Johannes Rudolf Wagner.

A handbook of chemical technology online

. (page 34 of 109)
Online LibraryJohannes Rudolf WagnerA handbook of chemical technology → online text (page 34 of 109)
Font size
QR-code for this ebook


purposes. At the present day these purposes are very varied, but consist chiefly of
the vulcanisation of caoutchouc, the extraction of fat from bones, and oils from oU
seeds and olives, the extraction of sulphur firom its concomitant rocks, and of fat
from crude wool. Sulphide of carbon is also used in electro-plating to obtain by its
addition to the silver-bath a bright and polished surface. It is highly valued for
killing vermin in com.

chiadde of sniphsr. Chlorido of sulphuT (ClaSa), important only in its technical use
lor the vulcanising of caoutchouc, is an oily fluid, sp. gr. i 60, of a brown colour,
fuming on exposure to air. It boils at 144°. On being mixed with water it is
decomposed, yielding sulphurous and hydrochloric acids, a very small quantity of
sulphuric add, and sulphur. Chloride of sulphur converts rape-seed oil into a mass
resembling caoutchouc, and linseed oil into a varnish. Chloride of sulphur is
prepared by passing chlorine gas over sulphur heated to 125'' to 130° ; the product is
rectified by distillation.

Hydbocbloeic Acid and Glauber's Sai.t, or Sulphate of Soda.
HydnMhiode Add. The commercial article known as hydrochloric or muriatic acid,
or spirits of salt, is, as has been explained in the manufacture of soda, a solution
of the gas given off during the decomposition of common salt by sulphuric acid.
Jn order to effect this condensation, the gas is conveyed to the coke columns, or in
many instances is prepared and condensed by the aid of the apparatus shown in
section in Figs. 102 and 103, and in plan in Fig. 104. This apparatus consists of
several cast-iron cylinders, 17 metres long by 07 metre diameter, closed similarly



Digitized by VjOOQIC



212 CHEMICAL TECHNOLOGY,

to gas retorts by lids Inted with clay. One of the lids is provided with an opening,
o, into which is fitted the stoneware or leaden pipe, a, conveying the hydrochloric
acid to the condensing apparatus. The other, or posterior lid, is also provided with
an opening, d, through which is passed the tube of a leaden funnel, so that after
the retort is filled with salt, sulphuric acid may be poured in. The construction of

FlO. 102.



the furnace, in which two retorts are usually placed, allows the flame of the fire at
o to play round the cylinders before reaching the flue leading to the chimney, f.
B is an arch covering the furnace. The first stage of the operation is to fill each
cylinder with 150 kilos, of salt or chloride of potassium, in localities where the latter
is abundant. The lids or covers are next luted on, and the fire kindled. The

Fio. 103.



required quantity of strong sulphuric acid is now poured into the retort, and the
funnel having been withdrawn from rf, the hole is closed by a clay plug. As soon
as the reaction is over, the 180 kilos, of sulphate of soda produced are removed, and
the operation repeated. The condensation apparatus. Figs. 102 and 104, consists of



Digitized by VjOOQIC



GLAUBER'S SALT,



213



rows of WotJfe*s bottles partly filled with water, care being taken to place the first
pair of these bottles in a tank of cold water. The condensation of the last portions

Fig. 104.



of the hydrochloric acid gas is effected either by the aid of coke columns, or in
leaden chambers, into which fine jets of cold water are injected on all sides.

PropflttiM o<^7<ixo«ii]oiie Cmde commercial hydrochloric acid is conmionly a yellow
Hqnid, this colour being dne to chloride of iron. It has a caustic sour taste, and
fames on exposure to air. At 20^ water is capable of absorbing 475 times its own
bulk of hydrochloric acid gas ; a saturated solution contains 4285 per cent of
gas, the sp. gr. being = i*2i. The following table shows the sp. gr. of hydrochloric
acid at various degress of concentration, and the quantity of pure acid (real
gas) contained at 70°: —



Specific
grayity.


Degrees
Baum6.


Degrees
Twaddle.


Percentage
of acid.


Specific
gravity.


Degrees
Baum6.


Degrees
Twaddle.


Percentage
of acid.


I'2I


26


42


4285


IIO


14-5


20


2020


120


25


40


40'8o


109


12


18


1818


119


24


38


3888


108


II


16


1616


118


23


36


3636


107


10


14


1414


117


22


34


3434


106


9


12


1212


116


21


32


3232


105


8


ID


ID* 10


115


20


30


3030


104


6


8


8-o8


114


19


28


2828


103


5


6


606


113


18


26


2626


I 02


3


4


404


112


17


24


2424


lOI


2


2


202


III


155


22


2222










UMt of Hydrochloric


Hvdroch


oric acid is v


erv larcrel


V emolovt


)d in the





of chlorine, sal-ammoniac, chloride of antimony, glue, phosphorus, in the prepara-
tion of carbonic acid for the manufacture of artificial mineral waters, in beet-root
sugar works, bleach works, hydro-metallurgy, and alone or mixed with nitric acid
for dissolving various metals.

oiuber'ssaiL Sulphate of soda, or Glauber's salt, consists in 100 parts of 19*3 soda,
247 sulphuric acid, and 56 water; formula, Na2S04+ioHaO ; anhydrous, Na^SO^,
in 100 parts — soda, 436 ; sulphuric acid, 56*4. It is prepared as described under
hydrochloric acid by decomposing common salt with sulphuric acid. It is also
found native as Thenardite (NaaS04), Brogniartine or Glauberite (Na2S04+CaS04),
and it occurs in sea-water and some mineral waters, as in those of Piillna and
Carlsbad.



Digitized by VjOOQIC



214 CHEMICAL TECHNOLOGY.

Sulphate of soda is indirectly obtained by yarious procefises, among which

1. The double decomposition of common salt and sulphate of magnesia or kieserite from.
the mother >Uquor of sea-water, or of salinea when exposed to a low temperature either
naturally in water or artificially by the assistance of Garr^^s ioe-midung machine.

2. Longmaid*8 process of roasting sulphuret of iron or copper with common sidt. 3. Cal-
cination of kieserite or magnesian sulphate with common salt. 4. Euhlmann's proceas,
the ciJcination of sulphate of magnesia and nitrate of soda, hyponitric acid and sulphate
of soda being formed. 5. As a by-product of paraffin and petroleum refining. The
sulphate of soda of the aUtali works contains on an average 93 to 97 per cent of the pure
salt, the remainder being chiefly chloride of sodium.

ums of snipiwto '^^^ ^^ ^ extensively employed in the manufactures of soda, ultra-
ot sodA. marine, and 'glass. In the last case the sulphate is mixed with coal and
BUica, and calcined, its sulphuric acid being reduced to sulphurous acid, which is Tolatiliaed,
whUe a silicate of soda is formed. Sulphate of soda when thus employed should be
purified from all traces of iron by being dissolved in water, some lime added to the
solution, and the clear liquid evaporated to dryness. Sulphate of soda is used in
metallurgy in the treatment of some kinds of antimonial ores, the sulphuret of antimony
found near Bono and Septemes, France, Ac, It is also employed in certain prooessee of
wool-dyeing.

BiBoiphato of Sod*. This Salt (NaHS04) is obtained in large crystals when i molecule

of sulphate of soda and i molecule of sulphuric acid are dissolved in water and

the solution left to evaporate slowly. One of the chief uses of the bisulphate is in

a mixture with abraum salt containing chloride of magnesium, employed for

removing zinc from .lead. As a by-product sulphate of soda is obtained in the

manufacture of nitric acid from nitrate of soda and sulphuric acid, and by heating

cryolite with sulphuric acid.

Bleaching-Powder and Hypochlorites.

Chlorine. It is oue of the most valuable properties of chlorine that it destroys
organic pigments and miasmata, and is hence useful as a bleaching agent, and as a
disinfectant. It is also employed as an oxidising agent in the extraction of gold
from pyritical ores.

At the ordinary temperature and pressure of the atmosphere chlorine is a
greenish-yellow gas, its sp. gr. = 1*33; it possesses a peculiarly disagreeable,
irritating odour, and is very soluble in water, i volume absorbing 25 volumes of
gas, forming the well-known aqua chloriiy or acidum tnuriaticum oxygenatum aqua
solutum of the pharmaceutists, and the chlorine water of the scientific chemist.
The bleaching property of chlorine gas, possessed also by its solution, is due to the
great affinity of chlorine for hydrogen, so that the chlorine while seizing upon the
hydrogen of the organic body m most instances causes the simultaneous decom-
position of water, and by the formation of ozone destroys the organic colouring
matter, hydrochloric acid being at the same time formed, a fact requiring attention
in the use of chlorine as a bleaching agent. When linen, or rather flax, raw cotton,
and paper pulp are bleached by chlorine, the fibre, really cellulose, is not acted upon,
but only the colouring matter is oxidised b^ the ozone formed. Chlorine cannot be
used to bleach animal matters, or such as contain nitrogen, these becoming yellow
by its action. Chlorine is not suited for transport either as gas or in aqueous
solution, therefore one of its combinations with oxygen and a base, viz., a hypo-
chlorite, is used. Hydrated oxide of calcium or slaked lime is the chief constituent
of bleaching-powder. Usually the alkali manufacturers prepare bleaching-powder.

Prcparati^on^o^f^Bieaching- Bleachiug-powder is prepared on the large scale in the
following manner : — In works where soda and chloride of lime are to be manu-
factured simultaneously, the chlorine is obtained by mixing the common salt to be



Digitized by VjOOQIC



BLEACHINQ-POWDER. 215

amverted into sulphate of soda by the action of sulphuric acid with peroxide of
manganese, heat being applied.
The process is as follows: —

Common salt, 2NaCl, ] (Glauber's salt, NaaSO^,

Peroxide of manganese, MnO^, Y yield i Sulphate of manganese, MnSO^,
Sulphuric acid, 2H2SO4 J I Chlorine, 2CI, and 2HaO.

In some works chlorine is prepared by the reaction of hydrochloric acid and
manganese, and sometimes with the addition of sulphuric acid. In the first instance
only half the chlorine contained in the hydrochloric acid is given up, because the
other half forms chloride of manganese ; for —

Chlorine, Cl^,
- Manganic chloride, MnCl^,
IWater, 2HaO.

In the second instance all the chlorine contained in the hydrochloric acid is
obtained —



Manganese, MnOa, i . , ,

Hydrochloric acid, 4CIH,r ^^^^^



4



Manganese, MhO^, ]

Hydrochloric acid, 2CIH, L yield
Sulphuric acid, HaS04,



Sulphate of manganese, MnS04,
Chlorine, Clj,
Water, 2HaO.



As proposed by Clemm, a chloride of magnesium solution, as largely obtained at
Stassfort, may be employed by concentrating the solution to 44° B (=1*435 SP- P^)>
and adding manganese, so that to i mol. of MnO^, 2 mols. of MgCl^ are taken. The
cooled, solid mass, when exposed to the action of superheated steam at 200"" to 300"*,
yields chlorine gas.

^*^3IEit MMgSSL*"* The following methods are selected as being the most scientific
and interesting: — •

1. Mac Dougal, Hawson, and Shanks's process, consisting in the decomposition of
chromate of lime by hydrochloric acid, the result being the formation of chloride of
chromium, chloride of calcium, and the evolution of free chlorine—

(2CaCr04+i6HCl=CraCl6-|-2CaCU+3H20-f6Cl).
158 parts of chromic add yield 106 parts of chlorine. The chloride of chromium is
again precipitated with carbonate of lime, and by ignition converted into chromate of
lime. Only three-eighths of the chlorine contained in the hydrochloric acid is given
up, while manganese yields one-half.

2. Schlbsing*s method consists in acting upon manganese with a mixture of hydro-
chloric and nitric acids, the degree of concentration of the acids being so regulated by
the addition of water that the mixture yields only chlorine, while nitrate of protoxide
of manganese is formed; this salt being calcined yields manganese, peroxide, and
nitric acid. The nitric acid aids the oxygen of the air in decomposing the hydro-
chloric acid. The nitrate of manganese begins to decompose at 150'', and the decom-
position is completed at 175° to i8o^ yielding much peroxide, in some cases even
93 per cent.

3. Vogel's method of decomposing chloride of copper by heat. 3 mols. of
chloride yield i mol. of chlorine ; according to Laurens the process is: —

2CuCl2=Cla+CuaCl2.
The chloride in crystalline state is mixed with half its weight of sand, and heated in
earthenware retorts to 200^ to 300°, yielding chlorine gas, while the remaining proto-
chloride of copper is re-converted into perchloride by the action of hydrochloric
acid. Mallet has constructed a peculiar rotating apparatus for the decomposition of



Digitized by VjOOQIC



2i6 CHEMICAL TECHNOLOGY.

this salt, the same apparatus serving to prepare oxygen. loo kilos, of cnpric
chloride yield 6 to 7 cubic metres of chlorine gas.

4. P61igot's method. When 3 parts of bichromate of potassa and 4 parts of con-
centrated hydrochloric acid are gently heated, the fluid yields on cooling crystals of
bichromate of chloride of potassium, KCl,Cr03 ; at 100° this salt yields chlorine.

5. Dunlop's process is followed at Mr. Tennant's works, Glasgow. Sulphuric acid
is made to act upon a mixture of 3 mols. of common salt, and i moL of nitrate of
soda, the result being the formation of chlorine and hyponitric add. The latter ia
absorbed by passing the mixed gases through strong sulphuric acid.

6. Mr. Walter Weldon^s process is performed by means of an apparatus eomprifflng
five yessels arranged at succesBiye eleTations, so that after having been pumped up to the
highest of them, the liquor operated upon can afterwards descend to all the others by its
own gravity. The lowest of these vessels is a well, which is furnished with a mechanical
agitator. The slightly acid chloride of manganese liquor with which the process oom-
menoes runs from the stills in which it is produced into this well, and is there treated wiUi
finely divided carbonate of lime, the action of whioh is facilitated by the energetic
agitation. When the neutralisation of the free add which is at first contained in this
liquor and the decomposition of the sesquiehloride of iron and sesqniohloridaof aluminium,
which are also at first contained in it, are completed, the liquor is pumped up into
settling tanks, placed nearly at the top of the apparatus, and known as the " chloride of
manganese settlers." It now consists of a quite neutral mixed solution of chloride of
manganese and chloride of calcium, containing in suspension considerable quantities of
sulphate of lime, and Bm&R quantities of oxide of iron and alumina. These solid
matters rapidly deposit in the chloride of manganese settlers, leaving the bulk of the
liquor perfectly bright and clear, and of a faint rose-colour. The next step is to run o£f
the clear portion of the contents of the settlers into a vessel immediately bdow, called
the oxidiser. This is usually a cyUndrical iron vessel about 12 feet in diameter, and about
22 feet deep. Two pipes go down nearly to*the bottom of the oxidiser, a la^g® pne for
conveying a blast of air from a blowing engine, and a smaller one for the injection of
steam. The latter is for the purpose of raising the temperature of the contents of the
oxidiser when necessary; for sopietimes the chloride of mangsmese liquor reaches
the oxidiser sufficiently hot — between 130^ and 160° or 170° F. Immediateiy above the
oxidiser is a reservoir containing milk of lime. The oxicUser having received a charge of
clear liquor from the settlers, and this liquor having been heated up to the proper point, if
it was not already hot enough, blowing is began, and milk of lime is then run into
the oxidiser as rapidly as possible, until the filtrate from a sample taken at a tap placed
nearly at the bottom of the oxidiser, ceases to give a manganese reaction with solution of
bleaching-powder. A certain quantity of Tnillc of lime is then added, and the blowing
continued until peroxidation ceases to advance. That point is usually attained when
from about 80 to 85 per cent of the manganese present has become converted into
peroxide. The contents of the oxidiser are now a thin black mud, consisting of solution
of chloride of calcium containing in suspension about 2 lbs. of peroxide of manganese
per cubic foot, these 2 lbs. of peroxide of manganese being combined with varying quan-
tities of protoxide of manganese and lime. This thin mud is now run off from the
oxidiser into one or other of a range of settling tanks or " mud settlers," placed below it,
and is there left at rest until it has settled as far as it will, usually until about one-half of
its volume has become clear. The clear part is then decanted, and the remainder,
containing about 4 lbs. of peroxide of manganese per cubic foot, is then ready to be used
in the stillB, There it reacts upon hydrochloric acid, liberating chlorine, with repro-
duction of exactly such a residual solution as was commenced with. With that solution
the round of operations is begun again ; and so on, time after time, indefinitely.

AppaimtM^fOTPreiwring When hydrochloric add and manganese are used, the apparatus
is that delineated in Fig. 105. It consists of a large stoneware jar, a, provided with
an opening, a, over which an air-tight cap is fitted when the apparatus is at work, and
by which the jar is filled with manganese and add ; b is another opening fitted with
a leaden or earthenware gas tube ; c is a tube serving to run off the spent manganese
liquor, b is a wooden box into which steam is admitted for the purpose of heating
A and its contents sufficiently to promote the reaction between the hydrochloric add
and the manganese.



Digitized by VjOOQIC



BLEACHINQ-POWDER. 317

When oblorine is prepared from a mixture of common salt, snlphorio aeid, and man-
ganese, the apparatus is required to withstand more heat, and is therefore oonstructed
entirely of metal, a a. Fig. 106, is a shallow iron pan, fitted with the tube h for the purpose
of emptying the contents of the leaden cylinder, dd. This iron vessel serves as the lower
part of the leaden cylinder, dd, the top of which is provided with an opening tor a
fnnnel syphon- tube for the introduction of the acid, and another opening, /, for the man-
ganeee. The entire apparatus stands on a flue leading from a furnace.

Fio 106.



Fig. 105.



condenainK Appumtiu. The ohlorine passes from the generator through the tube, m,
Fig. 107, into a room constructed of large blocks and slabs of sandstone joined by means
of asphalt cement, or a mixture of coal-tar and fire-clay. Sometimes the room is built
of bricks laid in a similar cement, the interior being lined with asphalt ; leaden chambers
also are used for this pxurpose. The room is fitted with several shelves upon which slaked
Ume is placed in layers of three to four inches and more in thickness. The chlorine gas

Fio. 107.



is readily absorbed, heat being evolved. Care is to be taken that the temperature does
not exceed 25°, because then chlorate of lime is formed ; this is prevented by admitting
the gas slowly. As soon as the absorption ceases, the bleaching-powder is removed with
rakes from the shelves, and fre^ lime introduced. Frequently the chloride of lime is
somewhat diluted by an admixture of slaked lime.

When it is desired to prepare a solution of chloride of lime, the apparatus shown in
Fig. 108 is employed. Two or four earthenware vessels, a, about 2 hectolitres capacity,
are placed in the leaden trough, b, the bottom of which is protected by a cast-iron plate
and a stoneware slab, r, from the direct action of the fire at d. b represents a ooncen-



Digitized by VjOOQIC



2i8 CHEMICAL TECHNOLOGY,

trated solution of chloride of calcium serving the purpose of a bath, such a solution boiling
at 179-5°. By the syphon funnel, k, the hydrochloric acid is poured into a. i is a per-
forated cistern filled with manganese, s is the leaden gas tube. The chlorine being first
washed in b, passes through n into t, filled with pieces of manganese, to decompose any
vapours of hydrochloric acid carried over, and lastly, the chlorine passing through m
reaches the absorption vessel, s. This vessel is a lead-lined wooden cask, fitted with an
axle bearing spokes to which are fastened gutta-percha floats. The bearing and plnmmer-
blocks of the axle are made of guaiacum wood and ebonite. The axle, o, gears with a suit-
able motive power, the purpose being to keep the milk of lime in continuous motion "while
the gas is being admitted.

Fio. 108.



The chlorine gas enters above the level of the fluid, which is kept constantly stirred, to
assist in the absorption. From the vessel wherein the absorption takes place a small tube
leads into another vessel filled with water to a depth of 18 to 24 oentims. ; a tube fitted
to this vessel leads into the open air to convey away any unabsorbed chlorine. As in the
preparation of solid chloride of lime, it is here necessary to guard against an increase in
temperature and also saturation ; Schlieper has proved that too concentrated solutions
evolve oxygen, while too dilute solutions yield chlorate of lime.

'^ftSfiSo'ia^^S?"* ^ the chlorine required for the preparation of chloride of
lime is generally obtained by the aid of manganese and hydrochloric acid, the resi-
dues consist chiefly of free acid and protochloride of manganese. The principal
suggestions as to the utilisation of these substances are : —
a. Those aiming at the regeneration of peroxide of manganese ; and
p. Those not proceeding with this view. The former are of course the more
important.

Dnniop'B Procow. This process is one of the oldest and the best, excepting perhaps,
Balmain's, in which the chloride of manganese is neutralised with the ammoniacal water
of gas-works, the supernatant liquor being employed for preparing sal-ammoniao, while
the precipitate is ignited in a reverberatory furnace and converted into peroxide of
manganese. Dunlop^s process, as practised at Tennant's works at Glasgow, is based upon
the fact, first observed by Forchhammer, that carbonate of manganese, when heated to
260°, is converted into peroxide of manganese ; that is, the carbonic acid is driven off,
and the compound, 2Mii02+MnO, obtained. The process consists in the following
operations : —

1. Conversion of the chloride of manganese into carbonate of manganese.

2. Conversion of the carbonate into peroxide of manganese.

To the chlorine preparation residues, when they have become clear, either chalk or milk
of lime is added to neutralise the excess of acid and precipitate the oxide of iron. This
precipitate having settled, the clear liquid, a rather pure solution of protochloride of man-
ganese, is poured into shallow troughs and intimately mixed with finely powdered chalk.
The magma thus formed is transferred for further decomposition to a large oast-iron
trough, 27 metres long by 3 metres wide. Parallel to the length of this vessel, a stout
wrought-iron axle is carried, to which are fitted cast-iron branches serving as stirrers.



Digitized by VjOOQIC



BLEACEING-POWDER. 219

The axle paBsing through staffing boxes at each end of the trough, gears with a motiTo
power, whereby the stirrers are oansed to keep the chalk constantly suspoided in the
manganese solution. High pressure steam is conveyed into the trougn and aids decom-
position. The carbonate of manganese obtained is freed by washing from chloride of
ealdom, and having been well drained, is calcined in a peculiarly constmoted fomaoe, in
which the carbonate is first dried on a higher stage, and then is transferred to a lower and
hotter stage, w^ere oxidation is commenced. The oxidation is completed at the lowest
stage of the fnmaoe, to which plenty of air is admitted. The fire-place is oonstmcted to
admit of the regulation of the heat with great nicety, because too high a temperature would
cause the formation of protosesquioxide, and too low a temperature would leave the
carbonate undecomposed.

GmttT^pmeeM. In this proosss the residues are converted into nitrate of manganese,
which is next decomposed by heat. The residues are evaporated to the oonsistenoy of a
gyrnp, and mixed with nitrate of soda : —

To 76 kilos, of protochloride of manganesej ^ ^ , ^^^ ^ ^ ^
and to 95 kilos, of sulphate of manganese j *"" '"* *"w»»o u* »vua arc uulcu.

The mixture is dried, and then heated to a dull red heat in an iron retort, the fumes of
nitric acid given off being used in the manufacture of sulphuric acid. The residue in the



Online LibraryJohannes Rudolf WagnerA handbook of chemical technology → online text (page 34 of 109)