Mrs. (Jane Haldimand) Marcet.

Conversations on chemistry .. online

. (page 15 of 43)
Online LibraryMrs. (Jane Haldimand) MarcetConversations on chemistry .. → online text (page 15 of 43)
Font size
QR-code for this ebook

of a candle?^

Jlfrt. B./rhe regular steam of hydrogen ga3, which exhales from
its combusQble matter.\

Caroline. But the h^rogen m must, from its great levity, as-
cend into the upper regions of the atmosphere ; why, therefore,
does not the flame continue to accompany it ?

Jin. B. The combustion of the hydrogen gas is completed at the
point where the flame terminates : it then ceases to be hydrogen
gas, as it is converted, by its combination with oxygen, into watery
,vapour ; but in a state of such mmute division as to be invisible.

Caroline. I do not understand what is the use of the wick of a
candle, since^the hydrogen gas bums so well without it.

Mrs, B, /The combustible matter of the candle must be decom-
posed in order to emit the hydrogen gas : and the wick is instru-
mental in effecting this decomposition. Its combustion first melts
the combustible matter, and—

CaroUne. But, in lamps, thexombustible matter is already ^nid,
and vet tbey also require wicks.

Jttrt . B. I am gomg to add, that afterwards, the burning wick
(by the power of capillary attraction) gradually draws up the fluid
to the point where combustion takes place ; foi you must have ob-
served that the wick does not burn quite to the bottom.}

'^Or rather kudro-earhonai^ a gas composed of hydr^eil and car-
bon, which will be noticed under the head Carbon,

f/The candle also contains carbon, which fives brilliancy to the
flaiAe, and the product of combination besi&s flame and water is
a quantity of carbonic acid.WC.

» I. I ■ II. ■ ■ " ■ / .^ I .. ■

481. WhiiU%i»aiidiiiiih»noUofthehvriwngofacmidU7
48t. What is flame >

483. How lonff will coals bum with flame ?

484. To what is the regular shape of the flameof a candle owing ?

485. If the flame of a candle is produced by Hydrogen gas, why
i« the wick iDiecesiaryf ^ ,

Digitized by LjOOQ IC


Caroline. Yes ; but I do not understsad wfa j it does Dot.

Mrs, B. Because the air has not so free an acceta to that part of
the wick which is immediately in contact frith the candle as to the
pdrt just aboye, so that the heat there is not sufficient to produce
Its decomposition ; the combustion, therefore, begins a little above
this point.*

Caroline. But, Mrs. B., in those beautiful lights, called gas
lights, which are now seen m so manj streets, and will, 1 hope, be
soon adopted erery where, I can perceive no wick at all. .How
are these lights managed ^

Mrs. B, I am glad you have put me in mind of saying a few
words on thisvery useful and important improvement In this mode
of lightingyfne gas is conveyed to the extremity of a tabe, where
it is kindled^nd burns as long as the supply continues^ There is
therefore, no occasion for a wick, or any other fuel whatever.

Emily. But how is this gas procured in such large quantities ?

Mrs. B. It is obtained from coal, by distillation. Coal, when
exposed to heat in a close vessel, is decomposed ; and hydrogen,
which is one of its constituents, rises in the state of gas, combined
with anothecof its component parts, carbon, forming a compound
gas, called (tydro-Carhonat^ihe nature of which we shall again
have an opportunity of noticing when we treat of carbon. This
gas, like hydrogen, i* perfectly transparent, invisible, and h ghly
inflammable ; and, in burning, it emits that vivid light which you
have so often observed.

Caroline. And does the process for procurrag it require nothing
but/neating the coals, and conveying the gas through tubes ?

Mk8 B. Nothing else, except that the gas must be made to pass,
immediately at its formation, through two or three large vessels of
water,! in which it deposits some other ingredients, and especially

ter, tar. and oil, which also arise from the distillation of cpalsS
. je gas-light apparatus, therefore, consists simply in a large ireor
essei, in which the coals are exposed to the heat of a furnace,-^
some reservoirs of water, in which the gas deposits its impurities,
and tubes that convey it to the desii^ spot, being propelled with
uniform velocity through the tubes by means of a certain degree of
pressure which is made upon the reservoir.N

* In the burning of a candle, the reason why combustion does not
take place in immediate contact with the tallow, is, thati^e caloric
is here employed in converting' a solid into a fluid, as explained in
the conversation on free calonc. In the burainr of a lamp, if the
same thing takes place, it is because the metaUictube through
which the wick passes, conducts off'the hcat.V C.

f The gas is passed through one vessel of ^cked lime and water
to absorb the carbonic acid gas, with which it is always more or
less mixed, when first distilM.— C.

486. Why is it that the wick of a candh does not bum to the bot-

487. How are gas lights made to bum without wicks?

488. What is the gas called, used in lighting the streets of some
large cities ?

489. How is it obtained ?

490* Of what does the gas light apparatus consist ?

Digitized byV^OOQlC


Emily, Wbatan admirable coDtriyanoef Doyon not think, Mrs.
B., that it will soon be uniyenally adopted?

Jlfr#. B. Most probably ; ^r the purpose oflighting' streets, offi-
ces, and public places, it rar sWpasses an v former inyeotion A but in
regard to the interior of prirate houses, this mode of lightingp4ias not
yet been sufficiently tricNl to knoir whether it will be found gene-
rally desirable/either with respect to economy or conrenience. It
may, however, be considered as one of the happiest applications of
chemistry to the comforts of life ; and there is every reason to sup-
pose that it will answer the full extent of public expectation. »

I have another experiment to show you with hydrogen pas, which,
1 think, will entertain you. Have you ever blown bubbles with
soap and water ?

Emily, Yes, often, when I was a child ; and I used to make them
float in the air by blowing them upwards.

Mrs, B, We shall fil some bubbles with hydrogen gasJinstead
of atmospheric air, md you will see with what ease and^pidity
they will ascend, without the assistance of blowing, from the light-
ness of the gas.— Will you mix some soap and water, whilst f fill
this bladder with the g^ contained in the receiver which stands on
the shelf in the water bath ?

CaroUne. What is the use of the brass-stopper and turn-cook at
the top of the receiver ?

Mr$, B. It is to atTord a passage to the gas, when reouired. There .
is, you see, a similar stop-cock fastened to this blaader, which is
made to fit on the receiver. I screw thekn one on the other, and
now turn the two cocks, to open a communication between the re-
ceiver and the bladder ; then, by sliding the receiver off the shelf,
and rently sinking into the bath, the water rises in the receiver,
and forces .the gas into the bladder. (Fig. 23, No. I.)

Caroline, Tes. I see the bladder swell as the water rises in the

Jlfrt . B» I think that we have already a sufficient quantity in the
bladder for our purpose ; we must be careful to stop both the cocks
before we separate the bladder from the receiver, lest the g^s should
escape. — Now I must ^;f. a pipe to the stopper of the bladder, and by
dippmg its mouth into the soap and water, take up a few drops : then .
I again turn tbe cock, and squeeze the bladder, m order to force the
gas into the soap and water, at the mouth of the pipe. (Fig. 23, No«

Emily, There is a bubble; but jt bucsta tefSow it leaves tb»
nouthof the pipe.

Mrs. B» We must have patience and try Ag^r; It is pot sp easy
to l^ow bubbles by means of a bladder, as simply with the bceath^

Psro/tne. F^rl^^ps there is not soap enopgh in the water. I sbonld
kavehad warm water ; it would have dissolved the soap better^,
^nii/y. Does jQQt some of the ^jeacapel>cttweeQ.||iieb]badd9riM|4

\ «k*^^

.^1. What is said of lighting streets, offices, and public places
^tb this g^ f

gt Hiow can bnbblesof soap and water be oiade (• float ia'lbe«il?
^ How can these bobbles be made so as to explode on settnr ^ .
tothsm? (See page 123.) n i

^H^ What is represented in 23, No. 1 and 2f ^ "^^ ^^ Google ^


Apfwrttat for tnuMftrriof fMc« from a R«oeiT«r into a bUddcr. No. 9. Appantot for
blowiof Smp bat>bIei.*N

Mrs. B, No ; Oi6y are perfect^' air ti^t ; we sball succeed pre-
setitty, I dare say.

CaroUne. Noir a babble ascends ; it moves irith the rapidity of a
balloon. Hoir beantifuil^ it refracts the light.

Emify, It has burst against the ceiHng — jou succeed now won-
derfully ; but why do they all ascend and burst against the ceilinr f

Mrs, B. Hym^n gas is so mdch hitter than atmospherical an*,
thttl it ascends rapidly with its very light envelope, which is burst
by the force with which it strikes tbe4:eiUnjg. ^

^r-bMOons are filled with, this gas^jandif they carry no <yther
w6Mt than their covering, would ascentfas rapidly as these bujbfbles*

OaroKne. Tet their covering most be much heavier than that of
these bobbles ?

Mrs. B. Not in proportion to the quantity of gas th^ contaift.
I lAo net know n^hetfaer you have ever neen present at the iilling of
Jk large balloon. The apparatus for that purpose is very simple.
Utconsfsts of a number of vesslels, either jars or barrels, in wbich the
\[iaterials for the formation of the gas are mixed, eacb of these be-
ing furnish^ wilba tube, and communici^^ng with a long flexible .
pipe ffWch conveys the gas into the baUoonij

EntHy. But the fire-ba^hxms which were flrst invented, and hate
been since abandoned, on aooount of their being so dangeroiil»
wQre constructed* I soApose, oa a Hi«M<mt principle. >.

Mr9. B. ^jfhey were filled simply with^tbnotpbencal airJoonskler-

494. With what are air ballooas filled ?

495. What it fheapparatnt for Wng m hfge battoon with 1iydf»-

49lrWith what wve fire balkmiffiM? r- i

497. Whywerathey^bandooelf Digitized by L^oogle

Mj rarefied by heat ; an^UtSe neoewity of baying a fire undemeatb
tbe balloon, in order to preserve the rarefaction ^ tbe air witbin it,
was the circumstance productive of so much daog^ei^

If yoa are not let tired of experiments, 1 have niother to show
you. It consists In filling soap*bubbles with a mixture of hydrogen
and oxygen g^asi^Hn the proportiooa that form water ; and after-
wards setting fire to thern^

EnUhf, They will detonate, I suppose.

Mrt, B, Tes, they will. As you haye seen the method of trans-
ferring tbe gas from the receiver into the bladder, it is not necessa-
ry to repeat it I haye therefore provided a bladder which coi^tainB
a due proportion of oxygen and hydrogen gases, autd we have only
to blow bubbles with it.

Caroline. Here is a fine large bubble rising— shall I set fire to it
with a candle ?

•Wir*. B. If you please—

Caroline, Heavens, what an explosion I* It was like tlie report
of a ^eo : [ confess it frightened me much. I never should have
inagined it could be so loud.

J5tfi%. And ^be flash was as vivid as lighting.

Mrs. B. The combination of the two gases take place during
that instant of time that you see the flash, and hear tbe detonation.

Emily, This has a strong resemblance to thunder and lightning.f

Mrs. B. These phenomena, however, are generally of an electri-
fitA. nature. Tet various meteproligical effects may be attributed
to accidental detonations of hydrogen gas in the atmosphere ; for
iiiatore abounds with hydroj^en ; it constitutes a very considerable
portion of ilie whole mass of water belonging to our globe, and from
that source almost every body obtains it. It enters into the com-
position of all animal su^ances, an4.flfa|^reat number of minerals ;
nut it is most abundan(fin v^etablesT^^rom this immense variety
of bodies it is often Jpontaneously ^scharged ; its gpreat levity
nmkes it rise into the superior regions of the atmosphere ; and
<wheo, either by an electrical spark, or any casual elevation of tem-
perature, it takes fire, it may produce such meteors or luminous
appearances as are occasionally seen io tbe atmosphere* Of this
kind are probably those broad flashes which i^m often see on a
summer evening, without hearing any detonationTl

Emily. Every flash, I suppose, must produce a ^antity of water?

Caroline. And this water, naturally, descends in the form of rain.

Mrs. B. That probably is often the case, though it is not aneces-

* In making this experiment, always be careful to turn the stop-
coek, or detach the bubble completely from tbe pipe before it is set
^f^ to ; otherwise a sad accident may happen from tbe gas takinfif
ire in the bladder.— C.

^ .^he report js owing to the air, rushing in to fill the vacuum,
^smtA by the condensation of the two gases, and the heat extrica-
ted tX the same instaotV-C.

'4i)8.i Row can babbles be made of soap and water so as to ex-
plode with a loud report, on setting fire to them ?
499. To %ohat Uil said in ik9noU thai lher^a<n^ is owing t\
fiOO, In what substances is hydrogen most abundant }
591. How may heat lightning be aeoonnted for f

Digitized by VjOOQIC -


sary coosequence ; for the water may be dissolved by the atmds-
pbere, as it descends towards the lower regions, and remain there
m the form of clouds.

The application of electrical attraction to chemical phenomena is
likely to lead to many very interesting discoveries in meteorology ;
for electricity evidently acts a most important part in the atmos-
phere. This subject, however/sj as yet, not sufficiently developed*\
for me to venture enlarging upA? it. The phenomena of the atmos-v^
phere are far from being well understood : and even with the little
that is known, 1 am but imperfectly acquainted.

But before we take leave of hydrogen, I must not omit to men-
tion to yon a mo^t interesting discovery of Sir H. Davy, which is
connected with this subject.

Caroline, You allude, I suppose, to the new miner's lamp, which
has of late been so much talked of. I have long been desirous oC
knowing what that discovery was, and what purpose it was intend-
ed to answer^

Mrs. Bylt often happens in coal-mines, that quantities of the gas
called by chemists hydro- carbonate or by the vomers fire damp, (the
same from which the gas lights are obtained,) ooze out from the fis-
sures in the beds of coal, and fill the cavities in which the men are
at work ; and this gas being inflammable, the consequence is, that
when the men approach those places, with a lighted candle, the g^
takes fire, and explosions happen, which destroy the men and horses
employed in that part of the coUiei^y, sometimes in great nnmbers'T)

Emily, What tremendous accidents these must be ! But whenS^
does that gas originate ?

Jtfrx. B, ^eing the chief product of the combustion of coal, no
wonder thaViDflammable gas should occasionally appear in situa-
tions in which this mineral abotinds, since there can be no doubt
that processes of combustion are frequently taking place at a great
depth under the surface of the earth ; and, therefore, these accumu-
lations of gas may arise either from combustions aetually going on,
or from former combustions, the gas having perhaps been confined
there from agesj|

Caroline. Auil how does Sir li. Davy*i lainp prevent those
drdadful explosions ?

Mrs. B, By a contrivance eqiially simple and ingenious ; and
one which does no less credit to the philosophical views from which
it was deduced, than to the philanthropic motives from which the
inquiry sprung. The principle of the lamp is shortly this : fli was
ascertained two or three years ago, both by Mr. Tenant, and^by Sir
Humphrey himself, that the combustion of inflami^iable gas could
not be propagated through small tubes; so that if a jet of an inflam-
mable gaseous mixture, issuing: from a bladder, or any other vessel,
through a small tube, be set fire to, it burns at the orifice of the
tube, but the flame never penetrates into the vessel.\ It is upon this
fact that Sir Humphrey's safety lamp is founded. J

Emily. But why does not the flame never penetrate through the

60^. Is it supposed that the subject of meteorology is well under-
stood ?

50% What disastrous eff'ects often happen in coal-mines ?

504. WhoDce does the hydrogen gas in mines originate ?

605. Upon what discovery of Mr. Tenant and SirH. Davy wat
the miner's safety lamp founded ? ° s'*'^^^ ^y ^OOg I


tube into the ▼•stel from which the gat isiaes, so ai to explode at
once the whole of the gta ?

Mrs. l(.Aecaa8e, no doubt, the inflamed gas is so much cooled
in its -passage through a small tube as to cease to burn before the
combustion reaches the reservoi^

Caroline, And how can this principle be applied to the construe*
tion of a lamp?

Jlfr#. B. Nothing easier. Tou need only suppos^Ai lamp enclo-
sed all round in glass or horn, but having a number 0^ small opea
labes at the bottom, and others at the .top, to let the air in and oun
/^ow, if such a lamp or lanthom be carried into an atmosphere ca<^
^pable of exploding, an explosion or combustion of the gas will take
place within the lamp ; and although the vent afforded by the tubes
will save the lamp from bursting, yet from the principle just ex-
plained, the combustion will not be propagated to the external air
through the tubes, so that no farther consequence will ensued
Emily. And is that all the mystery of that valuable lamp ?r
Mrs, j5. No ; in the early part of the inquiry, a lamp of this kind .
was actually proposed ; but it was but a naie sketch compared to
its present state of improvement. Sir H. Davy, after a succession *
of trials, by which he brought his lamp nearer and nearer to per-
/ection, at last conceived the happy idea that if the lamp were sur-
rounded %vith a wire-wick or wire-gauze, of a dose texture, instead
of glass or horn, the tubular contrivance 2 have just described
would be entirely superseded, since each of the insterstices of the
^nze would act as a tube in preventing the propagation of explo-
sions : so that this pervions metallic covering would answer tlie va-
rioos purposes of transparencv^ of permeability to air and of pro-
tection afi^ainst explosion. This idea, Sir Humphrey immediately
submitted to the test of experiment, and the result has answered
his most sanguine expectations, both in his laboratory and in the
colleries where it has already been extensively tried. And he has
now the happiness of thinking that his invention will probably be
the means of saving, every year a number of lives, which would
have been lost in digging out of the bowels of the earth one of the
most valuable necessaries of life. Here is oneof these l|J»ps, every
part of whic^ you will at once comprehend. /(Fig. 24.) )

Caroline. How very simple and ingenious LBut I do«ot yet well
see wliy an explosion takinr place within the lamp, should not
communicate to the external air around it, through the interstices
of the wire f

^frM. B. This has been a/nd is still a snbjeot of wonder^ even to *
philosophers ; and the on^ mode they have of explaining it isy that
flaeie or igoiti<3n cannot pass through a fine wire-work, liecause
the metallic wire cods the flame sufficieDtly to extinguish it in
pissing through the gsuze. This property of the wire-gauce is
Quite similar to that of the tubes wbicfa 1 mentioned on fntroduoing
the subject ; for you may consider, each iolerstKe of thegaoae as.
an extremely shdrt tube of a veny small diameter.

506. Why does not flame penetrate through a tube that oonveys
I*ydrogen gas so as to produce an explosion?
^. How would you describe the miner's lamp ? '
m^ What is the use of the miner^ lamp ?
509. Which figure represents tlte miner s lamp ?


Digitized by LjOOQ IC

126 flULPBlUXt

EmVy. Dot I should expect the Fig. 24.

wire would often become re
the buroiDg^of Ibegsis withio

Mrs, B, And this is acti
case ; for the top of the lam
apt to become red* hot. Bu
ately, such inflammable, g^as<
tures as are found in themin
be exploded by the red hot
intervention oi actual flame
quired for that purpose j si
wire does not set fire to me
gas around it.

Emily. I can understand
if the wire be red hot, how c
the flame within, and prevei
sing through the gauze ?

^rs, B, The gauze, thoug
is net so hot as the flame bj
. has been heated ; and as
wire is a good conductor*
does not much accuniulate i
passes ofl" quickly to the o'th<
the lamp, as well as to any c

Carfiine. This is indeed i
teresting discoFCry, and o
shows at once the immen
with which science may be
ly applied to some gf the m<
ti^Qt purposes*



Jtfr*. B, Sulphur is the
stftDce that comes under o
eratioD. It diifera in one
point/rom the preceding, \
in a solid forii^^^ the temp
tlie Mmospfaer^

Coi/twc. I arfii glad that

taftta 8(^id body to examine : one that a. th« «i«ura eonuiniar ih« oo. 9. am
we can see and touch. Pray, is it notri« <» amw by .h ch ib« i aus« c*^ « in4
with siHfibiir that the points of m^Uih^^^^'':\^,^;^r^^;;':j7Si'S,
es are covered, to make them easilyF.tiM«w*KattMe7i«iKi«r. g. »4t«Mki«upi
kindle .'


510. What is necessary to produce explosions in inflammable
gaseous mixtures ?

511. In what state dbes sulphur exist ?

Digitized by LjOOQ IC



•Wr#. B, Y«», it it ; and yoa therefore, already koovr, that sulphur
IS a very comlrastible substance. It is seldom discovered in nature
io a pure unmixed state ; sogreat is its affinity for other substances
that It is almost constantly found combined with some of them. It
18 most commonly united frilb metals, under various forms, and is
separated from them by a very simple process. It exists, likewise,
in many mineral waters, and some vegetables yield it in various pro-
portions, especially those of the cruciform tribe. It is also found
in animal matter ; in short, it may be discovered/in greater pr less
quantitv in the mineral, verelable, and animal kingdom^

Emily. I have heard otjlowerg of sulpkur-^sre they tlfi produce
of any plant ?

Mrs, B, By no means ; /hey consist of nothing more than com-
mon sulphur reduced in aVeiVfine powder by a process called
sublimQiioj^-^You see some of it in this phial ; it is exactly the
same substnice as the lump of sulphur, only its color is a paler yel-
low, owing to its state of very minute division,
^ini/y. Pray %?hat is sublimation ?

•^r*' .•/** '* ***® evaporation, or more properly speaking, the
yolatilizatidq of solid substances, which, in cooling condense agaia
into a concrete form^ The process, in this instance, must be per-
tormed in a closed vAsel,botb to prevent combustion, which would
Jake place if the access of air were not carefully precluded, and
likew ise> iix order to collect the substance after the operation. As it
IS rather a slow process we shall not try the experiment now ; but
you will understand it perfectly if I show you the apparatus used for
tbe pnrpo^. (fig. 25.) Some lumps of sulphur are put into a receiver
F17. 25. of this kind, which is called a cucurbit

Its shape you see somewhat resembles
that of a pear, and is open at the top, so
as to adapt itself exactly to a kind of con-
ical receiver of this sort, called the head.
The cucurbit, thus covered with its bead
is placed over a sand-bath ; this is nothing
more than a vessel full of sand, which ia
kept heated by a £umace,such as you see
here, so as to preserve the apparatus ipm
moderate and uniform temperature.^h«
sulphur then soon begins to melt,ana im-
mediately after this a thick white smoke
rises, which is g^mdually deposited within
the head, or upper part of the apparatus,
where it condenses ag^nst the sides,
somewhat in the form of vegetation,
whence it has obtained the name of flow*
^ "J* " ers of sulphuro This apparatus, which

c. Furoae*.'^ all kwds of distulations, as you will sot

* The sulphur of commerce is chiefly obtained^n the vicinity of

512. In what may it be found ?

513. How do the flowers of sulphur differ from sulphur in a solid

514. What is sublimation? [state!

515. What does figure 25 represent ?

516. From what is the name " Flowers of sulphurf-deri^d ?

138 •WLVBVM.

when we come to treat of those operatioDS. Alembics ara Bot
commonly made of glass^ like this which is apf^cable only to dis-
tillation upon a very small soale. Those nseo in manafactares are
generally made of copper, and are of coarse considerable larg^er.
The general constrnction, howeyer, is always the same, although
their shape admits of some variation.

Caroline. What is the use of that neck, or tube, which bends

Online LibraryMrs. (Jane Haldimand) MarcetConversations on chemistry .. → online text (page 15 of 43)