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vessel. As soon as the balloon becomes
warm, another is substituted for it; and
when the second becomes heated, the
first is again applied. The iodine is
withdrawn from the globes by a little
warm water, which dissolves it very
sparingl}', and it is purified by undergo-
ing a second sublimation. The test made
use of for the detection of iodine in any
solution, when it is suspected to be pre-
sent, is starch, with which iodine has the
property of uniting, and of forming with
It a compound, insoluble in cold water,
which is recognised with certainty by its
deep blue color. The solution should be
cold at the time of adding the starch; and
if the color does not become apparent
simply on the addition of the starch, a
few drops of sulphuric acid should be
cautiously added, when, if any iodine is
present, the blue color will make its ap-
pearance. This test is so exceedingly
delicate, that a liquid containing -^jo\ooq
of its weight of iodine, receives a blue
tinge from a solution of starch. — Iodine
has a powerful affinity for hydrogen,
which it takes from animal and vegetable
substances in the sanie manner as chlo-
rine, and uniting with it iorms hydriodic
acid.

The following are the methods for ob-
taining this acid in the gaseous and in the
liquid state: Into a flask to which a re-
curved tube is fitted, dipping under ajar
of mercury, are introduced eight parts of
iodine and one of phosphorus, and to the
mixture a few drops of water are added;
the water is immediately decomposed,
the phosphorus, seizing the oxygen, forms
phosphoric acid, while the hydrogen com
bines with the iodine



water present in sufficient quantity to
dissolve the hydriodic acid, it passes over
in the gaseous state, and is collected over
the mercury. In contact with air it
smokes or fumes like the muriatic acid,
and, like it, reddens vegetable blues. It
is distinguished, however, from that acid,
by the superior affinity possessed by
chlorine for hydiogen, in consequence of
which, if chlorine and hydriodic acid
gases are mingled together, the yellow
color of the former disappears, and the
violet vapor of iodine make? its ap-
pearance, which proves the decom-
position of the hydriodic acid by the
chlorine. If the decomposition is com-
plete, the vessel will be wholly occu-
pied by muriatic acid gas. To obtain the
hydriodic acid in a liquid state, we have
only to conduct the gas through water,
until it is fully charged with it; or it may
be obtained by transmitting a current of
sulphuretted hydrogen gas through water
in which iodine, in fine powder, is sus-
pended. The iodine, from a greater affi-
nity for hydrogen than the sulphur pos-
sesses, decon)poses the sulphuretted hy-
drogen; and hence sulphur is set free,
and hydriodic acid produced. The con-
stitution of hydriodic acid i.s.

By volume. By weight.
Iodine, - 50 - 124

Hydrogen, - 50 - 1



100 125

The solution of hydriodic acid is easily
decomposed. Thus, on exposure for a
few hours to the air, the oxygen of the
atmosphere forms water with the hydro-
gen of the acid, and liberates the iodine.
Nitric and sulphuric acids likewise de-
compose it by yielding oxygen, the for-
mer being converted into nitrous, and the
latter into sulphurous acid. The free
iodine becomes obvious on the applica-
tion of the above mentioned test; the com-
pounds of hydriodic acid with the solifia-
ble bases may be easily formed, either by
direct combination, or by acting on the
basis in water with iodine. Sulphurous
and muriatic acids, as well as sulphuret-
ted hydrogen, produce no change on the
hydriodates, at the usual temperature of
the air; but chlorine, nitre, and concen-
As there is not'trated sulphuric acid, instantly decom-



DEFINITION OF TERMS.



169



pose them, and separate the iodine. The
hydriodates of potash and soda are the
most interesting of their numhcr, hecause
they are the chief sources of iodine in
nature. The latter salt is prohalily the
one which affords the iodine obtained
from kelp; while it is believed, that it is
the hydriodate of potash which is most
generally found in mineral springs.
(Hence the necessity of adding sulphuric
acid to the residual liquor of the soap-
boiler, in order to procure the iodine,
which requires to be separated from its
combination with the alkali to which it is
united, in the condition of hydriodic acid ;
and peroxide of manganese is also added,
in order to facilitate the decomposition of
the hydriodic acid.) Iodine forms acids
also by uniting with oxj'gen and with
chlorine. When it is brought into con-
tact with protoxide of chlorine, imme-
diate action ensues; the chlorine of the
protoxide unites with one portion of io-
dine, and its oxygen with another, form-
ing two compounds — a volatile orange
colored matter, the chloriodic acid, and a
white solid substance, which is iodic acid.
Iodic acid acts powerfully on inflammable
substances; with charcoal, 'sulphur, sugar,
and similar combustibles, it forms mix-
tures which detonate when heated. It
enters into combination with metallic
oxides, giving rise to salts called iodales.
These compounds, like the chlorates,
yield pure oxygen by heat, and deflagrate
when thrown on burning charcoal: Iodic
acid is decomposed by sulphurous, phos-
phorous, and hydriodic acids, and by sul-
phuretted hydrogen. Iodine, in each
case, is set at liberty, and may be detect-
ed, as usual, in starch. Chloriodic acid,
which is also formed by simply immers-
ing dry iodine in chlorine gas, deliquesces
in the open air, and dissolves very freely
in water. Its solution is very sour to the
taste; and it reddens vegetable blues, but
afterwards destroys them. It does not
unite with alkaline bases; in which re-
spect it wants one of the characteristics
of an acid, and has hence been called by
Gay Lussac a chloride of iodine. Iodine
unites with nitrogen, forming a dark
powder, which is characterized chloride
of nitrogen, by its explosive property.
In order to form it, iodine is put into a



solution of ammonia; the alkali is decom-
posed; its elements unite with different
portions of iodine, and thus cause the
formation of hydriodic acid and iodide of
nitrogen. Iodine forms with suljjhur a
feeble compound, of a grayish black co-
lor. With phosphorus, also, it combines
with great rapidity at common tempera-
tures, attended with the emergence of
heat. It manifests little disposition to
combine with metallic oxides; but it has
a strong attraction for the pure metals,
producing compounds which are called
iodurels, or iodides. The iodides of
lead, copper, bismuth, silver and mer-
cury, are insoluble in water, while the
iodides of the very oxidizable metals are
soluble in that liquid. If we mix a hy-
driodate with the metallic solutions, all
the metals which do not decompose water
will give precipitates, while those which
decompose that liquid will give none.

Iodine, besides being employed for phi-
losophical illustrations, is used in the arts
for pigments, dj'es, and medicine. The
proto-ioduret of mercury is used in Eng-
land as a substitute for vermilion in the
preparation of paper-hangings ; and a
compound hydriodate of potassa G5, io-
date of potassa 2, and ioduret of mercury
33, is employed in printing calico. The
tincture of iodine, 48 grs. to 1 oz. of alco-
hol, is a powerful remedy in the goitre,
and other glandular diseases; but it is so
violent in its action on the system., as to
require great caution in its administra-
tion. The hydriodate of potash or of
soda is also applied to medical uses; and
it is inferred that the efficacy of many
mineral springs, in certain diseases, is
owing to the presence of one or the other
of* these salts.

Iridium; the name of a metal disco-
vered in 1S03, by M. Tennant, in the
black residuum from the solution of the
ore of platinum. Its name was bestowed
in allusion to the rainbow, (iris.) in con-
sequence of the changeable color it pre-
sents while dissolving in muriatic acid.
Its color is white; it is brittle, and very
difficult of fusion; specific gravity, 18.68.

Ipecacuanha, process to make Sirup of.
Take of Ipecac, bruised, - 1 part
Water, - - - 14 "



170



DEFINITION OF TERMS.



Boil in a covered vessel down to 12 parts
Then filter, and add sugar, - 24 "
Boil to a sirupy consistence.

The above is from the Paris Codex,
and contains about sixteen grains of ipe-
cac, to the ounce, or about two and a half
grains of emetia.

To get clear of the ^um and starch
which make a sirup soon spoil, other re-
cipes recommend alcoholic maceration,
and subsequent evaporation in making
the sirup, to dissipate the spirit.

As a better process than either of the
above mentioned, I would suggest the fol-
lowing, being an improvementupon them :

Take of ipecac, finely bruised, two
ounces; place in a small displacement-fil-
ter, and, to extract the soluble active prin-
ciples, pass over it a weak alcohol, (15)
lb. iss. Evaporate by a gentle heat to
four ounces, and add four pints of simple
sirup; then boil for a while, that the sirup
may be of proper consistence.

There are several compound sirups of
ipecac, combining its virtues with those
of senega, bark, and opium.

Sirup of ipecacuanha is employed to
stimulate the mucous membrane of the
bronchise in certain pulmonary affections,
and from its frequent use would seem to
form an indispensable ingredient in
French and German prescriptions for
this purpose. — Jour. Phar.

Iron, prope.rlies of. It has a styptic
taste, and emits a smell when rubbed.
Its specific gravity varies from 7.6 to 7.8.
It is attracted by the magnet or load-
stone, and is itself the substance which
constitutes the load-slone. But when
iron is perfectly pure, it retains the mag-
netic virtue a short time. It is mallea-
ble in every temperature, and its mallea-
bility increases in proportion as the tem-
perature augments; but it cannot be ham-
mered out nearly so thin as gold or silver,
or even copper. Its ductility, however,
is more perfect; for it may be drawn out
into wire as fine, at least, ns the human
hair. Its tenacity is such, that an iron
wire 0.078 of an inch in diameter, is ca-
pable of supporting 549.25 lbs. avoirdu-
pois without breaking. When heated to
about 158° Wedgewood, it melts. This
temperature being nearly the highest to
which it can be raised, it has been im-



possible to ascertain the point at which
this melted metal begins to boil and to
evaporate. Neither has the form of its
crystals been examined; but it is well
known that the texture of iron is fibrous;
that is, it appears when broken to be
composed of a number of fibres or strings,
bundled together.

When exposed to the air, its surface is
soon tarnished, and it is gradually chang-
ed into a brown or yellow powder, well
known under the name of rust; this
change takes place more rapidly if the
atmosphere is moist. It is occasioned
by the gradual combination of the iron
with the oxygen of the atmosphere, for
which it has a very strong affinity.

When iron filings are kept in water,
provided the temperature is not under
70°, they are gradually converted into a
black powder, while a quantity of hydro-
gen gas is emitted. This is occasioned
by the slow decomposition of the water.
The iron combines with its oxygen, while
the hydrogen makes its escape under the
form of a gas. If the steam of water is
made to pass through a red-hot iron tube,
it is decomposed instantly. The oxygen
combines with the iron, and the hydro-
gen gas passes through the tube, and may
be collected in proper vessels. This is
one of the easiest methods of procuring
pure hydrogen gas. — These facts are suffi-
cient to show that iron has a strong affi-
nity for oxygen, since it is capable of
taking it from air and water. It is capa-
ble also of taking fire, and burning with
great rapidity. Twist a small iron wire
into the form of a cork-screw, by rolling
it round a cylinder; fix one end of it into
a cork, and attach to the other a small bit
of cotton thread dipt in melted tallow.
Set fire to the cotton, and plunge it while
burning into ajar filled with oxygen gas.
The wire catches fire from the cotton,
and burns with great brilliancy, emitting
very vivid sparks in all directions. For
this very splendid experiment we are in-
debted to Dr. Ingenhouz. During this
combustion the iron combines with oxy-
gen, and is converted into an oxide.

INIr. Proust has proved that there are
only two oxides of iron; and the protox-
ide has usually a black color, but the per-
oxide is red.



DEFINITION OF TERMS.



171



The protoxide of iron may be obtained
by four different processes. 1. By keep-
ins: iron filings a sufficient time in water
at the temperature of 70°. The oxide
thus formed is a black powder, formerly
much used in medicine under the name
of martial ethiops, and seems to have been
first examined by Lemeri; but a better
process is that of De Roover. He ex-
poses a paste formed of iron filings and
water to the open air, in a stone-ware
vessel; the paste becomes hot, and the
water disappears. It is then moistened
again, and the process repeated till the
whole is oxydized. The mass is then
pounded, and the powder is heated in an
iron vessel till it is perfectly dry, stirring
it constantly. — 2. By making steam pass
through a red-hot iron tube, the iron is
changed into a brilliant black brittle sub-
stance, which, when pounded, assumes
the appearance of martial ethiops. This
experiment was first made by Lavoisier.
3. By burning iron wire in oxygen
gas. The wire as it burns is melted, and
falls in drops to the bottom of the vessel,
which ought to be covered with water,
and to be of copper. These metallic
drops are brittle, very hard, and black-
ish, but retain the metallic lustre. They
were examined by Lavoisier, and found
precisely the same with martial ethiops.
They owe their lustre to the fusion which
they underwent. — 4. By dissolving iron
in sulphuric acid, and pouring potass into
the solution. A green powder falls to
the bottom, which assumes the appear-
ance of martial ethiops, when dried quick-
ly in close vessels. This first oxide of
iron, however formed, is always com-
posed of 73 parts iron and 27 of oxygen,
as Lavoisier and Proust have demon-
strated. It is attracted by the magnet,
and is often itself magnetic. It is capa-
ble of crystallizing, and is often found
native in that state.

The peroxide or red oxide of iron may
be formed by keeping iron filings red-
hot in an open vessel, and agitating them
constantly till they are converted into a
dark red powder. This oxide was for-
merly called saffron of Mars. Common
rust of iron is merely this oxide combin-
ed with carbonic acid gas. The red
oxide may be obtained also by exposing



for a long time a diluted solution of iron
in sulphuric acid to the atmosphere, and
then dropping into it an alkali, by which
the oxide is precipitated. This oxide is
also found native in great abundance.
Proust proved it to be composed of 48
parts of oxygen, 52 of iron. Consequent-
ly the peroxide, wiien converted into red
oxide, absorbs 0.40 of oxygen; or which
is the same thing, the red oxide is com-
posed of 66.5 parts of black oxide and
33.5 parts of oxygen. One hundred parts
of iron, when converted into protoxide,
absorb 37 parts of oxygen, and the oxide
weighs 137 ; when converted into per-
oxide it absorbs 52 additional parts of
oxygen, and the oxide weighs 189. The
peroxide cannot be decomposed by heat;
but when heated along with its own
weight of iron filings, the whole, as
Vauquelin first observed, is converted
into black oxide. The reason of this
conversion is evident. This 100 parts
of peroxide are composed of 52 parts of
iron, combined with two different doses
of oxygen : 1, with 14 parts, which, with
the iron, makes 66 of protoxide ; 2, with
32 parts, 'vhich, with the protoxide, make
up the 100 parts of peroxide. Now, the
first of these doses has a much greater
affinity for the iron than the second has.
Consequently the 34 parts of oxygen,
which constitute the second dose, being
retained by a weak affinity, are easily
abstracted by the 100 parts of pure iron,
and combining with the iron, the whole
almost is converted into black oxide : for
100 parts of iron, to be converted into
black oxide, require only 27 parts of
oxygen. The peroxide of iron is not
magnetic. It is converted into black
oxide by sulphuretted hydrogen and
many other substances, which deprive it
of the second dose of oxygen for which
they have a stronger affinity, though they
are incapable of decomposing the pro-
toxide. Iron is capable of combining
with all the simple combustible bodies.
A small mixture of it constitutes that par-
ticular kind of iron, known by the name
of cold short iron, because it is brittle
when cold, though it is malleable when
hot. Rinman has shown that the brittle-
ness and bad qualities of cold short iron
may be removed by heating it strongly



173



DEFINITION OF TERMS.



with limestone, and with this the ex-
periments of Levasseur correspond.
There are a great many varieties ol iron,
which artists distinguish hy particular
names; but all of them may be reduced
under one or other of the three following
classes : cast iron, wrought or soft iron,
and steel. Cast iron, or pig iron, is the
name of the metal when first extracted
from its ores. The ores from which iron
is usually obtained are composed of oxide
of iron and clay. The object of the
manufacturer is to reduce the oxide to
the metallic state, and to separate all the
clay with which it is combined. These
two objects are accomplished at once by
mixing the ore reduced to small pieces
with a certain portion of limestone and
of charcoal, and subjecting the whole to
a very violent heat in furnaces construct-
ed for that purpose. The charcoal ab-
sorbs the oxygen of the oxide, flies off in
the state of carbonic acid gas, and leaves
the iron in the metallic state; the lime
combines with the clay, and both together
run into fusion, and form a kind of fluid
glass; the iron is also melted by the
violence of the heat and being heavier
than the glass, falls down and is collected
at the bottom of the furnace. Thus the
contents of the furnace are separated into
two portions ; the glass swims at the
surface, and the iron rests at the bottom,
A hole at the lower part of the furnace is
now opened, and the iron allowed to flow
out into moulds prepared for its reception.
The cast iron thus obtained is distin-
guished by the follovving properties: it
is scarcely malleable at any temperature.
It is generally so hard as to resist the file;
it can neither be hardened nor softened
by ignition and cooling. It is exceedingly
brittle. It melts at 130° Wedgewood.
It is more sonorous than steel. For the
most part it is of a dark-gray or blackish
color ; but sometimes it is whitish, and
then it contains a quantity of phosphuret
of iron, which considerably impairs its
qualities. A great number of utensils
are formed of iron in this state. To con-
vert it into wrought iron, it is put into a
furnace, and kept melted, by means of
the flame of the combustibles, which is
made to play upon its surface. While
melted every part of it is stirred by a



workman, that every part of it may be
exposed to the air. In about an hour the
hottest part of the mass begins to heave
and swell, and to emit a lambent blue
flame. This continues nearly an hourj
and by that time the conversion is com-
pleted. The heaving is evidently pro-
duced by the emission of an elastic fluid.
As the process advances, the iron gradu-
ally acquires more consistency; and at
last, notwithstanding the continuance of
the heat, it congeals altogether. It is
then taken while hot and hammered
violently, by means of a heavy hammer
driven by machinery. This not only
makes the particles of iron apj roach
nearer to each other, but drives away
several impurities which would other-
wise continue attached to the iron. In
this state it is the substance described
under the name of iron. As it has never
yet been decomposed, it is considered at
present, when pure, as a simple body;
but it has seldom or never been found
without some small mixture of foreign
substances. These substances are either
some of the other metals, or oxygen, car-
bon, or phosphorus. When small pieces
of iron are stratified in a close crucible,
with a sufficient quantity of charcoal
powder, and kept in a strong-red heat for
eight or ten hours, they are converted
into steel, which is distinguished from
iron by the following properties : It is
so hard as to be unmalleable while cold,
or at least, it acquires this property by
being immersed while ignited into a cold
liquid; for this immersion, though it has
no effect upon iron, adds greatly to the
hardness of steel. It is brittle, resists
the file, cuts glass, affords sparks with
flint, and retains the magnetic virtue for
any length of time. It loses this hard-
ness by being ignited and cooled very
slowly. It melts at above 130° Wedge-
wood. It is malleable when red-hot but
scarcely so when raised to a white heat.
It may be hammered out into much thin-
ner plates than iron. It is more sonorous,
and its specific gravity, when hammered,
is greater than that of iron. By being
repeatedly ignited in an open vessel, and
hammered, it becomes wrought iron,
which is a simple substance, and if per-
fectly pure would contain nothing but



DEFINITION OF TERMS.



173



iron. Steel is iron combined with a small
portion of carbon, and has been for that>
reason called carburetted iron. The pro-
portion of carbon has not been ascertained
with much precision.

From the analysis of Vaiiquelin, it
amounts, at an average, to ^l^ part. Mr.
Clouet seems to affirm that it amounts to
j\ part; but he has not published the
experiments which led him to a propor-
tion which so far exceeds what has been
obtained by other chemists. That steel
is composed of iron combined with pure
carbon, and not with charcoal, has been
demonstrated by Morveau, who formed
steel by combining together directly iron
and diamond. At the suggestion of Clouet,
he enclosed a diamond in a small crucible
of pure iron and exposed it, completely
covered up in a common crucible, to a
sufficient heat. The diamond disappear-
ed, and the iron was converted into steel.
The diamond weighed 907 parts, the iron
57800, and the steel obtained 56384 ; so
that 2313 parts of the iron had been lost
in the operation.

From this experiment it follows, that
steel contains about -^^0^ its weight of
carbon. This experiment was objected
to by Mr. Mushet, but the objections
were fully refuted by Sir George Mc-
Kenzie. Rinman, long ago, pointed out
a method by which steel may be dis-
tinguished from iron. When a little
diluted nitric acid is dropt upon a plate of
steel, allowed to remain a few minutes,
and then washed off, it leaves behind it
a black spot; whereas the spot formed
by nitric acid on iron is whitish green.
We can easily see the reason of the black
spot ; it is owing to the carbon of the
iron which is converted into charcoal by
the acid. This experiment shows us,
that carbon is much more readily oxidhz-
ed when combined with iron than when
crystallized in the diamond. Cast iron
is iron combined with a still greater pro-
portion of carbon than is necessary for
steel. The quantity has not yet been
ascertained with precision ; Mr. Clouet
makes it amount to | of the iron. The
blackness of the color and the fusibility
of cast iron, are proportional to the
quantity of carbon which it contains.
Cast iron is almost always contaminated



with foreign ingredients: these are chief-
ly oxide of iron, phosphuret of iron, and
silica. It is easy to see why iron is ob-
tained from its ore in the state of cast
ircn. The quantity of charcoal along
with which the ore is fused, is so great
that the iron hasan opportunity of saturat-
ing itself with it. The conversion of cast
iron into wrought, is effected by burning
away the charcoal, and depriving the iron
wholly of oxygen: this is accomplished
by heating it violently while exposed to
the air. Mr. Clouet has found that when
cast iron is mixed w'ith i of its weight
of black oxide of iron, and heated violent-
ly, it is equally converted into pure iron.
The oxygen of the oxide, and the carbon
of the cast iron, combine and leave the
iron in a state of purity. The conversion
of iron into steel is effected by combining
it with carbon. This combination is per-



Online LibraryD. PeirceObserver and record of agriculture, Science and art (Volume v.1) → online text (page 31 of 35)