Affinity and Solution, and the mechanical
Principle of Animal Life.



CHAP. L

Account of a Circumftance of a private Nature, by
which the Author has been induced to add this and
the following Chapters to the Second Edition of this
EJJay. Experimental Invejiigation of the Subjecl
continued. OIL found by Experiment to be a Non-
Conduclor of Heat. -MERCURY is likewife a Non-
Conductor. Probability that all FLUIDS are NON
CONDUCTORS, and that this Property is ESSEN
TIAL TO FLUIDITY. The Knowledge of thai
Fall may be of great Ufe in enablmg us to form
more juft Ideas with regard to the Nature of tbofe
mechanical Operations which take place in chemical
Solutions and Combinations ; in the Procefs of Vege
tation ; and in the 'various Changes effected by the
Powers of Life in the Animal Economy. Rapid
ity of Solution no Proof of the Exiftence of an At-

VOL. n. S s traction



312 Of the Propagation of Heat

tradlon of Affinity. Strata of frejh Water and of
fait Water may be made to rcpofe on each other in
adual Contact without mixing. Probability that
the Water at the Bottom of frcfo Lakes, that are
very deep, may be actually fait.

AT the end of a French trandation of the Firit
Edition of this Effay, publifhed at Geneva,,
Profeffor Piclet (the tranilator) has added the fol
lowing extract of one of my private letters to him,
(of the 9th of June, 1797,) written in anfwcr to
one from him to me, acknowledging the receipt of a
irjanufcript copy of the EflTay which I had fent him.

" I mould have been much furprifed if my Sev-
" enth Effay had not interefted you ; for in my
* life I never felt pleafure equal to that I enjoyed
" in making the experiments of which I have given
" an account in that performance. You will per-
" haps be furprifed when I tell you, that I have
" fuppreffed a whole Chapter of interefting fpecu-
" lation, merely with a view of leaving to others a
" tempting field of curious i-nveftigation untouched,
tc and to give more efFed to my concluding reflec-
" tion, which I confider as being by far the moft
" important of any I have ever publifhed."

As thefe aiTertions, (which were not originally
intended for the public eye,) are liable to leveral
interpretations, I think it my duty, not only to ex
plain them, but alfo to let the Public know precifely
how far I have pufhed my inquiries in the invefti-
gation of the fubjecl under confideration : This is
au act of juftice which I owe to thofe who may be

engaged



in Fluids. 313

engaged in the fame purfuits j for it would be very
unfair, by obfiure hints of important information kept
back, to keep others in doubt with refpecl to the
originality of the difcoveries they may make in the
profecution of their inveftigatkms. This would tend
to damp the fpirit of inquiry, inftead of exciting it ;
and throwing out fuch hints looks fo much like
lying in wait to feize on the fair fruits of the la
bours of others, that I cannot reft till I have fhewn
that I do not defer ve to be fufpected of fuch pitiful
views.

My worthy friend, Profeffor Piclet, certainly did
not fufpect any unhandfomc defign in any thing I
faid to him in my (private) letter ; but thofe who
are lefs acquainted with my character, may not be
difpofed to give me credit for candour and difin-
tereilednefs without proofs.

With regard to the aflcrtion in niy letter., " that'
" I had fuppreffed a whole Chapter of interefting
" fpeculation, with a view to leaving to others a
" tempting field, untouched, for curious inveftiga-
" tion ;" this is perfectly true in fact, as will, I
flatter myfelf, appear, by what I mall now lay be
fore the Public ; and I am confident that thofe who
will take the trouble to confidcr with attention
the reafons which induced me to do this, will find
them fuch as will deferve their approbation.

Having, as 1 flattered myfelf, laid open a new
and moft enticing profpecl: to thofe who are fond of
philofophical purfuits, I was afraid, if I advanced
too far, that others, inftead of ftriking out roads for
themfelves, might perhaps content themfelves with

following



314 Of the Propagation of Heat

following in my footfteps ; and confequently that
jnany,and probably the moft interefting parts of the
new field of inquiry, would remain a long time un
explored : And with regard to the reputation of
being a difcoverer, though I rejoice, J might fay, ex
ult and triumph in the progrefs of human knowl
edge, and enjoy the fweeteft delight in contem
plating the advantages to mankind which are de
rived from the introduction of ufeful improve
ments 5 yet I can truly fay, that I fet no very high
value on the honour of being the firft to {tumble
on thofe treafures which every where lie fo flightly
covered.

In refpecl: to the " concluding reflection" of the
Firft Edition of this EfTay ; though fome may
fmile in pity, and others frown at it, I am neither
afhamed nor afraid to own, that: I confider the fub-
ject as being of the utmoft Importance to the peace,
order, and happinefs of mankind, in our prefent ad
vanced ftate offodety. But to return from thefe di-
greflions-

Though it appeared to me that the important
fact I undertook to inveftigate, relative to the man
ner 9 in which heat is propagated in Fluids, is fully
eftablimed by the Experiments, of which an ac
count has been given in the preceding Chapters of
this Eflay ; yet, as a thorough examination of the
fubject is a matter of much importance, in many
refpects, I did not reft my inquiries here, but made
a number of Experiments with a view to throwing
flill more light upon it, and enabling us to form
jnore clear and diftinct ideas reflecting thofe curious

mechanical



in Fluids. 315

mechanical operations which appear to take place
in Fluids, when Heat is propagated in them.

Having frequently obferved when a quantity of
water in one of my glafs jars was frozen to a cake
of ice, by placing the jar in a freezing mixture 5
that, as the ice firft began to be formed at the fides
of the jar, and increafed gradually in thicknefs, the
portion of water in the axis of the jar (which laft
retained its fluidity) being comprefled by the ex-
panfion of the ice, was always forced upwards to
wards the end of the procefs, and formed a pointed
projection of ice in the form of a nipple, (papilla,)
which was fometimes above half an inch high in the
middle of the upper iide of the cake ; I was led by
that circumftance to make the following intereft-.
ing Experiments.

Experiment, No. 55.

A cake of ice, 3 inches thick, which had a
pointed projection, ^- an inch high, which arofe
from the centre of its upper furface, being frozen
faft in the bottom of a tall cylindrical glafs jar, 4^
inches in diameter ; this jar, {landing in an earthen
pan, and being furrounded by pounded ice and
water, to the height of an inch above the level of
the upper furface of the cake of ice, was placed on
a table, near a window, in a room where the air was
at the temperature of 3 1 of Farenheit's thermo
meter ; and fine olive oil, which had previouily
been cooled down to the temperature of 32, was

poured



3 1 6 Of the Propagation of Heat

poured into the jar till it flood at the height of 3
inches above the furface of the cake of ice.

Having ready a folid cylinder of wrought iron,
ii inch in diameter, and 12 inches long, with a
fmall hook at one end of it, by means of which it
could occafionally be fufpended in a vertical poll-
tion, and furnifhed with a fit hollow cylindrical
iheath of thick paper, into which it juft patted,
open at both ends, and about ~ of an inch longer
than the folid cylinder of iron, to which it ferved
as a covering for keeping it warm j this iron cyl
inder, being heated to the temperature of 210 in
boiling water, and being fuddenly introduced into
its fheath, was fufpended by an iron wire which de-
fcended from the ceiling of the room, in fuch a
manner, that its lower end entering the jar, (in the
direction of its axis,) was immerfed in the oil to
fuch a depth, that the middle of the flat furface of
this end of the hot iron, which was directly above
the point of the conical projection of ice, was dif-
tant from it only - of an inch. The end of the
{heath defcended of an inch lower than the end
of the hot metallic cylinder.

As the oil was very tranfparent, and the jar
placed in a favourable light, the conical projection
of ice was perfectly vifible, even after the hot cyl
inder was introduced into the jar ; and had any
Heat DESCENDED through the thin flratum of fluid
oil which remained interpofed between the hot fur-
face of the iron and the pointed projection of ice,
which was under it, there is no doubt but this
Heat muft have been apparent, by the melting of

the



in Fluids, 317

the ice ; which event would have been difcovered,
either by the diminution of the height of this pro
jection, or by an alteration of its form. But this
was not the cafe : the ice did not appear to be in the
fmalleft degree diminifhed, or otherwife affected by
the vicinity of the hot iron.

My reader will naturally fuppofe, without my
mentioning the circumftance, that due care was
taken in introducing the cylinder into the jar, to do
it in the moft gentle manner poffible, to prevent the
oil from being thrown into undulatory motions ;
and that proper means were ufed for con lining the
cylinder, motionlefs, in its place, when it had ar
rived there.

As this experiment appears to me to be unex
ceptionable, and its refult unequivocal and deciiive ;
in order that a perfect idea may the more eafily be
formed of it, I have added the Figure 4, where a
fection of the whole of the apparatus ufed in making
it may be ieen, expreffed in a clear and diftincl
manner.

If the general refult of the Experiments, of which
an account has been-given in the two firfc Chapters
of this Effay, afforded reafon to conclude that
water is a non-conductor of Heat, the refult of that
here defcribed certainly proves, in a manner quite
as fatisfactory, that oil is alfo a non-condulor ; and
ferves to give an additional degree of probability to
the conjecture, that all Fluids are neceffarily non
conductors of heat.

As mercury which is a metal in fuiion, is differ
ent in many refpects from all other Fluids, I

was



3 1 8 Of the Propagation of Heat

\vas very impatient to know if it agreed with them
in that eflential property, from which they have
been denominated non-conductors of Heat,and this
I found to be actually the cafe, by the refult of the
following decifive Experiment*

Experiment 9 No. 56.

Having emptied and cleaned out the cylindrical
glafs jar, ufed in the laft mentioned Experiment,
and replenimed it with a freih cake of ice, with a
conical projection in the middle of its upper lide, I
placed the jar, furrounded by pounded ice and
water, on the table, in the cold room,' where the
foregoing experiment had been made ; and poured
over the cake of ice as much ice-cold mercury, as
covered it to the height of about an inch. Having
cleaned the furface of the mercury in the jar with
blotting paper, I fuffered the whole to remain quiet,
about an hour ; and then very gently introduced
the end of the hot cylinder of iron (inclofed in its
paper meath) into the mercury, and fixed it im-
moveably in fuch a pofition, that its flat end, which
was naked, was immediately over the point of the
conical projection of ice, and diftant from it about
\ of an inch ; where I fuffered it to remain feveral
minutes.

It is necefiary that I mould mention, that, in
order to prevent the internal motions in the mafs of
mercury, which would other wife have been occa-
fioned by the rifmg and fpreading out on its furface
of thofe particles of that fluid, which, having

touched



in Fluids. 319

touched the flat end of the hot iron, became fpecif-
ically lighter in confequenee of their increafe of
temperature, the end of the hollow cylindrical
fheath, in which the foiid cylinder of iron was
placed, was made to project about ~ of an inch
below the flat end of the iron* This precaution
was like wife ufed, and for a fimilar reafon, in the
preceding Experiment ; when oil was ufed in the
place of the mercury 5 as was mentioned, though
without being explained, in giving an account of
that experiment-
As the cake of ice, on which the mercury repofed,
was at that temperature precifely at which ice is dif-
pofed to melt with the fmalleft additional quantity
of Heat, if any Heat had found its way downwards
through the mercury to the ice in this Experiment,
water would moil undoubtedly have been formed ;
and this water would as undoubtedly have appeared
on the furface of the mercury on taking away the
iron : but there was not the fmalleft appearance of
any ice having been melted,

To find out whether the cake of ice was really at
that temperature at which it was difpofed to melt
with any additional Heat, I thruft down the end of
my finger through the mercury, and touched the
ice ; and this Experiment removed all my doubts ;
for Ifound that, however expeditioufly Iperformed
that operation, it was hardly poffible for me to
touch the ice without evident figns of water having
been produced being left behind, on the clean and
bright furface of the mercury, on taking away my
finger.
VOL. ii. T t From



320 Of the Propagation of Heat

From the refults of all thefe experimental invefti-
gations it appears to me, that we may fafely con-
elude that ivatsr^ oil, and mercury are perfect non-
condudors of Heat ; or, that when either of thofe
iubftances takes the form of a fluid, all interchange
and communication of Heat among its particles , or
from one of them to the other, directly, becomes
from that moment abfolutely impoffible*

That this is alfo the cafe with refpecl to the par
ticles of air 9 has been rendered extremely probable,
I believe I might lay proved, by the Experi
ments of which I gave an account in one of my
Papers on Heat, publifhed in the Tranfaclions of
the Royal Society ; and I have {hewn elfe where
(in my Sixth Effay) how much reafon there- is to
conclude, that the particles of Steam and of Flame
are in the fame predicament.

But if all interchange and communication of
Heat, from particle to particle immediately, or de
froche en proche, be abfolutely impoffible in fo many
elaftic and unelaftic Fluids^ and in Fluids fo ef-
fentially different in many other refpects, is there
not mfficient grounds to conclude from hence, that
this property is common to all Fluids and that it
is even effential to fluidity ?

It is eafy to conceive, that the difcovery of fo im
portant a circumftance muft neceffarily occalion a
confiderable change in the ideas we have formed in
refpecl to the mechanical operations which take
place in many of the great phenomena of Nature ;
as vveli as in many of thofe Hill more interefting

chemical



in Fluids. 321

chemical operations, which we are able to direct,
but which we iind, alas ! very difficult to explain.
In my Paper on Heat,above mentioned,publifhed
in the Philofophical Tranfactions for the year 1 792,
I endeavoured to apply the difcovery of the non
conducting power of air in accounting for the
warmth of the hair of beafts ; of the feathers of
birds ; of artificial clothing ; and of fnow, the
winter garment of the earth ; and alfo, in explain
ing the caufes of the cold winds from the polar re
gions, and of their different directions in different
countries, which prevail at the end of winter, and
early in the fpring.

In my Sixth Eflay (on the Management of

Heat and the Economy of Fuel) I availed myfelf

of the knowledge of the non-conducting power of

Jleam and of fiame^ in explaining the effects of a

blow-pipe in increaiing the action of pure flame ;

and in inveftigating the molt advantageous forms

for boilers : and in the Third Chapter of this Effay

I have endeavoured to apply the difcoveries which

have been made, refpecting the manner in which

Heat is propagated in water Jm explaining the means

which appear to have been ufed by the Creator of

the world for equalizing the temperatures of the

different climates, and preventing the fatal effects

of the extremes of heat and of cold on the furface

of the globe. But a moft interefting application

remains to be made of thefe difcoveries^to chernijlry ;

\ vegetation ; and the animal economy ; and to

the learned in thofe branches of fcicncc I beg leave

moft earneitly to recommend them. If I am not

much



322 Of the Propagation of Heat

much miftaken they will throw a new light on
many of thofe myfterious operations of Nature, in
which inanimate bodies are put in motion^ their
forms changed their component parts feparated,
and new combinations formed ; and it is poffible
that they may even enable us to account, on me^
chanical principles, for thofe furprifing appearances
of preference and predilection among bodies, which,
without eyer having been attempted to be explain
ed, have been diftinguifhed by the appellation of
chemical affinity.

Perhaps it will be found that every change of
form, in every kind of fubftance, is owing to Heat ;
and to Heat alone : that every concretion is a true
congelation, effected by cold, or a diminution of
Heat ; and that every change from a folid to a
fluid form is a real/?//^. That the difference be
tween calcination in the wet and in the dry way, is,
in fact, much lefs than has hitherto been generally
imagined ; and that no metal is ever diflblved till it
\\zsjirft been melted.

Perhaps it will be found, that the apparent vio
lence with which folid bodies of fome kinds are at
tacked by their liquid folvents,- and which has, I
believe, been confidered as a proof of a ilrong che
mical affinity- is not owing to any particular at
traction, or election, but to the confiderable degree
of heat, or of cold, which is produced in their
union with their menftrua ; or to a great difference
in the fpecific gravity of the menftruum in its nat
ural ftate, and that of the fame fluid after it has
changed to a faturated foliation*

If



in Fluids. 323

If Fluids are non-conductors of Heat, it is evident
that, if any change of temperature takes place in
chemical folution, it muft neceffarily produce cur
rents in the folvent ; and that thefe currents muft
be the more rapid, as the change of temperature is
greater ; and as they necefiarily caufe a fucceffion
of frefli particles of the folvent to come into contact
with the folid, it is evident, all other things being
equal, that the rapidity of the procefs of folution
will be as the rapidity of thefe currents, or as the
change of temperature.

But the currents produced by the difference in
the fpecific gravities of the fluid menftruum, and
of the faturated folution, have perhaps, in general,
a ftill greater effect in bringing a rapid fucceffion of
freih particles of the menftruum into contact with
the folid body that is diffolved in it, than thofe pro
duced by the change of temperature.

When thefe two caufes confpire to accelerate the
motion of the fame current, or when their ten
dencies are in the fame direction, as is the cafe in
the folution of common fea-falt in water, the
folution ought to be mod rapid.

When common fait is diffolved in water, the fpe
cific gravity of the faturated folution is greater than
that of pure water, and will therefore defcend in it ;
and cold being produced in the procefs, and water
being a non-conductor of Heat, the fpecific gravity
of the faturated folution will btftill farther increafed,
in confequence of its condenfation with this cold,
by which its defcent in the water will be ftill farther
accelerated.

A curious



324 Of the Propagation of Heat

A curious quefticm here prefents itfelf, which,
could it be refolved, might greatly tend to elucidate
this abftrufe fubjed of philofophical inveftigation,
Suppofmg that, in a cafe where Heat is generated
in the folution of a folid in a fluid menftruum, the
addition to the fpecific gravity of the menftruum,
arifing from its chemical union with the folid,iliould
fo precifely counterbalance the diminution of the
fpeciiic gravity of the Fluid, by the Heat generated
in the procefs, that the hot faturated folution fliould
be precifely of the fame fpecific gravity as the cold
menftruum ; would, or would not the procefs
of folution be poffible under fuch circuit
fiances ?

If the apparent tendency to approach each other,
which we fometimes perceive in folids and their
fluid menftrua, were real ; if that peculiar kind of
attraction of predilection which has been called
chemical affinity, has a real exiftence, and if its in-
fluence reaches beyond the point of aftual contaft^ (as
has, I believe, been generally fuppofed,) as there is
no appearance of any attraction whatever, or affi
nity, between any folid body, and a faturated folu
tion of the fame body in its proper menftruum, it
feems probable that the folution would take place,
under the circumftances defcribed : but fliould
the attraction of affinity, according to the definition
of it here giveri, have no exiftence in fact, (which
is what I very much fufpect,) in that cafe it is evi
dent that the folution, though it would not be ab-
folutely impoffible, would.be fo very flow as hardly
to be perceptible.



in Fluids. 325

It would not be impoffible, becaufe the particles of
the menftruum in immediate contact with the folid 3
though, in the moment of their faturation, they
would have no tendency to move out of their places,
yet, as they would by degrees neceffarily give off,
to the undiffolved part of the folid, a part of the
Heat acquired in the chemical procefs by which
they were faturated, being condenfed by this lofs of
Heat, they would, at length, begin to defcend, and
give place to other particles of the menftruum ;
which, in their turns, would follow them, but with
velocities, however, continually decreafing ; on
account of the gradual augmentation of tempera
ture of the undiffolved part of the folid, and of the
Heat communicated by that folid fubftance to .the
whole mafs of the liquid menftruum.

Though it would, probably, be extremely diffi
cult to contrive any fingle experiment, from the re-
fult of which a fatisfactory dediion of this queftion
could be obtained, yet it does not appear to be im-
poflible to difcover by indirect means, the principal
fact on which its decifion muft depend.

It is a well known fact, that, when water which
holds fea-falt in folution is mixed, in any veiTel,
with freh water, the fait will, after a ihort time, be
found to be very equally diftributed in every part of
the whole mafs ; and I believe that it has been gen
erally confidered, that this equal diftribution of the
fait is owing to the affinity which is iuppofed toexift
between fea-falt and water.

Having doubts with refpecl to the exigence of
this fuppofed attraction ; and fufpecling that the

equal



326 Of the Propagation of Heat

equal diitribution of the fait was owing to a very
different caufe the internal motions among the
particles of the water, occafioned by accidental
changes of temperature I made the following
Experiment, which, I fancy, will be confidered as
decifive*



Experiment^ No. 57*

I took a cylindrical glafs jar, 4 ~ inches in diame
ter, and 7 1 inches high, and placing it in the
middle of another cylindrical glafs jar, j~ inches
in diameter, and 8 inches high, which flood in
a very mallow earthen difh, nearly filled with
pounded ice and water > I placed the dilh, with its
contents, on a ftrong table, in an uninhabited room,
in a retired part of the houfe, where the tempera
ture of the air, which was the fame, with very
little variation, day and night, was at about 36 F.
Having prepared, and at hand, a quantity of the
flrongeft brine I could make with fea-falt, which
was very clear, tranfparent, perfectly colourlefs,
and ice-cold ; and alfo, a quantity of frefh, or
pure water, ice-cold, lightly tinged of a red
colour with turnfol ; and fome ice> cold olive-oil ; I
firft poured as much of the frefh water into the
fmall cylindrical jar as was neeefTary to fill it up to
the height of above 2 inches ; and then, by means
of a glafs funnel, which ended in a long and narrow
tube, by introducing this tube into the frefh water,
and refting it on the bottom of the jar, I poured a

quantity



in Fluids. 327

quantity of the brine, equal to that of the frefh
water, into the jar ; and in performing this opera
tion I took fo much care to do it gently* and with
out difturbing the frefh water already in the jar,
that, when it was finilhed, the frefh water, which,