A B C D E F G H I J K L M N O P R S T U V W X Z

An Introduction to Chemical Science

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257. Uses.--Gypsum finds use as a fertilizer and as an adulterant
in coloring-materials, etc. CaSO4 is employed in making casts,
molds, statuettes, wall-plaster, crayons, etc.

How can CaCl2 be made? What is its use? See page 27. What else
is used for a similar purpose?

Symbolize and name the acid represented by Ca(ClO)2, and name
this salt (page 107). It is one of the constituents of bleaching-
powder, the symbol of which, though still under discussion, may
be considered Ca(ClO)2 + CaCl2. This is made by passing Cl over
Ca(OH)2 2 Ca(OH)2 + 4 Cl = Ca(ClO)2 + CaCl2 + 2 H2O.

CHAPTER XLVII.

MAGNESIUM, ALUMINIUM, AND ZINC.

MAGNESIUM AND ITS COMPOUNDS.

Examine magnesite, dolomite, talc, serpentine, hornblende,
meerschaum, magnesium ribbon, magnesia alba, Epsom salt.

258. Occurrence and Preparation.--Mg is very widely distributed,
but does not occur uncombined. Its salts are found in rocks and
soils, in sea water and in the water of some springs, to which
they impart a brackish taste.

The most common minerals containing Mg are magnesite, MgCO3,
dolomite, MgCO3 + CaCO3, and talc, serpentine, hornblende, and
meerschaum. The last four are silicates, and often are unctious
to the touch. What proportion of the earth's crust is composed of
Mg? See page 173.

259. Metallic Mg is prepared by fusing MgCl2 with Na. Why is the
process expensive? Write the reaction.

Experiment 120.--With forceps hold a short strip of Mg ribbon in
a flame. Note the brilliancy of the light, and give the reaction.
Examine and name the product.

Photographs of the interior of caverns, where sunlight does not
penetrate, are taken by Mg light. Gun-cotton sprinkled with
powdered Mg has recently been employed for that purpose. Mg
tarnishes slightly in moist air. Compounds of Mg.--MgO, magnesia,
like CaO, is very infusible, and is used for crucibles. Magnesia
alba, a variable mixture of MgCO2 and Mg(OH)2, is employed in
medicine, as is also Epsom salt, MgSO4 + 7 H2O.

ALUMINIUM AND ITS COMPOUNDS.

Examine aluminium, aluminium bronze, corundum, emery, feldspar,
argillite, clay. Note especially the color, luster, specific
gravity and flexibility of Al.

What elements are more common in the earth than Al? What metals?
Compare the abundance of Al with that of Fe.

260. Compounds of Al.--Al occurs only in combination with other
elements. Feldspar, mica, slate, and clay are silicates of it. It
occurs in all rocks except CaCO3 and SiO2, and in nearly 200
minerals. Though found in all soils, its compounds are not taken
up by plants, except by a few cryptogams. Corundum, Al2O3, is the
richest of its ores. Compute its percent of Al. Compounds of Al
are very infusible and difficult of reduction.

261. Reduction.--Like most other metals not easily reducible by C
or H, it was originally obtained by electrolysis, but more
recently from its chloride, by the reducing action of strongly
heated K or Na. Al2Cl6 + 6 Na = 6 NaCl + 2 Al.

What is the chief use of Na? As it takes three pounds of Na to
make one pound of Al, the cost of the latter has been fifteen
dollars or more per pound. Its use has thus been restricted to
light apparatus and aluminium bronze, an alloy of Cu 90, Al 10,
which is not unlike gold in appearance.

Al2O3 has lately been reduced by C. Higher temperatures than have
heretofore been known are obtained by means of the electric arc
and large dynamo machines. Afurnace made of graphite, because
fire-clay melts like wax at such a high temperature, is filled
with Al2O3--corundum, --C, and Cu. In the midst of this are
embedded large carbon terminals, connected with dynamos. The
reduction takes several hours.

The following reaction takes place: Al2O3 + 3 C = 2 Al + 3 CO. Cu
is also added, and an alloy of Al and Cu is thus formed. This
alloy is not easily separable into its elements. Explain the
action of the C. CO escapes through perforations in the top of
the furnace, burning there to CO2. Only alloys of Al have yet
been obtained by this process. This method has not been employed
before, simply because the highest temperatures of combustion,
2000 degrees or 2500 degrees, would not effect a reduction. In
the same way Si, B, K, Na, Ca, Mg, Cr, have recently been reduced
from their oxides; but a process has yet to be found for
separating them easily from their alloys.

262. Properties and Uses.--Al is a silvery white metal, lighter
than glass, and only one-third the weight of iron. It does not
readily rust or oxidize, it fuses at 1000 degrees (compare with
Fe), is unaffected by acids, except by HCl and, slightly, by
H2SO4, is a good conductor of electricity, can be cast and
hammered, and alloys with most metals, forming thus many valuable
compounds. Every clay-bank is a mine of this metal, which has so
many of the useful properties of metals and has so few defects
that, if it could be obtained in sufficient quantities, it might,
for many purposes, take the place of iron, steel, tin, and other
metals. From its properties state any advantages which it would
have over iron in ocean vessels, railroads, and bridges. Why is
it better than Sn or Cu for culinary utensils? An alloy of Al,
Cu, and Si is used for telephone wires in Europe, and the
Bennett-Mackay cable is of the same material. Washington
monument, the tallest shaft in the world, is capped with a
pyramid of Al,ten inches high.

For the uses of alumina, Al2O3, and its silicates, see page 133.

ZINC AND ITS COMPOUNDS.

Examine zincite, sphalerite, Smithsonite, sheet zinc, galvanized
iron, granulated zinc, zinc dust.

263. Compounds.--The compounds of zinc are abundant. Its chief
ores are zincite, ZnO, sphalerite or blende, ZnS, Smithsonite,
ZnCO3. For their reduction these ores are first roasted, i.e.
heated in presence of air. With ZnS this reaction takes place:
ZnS + 3 O = Zn0 + S02. The oxide is reduced with C, and then Zn
is distilled. State the reaction. Zinc is sublimed-in the form of
zinc dust-like flowers of S. Granulated Zn is made by pouring a
stream of the molten metal into water.

Experiment 121.--Burn a strip of Zn foil, and note the color of
the flame and of the product. State the reaction. The red color
of zincite is supposed to be imparted by Mn present in the
compound.

264. Uses.--Name any use of Zn in the chemical laboratory. It is
employed for coating wire and sheet iron --galvanized iron. This
is done by plunging the wire or the sheets of iron into melted
Zn. Describe the use of Zn as an alloy. See page 136.

ZnO forms the basis of a white paint called zinc white. White
vitriol, ZnSO4 + 7 H2O, is employed in medicine. Name two other
vitriols.

CHAPTER XLVIII.

IRON AND ITS COMPOUNDS.

Examine magnetite, hematite, limonite, siderite, pig-iron,
wrought-iron, steel.

265. Ores and Irons.--As Fe occurs native only in meteorites and
in small quantities of terrestrial origin, it is obtained from
its ores. There are four of these ores--magnetite (Fe3O4),
hematite (Fe2O3), limonite (2 Fe2O3 + 3 H2O), and siderite
(FeCO3). Which is richest in Fe? Compute the proportion. FeCO3
occurs mostly in Europe. The reduction of these ores, as well as
of other metallic oxides, consists in removing O by C at a high
tempera- ture. As ordinarily classified there are three kinds of
iron,--pig- or cast-iron, steel, and wrought-iron.

Study this table, noting the purity, the fusing-point, and the
per cent of C in each case.


Per Cent Fe Fusibility. Per Cent
(general). C.
Pig......... 90 1200 degrees 2-6
Steel........ 99 1400 degrees 0.5-2
Wrought....... 99.7 1500 degrees Fraction.


Pure iron melts at about 1800 degrees. Pig-iron is obtained from
the ore by smelting, and from this are made steel and wrought-
iron.

266. Pig-Iron.--The ore is reduced in a blast furnace (Fig. 47),
in some cases eighty or one hundred feet high, and having a
capacity of about 12,000 cubic feet. The reducing agent is either
charcoal, anthracite coal, or coke,bituminous coal being too
impure. Charcoal is the best agent, and is used in preparing
Swedish iron; but it is too expensive for general use.

Fig. 47. Blast furnace. F, entrance of tuyeres, or blast-pipes.
E, F, hottest part. C, conductor for gases, which are
subsequently used to heat the air going into the tuyeres. G,
upper portion, slag, lower portion, melted iron.

Were ores absolutely pure, only C would be needed to reduce them.
Complete: Fe3O4 + 4 C =? Fe3O4 + 2C=?

Much earthy material--gangue--containing silica and silicates is
always found with iron ores. These are infusible, and something
must be added to render them fusible. CaO forms with SiO2 just
the flux needed. See page 132. Ca0 + Si02 = ? Which of these is
the basic, and which the acidic compound? CaO results from
heating CaCO3; hence the latter is employed instead of the
former. In what case would Si02 be used as the flux?

Into the blast furnace are put, in alternate layers, the fuel,
the flux, and the ore. The fire, once kindled, is kept burning
for months or years. Hot air is driven in through the tuyeres
(tweers). O unites with C of the fuel, forming CO2 and CO. The C
also reduces the ore. Fe2O3 + 3 C = ? CO accomplishes the same
thing. 3 CO + Fe2O3 = ? The intense heat fuses CaO and SiO2 to a
silicate which, with other impurities, forms a slag; this, rising
to the surface of the molten mass, is drawn off. The iron is
melted, falls in drops to the bottom, and is drawn off into sand
molds. See Figure 47. This is pig-iron. It contains as
impurities, C, Si, S, P, Mn, etc. If too much S or P is present
in an ore, it is worthless. This is why the abundant mineral FeS2
cannot be used as a source of iron. From the top of the furnace
N, CO, CO2, H2O, etc., escape. These gases are used to heat the
air which is forced through the tuyeres, and to make steam in
boilers.

267. Steel.--The manufacture of steel and wrought-iron consists
in removing most of the impurities from pig-iron. It will be seen
that the most common compounds of C, S, Si, and P, are their
oxides, and these are for the most part gases. Hence these
elements are removed by oxidation.

Bessemer steel is prepared by melting pig-iron and blowing hot
air through it. A converter (Fig. 48) lined with siliceous sand,
and holding several tons, is partially filled with the molten
metal; blasts of hot air are driven into it, and the C and other
impurities, together with a little of the Fe, are oxidized. The
exact moment when the process has gone far enough, and most of
the impurities have been removed, is indicated by the appearance
of the escaping flame. It usually takes from five to ten minutes.
The blast is then stopped, and the metal has about the
composition of wrought-iron; it contains some uncombined O. A
white pig-iron (spiegeleisen), which contains a known quantity of
C and of Mn, is at once added. Mn removes part of the extra O,
and, though it remains, does not injure the metal. The C is
"dissolved" by the Fe, which is then run into molds (ingots).
This process, the Bessemer, invented in 1856, has revolutionized
steel manufacture. No less than ten tons of iron have been
converted into steel, in five minutes, in a single converter.

268. Wrought-Iron.--The chemical principle involved in making
wrought-iron is the same as that in making steel, but the process
is different. Impurities are burned out from pig-iron in an open
reverberatory furnace, by constantly stirring the metal in
contact with air. This is called puddling. A reverberatory
furnace is one in which the fuel is in one compartment, and the
heat is reflected downward into another, that holds the substance
to be acted upon (Fig. 49).

Steel may also be made by carburizing wrought-iron. Iron and
charcoal are packed together and heated for days, without
melting, when it is found that, in some unknown way, solid C has
penetrated solid Fe. The finer kinds of steel are made in this
way, but they are very expensive.

Wrought-iron may also be made directly from the ore in an open
hearth furnace, with charcoal. This was the original mode.

269. Properties.--The varying properties of pig-iron, steel, and
wrought-iron are due in part to the proportion of C and of other
elements present, either as mixtures or as compounds, and in part
to other causes not well understood. Wrought-iron is fibrous, as
though composed of fine wires, and hence is ductile, malleable,
tough, and soft, and cannot be hardened or tempered, but it is
easily welded. Pig-iron is crystalline, and so is not ductile or
malleable; it is hard and brittle, and cannot be welded. On
account of its low melting-point it is generally employed for
castings. Steel is crystalline in structure, and when suddenly
cooled from red heat by plunging into cold water, becomes hard
and brittle. The tempering can be varied by afterwards heating to
any required degree, indicated by the color of the oxide formed
on the exterior. The higher temperatures give the softer steel.

270. Salts of Iron.--Examine FeSO4, FeS, FeS2.

Fe has a valence of 2 or 4. This gives rise to two kinds of
salts, ferrous and ferric, as in FeCl2 and Fe2Cl6 The valence of
Fe in ferric salts is 4. Ferrous sulphate is FeSO4; ferric
sulphate, Fe2(SO4)3. Write the symbols for ferrous and ferric
hydrate; for the oxides; for the nitrates. Write the graphic
symbols for each.

271. Colors.--The characteristic color of ferrous salts is green,
as in FeSO4. These salts give the green color to the chlorophyll
in leaves and grass, and bottle glass owes its green color to
ferrous silicate. Ferric salts are a brownish red, as shown in
hematite and limonite, and in some bottles. Red sandstone, and
most soils and earths, are illustrations of this coloring action.
The blood of vertebrates owes its color to ferric salts. Bricks
are made from a greenish blue clay in which iron exists in the
ferrous state. On being heated, ferrous salts are oxidized to
ferric, and their color is changed to red. Iron rust is hydrated
ferric oxide, Fe2O3 and Fe2(OH)6.

272. Change of Valence.

Experiment 122.--Dissolve 2 g. of iron filings in diluted HCl.
Filter or pour off the clear liquid, divide it into two parts,
and add NH4OH to one part till a ppt. occurs. Notice the greenish
color of Fe(OH)2. Oxidize the other part by adding a few drops of
HNO3 and boiling a minute. Now add NH4OH, and observe the reddish
color of the ppt., Fe2(OH)6.

Solutions of ferrous salts will gradually change to ferric, if
allowed to stand, thus showing the greater stability of the
latter. In changing from FeCl2 to Fe2Cl6 oxidation does not
consist in adding O, but in increasing the negative element or
radical. This is possible only by changing the valence of Fe from
2 to 4. Hence oxidation, in its larger sense, means increasing
the valence of the positive element. To oxidize FeSO4 is to make
it Fe2(SO4)3, changing the valence of Fe as before. Reduction or
deoxidation diminishes the valence of the positive element.
Illustrate this by the same iron salts. Illustrate it by PbO and
Pb02; AuCl and AuCl3; Sb2S3 and Sb2S5. In this sense define an
oxidizing agent. A reducing agent.

273. Ferrous Sulphate.

Experiment 123.--Dissolve a few iron filings in dilute H2SO4, and
slowly evaporate for a few minutes. Write the equation.

Ferrous sulphate, green vitriol, or copperas, FeSO4 + 7 H2O, is
the source of what acid? See page 66. It is also one of the
ingredients in many writing inks. On being heated, or exposed to
the air, it loses its water of crystallization and becomes a
white powder. It is prepared as above, or by oxidizing moistened
FeS2 by exposure to the air.

Ferrous sulphide, protosulphide of iron, FeS, is how prepared?
See Experiment 6. State its use. See Experiment 108. It also
occurs native.

Ferric sulphide, pyrite, FeS2, occurs native in large quantities.
What is its use? See page 65.

CHAPTER XLIX.

LEAD AND TIN.

LEAD.

Examine galena, lead protoxide and dioxide, red-lead, lead
carbonate, acetate, and nitrate. Note especially the colors of
the oxides, the cubical crystallization and cleavage of galena,
the specific gravity of the compounds, the softness of Pb, and
the tarnish, Pb2O, which covers it,if long exposed.

274. Distribution of Pb.--Pb is widely distributed, occurring as
PbS and PbCO3. PbS, galenite or galena, is its main source. By
heating it in air, SO2 is formed, and Pb liberated and drawn off.

Pb is but little acted on by cold H2SO4, unless concentrated.
Describe its use in making that acid. See page 65. To show that a
little Pb has been dissolved, as PbSO4, in the manufacture of
that acid, perform this experiment.

Experiment 124.--To 5cc. of water in a clean t.t. add the same
volume of H2SO4, not C.P.; shake, and notice any fine powder
suspended. PbSO4, being insoluble in water, is precipitated. What
is the test for Pb? See Experiment 109.

275. Poisonous Properties.--Ph is very flexible and soft, and is
much used for water pipes. In moist air it is soon coated with
suboxide, Pb20, as may be seen by exposing a fresh surface. Some
portion of this is liable to dissolve in water, and, as all
soluble salts of Pb are poisonous, water that has stood in pipes
should not be used fordrinking. Lead is employed as an alloy of
tin for covering sheet-iron in "terne plate." T his plate is
rarely used except for roofing. The "bright plate," used for tin
cans and other purposes, scarcely ever contains any lead except
the small portion in solder. In soldering, ZnCl2 is employed for
a flux. Sn, Pb, and Zn are somewhat soluble in vegetable acids.
If citric acid be present, as it usually is, citrates of these
metals are formed, and all of them are poisonous. The action is
far more rapid after opening the can, since oxidation is
hastened. Hence the contents should be taken out directly after
opening.

Lead poisons seem to have an affinity for the tissues of the
body, and accumulate little by little. Painter's colic results
from lead poisoning. Epsom salt, or other soluble sulphate, is an
antidote, since with Pb it makes insoluble PbSO4.

276. Some Lead Compounds.--Lead salts form the basis of many
paints. White paint is a mixture of PbCO3 and Pb(OH)2 suspended
in linseed oil. It is often adulterated with BaSO4, ZnO, CaCO3.
Other lead compounds are used for colored paints. The two chief
soluble salts are Pb(NO3)2 and lead acetate, Pb(C2H302)2.

Red-lead, Pb3O4, and, to some extent, litharge, PbO, are employed
in glass manufacture. Name the kind of glass in which it is used,
describe its manufacture, and write a symbol for lead silicate.
What is the characteristic of lead glass? See page 132.

Experiment 125.--Put a small fragment of Pb on a piece of
charcoal, and blow the oxidizing flame against it for some time
with a mouth blow-pipe. Note the color of the coating on the
coal. PbO has formed.

Experiment 126.--Dissolve a small piece of lead in dilute HNO3.
Pour off the solution into a t.t. and add HCl or other soluble
chloride. Pb(NO3)2 + 2 HCl = ? What is the insoluble product?

Experiment 127.--Add to a solution of Pb(C2H3O2)2 some H2SO4.
Give the reaction and the explanation. TIN.

Examine cassiterite, tin foil, "terne plate," "bright plate."

277. Sn occurs as the mineral cassiterite, tin stone, Sn02, and
is found in only a few localities, as Banca, Malacca, and
England. It does not readily tarnish, and is used to cover thin
plates of copper and iron. Tin foil is generally an alloy of Pb
and Sn.

Sn is sometimes a dyad, at others a tetrad. Write symbols for its
two chlorides, stannous and stannic, also for its sulphides and
oxides.

CHAPTER L.

COPPER, MERCURY, AND SILVER.

COPPER.

Examine native copper, chalcopyrite, malachite, azurite, copper
acetate, copper nitrate, copper sulphate.

278. Occurrence.--Copper occurs both native and in many
compounds, being diffused in rocks and, in minute quantities, in
soils, waters, plants, and animals. Spain, Chili, and the United
States are the chief Cu producing countries. The extensive mines
of Michigan yield the native ore. The Calumet and Heela mine
alone produces 4,000,000 pounds per month. The most abundant
compound of Cu is chalcopyrite, or copper pyrites, CuFeS2.
Malachite, which is green, and azurite, which is blue, are
carbonates, the former being used for ornamental purposes.

Cu is, next to Ag, the best conductor of electricity and heat
among the elements; it is very ductile, malleable, and tenacious.

Cu has two valences, 1 and 2. Symbolize and name its chlorides,
iodides, sulphides, and oxides. Cupric compounds, as a rule, are
more stable than cuprous.

279. Uses.--Thousands of tons of Cu find use in domestic
utensils, ocean vessels, electric wires, batteries, and plating.
Name the chief alloys of Cu and their uses. See page 136. How may
CuS be obtained? See Experiment 7. Cu2O, cuprous oxide, is used
to color glass red. CUSO4 is employed in calico-printing,
electric batteries, etc. It is called blue vitriol.

Paris green, used for killing potato-beetles, is composed chiefly
of copper arsenite. Write the symbol for this compound. All
soluble salts of Cu are poisonous; hence care should be taken not
to bring any acid in contact with copper vessels of domestic use.
With acetic acid, what would be formed?

MERCURY AND ITS COMPOUNDS.

Examine cinnabar, vermilion, mercury, red oxide, mercurous and
mercuric chloride.

280. Cinnabar, HgS, is practically the only source of mercury--
quicksilver. Austria, Spain, and California contain nearly all
the mines. In these mines the metal also occurs native to a small
extent. It is the only commonly occurring metal that is liquid at
ordinary temperatures; it solidifies at about -40 degrees. What
other common liquid element? See page 12. Hg is reduced from the
ore by Fe, Hg being distilled over and collected in water. Heat
regularly expands the metal.

281. Uses.--For uses see Reduction of Ag and Au, pages 165 and
170; amalgams, page 137; laboratory work, page 68. It is also
employed for thermometers and barometers, and as the source of
the red pigment vermilion, which is artificial HgS.

Compare the vapor density and the atomic weight of Hg, and
explain. See page 12. Hg is either a monad or a dyad. Symbolize
its ous and ic oxides and chlorides. Which of the following are
is salts, and which are ous, and why? HgNO3, Hg(NO3)2, HgCl,
HgCl2? Calomel, HgCl or Hg2Cl2, used in medicine, and corrosive
sublimate, HgCl2, are illustrations of the ous and ic salts. The
former is insoluble, the latter soluble. All soluble compounds of
Hg are virulent poisons, for which the antidote is the white of
egg, albumen. With it they coagulate or form an insoluble mass.

SILVER AND ITS COMPOUNDS.

282. Occurrence and Reduction.--Silver is found uncombined, and
combined, as Ag2S, argenite, and AgCl, horn silver. It occurs
usually with galena, PbS. It is abundant in the Western States,
Mexico, and Peru. Silver is separated from galena by melting the
two metals. As they slowly cool, Pb crystallizes, and is removed
by asieve, while Ag is left in the liquid mass. The principle is
much like crystallizing NaCl from solution and leaving behind the
salts of Mg, etc., in the mother liquor. When, by repeating the
process, most of the Pb is eliminated, the rest is oxidized by
heating in the air. Pb + O = PbO. Ag does not oxidize, and is
left in the metallic state.

Another mode of reduction is to change the silver salt to its
chloride, and then remove the Cl with Fe. Roasting with NaCl
makes the first change, 2 NaCl + Ag2S = Na2S + 2 AgCl, and with
Fe the second, 2 AgCl + Fe = FeCl2 + 2 Ag. Ag is separated from
the other products by adding Hg, with which it forms an amalgam.
By distilling this, Hg passes over and Ag remains. This is the
amalgamating process.

283. Salts of Silver are much employed in organic chemistry, and
AgCl, AgBr, and AgNO3 are used in photography. AgNO3 is a
soluble, colorless crystal, and is the basis of the silver salts.
It blackens when in contact with organic matter. Stains on a
photographer's hands are due to this substance, and the use of
AgNO3 in indelible inks depends on the same property. This may be
due to a reduction of AgNO3 to Ag4O. Stains can be removed from
the skin or from linen by a solution of Kl, or of CuCl2 followed
by sodium hyposulphite. Lunar caustic is made by fusing AgNO3
crystals, and is used for cauterizing (burning) the flesh. Much
AgCN finds use in electroplating.

Experiment 128.--Put 5 cc. AgNO3 solution in each of three t.t.
To the first add 3 cc. HCl, to the second 3cc.NaCl solution, and
to the third 3 cc. KBr solution. Write the reaction for each
case, and notice that the first two give the same ppt., as in
fact any soluble chloride would. Filter the second and third, on
separate filter papers, and expose half the residue to direct
sunlight, observing the change of color by occasionally stirring.
Solar rays reduce AgCl and AgBr, it is thought, to Ag2Cl and
Ag2Br. Try to dissolve the other half in Na2S2O3, sodium
thiosulphate solution. This experiment illustrates the main facts
of photography.

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