PRESENTED
THE UNIVERSITY OF TORONTO
. fa
/
CONVERSATIONS
CHEMISTRY;
THE ELEMENTS OF THAT SCIENCE
FAMILIARLY EXPLAINED
ILLUSTRATED BY EXPERIMENTS.
P b\j vVavsc. ^*<
k~ I .
IN TWO VOLUMES.
The Fiflh Edition, revised) comected, and considerably enlarged.
J
VOL. I.
ON SIMPLE BODIES.
LONDON:
PIUNTED FOR LONGMAN, HURST, BEES, ORA1B, AND BROWN
PATERNOSTE R-RQW.
1817.
Priated by A. Strahan,
Printers-Street, London.
ADVERTISEMENT.
THE Author, in this Jlfth edition, kas en-
deavoured to give an account of the principal
discoveries which have been made within the
last four years in Chemical Science, and of
the various important applications, such as
the gas-lights, and the miner* s-lamp, to which
they have given rise. But in regard to doc-
trines or principles, the work has undergone
no' material alteration.
London, Jidy, 1817*
PREFACE.
IN venturing to offer to the public, and
more particularly to the female sex, an In-
troduction to Chemistry, the author, her-
self a woman, conceives that some expla-
nation may be required; and she feels it
the more necessary to apologise for the pre-
sent undertaking, as her knowledge of the
subject is but recent, and as she can have
no real claims to the title of chemist.
On attending for the first time experi-
mental lectures, the author found it almost
impossible to derive any clear or satisfac-
tory information from the rapid demonstra-
tions which are usually, and perhaps neces-
sarily, crowded into popular courses of this
kind. But frequent opportunities having
A 3
VI PREFACE.
afterwards occurred of conversing with a
friend on the subject of chemistry, and of
repeating a variety of experiments, she be-
came better acquainted with the principles
of that science, and began to feel highly
interested in its pursuit. It was then that
she perceived, in attending the excellent
lectures delivered at the Royal Institution,
by the present Professor of Chemistry, the
great advantage which her previous know-
ledge of the subject, slight as it was, gave
her over others who had not enjoyed the
same means of private instruction. Every
fact or experiment attracted her attention,,
and served to explain some theory to which
she was not a total stranger ; and she had
the gratification to find that the numerous
and elegant illustrations, for which that
school is so much distinguished, seldom
failed to produce on her mind the effect
for which they were intended.
Hence it was natural to infer, that fami-
liar conversation was, in studies of this
kind, a most useful auxiliary source of in-
PREFACE. Vll
formation ; and more especially to the fe-
male sex, whose education is seldom cal-
culated to prepare their minds for abstract
ideas, or scientific language.
As, however, there are but few women
who have access to this mode of instruc-
tion j and as the author was not acquainted
with any book that could prove a substitute
for it, she thought that it might be useful
for beginners, as well as satisfactory to her-
self, to trace the steps by which she had
acquired her little stock of chemical know-
ledgej and to record, in the form of dia*
logue, those ideas which she had first de-
rived from conversation.
But to do this with sufficient method,
and to fix upon a mode of arrangement,
was an object of some difficulty. After
much hesitation, and a degree of embarrass-
ment, which, probably, the most compe-
tent chemical writers have often felt in
common with the most superficial, a mode
of division was adopted, which, though the
most natural, does not always admit of be-
A 4
Vlll PREFACE
ing strictly pursued it is that of treating
first of the simplest bodies, and then gra-
dually rising to the most intricate com-
pounds.
It is not the author's intention to enter
into a minute vindication of this plan. But
whatever may be its advantages or incon-
veniences, the method adopted in this
work is such, that a young pupil, who
should occasionally recur to it, with a view
to procure information on particular sub-
jects, might often find it obscure or unin-
telligible ; for its various parts are so con-
nected with each other as to form an unin-
terrupted chain of facts and reasonings,
which will appear sufficiently clear and con-
sistent to those only who may have patience
to go through the whole work, or have
previously devoted some attention to the
subject.
It will, no doubt, be observed, that in
the course of these Conversations, remarks
are often introduced, which appear much
too acute for the young pupils, by whom
PREFACE. IX
they are supposed to be made. Of this
fault the author is fully aware. But, in
order to avoid it, it would have been neces-
sary either to omit a variety of useful illus-
trations, or to submit to such minute expla-
nations and frequent repetitions, as would
have rendered the work tedious, and there-
fore less suited to its intended purpose.
In writing these pages, the author was
more than once checked in her progress
by the apprehension that such an attempt
might be considered by some, either as un-
suited to the ordinary pursuits of her sex,
or ill-justified by her own recent and im-
perfect knowledge of the subject. But, on
the one hand, she felt encouraged by the
establishment of those public institutions,
open to both sexes, for the dissemination
of philosophical knowledge, which clearly
prove that the general opinion no longer
excludes women from an acquaintance with
the elements of science ; and, on the other,
she flattered herself that whilst the impres-
sions made upon her mind, by the wonders
X PREFACE.
of Nature, studied in this new point of
view, were still fresh and strong, she might
perhaps succeed the better in communi-
cating to others the sentiments she herself
experienced.
The reader will soon perceive, in perus-
ing this work, that he is often supposed to
have previously acquired some slight know-
ledge of natural, philosophy, a circumstance,
indeed, which appears very desirable. The
author's original intention was to commence
this work by a small tract, explaining, on a
plan analogous to this, the most essential
rudiments of that science. This idea she
has since abandoned ; but the manuscript
was ready, and might, perhaps, have been
printed at some future period, had not an
elementary work of a similar description,
under the tide of " Scientific Dialogues,"
been pointed out to her, which, on a
rapid perusal, she thought very ingenious,
and well calculated to answer its intended
object.
CONTENTS
or
THE FIRST VOLUME.
ON SIMPLE BODIES.
CONVERSATION I.
Pag
OK THE GENERAL PRINCIPLES OF CHEMISTRY. 1
C/ONNJSXION between Chemistry and Natural Philosophy.
Improved State of modern Chemistry. Its use in the '
Arts. The general Objects of Chemistry. Definition
of Elementary Bodies. Definition of Decomposition.
Integrant and Constituent Particles. Distinction
between Simple and Compound Bodies. Classification \r
of Simple Bodies. Of Chemical Affinity, or Attraction
of Composition. Examples of Composition and De-
composition.
CONVERSATION II.
ON LIGHT AND HEAT. 26
Light and Heat capable of being separated. Dr. Her-
schel's Experiments. Phosphorescence. Of Caloric.
Its two Modifications. Free Caloric. Of the three
Xll CONTENTS.
Page
different States of Bodies, nolid, fluid, and aeriform.
Dilatation of solid Bodies. Pyrometer. Dilatation
of Fluids. Thermometer. Dilatation of Elastic
Fluids. Air Thermometer. Equal Diffusion of Ca-
loric. Cold a Negative Quality. Professor Prevost's
Theory of the Radiation of Heat. Professor Pictet's
Experiments on the Reflexion of Heat. Mr. Leslie's
Experiments on the Radiation of Heat.
CONVERSATION III.
CONTINUATION OF THE SUBJECT. 70
Of the different Power of Bodies to conduct Heat. At-
tempt to account for this Power. Count Rumford's
Theory of the non-conducting Power of Fluids. > Phe-
nomena of Boiling. Of Solution in general. Solvent
Power of Water. Difference between Solution and
Mixture. Solvent Power of Caloric. Of Clouds,
Rain, Dr. Wells' theory of Dew, Evaporation, &c.
Influence of Atmospherical Pressure on Evaporation.
Ignition.
CONVERSATION IV-
ON COMBINED CALORIC, COMPREHENDING SPECIFIC HEAT
AND LATENT HEAT. 122
Of Specific Heat. Of the different Capacities of Bodies
for Heat. Specific Heat not perceptible by the Senses.
How to be ascertained. Of Latent Heat. Distinc-
tion between Latent and Specific Heat. Phenomena
attending the Melting of Ice and the Formation of Va-
pour. Phenomena attending the Formation of Ice,
and the Condensation of Elastic Fluids. Instances of
Condensation, and consequent Disengagement of Heat,
produced by Mixtures, by the Slaking of Lime. Ge-
CONTENTS. Xlii
Page
neral Remarks on Latent Heat. Explanation of the
Phenomena of Ether boiling, and Water freezing, at
the same Temperature. Of the Production of Cold by
Evaporation. Calorimeter. Meteorological Remarks.
CONVERSATION V.
ON THE CHEMICAL AGENCIES OF E1ECTRICITY. 160
Of Positive and Negative Electricity. Gal vani's Dis-
coveries. Vollaic Battery. Electrical Machine.
Theory of Voltaic Excitement.
CONVERSATION VI,
ON OXYGEN AND NITROGEN. 181
The Atmosphere composed of Oxygen and Nitrogen in
the State of Gas. Definition of Gas. Distinction be-
tween Gas and Vapour. Oxygen essential to Combus-
tion and Respiration. Decomposition of the Atmo-
sphere by Combustion. Nitrogen Gas obtained by this
Process. Of Oxygenation in general. Of the Oxyda-
tion of Metals. Oxygen Gas obtained from Oxyd qf
Manganese. Description of a Water-Bath for collect-
ing and preserving Gases. Combustion of Iron Wire
in Oxygen Gas. Fixed and volatile Products of Cora-
bustion. Patent Lamps. Decomposition of the Atmo-
sphere by Respiration. Recomposition of the Atmo-
sphere.
CONVERSATION VII.
ON HYDROGEN. 214
Of Hydrogen. Of the Formation of Water by the Com- ^
bustion of Hydrogen. Of the Decomposition of Wa-
10
ERRATA.
Vol. I. page 56. last Hn but one, for " caloric," read " calorific."
179. Note, for PlateXII." r. " Plate XIII."
ON
CHEMISTRY.
CONVERSATION I.
ON THE GENERAL PRINCIPLES OP CHEMISTRY*
MRS. B.
you have now acquired some elementary no-
tions of NATURAL PHILOSOPHY, I am going to pro-
pose to you another branch of science, to which I
am particularly anxious that you should devote a
share of your attention. This is CHEMISTRY, which
is so closely connected with Natural Philosophy,
that the study of the one must be incomplete with-
out some knowledge of the other; for, it is ob-
vious that we can derive but a very imperfect
idea of bodies from the study of the general laws
by which they are governed, if we remain totally
ignorant of their intimate nature.
VOL. i. B
2 GENERAL PRINCIPLES
CAROLINE.
To confess the truth, Mrs. B., I am not disposed
to form a very favourable idea of chemistry, nor
do I expect to derive much entertainment from it.
I prefer the sciences which exhibit nature on a
grand scale, to those that are confined to the mi-
nutiae of petty details. Can the studies which we
have lately pursued, the general properties of mat-
ter, or the revolutions of the heavenly bodies, be
compared to the mixing up of a few insignificant
drugs? I grant, however, there may be enter-
taining experiments in chemistry, and should not
dislike to try some of them : the distilling, for in-
stance, of lavender, or rose water
MRS. B.
I rather imagine, my dear Caroline, that your
want of taste for chemistry proceeds from the
very limited idea you entertain of its object. You
confine the chemist's laboratory to the narrow pre-
cincts of the apothecary's and perfumer's shops,
whilst it is subservient to an immense variety of
other useful purposes. Besides, my dear, che-
mistry is by no means confined to works of art.
Nature also has her laboratory, which is the uni-
verse, and there she is incessantly employed in
chemical operations. You are surprised, Caroline,'
but I assure you that the most wonderful and
the most interesting phenomena of nature are
OF CHEMISTRY. 3
almost all of them produced by chemical powers.
What Bergman, in the introduction to his history
of chemistry, has said of this science, will give
you a more just and enlarged idea of it. The
knowledge of nature may be divided, he observes,
into three periods. The first was that in which the
attention of men was occupied in learning the ex-
ternal forms and characters of objects, and this
is called Natural History. In the second, they
considered the effects of bodies acting on each
other by their mechanical power, as their weight
and motion, and this constitutes the science of
Natural Philosophy. The third period is that in
which the properties and mutual action of the
elementary parts of bodies was investigated. This
last is the science of CHEMISTRY, and I have no
doubt you will soon agree with me in thinking it
the most interesting.
You may easily conceive, therefore, that with-
out entering into the minute details of practical
chemistry, a woman may obtain snch a knowledge
of the science as will not only throw an interest
on the common occurrences of life, but will en-
large the sphere of her ideas, and render the
contemplation of nature a source of delightful
instruction.
CAROLINE.
If this is the case, I have certainly been much
B 2
4 GENERAL PRINCIPLES
mistaken in the notion I had formed of chemistry.
I own that I thought it was chiefly confined to the
knowledge and preparation of medicines.
MRS. B.
That is only a branch of chemistry which is
called Pharmacy; and, though the study of it is
certainly of great importance to the world at large,
it belongs exclusively to professional men, and is
therefore the last that I should advise you to pursue.
EMILY.
But, did not the chemists formerly employ them-
selves in search of the philosopher's stone, or the
secret of making gold ?
MRS. B.
These were a particular set of misguided phi-
losophers, who dignified themselves with the name
of Alchemists, to distinguish their pursuits from
those of the common chemists, whose studies were
confined to the knowledge of medicines.
But, since that period, chemistry has undergone
so complete a revolution, that, from an obscure
and mysterious art, it is now become a regular
and beautiful science, to which art is entirely
subservient. It is true, however, that we are in-
debted to the alchemists for many very useful dis-
coveries, which sprung from their fruitless attempts
OP CHEMISTRY. 5
to make gold, and which, undoubtedly, have proved
of infinitely greater advantage to mankind than all
their chimerical pursuits.
The modern chemists, instead of directing their
ambition to the vain attempt of producing any of
the original substances in nature, rather aim at
analysing and imitating her operations, and have
sometimes succeeded in forming combinations, or
effecting decompositions, no instances of which
occur in the chemistry of Nature. They have
little reason to regret their inability to make gold,
whilst, by their innumerable inventions and dis-
coveries, they have so greatly stimulated industry
and facilitated labour, as prodigiously to increase
the luxuries as well as the necessaries of life.
EMILY.
But, I do not understand by what means che-
mistry can facilitate labour ; is not that rather the
province of the mechanic ?
MHS. B.
There are many ways by which labour may be
rendered more easy, independently of mechanics ;
but even the machine, the most wonderful in its
effects, the Steam-engine, cannot be understood
without the assistance of chemistry. In agricul-
ture, a chemical knowledge of the nature of soils,
and of vegetation, is highly useful ; and, in those
B 3
6 GENERAL PRINCIPLED
arts which relate to the comforts and conveniences
of life, it would be endless to enumerate the ad-
vantages which result from the study of this science.
CAROLINE.
But, pray, tell us more precisely in what man-
ner the discoveries of chemists have proved so
beneficial to society?
MRS. B.
That would be an injudicious anticipation ; for
you would not comprehend the nature of such
discoveries and useful applications, as well as you
will do hereafter. Without a due regard to me-
thod, we cannot expect to make any progress in
chemistry. I wish to direct your observations
chiefly to the chemical operations of Nature ; but
those of Art are certainly of too high importance
to pass unnoticed. We shall therefore allow them
also some share of our attention.
EMILY.
Well, then, let us now set to work regularly. I
am very anxious to begin.
MRS. B.
The object of chemistry is to obtain a know-
ledge of the intimate nature of bodies, and of their
mutual action on each other. You find therefore.
OF CHEMISTRY. 7
Caroline, that this is no narrow or confined science,
which comprehends every thing material within
our sphere.
CAROLINE.
On the contrary, it must be inexhaustible ; and
I am a loss to conceive how any proficiency can
be made in a science whose objects are so numerous.
MRS. B.
If every individual substance were formed of dif-
ferent materials, the study of chemistry would, in-
deed, be endless ; but you must observe that the
various bodies in nature are composed of certain
elementary principles, which are not very nu-
merous.
CAROLINE.
Yes ; I know that all bodies are composed of fire,
air, earth, and water ; I learnt that many years ago.
MRS. B.
But you must now endeavour to forget ik I
have already informed you what a great change
chemistry has undergone since it has become a
regular science. Within these thirty years espe-
cially, it has experienced an entire revolution, and
it is now proved, that neither fire, air, earth, nor
water, can be called elementary bodies. For an
B 4
GENERAL PRINCIPLES
elementary body is one that has never been de-
composed, that is to say, separated into other
substances; and fire, air, earth, and water, are
, all of them susceptible of decomposition.
EMILY.
I thought that decomposing a body was divid-
ing it into its minutest parts. And if so, I do not
understand why an elementary substance is not
capable of being decomposed, as well as any
other.
MRS. B,
You have misconceived the idea of decomposi-
tion ; it is very different from mere division. The
latter simply reduces a body into parts, but the
former separates it into the various ingredients,
or materials, of which it is composed. If we were
to take a loaf of bread, and separate the several in-
gredients of which it is made, the flour, the yeast,
the salt, and the water, it would be very different
from cutting or crumbling the loaf into pieces.
EMILY.
I understand you now very well. To decompose
a body is to separate from each other the various
elementary substances of which it consists.
CAROLINE.
But flour, water, and other materials of bread,
OF CHEMISTRY.
according to our definition, are not elementary
substances ?
MRS. B.
No, my dear ; I mentioned bread rather as a
familiar comparison, to illustrate the idea, than as
an example.
The elementary substances of which a body is
composed are called the constituent parts of that
body ; in decomposing it, therefore, we separate its
constituent parts. If, on the contrary, we divide
a body by chopping it to pieces, or even by grind-
ing or pounding it to the finest powder, each of
these small particles will still consist of a portion
of the several constituent parts of the whole body :
these are called the integrant parts ; do you un-
derstand the difference ?
EMILY.
Yes, I think, perfectly. We decompose a body
into its constituent parts ; and divide it into its in-
tegrant parts.
MRS. B.
Exactly so. If therefore a body consists of only
one kind of substance, though it may be divided
into its integrant parts, it is not possible to de-
compose it. Such bodies are therefore called
simple or elementary, as they are the elements of
which all other bodies are composed. Compound
B 5
10 GENERAL PRINCIPLES
bodies are such as consist of more than one of these
elementary principles.
CAROLINE.
But do not fire, air, earth, and water, consist,
each of them, but of one kind of substance ?
MRS. B.
No, my dear ; they are every one of them sus-
ceptible of being separated into various simple
bodies. Instead of four, chemists now reckon up-
Avards of forty elementary substances. The ex-
istence of most of these is established by the
clearest experiments ; but, in regard to a few of
them, particularly the most subtle agents of na-
ture, heat, light, and electricity, there is yet much
uncertainty, and I can only give you the opinion
which seems most probably deduced from the latest
discoveries. After I have given you a list of the
elementary bodies, classed according to their pro-
perties, we shall proceed to examine each of them
separately, and then consider them in their com-
binations with each other.
Excepting the more general agents of nature,
heat, light, and electricity, it would seem that
the simple form of bodies is that of a metal.
CAROLINE.
You astonish me! I thought the metals were only
OF CHEMISTRY. 11
one class of minerals, and that there were besides,
earths, stones, rocks, acids, alkalies, vapours,
fluids, and the whole of the animal and vegetable
kingdoms.
MRS. B.
You have made a tolerably good enumeration,
though I fear not arranged in the most scientific
order. All these bodies, however, it is now
strongly believed, may be ultimately resolved into
metallic substances. Your surprise at this circum-
stance is not singular, as the decomposition of some
of them, which has been but lately accomplished,
has excited the wonder of the whole philosophical
world.
But to return to the list of simple bodies these
being usually found in combination with oxygen, I
shall class them according to their properties when
so combined. This will, I think, facilitate their
future investigation.
EMILY.
Pray what is oxygen ?
MRS. B.
A simple body ; at least one that is supposed to
be so, as it has never been decomposed. It is al-
ways found united with the negative electricity.
It will be one of the first of the elementary bodies
whose properties I shall explain to you, and, as
B 6
12 GENERAL PRINCIPLES
you will soon perceive, it is one of the most im-
portant in nature; but it would be irrelevant to
enter upon this subject at present. We must now
confine our attention to the enumeration and classi-
fication of the simple bodies in general. They may
be arranged as follows :
CLASS I.
Comprehending the imponderable agents, viz.
HEAT Or CALORIC,
LIGHT,
ELECTRICITY.
CLASS II.
Comprehending agents capable of uniting with in-
t flammable bodies, and in most instances of Affecting
their combustion.
OXYGEN,
CHLORINE,
IODINE. *
CLASS III.
Comprehending bodies capable of uniting with oxy-
gen, and, forming with it various compounds. This
class may be divided as follows :
DIVISION 1.
HYDROGEN, forming water.
* It has been questioned by some eminent chemists, whe-
ther these two last agents should not be classed among the
OP CHEMISTRY. 13
DIVISION 2.
Bodies forming acids.
NITROGEN, . . .forming nitric acid.
SULPHUR, . . . .forming sulphuric acid.
PHOSPHORUS, . .forming phosphoric acid.
CARBON, forming carbonic acid.
BORACIUM, . . .forming boracic acid.
FLUORIUM, . . .forming fluoric acid.
MURIATIUM, . .forming muriatic acid.
DIVISION 3.
Metallic bodies forming alkalies*
POTASSIUM, . . .forming potash.
SODIUM, forming soda.
AMMONIUM, . . .forming ammonia.
DIVISION 4. ;
Metallic bodies forming earths.
CALCIUM, or metal forming lime.
MAGNIUM, forming magnesia.
BARIUM, forming barytes.
STRONTIUM, . . . .forming strontites.
SILICIUM, forming silex.
ALUMIUM, forming aluminc.
YTTRIUM, forming yttria.
inflammable bodies, as they are capable of combining with
oxygen, as well as with inflammable bodies. But they seem to
be more distinctly characterised by their property of support-
ing combustion than by any other quality.
14 GENERAL PRINCIPLES
GLUCIUM, forming glucina.
ZIRCONIUM, forming zirconi. *
DIVISION 5.
Metals, either naturally metallic^ or yielding their
oxygen to carbon or to heat alone.
Subdivision 1.
Malleable Metals.
GOLD, COPPER,
PLATINA, IRON,
PALLADIUM, LEAD,
SILVER, f NICKEL,
MERCURY, if ZINC.
TIN,
Subdiv. 2.
Brittle Metals.
ARSENIC, ANTIMONY,
BISMUTH, MANGANESE,
* Of all these earths, three or four only have as yet been
distinctly decomposed.
f These first four metals have commonly been distinguished
by the appellation of perfect or noble metals, on account of
their possessing the characteristic properties of ductility, mal-
leability, inalterability, and great specific gravity, in an emi-
nent degree.
J Mercury, in its liquid state, cannot, of course, be called a
malleable metal. But when frozen, it possesses a considerable
degree of malleability.
OF CHEMISTRY. 15
TELLURIUM, URANIUM,
COBALT, COLUMBIUM Or TAN-
TUNGSTEN, TALIUM,
MOLYBDENUM, IRIDIUM,
TITANIUM, OSMIUM,
CHROME, RHODIUM. *
CAROLINE.
Oh, what a formidable list ! You will have much
to do to explain it, Mrs. B. ; for I assure you it is
perfectly unintelligible to me, and I think rather
perplexes than assists me.
MRS. B.
Do not let that alarm you, my dear; I hope that
hereafter this classification will appear quite clear,
and, so far from perplexing you, will assist you in
arranging your ideas. It would be in vain to at-
tempt forming a division that would appear per-
fectly clear to a beginner: for you may easily
conceive that a chemical division being necessarily
founded on properties with which you are almost
wholly unacquainted, it is impossible that you
should at once be able to understand its meaning
or appreciate its utility.
* These last four or five metallic bodies are placed under
this class for the sake of arrangement, though some of their
properties have not been yet fully investigated.
Ifi GENERAL PRINCIPLES
But, before we proceed further, it will be neces-
sary to give you some idea of chemical attraction,
a power on which the whole science depends.
Chemical Attraction, or the Attraction of Com-
position, consists in the peculiar tendency which
bodies of a different nature have to unite with each
other. It is by this force that all the compositions,
and decompositions, are effected.
EMILY.
What is the difference between chemical attrac-
tion, and the attraction of cohesion, or of aggrega-
tion, which you often mentioned to us, in former
conversations ?
MRS. B.
The attraction of cohesion exists only between
particles of the same nature, whether simple or
compound ; thus it unites the particles of a piece
of metal which is a simple substance, and likewise
the particles of a loaf of bread which is a compound.
The attraction of composition, on the contrary,
unites and maintains, in a state of combination,
particles of a dissimilar nature; it is this power
that forms each of the compound particles of which
bread consists ; and it is by the attraction of co-
hesion that all these particles are connected into a
single mass.
OF CHEMISTRY. 17
EMILY.
The attraction of cohesion, then, is the power
which unites the integrant particles of a body : the
attraction of composition that which combines the
constituent particles. Is it not so ?
MRS. B.
Precisely: and observe that the attraction of
cohesion unites particles of a similar nature, with-
out changing their original properties ; the result
of such an union, therefore, is a body of the same
kind as the particles of which it is formed ; whilst
the attraction of composition, by combining par-
ticles of a dissimilar nature, produces compound
bodies, quite different from any of their constitu-
ents. If, for instance, I pour on the piece of copper,
contained in this glass, some of this liquid (which
is called nitric acid), for which it has a strong
attraction, every particle of the copper will combine
with a particle of acid, and together they will form
a new body, totally different from either the copper
or the acid.
Do you observe the internal commotion that
already begins to take place ? It is produced by
the combination of these two substances ; and yet
the acid has in this case to overcome not only the
resistance which the strong cohesion of the particles
of copper opposes to their combination with it, but
also to overcome the weight of the copper, which
18 GENERAL PRINCIPLES
makes it sink to the bottom of the glass, and
prevents the acid from having such free access to
it as it would if the metal were suspended in the
liquid.
EMILY.
The acid seems, however, to overcome both
these obstacles without difficulty, and appears to
be very rapidly dissolving the copper.
MRS. B.
By this means it reduces the copper into more
minute parts than could possibly be done by any
mechanical power. But as the acid can act only
on the surface of the metal, it will be some time
before the union of these two bodies will be com-
pleted.
You may, however, already see how totally dif-
ferent this compound is from either of its ingre-
dients. It is neither colourless, like the acid, nor
hard, heavy, and yellow like the copper. If you
tasted it, you would no longer perceive the sour-
ness of the acid. It has at present the appearance
of a blue liquid ; but when the union is completed,
and the water with which the acid is diluted is
evaporated, the compound will assume the form
of regular crystals, of a fine blue colour, and per-
fectly transparent *. Of these I can shew you a
* These crystals are more easily obtained from a mixture of
sulphuric with a little nitric acid.
OF CHEMISTRY. 19
specimen, as I have prepared some for that pur-
pose.
CAROLINE.
How very beautiful they are, in colour, form,
and transparency !
EMILY.
Nothing can be more striking than this example
of chemical attraction.
MRS. B.
The term attraction has been lately introduced
into chemistry as a substitute for the word affinity,
to which some chemists have objected, because it
originated in the vague notion that chemical com-
binations depended upon a certain resemblance,
or relationship, between particles that are disposed
to unite ; and this idea is not only imperfect, tout
erroneous, as it is generally particles of the most
dissimilar nature, that have the greatest tendency
to combine.
CAROLINE.
Besides, there seems to be no advantage in using
a variety of terms to express the same meaning ;
on the contrary it creates confusion; and as we
are well acquainted with the term Attraction in
natural philosophy, we had better adopt it in
chemistry likewise.
GENERAL PRINCIPLES
MRS. B.
If you have a clear idea of the meaning, I shall
leave you at liberty to express it in the terms you
prefer. For myself, I confess that I think the word
Attraction best suited to the general law that unites
the integrant particles of bodies ; and Affinity bet-
ter adapted to that which combines the constituent
particles, as it may convey an idea of the prefer-
ence which some bodies have for others, which
the term attraction of composition does not so well
express.
EMILY.
So I think ; for though that preference may not
result from any relationship, or similitude, between
the particles (as you say was once supposed), yet, as
it really exists, it ought to be expressed.
MRS. B.
Well, let it be agreed that you may use the
terms affinity ', chemical attraction^ and attraction of
composition., indifferently, provided you recollect
that they have all the same meaning.
EMILY.
I do not conceive how bodies can be decomposed
by chemical attraction. That this power should
be the means of composing them, is very obvious ;
but that it should, at the same time, produce exactly
the contrary effect, appears to me very singular.
OF CHEMISTRY.
MRS. B.
To decompose a body is, you know, to separate
its constituent parts, which, as we have just ob-
served, cannot be done by mechanical means.
EMILY.
No : because mechanical means separate only the
integrant particles ; they act merely against the at-
traction of cohesion, and only divide a compound
into smaller parts.
MRS. B.
The decomposition of a body is performed by
chemical powers. If you present to a body com-
posed of two principles, a third, which has a
greater affinity for one of them than the two first
have for each other, it will be decomposed, that
is, its two principles will be separated by means
of the third body. Let us call two ingredients,
of which the body is composed, A and B. If we
present to it another ingredient C, which has a
greater affinity for B than that which unites A and
B, it necessarily follows that B will quit A to
combine with C. The new ingredient, therefore,
has effected a decomposition of the original body
A B ; A has been left alone, and a new compound,
B C, has been formed.
EMILY.
We might, I think, use the comparison of two
22 GENERAL PRINCIPLES
friends, who were very happy in each other's so-
ciety, till a third disunited them by the preference
which one of them gave to the new-comer.
MRS. B.
Very well. I shall now show you how this takes
place in chemistry.
Let us suppose that we wish to decompose the
compound we have just formed by the combination
of the two ingredients, copper and nitric acid ; we
may do this by presenting to it a piece of iron, for
which the acid has a stronger attraction than for
copper ; the acid will, consequently, quit the copper
to combine with the iron, and the copper will be
what the chemists call precipitated, that is to say,
it will be thrown down in its separate state, and re-
appear in its simple form.
In order to produce this effect, I shall dip the
blade of this knife into the fluid, and, when I take
it out, you will observe, that, instead of being
wetted with a bluish liquid, like that contained in
the glass, it will be covered with a thin coat of
copper.
CAROLINE.
So it is really ! but then is it not the copper,
instead of the acid, that has combined with the iron
blade?
MRS. B.
No; you are deceived by appearances!? it is
OF CHEMISTRY. - 23
the aeid which combines with the iron, and, in so
doing, deposits or precipitates the copper on the
surface of the blade.
EMILY.
But,, cannot three or more substances combine
together, without any of them being precipitated ?
MRS. B.
That is sometimes the case ; but, in general, the
stronger affinity destroys the weaker; and it sel-
dom happens that the attraction of several sub-
stances for each other is so equally balanced as to
produce such complicated compounds.
CAROLINE.
But, pray, Mrs. B., what is the cause of the
chemical attraction of bodies for each other? It
appears to me more extraordinary or unnatural,
if I may use the expression, than the attraction
of cohesion, which unites particles of a similar
nature.
MRS. B.
Chemical attraction may, like that of cohesion
or gravitation, be one of the powers inherent in
matter which, in our present state of knowledge,
admits of no other satisfactory explanation than an
immediate reference to a divine cause. Sir H.
Davy, however, whose important discoveries have
24 GENERAL PRINCIPLES
opened such improved views in chemistry, has sug-
gested an hypothesis which may throw great light
upon that science. He supposes that there are two
kinds of electricity, with one or other of which all
bodies are united. These we distinguish by the
names of positive and negative electricity ; those
bodies are disposed to combine, which possess oppo-
site electricities, as they are brought together by
the attraction which these electricities have for each
other. But, whether this hypothesis be altogether
founded on truth or not, it is impossible to ques-
tion the great influence of electricity in chemical
combinations.
EMILY.
So, that we must suppose that the two electri-
cities always attract each other, and thus compel the
bodies in which they exist to combine ?
CAROLINE.
And may not this be also the cause of the at-
traction of cohesion ?
MRS. B.
No, for in particles of the same nature the same
electricities must prevail, and it is only the differ-
ent or opposite electric fluids that attract each
other.
CAROLINE.
These electricities seem to me to be a kind of
OF CHEMISTRY. 25
chemical spirit, which animates the particles of
bodies, and draws them together.
EMILY.
If it is known, then, with which of the electri-
cities bodies are united, it can be inferred which
will, and which will not, combine together ?
MRS. B.
Certainly. I should not omit to mention, that
some doubts have been entertained whether elec-
tricity be really a material agent, or whether it
might not be a power inherent in bodies, similar
to, or, perhaps identical with, attraction.
EMILY.
But what then would be the electric spark which
is visible, aud must therefore be really material ?
MRS. B.
What we call the electric spark, may, Sir H.
Davy says, be merely the heat and light, or fire
produced by the chemical combinations with which
these phenomena are always connected. We will
not, however, enter more fully on this important
subject at present, but reserve the principal facts
which relate to it to a future conversation.
Before we part, however, I must recommend
you to fix in your memory the names of the simple
bodies, against our next interview.
VOL. I. C
CONVERSATION II.
ON LIGHT AND HEAT OR CALORIC.
CAROLINE.
VV E have learned by heart the names of all the
simple bodies which you have enumerated, and
we are now ready to enter on the examination
of each of them successively. You will begin, I
suppose, with LIGHT?
MBS. B.
Respecting the nature of light we have little
more than conjectures. It is considered by most
philosophers as a real substance, immediately
emanating from the sun, and from all luminous
bodies, from which it is projected in right lines
with prodigious velocity. Light, however, being
imponderable, it cannot be confined and examined
by itself', and therefore it is to the effects it pro-
duces on other bodies, rather than to its immediate
nature, that we must direct our attention.
The connection between light and heat is very
bvioiis; indeed, it is such, that it is extremely
LIGHT. 27
difficult to examine the one independently of the
other.
EMILY.
But, is it possible to separate light from heat;
I thought they were only different degrees of the
same thing, fire ?
MRS. B.
I told you that fire was not now considered as
a simple element. Whether light and heat be
altogether different agents, or not, I cannot pre-
tend to decide; but, in many cases, light may
be separated from heat. The first discovery
of this was made by a celebrated Swedish chemist,
Scheele. Another very striking illustration of the
separation of heat and light was long after pointed
out by Dr. Herschell. This philosopher disco-
vered that these two agents were emitted in the
rays of the sun, and that heat was less refrangible
than light ; for, in separating the different coloured
rays of light by a prism (as we did some time ago),
he found that the greatest heat was beyond the
spectrum, at a little distance from the red rays,
which, you may recollect, are the least refrangible.
., EMILY.
J should lilte to try that experiment.
C 2
28 LIGHT.
MRS. B.
It is by no means an easy one : the heat of a ray
of light, refracted by a prism, is so small, that it
requires a very delicate thermometer to distin-
guish the difference of the degree of heat within
and without the spectrum. For in this experi-
ment the heat is not totally separated from the
light, each coloured ray retaining a certain por-
tion of it, though the greatest part is not suffi-
ciently refracted to fall within the spectrum,
EMILY.
I suppose, then, that those coloured rays which
are the least refrangible, retain the greatest quan-
tity of heat ?
MRS. B.
They do so.
EMILY.
Though I no longer doubt that light and heat
can be separated, Dr. Hersch ell's experiment does
not appear to me to afford sufficient proof that
they are essentially different; for light, which you
call a simple body, may likewise be divided into
^the various coloured rays. (
MRS. B.
No doubt there must be some difference in the
various coloured rays. Even their chemical powers
LIGHT. 29
are different. The blue rays, for instance, have
the greatest effect in separating oxygen from bo-
dies, as was found by Scheele; and there exist
also, as Dr. Wollaston has shown, rays more re-
frangible than the blue, which produce the same
chemical effect, and, what is very remarkable, are
invisible.
EMILY.
Do you think it possible that heat may be
merely a modification of light?
MRS. B.
That is a supposition which, in the present
state of natural philosophy, can neither be po-
sitively affirmed nor denied. Let us, therefore,
instead of discussing theoretical points, be con-
tented with examining what is known respecting
the chemical effects of light.
Light is capable of entering into a kind of tran-
sitory union with certain substances, and this is
what has been called phosphorescence. Bodies
that are possessed of this property, after being
exposed to the sun's rays, appear luminous in the
dark. The shells of n'sh, the bones of land ani-
mals, marble, limestone, and a variety of com-
binations of earths, are more or less powerfully
phosphorescent.
c 3
30 LIGHT.
CAROLINE.
I remember being much surprised last summer
with the phosphorescent appearance of some pieces
of rotten wood, which had just been dug out of the
ground; they shone so bright that I at first
supposed them to be glow-worms.
EMILY.
And is not the light of a glow-worm of a phos-
phorescent nature?
MRS. B.
It is a very remarkable instance of phospho-
rescence in living animals r this property, however,
is not exclusively possessed by the glow-worm. The
insect called the lanthorn-fly, which is peculiar to
warm climates, emits light as it flies, producing in
the dark a remarkably sparkling appearance. But
it is more common to see animal matter in a dead
state possessed of a phosphorescent quality; sea
fish is often eminently so.
EMILY.
I have heard that the sea has sometimes had the
appearance of being illuminated, and that the light
is supposed to proceed from the spawn of fishes
floating on its surface.
LIGHT. 31
MRS. B.
This light is probably owing to that or some
other animal matter. Sea water has been observed
to become luminous from the substance of a fresh
herring having been immersed in it ; and certain
insects, of the Medusa kind, are known to produce
similar effects.
But the strongest phosphorescence is produced
by chemical compositions prepared for the purpose,
the most common of which consists of oyster shells
and sulphur, and is known by the name of Can-
ton's Phosphorus.
EMILY.
I am rather surprised, Mrs. B., that you should
have said so much of the light emitted by phos-
phorescent bodies without taking any notice of that
which is produced by burning bodies.
MRS. B.
The light emitted by the latter is so intimately
connected with the chemical history of combustion,
that I must defer all explanation of it till we come
to the examination of that process, which is one of
the most interesting in chemical science.
Light is an agent capable of producing various
chemical changes. It is essential to the welfare
both of the animal and vegetable kingdoms; for
men and plants grow pale and sickly if deprived of
c 4
32 LIGHT.
its salutary influence. It is likewise remarkable
for its property of destroying colour, which ren-
ders it of great consequence in the process of
bleaching.
EMILY.
Is it not singular that light, which in studying
optics we were taught to consider as the source
and origin of colours, should have also the power
of destroying them ?
CAROLINE.
It is a fact, however, that we every day expe-
rience ; you know how it fades the colours of linens
and silks.
EMILY.
Certainly. And I recollect that endive is made
to grow white instead of green, by being covered
up so as to exclude the light. But by what means
does light produce these effects ?
MRS. B.
This I cannot attempt to explain to you until
you have obtained a further knowledge of che-
mistry. As the chemical properties of light can
be accounted for only in their reference to com-
pound bodies, it would be useless to detain you
any longer on this subject; we may therefore pass
on to the examination of heat, or caloric, with
which we are somewhat better acquainted.
FREE CALORIC. 33
HEAT and LIGHT may be always distinguished
by the different sensations they produce, Light
affects the sense of sight ; Caloric that of feeling ;
the one produces Vision, the other the sensation
of Heat.
Caloric is found to exist in a variety of forms or
modifications, and I think it will be best to consi-
der it under the two following heads, viz.
1. FREE OR RADIANT CALORIC.
2. COMBINED CALORIC.
The first, FREE or RADIANT CALORIC, is also
called HEAT OF TEMPERATURE ; it comprehends
all heat which is perceptible to the senses, and
affects the thermometer*
EMILY.
You mean such as the heat of the sun, of fire,
of candles, of stoves ; in short, of every thing that
burns ?
MRS. B.
And likewise of things that do not burn, as, for
instance, the warmth of the body ; in a word, all
heat that is sensible, whatever may be its degree,
or the source from which it is derived.
CAROLINE.
What then are the other modifications of calo-
c 5
34 FREE CALORIC.
ric ? It must be a strange kind of heat that can-
not be perceived by our senses.
MRS. B.
None of the modifications of caloric should pro-
perly be called heat ,- for heat, strictly speaking,
is the sensation produced by caloric, on animated
bodies ; this word, therefore, in the accurate lan-
guage of science, should be confined to express
the sensation. But custom has adapted it likewise
to inanimate matter, and we say the heat of an oven,
the heat of the sun t without any reference to the
sensation which they are capable of exciting.
It was in order to avoid the confusion which
arose from thus confounding the cause and effect,
that modern chemists adopted the new word ca-
loric, to denote the principle which produces
heat ; yet they do not always, in compliance with
their own language, limit the word heat to the ex-
pression of the sensation, since they still frequently
employ it in reference to the other modifications
of caloric which are quite independent of sensation.
CAROLINE.
But you have not yet explained to us what
these other modifications of caloric are.
MRS. B.
Because you are not acquainted with the pro-
FREE CALORIC. 35
perties of free caloric, and you know that we have
agreed to proceed with regularity.
One of the most remarkable properties of free
caloric is its power of dilating bodies. This fluid
is so extremely subtle, that it enters and pervades
all bodies whatever, forces itself between their
particles, and not only separates them, but fre-
quently drives them asunder to a considerable
distance from each other. It is thus that caloric
dilates or expands a body so as to make it occupy
a greater space than it did before.
EMILY.
The effect it has on bodies, therefore, is directly
contrary to that of the attraction of cohesion;
the one draws the particles together, the other
drives them asunder.
MRS. B.
Precisely. There is a continual struggle be-
tween the attraction of aggregation, and the ex-
pansive power of caloric ; and from the action of
these two opposite forces, result all the various
forms of matter, or degrees of consistence, from
the solid, to the liquid and aeriform state. And
accordingly we find that most bodies are capable
of passing from one of these forms to the other,
merely in consequence of their receiving different
quantities of caloric.
c 6
36 FREE CALORIC.
CAROLINE.
That is very curious ; but I think I understand
the reason of it. If a great quantity of caloric is
added to a solid body, it introduces itself between
the particles in such a manner as to overcome, in
a considerable degree, the attraction of cohesion ;
and the body, from a solid, is then converted into
a fluid.
MRS. B.
This is the case whenever a body is fused 'or
melted ; but if you add caloric to a liquid, can you
tell me what is the consequence ?
CAROLINE.
The caloric forces itself in greater abundance
between the particles of the fluid, and drives them
to such a distance from each other, that their at-
traction of aggregation is wholly destroyed: the
liquid is then transformed into vapour.
MRS. B.
Very well ; and this is precisely the case with
boiling water, when it is converted into steam or
vapour, and with all bodies that assume an aeri-
form state.
EMILY.
1 do not well understand the word aeriform ?
FREE CALORIC. 37
MRS. B.
Any elastic fluid whatever, whether it be merely
vapour or permanent air, is called aeriform.
But each of these various states, solid, liquid,
and aeriform, admit of many different degrees of
density, or consistence, still arising (chiefly at
least) from the different quantities of caloric the
bodies contain. Solids are of various degrees of
density, from that of gold, to that of a thin jelly.
Liquids, from the consistence of melted glue, or
melted metals, to that of ether, which is the
lightest of all liquids. The different elastic fluids
(with which you are not yet acquainted) are sus-
ceptible of no less variety in their degrees of
density.
EMILY.
But does not every individual body also admit
of different degrees of consistence, without chang-
ing its state ?
MRS. B.
Undoubtedly ; and this I can immediately show
you by a very simple experiment. This piece of
iron now exactly fits the frame, or ring, made to
receive it ; but if heated red hot, it will no longer
do so, for its dimensions will be so much increased
by the caloric that has penetrated into it, that it
will be much too large for the frame.
The iron is now red hot ; by applying it to the
frame, we shall see how much it is dilated.
38 FREE CALORIC.
EMILY.
Considerably so indeed ! I knew that heat had
this effect on bodies, but I did not imagine that it
could be made so conspicuous.
MRS. E.
By means of this instrument (called a Pyrome-
ter) we may estimate, in the most exact manner,
the various dilatations of any solid body by heat.
The body we are now going to submit to trial is
this small iron bar ; I fix it to this apparatus,
(PLATE I. Fig. I.) and then heat it by lighting the
three lamps beneath it : when the bar expands, it
increases in length as well as thickness; and, as
one end communicates with this whei-1-work,
whilst the other end is fixed and immoveable, no
sooner does it begin to dilate than it presses against
the wheel-work, and sets in motion the index,
which points out the degrees of dilatation on the
dial-plate.
EMILY.
This is, indeed, a very curious instrument ; but
I do not understand the use of the wheels : would
it not be more simple, and answer the purpose
equally well, if the bar, in dilating, pressed against
the index, and put it in motion without the inter-
vention of the wheels ?
FREE CALORIC. 39
MRS. B.
The use of the wheels is merely to multiply the
motion, and therefore render the effect of the
caloric more obvious ; for if the index moved no
more than the bar increased in length, its motion
would scarcely be perceptible; but by means of
the wheels it moves in a much greater proportion,
which therefore renders the variations far more
conspicuous.
By submitting different bodies to the test of the
pyrometer, it is found that they are far from di-
lating in the same proportion. Different metals
expand in different degrees, and other kinds of
solid bodies vary still more in this respect. But
this different susceptibility of dilatation is still more
remarkable in fluids than in solid bodies, as I shall
show you. I have here two glass tubes, terminated
at one end by large bulbs. We shall fill the
bulbs, the one with spirit of wine, the other with
water. I have coloured both liquids, in order that
the effect may be more conspicuous. The spirit of
wine, you see, dilates by the warmth of my hand
as I hold the bulb.
JEMILY.
It certainly does, for I see it is rising into the
tube. But water, it seems, is not so easily affected
by heat ; for scarcely any change is produced on
it by the warmth of the hand.
40 FREE CALORIC.
MRS. B.
True ; we shall now plunge the bulbs into hot
water, (PLATE I. Fig. 2.) and you will see both
liquids rise in the tubes; but the spirit of wine will
ascend highest.
CAROLINE.
How rapidly it expands ! Now it has nearly
reached the top of the tube, though the water has
hardly begun to rise.
EMILY.
The water now begins to dilate. Are not these
glass tubes, with liquids rising within them, very
like thermometers ?
MRS. B.
A thermometer is constructed exactly on the
same principle, and these tubes require only a scale
to answer the purpose of thermometers : but they
would be rather awkward in their dimensions. The
tubes and bulbs of thermometers, though of va-
rious sizes, are in general much smaller than these j
the tube too is hermetically closed, and the air
excluded from it. The fluid most generally used
in thermometers is mercury, commonly called
quicksilver, the dilatations and contractions of
which correspond more exactly to the additions,
and subtractions, of caloric, than those of any
other fluid.
FREE CALORIC. 41
CAROLINE.
Yet I have often seen coloured spirit of wine
used in thermometers.
MRS. B.
The expansions and contractions of that liquid
are not quite so uniform as those of mercury ; but
in cases in which it is not requisite to ascertain the
temperature with great precision, spirit of wine
will answer the purpose equally well, and indeed
in some respects better, as the expansion of the
latter is greater, and therefore more conspicuous.
This fluid is used likewise in situations and expe-
riments in which mercury would be frozen; for
mercury becomes a solid body, like a piece of lead
or any other metal, at a certain degree of cold :
but no degree of cold has ever been known to freeze
spirit of wine.
A thermometer, therefore, consists of a tube
with a bulb, such as you see here, containing a
fluid whose degrees of dilatation and contraction
are indicated by a scale to which the tube is fixed.
The degree which indicates the boiling point,
simply means that, when the fluid is sufficiently
dilated to rise to this point, the heat is such that
water exposed to the same temperature will
boil. When, on the other hand, the fluid is so
much condensed as to sink to the freezing point,
we know that water will freeze at that tempera-
42 FREE CALORIC.
ture. The extreme points of the scales are not the
same in all thermometers, nor are the degrees
always divided in the same manner. In different
countries philosophers have chosen to adopt differ-
ent scales and divisions. The two thermometers
most used are those of Fahrenheit, and of Reaumur ;
the first is generally preferred by the English, the
latter by the French.
EMILY.
The variety of scale must be very inconvenient,
and I should think liable to occasion confusion,
when French and English experiments are com-
pared.
MRS. B.
The inconvenience is but very trifling, because
the different gradations of the scales do not affect
the principle upon which thermometers are con-
structed. When we know, for instance, that
Fahrenheit's ecalc is divided into 212 degrees, in
which 32 corresponds with the freezing point,
and 212 with the point of boiling water : and that
Reaumur's is divided only into 80 degrees, in
which denotes the freezing point, and 80 that
of boiling water, it is easy to compare the two
scales together, and reduce the one into the other.
But, for greater convenience, thermometers are
sometimes constructed with both these scales, one
VOL.I.p.42.
PLAIE. H.
THERMOMETER .
FREE CALORIC. V 43
on either side of the tube ; so that the correspond-
ence of the different degrees of the two scales is
thus instantly seen. Here is one of these scales,
(PLATE II. Fig. 1.) by which you can at once per-
ceive that each degree of Reaumur's corresponds to
2| of Fahrenheit's division. But I believe the
French have, of late, given the preference to what
they call the centigrade scale, in which the space
between the freezing and the boiling point is divided
into 100 degrees.
CAROLINE.
That seems to me the most reasonable division,
and I cannot guess why the freezing point is
called 32, or what advantage is derived from
it.
MRS. B.
There really is no advantage in it ; and it ori-
ginated in a mistaken opinion of the instrument-
maker, Fahrenheit, who first constructed these
thermometers. He mixed snow and salt together,
and produced by that means a degree of cold
which he concluded was the greatest possible,
and therefore made his scale begin from that
point. Between that and boiling water he made
21 2 degrees, and the freezing point was found to
be at 32.
44 FREE CALORIC.
EMILY.
Are spirit of wine, and mercury, the only liquids
used in the construction of thermometers ?
MRS. 13.
I believe they are the only liquids now in use,
though some others, such as linseed oil, would
make tolerable thermometers : but for experiments
in which a very quick and delicate test of the
changes of temperature is required, air is the fluid
sometimes employed. The bulb of air thermo-
meters is filled with common air only, and its ex-
pansion and contraction are indicated by a small
drop of any coloured liquor, which is suspended
within the tube, and moves up and down, according
as the air within the bulb and tube expands or
contracts. But in general, air thermometers, how-
ever sensible to changes of temperature, are by no
means accurate in their indications.
I can, however, show you an air thermometer of
a very peculiar construction, which is remarkably
well adapted for some chemical experiments, as it
is equally delicate and accurate in its indications.
CAROLINE.
It looks like a double thermometer reversed, the
tube being bent, and having a large bulb at each
of its extremities. (PLATE II. Fig. 2.)
FREE CALORIC. 45
EMILY.
Why do you call it an air thermometer; the
tube contains a coloured liquid ?
MRS. B.
But observe that the bulbs are filled with air, the
liquid being confined to a portion of the tube, and
answering only the purpose of showing, by its
motion in the tube, the comparative dilatation or
contraction of the air within the bulbs, which
afford an indication of their relative temperature.
Thus if you heat the bulb A, by the warmth of
your hand, the fluid will rise towards the bulb B,
and the contrary will happen if you reverse the
experiment.
But if, on the contrary, both tubes are of the
same temperature, as is the case now, the coloured
liquid, suffering an equal pressure on each side, no
change of level takes place,
i
CAROLINE.
This instrument appears, indeed, uncommonly
delicate. The fluid is set in motion by the mere
approach of my hand.
MRS. B.
You must observe, however, that this ther-
mometer cannot indicate the temperature of any
particular body, or of the medinm in which 'it is
46 FREE CALORIC.
immersed; it serves only to point out the differ-
ence of temperature between the two bulbs, when
placed under different circumstances. For this
reason it has been called differential thermometer.
You will see by-and-bye to what particular purposes
this instrument applies.
EMILY.
But do common thermometers indicate the
exact quantity of caloric contained either in the
atmosphere, or in any body with which they are in
contact ?
MRS. B.
No : first, because there are other modifications
of caloric which do not affect the thermometer ;
and, secondly, because the temperature of a body,
as indicated by the thermometer, is only relative.
When, for instance, the thermometer remains
stationary at the freezing point, we know that the
atmosphere (or medium in which it is placed, what-
ever it may be) is as cold as freezing water ; and
when it stands at the boiling point, we know that
this medium is as hot as boiling water ; but we do
not know the positive quantity of heat contained
either in freezing or boiling water, any more than
we know the real extremes of heat and cold ; and
consequently we cannot determine that of the body
in which the thermometer is placed.
FREE CALORIC. 47
CAROLINE.
I do not quite understand this explanation.
MRS. B.
Let us compare a thermometer to a well, in
which the water rises to different heights, accord-
ing as it is more or less supplied by the spring
which feeds it: if the depth of the well is un-
fathomable, it must be impossible to know the ab-
solute quantity of water it contains; yet we can
with the greatest accuracy measure the number of
feet the water has risen or fallen in the well at any
time, and consequently know the precise quantity
of its increase or diminution, without having the
least knowledge of the whole quantity of water it
contains.
CAROLINE.
Now I comprehend it very well ; nothing appears
to me to explain a thing so clearly as a comparison.
EMILY.
But will thermometers bear any degree of heat ?
MRS. B.
No ; for if the temperature werq much above the
highest degree marked on the scale of the thermome-i
ter, the mercury would burst the tube in an attempt
to ascend. And at any rate, no thermometer can.
be applied to temperatures higher than the boiling
48" FREE CALORIC.
point of the liquid used in its construction, for
the steam, on the liquid beginning to boil, would
burst the tube. In furnaces, or whenever any
very high temperature is to be measured, a pyro-
meter, invented by Wedgwood, is used for that
purpose. It is made of a certain composition of
baked clay, which has the peculiar property of con-
tracting by heat, so that the degree of contraction
of this substance indicates the temperature to which
it has been exposed.
EMILY.
But is it possible for a body to contract by
heat ? I thought that heat dilated all bodies what-
ever.
MRS. B.
This is not an exception to the rule. You must
recollect that the bulk of the clay is not compared,
whilst hot, with that which it has when cold ; but
it is from the change which the clay has undergone
by having been heated that the indications of this
instrument are derived. This change consists in
a beginning fusion which tends to unite the particles
of clay more closely, thus rendering it less pervious
or spongy.
Clay is to be considered as a spongy body, hav-
ing many interstices or pores, from its having
contained water when soft. These interstices are
FREE CALORIC. 4V
by heat lessened, and would by extreme heat be
entirely obliterated.
CAROLINE.
And how do you ascertain the degrees of con-
traction of Wedgwood's pyrometer ?
MRS. B.
The dimensions of a piece of clay are measured
by a scale graduated on the side of a tapered
groove, formed in a brass ruler ; the more the clay
is contracted by the heat, the further it will de-
scend into the narrow part of the tube.
Before we quit the subject of expansion, I must
observe to you that, as liquids expand more readily
than solids, so elastic fluids, whether air or vapour,
are the most expansible of all bodies.
It may appear extraordinary that all elastic
fluids whatever, undergo the same degree of ex-
pansion from equal augmentations of temperature.
EMILY.
I suppose, then, that all elastic fluids are of the
same density ?
MRS. B.
Very far from it ; they vary in density, more
than either liquids or solids. The uniformity of
their expansibility, which at first may appear sin-
gular, is, however, readily accounted for. For if
the different susceptibilities of expansion of bodies
VOL, I. D
50 FREE CALORIC.
arise from their various degrees of attraction of
cohesion, no such difference can be expected in
elastic fluids, since in these the attraction of co-
hesion does not exist, their particles being on the
contrary possessed of an elastic or repulsive power ;
they will therefore all be equally expanded by equal
degrees of caloric.
EMILY.
True ; as there is no power opposed to the ex-
pansive force of caloric in elastic bodies, its effect
must be the same in all of them.
MRS. B.
Let us now proceed to examine the other pro-
perties of free caloric.
Free caloric always tends to diffuse itself
equally, that is to say, when two bodies are of
different temperatures, the warmer gradually
parts with its heat to the colder, till they are both
brought to the same temperature. Thus, when
a thermometer is applied to a hot body, it receives
caloric; when to a cold one, it communicates
part of its own caloric, and this communication
continues until the thermometer and the body
arrive at the same temperature.
EMILY.
Cold, then, is nothing but a negative quality,
ftimply implying the absence of heat.
FREE CALORIC. 5i
MRS. B.
Not the total absence, but a diminution of heat;
for we know of no body in which some caloric
may not be discovered.
CAROLINE.
But when I lay my hand on this marble table
I feel it positively cold, and cannot conceive that
there is any caloric in it.
MRS. B.
The cold you experience consists in the loss of
caloric that your hand sustains in an attempt to
bring its temperature to an equilibrium with the
marble. If you lay a piece of ice upon it, you
will find that the contrary effect will take place ;
the ice will be melted by the heat which it ab-
stracts from the marble.
CAROLINE.
Is it not in this case the air of the room, which
being warmer than the marble, melts the ice ?
MRS. B.
The air certainly acts on the surface which is
exposed to it, but the table melts that part with
which it is in contact.
CAROLINE.
But why does caloric tend to an equilibrium ?
D 2
52 FREE CALORIC.
It cannot be on the same principle as other fluids,
since it has no weight ?
MRS. B.
Very true, Caroline, that is an excellent objec-
tion. You might also, with some propriety, ob-
ject to the term equilibrium being applied to a
body that is without weight ; but I know of no
expression that would explain my meaning so
well. You must consider it, however, in a figura-
tive rather than a literal sense ; its strict mean-
ing is an equal diffusion. We cannot, indeed, well
say by what power it diffuses itself equally, though
it is not surprising that it should go from the
parts which have the most to those which have
the least. This subject is best explained by a
theory suggested by Professor Prevost of Geneva,
which is now, I believe, generally adopted.
According to this theory, caloric is composed
of particles perfectly separate from each other,
every one of which moves with a rapid velocity
in a certain direction. These directions vary as
much as imagination can conceive, the result of
which is, that there are rays or lines of these par-
ticles moving with immense velocity in every pos-
sible direction. Caloric is thus universally diffused,
so that when any portion of space happens to
be hi the neighbourhood of another, which con-
tains more caloric, the colder portion receives a
FREE CALORIC. 53
quantity of calorific rays from the latter, sufficient
to restore an equilibrium of temperature. This
radiation does not only take place in free space,
but extends also to bodies of every kind. Thus
you may suppose all bodies whatever constantly
radiating caloric : those that are of the same tem-
perature give out and absorb equal quantities, so
that no variation of temperature is produced in
them ; but when one body contains more free ca-
loric than another, the exchange is always in fa-
vour of the colder body, until an equilibrium is
effected ; this you found to be the case when the
marble table cooled yonr hand, and again when
it melted the ice.
CAROLINE.
This reciprocal radiation surprises me ex-
tremely ; I thought, from what you first said, that
the hotter bodies alone emitted rays of caloric
which were absorbed by the colder ; for it seems
unnatural that a hot body should receive any
caloric from a cold one, even though it should
return a greater quantity.
MRS. B.
It may at first appear so, but it is no more ex-
traordinary than that a candle should send forth
rays of light to the sun, which, you know, must
necessarily happen.
B 8
54 FREE CALORIC.
CAROLINE.
Well, Mrs. B , I believe that I must give up
the point. But I wish I could see these rays of
caloric; I should then have greater faith in them.
MRS. B.
Will you give no credit to any sense but that
of sight ? You may feel the rays of caloric which
you receive from any body of a temperature
higher than your own j the lops of the caloric you
part with in return, it is true, is not perceptible;
for as you gain more than you lose, instead of
suffering a diminution, you are really making an
acquisition of caloric. It is, therefore, only when
you are parting with it to a body of a lower tem-
perature, that you are sensible of the sensation of
cold, because you then sustain an absolute loss of
caloric.
EMILY.
And in this case we cannot be sensible of the
small quantity of heat we receive in exchange
from.the colder body, because it serves only to
diminish the loss.
MRS. B.
Very well, indeed, Emily. Professor Pictet, of
Geneva, has made some very interesting experi-
ments, which prove not only that caloric radiates
from all bodies whatever, but that these rays may
be reflected, according to the laws of optics^ in
CALORIC. 55
the same manner as light. I shall repeat these
experiments before you, having procured mirrors
fit for the purpose; and it will afford us an op-
portunity of using the differential thermometer,
which is particularly well adapted for these ex-
periments. I place an iron bullet, (PLATE III.
Fig. I.) about two inches in diameter, and heated
to a degree not sufficient to render it luminous,
in the focus of this large metallic concave mirror.
The rays of heat which fall on this mirror are re-
flected, agreeably to the property of concave
mirrors, in a parallel direction, so as to fall on a
similar mirror, which, you see, is placed opposite
to the first, at the distance of about ten feet ;
thence the rays converge to the focus of the se-
cond mirror, in which 1 place one of the bulbs of
this thermometer. Now, observe in what manner
it is affected by the caloric which is reflected on
it from the heated bullet. The air is dilated in
the bulb which we placed in the focus of the
mirror, and the liquor rises considerably in the
opposite leg,
EMILY.
But would not the same effect take place, if the
rays of caloric from the heated bullet fell directly
on the thermometer, without the assistance of the
mirrors ?
MRS. B.
The effect would in that case be so trifling, at
P 4
56' FREE CALORIC.
the distance at which the bullet and the thermo-
meter are from each other, that it would be almost
imperceptible. The mirrors, you know, greatly in-
crease the effect, by collecting a large quantity of
rays into a focus ; place your hand in the focus of
the mirror, and you will find it much hotter there
than when you remove it nearer to the bullet.
EMILY.
That is very true; it appears extremely singular
to feel the heat diminish in approaching the body
from which it proceeds.
CAROLINE.
And the mirror which produces so much heat,
by converging the rays, is itself quite cold.
MRS. B.
The same number of rays that are dispersed
over the surface of the mirror are collected by it
into the focus ; but, if you consider how large a
surface the mirror presents to the rays, and, con-
sequently, how much they are diffused in compa-
rison to what they are at the focus, which is little
more than a point, I think you can no longer won-
der that the focus should be so much hotter than
the mirror.
The principal use of the mirrors in this experi-
ment is, to prove that the caloric emanation is re-
flected in the same manner as light.
FREE CAJLORIC. 5?
CAROLINE.
And the result, I think, is very conclusive.
MRS. B.
The experiment may be repeated with a wax
taper instead of the bullet, with a view of separating
the light from the caloric. For this purpose a
transparent plate of glass must be interposed be-
tween the mirrors; for light, you know, passes
with great facility through glass, whilst the trans-
mission of caloric is almost wholly impeded by it.
We shall find, however, in this experiment, that
some few of the calorific rays pass through the
glass together with the light, as the thermometer
rises a little ; but, as soon as the glass is removed,
and a free passage left to the caloric, it will rise
considerably higher.
EMILY.
This experiment, as well as that of Dr. Her-
schell's, proves that light and heat may be sepa-
rated; for in the latter experiment the separation
was not perfect, any more than in that of Mr.
Pictet.
CAROLINE.
I should like to repeat this experiment, with the
difference of substituting a cold body instead of the
hot one, to see whether cold would not be reflected
as well as heat.
D 5
58 FREE CALORIC.
MRS. B.
That experiment was proposed to Mr. Pictet by
an incredulous philosopher like yourself, and he
immediately tried it by substituting a piece of ice
in the place of the heated bullet.
CAROLINE.
Well, Mrs. B., and what was the result ?
MRS. B.
That we shall see; I have procured som ice for
the purpose.
EMILY.
The thermometer falls considerably 1
CAROLINE.
And does not that prove that cold is not merely
a negative quality, implying simply an inferior de-
gree of heat ? The cold must be positive, since it
is capaWe of reflection.
MRS. B.
So it at first appeared to Mr. Pictet"; but upon
a little consideration he found that it afforded onjy
an additional proof of the reflection of heat: this I
shall endeavour to explain to you.
According to Mr. Prevost's theory, we suppose
that all bodies whatever radiate caloric ; the ther-
mometer used in these experiments therefore emits
calorific rays in the same manner as any other
FREld CALORIC. 59
substance. When its temperature is in equilibrium
with that of the surrounding bodies, it receives as
much caloric as it parts with, and no change of
temperature is produced. But when we introduce
a body of a lower temperature, such as a piece of
ice, which parts with less caloric than it receives,
the consequence is, that its temperature is raised,
whilst that of the surrounding bodies is propor-
tionally lowered.
EMILY.
If, for instance, I was to bring a large piece of
ice into this room, the ice would in time be melted,
by absorbing caloric from the general radiation
which is going on throughout the room ; and as
it would contribute very little caloric in return
for what is absorbed, the room would necessarily
be cooled by it.
MRS. B.
Just so ; and as in consequence of the mirrors,
a more considerable exchange of rays takes place
between the ice and the thermometer, than between
these and any of the surrounding bodies, the tem-
perature of the thermometer must be more lowered
than that of any other adjacent object,
CAROLINE.
I confess I do not perfectly understand your
explanation.
D 6
60 FREE CALORIC.
MRS. B.
This experiment is exactly similar to that made
with the heated bullet : for, if we consider the ther-
mometer as the hot body (which it certainly is in
comparison to the ice), you may then easily under-
stand that it is by the loss of the calorific rays which
the thermometer sends to the ice, and not by any
cold rays received from it, that the fall of the mer-
cury is occasioned : for the ice, far from emitting
rays of cold, sends forth rays of caloric, which di-
minish the loss sustained by the thermometer.
Let us say, for instance, that the radiation of
the thermometer towards the ice is equal to 20,
and that of the ice towards the thermometer to
10: the exchange in favour of the ice is as 20 is
to 10, or the thermometer absolutely loses 10,
whilst the ice gains 10.
CAROLINE.
But if the ice actually sends rays of caloric to
the thermometer, must not the latter fall still lower
when the ice is removed ?
MRS. B.
No ; for the space that the ice occupied, admits
rays from all the surrounding bodies to pass through
it ; and those being of the same temperature as the
thermometer, will not affect it, because as much
heat now returns to the thermometer as radiates
from it.
FREE CALORIC. Gl
CAROLINE.
I must confess that you have explained this in
so satisfactory a manner, that I cannot help being
convinced now that cold has no real claim to the
rank of a positive being.
MRS. B.
Before I conclude the subject of radiation I must
observe to you that different bodies, (or rather sur-
faces,) possess the power of radiating caloric in very
different degrees.
Some very curious experiments have been made
by Mr. Leslie on this subject, and it was for this
purpose that he invented the differential thermo-
meter ; with its assistance he ascertained that black
surfaces radiate most, glass next, and polished sur-
faces the least of all.
EMILY.
Supposing these surfaces, of course, to be all of
the same temperature.
MRS. B.
Undoubtedly. I will now show you the very
simple and ingenious apparatus, by means of which
he made these experiments. This cubical tin
vessel or canister, has each of its sides externally
covered with different materials ; the one is sim-
ply blackened; the next is covered with white
62 FREE CALORIC.
paper ; the third with a pane of glass, and in the
fourth the polished tin surface remains uncovered.
We shall fill this vessel with hot water, so that
there can be no doubt but that all its sides will be
of the same temperature. Now let us place it in
the focus of one of the mirrors, making each of its
sides front it in succession. We shall begin with
the black surface.
CAROLINE.
It makes the thermometer which is in the focus
of the other mirror rise considerably. Let us turn
the paper surface towards the mirror. The ther-
mometer falls a little, therefore of course this side
cannot emit or radiate so much caloric as the
blackened side,
EMILY.
This is very surprising ; for the sides are exactly
of the same size, and must be of the same tempera-
ture. But let us try the glass surface.
MRS. B.
The thermometer continues falling, and with the
plain surface it falls still lower ; these two surfaces
therefore radiate less and less.
CAROLINE.
I think I have found out the reason of this.
ii
FREE CALORIC. 63
MRS. B.
I should be very happy to hear it, for it has not
yet (to my knowledge) been accounted for.
CAROLINE.
The water within the vessel gradually cools, and
the thermometer in consequence gradually falls.
MRS. B.
It is true that the water cools, but certainly in
much less proportion than the thermometer de-
scends, as you will perceive if you now change the
tin surface for the black one.
CAROLINE.
I was mistaken certainly, for the thermometer
rises again now that the black surface fronts the
mirror.
MRS. B.
And yet the water in the vessel is still cooling,
Caroline.
EMILY.
I am surprised that the tin surface should ra-
diate the least carolic, for a metallic vessel filled
with hot water, a silver teapot, for instance, feels
much hotter to the hand than one of black earthen
ware.
54 FREE CALORIC.
MRS. B.
That is owing to the different power which
rarious bodies possess tor conducting caloric, a
property which we shall presently examine. Thus,
although a metallic vessel feels warmer to the hand,
a vessel of this kind is known to preserve the heat
of the liquid within, better than one of any other
materials ; it is for this reason that silver teapots
make better tea than those of earthen ware.
EMILY.
According to these experiments, light-coloured
dresses, in cold weather, should keep us warmer
than black clothes, since the latter radiate so much
more than the former.
MRS. B.
And that is actually the case.
EMILY.
This property, of different surfaces to radiate in
different degrees, appears to me to be at variance
with the equilibrium of caloric ; since it would
imply that those bodies which radiate most, must
ultimately become coldest.
Suppose that we were to vary this experiment,
by using two metallic vessels full of boiling water,
the one blackened, the other not ; would not the
black one cool the first ?
16
FREE CALORIC. 65
CAROLINE.
True; but when they were both brought down
to the temperature of the room, the interchange
of caloric between the canisters and the other
bodies of the room being then equal, their tem-
peratures would remain the same.
EMILY.
I do not see why that should be the case ; for if
different surfaces of the same temperature radiate
in different degrees when heated, why should they
not continue to do so when cooled down to the
temperature of the room ?
MRS. B.
You have started a difficulty, Emily, which cer-
tainly requires explanation. It is found by expe-
riment that the power of absorption corresponds
with and is proportional to that of radiation ; so
that under equal temperatures, bodies compen-
sate for the greater loss they sustain in conse-
quence of their greater radiation by their greater
absorption ; so that if you were to make your ex-
periment in an atmosphere heated like the ca-
nisters, to the temperature of boil ing water, though
it is true that the canisters would radiate in dif-
ferent degrees, no change of temperature would
be produced in them, because they would each
absorb caloric in proportion to their respective
radiation.
66 FREE CALORIC.
EMILY.
But would not the canisters of boiling water also
absorb caloric in different degrees in a room of the
common temperature ?
MRS. B.
Undoubtedly they would. But the various
bodies in the room would not, at a lower tem-
perature, furnish either of the canisters with a
sufficiency of caloric to compensate for the loss
they undergo ; for, suppose the black canister to
absorb 400 rays of caloric, whilst the metallic one
absorbed only 200 ; yet if the former radiate 800,
whilst the latter radiates only 400, the black
canister will be the first cooled down to the tem-
perature of the room. But from the moment the
equilibrium of temperature has taken place, the
black canister, both receiving and giving out 400
rays, and the metallic one 200, no change of tem-
perature will take place.
EMILY.
I now understand it extremely well. But what
becomes of the surplus of calorific rays, which
good radiators emit and bad radiators refuse to
receive ; they must wander about in search of a
resting-place ?
MRS. B.
They really do so ; for they are rejected and sen.t
FREE CALORIC. 67
back, or, in other words, reflected by the bodies
which are bad radiators of caloric ; and they are
thus transmitted to other bodies which happen to
lie in their way, by which they are either absorbed
or again reflected, according as the property of
reflection, or that of absorption, predominates in
these bodies.
CAROLINE.
I do not well understand the difference between
radiating and reflecting caloric, for the caloric
that is reflected from a body proceeds from it in
straight lines, and may surely be said to radiate
from it ?
MRS. B.
It is true that there at first appears to be a great
analogy between radiation and reflection, as they
equally convey the idea of the transmission of
caloric.
But if you consider a little, you will perceive
that when a body radiates caloric, the heat which
it emits not only proceeds from, but has its origin
in the body itself. Whilst when a body reflects
caloric, it parts with none of its own caloric, but
only reflects that which it receives from other
bodies.
EMILY.
Of this difference we have very striking ex-
amples before us, in the tin vessel of water, and the
concave mirrors; the first radiates its own heat.
68
the latter reflect the heat which they receive from
other bodies.
CAROLINE.
Now, that I understand the difference, it no
longer surprises me that bodies which radiate, or
part with their own caloric freely, should not have
the power of transmitting with equal facility that
which they receive from other bodies.
EMILY.
Yet no body can be said to possess caloric of
its own, if all caloric is originally derived from the
sun.
MRS. B.
When I speak of a body radiating its own ca-
loric, I mean that which it has absorbed and incor-
porated either immediately from the sun's rays, or
through the medium of any other substance.
CAROLINE.
It seems natural enough that the power of ab-
sorption should be in opposition to that of reflec-
tion, for the more caloric a body receives, the less
it will reject.
EMILY.
And equally so that the power of radiation
should correspond with that of absorption. It is,
in fact, cause and effect ; for a body cannot radiate
FREE CALORIC. 69
heat without having previously absorbed it; just
as a spring that is well fed flows abundantly.
MRS. B.
Fluids are in general very bad radiators of ca-
loric ; and air neither radiates nor absorbs caloric
in any sensible degree.
We have not yet concluded our observations on
free caloric. But I shall defer, till our next meet-
ing, what I have further to say on this subject. I
believe it will afford us ample conversation for
another interview.
CONVERSATION 111.
CONTINUATION OF THE SUBJECT.
MRS. B.
IN our last conversation, we began to examine
the tendency of caloric to restore an equilibrium
of temperature. This property, when once well
understood, affords the explanation of a great va-
riety of facts which appeared formerly unaccount-
able. You must observe, in the first place, that
the effect of this tendency is gradually to bring
all bodies that are in contact to the same tern*
perature. Thus, the fire which burns in the grate,
communicates its heat from one object to another,
till every part of the room has an equal propor-
tion of it.
EMILY.
And yet this book is not so cold as the table on
which it lies, though both are at an equal distance
from the fire, and actually in contact with each
other, so that, according to your theory, they
should be exactly of the same temperature.
FREE CALORIC. 71
CAROLINE.
And the hearth, which is much nearer the fire
than the carpet, is certainly the colder of the two.
MRS. B.
If you ascertain the temperature of these several
bodies by. a thermometer (which is a much more
accurate test than your feeling), you will find
that it is exactly the same.
CAROLINE.
But if they are of the same temperature, why
should the one feel colder than the other ?
MRS. B.
The hearth and the table feel colder than the
carpet or the book, because the latter are not such
good conductors of heat as the former. Caloric
finds a more easy passage through marble and
wood, than through leather and worsted; the two
former will therefore absorb heat more rapidly
from your hand, and consequently give it a
stronger sensation of cold than the two latter, al-
though they are all of them really of the same
temperature.
CAROLINE.
Soj then, the sensation I feel on touching a cold
body, is in proportion to the rapidity with which
my hand yields its heat to that body ?
7 FREE -CALORIC.
MRS. B.
Precisely; and, if you lay your hand succes-
sively on ever)' object in the room, you will disco-
ver which are good, and which are bad conductors
of heat, by the different degrees of cold you
feel. But, in order to ascertain . this point, it is
necessary that the several substances should be of
the same temperature, which will not be the case
with those that are very near the fire, or those
that are exposed to a current of cold air from a
window or door.
EMILY.
But what is the reason that some bodies are
better conductors of heat than others ?
MRS. B.
This is a point not well ascertained. It has
been conjectured that a certain union or adher-
ence takes place between the caloric and the par-
ticles of the body through which it passes. If this
adherence be strong, the body detains the heat,
and parts with it slowly and reluctantly ; if slight,
it propagates it freely and rapidly. The con-
ducting power of a body is therefore, inversely,
as its tendency to unite with caloric.
EMILY.
That is to say, that the best conductors are
those that have the least affinity for caloric.
FREE CALORIC. 73
MRS. B.
Yes; but the terra affinity is objectionable in
this case, because, as that word is used to express
a chemical attraction (which can be destroyed
only by decomposition), it cannot be applicable to
the slight and transient union that takes place be-
tween free caloric and the bodies through which
it passes ; an union which is so weak, that it con-
stantly yields to the tendency which caloric has to
an equilibrium. Now you clearly understand,
that the passage of caloric, through bodies that are
good conductors, is much more rapid than through
those that are bad conductors, and that the former
both give and receive it more quickly, and there-
fore, in a given time, more abundantly, than bad
conductors, which makes them feel either hotter
or colder, though they may be, in fact, both of the
same temperature.
CAROLINE.
Yes, I understand it now; the table, and the
book lying upon it, being really of the same tem-
perature, would each receive, in the same space
of time, the same quantity of heat from my hand,
were their conducting powers equal; but as the
table is the best conductor of the two, it will ab-
sorb the heat from my hand more rapidly, and
consequently produce a stronger sensation of cold
than the book.
VOL, I. E
74 FREE CALORIC.
AIRS. B.
Very well, my dear; and observe, likewise,
that if you were to heat the table and the book ail
equal number of degrees above the temperature of
your body, the table, which before felt the colder, K
would now feel the hotter of the two ; for, as in
the first case it took the heat most rapidly from
your hand, so it will now impart heat most rapidly
to it. Thus the marble table, which seems to us
colder than the mahogany one, will prove the
hotter of the two to the ice ; for, if it takes heat
more rapidly from our hands, which are warmer, it
will give out heat more rapidly to the ice, which
is colder. Do you understand the reason of these
apparently opposite effects?
EMILY.
Perfectly. A body which is a good conductor
of caloric, affords it a free passage; so that it
penetrates through that body more rapidly than
through one which is a bad conductor ; and con-
sequently, if it is colder than your hand, you lose
more caloric, and if it is hotter, you gain more than
with a bad conductor of the same temperature.
MRS. B.
But you must observe that this is the case only
when the conductors are either hotter or colder
than your hand; for, if you heat different con-
CAL6RIC. 75
tluctors to the temperature of your body, they
will all feel equally warm, since the exchange of
caloric between bodies of the same temperature
is equal. Now, can you tell me why flannel
clothing, which is a very bad conductor of heat,
prevents our feeling cold ?
CAROLINE.
It prevents the cold from penetrating
MRS. B.
But you forget that cold .is only a negative
quality.
CAROLINE.
True ; it only prevents the heat of jur bodies
from escaping so rapidly as it would otherwise do.
MRS. B.
Now you have explained it right; the flannel
rather keeps in the heat, than keeps out the cold.
Were the atmosphere of a higher temperature than
our bodies, it would be equally efficacious in keep-
ing their temperature at the same degree, as it'
would prevent the free access of the external
heat, by the difficulty with which it conducts it.
EMILY.
This, I think, is very clear. Heat, whether
external or internal, cannot easily penetrate flan-
E 2
76 FREE CALORIC,
nel; therefore in cold weather it keeps us warm;
and if the weather was hotter than our bodies, it
would keep us cool.
MRS. B.
The most dense bodies are, generally speaking,
the best conductors of heat ; probably because the
denser the body the greater are the number of
points or particles that come in contact with caloric.
At the common temperature of the atmosphere a
piece of metal will feel much colder than a piece
of wood, and the latter than a piece of woolJen
cloth ; this again will feel colder than flannel ; and
down, which is one of the lightest, is at the same
time one of the warmest bodies.
CAROL1NF.
This is, I suppose, the reason that the plumage
of birds preserves them so effectually from the in-
fluence of cold in winter ?
MRS. B.
Yes ; but though feathers in general are an ex^
celient preservative against cold, down is a kind
of plumage peculiar to aquatic birds, and covers
their chest, which is the part most exposed to the
water ; for though the surface of the water is not
of a lower temperature than the atmosphere, yet,
a& it is a better conductor of heat, it feels
FREE CALORIC. 77
Colder, consequently the chest of the bird requires
a warmer covering than any other part of its body.
Besides, the breasts of aquatic birds are exposed
to cold not only from the temperature of the water,
but also from the velocity with which the breast
of the bird strikes against it; and likewise from
the rapid evaporation occasioned in that part by
the air against which it strikes, after it has been
moistened by dipping from time to time into the
water.
If you hold a finger of one hand motionless in a
glass of water, and at the same time move a finger
of the other hand swiftly through water of the same
temperature, a different sensation will be soon per-
ceived in the different fingers.
Most animal substances, especially those which
Providence has assigned as a covering for animals,
such as fur, wool, hair, skin, &c. are bad con-
ductors of heat, and are, on that account, such ex-
cellent preservatives against the inclemency of
winter, that our warmest apparel is made of these
materials.
EMILY.
Wood is, I dare say, not so good a conductor as
metal, and it is for that reason, no doubt, that silver
teapots have always wooden handles.
MRS. B.
Yes; and it is the facility with which metals
E 3
78 FREE CALORIC.
conduct caloric that made you suppose that a silver
pot radiated more caloric than an earthen one.
The silver pot is in fact hotter to the hand when
in contact with it ; but it is because its conducting
power more than counterbalances its deficiency in
regard to radiation.
We have observed that the most dense bodies
are in general the best conductors; and metals,
you know*, are of that class. Porous bodies, such
as the earths and wood, are worse conductors,
chiefly, I believe, on account of their pores being
filled with air ; for air is a remarkably bad con-
ductor.
CAROLINE.
It is a very fortunate circumstance that air should
be a bad conductor, as it tends to preserve the heat
of the body when exposed to cold weather.
MRS. B.
It is one of the many benevolent dispensations of
Providence, in order to soften the inclemency of the
seasons, and to render almost all climates habitable
to man.
In fluids of different densities, the power of con-
ducting heat varies no less remarkably ; if you dip
your hand into this vessel full of mercury, you will
scarcely conceive that its temperature is not lower
than that of the atmosphere.
FREE CALORIC. 79
CAROLINE.
Indeed I know not how to believe it, it feels so
extremely cold. But we may easily ascertain its
true temperature by the thermometer. It is really
not colder than the air; the apparent difference
then is produced merely by the difference of the
conducting power in mercury and in air.
MRS. B.
Yes; hence you may judge how little the sense
of feeling is to be relied on as a test of the tem-
perature of bodies, and how necessary a thermo-
meter is for that purpose.
It has indeed been doubted whether fluids have
the power of conducting caloric in the same man-
ner as solid bodies. Count Rumford, a very few
years since, attempted to prove, by a variety of
experiments, that fluids, when at rest, were not at
all endowed with this property.
CAROLINE.
How is that possible, since they are capable of
imparting cold or heat to us ; for if they did not
conduct heat, they would neither take it from, nor
give it to us?
MRS. B.
Count Rumford did not mean to say that fluids
would not communicate their heat to solid bodies;
E 4
80 FREE CALORIC.
but only that heat does not pervade fluids, that
is to say, is not transmitted from one particle of
a fluid to another, in the same manner as in solid
bodies.
EMILY.
But when you heat a vessel of water over the
fire, if the particles of water do not communicate
heat to each other, how does the water become hot
throughout ?
MRS. B.
By constant agitation. Water, as you have
seen, expands by heat in the same manner as solid
bodies; the heated particles of water, therefore,
at the bottom of the vessel, become specifically
lighter* than the rest of the liquid, and conse-
quently ascend to the surface, where, parting with
some of their heat to the colder atmosphere, they
are condensed, and give way to a fresh succession
of heated particles ascending from the bottom,
which having thrown off their heat at the surface,
are in their turn displaced. Thus every particle
is successively heated at the bottom, and cooled at
the surface of the liquid ; but as the fire commu-
nicates heat more rapidly than the atmosphere cools
the succession of surfaces, the whole of the liquid
in time becomes heated. .
CAROLINE.
This accounts most ingeniously for the propa-
FREE CALORIC. 81
.gation of heat upwards. But suppose you were
to heat the upper surface of a liquid, the particles
being specifically lighter than those below, could
not descend : how therefore would the heat be
communicated downwards ?
MRS. B.
If there were no agitation to force the heated
surface downwards, Count Rumford assures us
that the heat would not descend. In proof of this
he succeeded in making the upper surface of a vessel
of water boil and evaporate, while a cake of ice
remained frozen at the bottom.
CAROLINE.
That is very extraordinary indeed !
MRS. B.
It appears so, because we are not accustomed to
heat liquids by their upper surface; but you will
understand this theory better if I show you the in-
ternal motion that takes place in liquids when they
experience a change of temperature. The motion
of the liquid itself is indeed invisible from the ex-
treme minuteness of its particles ; but if you mix
with it any coloured dust, or powder, of nearly
the same specific gravity as the liquid, you may
judge of the internal motion of the latter by that
;of the coloured dust it contains. Do you see the
JE 5
82 FREE CALORIC.
small pieces of amber moving about in the liquid
contained in this phial?
CAROLINE.
Yes, perfectly.
MRS. B.
We shall now immerse the phial in a glass of
hot water, and the motion of the liquid will be
shown, by that which it communicates to the amber.
EMILY.
I see two currents, the one rising along the sides
of the phial, the other descending in the centre:
but I do not understand the reason of this.
MRS. B.
The hot water communicates its caloric, through
the medium of the phial, to the particles of the
fluid nearest to the glass ; these dilate and ascend
laterally to the surface, where, in parting with
their heat, they are condensed, and in descending,
form the central current.
CAROLINE.
This is indeed a very clear and satisfactory ex-
periment; but how much slower the currents
now move than they did at first ?
MRS. B.
It is because the circulation of particles has
FREE CALORIC. 83
nearly produced an equilibrium of temperature be-
tween the liquid in the glass and that in the phial.
CAROLINE.
But these communicate laterally, and I thought
that heat in liquids could be propagated only up-
wards.
MRS. B.
You do not take notice that the heat is imparted
from one liquid to the other, through the medium
of the phial itself, the external surface of which
receives the heat from the water in the glass,
whilst its internal surface transmits it to the liquid
it contains. Now take the phial out of the hot
water, and observe the effect of its cooling.
EMILY.
The currents are reversed; the external cur-
rent now descends, and the internal one rises. I
guess the reason of this change: the phial being
in contact with cold air instead of hot water, the
external particles are cooled instead of being heat-
ed ; they therefore descend and force up the cen-
tral particles, which, being warmer, are conse-
quently lighter.
MRS. B.
It is just so. Count Rumford hence infers that
no alteration of temperature can take place in a
fluid, without an internal motion of its particles,
6
84 FREE CALORIC.
and as this motion is produced only by the com-
parative levity of the heated particles, heat cannot
be propagated downwards.
But though I believe that Count Rumford's
theory as to heat being incapable of pervading
fluids is not strictly correct, yet there is, no doubt,
much truth in his observation, that the commu-
nication is materially promoted by a motion of
the parts ;, and this accounts for the cold that is
founcfe to prevail at the bottom of the lakes in
Switzerland, which are fed by rivers issuing from
the snowy Alps. The water of these rivers being
colder, and therefore more dense than that of the
lakes, subsides to the bottom, where it cannot be
affected by the warmer temperature of the surface ;
the motion of the waves may communicate this
temperature to some little depth, but it can descend
no further than the agitation extends.
EMILY..
But when the atmosphere ia colder than the
lake, the colder surface of the water will descend,
for the very reason that the warmer will not.
MRS. B.
Certainly : and it is on this account that neither
a lake, nor any body of water whatever, can be
frozen until every particle of the water has risen
to the surface to give off its caloric to the colder
*$
"*- .
*S
T* t
il^
^^s 4'
I
i
S v
FREE CALORIC. , 85
atmosphere; therefore the deeper a body of wa-
ter is, the longer will be the time it requires to
be frozen.
EMILY.
But if the temperature of the whole body of
water be brought down to the freezing point, why
is only the surface frozen ?
MRS. B.
The temperature of the whole body is lowered,
but not to the freezing point. The diminution of
heat, as you know, produces a contraction in the
bulk of fluids, as well as of solids. This effect,
however, does not take place in water below the
temperature of 40 degrees, which is 8 degrees
above the freezing point. At that temperature,
therefore, the internal motion, occasioned by the
increased specific gravity of the condensed par-
ticles, ceases; for when the water at the surface
no longer condenses, it will no longer descend,
and leave a fresh surface exposed to the atmo-
sphere: this surface alone, therefore, will be fur-
ther exposed to its severity, and will soon be
brought down to the freezing point, when it be-
comes ice, which being a bad conductor of heat,
preserves the water beneath a long time from being
affected by the external cold.
CAROLINE.
And the sea does not freeze, I suppose, because
86 FREE CALORIC.
its depth is so great, that a frost never lasts long
enough to bring down the temperature of such a
great body of water to 40 degrees ?
MRS. B.
That is one reason why the sea, as a large mass
of water, does not freeze. But, independently of
this, salt water does not freeze till it is cooled
much below 32 degrees, and with respect to the
law of condensation, salt water is an exception,
as it condenses even many degrees below the
freezing point. When the caloric of fresh water,
therefore, is imprisoned by the ice on its surface,
the ocean still continues throwing off' heat into the
atmosphere, which is a most signal dispensation of
Providence to moderate the intensity of the cold in
winter.
CAROLINE.
This theory of the non-conducting power of
liquids, does not, 1 suppose, hold good with respect
to air, otherwise the atmosphere would not be
heated by the rays of the sun passing through it ?
MRS. B.
Nor is it heated in that way. The pure atmosphere
is a perfectly transparent medium, which neither
radiates, absorbs, nor conducts caloric, but trans-
mits the rays of the sun to us without in any way
FREE CALORIC. 87
diminishing their intensity. The air is therefore
not more heated, by the sun's rays passing through
it, than diamond, glass, water, or any other trans-
parent medium.
CAROLINE.
That is very extraordinary ! Are glass windows
not heated then by the sun shining on them ?
MRS. B.
No; not if the glass be perfectly transparent.
A most convincing proof that glass transmits the
rays of the sun without being heated by them is
afforded by the burning lens, which by converging
the rays to a focus will set combustible bodies on
fire, without its own temperature being raised.
EMILY.
Yet, Mrs. B., if I hold a piece of glass near the
fire it is almost immediately warmed by it; the
glass therefore must retain some of the caloric
radiated by the fire? Is it that the solar rays
alone pass freely through glass without paying
tribute ? It seems unaccountable that the radiation
of a common fire should have power to do what
the sun's rays cannot accomplish.
MRS. B.
It is not because the rays from the fire have
more power, but rather because they have less, that
8 FREE CALORIC.
they heat glass and other transparent bodies. It
is true, however, that as you approach the source of
heat the rays being nearer each other, the heat
is more condensed, and can produce effects of
which the solar rays, from the great distance of
their source, are incapable. Thus we should find it
impossible to roast a joint of meat by the sun's rays,
though it is so easily done by culinary heat. Yet ca-
loric emanated from burning bodies, which is com-
monly called culinary heat, has neither the intensity
nor the velocity of solar rays. All caloric, we
have said, is supposed to proceed originally from the
sun; but after having been incorporated with ter-
restrial bodies, and again given out by .them,
though its nature is not essentially altered, it retains
neither the intensity nor the velocity with which it
first emanated from that luminary ; it has there-
fore not the power of passing through transparent
mediums, such as glass and water, without being
partially retained by those bodies.
EMILY.
I recollect that in the experiment on the reflec-
tion of heat, the glass skreen which you interposed
between the burning taper and the mirror, arrested
the rays of caloric, and suffered only those of light
to pass through it.
CAROLINE.
Glass windows, then, though they cannot be
FREE CALORIC. 89
heated by the sun shining on them, may be heated
internally by a fire in the room ? But, Mrs. B.,
since the atmosphere is not warmed by the solar
rays passing through it, how does it obtain heat;
for all the fires that are burning on the surface of
the earth would contribute very little towards
warming it ?
EMILY.
The radiation of heat is not confined to burning
bodies : for all bodies, you know, have that property;
therefore, not only every thing upon the surface of
the earth, but the earth itself, must radiate heat; and
this terrestrial caloric, not having, I suppose, suffi-
cient power to traverse the atmosphere, communi-
cates heat to it.
MRS. B.
Your inference is extremely well drawn, Emily ;
but the foundation on which it rests is not sound ;
for the fact is, that terrestrial or culinary heat,
though it cannot pass through the denser trans-
parent mediums, such as glass or water, without
loss, traverses the atmosphere completely: so that
all the heat which the earth radiates, unless it
meet with clouds or any foreign body to intercept
its passage, passes into the distant regions of the
universe.
CAROLINA.
What a pity that so much heat should be
wasted !
90 FREE CALORIC.
MRS. B.
Before you are tempted to object to any law of
nature, reflect whether it may not prove to be one
of the numberless dispensations of Providence for
our good. If all the heat which the earth has re-
ceived from the sun, since the creation had been
accumulated in it, its temperature by this time
would, no doubt, have been more elevated than
any human being could have borne.
CAROLINE.
I spoke indeed very inconsiderately. But,
Mrs. B., though the earth, at such a high tempera-
ture, might have scorched our feet, we should
always have had a cool refreshing air to breathe,
since the radiation of the earth does not heat the
atmosphere.
EMILY.
The cool air would have afforded but very in-
sufficient refreshment, whilst our bodies were ex-
posed to the burning radiation of the earth.
MRS. B.
Nor should we have breathed a cool air; for
though it is true that heat is not communicated to
the atmosphere by radiation, yet the air is warmed
by contact with heated bodies, in the same manner
as solids or liquids. The stratum of air which is
immediately in contact with the earth is heated by
FREE CALORIC. 91
it ; it becomes specifically lighter and rises, making
way for another stratum of air which is in its turn
heated and carried upwards; and thus each suc-
cessive stratum of air is warmed by coming in con-
tact with the earth. You may perceive this effect
in a sultry day, if you attentively observe the strata
of air near the surface of the earth ; they appear
in constant agitation, for though it is true the air
is itself invisible, yet the sun shining on the vapours
floating in it, render them visible, like the amber
dust in the water. The temperature of the sur-
face of the earth is therefore the source from
whence the atmosphere derives its heat, though it
is communicated neither by radiation, nor trans-
mitted from one particle of it to another by the
conducting power ; but every particle of air must
come in contact with the earth in order to receive
heat from it.
EMILY.
Wind then by agitating the air should contribute
to cool the earth and warm tine atmosphere, by
bringing a more rapid succession of fresh strata of
air in contact with the earth, and yet in general
wind feels cooler than still air ?
MRS. B.
Because the agitation of the air carries off heat
from the surface of our bodies more rapidly than
9.2 PKEE CALORIC.
still air, by occasioning a greater number of points
of contact in a given time.
EMILY.
Since it is from the earth and not the sun that
the atmosphere receives its heat, I no longer
wonder that elevated regions should be colder than
plains and valleys ; it was always a subject of
astonishment to me, that in ascending a mountain
and approaching the sun, the air became colder
instead of being more heated.
MRS. B.
At the distance of about a hundred million of
miles, which we are from the sun, the approach of a
few thousand feet makes no sensible difference,
whilst it produces a very considerable effect with
regard to the warming the atmosphere at the sur-
face of the earth.
CAROLINE.
Yet as the warm air rises from the earth and
the cold air descends to it, I should have sup-
posed that heat would have accumulated in the
upper regions of the atmosphere, and that we
should have felt the air warmer as we ascended ?
MRS. B.
The atmosphere, you know, diminishes in density,
find consequently in weight, as it is more distant
FREE CALORIC. 93
from the earth ; the warm air, therefore, rises only
till it meets with a stratum of air of its own density;
and it will not ascend into the upper regions of the
atmosphere until all the parts beneath have been
previously heated. The length of summer even in
warm climates does not heat the air sufficiently to
melt the snow which has accumulated during the
winter on very high mountains, although they are
almost constantly exposed to the heat of the sun's
rays, being too much elevated to be often enve-
loped in clouds.
EMILY.
These explanations are very satisfactory; bat
allow me to ask you one more question respect-
ing the increased levity of heated liquids. You
said that when water was heated over the fire, the
particles at the bottom of the vessel ascended as
soon as heated, in consequence of their specific
levity: why does not the same effect continue
when the water boils, and is converted into steam ?
and why does the steam rise from the surface,
instead of the bottom of the liquid ?
MBS. B.
The steam or vapour does ascend from the
bottom, though it seems to arise from the surface
of the liquid. We shall boil some water in this
Florence flask, (PLATE IV. Fig. 1.) in order that
94 FREE CALORIC.
you may be well acquainted with the process of
ebullition; you will then see, through the glass,
that the vapour rises in bubbles from the bottom.
We shall make it boil by means of a lamp, which
is more convenient for this purpose than the
chimney fire.
EMILY.
I see some small bubbles ascend, and a great
many appear all over the inside of the flask ; does
the water begin to boil already ?
MRS. E.
No ; what you now see are bubbles of air, which
were either dissolved in the water, or attached to
the inner surface of the flask, and which, being
rarefied by the heat, ascend in the water.
EMILY.
But the heat which rarefies the air inclosed in
the water must rarefy the water at the same
time; therefore, if it could remain stationary in
the water when both were cold, I do not under-
stand why it should not when both are equally
heated ?
MRS. B.
Air being much less dense than water, is more
easily rarefied; the former, therefore, expands to
a great extent, whilst the latter continues to oc-
FREE CALORIC. 95
cupy nearly the same space; for water dilates
comparatively but very little without changing its
state and becoming vapour. Now that the water
in the flask begins to boil, observe what large
bubbles rise from the bottom of it.
EMILY.
I see them perfectly; but I wonder that they
have sufficient power to force themselves through
the water.
CAROLINE.
They must rise, you know, from their specific
levity.
MRS. B.
You are right, Caroline; but vapour has not in
all liquids (when brought to the degree of va-
porization) the power of overcoming the pressure
of the less heated surface. Metals, for instance,
mercury excepted, evaporate only from the sur-
face; therefore no vapour will ascend from them
till the degree of heat which is necessary to form
it has reached the surface ; that is to say, till the
whole of the liquid is brought to a state of ebul-
lition.
EMILY.
I have observed that steam, immediately issuing
from the spout of a teakettle, is less visible than
at a further distance from it ; yet it must be more
96 FREE CALORIC.
dense when it first evaporates, than when it be-
gins to diffuse itself in the air.
' MRS. B.
When the steam is first formed, it i so per-
fectly dissolved by caloric, as to be invisible. In
order however to understand this, it will be ne-
cessary for me to enter into some explanation re-
specting the nature of SOLUTION. Solution takes
place whenever a body is melted in a fluid. In
this operation the bod}' is reduced to such a mi-
nute state of division by the fluid, as to become
invisible in it, and to partake of its fluidity ; but
in common solutions this happens without any de-
composition, the body being only divided into its
integrant particles by the fluid in which it is
melted.
CAROLINE.
It is then a mode of destroying the attraction of
aggregation.
MRS. B.
Undoubtedly. The two principal solvent fluids
are water, and caloric. You may have observed
that if you melt salt in water, it totally disappears,
and the water remains clear, and transparent as
before; yet though the union of these two bodies
appears so perfect, it is not produced by any che-
mical combination;; both the salt and the water
remain unchanged; and if you were to separate
7
FREE CALORIC. ^7 '
them by evaporating the latter, you would find
the salt in the same state as before.
EMILY.
I suppose that water is a solvent for solid bo-
dies, and caloric for liquids ?
MRS. B.
Liquids of course can only be converted into
vapour by caloric. But the solvent power of this
agent is not at all confined to that class of bo-
dies ; a "great variety of solid substances are dis-
solved by heat: thus metals, which are insoluble
in water, can be dissolved by intense heat, being
first fused or converted into a liquid, and then
rarefied into an invisible vapour. Many other
bodies, such as salt, gums, &c. yield to either of
these solvents.
CAROLINE.
And that, no doubt, is the reason why hot
water will melt them so much better than cold
water ?
MRS. B.
It is so. Caloric may, indeed, be considered as
having, in every instance, some share in the solu-
tion of a body by water, since water, however
low its temperature may be, always contains more
or less caloric.
VOL. I. F
98 FKEE CALORIC.
EMILY.
Then, perhaps, water owes its solvent power
merely to the caloric contained in it ?
MRS. B.
That, probably, would be carrying the specu-
lation too far; 1 shduld rather think that water
and caloric unite their efforts to dissolve a body,
and that the difficulty or facility of effecting this,
.depend both on the degree of attraction of aggre-
gation to be overcome, and on the arrangement
of the particles which are more or less disposed
to be divided and penetrated by the solvent.
EMILY.
But have not all liquids the same solvent power
as water?
MRS. B.
The solvent power of other liquids varies ac-
cording to their nature, and that of the substances
submitted to their action. Most of these solvents,
indeed, differ essentially from water, as they do
not merely separate the integrant particles of the
bodies which they dissolve, but attack their con-
stituent principles by the power of chemical at-
traction, thus producing a true decomposition.
These more complicated operations we must con-
sider in another place, and confine our atten-
FREE CALORIC. 99
tion at present to the solutions by water and
caloric.
CAROLINE.
But there are a variety of substances which,
when dissolved in water, make it thick and muddy,
and destroy its transparency.
MRS. B.
In this case it is not a solution, but simply a
mixture. I shall show you the difference between'
a solution and a mixture, by putting some com-
mon salt into one glass of water, and some pow-
der of chalk into another ; both these substances
are white, but their effect on the water will be
very different.
CAROLINE.
Very different indeed! The salt entirely disap-
pears and leaves the water transparent, whilst the
chalk changes it into an opaque liquid like milk.
EMILY.
And would lumps of chalk and salt produce si-
milar effects on water?
MRS. B.
Yes, but not so rapidly; salt is, indeed, soon
jnelted though in a lump ; but chalk, which does
not mix so readily with water, would require a
F 2
100 FREE CALORIC.
much greater length of time ; I therefore pre-
ferred showing you the experiment with both
substances reduced to powder, which does not in
any respect alter their nature, but facilitates the
operation merely by presenting a greater quantity
of surface to the water.
I must not forget to mention a very curious
circumstance respecting solutions, which is, that
a fluid is not nearly so much increased in bulk by
holding a body in solution, as it would by mere
mixture with the body.
CAROLINE.
That seems impossible; for two bodies cannot
exist together in the same space.
MRS. B.
Two bodies may, by condensation, occupy less
space when in union than when separate, and this
I can show you by an easy experiment.
This phial, which contains some salt, I shall fill
with water, pouring it in quickly, so as not to
dissolve much of the salt; and when it is quite
full I cork it. If I now shake the phial till the
salt is dissolved, you will observe that it is no
longer full.
CAROLINE.
I shall try to add a little more salt. But now,
you see, Mrs. B., the water runs over.
FREE CALORIC.
MRS. B.
Yes ; but observe that the last quantity of salt
you put in remains solid at the bottom, and dis-
places the water; for it has already melted all the
salt it is capable of holding in solution. This is
called the point of saturation; and the water in
this case is said to be saturated with salt.
EMILY.
I think I now understand the solution of a solid
body by water perfectly : but I have not so clear
an idea of the solution of a liquid by caloric.
MRS. B.
It is probably of a similar nature ; but as caloric
is an invisible fluid, its action as a solvent is not
so obvious as that of water. Caloric, we may
conceive, dissolves water, and converts it into
vapour by the same process as water dissolves salt ;
that is to say, the particles of water are so mi-
nutely divided by the caloric as to become invi-
sible. Thus, you are now enabled to understand
why the vapour of boiling water, when it first
issues from the spout of a kettle, is invisible J it
is so, because it is then completely dissolved by
caloric. But the air with which it comes in con-
tact, being much colder than the vapour, the latter
yields to it a quantity of its caloric. The particles
of vapour being thus in a great measure deprived
F 3
102 FREE CALORIC.
of their solvent, gradually collect, and become
visible in the form of steam, which is water in a
state of imperfect solution ; and if you were fur-
ther to deprive it of its caloric, it would return to
its original liquid state.
CAROLINE.
That I understand very well. If you hold a
cold plate over a tea-urn, the steam issuing from
it will be immediately converted into drops of
water by parting with its caloric to the plate ; but
in what state is the steam, when it becomes invisi-
ble by being diffused in the air ?
MRS. B.
It is not merely diffused, but is again dissolved
by the air.
EMILY.
The air, then, has a solvent power, like water
and caloric ?
MRS. B.
This was formerly believed to be the case. But
it appears from more recent enquiries that the
solvent power of the atmosphere depends solely
upon the caloric contained in it. Sometimes the
watery vapour diffused in the atmosphere is but
imperfectly dissolved, as is the case in the form-
ation of clouds and fogs ; but if it gets into a region
sufficiently warm, it becomes perfectly invisible.
FREE CALORIC. 103
EMILY.
Can any water dissolve in the atmosphere with-
out its being previously converted into vapour by
boiling ?
MRS. B.
Unquestionably ; and thrs constitutes the differ-
ence between vaporization and evaporation. Water,
when heated to the boiling point, can no longer
exist in the form of water, and must necessarily be
converted into vapour or steam, whatever may
be the state and temperature of the surrounding
medium ; this is called vaporization. But the at-
mosphere, by means of the caloric it contains, can
take up a certain portion of water at any tempera-
ture, and hold it in a state of solution. This is
simply evaporation. Thus the atmosphere is con-
tinually carrying off moisture from the surface of
the earth, until it is saturated with it.
CAROLINE.
That is the case, no doubt, when we feel the
atmosphere damp.
MRS. B.
On the contrary, when the moisture is well dis-
solved it occasions no humidity : it is only when
in a state of imperfect solution and floating in the
atmosphere, in the form of watery vapour, that it
produces dampness. This happens more fre-
F 4
104 FREE CALORIC.
quently in winter than in summer ; for the lower
the temperature of the atmosphere, the less water
it can dissolve ; and in reality it never contains so
much moisture as in a dry hot summer's day.
CAROLINE.
You astonish me ! But why, then, is the air so dry
in frosty weather, when its temperature is at the
lowest ?
EMILY.
This, I conjecture, proceeds not so t much from
the moisture being dissolved, as from its being
frozen ; is not that the case?
MRS. B.
It is; and the freezing of the watery vapour
which the atmospheric heat could not dissolve,
produces what is called a hoar frost ; for the
particles descend in freezing, and attach themselves
to whatever they meet with on the surface of the
earth.
The tendency of free caloric to an equilibrium,
together with its solvent power, are likewise con-
nected with the phenomena of rain, of dew, &c.
When moist air of a certain temperature happens
to pass through a colder region of the atmo-
sphere, it parts with a portion of its heat to the
surrounding air; the quantity of caloric, there-
fore, which served to keep the water in a state of
CALORIfl. 105
Vapour, being diminished, the watery particles
approach each other, and form themselves into
drops of water, which being heavier than the at-
mosphere, descend to the earth. There are also
other circumstances, and particularly the variation
in the weight of the atmosphere, which may contri-
bute to the formation of rain. This, however, is
an intricate subject, into which we cannot more
fully enter at present.
I EMILY.
In what manner do you account for the form-
ation of dew?
MRS. B.
Dew is a deposition of watery particles or minute
drops from the atmosphere, precipitated by the
coolness of the evening.
CAROLINE.
This precipitation is owing, I suppose, to the
cooling of the atmosphere, which prevents its retain-
ing so great a quantity of watery vapour in solution
as during the heat of the day.
MRS. B.
Such was, from time immemorial, the generally
received opinion respecting the cause of dew; but
it has been very recently proved by a course of
ingenious experiments of Dr. Wells, that the depo-
F 5
106 FREE CALORIC.
sition of dew is produced by the cooling of the sur-
face of the earth, which he has shown to take place
previously to the cooling of the atmosphere ; for on
examining the temperature of a plot of grass just
before the dew-fall, he found that is was considerably
colder than the air a few feet above it, from which
the dew was shortly after precipitated.
EMILY.
Bmt why should the earth cool in the evening
sooner than the atmosphere ?
MRS. B.
Because it parts with its heat more readily than
the air; the earth is an excellent radiator of caloric,
whilst the atmosphere does not possess that pro-
perty, at least in any sensible degree. Towards even-
Ing, therefore, when the solar heat declines, and
when after sunset it entirely ceases, the earth ra-
pidly coolfc by radiating heat towards the skies ;
whilst the air has no means of parting with its heat
but by coming into contact with the cooled surface
of the earth, to which it communicates its caloric.
Its solvent power being thus reduced, it is unable
to retain so large a portion of watery vapour, and
deposits those pearly drops which we call dew.
EMILY.
If this be the cause of dew, we need not be appre-
FREE CALORIC. 107
hensive of receiving any injury from it; for it can
be deposited only on surfaces that are colder than
the atmosphere, which is never the case with our
bodies.
MRS. B.
Very true ; yet I would not advise you for this rea-
son to be too confident of escaping all the ill effects
which may arise from exposure to the dew ; for it
may be deposited on your clothes, and chill you
afterwards by its evaporation from them. Besides,
whenever the dew is copious, there is a chill in
the atmosphere which it is not always safe to en-
counter.
CAROLINE.
Wind, then, must promote the deposition of dew,
by bringing a more rapid succession of particles of
air in contact with the earth, just as it promotes the
cooling of the earth and warming of the atmosphere
during the heat of the day ?
MRS.B.
Yes; provided the wind be unattended with
clouds, for these accumulations of moisture not only
prevent the free radiation of the earth towards the
upper regions, but themselves radiate towards the
earth; under these circumstances much less dew is
formed than on fine clear nights, when the radiation,
of the earth passes without obstacle through the at-
mosphere to the distant regions of space, whence it
F 6
108 FREE CALOKIC*
receives no caloric in exchange. The dew contH
nues to be deposited during the night, and is gene-
rally most abundant towards morning, when the
contrast between the temperature of the earth and
that of the air is greatest. After sunrise the equili-
brium of temperature between these two bodies is
gradually restored by the solar rays passing freely
through the atmosphere to the earth; and later in the
morning the temperature of the earth gains the as-
cendency, and gives out caloric to the air by contact,
in the same manner as it receives it from the air dur-
ing the night. Can you tell me, now, why a bottle
of wine taken fresh from the cellar (in summer parti-
cularly), will soon be covered with dew ; and even
the glasses into which the wine is poured will be
moistened with a similar vapour ?
EMILY.
The bottle being colder than the surrounding air,
must absorb caloric from it ; the moisture therefore
which that air contained becomes visible, and forms
the dew which is deposited on the bottle.
MRS. 15.
Very well, Emily. Now, Caroline, can you in-
form me why, in a warm room, or close carriage, the
contrary effect takes place; that is to say, that the
inside of the windows is covered with vapour ?
7
CALOttld*
CAROLINE.
1 have heard that it proceeds from the breath of
those within the room or the carriage; and I sup-
pose it is occasioned by the windows which, being
colder than the breath, deprive it of part of its
caloric, and by this means convert it into watery
vapour.
MRS. B.
You have both explained it extremely well. Bodies
attract dew in proportion as they are good radiators
of caloric, as it is this quality which reduces their
temperature below that of the atmosphere ; hence
we find that little or no dew is deposited on rocksj
sand, water ; while grass and living vegetables, to
which it is so highly beneficial, attract it in abun-
dance another remarkable instance of the wise and
bountiful dispensations of Providence.
EMILY,
And we may again observe it in the abundance
of dew in summer, and in hot climates, when its
cooling effects are so much required ; but I do not
understand what natural cause increases the dew in
hot weather?
MRS. B.
The more caloric the earth receives during the
day, the more it will radiate afterwards, and conse-
quently the more rapidly its temperature will be re-
duced in the evening, in comparison to that of the
1 10 FREE CALORIC.
atmosphere. In the West-Indies especially, where
the intense heat of the day is strongly contrasted with
the coolness of the evening, the dew is prodigiously
abundant. During a drought, the dew is less plen-
tiful, as the earth is not sufficiently supplied with
moisture to be able to saturate the atmosphere.
CAROLINE.
I have often observed, Mrs. B., that when I
walk out in frosty weather, with a veil over my
face, my breath freezes upon it. Pray what is
, the reason of that ?
MRS. B.
It is because the cold air immediately seizes on
the caloric of your breath, and, by robbing it of
its solvent, reduces it to a denser fluid, which is
the watery vapour that settles on your veil, and
there it continues parting with its caloric till it is
brought down to the temperature of the atmo-
sphere, and assumes the form of ice.
You may, perhaps, have observed that the breath
of animals, or rather the moisture contained in it,
is visible in damp weather, or during a frost. In
the former case, the atmosphere being over-
saturated with moisture, can dissolve no more.
In the latter, the cold condenses it into visible
vapour; and for the same reason, the steam arising
from water that is warmer than the atmosphere,
8
FREE CALORIC. Ill
becomes visible. Have you never taken notice of the
vapour rising from your hands after having dipped
them into warm w.iter ?
CAROLINE.
Frequently, especially in frosty weather.
MRS. B.
We have already observed that pressure is an
obstacle to evaporation: there are liquids that
contain so great a quantity of caloric, and whose
particles consequently adhere so slightly together,
that they may be rapidly converted into vapour
without any elevation of temperature, merely by
taking off the weight of the atmosphere. In such
liquids, you perceive, it is the pressure of the at-
mosphere alone that connects their particles, and
keeps them in a liquid state.
CAROLINE.
I do not well understand why the particles of
such fluids should be disunited and converted into
vapour, without any elevation of temperature, in
spite of the attraction of cohesion.
MRS. B.
It is because the degree of heat at which we
usually observe these fluids is sufficient to overcome
their attraction of cohesion. Ether is of this de-
112 FREE CALORIC.
scription; it will boil and be converted into vapour^
at the common temperature of the air, if the pres-
sure of the atmosphere be taken offl
EMILY.
I thought that ether would evaporate without
either the pressure of the atmosphere being taken
away, or heat applied ; and that it was for that rea-
son so necessary to keep it carefully corked up ?
MRS. B.
It is true it will evaporate, but without ebulli*
tion ; what I am now speaking of is the vaporiza-
tion of ether, or its conversion into vapour by
boiling. I am going to show you how suddenly
the ether in this phial will be converted into va-
pour, by means of the air-pump. Observe with
what rapidity the bubbles ascend, as I take off the
pressure of the atmosphere.
CAROLINE.
It positively boils: how singular to see a liquid
boil without heat !
MRS. B.
Now I shall place the phial of ether in this
glass, which it nearly fits, so as to leave only a
small space, which I fill with water ; and in this
state I put it again under the receiver. (PLATE
FREE CALORIC. 1 13
IV. Fig. 1.) * You will observe, as I exhaust the
air from it, that whilst the ether boils, the water
freezes.
CAROLINE.
It is indeed wonderful to see water freeze in
contact with a boiling fluid !
EMILY.
I am at a loss to conceive how the ether can pass
to the state of vapour without an addition of ca-
loric. Does it not contain more caloric in a state
of vapour, than in a state of liquidity ?
MRS. B.
It certainly does ; for though it is the pressure
of the atmosphere which condenses it into a liquid,
it is by forcing out the caloric that belongs to it
when in an aeriform state.
* Two pieces of thin glass tubes, sealed at one end, might
answer this purpose better. The experiment, however, as here
described, is difficult, and requires a very nice apparatus. But
if, instead of phials or tubes, two watch-glasses be used, water
may be frozen almost instantly in the same manner. The two
glasses are placed over one another, with a few drops of water
interposed between them, and the uppermost glass is filled with
ether. After working the pump for a minute or two, the glasses
are found to adhere strongly together, and a thin layer of ice is
seen between them.
114 FREE CALORIC.
EMILY.
You have, therefore, two difficulties to explain,
Mrs. B. First, from whence the ether obtains the
caloric necessary to convert it into vapour when it
is relieved from the pressure of the atmosphere ;
and, secondly, what is the reason that the water, in
which the bottle of ether stands, is frozen ?
CAROLINE.
Now, I think, I can answer both these ques-
tions. The ether obtains the addition of caloric
required, from the water in the glass; and the
loss of caloric, which the latter sustains, is the
occasion of its freezing.
MRS. B.
You are perfectly right ; and if you look at the
thermometer which I have placed in the water,
whilst I am working the pump, you will see that
every time bubbles of vapour are produced, the
mercury descends; which proves that the heat of
the water diminishes in proportion as the ether
boils.
EMILY.
This I understand now very well; but if the
water freezes in consequence of yielding its caloric
to the ether, the equilibrium of heat must, in this
case, be totally destroyed. Yet you have told us,
that the exchange of caloric between two bodies of
REE CALORIC. 115
temperature, was always equal ; how, then, is
it that the water, which was originally of the same
temperature as the ether, gives out caloric to it, till
the water is frozen, and the ether made to boil ?
MRS. B.
I suspected that you would make these objec^
tions ; and, in order to remove themi I enclosed
two thermometers in the air-pump; one which
stands in the glass of water, the other in the phial
of ether; and you may see that the equilibrium of
temperature is not destroyed; for as the thermo-
meter descends in the water, that in the ether sinks
in the same manner; so that both thermometers
indicate the same temperature, though one of them
is in a boiling, the other in a freezing liquid.
EMILY.
The ether, then, becomes colder as it boils?
This is so contrary to common experience, that I
confess it astonishes me exceedingly.
CAROLINE.
It is, indeed, a most extraordinary circumstance.
But pray, how do you account for it ?
MRS. B.
I cannot satisfy your curiosity at present; for
before we can attempt to explain this apparent
116 FREE CALOIIIC.
paradox, it is necessary to become acquainted with
the subject of LATENT HEAT : and that, I think, we
must defer till our next interview.
CAROLINE.
I believe, Mrs. B., that you are glad to put off
the explanation; for it must be a very difficult
point to account for.
I hope, however, that I shall do it to your com-
plete satisfaction.
EMILY.
But before we part, give me leave to ask you
one question. Would not water, as well as ether,
boil with less heat, if deprived of the pressure of
the atmosphere?
MRS. B.
Undoubtedly. You must always recollect that
there are two forces to overcome, in order to
make a liquid boil or evaporate ; the attraction of
aggregation, and the weight of the atmosphere.
On the summit of a high mountain (as Mr. De
Saussure ascertained on Mount Blanc) much less
heat is required to make water boil, than in the
plain, where the weight of the atmosphere is
FREE CALORIC. 117
greater. * Indeed if the weight of the atmosphere
be entirely removed by means of a good air-pump,
and if water be placed in the exhausted receiver, it
will evaporate so fast, however cold it maybe, as to
give it the appearance of boiling from the surface.
But without the assistance of the air-pump, I can
show you a very pretty experiment, which proves
the effect of the pressure of the atmosphere in
this respect.
Observe, that this Florence flask is about half
full of water, and the upper half of invisible va-
pour, the water being in the act of boiling. I
take it from the lamp, and cork it carefully the
water, you see, immediately ceases boiling. I
shall now dip the flask into a bason of cold water, f
CAROLINE.
But look, Mrs. B., the hot water begins to boil
again, although the cold water must rob it more
and more of its caloric ! What can be the reason
of that?
* On the top of Mount Blanc, water boiled when heated
only to 187 degrees, instead of 212 degrees.
f The same effect may be produced by wrapping a cold wet
linen cloth round the upper part of the flask. In order to
show how much the water cools whilst it is boiling, a ther-
mometer, graduated on the tube itself, may be introduced
into the bottle through the cork.
118 FREE CALORIC.
MRS. B.
Let us examine its temperature. You see the
thermometer immersed in it remains stationary at
180 degrees, which is about 30 degrees below the
boiling point. When I took the flask from the
lamp, I observed to you that the upper part of it
was filled with vapour; this being compelled ta
yield its caloric to the cold water, was again con-
densed into water What, then, filled the upper
part of the flask ?
EMILY.
Nothing ; for it was too well corked for the air
to gain admittance, and therefore the upper part
of the flask must be a vacuum.
MRS. B.
The water below, therefore, no longer sustains
the pressure of the atmosphere, and will conse-
quently boil at a much lower temperature. Thus,
you see, though it had lost many degrees of heat,
it began boiling again the instant the vacuum was
formed above it. The boiling has now ceased,
the temperature of the wafcepj being still farther
reduced ; if it had been ether, instead of water, it
would have continued boiling much longer, for
ether boils, under the usual atmospheric pressure,
at a temperature as low as 1 00 degrees ; and in a
vacuum it boils at almost any temperature; but
FREE CALORIC. 119
water being a more dense fluid, requires a more
considerable quantity of caloric to make it evapo-
rate quickly, even when the pressure of the atmo-
sphere is removed.
EMILY.
What proportion of vapour can the atmosphere
contain in a state of solution ?
MRS. B.
I do not know whether it has been exactly as-
certained by experiment; but at any rate this
proportion must vary, both according to the tem-
perature and the weight of the atmosphere ; for
the lower the temperature, and the greater the
pressure, the smaller must be the proportion of
vapour that the atmosphere can contain.
To conclude the subject of free caloric, I should
mention Ignition, by which is meant that emission
of light which is produced in bodies at a very
high temperature, and which is the effect of ac-
cumulated caloric.
EMILY.
You mean, I suppose, that light which is pro-
duced by a burning body ?
MRS. B.
No: ignition is quite independent of combus-
tion. Clay, chalk, and indeed all incombustible
120 FREE CALORIC.
substances, may be made red hot. When a body
burns, the light emitted is the effect of a chemi-
cal change which takes place, whilst ignition is
the effect of caloric alone, and no other change
than that of temperature is produced in the ig-
nited body.
All solid bodies, and most liquids, are suscepti-
ble of ignition, or, in other words, of being-
heated so as to become luminous; and it is re-
markable that this takes place pretty nearly at
the same temperature in all bodies, that is, at about
800 degrees of Fahrenheit's scale.
EMILY.
But how can liquids attain so high a tempera-
ture, without being converted into vapour ?
MRS. B.
By means of confinement and pressure. Water
confined in a strong iron vessel (called Papin's di-
gester) can have its temperature raised to up-
wards of 400 degrees. Sir James Hall has made
some very curious experiments on the effects of
^eat assisted by pressure; by means of strong gun-
barrels, he succeeded in melting a variety of sub-
stances which were considered as infusible : and it
is not unlikely that, by similar methods, water
itse.lf might be heated to redness.
FRKL CALORIC. 121
I.MILY.
I am surprised at that : for I thought that the
force of steam was such as to destroy almost all
mechanical resistance.
MRS. B.
The expansive force of steam is prodigious;
but in order to subject water to such high tem-
peratures, it is prevented by confinement from
being converted into steam, and the expansion of
heated water is comparatively trifling. But we
have dwelt so long on the subject of free caloric,
that we must reserve tfie other modifications of
that agent to our next meeting, when we shall en-
deavour to proceed more rapidly.
VOL. I.
CONVERSATION IV.
ON COMBINED CALORIC, COMPREHENDING
SPECIFIC AND LATENT HEAT.
MRS. B.
WE are now to examine the other modifications
of caloric.
CAROLINE.
I am very curious to know of what nature they
can be ; for I have no notion of any kind of heat
that is not perceptible to the senses.
MRS. B.
In order to enable you to understand them, it
will be necessary to enter into some previous ex-
planations.
It has been discovered by modern chemists,
that bodies of a different nature, heated to the
same temperature, do not contain the same quan-
tity of caloric.
CAROLINE.
How could that be ascertained ? Have you not
told us that it is impossible to discover the abso-
lute quantity of caloric which bodies contain ?
.4*
COMBINED CALORIC. 123
MRS. B.
True ; but at the same time I said that we were
enabled to form a judgment of the proportions
which bodies bore to each other in this respect.
Thus it is found that, in order to raise the tem-
perature of different bodies the same number of
degrees, different quantities of caloric are re-
quired for each of them. If, for instance, you
place a pound of lead, a pound of chalk, and a
pound of milk, in a hot oven, they will be gra-
dually heated to the temperature of the oven ; but
the lead will attain it first, the chalk next, and the
milk last.
CAROLINE.
That is a natural consequence of their different
bulks; the lead being the smallest body, will be
heated soonest, and the milk, which is the largest,
will require the longest time.
MRS. B.
That explanation will not do, for if the lead be
the least in bulk, it offers also the least surface to
the caloric, the quantity of heat therefore which
can enter into it in the same space of time is pro-
portionally smaller.
EMILY.
Why, then, do not the three bodies attain the
temperature of the oven at the same time ?
G 2
124 COMBINED CALORIC.
MRS. B.
It is supposed to be on account of the different
capacity of these bodies for caloric.
CAROLINE.
What do you mean by the capacity of a body
for caloric ?
MRS. B.
I mean a certain disposition of bodies to require
more or less caloric for raising their temperature
to any degree of heat. Perhaps the fact may be
thus explained :
Let us put as many marbles into this glass as
it will contain, and pour some sand over them
observe how the sand penetrates and lodges be-
tween them. We shall now fill another glass with
pebbles of various forms you see that they ar-
range themselves in a more compact manner than
the marbles, which, being globular, can touch
each other by a single point only.* The pebbles,
therefore, will not admit so much sand between
them ; and consequently one of these glasses will
necessarily contain more sand than the other,
though both of them be equally full.
CAROLINE.
This I understand perfectly. The marbles and
the pebbles represent two bodies of different kinds,
and the sand the caloric contained in them ;
COMBINED CALORIC. 125
it appears very plain, from this comparison, that
; one body may admit of more caloric between its
particles than another.
MRS. B.
You can no longer be surprised, therefore, that
bodies of a different capacity for caloric should
require different proportions of that fluid to raise
their temperatures equally.
EMILY.
But I do not conceive why the body that con-
tains the most caloric should not be of the highest
temperature; that is to say, feel hot in propor-
tion to the quantity of caloric it contains ?
MRS. B.
The caloric that is employed in filling the capa
city of a body, js not free caloric; but is imprisoned
as it were in the body, and is therefore impercept-
ible: for we can feel only the caloric which the body
parts with, and not that which it retains.
CAROLINE.
It appears to me very extraordinary that heat
should be confined in a body in such a manner as
to be imperceptible.
G 3
12G COMBINED CALORIC.
MRS. E.
If you lay your hand on a hot body, you feel
only the caloric which leaves it, and enters your
hand ; for it is impossible that you should be sen-
sible of that which remains in the body. The ther-
mometer, in the same manner, is affected only by
the free caloric which a body transmits to it, and
not at all by that which it does not part with.
CAROLINE.
I begin to understand it : but I confess that the
idea of insensible heat is so new and strange to me,
that it requires some time to render it familiar.
MRS. B.
Call it insensible caloric, and the difficulty will
appear much less formidable. It is indeed a sort
of contradiction to call it heat, when it is so situ-
ated as to be incapable of producing that sensation.
Yet this modification of caloric is commonly called
SPECIFIC HEAT.
CAROLINE.
But it certainly would have been more correct to
have called it specific caloric.
EMILY.
I do not understand how the term tyeci/ic applies
to this modification of caloric?
COMBINED CALORIC. 1^
MRS. B.
It expresses the relative quantity of caloric
which different species of bodies of the same
weight and temperature are capable of containing.
This modification is also frequently called heat of
capacity, a term perhaps preferable, as it explains
better its own meaning.
You now understand, I suppose, why the milk
and chalk required a longer portion of time than
the lead to raise their temperature to that of the
oven ?
EMILY.
Yes : the milk and chalk having a greater ca-
pacity for caloric than the lead, a greater pro-
portion of that fluid became insensible in those
bodies : and the more slowly, therefore, their tem-
perature was raised.
CAROLINE.
But might not this difference proceed from the
different conducting powers of heat in these three
bodies, since that which is the best conductor must
necessarily attain the temperature of the oven
first?
MRS. B.
Very welt observed, Caroline. This objection
would be insurmountable, if we could not, by re-
versing the experiment, prove that the milk, the
chalk, and the lead, actually absorbed different
G 4
128 COMBINED CALORIC.
quantities of caloric, and we know that if the dif-
ferent time they took in heating, proceeded merely
from their different conducting powers, they would
each have acquired an equal quantity of caloric.
CAROLINE.
Certainly. But how can you reverse this expe-
periment ?
y
MR*; B.
It may be done by cooling the several bodies to
the same degree in an apparatus adapted to re-
ceive and measure the caloric which they give out.
Thus, if you plunge them into three equal quan-
tities of water, each at the same temperature, you
will be able to judge of the relative quantity of
caloric which the three bodies contained, by that,
which, in cooling, they communicated to their
respective portions of water: for the same quan-
tity of caloric which they each absorbed to raise
their temperature, will abandon them in lowering
it; and on examining the three vessels of water,
you will find the one in which you immersed the
lead to be the least heated ; that which held the
chalk will be the next ; and that which contained
the milk will be heated the most of all. The
celebrated Lavoisier has invented a machine to
estimate, upon this principle, the specific heat
of bodies in a more perfect manner ; but I cannot
COMBINED CALORIC. 1 29
explain it to you, till you are acquainted with the
next modification of caloric.
EMILY.
The more dense a body is, I suppose, the less is
Its capacity for caloric ?
MRS. B.
This is not always the case with bodies of dif-
ferent nature; iron, for instance, contains more
specific heat than tin, though it is more dense.
This seems to show that specific heat does hot
merely depend upon the interstices between the
particles ; but, probably, also upon some peculiar
constitution of the bodies which we do not com-
prehend.
EMILY.
But, Mrs. B., it would appear to me more
proper to compare bodies by measure, rather than
by weight, in order to estimate their specific heat.
Why, for instance, should we not compare pints
of milk, of chalk, and of lead, rather than pounds
o'f those substances ; for equal weights may be com-
posed of very different quantities?
MRS. B.
You are mistaken, my dear ; equal weight must
contain equal quantities of matter; and when we
wish to know what is the relative quantity of ca-
G 5
130 COMBINED CALORIC.
loric, which substances of various kinds are capable
of containing under the same temperature, we
must compare equal weights, and not equal bulks
of those substances. Bodies of the same weight
may undoubtedly be of very different dimensions ;
but that does not change their real quantity of mat-
ter. A pound of feathers does not contain one
atom more than a pound of lead.
CAROLINE.
I have another difficulty to propose. It appears
to me, that if the temperature of the three bodies
in the oven did not rise equally, they would never
reach the same degree; the lead would always
keep its advantage over the chalk and milk, and
would perhaps be boiling before the others had
attained the temperature of the oven. I think
you might as well say that, in the course of time,
you and I should be of the same age ?
MRS. B.
Your comparison is not correct, Caroline. As
soon as the lead reached the temperature of the
oven, it would remain stationary; for it would
then give out as much heat as it would receive.
You should recollect that the exchange of radiat-
ing heat, between two bodies of equal tempera-
ture, is equal : it would be impossible, therefore,
for the lead to accumulate heat after having at-
COMBINED CALORIC. 131
tained the temperature of the oven ; and that of
the chalk and milk therefore would ultimately
arrive at the same standard. Now I fear that this
will not hold good with respect to our ages, and
that, as long as I live, I shall never cease to keep
my advantage over you.
EMILY.
I think that I have found a comparison for spe-
cific heat, which is very applicable. Suppose that
two men of equal weight and bulk, but who re-
quired different quantities of food to satisfy their
appetites, sit down to dinner, both equally hungry ;
the one would consume a much greater quantity of
provisions than the other, in order to be equally
satisfied.
MRS. B.
Yes, that is very fair ; for the quantity of food
necessary to satisfy their respective appetites, varies
in the same manner as the quantity of caloric re-
quisite to raise equally the temperature of different
bodies.
EMILY.
The thermometer, then, affords no indication of
the specific heat of bodies ?
MRS. B.
None at all : no more than satiety is a test ,of
the quantity of food eaten. The thermometer, as
G 6
132 COMBINED CALORIC.
I have repeatedly said, can be affected only by free
caloric, which alone raises the temperature of
bodies.
But there is another mode of proving the ex-
istence of specific heat, which affords a very satis-
factory illustration of that modification. This,
however, I did not enlarge upon before, as I
thought it might appear to you rather compli-
cated. If you mix two fluids of different tempera-
tures, let us say the one at 50 degrees, and the
other at 100 degrees, of what temperature do you
suppose the mixture will be ?
CAROLINE.
It will be no doubt the medium between the two,
that is to say, 75 degrees.
MRS. 6.
That will be the case if the two bodies happen to
have the same capacity for caloric ; but if not, a
different result will be obtained. Thus, for in-
stance, if you mix together a pound of mercury,
heated at 50 degrees, and a pound of water heated
at 100 degrees, the temperature of the mixture,
instead of being 75 degrees, will be 80 degrees; so
that the water will have lost only 12 degrees, whilst
the mercury will have gained 38 degrees; from
which you will conclude that the capacity of mer-
cury for heat is less than that of water. -^
COMBINED CALORIC. 133
CAROLINE.
I wonder that mercury should have so little spe-
cific heat. Did we not see it was a much better
conductor of heat than water?
MRS. B.
And it is precisely on that account that its spe-
cific heat is less. For since the conductive power
of bodies depends, as we have observed before, on
their readiness to receive heat and part with it, it
is natural to expect that those bodies which are the
worst conductors should absorb the most calorie
before they are disposed to part with it to other
bodies. But let us now proceed to LATEST HEAT.
CAROLINE.
And pray what kind of heat is that ?
MRS. B.
It is another modification of combined caloric,
which is so analogous to specific heat, that most
chemists make no distinction between them ; but
Mr. Pictet, in his Essay on Fire, has so clearly
discriminated them, that I am induced to adopt
his view of the -subject. We therefore call latent,
heat that portion of insensible caloric which is em-
ployed in changing the state of. bodies; that is to
say, in converting solids into liquids, or liquids;
into vapour. When a body changes its state from
134 COMBINED CALORIC.
solid to liquid, or from liquid to vapour, its ex-
pansion occasions a sudden and considerable in-
crease of capacity for heat, in consequence of
which it immediately absorbs a quantity of caloric,
which becomes fixed in the body which it has
transformed; and, as it is perfectly concealed from
our senses, it has obtained the name of latent heat.
CAROLINE.
I think it would be much more correct to call
this modification latent caloric instead of latent
heat, since it does not excite the sensation of heat.
MRS. B.
This modification of heat was discovered and
named by Dr. Black long before the French che-
mists introduced .the term caloric, and we must
not presume to alter it, as it is still used by much
better chemists than ourselves. And, besides, you
are not to suppose that the nature of heat is al-
tered by being variously modified: for if latent
heat and specific heat do not excite the same sen-
sations as free caloric, it is owing to their being
in a state of confinement, which prevents them
from acting upon our organs; and consequently,
as soon as they are extricated from the body in
which they are imprisoned, they return to their
state of free caloric.
COMBINED CALORIC. 135
EMILY.
But I do not yet clearly see in what respect
latent heat differs from specific heat ; for they are
both of them imprisoned and concealed hi bodies.
MRS. B.
Specific heat is that which is employed in filling
the capacity of a body for caloric, in the state in
which this body actually exists ; while latent heat
is that which is employed only in effecting a change
of state, that is, in converting bodies from a solid
to a liquid, or from a liquid to an aeriform state.
But I think that, in a general point of view,
both these modifications might be comprehended
under the name of heat of capacity, as in both
cases the caloric is equally engaged in filling the
capacities of bodies.
I shall now show you an experiment, which I
hope will give you a clear idea of what is under-
stood by latent heat.
The snow which you see in this phial has been
cooled by certain chemical means (which I can-
not well explain to you at present), to 5 or 6 de-
grees below the freezing point, as you will find
indicated by the thermometer which is placed in
it. We shall expose it to the heat of a lamp, and
you will see the thermometer gradually rise, till
it reaches the freezing point
136 COMBINED CALORIC.
EMILY.
But there it stops, Mrs. B., and yet the lamp
burns just as. well as before. Why is not its heat
communicated to the thermometer ?
CAROLINE.
And the snow begins to melt, therefore it must
be rising above the freezing point ?
MRS. B.
The heat no longer affects the thermometer, be-
cause it is wholly employed in converting the ice
into water. As the ice melts, the caloric becomes
latent in the new-formed liquid, and therefore can-
not raise its temperature ; nnd the thermometer
will consequently remain stationary, till the whole
of the ice be melted.
CAROLINE.
Now it is all melted, and the thermometer begins
to rise again.
MRS. B.
Because the conversion of the ice into water be-
ing completed, the caloric no longer becomes
latent; and therefore the heat which the water
now receives raises its temperature, as you ::d ihe
thermometer indicates.
COMBINED CALORIC. 137
EMILY.
But I do not think that the thermometer rises so
quickly in the water as it did in the ice, previous to
its beginning to melt, though the lamp burns equally
well?
MRS. B.
That is owing to the different specific heat of ice
and water. The capacity of water for caloric be--
ing greater than that of ice, more heat is required
to raise its temperature, and therefore the thermo^-
meter rises slower in the water than in the ice.
EMILY.
True ; you said that a solid body always in-
creased its capacity for heat by becoming fluid ; and
this is an instance of it.
MRS. B.
Yes, and the latent heat is that which is absorbed
in consequence of the greater capacity which the
water has for heat, in comparison to ice.
1 must now tell you a curious calculation founded
on that consideration. I have before observed to
you that though the thermometer shows us the
comparative warmth of bodies, and enables us to
determine the same point at different times and
places, it gives us no idea of the absolute quantity
of heat in any body. We cannot tell how low it
ought to fall by the privation of all heat, but an
138 COMBINED CALORIC.
attempt has been made to infer it in the following
manner. It has been found by experiment, that the
capacity of water for heat, when compared with that
of ice, is as 10 to 9, so that, at the same temperature,
ice contains one tenth of caloric less than water.
By experiment also it is observed, that in order to
melt ice, there must be added to it as much heat,
as would, if it did not melt it, raise its tempe-
rature 140 degrees. This quantity of heat is
therefore absorbed when the ice, by being converted
into water, is made to contain one-ninth more ca-
loric than it did before. Therefore 140 degrees is
a ninth part of the heat contained in ice at 30 de-
grees ; and the point of zero, or the absolute priva-
tion of heat, must consequently be 1260 degrees
below 32 degrees.
This mode of investigating so curious a question
is ingenious, but its correctness is not yet established
by similar calculations for other bodies. The
points of absolute cold, indicated by this method in
various bodies, are very remote from each other; it
is however possible, that this may arise from some
imperfection in the experiments.
CAROLINE.
It is indeed very ingenious but we must now
attend to our present experiment. The water
begins to boil, and the thermometer is again sta-
tionary.
VoLl.paaf 138.
Plate V.
J-'Ul.
Ka.i.Thf air-pump X- receiver for JUTZftiult ejcprrtment.C j taufer With tnlphurit <7<vW.B a glass
IT fart/if/i ,-ii/t cpntaininii Water. IJ a stanJ for the cup with it.< leas made t>f Mass. A a. Thermometer.
m.z.K Wolt,i.<t,>ns iruophiirus.Fif.&.KJtfareelk me<1f of n.tinii 'the Cruophoriis.
.-i..\- f.the dit'f'mni fxirtj fi' l-'ia.&.itsn separate.
COMBINED CALORIC. 139
MRS. B.
Well, Caroline, it is your turn to explain the
phenomenon.
CAROLINE.
It is wonderfully curious ! The caloric is now
busy in changing the water into steam, in which it
hides itself, and becomes insensible. This is an-
other example of latent heat, producing a change
of form. At first it converted a solid body into a
liquid, and now it turns the liquid into vapour !
MRS. B.
You see, my dear, how easily you have become
acquainted with these modifications of insensible
heat, which at first appeared so unintelligible. If,
now, we were to reverse these changes, and con-
dense the vapour into water, and the water into
ice, the latent heat would re-appear entirely, in
the form of free caloric.
EMILY.
Pray do let us see the effect of latent heat re-
turning to its free state.
MRS. B.
For the purpose of showing this, we need simply
conduct the vapour through this tube into this ves-
sel of cold water, where it will part with its latent
heat and return to its liquid form.
140 COMBINED CALORIC.
EMILY.
How rapidly the steam heats the water !
MRS. B.
That is because it does not merely impart its free
: caloric to the water, but likewise its latent heat.
This method of heating liquids, has been turned to
advantage, in several economical establishments.
The steam-kitchens, which are getting into such
general use, ate upon the same principle. The
steam is conveyed through a pipe in a similar man-
ner, into the several ve&sels which contain the pro-
visions to be dressed, where it communicates to
them its latent caloric, and returns to the state of
water. Count Rumford makes great use of this
principle in many of his fire-places: his grand
maxim is to avoid all unnecessary waste of caloric,
for which purpose he confines the heat in such a
manner, that not a particle of it shall unnecessarily
escape ; and while he economises the tree caloric,
he takes care also to turn the latent heat to advan-
tage. It is thus that he is enabled to produce a
degree of heat superior to that which is obtained
in common fire-places, though he employs less fuel.
EMILY.
When the advantages of such contrivances are
so clear and plain, I cannot understand why they
are not universally used.
COMBINED CALORIC. 141
MRS. B.
A long time is always required before inno-
vations, however useful, can be reconciled with the
prejudices of the vulgar.
EMILY.
What a pity it is that there should be a preju-
dice against new inventions ; how much more
rapidly the world would improve, if such useful
discoveries were immediately and universally
adopted !
MRS. B.
I believe, my dear, that there are as many novel-
ties attempted to be introduced, the adoption of
which would be prejudicial to society, as there arc
of those which would be beneficial to it. The
well-informed, though by no means exempt from
error, have an unquestionable advantage over the
illiterate, in judging what is likely or not to prove
serviceable ; and therefore we find the former more
ready to adopt such discoveries as promise to be
really advantageous, than the latter, who having
no other test of the value of a novelty but time and
experience, at first oppose its introduction. The '
well-informed, however, are frequently disappointed
in their most sanguine expectations, and the pre-
judices of the vulgar, though they often retard the
progress of knowledge, yet sometimes, it nlusf'be
142 COMBINED CALORIC.
admitted, prevent the propagation of error. But
we are deviating from our subject.
We have converted steam into water, and are
now to change water into ice, in order to render the
latent heat sensible, as it escapes from the water on
its becoming solid. For this purpose we must
produce a degree of cold that will make water
freeze.
CAROLINE.
That must be very difficult to accomplish in this
warm room.
MRS. B.
Not so much as you think. There are certain
chemical mixtures which produce a rapid change
from the solid to the fluid state, or the reverse, in
the substances combined, in consequence of which
change latent heat is either extricated or absorbed.
EMILY.
I do not quite understand you.
MRS. B.
This snow and salt, which you see me mix toge-
ther, are melting rapidly ; heat, therefore, must be
absorbed by the mixture, and cold produced.
CAROLINE.
It feels even colder than ice, and yet the snow is
melted. This is very extraordinary.
COMBINED CALORIC. 143
MRS. B.
The cause of the intense cold of the mixture is
to be attributed to the change from a solid to a
fluid state. The union of the snow and salt pro-
duces a new arrangement of their particles, in con-
sequence of which they become liquid ; and the
quantity of caloric, required to effect this change, is
seized upon by the mixture wherever it can be ob-
tained. This eagerness of the mixture for caloric,
during its liquefaction, is such, that it converts part
of its own free caloric into latent heat, and it is
thus that its temperature is lowered.
EMILY.
Whatever you put in this mixture, therefore,
would freeze ?
MRS. B.
Yes; at least any fluid that is susceptible of
freezing at that temperature. I have prepared
this mixture of salt and snow for the purpose of
freezing the water from which you are desirous of
seeing the latent heat escape. I have put a ther-
mometer in the glass of water that is to be frozen,
in order that you may see how it cools.
CAROLINE.
The thermometer descends, but the heat which
the water is now losing, is its Jree^ not its latent
heat.
144 COMBINED CALORIC.
MRS. B.
, . Certainly; it does not pnrt with its latent heat
till it changes its state and is converted into ice.
EMILY.
But here is a very extraordinary circumstance !
The thermometer is fallen below the freezing point,
and yet the water is not frozen.
MRS. B.
That is always the case previous to the freezing
of water when it is in a state of rest. Now it be-
gins to congeal, and you may observe that the ther-
mometer again rises to the freezing point.
CAROLINE.
It appears to me very strange that the thermo-
meter should rise the very moment that the water
freezes ; for it seems to imply that the water was
colder before it froze than when in the act of freez-
ing.
MRS.' B.
It is so; and after our long dissertation on this
circumstance, I did not think it would appear so
surprising to you. Reflect a little, and I think you
will discover the reason of it.
CAROLINE.
It must be, no doubt, the extrications of latent
heat, at the instant the water freezes, that raises
the temperature.
COMBINED CALORIC. 145
MRS. B.
Certainly ; and if you now examine the thermo-
meter, you will find that its rise was but temporary,
and lasted only during the disengagement of the
latent heat now that all the water is frozen it fells
again, and will continue to fall till the ice and
mixture are of an equal temperature.
EMILY.
And can you show us any experiments in which
liquids, by being mixed, become solid, and disen-
gage latent heat ?
MRS. B.
I could show you several ; but you are not yet suf-
ficiently advanced to understand them well. I shall,
however, try one, which will afford you a striking
instance of the fact. The fluid which you see in
this phial consists of a quantity of a certain salt
called muriat of lime, dissolved in water. Now, if
I pour into it a few drops of this other fluid, called
sulphuric acid, the whole, or very nearly the whole,
will be instantaneously converted into a solid mass.
EMILY.
How white it turns ! I feel the latent heat es-
caping, for the bottle is warm, and the fluid is
changed to a solid white substance like chalk !
VOL. j. H
146 COMBINED CALORIC.
CAROLINE.
This is, indeed, the most curious experiment we
have seen yet. But pray what is that white vapour
that ascends from the mixture ?
MRS. B.
You are not yet enough of a chemist to under-
stand that. But take care, Caroline, do not ap-
proach too near it, for it has a very pungent smell.
I shall show you another instance similar to that
of the water, which you observed to become warmer
as it froze. I have in this phial a solution of a salt
called sulphat of soda or Glauber's salt, made very
strong, and corked up when it was hot, and kept
without agitation till it became cold, as you may
feel the phial is. Now when I take out the cork
and let the air fall upon it, (for being closed when
boiling, there was a vacuum in the upper part) ob-
serve that the salt will suddenly crystallize. . . .
CAROLINE.
Surprising ! how beautifully the needles of salt
have shot through the whole phial !
MRS. B.
Yes, it is very striking but pray do not forget
the object of the experiment. Feel how warm the
phial has become by the conversion of part of the
liquid into a solid.
COMBINED CALORIC. 147
EMILY.
Quite warm I declare ! this is a most curious
experiment of the disengagement of latent heat.
MRS. B.
The slakeing of lime is another remarkable in-
stance of the extrication of latent heat. Have you
never observed how quick-lime smokes when water
is poured upon it, and how much heat it produces ?
CAROLINE.
Yes ; but I do not understand what change of
state takes place in the lime that occasions its
giving out latent heat ; for the quick-lime, which
is solid, is (if I recollect right) reduced to powder,
by this operation, and is, therefore, rather ex-
panded than condensed.
MRS. B.
It is from the water, not the lime, that the latent
heat is set free. The water incorporates with, and
becomes solid in the lime; in consequence of which,
the heat, which kept it in a liquid state, is disen-
gaged, and escapes in a sensible form.
CAROLINE.
I always thought that the heat originated in the
lime. It seems very strange that water, and cold
water too, should contain so much heat.
H 2
148 COMBINED CALORIC.
EMILY.
After this extrication of caloric, the water must
exist in a state of ice in the lime, since it parts
with the heat which kept it liquid.
MRS. B.
It cannot properly be called ice, since ice im-
plies a degree of cold, at least equal to the freezing
point. Yet as water, in combining with lime, gives
out more heat than in freezing, it must be in a state
of still greater solidity in the lime, than it is in the
form of ice; and you may have observed that it
does not moisten or liquefy the lime in the smallest
degree.
EMILY.
But, Mrs. B., the smoke that rises is white ; if
it was only pure caloric which escaped, we might
feel, but could not see it.
MRS. B.
This white vapour is formed by some of the
particles of lime, in a state of fine dust, which are
carried off by the caloric.
EMILY.
In all changes of state, then, a body either ab-
sorbs or disengages latent heat?
COMBINED CALORIC. 149
MRS. B.
You cannot exactly say absorbs latent heat, as
the heat becomes latent only on being confined in
the body; but you may say, generally, that bo-
dies, in passing from a solid to a liquid form, or
from the liquid state to that of vapour, absorb
heat ; and that when the reverse takes place, heat
is disengaged. *
EMILY.
We can now, I think, account for the ether
boiling, and the water freezing in vacno, at the
same temperature, f
MRS. B.
Let me hear how you explain it.
EMILY.
The latent heat, which the water gave out in
freezing, was immediately absorbed by the ether,
during its conversion into vapour ; and therefore,
from a latent state in one liquid, it passed into a
latent state in the other.
MRS. B,
But this only partly accounts for the result of
the experiment ; it remains to be explained why the
* This rule, if not universal, admits of very few exceptions,
f See page 102.
H 3
COMBINED CALORIC.
temperature of the ether, while in a state of ebulli-
tion, is brought down to the freezing temperature
of the water. It is because the ether, during its
evaporation, reduces its own temperature, in the
same proportion as that of the water, by convert-
ing its free caloric into latent heat : so that, though
one liquid boils, and the other freezes, their tem-
peratures remain in a state of equilibrium.
EMILY.
But why does not water, as well as ether, re-
duce* its own temperature by evaporating ?
MRS. B.
The fact is that it does, though much less ra-
pidly than ether. Thus, for instance, you may
often have observed, in the heat of summer, how
much any particular spot may be cooled by water-
ing, though the water used for that purpose be as
warm as the air itself. Indeed so much cold may be
produced by the mere evaporation of water, that
the inhabitants of India, by availing themselves of
the most favourable circumstances for this process
which their warm climate can afford, namely, the
cool of the night, and situations most exposed to
the night breeze, succeed in causing water to
freeze, though the temperature of the air be as
high as 60 degrees. The water is put into shal-
low earthen trays, so as to expose an extensive
ftg.2.
Fig. 3.
Electrical Machine .
Fiq.3. Atfa CvlwJer.-K the Conductor _R the ubhtr._C the Chain .
floj..t. * 4. Voltaic JSatteriej
Onu-n by th,J,rthtr. TuHirhtd />/ Longman ir i? trt. r . iA. . EnfrareJ fy
COMBINED CALORIC. 151
surface to the process of evaporation, and in the
morning, the water is found covered with a thin
cake of ice, which is collected in sufficient quan-
tity to be used for purposes of luxury.
CAROLINE.
How delicious it must be to drink liquids so
cold in those tropical climates ! But, Mrs. B.,
could we not try that experiment ?
MRS. B.
If we were in the>country, I have no doubt but
that we should be able to freeze water, by the
same means, and under similar circumstances.
But we can do it immediately, upon a small
scale, in this very room, in which the thermome-
ter stands at 70 degrees. For this purpose we
need only place some water in a little cup under
the receiver of the air-pump (PLATE V. fig. 1.),
and exhaust the air from it. What will be the
consequence, Caroline?
CAROLINE.
Of course the water will evaporate more quickly,
since there will no longer be any atmospheric
pressure on its surface : but will this be sufficient
to make the water freeze ?
H 4
152 COMBINED CALORIC.
MRS. B.
Probably not, because the vapour will not be
carried off fast enough ; but this will be accom-
plished without difficulty if we introduce into the
receiver (fig. 1.), in a saucer, or other large shallow
vessel, some strong sulphuric acid, a substance
which has a great attraction for water, whether in
the form of vapour, or in the liquid state. This
attraction is such that the acid will instantly ab-
sorb the moisture as it rises from the water, so as
to make room for the formation of fresh vapour ;
this will of course hasten the process, and the cold
produced from the rapid evaporation of the water,
will, in a few minutes, be sufficient to freeze its
surface. * We shall now exhaust the air from the
receiver.
EMILY.
Thousands of small bubbles already rise through
the water from the internal surface of the cup ;
what is the reason of this ?
MRS. B.
These are bubbles of air which were partly
attached to the vessel, and partly diffused in the
water itself; and they expand and rise in con-
sequence of the atmospheric pressure being re-
moved.
* This experiment was first devised by Mr. Leslie, and has
since been modified in a variety of forms.
COMBINED CALORIC. 153
CAROLINE.
See, Mrs. B. ; the thermometer in the cup is
sinking fast; it has already descended to 40 de-
grees !
EMILY.
The water seems now and then violently agi-
tated on the surface, as if it was boiling ; and yet
the thermometer is descending fast !
MRS. B.
You may call it boiling, if you please, for this
appearance is, as well as boiling, owing to the
rapid formation of vapour; but here, as you have
just observed, it takes place from the surface, for
it is only when heat is applied to the bottom of
the vessel that the vapour is formed there. Now
crystals of ice are actually shooting all over the
surface of the water.
CAROLINE.
How beautiful it is ! The surface is now en-
tirely frozen but the thermometer remains at
32 degrees.
MRS. B.
And so it will, conformably with our doctrine
of latent heat, until the whole of tire water is
frozen; but it will then again begin to descend
lower and lower, in consequence of the evapora-
tion which goes on from the surface of the ice.
H 5
154 COMBINED CALORIC.
EMILY.
This is a most interesting experiment; but it
would be still more striking if no sulphuric acid
were required.
MRS. B.
I will show you a freezing instrument, con-
trived by Dr. Wollaston, upon the same principle
as Mr. Leslie's experiment, by which water may
be frozen by its own evaporation alone, without
the assistance of sulphuric acid.
This tube, which, as you see (PLATE V. fig. 2.),
is terminated at each extremity by a bulb, one of
which is half full of water, is internally perfectly
exhausted of air ; the consequence of this is, that
the water in the bulb is always much disposed to
evaporate. This evaporation, however, does not
proceed sufficiently fast to freeze the water ; but
if the empty ball be cooled by some artificial
means, so as to condense quickly the vapour
which rises from the water, the process may be
thus so much promoted as to cause the water to
freeze in the other ball. Dr. Wollaston has called
this instrument Cryophorus.
CAROLINE.
So that cold seems to perform here the same
part which the sulphuric acid acted in Mr. Leslie's
experiment ?
COMBINED CALORIC. 155
MRS. B.
Exactly so ; but let us try the experiment.
EMILY.
How will you cool the instrument ? You have
neither ice nor snow.
MRS. B.
True : but we have other means of effecting
this. * You recollect what an intense cold can be
produced by the evaporation of ether in an ex-
hausted receiver. We shall inclose the bulb in
this little bag of fine flannel (fig. 3.), then soke it
in ether, and introduce it into the receiver of the
air-pump. (Fig. 5.) For this purpose we shall find
it more convenient to use a cryophorus of this
shape (fig. 4.), as its elongated bulb passes easily
through a brass plate which closes the top of the
receiver. If we now exhaust the receiver quickly,
you will see, in less than a minute, the water freeze
in the other bulb, out of the receiver.
EMILY.
The bulb already looks quite dim, and small
drops of water are condensing on its surface.
* This mode of making the experiment was proposed, and
the particulars detailed, by Dr. Marcet, in the 34th vol. of
Nicholson's Journal, page 119.
H 6
156 COMBINED CALO1UC.
CAROLINE.
And now crystals of ice shoot all over the water.
This is, indeed, a very curious experiment !
MRS. B.
You will see, some other day, that, by a similar
method, even quicksilver may be frozen. But we
cannot at present indulge in any further di-
gression.
Having advanced so far on the subject of heat,
I may now give you an account of the calorime-
ter, an instrument invented by Lavoisier, upon
the principles just explained, for the purpose of
estimating the specific heat of bodies. It consists
of a vessel, the inner surface of which is lined
with ice, so as to form a sort* of hollow globe of
ice, in the midst of which the body, whose speci-
fic heat is to be ascertained, is placed. The ice
absorbs caloric from this body, till it has brought
it down to the freezing point; this caloric con-
verts into water a certain portion of the ice which
runs out through an aperture at the bottom of the
machine ; and the quantity of ice changed to water
is a test of the quantity of caloric which the body
has given out in descending from a certain tem-
perature to the freezing point.
CAROLINE.
In this apparatus, I suppose, the milk, chalk.
COMBINED CALORIC. 157
and lead, would melt different quantities of ice, in
proportion to their different capacities for caloric ?
MRS. B.
Certainly : and thence we are able to ascer-
tain, with precision, their respective capacities
for heat. But the calorimeter affords us no more
idea of the absolute quantity of heat contained in
a body, than the thermometer; for though by
means of it we extricate both the free and com-
bined caloric, yet we extricate them only to a
certain degree, which is the freezing point; and
we know not how much they contain of either
below that point.
EMILY.
According to thfe theory of latent heat, it ap-
pears to me that the weather should be warm
when it freezes, arid cold in a thaw: for latent
heat is liberated from every substance that it
freezes, and such a large supply of heat must
warm the atmosphere ; whilst, during a thaw,
that very quantity of free heat must be taken
from the atmosphere, and return to a latent state
in the bodies which it thaws.
MRS. B.
Your observation is very natural ; but consider
that in a frost the atmosphere is so much colder
than the earth, that all the caloric which it takes
158 COMBINED CALORIC.
from the freezing bodies is insufficient to raise its
temperature aboVe the freezing point ; otherwise
the frost must cease. But if the quantity of latent
heat extricated does not destroy the frost, it serves
to moderate the suddenness of the change of tem-
perature of the atmosphere, at the commencement
both of frost, and of a thaw. In the first instance,
its extrication diminishes the severity of the cold;
and, in the latter, its absorption moderates the
warmth occasioned by a thaw : it even some-
times produces a discernible chill, at the break-
ing up of a frost.
CAROLINE.
But what are the general causes that produce
those sudden changes in the weather, especially
from hot to cold, which we often experience ?
MRS. B.
This question would lead us into meteorological
discussions, to which I am by no means competent.
One circumstance, however, we can easily under-
stand. When the air has passed over cold coun-
tries, it will probably arrive here at a temperature
much below our own, and then it must absorb heat
from every object it meets with, which will produce
a general fall of temperature.
CAROLINE.
But pray, now that we know so much of the
16
COMBINED CALORIC.
effects of heat, will you inform us whether it is
really a distinct body, or, as I have heard, a peculiar
kind of motion produced in bodies ?
MRS. B.
As I before told you, there is yet much uncer-
tainty as to the nature of these subtle agents.
But I am inclined to consider heat not as mere
motion, but as a separate substance. Late expe-
riments too appear to make it a compound body,
consisting of the two electricities, and in our next
conversation I shall inform you of the principal
facts on which that opinion is founded.
( 160 )
t
CONVERSATION V.
ON THE CHEMICAL AGENCIES OF ELECTRICITY*
MRS. B.
JDEFORE we proceed further it will be necessary
to give you some account of certain properties of
electricity, which have of late years been disco-
vered to have an essential connection with the
phenomena of chemistry.
CAROLINE.
It is ELECTRICITY, if I recollect right, which
comes next in our list of simple substances ?
MRS. B.
I have placed electricity in that list, rather from
the necessity of classing it somewhere, than from
any conviction that it has a right to that situation,
for we are as yet so ignorant of its intimate nature,
that we are unable to determine, not only whether
it is simple or compound, but whether it is in fact
a material agent ; or, as Sir H. Davy has hinted,
whether it may not be merely a property inherent
ELECTRO-CHEMISTRY. 161
in matter. As, however, it is necessary to adopt
some hypothesis for the explanation of the disco-
veries which this agent has enabled us to make, I
have chosen the opinion, at present most preva-
lent, which supposes the existence of two kinds
of electricity, distinguished by the names of positive
and negative electricity.
CAROLINE.
Well, I must confess, I do not feel nearly so
interested in a science in which so much uncer-
tainty prevails, as in those which rest upon esta-
blished principles ; I never was fond of electricity,
because, however beautiful and curious the pheno-
mena it exhibits may be, the theories, by which
they were explained, appeared to me so various, so
obscure and inadequate, that I always remained
dissatisfied. I was in hopes that the new disco-
veries in electricity had thrown so great a light
on the subject, that every thing respecting it would
now have been clearly explained.
MRS. B.
That is a point which we are yet far from hav-
ing attained. But, in spite of the imperfection
of our theories, you will be amply repaid by the
importance and novelty of the subject. The num-
ber of new facts which have already been ascer-
tained, and the immense prospect of discovery
162 ELECTRO-CHEMISTRY.
which has lately been opened to us, will, I hope,
ultimately lead to a perfect elucidation of this
branch of natural science; but at present you
must be contented with studying the effects, and
in some degree explaining the phenomena, with-
out aspiring to a precise knowledge of the remote
cause of electricity.
You have already obtained some notions of elec-
tricity: in our present conversation, therefore, I
shall confine myself to that part of the science
which is of late discovery, and is more particu-
larly connected with chemistry.
It was a trifling and accidental circumstance
which first gave rise to this new branch of physi-
cal science. Galvani, a professor of natural phi-
losophy at Bologna, being engaged (about twenty
years ago) in some experiments on muscular irri-
tability, observed, that when a piece of metal was
laid on the nerve of a frog, recently dead, whilst
the limb supplied by that nerve rested upon some
other metal, the limb suddenly moved, on a com-
munication being made between the two pieces of
metal.
EMILY.
How is this communication made?
MRS. B.
Either by bringing the two metals into contact,
or by connecting them by means of a metallic con-
ELECTRO-CHEMISTRY. 163
doctor. But without subjecting a frog to any cruel
experiments, I can easily make you sensible of this
kind of electric action. Here is a piece of zine,
(one of the metals I mentioned in the list of el&-
mentary bodies) put it under your tongue, and
this piece of silver upon your tongue, and let both
the metals project a little beyond the tip of the
tongue very well now make the projecting
parts of the metals touch each other, and you will
instantly perceive a peculiar sensation.
EMILY.
Indeed I did, a singular taste, and I think a de-
gree of heat : but I can hardly describe it.
MRS. B.
The action of these two pieces of metal on the
tongue is, I believe, precisely similar to that made
on the nerve of a frog. I shall not detain you by
a detailed account of the theory by which Galvani
attempted to account for this fact, as his explana-
tion was soon overturned by subsequent experi-
ments, which proved that Galvanism (the name
this new power had obtained) was nothing more
than electricity. Galvani supposed that the virtue
of this new agent resided in the nerves of the frog,
but Volta, who prosecuted this subject with much
greater success, shewed that the phenomena did
not depend on the organ? of the frog, but upon
164 ELECTRO-CHEMISTRY.
the electrical agency of the metals, which is excited
by the moisture of the animal, the organs of the
frog being only a delicate test of the presence of
electric influence.
CAROLINE.
I suppose, then, the saliva of the mouth answers
the same purpose as the moisture of the frog, in
exciting the electricity of the pieces of silver and
zinc with which Emily tried the experiment on
her tongue.
MRS. B.
Precisely. It does not appear, however, neces-
sary that the fluid used for this purpose should
be of an animal nature. Water, and acids very
much diluted by water, are found to be the most
effectual in promoting the developement of elec-
tricity in metals; and, accordingly, the original
apparatus which Volta first constructed for this
purpose, consisted of a pile or succession of plates
of zinc and copper, each pair of which was con-
nected by pieces of cloth or paper impregnated
with water ; and this instrument, from its original
inconvenient structure and limited strength, has
gradually arrived at its present state of power
and improvement, such as is exhibited in the Vol-
taic battery. In this apparatus, a specimen of
which you see before you (PLATE VI. fig. 1.),
the plates of zinc and copper are soldered to-
gether in pairs, each pair being placed at regular
ELECTRO-CHEMISTRY. 165
distances in wooden throughs and the interstices
being filled with fluid.
CAROLINE.
Though you will not allow us to enquire into
the precise cause of electricity, may we not ask
in what manner the fluid acts on the metals so as
to produce it ?
MRS. B.
The action of the fluid on the metals, whether
water or acid be used, is entirely of a chemical
nature. But whether electricity is excited by this
chemical action, or whether it is produced by the
contact of the two metals, is a point upon which
philosophers do not yet perfectly agree.
EMILY.
But can the mere contact of two metals, with-
out any intervening fluid, produce electricity ?
MRS. B.
Yes, if they are afterwards separated. It is an
established fact, that when two metals are put in
contact, and afterwards separated, that which has
the strongest attraction for oxygen exhibits signs
of positive, the other of negative electricity.
CAROLINE.
It seems then but reasonable to infer that the
166 ELECTRO-CHEMISTRY.
power of the Voltaic battery should arise from the
contact of the plates of zinc and copper.
MRS. B.
It is upon this principle that Volta and Sir H.
Davy explain the phenomena of the pile ; but not-
withstanding these two great authorities, many
philosophers entertain doubts on the truth of this
theory. The principal difficulty which occurs in
explaining the phenomena of the Voltaic battery
on this principle, is, that two such plates show no
signs of different states of electricity whilst in
contact, but only on being separated after con-
tact. Now in the Voltaic battery, those plates
that are in contact always continue so, being sol-
dered together: and. they cannot therefore receive
a succession of charges. Besides, if we consider
the mere disturbance of the balance of electricity
by the contact of the plates, as the sole cause of
the production of Voltaic electricity, it remains
to be explained how this disturbed balance be-
comes an inexhaustible source of electrical energy,
capable of pouring forth a constant and copious
supply of electrical fluid, though without any
means of replenishing itself from other sources.
This subject, it must be owned, is involved in too
much obscurity to enable us to speak very de-
cidedly in favour of any theory. But, in order to
avoid perplexing you with different explanations,
ELECTRO-CHEMISTRY. 167
I shall confine myself to one which appears to me
to be least encumbered with difficulties, and most
likely to accord with truth.*
This theory supposes the electricity to be excited
by the chemical action of the acid on the zinc ; but
you are yet such novices in chemistry, that I think
it will be necessary to give you some previous ex-
planation of the nature of this action.
All metals have a strong attraction for oxygen,
and this element is found in great abundance both
in water and in acids. The action of the diluted
acid on the zinc consists therefore in its oxygen
combining with it, and dissolving its surface.
CAROLINE.
In the same manner I suppose as we saw an
acid dissolve copper?
MRS. B.
Yes; but in the Voltaic battery the diluted
acid is not strong enough to produce so complete
* This mode of explaining the phenomena of the Voltaic
pile is called i\\Q chemical theory of electricity, because it ascribes
the cause of these phenomena to certain chemical changes
which take place during their appearance. In the preceding
edition of this work, the same theory was presented in a more
elaborate, but less easy form than it is in this. The mode of
viewing the subject which is here sketched was long since sug-
gested by Dr. Bostock, of whose theory, however, this is by no
means to be considered as a complete statement.
168 ELECTRO-CHEMISTRY.
an effect ; it acts only on the surface of the zinc,
to which it yields its oxygen, forming upon it a
film or crust, which is a compound of the oxygen
and the metal.
EMILY.
Since there is so strong a chemical attraction
between oxygen and metals, I suppose they are
naturally in different states of electricity ?
MRS. B.
Yes; it appears that all metals are united with
the positive, and that oxygen is the grand source
of the negative electricity.
CAROLINE.
Does not then the acid act on the plates of cop-
per, as well as on those of zinc ?
MRS. B.
No ; for though copper has an affinity for oxy-
gen, it is less strong than that of zinc ; and there-
fore the energy of the acid is only exerted upon
the zinc.
It will be best, I believe, in order to render the
action of the Voltaic battery more intelligible, to
confine our attention at first to the effect produced
on two plates only. (PLATE VI. fig. 2.)
If a plate of zinc be placed opposite to one of
copper, or any other metal less attractive of oxy-
ELECTRO-CHEMISTRY.
geii, and the space between them (suppose of half
an inch in thickness), be filled with an acid or any
fluid capable of oxydating the zinc, the oxydated
surface will have its capacity for electricity dimi-
nished, so that a quantity of electricity will be
evolved from that surface. This electricity will
be received by the contiguous fluid, by which it
will be transmitted to the opposite metallic surface,
the copper, which is not oxydated, and is there-
fore disposed to receive it; so that the copper
plate will thus become positive, whilst the zinc
plate will be in the negative state.
This evolution of electrical fluid however will
be very limited; for as these two plates admit of
but very little accumulation of electricity, and
are supposed to have no communication with other
bodies, the action of the acid, and further de-
velopement of electricity, will be immediately
stopped.
EMILY.
This action, I suppose, can no more continue-
to go on, than that of a common electrical ma-
chine, which is not allowed to communicate with
other bodies ?
MRS. B.
Precisely; the common electrical machine, when
excited by the friction of the rubber, gives out
both the positive and negative electricities.
(PLATE VI. Fig. 3.) The positive, by the ro-
VOL. 1. I
] 70 ELECTRO-CHEMISTRV.
tation of the glass cylinder, is conveyed into the
conductor* whilst the negative goes into the rub-
ber. But unless there is a communication made
between the rubber and the ground, but a very
inconsiderable quantity of electricity can be ex-
cited; for the rubber, like the plates of the bat-
tery,, has too small a capacity to admit of an ac-
cumulation of electricity. Unless therefore the
electricity can pass out of the rubber, it will not
continue to go into it, and consequently no addi-
tional accumulation will take place. Now as one
kind of electricity cannot be given out without
the other, the developement of the positive elec-
tricity is stopped as well as that of the negative,
and the conductor therefore cannot receive a
succession of charges.
CAROLINE.
But does not the conductor, as well as the rub-
ber, require a communication with the earth, in
order to get rid of its electricity ?J
MRS. B.
No ; for it is susceptible of receiving and con-
taining a considerable quantity of electricity, as
it is much larger than the rubber, and therefore
has a greater capacity; and this continued ac-
cumulation of electricity in the conductor is what
is called a charge.
ELECTRO-CHEMISTRY. 1J1
EMILY.
I3ut when an electrical machine is furnished with
two conductors to receive the two electricities, I
suppose no communication with the earth is re-
quired ?
MRS. B.
Certainly not, until the two are fully charged ;
for the two conductors will receive equal quan-
tities of electricity.
CAROLINE.
I thought the use of the chain had been to eon-
vey the electricity from the ground into the ma-
chine ?
MRS. B.
That was the idea of Dr. Franklin, who sup-
posed that there was but one kind of electricity,
and who, by the terms positive and negative
(which he first introduced), meant only different
quantities of the same kind of electricity. The
chain was in that case supposed to convey elec-
tricity from the ground through the rubber into
the conductor. But as we have adopted the hy-
pothesis of two electricities, we must consider the
chain as a vehicle to conduct the negative elec-
tricity into the earth.
EMILY.
And are both kinds of electricity produced when-
ever electricity is excited ?
i 9
1 7- ELECTBO-CHEMISTIIY.
MRS. B.
Yes, invariably. If you rub a tube of glass with
a woollen cloth, the glass becomes positive, and
the cloth negative. If, on the contrary, you ex-
cite a stick of sealing-wax by the same means, it is
the rubber which becomes positive, and the wax
negative.
But with regard to the Voltaic battery, in or-
der that the acid may act freely on the zinc, and
the two electricities be given out without inter-
ruption, some method must be devised, by which
the plates may part with their electricities as fast
as they receive them. Can you think of any
means by which this might be effected ?
EMILY.
Would not two chains or wires, suspended from
either plate to the ground, conduct the electrici-
ties into the earth, and thus answer the purpose ?
MRS. B.
It would answer the purpose of carrying off the
electricity, I admit ; but recollect, that though it
is necessary to find a vent for the electricity, yet we
must not lose it, since it is the power which we
are endeavouring to obtain. Instead, therefore, of
conducting it into the ground, let us make the
wires, from either plate, meet : the two electricities
will thus be brought together, and will combine
ELECTRO-CHEMISTRY.
and neutralize each other ; and as long as this com.
munication continues, the two plates having a vent
for their respective electricities, the action of the
acid will go on freely and uninterruptedly.
EMILY.
That is very clear, so far as two plates only
are concerned ; but I cannot say I understand how
the energy of the succession of plates, or rather
pairs of plates, of which the Galvanic trough is com-
posed, is propagated and accumulated throughout a
battery ?
MRS. B. ~
In order to shew you how the intensity of the
electricity is increased by increasing the number of
plates, we will examine the action of four plates ;
if you understand these, you will readily compre-
hend that of any number whatever. In this figure
(PLATE VI. Fig. 4.), you will observe that the two
central plates are united ; they are soldered to-
gether, (as we observed in describing the Voltaic
trough,) so as to form but one plate which offers
two different surfaces, the one of copper, the other
of zinc.
Now you recollect that, in explaining the action
of two plates, we supposed that a quantity of elec-
tricity was evolved from the surface of the first zinc
plate, in consequence of the action of the acid, and
was conveyed by the interposed fluid to the copper
I 3
17 i ELECTRO-CHEMISTRT.
plate, No. 2, which thus became positive. This
copper plate communicates its electricity to the
contiguous zinc plate, No. 3, in which, conse-
quently, some" accumulation of electricity takes
place. When, therefore, the fluid in the next cell
acts upon the zinc plate, electricity is extricated
from it in larger quantity, and in a more concen-
trated form, than before. This concentrated elec-
tricity is again conveyed by the fluid to the next
pair of plates, No. 4 and 5, when it is farther in-
creased by the action of the fluid in the third cell,
and so on, to any number of plates of which the
battery may consist ; so that the electrical energy
will continue to accumulate in proportion to the
number of double plates, the first zinc plate of the;
series being the most negative, and the last copper
plate the most positive.
CAROLINE.
But does the battery become more and more
strongly charged, merely by being allowed to stand
undisturbed ?
MRS. 13.
No, for the action will soon stop, as was ex-
plained before, unless a vent be given to the accu-
mulated electricities. This is easily done, however,
by establishing a communication by means of the
wires (Fig. 1.), between the two ends of the bat-
tery : these being brought into contact, the two
ELECTRO-CHEMISTRY. I'JB
electricities meet and neutralize each other, pro-
ducing the shock and other effects of electricity;
and the action goes on with renewed energy, being
no longer obstructed by the accumulation of the
two electricities which impeded its progress.
EMILY.
Is it the union of the two electricities which pro-
duces the electric spark ?
MRS. B.
Yes; and it is, I believe, this circumstance which
gaVe rise to Sir H. Davy's opinion that caloric may
be a compound of the two electricities.
CAROLINE.
Yet surely caloric is very different from the elec-
trical spark ?
MRS. u.
The difference may consist probably only in in-
tensity : for the heat of the electric spark is con-
siderably more intense, though confined to a very
minute spot, than any heat we can produce by other
means.
EMILY.
Is it quite certain that the electricity of the Vot*
taic battery is precisely of the same nature as that
of the common electrical machine ?
i 4
1 76 ELECTRO-CHEMISTRY.
MRS. B.
Undoubtedly; the shock given to the human
body, the spark, the circumstance of the same sub-
stances which are conductors of the one being also
conductors of the other, and of those bodies, such
as glass and sealing-wax, which are non-conductors
of the one, being also non-conductors of the other,
are striking proofs of it. Besides, Sir H. Davy
has shewn in his Lectures, that a Leyden jar, and
a common electric battery, can be charged with
electricity obtained from a Voltaic battery, the
effect produced being perfectly similar to that ob-
tained by a common machine.
Dr. Wollaston has likewise proved that similar
chemical decompositions are effected by the elec-
tric machine and by the Voltaic battery ; and has
made other experiments which render it highly
probable, that the origin of both electricities is es-
sentially the same, as they show that the rubber of
the common electrical machine, like the zinc in the
Voltaic battery, produces the two electricities by
combining with oxygen.
CAROLINE.
But I do not see whence the rubber obtains
oxygen, for there is neither acid nor water
used in the common machine, and I always
understood that the electricity was excited by the
friction.
ELECTRO-CHEMISTRY. 177
MRS. B.
It appears that by friction the rubber obtains
oxygen from the atmosphere, which is partly com-
posed of that element. The oxygen combines with
the amalgam of the rubber, which is of a metallic
nature, much in the same way as the oxygen of the
acid combines with the zinc in the Voltaic battery,
and it is thus that the two electricities are disen-
CAROLINE.
But, if the electricities of both machines are
similar, why not use the common machine for
chemical decompositions ?
MRS. B.
Though its effects are similar to those of the
Voltaic battery, they are incomparably weaker.
Indeed Dr. Wollaston, in using it for chemical
decompositions, was obliged to act upon the most
minute quantities of matter, and though the result
was satisfactory in proving the similarity of its ef-
fects to those of the Voltaic battery, these effects
were too small in extent to be in any considerable
degree applicable to chemical decomposition.
CAROLINE.
How terrible, then, the shock must be from a
Voltaic battery, since it is so much more powerful
than an electrical machine !
I 5
178 ELECTRO-CHEMISTRY*
MRS. B.
It is not nearly so formidable as you think ; at
least it is by no moans proportional to the chemical
effect. The great superiority of the Voltaic battery
consists in the large quantity of electricity that
passes ; but in regard to the rapidity or intensity of
the charge, it is greatly surpassed by the common
electrical machine. It would seem that the shock
or sensation depends chiefly upon the intensity ;
whilst, on the contrary, for chemical purposes, it is
quantity which is required. In the Voltaic battery,
the electricity, though copious, is so weak as not to
be able to force its way through the fluid which
separates the plates, whilst that of a common ma-
chine will pass through any space of water.
CAROLINE.
Would not it be possible to increase the intensity
of the Voltaic battery till it should equal that of the
common machine?
MRS. B.
It can actually be increased till it imitates a weak
electrical machine, so as to produce a visible spark
when accumulated in a Leyden jar. But it can
never be raised sufficiently to pass through any
considerable extent of air, because of the ready
communication through the fluids employed.
By increasing the number of plates of a battery,,
ii
ELECTRO-CHEMISTRY.
you increase its intensity ', whilst, by enlarging the
dimensions of the plates, you augment its quantity ;
and, as the superiority of the battery over the com-
mon machine consists entirely in the quantity of
electricity produced, it was at first supposed that it
was the size, rather than the number of plates that
was essential to the augmentation of power. It was,
however, found upon trial, that the quantity of
electricity produced by the Voltaic battery, even
when of a very moderate size, was sufficiently co-
pious, and that the chief advantage in this appa-
ratus was obtained by increasing the intensity,
which, however, still falls very short of that of the
common machine.
I should not omit to mention, that a very
splendid, and, at the same time, most powerful
battery, was, a few years ago, constructed under
the direction of Sir H. Davy, which he repeatedly
exhibited in his course of electro-chemical lectures.
It consists of two thousand double plates of zinc
and copper, of six square inches in dimensions,
arranged in troughs of Wedgwood-ware, each of
which contains twenty of these plates. The troughs
are furnished with a contrivance for lifting the
plates out of them in a very convenient and expe-
ditious manner.*
* A model of this mode of construction is exhibited in
PLATE XII. Fig. i.
1 6
1 80 ELECTRO-CHEMISTRY.
CAROLINE.
Well, now that we understand the nature of tiie
action of the Votaic battery, I long to hear an ac-
count of the discoveries to which it has given rise.
MRS. B.
You must restrain your impatience, my dear, for
1 cannot with any propriety introduce the subject
of these discoveries till we come to them in the re-
gular course of our studies. But, as almost every
substance in nature has already been exposed to
the influence of the Voltaic battery, we shall very
soon have occasion to notice its effects.
CONVERSATION VI.
ON OXYGEN AND NITROGEN.
MRS. B.
J O-DAY we shall examine the chemical properties
of the ATMOSPHERE.
CAROLINE.
I thought that we were first to learn the nature
of OXYGEN, which come next in our table of
simple bodies ?
MRS. B.
And so you shall ; the atmosphere being com-
posed of two principles, OXYGEN and NITROGEN,
we shall proceed to analyse it, and consider its com-
ponent parts separately.
EMILY.
I always thought that the atmosphere had been
a very complicated fluid, composed of all the va-
riety of exhalations from the earth.
MRS. B.
Such substances may be considered rather as he-
10
182 OXYGEN AND NITROGEN.
tcrogcneous and accidental, than as forming any of
its component parts; and the proportion they bear
to the whole mass is quite inconsiderable.
ATMOSPHERICAL AIR is composed of two gasses,
known by the names of OXYGEN GAS and NITRO-
GEN or AZOTIC GAS.
EMILY.
Pray what is a gas ?
MRS. B.
The name of gas is given to any fluid capable of
existing constantly in an aeriform state, under the
pressure and at the temperature of the atmosphere.
CAROLINE.
Is not water, or any other substance, when eva-
porated by heat, called gas ?
MRS. B.
No, my dear ; vapour is, indeed, an elastic fluid,
and bears a strong resemblance to a gas ; there are,
however, several points in which they essentially
differ, and by which you may always distinguish
them. Steam, or vapour, owes its elasticity merely
to a high temperature, which is equal to that of
boiling water. And it differs from boiling water
only by being united with more caloric, which, as
we before explained, is in a latent state. When
OXYGEN AND NITROGEN". 18J5
steam is cooled, it instantly returns to the form of
water; but air, or gas, has never yet been rendered
liquid or solid by any degree of cold.
EMILY.
But does not gas, as well as vapour, owe its elas-
ticity to caloric ?
MRS. B.
It was the prevailing opinion ; and the difference
of gas or vapour was thought to depend on the dif-
ferent manner in which caloric was united with the
basis of these two kinds of elastic fluids. In vapour,
it was considered as in a latent state ; in gas, it was
said to be chemically combined. But the late re-
searches of Sir H. Davy have given rise to a new
theory respecting gasses ; and there is now reason
to believe that these bodies owe their permanently
elastic state, not solely to caloric, but likewise to
the prevalence of either the one or the other of the
two electricities.
EMILY.
When you speak, then, of the simple bodies
oxygen and nitrogen, you mean to express those
substances which are the basis of the two gasses ?
MRS. B.
Yes, in strict propriety, for they can properly
be called gasses only when brought to an aeriform
state.
184 OXYGEN AND NITROGENS
CAROLINE.
In what proportions are they combined in the
atmosphere ?
MRS. B.
The oxygen gas constitutes a little more than
one-fifth, and the nitrogen gas a little less than
four-fifths. When separated, they are found to
possess qualities totally different from each other.
For oxygen gas is essential both to respiration and
combustion, while neither of these processes can be
performed in nitrogen gas.
CAROLINE.
But if nitrogen gas is unfit for respiration, how
does it happen that the large proportion of it which
enters into the composition of the atmosphere is
not a great impediment to breathing ?
MRS. B.
We should breathe more freely than our lungs
could bear, if we respired oxygen gas alone. The
nitrogen is no impediment to respiration, and pro-
bably, on the contrary, answers some useful pur-
pose, though we do not know in what manner it
acts in that process.
EMILY.
And by what means can the two gasses, which
compose the atmospheric air, be separated ?
OXYGEN AND NITROGEN. 185
MRS. B.
There are many ways of analysing the atmo-
sphere : the two gasses may be separated first by
combustion.
EMILY.
You surprise me ! how is it possible that com-
bustion should separate them ?
MRS. B.
I should previously remind you that oxygen is
supposed to be the only simple body naturally com-
bined with negative electricity. In all the other
elements the positive electricity prevails, and they
have consequently, all of them, an attraction for
oxygen. *
CAROLINE.
Oxygen the only negatively electrified body !
that surprises me extremely; how then are the
combinations of the other bodies performed, if,
according to your explanation of chemical attrac-
tion, bodies are supposed only to combine in virtue
of their opposite states of electricity ?
* If chlorine or oxymuriatic gas be a simple body, according
to Sir H. Davy's view of the subject, it must be considered as
an exception to this statement ; but this subject cannot be dis-
cussed till the properties and nature of chlorine come under
examination.
ISC.' OXYGEN AND NITROGEN.
MRS. B.
Observe that I said, that oxygen was the only
simple body, naturally negative. Compound bo-
dies, in which oxygen prevails over the other
component parts, are also negative, but their
negative energy is greater or less in proportion as
the oxygen predominates. Those compounds into
which oxygen enters in less proportion than the
other constituents, are positive, but their positive
energy is diminished in proportion to the quantity
of oxygen which enters into their composition.
All bodies, therefore, that are not already com-
bined with oxygen, will attract it, and, under cer-
tain circumstances, will absorb it from the atmo-
sphere, in which case the nitrogen gas will remain
ulone, and may thus be obtained in its separate
state.
CAROLINE.
I do not understand how a gas can be absorbed ?
MRS. B.
It is only the oxygen, or basis of the gas, which
is absorbed ; and the two electricities escaping, that
is to say, the negative from the oxygen, the positive
from the burning body, unite and produce caloric,
EMILY.
And what becomes of this caloric '<*
OXYGEN AND NITROGEN. 187
MRS. B.
We shall make this piece of dry wood attract
oxygen from the atmosphere, and you will see
what becomes of die caloric.
CAROLINE.
You are joking, Mrs. B ; you do not mean to
decompose the atmosphere with a piece of dry
stick ?
MRS. B.
Not the whole body of the atmosphere, certainly;
but if we can make this piece of wood attract any
quantity of oxygen from it, a proportional quan-
tity of atmospherical air will be decomposed.
CAROLINE.
If wood has so strong an attraction for oxygen,
why does it not decompose the atmosphere spon-
taneously ?
MRS. 13.
It is found by experience, that an elevation of
temperature is required for the commencement of
the union of the oxygen and the wood.
This elevation of temperature was formerly
thought to be necessary, in order to diminish the
cohesive attraction of the wood, and enable the
oxygen to penetrate and combine with it more
readily. But since the introduction of the new
theory of chemical combination, another cause has
188 OXYGEN AND NITROGEN.
been assigned, and it is now supposed that the
high temperature, by exalting the electrical ener-
gies of bodies, and consequently their force of
attraction, facilitates their combination.
EMILY.
If it is true, that caloric is composed of the two
electricities, an elevation of temperature must ne-
cessarily augment the electric energies of bodies.
MRS. B.
I doubt whether that would be a necessary con-
sequence; for, admitting this composition of ca-
loric, it is only by its being decomposed that
electricity can be produced. Sir H. Davy, how-
ever, in his numerous experiments, has found it
to be an almost invariable rule that the electrical
energies of bodies are increased by elevation of
temperature.
What means then shall we employ to raise the
temperature of the wood, so as to enable it to at-
tract oxygen from the atmosphere ?
CAROLINE.
Holding it near the fire, I should think, would
answer the purpose.
MRS, B.
It may, provided you hold it sufficiently close
OXYGEN AND NITROGEN. 181)
to the fire; for a very considerable elevation of
temperature is required.
CAROLINE.
It has actually taken fire, and yet I did not let
it touch the coals, but I held it so very close that
I suppose it caught fire merely from the intensity
of the heat.
MRS. B.
Or you might say, in other words, that the ca-
loric which the wood imbibed, so much elevated its
temperature, and exalted its electric energy, as to
enable it to attract oxygen very rapidly from the
atmosphere.
EMILY.
Does the wood absorb oxygen while it is burning?
MRS. B.
Yes, and the heat and light are produced by
the union of the two electricities which are set at
liberty, in consequence of the oxygen combining
xvith the wood.
CAROLINE.
You astonish me ! the heat of a burning body
proceeds then as much from the atmosphere as
from the body itself?
MRS. B.
It was supposed that the caloric, given out
OXYGEN AND NITROGtN.
during combustion, proceeded entirely, or nearly
so, from the decomposition of the oxygen gas ; but,
according to Sir H. Davy's new view of the sub-
ject, both the oxygen gas, and the combustible
body, concur in supplying the heat and light, by
the union of their opposite electricities.
EMILY.
I have not yet met with any thing in chemistry
that has surprised or delighted me so much as this
explanation of combustion. I was at first wonder-
ing what connection there could be between the
affinity of a body for oxygen and its combustibi-
lity ; but I think I understand it now perfectly.
MRS. B.
Combustion then, you see, is nothing more than
the rapid combination of a body with oxygen, at-
tended by the disengagement of light and heat.
EMILY.
But are there no combustible bodies whose at-
traction for oxygen is so strong, that they will com-
bine with it, without the application of heat ?
CAROLINE.
That cannot be; otherwise we should see bodies
burning spontaneously.
AND NITROGEN. 191
MRS. B.
But there are some instances of this kind, such
as phosphorus, potassium, and some compound
bodies, which I shall hereafter make you ac-^
quainted with. These bodies, however, are pre-
pared by art, for in .general, all the combustions
that could occur spontaneously, at the tempera-
ture of the atmosphere, have already taken place;
therefore new combustions cannot happen with-
out the temperature of the body being raised*
Some bodies, however, will burn at a much lower
temperature than others*
CAROLINE*
But the common way of burning a body is not
merely to approach it to one already on fire, but
rather to put the one in actual contact with the
other, as when I burn this piece of paper by hold-
ing it in the flame of the fire.
MRS. B.
The. closer it is in contact with the source of
caloric, the sooner will its temperature be raised to
the degree necessary for it to burn. If you hold it
near the fire, the same effect will be produced ; but
more time will be required, as you found to be the
case with the piece of stick.
EMILY.
But why is it not necessary to continue apply-
li>2 OXYGEN AND NITROGEN.
ing caloric throughout the process of combustion,
in order to keep up the electric energy of the
wood, which is required to enable it to combine
with the oxygen ?
MRS. B.
The caloric which is gradually produced by the
two electricities during combustion, keeps up the
temperature of the burning body ; so that when
once combustion has begun, no further applica-
tion of caloric is required.
CAROLINE.
Since I have learnt this wonderful theory of com-
bustion, I cannot take my eyes from the fire; and
I can scarcely conceive that the heat and light,
which I always supposed to proceed entirely from
the coals, are really produced as much by the at-
mosphere.
EMILY.
When you blow the fire, you increase the com-
bustion, I suppose, by supplying the coals with a
greater quantity of oxygen gas ?
MRS. B.
Certainly; but of course no blowing will pro-
duce combustion, unless the temperature of the
coals be first raised. A single spark, however, is
sometimes sufficient to produce that effect; for,
as I said before, when once combustion has com-
OXYGEN AMD NITROGEN. 193
menced, the caloric disengaged is sufficient to ele-
vate the temperature of the rest of the body, pro-
vided that there be a free access of oxygen. It
however sometimes happens that if a fire be ill
made, it will be extinguished before all the fuel
is consumed, from the very circumstance of the
combustion being so slow that the caloric disen-
gaged is insufficient to keep up the temperature
of the fuel. You must recollect that there are
three things required in order to produce combus-
tion; a combustible body, oxygen, and a tempe-
rature at which the one will combine with the
other.
EMILY.
You said that combustion was one method of
decomposing the atmosphere, and obtaining the
nitrogen gas in its simple state; but how do you
secure this gas, and prevent it from mixing with
the rest of the atmosphere?
MRS. B.
It is necessary for this purpose to burn the body
within a close vessel, which is easily done. We
shall introduce a small lighted taper (PLATE VII.
Fig. 1.) under this glass receiver, which stands in
a bason over water, to prevent all communication
with the external air.
VOL. I. K
194 OXYGEN AND NITROGEN.
CAROLINE.
How dim the light burns already ! It is now
extinguished.
MllS. B.
Can you tell us why it is extinguished ?
CAROLINE.
Let me consider. The receiver was full of at-
mospherical air; the taper, in burning within it,
must have combined with the oxygen contained
in that air, and the caloric that was disengaged
produced the light of the taper. But when the
whole of the oxygen was absorbed, the whole of
its electricity was disengaged; consequently no
more caloric could be produced, the taper ceased
to burn, and the flame was extinguished.
MRS. B.
Your explanation is perfectly correct.
EMILY.
The two constituents of the oxygen gas being
thus disposed of, what remains under the receiver
must be pure nitrogen gas ?
MRS. B.
There are some circumstances which prevent
the nitrogen gas, thus obtained, from being per-
fectly pure; but we may easily try whether the
OXYGEN AND NITROGEN. 195
oxygen has disappeared, by putting another lighted
taper under it. You see how instantaneously the
flame is extinguished, for want of oxygen to supply
the negative electricity required for the formation
of caloric; and were you to put an animal under
the receiver, it would immediately be suffocated.
But that is an experiment which I do not think
your curiosity will tempt you to try.
EMILY.
Certainly not. But look, Mrs. B., the re-
ceiver is full of a thick white smoke. Is that
nitrogen gas?
MRS. B.
No, my dear; nitrogen gas is perfectly trans-
parent and invisible, like common air. This cloudi-
ness proceeds from a variety of exhalations, which
arise from the burning tape*, and the nature of
which you cannot yet understand.
CAROLINE.
The water within the receiver has now risen a
little above its level in the bason. What is the
reason of this ?
MRS. B.
With a moment's reflection, I dare say, you
would have explained it yourself. The water
rises in consequence of the oxygen gas within it
K 2
196 OXYGEN AND NITROGEN.
having been destroyed, or rather decomposed, by
the combustion of the taper.
CAROLINE.
Then why did not the water rise immediately
when the oxygen gas was destroyed ?
MRS. B.
Because the heat of the taper, whilst burning,
produced a dilatation of the air in the vessel, which
at first counteracted this effect.
Another means of decomposing the atmosphere
is the oxygenation of certain metals. This process
is very analogous to combustion; it is, indeed,
only a more general term to express the combina-
tion of a body with oxygen.
CAROLINE.
In what respect, then, does it differ from com-
bustion ?
MRS. B.
The combination of oxygen in combustion is
always accompanied by a disengagement of light
and heat ; whilst this circumstance is not a neces-
sary consequence of simple oxygenation.
CAROLINE.
But how can a body absorb oxygen without the
combination of the two electricities which produce
caloric ?
OXYGEN AND NITROGEN. 197
MRS. B.
Oxygen does not always present itself in a
gaseous state; it is a constituent part of a vast
number of bodies, both solid and liquid, in which
it exists in a much denser state than in the atmo-
sphere; and from these bodies it may be obtained
without much disengagement of caloric. It may
likewise, in some cases, be absorbed from the at-
mosphere without any sensible production of light
and heat; for, if the process be slow, the caloric
is disengaged in such small quantities, and so gra-
dually, that it is not capable of producing either
light or heat. In this case the absorption of oxy-
gen is called oxygenation or oxydation, instead of
combustion, as the production of sensible light and
heat is essential to the latter.
EMILY.
I wonder that metals can unite with oxygen;
for, as they are so dense, their attraction of
aggregation must be very great; and I should
have thought that oxygen could never have
penetrated such bodies.
MRS. B.
Their strong attraction for oxygen counter-
balances this obstacle. Most metals, however, re-
quire to be made red-hot before they are capable of
attracting oxygen in any considerable quantity.
K 3
OXYGEN AND NITROGEN.
By this combination they lose most of their metal-
lic properties, and fall into a kind of powder,
formerly called calx^ but now much more properly
termed an oxyd ,- thus we have oxyd of lead, oxyd
ofiron t &c.
EMILY.
And in the Voltaic battery, it is, I suppose, an
oxyd of zinc, that is formed by the union of the
oxygen with that metal?
MRS. B.
Yes, it is.
CAROLINE.
The word oxyd, then, simply means a metal
combined with oxygen ?
MRS. B.
Yes; but the term is not confined to metals,
though chiefly applied to them. Any body what-
ever, that has combined with a certain quantity
of oxygen, either by means of oxydation or com-
bustion, is called an oxyd t and is said to be oxy-
dated or oxygenated,
EMILY.
Metals, when converted into oxyds, become, I
suppose, negative?
MRS. B.
Not in general ; because in most oxyds the po-
sitive energy of the metal more than counterba-
OXYGEN AND NITROGEN. 199
lances the native energy of the oxygen with which
it combines.
This black powder is an oxyd of manganese, a
metal which has so strong an affinity for oxygen,
that it attracts that substance from the atmosphere
at any known temperature : it is therefore never
found hi its metallic form, but always in that of
an oxyd, in which state, you see, it has very little
of the appearance of a metal. It is now heavier
than it was before oxydation, in consequence of the
additional weight of the oxygen with which it has
combined.
CAROLINE.
I am very glad to hear that ; for I confess I
could not help having some doubts whether oxygen
was really a substance, as it is not to be obtained
in a simple and palpable state ; but its weight is, I
think, a decisive proof of its being a real body.
MRS. B.
It is easy to estimate its weight, by separating
it from the manganese, and finding how much the
latter has lost.
EMILY.
But if you can take the oxygen from the metal,
shall we not then have it in its palpable simple
state ?
MRS. B.
No ; for I can only separate the oxygen from
K 4
200 OXYGEN AND NITROGEN.
the manganese, by presenting to it some other
body, for which it has a greater affinity than for
the manganese. Caloric affording the two elec-
tricities is decomposed, and one of them uniting
with the oxygen, restores it to the aeriform state.
EMILY.
But you said jost now, that manganese would
attract oxygen from the atmosphere in which it
is combined with the negative electricity; how,
therefore, can the oxygen have a superior affinity
for that electricity, since it abandons it to combine
with the manganese ?
MRS. B.
1 give you credit for this objection, Emily ; and
the* only answer I can make to it is, that the mu-
tual affinities of metals for oxygen, and of oxygen
for electricity, vary at different temperatures; a
certain degree of heat will, therefore, dispose a
metal to combine with oxygen, whilst, on the con-
trary, the former will be compelled to part with
the latter, when the temperature is further in-
creased. 1 have put some oxyd of manganese
into a retort, which is an earthen vessel with a
bent neck, such as you see here. (PLATE VII.
Fig. 2.) The retort containing the manganese
you cannot see, as I have enclosed it in this fur-
nace, where it is now red-hot. But, in order to
OXYGEN AND NITROGEN. 201
make you sensible of the escape of the gas, which
is itself invisible, I have connected the neck of the
retort with this bent tube, the extremity of which
is immersed in this vessel of water. (PLATE VII.
Fig. 3.) Do you see the bubbles of air rise
through the water ?
CAROLINE.
Perfectly. This, then, is pure oxygen gas;
what a pity it should be lost ! Could you not pre-
serve it ?
MRS. B.
We shall collect it in this receiver. For this
purpose, you observe, I first fill it with water, iu
order to exclude the atmospherical air ; and then
place it over the bubbles that issue from the retort,
so as to make them rise through the water to the
upper part of the receiver.
EMILY.
The bubbles of oxygen gas rise, I suppose, from
their specific levity ?
MRS. B.
Yes; for though oxygen forms rather a heavy
gas, it is light compared to water. You see how
it gradually displaces the water from the receiver.
It is now full of gas, and I may leave it inverted
in water on this shelf, where I can keep the gas
K 5
202 OXYGEN AND NITROGEN.
as long as I choose, for future experiments. This
apparatus (which is indispensable in all experi-
ments in which gases are concerned) is called a
water-bath.
CAROLINE.
It is a very clever contrivance, indeed ; equally
simple and useful. How convenient the shelf is
for the receiver to rest upon under water, and the
holes in it for the gas to pass into the receiver ! I
long to make some experiments with this apparatus.
MRS. B.
I shall try your skill that way, when you have
a little more experience. I am now going to show
you an experiment, which proves, in a very striking
manner, how essential oxygen is to combustion.
You will see that iron itself will burn in this gas, in
the most rapid and brilliant manner.
CAROLINE.
Really ! I did not know that it was possible to
burn iron.
EMILY.
Iron is a simple body, and you know, Caroline,
that all simple bodies are naturally positive, and
therefore must have an affinity for oxygen.
MRS. B.
Iron will, however, not burn in atmospherical
OXYGEN AND NITROGEN. 203
air without a very great elevation of temperature ;
but it is eminently combustible in pure oxygen
gas ; and what will surprise you still more, it can
be set on fire without any considerable rise of tem-
perature. You see this spiral iron wire I fasten
it at one end to this cork, which is made to fit an
opening at the top of the glass-receiver. (PLATE VII.
Fig. 4.)
EMILY.
I see the opening in the receiver ; but it is care-
fully closed by a ground glass-stopper.
MRS. B.
That is in order to prevent the gas from escap-
ing; but I shall take out the stopper, and put
in the cork, to which the wire hangs. Now I
mean to burn this wire in the oxygen gas, but I
must fix a small piece of lighted tinder to the ex-
tremity of it, in order to give the first impulse to
combustion; for, however powerful oxygen is in
promoting combustion, you must recollect that
it cannot take place without some elevation qf
temperature. I shall now introduce the wire into
the receiver, by quickly changing the stoppers.
CAROLINE.
Is there no danger of the gas escaping while you
change the stoppers?
K 6
204 OXYGEN AND NITROGEN.
MRS. B.
Oxygen gas is a little heavier than atmospherical
air, therefore it will not mix with it very rapidly ;
and, if I do not leave the opening uncovered, we
shall not lose any
CAROLINE.
Oh, what a brilliant and beautiful flame !
EMILY.
It is as white and dazzling as the sun ! Now a
piece of the melted wire drops to the bottom : I
fear it is extinguished ; but no, it burns again as
bright as ever.
MRS. B.
It will burn till the wire is entirely consumed,
provided the oxygen is not first expended : for you
know it can burn only while there is oxygen to
combine with it.
CAROLINE.
I never saw a more beautiful light. My eyes
can hardly bear it ! How astonishing to think that
all this caloric was contained in the small quantity
of gas and iron that was enclosed in the receiver;
and that, without producing any sensible heat !
CAROLINE.
How wonderfully quick combustion goes on in
pure oxygen gas ! But pray, are these drops of
burnt iron as heavy as the wire was before ?
OXYGEN AND NITROGEN. 205
MRS. B.
They are even heavier ; for the iron, in burning,
has acquired exactly the weight of the oxygen
which has disappeared, and is now combined with
it. It has become an oxyd of iron.
CAROLINE.
I do not know what you mean by saying that the
oxygen has disappeared, Mrs. B., for it was always
invisible.
MRS. B.
True, my dear; the expression was incorrect.
But though you could not see the oxygen gas, I
believe you had no doubt of its presence, as the
effect it produced on the wire was sufficiently
evident.
CAROLINE.
Yes, indeed ; yet you know it was the caloric,
and not the oxygen gas itself, that dazzled us so
much.
MRS. B.
You are not quite correct in your t turn, in saying
the caloric dazzled you ; for caloric is invisible ; it
affects only the sense of feeling; it was the light
which dazzled you.
CAROLINE.
True; but light and caloric are such constant
companions, that it is difficult to separate them,
even in idea.
20G OXYGEN AND NITROGEN.
MRS. B.
The easier it is to confound them, the more
careful you should be in making the distinction.
CAROLINE.
But why has the water now risen, and filled
part of the receiver ?
MRS, B.
Indeed, Caroline, I did not suppose you would
have asked such a question ! I dare say, Emily,
you can answer it.
EMILY.
Let me reflect The oxygen has com-
bined with the wire ; the caloric has escaped ; con-
sequently nothing can remain in the receiver, and
the water will rise to fill the vacuum.
CAROLINE.
I wonder that I did not think of that. I wish
that we had weighed the wire and the oxygen gas
before combustion ; we might then have found whe-
ther the weight of the oxyd was equal to that of
both.
MRS. B.
You might try the experiment if you particularly
wished it ; but I can assure you, that, if accurately
performed, it never fails to show that the addi-
tional weight of the oxyd is precisely equal to that
OXYGEN AND NITROGEN. 207
of the oxygen absorbed, whether the process has
been a real combustion, or a simple oxygenation.
CAROLINE.
But this cannot be the case with combustions in
general ; for when any substance is burnt in the
common air, so far from increasing in weight, it is
evidently diminished, and sometimes entirely con-
sumed.
MRS. B.
But what do you mean by the expression con-
sumed ? You cannot suppose that the smallest par-
ticle of any substance in nature can be actually
destroyed. A compound body is decomposed by
combustion ; some of its constituent parts fly off in
a gaseous form, while others remain in a concrete
state ; the former are called the volatile, the latter
thejixed products of combustion. But if we collect
the whole of them, we shall always find that they
exceed the weight of the combustible body, by that
of the oxygen which has combined with them
during combustion.
EMILY.
In the combustion of a coal fire, then, I suppose
that the ashes are what would be called the fixed
product, and the smoke the volatile product ?
208 OXYGEN AND NITROGEN.
MRS. B.
Yet when the fire burns best, and the quantity of
volatile products should be the greatest, there is no
smoke ; how can you account for that ?
EMILY.
Indeed I cannot; therefore I suppose that I was
not right in my conjecture.
MRS. B.
Not quite : ashes, as you supposed, are a fixed
product of combustion ; but smoke, properly speak-
ing, is not one of the volatile products, as it con-
sists of some minute undecomposed particles of the
coals that are carried off by the heated air without
being burnt, and are either deposited in the form
of soot, or dispersed by the wind. Smoke, there-
fore, ultimately, becomes one of the Jixed products
of combustion. And you may easily conceive that
the stronger the fire is, the less smoke is produced,
because the fewer particles escape combustion. On
this principle depends the invention of Argand's
Patent Lamps ; a current of air is made to pass
through the cylindrical wick of the lamp, by which
means it is so plentifully supplied with oxygen,
that scarcely a particle of oil escapes combustion,
nor is there any smoke produced.
EMILY.
But what then are the volatile products of com-
bustion ?
OXYGEN AND NITROGEN. 209
MRS. B.
Various new compounds, with which you are
not yet acquainted, and which being converted by
caloric either into vapour or gas, are invisible;
but they can be collected, and we shall examine
them at some future period.
CAROLINE.
There are then other gases, besides the oxy-
gen and nitrogen gases.
MRS. B.
Yes, several : any substance that can assume and
maintain the form of an elastic fluid at the tempe-
rature of the atmosphere, is called a gas. We
shall examine the several gases in their respective
places ; but we must now confine our attention to
those that compose the atmosphere.
I shall show you another method of decompos-
ing the atmosphere, which is very simple. In
breathing, we retain a portion of the oxygen, and
expire the nitrogen gas ; so that if we breathe in
a closed vessel, for a certain length of time, the
air within it will be deprived of its oxygen gas.
Which of you will make the experiment ?
CAROLINE.
I should be very glad to try it.
210 OXYGEN AND NITROGEN^
MRS. B.
Very well; breathe several times through this
glass tube into the receiver with which it is con-
nected, until you feel that your breath is ex-
hausted.
CAROLINE.
I am quite out of breath already !
MRS. B.
Now let us try the gas with a lighted taper.
EMILY.
It is very pure nitrogen gas, for the taper is im-
mediately extinguished.
MRS. B.
That is not a proof of its being pure, but only
of the absence of oxygen, as it is that principle
alone which can produce combustion, every other
gas being absolutely incapable of it.
EMILY.
In the methods which you have shown us, for
decomposing the atmosphere, the oxygen always
abandons the nitrogen; but is there no way of
taking the nitrogen from the oxygen, so as to ob-
tain the latter pure from the atmosphere ?
MRS. B.
You must observe, that whenever oxygen is
OXYGEN AND NITROGEN. 211
taken from the atmosphere, it is by decomposing
the oxygen gas ; we cannot do the same with the
nitrogen gas, because nitrogen has a stronger
affinity for caloric than for any other known prin-
ciple : it appears impossible therefore to separate
it from the atmosphere by the power of affinities.
But if we cannot obtain the oxygen gas, by this
means, in its separate state, we have no difficulty
(as you have seen) to procure it in its gaseous
form, by taking it from those substances that have
absorbed it from the atmosphere, as we did with
the oxyd of manganese.
EMILY.
Can atmospherical air be recoroposed, by mix-
ing due proportions of oxygen and nitrogen
gases ?
MRS. B.
Yes : if about one part of oxygen gas be mixed
with about four parts of nitrogen gas, atmosphe-
rical air is produced. *
EMILY.
The air, then, must be an oxyd of nitrogen?
MRS. B.'
No, my dear ; for there must be a chemical
* The proportion of oxygen in the atmosphere varies from
21 to 22 per cent.
212 OXYGEN AND NITROGEN*
combination between oxygen and nitrogen in order
to produce an oxyd; whilst in the atmosphere
these two substances are separately combined with
caloric, forming two distinct gases, which are
simply mixed in the formation of the atmosphere.
I shall say nothing more of oxygen and nitro-
gen at present, as we shall continually have oc-
casion to refer to them in our future conversations.
They are both very abundant in nature ; nitrogen
is the most plentiful in the atmosphere, and exists
also in all animal substances; oxygen forms a
constituent part, both of the animal and vegetable
kingdoms, from which it may be obtained by a
variety of chemical means. But it is now time to
conclude our lesson. I am afraid you have learnt
more to-day than you will be able to remember.
CAROLINE.
I assure you that I have been too much inte-
rested in it, ever to forget it. In regard to nitro-
gen there seems to be but little to remember ; it
makes a very insignificant figure in comparison
to oxygen, although it composes a much larger
portion of the atmosphere.
MRS. B.
Perhaps this insignificance you complain of may
arise from the compound nature of nitrogen, for
though I have hitherto considered it as a simple
OXYGEN AND NITROGEN. 213
body, because it is not known in any natural pro-
cess to be decomposed, yet from some experi-
ments of Sir H. Davy, there appears to be reason
for suspecting that nitrogen is a compound body,
as we shall see afterwards. But even in its simple
state, it will not appear so insignificant when you
are better acquainted with it ; for though it seems
to perform but a passive part in the atmosphere,
and has no very striking properties, when con-
sidered in its separate state, yet you will see by-
and-bye what a very important agent it becomes,
when combined with other bodies. But no more
of this at present ; we must reserve it for its proper
place,
( 214 )
CONVERSATION VII.
ON HYDROGEN.
CAROLINE.
1 HE next simple bodies we come to are CHLORINE
and IODINE. Pray what kinds of substances are
these ; are they also invisible ?
MRS. B.
No ; for chlorine, in the state of gas, has a dis-
tinct greenish colour, and is therefore visible ; and
iodine, in the same state, has a beautiful claret-red
colour. The knowledge of these two bodies,
however, and the explanation of their properties,
imply various considerations, which you would
not yet be able to understand ; we shall therefore
defer their examination to some future conversation,
and we shall pass on to the next simple substance,
HYDROGEN, which we cannot, any more than
oxygen, obtain in a visible or palpable form. We
are acquainted with it only in its gaseous state, as
we are with oxygen and nitrogen.
CAROLINE.
But in its gaseous state it cannot be called a
HYDROGEN. 215
simple substance, since it is combined with heat
and electricity?
MRS. B.
True, my dear; but as we do not know in na-
ture of any substance which is not more or less
combined with caloric and electricity, we are apt
to say that a substance is in its pure state when
combined with those agents only.
Hydrogen was formerly called iriflammable air,
as it is extremely combustible, and burns with a
great flame. Since the invention of the new no-
menclature, it has obtained the name of hydrogen,
which is derived from two Greek words, the mean-
ing of which is, to produce water.
EMILY.
And how does hydrogen produce water ?
MRS. B.
By its combustion. Water is composed of
eighty-five parts, by weight, of oxygen, combined
with fifteen parts of hydrogen ; or of two parts, by
bulk of hydrogen gas, to one part of oxygen gas.
CAROLINE.
Really ! is it possible that water should be a
combination of two gases, and that one of these
216 HYDROGEN.
should be inflammable air ! Hydrogen must be a
most extraordinary gas that will produce both fire
and water.
EMILY.
But I thought you said that combustion could
take place in no gas but oxygen ?
MRS. B.
Do you recollect what the process of combustion
consists in ?
EMILY.
In the combination of a body with oxygen, with
disengagement of light and heat.
MRS. B.
Therefore when I say that hydrogen is com-
bustible, I mean that it has an affinity for oxygen ;
but, like all other combustible substances, it cannot
burn unless supplied with oxygen, and also heated
to a proper temperature.
CAROLINE.
The simply mixing fifteen parts of hydrogen,
with eighty-five parts of oxygen gas, will not, there-
fore, produce water ?
MRS. B.
No ; water being a much denser fluid than gases,
in order to reduce these gases to a liquid, it is
12
HYDROGEN. 21 7
necessary to diminish the quantity of caloric or
electricity which maintains them in an elastic form.
EMILY.
That I should think might be done by combin-
ing the oxygen and hydrogen together; for in
combining they would give out their respective
electricities in the form of caloric, and by this
means would be condensed.
CAROLINE.
But you forget, Emily, that in order to make
the oxygen and hydrogen combine, you must begin
by elevating their temperature, which increases, in-
stead of diminishing, their electric energies.
MRS. B.
Emily is, however, right ; for though it is neces-
sary to raise their temperature, in order to make
them combine, as that combination affords them
the means of parting with their electricities, it is
eventually the cause of the diminution of electric
energy.
CAROLINE.
You love to deal in paradoxes to-day, Mrs. B.
Fire, then, produces water ?
MRS. B.
The combustion of hydrogen gas certainly does;
VOL. I. L
218 HYDROGEN*.
but you do not seem to have remembered the
theory of combustion so well as you thought you
would. Can you tell me what happens in the com-
bustion of hydrogen gas ?
CAROLINE.
The hydrogen combines with the oxygen, and
their opposite electricities are disengaged in the
form of caloric. Yes, I think I understand it now
by the loss of this caloric, the gases are con-
densed into a liquid.
EMILY.
Water, then, I suppose, when it evaporates and
incorporates with the atmosphere, is- decomposed
and converted into hydrogen and oxygen gases ?
MBS. B.
No, my dear there you are quite mistaken :
the decomposition of water is totally different from
its evaporation ; for in the latter case (as you should
recollect) water is only in a state of very minute
division; and is merely suspended in the atmosphere,
without any chemical combination, and without any
separation of its constituent parts. As long as these
remain combined, they form WATER, whether in a
state of liquidity, or in that of an elastic fluid, as
vapour 9 or under the solid form of ice.
In our experiments on latent heat, you may re-
7
HYDROGEN. 219
collect that we caused water successively to pass
through these three forms, merely by an increase
or diminution of caloric, without employing any
power of attraction, or effecting any decomposition.
CAROLINE.
But are there no means of decomposing water ?
MRS. B.
Yes, several : charcoal, and metals, when heated
red hot, will attract the oxygen from water, in the
same manner as they will from the atmosphere.
CAROLINE.
Hydrogen, I see, is like nitrogen, a poor de-
pendant friend of oxygen, which is continually
forsaken for greater favourites.
MRS. B.
The connection, or friendship, as you choose to
call it, is much more intimate between oxygen and
hydrogen, in the state of water, than between oxygen
and nitrogen, in the atmosphere ; for, in the first
case, there is a chemical union and condensation
of the two substances ; in the latter, they are simply
mixed together in their gaseous state. You will
find, however, that, in some cases, nitrogen is quite
as intimately connected with oxygen, as hydrogen
is. But this is foreign to our present subject.
L 2
220 HYDROGEN.
EMILY.
Water, then, is an oxyd, though the atmo-
spherical air is not ?
MRS. B.
It is not commonly called an oxyd, though, ac-
cording to our definition, it may, no doubt, be
referred to that class of bodies.
CAROLINE.
I should like extremely to see water decomposed,
MRS. B.
I can gratify your curiosity by a much more
easy process than the qxydation of charcoal or
metals : the decomposition of water by these latter
means takes up a great deal of time, and is at-
tended with much trouble ; for it is necessary that
the charcoal or metal should be made red hot in
a furnace, that the water should pass over them
in a state of vapour, that the gas formed should
be collected over the water-bath, &c. In short, it
is a very complicated affair. But the same effect
may be produced with the greatest facility, by the
action of the Voltaic battery, which this will give
me an opportunity of exhibiting.
CAROLINE.
I am very glad of that, for I longed to see the
power of this apparatus in decomposing bodies.
&YDROGEN. 221
MRS. B.
'For this purpose I fill this piece of glass-tube
(PLATE VIII. fig. 1.) with water, and cork it up
at both ends ; through one of the corks I intro-
duce that wire of the battery which conveys the
positive electricity; and the wire which conveys
the negative electricity is made to pass through
the other cork, so that the two wires approach
each other sufficiently near to give out their re-
spective electricities.
CAROLINE.
It does not appear to me that you approach the
wires so near as you did when you made the bat-
tery act by itself.
MRS. B.
Water being a better conductor of electricity
than air, the two wires will act on each other
at a greater distance in the former than in the
latter.
EMILY.
Now the electrical effect appears : I see small
bubbles of air emitted from each wire.
MRS. B.
Each wire decomposes the water, the positive by
combining with its oxygen which is negative, the
negative by combining with its hydrogen which is
positive.
L 3
222 HYDROGEN.
CAROLINE.
Thai is wonderfully curious ! But what are the
small bubbles 1 of air ?
MRS. B.
Those that appear to proceed from the positive
wire, are the result of the decomposition of the
ivater by that wire. That is to say, the positive
electricity having combined with some of the
oxygen of the water, the particles of hydrogen
which were combined with that portion of oxygen
are set at liberty, and appear in the form of snaall
bubbles of gas or air.
EMILY.
And I suppose the negative fluid having in the
same manner combined with some of the hydrogen
of the water, the particles of oxygen that were
combined with it, are set free, and emitted in a
gaseous form.
MRS. B.
Precisely so. But I should not forget to ob-
serve, that the wires used in this experiment are
made of platina, a metal which is not capable of
combining with oxygen; for otherwise the wire
would combine with the oxygen, and the hydrogen
alone would be disengaged.
HYDROGEN. 223
CAROLINE.
But could not water be decomposed without the
electric, circle being completed? If, for instance,
you immersed only the positive wire in the water,
would it not combine with the oxygen, and the
hydrogen gas be given out ?
MRS. B.
No ; for as you may recollect, the battery can-
not act unless the circle be completed ; since the
positive wire will not give out its electricity, unless
attracted by that of the negative wire.
CAROLINE.
I understand it now. But look, Mrs. B., the
decomposition of the water which has now been
going on for some time, does not sensibly diminish
its quantity what is the reason of that ?
MRS. B.
Because the quantity decomposed is so extremely
small. If you compare the density of water with
that of the gases into which it is resolved, you
must be aware that a single drop of water is suffi-
cient to produce thousands of such small bubbles
as those you now perceive.
CAROLINE.
But in this experiment, we obtain the oxygen
224 HYDROGEN.
and hydrogen gases mixed together. Is there any
means of procuring the two gases separately ?
MRS. B.
They can be collected separately with great
ease, by modifying a little the experiment. Thus
if instead of one tube, we employ two, as you see
here, (c, d, PLATE VIII. fig. 2,) both tubes being
closed at one end, and open at the other ; and if
after filling these tubes with water, we place them
standing in a glass of water (e), with their open
end downwards, you will see that the moment we
connect the wires (a, b) which proceed upwards
from the interior of each tube, the one with one
end of the battery, and the other with the other
end, the water in the tubes will be decomposed ;
hydrogen will be given out round the wire in the
tube connected with the positive end of the bat-
tery, and oxygen in the other; and these gases
will be evolved, exactly in the proportions which
I have before mentioned, namely, two measures of
hydrogen for one of oxygen. We shall now begin
the experiment, but it will be some time before any
sensible quantity of the gases can be collected.
EMILY.
The decomposition of water in this way, slow as
it is, is certainly very striking; but I confess that
I should be still more gratified, if you could shew
it us on a larger scale, and by a quicker process.
HYDROGEN. 225
1 am sorry that the decomposition of water by
charcoal or metals is attended with so much incon-
venience.
MRS. B.
Water may be decomposed by means of metals
without any difficulty ; but for this purpose the in-
tervention of an acid is required. Thus, if we add
some sulphuric acid (a substance with the nature of
which you are not yet acquainted) to the water
which the metal is to decompose, the acid disposes
the metal to combine with the oxygen of the water
so readily and abundantly, that no heat is required
to hasten the process. Of this I am going to shew
you an instance. I put into this bottle the water
that is to be decomposed, as also the metal that is
to effect that decomposition by combining with the
oxygen, and the acid which is to facilitate the com-
bination of the metal and the oxygen. You will see
with what violence these will act on each other.
CAROLINE.
But what metal is it that you employ for this
purpose ?
MRS. B.
It is iron ; and it is used in the state of filings,
as these present a greater surface to the acid than
a solid piece of metal. For as it is the surface of
the metal which is acted upon by the acid, and is
disposed to receive the oxygen produced by the
i 5
226 HYDROGEN.
decomposition of the water, it necessarily follows
that the greater is the surface, the more consider-
able is the effect. The bubbles which are now
rising are hydrogen gas
CAROLINE.
How disagreeably it smells !
MRS. B.
It is indeed unpleasant, though, I believe, not
particularly hurtful. We shall not, however, suf-
fer any more to escape, as it will be wanted for
experiments. I shall, therefore, collect it in a
glass-receiver, by making it pass through this bent
tube, which will conduct it into the water-bath.
(PLATE VIII. fig. 3.)
EMILY.
How very rapidly the gas escapes ! it is perfectly
transparent, and without any colour whatever.
Now the receiver is full
MRS. B.
We shall, therefore, remove it, and substitute
another in its place. But you must observe, that
when the receiver is full, it is necessary to keep
it inverted with the mouth under water, otherwise
the gas would escape. And in order that it may
not be in the way, I introduce within the bath,
under the water, a saucer, into which I slide the
receiver, so that it can be taken out of the bath
HYDROGEN. 227
and conveyed any where, the water in the saucer
being equally effectual in preventing its escape as
that in the bath. (PLATE VIII. fig. 4.)
EMILY.
I am quite surprised to see what a large quan-
tity of hydrogen gas can be produced by such a
small quantity of water, especially as oxygen is
the principal constituent of water,
MRS. B.
In weight it is ; but not in volume. For though
the proportion, by weight, is nearly six parts of
oxygen to one of hydrogen, yet the proportion of
the volume of the gases, is about one part of
oxygen to two of hydrogen; so much heavier is
the former than the latter.
CAROLINE.
But why is the vessel in which the water is de-
composed so hot? As the water changes from a
liquid to a gaseous form, cold should be produced
instead of heat.
MRS. B.
No; for if one of the constituents of water is
converted into a gas, the other becomes solid in
combining with the metal.
EMILY.
In this case, then, neither heat nor cold should
\>e produced ?
I, 6
228 HYDROGEN.
MRS. B.
True : but observe that the sensible heat which
is disengaged in this operation, is not owing to
the decomposition of the water, but to an extrica-
tion of heat produced by the mixture of water
and sulphuric acid. I will mix some water and
sulphuric acid together in this glass, that you
may feel the surprising quantity of heat that is
disengaged by their union now take hold of the
glass
CAROLINE.
Indeed I cannot ; it feels as hot as boiling water.
I should have imagined there would have been
heat enough disengaged to have rendered the liquid
solid.
MRS. B.
As, however, it does not produce that effect,
we cannot refer this heat to the modification called
latent heat. We may, however, I think, con-
sider it AS heat of capacity, as the liquid is con-
densed by its loss ; and if you were to repeat the
experiment, in a graduated tube, you would find
that the two liquids, when mixed, occupy con-
siderably less space than they did separately.
But we will reserve this to another opportunity,
and attend at present to the hydrogen gas which
we have been producing.
If I now set the hydrogen gas, which is con-
tained in this receiver, at liberty all at once, and
I
j
HYDROGEN. 229
kindle it as soon as it comes in contact with the
atmosphere, by presenting it to a candle, it will so
suddenly and rapidly decompose the oxygen gas,
by combining with its basis, that an explosion, or
a detonation (as chemists commonly call it), will be
produced. For this purpose, I need only take up
the receiver, and quickly present its open mouth
to the candle so ....
CAROLINE.
It produced only a sort of hissing noise, with a
vivid flash of light. I had expected a much
greater report.
MRS. B.
And so it would have been, had the gases been
closely confined at the moment they were made
to explode. If, for instance, we were to put in
this bottle a mixture of hydrogen gas and atmo-
spheric air ; and if, after corking the bottle, we
should kindle the mixture by a very small orifice,
from the sudden dilatation of the gases at the
moment of their combination, the bottle must
either fly to pieces, or the cork be blown out with
considerable violence.
CAROLINE.
But in the experiment which we have just seen,
if you did not kindle the hydrogen gas, would it
not equally combine with the oxygen ?
23X) HYDROGEN.
'MRS. B.
Certainly not; for, as I have just explained to
you, it is necessary that the oxygen and hydrogen
gases be burnt together, in order to combine che^
mically and produce water.
CAROLINE.
That is true ; but I thought this was a different
combination, for I see no water produced.
MRS. B.
The water resulting from this detonation was so
small in quantity, and in such a state of minute
division, as to be invisible. But water certainly
was produced ; for oxygen is incapable of combin-
ing with hydrogen in any other proportions than
those that form water ; therefore water must always
be the result of their combination.
If, instead of bringing the hydrogen gas into
sudden contact with the atmosphere (as we did
just now) so as to make the whole of it explode
the moment it is kindled, we allow but a very
small surface of gas to burn in contact with the
atmosphere, the combustion goes on quietly and
gradually at the point of contact, without any de-
tonation, because the surfaces brought together
are too small for the immediate union of gases*
The experiment is a very easy one. This phial,
\vith a narrow neck, (PLATE VIII, fig. 5.) is full
HYDROGEN. 231
of hydrogen gas, and is carefully corked. If I
take out the cork without moving the phial, and
quickly approach the candle to the orifice, you
will see how different the result will be
EMILY.
How prettily it burns, with a blue flame ! The
flame is gradually sinking within the phial now
it has entirely disappeared. But does not this
combustion likewise produce water ?
MRS. B.
Undoubtedly. In order to make the formation
of the water sensible to you, I shall procure a
fresh supply of hydrogen gas, by putting into this
bottle (PLATE VIII. fig. 6.) iron filings, water,
and sulphuric acid, materials similar to those
which we have just used for the same purpose.
I shall then cork up the bottle, leaving only a
small orifice in the cork, with a piece of glass-tube
fixed to it, through which the gas will issue in a
continued rapid stream.
CAROLINE.
I hear already the hissing of the gas through
the tube, and I can feel a strong current against
my hand.
MRS. B.
This current I am going to kindle with the
candle . see how vividly it burns
232 HYDROGEN.
EMILY.
It burns like a candle with a long flame. But
Why does this combustion last so much longer than
in the former experiment?
MRS. B.
The combustion goes on uninterruptedly as long
as the new gas continues to be produced. Now if
I invert this receiver over the flame, you will soon
perceive its internal surface covered with a very
fine dew, which is pure water
CAROLINE.
Yes, indeed; the glass is now quite dim with
moisture! How glad I am that we can see the
water produced by this combustion.
EMILY.
It is exactly what I was anxious to see; for I
confess I was a little incredulous.
MRS. B.
If I had not held the glass-bell over the flame,
the water would have escaped in the state of va-
pour, as it did in the former experiment. We
have here, of course, obtained but a very small
quantity of water; but the difficulty of procuring
a proper apparatus, with sufficient quantities of
HYDROGEN. 233
gases, prevents my showing it you on a larger
scale.
The composition of water was discovered about
the same period, both by Mr. Cavendish, in this
country, and by the celebrated French chemist
Lavoisier. The latter invented a very perfect
and ingenious apparatus to perform, with great
accuracy, and upon a large scale, the formation
of water by the combination of oxygen and hy-
drogen gases. Two tubes, conveying due pro-
portions, the one of oxygen, the other of hydrogen
gas, are inserted at opposite sides of a large globe
of glass, previously exhausted of air; the two
streams of gas are kindled within the globe, by
the electrical spark, at the point where they come
in contact ; they burn together, that is to say, the
hydrogen combines with the oxygen, the caloric
is set at liberty, and a quantity of water is pro-
duced exactly equal, in weight, to that of the two
gases introduced into the globe.
CAROLINE.
And what was the greatest quantity of water
ever formed in this apparatus ?
MRS. B.
Several ounces ; indeed, very nearly a pound, if
I recollect right; but the operation lasted many
days.
234 HYDROGKN.
/
EMILY.
This experiment must have convinced all the
world of the truth of the discovery. Pray, if im-
proper proportions of the gases were mixed and
set fire to, what would be the result ?
MRS. B.
Water would equally be formed, but there would
be a residue of either one or other of the gases,
because, as I have already told you, hydrogen and
oxygen will combine only in the proportions requi-
site for the formation of water.
MILY.
Look, Mrs. B., our experiment with the Voltaic
battery (PLATE VIII. fig. 2.) has made great pro-
gress ; a quantity of gas has been formed in each
tube, but in one of them there is twice as much
gas as in the other.
MRS. B.
Yes; because, as I said before, water is com-
posed of two volumes of hydrogen to one of oxy-
gen and if we should now mix these gases
together and set fire to them by an electrical spark,
both gases would entirely disappear, and a small
quantity of water would be formed.
There is another curious effect produced by the
combustion of hydrogen gas, which I shall show
HYDROGEN. 235
you, though I must acquaint you first, that I can-
not well explain the cause of it. For this purpose,
1 must put some materials into our apparatus, in
order to obtain a stream of hydrogen gas, just as
we have done before. The process is already going
on, and the gas is rushing through the tube I
shall now kindle it with the taper
EMILY.
It burns exactly as it did before What is the
curious effect which you were mentioning ?
MRS. B.
Instead of the receiver, by means of which we
have just seen the drops of water form, we shall in-
vert over the flame this piece of tube, which is
about two feet in length, and one inch in diameter
(PLATE VIII. fig. 70; but you must observe that
it is open at both ends.
EMILY.
What a strange noise it makes ! something hke
the /Eolian harp, but not so sweet.
CAROLINE.
It is very singular, indeed ; but I think rather
too powerful to be pleasing. And is not
sound accounted for?
MRS. B.
That the percussion of glass, by a rapid stream
of gas, should produce a sound, is not extraor-
dinary: but the sound here is so peculiar, that
no other gas has a similar effect. Perhaps it is
owing to a brisk vibratory motion of the glass,
occasioned by the successive formation and con-
densation of small drops of water on the sides of
the glass tube, and the air rushing in to replace
the vacuum formed. *
CAROLINE.
How very much this flame resembles the burn-
ing of a candle.
MRS. B.
The burning of a candle is produced by much
the same means. A great deal of hydrogen is
contained in candles, whether of tallow or wax.
This hydrogen being converted into gas by the
heat of the candle, combines with the oxygen of
the atmosphere, and flame and water result from
this combination. So that, in fact, the flame of a
candle is owing to the combustion of hydrogen
gas. An elevation of temperature, such as is pro-
duced by a lighted match or taper, is required to
give the first impulse to the combustion ; but af-
* This ingenious explanation was first suggested by Dr. De-
larive. See Journals of the Royal Institution, vol. i. p. 259.
.
ft
^n
X
~\ /. ;
:)
'^
I
11
h
*"
11
H V DROOEtf. 237
terwards it goes on of iteelf, because the candle
finds a supply of caloric in the successive quan-
tities of heat which result* from the union of the
two electricities given out by the gases during
their combustion. But there are other circum-
stances connected with the combustion of candles
and lamps, which I cannot explain to you till you
are acquainted with carbon, which is one of their
constituent parts. In general, however, whenever
you see flame, you may infer that it is owing to the
formation and burning of hydrogen gas *; for flume
is the peculiar mode of burning hydrogen gas,
which, with only one or two apparent, exceptions,
does not belong to any other combustible.
EMILY.
You astonish me i I understood that flame was
the caloric produced by the union of the two elec-
tricities, in all combustions whatever ?
MRS. B.
Your error proceeded from your vague and in-
correct idea of flame; you have confounded it
with light und caloric in general. Flame always
implies caloric, since it is produced by the com-
bustion of hydrogen gas ; but all caloric does not
* Or rather, tiydro-carbonat, a gas composed of hydrogen
and carbon, which will be noticed under the head Carbon,
238 HYDROGEN
imply, flame. Many bodies burn with intense heat
without producing flame. Coals, for instance, burn
with flame until all the hydrogen which they con-
tain is evaporated ; but when they afterwards be-
come red hot, much more caloric is disengaged than
when they produce flame.
CAROLINE.
But the iron wire, which you burnt in oxygen gas,
appeared to me to emit flame ; yet, as it was a sim-
ple metal, it could contain no hydrogen ?
MRS. B.
It produced a sparkling dazzling blaze of light,
but no real flame.
EMILY.
And what is the cause of the regular shape of
the flame of a candle ?
' MRS. B.
The regular stream of hydrogen gas which ex-
hales from its combustible matter.
CAROLINE.
But the hydrogen gas must, from its great
levity, ascend into the upper regions of the at-
mosphere ; why therefore does not the flarae con-
tinue to accompany it ?
HYDROGEN. 239
MRS. B.
The combustion of the hydrogen gas is com-
pleted at the point where the flame terminates;
it then ceases to be hydrogen gas, as it is con-
verted by its combination with oxygen into watery
vapour; but in a state of such minute division
as to be invisible.
CAROLINE.
I do not understand what is the use of the wick
of a candle, since the hydrogen gas burns so well
without it ?
MRS. B.
The combustible matter of the candle must be
decomposed in order to emit the hydrogen gas,
and the wick is instrumental in effecting this de-
composition. Its combustion first melts the com-
bustible matter, and ....
CAROLINE.
But in lamps the combustible matter is already
fluhl, and yet they also require wicks ?
MRS. B.
I am going to add that, afterwards, the burning
wick (by the power of capillary attraction) gradually
. draws up the fluid to the point where combustion
240 HYDROGEN.
takes place ; for you must have observed that the
wick does not burn quite to the bottom.
/
CAROLINE.
Yes ; but I do not understand why it does not.
MRS. B.
Because the air has not so free an access to
that part of the wick which is immediately in
contact with the candle, as to the part just above,
so that the heat there is not sufficient to produce
its decomposition ; the combustion therefore be-
gins a little above this point.
CAROLINE.
But, Mrs. B., in those beautiful lights, called
gas-lights, which are now seen in many streets, and
will, I hope, be soon adopted every where. I can
perceive no wick at all. How are these lights
managed ?
MRS. B.
I am glad you have put me in mind of saying a
few words on this very useful and interesting im-
provement. In this mode of lighting, the gas is
conveyed to the extremity of a tube, where it is
kindled, and burns as long as the supply continues.
There is, therefore, no occasion for a wick, or
any other fuel whatever.
HYDROGEN. 24 1
EMILY.
But how is all this gas procured in such large
quantities ?
MRS. B.
It is obtained from coal, by distillation. Coal,
when exposed to heat in a close vessel, is decom-
posed; and hydrogen, which is one of its consti-
tuents, rises in the state of gas, combined with
another of its component parts, carbon, forming a
compound gas, called Hydrocarbonat t the nature of
which we shall again have an opportunity of no-
ticing when we treat of carbon. This gas, like
hydrogen, is perfectly transparent, invisible, and
Jiighly inflammable ; and in burning it emits that
vivid light which you have so often observed.
CAROLINE.
And does the process for procuring it require
nothing but heating the coals, and conveying the
gas through tubes ?
MRS. B.
Nothing else; except that the gas must be made
to pass, immediately at its formation, through two or
three large vessels of water, in which it deposits
some other ingredients, and especially water, tar,
and oil, which also arise from the distillation of coals.
The gas-light apparatus, therefore, consists simply
in a large iron vessel, in which the coals aie ex-
posed to the heat of a furnace, some reservoirs
VOL. J. M
242 HYDROGEN.
of water, in which the gas deposits its impurities, -
and tubes that convey it to the desired spot, being
propelled with uniform velocity through the tubes
by means of a certain degree of pressure which is
made upon the reservoir.
EMILY.
What an admirable contrivance ! Do you not
think, Mrs. B., that it will soon get into universal
use?
MRS. B.
Most probably, as to the lighting of streets, offices,
and public places, as it far surpasses any former
invention for that purpose ; but as to the interior
of private houses, this mode of lighting has not yet
been sufficiently tried to know whether itwill be found
generally desirable, either in regard to economy or
convenience. It may, however, be considered as
one of the happiest applications of chemistry to
the comforts of life ; and there is every reason to
suppose that it will answer the full extent of public,
expectation,
I have another experiment to show you with
hydrogen gas, which I think will entertain you.
Have you ever blown bubbles with soap and water ?
EMILY.
Yes, often, when I was a child ; and I used to
make them float in the air by blowing them upi
wards.
HYDROGEN. 243
MRS. B.
We shall fill some such bubbles with hydrogen
gas, instead of atmospheric air, and you will see
vnth what ease and rapidity they will ascend,
without the assistance of blowing, from the
lightness of the gas. Will you mix some soap
and water whilst I fill this bladder with the gas
contained in the receiver which stands on the
shelf in the water-bath ?
CAROLINE.
What is the use of the brass-stopper and turn-
cock at the top of the receiver ?
MRS. B,
It is to afford a passage to the gas when re-
quired. There is, you see, a similar stop-cock
fastened to this bladder, which is made to fit that
on the receiver. I screw them one on the other,
and now turn the two cocks, to open a commu-
nication between the receiver and the bladder;
then, by sliding the receiver off the shelf, and
gently sinking it into the bath, the water rises in
the receiver and forces the gas into the bladder.
(PLATE IX. fig. 1.)
CAROLINE.
Yes, I see the bladder swell as the water rises in
the receiver.
M2
244 HYDROGEN.
MRS. B.
I think that we have already a sufficient quan-
tity in the bladder for our purpose ; we must be
careful to stop both the cocks before we separate
the bladder from the receiver, lest the gas should
escape. Now I must fix a pipe to the stopper of
the bladder, and by dipping its mouth into the soap
and water, take up a few drops then I again turn
the cock, and squeeze the bladder in order to force
the gas into the soap and water at the mouth of
the pipe. (PLATE IX. fig. 2.)
EMILY.
There is a bubble but it bursts before it leaves
the mouth of the pipe.
MRS. B.
We must have patience and try again ; it is not
so easy to blow bubbles by means of a bladder, as
simply with the breath.
CAROLINE.
Perhaps there is not soap enough in the water ;
I should have had warm water, it would have
dissolved the soap better.
EMILY.
Does not some of the gas escape between the
bladder and the pipe ?
HYDROGEN. 245
MRS. B.
they are perfectly air tight ; we shall suc-
ceed presently, I dare say,
CAROLINE.
Now a bubble ascends ; it moves with the ra-
pidity of a balloon. How beautifully it refracts
the light !
EMILY.
It has burst against the ceiling you succeed
now wonderfully; but why do they all ascend
and burst against the ceiling?
MRS. B.
Hydrogen gas is so much lighter than atmo-
spherical air, that it ascends rapidly with its very
light envelope, which is burst by the force with
which it strikes the ceiling.
Air-balloons are filled with this gas, and if they
carried no other weight than their covering, would
ascend as rapidly as these bubbles.
CAROLINE.
Yet their covering must be much heavier than
that of these bubbles ?
MRS. B.
Not in proportion to the quantity of gas they
contain. I do not know whether you have ever
M 3
246 HYDROGEN.
been present at the filling of a large balloon. The
apparatus for that purpose is very simple. It
consists of a number of vessels, either jars or bar-
rels, in which the materials for the formation of
the gas are mixed, each of these being furnished
with a tube, and communicating with a long
flexible pipe, which conveys the gas into the
balloon.
EMILY.
But the fire-balloons which were first invented,
and have been since abandoned, on account of
their being so dangerous, were constructed, I sup-
pose, on a different principle.
MRS. B.
They were filled simply with atmospherical air,
considerably rarefied by heat ; and the necessity of
having a fire underneath the balloon, in order to
preserve the rarefaction of the air within it, was the
circumstance productive of so much danger.
If you are not yet tired of experiments, I have
another to show you. It consists in filling soap-
bubbles with a mixture of hydrogen and oxygen
gases, in the proportions that form water; and
afterwards setting fire to them.
EMILY.
They will detonate, I suppose ?
247
MRS. B.
Yes, they will. As you have seen the method
of transferring the gas from the receiver into the
bladder, it is not necessary to repeat it. I have
therefore provided a bladder which contains a due
proportion of oxygen and hydrogen gases, and
we have only to blow bubbles with it.
CAROLINE.
Here is a fine large bubble rising shall I set
fire to it with the candle ?
MRS. B.
If you please ....
CAROLINE.
Heavens, what an explosion ! It was like the
report of a gun : I confess it frightened me much.
I never should have imagined it could be so loud.
EMILY.
And the flash was as vivid as lightning.
MRS. B.
The combination of the two gases takes place
during that instant of time that you see the flash,
and hear the detonation.
M 4
248 HYDROGEN.
EMILY.
This lias a strong resemblance to thunder and
lightning.
MRS. B.
These phenomena, however, are generally of
an electrical nature. Yet various meteorological
effects may be attributed to accidental detonations
of hydrogen gas in the atmosphere; for nature
abounds with hydrogen: it constitutes a very
considerable portion of the whole mass of water
belonging to our globe, and from that source
almost every other body obtains it. It enters into
the composition of all animal substances, and of a
great number of minerals ; but it is most abun-
dant in vegetables. From this immense variety of
bodies, it is often spontaneously disengaged; its
great levity makes it rise into the superior regions
of the atmosphere ; and when, either by an electri-
cal spark, or any casual elevation of temperature,
it takes fire, it may produce such meteors or lu-
minous appearances as are occasionally seen m
the atmosphere. Of this kind are probably those
broad flashes which we often see on a summer-even-
ing, without hearing any detonation.
EMILY.
Every flash, I suppose, must produce a quantity
of water?
HYDROGEN. 249
CAROLINE.
And this water, naturally, descends in the form
f rain?
MRS. B.
That probably is often the case, though it is not
a necessary consequence ; for the water may be dis-
solved by the atmosphere, as it descends towards
the lower regions, and remain there in the form of
clouds.
The application of electrical attraction to che-
mical phenomena is likely to lead to many very in-
teresting discoveries in meteorology; for electri-
city evidently acts a most important part in the
atmosphere. This subject however, is, as j'et, not
sufficiently developed for me to venture enlarging
upon it. The phenomena of the atmosphere are
far from being well understood; and even with
the little that is known, I am but imperfectly
acquainted.
But before we take leave of hydrogen, I must
not omit to mention to you a most interesting dis-
covery of Sir H. Davy, which is connected with
this subject.
CAROLINE,
You allude, I suppose, to the new miner's lamp,
which has of late been so much talked of? I have
long been desirous of knowing what that discovery
was, and what purpose it was intended to answer.
JM 5
250 HYDROGEN.
MRS. B.
It often happens in coal-mines, that quantities
of the gas, called by chemists hydro-carbonat, or
by the miners Jlre~damp t (the same from which the
gas-lights are obtained,) ooze out from fissures in
the beds of coal, and fill the cavities in which the
men are at work ; and this gas being inflammable,
the consequence is, that when the men approach
those places with a lighted candle, the gas takes
fire, and explosions happen which destroy the men
and horses employed in that part of the colliery,
sometimes in great numbers.
EMILY.
What tremendous accidents these must be !
But whence does that gas originate ?
MRS. B.
Being the chief product of the combustion of
coal, no wonder that inflammable gas should occa-
sionally appear in situations in which this mineral
abounds, since there can be no doubt that processes
of combustion are frequently taking place at a
great depth under the surface of the earth; and
therefore those accumulations of gas may arise
either from combustions actually going on, or from
former combustions, the gas having perhaps been
confined there for ages.
HYDROGEN. 251
CAROLINE.
And how does Sir H. Davy's lamp prevent
those dreadful explosions ?
\
MRS. B.
By a contrivance equally simple and ingenious ;
and one which does no less credit to the philoso-
phical views from which it was deduced, than to
the philanthropic motives from which the enquiry
sprung. The principle of the lamp is shortly this :
It was ascertained, two or three years ago, both by
Mr. Tennant and by Sir Humphry himself, that
the combustion of inflammable gas could not be
propagated through small tubes ; so that if a jet of an
inflammable gaseous mixture, issuing from a bladder
or any other vessel, through a small tube, be set
fire to, it burns at the orifice of the tube, but the
flame never penetrates into the vessel. It is upon
this fact that Sir Humphry's safety-lamp is
founded.
EMILY.
But why does not the flame ever penetrate
through the tube into the vessel from which the gas
issues, so as to explode at once the whole of the
gas?
MRS. B.
Because, no doubt, the inflamed gas is so much
cooled in its passage through a small tube as to
M 6
252 HYDROGEN.
cease to burn before the combustion reaches the
reservoir,
CAROLINE.
And how can this principle be applied to the
construction of a lamp ?
. fc.
Nothing easier. You need only suppose a lamp
enclosed all round in glass or horn, but having a
number of small open tubes at the bottom, and
others at the top, to let the air in and out. Now,
if such a lamp or Ian thorn be carried into an
atmosphere capable of exploding, an explosion or
combustion of the gas will take place within the
lamp; and although the vent afforded by the tubes
will save the lamp from bursting, yet, from the
principle just explained, the combustion will not be
propagated to the external air through the tubes,
so that no farther consequence will ensue.
EMILY.
And is that all the mystery of that valuable
lamp?
MRS. B.
No ; in the early part of the enquiry a lamp of this
kind was actually proposed ; but it was but a rude
sketch compared to its present state of improve-
ment. Sir H. Davy, after a succession of trials,
by which he brought his lamp nearer and nearer
figJ.A . the astern containing the Oil . . B. the ri/n or screw by which the
gouzt cage, if fix<o the cistern. C .oppcrture Tor supplying Oii.
^..awire for trimming the wick D. _ F. ike wirt gauze affinJa: -&.a double top.
FyZ.A..the. reservoir of condensed air . _B.rt< condensing Syrin,f? .
C . the bladder tor Oxygen . _ D . the moveable jet .
Lamy
HYDROGEN. 2.>*
to perfection, at last conceived the happy idea that
if the lamp were surrounded with a wire-work or
wire-gauze, of a close texture, instead of glass or
horn, the tubular contrivance I have just described
would be entirely superseded, since each of the
interstices of the gauze would act as a tube in pre-
venting the propagation of explosions; so that
this pervious metallic covering would answer the
various purposes of transparency, of permeability
to air, and of protection against explosion. This
idea, Sir Humphry immediately submitted to the
test of experiment, and the result has answered his
most sanguine expectations, both in his laboratory
and in the collieries, where it has already been
extensively tried. And he has now the happiness
of thinking that his invention will probably be the
means of saving every year a number of lives,
which would have been lost in digging out of the
bowels of the earth one of the most valuable neces-
saries of life. Here is one of these lamps, every
part of which you will at once comprehend. (See
PLATE X. fig. 1.)
CAROLINE.
How very simple and ingenious ! But I do not
yet well see why an explosion taking place within
the lamp should not communicate to the ex-
ternal air around it, through the interstices of the
wire ?
254 HYDROGEN.
MRS. B.
This has been and is still a subject of wonder,
even to philosophers; and the only mode they
have of explaining it is, that flame or ignition
cannot pass through a fine wire-work, because the
metallic wire cools the flame sufficiently to extin-
guish it in passing through the gauze. This pro-
perty of the wire-gauze is quite similar to that of
the tubes which I mentioned on introducing the
subject; for you may consider each interstice of
the gauze as an extremely short tube of a very
small diameter.
EMILY.
But I should expect the wire would often become
red-hot, by the burning of the gas within the lamp ?
MRS. B.
And this is actually the case, for the top of the
lamp is very apt to become red-hot. But, fortu-
nately, inflammable gaseous mixtures cannot be
exploded by red-hot wire, the intervention of
actual flame being required for that purpose ; so
that the wire does not set fire to the explosive gas
around it.
EMILY.
I can understand that ; but if the wire be red-
hot, how can it cool the flame within, and prevent
its passing through the gauze ?
HVPROGEN. 255
MRS. B.
The gauze, though red-hot, is not so hot as the
flame by which it has been heated ; and as metallic
wire is a good conductor, the heat does not much
accumulate in it, as it passes off quickly to the other
parts of the lamp, as well as to any contiguous
bodies.
CAROLINE.
This is indeed a most interesting discovery, and
one which shows at once the immense utility with
which science may be practically applied to some of
the most important purposes.
( 256' )
CONVERSATION VIII.
ON SULPHUR AND PHOSPHORUS.
MRS, B.
OULPHUR is the next substance that comes under
our consideration. It differs in one essential point
from the preceding, as it exists in a solid form at
the temperature of the atmosphere.
CAROLINE.
I am glad that we have at last a solid body to
examine; one that we can see and touch. Pray,
is it not with sulphur that the points of matches
are covered, to make them easily kindle ?
MRS. B.
Yes, it is; and you therefore already know that
sulpur is a very combustible substance. It is sel-
dom discovered in nature in a pure unmixed
state ; so great is its affinity for other substances,
that it is almost constantly found combined with
some of them. It is most commonly united with
SULPHUR. 257
metals, under various forms, and is separated
from them by a very simple process. It exists
likewise in many mineral waters, and some vege-
tables yield it in various proportions, * especially
those of the cruciform tribe. It is also found in
animal matter ; in short, it may be discovered in
greater or less quantity, in the mineral, vegetable,
and animal kingdoms.
EMILY.
I have heard ofjftowers of sulphur, are they the
produce of any plant?
MRS. B.
By no means: they consist of nothing more
than common sulphur, reduced to a very fine
powder by a process called sublimation. You see
some of it in this phial ; it is exactly the same
substance as this lump of sulphur, only its colour
is a paler yellow, owing to its state of very mi-
nute division.
EMILY.
Pray what is sublimation ?
MRS. B.
It is the evaporation, or, more properly speak-
ing, the volatilisation of solid substances, which,,
in cooling, condense again in a concrete form.
2S8 SULPHUR.
The process, in this instance, must be performed
in a closed vessel, both to prevent combustion,
which would take place if the access of air were
not carefully precluded, and likewise in order to
collect the substance after the operation. As it
is rather a slow process, we shall not try the ex-
periment now; but you will understand it per-
fectly if I show you the apparatus used for the
purpose. (PLATE XL fig. 1.) Some lumps of
sulphur are put into a receiver of this kind,
which is called a cucurbit. Its shape, you see,
somewhat resembles that of a pear, and is open at
the top, so as to adapt itself exactly to a kind of
conical receiver of this sort, called the head. The
cucurbit, thus covered with its head, is placed
over a sand-bath ; this is nothing more than a ves-
sel full of sand, which is kept heated by a furnace,
such as you see here, so as to preserve the appa-
ratus in a moderate and uniform temperature.
The sulphur then soon begins to melt, and im-
mediately after this, a thick white smoke rises,
which is gradually deposited within the head, or
uppe~r part of the apparatus, where it condenses
against the sides, somewhat in the form of a vege-
tation, whence it has obtained the name of flowers
of sulphur. This apparatus, which is called an
alembic, is highly useful in all kinds of distilla-
tions, as you will see when we come to treat of
those operations. Alembics are not commonly
SULPHUR. 259
made of glass, like this, which is applicable only
to distillations upon a very small scale. Those
used in manufactures are generally made of cop-
per, and are, of course, considerably larger. The
principal construction, however, is always the
same, although their shape admits of some va-
riation.
CAROLINE.
What is the use of that neck, or tube, which
bends down from the upper piece of the appa-
ratus ?
MRS. B.
It is of no use hi sublimations ; but in distilla-
tions (the general object of which is to evaporate,
by heat, in closed vessels, the volatile parts of a
compound body, and to condense them again into
a liquid,) it serves to carry off the condensed
fluid, which otherwise would fall back into the
cucurbit. But this is rather foreign to our pre-
sent subject. Let us return to the sulphur. You
now perfectly understand, I suppose, what is
meant by sublimation ?
EMILY.
I believe I do. Sublimation appears to consist
in destroying, by means of heat, the attraction of
aggregation of the particles of a solid body, which
are thus volatilised ; and as soon as they lose the
260 SULPHUR.
caloric which produced that effect, they are de-*
posited in the form of a fine powder.
CAROLINE.
It seems to me to be somewhat similar to the
transformation of water into vapour, which returns
to its liquid state when deprived of caloric.
EMILY.
There is this difference, however, that the sul-
phur does not return to its former state, since, in-
stead of lumps, it changes to a fine powder.
MRS. B.
Chemically speaking, it is exactly the same sub-
stance, whether in the form of lump or powder.
For if this powder be melted again by heat, it will,
in cooling, be restored to the same solid state in
which it was before its sublimation.
CAROLINE.
But if there be no real change, produced by the
sublimation of the sulphur, what is the use of that
operation ?
MRS. B.
It divides the sulphur into very minute parts,
and thus disposes it to enter more readily intQ
combination with other bodies. It is used also as
a means of purification.
SULPHUR. 261
CAROLINE.
Sublimation appears to me like the beginning of
combustion, for the completion of which one cir-
cumstance only is wanting, the absorption of
oxygen.
MRS. B.
But that circumstance is every thing. No essen-
tial alteration is produced in sulphur by sublima-
tion; whilst in combustion it combines with the
oxygen, and forms a new compound totally dif-
ferent in every respect from sulphur in its pure
state. We shall now burn some sulphur, and you
will see how very different the result will be. For
this purpose I put a small quantity of flowers of
sulphur into this cup, and place it in a dish, into
which I have poured a little water : I now set fire
to the sulphur with the point of this hot wire; for
its combustion will not begin unless its temperature
be considerably raised. You see that it burns
with a faint blueish flame ; and as I invert over it
this receiver, white fumes arise from the sulphur,
and fill the vessel. You will soon perceive that
the water is rising within the receiver, a little above
its level in the plate. Well, Emily, can you ac-
count for this ?
EMILY.
I suppose that the sulphur has absorbed the
oxygen from the atmospherical air within the re-
ceiver, and that we shall find some oxygenated
262 SULPHUR.
sulphur in the cup. As for the white smoke, I am
quite at a loss to guess what it may be.
MRS. B.
Your first conjecture is very right : but you are
mistaken in the last ; for nothing will be left in the
cup. The white vapour is the oxygenated sulphur,
which assumes the form of an elastic fluid of a
pungent and offensive smell, and is a powerful
acid. Here you see a chemical combination of
oxygen and sulphur, producing a true gas, which
would continue such under the pressure and at the
temperature of the atmosphere, if it did not unite
with the water in the plate, to which it imparts its
acid taste, and all its acid properties. You see,
now, with what curious effects the combustion of
sulphur is attended.
CAROLINE.
This is something quite new ; and I confess that
I do not perfectly understand why the sulphur turns
acid.
MRS. B,
It is because it unites with oxygen, which is the
acidifying principle. And, indeed, the word oxygen
is derived from two Greek words signifying to pro~
duce an acid.
CAROLINE.
Why, then, is not water, which contains such a
quantity of oxygen, acid ?
SULPHUR. 263
MRS. B.
Because hydrogen, which is the other consti-
tuent of water, is not susceptible of acidification.
I believe it will be necessary, before we proceed
further, to say a few words of the general nature
of acids, though it is rather a deviation from our
plan of examining the simple bodies separately,
before we consider them in a state of combination.
Acids may be considered as a peculiar class of
burnt bodies, which during their combustion, or
combination with oxygen, have acquired very
characteristic properties. They are chiefly dis-
cernible by their sour taste, and by turning red
most of the blue vegetable colours. These two
properties are common to the whole class of
acids ; but each of them is distinguished by other
peculiar qualities. Every acid consists of some
particular substance, (which constitutes its basis,
and is different in each,) and of oxygen, which Is
common to them all.
EMILY.
But I do not clearly see the difference between
acids and oxyds.
MRS. B.
Acids were, in fact, oxyds, which, by the addi-
tion of a sufficient quantity of oxygen, have been
converted into acids. For acidification, you must
observe, always implies previous oxydation, 'as a
body must have combined with the quantity of
14
264 SULPHUR.
oxygen requisite to constitute it an oxyd, before it
can combine with the greater quantity that is
necessary to render it an acid.
CAROLINE.
Are all oxyds capable of being converted into
acids ?
MRS. B.
Very far from it; it is only certain substances
which will enter into that peculiar kind of union
with oxygen that produces acids, and the number
of these is proportionally very small ; but all burnt
bodies may be considered as belonging either to
the class of oxyds, or to that of acids. At a future
period, we shall enter more at large into this sub-
ject. At present, I have but one circumstance
further to point out to your observation respecting
acids : it is, that most of them are susceptible of
two degrees of acidification, according to the dif-
ferent quantities of oxygen with which their basis
combines.
EMILY.
And how are these two degrees of acidification
distinguished ?
MRS. B.
By the peculiar properties which result from
them. The acid we have just made is the first or
weakest degree of acidification, and is called sul-
ghurccnis acid ; if it were fully saturated with oxy-
7
SULPHUR. 265
gen, it would be called sulphuric acid- You must
therefore remember, that in this, as in all acids,
the first degree of acidification is expressed by the
termination in ous ; the stronger, by the termination
in ic.
CAROLINE.
And how is the sulphuric acid made ?
MRS. B.
By burning sulphur in pure oxygen gas, and
thus rendering its combustion much more conv
plete. I have provided some oxygen gas for this
purpose; it is in that bottle, but we must first
decant the gas into the glass receiver which
stands on the shelf in the bath, and is full of
water.
CAROLINE.
Pray, let me try to do it, Mrs. B.
MRS. B.
It requires some little dexterity hold the bottle
completely under water, and do not turn the
mouth upwards, till it is immediately under the
aperture in the shelf, through which the gas is
to pass into the receiver, and then turn it up gra-
dually. Very well, you have only let a few bubbles
escape, and that must be expected at a first trial.
Now I shall put this piece of sulphur into the
receiver, through the opening at the top, and
VOL, I. N
266 SULPHUR.
introduce along with it a small piece of lighted
tinder to set fire to it. This requires being done-
very quickly, lest the atmospherical air should get
in, and mix with the pure oxygen ga.
EMILY.
How beautifully it burns !
CAROLINE.
But it is already buried in the thick vapour.
This, I suppose, is sulphuric acid ?
EMILY.
Are these acids always in a gaseous state ?
MRS. B.
Sulphureous acid, as we have already observed,
is a permanent gas, and can be obtained in a
liquid form only by condensing it in water. In its
pure state, the sulphureous acid is invisible, and
it now appears in the form of a white smoke, from
its combining with the moisture. But the vapour
of sulphuric acid, which you have just seen to
rise during the combustion, is not a gas, but only
a vapour, which condenses into liquid sulphuric
acid, by losing its caloric. But it appears from
Sir H, Davy's experiments, that this formation and
condensation of sulphuric acid requires the presence
of water^ for which purpose the vapour is received
SULPHUU. 267
into oold water, which may afterwards be separated
from the acid by evaporation.
Sulphur has hitherto been considered as a simple
substance; but Sir H. Davy has suspected that
it contains a small portion of hydrogen, and per-
haps also of oxygen.
On submitting sulphur to the action of the
Voltaic battery, he observed that the negative
wire gave out hydrogen; and the existence of
hydrogen in sulphur was rendered still more pro-
bable by his observing that a small quantity of
water was produced during the combustion of
sulphur.
EMILY.
And pray of what nature is sulphur when per-
fectly pure ?
MRS. B.
Sulphur has probably never been obtained per-
fectly free from combination, so that its radical
may possibly possess properties very different from
those of common sulphur. It has been suspected
to be of a metallic nature ; but this is mere con-
jecture.
Before we quit the subject of sulphur, I must
tell you that it is susceptible of combining with a
great variety of substances, and especially with
hydrogen, with which you are already acquainted.
Hydrogen gas can dissolve a small portion of itt
N 2
SULPHUR.
EMILY.
What ! can a gas dissolve a solid substance ?
MRS. B.
Yes ; a solid substance may be so minutely di-
vided by heat, as to become soluble in a gas : and
there are several instances of it. But you must
observe, that, in this case, a chemical union or
combination of the sulphur with the hydrogen
gas is produced. In order to effect this, the sul-
phur must be strongly heated in contact with the
gas ; the heat reduces the sulphur to such a state
of extreme division, and diffuses it so thoroughly
through the gas, that they combine and incorpo-
rate together. And as a proof that there must be
a chemical union between the sulphur and the gas,
it is sufficient to remark that they are not separated
when the sulphur loses the caloric by which it was
volatilized. Besides, it is evident, from the peculiar
fetid smell of this gas, that it is a new compound
totally different from either of its constituents ; it is
called sulphuretted hydrogen gas, and is contained in
great abundance in sulphureous mineral waters.
CAROLINE.
Are not the Harrogate waters of this nature?
MRS. B.
Yes; they are naturally impregnated with sul-
SULPHUR.
Ipimretted hydrogen gas, and there are many other
springs of the same kind, which shows that this gas
must often be formed in the bowels of the earth by
spontaneous processes of nature.
CAROLINE.
And could not such waters be made artificially
by impregnating common water with this gas ?
MRS. B.
Yes ; they can be so well imitated, as perfectly
to resemble the Harrogate waters.
Sulphur combines likewise with phosphorus, and
with the alkalies, and alkaline earths, substances
with which you are yet unacquainted. We can-
not, therefore, enter into these combinations at
present. In our next lesson we shall treat of phos-
phorus.
EMILY.
May we not begin that subject to-day ; this lesson
has been so short ?
MRS. B.
T have no objection, if you are not tired. What
do you say, Caroline ?
CAROLINE.
I am as desirous as Emily of prolonging the les-
son to-day, especially as we are to enter on a new
N 3
270 SULPHUR.
subject ; for I confess that sulphur has not appeared
to me so interesting as the other simple bodies.
MRS. B.
Perhaps you may find phosphorus more enter-
taining. You must not, however, be discouraged
when you meet with some parts of a study less
amusing than others; it would answer no good
purpose to select the most pleasing parts, since,
if we did not proceed with some method, in order
to acquire a general idea of the whole, we could
scarcely expect to take interest in any particular
subjects.
PHOSPHORUS.
PHOSPHORUS is considered as a simple body ;
though, like sulphur, it has been suspected of
containing hydrogen. It was not known by the
earlier chemists. It was first discovered by Brandt,
a chemist of Hamburgh, whilst employed in re-
searches after the philosopher's stone; but the
method of obtaining it remained a secret till it was
a second time discovered both by Knnckel and
Boyle, in the year 1680. You see a specimen of
phosphorus in this phial ; it is generally moulded
into small sticks of a yellowish colour, as you find
it here.
PHOSPHORUS.
CAROLINE*
I do not understand in what the discovery con-
sisted ; there may be a secret method of making
an artificial composition, but how can you talk ot
-making a substance which naturally exists ?
MRS. B.
A body may exist in nature so closely combined
with other substances, as to elude the observation
of chemists, or render it extremely difficult to ob-
tain it in its separate state. This is the case with
phosphorus, which is always so intimately com-
bined with other substances, that its existence re-
mained unnoticed till Brandt discovered the means
of obtaining it free from other combinations. It
is found in all animal substances, and is now
chiefly extracted from bones, by a chemical pro-
cess. It exists also in some plants, that bear a
strong analogy to animal matter in their chemical
composition.
EMILY.
But is it never found in its pure separate state?
MRS. B.
Never, and this is the reason that it has re-
mained so long undiscovered.
Phosphorus is eminently combustible; it melts
and takes fire at the temperature of one hundred
N 4
27- PHOSPHORUS.
degrees, and absorbs in its combustion nearly once
and a half its own weight of oxygen.
CAROLINE.
What ! will a pound of phosphorus consume a
pound and half of oxygen ?
MRS. B.
So it appears from accurate experiments. I can
sljow you with what violence it combines with
oxygen, by burning some of it in that gas. We
must manage the experiment in the same manner
as we did the combustion of sulphur. You see
>J am obliged to cut this little bit of phosphorus
under water, otherwise there would be danger of
its taking fire by the heat of my fingers. I now
put into the receiver, and kindle it by means of a
hot wire.
EMILY.
What a blaze ! I can hardly look at it. I
never saw any thing, so brilliant. Does it not
hurt your eyes, Caroline ?
CAROLINE.
Yes ; but still I cannot help looking at it. A
prodigious quantity of oxygen must indeed be
absorbed, when so much light and caloric are dis-
engaged !
VHOSPHORUS. fjf3
MRS. B.
In the combustion of a pound of phosphorus, a
sufficient quantity of caloric is set free to melt up-
wards of a hundred pounds of ice; this has Joeen
computed by direct experiments with the calori-
meter.
EMILY.
And is the result of this combustion, like that
of sulphur, an acid ?
MRS. B.
Yes ; phosphoric acid. And had we duly pro-
portioned the phosphorus and the oxygen, they
would have been completely converted into phos-
phoric acid, weighing together, in this new state,
exactly the sum of their weights separately. The
water would have ascended into the receiver, on
account of the vacuum formed, and would have
filled it entirely. In this case, as in the combus-
tion of sulphur, the acid vapour formed is absorbed
and condensed in the water of the receiver. But
when this combustion is performed without any
water or moisture being present, the acid then ap-
pears in the form of concrete whitish flakes, which
are, however, extremely ready to melt upon the
least admission of moisture.
EMILY.
Does phosphorus, in burning in atmospherical
5
4 PHOSPHORUS.
air, produce, like sulphur, a weaker sort of the
same acid ?
MRS. B.
No : for it burns in atmospherical air, nearly at
the same temperature as in pure oxygen gas ; and
it is in both cases so strongly disposed to combine
with the oxygen, that the combustion is perfect,
and the product similar ; only in atmospherical air,
being less rapidly supplied with oxygen, the pro-
cess is performed in a slower manner.
CAROLINE.
But is there no method of acidifying phosphorus
in a slighter manner, so as to form pkospkorus
acid?
MRS. B.
Yes, there is. When simply exposed to the
atmosphere, phosphorus undergoes a kind of slow
combustion at any temperature above zero.
EMILY.
But is not the process in this case rather an
oxydation than a combustion? For if the oxy-
gen is too slowly absorbed for a sensible quantity
of light and heat to be disengaged, it is not a true
combustion.
MRS. B.
The case is not as you suppose : a faint light is
PHOSPHORUS. 275
emitted which is very discernible in the dark;
but the heat evolved is not sufficiently strong to be
sensible: a whitish vapour arises from this com-
bustion, which, uniting with water, condenses into
liquid phosphorus acid.
CAROLINE.
Is it not very singular that phosphorus should
burn at so low a temperature in atmospherical air,
whilst it does not burn in pure oxygen without the
application of heat?
MRS. B.
So it at first appears. But this circumstance
seems to be owing to the nitrogen gas of the at-
mosphere. This gas dissolves small particles of
phosphorus, which being thus minutely divided
and diffused in the atmospherical air, combines
with the oxygen, and undergoes this slow com-
bustion. But the same effect does not take place
in oxygen gas, because it is not capable of dis-
solving phosphorus; it is therefore necessary, in
this case, that heat should be applied to effect that
division of particles, which, in the former instance,
is produced by the nitrogen.
EMILY.
I have seen letters written with phosphorus,
which are invisible by day-light, but may be read
N 6
PHOSPHORUS.
in the dark by their own light. They look as if
they were written with fire ; yet they do not seem
to burn.
MRS. B,
But they do really burn ; for it is by their slow
combustion that the light is emitted; and phos-
phorus acid is the result of this combustion.
Phosphorus is sometimes used as a test to esti-
mate the purity of atmospherical air. For this
purpose, it is burnt in a graduated tube, called an
Eudiometer (PLATE XI. fig. 2.), and from the quan-
tity of arr which the phosphorus absorbs, the pro-
portion of oxygen in the air examined is deduced;
for the phosphorus will absorb all the oxygen, and
the nitrogen alone will remain.
EMILY,
And the more oxygen is contained in the atmo-
the purer, I suppose, it is esteemed?
MRS. B,
Certainly. Phosphorus, when melted, com-
bines with a great variety of substances. With
sulphur it forms a compound so extremely com-
bustible, that it immediately takes fire on coming
in contact with the air. It is with this composi-
tion that phosphoric matches are prepared, which
kindle as soon as they are taken out of their ease
and are exposed to the air.
7
PHOSPHORUS. 277
EMTLY.
I have a box of these curious matches ; but I
have observed, that in very cold weather, they will
ftot take fire without being previously rubbed.
MRS. B.
By rubbing them you raise their temperature 5
for, you know, friction is one of the means of ex-
tricating heat.
EMILY.
Will phosphorus combine with hydrogen gas,
as sulphur does ?
MRS. B.
Yes ; and the compound gas which results front
this combination has a smell still more fetid than
the sulphuretted hydrogen ; it resembles that of
garlic.
The phosphoretted hydrogen gas has this remark-
able peculiarity, that it takes fire spontaneously
in the atmosphere, at any temperature. It is thus,
probably, that are produced those transient flames,
or flashes of light, called by the vulgar Will-of-tke
Whisp, or more properly Ignes-fatui, which are
often seen in church-yards, and places where the
putrefactions of animal matter exhale phosphorus
and hydrogen gas.
CAROLINE.
Country people, who are so much frightened by
PHOSPHORUS.
those appearances, would soon be reconciled to
them, if they knew from what a simple cause they
proceed.
MRS. B.
There are other combinations of phosphorus
that have also very singular properties, particularly
that which results from its union with lime.
EMILY.
Is there any name to distinguish the combina-
tion of two substances, like phosphorus and lime,
neither of which are oxygen, and which cannot
therefore produce either an oxyd or an acid ?
MKS. B.
The names of such combinations are composed
from those of their ingredients, merely by a slight
change in their termination. Thus the combina-
tion of sulphur with lime is called a sulphuret, and
that of phosphorus, a phosphuret of lime. This
latter compound, I was going to say, has the sin-
gular property of decomposing water, merely by
being thrown into it. It effects this by absorbing
the oxygen of water, in consequence of which bub-
bles of hydrogen gas ascend, holding in solution a
small quantity of phosphorus.
PHOSPHORUS. 279
EMILY.
These bubbles then are pJiosphoretted hydrogen
gas ?
MRS. B.
Yes ; and they produce the singular appearance
of a flash of fire issuing from water, as the bub-
bles kindle and detonate on the surface of the
water., at the instant that they come in contact
with the atmosphere.
CAROLINE.
Is not this effect nearly similar to that produced
by the combination of phosphorus and sulphur, or,
more properly speaking, the phosphuret of sulphur ?
MRS. B.
Yes ; but the phenomenon appears more extra-
ordinary in this case, from the presence of water,
and from the gaseous form of the combustible com-
pound. Besides, the experiment surprises by its
great simplicity. You only throw a piece of phos-
phoret of lime into a glass of water, and bubbles of
fire will immediately issue from it.
CAROLINE.
Cannot we try the experiment ?
280 PHOSPHORUS.
MRS. B.
Very easily: but we must do it in the open
air ; for tho smell of the phosphorated hydrogen
gas is so extremely fetid, that it would be intoler-
able in the house. But before we leave the room,
we may produce, by another process, some bub-
bles of the same gas, which are much less offen-
sive.
There is in this little glass retort a solution of
potash in water ; I add to it a small piece of phos-
phorus. We must now heat the retort over the
lamp, after having engaged its neck under water
you see it begins to boil ; in a few minutes bub-
bles will appear, which take fire and detonate as
they issue from the water.
CAROLINE.
There is one and another. How curious it is !
But I do not understand how this is produced.
MRS. B.
It is the consequence of a display of affinities
too complicated, I fear, to be made perfectly intel-
ligible to you at present.
In a few words, the reciprocal action of the pot-
ash, phosphorus, caloric, and water are such, that
some of the water is decomposed, and the hydro-
gen gas thereby formed carries off some minute
particles of phosphorus, with which it forms phos-
PHOSPHORUS. 281
phoretted hydrogen gas, a compound which spon-
taneously takes fire at almost any temperature.
EMILY.
What is that circular ring of smoke which slowly
rises from each bubble after its detonation.
MRS. B.
It consists of water and phosphoric acid in va-
pour, which are produced by the combustion of
hydrogen and phosphorus.
( 282 )
CONVERSATION IX.
ON CARBON,
CAROLINE.
1 O-DAY, Mrs. B., I believe we are to learn
the nature and properties of CARBON. This sub-
fetance is quite new to me ; I never heard it men-
tioned before.
MRS. B.
Not so new as you imagine ; for carbon is no-
thing more than charcoal in a state of purity, that is
to say, unmixed with any foreign ingredients.
CAROLINE.
But charcoal is made by art, Mrs. B., and a
body consisting of one simple substance cannot be
fabricated?
MRS. B.
You again confound the idea, of making a sim-
ple body, with that of separating it from a com-
pound. The chemical processes by which a sim-
ple body is obtained in a state of purity, consist in
unmaking the compound in which it is contained,
CARBON. 283
in order to separate from it the simple substance
in question. The method by which charcoal is
usually obtained, is, indeed, commonly called
making it; but, upon examination, you will find
this process to consist simply in separating it from
other substances with which it is found combined
in nature.
Carbon forms a considerable part of the solid
matter of all organised bodies ; but it is most
abundant in the vegetable creation, and it is chiefly
obtained from wood. When the oil and water
(which are other constituents of vegetable matter)
are evaporated, the black, porous, brittle sub-
stance that remains, is charcoal.
CAROLINE.
But if heat be applied to the wood in order to
evaporate the oil and water, will not the tempe-
rature of the charcoal be raised so as to make it
burn ; and if it combines with oxygen, can we any
longer call it pure ?
MRS. B.
1 was going to say, that, in this operation, the
air must be excluded.
CAROLINE.
How then can the vapour of the oil and water
fly off?
MRS. B.
In order to produce charcoal in its purest state 4
(which is, even then, but a less imperfect sort of
carbon), the operation should be performed in an
earthen retort. Heat being applied to the body
of the retort, the evaporable part of the wood will
escape through its neck, into which no air can
penetrate as long as the heated vapour continues
to fill it. And if it be wished to collect these
volatile products of the wood, this can easily be
done by introducing the neck of the retort into the
water-bath apparatus, with which you are ac-
quainted. But the preparation of common char-
coal, such as is used in kitchens and manufactures*
is performed on a much larger scale, and by an
easier and less expensive process.
EMILY.
I have seen the process of making common
charcoal. The wood is ranged on the ground in
a pile of a pyramidical form, with a fire under-
neath ; the whole is then covered with clay, a few
holes only being left for the circulation of air.
MRS. B.
These holes are closed as soon as the wood is
fairly lighted, so that the combustion is checked,
or at least continues but in a very imperfect man-
ner; but the heat produced by it is sufficient to
CARBON. 285
force out and volatilize, through the earthy cover,
most part of the oily and watery principles of the
wood, although it cannot reduce it to ashes.
EMILY.
Is pure carbon as black as charcoal ?
MRS. B.
The purest charcoal we can prepare is so ; but
chemists have never yet been able to separate it
entirely from hydrogen. Sir H. Davy says, that
the most perfect carbon that is prepared by art
contains about five per cent, of hydrogen ; he is
of opinion, that if we could obtain it quite free
from foreign ingredients, it would be metallic, in
common with other simple substances.
But there is a form in which charcoal appears,
that I dare say will surprise yon. This ring,
which I wear on my finger, owes its brilliancy to
a small piece of carbon.
CAROLINE.
Surely, you are jesting, Mrs. B. ?
EMILY.
I thought your ring was diamond ?
MRS.B.
It is so. But diamond is nothing more than
carbon in a crystallized state.
286 CARBON.
EMILY.
That is astonishing ! Is it possible to see two
things apparently more different than diamond
and charcoal ?
CAROLINE.
It is, indeed, curious to think that we adorn our-
selves with jewels of charcoal !
MRS. B.
There are many other substances, consisting
chiefly of carbon, that are remarkably white. Cot-
ton, for instance, is almost wholly carbon.
CAROLINE.
That, I own, I could never have imagined !
But pray, Mrs. B., since it is known of what
substance diamond and cotton are composed, why
should they not be manufactured, or imitated, by
some chemical process, which would render them
much cheaper, and more plentiful than the present
mode of obtaining them ?
B*
You might as well, my dear, propose that we
should make flqj^rs and fruit, nay, perhaps even
animals, by a chemical process; for it is known
of what these bodies consist, since every thing
which we are acquainted with in nature is formed
from the various simple substances that we have
CARBON. 287
enumerated. But you must not suppose that a
knowledge of the component parts of a body will
in every case enable us to imitate it. It is much
less difficult to decompose bodies, and discover of
what materials they are made, than it is to recom-
pose them. The first of these processes is called
analysis, the last synthesis. When we are able to
ascertain the nature of a substance by both these
methods, so that the result of one confirms that of
the other, we obtain the most complete knowledge
of it that we are capable of acquiring. This is
the case with water, with the atmosphere, with
most of the oxyds, acids, and neutral salts, and
with imny other compounds. But the more com-
plicated combinations of nature, even in the mi-
neral kingdom, are in general beyond our reach,
and any attempt to imitate organised bodies must
ever -prove fruitless; their formation is a secret
that rests in the bosom of the Creator. You see,
therefore, how vain it would be to attempt to
make cotton by chemical means. But, surely, we
have no reason to regret our inability in this in-
stance, when nature has so clearly pointed out a
method of obtaining it in perfection and abundance.
CAROLINE.
I did not imagine that the principle of life could
be imitated by the aid of chemistry; but it did not
appear 4o me ridiculous to suppose that chemists
288 CARBON,
might attain a perfect imitation of inanimate
nature.
MRS. B.
They have succeeded in this point in a variety
of instances; but, as you justly observe, the prin-
ciple of life, or even the minute and intimate or-
ganisation of the vegetable kingdom, are secrets
that have almost entirely eluded the researches of
philosophers; nor do I imagine that human art
will ever be capable of investigating them with
complete success.
EMILY.
But diamond, since it consists of one simple un-
organised substance, might be, one would think,
perfectly imitable by art ?
MRS. B.
It is sometimes as much beyond our power to
obtain a simple body in a state of perfect purity, as
jit is to imitate a complicated combination ; for the
operations by which nature separates bodies are
frequently as inimitable as those which she uses for
their combination. This is the case with carbon ;
all the efforts of chemists to separate it entirely
from other substances have been fruitless, and in
the purest state in which it can be obtained by art,
it still retains a portion of hydrogen, and probably
of some other foreign ingredients. We are igno-
CARBON. 289
rant of the means which nature employs to crystallize
it. It may probably be the work of ages, to purify,
arrange, and unite the particles of carbon in the
form of diamond. Here is some charcoal in the
purest state we can procure it : you see that it is a
very black, brittle, light, porous substance, entirely
destitute of either taste or smell. Heat, without
air, produces no alteration in it, as it is not volatile ;
but, on the contrary, it invariably remains at the
bottom of the vessel after all the other parts of the
vegetable are evaporated.
EMILY.
Yet carbon is, no doubt, combustible, since you
say that charcoal would absorb oxygen if air were
admitted during its preparation ?
CAROLINE.
Unquestionably. Besides, you know, Emily,
how much it is used in cooking. But pray what
is the reason that charcoal burns without smoke,
whilst a wood fire smokes so much?
MRS. B.
Because, in the conversion of wood into char-
coal, the volatile particles of the former have been
evaporated.
CAROLINE.
Yet I have frequently seen charcoal burn with
TOL. J. o
290 CARBON.
flame ; therefore it must, in that case, contain some
hydrogen.
MRS. B.
Very true; but you must recollect that char-
coal-, especially that which is used for common
purposes, is not perfectly pure. It generally re-
tains some remains of the various other component
parts of vegetables, and hydrogen particularly,
which accounts for the flame in question.
CAROLINE.
But what becomes of the carbon itself during its
combustion ?
MRS. B.
It gradually combines with the oxygen .of the
atmosphere, in the same way as sulphur and phos-
phorus, and, like those substances, it is converted
into a peculiar acid, which flies off in a gaseous
form. There is this difference, however, that the
acid is not, in this instance, as in the two cases just
mentioned, a mere condensable vapour, but a per-
manent elastic fluid, which always remains in the
state of gas, under any pressure and at any tem-
perature. The nature of this acid was first ascer-
tained by Dr. Black, of Edinburgh ; and, before
the introduction of the new nomenclature, it was
called Jixed air. It is now distinguished by the
snore appropriate name of carbonic acid gas.
CARBON. 291
EMILY.
Carbon, then, can be volatilized by burning,
though, by heat alone, no such effect is produced ?
MRS. B.
Yes; but then it is no longer simple carbon, but
an acid of which carbon forms the basis. In this
state, carbon retains no more appearance of solidity
or corporeal form, than the basis of any other gas.
And you may, I think, from this instance, derive
a more clear idea of the basis of the oxygen, hydro-
gen, and nitrogen gases, the existence of which, as
real bodies, you seemed to doubt, because they were
not to be obtained simply in a solid form.
EMILY.
That is true ; we may conceive the basis of the
oxygen, and of the other gases, to be solid, heavy
substances, like carbon ; but so much expanded by
caloric as to become invisible.
CAROLINE.
But does not the carbonic acid gas partake of the
blackness of charcoal ?
MRS. B.
Not iii the least. Blackness, you know, does not
appear to be essential to carbon, and it is pure
carbon, and not charcoal, that we must consider
o 2
292 CARBON.
as the basis of carbonic acid. We shall make some
carbonic acid, and, in order to hasten the process,
we shall burn the carbon in oxygen gas.
EMILY.
But do you mean then to burn diamond ?
MRS. B.
Charcoal will answer the purpose still better,
being softer and more easy to inflame ; besides the
experiments on diamond are rather expensive.
CAROLINE. ,
But is it possible to burn diamond ?
MRS. B.
Yes, it is ; and in order to effect this combustion,
nothing more is required than to apply a sufficient
degree of heat by means of the blow-pipe, and of
a stream of oxygen gas. Indeed it is by burning
diamond that its chemical nature has been ascer-
tained. It has long been known as a combustible
substance, but it is within these few years only that
the product of its combustion has been proved to
be pure carbonic acid. This remarkable discovery
is due to Mr. Tennant.
Now let us try to make some carbonic acid.
Will you, Emily, decant some oxygen gas from
this large jar into the receive* in which we are to
CARBON. 293
bnrn the carbon ; and I shall introduce this small
piece of charcoal, with a little lighted tinder, which
will be necessary to give the first impulse to the
combustion.
EMILY.
I cannot conceive how so small a piece of tinder,
and that but just lighted, can raise the temperature
of the carbon sufficiently to set fire tojt; for it can
produce scarcely any sensible heat, and it hardly
touches the carbon.
MRS. B.
The tinder thus kindled has only heat enough
to begin its own combustion, which, however, soon
becomes so rapid in the oxygen gas, as to raise the
temperature of the charcoal sufficiently for this to
burn likewise, as you see is now the case.
EMILY.
I am surprised that the combustion of carbon is
not more brilliant ; it does not give out near so
much light or caloric as phosphorus, or sulphur.
Yet since it combines with so much oxygen, why
is not a proportional quantity of light and heat
disengaged from the decomposition of the oxygen
gas, and the union of its electricity with that of the
charcoal ?
MRS. B.
It is not surprising that less light and heat should
be liberated in this than in almost any other com-
o 3
294 CARBON,
bustion, since the oxygen, instead of entering into
a solid or liquid combination, as it does in the
phosphoric and sulphuric acids, is employed in
forming another elastic fluid; it therefore parts with
less of its caloric.
EMILY.
True ; and, on second consideration, it appears,
on the contrary, surprising that the oxygen should,
in its combination with carbon, retain a sufficient
portion of caloric to maintain both substances in a
gaseous state.
CAROLINE.
We may then judge of the degree of solidity in
which oxygen is combined in a burnt body, by the
quantity of caloric liberated during its combustion ?
MRS. B.
Yes; provided that you take into the account
the quantity of oxygen absorbed by the combusti-
ble body, and observe the proportion which the
caloric bears to it.
CAROLINE.
But why should the water, after the combustion
of carbon, rise in the receiver, since the gas within
it retains an aeriform state ?
MRS. B.
Because the carbonic acid gas is gradually ab-
CARBON. 295
Sorbed by the water ; and this effect would be pro-
moted by shaking the receiver.
EMILY.
The charcoal is now extinguished, though it is
not nearly consumed ; it has such an extraordinary
avidity for oxygen, I suppose, that the receiver did
not contain enough to satisfy the whole.
MRS. B.
That is certainly the case ; for if the combustion
were performed in the exact proportions of 28
parts of carbon to 72 of oxygen, both these in-
gredients would disappear, and 100 parts of car-
bonic acid would be produced.
CAROLINE.
Carbonic acid must be a very strong acid, since
it contains so great a proportion of oxygen ?
MRS. B.
That is a very natural inference ; yet it is erro-
neous. For the carbonic is the weakest of all the
acids. The strength of an acid seems to depend
upon the nature of its basis, and its mode of com-
bination, as well as upon the proportion of the
acidifying principle. The same quantity of oxygen
that will convert some bodies into strong acids, will
only be sufficient simply to oxydate others,
o 4
2J)6 CARBON.
CAROLINE,
Since this acid is so weak, I think chemists
should have called it the carbonous, instead of the
carbonic acid.
EMILY.
But, I suppose, the carbonous acid is still weaker,
and is formed by burning carbon in atmospherical
air.
MRS. B.
It has been lately discovered, that carbon may be
converted into a gas, by uniting with a smaller pro-
portion of oxygen ; but as this gas does not possess
any acid properties, it is no more than an oxyd j it
is called gaseous oxyd of carbon.
CAR.OMNE.
Pray is not carbonic acid a very wholesome gas
to breathe, as k contains so much oxygen ?
MRS. B.
On the contrary, it is extremely pernicious.
Ofcygen, when in a state of combination with other
substances, lose*, in almost every instance, its
respirable properties, and the salubrious effects
which it has on the animal economy when in its
unconfined state. Carbonic acid is not only unfit
for respiration, but extremely deleterious if taken
into the lungs.
CARBON. 297
EMILY.
You know, Caroline, how very unwholesome the
fumes of burning charcoal are reckoned.
CAROLINE.
Yes ; but, to confess the truth, I did not con-
sider that a charcoal fire produced carbonic acid
gas. Can this gas be condensed into a liquid ?
i
MRS. B.
No : for, as I told you before, it is a permanent
elastic fluid. But water can absorb a certain
quantity of this gas, and can even be impregnated
with it, in a very strong degree, by the assistance
of agitation and pressure, as I am going to show
you. I shall decant some carbonic acid gas into
this bottle, which I fill first with water, in order to
exclude the atmospherical air ; the gas is then in-
troduced through the water, which you see it dis-
places, for it will not mix with it in any quantity,
unless strongly agitated, or allowed to stand over it
for some time. The bottle is now about half full of
carbonic acid gas, and the other half is still occupied
by the water. By corking the bottle, and then
violently shaking it, in this way, I can mix the gas
and water together. Now will you taste it ?
EMILY.
It has a distinct acid taste.
O 5
CARBON.
CAROLINE.
Yes, it is sensibly sour, and appears full of little
bubbles.
MRS. B.
It possesses likewise all the other properties of
acids, but, of course, in a less degree than the pure
carbonic acid gas, as it is so much diluted by water.
This is a kind of artificial Seltzer water. By
analysing that which is produced by nature, it
was found to contain scarcely any thing more than
common water impregnated with a certain pro-
portion of carbonic acid gas. We are, therefore,
able to imitate it, by mixing those proportions of
water and carbonic acid. Here, my dear, is an
instance, in which, by a chemical process, we can
exactly copy the operations of nature; for the
artificial Seltzer waters can be made in every respect
similar to those of nature ; in one point, indeed,
the former have an advantage, since thay may be
prepared stronger, or weaker, as occasion requires.
CAROLINE.
I thought 1 had tasted such water before. But
what renders it so brisk and sparkling ?
MRS. B.
This sparkling, or effervescence, as it is called,
is always occasioned by the action of an elastic
fluid escaping from a liquid; in the artifical Selt-
CARBON. 2.99
"Zer water, it is produced by the carbonic acid,
which being lighter than the water in which it
was strongly condensed, flies off with great ra-
pidity the instant the bottle is uncorked; this
makes it necessary to drink it immediately. The
bubbling that took place in this bottlt- was but
trifling, as the water was but very slightly im-
pregnated with carbonic acid. It requires a par-
ticular apparatus to prepare the gaseous artificial
mineral waters.
EMILY.
If, then, a bottle of Seltzer water remains for
any length of time uncorked, I suppose it returns
to the state of common water ?
MRS. B.
The whole of the carbonic acid gas, or very
nearly so, will soon disappear ; but there is like-
wise in Seltzer water a very small quantity of
soda, and of a few other saline or earthy ingre-
dients, which will remain in the water, though it
should be kept uncorked for any length of time.
CAROLINE.
I have often heard of people drinking soda-
water. Pray what sort of water is that ?
MRS. B.
It is a kind of artificial Seltzer water, holding
o 6
300 CARBON.
in solution, besides the gaseous acid, a particular
saline substance, called soda, which imparts to the
water certain medicinal qualities.
CAROLINE.
But how can these waters be so wholesome, since
carbonic acid is so pernicious ?
MRS. B.
A gas, We may Conceive, though very prejudicial
to breathe, may be beneficial to the stomach.
But it would be of no use to attempt explaining
this more fully at present.
CAROLINE,
Are waters never impregnated with other gases ?
MRS. B.
Yes ; there are several kinds of gaseous waters*
1 forgot to tell you that waters have, for som6
years past, been prepared, impregnated both with
oxygen and hydrogen gases. These are not an
imitation of nature, but are altogether obtained
by artificial means. They have been lately used
medicinally, particularly on the continent, where,
J understand, they have acquired some reputa-
tion.
EMILY.
If I recollect right, Mrs. B., you told us that
7
Apparatus for the combustion of
metals by Tneans of oxygen gas .
, Ljnctitig ,/i,ii ,,'.!/ with, a, -taper & blvw-pipc. __ "big. 2, Combustion of mchds by
A T>l0w-pipe, convey inq a stream of lucygen qa* jhwt, a ytw holder.
of
CARBON. 301
carbon was capable of decomposing water; the
affinity between oxygen and carbon must, there-
fore, be greater than between oxygen and hy-
drogen ?
MRS. B.
Yes ; but this is not the case unless their tem-
perature be raised to a certain degree. It is only
when carbon is red-hot, that it is capable of sepa-
rating the oxygen from the hydrogen. Thus, if
a small quantity of water be thrown on a red-hot
fire, it will increase rather than extinguish the
combustion ; for the coals or wood (both of which
contain a quantity of carbon) decompose the wa-
ter, and thus supply the fire both with oxygen
and hydrogen gases. If, on the contrary, a large
mass of water be thrown over the fire, the dimi-
nution of heat thus produced is such, that the com-
bustible matter loses the power of decomposing the
water, and the fire is extinguished.
EMILY.
I have heard that fire-engines sometimes do
more harm than good, and that they actually in-
crease the fire when they cannot throw water
enough to extinguish it. It must be owing, no
doubt, to the decomposition of the water by the
carbon during the conflagration.
302 CARBON.
MRS. B.
Certainly. The apparatus which you see
(PLATE XI. fig. 3.), may be used to exemplify
what we have just said. It consists in a kind of
open furnace, through which a porcelain tube,
containing charcoal, passes. To one end of the
tube is adapted a glass retort with water in it;
and the Other end communicates with a receiver
placed on the water-bath. A lamp being applied
to the retort, and the water made to boil, the va-
pour is gradually conveyed through the red-hot
charcoal, by which it is decomposed ; and the
hydrogen gas which results from this decomposi-
tion is collected in the receiver. But the hydro-
gen thus obtained is far from being pure; it re-
tains in solution a minute portion of carbon, and
contains also a quantity of carbonic acid. This
renders it heavier than pure hydrogen gas, and
gives it some peculiar properties; it is distin-
guished by the name of carbonated hydrogen
gas.
CAROLINE.
And whence does it obtain the carbonic acid
-that is mixed with it ?
EMILY.
I believe I can answer that question, Caroline,
From the union of the oxygen (proceeding from
CARBON. 303
the decomposed water) with the carbon, which,
you know, makes carbonic acid.
CAROLINE.
True ; I should have recollected that. The
product of the decomposition of water by red-hot
charcoal, therefore, is carbonated hydrogen gas,
and carbonic acid gas.
MRS. B.
You are perfectly right now.
Carbon is frequently found combined with hy-
drogen in a state of solidity, especially in coals,
which owe their combustible nature to these two
principles.
EMILY.
Is it the hydrogen, then, that produces the
flame of coals?
MRS. B.
It is so ; and when all the hydrogen is consum-
ed, the carbon continues to burn without flame.
But again, as I mentioned when speaking of the
gas-lights, the hydrogen gas produced by the
burning of coals is not pure ; for, during the com-
bustion, particles of carbon are successively vola-
tilized with the hydrogen, with which they form
what is called a hydro-carbonat, which is the prin-
cipal product of this combustion.
Carbon is a very bad conductor of heat; for
304 CARBON.
this reason, it is employed (in conjunction with
other ingredients) for coating furnaces and other
chemical apparatus.
EMILY.
Pray what is the use of coating furnaces ?
MRS. B.
In most cases, in which a furnace is used, it is
necessary to produce and preserve a great degree
of heat, for which purpose every possible means
are used to prevent the heat from escaping by
communicating with other bodies, and this object
is attained by coating over the inside of the fur-
nace with a kind of plaster, composed of materials
that are bad conductors of heat.
Carbon, combined with a small quantity of iron,
forms a compound called plumbago, or black-lead,
of which pencils are made. This substance, agree-
ably to the nomenclature, is a carburet of iron.
EMILY.
Why, then, is it called black-lead ?
MRS. B.
It is an ancient name given to it by ignorant
people, from its shining metallic appearance ; but
it is certainly a most improper name for it, as
there is not a particle of lead in the composition ,
CARBON. 305
There is only one mir,e of this mineral, which is
in Cumberland. It is supposed to approach as
nearly to pure carbon as the best prepared char-
coal does, as it contains only five parts of iron,
unadulterated by any other foreign ingredients.
There is another carburet of iron, in which the
iron, though united only to an extremely small
proportion of carbon, acquires very remarkable
properties ; this is steel.
CAROLINE.
Really ; and yet steel is much harder than iron ?
MRS. B.
But carbon is not ductile like iron, and there-
fore may render the steel more brittle, and pre-
vent its bending so easily. Whether it is that the
carbon, by introducing itself into the pores of the
iron, and, by filling them, makes the metal both
harder and heavier; or whether this change de-
pends upon some chemical cause, I cannot pre-
tend to decide. But there is a subsequent opera-
tion, by which the hardness of steel is very much
increased, which simply consists in heating the
steel till it is red-hot, and then plunging it into
cold water.
Carbon, besides the combination just mention-
ed, enters into the composition of avast number
of natural productions, such, for instance, as all
306
CARBON.
the various kinds of oils, which result from the
combination of carbon, hydrogen, and caloric, in
various proportions.
EMILY.
I thought that carbon, hydrogen, and caloric,
formed carbonated hydrogen gas ?
MRS. B.
That is the case when a small portion of car-
bonic acid gas is held in solution by hydrogen gas.
Different proportions of the same principles, to-
gether with the circumstances of their union, pro-
duce very different combinations ; of this you will
see innumerable examples. Besides, we are not
now talking of gases, but of carbon and hydro-
gen, combined only with a quantity of caloric
sufficient to bring them to the consistency of oil
or fat.
CAROLINE.
But oil and fat are not of the same consistence ?
MRS. B.
Fat is only congealed oil; or oil, melted fat.
The one requires a little more heat to maintain it
in a fluid state than the other. Have you never
observed the fat of meat turned to oil by the ca-
loric it has imbibed from the fire ?
CARBON. 307
EMILY.
Yet oils in general, as salad-oil, and lamp-oil, do
not turn to fat when cold ?
MRS. B.
Not at the common temperature of the atmo-
sphere, because they retain too much caloric to
congeal at that temperature; but if exposed to a
sufficient degree of cold, their latent heat is ex-
tricated, and they become solid fat substances.
Have you never seen salad oil frozen in winter ?
EMILY.
Yes ; but it appears to me in that state very dif-
ferent from animal fat.
MRS. B.
The essential constituent parts of either vege-
table or animal oils are the same, carbon and hy-
drogen ; their variety arises from the different
proportions of these substances, and from other
accessory ingredients that may be mixed with
them. The oil of a whale, and the oil of roses,
are, in their essential constituent parts, the same;
but the one is impregnated with the offensive par-
ticles of animal matter, the other with the deli-
cate perfume of a flower.
The difference ofjixed oils, and volatile or essen-
tial oils, consists also in the various proportions of
carbon and hydrogen. Fixed oils are those which
308 CARBON.
will not evaporate without being decomposed j
this is the case with all common oils, which
contain a greater proportion of carbon than the
essential oils. The essential oils (which compre-
hend the whole class of essences and perfumes)
are lighter ; they contain more equal proportions
of carbon and hydrogen, and are volatilized or
evaporated without being decomposed.
EMILY.
When you say that one kind of oil will evapo-
rate, and the other be decomposed, you mean, I
suppose, by the application of heat ?
MRS. B. '
Not necessarily ; for there are oils that will eva-
porate slowly at the common temperature of the
atmosphere ; but for a more rapid volatilization, or
for their decomposition, the assistance of heat is
required.
CAROLINE.
I shall now remember, I think, that fat and oil
are really the same substance's, both consisting of
carbon and hydrogen ; that in fixed, oils the car-
bon preponderates, and heat produces a decom-
position ; while, in essential oils, the proportion of
hydrogen is greater, and heat produces a volatili-
zation only.
EMILY.
I suppose the reason why oil burns so well in
CARBON. 309
lamps is because its two constituents are so com-
bustible ?
MRS. B.
Certainly ; the combustion of oil is just the same
as that of a candle ; if tallow, it is only oil in a con-
crete state ; if wax, or spermaceti, its chief chemi-
cal ingredients are still hydrogen and carbon.
EMILY.
I wonder, then, there should be so great a dif-
ference between tallow and wax ?
MRS. B. %
I must again repeat, that the same substances,
in different proportions, produce results that
have sometimes scarcely any resemblance to each
other. But this is rather a general remark that I
wish to impress upon your minds, than one which
is applicable to the present case ; for tallow and
wax are far from being very dissimilar; the chief
difference consists in the wax being a purer com-
pound of carbon and hydrogen than the tallow,
which retains more of the gross particles of animal
matter. The combustion of a candle, and that of
a lamp, both produce water and carbonic acid gas.
Can you tell me how these are formed?
EMILY.
Let me reflect .... Both the candle and lamp
310 CARBON.
burn by means of fixed oil this is decomposed as
the combustion goes on ; and the constituent parts
of the oil being thus separated, the carbon unites
to a portion of, oxygen from the atmosphere to
form carbonic acid gas, whilst the hydrogen com-
bines with another portion of oxygen, and forms
with it water. The products, therefore, of the
combustion of oils are water and carbonic acid
CAROLINE.
But we see neither water nor carbonic acid pro-
duced by the combustion of a candle.
MRS. B.
The carbonic acid gas, you know, is invisible,
and the water being in a state of vapour, is so like-
wise. Emily is perfectly correct in her explana-
tion, and I am very much pleased with it.
All the vegetable acids consist of various pro-
portions of carbon ( and hydrogen, acidified by
oxygen. Gums, sugar, and starch, are likewise
composed of these ingredients ; but, as the oxygen
which they contain is not sufficient to convert them
into acids, they are classed with the oxyds, and
called vegetable oxyds.
CAROLINE.
I am very much delighted with all these new
M
CARBON. 311
ideas ; but, at the same time, I cannot help being
apprehensive that I may forget many of them.
MRS. B.
I would advise you to take notes, or, what would
answer better still, to write down, after every lesson,
as much of it as you can recollect. And, in order
to give you a little assistance, I shall lend you the
heads or index, which 1 occasionally consult for
the sake of preserving some method and arrange-
ment in these conversations. Unless you follow
some such plan, you cannot expect to retain nearly
all that you learn, how great soever be the impres-
sion it may make on you at first.
EMILY.
I will certainly follow your advice. Hitherto
I have found that I recollected pretty well what
you have taught us ; but the history of carbon is
a more extensive subject than any of the simple
bodies we have yet examined.
MRS. B.
I have little more to say on carbon at present ,*
but hereafter you will see that it performs a con-
siderable part in most, chemical operations.
CAROLINE.
That is, I suppose, owing to its entering into
312 CARBON.
the composition of so great a variety of sub-
stances ?
MRS. B.
Certainly ; it is the basis, you have seen, of all
vegetable matter ; and you will find that it is very
essential to the process of animalization. But in
the mineral kingdom also, particularly in its forra
of carbonic acid, we shall often discover it com-
bined with a great variety of substances.
In chemical operations, carbon is particularly
useful, from its very great attraction for oxygen,
as it will absorb this substance from many oxyge-
nated or burnt bodies, and thus deoxygenjrte,
or unburn them, and restore them to their original
combustible state.
CAROLINE.
I do not understand how a body can be unburnt,
and restored to its original state. This piece of
tinder, for instance, that has been burnt, if by
any means the oxygen were extracted from it,
would not be restored to its former state of linen ;
for its texture is destroyed by burning, and that
must be the case with all organized or manufac-
tured substances, as you observed in a former con*
versation.
MRS. B.
A compound body is decomposed by combus-
tion in a way which generally precludes the pos-
CARBON. 313
sibility of restoring it to its former state; the
oxygen, for instance, does not become fixed in
the tinder, but it combines with its volatile parts,
and flies off in the shape of gas, or watery vapour.
You see, therefore, how vain it would be to at-
tempt the recomposition of such bodies. But,
with regard to simple bodies, or at least bodies
whose component parts are not disturbed by the
process of oxygenation or deoxygenation, it is often
possible to restore them, after combustion, to their
original state. The metals, for instance, undergo
no other alteration by combustion than a combina-
tion with oxygen ; therefore, when the oxygen is
taken from them, they return to their pure metallic
state. But I shall say nothing further of this at
present, as the metals will furnish ample subject for
another morning ; and they are the class of simple
bodies that come next under consideration.
VOL. i.
CONVERSATION X,
ON METALS.
MRS. B.
J HE METALS, which we are now to examine,
are bodies of a very different nature from those
which we have hitherto considered. They do not,
like the bases of gases, elude the Immediate ob-
servation of our senses; for they are the most
brilliant, the most ponderous, and the most pal-
pable substances in nature.
CAROLINE.
I doubt, however, whether the metals will appear
to us so interesting, and give us so much entertain-
ment as those mysterious elements which conceal
themselves from our view. Besides, they cannot
afford so much novelty ; they are bodies with which
we are already so well acquainted.
MRS. B.
You are not aware, my dear, of the interesting
discoveries which were a few years ago made by
Sir H. Davy respecting this class of bodies. By
the aid of the Voltaic battery, he has obtained from
METALS. 315
a variety of substances, metals before unknown, the
properties of which are equally new and curious.
We shall begin, however, by noticing those metals
with which you profess to be so well acquainted.
But the acquaintance, you will soon perceive, is but
very superficial; and I trust that you will find
both novelty and entertainment in considering the
metals in a chemical point of view. To treat of
this subject fully, would require a whole course of
lectures; for metals form of themselves a most
important branch of practical chemistry. We
must, therefore, confine ourselves to a general
view of them. These bodies are seldom found
naturally in their metallic form : they are gene-
rally more or less oxygenated or combined with
sulphur, earths, or acids, and are often blended
with each other. They are found buried in the
bowels of the earth in most parts of the world,
but chiefly in mountainous districts, where the
surface of the globe has suffered from the earth-
quakes, volcanos, and other convulsions of nature.
They are spread in strata or beds, called veins,
and these veins are composed of a certain quantity
of metal, combined with various earthy substances,
with which they form minerals of different nature
and appearance, which are called ares.
CAROLINE.
I now feel quite at home, for my father has
p 2
316 METALS.
a lead-mine in Yorkshire, and I have heard a
great deal about veins of ore, and of the roast-
ing and smelting of the lead ; but, 1 confess, that
I do not understand in what these operations
consist.
MRS. B.
Roasting is the process by which the volatile
parts of the ore are evaporated ; smelting, that
by which the pure metal is afterwards separated
from the earthy remains of the ore. This is. done
by throwing the whole into a furnace, and mixing
with it certain substances that will combine with
the earthy parts and other foreign ingredients of
the ore ; the metal being the heaviest, falls to the
bottom, and runs out by proper openings in its
pure metallic state.
EMILY.
You told us in a preceding lesson that metals
had a great affinity for oxygen. Do they not,
therefore, combine with oxygen, when strongly
heated in the furnace, and ran out in the state of
oxyds ?
MRS. B.
No ; for the scoriae, or oxyd, which soon forms
on the surface of the fused metal, when it is oxyd-
able, prevents the air from having any further in-
fluence on the mass; so that neither combustion
Aor oxygenation can take place.
METALS. 317
CAROLINE.
Are all the metals equally combustible ?
MRS. B.
No ; their attraction for oxygen varies extremely.
There are some that will combine with it only
at a very high temperature, or by the assistance
of acids ; whilst there are others that oxydate spon-
taneously and with great rapidity, even at the lowest
temperature; such is in particular manganese,
which scarcely ever exists in the metallic state, as
it immediately absorbs oxygen on being exposed
to the air, and crumbles to an oxyd in the course
of a few hours.
EMILY.
Is not that the oxyd from which you extracted
the oxygen gas ?
MRS. B.
It is : so that, you see, this metal attracts
oxygen at a low temperature, and parts with it
when strongly heated.
EMILY.
Is there any other metal that oxydates at the
temperature of the atmosphere ?
MRS. B.
They all do, more or less, excepting gold, silver,
and platina.
p 3
318 METALS.
Copper, lead, and iron, oxydate slowly in the
air, and cover themselves with a sort of rust, a
process which depends on the gradual conversion
of the surface into an oxyd. This rusty surface
preserves the interior metal from oxydation, as it
prevents the air from coming in contact with it.
Strictly speaking, however, the word rust applies
only to the oxyd, which forms on the surface of
iron, when exposed to air and moisture, which
oxyd appears to be united with a small portion of
carbonic acid.
TZMTT.V.
When metals oxydate from the atmosphere
without an elevation of temperature, some light
and heat, I suppose, must be disengaged, though
not in sufficient quantities lo be sensible.
MRS. B.
Undoubtedly ; and, indeed, it is not surprising
that in this case the light and heat should not be
sensible, when you consider how extremely slow,
and, indeed, how imperfectly, most metals oxydate
by mere exposure to the atmosphere. For the
quantity of oxygen with which metals are capable
of combining, generally depends upon their tem-
perature ; and the absorption stops at various points
of oxydation, according to the degree to which
their temperature is raised.
MEfALS. 319
EMILY.
That seems very natural ', for the greater the .
quantity of caloric introduced into a metal, the
more will its positive electricity be exalted, and
consequently the stronger will be its affinity for
oxygen.
MRS. B.
Certainly. When the metal oxygenates with
sufficient rapidity for light and heat to become
sensible, combustion actually takes place. But
this happens only at very high temperatures, and
the product is nevertheless an oxyd ; for though,
as I have just said, metals will combine with -dif-
ferent proportions of oxygen, yet with the excep-
tion of only five of them, they are not susceptible
of acidification.
Metals change colour during the different de-
grees of oxydation which they undergo. Lead,
when heated in contact with the atmosphere, first
becomes grey ; if its temperature be then raised, it
turns yellow, and a still stronger heat changes it
to red. Iron becomes successively a green, brown,
and white oxyd. Copper changes from brown to
blue, and lastly green.
EMILY.
Pray, is the white lead with which houses are
painted prepared by oxydating lead ?
p 4
320 METALS.
MRS. B.
Not merely by oxydating, but by being also
united with carbonic acid. It is a carbonat of
lead. The mere oxyd of lead is called red lead.
Litharge is another oxyd of lead, containing less
oxygen. Almost all the metallic oxyds are used
as paints. The various sorts of ochres consist
chiefly of iron more or less oxydated. And it is a
remarkable circumstance, that if you burn metals
rapidly, the light or flame they emit during com-
bustion partakes of the colours which the oxyd
successively assumes.
CAROLINE.
How is that accounted for, Mrs. B. ? For light,
you know, does not proceed from the burning body,
but from the decomposition of the oxygen gas ?
MRS. B.
The correspondence of the colour of the light
with that of the oxyd which emits it, is, in all pro-
bability, owing to some particles of the metal which
are volatilised and carried off by the caloric.
CAROLINE.
It is then a sort of metallic gas.
EMILY.
Why is it reckoned so unwholesome to breathe
tire air of a place in which metals are melting ?
METALS, 321
MRS. B.
Perhaps the notion is too generally entertained.
But it is true with respect to lead, and some other
noxious metals, because, unless care be taken, the
particles of the oxyd which are volatilised by the
heat are inhaled in with the breath, and may pro-
duce dangerous effects.
I must show you some instances of the combus-
tion of metals; it would require the heat of a fur-
nace to make them burn in the common air, but
if we supply them with a stream of oxygen gas, we
may easily accomplish it.
CAROLINE.
But it will still, I suppose, be necessary in some
degree to raise their temperature ?
MRS. B.
This, as you shall see, is very easily done, parti-
cularly if the experiment be tried upon a small
scale. I begin by lighting this piece of charcoal
with the candle, and then increase the rapidity of
of its combustion by blowing upon it with a blow-
pipe. (PLATE XII. fig. 1.)
That I do not understand ; for it is not every
kind of air, but merely oxygen gas, that produces
combustion. Now you said that in breathing we
p 5
322 METALS.
inspired, but did not expire oxygen gas. Why,
therefore, should the air which you breathe
through the blow-pipe promote the combustion
of the charcoal ?
MRS. B.
Because the air, which has but once passed
through the lungs, is yet but little altered, a small
portion only of its oxygen being destroyed; so
that a great deal more is gained by increasing the
rapidity of the current, by means of the blow-
pipe, than is lost in consequence of the air passing
once through the lungs, as you shall see
EMILY.
Yes, indeed, it makes the charcoal burn much
brighter.
MRS. B.
"Whilst it is red-hot, I shall drop some iron
filings on it, and supply them with a current of
oxygen gas, by means of this apparatus, . PLATE
XII. fi# 2.) which consists simply of a closed tin
cylindrical vessel, full of oxygen gas, with two
apertures and stop-cocks, by one of /which a stream
of water is thrown into the vessel through a long
funnel, whilst by the other the gas is forced out
through a blow-pipe adapted to it, as the water
gains admittance. Now that I pour water into
the funnel, you may hear the gas issuing from the
1.6
METALS. 323
blow-pipe I bring the charcoal close to the cur-
rent, and drop the filings upon it -^
CAROLINE.
They emit much the same vivid light as the com-
bustion of the iron wire in oxygen gas.
MRS. B.
The process is, in fact, the same ; there is only
some difference in the mode of conducting it. Let
us burn some tin in the same manner you see
that it is equally combustible. Let us now try
some copper
CAROLINE.
This burns with a greenish flame; it is, I sup-
pose, owing to the colour of the oxyd 'i
EMILY.
Pray, shall we not also burn some gold ?
MRS. B.
That is not in our power, at least in this way.
Gold, silver, and platina, are incapable of being
oxydated by the greatest heat that we can produce
by the common method. It is from this circum-
stance, that they have been called perfect metals.
Even these, however, have an affinity for oxygen ;
but their oxydation or combustion can be per-
formed only by means of acids or by electricity,
p 6
324 JVI&TALS.
The spark given out by the Voltaic battery pro-
duces at the point of contact a greater degree of
heat than any other process ; and it is at this very
high temperature only that the affinity of these
metals for oxygen will enable them to act on each
other.
I am sorry that I cannot show you the combus-
tion of the perfect metals by this process, but it
requires a considerable Voltaic battery. You will
see these experiments performed in the most perfect
manner, when you attend the chemical lectures of
the Royal Institution. But in the mean time I
can, without difficulty, show you an ingenious
apparatus lately contrived for the purpose of pro-
ducing intense heats, the power of which nearly
equals that of the largest Voltaic batteries. It
simply consists, you see, in a strong box, made of
iron or copper, (PLATE X. fig. 2.) to which may be
adapted this air-syringe or condensing-pump, and
a stop-cock terminating in a small orifice similar to
that of a blow-pipe. By working the condensing
syringe, up and down in this manner, a quantity of
air is accumulated in the vessel, which may be
increased to almost any extent ; so that if we now
turn the stop-cock, the condensed air will rush
out, forming a jet of considerable force; and if
we place the flame of * lamp in the current, you
\vill see how violently the flame is driven in that
direction.
METALS. 325
CAROLINE.
It seems to be exactly the same effect as that of
a blow-pipe worked by the mouth, only much
stronger.
EMILY.
Yes ; and this new instrument has this additional
advantage, that it does not fatigue the mouth and
lungs like the common blow-pipe, and requires no
art in blowing.
MRS. B.
Unquestionably ; but yet this blow-pipe would
be of very limited utility, if its energy and power
could not be greatly increased by some other con-
trivance. Can you imagine any mode of producing
such an effect?
EMILY.
Could not the reservoir be charged with pure
oxygen, instead of common air, as in the case of
the gas-holder ?
MRS. B.
Undoubtedly; and this is precisely the con-
trivance I allude to. The vessel need only be
supplied with air from a bladder full of oxygen,
instead of the air of the room, and this, you see,
may be easily done by screwing the bladder on the
upper part of the syringe, so that in working the
syringe the oxygen gas is forced from the bladder
into the condensing vessel.
326 METALS.
CAROLINE.
With the aid of this small apparatus, therefore, we
could obtain the same effects as those we have just
produced with the gas-holder, by means of a column
of water forcing the gas out of it ?
MRS. B.
Yes ; and much more conveniently so. But there
is a mode of using this apparatus by which more
powerful effects still may be obtained. It consists
in condensing in the reservoir, not oxygen alone,
but a mixture of oxygen and hydrogen in the exact
proportion in which they unite to produce water; and
then kindling the jet formed by the mixed gases.
The heat disengaged by this combustion, without
the help of any lamp, is probably the most intense
known ; and various effects are said to have been
obtained from it which exceed all expectation.
CAROLINE.
But why should we not try this experiment ?
MRS. B.
Because it is not exempt from danger ; the com-
bustion (notwithstanding various contrivances which
have been resorted to with a view to prevent acci-
dent) being apt to penetrate into the inside of
the vessel, and to produce a dangerous and violent
METALS. 327
explosion. We shall, therefore, now proceed iu
our subject.
CAROLINE.
I think you said the oxyds of metals could be
restored to their metallic state ?
MRS. B.
Yes; this is called reviving a metal. Metals
are in general capable of being revived by charcoal,
when heated red hot, charcoal having a greater
attraction for oxygen than the metals. You need
only, therefore, decompose, or unburn the oxyd, by
depriving it of its oxygen, and the metal will be
restored to its pure state.
EMILY.
But will the carbon, by this operation, be burnt,
and be converted into carbonic acid ?
MRS. B.
Certainly. There are other combustible sub-
stances to which metals at a high temperature will
part with their oxygen. They will also yield it to
each other, according to their several degrees of
attraction for it ; and if the oxygen goes into a more
dense state in the metal which it enters, than it
existed in that which it quits, a proportional disen-
: gagement of caloric will take place.
328 METALS.
CAROLINE.
And cannot the oxyds of gold, silver, and pla-
tina, which are formed by means of acids or of the
electric fluid, be restored to their metallic state ?
MRS. E.
Yes, they may ; and the intervention of a com-
bustible body is not required ; heat alone will take
the oxygen from them, convert it into a gas, and
revive the metal.
EMILY.
You said that, rust was an oxyd of iron ; how is
it, then, that water, or merely dampness, produces
it, which, you know, it very frequently does on
steel grates, or any iron instruments ?
MRS. B.
In that case the metal decomposes the water,
or dampness (which is nothing but water in a state
of vapour), and obtains the oxygen from it.
CAROLINE.
I thought that it was necessary to bring metals
to a very high temperature to enable them to de-
compose water.
MRS. B.
It is so, if it is required that the process should
be performed rapidly, and if any considerable
quantity is to be d ecomposed. Rust, you knew,
METALS. 329
is sometimes months in forming, and then it is only
the surface of the metal that is oxydated.
EMILY.
Metals, then, that do not rust, ar incapable of
spontaneous oxydation, either by air or water ?
MRS. B.
Yes ; and this is the case with the perfect metals,
which, on that account, preserve their metallic
lustre so well.
EMILY.
Are all metals capable of decomposing water,
provided their temperature be sufficiently raised ?
MRS. B.
No; a certain degree of attraction is requisite,
besides the assistance of heat. Water, you recol-
lect, is composed of oxygen and hydrogen ; and,
unless the affinity of the metal for 6xygen be
stronger than that of hydrogen, it is in vain that
we raise its temperature, for it cannot take the
oxygen from the hydrogen. Iron, zinc, tin, and
antimony, have a stronger affinity for oxygen than
hydrogen has, therefore these four metals are
capable of decomposing water. But hydrogen
having an advantage over all the other metals with
respect to its affinity for oxygen, it not only with-
holds its oxygen from them, but is even capable.
330 METALS.
under certain circumstances, of taking the oxygen
from the oxyds of these metals.
EMILY.
I confess that I do not quite understand why
hydrogen can take oxygen from those metals that
do not decompose water.
CAROLINE.
Now I think I do perfectly. Lead, for instance,
will not decompose water, because it has not so
strong an attraction for oxygen as hydrogen has.
Well, then, suppose the lead to be in a state of
oxyd ; hydrogen will take the oxygen from the
lead, and unite with it to form water, because
hydrogen lias a stronger attraction for oxygen,
than oxygen has for lead ; and it is the same
with all the other metals which do not decompose
water.
EMILY.
I understand your explanation, Caroline, very
well; and I imagine that it is because lead cannot
decompose water that it is so much employed for
pipes for conveying tluit fluid.
MRS. B.
Certainly; lead is, I.L .n.i uicount, particularly
appropriate to such purposes; whilst, on the con-
trary, this metal, if it was oxydable by water,
METALS. 331
would impart to it very noxious qualities, as all
oxyds of lead are more or less pernicious.
But, with regard to the oxydation of metals, the
most powerful mode of effecting it is by means of
acids. These, you know, contain a much greater
proportion of oxygen than either air or water j
and will, most of them, easily yield it to metals.
Thus, you recollect, the zinc plates of the Voltaic
battery are oxydated by the acid and water, much
more effectually than by water alone.
CAROLINE.
And I have often observed that if I drop vine-
gar, lemon, or any acid on the blade of a knife, or
on a pair of scissars, it will immediately produce a
spot of rust.
EMILY.
Metals have, then, three ways of obtaining oxy-
gen ; from, the atmosphere, from water, and from
acids.
MRS. B.
The two first you have already witnessed, and
I shall now show you how metals take the oxygen
from an acid. This bottle contains nitric acid;
I shall pour some of it over this piece of copper-
leaf
CAROLINE.
Oh, what a disagreeable smell !
332 . METALS.
EMILY.
And what is it that produces the effervescency
and that thick yellow vapour ?
MRS. B.
It is the acid, which being abandoned by the
greatest part of its oxygen, is converted into a
weaker acid, which escapes in the form of gas,
CAROLINE.
And whence proceeds this heat ?
MRS. B. .
Indeed, Caroline, I think you might now be able
to answer that question yourself.
CAROLINE.
Perhaps it is that the oxygen enters into the
metal in a more solid state than it existed in the
acid, in consequence of which caloric is disen-
MRS. B.
If the combination of the oxygen and the metal
results from the union of their opposite electricities,
of course caloric must be given out.
EMILY.
The effervescence is over; therefore I suppose
that the metal is now oxydated.
METALS. 333
MRS. B.
Yes. But there is another important connection
between metals and acids, with which I must now
make you acquainted. Metals, when in the state
of oxyds, are capable of being dissolved by acids.
In this operation they enter into a chemical com-
bination with the acid, and form an entirely new
compound.
CAROLINE.
But what difference is there between the oxyda-
tion and the dissolution of the metal by an acid ?
MRS. B.
In the first case, the metal merely combines with
a portion of oxygen taken from the acid, which is
thus partly deoxygenated, as in the instance you
have just seen; in the second case, the metal, after
being previously oxydated, is actually dissolved in
the acid, and enters into a chemical combination
with it, without producing any further decompo-
sition or effervescence. This complete combina-
tion of an oxyd and an acid forms a peculiar and
, important class of compound salts.
EMILY.
The difference between an oxyd and a com-
pound salt, therefore, is very obvious: the one
consists of a metal and oxygen; the other of an
oxyd and an acid.
334 METALS.
MRS. B.
Very well : and you will be careful to remem-
ber that the metals are incapable of entering into
this combination with acids, unless they are pre-
viously oxydated ; therefore, whenever you bring
a metal in contact with an acid, it will be first
oxydated and afterwards dissolved, provided that
there be a sufficient quantity of acid for both
operations.
There are some metals, however, whose solu-
tion is more easily accomplished, by diluting the
acid in water; and the metal will, in this case, be
oxydated, not by the acid, but by the water, which
it will decompose. But in proportion as the oxy-
gen of the water oxydates the surface of the me-
tal, the acid combines with it, washes it off, and
leaves a fresh surface for the oxygen to act upon :
then other coats of oxyd are successively formed,
and rapidly dissolved by the acid, which continues
combining with the new- formed surfaces of oxyd
till the whole oi the metal is dissolved. During
this process the hydrogen gas of the water is dis-
engaged, and flies off with effervescence.
EMILY.
Was not this the manner in which the sul-
phuric acid assisted the iron filings in decomposing
water?
METALS. 335
MRS. B.
Exactly; and it is thus that several metals,
which are incapable alone of decomposing water,
are enabled to do it by the assistance of an acid,
which, by continually washing off the covering of
oxyd, as it is formed, prepares a fresh surface of
metal to act upon the water.
CAROLINE.
The acid here seems to act a part not very
different from that of a scrubbing-brush. But
pray would not this be a good method of clean-
ing metallic utensils?
MRS. B.
Yes ; on some occasions a weak acid, as vinegar,
is used for cleaning copper. Iron plates, too, are
freed from the rust on their surface by diluted
muriatic acid, previous to their being covered
with tin. You must remember, however, that in
this mode of cleaning metals the acid should be
quickly afterwards wiped off, otherwise it would
produce fresh oxyd.
CAROLINE.
Let us watch the dissolution of the copper in
the nitric acid ; for I am very impatient to see the
salt that is to result from it. The mixture is now
of a beautiful blue colour; but there is no ap-
336* METALS.
pearance of the formation of a salt; it seems to
be a tedious operation.
MRS. B.
The crystallisation of the salt requires some
length of time to be completed; i however, you
are so impatient, I can easily show you a metallic
salt already formed.
CAROLINE.
But that would not satisfy my curiosity half so
well as one of our own manufacturing.
MRS. B.
It is one of our own preparing that I mean to
show you. When we decomposed water a few
days since, by the oxydation of iron filings through
the assistance of sulphuric acid, in what did the
process consist?
CAROLINE.
In proportion as the water yielded its oxygen to
the iron, the acid combined with the new-formed
oxyd, and the hydrogen escaped alone.
MRS. B.
Vary well; the result, therefore, was a com-
pound salt, formed by the combination of sul-
phuric acid with oxyd of iron. It still remains in
METALS. 337
the vessel in which the experiment was performed.
Fetch it, and we shall examine it.
EMILY.
What a variety of processes the decomposition
of water, by a metal and an acid, implies; 1st,
the decomposition of the water; 2dly, the oxy-
dation of the metal ; and 3dly, the formation of
a compound salt.
CAROLINE.
Here it is, Mrs. B. What beautiful green crys-
tals ! But we do not perceive any crystals in the
solution of copper in nitrous acid ?
MRS. B.
Because the salt is now suspended in the water
which the nitrous acid contains, and will remain
so till it is deposited in consequence of rest and
cooling.
EMILY.
I am surprised that a body, so opake as iron can
be converted into such transparent crystals.
MRS. B.
It is the union with the acid that produces the
transparency ; for if the pure metal were melted,
and afterwards permitted to cool and crystallise, it
would be found just as opake as before.
VOL. i.
338 METALS.
EMILY.
I do not understand the exact meaning of crys-
tallisation ?
MRS. B.
You recollect that wken a solid body is dis-
solved either by water or caloric it is not de-
composed; but that its integrant parts are only
suspended in the solvent. When the solution is
made in water, the integrant particles of the body
will, on the water being evaporated, again unite
into a solid mass by the force of their mutual at-
traction. But when the body is dissolved by ca-
loric alone, nothing more is necessary, in order
to make its particles reunite, than to reduce its
temperature. And, in general, if the solvent,
whether water or caloric, be slowly separated
by evaporation or by cooling, and care* taken
that the particles be not agitated during their
reunion, they will arrange themselves in regular
masses, each individual substance assuming a pe-
culiar form or arrangement; and this is what is
called crystallisation.
EMILY.
Crystallisation, therefore, is simply the reunion
of the particles of a solid body that has been
dissolved in a fluid.
METALS. 339
MRS. B.
That is a very good definition of it. But I
must not forget to observe, that heat and "water
may unite their solvent powers ; and, in this case,
crystallisation may be hastened by cooling, as
well as by evaporating the liquid ?
CAROLINE.
But if the body dissolved is of a volatile nature,
will it not evaporate with the fluid ?
MRS. B.
A crystallised body held in solution only by
water is scarcely ever so volatile as the fluid it-
self, and care must be taken to manage the heat
so that it may be sufficient to evaporate the water
only.
I should not omit also to mention that bodies,
in crystallising from their watery solution, always
retain a small portion of water, which remains
confined in the crystal in a solid form, and does
not reappear unless the body loses its crystalline
state. This is called the water of crystallisation.
But you must observe, that whilst a body may be
separated from its solution in water or caloric
simply by cooling or by evaporation, an acid can
be taken from a metal with which it is combined
only by stronger affinities, which produce a decom-
position.
e 2
340 METALS.
EMILY.
Are the perfect metals susceptible of being dis-
solved and converted into compound salts by
acids ?
MRS. B.
Gold is acted upon by only one acid, the oxy-
genated muriatic^ a very remarkable acid, which,
when in its most concentrated state, dissolves gold
or any other metal, by burning them rapidly.
Gold can, it is true, be dissolved likewise by a
mixture of two acids, commonly called aqua regia ;
but this mixed solvent derives that property from
containing the peculiar acid which I have just men-
tioned. Platina is also acted upon by this acid
only ; silver is dissolved by nitric acid.
CAROLINE.
I think you said that some of the metals might
be so strongly oxydated as to become acid ?
MRS. B.
There are five metals, arsenic, molybdena,
chrome, tungsten, and columbium, which are sus-
ceptible of combining with a sufficient quantity of
oxygen to be converted into acids.
CAROLINE.
Acids are connected with metals in such a variety
of ways, that I am afraid of some confusion in re
MUTALS. 341
>nembering them. In the first place, acids will
yield their oxygen to metals. Secondly, they will
combine with them in their state of oxyds, to form,
compound salts ; and lastly, several of the metals
are themselves susceptible of acidification.
MRS. B.
Very well ; but though metals have so great an
affinity for acids, it is not with that class of bodies
alone that they will combine. They are most of
them, in their simple state, capable of uniting
with sulphur, with phosphorus, with carbon, and
with each other ; these combinations, according
to the nomenclature which was explained to you
on a former occasion, are called sulphurets, plios-
phorets, carburets, &c.
The metallic phosphorets offer nothing very re-
markable. The sulphurets form the peculiar
kind of mineral called pyrites, from which certain
kinds of mineral waters, as those of Harrogate,
derive their chief chemical properties. In this
combination, the sulphur, together with the iron,
have so strong an attraction for oxygen, that they
obtain it both from the air and from water, and
by condensing it in a solid form, produce the heat
which raises the temperature of the water in such a
remarkable degree.
EMILY.
But if gyrites obtain oxygen from water, that
2
342 METALS.
water must suffer a decomposition, and hydrogen
gas be evolved.
MRS. B.
That is actually the case in the hot springs alluded
to, which give out an extremely fetid gas, composed
of hydrogen impregnated with sulphur.
CAROLINE.
If I recollect right, steel and plumbago, which
you mentioned in the last lesson, are both car-
burets of iron ?
MRS. B.
Yes ; and they are the only carburets of much
consequence.
A curious combination of metals has lately very
much attracted the attention of the scientific
world : I mean the meteoric stones that fall from the
atmosphere. They consist principally of native
or pure iron, which is never found in that state in
the bowels of the earth ; and contain also a small
quantity of nickel and chrome, a combination like-
wise new in the mineral kingdom.
These circumstances have led many scientific
persons to believe that those substances have fallen
from the moon, or some other planet, while
others are of opinion either that they are formed
in the atmosphere, or are projected into it by
some unknown volcano on the surface of our
globe.
METALS. 343
CAROLINE.
I have heard much of these stones, but I befieve
many people are of opinion that they are formed
on the surface of the earth, and laugh at their pre-
tended celestial origin.
MRS. B.
The fact of their falling is so well ascertained,
that I think no person who has at all investigated
the subject, can now entertain any doubt of it.
Specimens of these stones have been discovered
in all par{s of the world, and to each of them some
tradition or story of its fall has been found con-
nected. And as the analysis of all those specimens
affords precisely the*same results, there is strong
reason to conjecture that they all proceed from the
same source. It is to Mr. Howard that philoso-
phers are indebted for having first analysed these
stones, and directed their attention to this inter-
esting subject.
CAROLINE.
But pray, Mrs. B., how can solid masses of iron
and nickel be formed from the atmosphere, which
consists of the two airs, nitrogen and oxygen ?
MRS. B.
I really do not see how they could, and think it
much more probable that they fall from the moon.
But we must not suffer this digression to take up
too much of our time.
344 METALS.
The combinations of metals with each other are
called alloys ; thus brass is an alloy of copper and
zinc ; bronze, of copper and tin, &c.
EMILY.
And is not pewter also a combination of metal ?
MRS. B.
It is. The pewter made in this country is
mostly composed of tin, with a very small pro-
portion of zinc and lead.
CAROLINE.
Block-tin is a kind of pewtei% I believe ?
MRS. B.
Properly speaking, blocl^-tin means tin in blocks,
or square massive ingots ; but in the sense in which
it is 'used by ignorant workmen, it is iron plated
with tin, which renders it more durable, as tin will
not so easily rust. Tin alone, however, would
be too soft a metal to be worked for common use,
and all tin^vessels and utensils are in fact made of
plates of iron, thinly coated with tin, which pre-
vents the iron from rusting.
CAROLINE.
Say rather oxydating, Mrs. B. Rust is a word
that should be exploded in chemistry.
METALS. 345
MRS. B.
Take care, however, not to introduce the word
oxydate, instead of rust, in general conversation ;
for you would probably not be understood, and you
might be suspected of affectation.
Metals differ very much in their affinity for each
other; some will not unite at all, others readily
combine together, and on this property of metals
the art of soldering depends.
EMILY.
What is soldering ?
"MRS. B.
It is joining two pieces of metal together, by a
reiore fusible metal interposed between them.
Thus tin is a solder for lead ; brass, gold, or silver,
are solder for iron, &c.
CAROLINE.
And is not plating metals something of the same
nature ?
MRS. B.
In the operation of plating, two metals are united,
one being covered with the other, but without the
intervention of a third ; iron or copper may thus
be covered with gold or silver.
346 METALS.
EMILY.
EMILY.
Mercury appears to me of a very different nature
from the other metals.
MRS. B.
One of its greatest peculiarities is, that it re-
tains a fluid state at the temperature of the atmo-
sphere. All metals are fusible at different degrees
of heat, and they have likewise each the property
of freezing or becoming solid at a certain fixed
temperature. Mercury congeals only at seventy-
two degrees below the freezing point.
EMILY.
That is to say, that in order to freeze, it requires
a temperature of seventy-two degrees colder than
that at which water freezes. ,
MRS. B.
Exactly so.
CAROLINE.
But is the temperature of the atmosphere ever so
low as that?
MRS. B.
Yes, often in Siberia; but happily never in this
part of the globe. Here, however, mercury may
be congealed by artificial cold ; I mean such in-
tense cold as can be produced by some chemical
METALS. 347
mixtures, or by the rapid evaporation of ether
under the air-pump..*
CAROLINE.
And can mercury be made to boil and evapo-
rate ?
MRS. B.
Yes, like any other liquid ; only it requires a
much greater degree of heat. At the temperature
of six hundred degrees, it begins to boil and eva-
porate like water.
Mercury combines with gold, silver, tin, and with
several other metals; and, if mixed with any of
them in a sufficient proportion, it penetrates the
solid metal, softens it, loses its own fluidity, and
forms an amalgam^ which is the name given to the
combination of any metal with mercury, forming a
substance more or less solid, according as the mer-
cury or the other metal predominates.
EMILY.
In the list of metals there are some whose names
I have never before heard mentioned.
MRS. B.
Besides those which Sir H. Davy has obtained,
there are several that have been recently disco-
* By a process analogous to that described, page 155. of this
volume.
2 6
348 METALS.
vered, whose properties are yet but little known,
as for instance, titanium, which was discovered
by the Rev. Mr. Gregor, in the tin-mines of Corn-
wall; columbium or tantalium, -which has lately
been discovered by Mr. Hatchett; and osmium,
iridium, palladium, and rhodium, all of which
Dr. Wollaston and Mr. Tennant found mixed in
minute quantities with crude platina, and the dis-
tinct existence of which they proved by curious
and delicate experiments.
CAROLINE.
Arsenic has been mentioned amongst the metals,
1 had no notion that it belonged to that class of
bodies, for I had never seen it but as a powder, and
never thought of it but as a most deadly poison.
MRS. 6.
In its pure metallic state, I believe, it is not so
poisonous; but it has such a great affinity for
oxygen, that it absorbs it from the atmosphere at
its natural temperature : you have seen it, there-
fore, only in its state of oxyd, when, from its
combination with oxygen, it has acquired its very
poisonous properties.
CAROLINE.
Is it possible that oxygen can impart poisonous
qualities? That valuable substance which pro-
METALS*
duces light and fire, and which all bodies in na-
ture are so eager to obtain ?
MRS. 6.
Most of the metallic oxyds are poisonous, and
derive this property from their union with oxy-
gen. The white lead, so much used in paint,
owes its pernicious effects to oxygen. In general,
oxygen, in a concrete state, appears to be parti-
cularly destructive in its effects on flesh or any
animal matter; and those oxyds are most caustic
that have an acrid burning taste, which proceeds
from the metal having but a slight affinity for
oxygen, and therefore easily yielding it to the flesh,
which it corrodes and destroys.
EMILY.
What is the meaning of the word caustic^ which
you have just used ?
MRS. B.
It expresses that property which some bodies
possess, of disorganizing and destroying animal
matter, by operating a kind of combustion, or at
least a chemical decomposition. You must often
have heard of caustic used to burn warts, or other
animal excrescences; most of these bodies owe
their destructive power to the oxygen with which
they are combined. The common caustic, called
350 METALS.
lunar caustic, is a compound formed by the union
of nitric acid and silver; and it is supposed to
owe its caustic qualities to the oxygen contained
in the nitric acid.
CAROLINE.
But, pray, are not acids still more caustic than
oxyds, as they contain a greater proportion of
oxygen ?
MRS. B.
Some of the acids are ; but the caustic property
of a body depends not only upon the quantity of
oxygen which it contains, but also upon its slight
affinity for that principle, and the consequent faci-
lity with which it yields it.
EMILY.
Is not this destructive property of oxygen ac-
counted for ?
MRS. B.
It proceeds probably from the strong attraction
of oxygen for hydrogen ; for if the one rapidly
absorb the other from the animal fibre, a disor-
ganisation of the substance must ensue.
EMILY.
Caustics are, then, very properly said to burn
the flesh, since the combination of oxygen and
hydrogen is an actual combustion.
12
METALS. 351
CAROLINE.
Now, I think, this effect would be more pro-
perly termed an oxydation, as there is no disen-
gagement of light and heat.
MRS. 6.
But there really is a sensation of heat produced
by the action of caustics.
EMILY.
If oxygen is so caustic, why does not that which
is contained in the atmosphere burn us ?
MRS. B.
Because it is in a gaseous state, and has a
greater attraction for its electricity than for the
hydrogen of our bodies. Besides, should the air
be slightly caustic, we are in a great measure
sheltered from its effects by the skin ; you know
how much a wound, however trifling, smarts on
being exposed to it.
CAROLINE.
It is a curious idea, however, that we should
live in a slow fire. But, if the air was caustic,
would it not hare an acrid taste ?
MRS. B.
It possibly may have such a taste ; though in so
352 METALS*
slight a degree, that custom has rendered it in-
sensible.
CAROLINE.
And why is not water caustic ? When I dip my
hand into water, though cold, it ought to burn me
from the caustic nature of its oxygen.
MRS. B.
Your hand does not decompose the water ; the
oxygen in that state is much better supplied with
hydrogen than it would be by animal matter, and
if its causticity depend on its affinity- for that
principle, it will be very far from quitting its
state of water to act upon your hand. You must
not forget that oxyds are caustic in proportion as
the oxygen adheres slightly to them.
EMILY.
Since the oxyd of arsenic is poisonous, its acid,
I suppose, is fully as much so ?
MRS. B.
Yes ; it is one of the strongest poisons in nature.
EMILY.
There is a poison called verdigris, which forms
on brass and copper when not kept very clean ;
and this, I have heard, is an objection to these
METALS. 353
metals being made into kitchen utensils. Is this
poison likewise occasioned by oxygen ?
MRS. B.
It is produced by the intervention of oxygen ;
for verdigris is a compound salt formed by the
union of vinegar and copper ; it is of a beautiful
green colour, and much used in painting.
EMILY.
But, I believe, verdigris is often formed on cop-
per when no vinegar has been in contact with it.
MRS. B.
Not real verdigris, but compound salts, somewhat '
resembling it, may be produced by the action of
any acid on copper.
The solution of copper in nitric acid, if evapo-
rated, affords a salt which produces an effect on
tin that will surprise you, and I have prepared
some from the solution we made before, that I
might show it to you. I shall first sprinkle some
water on this piece of tin-foil, and then some of
the salt. Now observe that I fold it up suddenly,
and press it into one lump.
CAROLINE.
What a prodigious vapour issues from it and
sparks of fire I declare !
354 METALS.
MRS. B.
I thought it would surprise you. The effect,
however, I dare say you could account for, since
it is merely the consequence of the oxygen of the
salt rapidly entering into a closer combination with
the tin.
There is also a beautiful green salt too curious to
be omitted ; it is produced by the combination of
cobalt with muriatic acid, which has the singular
property of forming what is called sympathetic ink.
Characters written with this solution are invisible
when cold, but when a gentle heat is applied, they
assume a fine bluish green colour.
CAROLINE.
I think one might draw very curious landscapes
with the assistance of this ink ; I would first make
a water-colour drawing of a winter-scene, in
which the trees should be leafless, and the grass
scarcely green : I would then trace all the verdure
with the invisible ink, and whenever I chose to
create spring, I should hold it before the fire, and
its warmth would cover the landscape with a rich
verdure.
MRS. B.
That will be a very amusing experiment, and
I advise you by all means to try it.
Before we part, I must introduce to your ac-
quaintance the curious metals which Sir H. Davy
METALS. 355
has recently discovered. The history of these
extraordinary bodies is yet so much in its infancy,
that I shall confine myself to a very short account
of them ; it is more important to point out to you
the vast, and apparently inexhaustible, field of re-
search which has been thrown open to our view by
Sir H. Davy's memorable discoveries, than to enter
into a minute account of particular bodies or ex-
periments.
CAROLINE.
But I have heard that these discoveries, however
splendid and extraordinary, are not very likely to
prove of any great benefit to the world, as they
are rather objects of curiosity than of use.
MRS. B.
Such may be the illiberal conclusions of the ig-
norant and narrow-minded ; but those who can duly
estimate the advantages of enlarging the sphere of
science, must be convinced that the acquisition of
every new fact, however unconnected it may at first
appear with practical utility, must ultimately prove
beneficial to mankind. But these remarks are
scarcely applicable to the present subject ; for some
of the new metals have already pro-ved eminently
useful as chemical agents, and are likely soon to be
employed in the arts. For the enumeration of
these metals, I must refer you to our list of simple
bodies; they are derived from the alkalies, the
356 METALS,
earths, and three of the acids, all of which had beert
hitherto considered as undecompoundable or simple
bodies.
When Sir H. Davy first turned his attention to
the effects of the Voltaic battery, he tried its power
on a variety 'of compound bodies, and gradually
brought to light a number of new and interesting
facts, which led the way to more important dis-
coveries. It would be highly interesting to trace
his steps in this new department of science, but it
would lead us too far from our principal object. A
general view of his most remarkable discoveries is
all that I can aim at, or that you could, at present,
understand.
The facility with which compound bodies yielded
to the Voltaic electricity, induced him to make trial
of its effects on substances hitherto considered as
simple, but which he suspected of being compound,
and his researches were soon crowned with the most
complete success.
The body which he first submitted to the Voltaic
battery, and which had never yet been decomposed,
was one of the fixed alkalies, called potash. This
substance gave out an elastic fluid at the positive
wire, which was ascertained to be oxygen, and at
the negative wire, small globules of a very high
metallic lustre, very similar in appearance to mer-
cury ; thus proving that potash, which had hitherto
been considered as a simple incombustible body,
METALS. 357
was in fact a metallic oxyd; and that its incom-
bustibility proceeded from its being already com-
bined with oxygen.
EMILY.
I suppose the wires used in this experiment were
of platina, as they were when you decomposed
water ; for if of iron, the oxygen would have com-
bined with the wire, instead of appearing in the
form of gas.
MRS. B.
Certainly : the metal, however, would equally
have been disengaged. Sir H. Davy has distin-
guished this new substance by the name of PO-
TASSIUM, which is derived from that of the alkali,
from which it is procured. I have some small
pieces of it in this phial, but you have already seen
it, as it is the metal which we burnt in contact with
sulphur.
What is the liquid in which you keep it ?
MRS. B.
It is naptha, a bituminous liquid, with which I
shall hereafter make you acquainted. It is almost
the only fluid in which potassium can be preserved,
as it contains no oxygen, and this metal has so
powerful an attraction for oxygen, that it will not
only absorb it from the air, but likewise from water,
or any body whatever that contains it,
358 METALS,
EMILY.
This, then, is one of the bodies that oxydate*
spontaneously without the application of heat ?
MRS. B.
Yes; and it has this remarkable peculiarity that
it attracts oxygen much more rapidly from water
than from air ; so that when thrown into water, how-
ever cold, it actually bursts into flame. I shall now
throw a small piece, about the size of a pin's head,
on this drop of water.
CAROLINE.
It instantaneously exploded, producing a little
flash of light ! this is, indeed, a most curious sub-
stance !
MRS. B.
By its combustion it is reconverted into potash ;
and as potash is now decidedly a compound body,
I shall not enter into any of its properties till we
have completed our review of the simple bodies ;
but we may here make a few observations on its
basis, potassium. If this substance is left in con-
tact with air, it rapidly returns to the state of pot-
ash, with a disengagement of heat, but without any
flash of light.
EMILY.
But is it not very singulr that it should burn
better in water than in air ?
METALS. 359
CAROLINE.
I do not think so : for if the attraction of pot-
assium for oxygen is so strong that it finds no more
difficulty in separating it from the hydrogen in
water, than in absorbing it from the air, it will no
doubt be more amply and rapidly supplied by water
than by air.
MRS. B.
That cannot, however, be precisely the reason,
for when potassium is introduced under water,
without contact of air, the combustion is not so
rapid, and indeed, in that case, there is no lumin-
ous appearance ; but a violent action takes place,
much heat is excited, the potash is regenerated,
and hydrogen gas is evolved.
Potassium is so eminently combustible, that in-
stead of requiring, like other metals, an elevation
of temperature, it will burn rapidly in contact with
water, even below the freezing point. This you
may witness by throwing a piece on this lump of
ice.
CAROLINE.
It again exploded with flame, and has made a
deep hole in the ice.
MRS. B.
This hole contains a solution of potash ; for the
alkali being extremely soluble, disappears in the
860 METALS.
water at the instant it is produced. Its presence,
however, may be easily ascertained, alkalies having
the property of changing paper, stained with tur-
meric, to a red colour ; if you dip one end of this
slip of paper into the hole in the ice you will see
it change colour, and the same, if you wet it with
the drop of water in which the first piece of po-
tassium was burnt.
CAROLINE.
It has indeed changed the paper from yellow to
red.
MRS. B.
This metal will burn likewise in carbonic acid
gas, a gas that had always been supposed incapable
of supporting combustion, as we were unacquainted
with any substance that had a greater attraction for
oxygen than carbon. Potassium, however, readily
decomposes this gas, by absorbing its oxygen, as I
shall ;show you. This retort is filled with carbonic
acid gas. I will put a small piece of potassium in
it ; but for this combustion a slight elevation of
temperature is required, for which purpose I shall
hold the retort over the lamp.
CAROLINE.
NOW it has taken fire, and burns with violence !
It has burst the retort.
METALS. 36 /
MRS. B.
Here is the piece of regenerated potash ; can you
tell me why it is become so black ?
EMILY.
No doubt it is blackened by the carbon, which,
when its oxygen entered into combination with the
potassium, was deposited on its surface.
MRS. B.
You are right. This metal is perfectly fluid at
the temperature of one hundred degrees ; at fifty
degrees it is solid, but soft and malleable ; at thirty-
two degrees it is hard and brittle, and its fracture
exhibits an appearance of confused crystallization.
It is scarcely more than half as heavy as water ; its
specific gravity being about six when water is
reckoned at ten ; so that this metal is actually
lighter than any known fluid, even than ether.
Potassium combines with sulphur and phos-
phorus, forming sulphurets and phosphurets; it
likewise forms alloys with several metals, and
amalgamates with mercury.
EMILY.
But can a sufficient quantity of potassium be ob-
tained, by means of the Voltaic battery, to admit
of all its properties and relations to other bodies
being satisfactorily ascertained?
VOL. i. R
362 METALS,
MRS. B.
Not easily; but I must not neglect to inform
you that a method of obtaining this metal in con-
siderable quantities has since been discovered. Two
eminent French chemists, Thenard and Gay Lussac,
stimulated by the triumph which Sir H. Davy had
obtained, attempted to separate potassium from its
combination with oxygen, by common chemical
means, and without the aid of electricity. They
caused red hot potash in a state of fusion to filter
through iron turnings in an iron tube, heated to
whiteness. Their experiment was crowned with
the most complete success; more potassium was
obtained by this single operation, that could have
been collected in many weeks by the most diligent
use of the Voltaic battery.
EMILY.
In this experiment, I suppose, the oxygen
quitted its combination with the potassium to unite
with the iron turnings ?
MRS. B.
Exactly so; and the potassiflm was thus obtained
in its simple state. From that time it has become
a most convenient and powerful instrument of
deoxygenation in chemical experiments. This
important improvement, engrafted on Sir H.
Davy's previous discoveries, served but to add to
his glory, since the facts which he had established,
METALS. 363
\vhen possessed of only a few atoms of this curious
substance, and the accuracy of his analytical state-
ments, were all confirmed when an opportunity
occurred of repeating his experiments upon this
substance, which can now be obtained in unlimited
quantities.
CAROLINE.
What a satisfaction Sir H. Davy must have felt,
when by an effort of genius he succeeded in bring-
ing to light and actually giving existence, to these
curious bodies, which without him might perhaps
have ever remained concealed from our view !
MRS. B.
The next substance which Sir H. Davy submitted
to the influence of the Voltaic battery was Soda,
the other fixed alkali, which yielded to the same
powers of decomposition ; from this alkali too, a
metallic substance was obtained, very analogous in
its properties to that which had been discovered in
potash ; Sir H. Davy has called it SODIUM. It is
rather heavier than potassium, though considerably .
lighter than water; it is not so easily fusible as
potassium.
Encouraged by these extraordinary results, Sir
H. Davy next performed a series of beautiful ex-
periments on Ammonia, or the volatile alkali, which,
from analogy, he was led to suspect might also con-
tain oxygen. This he soon ascertained to be the
R 2
364 METALS.
fact, but he has not yet succeeded in obtaining the
basis of ammonia in a separate state ; it is from ana-
^gy> an d fr m the power which the volatile alkali
has, in its gaseous form, to oxydate iron, and also
from the amalgams which can be obtained from
ammonia by various processes, that the proofs of
that alkali being also a metallic oxyd are deduced.
Thus, then, the three alkalies, two of which had
always been considered as simple bodies, have now
lost all claim to that title, and I have accordingly
classed the alkalies amongst the compounds, whose
properties we shall treat of in a future conversation.
EMILY.
What are the other newly discovered metals
which you have alluded to in your list of simple
bodies ?
MRS. B.
They are the metals of the earths which became
next the object of Sir H. Davy's researches ; these
bodies had never yet been decomposed, though
they were strongly suspected not only of being
compounds, but of being metallic oxyds. From
the circumstance of their incombustibility it was
conjectured, with some plausibility, that they might
possibly be bodies that had been already burnt.
CAROLINE.
And metals, when oxydated, become, to all ap-
pearajice, a kind of earthy substance.
METALS. 365
MRS. B.
They have* besides, several features of resem-
blance with metallic oxyds; Sir H. Davy had
therefore great reason to be sanguine in his ex-
pectations of decomposing them, and he was not
disappointed. He could not, however, succeed
in obtaining the basis of the earths in a pure se-
parate state ; but metallic alloys were formed with
other metals, which sufficiently proved the exist-
ence of the metallic basis of the earths.
The last class of new metallic bodies which Sir
H. Davy discovered was obtained from the three
undecompounded acids, the boracic, the fluoric,
and the muriatic acids ; but as you are entirely
unacquainted with these bodies, I shall reserve the
account of their decomposition till we come to
treat of their properties as acids.
Thus in the course of two years, by the unpa-
ralleled exertions of a single individual, chemical
science has assumed a new aspect. Bodies have
been brought to light which the human eye never
before beheld, and which might have remained
eternally concealed under their impenetrable dis-
guise.
It is impossible at the present period to appre-
ciate to their full extent the consequences which
science or the arts may derive from these disco-
veries; we may, however, anticipate the most
important results.
366 METALS.
In chemical analysis we are now in possession of
more energetic agents of decomposition than were
ever before known.
In geology new views are opened, which will
probably operate a revolution in that obscure and
difficult science. It is already proved that all the
earths, and, in fact, the solid surface of this globe,
are metallic bodies mineralized by oxygen, and
as our planet has been calculated to be consider-
ably more dense upon the whole than on the sur-
face, it is reasonable to suppose that the interior
part is composed of a metallic mass, the surface of
which only has been mineralized by the atmosphere.
The eruptions of volcanos, those stupendous pro-
blems of nature, admit now of an easy explanation.
For if, the bowels of the earth are the grand recess
of these newly discovered inflammable bodies, when-
ever water penetrates into them, combustions and
explosions must take place ; and it is remarkable
that the lava which is thrown out, is the very kind
of substance which might be expected to result from
these combustions.
I must now take my leave of you ; we have had
a very long conversation to-day, and I hope you will
be able to recollect what you have learnt. At our
next interview we shall enter on a new subject.
END OF THE FIRST VOLUME.
Printed by A. Strahan,
Pi inters-Street, London.
iH
13
0)
*
30
h
O
4= a>
UNIVERSITY OF TORONTO
LIBRARY -
Acme Library Card Pocket
Under Pat. " Ref . Index File.
Made by LIBRARY BUREAU
