What is water made of?
What is iron made of?
Is everything made out of dust?
One of the most natural questions in the world is, "What is this
made of?" If we are talking about a piece of bread, the answer is, of
course, "flour, water, milk, shortening, sugar, salt, and yeast." But
what is each of these made of? Flour is made of wheat, and the wheat
is made of materials that the plant gets from the earth, water, and
air. Then what are the earth, water, and air made of? A chemist is
a person who can answer these questions and who can tell what almost
everything is made of. And a strange thing that chemists have found
out is this: Everything in the world is made out of one or more of
about eighty-five simple substances called _elements_.
WHAT AN ELEMENT IS. An element is a substance that is not made of
anything else but itself. Gold is one of the eighty-five elements;
there are no other substances known to man that you can put together
to make gold. It is made of gold and that is all. There is a theory
that maybe all the elements are made of electrons in different
arrangements, or of electrons and one other thing; but we do not know
that, it is only a theory. Carbon is another element; pure charcoal
is carbon. The part of the air that we use when we breathe or when we
burn things is called _oxygen_. Oxygen is an element; it is not made
of anything but itself. There is another gas which is often used to
fill balloons that are to go very high; it is the lightest in the
world and is called _hydrogen_. Hydrogen is an element.
For a long time people thought that water was an element. Water
certainly looks and seems as if it were made only of itself. Yet
during the thousands of years that people believed water was an
element, they were daily putting two elements together and making
water out of them. When you put a kettle, or anything cold, over a
fire, tiny drops of water always form on it. These are not drops of
water that were dissolved in the air, and that condense on the sides
of the cold kettle; if they were, they would gather on the kettle
better in the open air than over the hot fire. Really there is some
of that very light gas, hydrogen, in the wood or coal or gas that
you use, and this hydrogen joins the oxygen in the air to make water
whenever we burn ordinary fuel.
But the best way to prove that water is made of two gases is to take
the water apart and get the gases from it. Here are the directions for
doing this:
EXPERIMENT 90. A regular bought electrolysis apparatus may be
used, or you can make a simple one as follows:
Use a tumbler and two test tubes. If the test tubes are rather
small (3/8'' X 3'') they will fill more quickly. Dissolve a
little lye (about 1/8 teaspoonful) in half a pint of water
to make the water conduct electricity easily, or you may use
sulfuric acid in place of lye. Pour half of this solution
into the tumbler. Pour as much more as possible into the test
tubes, filling both tubes brim full. Cover the mouth of each
test tube with a small square of dry paper or cardboard, and
turn it upside down, lowering it into the tumbler.
The "electrodes" are two 3/4'' pieces of platinum wire (#30),
which are soldered to two pieces of insulated copper wire,
each about 2 feet long.[8] The other ends of the copper wire
are bare. Fasten the bare end of one copper wire to one nail
of the nail plug if you have direct current (d. c.) in the
laboratory, and fasten the bare end of the other wire to the
other nail; then turn on the electricity. If you do not have
direct current in the laboratory, attach the copper wires to
the two poles of a battery instead.
[Footnote 8: If the copper wire is drawn through a piece of
1/4-inch soft glass tubing so that only the platinum wire
projects from the end of the tube, and the tube is then sealed
around the platinum by holding it in a Bunsen burner a few
minutes, your electrodes will be more permanent and more
satisfactory. The pieces of glass tubing should be about 6
inches long (see Fig. 160).]
Bend the platinum electrodes up so that they will stick up
into the test tubes from below. Bubbles should immediately
begin to gather on the platinum wire and to rise in the test
tubes. As the test tubes fill with gas, the water is forced
out; so you can tell how much gas has collected at any time by
seeing how much water is left in each tube.
One tube should fill with gas twice as fast as the other. The
gas in this tube is hydrogen; there is twice as much hydrogen
as there is oxygen in water. The tube that fills more slowly
contains oxygen.
When the faster-filling tube is full of hydrogen--that is,
when all of the water has been forced out of it--take the
electrode out and let it hang loose in the glass. Put a piece
of cardboard about 1 inch square over the mouth of the test
tube; take the test tube out of the water and turn it right
side up, keeping it covered with the cardboard. Light a match,
remove the cardboard cover, and hold the match over the open
test tube. Does the hydrogen in it burn?
When the tube containing the oxygen is full, take it out,
covered, just as you did the hydrogen test tube. But in this
case make the end of a stick of charcoal glow, remove the
cardboard from the tube, and then plunge the glowing charcoal
into the test tube full of oxygen.
[Illustration: FIG. 160. The electrodes are made of loops of platinum
wire sealed in glass tubes.]
Only oxygen will make charcoal burst into flame like this.
When people found that they could take water apart in this way and
turn it into hydrogen and oxygen, and when they found that whenever
they combined hydrogen with oxygen they got water, they knew, of
course, that water was not an element. Maybe some day they will find
that some of the eighty-five or so substances that we now consider
elements can really be divided into two or more elements; but so far
the elements we know show no signs of being made of anything except
themselves.
The last section of this book will explain something about the way
the chemist goes to work to find out what elements are hidden in
compounds.
[Illustration: FIG. 161. Water can be separated into two gases by a
current of electricity.]
THE QUICK WAY CHEMISTS WRITE ABOUT ELEMENTS. Since everything in the
world is made of a combination or a mixture of elements, chemists have
found it very convenient to make abbreviations for the names of the
elements so that they can quickly write what a thing is made of.
They indicate hydrogen by the letter H. O always means oxygen to the
chemist; C means carbon; and Cl means chlorine, the poison gas so much
used in the World War. The abbreviation stands for the Latin name of
the element instead of for the English name, but they are often almost
alike. The Latin name for the metal sodium, however, is _natrum_, and
chemists always write Na when they mean sodium; this is fortunate,
because S already stands for the element sulfur. Fe means iron (Latin,
_ferrum_). But I stands for the element iodine. (The iodine you use
when you get scratched is the element iodine dissolved in alcohol.) It
is not necessary for you to remember the chemical symbols unless
you mean to become a chemist or unless you read a good deal about
chemistry. But almost every one knows at least that H means hydrogen,
O means oxygen, and C means carbon.
When a chemist wants to show that water is made of hydrogen two
parts and oxygen one part, he writes it very quickly like this: H_2O
(pronounced "H two O"). "H_2O" means to a chemist just as much as
"w-a-t-e-r" means to you; and it means even more, because it tells
that water is made of two parts hydrogen and one part oxygen. If a
chemist wanted to write, "You can take water apart and it will give
you two parts of hydrogen and also one part of oxygen," this is what
he would put down:
H_2O -> 2H+O.
If he wanted to show that you could combine two parts of hydrogen and
one part of oxygen to form water, he would write it quickly like this:
2H+O -> H_2O.
These are called _chemical equations_. You do not need to remember
them; they are put here merely so that you will know what they look
like. Some of them are much longer and more complicated, like this:
HC_2H_3O_2+NaHCO_3 -> H_2O+CO_2+NaC_2H_3O_2.
This is the chemist's way of saying, "Vinegar is made of one part
of hydrogen gas that will come off easily and that gives it its sour
taste, two parts of carbon, three parts of hydrogen that does not come
off so easily, and two parts of oxygen. When you put this with baking
soda, which is made of one part of the metal sodium, one part of
hydrogen, one part of carbon, and three parts of oxygen, you get water
and carbon dioxid gas and a kind of salt called sodium acetate." Or,
more briefly, "If you put baking soda with vinegar, you get water, a
gas called carbon dioxid, and a salt." You can see how much shorter
the chemist's way of writing it is.
SOME ELEMENTS YOU ALREADY KNOW. Here is a list of some elements that
you are already pretty well acquainted with. The abbreviation is put
after the name for each. This list is only for reference and need not
be learned.
Aluminum (Al)
Carbon (C) Charcoal, diamonds, graphite (the lead in a
pencil is graphite), hard coal, and soot are
all made of carbon.
Chlorine (Cl) A poison gas that was used in the war.
Copper (Cu)
Gold (Au)
Hydrogen (H) The lightest gas in the world; you got it from
water in the last experiment and will get it
from an acid in the next.
Iodine (I) It is a solid; what you use is iodine dissolved
in alcohol.
Iron (Fe)
Lead (Pb)
Mercury (Hg) This is another name for quicksilver.
Nickel (Ni)
Nitrogen (N) About four fifths of the air is pure nitrogen.
Oxygen (O) This is the part of the air we use in breathing.
You got some out of water, and you will
have it to deal with in another experiment.
Phosphorus (P) Phosphorus makes matches glow in the dark,
and it makes them strike easily.
Platinum (Pt)
Radium (Ra)
Silver (Ag)
Sodium (Na) You are not acquainted with sodium by itself,
but when it is combined with the poison
gas, chlorine, it makes ordinary table salt.
Sulfur (S)
Tin (Sn)
Zinc (Zn)
For the rest of the elements you can refer to any textbook on
chemistry.
HOW ELEMENTS HIDE IN COMPOUNDS. One strange thing about an element
is that it can hide so completely, by combining with another
element, that you would never know it was present unless you took the
combination apart. Take the black element carbon, for instance. Sugar
is made entirely of carbon and water. You can tell this by making
sugar very hot. When it is hot enough, it turns black; the water part
is driven off and the carbon is left behind. Yet to look at dry, white
sugar, or to taste its sweetness, one would never suspect that it was
made of pure black, tasteless carbon and colorless, tasteless water.
Mixing carbon and water would never give you sugar. But combining them
in the right proportions into a chemical compound does produce sugar.
Not only is carbon concealed in sugar, but it is present in all plant
and animal matter. That is why burning almost any kind of food makes
it black. You drive off most of the other elements and separate the
food into its parts by getting it too hot; the water evaporates and so
does the nitrogen; what is left is mainly black carbon.
MAKING HYDROGEN COME OUT OF HIDING. The light gas, hydrogen, conceals
itself as perfectly as carbon does by combining with other elements.
It is hiding in everything that is sour and in many things that are
not sour. And you can get it out of sour things with metals. In
some cases it is harder to separate than in others; and some metals
separate it better than others do. But one sour compound that you can
easily get the hydrogen out of is hydrochloric acid (HCl), which
is hydrogen combined with the poison gas, chlorine. One of the best
metals to get the hydrogen out with is zinc. Here are the directions
for doing it and incidentally for making a toy balloon:
EXPERIMENT 91. _Do this experiment on the side of the
laboratory farthest from any flames or fire. Do not let any
flame come near the flask in which you are making hydrogen._
In the bottom of a flask put two or three wads of zinc
shavings, each about the size of your thumb. Fit a one-hole
rubber stopper to the flask. Take the stopper out and put a
piece of glass tubing about 5 inches long through the hole of
the stopper, letting half an inch or so stick down into the
flask when the stopper is in place (Fig. 162). With a rubber
band fasten the mouth of a rubber balloon over the end of the
glass tube that will be uppermost. Fill the balloon by blowing
through the glass tube to see if all connections are tight,
and to see how far it may be expanded without danger of
breaking. You can tell when the balloon has about all it will
hold, by pressing gently with your fingers. If the rubber
feels tight, do not blow any more. Let the air out of the
balloon again.
Now get some hydrochloric acid (HCl) diluted with three parts
of water. Find the bottle marked "HCl, dilute 1-3," in which
the acid is already diluted. Before you open the bottle,
get some solution of soda, and keep it near you; if in this
experiment or any other you spatter acid on your hands or
face or clothes, wash it off _immediately_ with soda solution.
_Remember this._ Ammonia will do as well as the soda solution
to wash off the acid, but be careful not to get it into your
eyes.
Pour the hydrochloric acid (HCl) on the zinc shavings in the
bottom of the flask, until the acid stands about an inch deep.
Then quickly put the rubber stopper with its attachments into
the flask, so that the gas that bubbles up will blow up the
balloon.
If the bubbles do not form rapidly, ask the teacher to pour a
little strong hydrochloric acid into the flask; but this will
probably not be necessary. Let the balloon keep filling until
it is as large as you blew it. But if the bubbles stop coming
before it gets as large as that, close the neck of the balloon
by pinching it tightly, and take the stopper out. Let some
one add more zinc shavings and more acid to the flask; put the
stopper back in, and stop pinching the neck of the balloon.
_In this and all other experiments when you use strong acids,
pour the used acids into the crockery jar that is provided
for such wastes. Do not pour them into the sink, as acids ruin
sink drainpipes._
When the balloon is full, close the neck by slipping the
rubber band up from the part of the neck that is over the
glass tube on to the upper part of the neck. Pull the balloon
off the glass tube and pinch the neck firmly shut. Take the
stopper out and rinse the flask several times with running
water. Any zinc that is left should be rinsed thoroughly,
dried, and set aside so that it may be used again. Now tie one
end of a long thread firmly around the mouth of the balloon
and let the balloon go. Does it rise? If it does not, the
reason is that you did not get it full enough. In that case
make more hydrogen and fill it fuller, as explained above.
[Illustration: FIG. 162. Filling a balloon with hydrogen.]
[Illustration: FIG. 163. Adding more acid without losing the gas.]
Here is another experiment with hydrogen:
EXPERIMENT 92. Put a wad of zinc shavings, about the size of
the end of your little finger, into the bottom of a test tube.
Cover it with hydrochloric acid (HCl) diluted one to three,
as in the preceding experiment. After the bubbles have been
rising for a couple of minutes, take the test tube to the side
of the laboratory where the burners are, and hold a lighted
match at its mouth. Will hydrogen burn?
Remember that the hydrogen which the zinc is driving out of the acid
is exactly the same as the hydrogen you drove out of water with an
electric current. There is a metal called _sodium_ (Na) and another
called _potassium_ (K) which are as soft as stiff putty and as shiny
as silver; if you put a tiny piece of sodium (Na) or potassium (K) on
water, it will drive the hydrogen out of the water just as zinc drove
it out of the acid. The action is so swift and violent and releases so
much heat that the hydrogen which is set free catches fire. This makes
it look as if the metal were burning as it sputters around on top
of the water. There is so much sputtering that the experiment
is dangerous; people have been blinded by the hot alkaline water
spattering into their eyes. So you cannot try this until sometime when
you take a regular course in chemistry.
[Illustration: FIG. 164. Trying to see if hydrogen will burn.]
GETTING OXYGEN, A GAS, FROM TWO SOLIDS. Oxygen (O) can hide just as
successfully as hydrogen. Practically all elements can do the same by
combining with others. Here is an experiment in which you can get the
gas, oxygen, out of a couple of solids. If you went to the moon or
some other place where there is no air, you could carry oxygen
very conveniently locked up in these solid substances. Oxygen, you
remember, is the part of the air that keeps us alive when we breathe
it.
EXPERIMENT 93. In a test tube mix about one half teaspoonful
each of white potassium chlorate crystals and black grains of
manganese dioxid. Put a piece of glass tubing through a cork
so that the tubing will stick down a little way into the test
tube. _Do not put the glass tubing through the cork while the
cork is in the test tube: insert the glass tubing first, then
put the cork into the test tube._ Put one end of a 2-foot
piece of rubber tubing over the glass tube and put the other
end into a pan of water.
Fill a flask or bottle to the brim with water, letting it
overflow a little; hold a piece of cardboard firmly over the
mouth of the bottle; turn the bottle upside down quickly,
putting the mouth of it under water in the pan; take the
cardboard away. The water should all stay in the bottle.
Now shove the rubber tube into the neck of the bottle until it
sticks up an inch or two. During this experiment, be careful
not to let the neck of the bottle or flask pinch the rubber
tubing; small pieces of wood or glass tubing laid beside the
rubber tubing where it goes under the run of the neck will
prevent this.
Hold, the test tube, tightly corked, over the flame of a
burner, keeping the tube at a slant and moving it slightly
back and forth so that all the material in it will be
thoroughly heated. If you stop heating the test tube even for
a couple of seconds, take the cork out; if you do not remove
the cork, the cooling gas in the test tube will shrink and
allow the water from the pan to be forced through the rubber
tube into the test tube, breaking it into pieces.
When enough gas has bubbled up into the bottle to force all
the water out, and when bubbles begin to come up outside the
bottle, uncork the test tube and lay it aside where it will
not burn anything; then slide the cardboard under the mouth of
the bottle and turn it right side up; leave the cardboard on
the bottle.
Light a piece of charcoal, or let a splinter of wood burn a
few minutes and then blow it out so that a glowing coal will
be left on the end of it. Lift the cardboard off the bottle
and plunge the glowing stick into it for a couple of seconds.
Cover the bottle after taking out the stick, and repeat, using
a lighted match or a burning piece of wood instead of the
glowing stick. If you dip a piece of iron picture wire in
sulfur and light it, and then plunge it into the bottle, you
will see iron burn.
[Illustration: FIG. 165. Filling a bottle with oxygen.]
[Illustration: FIG. 166. The iron really burns in the jar of oxygen.]
Both manganese dioxid and potassium chlorate have a great deal of
oxygen bound up in them. When they join together, as they do when you
heat them, they cannot hold so much oxygen, and it escapes as a gas.
In the experiment, the escaping oxygen passed through the tube, filled
the bottle, and forced the water out.
WHAT BURNING IS. When anything burns, it is simply joining oxygen.
When a thing burns in air, it cannot join the oxygen of the air very
fast, for every quart of oxygen in the air is diluted with a gallon of
a gas called _nitrogen_. Nitrogen will not burn and it will not
help anything else to burn. But when you have pure oxygen, as in the
bottle, the particles of wood or charcoal or picture wire can join it
easily; so there is a very bright blaze.
Although free oxygen helps things to burn so brilliantly, a match
applied to the solids from which you got it would go out. And while
hydrogen burns very easily, you cannot burn water although it is
two-thirds hydrogen. Water is H_2O, you remember.
WHAT COMPOUNDS ARE. When elements are combined with other elements,
the new substances that are formed are called _compounds_. Water
(H_2O) is a compound, because it is made of hydrogen and oxygen
combined.
When elements unite to form compounds, they lose their original
qualities. The oxygen in water will not let things burn in it; the
hydrogen in water will not burn. Salt (NaCl) is a compound. It is made
of the soft metal sodium (Na), which when placed on water sputters and
drives hydrogen out of the water, and the poison gas chlorine (Cl),
combined with each other. And salt is neither dangerous to put in
water like sodium, nor is it a greenish poison gas like chlorine.
MIXTURES. But sometimes elements can be mixed without their combining
to form compounds, in such a way that they keep most of their original
properties. Air is a mixture. It is made of oxygen (O) and nitrogen
(N). If they were _combined_, instead of _mixed_, they might form
laughing gas,--the gas dentists use in putting people to sleep when
they pull teeth. So it is well for us that air is only a _mixture_ of
oxygen and nitrogen, and _not_ a compound.
You found that things burned brilliantly in oxygen. Well, things burn
in air too, because a fifth of the air is oxygen and the oxygen of
the air has all its original properties left. Things do not burn as
brightly in air as they do in pure oxygen for the same reason that a
teaspoonful of sugar mixed with 4 teaspoonfuls of boiled rice does not
taste as sweet as pure sugar. The sugar itself is as sweet, but it is
not as concentrated. Likewise the oxygen in the air is as able to help
things burn as pure oxygen is; but it is diluted with four times its
own volume of nitrogen.
A solution is a mixture, too; for although substances disappear when
they dissolve, they keep their own properties. Sugar is sweet whether
it is dissolved or not. Salt dissolved in water makes brine; but the
water will act in the way that it did before. It will still help to
make iron rust; and salt will be salty, whether or not it is dissolved
in water. That is why solutions are only mixtures and are not chemical
compounds.
EVERYTHING IN THE WORLD IS MADE OF ATOMS. Everything in the world is
either an element or a compound or a mixture. Most plant and
animal matter is made of very complicated compounds, or mixtures of
compounds. All pure metals are elements; but metals, when they are
melted, can be dissolved in each other to form alloys, which really
are mixtures. Most of the so-called gold and silver and nickel
articles are really made of alloys; that is, the gold, silver, or
nickel has some other elements dissolved in it to make it harder,
or to impart some other quality. Bronze and brass are always alloys;
steel is generally an alloy made chiefly of iron but with other
elements such as tungsten, of which electric lamp filaments are made,
dissolved in it to make it harder. An alloy is a special kind of
solution not quite like an ordinary solution.
You remember that in the opening chapters we often spoke of molecules,
the tiny particles of matter that are always moving rapidly back
and forth. Well, if you were to examine a molecule of water with the
microscope which we imagined could show us molecules, you would find
that the molecule of water was made of three still smaller particles,
called _atoms_. Two of these would be atoms of hydrogen and would
probably be especially small; the third would be larger and would be
an oxygen atom.
In the same way if you looked at a _molecule_ of salt under this
imaginary microscope, you would probably find it made of _two atoms_,
one of sodium (Na) and one of chlorine (Cl), held fast together in
some way which we do not entirely understand.
The smallest particle of an _element_ is called an _atom_.
The smallest particle of a _compound_ is called a _molecule_.
Molecules are usually made of two or more atoms joined together.
_APPLICATION 68._ In the following list tell which things
are elements, which are compounds, and which are mixtures,
remembering that both solutions and alloys are mixtures:
Air, water, salt, gold, hydrogen, milk, oxygen, radium,
nitrogen, sulfur, baking soda, sodium, diamonds, sweetened
coffee, phosphorus, hydrochloric acid, brass.
INFERENCE EXERCISE
Explain the following:
431. Although in most electric lamps there is a vacuum between
the glowing filaments and the glass, the glass nevertheless
becomes warm.
432. Clothes left out on the line overnight usually become
damp.
433. You can separate water into hydrogen and oxygen, yet
you cannot separate the hydrogen or the oxygen into any other
substances.
434. Wet paper tears easily.
435. Windows are soiled on the outside much more quickly in
rainy weather than in clear weather.
436. If you stir iron and sand together, the iron will rust as
if alone.
437. Rust is made of iron and oxygen, yet you cannot separate
the iron from the oxygen with a magnet.
438. A reading glass helps you to read fine print.
439. Stretching the string of a musical instrument more
tightly makes the note higher.
440. Mayonnaise dressing, although it contains much oil, can
readily be washed off a plate with cold water.