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sulphate of potash, and sulphuret of potassium. When the
salt was heated on platinum foil in the air, it burnt with a
dense flame, leaving a slightly alkaline sulphate of potash.

Soda yields a salt in most properties resembling that of
potash, crystalline, white, pearly, and unaltered in the air. I
thought that, in it, the metallic taste which frequently occurred
with this acid and its compounds was very decided. The
action of heat was the same as before.

Ammonia formed a neutral salt imperfectly crystalline, not
deliquescent, but drying in the atmosphere. Its taste was
saline and cooling. It was readily soluble in water and alcohol.
When heated on platinum foil it fused, blackened, burnt with
flame, and left a carbonaceous acid sulphate of ammonia, which
by further heat was entirely dissipated. Its general habits



190 On Sulphuric Acid and Naphthaline. [1826.

were those of ammoniacal salts. When its solutions, though
previously rendered alkaline, were evaporated to dryness at
common temperatures, and exposed to air, the salt hecame
strongly acid to litmus paper. This however is a property
common to all soluble ammoniacal salts, I believe, without
exception.

Baryta. It is easy by rubbing carbonate of baryta with
solution of the impure acid, to obtain a perfectly neutral solu-
tion, in which the salt of baryta, containing the acid already
described, is very nearly pure. There is in all cases an undis-
solved portion, which being washed repeatedly in small quan-
tities of hot water, yields to the first portions a salt, the same
as that in the solution. As the washings proceed, it is found
that the salt obtained does not burn with so much flame on
platina foil, as that at first separated ; and the fifth or sixth
washing will perhaps separate only a little of a salt, which, when
heated in the air in small quantities, burns without flame in
the manner of tinder. Hence it is evident that there are two
compounds of baryta, which as they are both soluble in water,
both neutral, and both combustible, leaving sulphate of baryta,
differ probably only in the quantity of combustible matter pre-
sent, or its mode of combination in the acid.

It is this circumstance, of the formation of a second salt in
small but variable quantities with the first, which must be
guarded against, as before mentioned, in the preparation of
salts from the impure acid. It varies in quantity according to
the proportions of materials, and the heat employed ; and I
have thought that when the naphthaline has been in large
quantity, and the temperature low, the smallest quantity is
produced. When the impure acid is used for the preparation
of the salts now under description, a small portion of it should
be examined by carbonate of baryta as above, and rejected if
it furnish an important quantity of the flameless salt.

These bodies may be distinguished from each other provi-
sionally, as the flaming and the glowing salts of baryta, from
their appearances when heated in the air. The latter is more
distinctly crystalline than the former, and much less soluble,
which enabled me by careful and repeated crystallizations to
obtain both in their pure states.

The flaming salt (that corresponding to the acid now under



1826.] SulpJiO'Naphthalic Acid. 191

description), when obtained by the slow evaporation of the satu-
rated solution, formed tufts, which were imperfectly crystalline.
When drops were allowed to evaporate on a glass plate, the
crystalline character was also perceived ; but when the salt
was deposited rapidly from its hot saturated solution, it ap-
peared in the form of a soft granular mass. When dry, it was
white and soft, not changing in the atmosphere. It was rea-
dily soluble in water and alcohol, but was not affected by ether.
Its taste was decidedly bitter. When heated in the air on
platinum foil it burnt with a bright smoky flame, like naphtha-
line, sending flocculi of carbon into the atmosphere, and leaving
a mixture of charcoal, sulphuret of barium, and sulphate of
baryta.

After being heated to 212 for some time, the salt appeared
to be perfectly dry, and in that state was but very slightly
hygrometric. When heated in a tube, naphthaline was evolved ;
but the substance could be retained for hours at a temperature
of 500 F. before a sensible portion of naphthaline had sepa-
rated : a proof of the strength of the affinity by which the
hydrocarbon was held in combination. When a higher tempe-
rature was applied, the naphthaline, after being driven off,
was followed by a little sulphurous acid, a small portion of
tarry matter, and a carbonaceous sulphate and sulphuret were
left.

This salt was not affected by moderately strong nitric or
nitromuriatic acid, even when boiled with them ; and no pre-
cipitation of sulphate took place. When the acids were very
strong, peculiar and complicated results were obtained. When
put into an atmosphere of chlorine, at common temperatures,
it was not at all affected by it. Heat being applied, an action
between the naphthaline evolved, and chlorine, such as might
be expected, took place.

When a strong solution of the pure acid was poured into
a strong solution of muriate of baryta, a precipitate was formed,
in consequence of the production of this salt. It was re-dis-
solved by the addition of water. The fact indicates that the
affinity of this acid for baryta is stronger than that of muriatic
acid.

The second, or glowing salt of haryta, was obtained in small
crystalline groups. The crystals were prismatic, colourless,



192 On Sulphuric Acid and Naphthaline. [1826.

and transparent : they were almost tasteless, and by no means
so soluble either in hot or cold water as the former salts. They
were soluble in alcohol, and the solutions were perfectly neutral.
When heated on platinum foil, they gave but very little flame,
burning more like tinder, and leaving a carbonaceous mixture
of sulphuret and sulphate. When heated in a tube, they gave
off a small quantity of naphthaline, some empyreumatic fumes,
with a little sulphurous acid, and left the usual product.

This salt seemed formed in largest quantity when one volume
of naphthaline and two volumes of sulphuric acid were shaken
together, at a temperature as high as it could be without
charring the substances. The tint, at first red, became olive-
green ; some sulphurous acid was evolved, and the whole would
ultimately have become black and charred, had it not been
cooled before it had proceeded thus far, and immediately dis-
solved in water. A solution was obtained, which though dark
itself, yielded, when rubbed with carbonate of baryta, colour-
less liquids ; and these when evaporated furnished a barytic
salt, burning without much flame, but which was not so crystal-
line as former specimens. No attempt to form the glowing
salt from the flaming salt by solution of caustic baryta, suc-
ceeded.

Strontia. The compound of this earth with the acid already
described very much resembled the flaming salt of baryta.
When dry it was white, but not distinctly crystalline : it was
soluble in water and alcohol; not alterable in the air, but when
heated burnt with a bright flame, without any red tinge, and
left a result of the usual kind.

Lime gave a white salt of a bitter taste, slightly soluble in
water, soluble in alcohol, the solutions yielding imperfect crystal-
line forms on evaporation : it burnt with flame ; and both in
the air and in tubes, when heated, gave results similar to those
of the former salts.

Magnesia formed a white salt with a moderately bitter taste ;
crystallizing under favourable circumstances, burning with
flame, and giving such results by the action of heat as might
be expected.

Iron. The metal was acted upon by the acid, hydrogen
being evolved. The moist protoxide being dissolved in the
acid gave a neutral salt capable of crystallization. This by



1S2G.] Sulpho-Naphthalic Acid. 193

exposure to air slowly acquired oxygen, and a portion of per-
salt was found.

Zinc was readily acted upon by the acid, hydrogen evolved,
and a salt formed. The same salt resulted from the action of
the acid upon the moist oxide. It was moderately soluble
in hot water, the solution on cooling affording an abundant
crop of acicular crystals. The salt was white and unchangeable
in the air ; its taste bitter. It burnt with flame, and gave the
usual results by heat.

Lead. The salt of this metal was white, solid, crystalline,
and soluble in water and alcohol. It had a bitter metallic
taste, with very little sweetness. The results by heat were
such as might be expected.

Manganese. The protoxide of this metal formed a neutral
crystalline salt with the acid. It had a slightly austere taste,
was soluble in water and alcohol, and was decomposed by heat,
with the general appearances already described.

Copper. Hydrated peroxide of copper formed an acid salt
with the acid, and the solution evaporated in the air left radi-
ated crystalline films. The dry salt when heated fused, burnt
with flame, and exhibited the usual appearances.

Nickel. The salt of this metal was made from the moist
carbonate. It was soluble, crystalline, of a green colour, and
decomposed by heat in the usual manner. In one instance an
insoluble subsalt was formed.

Silver. Moist carbonate of silver dissolved readily in the
acid, and a solution, almost neutral, was quickly obtained. It
was of a brown colour, and a powerful metallic taste. By
evaporation it gave a splendent, white, crystalline salt ; not
changing in the air except when heated, but then burning
with flame and ultimately leaving pure silver. When the solu-
tion of the salt was boiled for some time, a black insoluble
matter was thrown down, and a solution obtained, which by
evaporation gave abundance of a yellow crystalline salt. The
changes which took place during the action of heat in the moist
way were not minutely examined.

Mercury. Moist protocarbonate of mercury dissolved in
the acid, forming a salt not quite neutral, crystallizing feebly in
the air, white, of a metallic taste, not deliquescent, and decom-
posed with various phenomena by heat. By re-solution in

o



194 On Sulphuric Acid and Naphthaline. [1826.

water or alcohol, and heat, a subsalt of a yellow colour was
formed.

The moist hydrated peroxide of mercury also dissolved
in the acid, forming an acid solution, which by evaporation
gave a yellowish deliquescent salt, decomposed by heat, burning
in the air, and entirely volatile.

3. Analysis of the acid and salts. When solution of the
pure acid was subjected to the voltaic battery, oxygen and
hydrogen gases were evolved in their pure state : no solid
matter separated, but the solution became of a deep yellow
colour at the positive pole, occasioned by the evolution of free
sulphuric acid, which reacted upon the hydrocarbon. A solu-
tion of the barytic salts gave similar results.

The analytical experiments upon the composition of this acid
and its salts were made principally with the compound of baryta.
This was found to be very constant in composition, could be
obtained anhydrous at moderate temperatures, and yet sustained
a high temperature before it suffered any change.

A portion of the pure salt was prepared and dried for some
hours on the sand-bath, at a temperature of about 212. Known
weights were then heated in a platinum crucible to dissipate
and burn off the combustible matter ; and the residuum being
moistened with sulphuric acid to decompose any sulphuret of
barium formed, was heated to convert it into a pure sulphate of
baryta. The results obtained were very constant, and amounted
to 41*714 of sulphate of baryta per cent, of salt used, equivalent
to 27*57 baryta per cent.

Other portions of the salt were decomposed by being heated
in a flask with strong nitromuriatic acid, so as to liberate the
sulphuric acid from the carbon and hydrogen present, and yet
retain it in the state of acid. Muriate of baryta was then
added, the whole evaporated to dryness, heated red-hot, washed
with dilute muriatic acid to remove the baryta uncombined with
sulphuric acid, and the sulphate collected, dried and weighed.
The results were inconstant; but the sulphate of baryta ob-
tained always much surpassed that furnished by the former
method. Judging from this circumstance that the sulphuric
acid in the salt was more than an equivalent for the baryta pre-
sent, many processes were devised for the determination of its
quantity, but were rejected in consequence of difficulties and



1826.] Sulpho-Naphthalic Acid. 195

imperfections, arising principally from the presence and action
of so much carbonaceous matter. The following was ultimately
adopted.

A quantity of peroxide of copper was prepared by heating
copper plates in air and scaling them. A sufficient quantity
of pure muriatic and nitric acids were provided, and also a
specimen of pure native carbonate of baryta. Seven grains of
the salt to be examined were then mixed with seven grains of
the pulverized carbonate of baryta, and afterwards with 312
grains of the oxide of copper. The mixture being put into a
glass tube was successively heated throughout its mass, the
gas liberated being passed through a mixture of baryta water
and solution of muriate of baryta. It was found that no sul-
phurous or sulphuric acids came off, or indeed sulphur in any
state. The contents of the tube were then dissolved in an ex-
cess of nitric and muriatic acids, above that required to take up
all that was soluble ; and a little solution of muriate of baryta
was added for the sake of greater certainty. A portion of sul-
phate of baryta remained undissolved, equivalent to the sul-
phuric acid of the salt experimented upon, with that contained
accidentally in the oxide of copper acids, &c. This sulphate
was collected, washed, dried and weighed. Similar quantities
of the carbonate of baryta and oxide of copper were then dis-
solved in as much of the nitric and muriatic acids as was used
in the former experiment ; and the washings and other opera-
tions being repeated exactly in the same way, the quantity of
sulphate of baryta occasioned by the presence of sulphuric acid
in the oxide, acids, c. was determined. This, deducted from
the weight afforded in the first experiments, gave the quantity
produced from the sulphuric acid actually existing in the salt.
Experiments so conducted gave very uniform results. The
mean of many indicated 8*9 grains of sulphate of baryta for 10
grains of salt used, or 89 grains per cent., equivalent to 30*17 of
sulphuric acid for every 100 of salt decomposed.

In the analytical experiments relative to the quantity of car-
bon and hydrogen contained in the salt, a given weight of the
substance being mixed with peroxide of copper, was heated
in a green glass tube. The apparatus used consisted of Mr.
Cooper's lamp furnace, with Dr. Prout's mercurial trough ; and
all the precautions that could be taken, and which are now



196 On Sulphuric Acid and Naphthaline. 1826.]

well known, were adopted for the purpose of obtaining accu-
rate results. When operated upon in this way, the only sub-
stances evolved from the salt were carbonic acid and water.
As an instance of the results, 3*5 grains of the salt afforded
1 1 P 74 cubic inches of carbonic acid gas, and 0*9 of a grain of
water. The mean of several experiments gave 32'93 cubic
inches of carbonic acid gas, and 2*589 grains of water for every
10 grains of salt decomposed.

On these data, 100 grains of the salt would yield 329*3 cubic
inches of carbonic acid, or 153*46 grains, equivalent to 41*9
grains of carbon, and 25*89 grains of water, equivalent to 2*877
grains of hydrogen. Hence 100 grains of the salt yielded

Baryta .... 27-57 ... 78

Sulphuric acid . . 30'17 . . . 85*35

Carbon .... 41*90 ... 118*54

Hydrogen . . . . 2*877 . . . 8*13

102*517

In the second numerical column the experimental results are
repeated, but increased, that baryta might be taken in the
quantity representing one proportional, hydrogen being unity ;
and it will be seen that they do not differ far from the following
theoretical statement :

Baryta ... 1 proportional . . 78

Sulphuric acid . 2 ditto . . 80

Carbon .... 20 ditto . .120

Hydrogen ... 8 ditto . . 8

The quantity of sulphuric acid differs most importantly from
the theoretical statement, and it probably is that element of the
salt in the determination of which most errors are involved.
The quantity of oxide of copper and of acids required to be
used in that part of the analysis, may have introduced errors,
affecting the small quantity cf salt employed, which when mul-
tiplied, as in the deduction of the numbers above relative to
100 parts, may have created an error of that amount.

As there is no reason to suppose that during the combination
of the acid with the baryta any change in its proportions takes
place, the results above, minus the baryta, will represent its
composition: from which it would appear, that one proper-



1826.] Sulpho-Naphthalic Acid. 197

tional of the acid consists of two proportionals of sulphuric
acid, twenty of carbon, and eight of hydrogen ; these consti-
tuents forming an acid equivalent in saturating power to one
proportional of other acids. Hence it would seem, that half
the sulphuric acid present, at least when in combination, is
neutralized by the hydrocarbon; or, to speak in more general
terms, that the hydrocarbon has diminished the saturating
power of the sulphuric acid to one half. This very curious and
interesting fact in chemical affinity was, however, made known
to me by Mr. Hennell of Apothecaries' Hall, as occurring in
some other compounds of sulphuric acid and hydrocarbon,
before I had completed the analysis of the present acid and
salts ; and a similar circumstance is known with regard to mu-
riatic acid, in the curious compound discovered by M. Kind,
which it forms with oil of turpentine. Mr. Hennell is, I believe,
on the point of offering an account of his experiments to the
Royal Society, and as regards date they precede mine.

It may be observed, that the existence of sulphuric acid in
the new compounds, is assumed, rather than proved ; and that
the non-appearance of sulphurous acid, when sulphuric acid
and naphthaline act on each other, is not conclusive as to the
non-reaction of the bodies. It is possible that part of the
hydrogen of the naphthaline may take oxygen from one of the
proportions of the sulphuric acid, leaving the hyposulphuric
acid of Welter and Gay-Lussac, which with the hydrocarbon
may constitute the new acid. I have not time at present to
pursue these refinements of the subject, or to repeat the ana-
lyses which have been made of naphthaline, and which would
throw light upon the question. Such a view would account for
a part of the overplus in weight, but not for the excess of the
sulphuric acid obtained, above two proportionals.



The glowing salt of baryta was now analysed by a process
similar to that adopted for the flaming salt. The specimen
operated upon was pure, and in a distinctly crystalline state.
It had been heated to about 440 F. for three hours in a me-
tallic bath. Ten grains of this salt, exposed to air for forty
hours, increased only 0*08 of a grain in weight. These, when
converted into sulphate of baryta by heat and sulphuric acid,
gave 4*24 grains. Seven grains by carbonate of baryta, oxide



198 On Sulphuric Acid and Naphthaline. [1826.

of copper, heat, &c., gave 6'02 grains of sulphate of baryta :
hence 10 grains of the salt would have afforded 8*6 grains of
the sulphate, equivalent to 2*915 grains of sulphuric acid. Five
grains, when heated with oxide of copper, gave 16'68 cubic
inches of carbonic acid gas, equal to 7*772 grains, and equiva-
lent to 2*12 grains of carbon. The water formed amounted to
1-2 grain, equivalent to 0*133 of a grain of hydrogen.

From these data, 100 grains of the salt would appear to
furnish

Baryta . . . 28'03 . 78 or 1 proportional.

Sulphuric acid 29*13 . 81-41 nearly two proportionals.

Carbon. . . 42*40 . 118* approaching to 20 ditto.

Hydrogen . . 2*66 . 7*4 or 7-4 proportionals.

102*22

results not far different from those obtained with the former
salt.

I have not yet obtained sufficient quantities of this salt in a
decidedly crystalline state to enable me satisfactorily to account
for the difference between it and the flaming salt.



Attempts were made to form similar compounds with other
acids than the sulphuric. Glacial phosphoric acid was heated
and shaken in naphthaline, but without any particular results.
A little water was then used with another portion of the mate-
rials, to bring the phosphoric acid into solution, but no decided
combination could be obtained. Muriatic acid gas was brought
into contact with naphthaline in various states, and at various
temperatures, but no union could be effected either of the sub-
stances or their elements.

Very strong solution of potash was also heated with naph-
thaline, and then neutralized by sulphuric acid ; nothing more,
however, than common sulphate of potash resulted.

As the appropriation of a name to this acid will much facili-
tate future reference and description, I may perhaps be allowed
to suggest that of sulpho-naphthalic acid, which sufficiently
indicates its source and nature without the inconvenience of
involving theoretical views.

Royal Institution, January 10, 1826.



1826.] On the existence of a Limit to Vaporization. 199

On the existence of a Limit to Vaporization*.
[Read June 15, 1826.]

IT is well known that within the limits recognized by experi-
ment, the constitution of vapourf in contact with the body
from which it rises, is such, that its tension increases with in-
creased temperature, and diminishes with diminished tempe-
rature; and though in the latter case we can, with many sub-
stances, so far attenuate the vapour as soon to make its presence
inappreciable to our tests, yet an opinion is very prevalent, and
I believe general f, that still small portions are produced ; the
tension being correspondent to the comparatively low tempera-
ture of the substance. Upon this view it has been supposed
that every substance in vacua or surrounded by vapour or gas,
having no chemical action upon it, has an atmosphere of its own
around it ; and that our atmosphere must contain, diffused
through it, minute portions of the vapours of all those sub-
stances with which it is in contact, even down to the earths and
metals. I believe that a theory of meteorites has been formed
upon this opinion.

Perhaps the point has never been distinctly considered, and
it may therefore not be uninteresting to urge two or three
reasons, in part dependent upon experimental proof, why this
should not be the case. The object, therefore, which I shall
hold in view in the following pages, is to show that a limit
exists to the production of vapour of any tension by bodies
placed in vacuo, or in elastic media ; beneath which limit they
are perfectly fixed.

Dr. Wollaston, by a beautiful train of argument and obser-
vation, has gone far to prove that our atmosphere is of finite
extent, its boundary being dependent upon the opposing
powers of elasticity and gravitation . On passing upwards,
from the earth's surface, the air becomes more and more atte-
nuated, in consequence of the gradually diminishing pressure
of the superincumbent part, and its tension or elasticity is pro-

* Philosophical Transactions, 1826, p. 484.

t By the term vapour, I mean throughout this paper that state of a body
in which it is permanently and indefinitely elastic.

J See Sir H. Davy's paper on Electrical Phenomena exhibited in vacuo.
Phil. Trans. 1822, p. 70.

Ibid. p. 89.



#00 On the existence of a Limit to Vaporization. [1826.

portionally diminished : when the diminution is such that the
elasticity is a force not more powerful than the attraction of
gravity, then a limit to the atmosphere must occur. The par-
ticles of the atmosphere there tend to separate with a certain
force; but this force is not greater than the attraction of gravity,
which tends to make them approach the earth and each other ;
and as expansion would necessarily give rise to diminished ten-
sion, the force of gravity would then be the strongest, and conse-
quently would cause contraction, until the powers were balanced
as before.

Assuming this state of things as proved, the air at the limit
of the atmosphere has a certain degree of elasticity or tension ;
and although it cannot there exist of smaller tension, yet if
portions of it were removed to a farther distance from the earth,



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