John Lee Comstock Mrs. Marcet (Jane Haldimand).

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hole in the ice.

Mrs. B, This hole contains a solution of potash : for the alkali
being extremely soluble, disappears in the water the instant it is
produced. Its presence, however, may be easiljr aficertained, alka-
lies having the properties of changing paper, stained with turmeric,
to a red color ; if you dip one end of this slip of paper into the hole
in the ice, you wiU see it change color : and the same if you Vet it
with the mrop of water in which the first piece of potassium was

Caroline. It has indeed changed the paper from yellow to red.

Mrs. B. This metal will bum likewise, in carbonic acid gas, a
g^ that has always been supposed incapable of supporting combus-
tion, as we were unacquainted with any substance tnat had a greater
attraction for oxygen than carbon. Potassium, however, readily
decomposes this gas by absorbing its oxygeiK as I shall show you.
This retort is fillM wim carbonic acid gas. I will put a small piece
of potassium in it ; but for this combustion a slight elevation of
temperature is required^ for which purpose I shall hold the retort
over the lamp.

Caroline. Now it has taken fire and bums with violence ! It has
burst the retort.

Mrs. B. Here is a piece of regenerated potash ; can you tell me
why it has become so black ?

JEndfy. No doubt it is blackened by the carbon-, which, when its
oxygen entered into combination with the potassium, was deposited
on its surface.

Mrs. B. You are right. This metal is perfectly fluid at the tem-
perature of one hundred, degrees ; at fifty degrees it is solid, but
soft and malleable ; at thirty-two degrees it is hard and brittle, and
its fracture exhibits an appearance of confrised crystallization. It is
scarcely more than half as heavy as water ; its specific ^avity be-
ing about six, when water is reckoned at ten ; so that tms metal is
actiuilly lighter than any known fluid, even than ether.

Potassium combines with sulphur and phosphoms, forming suK
phurets apd phosphorets ; It likewise forms alloys with several met?
ids, and amalgamates with mercury.

Emify. But can a suflicient quantitj of potassium be obtained, by
means of the Voltaic battery, to admit of all its properties and re
lations to other bodies, being satisfactorily ascertained?

Mrs. B^ Not easily , but I must not neglect to inform you that a
method of Qbtainingthis metal in considerable quantities, \\9s since
been discovered. Two eminent French chemists, Thenard and
Gay Lussac, stimulated by the triumph which Sir H. Davy had ob-

693. At how low a temperature will potasdum bum in contact with
water ?

694. Whv, until the didcoveiy of potasdum, had carbonic acid gas
been considered incapable of supportuig combustion ?

695. How does potasuum decompose this gas ?
096. WhtX metal is lighter than any known fluid ?

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MSTAIiS. 109

tBiaed, attempted to separate potasaiiuQ jfrom its combin0,tj0n with
oxygen^ by common chemical means, and without the aid of elec^
tmity. They caused red hot potash in a state of fusion, to lUtet
through iron turnings in an iron tube, heated to whiteness. Theif
experiment was crowned with the most complete success ; more
potassium was obtained by a single operation, tiinan could have been
collected in manji^eeks by the most dihgent use of the Voltaic

EmJy, In this experiment, I suppose the oxygen quitted its com-
bination with the potassium, to unite with the iron turning ?

Mn, B, Exactly so ; and thus the potassium-waS obtamed in its
simple state. From that time it has become a most convenient and
powerful instrument of deoxygenation in chemical experiments.— ^
This important improvement, enffrafted on Sir H. Da^'s previous
discovenes, served but to add to his glory, since the fjfccts which he
had established, when possessed only of a few atoms of this curious
substance, and the accuracy of his analytical statements were all
Confirmed, when an opportunity occurred of repeating his experi-
ments upon this substance, which can now be obtained in unlimited

Caroline, What a satisfaction Sir H. Dav^ must have felt, when
by an efibrt of genius he succeeded in bringing to light, and actu^
afly giving existence to these curious bodies, which without him,
might perhaps have ever remained concealed from our view !

Mrs, B, The next substance which Sir H. Davy subniitted to
the influence of the Voltaic battery, was Soda, the other fixed alkali,
which yielded to the same powers of decomposition ; from this alkaU,
too, a metallic substance was obtained^ vety analogous in its prop-
erties to that which had been discovered in potash ; Sir H. Davy has
called it sodium. It is rather heavier than potassium, though con-
siderably lighter than water ; it is not so easily fusible as potassium.

Encouraged by these extraordinary results, Sir H. Davy next
performed a -series of beautiful experiments on" Ammonia, or the vol-
atile alkali, which from analogy, he was led to suspect, might also
contain oxygen. This he soon ascertained to be the fact, but he has
not yet succeeded in obtaining the basis of ammonia in a separate
state : it is from analogy, and from the power which the volatile alkali
nas, in its gaseous form, to oxydate iron, and also from the amalgams
which can be obtained from ammonia by various processes, that the
proofs of alkali being also a metallic oxyd are deduced.

Thus, ihen, the ihriee alkalies, two of which had always been
considered as simple bodies, have now lost all claim to that title, and

have accordingly classed the alkalies amongst the compounds,
whose properties 1 shall treat of in a future conversation.

Emily, What are the oth^r newly discovered metals which you
have afiuded to in your list jf simple bodies ?

697. How may potassium be obtained In large quantities ?

698. In the experiment for obtaining potassium, why did the oxygen-
quit that substance ?

699. What waff the next substance submitted to tiie ^ifiuence of \hei^
Voltaic battery ?

700. What was the effect .'

'701. What is the substance produced by the decomposition of iod#

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170 MSTAIiS.

A^. 3, Theyaie the metals of the earth which hecame niezt the
object of Sir H. I)ayy 's researches ; these bodies had never jet been
decomposed, though they were strongly suspected, not only of being
compounds, but or being metaUic oxyds. From the circumstance
of their incombustibili^, it was coniectured with some plausibility,
that they might possibly be bodies that had been already^boxnt.

Caro&ne And metals, when oxydated , beconti, to all appeaianoe,
a Idnd of earthy substance.

Mrs. B, They haVe besides, several features of resemblance with
metallic oxyds; Sir H. Davy had, therefore, great reason to be
sanguine in hk e^qpectations of decomposing them^ and he was not
disappointed. He could not, however, succeed' m obtaining the
basis of the earths in a pure separate state ; but metallic alloys
were formed with oth^ metals, which sufficiently proved the ex-
istence of the metaHio basis of the earths.

The last class of new metalUc bodies whieh Sir H. Bav]^^ discov-
ered, waa obtained &pmth% three, undecompounded acida, the bo-
xacic, the'fluori^, and' the muriatic acids; but as you are entirely
unacquainted with these bodies, I shall reserve the account of thenr
decomposition^ till we come to treat of their properties as acids.

Thus in the course of two years, by. the unparalleled exertions
of a single individual, chemical science has assumed a new aspect.
Bodies have been brought to light which the human eye never be-^
fi>re beheld, and which might have remained eternally concealed,
under their impenetrable disguise.

It is impossoble, at the. present period^ to appreciate, to their full
extent, the consequences which science or the arid may derive from
these discbveiies ; we may, however, antipipate the most important

In chemical analysis, we in possession of more energetie.
agents- of decomposition than were ever before known.

In geology, new views are opeped, which will probably operate,
a revolution in that obscnee imd difficult science. It is ahrea^
proved that all the earths, and, i^ ^t, the solid surface. of this.,
globe, are metallic bodies.nuneralized by oxygen, and as our planet
Has been calculated to be considerably more: dense .upon the whole,
than it is on the surface, it is more reasonable to suppose that the
interior of the earth is composed of a. metallic mass, the surface of
^ which only has hipei^ mineralized by the atmosphere.

The erujption of volcanoes, those stupendous problems of nature,
admit' now of.'an easy expkuia^ion.* For if the oowels of the earUi
are the grand recess of mese- newly discovered inflammable bodies,
whenever water; penetrat«s,i|^,t^em, combustions and explosioiiB.

* It is always easy to form a thepry,. But an explanation of these ,
''stupendous problems of. nature," we believe has not yet been
demonstrated to the satisfaction of all^. though great learning and

702. What peculiarities havg the new-metals, discovered by Sir H.

703. What reason had Sir H. Davy for supposing thattUielAls might
be decomposed ? *

704. What are earths supposed to be ?

705. What if supposed u>' fOrm the principal interior part of o\a^
globe ?


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■mfltjl tiftke pkce ; and it is remarkable that the lara which is thrown
out, is the very kind of sabstance which might be expected to
result from these combustions.

I must now take my leaye of you ; we haye had a yery long
oonyersation to-day, and I hope you will be able to recollect what
you haye learnt. At our nei^ inl^nciew, we shall enter on a new



Mrs, B, Haying completed pur examination of the simple or
elementary bodies, we are now to proceed to those of a com])ound
nature ; but, before we enter on this extensiye subject, it will be
necessary to make yoi; acquainted with the principal laws by which
chemical combinations are governed.

You recoHect, I hope, what we formerly said of the nature of
t^e attraction' of composition, or chemical attraction, or affinity, as
It is also called.

Unify, Yes, I think, perfectly ; it is the attraction that sub8ist9
between bodies of a difierent| nature, which oocasions them to com-
bine and form a compound', \i4ien the^ come in contact ; and, bo-
^rdin^ to Sir H. I^ayy's. opinion, this effect is produced by the
attraction of the opposite electricities, whiit;h prevailed in bodies of
difierent kinds.

Mrs. Bi Veiry well; your definition comprehends the first law
of chemical attraction, which is, that t^* takes place onfy between
bodies of a different nature;, as, for instance, b^iw^een an acid and
an alkali ; between oxygen and a metal, &c..

Caroline. That we understand, of course ; for the attraction be-
tween particles of a similar nature is that of aggregation, or cohe-
sion, which is independent of any chemical power.

Mrs. B. The second law of chemical attraction is, that it takes
place onfy between the most minute particles of bodies; therefore the-

immense labor has been bestowed on the subject. If the " feasy
explanation " is founded on the data here proposed, viz. that the
9plid soT&ce of opr globe consists of nothing except metals and
oxygen, such a ^eory in the present state- of knowledge, must
duefly consist of supposition piled on supposition; there being as
yet no proof that th^ crust of the earth is- roimed only of diese two

706. How are volcanoes accounted for ?

707. What do you understand by the attraction of composition?

708. What cause does SirH. Davy amign for the attraction between
bodies of a different nature ?

709. What is the fii^st law of chemical attraction ?

710. What is the attraction between particles of a nmilar naturft-

7^. What is the second law of chemical attraction f


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IVfl en THE ATVEACvroir

nore you divide the paitioleB of the Iwdies to be oamUned, ithe
more readily they act upoa each other.

QiroUne. That is again a circumstanoe nduch wo mi^ht h&Ve
mferred ; for &e finer the particles of the two sabstanees are, ithe
more eamly and perfectly they will come in contact with eadi
other, which must greatly fau^tate their union, it was for this
purpose, you said, that you used iron filings, in preference to wises
or pieces of iron, for the decomposition of water.

Mrs. B, It was once supposed, that no mechanical power conld
divide bodies into particles sufficiently minute for them to act on
each other ; and that in order to produce the extreme division re-
quisite for a chemical action, one, if not both of the bodies, should
be in a fluid state. There are, however, a few instances in which
two solid bodies, very finely pulverized, exert a chemical action
on one another ; * but such exceptions to the general rule are very
rare indeed.

JBmify. In all the oombioations that we have hitherto seen^ one
of the constituents has, I believe, been either liquid or (triform.—'
In combustion, for instance, the oxygen is taken from the atmos*
phere, in which it existed in a state of gas ; and whenever we have
seen acids combine with metals or with alkalies, they were either
in a liquid or an serifbrm state. '

Mrs. B. The third law of chemical attraction is, that it can take
place between two, three, four, or even a greater number of bodies.

Caroline. Oxyds and acids are bodies composed of two constitu-
ents, but I recollect no instance of the combination of a greater
number of principles.

Mrs. B. The compound salts, formed by the union of the metals
with acids, are composed of three principles. And there are salts
formed by the combination of the alkalies with the earths which
are of a similar description.

Caroline. Are they of the same kind as the metallic salts ?

Mrs. B. Yes ; they are very analogous in their nature, althouglr
different in many of their properties.

A methodical nomenclature, similar to that of the acids, has been
adopted for the compound salts. Each individual salt derives its-
name froxi;i its constituent parts, so that every name implies a
knowledge of the composition of the salt.

The t&ee alkalies, the alkaline earths, and the metals are called
saiifiable bases, or radicals, and the acids, saiiftfing principles. The
name of each salt is composed both of that of the acid and the sali,-
.fiable base ; and it terminates in at or it, according to the degree
orthe oxygenation of the acid. Thus, for instance, all those salts
which are formed by the comtbination of sulphuric acid with any of
the salifiable bases, are called sulphals, and the name of the radical i»-

* This is the case with muriate of ammonia and quick lime. — C.

712. What is necessary in order that chemical action take place be^
Iween different bodies ?

713. What is the third law of chemical attraction ?

714. How aife compound salts formed?

715. What are called salifiable bases or radicals ?

716. What are called salifying principles ?

HZ. How do salts ending in ate di&r finxn those ending^ in els>t'


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OF coMPosiTioir. 173

> added for the specific distinction of the salt ; if it be potash, it will
compose a sulphat of potash ; if ammonia, sulphat of ammonia, &c.

Mnili/., The crystals which we obtained from the combination of
iwn and sulphuric acid were therefore called sulphat of iron.

Mrs,. B^ rrecisely ; and those which we prepared by dissolving
copper in nitric acid, Tiitrat of copper, aad so on. But this is not
ajl ; if the salt be formed by that land of acids whibh ends in ous,
(which you know indicates a less degree of oxygenation) the termi-
nation of the name of the salt will be in tr, as sulphit of potash, stU-
phit of ammonia, &q.

Emily. There must be an immense number of compound salts,
since there is so great a variety of salifiable radicals, as well as of
salifying principles.

Mrs. B. Their real number cannot be ascertained, since it in-
creases every day. But we must not proceed further in the inves-
tigation of the compound salts, until we have completed the exami-
nation of the nature of the ingredients of which they are composed.

The fourth law of chemical attraction is, that a mange of temper-
ature always takes place at the moment of combination. This arises
from the extrication of the two electricities in the form of caloric,
which ajways occurs when bodies unite ; and also sometimes in part
from a change of capacitor in the bodies for heat, which always takes

Elace when the combination is attended with an increase of density,
ut more especially when the compound passes from the liquid to
the solid form. I shall now show you a striking instance of a change
of temperature from chemical union, merely by pouring som^e ni-
trous acid on this small quantity of oil of turpentine, the oil will
instantly combine with the oxygen of the sbcid, an4 produce ^
considerable change of temperature.

Ckiroline. What a blaze ! The temperature of the oil and the
acid must be greatly raised, indeed, tp procure such a violent com-

Mrs. B. There is, however, a peculiarity in this combustion,
which is, that the oi^gen, instead of being derived from the atmos^
pheric air alone, is principally supplied by the acid itself.

Emily. And are not all combustions instances of the change of
temperature produced by the chemical combination of two homes ?

Mrs. B. Undoubtedly ; when oxygen loses its gaseous form, in
order to combine with a solid body, it becomes condensed, and the
caloric evolved produces the elevation of temperature. The spe-
cific ^[ravity of bodies is at the same time altered by chemical com-
bination ; for in consequence of a change of capacity for heat, a
change of density must be produced.

Caroline, That was the case with the sulphuric acid and wateX|
which, by being mixed together, gave out a great deal of heat, an4
increa^a in density .

718. How do acida ending in ic, <^ifier from those ending in ous f

719. What is the fourth fitw of chemical attraction ?

720. From what does the change of teniperature arise ?

721. What is an instance of increase or temperature from chemical

722. Is th^ «|)6ci$c gravity of bodies affected by chemioal ooo^ii^-


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Mr», B. The fifth law of chemical attraction is, that $he proper*
ties which characterize bofUes, when separate, are aUered or destroyed
by their combination,

Caroline, Certainly ; what, for instance, can he so different &om
water, as the hydrogen and oxygen gases ?

Emib/. Or what more unliKe 8ii^>hat of iron, than iron or sul-
phuric add ?

Mrs, B, Every chemical combination is aa illustration of this
rule. But let us proceed —

The sixth law is, that the force of chemical qffiniiy baween the con-
stitttents of a body, is estimated by that which is required for their sep-
aration. This force is not always proportional to the ^ility with
which bodies unite ; for manganese,- for instance, which you know,
is so much disposed to unite with oxygen, that it is never found in
a metallic state, yields it more easily than any other metal.

Eamky, But, Mrs. B., you speak of estimating the force of attrac-
tion between bodies, by the force required to separate them ; now
can you measure these forcen ?

Mrs. B. They cannot be precisely measured, but they are com-
paratively ascertained by experiment, and can be represented by
numbers which express, at least by approximation, the relative de-
grees of attraction.

The seventh law is, that bodies have amongst themselves different
degrees ^attraction. Upon this law, (which you may have discover-
ed yourselves, long sinc6,) the whole science of chemistr]^ depends,
far it is by means of the various degprees of alhnity which bodies
have for each other, that all the chemical compositions and decom-
l^ositions^ are effected. Every chemical fact or experiment is ah
mstance of the same kind ; and whenever the decomposition of a
body is performed by the addition of any single new substance, it is
«aid to be efiected by simple elective attractions. But it often happens
that no simple substance will decompose a body, and that in order
to effect this, you must offer to the compound a body whidi is itself
composed of two, or sometimes three principles, which would not,
each separately, perform the decomposition. In this case there are
two new compounds formed in consequence of a reciprocal decom^
position and recomposition. All instances of this kind are called
double elective attractions,

Caroline, I confess I do not understand this clearly.

Mrs, B, You will easily comprehend it, by the assistance of this
diagram, in wUch the reciprocal forces of attraction are represented
by numbers :

723. What is the fifth law of ehemieal attraction ?

724. What is the sixth law of chemical attraction ?

725. What is the seventh law of chemical attraction.^

726. Upon what does the whole science of chemistry depend ^

727. What is a simple elective attraction ?

728. What is a double elective attraction ?


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ov coofvasinoN.


Original Compownd,
Sulphat of Soda.



of Soda.


8 Sulphuric Acid

7 Divellent § Attractions 6.13 y Salphat

of Lime.

Nitric Acid 4 Lime


Original Compound,
Nitrate of Lime.

We here suppose that we are to decompose sulphat of soda; that
Is, to separate the acid from the alkali : if for this purpose, we add
some lime, in order to make it combine with the acid, we shall fail
in our attempt, because the soda and the sulphuric acid attract each"
other by a force which is superior, and, (by the way of supposition)
is represented by the number 8 ; while the lime tends to unite with
this acid by an affinity equal only to the number 6. It is plain »
therefore, that the sulphat of soda will not be decomposed, since a
force equal to 8 cannot be overcome by a force equal only to 6.

Caroline, So far, this appears very clear.

Mrs, B. If on the other hand we endeavor to decompose this
salt by nitric acid, which tends to combine with soda, we shall be
equally unsuccessful, as nitric acid tends to unite with the alkali by
a force equal only to 7.

In neither of these cases of simple elective attraction, therefore,
can we accomplish our purpose. But let us previously combine
together the lime and nitric acid, so as to form a nitrate of lime,- a
compound salt, the constituents of which are united by a power
equal to 4. If then we pesent this compound to, the sulphat of
soda, a decomposition will ensue, because the sum of the forces
which tend to preserve the two salts in their actual state is not
equal to that of^the forces which tend to decompose them, and to
form new combinations. The nitric acid, therefore, will combine
with the soda, and the sulphuric acid with the lime.*

* Suppose we say thus. The sul^phuric acid attracts soda with a
stronger force than it does litnej and soda has a stronger affinity foi
sulphuric acid than it has for nitric acid. It is plain', then, that nei-
ther lime nor nitric acid alone will decompose the sulphat of soda.
Now if we unite the nitric acid and lime, we form nitrate of lime,—'

729. What is represented in the diagram ?

730. What is said in the note of the subject of tltis diagram f


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OaroSne. I nndarstaiid you now veiy well. This doable e&xi
takes place because the numbers 8 and 4, which represent the de
giees of attraction of the constituents of th^ two original salts,
make a sum less than the numbers 7 and 6, which represent the
degrees of attraction of the two new compounds that will in conse-
quence be formed,
g Mrs, B, Precisely so.

CaroUne, But what is the meaning of quiescent and dweUent
forces which are written in the diagram ?

Mrs, B. Quiescent forces are those which tend to preserve com-
pounds in a state of rest, or such as they actually are; divellent
forces, those which tend to destroy that state of combination, and
to form new compounds.

These are the principal circumst-ances relative to the doctrine of
chemical attractions, which have been laid down as rules by mod-
em chemists : a few others might be mentioned respecting the same
theory, but of less importance, and such as would take us too far
from our plan. I should, however, not omit to mention that Mr,
Berthollet, a celebrated French chemist, has questioned the uniform

Online LibraryJohn Lee Comstock Mrs. Marcet (Jane Haldimand)Conversations on chemistry: in which the elements of that science are ... → online text (page 20 of 43)