Vegetable and animal oils.
From the earliest times the burning of oil has been a source of light,
but until the middle of the 19th century only oils of vegetable and
animal origin were employed in indoor lamps for this purpose. Although
many kinds were used locally, only colza and sperm oils had any very
extended use, and they have been practically supplanted by mineral oil,
which was introduced as an illuminant in 1853. Up to the latter half of
the 18th century the lamps were shallow vessels into which a short
length of wick dipped; the flame was smoky and discharged acrid vapours,
giving the minimum of light with the maximum of smell. The first notable
improvement was made by Ami Argand in 1784. His burner consisted of two
concentric tubes between which the tubular wick was placed; the open
inner tube led a current of air to play upon the inner surface of the
circular flame, whilst the combustion was materially improved by placing
around the flame a chimney which rested on a perforated gallery a short
distance below the burner. Argand's original burner is the parent form
of innumerable modifications, all more or less complex, such as the
Carcel and the moderator.
[Illustration: FIG. 1.]
A typical example of the Argand burner and chimney is represented in
fig. 1, in which the burner is composed of three tubes, d, f, g. The
tube g is soldered to the bottom of the tube d, just above o, and the
interval between the outer surface of the tube g and the inner surface
of the tube d is an annular cylindrical cavity closed at the bottom,
containing the cylindrical cotton wick immersed in oil. The wick is
fixed to the wick tube ki, which is capable of being moved spirally;
within the annular cavity is also the tube f, which can be moved
round, and serves to elevate and depress the wick. P is a cup that
screws on the bottom of the tube d, and receives the superfluous oil
that drops down from the wick along the inner surface of the tube g.
The air enters through the holes o, o, and passes up through the tube
g to maintain the combustion in the interior of the circular flame.
The air which maintains the combustion on the exterior part of the
wick enters through the holes m, with which rn is perforated. When the
air in the chimney is rarefied by the heat of the flame, the
surrounding heavier air, entering the lower part of the chimney,
passes upward with a rapid current, to restore the equilibrium. RG is
the cylindrical glass chimney with a shoulder or constriction at R, G.
The oil flows from a side reservoir, and occupies the cavity between
the tubes g and d. The part ki is a short tube, which receives the
circular wick, and slides spirally on the tube g, by means of a pin
working in the hollow spiral groove on the exterior surface of g. The
wick-tube has also a catch, which works in a perpendicular slit in the
tube f; and, by turning the tube f, the wick-tube will be raised or
lowered, for which purpose a ring, or gallery, rn, fits on the tube d,
and receives the glass chimney RG; a wire S is attached to the tube f,
and, bending over, descends along the outside of d. The part rn, that
supports the glass chimney, is connected by four other wires with the
ring q, which surrounds the tube d, and can be moved round. When rn is
turned round, it carries with it the ring q, the wire S, and the tube
f, thus raising or depressing the wick.
A device in the form of a small metallic disk or button, known as the
Liverpool button from having been first adopted in the so-called
Liverpool lamp, effects for the current of air passing up the interior
of the Argand burner the same object as the constriction of the
chimney RG secures in the case of the external tube. The button fixed
on the end of a wire is placed right above the burner tube g, and
throws out equally all round against the flame the current of air
which passes up through g. The result of these expedients, when
properly applied, is the production of an exceedingly solid brilliant
white light, absolutely smokeless, this showing that the combustion of
the oil is perfectly accomplished.
[Illustration: FIG. 2.--Section of Reading Lamp.]
The means by which a uniformly regulated supply of oil is brought to
the burner varies with the position of the oil reservoir. In some
lamps, not now in use, by ring-formed reservoirs and other expedients,
the whole of the oil was kept as nearly as possible at the level of
the burner. In what are termed fountain reading, or study lamps, the
principal reservoir is above the burner level, and various means are
adopted for maintaining a supply from them at the level of the burner.
But the most convenient position for the oil reservoir in lamps for
general use is directly under the burner, and in this case the stand
of the lamp itself is utilized as the oil vessel. In the case of fixed
oils, as the oils of animal and vegetable origin used to be called, it
is necessary with such lamps to introduce some appliance for forcing a
supply of oil to the burner, and many methods of effecting this were
devised, most of which were ultimately superseded by the moderator
lamp. The Carcel or pump lamp, invented by B. G. Carcel in 1800, is
still to some extent used in France. It consists of a double piston or
pump, forcing the oil through a tube to the burner, worked by
clockwork.
A form of reading lamp still in use is seen in section in fig. 2. The
lamp is mounted on a standard on which it can be raised or lowered at
will, and fixed by a thumb screw. The oil reservoir is in two parts,
the upper ac being an inverted flask which fits into bb, from which
the burner is directly fed through the tube _d_; _h_ is an overflow
cup for any oil that escapes at the burner, and it is pierced with
air-holes for admitting the current of air to the centre tube of the
Argand burner. The lamp is filled with oil by withdrawing the flask
ac, filling it, and inverting it into its place. The under reservoir
_bb_ fills from it to the burner level ee, on a line with the mouth of
ac. So soon as that level falls below the mouth of _ac_, a bubble of
air gets access to the upper reservoir, and oil again fills up bb to
the level _ee_.
[Illustration: FIG. 3.--Section of Moderator Lamp.]
The moderator lamp (fig. 3), invented by Franchot about 1836, from the
simplicity and efficiency of its arrangements rapidly superseded
almost all other forms of mechanical lamp for use with animal and
vegetable oils. The two essential features of the moderator lamp are
(1) the strong spiral spring which, acting on a piston within the
cylindrical reservoir of the lamp, serves to propel the oil to the
burner, and (2) the ascending tube C through which the oil passes
upwards to the burner. The latter consist of two sections, the lower
fixed to and passing through the piston A into the oil reservoir, and
the upper attached to the burner. The lower or piston section moves
within the upper, which forms a sheath enclosing nearly its whole
length when the spring is fully wound up. Down the centre of the upper
tube passes a wire, "the moderator," G, and it is by this wire that
the supply of oil to the burner is regulated. The spring exerts its
greatest force on the oil in the reservoir when it is fully wound up,
and in proportion as it expands and descends its power decreases. But
when the apparatus is wound up the wire passing down the upper tube
extends throughout the whole length of the lower and narrower piston
tube, obstructing to a certain extent the free flow of the oil. In
proportion as the spring uncoils, the length of the wire within the
lower tube is decreased; the upward flow of oil is facilitated in the
same ratio as the force urging it upwards is weakened. In all
mechanical lamps the flow is in excess of the consuming capacity of
the burner, and in the moderator the surplus oil, flowing over the
wick, falls back into the reservoir above the piston, whence along
with new supply oil it descends into the lower side by means of
leather valves a, a. B represents the rack which, with the pinion D,
winds up the spiral spring hard against E when the lamp is prepared
for use. The moderator wire is seen separately in GG; and FGC
illustrates the arrangement of the sheathing tubes, in the upper
section of which the moderator is fixed.
Mineral oils.
As early as 1781 the idea was mooted of burning naphtha, obtained by the
distillation of coal at low temperatures, for illuminating purposes, and
in 1820, when coal gas was struggling into prominence, light oils
obtained by the distillation of coal tar were employed in the Holliday
lamp, which is still the chief factor in illuminating the street barrow
of the costermonger. In this lamp the coal naphtha is in a conical
reservoir, from the apex of which it flows slowly down through a long
metal capillary to a rose burner, which, heated up by the flame,
vaporizes the naphtha, and thus feeds the ring of small jets of flame
escaping from its circumference.
It was in 1847 that James Young had his attention drawn to an exudation
of petroleum in the Riddings Colliery at Alfreton, in Derbyshire, and
found that he could by distillation obtain from it a lubricant of
considerable value. The commercial success of this material was
accompanied by a failure of the supply, and, rightly imagining that as
the oil had apparently come from the Coal Measures, it might be obtained
by distillation from material of the same character, Young began
investigations in this direction, and in 1850 started distilling oils
from a shale known as the "Bathgate mineral," in this way founding the
Scotch oil industry. At first little attention was paid to the fitness
of the oil for burning purposes, although in the early days at Alfreton
Young attempted to burn some of the lighter distillates in an Argand
lamp, and later in a lamp made many years before for the consumption of
turpentine. About 1853, however, it was noticed that the lighter
distillates were being shipped to Germany, where lamps fitted for the
consumption of the grades of oil now known as lamp oil were being made
by Stohwasser of Berlin; some of these lamps were imported, and similar
lamps were afterwards manufactured by Laidlaw in Edinburgh.
In Pennsylvania in 1859 Colonel E. L. Drake's successful boring for
petroleum resulted in the flooding of the market with oil at prices
never before deemed possible, and led to the introduction of lamps from
Germany for its consumption. Although the first American patent for a
petroleum lamp is dated 1859, that year saw forty other applications,
and for the next twenty years they averaged about eighty a year.
English lamp-makers were not behind in their attempts to improve on the
methods in use for producing the highest results from the various grades
of oil, and in 1865 Hinks introduced the duplex burner, while later
improvements made in various directions, by Hinks, Silber, and Defries
led to the high degree of perfection to be found in the lamps of to-day.
Mineral oil for lamps as used in England at the present time may be
defined as consisting of those portions of the distillate from shale oil
or crude petroleum which have their flash-point above 73° F., and which
are mobile enough to be fed by capillarity in sufficient quantity to the
flame. The oil placed in the lamp reservoir is drawn up by the
capillarity of the wick to the flame, and being there volatilized, is
converted by the heat of the burning flame into a gaseous mixture of
hydrogen and hydrocarbons, which is ultimately consumed by the oxygen of
the air and converted into carbon dioxide and water vapour, the products
of complete combustion.
To secure high illuminating power, together with a smokeless flame and
only products of complete combustion, strict attention must be paid to
several important factors. In the first place, the wick must be so
arranged as to supply the right quantity of oil for gasification at
the burner-head--the flame must be neither starved nor overfed: if the
former is the case great loss of light is occasioned, while an excess
of oil, by providing more hydrocarbons than the air-supply to the
flame can completely burn, gives rise to smoke and products of
incomplete combustion. The action of the wick depending on the
capillary action of the microscopic tubes forming the cotton fibre,
nothing but long-staple cotton of good quality should be employed;
this should be spun into a coarse loose thread with as little twist in
it as possible, and from this the wick is built up. Having obtained a
wick of soft texture and loose plait, it should be well dried before
the fire, and when put in position in the lamp must fill the
wick-holder without being compressed. It should be of sufficient
length to reach to the bottom of the oil reservoir and leave an inch
or two on the bottom. Such a wick will suck up the oil in a regular
and uniform way, provided that the level of the oil is not allowed to
fall too low in the lamp, but it must be remembered that the wick acts
as a filter for the oil, and that if any sediment be present it will
be retained by and choke the capillaries upon which the action of the
wick depends, so that a wick should not be used for too long a time. A
good rule is that the wick should, when new, trail for 2 in. on the
bottom of the oil vessel, and should be discarded when these 2 in.
have been burnt off.
When the lamp is lighted the oil burns with a heavy, smoky flame,
because it is not able to obtain sufficient oxygen to complete the
combustion, and not only are soot flakes produced, but products of
incomplete combustion, such as carbon monoxide and even petroleum
vapour, escape--the first named highly injurious to health, and the
second of an offensive odour. To supply the _necessary amount of air_
to the flame, an artificial draught has to be created which shall
impinge upon the bottom of the flame and sweep upwards over its
surface, giving it rigidity, and by completing the combustion in a
shorter period of time than could be done otherwise, increasing the
calorific intensity and thus raising the carbon particles in the
flame to a far higher incandescence so as to secure a greater
illuminating power. This in practice has been done in two ways, first
by drawing in the air by the up-suck of the heated and expanded
products of combustion in a chimney fitted over the flame, and
secondly by creating a draught from a small clockwork fan in the base
of the lamp. It is necessary to break the initial rush of the draught:
this is mostly effected by disks of perforated metal in the base of
the burner, called _diffusers_, while the metal dome which surrounds
and rises slightly above the wick-holder serves to deflect the air on
to the flame, as in the Wanzer lamp. These arrangements also act to a
certain extent as regenerators, the air passing over the heated metal
surfaces being warmed before reaching the flame, whilst disks, cones,
buttons, perforated tubes, inner air-tubes, &c., have been introduced
to increase the illuminating power and complete the combustion.