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HE white substance left by the burning magnesium had been
wrapped in paper, and Uncle Paul took it up again as
his opening topic in the next lesson.
"Judging from looks only," said he, "we compared this
powder to flour and also to very finely ground chalk.
If we considered its properties, we ought rather to
compare it to lime. This latter, at first a rough and
shapeless stone, swells on being soaked in water, and
then cracks to pieces and turns into a white powder
closely resembling burnt magnesium. Nor is this
resemblance misleading, for chalk is also a burnt
"A burnt metal!" repeated Emile, in surprise. "I never
knew chalk was made by burning a metal."
"Naturally not," replied his uncle, "for that is not
the way it is obtained. If, in order to get lime, we
had to burn the metal that enters into its formation,
the mason would never venture to use a trowelful
of mortar, because of its excessive price."
"I know how lime is made," put in Jules. "Out in the
country they pile up stones and charcoal in a
lime-kiln, and the fire bakes the stones and
turns them to lime all ready for use."
 "That is it. The stone they use is called limestone,
and it contains lime and something else; this latter
the fire drives out, so that, after the burning is
finished, the lime is left by itself, ready for the
mason and very different from the original stone. It is
really a burnt metal, though the lime-burner
knows nothing about the burning of metals, and does not
even suspect the presence of a metal in the product of
his kiln. The honest lime-burner would be greatly
surprised to be told that his lime contains a metal;
he would laugh in your face and say you were joking.
But nothing could be further from joking; lime comes
from the burning of a metal or, in other words, from
the combining of a metal with oxygen. Its particles may
be likened to the tiny scales that fall from
red-hot iron as it comes from the forge, and to
the flakes that fly off from zinc burning in the bed of
glowing charcoal, and also to that floury powder left
on the sheet of paper by the brilliant magnesium flame.
In a word, lime is an oxid. "It is true that in
producing this oxid the hand of man played no part, the
combustion having taken place of itself, perhaps at the
very beginning of things; and, since the creation of
the world, the metallic part of lime has never been
found alone anywhere in nature. It abounds nearly
everywhere, but so greatly changed, so completely
disguised in the combinations of which it forms a part,
that it has required much shrewdness on the part of
science to guess its existence, and still greater skill
to restore some particles of it to their primitive
 state, that of a real metal. Here is a pinch of burnt
magnesium, and here one of powdered lime; look at them
well and tell me, if you can, in what the two differ."
"We can't see any difference," the boys agreed, after a
careful examination. "Both are white, and both look
"I see no difference, either," their uncle rejoined.
"We are all three of one mind as to this close
resemblance, though we know the two to be different
substances. Let us, then, say, with those who are wiser
than we, that this powder, lime, is the oxid of a
metal, just as this other powder is the oxid of another
"What is this lime metal called?" asked Jules.
"It is called calcium."
"Why, that is n't so very different from what the
farmers round here call lime; they call it
"I will tell you, my boy, that the common speech of our
part of the country, like that of other southern
provinces, contains the relics of a tongue spoken long
ago, venerable relics that, instead of being ridiculed
as they are by the foolish, should be preserved with
veneration. Our popular terms reproduce, though
corrupted by centuries of use, the superb Latin tongue
that came from Rome with civilization. In that language
lime was called calx, and this word has been
preserved almost unchanged in the common term you just
named. So, you see, the rustic term needs no apology,
its parentage being one of the noblest. He who speaks
the native tongue of the South speaks something very
 Latin. Men of learning, who delight, not without
reason, in going back to ancient usages, have made
calx into calcium, a sonorous and
pleasing term, to designate the metal that enters into
the formation of lime; but they might just as well
have started with our popular word, cals.
"Well, then, the metal element in lime is calcium, the
name coming from the Latin word calx, which
"Will you show us some of this metal?" asked Jules,
"Alas, no, my lad! Our humble laboratory cannot afford
so costly a curiosity. Not that calcium is rare, for it
is to be found almost everywhere, the very rocks in
many regions abounding in it, and whole mountain chains
being largely made of it; but the difficulty is to
extract it from the compounds that contain it, to bring
it back to its original state of a simple metal. If we
were to ransack all the chemical laboratories in
France, we should perhaps find not more than a handful
or two, so difficult and expensive is its preparation.
That is why your Uncle Paul's collection of chemicals
is now and always will be destitute of such treasures.
But, at any rate, I can tell you about it. Imagine
something white and shiny, almost like silver in
appearance, and as soft as wax, so that it can be
kneaded and molded with the fingers. That is calcium."
Here Emile interrupted his uncle. "What!" he cried,
"calcium a metal that can be kneaded with the fingers
like a piece of soft wax or a lump of clay?"
 "Yes, my child, this curious metal is soft enough to
yield to the pressure of the fingers and be molded at
"I wish I had some to make into little men that would
look like silver statues.”
"It would be a very expensive amusement, and I have
told you why. Also, it would be hard on your hands, for
this terrible stuff catches fire more easily than
anything you have ever seen. If, while you were molding
it, your little statue were all at once to burst into
flames, what would become of the sculptor?"
"That would n't be so much fun, would it?"
"Beware, then, of burns! Calcium catches fire by merely
touching water. Burning coal, sulphur, and phosphorus
are extinguished by water; calcium, on the contrary,
is set on fire by it. Let it get a little damp and,
behold, it begins to burn. Do not look incredulous when
I tell you this, for it is nothing but the exact truth.
In a lesson soon to follow I will show you that water
is not, as you think it to be, always effectual in
putting out a fire; and who
knows—perhaps—well, we will see whether my
purse will allow it."
"What is your purse going to allow?"
"The purchase, it may be, of a metal that, like
calcium, has the peculiarity of catching fire in
"There are others, then?"
"Yes, three or four."
"And will you really show us one of them?"
"I make no promise. I will see, I will do my
 best, if you continue to take as much pleasure in these
studies as you have taken so far."
"We should be hard to please if we did n't like to see
magnesium burn, phosphorus and zinc turn to snow, and
other metals catch fire in water."
"To return to Emile's wish, calcium's readiness to take
fire on touching water being now known to you, you see
how dangerous it would be to mold it in your fingers,
damp as these always are with their natural moisture.
If we had any calcium, it is not a thing to hold in the
hands and knead with the fingers; it is a dangerous
substance to be left quietly reposing in its bottle.
"But now let us pass on from calcium to its oxid, lime.
We find that this has a taste of its own, which the
oxid of iron, zinc, and magnesium have not; and this
taste is strong, disagreeable, and of a burning nature.
The taste of phosphorus, after combustion, is sour,
acid, whereas that of burnt calcium is caustic or
fiery. Furthermore, it is not the sense of taste alone
that lime affects unpleasantly; it exerts its
corrosive energy on every part of the body. Handled
carelessly for any length of time, it would gnaw the
hands. Like the metal it comes from, it is a harsh
substance, and prolonged contact with it is to be
"Not lacking in flavor, lime ought to be soluble in
water; and in fact it is, though not to any great
extent, but merely enough to give the water an
unbearable taste. If we dilute in water a little lime
previously reduced to a paste, the liquid will turn
white like milk; then, after it has stood a while, the
 undissolved lime will settle to the bottom and the
water will resume its former clearness; but in this
clear water, this water showing no trace of any
foreign substance, there is dissolved lime, just as
there is dissolved sugar in sweetened water. This we
know from the burning, lime-like taste of the
Illustrating by experiment while he talked, Uncle Paul
made his hearers taste of the water in which he had
dissolved a little lime. A drop of the liquid on the
tip of the finger and touched to the tongue was enough
to convince them of its disagreeable taste. Emile made
a grimace of disgust, spitting several times and rather
overdoing his show of repugnance, for the flavor is not
so offensive as his actions indicated. Uncle Paul then
"Here are some violets that I picked just now in the
garden. I showed you how these flowers and others of
the same color lose their blue and turn red when acted
upon by a burnt metalloid, an acid, notably phosphoric
acid, which you have experimented with to the nearly
complete devastation of the garden, so far as its blue
flowers are concerned. Now, what will happen to violets
when acted upon by a burnt metal, an oxid? That is what
this lime here is going to show us."
Uncle Paul selected a violet and pressed it lightly
between his fingers with a little moistened lime,
whereupon the flower instantly turned a brilliant
"Chemistry seems to be a dye factory," observed Emile,
astonished at this new transformation.
 "You took a little acid and made the blue of the violet
turn red, and now you take lime and make the same blue
turn green. When I know enough about chemistry I'm
going to make no end of colors for painting my
"You will be able to make as many as you please, for
chemistry teaches, among other things, how from a
colorless substance a bright color may be obtained by
certain combinations of elements; and it also teaches
how a colored substance may be made to lose its color
or change it into such and such another color. Yes, the
making of dyes is an important part of chemistry's
work, and as the opportunity now occurs to give you
some acquaintance with this interesting subject, I am
glad to make the most of it. By using an acid we change
the blue of the violet to red, and by using lime we
change it to green. These two transformations, so
complete and so instantaneous, give you an idea of how
chemistry, with all the various drugs at is disposal,
can produce the many different colors used by the
painter and the dyer.
"I again take up my violet, turned green by the action
of the lime, and dip it into this glass of water
containing a few drops of some acid or other, no matter
what, though in this instance it happens to be the acid
that results from burning sulphur and is called
sulphuric acid. We shall get better acquainted with it
later. I could make phosphoric acid serve equally well
if you had not used up our supply in your experiments
with flowers. Now keep your eyes open for what happens.
 liquid acid the violet turns red, just as it would have
done had it not been first subjected to the action of
lime. When it is changed to red, I take it out of the
glass and place it a second time in contact with lime,
whereupon it turns green again. If it were dipped into
the acid once more, it would turn red, and then if
touched with moist lime a third time it would again
change to green. Thus the flower would continue to turn
alternately green and red from being alternately
subjected to the action of lime and of acid."
"Could these changes from green to red and from red to
green go on a good many times?" asked Emile.
"As many times as you pleased. On coming out of the
acid the violet would be red, and after touching moist
lime it would be green. Oxids of iron, zinc, and
magnesium do not have this property of turning violets
and other blue flowers green, whereas the oxid of
calcium, or lime, does. Whence comes this difference in
the properties of these various metals? It comes from
the same cause that determines the presence or the
absence of taste. Lime, which dissolves in water, acts
on the organs of taste, and it also acts on blue
flowers by turning them green. The other three oxids,
those of iron, zinc, and magnesium, do not dissolve in
water, are tasteless, and do not turn blue flowers
green, but leave them unchanged.
"But if these oxids were soluble in water, it is
probable that they would have a burning taste, more or
less like that of lime, and would turn violets and
 other blue flowers green. Indeed, we know that, besides
lime, some other oxids are soluble in water, and all
these oxids without exception have the burning taste of
lime, but much more pronounced; also, they all turn
blue flowers green. Taking for the present no account
of any but the soluble compounds, we may sum up in a
few words what we have learned about acids and oxids.
"An acid, which is a metalloid combined with oxygen,
has a sour taste, and turns blue flowers red. An oxid,
which is a metal combined with oxygen, has a burning
taste, and turns blue flowers green.
"I must now tell you that an acid and an oxid can
combine and thus produce a compound substance, whose
properties are, of course, different from those of
either the acid or the oxid. You have not forgotten, I
trust, that after chemical combination has taken place
one must not expect to find in the resulting compound
the same properties that were in the separate
substances before they united. You have a fairly good
notion of phosphoric acid, having seen it made by
burning phosphorus and having ascertained its
unbearable sourness by tasting it. Lime, a very common
substance, is still better known to you, and its
burning taste is even at this moment on the tip of your
tongue. Now, you would never guess what happens when we
combine these two, this acid and this oxid, both of
them harmful substances that must needs inspire us with
grave mistrust. They are changed into something of the
most harmless nature imaginable,—into something,
indeed, that is most
neces-  sary in the animal body: they become the rigid
material that gives strength to our bones.
"Throw the bone from a leg of mutton or from a mutton
chop into the fire, and you will see it burn; but what
takes fire in this fashion is the grease and other
animal matter that impregnate the bone. When this flame
has subsided, the bone will be found in its original
shape, pure white, and so fragile as to crush under the
pressure of your fingers. There we have the essential
elements that go to make bone, and they are alone by
themselves, purged by fire so as to contain no alien
matter. Being incombustible, they have undergone no
change by heart, whereas all else has been consumed.
"Now, chemistry tells us that this white, stony
material to which the burnt bone has been reduced is
formed—not entirely, but nearly so—of
phosphoric acid and lime in combination. Grind this
hard, white substance to a powder and taste it, and you
will find it has no taste, whether sour or caustic. It
is as if the substance contained neither phosphoric
acid nor lime. It has no effect on either violets or
any other blue flowers, their natural color remaining
unchanged and without the slightest trace of red or
green. In short, the properties of both acid and oxid
have disappeared; what was active has become inert,
and what was salt and what was caustic no longer have
any taste. This stony material of bones, a combination
of phosphoric acid and lime, is called phosphate of
lime. It contains three elements, phosphorus, calcium,
and oxygen, and therefore is, as we say, a
 "There are innumerable similar
compounds,—compounds, that is, made by combining
an acid with an oxid. Chemistry calls them salts. Thus,
the white, stone-like substance left after a bone
is burned, and known as phosphate of lime, is a salt."
"You call that salt, that bone powder that has no salt
taste at all?" exclaimed the boys, surprised to hear
thus used a word they thought they knew the meaning of.
"Notice my young friends," their uncle corrected them,
"I do not say the hard substance of the bone is salt;
I say it is a salt. In common language the word
'salt' is used as the name of what we add to our food
to heighten its flavor, as when we salt our soup or
fish; but chemistry gives to this term a much wider
meaning, applying it to every compound resulting from
the union of an acid with an oxid. Every acid—
and the number of acids is large—can combine with
one or another of the oxids, which are still more
numerous, and thus are formed salts in great number.
Kitchen or common salt has given us a general name
which we apply to a great many other compounds; but it
is an unfortunate misnomer in its common use, for our
ordinary salt really does not belong in the class of
salts as I have just defined them, not being composed
of an acid and an oxid. Let us, then, disregard the
salt we all know so well, let us forget its
so-called salt taste and its household use, and
henceforth let us understand by salt in chemical
language any compound of an acid and an oxid, no matter
what its taste, color, or appearance may be.
 "All these particulars, as a matter of fact, vary a
good deal in the different salts. There are numerous
salts that resemble kitchen salt in appearance, being
colorless, vitreous (or glass-like), and soluble
in water; and from this superficial resemblance to
common salt they get their general name. Others are
blue, containing oxid of copper; and others green,
containing oxid of iron; while others still are
yellow, reddish, or violet. In fact, we may find among
them almost any color, but not one of these true salts
has the peculiar taste of our kitchen salt. Some are
bitter, some sour, some caustic, and some of an
indescribable taste, but nearly all are intensely
disagreeable. There are many, too, that will not
dissolve in water, and so are tasteless; such is the
hard material of which bones are chiefly made, and
such, also, the freestone used for building. To this
list we may add the plaster of Paris used in the
ceilings of our rooms. Here, then, are three
things—the mineral substance of bones, freestone,
and plaster of Paris—that you certainly did not
suspect of being salts."
"I had no idea of it," replied Emile. "If houses are
built of salts such as freestone and plaster, I see
that from a chemical standpoint the salt in sausage and
ham must be something very different."
"Yes, very different indeed, for what chemists call a
salt is to be found in almost any stone on the road,
rock on the mountain, or handful of earth in the
"Then there must be quantities and quantities of those
compounds of acid and oxid."
 "Yes, some are very abundant, forming the greater part
as they do of rocks and stones and other minerals. The
salt called carbonate of lime is one of them.
Freestone, rubble-stone, limestone, from which we
get lime, and also marble and many other kinds of stone
are composed chiefly of carbonate of lime."
"And what is plaster of Paris called in chemistry?"
"Sulphate of lime. But these words mean nothing to you,
and so we must stop here and have a little lesson in
"Does chemistry have a grammar?"
"It has a language of its own, and therefore it has
rules for correct speaking when referring to the things
it has to do with. But Emile has no need to be
frightened at this word 'grammar'; it has nothing to
do with his hated conjugations. A few simple rules will
make us master of it. Let us begin with the name of the
acids. We know that an acid is a burnt metalloid, or,
in more precise terms, a metalloid combined with
oxygen. That of phosphorus is called phosphoric acid,
and this example gives us our rule: to the name of the
metalloid, or to the chief part of that name, is added
the ending ic, and we have the name of the acid.
Surely, there's nothing hard about that.
Phosphorus and ic, with the omission of
us to make a pleasanter sound, unite and give us
phosphoric, and that's all there is to it; we
have the name of the acid of phosphorus.
"Let us take another metalloid. You are
ac-  quainted with nitrogen. I told you of its unwillingness
to combine with oxygen. Nevertheless, by using skill
and ingenuity enough, we may overcome this
unwillingness and make the two elements unite. What
will the acid thus formed be called?"
"According to the rule, I should say nitric acid,"
answered Emile. "Is that right?"
"Perfectly. Another metalloid is called chlorin, which
you know nothing about as yet; but no matter, you can
give the name of its acid."
"It must be chloric acid, or I am much mistaken."
"You are not in the least mistaken. Chloric acid is the
"That's easy enough. Oh, I wish our grammar at
"Never mind your grammar at school just now, but let us
proceed with our grammar of chemistry. From carbon we
get an acid that you can name by following the rule
"Carbon and the ending ic make
carbonic," volunteered Jules. "It must be
"In the same way you will be able to name the acid
derived from sulphur."
"Oh, I have it!" cried Emile. "It is sulphuric acid."
"Yes, that is right. But enough, now, on the naming of
acids. Let us pass on to that of oxids, which is
simpler still. We say oxid of iron, oxid of zinc, oxid
of copper, and so on, according to the metal in the
compound we wish to name. I need only tell you to
notice that certain oxids have retained their common
name; familiar to people in
 general from time immemorial, they have kept in
chemistry the name acquired by long use. Thus, oxid of
calcium is simply lime, both to the chemist and to the
mason. The learned term gives way to the popular one.
As we go on we shall meet with other oxids of the same
exceptional sort in respect to name.
"There still remain to be considered in this connection
the salts. They are formed, as we have already seen, by
combining an acid and an oxid; and the rule to be
followed in naming them is simple enough. In the name
of the acid replace the ending ic by ate,
follow it with the name of the metal supplying the
oxid, and you will have the term denoting the salt.
Thus nitric acid and oxid of zinc form a salt called
nitrate of zinc; carbonic acid and oxid of lead form
another called carbonate of lead."
"I see," said Emile; "and so, phosphoric acid and
oxid of zinc would make the salt called phosphorate of
"According to the rule that is quite right, but not
right according to usage. The ear is hard to please,
even that of a chemist, who, without boggling over the
trifles of language, nevertheless finds
phosphorate a little disagreeable; and so for
the sake of euphony the word is shortened to
phosphate, as phosphate of zinc, phosphate of
copper, etc. In the same way sulphurate is
shortened to sulphate, as sulphate of iron,
sulphate of lead, and so on.
"One word more and we shall have done with the subject.
When a salt contains an oxid that has
 kept its common name instead of the name of the metal,
this common name is still retained. Take as an
illustration the salts whose oxid is furnished by
calcium. We do not say sulphate of calcium, carbonate
of calcium, but sulphur of lime, whish is plaster of
Paris, and carbonate of lime, which is limestone.
Herewith ends our grammar."
"The whole of it?"
"Not the whole, but the most important part."
"Oh, I wish our school grammar—"
"Tush! Don't worry about that."