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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Solidifying Points: Cl -102 degrees; HCl -115 degrees; Ether -129
degrees; Alcohol -130 degrees.

Chapter XXXVII.

SULPHUR.

Examine brimstone, flowers of sulphur, pyrite, chalcopyrite,
sphalerite, galenite, gypsum, barite.

182. Separation.

Experiment 103.--To a solution of 2 g. of sodium sulphide,, Na2S2
in 10 cc. H2O add 3 or 4cc. HCl, and look for a ppt. Filter, and
examine the residue. It is lac sulphur, or milk of sulphur.

183. Crystals from Fusion.

Experiment 104.--In a beaker of 25 or 50 cc. capacity put 20 g.
brimstone. Place this over a flame with asbestos paper
interposed, and melt it slowly. Note the color of the liquid,
then let it cool, watching for crystals. When partly solidified
pour the liquid portion into an evapo- rating-dish of water, and
observe the crystals of S forming in the beaker (Fig. 42). The
hard mass may be separated from the glass by a little HNO3 and a
thin knife-blade, or by CS2.

184. Allotropy.

Experiment 105.--Place in a t.t. 15g of brimstone, then heat
slowly till it melts. Notice the thin amber-colored liquid. The
temperature is now a little above 100 degrees. As the heat
increases, notice that it grows darker till it becomes black and
so viscid that it cannot be poured out. It is now above 200
degrees. Still heat, and observe that it changes to a slightly
lighter color, and is again a thin liquid. At this time it is
above 300 degrees. Now pour a little into an evaporating dish
containing water. Examine this, noticing that it can be stretched
like rubber. Leave it in the water till it becomes hard. Continue
heating thebrimstone in the t.t. till it boils at about 450
degrees, and note the color of the escaping vapor. Just above
this point it takes fire. Cool the t.t., holding it in the light
meantime, and look for a sublimate of S on the sides.

185. Solution.

Experiment 106.--Place in an evaporating-dish a gram of powdered
brimstone, and add 5cc, CS2, carbon disulphide. Stir, and see
whether S is dissolved. Put this in a draft of air, and note the
evaporation of the liquid CS2, and the deposit of S crystals.
These crystals are different in form from those resulting from
cooling from fusion.

186. Theory of Allotropy.--The last three experiments well
illustrate allotropy. We found S to crystallize in two different
ways. Substances can crystallize in seven different systems, and
usually a given substance is found in one of these systems only;
e.g. galena is invariably cubical. An element having two such
forms is said to be dimorphous. If it crystallizes in three
systems, it is trimorphous. A crystal has a definite arrangement
of its molecules. If without crystalline form, a substance is
called amorphous. An illustration of amorphism was S after it had
been poured into water. Thus S has at least three allotropic
forms, and the gradations between these probably represent
others. Allotropy seems to be due to varied molecular structure.
We know but little of the molecular condition of solids and
liquids, since we have no law to guide us like Avogadro's in
gases; but, from the density of S vapor at different
temperatures, we infer that liquids and solids have their
molecules very differently made up from those of gases. The least
combining weight of S is 32. Its vapor density at 1,000 degrees
is 32; hence its molecular weight is 64, i.e. vapor density x 2;
and there are 2 atoms in its molecule at that temperature,
molecular weight / atomic weight. At 500 degrees, however, the
vapor density is 96and the molecular weight 192. At this degree
the molecule must contain 6 atoms. How many it has in the
allotropic forms, as a solid, is beyond our knowledge; but it
seems quite likely that allotropy is due to some change of
molecular structure.

The above experiments show two modes of obtaining crystals, by
fusion and by solution.

187. Occurrence and Purification.--Sulphur occurs both free and
combined, and is a very common element. It is found free in all
volcanic regions, but Sicily furnishes most of it. Great
quantities are thrown up from the interior of the earth during an
eruption. The heat of volcanic action probably separates it from
its compound, which may be CaSO4. Vast quantities of the
poisonous SO2 gas are also liberated during an eruption, this
being, in volume of gases evolved, next to H2O. S is crudely
separated from its earthy impurities in Sicily by piling it into
heaps, covering to prevent access of air, and igniting, when some
of the S burns, and the rest melts and is collected. After
removal from the island it is further purified by distilling in
retorts connected with large chambers where it sublimes on the
sides as flowers of sulphur (Fig. 43). This is melted and run
into molds, forming roll brimstone. S also occurs as a
constituent of animal and vegetable compounds, as in mustard,
hair, eggs, etc. The tarnishing of silver spoons by eggs is due
to the formation of silver sulphide, Ag2S. The yellow color of
eggs, however, is due to oils, not to S.

The main compounds of S are sulphides and sulphates. What acids
do they respectively represent? Metallic sulphides are as common
as oxides; e.g. FeS2, or pyrite, PbS, or galenite, ZnS, or
sphalerite, CuFeS2, or chalcopyrite, etc. The most abundant
sulphate is CaSO4, or gypsum. BaSO4, or barite, and Na2SO4, or
Glauber's salt, are others.

The only one of these compounds that is utilized for its S is
FeS2. In Europe this furnishes a great deal of the S for H2SO4. S
is obtained by roasting FeS2. 3 FeS2 = Fe3S4 + 2 S.

188. Uses. -The greatest use of S is in the manufacture of H2SO4.
A great deal is used in making gunpowder, matches, vulcanized
rubber, and the artificial sulphides, like HgS, H2S, CS2, etc.
The last is a very volatile, ill- smelling liquid, made by the
combination of two solids, S being passed over red-hot charcoal.
It dissolves S, P, rubber, gums, and many other substances
insoluble in H2O.

189. Sulphur Dioxide, SO2, has been made in many experiments. It
is a bleaching agent, a disinfectant, and a very active compound,
having great affinity for water, but it will not support
combustion. Like most disinfectants, it is very injurious to the
system. It is used to bleach silk and wool--animal substances--
and straw goods, which Cl would injure; but the color can be
restored, as the coloring molecule seems not to be broken up, but
to combine with SO2, which is again separated by reagents. Goods
bleached with SO2 often turn yellow after a time.

190. SO2 a Bleacher.

Experiment 107.-Test its bleaching power by burning S under a
receiver under which a wet rose or a green leaf is also placed.

Chapter XXXVIII.

HYDROGEN SULPHIDE.

Examine ferrous sulphide, natural and artificial.

191. Preparation.

Experiment 108.--Put a gram of ferrous sulphide (FeS) into a t.t.
fitted with a d.t., as in Figure 32. Add 10cc. H2O and 5cc.
H2SO4. H2S is formed. Write the equation, omitting H2O. What is
left in solution?

192. Tests.

Experiment 109.-(1) Take the odor of the escaping gas. (2) Pour
into a t.t. 5cc.solution AgNO3, and place the end of the d.t.
from a H2S generator into the solution and note the color of the
ppt. What is the ppt.? Write the equation. (3) Experiment in the
same way with Pb(NO3)2 solution. Write the equation. (4) Let some
H2S bubble into a t.t. of clean water. To see whether H2S is
soluble in H2O, put a few drops of the water on a silver coin.
Ag2S is formed. Describe, and write the equation. Do the same
with a copper coin. (5) Put a drop of lead acetate solution,
Pb(C2H3O2)2, on a piece of unglazed paper, and hold this before
the d.t. from which H2S is escap- ing. PbS is formed. Write the
equation. This is the characteristic test of H2S.

193. Combustion of H2S

Experiment 110.--Attach a philosopher's lamp tube to the H2S
generator, and, observing the same precautions as with H, light
the gas. What two products must be formed? State the reaction.
The color of the flame. Compute the molecular weight and the
vapor density of H2S. 194. Uses. -Hydrogen sulphide or
sulphuretted hydrogen, H2S, is employed chiefly as a reagent in
the chemical laboratory. It forms sulphides with many of the
metals, as shown in the last experiment. These are precipitated
from solution, and may be separated from other metals which are
not so precipitated, as was found in the case of HCl and NH4OH.
The subjoined experiment will illustrate this. Suppose we wished
to separate Pb from Ba, having salts of the two mixed together,
as Pb(NO3)2 and Ba(NO3)2.

195. H2S an Analyzer of Metals.

Experiment 111.--Pass Some H2S gas in to 5cc.solution Ba(NO3)2.
No ppt. is formed. Do the same with Pb(NO3)2 solution. A ppt.
appears. Now mix 5cc.of each of these solutions in a t.t. and
pass the gas from a H2S generator into the liquid. What is
precipitated, and what is unchanged? When fully saturated with
the gas, as indicated by the smell, filter. Which metal is on the
filter and which is in the filtrate? Other reagents, as Na2CO3
solution, would precipitate the latter.

196. Occurrence and Properties. -- H2S is an ill-smell- ing,
poisonous gas, formed in sewers, rotten eggs, and other decaying
albuminous matter. It is formed in the earth, probably from the
action of water on sulphides, and issues with water from sulphur
springs.

A characteristic property is the formation of metallic sulphides,
as above. A skipper one night anchored his newly painted vessel
near the Boston gas-house, where the refuse was deposited, with
its escaping H2S. In the morning, to his consternation, the craft
was found to be black. H2S had come in contact with the lead in
the white paint, forming black PbS. This gradually oxidized after
reaching the open sea, and the white color reappeared.

Chapter XXXIX.

PHOSPHORUS.

NOTE.--Phosphorus should be kept in water, and handled with
forceps, never with the fingers, except under water, as it is
liable to burn the flesh and produce ulcerating sores. Pieces not
larger than half a pea should be used, and every bit should
finally be burned.

197. Solution and Combustion. Experiment 112. -Put 1 or 2 pieces
of P into an evaporating- dish, and pour over them 5 or 10cc.CS2
carbon disulphide. This will be enough for a class. When
dissolved, dip pieces of unglazed paper into it, and hold these
in the air, looking for any combustion as they dry. The P is
finely divided in solution, which accounts for its more ready
combustion then. Notice that the paper is not destroyed. This is
an example of so-called "spontaneous combustion." The burning-
point of P, the combustible, in air, the supporter, is about 60
degrees.

198. Combustion under Water.

Experiment 113. -Put a piece of P in a t.t. which rests in a
receiver, add a few crystals KClO3 and 5cc. H2O. Now pour in
through a thistle-tube 1cc.or more of H2SO4. Look for any flame.
H2SO4 acts very strongly on KClO3. What is set free? From this
fact explain the combustion in water.

199. Occurrence.--P is very widely disseminated, but not
abundant, and is found only in compounds, the chief of which is
calcium phosphate Ca3(PO4)2. It occurs in granite and other
rocks, as the mineral apatite, in soils, in plants, particularly
in seeds and grains, and in the bones, brains, etc., of
vertebrates. From the human system it is excreted by the kidneys
as microcosmic salt, HNaNH4PO4; and when the brain is hard-
worked, more than usual is excreted. Hence brain-workers have
been said to "burn phosphorus."

200. Sources.--Rocks are the ultimate source of this element.
These, by the action of heat, rain, and frost, are disintegrated
and go to make soils. The rootlets of plants are sent through the
soil, and, among other things, soluble phosphates in the earth
are absorbed, circulated by the sap, and selected by the various
tissues. Animals feed on plants, and the phosphates are
circulated through the blood, and deposited in the osseous
tissue, or wherever needed.

Human bones contain nearly 60 per cent of Ca3(PO4)2; those of
some birds over 80 per cent.

The main sources of phosphates and P are the phosphate beds of
South Carolina, the apatite beds of Canada, and the bones of
animals.

201. Preparation of Phosphates and Phosphorus.--Bone ash,
obtained by burning or distilling bones, and grinding the
residue, is treated with H1SO4, and forms soluble H4Ca(PO4)2,
superphosphate of lime, and insoluble CaSO4.

Ca3(PO4)2 + 2 H2SO4 = H4Ca(PO04)2 + 2 CaSO4. This completes the
process for fertilizers. If P is desired, the above is filtered;
charcoal, a reducing agent, is added to the filtrate; the
substance is evaporated, then very strongly heated and distilled
in retorts, the necks of which dip under water. It is then
purified from any uncombined C by melting in hot water and
passing into molds in cold water.

The work is very dangerous and injurious, on account of the low
burning-point of P, and its poisonous properties. While its
compounds are necessary to human life, P itself destroys the
bones, particularly the jaw bones, of the workers in it.

Between 1,000 and 2,000 tons are made yearly, mostly for matches,
but almost all at two factories, one in England, and one in
France. 202. Properties.--P is a colorless, transparent solid,
when pure; the impure article is yellowish, translucent, and
waxy. It is insoluble in water, slightly soluble in alcohol and
ether, and it readily dissolves in CS2, oil of turpentine, etc.
Fumes, having a garlic odor, rise when it is exposed to the air,
and in the dark it is phosphorescent, emitting a greenish light.

203. Uses. -The uses of this element and its compounds are for
fertilizers, matches, vermin poisons, and chemical operations.

204. Matches.-The use of P for matches depends on its low
burning-point. Prepared wood is dipped into melted S, and the end
is then pressed against a stone slab having on it a paste of P,
KClO3, and glue. KNO3 is often used instead of KClO3. In either
case the object is to furnish O to burn P. Matches containing
KClO3 snap on being scratched, while those having KNO3 burn
quietly. The friction from scratching a match generates heat
enough to ignite the P, that enough to set the S on fire, and the
S enough to burn the wood. Give the reaction for each. Paraffine
is much used instead of S. Safety matches have no P, and must be
scratched on a surface of red P and Sb2S3, or on glass.

205. Red Phosphorus.-Two or three allotropic forms of P are
known, the principal one being red. If heated between 230 degrees
and 260 degrees, away from air, the yellow variety changes to
red, which can be kept at all temperatures below 260 degrees.
Above that it changes back. Red P is not poisonous, ignites only
at a high temperature, and is not phosphorescent, like the
yellow. 206. Spontaneous Combustion of Phosphene, or Hydrogen
Phosphide, PH3.

Experiment 114.--Put into a 20cc.flask 1 g. P and 50cc.saturated
solution NaOH or KOH. Connect with the p.t. by a long d.t., as in
Figure 44, the end of which must be kept under water. Pour 3 or
4cc.of ether into the flask, to drive out the air. It is
necessary to exclude all air, as a dangerously explosive mixture
is formed with it. Heat the mixture, and as the gas passes over
and into the air, it takes fire spontaneously, and rings of smoke
successively rise. It will do no harm if, on taking away the
lamp, the water is drawn back into the flask; but in that case
the flask should be slightly lifted to prevent breakage by the
sudden rush of water. On no account let the air be drawn over.

The experiment has no practical value, but is an interesting
illustration of the spontaneous combustion of PH3 and of vortex
rings. What are the products of the combustion? An admixture of
another compound of P and H causes the combustion.

Chapter XL.

ARSENIC.

Examine metallic arsenic, realgar, orpiment, arsenopyrite,
arsenic trioxide, copper arsenite.

The compounds of arsenic are very poisonous if taken into the
system, and must be handled with care.

207. Separation. Experiment 115.--Draw out into two parts in the
Bunsen flame a piece of glass tubing 20cm long and 1 or 2cm in
diameter. Into the end of one of the ignition tubes thus formed,
when it is cool, put one-fourth of a gram of arsenic trioxide,
As2O3, using paper to transfer it. Now put into the tube a piece
of charcoal, and press it down to within 2 or 3cm of the AS2O3
(Fig. 45). Next heat the coal red-hot, and then at once heat the
As203. Continue this process till you see a metallic sublimate-
metallic mirror-on the tube above the coal. Break the tube and
examine the sublimate. It is As. Heat vaporizes the As2O;3.
Explain the chemical action. What is the agency of C in the
experiment? Of As2O3? 2 As2O3 + 3 C = ?

208. Tests.-Experiments 115 and 116 are used as tests for the
presence of arsenic.

Experiment 116.--Prepare a H generator, - a flask with a thistle-
tube and a philosopher's lamp tube (Fig. 46), put in some
granulated Zn, water, and HCl. Test the purity of the escaping
gas (Experiment 23), and when pure, light the jet of H. H is now
burning in air. To be sure that there is no As in the ingredients
used, hold the inside of a porcelain evaporating-dish directly
against the flame for a minute. If no silvery-white mirror is
found, the chemicals are free from As. Then pour through the
thistle-tube, while the lamp is still burning, 1cc.solution of
AS2O3 in HCl or H2O a bit of As2O3 not larger than a grain of
wheat in 10 cc. HCl.

See whether the color of the flame changes; then hold the
evaporating-dish once more in the flame, and notice a metallic
deposit of As. Set away the apparatus under the hood and leave
the light burning.

This experiment must not be performed unless all the cautions are
observed, since the gas in the flask (AsH3) is the most poisonous
known, and a single bubble of it inhaled is said to have killed
the discoverer. By confining the gas inside the flask there is no
danger.

Instead of using As2O3 solution, a little Paris green, wall paper
suspected of containing arsenic, green silk, or green paper
labels, etc., may be soaked in HCl, and tested.

209. Explanation.--The chemical changes are as follows: The
compounds of As, in this case As2O3, in presence of nascent H,
are immediately converted into the deadly hydrogen arsenide
(arsine, arseniuretted hydrogen), AsH3. As2O3 + 12 H = 2 AsH3 + 3
H2O. The AsH3 mixed with excess of H tends to escape and is
burned to As2O3 and H2O, and thus is rendered comparatively
harmless as it passes into the air. This is why the flame must be
burning when the arsenic compound is introduced. 2 AsH3 + 6 O =
As2O3 + 3 H2O.

In the combustion of AsH3, H burns at a lower point than As. The
introduction of a cold body like porcelain cools the flame below
the kindling-point of As, and this is deposited, while H burns,
in exactly the same way as lamp- black was collected in
Experiment 26.

210. Expert Analysis.--A modification of this experiment is
employed by experts to test for AS2O3 poisoning. The organs.--
stomach or liver--are cut into small pieces dissolved by nascent
Cl, or HClO, made from KC1O3 and HCl, and the solution is
introduced into a H generator, as above. AS2O3 preserves the
tissues it comes in contact with, for a long time, and the test
can be made years after death. All the chemicals must be pure,
since As is found in small quantities in most ores, and the Zn,
HCl, and H2SO4 of commerce are very likely to contain it. The
above is called Marsh's test, and is so delicate that a mere
trace of arsenic can be detected.

211. Properties and Occurrence.--As is a grayish white solid, of
metallic luster, while a few of its characters are non-metallic.
It is very widely distributed, being sometimes found native, and
sometimes combined, as AsS, realgar, As2S8, orpiment, and FeAsS,
arsenopyrite. Its chief source is the last, the fine powder of
which is strongly heated, when As separates and sublimes. It has
the odor of garlic, as may be observed by heating a little on
charcoal with the blow-pipe.

212. Atomic Volume.--As is peculiar in that its atomic volume, so
far as the volume can be determined, is only half that of the H
atom. Its vapor density is 150, which gives 300 for the molecular
weight, while its least combining or atomic weight is 75. 300,
the molecular weight = 75, the atomic weight =4, the number of
atoms in the molecule. All gaseous molecules being of the same
size, represented by two squares, the atomic volume of As must be
one-fourth of this size, represented by half of one square. Of
what other element is this true? 213. Uses of As2O3.-Arsenic is
used in shot-manufacture, for hardening the metal. Its most
important compound is As2O3, arsenic trioxide, called also
arsenious anhydride, arsenious acid, white arsenic, etc. So
poisonous is this that enough could be piled on a one-cent piece
to kill a dozen persons. Taken in too large quantities it acts as
an emetic. The antidote is ferric hydrate Fe2(OH)6 and a mustard
emetic, followed by oil or milk.

The vapor density of this compound shows that its symbol should
be As4O6, but the improper one, As2O3, is likely to remain in
use. Another oxide, As2O5, arsenic pentoxide, exists, but is less
important. Show how the respective acid formulae are obtained
from these anhydrides. See page 50.

AS2O3 is used in making Paris green; in many green coloring
materials, in which it exists as copper arsenite; in coloring
wall papers, and in fly and rat poisons. It is employed for
preserving skins, etc. Fashionable women sometimes eat it for the
purpose of beautifying the complexion, to which it imparts a
ghastly white, unhealthy hue. Mountaineers in some parts of
Europe eat it for the greater power of endurance which it is
supposed to give them. By beginning with small doses these
arsenic-eaters finally consume a considerable quantity of the
poison with apparent impunity; but as soon as the habit is
stopped, all the pangs of arsenic-poisoning set in. Wall paper
containing arsenic is said to be injurious to some people, while
apparently harmless to others.

Chapter XLI.

SILICON, SILICA, AND SILICATES.

214. Comparison of Si and C.--The element Si resembles carbon in
valence and in allotropic forms. It occurs in three forms like C,
a diamond form, a graphite, and an amorphous. C forms the basis
of the vegetable and animal world; Si, of the mineral. Most soils
and rocks, except limestone, are mainly compounds of O, Si, and
metals. While O is estimated to make up nearly one- half of the
known crust of the earth, Si constitutes fully a third. The two
are usually combined, as silica, SiO2, or silicates, SiO2
combined with metallic oxides. This affinity for O is so strong
that Si is not found uncombined, and is separated with great
difficulty and only at the highest temperatures. No special use
has yet been found for it, except as an alloy with Al. Its
compounds are very important.

215 Silica.--Examine some specimens of quartz, rock crystal,
white and colored sands, agate, jasper, flint, etc.; test their
hardness with a knife blade, and see whether they will scratch
glass. Notice that quartz crystals are hexagonal or six-sided
prisms, terminated by hexagonal pyramids. The coloring matters
are impurities, often Fe and Mn, if red or brown. When pure,
quartz is transparent as glass, infusible except in the oxy-
hydrogen blow- pipe, and harder than glass. Rock crystal is
massive Si02. Sand is generally either silica or silicates.

The common variety of Si02 is not soluble in water or in acids,
except HF. An amorphous variety is to some extent soluble in
water. Most geysers deposit the latter in successive layers about
their mouths. Agate, chalcedony, and opal have probably an origin
similar to this. A solution of this variety of SiO2 forms a
jelly-like masscolloid--which will not diffuse through a membrane
of parchment -dialyzer--when suspended in water. Crystalloids
will diffuse through such a membrane, if they are in solution.
This principle forms the basis of dialysis.

All substances are supposed to be either crystalloids, i.e.
susceptible of crystallization, or colloids-jelly-like masses.
HCl is the most diffusible in liquids of all known substances;
caramel is one of the least so. To separate the two, they would
be put into a dialyzer suspended in water, when HCl will diffuse
through into the water, and caramel will remain. As2O3, in cases
of suspected poisoning, was formerly separated from the stomach
in this way, as it is a crystalloid, whereas most of the other
contents of the stomach are colloidal.

216. Silicates.--Si is a tetrad. SiO2 + 2 H2O =? Si02 + H2O =? In
either case the product is called silicic acid. Replace all the H
with Na, and name the product. Replace it with K; Mg; Fe; Ph; Ca.
Na4SiO4 and Na2SiO3 are typical silicates of Na, but others
exist.

217. Formation of SiO2 from Sodium Silicate. Experiment 117.--To
5cc.Na4SiO4 in au evaporating-dish add 5cc. HCl. Describe the
effect. Pour away any extra HCl. Heat the residue gently, above a
flame, till it becomes white, then cool it and add water. In a
few minutes taste a drop of the water, then pour it off, leaving
the residue. Crush a little in the fingers, and compare it with
white sand, SiO2. Apply to the experiment these equations: -
Na4SiO4 + 4 HCl = 4 NaCl + H4SiO4. H4SiO4 + 2 H2O = Si02. Why was
H4Si04 heated? Why was water finally added?

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