Friedrich Ludwig Knapp.

Chemical technology; or, Chemistry, applied to the arts and to manufactures online

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been instituted by Anthon which prove how very objectionable the]

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[practice must be of concentrating the acid in leaden pans beyond
the prescribed limits. Anthon found in acid thus concentrated
and afterwards cooled down to 68° F. the following quantities of
sulphate of lead :

Acid of sp. gr. 1.724 contained Tfo^hs sulphate of lead.

„ „ 1.805 „ -j-J-jjths „ „

The annexed wood cut (Fig. 96) shows the manner in which the
platinum still is erected in the concentrating house of the vitriol

Fio. 96.

The high price of platinum vessels renders it very much to tlie
interest of the manufacturer that they should be in constant use ;
yet it is impossible to draw off so powerful an acid at that tempe-
rature into the glass carboys, in which it is sent out^ and leaden
coolers cannot be used. Hence arises the necessity for the plati-
num syphons^ Figs. 97 and 98^ which at the same time answer
the purpose of coolers. The syphon abc is let into a wide tube
dd, which is supplied with a current of cold water through e.

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The water, after becommg wann^ flows off at g. The cooling is,
therefore, effected by surrounding the hot acid in ic with a

Fio. 97.

PIG. 98.

current of cold water passing in an opposite direction, the effect of
which is very much increased by making the longer limb in four
distinct tubes, as in Fig. 98. To fill the syphon, the cock n is
stopped, and acid is poured first into o, and then into o', until it
runs down into the retort through b a. When o and o* are now
closed, and n opened, the syphon comes into play.

[The process of concentrating sulphuric acid in a series of open
leaden pans by applying tbe heat below, has been abandoned in
most manufactories, in consequence of the great waste of the pans
themselves (v. p. 249), and the loss of acid, where the chambers have
been worked with an excess of sulphurous acid. Two modifications
have been introduced with great advantage. One of these
modifications consists in covering the leaden pan with a moveable
hood of sheet-lead, suspended from a wooden framework, con-
structed in the same way as the ordinary sulphuric acid]

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[chamber : and this
FIG. 99. y '

improvement gene-
rally effects a saving
of lOper cent of acid.
The other modifica-
tion is shown in the
drawing, Fig. 99, by
means of which a
larger quantity of acid is concentrated in the same time, and the
leaden pans protected from the serious corrosion to which they are
liable under both the other systems. This arrangement consists
of a leaden pan a, built in brickwork, and enclosed in a furnace b,
when the heat from the furnace c is applied from above, and
passes along, with all the fiimes, into the flues d. The advantages
of this latter plan are too obvious to require any notice.]

Produce, — In a manufactory like that described, from 100 lbs.
of sulphur, 308, 310, or even 320 lbs. of concentrated commercial
acid, according to the management of the process, may be obtained,
of 66^ B. (= 1.816 specific gravity), and for the production of
this quantity, from 10 to 12 lbs. of nitric acid are requisite,
whilst upon the old plan the produce would not have exceeded
150 to 200 lbs. of sulphuric acid. As the commercial acid is not
pure hydrate (SO3, HO), but, on account of about 7 per cent
residual water, is probably a mixture of SO3, HO, with some
SO3, 2 HO, the mean produce of 310 lbs. will correspond with
288 lbs. of actual hydrate. Now as 100 lbs. of sulphur in becom-
ing sulphuric acid, require 150 lbs. of oxygen (=3 equivs.), and
56 lbs. (= 1 equiv.) of water, which, according to theory, would
give 306 lbs. of hydrate, we see to what a high state of perfection
this branch of manufacture has arrived, when only (18 per cent of
hydrate =) 6 per cent of sulphur have been lost in the process.

[The manufactory described at page 240, is capable of burning
40 tons of sulphur per week, with a produce of 8 of oil of vitriol
for 1 of sulphur, and a consumption of only 3 lbs. of nitrate of
soda for every 100 lbs. of sulphur.]

To produce this mean quantity of acid (310 lbs.) 48 cwts. of
sulphur are burned, on an average, daily, therefore, 2 cwts. per
hour, which take up 2 cwts. of oxygen from 8.5 cwts. = 21000
cubic feet of air, in order to be converted into 4 cwts. = (about
4400 cubic feet at 0^ C.) of sulphurous acid ; in which case there
will remain 6.5 cwts. of nitrogen from the air, = 16,400 cubic

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feet. On its arrival in the chamber, the sulphurous acid requires
10,700 cubic feet of air, in order, by the separation of another
quantity of nitrogen (8401 cubic feet), to combine with 1 cwt. of
oxygen = 2200 cubic feet, and become converted into sulphuric
acid. From the sudden condensation of the latter, which is
almost equivalent to its complete removal, the chamber, upon the
old plan, was exposed to the risk of being crushed in — ^inasmuch
as it was closed for a time.

The excess of air which enters the chambers being left out of
calculation, there will pass through them altogether in an hour
(4400+16400 + 10700=) 31500 cubic feet of the mixture of
gases,* so that during the lapse of twenty-four hours their con-
tents will be changed four or five times. The gases which escape
carry with them the nitric oxide, which is each time generated,
about 5 or 6 lbs. in the hour (to 2 cwts. of sulphur). To regain
this, at least, the greater part, the gases, in escaping from the
chamber are brought into contact with a current of strong
sulphuric acid, in the form of rain, which absorbs nitric oxide
with great avidity, as described at page 244.

Impurity. — English commercial oil of vitriol is not sufl&ciently
pure for all purposes : it contains, besides hydrochloric acid (from
the common salt of the impure saltpetre), traces of nitrous acid,
nitric acid, and particularly nitric oxide, which are detected by
the purple colour which it assumes with green vitriol. On dis-
tilling the acid, sulphate of nitric oxide being less volatile, is
contained in the residue. The presence of the oxides of nitrogen
is objectionable to the manufacturer, on account of their com-
municating to the acid the property of attacking platinum. To
get rid of that portion which would otherwise reach the platinum
retort, tV to 5 per cent of sulphate of ammonia may be added
before the heat is applied ; the ammonia, and the oxides of nitrogen,
are then converted into water and nitrogen gas (Pelouze). Besides
these, impurities, there are also sulphate of lead, (which is not sepa-
rated by sulphuretted hydrogen, but only by dilution), anhydrous
persulphate of iron (as a white deposit, which vanishes on dilu-
tion), selenium, and arsenic (from the sulphur, or pyrites) in the
acid, which is likewise frequently coloured brown by straw, or
cement that has fallen into it.

Fuming oil of vitriol. — Of those sulphates which part with their
acid at a red heat, without decomposition of the latter into sulphu-
* At a temperature of 0« C. (32« F.)

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reus acid and oxygen, the persulphate of iron is the only one that
can be used in the manufacture of the fuming acid. This substance
is always evolved when green vitriol, a cheap, easily obtainable
salt, is heated to redness. The starting point of the manufacture
is, therefore, green vitriol, (hence the name, oil of vitriol), or
crystallized proto-sulphate of iron, (Fe 0, SO34-7 HO), 6 equivs.
of its water being driven off, before decomposition ensues ; the
seventh equiv., which is more intimately combined, is only expelled
when that process begins. In the vitriol manufactories, the impure
vitriol obtained by evaporation of the mother liquors, which has
no commercial value, is subjected to two consecutive operations,
the one of which removes its water, the other its acid.

The furnaces, — ^Both these operations are effected simultaneously
in the same furnace, the arrangement of which, as constructed
at Hermsdorf, is seen in profile at Fig. 100. The furnace used at
Radnitz, in Bohemia, is represented at Fig. 101. In the gallery

PIG. 100.

FIG. 101.

furnaces (Galeerenofen) in general, as represented in Fig. 100,
the same firing heats two rows of vessels a a, in which the decom-
position is effected ; these pots are walled in at the necks c c, and
in such a manner that the moveable receivers b b can easily be
inserted, and made tight by cement. If, on the contrary, the
necks of the retorts a were inverted into the receivers 6, the
cement would be liable to fall into the acid. The grate d is carried
throughout the whole length of the furnace to the chimney /; e

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is the ash-pit^ and m the drying chamber for separating the water
from the vitriol, which is heaped up upon the projecting plate n.
The walls cc are overlaid at top with plates of clay A. The
Bohemian furnace is not essentially different from the one described,
except that it is calculated for a double range of retorts. The
retorts are 1^ feet long, and 4 inches wide at the neck ; the
receivers are of the same length, and are 1^ inch wide at the
mouth ; both retorts and receivers are from 5 to 6 lines thick,
and composed of crucible ware. The furnaces accommodate from
twelve (as in Fig. 101) to thirty retorts on each side, which are
placed 8 inches apart.

Process of distillation. — When the retorts are charged, each
with about 2 to 2^ lbs. of calcined vitriol, a flame-fire is made
with dry pine wood. The first portions that pass off, consisting
of very weak sulphuric acid, and much sulphurous acid, are not
collected. As soon, however, as the grey, fog-like vapours of
anhydrous sulphuric acid appear, the receivers are connected, each
containing about an ounce of rain-water, and the distillation begins.
The heat is kept up until the retorts have been exposed for some
time to a white-heat, in all about thirty-six hours ; as long, indeed,
as acid passes over. When this ceases, and the receivers have
become cool, they are at once removed, the retorts emptied, and
charged anew, which is done by means of iron shovels ; the same
receivers are again adapted (without having been emptied), and
the process is then repeated. The acid in the receivers is
not so saturated with anhydrous sulphuric acid, as to attain
the strength of commercisd oil of vitriol, until this process
has been repeated four times. In this manner, 45 to 50 per
cent of the dry vitriol is obtained as acid, which is sent out in
stoneware jars, with screw stoppers, covered with cement. The
residue is a reddish-brown earthy mass, called Colcothar, or CaptU
mortuum vitrioli, and may be used as a paint.

When anhydrous vitriol (FeO, SO3) is heated to redness, the
protoxide is converted into peroxide, by taking from a portion of
the sulphuric add, the requisite quantity of oxygen, the former
becoming reduced to sulphurous acid. For 2 Fe 0, SO3, or
2Fe+2 0+S0s + S03 = Fe^ O3, SOa + SO^.

Basic persulphate of iron is, therefore, formed^ which at a still
higher temperature parts directly with its acid. From the great
tendency which protoxide of iron has to combine with oxygen,
or to be converted into peroxide, more exposure to the air, or slight

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roasting^ is sufficient to eflFect this conversion^ when 2 Fe O, SO3,
or2Fe-|-2 + 2SOs-l-0 (from the air), become Fe2 03 + 2S03,
or f basic persulphate of iron, which at a high temperature parts
with the whole of its sulphuric acid without any formation of
sulphurous acid, and, therefore, without loss. This is the case
in the vitriol works, where vitriol is employed that has become
nearly entirely peroxidised by exposure to the air; for every
portion of oxygen taken up, five portions more anhydrous acid
are obtained. The chambers m, therefore, besides separating the
water from the vitriol, roast it also to a certain extent. The
amount of produce proves what is here stated ; for whilst proto-
sulphate of iron ought to produce 30.3 per cent, and the persalt
53.3 per cent of dry acid, 50 per cent of oil of vitriol is obtained,
which is equivalent to much more than 30.6 per cent of anhydrous

Since English sulphuric acid has become so cheap, manufac-
turers have begun to use it in the vitriol works, either for dissolv-
ing colcothar, (to form persulphate of iron), which is then decom-
posed in the manner described, or for replacing the water in the
receivers. In the latter case, the product is of course contami-
nated with all the impurities of the English acid.

Fuming oil of vitriol is an oily, brownish fluid of 1.9 specific
gravity. Its chief constituent is the hydrate 2 SO3, HO ; in the
weaker acid this is mixed with the simple hydrate SO3, HO, in
the stronger it contains anhydrous sulphuric acid SO3 in solution.
The latter substance is so volatile, that it escapes even at ordinary
temperatures from the oil of vitriol, and uniting with the moisture
of the atmosphere, is condensed in the form of a visible cloud to
SO3, HO. Hence the fuming. Together with selenium, and
earthy particles, sulphurous acid is never missing amongst the
impurities, and is only gradually evolved on dilution, destroying,
for instance, the spongy platinum in the platinum lamp, when
fuming acid is used to supply it.


Occurrence. — Sea-salt, or culinary salt, (chloride of sodium
NaCl), is not an artificial product, but is found even lavishly
prepared and stored up in the earth by nature. Nevertheless,
the manner in which it is obtained is interesting, and the more
so, as it is the source of the most important compounds of soda.

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As a rock — rock-salt — for so it is called by mineralogists — forms
a distinct member in the series of stratified rocks, occurring with
limestone, clay, chalk, gypsum, marl, stinkstone, slate, and not
imfrequently with bituminous formations. The great deposit
of salt which extends from Upper Austria through Styria, Salz-
burg, and Berchtesgaden, as well as that of Wimpfen, in Wiirtem-
berg, are the most extensive and productive in Grermany.* From
the section of the latter. Fig. 102, it will be seen how the gypsum

FIG. 102.

is enclosed by a deep layer of shell-limestone, containing the
rock-salt as a separate mass. It is highly probable that the
rock-salt in this, and similar basins, has been deposited from
saline lakes, and this explains why it should occur in more defined
and rounded masses, as compared with the enormous extent of
the other members of the same formation. In the high lands of
Asia and Africa there are often extensive wastes, the soil of which
is covered and impregnated with salt, without having ever been
covered by other deposits. Salt lakes themselves are not uncommon,
and occur on the banks of the Wolga, in South Africa, in England,
and in the neighbourhood of the Caspian Sea. In the water of
one of these lakes near Sympheropol, in the Crimea, Gobel found
16.12 per cent chloride of sodium, 2.444 sulphate of soda, 7.55
chloride of magnesium, 0.276 chloride of calcium, and 0.7458
sulphate of potash. The simultaneous occurrence of soluble
sulphates, or other chlorides, as well as the corresponding com-
pounds of bromine and iodine, which has everywhere been
observed, is of equal importance as regards the history of its
origin, as also of the mode of obtaining sea-salt. Lastly, the water
of the ocean — ^which, from the geological processes concurring

[* The chief deposit of rock-salt in England is at Northwich, in Cheshire, where the
mineral occurs in two beds, one above the other, and separated by about 30 feet of
clay and marl, intersected with veins of rock-salt. The two beds together arc not
less than 60 feet thick, and probably extend \\ miles, and are 1300 yards broad.]

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in its formation^ is necessarily a solution of salt — contains chloride
of sodium as its chief saline ingredient. On account of the
unequal amount of evaporation, however, the water of the sea
has not always the same composition ; thus there has been found
in 1000 parts :

(N. Sea).


Chloride of sodium . .

„ magnesium

9, potassium
Sulphate of lime . . . .

„ magnesia

„ soda . . . .
Carbonate of lime and magnesia.







Total amount of salts.




to which must be added 6.2 vol. per cent of earbonic acid, traces
of proto-carbonate of iron and manganese, phosphate of lime,
silica, bromides and iodides of the metals, some organic matter,
and ammonia.

Production of salt from sea-water. — It is seldom that artificial
evaporation is had recourse to for separating the salt from sea-
water ; when it is practised, the same mode is adopted as will
be described hereafter with reference to the brine springs ; some-
times, as in Siberia, frost is made subservient to this object — for
salt water separates on freezing into ice, (containing no salt)^ and
a strong saline lye; but most generally evaporation is eflFected
by the air and sun in the "salt gardens/' Fig. 103, which are laid
out upon a clay soil on the sea coasts of southern climates,^ and
being secured from the influence of the tides, are cultivated
during the summer months, from about March to September.
These salt-gardens are nothing more than a series of very shallow
ponds, intended to spread the water over a very large surface
with hardly any depth of liquid, so that by increasing as much
as possible the evaporating surface> the drying action of the air may
be more fully exerted, and salt may be deposited in the hindermost
pools, whilst the foremost ones are constantly supplied with fresh
sea water. Advantage is taken of the flow of the tide to fill
the collecting pond A^ through the flood gate a, to the height
of from 2 to 6 feet, in which the evaporation begins, but the
principal object of this first pond is, to allow the water to deposit
its mud. The pipe h then carries the clear water from the


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collecting pond to the perfectly horizontal but very shallow front

no. 103.

pool c, Cy Cy from whence^ by means of a second pipe rf, it is
circulated through a channel e, e, 16000 feet long, from this it
enters the ponds /, f, /, and lastly runs through the open channel
^ to a third series of ponds hj. h, h. At this point, the evaporation
has proceeded so far that the salts begin to crystalUze in the
hindermost reservoirs o,- o, o, of which there are four rows. From
the reservoii's A, A, numerous channels », t,. branch out, which
supply the crystallizing ponds o, o. The manner in which the
water arrives in these through the gutters in the sides, is clearly
shown in the drawing. The saline incrustation with which the
surface of o, o, o, becomes gradually covered, is broken up and
collected with rakes into small heaps r, r,. r, on the sides, and
from these the mother liquor runs off into the ponds o, o,
and h, h. When no more salt separates by crystallization, the
lye is allowed to run off through x into the sea. The salt
as at first collected, would contain too much impurity, chiefly
consisting of chloride of magnesium, the smaller heaps r, r, are
therefore made up into larger square (m, m), or round heaps
(n, n), which are allowed to remain for a time covered with
straw. The rain is thus kept off, and the moisture of the atmos-

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phere suffices to liquify the chloride of magnesium, which is
thus gradually separated from the saline mass.

Although the entire surface of the ponds amounts together to
many hundred acres, yet the process depends so entirely upon
the sun and wind, that in wet weather the evaporation sometimes
entirely ceases. The following analyses of sea-salt show the
nature and amotmt of its impurities.



• « .







o S


Salt from St. Ubea in


I. Sort .





— ■

IL „ . . .






. Berthier

m. „ . . .







Salt from Figueras .






„ EymingtoD





0.20 •



salt) ....






0.10 .

Rock-salt, — The mode in which salt is obtained from the
deposits of rock-salt depends very much upon the locality, upon
the depth of the deposit, the price of fuel, the rate of wages,
&c. &c. In some places, it is a mining operation, and is carried
on by means of shafts and horizontal galleries, as at Wieliczka
in Grahcia (where the layer is 500 miles long, 20 miles broad, and
1200 feet deep), near Liverpool, in England, and in other places.
It depends upon the degree of purity of the rock-salt, whether
it can at once be brought into the market, or must first be
purified by solution and recrystallization. Near Liverpool, for
instance, it is obtained as clear as glass and colourless; in
general, however, it varies throughout the mass, is often coloured
red, either from clay or bitumen, and particularly from the same
kind of infusoria, which are still found inhabiting salt-lakes.
Rose has also observed a particular kind of carbo-hydrogen
Cji Hg in the rock-salt of Wieliczka, which is enclosed in a high
state of condensation, and is evolved on dissolving the salt with
% peculiar crackling sound. Henry found in the rock-salt from
Chester 98.3 per cent chloride of sodium, 0.05 chloride of mag-
nesium, 0.65 gypsum, and 1 per cent of insoluble matter. In
other places, as at Wimpfen, fresh water is let down through a
bore extending to the middle of the salt bed, and pumped up


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again as a saturated solution. For this purpose pumps and pipes
descend the whole depth of the bore. The solution of salt is
raised in the pipes^ whilst between these and the sides of the
bore fresh water flows down. Thus a wide cavity is gradually
left in the bed of salt^ in which fresh water and a solution of
salt is contained. Now^ as 1 cubic foot of the saturated solution
weighs 6.4 lbs. more than the same volume of fresh water^ the latter
will chiefly occupy the surface of the fluid in the cavity. The
pump must^ therefore^ work from the bottom of the cavity^ and
the suction pipe be sufficiently deep for that purpose. The valves^
however^ may be placed much higher up^ because the fluids on
the inside and outside will balance each other^ and the solution
of salt will be as much below the level of the water as its
specific gravity is greater.'*' At 1200 feet depth of bore^ for
instance^ the saturated solution of salt will of itself stand at
1000 feet^ and the pump will only have to raise it 200 feetr

Natural brine welk. — Salt wells^ which may thu? be artificially
constructed, are alsc^ frequently found ready formed in- nature^
wherever a springs during its course^ has come in contact with
a bed of rock-salt (Soolen). It is rare^ however^ that these
are so highly saturated as the artificial springs^ although this
is actually the case with that of Liineburg^ whicb contains 25 per
cent; but they are generally very slightly impregnated^ or have
become weakened by an after addition of fresh water. This diffe-
rence in the strength^ and many other circumstances attending
the occurrence of salt will be seen from the following tabular

* Specific gravity of tAe satunted soration » T.2046. 100 parts of saturated
solution contain :

At V^ 26.53 Chloride of sodium according to Unger, Gay-Lussac.

— 17" 26.40 „ „ Gay-Lussac.
— 18.8" 26.76 „ „ Karsten

— 25<» 26.30 „ „ Kopp.

— 100" 28.22 „ „ Unger, Gay-Lussac.

And at every temperature 27.00 „ „ Fuchs.

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Brine springs.

Salt (chloride of sodium)
Chloride of potassium.

tf magnesium,

„ calcium.

M .ammonivm.

M lithium.

Bromide of magnesium.

I, sodium

Iodide of magnesium .

Online LibraryFriedrich Ludwig KnappChemical technology; or, Chemistry, applied to the arts and to manufactures → online text (page 24 of 56)