Mrs. (Jane Haldimand) Marcet.

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variety of raioeral products, may be referred to some of these
earths, either in a simple state, or combined the one with the other,
or blended with other ingredients.

Caro/m«yPreciou8 stooesVxjm posed of earth ! That seems very
difficult to c^ceive. ^

Emily. Is it more extraordinary than that the most precious of
all jewels, diamond, should be composed of carbon ? But diamond
forms an exception, Mrs. B. ; for, though ^ stone, it is not com-
posed of earth.

Mrs. B. I did not specify the exception, as I knew you were sa
well acquainted with it. Besides, I would call a diamond a mineral
rather than a stone, as the latter term always implies the presence
of some earth.

Caroline, I cannot conceive how such coarse materials can be
converted into such beautiful productions.

JJfrjr. B. We arej^ery far from understanding all the secret re-
sources of nature ;(but 1 do not think the spontaneous formation of
the crystals, whichVe call precious stones, one of the most di&cult
pbenomena to co^preheodl

By the slow and regularwork of ages, perhaps of hundreds of
a^es. these earths may be. gradually dissolved by water, and 28
gradually deposited by their solvent m the undisturbed proce^, of
crystallization. The regular arrangement of their particles, during
their re-union in a solid mass, gives them that brilliancy, transpa-
rency, and beauty, for which they are so much admired ; and ren-
ders them in appearance so totally different from their rude and
primitive ingredients.

Caroline, But bow does it happen that they are spontaneously
dissolved, and afterwards crystallized f

Jirs. B. The scarcity of many kinds of crystals, as rubies, eme-
ralds, topazes, &c.,^ows that their formation is not an operation
▼ery easily carried ob in nature! But cannot you imagme/nTat
when water holding in solution^ some particles of earth filters
through the crevices of hills or mountains, and at length dripples
into some cavern, each successive drotp m?ij. be slowiv evaporat^,
leaving behind it the particle of earib which it held in solntionf
You koow that erystallizaticm is more re^lar and perfect, in prg^
portion as the evaporation ,of the solvent is^slow and upiforro ; na-
t^re* therefore, who Imows no limit of ti|XKe» has, in all works of tliis
kind, an infinite advantage over any artiBt who attempts to. imitate
snob productions.

Emily, I can now conceive that the arrangtepieot of the particles
ci earth dnripg crystalUxalMn, may be ^och asi to occasion transpa-
Deocy, by admitting a free passage totherav&of Ifght; botlcan-
oot nnderiBtaod why orystaUiaed earths should assume such beauti-
ful cc^Qrs as iiK>st of (hero 4o. Sapphire, for instance, is of a ce-
lestial blue ; ruby, a deep red ; topaz, a brilliant yellow ?



308. What vaMmbleteJbttettoe do the ^rtbt compose?

809. Is it deemed difficalt to anderstand the spontaneoof forma-
tion of crystal?

810. what does the scarcity of many kin<U of crystals ahow ?
81 1 • How may it be supposed that Ibey ,ar« formed ?

17



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194 EAETHS.

Jlfr«. B. Nothing is more simple than to suppose that pe ar-
raDgeinent of their particles, is such^ as to transmit someVof the
coloured, rays of light, and. to reflect others, io which case the stone
must appear of thi colour of the rays which it reflects. But be-
sides, it frequently happens that ihe colour of a stone is owing to
a mixture of some metallic matterTS^

Caroline. Pray, are the differenfTiinds of precious stones 'each
composed of One individual earth, or are they formed of a combina-
tion of se?eral earths ?

Mts. B. A great variety of materials enters into the composition
of most of them ; not only several earths, but sometimes salts and
metals. The earths, however, in their simple state, frequently
form very beautiful crystals ; and, indeed, it is in that stale only
that they can be obtained perfectly pure.

Emily. Is not ihe/Derby shire spaKproduced by the crystalliza-
tion of earths, in theSfay you have jAt explained ? I have been in
some of the subterraneous caverns where it is found, which are
similar to those you have described.

Mrs. B. Yes ; but this spar is a very imperfect specimen- of
crystallization \* it consists of a variety of ingredients confusedly
blended together, as you may judgQ by its opacity, and by the
various colours and appearances which it exhibits.

But, in examining the earths in their most perfect and agreeable
form, we must not lose sight of that stale in which they are com-
monly found, and which, if less pleasing to the eye, is far more in-
teresting by its utility. ,

All the earths are mora^or less endowed with alkaline proper-
ties ; but there are four,^ar^ea^ magnesia, lime, and strontites,
which are called alkaline ^^^AS^^ecause they possess those quali-
ties in so great a degree, as to entitle them, in most respects, to the
rank of alkaliesS They combine and form compound salts with
acids, in the samor way as alkalies ; they are, like them, susceptible
of a considerable degree of causticity, and are acted t]pon in a simi-
lar manner by chemical tests. — ^The remaining earths, silex and
alumine, with one or two others of late discovery, are in some de-
gree more earthy, that is to say, they possess nujre completely the
properties common to all the earths, which areQnsipidity, dryness,
unalterableness in the fire, infusibility, &c^

' Caroline. Yet, did you not tell us thaVsilex, or siliceous earth, *
when mixed with an alkali, was fusible, and run into glass ?

J^rs. B. Yes, my dear ; but the cbcuracteristio properties of earths,

"^^le Derbyshire spar is composed of lime ^ndjluoria ficid ; hence
il is^alled /W^e of lime. The colours are owing to intermixture
with metallic oxides. It is a very beautiful mineral, and instead of
being opaque, it is generally translucent, or nearly transparentV-C.

812. Whence may it be supposed they receive their beautiful
colours ?

813. What is an instance of simple earths io a state of crystal-
lization ?

814. JVhat is the eompasition i^ Derbyshite tptwf

815. What are alkaline earths ?

816. Whyaretheysocalted?

8 1 7. What properties are common to all earths ?

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SILEX. . 195

which I have meDtiooed, are to be considered as belongio^ to them
in a state of purity only ; a state in which they are very seldom to
be met with in nature. Besides these p^enerai properties, each earth
has its own specific characters, by which it is distinguished from
anv other substance. Let us, therefore, review them separately.
rbii.EX,,or SILICA, aboupds in flint, sand, sand-stone, agate, jas-
per, &c. ; it forms the basis of many precious stones, and partica-
iarly of those which strike fire wiih'stee® It is rough to the touch,
scratches and wears away metals ; it h acted upon by no acid but
the fluoric, and it is not soluble in water by any known proqess; but
nature certainly dissolves it by means with which we are unac-
quainted, and t{ws produces a variety of siliceous crystals, and
Sixnongst these, &ock erj/stcuS which is the purest specimen of this
earth. Silex appears to hanre been intended by Providence to form
the solid basis of the globe, to senre as the foundation for the origi-
nal mountains, and give them that hardness and durability "which
has enabled them to resist the various revolutions which the surface
of the earth has successively undergone. From these mountains
silicious rocks have, during the course of ages, been gradually -^e-*
tached by torrents of water, and brought down in fragments ; tnes6,
in the violence and rapidity of their descent, are sometimes crum-
bled to sand, and in this state form the beds of rivers and of the sea,
chiefly composed of siliceous materials. Sometimes the fragments
are broken without being pulverized by their fall, and assume the
form of pebbles, which gradually become rounded and polished.

Emily, P'^si^* what is the true colour of silez, which forms such a
variety of difl^rent coloured substances ? Sand is brown, flint is
nearly black, and precious stones are of all colours.

Jdrs.^, Pure silex, such as is found only in the chemist's labo-
ratory ^^ perfectly white, and the various colours which it assumes
in the different substances you have just mentioned, proceed from
the different ingredients with which it is mixed in therm

Caroline. ,1 wonder that silex is not more valuable, siAce it forms
the basis of so many precious stones.*

Mrs. B, You must not forget that the value we set upon precious
stones dependsnn a great measure upon the scarcity with which
nature affords tnbiM for, were those productions either common or
perfectly imitable Jl^ art, they would no longer, notwithstanding
their beauty, be so highly esteemed. But the real value of siiifieous
earth in many of the most useful arts, is very extensive, ^ixed
with clay, it forms the basis of all the various kinds of earthern
ware, from the most common utensils to the most refined ornaments)

Emitt/. And we must recollect its importance in the formation of
glass with potash,

Mrs. B. Nor should we omit to mention, likewise, many other

* The bases of some of the moat costly gems, as sapphire, ruby,
and topaz, are alumine. — C.



818. In what is silex chiefly found ?

819. What is the purest specimen of silex ?
8^. What is the colour of silex ^

821. Upon what does the value of precious stones depend ?
822* For what important uses is silex chiefly valuably f



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106 AXintlNB.

important uses of silez, such as being the chief ingpredient of soiD^
of the most durable cements, of mortar, &c.

r said before that^liceous earth combined with no acid but the
fluoric ; it is for tbis^eason that glass is liable to be attacked by
that acid onlj, which, from its strong affinity to silex, forces that
^ubstanqe from its combination with the potash, and thus destroys
the glassj

We shifll now hasten to proceed to the other earths, for I am ra-
ther apprehensive of your growing weary of this part of our subject.

Caroline. 1 confess that the history of the earths is not quite do
entertaming as that of the simple substances.

Mr», B. Perhaps not ; but it is absolu^ly indispensable that you
should know something of them ; for {hey form the basis of so
many interesting and important compouods, that their total omis-
sion would Jthrow great obscurity on oiir general outline of chemi-
tjal 8cience\ We shall, however, review them in as cursory a
mapper as ibe subject can admit of.

^Slumint derives its name from a compound salt called alum^ of
wnich it forms the basis!!

Caroline. But it ought to be just the contrary, Mrs. B. ; the sirta-
ple body should give, instep of taking, its name from the compound.

Mrs. B, That is true ; wut as the compound salt was known long
"before its basis was discoVered, it was very natural that when the
earth was at length separated from the acid, it should derive its
4iame from the compound from which it was obtained. However*
to remove your scruples, we will call the salt according to the new
nomenclature, rulphat of alumine^ From this combination, alu-
roine may be obtained in its pure>^tate ; it is then soft to the touch,
makes a paste with water, and hardens in the fire. /Tn nature it is
found chiefly in clay, which contains a considerable proportion of
this earth ; it is very abundant in fullers' earth, slate, and a variety
of other mineral productions^ There is indeed scarcebLany mine-
ral substance more useful tj/mankind than alumine. lln the state
of clay, it forms large strata of the earthi gives coosisfbncy to (he
soil of valleys, and of all low and damp spots, such as swamps and
marshes. The beds of lakes, ponds, and springs, are almost en-
tirely of clay ; instead of allowing of the filtration of water, as sand
does, it forms an impenetrable bottom, and by this means water is
accumulated in the caverns of the earth, producing those reservdirs
whence springs issue, and spout out at the surface.

Emily. I always thought that these subterraneous reservoirs of
water were bedded by some hard stone, or rock, which the water
tsould not penetrate.

Mrs. B. That is not the case ; for in the course of time water
^ould penetrate, or wear away silex, or any other kind of stone,
while it is efiectually stopped by clay, or alumine.

The solid compact soils such as are fit for com, owe their consist-



8^3. How, and why does the fluoric acid destroy glass f

fi24. Why is it necessary to understand the nature of the earths ?

8i5. From what does alumine derive its name ?

o»S' f^**** »8 the sulphat of alumine .'

oir T ^^^^ '^ alumine chiefly found ?

828. In what kind of sbil does it occur most abundantly ?



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s



BABYT^S* 107

eace in a great measure to alumine ;/(&i9 earth is therefore used to
improve sandy or chalkjr soils, which oo not retain a sufficient quan-
tity of water for the purpose of vegetation) -,

Alumine is the most essential ingredienjTin all potteries, (u en-
ters into the composition of brick, as well as that of the finest pbrce-
lain : the additiou of silex and water hardens it, renders it suscept-
ible of a degree of yitriiicatioo, and makes it j^erfecily fit for its
various purposesN

Caroline. I c^ scarcely conceive that brick and china should
be made of the same m&terials.

Mrs. B. Brick consists almost entirely of baked clay ; but a cer-
tain proportion of silex is essential to the formation of earthen or
stone ware. In the common potteries sand is used for that purpose ;
a more pure silex is,* I belii»ve, necessary for tiie composition of
porcelain, as well as a finer kind of clay ; and these niateriab are,
no doubt, more earefully prepared, and curiously wrought, in the
one case than in the other. Porcelain owes its beautiful semi*
transparencyVtQ a commencement of vitrification^

Emily- BuNbe commonest eaKhenware, thougn not transparent,
is covered with a kind of glazing.

Mrs. B. That precaution is equally necessary for use as for beaa-
ty, as the ware'would be liable to be spoiled and corroded by a va-
riety of substances, if not covered with a coating of this kind. In
porcelain it consists of enamel, which is a fine white opaque glass,
formed of metallic oxyds, sandSyMilts, and such other materials as
are suseeptible of vitrification. ^!Tie glaring of common earthen*
ware is made chiefly of oxyd of lead, or sometimes merely of sa't,
irhich, when thinly spread o¥er earthen vessels, will, at a certain
beat, run mto opaque glasA

Caroline. And of what nAture are the colours which are used for
painting pofcelain f ^

Mrt. B.fvYkey are all composed of metallic oxyds ; so that these
colours, instead of receiving injury from the application of fire, are
strengthened and developed by its acUon, which causes them to
undergo different degrees of oxvdatiou

Alumine and silex are not only oftejl combined by art, but they
bare in nature a very strong tendency to unite, and are found com-
bined, in different proportions, in various gems and other minerals*
Indeed,many of the precious stones, such as ruby, oriental sapphire*
amelbyst^f w. consist chiefly of alumine.

We may now proceed to the alkaline earths. I shall say butaGaw
words-on Barttss, as it is hardly ever used, except in chemics^

'p ■■ >

* Porcelain clay, of which china ware is made, is found among
g^nite roc^s, and seems to owe its ori^n to the decomposition of a
mineral tmdXei^feldfpar. Its composition is silex and alumine, si-
lex 'being the predominant ingredient.— C.
' f The amethyst is almost entirely composed of silex.—C.

829. What is tbe.use of alumine for purposes of vegetation ?

890. What is tbeiise of it in works of art ?

631. TofVhat is the transparency of porcelain owing .>

832. Of what is the glazing of common earthen- ware made ?

833. What is the naiure of the colours which are used for pak^
ipg BDrcelaip .'

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196 LtKS.

laboratories. \t is remarkable for its great weight, and its stroDg
alkaline properties, such as destroying animal substances, turaing
green some bhie vegetable cdlours, and showing a powerful attrsic-
tton for acids ; this last property it possesses to sui^h a degree, par-
ticularly with regard to the sulphuric acid, that it will always de-
tect its presence in any substance or combination whatever, bvjm-
mediately uniting with it, and forming a solphat of baryte^ /This
renders it a very valuable chemical tes^, m is found pretty abutf-
dantly in nature in the state of carbona^* from which the pure
«arth can be easily separated)

The next earth we have toxonsider is Lime. This is a substance
of too great and general importance to be passed over so lightly ai
the last.

Lime is strongly alkaline. In nature it is not met with in its
simple state/Us its affinity for water and carbonic acid is so great
that it is alf^ys found combined with these substances, with which
it forms the common lime-stonSjc but it is separated in the kiln from
these ingredients, which are vmatilized whenever a sufficient de-
tgree of lieat is applied.

Emily^xxre lime, then, is nothing but lime-stone, which has been
4eprivcd, m the kiln, of its water and carbonic acid^

Mrt. B. Precisely : in this state il is called quick-wney and^ is so
caustic, that it is capable of decomposing the dead bodies of animak
v«ry rapidly, without their undergoing the process of putrefactiooS
I have here some quick-lime, which is kept carefully corked up iinr
bottle to prevent the access of air ; for^re it all exposed to the at-
mosphere, it would ab^rb both moisture and carbonic acid gas from
it, and be soon slakedlj Here is also some lime stone—we shall
pour a little water on tfach^ and observe the effects that result from
it.

Carcdine* How the quick-lime hisses ! It is become excessively
hot !-/rt swells, and now it bursts and crumbles to powder, while
the water appears to produce no kind of alteration on the lioae-
stone.] ^

MtL B. fljecanse the lime-stone is already saturated with water,
whilst the qbicklime, which has been deprived of it in the kHo,
combines with it with very great avidity, and produces- this prodi-
gious disengagement of heat\the cause of which I formerly ex-
plained to you ; do you recollect it ?

Emily, Yes; you said i^a^xMk^ heat did not proceed from theliaio

* The native carhonai of barytes is a rare mineral. It is a viru-
lent poison. The ntlphat of barytes is found in considerable abim-
dance.— C.

...; 1 ^ "I ' . ' . ' '

834. For what is barytes remarkable?

835. For what is it valuable ?

836. Where is it abundantly found ?

837. What is the reason that lime is not found in its simple state?

838. How does lime-stone differ from pure lime?

839. What effect will quick-lime have upon the dead bodies of
animals ?

840. What effect does the air produce on quick-lime f

84 1 . What effect has water on it ? /

842. Why iviH not water have an effect on lime^stone as well M
upon quick-liine ?

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BARlr«B». }99

bat from the water which was tolidifiedi^ and thus ^rted with its
heat of liquidity!

Mra. B. Verf well. If we continae to add successiye quantities
of water to the lime, after being siaked and crumbled, as yon see,
it will then gradually be diffused in the water, till it will at length
be dissolved in it, andentirely disaft^ear ; but for this purpose it
requires no less tbanJ^OO times its weight of water! This solution
is called lime water.'^ J

Caroling, How very small, then, is the proportion of lime dissoU
ved ! j^

Mra.B, rBarytes is also of very difficult solution ; but it is much
more soluAe in the state of crystalsA The liquid contained in this
bottle is lime-water: it is often usee as a medicine, chiefly, X be-
lieve, for the purpose of combining with and neutralizing tiie super-
abundant acid which it meets with in the stomach.

Emily » 1 am surprised th^t it is so perfectly clear : it does not
at all partake of the whiteness'of the lime. .

Jlfri. B. ilave yoy forgotten that, in soIutionSf/The solid body it
so minutely subdivided by the fluid as to becomte invisible, and
therefore, wHl not, in the least degree impair the transparency of
the solven!j^ ^^ v

I said tb&t the attraction oflimenor carbonic acidJwas so strongs
that it would absorb it from the atmosphere. We m/y see this effect
A6y exposing a glassof lime-water to the air ; the lime will then se-
parate from the water, combine with the carbonic acid, and re ap-
pear on the surface in the form ^ a white film, which is carbonat
of lime, commonlv called chalkA

Caroline, Chalk is, then, a c<fm pound salt ! I never slioilld have
supposed that those immense beds of chalk, that we see in many
parts of the country were a salt. Now the white film begins to ap-
pear on the surface of the water : but it is far from resembling hard
solid chalk.

J^rs.B. That i^ owing to its state of extreme division : in a lit-
tle time it will collect into a more compact mass, and subside at the
bottom of the glais.

If you breathe into lime-water/fbe carbonic acid, whi<^ is mixed
with the air that you expire, will produce the same effectij It is an
experiment very easily made :— ?! shall pour some lime-Fater into
this glass tube, and, by bi'eathing repeatedly into it, you will soon
perceive a precipittftion of chalk.

*fvq make lime-water, take a piece of well burned lime, about
theVze of a hen's egg, put it into an earthen dish, and sprinkle wa-
ter on it, till it falls into powder : Then pour on two quarts of boil-
ing water, and stir it several times, af^r the lime has settled ; pour
off the clear water and cork it for use.- '^



s, after the li
use.VC.

len w^ter is (



843. Why is heat disengaged when w^ter is put upon quick-lime?

844. How much 'Water does it take to dissolve lime?

845. Is Barytes easily dissolve^ in water ?

846. Why does not lime-water partake of the whiteness of lime ?

847. For what has lime a very strong attraction ?

348. Why does a white film collect on the surface of lime^wat^r
on beinf? exposed to the air ?
^49. Why will lime-w|tter turn white if you breathe into it ?



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200 xms.

Emily. I see already a smaH white cloud formed.

Mrs, B. It 18 composed of minute particles of chalk ; at present
itfl fta ts in the water, but it will soon subside
^Carbonat of limeAor'cbalf,k,jou see, is insoluble in water, since
tke lime which wa&iGissolved reappears when converted into chalk;
bu^ou must take notice of a very singular circumstance, whijjh
is/Sat chalk is soluble in water impregnated with carbonic acioT)

\aroline. It is very curious, indeed, that carbonic acid and gas
.should render lime soluble in one instance, and insoluble in the
other !

J^rt, B. I have here a bottle of Seltzer water, which you know,
is strongly impre^natt^d with carbonic acid i let us pour a little of
it into a glass of Ume water. You see thatat immediately forms a
precipitation of carbonat of lime^ ^

Emily. Yes, ^ white cloud appears.

Mra.B. I shall now pour an additional quantity of the Seltzer
water j'nto the lime waiter..-^

Emtly. How singular ! The cloud is re-dissolved, and the liquid
is again transparent.

Mfs/6. >\11 the mystery depends upon this circumstance, that
carbonat of lime is soluble in carbonic acid, whilst it is insoluble ia
water; the first quantity of carbonic acid, thei>efore,'which 1 intro-
duced into the lime water, was employed in forming the carbonat
of lime, which remained visible, until an additional quantity of car-
bonic acid dissolved it. Thus, you see, when the lime and carbonic
'acid are in proper proportions to form chalk, the white cloud ap-
pears ; ^ut when the acid predominates, the chalk ds no sooner
formed than it is dissolved.

Caroline. That is now the case ; but let us try whether a further
addition of lime-water will agiin precipitate the chalk.

Emily. It does, indeed ! The cloud re-appears, Uscause, I sup-
pose, 'there is now no more of the carbonic acid than is necessary
to form chalk; and, in order to dissolve the chalk, a superabun-
dance of acid is required.

Mrs. B. iVe have. I think, carried this experiment far enough;
every >epetition would but exhibit the same appearance.

Lime cbmbihes with most of the acids, to which the carbonic (as
beMig the weakest) readily yields it ; but these usombinations we
shall have^an opportunity of noticing mere particularly hereafter.
It unites with phosphoru8^n4j^fh sulphur, in their simple state;
in short, of all the earthmimels that which nature employs most



Online LibraryMrs. (Jane Haldimand) MarcetConversations on chemistry .. → online text (page 24 of 43)