Mrs. (Jane Haldimand) Marcet.

Conversations on chemistry .. online

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JUrs. B» I have now drawn it asunder, and am going to blow a
ball at one of the heated ends ; bat 1 must previously close it np
and flatten it with this little metallic instrument, otherwise the
breath would pass through the tube without dilating any part of it.
— NoiV" Caroline, will you blow strongly into the lube whilst the
. tlosed end is red hot ?

Emily, You b\ow too hard; for the ball suddenly dilated to a
great size, and then burst into pieces.

Mrt, B. You will be more expert another time ; butl must cau-
tion you, should you ever use this blow-pipe, to be very careful that
the combustion of the alcohol does not go on with too great vio-
lence, for I have seen the flame sometimes dart out with such force
as to reach the opposite wall of the room^ and set the paint on fire.
There is, however, no danger of the vessel bursting, as it is provi-
ded with a safety tube, which affords an additional vent for the va-
pour of alcohol when required.

The products of the combustion of alcohol consist in^ great pro-
portion of water, and a small quantity of carbonic acid^ There is
DO smoke or fixed remains whatever — How do you account for
that, Emilv I

Emily. I suppose that the oxygen which the alcohol absorbs in
burning, converts its hydrogen mto water, and its carbon into car-
bonic acid ffas, and thus it is completely consumed.

Mrs, B, Very well.— iJ/Aer, the lightest of all fluids^ and with
which you are well acquainted, is obtaine4(?com alcohoH ot which
it forms the lightest and most volatile part.^ ^

Emily. Ether, then, is to alcohol, what alcohol is to brandy.

Mrs. B. No ; there is an essential difference. /In order to ob-
tain alcohol from brandy, ypu need only deprive the latter of its
water; but ioj the fprmati^^ ^f ether; the alcohol ^ust be decom-
posed, and one of its cortstitacfnts partly subtracted^ I leave you to
guess which of them it is. ^

Emily. It cannot be hydrogen, as etber is more volatile than al-
cohol, and hydrogen is the lightest of all its ingredients .* nor do I
suppose that it can be oxygen, as alcohol contains so small a propor-
tion of that principle ; it is, therefore, most probably, carbon, a di-
minution of which would not render the new compound more
volatile. ■*« .

Mrt. B. You are perfectly right. iSW ibmoation of ether con-
sists simply in subtracting from the alcoEol a certain proportion bf
carbon ; this is effected^by the action of the sulphuric, nitnc, or mu-

goosequill. Let the tube rise an inch or two above the cork —
pass some cotton wick through the tube— then fill the vial with al-
cohoL and put the cork and tube in their places. The lamp is then
readyl ^

oL and p

1194. What is the composition of alcohol ?

1195. From what is ether obtained ?

1196. How does it differ from alcohol ?

1197. In what does the formatioo of ether consist ?r^ i

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riatic acidt, on alcohoL) The acid and carbon remain at the bot-
tom of the vessel, wbiist (be decarbonized alcohol flies off in the
form of a condensable vapour, whicb is ether,
(^ther is the most inflammable of all fluids) and burns at so low a
tehiperature that the heat evolved during^'^its combustion is more
than is required for its support, so that a quantity of ether is volati-
lized, which takes fire, and gradually increases the violence of the

fSir Humphrey Davy has lately discovered a very singular fact re*
specting the vapour of ether. If a few drops of ether be poured in-
to a wine-glass, and a fine platina wire, heated almost to redness, be
held suspended in the glass, close to the surface of the ether, the
wire soon becomes intensely red hot, and remains so for any length
of time^ We may easily try the experiment.
■ Carmine. How very curious ! The wire is almost white hot, and
a pungent smell rises from the glass. Pray liow is this accounted

JUIrs. B, This is owing to a very peculiar property of the vapour
of etheri and indeed of many other combustible gaseous bodies. At
a certain temperature lower than that of ignition, these vapours un-
dergo a slow and imperfect combustion, which does not give rise,
ib any sensible degree, to the phenomena of light and flame, and
yet extricates a quantity of caloric sufficient to re-act upon the
wire, and make it red hot, and the wire in its turn keeps up the ef-
fect as long as the emission of vapour continues.

This singular effect, which is also produced by the alcohol, may
be rendered more striking, and kept up for an indefinite length of
time, by rolling a few coils of platina wire, of the diameter of from
about l-60th to l-70th of an inch, round the wick of a spirit-lamp.
If this lamp be lighted for a moment, and blown out again, the wire,
after ceasing for an instant to be luminous, becomes red hot again,
though the lamp Is extinguished, and remains glowing vividly, till
the whole of the Spirit contained in the lamp has been evaporated
and consumed in this peculiar manner. ,

Caroline. This is extremely- curioui. But why should not an
iron or silver wire produce the same effect ?

JUrs: B.\ Because either iron or silver, being nuch better con-
djuctors of beat than platina, the heat is carried off too fost by those
metals to allow the accumulation of caloric necessary to produce
thj& effect in questioo«

Ether is so light that it evaporates at the common temperature of
the atmosphere ; it is therefore necessary to keep it confined by a
well ground glass stopper; No degree of cold known has ever m>-

'^ Ether freezes and shoots into crystals, at 46^ below the zero of

< 198. W hat is theifiost inflammable of all bodies ?
1 1 99. What singular effect has Sir H. Davy lately discovered re-
specting the vapour of ether ?
l^OD. How may this effect be rendered more striking?

1201. Why would not an iron or silver wire produce the

1202. At what deg^ofcoldwiUetlMr freeze?

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Caroline. U it not often taken medi^inallj ?

Mrs B, Yes ; it is one of the most effectual antispasmodic medi^
cines, and the quickness of its effects^ as auch, prohably depends on
its being instantly converted into yapour by the heat of the stomach,
through. the intervention of which it acts on the nervous system.
But the frequent use of ether, like thatof spiritous liquors, becomes
prejudicial, and, if taken to excess, it produces effects similar to
those of intoxication.

We may now take our leave of the vinous fermentation, of which,
I hope, you have acquired a clear idea ; as well as of the several
products that are derived from it.

Caroline. Though this process appears, at first sight, so much
complicated, it may, I think, be summed up in a few words,/a8 it
consists in the conversion of sugar and fermentable bodies into alco-
hol and carbonic acid, which gives rise both to the formation of
wine, and of all kinds of spiritous liquors^

Mr»: B We shall now proceed to the ncelous fermentation, which
is thus called^ccause it converts wine into vinegar, by the forma-
tion of the acdtous acid, which is the basis or radical of vin^gaK

Caroline. But is not the acidifying principle of the acetou/acid
the same as that of all other acids, oxygen P

Mrs. B. Certainly : and on that account the contact of air is es-
sentia^l to this fermentation, (s^ it affords the necessary supply of ox-
ygeiA Vinegar, in order t(robtain pui"e acetous acid from it, inust
be distilled and rectified by certain processes.

Emily. But pray, Mrs. B. ■ is not the acetous acid frequently
formed without this fermentation taking place ? is it not, for in-
stance, contained in acid fruits, and in every substance that be-
comes sour P

Mrs, B. No, not in fruits; you confound it with the citric, he
malic, the oxalic, and other vegetable acids, to which living vege-
tables owe their acidity. But whenever a vegetable substance
turns sour, after it has ceased to live, the acetous acid is developed
by means of the acetous fermentation, in which the substance ad-
vances a step towards its final decomposition^^

Amongst the various instances of acetous fermentation thatof
bread is usually classed

Caroline. But the fernuBntation of bread is produced by yeast ;
how does that effect it ? '

Mrs. B. It is found by experience that any substance that has
already undergone a fermentation, will readily excite it in one that
is susceptible of that process. If, for instance, 'you mix a little vine-
gar with wine, that is intended to be acidified, it will absorb oxygen
more rapidly, and the procesibe completed much sooner, than if lef^
to ferment spoil taneou sly. -Thus yeast, which is a product of th^
fermentation of beer, is usetr to excite and accelerate the fermenta .

1203. How may the process of the vinous fermentation be ex-
pressed in a few words ?

1204. Why is the third fermentation called acetous ?

1^5. Why is the contact of air necessary to produce the acetous
fermentation ?

1206. What is the reason that wine, or cider, when corked tight
does not turn to vinegar ?

1207. How is the fermentatton of bread produced by yeast ?

268 BEC01IP08ITI0N

tion of malt, which is to be convertediiito beer, as well as that of
paste, which is to be made into bread)

Caroline, I^ut if bread undergoes the acetous fermeutatioD, why
is it act sour?

Jttrt. j3. /It acquires a certain savour which corrects the heavy
insipidity or flour, and may be reckoned a first degree of acidifica-
tion, or if the process were carried further, the bread would become
decidedly acidu)

There are, however, some chemists who' do not consider the fer-
mentation of bread as being of the acetous kind, but suppose, that it
is ^..process of fermentation peculiar to that substance.

f'Theputridfermmtationis the final operation of Nature and her
last step towards reducing organized bodies to their simplest combi-
naliona. All veis^etables spontaneously undergo this fermentation
after death, provided there be a sufficient degree of heat and mois-
ture, together with access of air ; for it is well known that dead
plants may be preserved by drying, or by the total exclusion of air.

Caroline. But do dead plants undergo the Other fermentatioos
previous to this last ; or do they immediately suffer the putrid fer->
mentation ? .

Jlrg. B. That depends on a variety of circumstances, such as the
degrees of temperature and of moisture,the nature of the plant itself,
&c. But if you were carefully to follow and examine the decompo-
sition of plants from their death to their final dissolution, ^rou would
generally find a sweetness d'eveloped in the seeds, and a spiritous fla-
vour in the fruits (which have undergone the saccharine fermenta-
tion,)previous to the total disorganization and separation of the parts.

Emily. I have sometimes remarked a kind of spiritous taste in
fruits that were over-ripe, especially oranges, and this was just be-
fore they became rotten.

Mrs. B.f It was then the vinous fermentation, which bad succeed-
ed^e saccharine and had you followed up these changes attentive-
ly, you would probably have found the spiritous taste followed by
acidity, previous to the fruit passing to the state of putrefactioh^

;\Vhen the leaves fall from the trees in the autumn, they do not (if
there is no great moisture in the atmosphere) immediately on<iergo
a decomposition, but are ,first dried and withered ; as soon, howev-
er, as the rain sets in, fermentation Qommences, their gaseous pro-
ducts are imperceptibly evolved into the atmosphere, and their fixed
remains mixed with their kindred earthj

Wood, when exposed to moisture, als6 undergoes the putrid fer-
mentation, and becomes rotten.

EmUy. But I have heard that the dry rpt^ which is to liable to de-
stroy the beams of houses, is prevented^by a current of air ]^, and yet
you said that the air was essential to th^ putrid ferm^eptatibo ?

Mrs. B. True ; J>ut it must not be in such a proportion to the
moisture as to dissolve the lattei^> and this is generally the case when

120B. Why then is it not sour ?

1209. What is the final fermentation in reducing organized bodies
to their simplest combinations ?

1210. What is mentioned of oranges, and other over-ripe fruit, as
illustrating the above principles of fermentation ?

121 1 What is said of the fermentation of leaves ?

1212. How may the dry rot be prevente4i|tized by Google

1^ vi^aEXAnuBS*

the rotting of wood ia preveoted or stopped by thd free access of air.
What is commonly calle(}j(rj rot, however, is not, I believe, a true
process of putrefaclioti. It is supposed to depend on a peculiar kind
ofvegetation, which, by^ feeding^ on the wood, gradually destroys iS
/(Straw and all other kinds of vegetable matter undergo the putria
jTermentation more rapidly when mixed with animal matter. Much
heat is evolved during this process, and a variety of volatile products
are disengaged, as carbonic acid -and hydrogen gas, the latter of
which is frequently either sulphurated or phosphorated. When all
these gases have been^evblved, the fixed products, consisting of car-
bon, small quantities of salts, potash, &c. form a kind of vegetable
earth, which makes very fine manure, as it is composed of those ele-
ments which form the immediate materials of plants^

Caroline. Pt^y are not vegetables sometimes preserved from de-
composition by petrifaction ? 1 have seen very curious specimens of
petrified vegetables, in which state they perfectlv preserve their form
and organization, though in appearance they are changed to stone.
J^rs. B. That is a kind of metamorphosis, which, now that you
are tolerably well versed in the history of mineral and vegetable
substances, I leave to your judgment to explain. Do yoti imagine
that vegetables can be converted into stone P

JBmi/y. No, certainly ; but they might, perhaps, be changed to a
substance in appearance resembling stone.

Mrs. B: It is not so, however, with the substances that are called
petrified reffetables ; for these arfe really stone, and generally of the
hardest kind, often consisting chiefly of silex.) The case is this :
(^hen a vegetable is buried under water, or \9tt in earth, it is slowly
and gradually decomposed^ As each successive particle of the veg-
etable is destroyed, its place is supplied by a particle of silicious
earth, conveyed thither by the water. In the course of time the
vegetable is entirely destroyed, but, the silex has completely re-
placed it, having assumed its fortn and apparent texture, as if the
vegetable itself were changed to stone^

Caroline, That is verv-curiousl iandl suppose that petrified ani»
mal substances are of the same nature ?

Mn. B. Precisely. It is equally impossible for either animal or
Vegetable substances to be converted into stone. They may be re-
duced, as we find they are, by decomposition, to their constituent
elements, but cannot be changed to elements which do not enter
into their com positioDf.

* ■

' Petrefactions are ofiwo kinds] viz. \0ticeou8, when flinty parti-
cles take the place of the original substance, and co/carecm*, where
the substance appears to be changed to lime-stone. The first kind
gives fire with steel, and the other effervesces with acids;*-C.

1213. On what is the dry rot supposed to depend P
12 J4. Why will animal matter, mixed with straw and other veg*
etable substances, hasten fermentation ?
•1215. What are vegetable petrifactions ?
1^16. How are vegetaible petrifactions formed ?

1217. How many kinds of petrifaeiions are there ?

1218. Wha,t are they called^ and what are their propertieisj

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^ There are, however, bircumstskiices which frequently prevent the
T^ularand final decomposition of vegetables : as for instanoe, wheo
th^y are buried either in the sea, or in the earth, where they -cannot
undergo the putrid fermentation for want of air. ' In these cases
^hey are subject to a peculiar change, by which they are converted
"into a new class of compounds, called 6i/um«Ai.

Caroline* These are substances 1 eever heard of before.

Mrs. B, You will find, however, that some of ihem are v«ry fa-
miliar to you. ^itumens are vegetables so far decomposed as to re-
tain no organ ic^appearance ; but their origin is easily detected by
their oily nature, their conybustibility, the products of their analy-
sis, and the impression of the forms of leaves, grains, fibres of wood,
and even of animals, which they frequently bear^

They are sometimes of an oily^ liquid consistence, as the sub-
stance called naptka,* in which we preserved potassium ; it is a fine
transparent, colourless fluid, that issues out of clays in some parts of
Persia. But more frequently bitumens are solid, as asphaltumf^
smooth, bard, brittle substance, which easily melts, and forms, in^ib
liquid state, a beautrf'ul dark brown oolor for oil painting^ Jety
which is of a still harder texture, is a peculiar bitumen, susceptible
of so fine a polish, that it is used for many ornamental purpose^

{pool is also a bituminous substance, to. the cpm position of which
both the mineral and animal kingdoms seem to concur. This moat
useful mineral appears to consist chiefly of vegetable matter, mixed
with the remains of marine animals and marine salts, and occasion-
ally containing a quantity of sulphuret of iron, commonly called

EmUi. ^^ is* I suppose, th^ earthy, ihe metallic, and the saline
parts of coals, that compose the cinders or fixed products of their
combustion: whilst the hydrogen and carbon, which they derive
from vegetables, constitu te their volatile prod ucts.

Caroline, Pray is not cofce, (which I have heard is much used in
some manufactures,) also a bituminous substance f
_ J\Irs, B. No ; it is a kind of fuel artificially prepared from coals.

S consists of coals reduced to a substance analagous to charcoal by
e evaporatioq of their bituminous parts. Coke, therefore, is com*
posed of caroon, with some earthy and saline ingredients^

ySuceihy or. yelliyw amber^'is a bitumen which the ancients called
tleetrvmy from whence the word electricity is derived, as that sub-
gtanceis peculiarly ,. and was once supposed to be exclusively, elec-
tric) (It is found either deeply buried in the bowels of the earth, or

^^^aptha appears to be the only fluid in which oxygen does not
exist;, heoce its property of preserving potassium which h^ so strong
an affinity for oxygen as to absorb it from all other fluids^ It bow-
.^ver loses this property by exposure to the atmosphere, probably,
because it absorbs a small quantity of air$ or moisture. It is agaia
restored' by distillation. — C,

1^19. What are bitumens, and howave they formed .^

1220. What is^asphaltum .?

1221. What is jet?

1222. What is coal?

11224. What is yellow amber ? « d


floating on the sea, aadis supposed to be a resinoas body which has
beeo acted on by saiphuric acid, as its analysis shows it to consist
of an oil and an acid. The oil is called oil rf ambor^ the acid the

Emi^^ThiA oil I ha^e sometimes used in painting, as it is reck-
oned to change less than the other -kinds of oil.

Mrs. B. The last Class of vegetable substances that have chang-
ed their nature are faetU-iwood^ peat* and turf* /^hese are com-
posed of wood and roots of shrubs, that are partly decomposed by
being exposed to the moisture under ground, and yet in some meas-
ure, preserve their form and organic appearance. The peat, or
black earth of the moors, retains but few vestiges of the roots to
which it owes its richness and combustibility, these substances be-
ing in the course of time,, reduced to the state of vegetable earth.
But in turf the roots of plants are still discernible, and it equally .an-
swers the purpose of fuel. It is the combustible ^used by the poor in
heathy countries, which supply it abundantly

U is too late this morning to enter upon the history of vegetatioiw
We shall reserve this subject, therefore, to our next interview,
when I expect that it will furnish us with ample matter for another



J\tr8. B. u^he vegetable kingdo^may be considered as i^he link
which unites the mineral and animal creation into one common
chain of beings ; for it is through the means of vegetation alone that
mineral substances aj^ introduced into the animal system ; since,
generally speakingMt is from vegetsa>les thatall animals ultimately
derive their $ustenalkc<^

Carolina. 1 do not understand that ; the human species w^siit at
much on animal as on vegetable food.

Jlfr». J3. That is true ; but you do not consider that those that live
on animal^ food, derive their sustenance equally, though not so im-
jnediately^ from vegetables. The meat which we eat is formed
from the herbs of the field, and the ^cey of carnmrous animals pro-
ceeds either directly or indirectly iCrom .the same source. It is,
therefore, through this channel, that ihe simple -elements become a
part of the animal frame. We should in vain -attempt to derive
noorishment from oarbdn, hydrogen, and oxygen, either in their
separate state or combined in the mineral kmgdom ; for it is onlji^

1225. Where is it found ?

1226. What are fossil- wood, peat and turf?

1227. Why does naptha preserve potassium ?

1228. Wlmt is considered as uniting the mineral and animal cre-
ation ?

1229. From whence do all anitnale derive their ^sustenance?

1230. In what state are carbon, 'hydrogen, and oxygen capabia
«iif afibrding nourishment ?

272 ina&BK±TioifU

being united in the form of reg^etaWe combination that tb^ become
capable of conreyioff nourishmeop .,. ^ _:..,. ,0^ .

Emily. Vegetation, then, seems to be ihe method which Nature
employs to prepare the food of animals ?

jkrs.B. That is certainly its principal object. The vegetable
creation does not exhibit more wisdom in that admirable system of
organization, by which it is enabled to answer its oWn immediate
ends of preservation, nutrition and propagation, than in its grand
and ultimate object of forming those arrangements and combina-
tions of principles, which are so well adapted for the nourishment of

Emily. But T am very curious to know whence vegetables obtaia
those principles which form their immediate materiaasr

Mrs. B. This is a point on which we are yet po much in the dark
that 1 cannot hope fully to satisfy your curiosity ; but what little I
know on this subject, 1 ^hall endeavor to explain to you.

rfhe soil which at first view, appears lo be the element of vegeta-
bles, is found on a<jloser4nve8tigation,to'be little more tharf the
♦ channel through which they receive their nourishment so that it
is very possible to ifear plants without any earth or 8017.*

♦ The opinion that water is the only food of plants, was adopted
by the learned on this subject in the 17th century ; and inany ex-
periments were made which seemed to prove that this was the
-toulh. Among others was a famous one by Van Hehnout, which
for a long time 'was supposed to have established the point beyond
all doubt. tJie planted a willow which weighed five pounds, in an
earthen vealel containing SOOlbs. of dried earth. This vessel was
sunk into the ground, and the tree was watered, sometimes with
^distilled, and sometimes with rain water. . ^ ^ ^^;^,^

At the end of five years the willow weighed 169 lbs. ; and on
weighing the soil, dried as before, it was found to have lost only two
ounces. Thus the willow had gained 464 Ibs.^ and yet its food had
been only water. The induction from this experiment was obvious.
Plants live on pure wate^ . This, therefore, was the general opinion
uutil the progress of chwistry detected its fallacy. Ber|^man* in
1763, showed by some experiments, that the water which Van
Helmout had used, contained as much earth as could exist in the
tree at the end of the five years:; a pound of watercontained about
a grain of earth. So that this experiment by no means proved
that the willow lived on water alone. Since this time a great
variety of experiments have been made for the purpose of deciding
what was the food of plants. ^Jn the course of these it has been
found, that although seeds do vegetate in pure distilled water, yet
the plant is weakly and finally dies before the fruit is matured)

It is pretty certain, then, that earth is absolutely necessary lo the
growth of plants, and that a part of their food is taken from thesoiL
Indeed, the weH'known fact, that a soil is worn out by a longsucces*

Online LibraryMrs. (Jane Haldimand) MarcetConversations on chemistry .. → online text (page 33 of 43)