I will tell you in five lectures the Chemical
History of a Candle. There is not a law under
which any part of the universe is governed
which does not come into play, and is touched
upon in the chemistry of a candle. There is
no better, there is no more open door by which
you can enter into the study of science, than
by considering the physical phenomena of a
candle. I trust, therefore, I shall not disappoint
you in choosing this for my subject rather
than any newer topic, which could not be better,
were it even so good. So, now, as to the light
of the candle. Notice that when the flame
runs down the wick to the wax, it gets extinguished,
but it goes on burning in the part above.
Now, I have no doubt you will ask, how is
it that the wax, which will not burn of itself,
gets up to the top of the wick, where it will
burn? We shall presently examine that; but
there is a much more wonderful thing about
the burning of a candle than this. You have
here a solid substance—the fuel—with no
vessel to contain it; and how is it that this
can get up to the place where the flame is?
How is it that this solid gets there, it not
being a fluid? Or, when it is made a fluid,
then how is it that it keeps together? This
is a wonderful thing about a candle. You see
that a beautiful cup is formed. As the air
comes to the candle it moves upwards by the
force of current which the heat of the candle
produces, and it so cools all the sides of
the wax, as to keep the edge much cooler than
the part within; the part within melts by
the flame that runs down the wick as far as
it can go before it is extinguished, but the
part on the outside does not melt. The same
force of gravity which holds worlds together
holds this fluid in a horizontal position,
and if the cup be not horizontal, of course
the fluid will run away in guttering. You
see, therefore, that the cup is formed by
this beautifully regular ascending current
of air playing upon all sides, which keeps
the exterior of the candle cool. No fuel would
serve for a candle which has not the property
of giving this cup. These beautiful candles
which are irregular and intermittent in their
shape cannot have that nicely-formed edge
to the cup which is the great beauty in a
candle. I hope you will now see that the perfection
of a process—that is, its utility—is the
better point of beauty about it. It is not
the best looking thing, but the best acting
thing, which is the most advantageous to us.
These good-looking candles are bad-burning
ones. There is guttering because of the irregularity
of the stream of air and the badness of the
cup which is formed thereby. You may see some
pretty examples (and I trust you will notice
these instances) of the action of the ascending
current when you have a little gutter running
down the side of a candle, making it thicker
there than it is elsewhere. As the candle
goes on burning, that keeps its place and
forms a little pillar sticking up by the side,
because, as it rises above the rest of the
fuel or wax, the air gets better round it,
and it is more cooled and better able to resist
the action of the heat at a little distance.
Now, the great mistakes and faults with regard
to candles, as in many other things, often
brings with them instruction which we should
not receive if they had not occurred. We come
here to be scientists; and I hope you will
always remember that whenever a result happens,
especially if it be new, you should say, “What
is the cause? Why does it occur?” and you
will in the course of time find out the reason.
Then, there is another point about these candles
which will answer a question; that is, as
to the way in which this fluid gets out of
the cup, up the wick, and into the place of
combustion. You see that the flames on these
burning wicks do not run down to the wax and
melt it all away, but keep to their own right
place. They are fenced off from the fluid
below, and do not encroach on the cup at the
sides. I cannot imagine a more beautiful example
than the condition of adjustment under which
a candle makes one part subserve to the other
to the very end of its action. A combustible
thing like that, burning away gradually, never
being intruded upon by the flame, is a very
beautiful sight; especially when you come
to learn what a vigorous thing flame is—what
power it has of destroying the wax itself
when it gets hold of it, and of disturbing
its proper form if it comes only too near.
But how does the flame get hold of the fuel?
Capillary action conveys the fuel to the part
where combustion goes on, and it is deposited
there, not in a careless way, but very beautifully
in the very midst of the center of action
which takes place around it. Now, I am going
to give you two instances of capillary action.
It is that kind of action or attraction which
makes two things that do not dissolve in each
other still hold together. When you wash your
hands, you take a towel to wipe off the water;
and it is by that kind of wetting, or that
kind of attraction which makes the towel become
wet with water, that the wick is made wet
with the wax. If you throw the towel over
the side of the basin, before long it will
draw the water out of the basin like the wick
draws the wax out of the candle. Let me show
you another application of the same principle.
You see this hollow glass tube filled with
table salt. I’ll fill the dish with some
alcohol colored with red food coloring.
You see the fluid rising through the salt. There
being no pores in the glass, the fluid cannot
go in that direction, but must pass through
its length. Already the fluid is at the top
of the tube: now I can light it and make it
serve as a candle.
The fluid has risen by the capillary action of the salt, just as
it does through the wick in the candle. Now,
the only reason why the candle does not burn
all down the sides of the wick is that the
melted wax extinguishes the flame. You know
that a candle, if turned upside down, so as
to allow the fuel to run upon the wick, will
be put out. The reason is that the flame has
not had time to make the fuel hot enough to
burn, as it does above, where it is carried
in small quantities into the wick, and has
all the effect of the heat exercised upon
it. There is another condition which you must
learn as regards the candle, without which
you would not be able fully to understand
the science of it, and that is the vaporous
condition of the fuel. In order that you may
understand that, let me show you a very pretty
experiment. If you blow a candle out carefully,
you will see the vapor rise from it. You have,
I know, often smelled the vapor of a blown-out
candle—and a very bad smell it is; but if
you blow it out lightly, you will be able
to see pretty well the vapor into which this
solid matter is transformed. When I hold a
lighted match two or three inches from the
wick, you can observe a train of fire going
through the air till it reaches the candle.
I am obliged to be quick and ready, because,
if I allow the vapor time to cool, it becomes
condensed into a liquid or solid, or the stream
of combustible matter gets disturbed.
Now, to the shape or form of the flame. It concerns
us much to know about the condition which
the matter of the candle finally assumes at
the top of the wick—where you have such
beauty and brightness as nothing but combustion
or flame can produce. You have the glittering
beauty of gold and silver, and the still higher
luster of jewels, like the ruby and diamond;
but none of these rival the brilliancy and
beauty of flame. What diamond can shine like
flame? It owes its luster at night-time to
the very flame shining upon it. The flame
shines in darkness, but the light which the
diamond has is as nothing until the flame
shines upon it, when it is brilliant again.
The candle alone shines by itself, and for
itself, or for those who have arranged the
materials. The flame is a bright oblong—brighter
at the top than toward the bottom—with the
wick in the middle, and besides the wick in
the middle, certain darker parts toward the
bottom, where the ignition is not so perfect
as in the part above. Now, let me show you
there is a matter rising about it which you
do not see. You can actually see streaming
around the flame something which is not part
of the flame, but is ascending and drawing
the flame upwards. There is a current formed,
which draws the flame out—for the flame
which you see is really drawn out by the current,
and drawn upward to a great height. How remarkable
it is that the thing which is light enough
to produce shadows of other objects, can be
made to throw its own shadow. You observe
the shadow of the candle and of the wick;
then there is a darkish part and then a part
which is more distinct. Curiously enough,
however, what we see in the shadow as the
darkest part of the flame is, in reality,
the brightest part; and here you see streaming
upward the ascending current of hot air, which
draws out the flame, supplies it with air,
and cools the sides of the cup of melted fuel.
You know the flame goes up or down; according
to the current. You see, then, that we have
the power in this way of varying the flame
in different directions. Many of the flames
you see here vary in their shape by the currents
of air blowing around them in different directions;
but we can, if we like, make flames so that
they look like fixtures, and we can photograph
them—indeed, we have to photograph them,
so that they become fixed to us, if we wish
to find out everything concerning them. If
I take a flame sufficiently large, it does
not keep that homogeneous, that uniform condition
of shape, but it breaks out with a power of
life which is quite wonderful. In what way
does it differ from an ordinary candle? It
differs very much in one respect: we have
a vivacity and power about it, a beauty and
a life entirely different from the light presented
by a candle. You see those fine tongues of
flame rising up. You have the same general
disposition of the mass of the flame from
below upwards; but, in addition to that, you
have this remarkable breaking out into tongues
which you do not perceive in the case of a
candle. Now, why is this? You have the air
creeping in over the edge of the dish forming
these tongues. Why? Because, through the force
of the current and the irregularity of the
action of the flame, it cannot flow in one
uniform stream. The air flows in so irregularly
that you have what would otherwise be a single
image, broken up into a variety of forms,
and each of these little tongues has an independent
existence of its own. Indeed, I might say,
you have here a multitude of independent candles.
You must not imagine, because you see these
tongues all at once, that the flame is of
this particular shape. A flame of that shape
is never so at any one time. Never is a body
of flame, like that which you just saw rising
from the ball, of the shape it appears to
you. It consists of a multitude of different
shapes, succeeding each other so fast that
the eye is only able to take cognizance of
them all at once. They do not occur all at
once: it is only because we see these shapes
in such rapid succession, that they seem to
us to exist all at one time. We have thus
far spent our time considering the light of
the candle, discussing how the fuel gets to
the wick and the form of the flame upon combustion.
But we have more questions to ponder. From
where does the brightness come? And where
does the candle eventually go? And in a larger
sense, how do the products of combustion lead
us to a discussion of the atmosphere? And
what is the relationship between combustion
and respiration? I started this lecture by
claiming that there is no more open door by
which to enter into the study of science than
by considering the physical phenomena of the
candle. Over the next four lectures, I hope
to prove this to you.
