Michael Faraday.

A course of six lectures on the chemical history of a candle : to which is added a lecture on platinum online

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THE



CHEMICAL HISTORY OF A CANDLE.



^



COURSE OF SIX LECTURES



CHEMICAL HISTORY OF A CANDLE



TO M-niCU IS ADDED



A LECTURE ON PLATINUM.



BY

MICHAEL FARADAY, D.C.L., F.R.S.,

FULLERIAN PKOFESSOE OP CHEMISTBY, EOYAl, INSTITtXTION ; FOBEIQN
ASSOCIATE OF THE ACADEMY OF SCIENCES, ETC.



Delivered be/ore a Jttvenile Axjditoey at the Eoyal Institution of
Gbeat Beitain during the Christmas Holidays of 1S60-1.



EDITED BY WILLIAM CROOKES, F.C.S.



WITH NUMEROUS ILLUSTRATIONS.



NEW YORK:

HARPER & BROTHERS, PUBLISHERS,

FBANKMN SQfTABK.



i-f-^ of riiss Helt-rv SVevf VIS
March a 19^V



PREFACE.



Feom the primitive pine torch to the paraf-
fine candle, how "wide an interval! between
them how vast a contrast ! The means adopt-
ed by man to illuminate his home at night
stamp at once his position in the scale of civili-
zation. The fluid bitumen of the far East,
blazing in rude vessels of baked earth; the
Etruscan lamp, exquisite in form, yet ill adapt-
ed to its office; the whale, seal, or bear fat,
filling the hut of the Esquimaux or Lap with
odor rather than light ; the huge wax candle
on the glittering altar ; the range of gas-lamps
in our streets, all have their stories to tell. All,
if they could speak (and after their own man-
ner they can), might warm our hearts in telling
how they have ministered to man's comfort,
love of home, toil, and devotion.

Surely, among the millions of fire-worshipers
and fire-users who have passed away in earlier



vi TREFACE.

ages, some have pondered over the mystery of
fire ; perhaps some clear minds have guessed
shrewdly near the truth. Think of the time
man has lived in hopeless ignorance; think
that only during a period which might be
spanned by the life of one man has the truth
been known !

Atom by atom, link by link, has the reason-
ing chain been forged. Some links too quickly
and too slightly made have given way, and
been replaced by better work; but now the
great phenomena are known, the outline is cor-
rectly and firmly drawn, cunning artists are
filling in the rest, and the child who masters
these Lectures knows more of fire than Aris-
totle.

The candle itself is now made to light up the
dark places of nature ; the blowpipe and the
prism are adding to our knowledge of the
earth's crust, but the torch must come first.

Among the readers of this book, some few
may devote themselves to increasing the stores
of knowledge : the Lamp of Science must burn.
" Alere flammam." W. C.



CONTENTS.



LECTURE I.

PAGE
A candle: the flame — ITS SOURCES — STRUCTURE —

MOBILITY — BRIGHTNESS 9



LECTURE II.

BRIGHTNESS OF THE FLAME. — AIR NECESSARY FOR

COMBUSTION. — PRODUCTION OF WATER 39

LECTURE III.

PRODUCTS : WATER FROM THE COMBUSTION. — NATURE

OF WATER. — A COMPOUND. — HYDROGEN 64

LECTURE IV.

HYDROGEN IN THE CANDLE. BURNS INTO WATER. —

THE OTHER PART OF WATER. — OXYGEN 94

LECTURE V.

OXYGEN PRESENT IN THE AIR. — NATURE OF THE AT-
MOSPHERE. ITS PROPERTIES. OTHER PRODUCTS

FROM THE CANDLE. — CARBONIC ACID. — ITS PROPER-
TIES 121



VIU CONTENTS.



LECTURE VI.

PAGE
CARBON OR CHARCOAL. — COAL - GAS. — RESPIRATION

AND ITS ANALOGY TO THE BURNING OF A CANDLE.

— CONCLUSION 153



LECTURE ON PLATINUM 185



NOTES 219



LECTURES



CHEMICAL HISTORY OF A CANDLE.



LECTUEE I.

A CANDLE: THE FLAME — ITS SOURCES —
STRUCTURE — MOBILITY — BRIGHTNESS.

I PURPOSE, in return for the honor you do
us by coming to see what are our proceedings
here, to bring before you, in the course of
these lectures, the Chemical History of a Can-
dle. I have taken this subject on a former oc-
casion, and, were it left to my own will, I
should prefer to repeat it almost every year,
so abundant is the interest that attaches itself
to the subject, so wonderful are the varieties
of outlet which it offers into the various de-
partments of philosophy. There is not a ]aw
under which any part of this universe is gov-
erned which does not come into play and is'



10 PRIMITIVE CANDLES.

touched upon in these phenomena. There is
no better, there is no more open door by which
you can enter into the study of natural phi-
losophy than by considering the physical phe-
nomena of a candle. I trust, therefore, I shall
not disappoint you in choosing this for my sub-
ject rather than any newer topic, which could
not be better, were it even so good.

And, before proceeding, let me say this also :
that, though our subject be so great, and our
intention that of treating it honestly, seriously,
and philosophically, yet I mean to pass away
from all those who are seniors among us. I
claim the privilege of speaking to juveniles as
a juvenile myself. I have done so on former
occasions, and, if you please, I shall do so again.
And, though I stand here with the knowledge
of having the words I utter given to the world,
yet that shall not deter me from speaking in
the same familiar way to those whom I esteem
nearest to me on this occasion.

And now, my boys and girls, I must first tell
you of what candles are made. Some are great
curiosities. I have here some bits of timber,
branches of trees particularly famous for their



CANDLE- WOOD. H

burning. And here you see a piece of that
f very curious substance, taken out of some of
the bogs in Ireland, called candle-wood; a hard,
strong, excellent wood, evidently fitted for good
work as a register of force, and yet, withal,
burning so well that where it is found they
make splinters of it, and torches, since it burns
like a candle, and gives a very good light in-
deed. And in this wood we have one of the
most beautiful illustrations of the general na-
ture of a candle that I can possibly give. The
fuel provided, the means of bringing that fuel
to the place of chemical action, the regular and
gradual supply of air to that place of action —
heat and light— all produced by a little piece
of wood of this kind, forming, in fact, a natu-
ral candle.

But we must speak of candles as they are in
commerce. Here are a couple of candles com-
monly called dips. They are made of lengths
of cotton cut off, hung up by a loop, dipped
into melted tallow, taken out again and cooled,
then redipped, until there is an accumulation
of tallow round the cotton. In order that you
may have an idea of the various characters of



12

these candles, you see these which I hold in
my hand — they are very small and very curi-
ous. They are, or were, the candles used by
the miners in coal mines. In olden times the
miner had to find his own candles, and it was
supposed that a small candle would not so soon
set fire to the fire-damp in the coal mines as a
large one ; and for that reason, as well as for
economy's sake, he had candles made of this
sort— 20, 30, 40, or 60 to the pound. " They
have been replaced since then by the steel-mill,
and then by the Davy lamp, and other safety-
lamps of various kinds. I have here a candle
that was taken out of the Royal Oeorge^i^) it
is said, by Colonel Pasley. It has been sunk
in the sea for many years, subject to the action
of salt water. It shows you how well candles
may be preserved; for, though it is cracked
about and broken a good deal, yet when light-
ed it goes on burning regularly, and the tallow
resumes its natural condition as soon as it is
fused.

Mr. Field, of Lambeth, has supplied me
abundantly with beautiful illustrations of the
candle and its materials ; I shall therefore now



STEARIN CANDLES. 13

refer to them. And, first, there is the suet —
the fat of the ox — Kussian tallow, I believe,
employed in the manufacture of these dips,
which Gay-Lussac, or some one who intrusted
him with his knowledge, converted into that
beautiful substance, stearin, which you see ly-
ing beside it. A candle, you know, is not now
a greasy thing like an ordinary tallow candle,
but a clean thing, and you may almost scrape
off and pulverize the drops which fall from it
without soiling any thing. This is the process
be adopted :(^) The fat or tallow is first boiled
with quick-lime, and made into a soap, and then
the soap is decomposed by sulphuric acid, which
takes away the lime, and leaves the fat rear-
ranged as stearic acid, while a quantity of gly-
cerin is produced at the same time. Glycerin
— absolutely a sugar, or a substance similar to
sugar — comes out of the tallow in this chemical
change. The oil is then pressed out of it; and
you see here this series of pressed cakes, show-
ing how beautifully the impurities are carried
out by the oily part as the pressure goes on in-
creasing, and at last you have left that sub-
stance, which is melted, and cast into candles



14 PARAFFINE CANDLES.

as here represented. The candle I have in my
hand is a stearin candle, made of stearin from
tallow in the way I have told you. Then here
is a sperm candle, which comes from the puri-
fied oil of the spermaceti whale. Here, also, are
yellow bees'-wax and refined bees'-wax, from
which candles are made. Here, too, is that
curious substance called paraffine, and some
parafiine candles, made of parafiine obtained
from the bogs of Ireland. I have here also a
substance brought from Japan since we have
forced an entrance into that out-of-the-way
place — a sort of wax which a kind friend has
sent me, and which forms a new material for
the manufacture of candles.

And how are these candles made ? I have
told you about dips, and I will show you how
moulds are made. Let us imagine any of these
candles to be made of materials which can be
cast. " Cast !" you s^j. " Why, a candle is a
thing that melts, and surely if you can melt it
you can cast it." Not so. It is wonderful, in
the progress of manufacture, and in the consid-
eration of the means best fitted to produce the
required result, how things turn up which one



TALLOW CANDLES. 15

would not expect beforehand. Candles can
not always be cast. A wax candle can never
be cast. It is made by a particular process
which I can illustrate in a minute or two, but
I must not spend much time on it. Wax is a
thing which, burning so "well, and melting so
easily in a candle, can not be cast. However,
let us take a material that can be cast. Here
is a frame, with a number of moulds fastened in
it. The first thing to be done is to put a wick
through them. Here is one — a plaited wick,
which does not require snuj3ing(^) — supported
by a little wire. It goes to the bottom, where
it is pegged in ; the little peg holding the cot-
ton tight, and stopping the aperture so that
nothing fluid shall run out. At the upper part
there is a little bar placed across, which stretch-
es the cotton and holds it in the mould. The
tallow is then melted, and the moulds are filled.
After a certain time, when the moulds are cool,
the excess of tallow is poured off at one corner,
and then cleaned off altogether, and the ends
of the wick cut away. The candles alone then
remain in the mould, and you have only to
upset them, as I am doing, when out they tum-



16 WAX CANDLES.

ble, for the candles are made in the form of
cones, being narrower at the top than at the
bottom ; so that, what with their form and their
own shrinking, they only need a little shaking
and out they fall. In the same way are made
these candles of stearin and of paraffine. It is
a curious thing to see how wax candles are
made. A lot of cottons are hung upon frames,
as you see here, and covered with metal tags at
the ends to keep the wax from covering the
cotton in those places. These are carried to a
heater, where the wax is melted. As you see,
the frames can turn round ; and, as they turn,
a man takes a vessel of wax and pours it first
down one, and then the next, and the next,
and so on. When he has gone once round, if
it is sufficiently cool, he gives the first a second
coat, and so on until they are all of the required
thickness. When they have been thus clothed,
or fed, or made up to that thickness, they are
taken off and placed elsewhere. I have here,
by the kindness of Mr. Field, several specimens
of these candles. Here is one only half finish-
ed. They are then taken down and well roll-
ed upon a fine stone slab, and the conical top



OliNAMENTAL CANDLES. 17

is moulded by properly shaped tubes, and tlie
bottoms cut off and trimmed. This is done so
beautifully that they can make candles in this
way weighing exactly four or six to the pound,
or any number they please.

"We must not, however, take up more time
about the mere manufacture, but go a little
farther into the matter. I have not 3^et refer-
red you to luxuries in candles (for there is such
a thing as luxury in candles). See how beau-
tifully these are colored ; you see here mauve,
Magenta, and all the chemical colors recently
introduced, applied to candles. You observe,
also, different forms employed. Ilere is a
fluted pillar most beautifully shaped; and I
have also here some candles sent me by Mr.
Pearsall, which are ornamented with designs
upon them, so that, as they burn, you have, as
it were, a glowing sun above, and a bouquet of
flowers beneath. All, however, that is fine and
beautiful is not useful. These fluted candles,
pretty as they are, are bad candles ; they are
bad because of their external shape. Never-
theless, I show you these specimens, sent to me
from kind friends on all sides, that you may
B



18 MODE OF BURNING.

see what is done and what may be done in thi3
or that direction ; although, as I have said,
when we come to these refinements, we are
obliged to sacrifice a little in utility.

ISTow as to the light of the candle. "We will

light one or two, and set them at work in the

performance of their proper functions. You

observe a candle is a very different thing from

a lamp. With a lamp you take a little oil, fill

your vessel, put in a little moss or some cotton

prepared by artificial means, and then light the

top of the wick. When the flame runs down

the cotton to the oil, it gets extinguished, but

it goes on burning in the part above. Kow I

have no doubt you will ask how it is that the

oil which will not burn of itself gets up to the

top of the cotton, 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 with no vessel to contain it; and

how is it that this solid substance 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



THE CUP. 19

it keeps together ? This is a wonderful thing
about a candle.

We have here a good deal of wind, which
will help us in some of our illustrations, but
tease us in others ; for the sake, therefore, of a
little regularity, and to simplify the matter, I
shall make a quiet flame, for who can study a
subject when there are difficulties in the way
not belonging to it? Here is a clever inven-
tion of some costermonger or street-stander in
the market-place for the shading of their can-
dles on Saturday nights, when they are selling
their greens, or potatoes, or fi^h. I have very
often admired it. They put a lamp-glass round
the candle, supported on a kind of gallery,
which clasps it, and it can be slipped up and
down as required. By the use of this lamp-
glass, employed in the same way, you have a
steady flame, which you can look at, and care-
fully examine, as I hope you will do, at home.

You see then, in the first instance, that a
beautiful cup is formed. As the air comes to
the candle, it moves upward by the force of the
current which the heat of the candle produces,
and it so cools all the sides of the wax, tallow,



20 CANDLES OF IRREGULAR SHAPE.

or fuel 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. If I made a current
in one direction, my cup would be lop-sided,
and the fluid would consequently run over;
for 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 beau-
tifully regular ascending current of air playing
upon all sides, which keeps the exterior of the
candle cool. Ko fuel would serve for a candle
which has not the property of giving this cup,
except such fuel as the Irish bog- wood, where
the material itself is like a sponge and holds its
own fuel. You see now why you would have
had such a bad result if you were to burn these
beautiful candles that I have shown you, which
are irregular, intermittent in their shape, and
can not, therefore, have that nicely-formed edge
to the cup which is the great beauty in a can-
dle. I hope you will now see that the perfec-



CAUSE OF GUTTERING. 21

tien of a process — that is, its utility — is the bet-
ter point of beauty about it. It is not the best
looking thing, but the best acting thing, which
is the most advantageous to us. This good-
looking candle is a bad-burning one. There
will be a guttering round about it because of
the irregularity of the stream of air and the bad-
ness 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
run down the side of a candle, making it thick-
er 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 higher above the rest of the wax or
fuel, 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. ISTow the greatest mis-
takes and faults with regard to candles, as in
many other things, often bring with them in-
struction which we should not receive if they
had not occurred. We come here to be philos-
ophers, and I hope you will always remember
that whenever a result happens, especially if it



22 RISE OF FLUID IN THE WICK.

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 can-
dles 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 com-
bustion. You know that the flames on these
burning wicks in candles made of bees'-wax,
stearin, or spermaceti, do not run down to the
wax or other matter, 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 can not 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, burn-
ing away gradually, never being intruded upon
by the flame, is a very beautiful sight, especial-
ly when you come to learn what a vigorous
thing flame is — what power it has of destroy-
ing the wax itself when it gets hold of it, and
of disturbing its proper form if it come only too
near.



CAPILLARY ATTRACTION. 23

But how does tlie flame get hold of the fael ?
There is a beautiful point about that — capillary
attr action. {^) "Capillary attraction!" you say
— " the attraction of hairs." Well, never mind
the name ; it was given in old times, before we
had a good understanding of what the real
power was. It is by what is called capillary
attraction that the fuel is conveyed to the part
where combustion goes on, and is deposited
there, not in a careless way, but very beauti-
fully in the very midst of the centre of action,
which takes place around it. Now I am going
to give you one or two instances of capillary
attraction. It is that kind of action or attrac-
tion which makes two things that do not dis-
solve in each other still hold together. When
you wash your hands, you wet them thorough-
ly ; you take a little soap to make the adhesion
better, and you find your hand remains wet.
This is by that kind of attraction of which I
am about to speak. And, what is more, if your
hands are not soiled (as they almost always are
by the usages of life), if you put your finger
into a little warm water, the water will creep a
little way np the finger, though ^you may not



24 CAPILLARY ACTION.

stop to examine it. I have here a substance
■whicli is rather porous — a column of salt —
and I -will pour into the plate at the bottom,
not water, as it appears, but a saturated solution
of salt which can not absorb more, so that the
action which you see will not be due to its
dissolving any thing. We may consider the
plate to be the candle, and the salt the wick,
and this solution the melted tallow. (I have
colored the fluid, that you may see the action
better.) You observe that, now I pour in the
fluid, it rises and gradually creeps up the salt
higher and higher ; and provided the column
does not tumble over, it will go to the top. If



Fig. 1.




this blue solution were combustible, and we
were to place a wick at the top of the salt, it
would burn as it entered into the wick. It is



ACTION OF THE SIPHON. 25

a most curious thing to see this kind of action
taking place, and to observe how singular some
of the circumstances are about it. 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 tallow. I have known some care-
less boys and girls (indeed, I have known it
happen to careful people as well) who, having
washed their hands and wiped them with a
towel, have thrown the towel over the side of
the basin, and before long it has drawn all the
water out of the basin and conveyed it to the
floor, because it happened to be thrown over
the side in such a way as to serve the purpose
of a siphon.(^) That you may the better see
the way in whicb the substances act one upon
another, I have here a vessel made of wire
gauze filled with water, and you may compare
it in its action to the cotton in one respect, or
to a piece of calico in the other. In fact, wicks
are sometimes made of a kind of wire gauze.
You will observe that this vessel is a porous
thing ; for if I pour a little water on to the top.



26 RISE OF FLUID THROUGH CANE.

it will run out at the bottom. You would be
puzzled for a good while if I asked you what
the state of this vessel is, what is inside it, and
why it is there ? The vessel is full of water,
and yet you see the water goes in and runs out
as if it were empty. In order to prove this to
you I have only to empty it. The reason is
this : the wire, being once wetted, remains wet;
the meshes are so small that the fluid is at-
tracted so strongly from the one side to the
other as to remain in the vessel, although it is
porous. In like manner, the particles of melted
tallow ascend the cotton and get to the top ;
other particles then follow by their mutual at-
traction for each other, and as they reach the
flame they are gradually burned.

Here is another application of the same prin-
ciple. You see this bit of cane. I have seen
boys about the streets, who are very anxious to
appear like men, take a piece of cane, and light
it, and smoke it, as an imitation of a cigar.
They are enabled to do so by the permeability
of the cane in one direction, and by its capil-
larity. If I place this piece of cane on a plate
containing some camphene (which is very much



WHY FLAME DOES NOT REACH THE CUP. 27

like paraffine in its general character), exactly
in the same manner as the blue fluid rose
through the salt will this fluid rise through the
piece of cane. There being no pores at the
side, the fluid can not go in that direction, but
must pass through its length. Already the
fluid is at the top of the cane ; now I can light
it and make it serve as a candle. The fluid
has risen by the capillary attraction of the
piece of cane, just as it does through the cotton
in the candle.

Now the only reason why the candle does
not burn all down the side of the wick is that
the melted tallow extinguishes the flame. You
know that a candle, if turned upside down, so
as to allow the fuel to run upon the wick, will


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Online LibraryMichael FaradayA course of six lectures on the chemical history of a candle : to which is added a lecture on platinum → online text (page 1 of 10)