Charles Tomlinson.

Cyclopædia of useful arts, mechanical and chemical, manufactures, mining, and engineering (Volume 2) online

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be conducted successfully, the acid continues to be
formed and to trickle down the sides of the chamber
to the bottom, gradually increasing in density. When
the density of the acid varies from T350 to T450 it
is drawn off from the bottom of the chamber by a
leaden pipe into large leaden boilers, where, by the
action of heat, a portion of the water of the acid is
driven off, and the strength of the acid thus increased.
These boilers are made of large rectangular plates of
thick lead, the edges being folded up so as to form
pans of the depth of 10 or 12 inches. Each boiler
rests on a close grating of strong iron bars, and has
a separate fire. As the acid in the top boiler becomes
stronger by the evaporation of the water, it is trans-
ferred by means of a syphon tube to the middle boiler,
and thence to the lowest. When the acid has ac-
quired the density of T650, or 1700, it must be
removed from the leaden vessels, because at a little
over this strength the acid corrodes lead. In order
to raise it to the commercial strength it must be con-
centrated in glass or platinum retorts, for which pur-
pose it is removed from the boilers into coolers, or run
through a long worm pipe surrounded by cold water.
When glass retorts are used, they are arranged in a
long gallery furnace in a double row, each retort being
placed in a sand-bath supported by fire-tiles and fur
nished with a separate fire. The vapour given off




usually contains some acid, especially when the con-
centration is nearly complete, and this vapour is con-
ducted into the chamber or into the leaden boilers.
In some sulphuric acid works near Salisbury, which
the Editor visited a few years ago, and described in
the second volume of his work on the " Useful Arts
and Manufactures of Great Britain," the glass retorts
were each of the capacity of 4 or 5 gallons, with the
necks fitting on separately like the top of an alembic.
The retorts were arranged in a double row of 10, and
while in operation the parts of the retort project-
ing from the sand-bath were covered
with a hood of tin plate. Eroin 12
to 16 hours were required for the
concentration: this being completed,
the fires were extinguished and the
retorts left to cool ; after which the
acid was drawn off into large brown
earthenware vessels by means of a
syphon of lead pipe, Eig. 2122, re-
curved at the shorter arm. This -Ffy. 2122.
syphon was first inverted and filled with water; then
closing the long end with the finger, the short limb
was inserted into the body of the retort. On removing
the finger, the water in the syphon was set in motion,
bringing after it the acid. The water was caught in
a small cup held under the end of the syphon ; this
flowed out with a gurgling sound, and the moment it
ceased the cup was removed, and the acid appeared;
it fell down into the deep jar in a full, smooth, quiet
stream, very much resembling oil, and reminding one
of the origin of the old name of oil of vitriol, applied
to it from this circumstance. The acid was next
transferred into large globular green glass bottles,
called carboys, securely packed with straw in wicker
baskets. Each carboy contained from 80 to 100 Ibs.
weight of the acid ; the necks were closed with glass
or earthen stopples, luted on with clay or loam, and
tied over with coarse canvas. In this way sulphuric
acid is sent into the market.

In the above works the glass retorts arc found
to answer very well. No retort is ever disturbed
in its sand-bath while it remains entire ; but when,
from exposure to draught or to too much heat, a re-
tort is cracked, it is removed at once, unless the crack
is situated in the upper part, where it admits of patch-
ing with white lead.

In large acid works, where the quantities produced
require the incessant working of the apparatus, this
system of glass-retortiny is not practicable. The
danger and great loss arising from breakage induced
the late Mr. Samuel Parkcs to introduce stills of
platinum, a metal which resists the action of sul-
phuric acid even at high temperatures. The stills
are made of thin sheets of platinum soldered together
with pure gold: 1 they are oval in shape, and of

(1) These stills are nearly all made in Paris, and are of the
capacity of from 5 to 20 cwt. ; they cost from 1,7001. to 2,600 J. each ;
and although one of these retorts wears out in two or three years,
yet it is found more economical in large works to use these costly
vessels than the cheap and abundant material, glass.

The following calculations by M. Payen prove that where glass re-
torts o r the capacity of 80 litres do not cost more than 1 franc GOcen-

3 F2



804



SULPHUR




Fig. 2123.



various sizes, and are preserved from the direct action
of the fire by being set in cast-iron jackets, arranged
over the flue of a furnace. The stills have platinum
heads and beaks like common stills, and the beaks
are inserted into leaden worms, in which the watery,
sulphurous, and nitrous acid vapours given off during
the concentration are condensed and conveyed to the
water on the floor of the chamber.

When the acid is sufficiently concentrated in the
platinum retorts, they are in some cases lifted off the
lire, together with their iron jackets, and let down
into a cistern of cold water. The boiling hot acid
is in this way speedily cooled ; but this clumsy and
dangerous contrivance has been superseded in many
works by a platinum syphon, Fig. 2123, one leg of
which is twisted into a
worm, and contained in
a vessel of cold water v,
The acid is cooled in
passing through this
worm, thereby render-
ing it unnecessary to
disturb the retort. In
order to fill this syphon,
the shorter leg t is
plunged to nearly the
bottom of the still ; the
stop-cock c to the longer
leg, or worm, is closed ;
the worm is filled with
cold acid through the
funnel/. The stop-cock to this funnel is then closed,
and that at c suddenly opened ; a quantity of acid
then flows out sufficient to rarify the small portion of
air in the upper part of the pipe, and to cause the hot
acid to rise over the bend, and thus produce a con-
tinuous stream. The flow of the acid can be regu-
lated by opening the stop-cock c more or less, and
a constant supply of cold water may be kept up in
the outer vessel v by the pipe #>, which constantly
supplies colder and heavier water to the bottom of
the vessel v, while the water heated by the worm



times each, as at Montpellier and the neighbourhood of large glas_s
works, then glass retorts and platinum are about eqaal in cost";
Init when, as at Paris, Rouen, &c., a glass retort of the capacity of
80 kilogrammes costs 6 francs, and can only be used on an average
5 times, thus yielding 400 kilogs. of concentrated acid, the addi-
tional charge on every 100 kilogs. for expense of retorts is GO
centimes at Montpellier, &c , and 1 franc 50 centimes at Paris,
llouen, &c. In the latter case platinum is much less costly than
glass. For example, in a platinum-still the body weighs 63
kilogs. the capital 6 kilogs. the adjutages, gage, &c. 2 kilogs. the
syphon 10 kilogs. making altogether 81 kilogs. and the cost
about 80,000 francs (3,200f.). The interest on this sum, and the
wear and tear, may be represented at 24 francs per day. This sum,
spread over 4,000 kilogs., the quantity of concentrated acid pro-
duced daily by the platinum apparatus, causes an additional
charge of GO centimes on every 100 kilogs. of acid ; for
Kilog. Fr. Kilog. Cent.

4,000 : 24 : : 100 : GO

Which shows an advantage of 90 cents per 100 kilogs. of acid in
favour of platinum, when the retorts cost 6 fr. each ; but when
the retorts cost only 1 fr. 60 cents each, the expense of platinum
and glass is the same, with the advantage in favour of platinum,
that it is not liable to break by the heat, as glass is, and so entail
loss of acid and danger to the operatives.



' escapes through the side opening at e. The platinum
retorts can be charged from 4 to 6 times a-day, which

1 gives them a great advantage over glass retorts.
The French method of concentrating the acid is

j more elaborate than the English. It is conducted by
means of two leaden boilers or evaporators, B B',
Fig. 2124, and a platinum still p, as in the English
method ; but the first of the two boilers B is closed
in at the top for the purpose of passing a current of
sulphurous acid gas through the weak acid, and the
close cover to this boiler is supported by curtains or
partitions c c, which cause the sulphurous acid gas to
travel by a circuitous route, and thus multiply the
points of contact. The boilers are heated by the
flues of the lire F, and the lead is supported by an
outer casing of sheet iron, which also prevents the
flame from coming in contact with the lead. :

The acid to be concentrated is conveyed from the
sulphuric acid chambers by a leaden pipe p, into the
boiler B, and when it has attained a certain height
therein it flows off by a waste-pipe. The sulphurous
acid gas mixed with atmospheric air is conducted into
the boiler from the furnaces Aa in the steel engraving
by means of a pipe s, Fig. 2124, and the gases which
remain after having circulated through the boiler,
together with vapour of water from the weak acid,
are returned by another pipe s' into the chimney c' D,
and thence into the first chamber E E' of the steel
engraving. Within the chimney is shown a portion
of this pipe enclosing a steam jet x, which acts as
a moving power, setting the sulphurous acid gas in
motion from the furnaces A a along the pipe s, through
the boiler B in the direction of the arrows, then along
the tube s' into the chimney D, and so into the
chamber EE'. The sulphurous acid gas, mixed with
common air and assisted by the heat of the flue/",
reacting on the nitrous and nitric acids contained in
the weak acid in the boiler, forms sulphuric acid, and
discharges by the tube s' into the chamber E E' nitric
oxide and nitrous acid, by which means the acid in
the boiler B is denitrified, and the nitrous products,
instead of being discharged into the air, are usefully
employed in producing the reactions above described.
The acid thus made stronger and purer is passed by
a waste-pipe or a syphon o into the open boiler B',
which being nearer the fire F, is evaporated at a
higher temperature, and concentrated to about 00 B.
From this boiler the acid is passed into the platinum
still by means of a syphon n, one leg of which is im-
mersed in a beaked vessel, on raising or lowering
which the discharge may be regulated or arrested
altogether. The concentration of the acid in the
platinum-still may be intermittent or continuous. In
the first case the platinum-still is filled f of its capa-
city as indicated by a floating-gage y, fresh acid being
let in when the evaporation has lowered the surface
of the acid in the still about -^ths of the depth of the
liquid. A brisk fire is kept up in F', and the contents
of the platinum-still are made to boil until the acid is
sufficiently concentrated : this is known by the state
of the acid water, which, distilling over from p in the
state of vapour, is condensed by the worm w w con-



SULPHUR.



805



tallied in the refrigerator n, and is received into a
small reservoir lined with lead. The liquor thus dis-
tilled over contains at first much water, and very little
acid, but in proportion as the acid in P loses water,
its boiling point rises, more acid passes over, until at
length acid containing only a single equivalent of
water (S03,HO) would pass over. When such acid
begins to pass over it is known that the contents of
the still have attained that degree of concentration;



but the process is nearly always arrested long before
this limit is attained, unless where acid of extra
strength is required, and which fetches a higher price
in the market. It is, however, a loss to the manu-
facturer to produce such acid, not only on account of
the smaller quantity which can thus be formed, but
on account of the extra consumption of fuel and the
high temperature, which towards the end of the pro-
cess is near 020: this induces a great amount of ex-



ELEVATION OP BOILEKS FOB EVAPORA.TIKG SULPHURIC ACID.




Fig. 2125.



pansion in the platinum, and endangers its cracking by
its subsequent contraction on admitting a fresh charge.
The operation is generally arrested when the condense
water is of the sp. gr. 45 B. The acid in the still
is then at GG? 13., and forms the sulphuric acid of
commerce.

The operation is, however, more economical when
made continuous; for which purpose a constant stream
of acid is made to pour into the still P, and a constant
stream is at the same time being drawn off. In such
case the product docs not mark a higher degree than
G4 t 5 <? to 65 B., and contains at least 1| equivalent
of water. By this plan, however, the level of the
acid in the still is kept constant, and the temperature
is always the same, two conditions which contribute
largely to the durability of the still. When the acid
is sufficiently concentrated it is drawn off by means
of the syphon aee' d, one leg of which, ae, is fixed
into the boiler r by a screw-joint, its open mouth
a nearly touching the bottom of P. When it is
required to draw off the concentrated acid this
syphon must be primed ; for which purpose platinum



Plan.



plugs are taken out of the platinum cups c e, and
strong sulphuric acid being poured into one of them
it gradually descends and occupies the long limb e' d,
while the air escapes by the other cup e. When the
acid has risen up into one of the cups it is known
that the long limb is full. The two plugs arc then
restored to their place, the cock K is opened, and the
acid flows down the long branch of the syphon, which
being immersed in a refrigerator n' of cold water,
which is being constantly renewed, reduces the acid
to the temperature of the air, or thereabouts, and in
order to increase the cooling-surface the syphon is
divided into 2 or 4 branches. The acid is received
into carboys c c or into a reservoir of lead.

The sulphuric acid of commerce is not quite pure.
It contains persulphate of iron and sulphate of lead,
and other fixed salts, some of which are deposited by
repose. In order to obtain it pure, as it is required
fur many purposes of the laboratory, it must be
distilled, and the most concentrated portion of the
product reserved for use.

The sulphuric acid which has hitherto been referred



806



SULPHUR



to is the monohydrated, or one-watered acid (SOsJiO).
It has a very strong attraction for water, and mixes
with it in any proportion. As the mono-hydrated
acid, however, is much less volatile than water, (not
boiling below 600,) these dilnte mixtures may be
concentrated by boiling, which drives away the sur-
plus water, as already noticed. But by this method
the acid can never be made stronger than the mono-
hydrate, which boils at 620, and distils without
change. Acid containing less water than this can
only be obtained by Valentine's process of distillation
from vitriol, (as is practised at the present day in
obtaining what is called the Nordliausen acid;} and
the reason is, that the monohydrate, SOa+HO, is a
chemical compound, having properties not interme-
diate between those of its ingredients. The anhy-
drous, or waterless acid, S0 3 , which is a solid, is
extremely volatile, being entirely vapourized below
100 : yet, by uniting with 1 equivalent of water (the
boiling point of which is 212), it forms a liquid that
does not evaporate below 600. Compounds contain-
ing either more or less water than this, boil at lower
temperatures, but with this difference, that the former
give out only their surplus water, and the latter
only their, surplus acid ; so that, although boiling
strengthens the one, it weakens the other. At com-
mon temperatures, however, both kinds of acid be-
come weakened, but in different modes ; for while the
common acid emits no vapour whatever, but greedily
attracts moisture from the air, the Nordliausen acid
emits dry acid vapour, which, meeting with the moist-
ure of the air, instantly combines with it and con-
denses, forming the white fumes above mentioned;
and this continues until both the liquid and the
vapour (the former by losing acid, and the latter by
gaining water) become reduced to the state of mono-
hydrate, or common acid.

The Nordhausen, 1 or famine) sulphuric acid, as it is also
called, is indeed a solution of anhydrous in the mono-
hydrated acid. If the Nordhausen acid be carefully
heated in a glass retort, it separates into anhydrous
acid, which comes over in the state of vapour, and
monohydrated acid, which remains in the retort. If
these vapours be received into a small matrass with a
long neck [see MATRASS, Fig. 14261, surrounded by
a freezing mixture, they will condense under the form
of long, white, brilliant needles, and form masses
resembling asbestos. It fuses at about 77, and
boils at between 86 and 95 ; its vapour is colourless.
It is so greedy of water, that if a small piece of the
acid be thrown into it, it produces a noise similar to
that of a red-hot iron plunged into water ; the hissing
noise being produced by the great heat developed,
the instant formation of steam by the contact of the
acid and the water, and the condensation of the steam
by the cold water closing in upon the bubbles. Reg-
nault states that if a drop of water be allowed to fall
into a bottle of the anhydrous acid, a flash of light is
produced and an explosion. When the Nordhausen
acid is exposed to a low temperature, a white crystal-

(1) Nordhausen is in Prussian Saxony. The manufacture,
however, is chiefly carried on near Prague, in Bohemia.



line substance separates, \\hich is a hydrate contain-
ing half as much water as the common liquid acid.

For the preparation of the Nordhausen acid, iron
pyrites, or native bisulphuret of iron, are collected,
washed in water for the purpose of getting rid of clay
and earthy matters, and then calcined in clay retorts,
similar in composition to glass pots [see GLASS, Fig.
1056]. The object of this operation is, first, to obtain
sulphur, and second!}', to reduce the pyrites to that
friable condition which is favourable to the subse-
quent process. The pyrites contain 53'33 per cent,
of sulphur, half of which may be obtained by distilla-
tion in close vessels ; but in such case, the heat must
be sufficiently intense to fuse the monosulphuret
which remains ; but in so doing, the monosulphuret
penetrates the body of the retort, and quickly de-
stroys it. This inconvenience is avoided by employ-
ing less heat ; but in such case only about 13 to 14
per cent, of sulphur is obtained, and there remains in
the retort a sulphuret of iron composed of Fe 2 S 3 .
The retorts are arranged in double rows, six in each
row, and are heated by 3 to 6 fires, the whole ar-
rangement being similar to that of gas-retorts [see
GAS-LIGHTING, Fig. 1020] ; and the vapour of sulphur
which is disengaged is passed down a wide tube into
cold water, where it is condensed. The residue in the
retorts is exposed in heaps to the action of the atmo-
sphere, and in the course of some years it undergoes
a slow combustion, the sulphur and the iron absorb
oxygen, the one forming sulphuric acid, and the other
oxide of iron : the combination of these two com-
pounds forms sulphate of iron, or green vitriol, which
is obtained by washing the pyrites with water, and
evaporating the solution. The mother liquors result-
ing from many similar operations are slowly evapo-
rated ; they deposit a basic sulphate of peroxide of
iron, and retain in solution a mixture of sulphate of
protoxide and sulphate of the sesquioxide of iron. The
solution is evaporated nearly to dryness, and is lastly
dried by the waste heat of the furnace, during which
operation the protosulphate becomes oxidized by ex-
posure to the air.

The furnace used in the distillation of the green
vitriol, is a long gallery, containing 2 or 3 rows of 100
retorts in each,
heated by the
flame of a single
fire. Each retort
RE, Fig. 2126, is
about 8 inches in
diameter, and 32
inches long, and
communicates
with a receiver c
of the same capa-
city, and of similar form. 200 retorts in the course
of 48 hours, during which about 1^ ton of lignite is
burnt as fuel, decompose about 560 Ibs. of green
vitriol. Vapour of water is first disengaged, and
this is allowed to escape ; then sulphurous acid and
oxygen ; and after these sulphuric acid, partly anhy-
drous, and partly hydrated, which is collected. About




SULPHUR.



807



225 Ibs. of this mixed acid is thus obtained, and
about 282 Ibs. of peroxide of iron or coicothar re-
main in the retorts.

Of late years a similar acid has been obtained in
Prance, by distilling dry bisnlphate of potash, or of
soda, in earthenware retorts.

The chief use of the Nordhausen sulphuric acid is
to make the solution of indigo so much used in dyeing
blue colours. 4 parts of the fuming sulphuric acid
dissolve 1 part of indigo, which is soluble in not less
than 8 parts of common sulphuric acid ; not only is
the excess of acid lost, but its presence exerts an
injurious action on the dye stuffs, and the articles to
be dyed.

Iron pyrites is also used in the manufacture of
ordinary sulphuric acid, as a source of sulphur, for
the production of sulphurous acid. It is applied in
two ways : in the first, the pyrites are washed at the
stamping mill, and then spread in layers of about
2 inches deep, on plates of iron heated to redness,
in a furnace similar to that shown at A or a of the
sulphuric chambers, represented in the steel engrav-
ing. The pyrites is frequently stirred with an iron
rake, for the purpose of renewing the*poinfs of con-
tact with the draught of air ; and after G hours the
charge is let down into a cavity under the furnace,
where it continues to burn for some time, and fur-
nishes sulphurous acid, which passes up the chimney
c' D, and so into the chamber E f .

In places where fuel is scarce, the second plan is
adopted, viz. to make the sulphur of the burning
pyrites serve as fuel to a new charge. Eor this
purpose a kind of running kiln, Pig. 2127, is used;
a, fire is lighted on the hearth sufficient to raise the




Fig. 2127.

interior of the furnace to a red heat ; the first charge
of pyrites, r, previously reduced to small lumps, is
then filled in through an opening o in the top, and
as it becomes ignited, fresh quantities are gradually
added, until a height of nearly 3 feet is attained. The
supply of air is regulated by the sliding door D, and
as the pyrites is thoroughly burnt, they are hooked
out by means of a long iron rod from between the
bars, and they fall into the ash pit below. As the
charge sinks in the furnace, more pyrites is added
through o. Six of these furnaces are arranged round
a central shaft, into which they discharge their pro-
ducts of combustion, consisting chiefly of sulphurous
acid and air, by channels such as t, and from the
central shaft the sulphuric acid chambers are supplied



with sulphurous acid. For further details we must
refer to Paycn's " Chimie Industrielle."

In addition to sulphurous acid, SCX,, and sulphuric
acid, 863, sulphur and oxygen combine in other pro-
portions. Ilyposulphurous acid, S-jOj, is interesting,
fiom the property of hyposulphite of soda dissolving
certain insoluble salts of silver, such as the chloride,
on which account it is of importance in PnoTOGiurjiY,
as noticed in that article. The acid has not been
isolated, but by digesting sulphur with a solution of
sulphite of potash or soda, a portion of sulphur is
dissolved, and the liquid by slow evaporation yields
crystals of the new salt. HyponUphtric acid, S a 5 ,
Sulphuretted Jiyposulphuric acid, SsOo, and Jiisulphu-
retted hyposulphnric acid, S 4 O 5 , do not require further
notice in this place.

Sulphur combines with hydrogen, forming sulphu-
retted hydrogen, or hydrosulphuric acid, IIS. It is
a frequent product of the putrefaction of organic
matter, both animal and vegetable ; and it occurs in
certain mineral springs. It is readily prepared in a
gas bottle, such as is used for making common hydro-
gen, by the action of dilute sulphuric acid on sul-
phuret of iron, or of dilute hydrochloric acid on
sulphuret of antimony. The action will be understood
in cither case from the following diagrams :



Sulphuretted hydrogen.



Sulphuret of iron J

Water (Hydrogen

>ter \0xygen

Sulphuric acid



Sulphuret of an-fSulphur
timony \Antimony



Online LibraryCharles TomlinsonCyclopædia of useful arts, mechanical and chemical, manufactures, mining, and engineering (Volume 2) → online text (page 187 of 245)