IRON AND METAL-WORK GENERALLY.—LAMPS.—PRINCIPLES OF COMBUSTION.
In addition to the foregoing, a large quantity of expensive ironwork
is used in the construction of carriages; the principal cause of
which expense is not the cost of the material, but the highly skilled
labour which is necessary in preparing it.
In carriages suspended from C springs, the front and hind wheels are
connected by a central longitudinal timber, called a perch. This has
to be plated with iron in order to prevent its breaking when running
over bad ground; and without this precaution there is great danger
of the perch giving way, as owing to its curved form, which follows
the contour of the body, it is necessary to cut across the grain, and
thus weaken the timber.
These wooden perches have, to some extent, been superseded by
wrought-iron perches, as previously mentioned, and these have been
found to answer admirably.
In C spring carriages there are the loops, which serve to suspend the
body; and these require very good workmanship, for they are curved
in many opposite directions, are tapered and irregularly formed
every way, yet requiring to have bearing bolts accurately adjusted,
and sundry contrivances for affixing ironwork to them, and all this
without a single square side for the mechanic to work from. They are
samples of great mechanical skill and dexterity of hand.
Other carriage ironwork may be generally divided into stays, plates,
hoops, clips, bolts, steps, treads, joints, shackles, and jacks.
Stays are iron brackets of various forms, bolted by their extremities
to such parts as they are intended to sustain or strengthen, but they
do not take a bearing on any part.
Plates are irons which take a bearing throughout their length and
breadth on the part they are intended to strengthen, and to which
they are fastened by bolts, screws, or rivets.
Hoops are flat straps of iron riveted or welded together, for the
purpose of securing timbers together side by side.
Clips are a kind of open hoops, the ends of which have a thread run
upon them in order to take nuts. The purposes for which they are
used is to screw springs and axles in their places without having to
weaken them by drilling holes through them.
[Illustration: Fig. 32.
AXLE CLIP
CARRIAGE BOLT
POINTED TIRE BOLT
STEP BOLT
ELLIPTIC HEAD PERCH BOLT
=T= HEAD OR SHAFT BOLT
CONE HEAD BOLT
]
Bolts are cylindrical pieces of iron of various sizes (Fig. 32), one
end of which is flattened out to form a head, and the other is formed
into a screw to receive a nut. The use to which they are applied is
to secure the ironwork and heavy framework.
Steps may be single, double, or treble. In the two latter cases they
are made to fold up, and are called folding steps, and may be made to
fold up outside or into the body; this latter is the best way, and if
they be well managed they do not incommode the sitters inside.
Treads are small single steps a few inches square, fixed for the most
part on a single iron stem.
Joints are jointed iron stays, made in the form of the letter S, and
serve to keep the leather heads or hoods of open carriages, such as
landaus, stretched firmly out when required.
Shackles are iron staples, which serve to receive the leather
suspension braces of C spring carriages on the springs; they are also
used for coupling springs together.
Jacks are small windlasses, which serve to receive the ends of the
leather suspension braces after passing round the backs of the
springs. By means of a wrench or winch handle the jacks may be wound
up or let down so as to lengthen or shorten the brace.
Then we have the hinges, which are now concealed in the door pillar,
effecting a great improvement in the appearance of the vehicle,
though it necessitates a somewhat stouter pillar than would otherwise
be necessary.
To preserve the ironwork and steelwork of carriages from rusting,
it is either painted or plated with some metal on which the oxygen
of the air does not act. When it is wished to make it ornamental,
carriage ironwork is plated, in which case it is first covered with
a coat of tin laid on by means of a soldering iron, with rosin and
a small portion of sal-ammoniac in order to promote union between
the two metals. The tin being smoothed, a small portion of silver
or brass, rolled exceedingly thin, is laid on, and by means of the
soldering iron is made to adhere to the tin; more of the plating
metal is then added to join the first by the edges, till the whole
surface is covered. It is then burnished and polished by means of
the proper tools. All articles of iron requiring to be covered with
silver are treated in the same way; small articles of ornament in
brass, which do not require strength, are cut in solid metal, as
it is cheaper by the saving in labour; but for heavy articles, the
weight of the metal would considerably enhance the price, supposing
that strength were not required. Wheel nave hoops, axletree caps,
loops, brace buckles, check rings, and door handles are generally
plated.
The beading, which is used to cover the joints, is of three kinds,
brass, copper, and plated copper. It is formed by strips of metal
being drawn into a circular or angular form by means of a die,
the hollow space being filled with solder, into which small pins
of pointed wire are fixed to attach it by. The brass beading is
polished; the copper is painted, for which purpose the surface
is roughened. As the quantity of beading used is often very
considerable, the labour of silvering by means of a soldering iron
would be too great, and therefore the plated or silvered beading
is prepared from metal silvered in the sheet. The process is very
simple:—A bar of copper being reduced to the proper thickness, a bar
of silver is then united to it by means of heat. They are then passed
through the rolls together, and occasionally annealed in the fire
until the requisite thickness be obtained, the two metals spreading
equally. This kind of metal is much used in the manufacture of
carriage lamps.
Several kinds of lamps are used in carriages, both as regards
principle of construction and form and ornament. In the simplest kind
the light is furnished by the combustion of wax candles, which are
contained in tin tubes, through a hole in the upper part of which the
wick passes, the candle being pressed upwards as fast as it consumes
by a spiral spring. In dress carriages, where the lamps are somewhat
ornamental, wax candles are invariably used on account of their
superior cleanliness, though the light is inferior to that of oil.
Oil is often used on account of its superior illuminating power. The
lamp then simply consists of a tin reservoir for holding the oil, and
a round wick of the most ordinary kind, though sometimes flat for
the sake of spreading the flame. Reflectors of many kinds are used
in every variety of carriage lamps, formed of silvered metal highly
burnished.
Attempts have been made to bring the argand lamp, with a current
of air through the wick, into use, but sufficient success has not
attended these efforts to make them general, owing to their liability
to be suddenly extinguished by violent draughts of wind. This may,
however, be accomplished when the scientific principles of combustion
and the regulation of the draught shall be better understood.
By a common lamp is understood one that feeds the wick with oil by
capillary attraction, the column of oil being below the level of
the flame. An argand lamp, on the contrary, has a column of oil
considerably above the level of the flame and constantly pressing
upwards to it like a fountain. The motion of a carriage has a
tendency to make oil at times flow too rapidly and extinguish the
flame, and sometimes to cause too sudden a rush of air up the central
tube, which blows away the flame from the wick; and when these
difficulties are overcome by ingenuity they become such complicated
pieces of work that it is beyond the ordinary “gumption” of the
servants to trim them properly, and if this be not done the object of
the improvements is defeated.
The principle of constructing an argand lamp, so that it may regulate
its own air draught, is set forth by Lord Cochrane in one of his
patents. It is to divide the lamp into three chambers—one in the
centre, which contains the reflectors and light, surrounded by the
chimney glass, and is pierced with holes at the sides to permit the
egress of the heated air and the ingress of the fresh air. From
this chamber a tube or tubes communicate with the lower chamber,
into which the air tube of the burner descends, and thus furnishes
a regulated supply of air. It is evident by this process the air
rushing in must be regulated by the air rushing out, and _vice versâ_.
The flame of the lamp is not produced by oil or tallow alone, it
requires the oxygen of the air to mix with it in order to sustain
combustion. This may be proved by putting a glass bowl over a candle,
when, as soon as the oxygen is consumed, the light will be seen to
go out, the bowl having the remaining constituent of air left in it,
viz. nitrogen, which will neither support nor assist combustion.
Herein consists the advantage of the argand lamp in furnishing
atmospheric air in the centre of the flame. The flame arising from a
thick wick is hollow, _i.e._ it is a film of light, like a bladder,
and not continuous, the inner portion of the flame being filled with
gas.
It is well known that if the flames of two candles be brought in
contact they will produce a greater intensity of light than if
burned separately. Upon this principle what are technically termed
“cobblers’ candles” are made. For the same reason lamps are sometimes
made to burn two or three wicks, placed just so far apart that the
flames may come in contact. This is an approximation to the argand
principle, by admitting air between them. But there is one difficulty
attending them, viz. the regulating of all the wicks to an equal
height, which would be considerable unless the lamp were so contrived
that all could be regulated by one movement. If this difficulty can
be overcome a very excellent lamp might be made by placing four wicks
in a square.