Edward Turner.

Elements of chemistry : including the history of the imponderables and the inorganic chemistry online

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yellow colour when concentrated. Its odour is strong and penetrating, and dif-
ferent though somewhat similar to chlorine. Its action on the skin is exceed-
ingly active, the effect being similar to but greater than that produced by nitric
acid. It is a highly bleaching compound. In a concentrated state it is very
unstable, a slow decomposition taking place at common temperatures, by which
chlorine is evolved and chloric acid produced. This change is promoted by
light, and is effected almost instantly by exposure for a few moments to the
direct rays of the sun. It is also decomposed by agitation with angular bodies ;
and on throwing into the acid a portion of pounded glass, a brisk effervescence
is observed from the escape of chlorine.

It is one of the most powerful oxidizing agents. Its action in this respect,
however, is various, and is principally observed in relation to the simple non-
metallic elements. Thus sulphur and phosphorus are readily brought to their
highest state of oxidation, and even selenium is converted into selenic acid, an
effect which the nitric acid cannot accomplish. Iodine and bromine are also in-
stantly changed into iodic and bromic acids. Its action on the more perfect metals,
on the contrary, is slight: iron and silver, however, are remarkable exceptions to
this rule ; for when either of them is brought in a finely divided state in contact
with hypochlorous acid, the latter suffers instantaneous decomposition. When iron
is used, it is oxidized at the expense of the acid, and chlorine is evolved ; with
silver the oxygen escapes, and the chlorine unites exclusively with the metal.
The decomposition of hypochlorous acid may also be produced by metallic mer-
cury, but the decomposition is unattended by the evolution of either gas. Both






CHLORINE. 225

the chloride and oxide of mercury are produced, and instantly unite to form the^\
oxychloride. -*

Balard has also succeeded in obtaining hypochlorous acid in the gaseous form.
A small quantity of a concentrated solution is introduced into a bell jar over
mercury, and fragments of dry nitrate of lime are successively added. The
nitrate of lime being highly deliquescent, unites with the water, and the acid
gas escapes with effervescence : the presence of the saline solution is essential,
as it prevents the decomposition of the gas by the mercury.

[M. Pelouse has found that when chlorine, and the common crystallized red
oxide of mercury, both quite dry, are presented to each other, the reaction is
such as not to form hypochlorous acid, but simply chloride of mercury, with the
liberation of free oxygen gas. When, however, the oxide used is prepared by
precipitation, and subsequent exposure to a temperature of about 550 F. this
acid is readily produced. By passing over the oxide so prepared, and placed in a
glass tube, a gentle current of dry chloride gas an active reaction ensues, chloride
of mercury is formed, which remains in the tube, and hypochlorous acid gas is
evolved, which may be collected, by displacement, from the open end of the
tube, so bent as to reach to the bottom of a dry flask, or bottle. By exposure to
the cold arising from a mixture of ice and snow, the hypochlorous acid gas con-
denses as a deep red liquid, which is slowly dissolved by water, and readily
decomposed by heat, often with explosive violence. (Ann. de Ch. et Ph. 3rd
se. p. 179.)]

The gas is of a yellowish green colour, and is very similar to chlorine in ap-
pearance. It unites rapidly with water, which absorbs at least 100 times its own
volume of gas. It detonates by a slight increase of temperature ; and though
less explosive than the chlorous acid, there is a probability of an accident in
transferring it from one vessel to another. The results of explosion are oxygen
and chlorine; and Balard found that 100 measures produced 100 of chlorine and
50 of oxygen. From these data its sp. gr. is 3-0212; its eg. 43*42; eq. vol.

100; symb. Cl + O, Cl or CIO.

Chlorous Acid. Hist, and Prep. This compound was discovered by Davy in
1815 (Phil. Trans.), and soon after by Count Stadion of Vienna. It is formed
by the action of sulphuric acid on chlorate of potassa. A quantity of this salt,
not exceeding 50 or 60 grains, is reduced to powder, and made into a paste by
the addition of strong sulphuric acid. The mixture, which acquires a deep yel-
low colour, is placed in a glass retort, and heated by warm water, the tempera-
ture of which is kept under 212 F. A bright yellowish green gas of a richer
colour than chlorine is disengaged, which has an aromatic odour without any
smell of chlorine, is absorbed rapidly by water, to which it communicates its
tint. This gas, which has Jong been described as the peroxide of chlorine, must
now be called chlorous acid, as it has been shown to possess acid properties,
and to form definite compounds with the alkaline bases.

The chemical changes which take place in the process are explained in the
following manner. The sulphuric acid decomposes some of the cftorate of
potassa, and sets chloric acid at liberty. The chloric acid, at the moment of
separation, resolves itself into peroxide of chlorine and oxygen ; the last of
which, instead of escaping as free oxygen gas, goes over to the acid of some
undecomposed chloride of potassa, and converts it into perchloric acid. The
products are bisulphate and perchlorate of potassa, and chlorous acid. It is

17



226 CHLORINE.

most probable, from the data contained in the preceding table, that every 3 eq.
ofchloride acid yield 1 eq. of perchloric acid and 2 eq. of chlorous acid.

*rop. Chlorous acid unites readily with the alkalies and alkaline earths,
forming salts which are more stable than those of the hypochlorous acid. They
are produced by transmitting the gas into the alkaline solutions, which may
thus be rendered perfectly neutral (Martens, An. de Ch. et Ph. Ixi. 293.) All
the salts hitherto examined are soluble in water, and are possessed, like the acid
itself, of bleaching properties. The neutral salts pass readily into a metallic
chloride and chlorate of the base, particularly such as the chlorite of potassa,
which form a sparingly soluble chlorate. This change does not so readily ensue
when alkali is in excess. The proportion in which the chloride and chlorate
are produced indicate that 6 eq. of chlorite are decomposed, by which 1 eq. of
metallic chloride and 5 eq. of chlorate are produced : thus 6KO C10 4 yields
KC1 and 5 KO C1O 6 . The solution of the pure acid gradually yields chloric
acid and chlorine. It is a powerful oxidizing agent, and in this respect is very
similar to the hypochlorous acid. It causes a precipitate with nitrate of silver ;
but it is best recognized by the evolution of chlorous acid gas on the addition of
an acid to its salts.

Phosphorus takes fire when introduced into the gas, and occasions an explo-
sion. It explodes violently when heated to a temperature of 212, emits a
strong light, and undergoes a greater expansion than protoxide of chlorine. Ac-
cording to Davy, whose result is confirmed by Gay-Lussac, 40 measures of the
gas occupy after explosion the space of 60 measures ; and of these, 20 are
chlorine and 40 oxygen. The peroxide is therefore composed of 36-42 parts, or
1 eq. of chlorine, united with 32 or 4 eq. of oxygen; and its sp. gr. must be
23-375.

Its eq. is 67-42 ; eq. vol. = 100; symb. Cl + 40, Cl, or C10 4 .

Chloric Acid. Prep. If a current of chlorine gas be transmitted into a strong
solution of pure potassa, a portion of the alkali is decomposed, and chloride of
potassium and hypochlorite of potassa are generated. On bringing the solution
to the boiling point, the latter salt is decomposed. ^The changes which occur
are complicated, and give rise to the evolution of oxygen, and the formation of
chlorate of potassa and chloride of potassium. According to the experiments of
Morin and Soubeiran, which accord entirely with the observations of Balard, 9
eq. of hypochlorite of potassa produce 1 eq. of chlorate of potassa, 8 eq. of chlo-
ride of potassium, and 12 eq. of oxygen; or thus,

9(KOfC10) yield (KO-J-Clo 6 ), 8KC1, and 120.

Hence for every eq. of chlorate, 17 eq. ofchloride are formed.

When to a dilute solution of chlorate of baryta a quantity of weak sulphuric
acid, exactly sufficient for combining with the baryta, is added, the insoluble
sulphate of baryta subsides, and pure chloric acid remains in the liquid. This
acid, the existence of which was originally observed by Mr. Chenevix, AVQS first
obt|fnecr*ln a separate state by Gay-Lussac.

Prop. Chloric acid reddens vegetable blue colours, has a sour taste, and forms
neutral salts, called chlorates (formerly hyperoxy muriates,} with alkaline bases.
It possesses no bleaching properties, a circumstance by which it is distinguished
from chlorine, hypochlorous, and chlorous acids. It gives no precipitate in solu-
tion of nitrate of oxide of silver, and hence cannot be mistaken for hydrochloric



CHLORINE.

acid. Its solution may be concentrated by gentle heat till it acquires an oily
consistence without decomposition: in this state of highest concentration it
acquires a yellowish tint, emits an odour of nitric acid, sets fire to paper and
other dry organic matter, and converts alcohol into acetic acid. When sharply
heated in a retort, part of the acid is resolved into chlorine and oxygen ; but
another portion, acquiring oxygen from that which is decomposed, is converted
into perchloric acid, and then passes over into the receiver in the form of a dense
colourless liquid (Serullas.) Chloric acid is easily decomposed by deoxidizing
agents. Sulphurous acid, for instance, deprives it of oxygen, with formation of
sulphuric acid and evolution of chlorine. By the action of hydrosulphuric acid,
water is generated, while sulphur and chlorine are set free. The power of
hydrochloric acid in effecting its decomposition has already been explained.

Chloric acid is readily known by forming a salt with potassa, which crystal-
lizes in tables and has a pearly lustre, deflagrates like nitre when flung on burn-
ing charcoal, and yields peroxide of chlorine by the action of concentrated
sulphuric acid. Chlorate of potassa, like most of the chlorates, gives off pure
oxygen when heated to redness, and leaves a residue of chloride of potassium.
By this mode Gay-Lussac ascertained the composition of chloric acid, as stated
in the preceding table. (An. de Chimie, xci.)

Its eg. is 75-42; symb. Cl f 50, Cl, or.C10 5 .

Perchloric Acid. The saline matter which remains in the retort after forming
chlorous acid, is a mixture of perchlorate and bisulphate of potassa; and by
washing it with cold water, the bisulphate is dissolved, and the perchlorate is
left. Perchloric acid may be prepared from this salt by mixing it in a retort
with half its weight of sulphuric acid, diluted with one-third of water, and ap-
plying heat to the mixture. At the temperature of abcjjit 284 F. white vapours
rise, which condense as a colourless liquid in the receiver. This is a solution
of perchloric acid.

The existence of perchloric acid was first ascertained by Count Stadion, who
found it to be a compound of 2 volumes or 1 eq. of chlorine and 7 of oxygen ;
and this view of its constitution has been confirmed by Gay-Lussac, Serullas,
and Mitscherlich. (An. de Ch. et Ph. viii. ix. xlvi. 297, and xlix. 113.) Ac-
cording to Serullas, it is a very stable compound : it may be heated with hydro-
chloric or sulphuric acid without change, does not set fire to organic substances,
and is not decomposed by alcohol. When concentrated it has a density of 1'65,
in which state it emits vapour when exposed to the air, absorbs hygrometric
moisture powerfully, and boils at 392 F. By admixture with strong sulphuric
acid and distilling, Serullas obtained it in the solid form, both massive and in
elongated prisms. It hisses when thrown into water, like red-hot iron when
quenched.

Of all the salts of perchloric acid, that with potassa is the most insoluble, re-
quiring 65 times its weight of water at 60 for solution. This salt is readily
and safely formed by adding chlorate of potassa, well dried and in fine powder,
in small portions at a time, to an equal weight of concentrated sulphuric acid,
gently warmed in an open vessel. The chlorous acid gas escapes without dan-
ger, and the chlorate is entirely converted into perchlorate and bisulphate of po-
tassa, the latter of which, being very soluble, is easily removed by cold water.
Serullas finds that chlorate of potassa, when decomposed by a low heat, is con-
verted into chloride of potassium and perchlorate of potassa ; but the temperature



228 CHLORINE.

must be carefully managed, otherwise the perchl orate itself would be resolved
into oxygen and chloride of potassium. The perchlorate thus procured is puri-
fied by solution in hot water and crystallization.* It is distinguished from chlo-
rate of potassa by not acquiring a yellow tint on the addition of hydrochloric acid.
The primary form of its crystals, according to Mitscherlich, is a right rhomboidal
prism isomorphus with premanganate of potassa.

Its eq. is 91-42; symb. Cl f 70, Cl, or C10 7 .

[In reference to -the oxygen compounds of chlorine it must be observed that
our knowledge is far from being entirely complete. The recent elaborate re-
searches of Gay-Lussac and Millon have tended to prove the existence of a greater
number than has been heretofore recognized, and to modify our views respecting
their constitution. These researches are still in progress and require confirma-
tion. The following table presents the composition of these compounds accord-
ing to the views of Millon.

Hypochlorous Acid, .... CIO

Chlorous Acid, ..... C1O S

Hypochloric Acid, .... C10 4 = C1 4 0| 6 = SClOa -f CIO?

Chloric Acid, .... C10 6 = Cl a Oio= C1O S f ClOt

Chlorochloric Acid, .... Cl 3 0i3 = 2C10 3 -f C10 7

Chloroperchloric Acid, . . . Cl 3 0n = ClOa -f 2C10 7

Perchloric Acid, . . . . C1O 7 ]

Quadrochloride of Nitrogen. Hiit. and Prep. This compound was discovered
by Dulong in 1811. Its elements have a feeble mutual affinity, and do not unite
when presented to each other in their gaseous form. The condition which leads
to their union is the decomposition of ammonia by chlorine, during which hydro-
chloric acid is generated t)y chlorine combining with the hydrogen of ammonia ;
while the nitrogen of thatj alkali, in its nascent state, enters into combination
with another portion of chlorine. A convenient mode of preparing the quadro-
chloride of nitrogen is the following. An ounce of hydrochlorate of ammonia is
dissolved in 12 or 16 ounces of hot water; and when the solution has cooled to
the temperature of 90, a glass bottle with a wide mouth, full of chlorine, is in-
verted in it. The solution gradually absorbs the chlorine, and acquires a yellow
colour ; and in about 20 minutes globules of a yellow fluid are seen floating like
oil upon its surface, which, after acquiring the size of a small pea, sink to the
bottom of the liquid. The drops of the chloride, as they descend, should be col-
lected in a small saucer of lead, placed for that purpose under the mouth of the
bottle. It is also readily obtained by suspending a fragment of sal-ammonia in
a solution of hypochlorous acid.

Prop. It is one of the most explosive compounds yet known, having been
the cause of serious accidents both to its discoverer and to Davy. (Phil. Trans.
1813; An. de Ch. Ixxxvi.) Its specific gravity is 1-653. It does not congeal
in the intense cold produced by a mixture of snow and salt. It may be distilled

* All possibility of danger, as first shown by Professor Penny, is avoided by adding the
chlorate to dilute nitric acid, and applying a gentle heat. The change which occurs is
similar to that which takes place when sulphuric acid is used ; but in this case the oxygen
and chlorine are evolved merely in a state of mixture, and not in union as an explosive
compound. The resulting salts, nitrate and perchlorate of potassa, are readily separated by
water, on account of the much greater solubility of the former (R.)



CHLORINE. 2<J9

at 160 ; but at a temperature between 200 and 212 it explodes. It appears
from the investigation of Messrs. Porrett, Wilson, and Kirk, that its mere con-
tact with some substances of a combustible nature causes detonation even at com-
mon temperatures. This result ensues particularly with oils, both volatile and
fixed. I have never known olive oil fail in producing the effect. The products
of the explosion are chlorine and nitrogen. (Nicholson's Journal, xxxiv.)

Sir H. Davy analyzed chloride of nitrogen by means of mercury, which unites
with chlorine, and liberates the nitrogen. He inferred from his analysis that its
elements are united in the proportion of four measures of chlorine to one of nitro-
gen ; and it hence follows that, by weight, it consists of 4 eq. of chlorine and 1
eq. of nitrogen. [Chemists are, however, still undecided, respecting the true
constitution of this substance. From the researches of Millon, Kane, and others,
it would appear to contain hydrogen, and may be a compound of chlorine and
amidogen ; represented thus, NH 2 , CL]

Perchloride of Carbon. Hist, and Prep. The discovery of this compound is
due to Mr. Faraday. When olefiant gas (a compound of carbon and hydrogen)
is mixed with chlorine, combination takes place between them, and an oil-like
liquid is generated, which consists of chlorine, carbon, and hydrogen. On ex-
posing this liquid in a vessel full of chlorine gas to the direct solar rays, the
chlorine acts upon and decomposes the liquid, hydrochloric acid is set free, and
the carbon, at the moment of separation, unites with the chlorine. (Phil. Trans.
1821.)

Prop. Perchloride of carbon is solid at common temperatures, has an aromatic
odour approaching to that of camphor, is a non-conductor of electricity, and re-
fracts light very powerfully. Its sp. gr. is exactly double that of water. It fuses
at 320, and after fusion it is colourless and very transparent. It boils at 360,
and may be distilled without change, assuming a crystalline arrangement as it
condenses. It is sparingly soluble in water, but dissolves in alcohol and ether,
especially by the aid of heat. It is soluble also in fixed and volatile oils.

It burns with a red light when held in the flame of a spirit-lamp, giving out
acid vapours and smoke ; but the combustion ceases as soon as it is withdrawn.
It burns vividly in oxygen gas. Alkalies do not act upon it ; nor is it changed
by the stronger acids, such as the hydrochloric, nitric, or sulphuric acids, even
with the aid of heat. When its vapour, mixed with hydrogen, is transmitted
through a red-hot tube, charcoal is separated, and hydrochloric acid gas evolved.
On passing its vapour over the peroxides of metals, such as that of mercury and
copper, heated to redness, a chloride of the metal and carbonic acid are gene-
rated. Protoxides, under the same treatment, yield carbonic oxide gas and me-
tallic chlorides. Most of the metals decompose it also at the temperature of
ignition, uniting with its chlorine, and causing deposition of charcoal.

The composition of the perchloride of carbon was inferred by Faraday from
the proportions of chlorine and olefiant gas employed in its production, and from
the quantity of chloride of copper and carbonic acid generated when its vapour
was transmitted over oxide of copper at a red heat.

Its eq. is 118-50; symb. 2C -f- 3C1, or C 2 C1 3 .

Protochloride of Carbon. When the vapour of the perchloride is passed through
a red-hot glass or porcelain tube, filled with fragments of rock crystal to increase
the quantity of heated surface, partial decomposition occurs, chlorine gas escapes,
and a vapour which, analyzed by Faraday, by means of oxide of copper, proved
to be protochloride of carbon. At common temperatures it is a limpid colourless



230 CHLORINE.

liquid, which has a density of 1-5526, does not congeal at F., and at 160 or
170 is converted into vapour. It may be distilled repeatedly without change ;
but when exposed to a red heat, some of it is resolved into its elements. In its
chemical relations it is very analogous to perchloride of carbon.

Its eq. is 41-54; symb. C -f- Cl, or C Cl.

Dichloride of Carbon. The first sample of this substance yet obtained was
brought from Sweden by M. Julin, and is said to have been formed during the
distillation of nitric acid from crude nitre and sulphate of iron. It occurs in small,
soft, adhesive fibres of a white colour, which have a peculiar odour, somewhat
resembling spermaceti. It fuses on the application of heat, and boils at a tem-
perature between 350 and 450 F. At 250 it sublimes slowly, and condenses
again in the form of long needles. It is insoluble in water, acids, and alkalies ;
but is dissolved by hot oil of turpentine or. by alcohol, and forms acicular crys-
tals as the solution cools. It burns with a red flame, emitting much smoke and
fumes of hydrochloric acid gas. It has since been obtained among the products
of the action of chlorine, aided by light, on some organic compounds.

The nature of this substance is shown by the following circumstances. When
its vapour is exposed to a red heat, evolution of chlorine gas ensues, and char-
coal is deposited. A similar deposition of charcoal is produced by heating it
with phosphorus, iron, or tin ; and a chloride is formed at the same time. Po-
tassium burns vividly in its vapour with formation of chloride of potassium and
separation of charcoal. On detonating a mixture of its vapour with oxygen gas
over mercury, a chloride of that metal and carbonic acid are generated. By these
means Phillips and Faraday ascertained its composition. (An. of Phil, xviii.
150). Us eq. is 47-66 ; symb. 2C -|- Cl, or C 2 Cl.

Chlorocarbonic Acid Gas. Hist, and Prep. This compound was discovered in
1819 by John Davy, who described it in the Philosophical Transactions for that
year, under the name of phosgene gas. (From $^$ light, and ysivcuiv to produce.)
It is made by exposing a mixture of equal measures of dry chlorine and carbonic
acid gases to sunshine, when rapid but silent combination ensues, and they con-
tract to one half their volume. Diffused day-light also affects their union slowly;
but they do not combine at all when the mixture is wholly excluded from light.

Prop. It is colourless gas, has a strong odour, and reddens dry litmus paper.
It combines with four times its volume of ammoniacal gas, forming a white solid
salt ; so that it possesses the characteristic property of acids. It is decomposed
by contact with water. One equivalent of each compound undergoes decompo-
sition ; and as the hydrogen of the water unites with chlorine, and its oxygen
with carbonic oxide, the products are carbonic and hydrochloric acids. When
tin is heated in this gas, chloride of tin is generated, and carbonic oxide gas set
free, which occupies exactly the same space as the chlorocarbonic acid which
was employed. A similar change occurs when it is heated in contact with anti-
mony, zinc, or arsenic.

As chlorocarbonic acid gas contains its own volume of each of its constituents,
it follows that 100 cubic inches of that gas at the standard temperature and pres-
sure must weigh 106-806 grains; namely, 76-599 of chlorine added to 30-207 of
carbonic oxide. Its sp. gr. is therefore 3-4427, and it consists of 35*42 parts or
1 eq. of chlorine, and 14-15 parts or 1 eq. of carbonic oxide.

Itseq. is 49-54; symb. C f O f Cl, or CO Cl.

Dichloride of Sulphur. This compound was discovered in the year 1804 by



CHLORINE. 231

Thomson,* and was afterwards examined by Berthollet. j It is most conveniently
prepared by passing a current of chlorine gas over flowers of sulphur gently
heated, until nearly all the sulphur disappears. Direct combination ensues, and
the product, distilled off from uncombined sulphur, is obtained under the form
of a liquid which appears red by reflected, and yellowish green by transmitted
light. It% density is 1-687. It is volatile below 200, boils at 280, yielding
vapour which has a density of 4*70, and condenses again without change in cool-
ing. When exposed to the air it emits acrid fumes, which irritate the eyes pow-
erfully, and have an odour somewhat resembling sea-weed, but much stronger.
Dry litmus paper is not reddened by it, nor does it unite with alkalies. It acts
with energy on water : mutual decomposition ensues, with formation of hydro-
chloric and hypos ulphurous acids, a,nd deposite of sulphur, by which the water
is rendered cloudy. From a recent analysis by Rose it consists of 35-42 parts



Online LibraryEdward TurnerElements of chemistry : including the history of the imponderables and the inorganic chemistry → online text (page 34 of 119)