
chimney. By these means the risk of accident would be so reduced as to
compare favourably with other illuminants.
Candles, oil and coal gas all emit the same products of complete
combustion, viz. carbon dioxide and water vapour. The quantities of
these compounds emitted from different illuminants for every candle of
light per hour will be seen from the following table:
Cubic Feet per Candle
Illuminant. Carbon Dioxide. Water Vapour.
Sperm candle 0.41 0.41
Oil lamp 0.24 0.18
Gas--Flat flame 0.26 0.67
Argand 0.17 0.45
Regenerative 0.07 0.19
Incandescent 0.03 0.08
From these data it appears that if the sanitary condition of the air
of a dwelling-room be measured by the amount of carbon dioxide
present, as is usually done, candles are the most prejudicial to
health and comfort, oil lamps less so, and gas least, an assumption
which practical experience does not bear out. The explanation of this
is to be found in these facts: First, where we illuminate a room with
candles or oil we are contented with a less intense and more local
light than when we are using gas, and in a room of ordinary size would
be more likely to use a lamp or two candles than the far higher
illumination we should demand if gas were employed. Secondly, the
amount of water vapour given off during the combustion of gas is
greater than in the case of the other illuminants, and water vapour
absorbing radiant heat from the burning gas becomes heated, and,
diffusing itself about the room, causes great oppression. Also the
air, being highly charged with moisture, is unable to take up so
rapidly the water vapour which is always evaporating from the surface
of our skin, and in this way the functions of the body receive a
slight check, resulting in a feeling of depression.
Oil-spray lamps.
A very successful type of oil lamp for use in engineering is represented
by the Lucigen, Doty, and Wells lights, in which the oil is forced from
a reservoir by air-pressure through a spiral heated by the flame of the
lamp, and the heated oil, being then ejected partly as vapour and partly
as spray, burns with a large and highly luminous flame. The great
drawback to these devices is that a certain proportion of the oil spray
escapes combustion and is deposited in the vicinity of the light. This
form of lamp is often used for heating as well as lighting; the rivets
needed for the Forth Bridge were heated in trays by lamps of this type
at the spot where they were required. The great advantage of these lamps
was that oils of little value could be employed, and the light obtained
approximated to 750 candles per gallon of oil consumed. They may to a
certain extent be looked upon as the forerunners of perhaps the most
successful form of incandescent oil-burner.
Oil applied to incandescent lighting.
As early as 1885 Arthur Kitson attempted to make a burner for heating
purposes on the foregoing principle, i.e. by injecting oil under
pressure from a fine tube into a chamber where it would be heated by the
waste heat escaping from the flame below, the vapour so produced being
made to issue from a small jet under the pressure caused by the initial
air-pressure and the expansion in the gasifying tube. This jet of gas
was then led into what was practically an atmospheric burner, and drew
in with it sufficient air to cause its combustion with a non-luminous
blue flame of great heating power. At the time when this was first done
the Welsbach mantle had not yet reached the period of commercial
utility, and attempts were made to use this flame for the generation of
light by consuming it in a mantle of fine platinum gauze, which,
although giving a very fine illuminating effect during the first few
hours, very soon shared the fate of all platinum mantles--that is,
carbonization of the platinum surface took place, and destroyed its
power of light emissivity. It was not until 1893 that the perfecting of
the Welsbach mantle enabled this method of consuming the oil to be
employed. The Kitson lamp, and also the Empire lamp on a similar
principle, have given results which ought to ensure their future
success, the only drawback being that they need a certain amount of
intelligent care to keep them in good working order.
Incandescent table-lamps.
Oil gas and oil vapours differ from coal gas merely in the larger
proportion and greater complexity of the hydrocarbon molecules present,
and to render the oil flame available for incandescent lighting it is
only necessary to cause the oil gas or vapour to become mixed with a
sufficient proportion of air before it arrives at the point of
combustion. But with gases so rich in hydrocarbons as those developed
from oil it is excessively difficult to get the necessary air intimately
and evenly mixed with the gas in sufficient proportion to bring about
the desired result. If even coal gas be taken and mixed with 2.27
volumes of air, its luminosity is destroyed, but such a flame would be
useless with the incandescent mantle, as if the non-luminous flame be
superheated a certain proportion of its luminosity will reappear. When
such a flame is used with a mantle the superheating effect of the mantle
itself very quickly leads to the decomposition of the hydrocarbons and
blackening of the mantle, which not only robs it of its light-giving
powers, but also rapidly ends its life. If, however, the proportion of
air be increased, the appearance of the flame becomes considerably
altered, and the hydrocarbon molecules being burnt up before impact
with the heated surface of the mantle, all chance of blackening is
avoided.
On the first attempts to construct a satisfactory oil lamp which could
be used with the incandescent mantle, this trouble showed itself to be
a most serious one, as although it was comparatively easy so to
regulate a circular-wicked flame fed by an excess of air as to make it
non-luminous, the moment the mantle was put upon this, blackening
quickly appeared, while when methods for obtaining a further air
supply were devised, the difficulty of producing a flame which would
burn for a considerable time without constant necessity for regulation
proved a serious drawback. This trouble has militated against most of
the incandescent oil lamps placed upon the market.
It soon became evident that if a wick were employed the difficulty of
getting it perfectly symmetrical was a serious matter, and that it
could only be utilized in drawing the oil up to a heating chamber
where it could be volatilized to produce the oil gas, which on then
being mixed with air would give the non-luminous flame. In the earlier
forms of incandescent oil lamps the general idea was to suck the oil
up by the capillarity of a circular wick to a point a short distance
below the opening of the burner at which the flame was formed, and
here the oil was vaporized or gasified by the heat of the head of the
burner. An air supply was then drawn up through a tube passing through
the centre of the wick-tube, while a second air current was so
arranged as to discharge itself almost horizontally upon the burning
gas below the cap, in this way giving a non-luminous and very hot
flame, which if kept very carefully adjusted afforded excellent
results with an incandescent mantle. It was an arrangement somewhat of
this character that was introduced by the Welsbach Company. The lamps,
however, required such careful attention, and were moreover so
irregular in their performance, that they never proved very
successful. Many other forms have reached a certain degree of
perfection, but have not so far attained sufficient regularity of
action to make them commercial successes. One of the most successful
was devised by F. Altmann, in which an ingenious arrangement caused
the vaporization of oil and water by the heat of a little oil lamp in
a lower and separate chamber, and the mixture of oil gas and steam was
then burnt in a burner-head with a special arrangement of air supply,
heating a mantle suspended above the burner-head.
The perfect petroleum incandescent lamp has not yet been made, but the
results thus obtained show that when the right system has been found a
very great increase in the amount of light developed from the
petroleum may be expected. In one lamp experimented with for some time
it was easy to obtain 3500 candle hours per gallon of oil, or three
times the amount of light obtainable from the oil when burnt under
ordinary conditions.
Air-gas.
Before the manufacture of coal-gas had become so universal as it is at
present, a favourite illuminant for country mansions and even villages
where no coal-gas was available was a mixture of air with the vapour of
very volatile hydrocarbons, which is generally known as "air-gas." This
was produced by passing a current of dry air through or over petroleum
spirit or the light hydrocarbons distilled from tar, when sufficient of
the hydrocarbon was taken up to give a luminous flame in flat flame and
Argand burners in the same way as coal-gas, the trouble being that it
was difficult to regulate the amount of hydrocarbon held in suspension
by the air, as this varied very widely with the temperature. As coal-gas
spread to the smaller villages and electric lighting became utilized in
large houses, the use of air-gas died out, but with the general
introduction of the incandescent mantle it again came to the front. In
the earlier days of this revival, air-gas rich in hydrocarbon vapour was
made and was further aerated to give a non-luminous flame by burning it
in an atmospheric burner.
One of the best illustrations of this system was the Aerogene gas
introduced by A. I. van Vriesland, which was utilized for lighting a
number of villages and railway stations on the continent of Europe. In
this arrangement a revolving coil of pipes continually dips into
petroleum spirit contained in a cylinder, and the air passed into the
cylinder through the coil of pipes becomes highly carburetted by the
time it reaches the outlet at the far end of the cylinder. The
resulting gas when burnt in an ordinary burner gives a luminous flame;
it can be used in atmospheric burners differing little from those of
the ordinary type. With an ordinary Welsbach "C" burner it gives a
duty of about 30 candles per foot of gas consumed, the high
illuminating power being due to the fact that the gas is under a
pressure of from 6 to 8 in. With such a gas, containing a considerable
percentage of hydrocarbon vapour, any leakage into the air of a room
would give rise to an explosive mixture, in the same way that coal-gas
would do, but inasmuch as mixtures of the vapour of petroleum spirit
and air are only explosive for a very short range, that is, from 1.25
to 5.3%, some systems have been introduced in which by keeping the
amount of petroleum vapour at 2% and burning the gas under pressure in
a specially constructed non-aerating mantle burner, not only has it
been found possible to produce a very large volume of gas per gallon
of spirit employed, but the gas is itself non-explosive, increase in
the amount of air taking it farther away from the explosive limit. The
Hooker, De Laitte and several other systems have been based upon this
principle.