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or if the force of gravity over it could in any other way be
diminished, then it would expand, and exist of a lower tension ;
upon the renewal of the gravitating force, either by approxima-
tion to the earth's surface or otherwise, the particles would ap-
proach each other, until the elasticity of the whole was again
equal to the force of gravity.

Inasmuch as gases and vapours undergo no change by mere
expansion or attenuation, which can at all disturb the analogy
existing between them in their permanent state under ordinary
circumstances, all the phenomena which have been assumed as
occurring with the air at the limit of our atmosphere may, with
equal propriety, be admitted with respect to vapour in general
in similar circumstances ; for we have no reason for supposing
that the particles of one vapour more than another sxtfree from
the influence of gravity, although the force may, and without
doubt does, vary with the weight and elasticity of the particles
of each particular substance.

It will be evident also, that similar effects would be produced
by the force of gravity upon air or vapour of the extreme tenuity
and feeble tension referred to, whatever be the means taken to
bring it into that state ; and it is not necessary to imagine the
portion of air operated upon, as taken from the extremity of
our atmosphere, for a portion of that at the earth's surface, if
it could be expanded to the same degree by an air-pump, would
undergo the same changes : when of a certain rarity it would
just balance the attraction of gravitation and fill the receiver



1826.] On the existence of a Limit to Vaporization. 201

with vapour ; but then, if half were taken out of the receiver,
the remaining portion, in place of filling the vessel, would sub-
mit to the force of gravity, would contract into the lower half
of the receiver, until, by the approximation of the particles,
the vapour there existing should have an elasticity equal to the
force of gravity to which it was subject. This is a necessary
consequence of Dr. Wollaston's argument.

There is yet another method of diminishing the elasticity of
vapour, namely, by diminution of temperature. With respect
to the most elastic substances, as air and many gases, the com-
paratively small range which we can command beneath common
temperatures, does nothing more at the earth's surface than
diminish in a slight degree their elasticity, though two or three
of them, as sulphurous acid and chlorine, have been in part
condensed into liquids. But with respect to innumerable
bodies, their tendency to form vapour is so small, that at com-
mon temperatures the vapour produced approximates in rarity
to the air upon the limits of our atmosphere ; and with these,
the power we possess of lessening tension by diminution of
temperature, may be quite sufficient to render it a smaller force
than its opponent, gravity; in which case it will be easy to com-
prehend that the vapour would give way to the latter, and be
entirely condensed. The metal, silver for instance, when vio-
lently heated, as on charcoal urged by a jet of oxygen, or by
the oxy-hydrogen or oxy-alcohol flame, is converted into
vapour ; lower the temperature, and before the metal falls
beneath a white heat, the tension of the vapour is so far dimi-
nished, that its existence becomes inappreciable by the most
delicate tests. Suppose, however, that portions are formed,
and that vapour of a certain tension is produced at that tem-
perature ; it must be astonishingly diminished by the time the
metal has sunk to a mere red heat ; and we can hardly conceive
it possible, I think, that the silver should have descended to
common temperatures, before its accompanying vapour will, by
its gradual diminution in tension, if uninfluenced by other
circumstances, have had an elastic force far inferior to the force
of gravity ; in which case, that moment at which the two forces
had become equal, would be the last moment in which vapour
could exist around it ; the metal at every lower temperature
being perfectly fixed.



On the existence of a Limit to Vaporisation. Q1826.

I have illustrated this case by silver, because from the high
temperature required to make any vapour appreciable, there
can be little doubt that the equality of the gravitating and elas-
tic forces must take place much above common temperatures,
and therefore within the range which we can command. But
there is, I think, reason to believe that the equality in these
forces, at or above ordinary temperatures, may take place
with bodies far more volatile than silver ; with substances
indeed which boil under common circumstances at 600 or
700 F.

If, as I have formerly shown*, some clean mercury be put at
the bottom of a clean dry bottle, a piece of gold-leaf attached
to the under part of the stopper by which it is closed, and the
whole left for some months at a temperature of from 60 to 80,
the gold-leaf will be found whitened by amalgamation, in con-
sequence of the vapour which rises from the mercury beneath ;
but upon making the experiment in the winter of 1824-25, 1 was
unable to obtain the effect, however near the gold-leaf was
brought to the surface of the mercury ; and I am now inclined
to believe it was so because the elastic force of any vapour which
the mercury could have produced at that temperature, was less
than the force of gravity upon it, and that consequently the
mercury was then perfectly fixed.

Sir Humphry Davy, in his experiments on the electrical phe-
nomena exhibited in vacuo, found, that when the temperature
of the vacuum above mercury was lowered to 20 F. no further
diminution, even down to 20 F., was able to effect any change,
as to the power of transmitting electricity, or in the luminous
appearances ; and that these phenomena were then nearly of
the same intensity as in the vacuum made over tint- Hence,
in conjunction with the preceding reasoning, I am led to con-
clude that they were then produced independent of any vapour
of the metals, and that under the circumstances described ; no
vapour of mercury existed at temperatures beneath 20 F.

Concentrated sulphuric acid boils at about 600 F. 3 but as
the temperature is lowered the tension of its vapour is rapidly
diminished. Signer BellaniJ placed a thin plate of zinc at the
upper part of a closed bottle, at the bottom of which was some

* Quarterly Journal of Science, x. 354. See page 57.

f Phil. Trans. 1822, p. 71. J Giornale di Fisica, v. 197.



1826.] On the existence of a Limit to Vaporization. 203

concentrated sulphuric acid. No action had taken place at
the end of two years, the zinc then remaining as bright as at
first ; and this fact is very properly adduced in illustration of
the fixedness of sulphuric acid at common temperatures. Here
I should again presume, that the elastic force which tended to
form vapour was surpassed by the force of gravity.

Whether it be admitted or not, that in these experiments
the limit of volatilization, according to the principle of the
balance of forces before stated, had been obtained, I think we
can hardly doubt that such is the case at common temperatures
with respect to the silver and with all bodies which bear a
high temperature without appreciable loss by volatilization, as
platina, gold, iron, nickel, silica, alumina, charcoal, c. ; and
consequently, that, at common temperatures, no portion of
vapour rises from these bodies or surrounds them ; that they
are really and truly fixed ; and that none of them can exist in
the atmosphere in the state of vapour.

But there is another force, independent of that of gravity,
at least of the general gravity of the earth, which appears to
me sufficient to overcome a certain degree of vaporous elasticity,
and consequently competent to the condensation of vapour of
inferior tension, even though gravity should be suspended ; I
mean the force of homogeneous attraction.

Into a clean glass tube, about half an inch in diameter, in-
troduce a piece of camphor ; contract the tube at the lamp
about 4 inches from the extremity ; then exhaust it, and
seal it hermetically at the contracted part; collect the camphor
to one end of the tube ; and then, having placed the tube in a
convenient position, cool the other end slightly, as by covering
it with a piece of bibulous paper preserved in a moist state by
a basin of water and thread of cotton ; in this way, a difference
in temperature of a few degrees will be occasioned between
the ends of the tube, and after some days, or a week or two,
crystals of camphor will be deposited in the cooled part ; there
will not, however, be more than three or four of them, and
these will continue to increase in size as long as the experiment
is undisturbed, without the formation of any new crystals, unless
the difference of temperature be considerable.

A little consideration will, I think, satisfy us that, after
the first formation of the crystals in the cooled part, they have



04- On the existence of a Limit to Vaporization. [1826.

the power of diminishing the tension of the vapour of camphor
below that point at which it could have remained unchanged
in contact with the glass, or in space ; for the vapour of the
camphor is of a certain tension in the cooled end of the tube,
which it can retain in contact with the glass, and therefore it
remains unchanged ; but which it cannot retain in contact with
the crystal of camphor, for there it is condensed, and con-
tinually adds to its mass. Now this can only be in conse-
quence of a positive power in the crystal of camphor of
attracting other particles to it; and the phenomena of the
experiment are such as to show that the force is able to over-
come a certain degree of elasticity in the surrounding vapour.
There is therefore no difficulty in conceiving, that, by dimi-
nishing the temperature of a body and its atmosphere of
vapour, the tension of the latter may be so far decreased, as
at last to be inferior to the force with which the solid portion,
by the attraction of aggregation, draws the particles to it ; in
which case it would immediately cause the entire condensation
of the vapour.

The preceding experiment may be made with iodine, and
many other substances ; and indeed there is no case of distinct
crystallization by sublimation * which does not equally afford
evidence of the power of the solid matter to overcome a
positive degree of tension in the vapour from which the
crystals are formed. The same power, or the force of aggre-
gation, is also illustrated in crystallizing solutions ; where the
solution has a tendency to deposit upon a crystal, when it has
not the same tendency to deposit elsewhere.

It may be imagined that crystallization would scarcely go on
from these attenuated vapours, as it does in the denser states
of the vapours experimented upon. There is, however, no
good reason for supposing any difference in the force of aggre-
gation of a solid body, dependent upon changes in the tension
of the vapour about it ; and indeed, generally speaking, the
method I have assumed for diminishing the tension of the
vapour, namely, by diminishing temperature, would cause in-
crease in the force of aggregation.

* Calomel, corrosive sublimate, oxide of antimony, naphthaline, oxalic
acid, &c. &c.



1830.] On the Limits of Vaporization. 205

Such are the principal reasons which have induced me to
believe in the existence of a limit to the tension of vapour.
If I am correct, then there are at least two causes, each of
which is sufficient to overcome and destroy vapour when re-
duced to a certain tension ; and both of which are acting
effectually with numerous substances upon the surface of the
earth, and retaining them in a state of perfect fixity. I have
given reasons for supposing that the two bodies named, which
boil at about 600 F., are perfectly fixed within limits of low
temperature which we can command ; and I have no doubt,
that nearly all the present recognized metals, the earths, car-
bon, and many of the metallic oxides, besides the greater
number of their compounds, are perfectly fixed bodies at com-
mon temperatures. The smell emitted by various metals when
rubbed may be objected to these conclusions, but the circum-
stances under which these odours are produced, are such as
not to leave any serious objections on my mind to the opinions
above advanced.

I refrain from extending these views, as might easily be
done, to the atomic theory, being rather desirous that they
should first obtain the sanction or correction of scientific men.
I should have been glad to have quoted more experiments
upon the subject, and especially relative to such bodies as
acquire their fixed point at, or somewhat below common tem-
peratures. Captain Franklin has kindly undertaken to make
certain experiments for me in the cold regions to which he has
gone, and probably when he returns from his arduous under-
taking, he may have some contributions towards this subject.

Royal Institution, May 4, 1826.



On the Limits of Vaporisation*.

I WAS induced some time since to put together a few remarks
and experiments on the existence of a limit to vaporization,
which were favoured with a place in the Philosophical Transac-
tions for the year 1826f. When the experiments there men-
tioned were published, I arranged some others bearing upon
the same subject, but which required great length of time for

* Royal Institution Journal, 1830, i, 70. t See page 199.



206 On the Limits of Vaporisation. [1830.

the development of their result. Four years have since
elapsed, during which, the effects, if any, have been accumu-
lating, and it is the object of this brief paper to give an account
of them.

The point under consideration originally was, whether there
existed any definite limit to the force of vaporization. Water
at 220 sends off vapour so powerfully, and in such abundance
as to impel the steam-engine; at 120 it sends off much less;
at 40, though cold, still vapour rises ; below 32, when the
water becomes ice, yet the ice evaporates ; and there is no cold,
either natural or artificial, so intense as entirely to stop the
evaporation of water, or in the open air prevent a wet thing
from becoming dry.

The opinion of many, among whom were the eminent names
of Sir H. Davy and Mr. Dalton, was, that though the power
of evaporating became continually less with diminution of tern-'
perature, it never entirely ceased, and that therefore every
solid or fluid substance had an atmosphere of its own nature
about it and diffused in its neighbourhood ; but which being
less powerful as the body was more fixed, and the existing
temperature lower, was, with innumerable substances, as the
earths, metals, &c., so feeble as to be quite insensible to ordi-
nary or even extraordinary examination, though in certain cases
they might affect the transmission of electricity ; or, rising into
the atmosphere, produce there peculiar and strange results.

The object of my former paper was to show that a real and
distinct limit to the power of vaporization existed, and that at
common temperatures we possess a great number of substances
which are perfectly fixed. The arguments adduced, were drawn
first from the power of gravity, as applied by Dr. Wollaston,
to show that the atmosphere around our globe had an external
limit, and then from the power of cohesion ; either of these
seemed to me alone sufficient to put a limit to vaporization, and
experiments upon the sufficiency of the latter force were de-
tailed in the paper.

The conclusion was, that although such substances as ether,
alcohol, water, iodine, &c. could not as such be entirely de-
prived of their vaporizing force, by any means we could apply
to them, but, if in free space or in air, would send off a
little vapour, yet there were other bodies, as iron, silver, copper,



1830.] On the Limils of Vaporization. 207

&c., most of the metals, and also the earths, which were abso-
lutely fixed under common circumstances, the limit of their
vaporization being passed ; and further, that there were a few
bodies, the limits of whose vaporization occurred at such tem-
peratures as to be within our command, and therefore passable
in either direction. Thus mercury is volatile at temperatures
above 30, but fixed at temperatures below 20, and concentrated
sulphuric acid, which boils at temperatures about 600, is fixed
at the ordinary temperature of the atmosphere.

It is well known in the practical laboratory that vaporization
may be very importantly assisted so as to make certain pro-
cesses of distillation effectual, which otherwise would fail.
Thus with the essential oils, many of them which would re-
quire a high temperature for their distillation if alone, and be
seriously injured in consequence, will, when distilled with water,
pass over in vapour with the vapour of the water at a much
lower temperature, and, being condensed, may be obtained
in their unaltered state.

It has been supposed that the vapour of the water, either by
affinity for the vapour of the essential oil or in some other way,
has increased the vaporizing force of the latter at the tem-
perature applied, and so enabled it to distil over; but there is
no doubt that if air or any other similar elastic medium were
made to come in contact with the mass of essential oil at 212
in equal quantity, and in a manner to represent the vapour of
water, it would, according to well-known laws, carry up the
vapour of the essential oil perhaps to an equal extent, and pass
it forward ; only the facility with which the carrying agent
is condensed when it consists of steam, allows of the condensa-
tion of every particle of the essential oil vapour, whereas the
permanency of the elastic state of the air would cause it to
retain a large proportion of the vapour of the oil when cold,
and consequently a diminished result would be obtained.

There are, nevertheless, some appearances which seem to
favour the idea that water occasionally favours vaporization,
not merely in the manner referred to above, but by some pecu-
liar process ; and it was to ascertain whether substances which,
from a consideration of the general reasoning already referred
to, and the high temperature at which they sensibly volatilized,
might be considered as fixed at common temperatures, could,



208 On the Limits of Vaporization. [1830.

by reason of this peculiarity, have any sensible degree of vola-
tility, in conjunction with water or its vapour, conferred upon
them at ordinary temperatures, that the following experiments
were made. It is well known that a theory of meteoric stones
has been founded on the supposition that the earthy and metallic
matter found in them had been raised in vapour from similar
matter upon the earth's surface ; which vapours, though ex-
tremely attenuated and dilute at first, gradually accumulated,
and by some natural operation in the upper regions of the atmo-
sphere became condensed, forming those extraordinary masses
of matter which occasionally fall to us from above. The theory
has in its favour the remarkable circumstance, that, notwith-
standing many substances occur in meteoric iron and stones,
yet there is none but what also occur on this our earth* ; and
it also has a right to the favouring action of water, if there be
such an action ; because vaporization is one of the most import-
ant, continual, and extensive operations that go on between the
surface of the globe and the atmosphere around it.

In September 1826, several stoppered bottles were made
perfectly clean, and several wide tubes closed at one extremity,
so as to form smaller vessels capable of being placed within the
bottles, were prepared. Then selected substances were put
into the tubes, and solutions of other selected substances into
the bottles : the tubes were placed in the bottles so that nothing
could pass from the one substance to the other, except by way
of vaporization. The stoppers were introduced, the bottles tied
over carefully and put away in a dark safe cupboard, where,
except for an occasional examination, they have been left for
nearly four years, during which time such portion of the sub-
stances as could vaporize have been free to act and produce
accumulation of their specific effects.

No. 1. The bottle contained a clear solution of sulphate of
soda with a drop of nitric acid, the tube, crystals of muriate
of baryta. One half or more of the water has passed by eva-
poration into the tube, and formed a solution of muriate of

* This very striking circumstance does not prove that aerolites in any way
originate from our planet ; but then, if we could by other arguments deduce
that they were extraneous, it would lead to the conclusion that the substances
which have been used in the construction of this our globe, are the same with
those which have been used extensively elsewhere in the material creation.



1830.] On the Limits of Vaporization. 209

baryta above crystals, but both that and the remaining solution
of sulphate of soda is perfectly clear ; there is not the slightest
trace of sulphate of baryta in either the one or the other, so
that neither muriate of baryta nor sulphate of soda appear to
have volatilized with the water.

No. 2. Bottle, solution of nitrate of silver ; tube, fused chlo-
ride of sodium. All the water has passed from the nitrate of
silver to the salt ; but there is no trace of chloride of silver
either in one or the other. No nitrate of silver has sublimed
with the water, nor has any chloride of sodium passed over to
the nitrate.

No. 3. Bottle, solution of muriate of lime ; tube, crystals of
oxalic acid. The water here remained with the muriate of lime.
In the tube, the oxalic acid when put in had formed a loose
aggregation, with numerous vacancies, and with a very irregular
upper surface about an inch below the upper edge of the tube.
No particular appearances occur in the vacancies ; but at the
top there has evidently been a sublimation of the oxalic acid,
for upon the crystals and glass new crystals in exceedingly thin
plates and reflecting colour have been formed ; these rise no
higher in the tube than to the level of the most projecting part
of the original portion of oxalic acid ; no appearance of sublima-
tion is evident above this, and it seems as if the most elevated
parts of the salt have given off vapour, which has sunk and
formed crystals on the neighbouring lower surfaces, but that
no vapour has risen to the upper part of the tube. On exa-
mining the solution by a drop or two of pure ammonia, it was
found that a slight precipitate of oxalate of ammonia occurred.
The experiment shows, therefore, that oxalic acid is volatile
at common temperatures, and had not only formed crystals in
the tube, but had passed over to the solution of lime.

No. 4. Bottle, solution half sulphuric acid, half water ; tube,
crystallized common salt. No water has passed to the salt.
On opening the bottle, the clear diluted sulphuric acid was
examined for muriatic acid, but no trace could be found.
Hence chloride of sodium has not been volatilized under these
circumstances.

No. 5. Bottle, solution of muriate of lime ; tube, crystals of
oxalate of ammonia. The oxalate of ammonia appeared quite
unchanged. The solution of muriate of lime was perfectly clear ;

p



210 On the Limits of Vaporization. [1830.

but when a little pure ammonia was added to it, a very faint
precipitate of oxalate of lime was produced.

No. 6. Bottle, little solution of potash ; tube, white arsenic
in pieces and powder. This bottle was opened because of the
appearances, in October 1829, having then remained three
years undisturbed. The arsenious acid was to all appearance
unchanged. The solution of potash was turbid and foul. On
chemical examination, it proved to have acted powerfully on
the glass. It had dissolved so much silica as to become a soft
solid, by the action of an acid, and it had also dissolved a con-
siderable quantity of lead ; but there was no trace of arsenious
acid in it ; so that this substance, although abundantly volatile
at 600, had not risen in vapour when aqueous vapour and air
were present at common temperatures.

No. 7 was some of the sulphuric acid used in these expe-
riments, preserved for comparison.

No. 8. Bottle, solution half sulphuric acid, half water ; tube,
pieces of muriate of ammonia. When this bottle was opened,
the pieces of muriate of ammonia presented no appearance
of change ; there was no moisture about them, nor any ap-
pearances of dissection that I could distinguish. The diluted



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