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LL the blue flowers in the garden had been tested with
phosphoric acid. After the violet had come the iris,
after the iris the periwinkle, then the veronica, and
others besides; and all had lost their natural color
and turned red. Yellow flowers, on the other hand,
such as the marigold, and white ones like the Easter
daisy, and red ones such as the poppy, did not change
color at all when dipped into the acid liquid. For
some time, now, the contents of the glass had been used
in these experiments when Uncle Paul invited his pupils
to take part in some new investigations; and the
summons was responded to with an outburst of joy. This
time the equipment consisted of a small portable stove
full of charcoal and set to burn in the fireplace,
while on the table were some bits of zinc, doubtless
the remnants of a worn-out watering-can. There was
also an old iron spoon, in so sorry a condition that no
beggar would have stopped to pick it up in the street.
A bottle hardly longer than your finger contained
something grayish, of metallic appearance, shaped like
a narrow ribbon and wound about in the form of a skein.
The boys puzzled in vain to guess what this could be.
Their uncle told
 them in due time, but before doing so he resumed his
talk as follows:
"How to obtain pure oxygen freed from the nitrogen with
which it is mixed in the atmosphere was the difficult
problem engaging our attention at our last lesson, and
it will continue to do so to-day. We know that the
sour-tasting compounds, the acids, made by burning
various metalloids, notably phosphorus, contain an
abundance of oxygen taken from the air and stored up.
That is the first stage of the journey toward our
destination. Another lies ahead, and when we have
accomplished it we can, with better understanding,
avail ourselves of the means offered us by chemical
science. Perhaps you will say I am straying from the
road that leads straight to the element, oxygen, which
you are so eager to learn about, and you will reproach
me for dividing the journey into more stages than
"Oh, never fear," Jules hastened to reply; "you may
make the journey as many stages long as you like. If
they are all as interesting as the last one, when you
showed us snowflakes made by fire, we shan't be the
ones to complain. Oxygen will have its turn all in
"To-day's stage in our journey, my young friends, will
be no less interesting than the one that preceded it.
I think it will give you an even greater surprise; and
in the end it will show us how to obtain pure oxygen,
which is what we started out for. Let us talk a little
more about the burning of various substances.
 "A piece of phosphorus on fire is certainly a fine
sight. The vigor with which it burns, the dazzling
brightness of its flame, the snowy flakes of phosphoric
acid resulting from the combustion—all these
cannot fail to arouse interest. But, accustomed as you
already were by the use of matches to seeing phosphorus
burn, this spectacle had in your eyes none of the
fascination of the new and unexpected. To witness the
burning of a substance well known to be highly
inflammable is nothing very thrilling. But to-day you
will be rather surprised to see things burn that you
have always thought to be fireproof. We are going to
set metals on fire."
"Metals!" cried Emile with a start of astonishment.
"I said that would rather surprise you. Yes, my boy,
metals, real metals."
"But metals don't burn."
"Who told you so?"
"Nobody told me, but I know what I see every day.
Tongs, fire-shovel, andirons are made of iron, which is
a metal; and even in the hottest kind of a fire, I have
never seen any of these things burn. The stove is
metal, and in winter when it gets red-hot with a
roaring fire inside I have never seen a particle of it
burn. Why, the whole stove would have burnt up long
ago if metals could take fire as you say they do!"
"Then Emile does not believe me when I say that metals
"What can I say, Uncle Paul? You put my faith
 in you
to a hard test. You might as well tell me that water
can burn, too."
"And why not, as I am going to show you some day that
"Yes, my child; I propose to show you some day that
water contains the very best kind of material for
Astounded at this promise, made with undoubted
sincerity, Emile said no more, but waited to see metals
burn, before believing what seemed to him incredible.
His uncle continued:
"If the tongs, shovel, andirons, stove, and other
things made of iron do not burn in our fireplaces and
kitchens, it is because the heat is not intense enough.
Make more heat, and metal will not fail to take fire.
You have often seen this burning of iron, but without
suspecting what it really was. Let us recall what we
see from time to time at the blacksmith's shop when we
pass his door. The smith has just taken from the forge
a bar of iron, glowing hot. As soon as it comes to the
air this bar of dazzling brightness throws out showers
of brilliant sparks in every direction, so that one
might mistake it for a piece of fireworks. The dark
shop is all ablaze with blinding flashes. What are
these sparks that fly off in showers? Little scales of
iron that become detached from the bar and burn as they
shoot through the air. Does Emile begin to believe me
"Yes, I am beginning to. I see more and more every day
that anything may be expected in chemistry."
 "I will tell you further that when the makers of
fireworks wish their pinwheels, Roman candles, rockets,
and squibs to throw out splendid sparks like sprays of
water from a fountain, they mix with gunpowder a
quantity of filings of various metals according to the
colors they wish to obtain. Copper gives green sparks,
iron white. Each particle of these metal filings turns
into a spark as soon as it touches fire. I am planning
to show you, one of these days, a conflagration of iron
that will make the blacksmith's shop look dull and
tame. So I will say but little more at present about
this metal, merely adding a third example to the two I
have just cited.
"You both know how to get bright sparks by striking
flint and steel together, or flint and the back of a
knife-blade. Those sparks are particles of metal, of
steel, which is a variety of iron, that are struck off,
becoming heated by the shock and burning as they fly
through the air. In exactly the same way sparks fly
off from the stone of the scissors-grinder when he
sharpens a piece of cutlery on it, and from an iron
horseshoe when it strikes a pebble. The violent
friction of the grindstone and the shock of the
horseshoe's hitting the hard pebble break off fine
scales of iron, and these, raised to intense heat by
the friction, catch fire as they dart off through the
air. You see, you don't have to go very far to find
plain proofs that iron really will burn, which at first
seemed so impossible to you. The scissors-grinder
sharpening a knife and the mule stumbling on a stone
teach us what Emile found so hard to believe;
 they perform for the wide-awake observer one of
chemistry's fine experiments.
"I pass now to another metal, zinc. Here are some
pieces, the remains of an old watering-can that has
been thrown away. This metal is grayish on the
surface, but if I scratch it a little with a file of
the point of a knife, we get a glimpse of metallic
luster like that of tin or silver. Now what we wish to
do is to make this zinc burn,—quite an easy
operation and readily performed with the help of a few
live coals. It is the same with metals as with the
things we commonly think of as inflammable, such as
sulphur and phosphorus and charcoal, for example: some
catch fire easily, others with difficulty. At the mere
touch of a lighted match phosphorus is instantly
ablaze, while sulphur is much slower and charcoal more
obstinate still. In the same way, while iron requires
the heat of a forge to make it burn, zinc needs only a
few live coals. There are some metals that burn still
more easily, as we shall soon see.
"Let us proceed, now, to make zinc burn. I place a few
pieces of it in this old and discarded iron spoon, and
thrust the spoon thus filled into the midst of the
glowing coals in this little stove. If you have any
doubts, our experiment will settle them for you."
Everything being arranged as Uncle Paul had indicated,
they waited a little while. The zinc melted almost as
readily as lead, and when the spoon was red-hot the
coals were pushed aside a little to show the melted
zinc without cooling it off. Then with a stout piece
of iron wire Uncle Paul began to stir the
 molten metal so as to bring it into better contact with
the air. A flame burst forth, of a superb bluish
white, dazzling to the eyes, though of no great volume.
It flickered on the surface of the liquid metal,
springing up brighter or dying down, according to the
briskness with which the matter was stirred. The boys
marveled at the brilliance of the burning zinc, and
their wonder was heightened as they saw a kind of snow
rise from the flame, float lightly in the air, and
spread all about the room. One might have taken it for
the finest of incomparably white down, or those
delicate shreds of cobweb that one sees fluttering over
the fields on a fine autumn morning. At the same time,
on the surface of the metal in the spoon, there
collected a kind of cotton-wool of unparalleled
fineness. The current of hot air from the stove moved
it lightly, detaching the flakes they saw rising and
spreading through the room.
"This white fluff," resumed Uncle Paul, "this down or
cotton, is burnt zinc, zinc combined with oxygen from
the atmosphere, and it bears the same relation to this
metal that the snowy flakes bear to phosphorus. We
will ascertain its chief properties as soon as there is
enough in the spoon."
Jules took his uncle's place in stirring the molten
metal, while Emile began to blow the flakes before him,
taking care not to blow hard enough to drive them too
fast, even the largest of them floating so lightly in
the air, despite their size, that it seemed as if they
would never settle down. Soon there was no more of the
shiny liquid left in the spoon, all the
 zinc having turned into this white material. When the
residue of this in the spoon had cooled off and been
emptied out, Uncle Paul continued:
"Burnt zinc is a white substance such as you now see
before you. It is also quite tasteless. Put some on
your tongue and it will convey no sense of taste."
"That's so," affirmed Emile, after trying it
cautiously, warned by his previous experience with
burnt phosphorus. "It hasn't any more taste than a
pinch of sand or sawdust."
"I don't taste anything, either," Jules chimed in; "and
yet the burnt phosphorus, the phosphoric acid, was so
sour you couldn't bear it. Now, here's something else
that we've burnt, and it hasn't any taste at all."
"Let us seek the reason for this lack of taste,"
suggested his uncle. "I drop a good pinch of the white
substance into this glass of water and stir it well
with a stick. It does not dissolve, does not melt in
the water; it is, as we say, insoluble. You remember
how readily, on the other hand, the burnt phosphorus or
phosphoric acid dissolved in water."
"We are not likely," replied Emile, "to forget very
soon that terrible stuff that melts in water with a
hissing sound like red-hot iron, and that has to have
dried air if you want to keep it."
"Let us put together these various facts: burnt
phosphorus dissolves in water and has a taste; burnt
zinc does not dissolve in water and has no taste. In
the same way, salt and sugar readily dissolve in water,
and both have a taste, the first a salt taste, the
second a sweet taste. Marble and brick do
 not dissolve in water, nor has either of them the
slightest taste. Do you begin to see what these facts
"It seems to me from all that," replied Julies, "that
to have any taste a thing must be able to melt in
"I have no fault to find with that answer. Yes, my
boy, what a substance must have in order to possess any
taste at all, whether strong or weak, sweet or sour,
salt or bitter, or whatever flavor, is solubility in
water. Anything that cannot be dissolved in water is
by that very fact tasteless, and for this reason: to
act on the sense of taste, to make an impression on
tongue or palate, a substance must necessarily, unless
it be a liquid, dissolve in the saliva, being thus
divided into extremely small particles and brought into
contact with the organs designed to perceive it. Now,
saliva is almost entirely composed of water. If, then,
a substance is insoluble in water, it is also insoluble
in saliva, and therefore has no taste. In future, when
you see a substance that will not dissolve in water,
don't try to see how it tastes, for it has no taste and
cannot have any. But if it yields to the action of
water, it has a taste,—sometimes very insipid, it
is true, and hardly perceptible, as gum Arabic, for
"To return to our two burnt substances: the white
material left by the burning zinc has no taste, because
it is not soluble in water, whereas the white material
left by burning phosphorus is easily soluble and
consequently has a very decided taste."
"Yes, very decided," assented Emile, "for it eats
 away the part of the tongue it touches. But tell me,
Uncle, if burnt zinc could melt in water, so as to have
a taste, what sort of taste would it be? Would it be
as strong as the taste of burnt phosphorus?"
"As to that, my little friend, neither I nor any one
else can give you a sure answer, no one having
experimented with such an impossibility. All we can
say is that probably the taste would be detestable, as
is the taste of ninety-nine chemicals out of a hundred.
"When we exhibit fireworks, we keep for the last the
most beautiful piece of all, the star number on our
program. This I am doing to-day, reserving to the end
the prize piece in our collection, the most splendid
example of metal burning. The material for this
display is there in that little bottle."
"That thing that looks like a skein of narrow gray
ribbon?" asked Emile.
"Yes, that's it."
"It doesn't look as if it could do anything."
"It can do much more than its appearance promises. Let
us examine it closely."
So saying, Uncle Paul took the skein out of the bottle.
It was a dull gray ribon[should be ribbon], narrow,
very thin, and as flexible as tinfoil. When scratched
with a knife it showed the brightness peculiar to
metals. By this brightness and the whitish color the
children though they recognized the metal.
"It is either lead or tin," declared Emile.
"I should rather say zinc or iron," said Jules.
"It is not any of those metals," their uncle told
 them. "This is a metal you have never seen before, nor
have you even heard of it."
"And what is it called, please?" was Emile's eager
"It is called magnesium."
"Ma-ma—" stammered the boy. "Please say it
"Oh, what a funny name!"
"No funnier than bismuth, barium, or titanium."
"Are those the names of metals?"
"Yes, my child, they are the names of metals. If they
sound strange to you, it is because you now hear them
for the first time. One gets used to bismuth and
titanium just as much as to copper and lead. As I have
already told you, there are about fifty metals. Most
of them remain unknown to us, not being in common use;
their names, being seldom heard in ordinary
conversation, strike the ear rather strangely at first.
After you have become acquainted with magnesium, you
will find its name easy to remember and it will cease
to have the unwonted sound it has at present.
"A few live coals are enough to make zinc burn; a
candle-flame will set fire to magnesium, and the metal
will go on burning of its own accord when once it is
started. It lights almost as easily as a paper spill."
"And where do they find this queer metal?" Emile
inquired. "I should be willing to spend some of the
pennies I have saved up if I could buy a piece."
"Magnesium is not a metal in common use. It is
to the blacksmith, the tinsmith, and the coppersmith.
It is a substance used chiefly in scientific research
and in chemical experiments of an entertaining sort.
It can be procured at city drug shops and toy-shops,
where it is sold as one of those curiosities that
instruct and amuse at the same time; and it is from the
city that I brought it home for your benefit."
A candle having been lighted, the shutters were closed
so as not to let the daylight lessen the brilliant
effect of the burning metal. Then Uncle Paul cut off a
short strip of the magnesium ribbon, and, taking hold
of one end with a pair of pincers, touched the other to
the candle-flame. A sheet of paper was spread on the
table to receive what might fall from the burning
metal. Catching fire very quickly, the ribbon was
withdrawn from the candle and held in an upright
position over the sheet of paper, after which it needed
no further assistance; the magnesium burned alone. It
was as if a sudden burst of dazzling sunlight had
illuminated the darkened room. A superb white light,
intense enough to penetrate every corner and render all
objects clearly visible, came in waves from the
splendid torch. No sputtering, no noise whatever, no
flying sparks. It was the calm, sustained illumination
of daylight. Dumb with astonishment at this brilliant
display, the boys gazed in fascination. The burning
continued, the flame approaching ever nearer to the
pincers, while the burnt part fell off in pieces that
looked like chalk. In a few seconds it was finished;
the radiant flame died down for want of fuel.
 "Oh, how beautiful, how splendid that was!" cried the
children, rubbing their eyes, dazzled by the glare.
Their uncle opened the shutters to let in the
"Why, I can't see;" said Emile, still rubbing his eyes.
"I'm nearly blind from looking at the magnesium flame.
"And, I," added Jules, "am almost as dazzled as if I
had been staring at the sun."
"That will pass off in a few minutes," their uncle
assured them. "Wait until your eyes recover from the
fatigue caused by the too-bright light of the magnesium
The dazzling effect having worn off, as it did in a
short time, Emile spoke of something that had struck
him while the magnesium was burning.
"I was looking," said he, "at the flame of the candle,
which you had left burning after setting fire to the
magnesium, and all I saw was something of a reddish
color, smoky and dull. How pale the candle looked, and
it had been bright enough before! I could hardly made
out any flame at all. Is it possible, I asked myself,
that that can give light?"
"If you set a lighted candle in the full glare of the
sunshine, can you see the flame?" asked Uncle Paul.
"No; it looks as pale and dim as it did in the
"That, my little friend, comes from the inability of
the eye, when exposed to a bright light, to see, except
imperfectly, a dim one. In full sunlight one cannot
tell whether live coals are really alive or not. The
flame that gave light in the dark ceases to do so
 when overpowered by a greater brilliance. Our dazzled
eyes and the apparently dulled flame of the candle
prove to us that the magnesium light is one of the
brightest possible; it bears comparison only with the
"I hope I have now convinced you, including even the
skeptical Emile, that metals are not hard to burn. The
flying sparks of burning iron in the blacksmith's shop,
the firing of zinc in our old spoon, and finally the
dazzling magnesium flame, have furnished proof upon
proof. Furthermore, the last experiment shows us that
among the metals there are some that would give us
splendid light if it were not for their price and
scarcity. Instead of lamp oil or candle grease we
could use a magnesium ribbon for lighting. Who knows
what the future may have in store for us in this field?
The history of chemistry is full of wonderful
discoveries, and we already owe so many and important
improvements to this science that we may well look to
it for still greater things.
"But without dwelling longer on the brilliant splendors
of magnesium let us see what has become of the metal
after burning. The substance that has fallen on to the
paper over which the ribbon burned is a white material
which, when touched, crumbles into a soft powder like
flour, or, better, like ground chalk of a very fine
quality. It does not dissolve in water, and
consequently has no taste. In addition to the metal
itself, it contains, as does everything else after
burning, oxygen taken from the air in the process of
burning. So here is another storehouse
 of oxygen from which this gas could be obtained by
using the proper means, but not without some
"Iron burns. Hammered on the anvil when red-hot, it
gives out sparks which are tiny scales of this metal on
fire. Let us get some of these particles of burnt iron
from the smith, and we shall find them to be of a black
material, rather hard, but still yielding to the
pressure of our fingers. This black material, this
burnt iron, is called oxid or iron.
"Zinc burns, being changed by the process into a white
substance of which part is wafted upward from the flame
and floats in the air like shreds of cotton or down.
This white substance, this burnt zinc, is called oxid
"Magnesium burns, and becomes thereby a white substance
looking much like very fine chalk and extremely soft to
the touch. This chalk-like substance, this burnt
magnesium, is called oxid of magnesium.
"As a rule, metals are combustible, though there are
exceptions; and in burning they combine with oxygen
from the air or elsewhere, being thus changed into
compounds which have non of the luster of metals and
which take the name of oxid. An oxid is a burnt metal,
just as an acid is a burnt metalloid, and both contain