Mrs. (Jane Haldimand) Marcet.

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state of carbonat, or mixed with water, M^ld prove the best anti-
dote)

Bmily, In those cases then, I suppose, the potash and the mag-
nesia would quit their combinations to form salts with the sulphurie
acid ?

Mrs. B. Precisely.

We may now make a few observations on the sulphureous acid,
which/^e have found to be the product of sulphur slowly and im-
perfeciif burntA This acid is distinguished by its pungent smell,
and its gaseous Arm.

Caroline. Its kriform state is, I suppose, owing to the smaller
proportion of oxvgen, which renders it lighter than sulphuric acid?

Mrs. B, Probably ; for by adding oxygen to the weaker acid,
it may be converted into the stronger kind. But this change of
state may also be connected jrith a change of affinity with regard
to caloric*

EmUy. And may sulphureous acid be obtained frpm sulphurie
acid^ a diminution of oxygen>|

Mjrs. B. Yes ; it can be dono/by bringing an^ combustible sub-
stance in contact with the acid. This decomposition is most easily
performed by some of the acids ; these absorb a portion of the oxy-
gen from the sulphuric acid, which is thus converted into the sul-
phureous, and flies oflTin its gaseous form.

Caroline. And cannot the sulphureous acid itself be decomposed
aod reduced to sulphur?

Mrs, B. Yes ;/1rOiis gfas be heated in contact with charcoal, the
oxygen of the m will combine with it, and the pure sulphur will
be regeneratedTj
— * ^ -,.« . — •

908. How does sulphureous acid differ from sulphuric ?

909. What would prove the best remedy to a person who had
swallowed sulphuric acid ?

910. How may sulphureous acid be obtained I

911. How can the sulphuric acid be changed to the sulphureoui?
913. How caa lulphureous^cid be reduced to sulphur ?

18*

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210



OF THE STJLPHtJKEOtJS ACID.



Sul|3Jiureous acid is readily absorbed by water ; and id this liquid
state^ is fouud particularly useful in bleaching linen and woollen
clothsAand is much used in manufactures for those purposes. I
can skow you its effect in destroying^ colours, by taking out vegeta-
ble stains — I think I see a spot on your gown, Emily, on which we
may try the experiment.

Emily, It is the stain of mulberries ; but I shall be almost afraid
of exposing my gown to the experiment, after seeing the effect
which the sulphuric acid produced on that of Caroline —

Mrs, B, There is no such danger from the sulphureous ; but the
experiment must be made with great caution, for during the forma-
tion of sulphureous acid by combustion, there is always some sul-
phuric produced.

Caroline, But where is your sulphureous acid ? —

Mrs, B, We may easily prepare some ourselves, simplj/py burn-
ing a match ; we must first wet the stain with water, ancfi^ow hold
it in this way, at a distance over the lighted match; the vapour
that arises from it is sulphureous acid, and the stain, you see, gradu-
al! r di8appears7\

ilmily. I ha^ frequently taken out stains by this means, with-
out understanding the nature of the process. But why is it neces-
sary to wet the stain before it is exposed to the acid fumes ?

Mrs, B, The moi&ture attracts and absorbs the sulphureotis
acid ^ and it serves likewise to dilute any particles of sulphuric acid
which might injure the linen.

Sulphur appears to be susceptible of a third combination of oxy-
gen, in which|ffie proportion of the latter is too smalt to render the
sulphur acid, y it acquires this slight oxygenation bjrmere exposure
to the atmosphere, without any application of heaK; in this case
the sulphur does not change its'^natural form, but i^nly discolour*
ed, being changed to red or brown, a state in which it may be
considered an oxyd of sulphur.

Before we take leave of the sulphyric acid, we sba:!! say a few
words of its principal combinations. /It unites with all the alkalies*
/ alkaline earths and metals, to form dompound saltsV

Caroline, Pray, give me leave to interrupt yoy/for a moment i
you have never mentioned any other salts than the compound or
neutral salts ; is there no other kind ^

^ Mrs, B, The term soli has been used, from time immemorial, as
/a kind of a general name for any substance that has favour, odour,
IS soluble in water, and crystallizable, whether it be of an acfid, an
alkaline or compound natur^ but the compound salts alone retftin
that appellation in modem cl/emistry.

The most important of the salts formed by the combinations of the
sulphuric acid, are, first, sulphat of potash^ formerly called sal poly'
ehrest : this is a very bitter salt, much used in medicine ; it is found
iln the ashes of most vegetables, but it may be prepared artificially
by the immediate combmation of sulphuric acid and potash. This



9.J3. What important use is made of this acid ?

914;^^ What is the easiest process for making this acid ?

915. Hqw would you describe a third combination of sulphv
with oxygelT'?

9 1 6. W ith Itfiat does sulphuric acid unite ?

917. What is the meaning of the term salt /

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OF THE BVLPHATS. 21 1

salt 18 easily soluble in boiling water. Solubility is, indeed, a prop-
erty common to all salts^and they always produce cold in meltin|f.

Emily. That must be/owing to tl^e caloric which they absorb m
passing from a solid toVk^uid form j

J\ilrs, B. That is, certain Iv, the,»o8| probable explanation.

Sulphat ofSoday commonly calledfGlauber's saltlis another me-
dicinal salt, which'is still more bitteAhan the precefling. We must
prepare some of these compounds, that you may observe the phe-
nomena which take place during their formation. We need only
/pour some sulphuric acid brer tbesodaVhich I have put into this
glass. I

Caroline. What an amazing heat is d^isengaged ! — I thought yon
said that cold was produced by the melting of salts?

Jtfrs. jB. But you must observe that we are now makings not meli-
ing^ a salt. Heat is disengaged during the formation of compound
salts, and a faint light is also emitted, which may sometimes be per*
ceivcd in the dark.

Emily, And is this heat and light produced by the union of the
opposite electricities of the alkali and the acid r

J\irt. B. No doubt it is, if that theory be true.

Caroline, The union of an acid and an alkali is then an actual
combustion ?

J^rs.B. Not precisely, though there is certainly much analogy
in these processes.

Caroline. Will this sulphat of soda become solid ?

JIfrf. B. We have not, I suppose, mixed the acid and the alkali
in the exact proportions which are required for the formation of
the salt, otherwise the mixture would have been almost immediate-
ly changed to a solid mass ; but in order to obtain it in crystals, as
you see it in this bottle, it would be necessary first to dilute it with
water, and afterwards to evaporate the water, during which opera-
tion the salt would rradaally crystahize.

Caroline. But of what use is the addition of water, if it is after-
wards to be evaporated ?

Jtfr«. B. When suspended in water, the acid andihe alkaU tarn
more at liberty to act on each other, ^ir miie^^ore complete,
and the salt assumes the regular form of CfjpeflRi during the alow
evaporation of its solrent.

Sulphat of soda liquefies by heat and effloresces in the air.

Emily. Pray what is the meaning of the word ^gUretoes / I do
not recollecjt your having mentioned it before.

Mr». B.fk 'salt is said to effloresce when it totes its water of cr]fs«
taUi^ation Vn being exposed to the atmosphere, and is thus grad«al-
ly converted into a dry powder\ yon may observe that these crys-
tals of sulphat of soda are farArom possessing the transparenof
which belongs to their crvstalUne state { they are covered with a
white powder, occasioned by their having beeAex posed to the At-
mosphere, which has depri^ their sarfaMce of ick lustre, by absorb-
ing Its water of crystallization. SaHs are^ in gelieral, either ^ffif
eteent or deHqueueni : this latter propertyHs preeisely the reverse of

918. Why do the salts prodace cold in melting ?

919. By what name is the sulphat of soda called ?
9^. How can sulphat of soda be formed ?

9^1. What is the signification of the word effloresces ?



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212 OF TUB BVhPIULt8.

the former ; that U to say, deliqaescent salts absorb water^rom the
atmosphere, and are moistened and gradually melted by itJ M ariat
of time is an instance of great deliquescence. ^

. Emily But are there bo salts that have the same degpree of at-
traction for water as the atmosphere, and that will consequently
not be affected by it ?

J(fr«. B. Yes : there are many such salts, as, for instance, com-
mon salt, sulphat of magnesia, and a variety of others.

Sulphat o/limeis very frequently metwitb in nature, and consti-
tutes the well known substance called^^iom or />^/er^l»amA

Sulphat tf magnesia, commonly caLlecK^/^fomM^, is another ^ry
bitter medicine, which is obtainednrom sea- water and from sevenu
spring, or may be prepared by thVdirect combination of its ingre-
dients^

We €ave formerly mentioned ntZjoAa/o/'a/uiiitne as constituting
the common alum; it is found in naturepTiiefly in the neighborhood
of volcaooes^nnd is particularly useful '\ the arts, from its strong
astringent qifoities. ^ is chiefly employed bv dyers and calico-
printers, to fix coIoui:s\ and is used also in the manufacture of
some kinds of leatherr\

Sulphuric acid combines also with the metals.

Cardline, One of these combinations, «u/p^/ o/'tron, we are al-
ready well ac()uainted with.

Mrs. B. This i<) the most important metallic salt formed by sul-
phuric acid, and the only one which we shall here notice. It is of
great use in the arts ; and in medicine, it affords a very valuable
tonic ; it is of this salt that most of those preparations called iitd
medieirut are composed.

Caroline* But does any carbon enter into these compositions to
form steel ?

Mrs. B. Not an atom : they are, therefore, very improperly cal-
ted steel ; but it is the vulgar appellation, and meiical ^nen them-
selves often comply with the general custom.

Sulphat of iron mav be prepared, as you have seen, by dissolving

iron in sulphuric acid : but is generally obtained from the natural

production call^k^^i/e«,Vhicn being a sulphuret of iron, requires

/'only ei^nosureto^ie atmosphere to be oxydated, in order to form

Hhe sain this, therefore, is much the most easy way of procuring

it on a mrge scale.

Emi^f, 1 am surprised to find that both acids and compound salts
are generally obtained from their various combinations, rather tbao
from the immediate union of their ingredients.

Mrs. B. Were the simple bodies always at hand, their combioa-
Uons would naturally be the most convenient method of forming
compounds ; but you must consider that, in most instances, there is
great difficulty and expense in obtaining the Simple ingredient from

92t. What is the signification of the word deliquescent?
9S3. What substance is frequently found in nature, the same as
sulphat of lime f

994. From what is the sulphat of magnesia obtained ?

925. Where is the sulphat of alumine chiefly found?

926. For what purpose is it used ?

927. From what is the sulphat of iron obtained ?

928. How is sulphat of iron manufactured in the large way ?

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OF THE 8ULPHATS. 2l3

their combinations ; it is, therefore, often more expedient to procure'
compounds from the decomposition of other compounds. But, to
return to the sulphat of iron. There is a certain vegetable acid
called gallic acirf,n bieh has the remarkable property of precipitat-
ing this salt black — I shallJpour a few drops of the gallic acid into
this solution of sulphat of ¥onV

CaroliTie. It is become asbiaek as ink !

.^/r? B- And it is ink in reality. Common writing ink is a pre-
cipitate of sulphat of fron bj gallic acid ;^e black color is owing
tb the formation of gallat of iron, which fcing insoluble, remains
suspended in the fluid.

This acid has also the property of alterrog the color of iron in
its metnllic state. You may frequently see its effect on the blade of
a kniie, that has been used to cut certain kinds of fruit^

CaruUrie. True; and that is, perhaps, the reason that a silver
knife is preferred to cut fruits ; the gallic acid, 1 suppose, does not
act upon silver.— Is thi« acid found in all fruits ?

J\Irs. B. it is contain- d, more or less, in the rind of most fruits
and roots, especially th* radish, which, if scraped with a steel or iron
knife, has its briglit red color changed to a deep purple, the knife
bein": nt the same time blackened. But the vegetable substance
in which the gallic, acid most abounds, is ^utgali\2k kind of ex-
creserjce that grows on oaks, and from wbicnf^the aoidis commonly
obtained for its various purposes.

Mrs B. We now come to the phosphoric aud phosfhorous
ACIDS, In treating of phosphorus, you have seen how these acids
may be obtained from it by combustion.

Emilij. Yes; but I should be much surprised if it was the usual
method* of obtaining them, since it is so very difficult to procure
phosphorus in its pure state.

J\Irs, B, You are right, my dear ;/fTf)e phosphoric acid, for gene-
ral purposes, is extracted from bones^n which it is contained in the
state of pliosphat of lime ; from this «Llt the phosphoric acid is sepa-
rated by means of the sulphuric, which combines with the lime. In
its pure slate, phosphoric acid is either liquid or solid, according to
its depfree of concentration.

Among- the salts formed by this acid, phosphat of lime is the only
one that affords much interest ; and this, we have already observed,
constitutes the basis of all bones, fit is also found in very small
quantities in some vegetables! \

929. How may the sulphat of iron be turned black ?

930. Why is a knife turned black in cutting fruit ?

93 1 . In what vegetable substance does gallic acid mostly abound ^

932. Where is the phosphat of lime found ^

V



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214 ON THE NITBIO

CONVERSATION JITIII.

OP THE NITBIC AND CAKBONIC ACID&; OK THE COXBINATIONB
OF OXYGEN WITH NTFROOEN AND CABVON ; AND OF THB
NITRATS AND CARBONATS.

Mr*. B. I am almost afraid of introducipg^ the subject of the
siTRic ACID, as I am sure (hat I shall be blamed by Caroline for
not having- made her acquainted with it before.

Caroline. Wh} so, Mrs. B. ? ^ . . J.

Jifrs, B. Because you have Ipng known its radical, which iani-
trogem or azot^ and in treating of that element, I did not evbn
bint (hat it was M basis of an acid.

Caroline. And what could be jrour reason for not mentioning this
acid sooner ?

J^rg. B. I do not know whether you will think the reason suffi-
ciently good to acquit me ; but the omission, I assure you, did not
proceed from negligence^ You may recollect that nitrogen was one
of the first simple bodies which we examined ; you were then igno-
rant of the theory of combustion, which 1 believe was, for the first
time, mentioned in that lesson ; and therefore it would have been
in vain, at that time, to have attempted to explain the nature and
formation of acids.

Caroline. 1 wonder, however, that it never occurred to us to in*
quire whether nitrogen could be acidified ; for, as we knew it was
classed among the combustible bodies, it was natural to suppose that
it might produce an acid.

Mrs. B. That is not a necessary consequence ; for it might com-
bine with oxygen only in the degree requisite to form an oxyd. Bat
you will find'that nitrojren is susceptible of various degrees of oxy-
genation, some of which convert it merely into an oxyd, and others
give it all the acid properties.

The acids, resulting from the combination of oxygen and nitro-
gen, are calledThe nitrous and nitric acid» We will begin with
^e nitric, in wkich nitrogen is in the highcsTstate of oxygenation.
vThis acid has so powerful an attraqtion for water that it has never
Been obtained perfectly free from iu\ But water may be so stronrlj
impregnated with it as to form an esteedingly powerful acid -solu-
tion. Here is a bottle of this acid^ which you see, is quite limpid.

Caroline.g^h^i a strong offensive smell it has !

Mrs. B.trh\s acid contains a greater abundance of oxygen than
any other ;N>ut it retains it with very little foroa ^

Emily. Then it must be a powerful caustic, Mih fromthe facility
with which it parts with its oxygen, and the quantity whicn^t afford^

933. What is the radical of nitric acid ?

934. What acids are formed by the combination of nitrogen and
oxygen f

QJS. How does nitric acid naturally exist ?

936. How does this compare with other acids as to the quantity
of oxygen contained in it f

937. To what is the great causticity of nitric acid owing ?



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▲NB lOTBOnS ACIDS. 215

Mrt. B» Very well, Emily ; both causes and effects are exactly
such as you describe ; nitric acid burns aod destroys all kiads of
erranized matter. It even sets fire to some of the most combustible
sabstances.— -We shall pour a little of it over this piece of dry
warm charcoal* — ^you see it inflames it immediately ; it would do
the same with oil of t^igpenimey phosphorus, and several other very
combustible bodies. /This shows you how easily this acid is decom-
posed by combustib1e4)odi^ since these effects must depend upon
the absorption of its oxyge^

Nitric acid has been usetrin the arts from time immemorial ; but
it is only within those twenty-five years that its chemical nature has
been ascertained. The celebrated Mr. Cavendish discovfn*ed that
it consisted of aboutflO parts of nitrogen and 2$ of oxygen.f\ These
principles, in their g^eous state, combine at a high temperature;
and this may be effected by repeatedly passing the electoral spark
through a mixture of the two gases.

Emily. The nitrogen and oxygen gases^of which the atmosphere
is composed, do not com^jai I suppose/Cecause their temperature
is not sufficiently^ elevatedj V^

Coiroline, But in a thumflr-storm, when the lightning repeatedly
passes through them, may it not produce nitric acid ? We should be
in a strange situation, if a violent «torm should at once convert the
atmosphere into nitric acid.

Mrs. B. There is no danger of it, my dear *^Qne lightning can af
feet but a very small portion of the atmosphe^and though it wer
occasionally to produce a little niti;ic acid, it never could happen to
such an extent as to be perceivable^

Emily, But how could the nitric^clcid beknown, and used, before
the method of combining its constituent was -discovered-?

Jtfrx. B. Previous to that period the nitric acid was obtained,
and it is indeed still extracted, for the <commoa purposes of art,
from the compoand salt which it forms with pot-ash, commonly ctdU
ad nitre,

Caroline' Why is it so called ? Pray, Mrs. B., let these old un-
meaning names be entirely given^ «p, bj us at least ; and let as call
this saltintral of pot-ath.

* To inflame charcoal, a stronger acid than that sold at the shops
is necessary. The experiaient with oil, turpentine, and phospho-
rus, succeeds, if about a sixth part of sitlpb. acid is added to the ni-
tric acid. The experiment with the turpentine requires caatioo.
The vial containing the acid must be tied to a stick, a yard or two
long, the operator pouring it into a small quantity of the tarpentiBe
standing at a distance. — C«

TThe proportion stated by Sir H. DaTj« in his Chemical Re-
teftrches, is as 1 to 2,389^

938. What is the reason why nitric acid inflames charcoal, oil of
turpentine, kc. ?

939. What are the proportions of oxygen and Bitrogfensn nitrie
aeid?

940. What is the reason, that the oxygen and nitrogen «f which
tbe atmosflhere is composed, do not combine and form nitric acid f

941. Why does not lightning prodnce this elevation of 4empera-
tnra?

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216 ON THE NiTBIC

Mr*, B. With all my heart; but it is necessary that I shotfid, at
least, mention the old Dames, and more especially those which are
yet in common use ; otherwise, when you meet "with them, you
would not be able to understand their meaning^.

Emily. And how is the acid obtained from this salt ?

Jdrs,B»^y the intervention of sulphuric acid, which ^combines
with the pot-ash, and sets the nitric acid at libert^ This 1 can
easily show you, by mixing^some nitrat of potash aoA^ulphuric acid
in this retort, and heating^ it over a lamp ; the nitric acid will come
over in the form of vapour, which we shall collcpt in a g^4ss bell.
This acid diluted in water, is commonly c2i\iedm^uaforlifi\( Car-
oline will allow me to mention that name. ^^^ >r

Caroline. I have often .heard that aqua fortiJmill dissoWe almost
all metals ; it i$ bo d ciubt bi ' i! i ius«. itj;4fl||^tent wryg,Bii nu t iU i l} !*'

•Mrs, B.,Y9^^ and from this powerful solveojtoroperty, it deriy-
ed the name of aqua tortis, or strong wate^ Do you not recol-
lect, that weoxydated, and aAerwards dissolv^, some copper in this
acid ?

Emily, If 1 remember right, the nitrat of copper was the first in-
stance you gave us of a compound salt. —

Caroline. Can the nitric acid be completely decomposed and con-
verted into nitrogen and oxygen ?

Emily, That cannot be the case, Caroline ; since the acid can be
decomposed only by the combination of its.coDstituents with other
-bodies.

Mrs* B. True ; but caloric is sufficient for this purpose.
rSy making the acid pass through a red hot porcelain tube, it is
ddeompose^ the nitrogen and oxygen regain the caloric which
they had Id^ in combining, and are thus both restored to their gas-
eoj^ state.

filie nitric acid may also be parthr decomposed, and is by this
.mesAs converted into nitrous acii^

' Caroline. This conversion must b^easily effected, as the oxygea
is so slightly combined with the nitrogen.

Mrs, B, The partial decomposition of nitric acid is readil^r ef-
fected by roost metals; but it is sufficient to expose tbe nitric acid to
ft very strong light tomake it giye outoxygfen g^asand thus be coo-
yerted into nitrous acid. This latter acid appears i&^arious degrees
of strength, {Uncording to the proportions of nitrous acid gas and
water of which it is composed ; the strongest is a yellow color, as
jpu see in this bottle.

Caroline. How it fumes when tbe stopper is taken out !

Mrs. B. The acid exists naturally in a gaseous state, and is hero
so strongly concentrated in water, that it is constantly esc^ing.

Here is anotber bottle of nitrous acid, which, you see, i^of an or-
ange red : this acid is weaker, that is^contains a smaller <pantity of
the acid gas ; and with a still less proportion of the gas it is of an



942. How is nitric acid obtained from the nitrate of potash ? .

943. What is the common name of nitric acid diluted in water ?

944. What is the propriety of the name aaua fortisf

945. How may nitric acid be decomposed f

946. How can nitrous acid be formed ?

947. How may the color of water be effected by tb<9 di^rejit
portions of nitrous acid with which it Is combined ?

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43X1} NUTtotrs ^oisf . 217

olive green colour, as it appears ia thift4bird bottle. In short, the
weaker the acid, the deeper is its colour^^

Nitrous acid acts ^tijl more powerfuily^n some inflammable sub-
stances than the niti^.

Emily. I am surprised at that, as it contains less oxyg^eo.

Mrs.JB. But, on ihe other handiTT parts with its oxygen much
more readil^ you may recollect tOat we once inflamed oil with
this acid. I

The next combinations of nitrogen and oxygen form only oxyds
of nitrogen, the first of which is^mmonly called nitrous air ; or
more properly nitric oxydgas.* /This may be obtained from nitric
.acid, by exposing the latter to thVaction of metalsias in dissolving
them it does^not yield the jnrhole of its oxygen, ba^etaios a portion
of this principle sufficient to convert it into this peculiar gas, a spe-
cimen of which I hai^e prepared, .and preserved/^ith this inverted
^lass bellJ V.

^mi^yrlti? a perfectly invisible elastic fluid.

JITrf. B, Yes ; and it may be kept any length of time in this man-
vHer over water> as it is not, like the nitric and nitrous acids, absorb-
. able by it. It is rather heavier than atmospherical air, and is inca-
pable of supporting either combustion or respiration. I am going
vto incline the glass gently on one side, so as to let some of the gas
/escape —

Emily, H(^ very curious !— It produces orange fumes like the
..nitrous acid ! that is the mor^ extraordinary, as the gas within the
glass is perfectly invisible.

Jits.^B. It would give me much pleasure \( you could make out
the reason of this curious change^ without ^.re^iHng any further



Online LibraryMrs. (Jane Haldimand) MarcetConversations on chemistry .. → online text (page 26 of 43)