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An Introduction to Chemical Science

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Lime water, Ca(OH)2 solution, is therefore a test for the
presence of CO2. To show that carbon dioxide is formed in
breathing, and in the combustion of C, and that it is present in
the air, perform the following experiment:

Experiment 77.--(1) Put a little lime water into a t.t., and blow
into it through a piece of glass tubing. Any turbidity shows
what? (2) Burn a candle for a few minutes in a receiver of air,
then take out the candle and shake up lime water with the gas.
(3) Expose some lime water in an e.d. to the air for some time.

133. Oxidation in the Human System.--Carbon dioxide, or carbonic
anhydride, carbonic acid, etc., CO2, is a heavy gas, without
color or odor. It has a sharp, prickly taste, and is commonly
reckoned as poisonous if inhaled in large quantities, though it
does not chemically combine with the blood as CO does. Ten per
cent in the air will sometimes produce death, and five per cent
produces drowsiness. It exists in minute portions in the
atmosphere, and often accumulates at the bottom of old wells and
caverns, owing to its slow diffusive power. Before going down
into one of these, the air should always be tested by lowering a
lighted candle. If this is extinguished, there is danger. CO2 is
the deadly "choke damp" after a mine explosion, CH4 being
converted into CO2 and H2O; a great deal is liberated during
volcanic eruptions, and it is formed in breathing by the union of
O in the air with C in the system. This union of C and O takes
place in the lungs and in all the tissues of the body, even on
the surface. Oxygen is taken into the lungs, passes through the
thin membrane into the blood, forms a weak chemical union with
the red corpuscles, and is conveyed by them to all parts of the
system. Throughout the body, wherever necessary, C and H are
supplied for the O, and unite with it to form CO2 and H2O. These
are taken up by the blood though they do not form a chemical
union with it, are carried to the lungs, and pass out, together
with the unused N and surplus O. The system is thus purified, and
the waste must be supplied by food. The process also keeps up the
heat of the body as really as the combustion of C or P in O
produces heat. The temperature of the body does not vary much
from 99 degrees F., any excess of heat passing off through
perspiration, and being changed into other forms of energy.

If, as in some fevers, the temperature rises above about 105
degrees F., the blood corpuscles are killed, and the person dies.
During violent exercise much material is consumed, circulation is
rapid, and quick breathing ensues. Oxygen is necessary for life.
A healthy person inhales plentifully; and this element is one of
nature's best remedies for disease. Deep and continued
inhalations in cold weather are better than furnace fires to heat
the system. All animals breathe O and exhale CO2. Fishes and
other aquatic animals obtain it, not by decomposing H2O, but from
air dissolved in water. Being cold-blooded, they need relatively
little; but if no fresh water is supplied to those in captivity,
they soon die of O starvation.

124. Oxidation in Water.--Swift-running streams are clear and
comparatively pure, because their organic impurities are
constantly brought to the surface and oxidized, whereas in
stagnant pools these impurities accumulate. Reservoirs of water
for city supply have sometimes been freed from impurities by
aeration, i.e. by forcing air into the water.

125. Deoxidation in Plants.--Since CO2 is so constantly poured
into the atmosphere, why does it not accumulate there in large
quantity? Why is there not less free O in the air to-day than
there was a thousand years ago? The answer to these questions is
found in the growth of vegetation. In the leaf of every plant are
thousands of little chemical laboratories; CO2 diffused in small
quantities in the air passes, together with a very little H2O,
into the leaf, usually from its under side, and is decomposed by
the radiant energy of the sun. The C is built into the woody
fiber of the tree, and the O is ready to be re-breathed or burned
again. CO2 contributes to the growth of plants, O to that of
animals; and the constituents of the atmosphere vary little from
one age to another. The compensation of nature is here well
shown. Plants feed upon what animals discard, transforming it
into material for the sustenance of the latter, while animals
prepare food for plants. All the C in plants is supposed to come
from the CO2 in the atmosphere. Animals obtain their supply from
plants. The utility of the small percentage of CO2 in the air is
thus seen.

126. Uses.--CO2 is used in making "soda-water," and in chemical
engines to put out fires in their early stages. In either case it
may be prepared by treating Na2CO3 or CaCO3 with H2SO4. Give the
reactions. On a small scale CO2 is made from HNaCO3. CO2 has a
very weak affinity for water, but probably forms with it H2CO3.
Much carbon dioxide can be forced into water under pressure. This
forms soda-water, which really contains no soda. The
justification for the name is the material from which it is
sometimes made. Salts from H2CO3, called carbonates, are
numerous, Na2CO3 and CaCO3 being the most important.

Chapter XXVI.

OZONE.

127. Preparation.

Experiment 78.--Scrape off the oxide from the surface of a piece
of phosphorus 2 cm long, put it into a wide-mouthed bottle, half
cover the P with water, cover the bottle with a glass, and leave
it for half an hour or more.

128. Tests.

Experiment 79.--Remove the glass cover, smell the gas, and hold
in it some wet iodo-starch paper. Look for any blue color. Iodine
has been set free, according to the reaction, 2 KI + 03= K20 + O2
+ I2, and has imparted a blue color to the starch, and ordinary
oxygen has been formed. Why will not oxygen set iodine free from
KI?. What besides ozone will liberate it?

129. Ozone, oxidized oxygen, active oxygen, etc., is an
allotropic form of O. Its molecule is 03, while that of ordinary
oxygen is 02.

Three atoms of oxygen are condensed into the space of two atoms
of ozone, or three molecules of O are condensed into two
molecules of ozone, or three liters of O are condensed into two
liters of ozone. Ozone is thus formed by oxidizing ordinary
oxygen. 02 + O = 03. This takes place during thunder storms and
in artificial electrical discharges. The quantity of ozone
produced is small, five per cent being the maximum, and the usual
quantity is far less than that.

Ozone is a powerful oxidizing agent, and will change S, P, and As
into their ic acids. Cotton cloth was formerly bleached, and
linen is now bleached, by spreading it on the grass and leaving
it for weeks to be acted on by ozone, which is usually present in
the air in small quantities, especially in the country. Ozone is
a disinfectant, like other bleaching agents, and serves to clear
the air of noxious gases and germs of infectious diseases. So
much ozone is reduced in this way that the air of cities contains
less of it than country air. A third is consumed in uniting with
the substance which it oxidizes, while two-thirds are changed
into oxygen, as in Experiment 79.

It is unhealthful to breathe much ozone, but a little in the air
is desirable for disinfection.

Ozone will cause the inert N of the air to unite with H, to form
ammonia. No other agent capable of doing this is known, so that
all the NH3 in the air, in fact all ammonium compounds taken up
by plants from soils and fertilizers, may have been made
originally through the agency of ozone. At a low temperature
ozone has been liquefied. It is then distinctly blue.

Electrolysis of water is the best mode of preparing this
substance in quantity. When prepared from P it is mixed with
P2O3.

Chapter XXVII.

CHEMISTRY OF THE ATMOSPHERE.

130. Constituents.--The four chief constituents of the atmosphere
are N, O, H2O, CO2, in the order of their abundance. What
experiments show the presence of N, O, and CO2 in the air? Set a
pitcher of ice water in a warm room, and the moisture that
collects on the outside is deposited from the air. This shows the
presence of H2O. Rain, clouds, fog, and dew prove the same. H2SO4
and CaCl2, on exposure to air, take up water. Experiment 18 shows
that there is not far from four times as much N as O by volume in
air. Hence if the atmosphere were a compound of N and O, and the
proportion of four to one were exact, its symbol would be N4O.

131. Air not a Compound.--The following facts show that air is
not a compound, but rather a mixture of these gases.

1. The proportion of N and O in the air, though it does not vary
much, is not always exactly the same. This could not be true if
it were a compound. Why?

2. If N4O were dissolved in water, the N would be four times the
O in volume; but when air is dissolved, less than twice as much N
as O is taken up.

3. No heat or condensation takes place when four measures of N
are brought in contact with one of O. It cannot then be N4O, for
the vapor density of N4O would be 36--i.e. (14 x 4 + 16) / 2; but
that of air is 14 1/2 nearly --i.e. (14 x 4 + 16) / 5. Analysis
shows about 79 parts of N to 21 parts of O by volume in air.

132. Water.--The volume of H2O, watery vapor, in the atmosphere
is very variable. Warm air will hold more than cold, and at any
temperature air may be near saturation, i.e. having all it will
hold at that temperature, or it may have little. But some is
always present; though the hot desert winds of North Africa are
not more than 1/15 saturated. A cubic meter of air at 25 degrees,
when saturated, contains more than 22 g. of water.

133. Carbon Dioxide.--Carbon dioxide does not make up more than
three or four parts in ten thousand of the air; but, in the whole
of the atmosphere, this gives a very large aggregate. Why does
not CO2 form a layer below the O and N?

134. Other Ingredients.--Other substances are found in the air in
minute portions, e.g. NH3 constitutes nearly one-millionth. Air
is also impregnated with living and dead germs, dust particles,
unburned carbon, etc., but these for the most part are confined
to the portion near the earth's surface. In pestilential regions
the germs of disease are said sometimes to contaminate the air
for miles around.

Chapter XXVIII.

THE CHEMISTRY OF WATER.

135. Pure Water.--Review the experiments for electrolysis, and
for burning H. Pure water is obtained by distillation.

Experiment 80.--Provide a glass tube 40 or 50 cm long and 3 or 4
cm in diameter. Fit to each end a cork with two perforations,
through one of which a long tube passes the entire length of the
larger tube (Fig. 32a). Connect one end of this with a flask of
water arranged for heating; pass the other end into an open
receptacle for collecting the distilled water. Into the other
perforations lead short tubes,-- the one for water to flow into
the large tube from a jet; the other, for the same to flow out.
This condenses the steam by circulating cold water around it. The
apparatus is called a Liebig's condenser. Put water into the
flask, boil it, and notice the condensed liquid. It is
comparatively pure water; for most of the substances in solution
have a higher boiling-point than water, and are left behind when
it is vaporized.

(Fig. 32a.)

136. Test.

Experiment 81.--Test the purity of distilled water by slowly
evaporating a few drops on Pt foil in a room free from dust.
There should be no spot or residue left on the foil. Test in the
same way undistilled water. 137. Water exists in Three States,--
solid, liquid, and vaporous. It freezes at 0 degrees, suddenly
expanding considerably as it passes into the solid state. It
boils, i.e. overcomes atmospheric pressure and is vaporized, at
100 degrees (760 mm pressure). If the pressure is greater, the
boiling-point is raised, i.e. it takes a higher temperature to
overcome a greater pressure. If there be less pressure, as on a
mountain, the boiling-point is lowered below 100 degrees. Salts
dissolved in water raise its boiling-point, and lower its
freezing-point to an extent depending on the kind and quantity of
the salt. Water, however, evaporates at all temperatures, even
from ice.

Pure water has no taste or smell, and, in small quantities, no
color. It is rarely if ever found on the earth. What is taken up
by the air in evaporation is nearly pure; but when it falls as
rain or snow, impurities are absorbed from the atmosphere. Water
falling after a long rain, especially in the country, is
tolerably free from impurities. Some springs have also nearly
pure water; but to separate all foreign matter from it, water
must be distilled. Even then it is liable to contain traces of
ammonia, or some other substance which vaporizes at a lower
temperature than water.

138. Sea-Water.--The ocean is the ultimate source of all water.
From it and from lakes, rivers, and soils, water is taken into
the atmosphere, falls as rain or snow, and sinks into the ground,
reappearing in springs, or flowing off in brooks and rivers to
the ocean or inland seas. Ocean water must naturally contain
soluble salts; and many salts which are not soluble in pure water
are dissolved in sea-water. In fact, there is a probability that
all elements exist to some extent in sea-water, but many of them
in extremely minute quantities. Sodium and magnesium salts are
the two most abundant, and the bitter taste is due to MgSO4 and
MgCl2. A liter of sea- water, nearly 1000 g., holds over 37 g. of
various salts, 29 of which are NaCl. See Hard Water.

139. River Water.--River water holds fewer salts, but has a great
deal of organic matter, living and dead, derived from the regions
through which it flows. To render this harmless for drinking,
such water should be boiled, or filtered through unglazed
porcelain. Carbon filters are now thought to possess but little
virtue for separating harmful germs.

140. Spring Water.--The water of springs varies as widely in
composition as do the rocks whence it bubbles forth. Sulphur
springs contain much H2S; many geysers hold SiO2 in solution;
chalybeate waters have compounds of Fe; others have Na2SO4, MgSO4
NaCl, etc.

CHAPTER XXIX.

THE CHEMISTRY OF FLAME.

141. Candle Flame.

Experiment 82.--Examine a candle flame, holding a dark object
behind it. Note three distinct portions: (1) a colorless interior
about the wick, (2) a yellow light-giving portion beyond that,
(3) a thin blue envelope outside of all, and scarcely
discernible. Hold a small stick across the flame so that it may
lie in all three parts, and observe that no combustion takes
place in the inner portion.

142. Explanation.--A candle of paraffine, or tallow, is chiefly
composed of compounds of C and H, in the solid state. The burning
wick melts the solid; the liquid is then drawn up by the wick
till the heat vaporizes and decomposes it, and O of the air comes
in contact with the outer heated portion of gas, and burns it
completely. Air tends to penetrate the whole body of the flame,
but only N can pass through uncombined, for the O that is left
after combustion in the outer portion seizes upon the compounds
of C and H in the next, or yellow, part. There is not enough O
here for complete combustion; at this temperature H burns before
C, and the latter is set free. In that state it is of course a
solid. Now an incandescent solid, or one glowing with heat, gives
light, while the combustion of a gas gives scarcely any light,
though it may produce great heat. While C in the middle flame is
glowing, during the moment of its dissociation from H, it gives
light. In the outer flame the temperature is high enough to burn
entirely the gaseous compounds of C and H together, so that no
solid C is set free, and hence no light is given except the faint
blue. No combustion takes place in the inner blue cone, because
no O reaches there.

By packing a wick into a cylindrical tin cup 5 or 10 cm high and
4 cm in diameter, containing alcohol, and lighting it, gunpowder
can be held in the middle of the flame in a def. spoon, without
burning. This shows the low temperature of that portion. Burning
P will also be extinguished, thus showing the exclusion of O.

143. Bunsen Flame.

Experiment 83.--Examine a Bunsen burner. Unscrew the top, and
note the orifices for the admission of gas and of air. Make a
drawing. Replace the parts; then light the gas at the top,
opening the air-holes at the base. Notice that the flame burns
with very little color. Try to distinguish the three parts, as in
the candle flame. These parts can best be seen by allowing direct
sunlight to fall on the flame and observing its shadow on a white
ground. Make a drawing of the flame. Hold across it a Pt wire and
note at what part the wire glows most. Also press down on the
flame for an instant with a cardboard or piece of paper; remove
before it takes fire, and notice the charred circle. Put the end
of a match into the blue cone, and note that it does not burn.
Put the end of a Pt wire into this blue cone, and observe that it
glows when near the top of the cone. What do these experiments
show? Ascertain whether this inner portion contains a combustible
material, by holding in it one end of a small d.t., and trying to
ignite any gas escaping at the other end. It should burn. This
shows that no combustion takes place in the interior of the
flame, because sufficient free O is not present.

Next, close the air-holes, and note that the flame is yellow and
gives much light. From this we infer the presence of solid
particles in an incandescent state. But these could not come from
the air. They must be C particles which have been set free from
the C and H compounds of the gas, just as in the candle flame.
The smoke that rises proves this. Hold an e.d. in the flame and
collect some C. Try the same with the air-holes open. 144. Light
and Heat of Flame.--Which of the two flames is hotter, the one
with the air-holes open, or that with them closed? Evidently the
former; for air is drawn in and mixes with the gas as it rises in
the tube, and, on reaching the flame at the top, the two are well
mingled, and the gaseous compounds of C and H burn at so high a
temperature that solid C is not freed; hence there is little
light. On closing the air-holes, no O can reach the flame except
from the outside, and the heat is much less intense.

(Fig 33.) (Fig 34.)

The H burns first, and sets the C free, which, while glowing,
gives the light. This again illustrates the facts (1) that flame
is caused by burning gas; (2) that light is produced by
incandescent solids. Charcoal, coke, and anthracite coal burn
without flame, or with very little, because of the absence of
gases.

145. Temperature of Combustion.

Experiment 84.--Light a Bunsen flame, with the basal orifices
open, and hold over it a fine wire gauze. Notice that the flame
does not rise above the gauze. Extinguish the light, and try to
ignite the gas above the gauze, holding the latter within 5 or 6
cm of the burner tube. Notice that it does not burn below the
gauze (Fig. 33).

Gas and O are both present. Evidently, then, the only condition
wanting for combustion is a sufficiently high temperature. The
gauze cools the gas below its kindling- point.

This principle is made use of in the miner's lamp of Davy (Fig.
34). In coal mines a very inflammable gas, CH4, called fire-damp,
issues from the coal. If this collects in large quantities and
mixes with O of the air, a kindling-point is all that is needed
to make a violent explosion. An ordinary lamp would produce this,
but the gauze lamp prevents it; for, though the inside may be
filled with burning gas, CH4, the flame cannot communicate with
the outside.

(Fig 35.) (Fig 36.)
a, reducing flame b, oxidizing flame

146. Oxidizing and Reducing Flames.--The hottest part of a Bunsen
flame is just above the inner blue cone (b, Fig. 36). Evidently
there is more O at that point. If a reducing agent, i.e. a
substance which takes up O, be put into this part of the flame,
the latter will remove the O and appropriate it, forming an
oxide. Cu heated there would become copper oxide. This part is
called the oxidizing flame. The inner blue part of the Bunsen
flame is devoid of O. It ought to remove O from an oxidizing
agent, i.e. a substance which supplies O. If copper oxide be
heated there (a, Fig. 36) by means of a mouth blow-pipe (Fig.
35), the flame will appropriate the O and leave the copper. This
is called the reducing flame. Only the upper part of this blue
central cone has heat enough to act in this way. By using a
prepared piece of metal, to make the flame thin and to shut off
the air, and then blowing the flame with a blow-pipe, greater
strength can be obtained in both oxidizing and reducing flames
(Fig. 36).

147. Combustible and Supporter Interchangeable.-- H was found to
burn in O. H was the combustible, O the supporter. Would O itself
burn in H?--i.e. would the combustible become the supporter, and
the supporter the combustible? As illuminating gas consists
largely of H, and as air is part O, we may try the experiment
with gas and air. Gas will burn in air. Will air burn in gas?

Experiment 85.--Fit a cork with two holes in it to the large end
of a lamp chimney. Through each hole pass a short piece of
tubing, and connect one of these with a rubber tube leading to a
gas-jet. Pass a metallic tube, long enough to reach the top of
the chimney, through the other, so that it will move easily up
and down. Turn on the gas, and light it at the top of the
chimney. Hold the end of the tube passing through the cork in the
flame for a minute, then draw it down to the middle of the
chimney (Fig. 37, a) and finally slowly remove it (b). Note that
O from the air is burning in the gas. Which is the supporter, and
which the combustible in this case? O will burn equally well in
an atmosphere of H, as can be shown by experiment.

148. Explosive Mixture of Gases.

Experiment 86.--Slowly turn down the burning gas of a Bunsen
lamp, having the orifices open, and notice that it suddenly
explodes and goes out at the top, but now burns at the base. As
the gas was gradually turned off, more air became mixed with it,
until there was the right proportion of each gas for an
explosion. Figure 38 shows the same thing. Light the gas at the
top a, when the tube c covers the jet b. Then gradually raise the
tube c. At a certain place there is the same explosion as with
the lamp.

149. Generalizations.--These experiments show (1) that three
conditions are necessary for combustion,--a combustible, a
supporter, and a burning temperature which varies for different
substances. Given these, "a fire" always results. The conditions
for "spontaneous combustion" do not differ from those of any
combustion. See Experiments 34, 112, 113, 114. (2) That
combustible and supporter are interchangeable. If H burns in O, O
will burn in H, the product, being the same in each case. (3) For
any combustion there must be a certain proportion of combustible
and of supporter. Twenty per cent of CO2 in the air dilutes the O
to such an extent that C will not burn. Hence the utility of the
chemical engine for putting out fires. (4) When two

gases, a combustible and a supporter, are mixed in the requisite
proportion, they form an explosive mixture, needing only the
kindling temperature to unite them.

Chemical combination is always accompanied by disengagement of
heat. Chemical dissociation is always accompanied by absorption
of heat. The disengagement, or the absorption, is not always
evident to the senses.

Combustion is the chemical combination of two or more substances
with the self-evident disengagement of great heat, and usually of
light.

The temperature of ignition varies greatly with different
substances. PH3 burns spontaneously at the usual temperatures of
the air. P takes fire at 60 degrees, but even at 10 degrees it
oxidizes with rapidity enough to produce phosphorescence. The
vapor of CS2 may be set on fire by a glass rod heated to 150
degrees, but a red-hot iron will not ignite illuminating gas.

Spontaneous combustion often takes place in woolen or cotton rags
which have been saturated with oil. The oil rapidly absorbs O,
and sets fire to the cloth. This is thought to be the origin of
some very destructive fires.

CHAPTER XXX.

CHLORINE.

150. Preparation.

Experiment 87.--Put into a t.t. 5 g. of fine granular MnO2 and 10
cc. HCl. Apply heat carefully, and collect the gas by downward
displacement in a receiver loosely covered with paper (Fig. 39).
Add more HCl if needed. Have a good draft of air, and do not
inhale the gas. If you have accidentally breathed it, inhale
alcohol vapor from a handkerchief; alcohol has great affinity for
Cl. Note the color of the gas, and compare its weight with that
of air.

MnO2 + 4 HCl = MnCl2 + 2 H2O + 2 Cl. How much Cl can be separated
with 5 g. MnO2?

If preferred, a flask may be used for a generator instead of a
t.t. Cl can be obtained directly from NaCl by adding H2SO4 (which
produces HCl) and MnO2. 2 NaCl + 2 H2SO4 + MnO2 = MnSO4 + Na2SO4
+ 2 H2O + 2 Cl. Try the experiment, using a t.t. and adding
water.

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