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sulphuric acid being examined by sulphate of silver, gave no
evidence of muriatic acid ; so that muriate of ammonia appears
fixed under these circumstances.

No. 9. Bottle, a little solution of persulphate of iron ; tube,
crystals of the ferro-prussiate of potash. Both were unchanged ;
there was no appearance of prussian blue about either the
crystals or solution ; neither of the salts had been volatilized.

No. 10. Bottle, a little solution of potash; tube, fragments
of calomel. Here the potash had acted upon the glass, as in
No. 6 ; but, with respect to the calomel, the volatility of which
was in question, there was not the slightest trace of such an
effect. No black oxide nor other substance existed in the
potash solution, which could allow the presumption that any
calomel had passed.

No. 11. Bottle, solution of potash; tube, fragments of cor-
rosive sublimate. Here the potash had acted on the glass as
before ; carbonic acid had also gained access by the stopper ;
so that no caustic potash was present ; but there were distinct
appearances of the sublimation of corrosive sublimate, and



1830.] On the Limits of Vaporization. 211

minute crystals of the substance were even attached to the
under part of the stopper in the bottle. Hence corrosive
sublimate is volatile at common temperatures.

No. 12 and 13. Bottles, solution of chromate of potash;
tubes, in one, chloride of lead in powder, in the other nitrate
of lead in crystals. In both these experiments the chromate of
potash had acted upon the lead of the glass, and rendered it
yellow and dim ; so that no indication could be gathered re-
lating to the volatility of the compounds of lead.

No. 14. Bottle, solution of iodide of potassium ; tube, chloride
of lead. Both remained unaltered ; the solution of iodide was
perfectly clear and colourless ; no trace of the chloride of lead
had passed over in vapour.

No. 15. Bottle, solution of muriate of lime; tube, crystals of
carbonate of soda. A part of the water has passed to the car-
bonate of soda ; but both it and the remaining solution of mu-
riate of lime are perfectly clear. No portion of either salt has
volatilized from one place to another.

No. 16. Bottle, dilute sulphuric acid ; tube, nitrate of am-
monia in fragments. The nitrate was slightly moist. The
acid being examined was found to contain nitric acid, whilst the
test acid, No. 7, was perfectly free from it. It would therefore
appear that nitrate of ammonia is a salt volatile at common
temperatures ; although it is just possible that slow decom-
position may take place in it, and so nitric acid or its elements
pass over. ,

No. 17. Bottle, solution of persulphate of copper; tube,
crystals of ferro-prussiate of potash. The crystals had attracted
most of the water from the cupreous salt ; but the solution of
ferro-prussiate and that of the copper had their proper colour;
neither were rendered brown ; no salts had been volatilized.

No. 18. Bottle, solution of acetate of lead; tube, iodide of
potassium. The acetate of lead is now dry ; the iodide of
potassium has taken all the water and formed a brown solution,
in which there is free iodine ; probably a little acetic acid has
passed over and caused the change in the iodide of potassium.
There is no appearance of iodide of lead in the tube, but there
is in the bottle, and most probably in consequence of the vapo-
rization of the free iodine from the solution in the tube.

From these experiments it would appear that there is no



Fluidity of Sulphur at Common Temperatures. [1826.

reason to believe that water or its vapour confer volatility, even
in the slightest degree, upon those substances which when alone
have their limits of vaporization at temperatures above ordinary
occurrence, and that consequently natural evaporation can
produce no effects of this kind in the atmosphere.

It would also appear that nitrate of ammonia, corrosive sub-
limate, oxalic acid, and perhaps oxalate of ammonia, are sub-
stances which evolve vapour at common temperatures.

Royal Institution) Aug. 30, 1830.



Fluidity of Sulphur at Common Temperatures*.

HAVING placed a Florence flask containing sulphur upon a hot
sand-bath, it was left to itself. Next morning, the bath being
cold, it was found that the flask had broken, and in consequence
of the sulphur running out, nearly the whole of it had disap-
peared. The flask being broken open, was examined, and
was found lined with a sulphur dew, consisting of large and
small globules intermixed. The greater number of these,
perhaps two-thirds, were in the usual opake solid state ; the
remainder were fluid, although the temperature had been
for some hours that of the atmosphere. On touching one of
these drops, it immediately became solid, crystalline, and
opake, assuming the ordinary state of sulphur, and perfectly
resembling the others in appearance. This took place very
rapidly, so that it was hardly possible to apply a wire or other
body to the drops quick enough to derange the form before
solidity had been acquired ; by quick motion, however, it might
be effected, and by passing the finger over them, a sort of
smear could be produced. Whether touched by metal, glass,
wood, or the skin, the change seemed equally rapid ; but it
appeared to require actual contact ; no vibration of the glass
on which the globules lay rendered them solid, and many of
them were retained for a week in their fluid state. This state
of the sulphur appears evidently to be analogous to that of
water cooled whilst quiescent below its freezing-point. The
same property is also exhibited by some other bodies, but I
believe no instance is known where the difference between the

* Quarterly Journal of Science, xxi. 392.



1827.'] Fluidity of Sulphur at Common Temperatures. 213

usual point of fluidity and that which could thus be obtained
is so great: it, in the present instance, amounts to 130, and
it might probably have been rendered greater if artificial cold
had been applied.



On the Fluidity of Sulphur and Phosphorus at Common

Temperatures *.

I PUBLISHED some time ago a short account of an instance of
the existence of fluid sulphur at common temperaturesf ;
and though I thought the fact curious, I did not esteem it of
such importance as to put more than my initials to the account.
I have just learned, through the * Bulletin Universel' for Sep-
tember, p. 178, that Signor Bellani had observed the same
fact in 1813, and published it in the ' Giornale di FisicaJ,'
vol. vi. (old series). I also learn, by the same means, that
M. Bellani complains of the manner in which facts and theories,
which have been published by him, are afterwards given by
others as new discoveries ; and though I find myself classed
with Gay-Lussac, Sir H. Davy, Daniell, Bostock, c., in having
thus erred, I shall not rest satisfied without making restitution,
for M. Bellani in this instance certainly deserves it at my
hand.

Not being able to obtain access to the original journal, I shall
quote M. Bellani's very curious experiments from the ' Bulletin,'
in which they appear to be fully described. " The property
which water possesses of retaining its fluid state, when in
tranquillity, at temperatures 10 or 15 below its freezing-point,
is well known ; phosphorus behaves in the same manner ;
sometimes its fluidity may be retained at 13 (Centigrade?) for
a minute, an hour, or even many days. What is singular is,
that, though water cooled below its freezing-point congeals
easily upon slight internal movement, however communicated,
phosphorus, on the contrary, sometimes retains its liquid state
at 3, even though it be shaken in a tube, or poured upon
cold water. But, as soon as it has acquired the lowest tempe-
rature which it can bear without solidifying, the moment it is
touched with a body at the same temperature, it solidifies so

* Quarterly Journal of Science, xxiv. 469. t Ibid, xxi. 392 j or page 212.
J The Italian Journal has not yet arrived in this country.



214) Fluidity of Sulphur at Common Temperatures. [1827.

quickly, that the touching body cannot penetrate its mass. If
the smallest morsel of phosphorus is put into contact with a
liquefied portion, the latter infallibly solidifies, though it be
only a single degree below the limit of temperature necessary ;
this does not always happen when the body touching it is hete-
3neous.

Sulphur presented the same phenomena as phosphorus ;
fragments of sulphur always produced the crystallization of
cold fluid portions. Having withdrawn the bulb of a thermo-
meter which had been plunged into sulphur at 120, it came out
covered with small globules of sulphur, which remained fluid at
60; and having touched these one after another with a thread
of glass, they became solid : although several seemed in contact,
yet it required that each should be touched separately. A drop
of sulphur, which was made to move on the bulb of the thermo-
meter by turning the instrument in a horizontal position, did
not congeal until nearly at 30 ; and some drops were retained
fluid at 15, i. e. 75 of Reaumur below the ordinary point of
liquefaction."

The ' Bulletin Universel ' then proceeds to describe some
late and new experiments of M. Bellani, on the expansion in
volume of a cold dense solution of sulphate of soda during the
solidification of part of the salt in it. The general fact has,
however, been long and well known in this country and in
France ; and the particular form of experiment described is
with us a common lecture illustration. The expansion, as
ascertained by M. Bellani, is - 7 of the original volume of
fluid.

According to the ' Bulletin,' M. Bellani also claims, though
certainly in a much less decided manner than the above, the
principal ideas in a paper which I have published on the exist-
ence of a limit to vaporization ; and I referred back to the
6 Giornale diFisica'for 1822 (published prior to my paper),
for the purpose of rendering justice in this case also. Here,
however, the contact of our ideas is so slight, and for so brief
a time, that I shall leave the papers in the hands of the public
without further remarks. It is rather curious to observe how
our thoughts had been simultaneously engaged upon the same
subject. Being charged in the ( Bulletin' with quoting an ex-
periment from a particular page in M. Bellani's memoir (which



1826.] Perspective Aerial Light and Shade. 215

I did from another journal, in which the experiment only was
described), I turned to the original place, and there, though I
found the experiment I had transferred, I also found another
which I had previously made on the same suhject, and which
M. Bellani had quoted.

I very fully join in the regret which the ' Bulletin Universel'
expresses, that scientific men do not know more perfectly what
has been done, or what their companions are doing ; but I am
afraid the misfortune is inevitable. It is certainly impossible
for any person who wishes to devote a portion of his time to
chemical experiment, to read all the books and papers that are
published in connexion with his pursuit ; their number is im-
mense, and the labour of winnowing out the few experimental
and theoretical truths which in many of them are embarrassed
by a very large proportion of uninteresting matter, of imagination,
and of error, is such, that most persons who try the experiment
are quickly induced to make a selection in their reading, and
thus inadvertently, at times, pass by what is really good.



On a peculiar Perspective Appearance of Aerial Light and

Shade*.

ONE evening last month (Aug. 19, 1826), a curious aerial phe-
nomenon was observed from the undercliffat the back of the
Isle of Wight, just above Puckaster Cove. The sky was clear,
the sun had just set to those who were standing where the ap-
pearance was observed, when several enormous rays of light and
shade were remarked towards the E., N.E., and S.E., all radi-
ating in strait lines from a spot rather south of east, and just
upon the horizon. They were ten or twelve in number, did not
join at the place from whence they appeared to originate, but
seemed to emerge from an obscure portion of surface of a convex
form 8 or 9 in horizontal extent, and about the third of that
in height. The rays extended from 30 to 40 on the right and
left from the centre, but were of less extent as they became
more vertical. They diminished gradually in intensity at the
extremities until they could be traced no further. The ap-
pearance slowly faded away, some of the rays disappearing

* Quarterly Journal of Science, xxii. 81.



216 Perspective Aerial Light and Shade. [1826.

before others, but was observed upon the whole for about half
an hour.

At first the phenomenon seemed inexplicable, but after a
little consideration, was referred (and as it appeared from
after observations correctly) to an effect of aerial perspective.
The rays which seemed to originate from a common centre on
the east, were really only the intervals between long shadows
caused by the occurrence of clouds far to the west, and were
in fact passing to the place from whence they seemed to
originate, and the circumstances of the case seem to have been
as follow: the atmosphere contained a slight haze, which
allowed the sun's beams to pass forward with but little inter-
ruption, but was yet in sufficient quantity to reflect a consider-
able portion of light to the eye. The sun was just setting;
clouds, very far to the west and out of sight from the place
where the observer stood, stopped the light wherever they
interfered, and cast immense horizontal or nearly horizontal
shadows along the sky, parallel to each other, and over the
head of the observer. The difference between these shadows
and the intervening illuminated parts, could not be observed
over head or on the right or left hand, i. e. perpendicular to
their direction, because of the want of sufficient depth, as it
were, in the parts thus circumstanced, to make them visible ;
but as they receded from the observer in the direction from
the sun, they became fore-shortened, and then, from the greater
depth of mass, and consequently greater number of particles
looked at, became visible. This is at least one reason why
they were so visible towards the east; but another is the pro-
bable existence of more haze in that direction than towards
the west, or to the right or left of the observer's situation :
the rays could not be seen between the sun and the observer,
though the sun was out of sight, and consequently the general
light; it may be supposed, not too great ; which seems to imply
that less haze existed in that direction ; and its presence was
fully proved towards the east by the dull red colour which the
moon assumed upon rising a short time after the appearance
had ceased. The convergence of the rays to one spot, and
that opposite the sun, was merely an effect of perspective,
and requires no explanation here. (See Plate I. fig. 6.)

Although the appearance on this evening was exceedingly



1826.] On the confinement of Dry Gases over Mercury. 217

beautiful and rare, and the more striking from the absence, to
the observer, of the sun or clouds, and the complete insula-
tion of the phenomenon, yet by close observation upon other
evenings, it was found that partial effects of the same kind
were very common, and, from the manner in which these could
be observed, the explanation above given was fully confirmed.
On several evenings after, when observing the sun- set from the
neighbouring hill of St. Catherine, it was found that if the
atmosphere was generally clear, but with compact and di-
stinctly-formed clouds floating in it, the effect was produced.
The usual appearance of rays at sun-set, diverging amongst the
clouds in the west, from the sun, is well known ; but even when
these were not visible, upon looking to the eastern half of the
hemisphere, and especially to the north or south of east towards
the horizon, it was rare that some clouds could not be di-
stinguished with long shadowy projections behind them, always
converging to the spot opposite to the sun. Frequently clouds
could be selected moving more immediately in the neighbour-
hood of the observer : of those which passed overhead, the
shadows could not be observed close. to the clouds; but
carrying the eye onwards towards the east, the same shadows
became visible, when considerably fore-shortened, and could
be observed moving on and changing with the clouds them-
selves. All these phenomena, with their variations, were
easily referable to their causes, and may be observed at almost
any sun-set in fine weather ; but the effect of the first evening,
so similar in kind, though so different in appearance, was not
again remarked. It is with a view of guarding persons who
may observe the same effect, against any mistake as to its
origin, that the appearance, with its nature, has been thus
particularly described.



On the confinement of Dry Gases over Mercury *.
THE results of an experiment made by myself, and quoted as
such, having been deemed of sufficient interest to be doubted,
I have been induced to repeat it ; and though the original ex-
periment was not published by me, I am inclined to put the
latter and more careful one upon record, because of the strong

* Quarterly Journal of Science, xxii, 220.



218 On the confinement of Dry Gases over Mercury. [1826.

illustration it affords of the difficulty of confining dry gases
over mercury alone. Two volumes of hydrogen gas were
mixed with one volume of oxygen gas, in a jar over the mer-
curial trough, and fused chloride of lime introduced, for the
purpose of removing hygrometric water. Three glass bottles,
of about three ounces capacity each, were selected for the
accuracy with which their glass stoppers had been ground into
them; they were well cleaned and dried, no grease being
allowed upon the stopper. The mixture of gases was trans-
ferred into these bottles over the mercurial trough, until they
were about four-fifths full, the rest of the space being occupied
by the mercury. The stoppers were then replaced as tightly
as could be, the bottles put into glasses in an inverted position,
and mercury poured round the stoppers and necks, until it
rose considerably above them, though not quite so high as the
level of the mercury within. Thus arranged they were put
into a cupboard, which happened to be dark, and were sealed
up. This was done on June 28, 1825, and on September the
15th, 1826, after a lapse of fifteen months, they were examined.
The seals were unbroken, and the bottles found exactly as
they were left, the mercury still being higher on the inside
than the outside. One of them was taken to the mercurial
trough, and part of its gaseous contents transferred ; upon ex-
amination it proved to be common air, no traces of the original
mixture of oxygen and hydrogen remaining in the bottle. A
second was examined in the same manner ; it proved to contain
an explosive mixture. A portion of the gas introduced into a
tube, with a piece of spongy platina, caused dull ignition of
the platina; no explosion took place, but a diminution to
rather less than one-half. The residue supported combustion
a little better than common air. It would appear, therefore,
that nearly a half of the mixture of oxygen and hydrogen had
escaped from it, and been replaced by common air. The third
bottle, examined in a similar manner, yielded also an explosive
mixture, and upon trial was found to contain nearly two-fifths
of a mixture of oxygen and hydrogen, the rest being very little
better in oxygen than common air.

There is no good reason for supposing that this capability
of escape between glass and mercury is confined to the mixture
here experimented with ; probably every other gas, having no



1837.] On the Decomposition of certain Hydrocarbons. 219

action on the mercury or the glass, would have made its way
out in the same manner. There is every reason for believing
that a small quantity of grease round the stoppers would have
made them perfectly tight.



On the probable Decomposition of certain Gaseous Compounds
of Carbon and Hydrogen during sudden expansion* .

SOME very singular appearances have been observed by Mr.
Gordon, of the Portable-Gas Works, which have led him to
believe that chemical changes are occasioned by the sudden
expansion of oil-gas, which do not happen when the expansion
is gradual ; a striking result of the change being the separa-
tion of carbon from the gas. The effect referred to is ex-
hibited when oil-gas, compressed into vessels by a power equal
to that of thirty atmospheres, is suddenly allowed to escape
through a small aperture into the air. It was first observed
accidentally, in consequence of the derangement of the valve of
a large apparatus, into which the gas had been compressed to
twenty-seven atmospheres. The gas escaped with immense
velocity, and when an examination took place of what had
happened, it was found that all the metallic part of the valve
upon which the gas had rushed was covered with a black, moist
carbonaceous substance, and the contiguous brick wall with dry,
black carbon, the moisture in this case having been absorbed
by the brick. Since that time, Mr, Gordon has repeatedly
shown the effect, by allowing the gas to rush out with very
great violence from a portable lamp against a piece of white
paper, which becomes immediately covered with black carbo-
naceous deposit.

The general conclusion is, that as the gas thus rapidly ex-
pands, a partial decomposition takes place and carbon is sepa-
rated. If this explanation should ultimately prove by further
experiments to be true, it will be highly important, as affording
an instance of the exertion of mechanical and chemical powers
in those circumstances where they most closely verge upon
each other. At present, we have but little knowledge of such
phenomena, though the announcement in France of the pro-
duction of several new compound bodies, possessed of peculiar

* Quarterly Journal of Science, xxiii. 204.



220 On the Decomposition of certain Hydrocarbons, [ 1 827.

properties, solely by the exertion of physical powers, may lead
us to hope for an accession of information on the subject; that
which we thought we had, was in part rendered uncertain by
the contrary conclusions arrived at by Mr. Perkins and Dr.
Brewster, the one believing that in a case of crystallization the
effect was produced entirely in consequence of pressure*; the
other, that pressure had been the only cause why bodies,
otherwise ready to crystallize, had retained the fluid state.

A natural suspicion, upon first hearing of and seeing the
results obtained by Mr. Gordon, was, that the rapidity of the
current of gas had carried away a minute portion of the metal
from the surface of the valve past which it rushed, or of the
interior of the air-way against which it was thrown, and that
that metal had caused the stain upon the paper ; but upon
examination this proved not to be the case ; for the black
deposit upon a card, when subjected to acids, remained in-
soluble, and when burnt and tested chemically, gave no traces
of copper.

Further examination of the substance showed that it was not a
pure carbon, but one of those compounds, containing a very large
proportion of carbon, combined with a small quantity of hydro-
gen ; being analogous to tar, pitch, or asphaltum. It dissolved
readily in the fluid hydrocarbons obtained by the compression
of oil-gas. As these black carbonaceous compounds are formed
in the process of making oil-gas, a suspicion cannot but arise,
that the effect observed may have been produced by the
current of gas having swept off small portions of such sub-
stances previously deposited, or slowly formed in the interior
of the vessels at former periods ; and have left them upon the
wall in the accidental result, or upon the paper placed in the
current of the gas, when the effect has been purposely shown.

It may, however, be remarked, that in experiments made in
the laboratory of the Royal Institutionf upon the fluid pro-
duct obtained by condensing oil-gas at high pressures, it was
observed, after rectifying the products and separating the
more fixed from the more volatile, that although they were
perfectly clear and transparent at first, yet by spontaneous
evaporation through the corks which closed the vessels, and
after a lapse of time, chemical changes were produced ; for
* Philosophical Transactions. t page 154.



1827.] Transference of Heat by change of Capacity.

ultimately there remained nothing in several of the receivers



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