Mrs. (Jane Haldimand) Marcet.

Conversations on chemistry .. online

. (page 13 of 43)
Online LibraryMrs. (Jane Haldimand) MarcetConversations on chemistry .. → online text (page 13 of 43)
Font size
QR-code for this ebook

the oxygen with which it combineslX ., , .

This black powder is an oxyd of mkng^ese, a metal which has so

* Red Lead and Rust of Iron, — C.

417. Does oxygen always exist in a gaseous state ?

418. When is the absorption of oxygen called oxygenation, or
oxvdation ? .

419. How can oxygen penetrate metals, since their attraction of
aggregation is so great f

420. What ib the ofaenmnd same Ibr red lead and mst of iron?

421. What is an oxyd ?

422. If oxyds are a combination of taetali and oxygen, why are
they not negative?

Digitized byV^OOQlC


Strong: an affinity for oxygen, that it attracts that substance from -
the atmosphere at any known temperature ; it is therefore ne^er
found in its metallic form, but always in that of an ozyd; in which
state, you see it has very little of the appearance of a metal. It is
now heavier than it was before oxydation,in consequence of the ad-
ditional weight of the ozvgen, with which it has combined.

Caroline. I am very glsul to hear that ; for I confess I could not
help having some doubts whether oxygen was really a substance, as
it is not to be obtained in a simple and palpable state : but its weight
is, 1 think, a decisive proof of its being a real body.

Mrs. B. It is easy to estimate its weight, fBy separating it from
the manganese, and finding how much the Is^er has loscj

Emily. But if you can take the oxygen from the moMl, shall we
not then have it in its palpable simple state ?

»Vr*. B. No ; for I can 6nly separate the oxygen from the man-
gfanese/By presenting to it some other body, for which it has a great-
er affinity tnan for the manganese^ Caloric affording the two elec-
tricities is decomposed, and one or them uniting with the oxygen,
restores it to the aeriform state.

Emily. But you said just now, that manganese would attract ox-
ygen from the atmosphere in which it is combined with the nega.-
tive electricity ; how, therefore, can the oxji^gen have a superior
affinity for that electricity, since it abandons it to combine with the
manganese ?

J^rs. B. I give you credit for this objection, Emily ; and the on*
ly answer 1 can make to it is, that the mutual affinities of metals for
oxygen, and of oxygen for electricity, vary at different tempera-
tures ; a certain degree of heat will, therefore, dispose a metal to
combine with oxygen, whilst on the contrary, the former will be
compelled to part with the latter, when the temperature is further
increased. I have jffat some oxyd of manganese into a retort,"^
which is an earthen vessel with a bent neck, such as you see here.
(See Fig 17, No. 1.) The retort containing the manganese you can-
not see, as 1 have enclosed it in this furnace, where it is now red-hot.
But, in order to make you sensible of the escape of the gas, which
is itself invisible, I have connected the neck of the retort with this
bent tube, the extremity of which is immersed in a vessel of water.
(See Fig. 17, No. 2.) Do you see the bubbles of air rise through
the water ?S

Carolini. Perfectly. This, then, is pure oxygen gas ? What a
pity it should be lost. Could you not preserve it ?

)^o collect oxygen gas. take an oil flask, and having fitted a cork
to it, pierce the cork so as to admit a bent glass tube ; (the bending
is done over a spirit lamp.) Put into the flask some black oxyd of
roang^ese, and poar on sulphuric acid enough to make it into a
paste. Then put in the cork and tube, and having connected the
other end of tne tube with a receiver, in the tub of water, apply the
heat of an Argand lamp.V-C

423. How can it be determined that oxygen has weight ?

424. How can oxygen be separated from manganese after having
been oxydated ?

425. Haw may fnere oxygen be ooUected ?

426. How would you describe the experiment represented in fig^
ure 17 ?


Fig. 17.

2 (s:::::;^^

No. 1. A, retort on a tUnd.— No. 2. A, Furnace. B, Earthen Retort io the : .^..

C, Water Bath. D .Receirer. E E, Tube conTejio; the fas from the Retort through the
water into the Receiver. F F Fi Shelf perforated on which the Receiver atandt.

Mrs. B. We shall collect it in this receiver. For this purpose,
you observe, I first fill it with water, ia order to exclude the at-
mospherical air ; and then place it over the bubbles which issue
from the retort, so as to make them rise through the water to the
upper part of the receiver.

Emily The bubbles of oxygen gas rise, I suppose, from their
specific levity ?

Jkfr* B. Yes ; for though oxygen forms rather a heavy g^,«t
is light compared to watei^ You see how it gradually displaces tlS
water from the receiver. It is now full of s^, and I may leave it
inverted in water on this shelf, where I can keep the gas as long as
I choose, for future experiments. This apparatus (which is indis-
pensable in all experiments in which g^es are concerned) is called
a water- bath.*

Caroline. It is a very clever contrivance, indeed ; equally simple
and useful. How convenient the shelf is for the receiver to rest
upon under water, and the holes in it for the ^as to pass mto the re-
ceiver ! I long to make some experiments with this apparatus..

J\irs. B. 1 shalllry your skill that way, when you have a little
more experience, fl am now going to show you an experiment,
which proves, in a Very striking manner, how essential oxy^n is
to combustion. You will see that irqa itself will burn in this gas,
in the most rapid and brilliant mannerA

* A common large sized wash-tub, with a board 4 or 5 inches wide
fixed through the middle, and about 6 inches from the top, and filled
with water, will answer very well for a great variety of experiments
on the gases.— C.

427. How does the weight of oxygen g^ compare with that of

428. How may the great tendency of oxygea to produce corobut-
tion, be proved .^

Digitized by LjOOQIC



CaroUne, Really ! I did not kooir that it was possible to barn iroD.

Emily* Iron i6 a simple body, and you know, Caroline, tbat^ill
simple bodies are naturally positiridland therefore must ha^e airaf-
finity for oxygen. J

Mrs, B. Iron will, bowerer, not burn in atmospherical air with-
out a Terv great elevation of temperature ; but it is eminently com-
bustible in pure oxygen gas ; and what will surprise you still mor§.
m can be set on fire witTOut any considerable rise of temperature^
Vou see this spiral iron wire.* — I fasten it at one end to this cork;
which is made to fill an opening at the top of the glass receiver.

Fig. 18.

Emily, I see the opening in the receiver ;
but it is carefully closed by a ground glass-

Mrs. B, That is in order to prevent the gas
from escaping ; but I shall take out the stop-
per, and put in the cork, to which the wire
hangs. Now I mean to bum this wire in the
oxygen g^s, but I must fix a small piece of
lighted tinder to the extremity of it in order
to give the first impulse to combustion ; for,
however powerful oxygen is in promoting
combustion, you must recollect that it cannot
take place without some elevation of tempera- combaition of iron wirt u
ture. I shall now introduce the wire into the •*''«•" »"•

receiver, by quickly changing the stoppers.

Caroline, Is there no danger of the gas escaping while you
change the stoppers ? ^

Mrs. B. Oxygen gas is a little heavier than i^mospherical ai^
therefore it ^11 not mix with it very rapidly ; and if I do not leavC
the opening uncovered, we shall not lose aaj

Caroline. Oh, what a brilliant and beautiful flame !

Emily. It is as white and dazzling as the sun ! — Now a piece of
the melted wire drops to the bottom ; I fear it is extinguished ; but
no, it bums^igain as bright as ever.

Mrs. B. Qt will burn till the wire is entirely consumed, provided
the oxygenis not first expendedj for you know it can burn only
while there is oxygen to combine with it.

Caroline. I never saw a more beautiful light. My eyes can
hardly bear it ! How astonishing to think that all this caloric was
contained in the small quantity of g^ and iron that was enclosed
in the receiver ; and that without prodacing any visible heat !

Emily. How wonderfully quick combustion goes on in pure oxy-

* The combustion of steel, as a watch spring, is much more vivid
than that of iron. This affords a very beautiful experiment, and
w easily made after the pxygen is collected. A bottle of white glass
of a quart capacity does well as a receiver. An inch of water at
toe bottom will prevent its breaking. — C.

429. Why have all simple bodies an affinity for oxygen ?

430. Will iron burn in oxygen gas without an elevation of tem-

431. Which is lightest, oxygen gas or atmospherical air ?

432. How long will a piece of iron burn in oxygen gas)Dgle


gen gas I But pray, are these drops of burnt iron as beavy as the
wire was before ? ^

Mrs. B. They are even heavier ; for the iron^ burning, has ac-
quired exactly the weighti^f the oxygen whicnbas disappeared,
and is now combined with itl It has become an oxyd of iron:

Caroline. I do not know wriat you mean by saying that the oxy-
gen has disappeared^ Mrs. B , for it was always invisible.

Mrs. B. True, my dear ; the expression was incorrect. But
though you could not see the oxygen gas, I believe you had nodotibt
of its presence, as the effect it produced on the wire was sufficiently

Caroline Yes, indeed ; yet you know it was the caloric, and not
the oxygen gas itself, that dazzled us so much.

Mrs.B. You are nat quite correct in your turn, in saying the
caloric dazzled you ;\^r caloric is invisible ; it effects only the sense
of feeling ; it was the light which dazzled you|

Caroline. True ; but light and caloric are such constant com-
painions, that it is difficult to separate them, even in idea.

Mrs. B. The easier it is to confound them, the more careful you
should be in making the distinction

Caroline. But why has the water now risen and filled part of the
receiver ?

Mrs. B. Indeed, Carohne, 1 did not suppose you would have ask-
ed such a question ! I dare say, Emily, you can answer it.

Emily Let me reflect . . The oxygen has combined with the
wire ; the caloric has escaped ; consequently nothing can remain
in the receiver, and the water will rise to fill the vacuum.

Caroline. I wonder that I did not thinly of that. I wish that we
had weighed the wire and the oxygen gas before the combustion ;
we might then have found whether tho vreight of the oxyd was equal
to that of both-

Mrs.B. You might try the experiment if you particularly wish-
ed it ; but I can assure you that, if accurately performed, it never
fails to show that the additional weight of the oxyd is precisely equal
to that of the oxygen absorbed, whether the process has been a real
combusiion or a simple oxygenation.

Caroline. But this cannot be thf case with all combustions in
general ; for when any substance 's burnt in the common air so far
from increasing in weight, it is evidently, diminished, and sometimes
entirely consumed.

Mrs. B. But what do you menu by the expression consumed.^ You
cannot suppose that the smallest particle of »ny substance n nature
can be actually destroyed. A compound body is decomposed b^
combustion ;(some n( its constituent parts fly off in a gaseous form
nvhile others KMnain in a concrete state ; the former are called th^
\olalile^ the latter {\\e fixed products of combustioin But if we col-
lect the whole of them, we sh^ll always fin(J thatTthey exceed the


433. Why will the component parts of a compound body that has
been decomposed by combuKtion, weigh more than the compound
body did ?

434. What is the impropriety in saying that a person is dazzled
by caloric ?

435 Can a particle of any substance be actually destroyed ? /I P

436. What is the fixed product in combustion ?

437. What is the volatile product in combustioiiGoogle


weight of the combustible body, by that of the oxygen which has
combined with them during combustion.

Emily. In the combustion of a coal fire, then, I suppose that the
ashes are what would be called the fixed product, and the smoke
the volatile product ?

Mrs, B. Yet when the fire bums best, and the quantity of vola-
tile products should be the greatest, there is no smoke ; how can
you account for that ?

Emily, Indeed 1 cannot ; therefore I suppose that I was not right
in my conjecture.

•Hrs, B. Not quite ; ashes as you supposed, are a fixed product
of combustion ; but smoke, properly speaking, is not one of the vo-
latile products, as it consists of some minute undecomposed particles
of coals which are carried off by the heated air without being
burnt, and are either deposited in the form of soot, or dispersed by
the wind. Smoke, therefore, ultimately becomes one of the fixed
products of combustion. As you may easily conceive that the
^ronger the fire is, the legs smoke is produced, because the fewer
7)articles escape combustio^ On this principle depends the inven-
tion of Argand's Patent Lamps ; a current of air is made to pass
through the cylindrical wick of the lamp, by which means it is so
plentifully supplied with oxygen, that scarcely a particle of oil es-
capes combustion, nor is there any smoke. produced.

Emily, But what then are the volatile products of combustion ?

Mrs. B, Various new compounds with which you are not yet ac-
quainted, and which being converted by caloric either into vapour
or gpas, are invisible : but they can be collected, and We shall exam-
ine them at some future period.

Caroline. There are then other gases, besides the oxygen and ni-
trogen gases.

Mrs. B, Yes, several ; any substance that can assume and main-
tain the form of an elastic fiuid at the temperature of the atmos-
phere, is called a gas. We shall examine the several gases in their
respective places ; but we must now confine our attention to those
which compose the atmosphere.

I shall show you another method of decomposing the atmosphere,
which is very simple. Ho breathing, we retain a portion of the ox-
ygen, and expire the nHrogen gas ; so that if we oreathe in a clos-
ed vessel, for a certain ]ength of time, the air within it will be de-
prived of its oxygen ffaw which of you will make the experiment?

Caroline. I should bowery glad to try it.

Mrs. B. Very well; breathe several times through this glass tube
into the receiver with which it is connected, until you feel that your
breath in exhausted.

Caroline. 1 am quite out of breath already !

Mrs, B. Now let us try the gas with a lighted taper.

Emily, It is very pure nitrogen gas, for the taper is immediately

Mrs. B. That is not a proof of its being pure, but only of the ab-
sence of oxygen, as it is that principle alone which can produce
combustion, every other gas being absolutely incapable of it*

* This does not agree with the opinion that chlorine and iodine
are simple bodies, since they are both supporters of combustion.-C

438. Why is there no smoke when the fire bums best ?

439. How c^u the atmosphere be decomposed by breathing |


EmUy* Id (he methods which yoa have riiown as, for decompo^
sing the atmosphere, the oxygen always abaadons the nitrogen ;
but is there no way of taking the nitrogen from oxygen, so as to
obtain the latter pure from the atmosphere?

JIfrf. B. You mustobserre, that whenever oxygen is taken from
the atmosphere, it is by decomposing the oxygen gas ; we cannot do
the same with the nitrogen gfas^ecause nitrogen has a stronger af-
finity for caloric than for any Mher known principle ; it appears
impossible, th^fore, to separate it from the atmosphere by the pow-
er of affinities^ But if we canngt obtain the oxygen g^ by this
means, in its ^arate state, we have no difficulty (as you have seen)
to procure it in its gaseous form, by mken it firom those substances
that have absorbed it from the atmosphere, as we did with the oxyd
of manganese.

' Emiiy. Can atmospherical air be recomposed, by mixing due
proportiona,of oxygen and nitrogen gases ?

Mrs. B^TYcs : if about one part of oxygen g^as be mixed vUh
about founparts of nitrogen gas, atmosplierical air is produced^

Emily, The air, then, myst be an oxyd of nitrogen ?

Mrs. B. No, my dear i^r it requires a chemical combination
between oxygen and nitral^eD io order to produce an oxyda whilst
in the atmosphere these two substances were separately clmibined
with caloric, forming two distinct gases, which are simply mixed in
the formation of the atmosphere.

I shall say nothing more of oxygen and nitrogen,' at present, as
we shall continually have occasion to refer to Uiem in our future
conversations^ They are both very abundant in nature ; £itrogen
is the most plentiful m the atmosphere, and exists also in ali animal
substances ; oxvgen forms a constituent part both of the animal and
vegetable kingdoms^ from which it may oe obtained bv a variety of
chemical meansS But it is now time to conclude our lesson. I am
afraid you have learnt more to-day than yon will be able to remem-

Caroline, 1 assure you that I have been too much interested in
it, ever to forget it. In regard to nitrogen th^re seems to be but
little to remember ; it makes but a very insigfnificant figure in com-
parison to oxygen, although it composes a much larger portion of
the atmosphere.

Jirr«. B^ Perhapsthis insignificance you complain of, may arise
from th^ompouna\iature of nitrogen, for though I have hitherto
considered it as a simple body, because it is not known in any nat-
ural process to be decomposed, yet from some experiments of Sir H.
Davy, there appears to be reason for suspecting that nitrogen is a

* The proportion of oxygen in the atmosphere varies from 21 to
22 per cent.

440. Why may not oxygen be taken from the atmosphere so as to
Itaxe the nitrogen pure ?

441. How can atmospheric air be produced by the union of oxy-
gen and nitrogen ?

442. Why is not the union that takes place between oxygen and
nitrogen in the production of atmospheric air, an oxyd ?

443. Where do oxygen and nitrogen exist?

444. Is nitrogen a simple or a compound substance^^ i

Digitized by VjOOQIC


oompoiuk] body» as we ahaU Me afierwerds. But eren in its simple
state it will not appear so insigpnficant when you are better ac-
qoainted with it ; loir though it seems to perform but a passive part
in the atmosphere, and has no yery striking properties, when con-
sidered in its separate state, yet you will see oj and by what a very
important agent it becomes, when combing with other bodies. But'
no more of this at present ; we must reserve it for its properplace.



Caroline. The next simple bodies we come to are chlorine and
lODms. Pray what kind of substances are these ? Are they also
invisible ?

Jirs. B, No; /lor chlorine, in the state of g^, has a distinct
greenish color, Md is therefore visibly and iodine, in the same
state, has a beautiful claret-red colour J These bodies, 1 have al-
ready informed you, are, like oxygen ,jindowed with the negative
electricity ; but the explanation of their properties, implies various
considerations, which yon would not yet oe able to understand ; we
shall therefore defer their examination to some future conversation,
and we shaH go on to the next simple substance, htbrogem, which
we cannot, any more than oxygen, obtain in a visible or palpable
form. We are acquainted with it only in its gaseous state, as we
are with oxygen and nitrogen.

Caroline. But in its gaseous state it cannot be called a simple
substance, since it is combined with heat and electricity P

JIfrt. B. Tnie, my dear; but as we do not know in nature, of any
substance which is not more or less combined with caloric and elec-
triqit]r, we are apt to say that a substance is in its pure state when
conibined with tnose ag^ents only.

Hydrogen was formerly c^WeA/r^mmabU airi as it is extremely
combustible, and bums with a gfiieat flame. Siute the invention of
the new nomenclature, it has obtained the name of hydrogen, which
is derived from two Greek words, the meaning of which wno prO'
duee vfate/\ V

Emiiy^kud how does hydr^ejLj>roduce water ?

J^rt. B. /By its combustionT /Water is composed of 89 parts, by
weigh . of oxygen, combined witti 11 parts of hydrogen ; £r of two
parts, by bulk, of hydrogen gas, to one part of oxyg^en gasfS

Caroline. ReaHy ! is it possible that water should be a c/nbina-
tioD of two gfases^ and that one of these should be mflammable air !
Hydrogen must be a most extraordinary gas that will produce botU
fire ana water.

Emhf. But I thought ^ou said that combustion could take place
in no gas but oxygen.

445. Of what color are chlorine and iodine ?

446. What d' esthe term hydrogen signify ^

447. What was it formerly called f

448. How doeshydro|nen produce water ?

449. In what proportums do oxygen and hydrogen conibineto
produce water .> 10 Cc^f^aXo

Digitized by VjOOQ IC


Jtfrf • JB. Do you recollect what the process of combustion coD'

sists in i

Emily, In the combinatioii of a body with oxygen, with diseu'
gagement of light and heat

Jdrs. B. Thi^'efore when 1 say thi^ hydrojpen is combustible, I
mean/l^at it has an affiaitf for oxygen^ bnt, like all other combnsti-
ble substances, it cannot burn unless supplied with oxygen, and also
heated to a proper temperature.

Caroline. I'he simply mixing 1 1 parts of hydrogen, with 89 parts
rof oxygen ffas, will not. therefore, produce water.

Jlfr« BfSoi water being a muchdenser fluid than rases, in or-
der to reduce these g^ases to a liquid/tt is necessary to diminish the
quai^ity of caloric or electricity whibb maintains tnem in an elastic
form, j

Emily. That I should think mieht be done by combining the
oxygen and hydrogen together ; for in combining, they would give
out their respectiye electricities in the form of caloric, and by this
means would be condensed.

CaroUrv, But you forget, Emily, that in order to make the oxy-
gen and hydrogen combine, you must be^in by elevating their tem-
perature, which increases, instead of dimmishmg, their electric en-

Mrs B. Emily is, however, right ; for though it is necessary to
jraise their temperature, in order to make them combine, as that
combination affords them the means of parting with their electrici-
ties, it 18 eventually the cause of the diminution of electric energy.

Caroline. You love to deal in paradoxes to-day, Mrs. B, Fire,
then, produces water.

Mrs. B. The combustion of hydrogen eas certainly does ; but
you do not seem to have remembered the theory of combustion so
well as you thought you would. Can you tell me what happens in
the comoustion of hydrogen gas ?

Caroline. (The hydrogen combines with the oxygen, an4their op-
posite electmities are disengaged in the form of caloricJ Yes, I
think I understand it now— by the loss of this caloric, thegases are
condensed into a liquid.

Emily- Water, then, I suppose, when it evaporates and incorpo-
rates with the atmosphere, is decomposed, and converted into by-
drcM^en and oxygen gases.

Mrs. B. No, my dear— 4here you are quite mistaken : itne de-
composition of water is totally different from its evaporatmn ; for
in the latter case (as you should recollect) water is only in a state of
very minute division ; and is merely suspended in the atmosphere,
witnout any chemic^ combination, and without any separation of
its constituent parts* \ As long as these remain combined, they form
WATER, whether interstate of liquidity, or in that of an elastic fluids
aa vapor, or Under the solid form of ice.

450. When it is said that hydrogen is combustible, what is inten-

461 . Will simply mixing eighty five.ptrts of oxygen and fifteen
of hydrogen, produce water f

452* What U necessary ?

453. What happens in the combustion of hydrogen gas ?

454. What is the difference between the decompositioa and erap-
oration of water? ^ ^ . *^ ,

Digitized by VjOOQIC



In our experiments on latent heat, yon may recollect that we
caused water successively to pass throo|^h tbese three forms, merely
by an increase or diminution of caloric, without employing any
power of attraction, or effecting any decomposition

Caroline. But are there np iiiean.« of decomposiog water ?

J^rs. B. Yes. seyeral ; feharcoal, and metals, when heat ed red hot,
will attract the oxyren from water, in the same manner as they will
from the atmospheroN

Caroline, Hydrogen, I see, is like nitrogen, a poor dependant

Online LibraryMrs. (Jane Haldimand) MarcetConversations on chemistry .. → online text (page 13 of 43)