Johannes Rudolf Wagner.

A handbook of chemical technology online

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plants in a soluble state, the quantity must of necessity be greatest in the juicy
and snccnlent parts.

Dr. Bottger found the ash of beech-wood to contain —

21-27 per cent of soluble salts,
7^73 M M of insoluble salts.
The soluble salts were found to be —

Carbonate of potassa . . . . 15*40 per cent
Sulphate of potassa . . 2-27 „ „

Carbonate of soda 3*40 ,, „

Chloride of sodium . . . . 0*20 „ „



21*27 per cent
The value of an ash for the manufacture of potash is chiefly dependent, in the first
place, upon the quantity of potassic carbonate it will yield, upon the abundance of the
wood or other vegetable product, and the cost of labour. The undermentioned woods
yield, on an average, for 1000 parts, the following quantities of potash —

Pine 0*45 Beech-bark 6*oo

Poplar 0-75 Dried ferns 6*26

Beech 1*45 Stems of maize (Indian com) . . . . 17*50

Oak . . 1-53 Bean-straw 20*00

Box-wood 2*26 Sunflower-stems 20*00

Willow 2*85 Nettles 25*03

Elm 3-90 Vetch-straw 27*50

Wheat-straw 3-90 Thistles 35'37

Bark from oak-knots 4*20 Dried wheat-plant previous to

Cotton-gra88(£riop^rumva^inatum) 5*00 blooming 47*00

Bushes 5*o8 Wormwood 73*00

Vine-wood 5-50 Fumitory 79*00

Bailey-straw ., 5-80

According to M, Hoss, 1000 parts of the following kinds of wood yield —

Ash. Potash. Ash. Potash.

Pine 3*40 045 Willow 280 2*85

Beech 5-80 1*27 Vine 34*0 5*50

Ash i2*2o 0*74 Dried ferns . . . . 36*4 4*25

Oak 13*50 1*50 Wormwood .. .. 97*4 73*00

Elm 25*50 3*90 Fumitory .. ., 219*0 -79*90

The preparation of potash from vegetable matter is effected in three operations, viz. : —

a. The lisiviation of the ash.

6. The boiling down of the crude liquor.

c. The calcination of the crude potash.
The combustion of the vegetable matter should be so conducted as to prevent its
becoming too violent and giving rise to the combustion of some of the reduced potassa-
salt ; nor should too strong a current of air be admitted for fear of the ash being mechani-
cally carried off. A distinction is made abroad — ^no potash from wood or other vegetable
matter being produced in the United Kingdom, nor wood used as fuel in sufiicient quanti-
ties to yield ash for the preparation of potash — between the ash obtained by the com-
bustion of the refuse wood of forests and the ash from wood used as fuel, the former
being termed /or<«(- and the latter /tteZ-ash. As ash from other fuel than wood may be
ipixed with fuel-ash, a sample may be roughly tested by liziviation, and the density of the
liquor taken by the areometer, the higher the specific gravity the larger the quantity of
fioluble saltfl. Formerly the forest-ash was purposely prepared, and sold to potash-
boilen. There is stiU known in Eastern Prussia and Sweden a material termed okras or
ochratf holding a position intermediate to crude ash and potash.

0. The liziviation of the ash effects the separation of the soluble from the insoluble saline
matter, the former amounting to about 25 to 30 per cent of the entire weight of the ash.
^e operation is carried on in wooden vessels shaped like an inverted truncated cone, and
provided with a perforated false bottom, which is covered with straw ; in the real bottom
» tap is fixed for removing the liquor. If the lixiviation is systematically carried on,



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124 • CHEMICAL TECHNOLOGY.

several of these yeflsels are placed together, forming what is termed a battery, and mider
eaoh a tank to receiye the liquor. The ash to be lixiviated is first sifted from the coarse
particles of charcoal, next put into a small square water-tight wooden box, and thoroughly
saturated with water for at least twenty-four hours. By this proceeding the lixiviatilon is
greatly assisted, and the silicate of potassa to some extent decomposed by the action of
ihe carbonic acid of the atmosphere. The next step is to transfer the wet ash to the
lixiviation vessel, care being taken to press it tightly down on to the false bottom ; cold
water is then poured in, until the liquor begins to run off at the taps left open for that
purpose. The liquor which runs off, after the water has remained some little time in
contact with the ash, is found to contain about 30 per cent of soluble salts, afterwards
decreasing to about 10 per cent, when hot water is employed to complete the lixiviation.
The insoluble residue left in the lixiviation-tub is of value as a manure, on account of the
phosphate of lime it contains, and is also used in maklog green bottle-glass, and for
building up saltpetre-beds.

5. BoUing down the liquor. The liquor obtained by lixiviation is of a brown colour,
owing to organic matter, humiu or ulooine, which the carbonate of potassa has dissolved
from the small chips of imperfectly burnt charcoal. The evaporation is carried on in
large shallow iron pans, fresh liquor being from time to time added, and the operation
continued until a sam|»le of the hot concentrated liquor exhibits on cooling a crystiUline
solid mass. When this point is reached the fire is gradually extinguished, and as soon as
the contents of the pan are sufficiently cold to handle, the solid salt mass is broken up ;
its colour is a deep brown. This crude product, containing about 6 per cent water, is
known in the trade as crude, or lump-potash. It is evident titiat this method of boiling
down may cause considerable damage to the iron pans, therefore in many instances the
operation is conducted in a somewhat different manner. The Uquid is kept stirred with
iron rakes, and the salt, instead of forming a hard solid mass, is obtained as a granular
powder, containing upwards of 12 per cent water. Some manufacturers first separate the
sulphate of potash, which, being less soluble, crystallises before the carbonate, a deli-
quescent salt, is separated from the liquor ; in most cases, however, this operation is only
carried on where the sulphate of potadi is required for alum-making. The pearl-ash or
potash of commerce almost invariably contains a large quantity of sulphate of potash.

c. In order to expel all the water and to destroy the organic matter, the saline mass is
calcined, and as this operation was formerly performed in oast-iron pots, the salt has
obtained the name of potash. A calcining furnace. Fig. 62, is now used, distinguished
from ordinary reverberatory furnaces by being provided with a double fire-place. These

Fxo. 62.



hearths, one of which is exhibited in section at a. Fig. 62, are placed at right angles to
each other, and the fiame and smoke meeting in the centre of the furnace, pass off at 0,
the work-hole, into the chimney, x. Wood is used as fuel, and as the heating of the
furnaces requires a very large quantity, they are on^ in use when a sufficient supply of
crude potash is ready for being operated upon. The furnace is thoroughly heated in
about five to six hours, care being taken to fire gradually, and to bring the interior of the
furnace to nearly red heat, so that the vapour due to the combustion of the wood may not
condense inside the furnace, but be carried off by the flue. The crude potash, broken up
to egg-sized lumps, is next placed in such quantities at a time as may suit the size of the
calcining hearth ; for instance, if the hearth is roomed to contain 3 cwts., that quantity is
divided into three portions and put in at intervals of a few minutes. The first effect of
the heat is to expel the water from the potash, the escape of the steam being promoted by



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CARBONATE OF P0TA88A. 125

Btirring the nutss niih iron rakes. In abont an hour all the water is driven off, and the
maae takes fire in couseqnenoe of the burning of the organic matter, the salt at first being
falaekened, bat gradoally beooming white as the carbon bnms off. As soon as this stage
is reached, the potash is remoyed to the cooling-hearth, and when cold, packed in well-
made wooden-casks, which, as this salt is Tery nygroscopic, are rendered as air-tight as
possible. The heat of the fomace has to be well regulated to prevent the potash
beooming semi-fased, in which case it wonld attack the siliceous matter of the fire-
brioka ; the workmen from time to take a small sample to test how far the calcination is
eomplete.

We, in Europe, obtain a considerable quantity of potash from the United States and
Canada, known as American potash, of which there are three different kinds, viz. : —
I. Potflksh prepared as described. 2. Pearl-ash, or potash, purified by lixiTiation, decan*
taiion from sediment, boiling down, and the calcination of the salt thus obtained.
3. Stone-ash, a mixture of uncaloined potash (potassic carbonate), and caustic potash
obtained by treating the crude potash liquor with caustic lime, and boiling down the mass
to dryness ; this article has the appearance of the crude caustic soda of this country, but
is nsnally ooloured red by oxide of iron; the lumps, stone-hard, are frdm 6 to 10
eentims. in thickness, and contain upwards of 50 per cent caustic potash. The under-
mentioned analyses exhibit the vaiying composition of the potash of commerce : — Sample
I is from Kasan (Bussia) ; analyst, M. Hermann. 2. Tuscany. 3 and 4— the latter of
a reddish colour — from North America. 5. Bussia. 6. Yosges fFrance) ; analyst of
2* 3i 4t 5> And 6, M. Pesier. 7. Helmstedt, in Brunswick ; analyst, M. Lmipricht. 8. Bussia ;
analyst, M. Bastelaer.





I.


2.


3.


4-


5.


6.


7.


8.


Carbonate of potash


. 78-0


741


71-4


680


69-9


38-6


490


50-84


Carbonate of soda . .





30


23


5-8


3*1


4-2




I2'I4


Sulphate of potash


. 17*0


13-5


14-4


153


I4-I


388


40-5


17-44


Chloride of potassium


. 30


0'9


3-6


81


2-1


91


lo-o


5-8o


Water




72


4*5





8-8


5*3





xo-i8


Insoluble residue ..


.. 0*2


O'l


27


2-3


2-3


3-8





3-60



The calcined potash Taries in eolour, being either white, pearl-grey, or tinged with
yellow, red, or blue. The red colour is due to oxide of iron, the blue to the manganates
of potash, a hard, light porous, non-crystalline mass, neyer entirely soluble in water.
Formerly, a large quantity of potash was obtained from the residues of wine-making, and
Cfldled Tinasse, Uie semi-liquid left after the alcohol has been distilled from the wine, and
containing, among other substances, argol, or crude bitartrate of potash ; it was boiled
down, and next calcined, yielding a kilo, of yery good potash for every hectolitre of yinasse.
The large quantity of potash thus formerly produced may be judged from the fact that
19 of the wine-produdng departments of France, those only where large quantities of
wine are conyerted into alcohol, technically termed troia six and einq Imit, yield annually
aboat 9 to xo million hectolitres of yina8se,'at the present time employed for the prepara-
tion on the large scale of cream of tartar, glycerine, and tartaric acid.

FotoAtemMniwm Y. Of late years, the mana£EU)ture of potajsh salts from the
Tinasse left after the distillation of fermented beet-root molasses has been added as a
new branch of industry by M. DubrunfEmt, and introduced into Germany by M.
Yamhagen, in the year 1840, at Mucrena, Prussian Saxony.

Beet-root, on being subjected to ignition, yields an ash eontaining a large percentage of
potash, a fact first obseryed in the early part of this century by M. Mathieu de Dombasle,
a celebrated French agriculturist, who discoyered that 100 kilos, of dried beet-root leayes
yield 10*^ kilos, of ash, containing 5-1 kilos, of potash ; but this author's idea that the
leayes might be cut off and gathered for the purpose of potash manufacture, proyed
erroneous, in so far that the growth of the roots was greatly impeded. After the publica-
tion of M. Dubrunfaut*s researches on this subject, in 1838, the yinasse of the beet-root
molasses distillation was eyaporated to diyness, next calcined, and the calcined mass
refined for the production of potash and otiier salts of that base, an industry which has
obtained a great deyelopment, as may be judged from the fact that the quantity of these
materials produced on the European contment in 1865 amounted to 240,000 cwts.

The reader who desires details on this subject, is r^erred to the work, ** On the Manu-
facture of Beet-Boot Sugar in England and Ireland," by Wm. Orookes, F.B.S., Ac., p. 250
sttsq.



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126 CHEMICAL TECHNOLOOT,

The molasses from beet-root sugar consists, previous to the fermentation and dis-
tillation, of the undermentioned substances, as recorded by the several analysts whose

names are subjoined : —

Brmmer. Fricke. Lunge. Heidenpriem.

^ ' >

Water 152 180 185 190 197

Sugar 490 480 507 469 49-8 '

Salts and organic substances 35-8 340 308 34" i 305

The following analyses by M. Heidenpriem exhibit the average composition of the

ashes of molasses : —

I. 2. 3

Potassa 5172 4767 5038

Soda 800 1 143 829

Lime 504 360 312

Magnesia 018 010 018

Carbonic acid 2890 2794 2870

The remainder of the 100 parts consists of phosphoric and silicic acids, chlorine,
oxide of iron, &c. The quantity of ash amounts to 10 or 12 per cent. According to
Dubrunfaut the alkalimetrical degree of the ash of beet-root sugar molasses is a
constant, as the ash obtained from 100 grms. of molasses neutraKses on an average
7 grms. of sulphuric acid (H2SO4).

The molasses is generally treated in the following manner : — ^It is first diluted with
either water or vinasse to 8° or 11° B. = 1056 or 1078 sp. gr., and mixed with 05 to
15 per cent of a pure mineral acid, the object of this addition being not simply the
neutralisation of the alkali, but also the conversion of dextrine and such unfermentable
sugar into fermentable sugar. Formerly, sulphuric acid was used, but upon the
recommendation of M. Wurtz, hydrochloric acid is now generally employed, the
advantage being the formation of readily soluble chlorides, instead of comparative
insoluble alkaline sulphurets, the action of the organic matter present in the molasses.

The diluted molasses is next mixed with yeast, left to ferment, and the alcohol
distilled off; the residue is a liquid of about 4* B. density [=1027 sp. gr.] containing
imdecomposed yeast, ammoniacal salts, various organic substances, and all the inorganic
salts of the beet-root juice. The potassa is present in this liquid as nitrate chiefly,
although by the addition of hydrochloric acid a portion of this salt is decomposed,
red nitrous fumes sometimes being seen in the fermentation room. Evrard suggests
that the saltpetre should be separated from the beet-root molasses by evaporation,
and further purified by tlie aid of the centrifugal machine. The acidity of the
vinasse is neutralised by chalk, and afterwards it is evaporated to dryness in an iron
vessel, the total length of which is 203 metres, by an average widih of 1*6 metre,
extended at the top to 2 metres, the deptli being 034 metre. The vessel is made of stout
boiler plate, strengthened by stays and angle irons, and is divided into two divisions,
the larger of which has a length of 14-3 metres, and is the real evaporating pan,
wliile tlie other is used as a calcining furnace, and covered with an arch of fire-
bricks o"6 metre high. The fire-place is 13 metre wide, and the fire-box has a
surface of 3*3 square metres. The evaporation is effected by surface lieating, that
is to say, tlie flame and hot gases from the burning fuel after passing across the fire-
bridge arc conduc-ted over the surface of tlie vinasse, the calcining pan being nearest
to the fire, while the evaporating pan is at its other extremity in contact with the



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CARBONATE OF POT ASS A. 127

flue or chimney. The vinasse, having been run off from the still, is kept in cisterns,
from which it is forced by means of a pump into a reserv^oir so placed as to admit of
the liquid running in a constant sti-eam into the evaporating pan. At a first operation
both the evaporating and the calcining pan are filled with vinasse, but afterwards
the latter is filled regularly with concentrated thick liquor, which is simply carbonised,
the organic matter being only destroyed.

The daOy average of carbonised vinasse is about 5 to 5i cwts. The composition
of that substance may be gleaned from the following approximative analysis : —

Insoluble matter = 23 per cent.

Sulphate of potassa =1107 „

Chloride of potassium = ii-6i „

Carbonate of potassa — 3i'40 „

Carbonate of soda = 23"26 „

Silicic acid and h}T}osulphite of potassa = traces „

9934 M
In Germany, the calcined vinasse is generally sold to saltpetre manufacturers, but
in Belgium and France this material is calcined, lixiviated, and the salts it contains
separately obtained. For this purpose the vinasse is first evaporated to 38° or 40°
B. (I '33 to 1*35 sp. gr.), and next carbonised and calcined in a furnace constructed
as exhibited in Fig. 63. v is a reservoir containing the concentrated vinasse, which
by means of a tube is gradually run into the furnace, of which g is the fire-place, m
the calcination space, destined to contain the concentrated or carbonised vinasse,

Fio. 63.



which is evaporated to dr^Ticss and calcined in m' ; a door is fitted to each com-
partment, and at p, the end of the furnace opposite to the fire-place. The air required
for the calcination is admitted partly through the ash-pit, pai*tly through the
openings, b, in the brickwork. The thickish liquid vinasse admitted into m' is
constantly stirred, and, as soon as it is quite dry, it is shovelled across the brickwork
ridge, a', into the calcining space, m, care being taken to agatu fill m' wdth concen-
trated vinasse. The organic matter of the saline mass soon takes fire, emitting
noxious fumes. The calcination is greatly aided by the access of air at b, and also
to some extent by the nitrate of potassa present. The temperature has to be regulated
to prevent the salts becoming fused and forming a hard compact mass, in which case
the sulphate of potassa would be reduced to sulphuiet of potassium, a salt which



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Google



a.


b.


e.


d.


26*22


19*82


17*47


13*36


"•95


9-88


2'55


3*22


15-87


20*59


i8'45


16*62


0-I3


015


o*i8


0*21


25'5a


1966


1922


i6*54


2340


2990


4313


5005



128 CHEMICAL TECHNOLOGY.

could not be removed. The caloined vinasse, technicftlly termed 9aUn, contains,
when removed from the furnace, 10 to 25 per cent of insoluble substances, viz.,
carbonate and phosphate of lime, more or less charcoal, and in addition, 3 to 4 per
cent moisture ; the remainder consists of carbonates of potash and soda, sulphate of
potassa, chloride of potassium, and sometimes cyanide of potassium in considerable
quantity. The relative quantities of potassa and soda are, of course, not at all
constant, but vary according to the soil on which the beets hav» grown ; it has been
observed in France that the molasses obtained from beets grown in the D6partement
du Nord are less rich in potassa than those grown in the I>6partements de TOise et de
la Somme. The average composition of the salin is : —

7 to 12 per cent of sulphate of potassa.

18 to 20 „ of carbonate of soda.

17 to 22 „ of chloride of potassium.

30 to 35 „ of carbonate of potassa.
The complete composition of the salin may be gathered from the following
tabulated results : —

Water and insoluble matter

Sulphate of potassa

Chloride of potassium

Chloride of rubidium

Carbonate of soda

Carbpnate of potassa

100*00 lOOOO 100*00 lOO'OO

The method of separating the soluble salts from each other, invented by M. Euhl-
mann, is generally executed as follows : — The saline mass is first broken up and
granulated by the aid of grooved iron rollers, after which it is placed in lixiviation-
tanks, each containing 26*4 cwts., and arranged precisely in the same manner as
those in use in soda works. The liquor tapped from the tanks has a sp. gr. of 1*229
(= 27"* B.) ; the insoluble residue is used as manure. The liquor having been col-
lected in a large reservoir, capable of containing some 210 hectolitres, is concentrated
by waste heat {abgSngiger w&rme) to a density of 1*26 (= 30° B.) ; on cooling, the
greater part of the sulphate of potassa cxystallises, and is removed, care being taken
to wash off the adhering mother-liquor. The sulphate thus obtained contains 80 per
cent pure potassio sulphate, the rest being carbonate of potassa and organic matter:
this material is converted into potash by Leblanc's process. The liquor at 30® B. is
next poured into evaporating>pans, each capable of containing 90 hectolitres, and
concentrated by means of heat and a steam pressure of 3 atmospheres (= 45 lbs. to
the square inch) to a density of 42** B. (= 1*408). By this operation a mixture of
carbonate of soda and sulphate of potassa is separated, which frequently exhibits
30 alkalimetrical degrees; the liquor is transferred from the evaporating-pans to
crystallising vessels, in which it is cooled down to not less than 30^ If, by careless-
ness, the temperature should fall below- 30°, the chloride of potassium ciystals become
mixed with a layer of carbonate of soda. The liquor at a temperature of 30°, and
having a density of 42° B., is again transferred to evaporating-pans, each capable of
containing 20 hectolitres, and evaporated

In winter to a sp. gr. of 1494 (= 48^ B.), and

In summer to a sp. gr. of 1-51 (= 49° B.)



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CARBONATE OF POTASSA. 129

B7 tliis operation sodic carbonate separates, the first and purer portions of which
are of 82 alkalimetrical degrees, and the last of 50"" only. After the separation of
the salt, the remaining liquor is poured into small cr>'stallising vessels, each capable
of holding 2i hectolitres, and, having been left standing for some time, yields in each
vessel about 130 kilos, of a crystalline salt, mainly composed according to the
fommla (KsCOs+NacGOj-j-i^HaO). The remaining mother-liquor, when evapo-
rated to dryness and calcined, yields a semi-refined potash, tinged with red by oxide
of iron. This product is again lixiviated with water, and the liquor having been
concentrated to 1*51 to 1*525 sp. gr. (= 49^" to 50** B.), deposits a large quantity of
sulphate of potassa and carbonate of soda. The mother-liquor having been again
evaporated and calcined, yields a potash consisting in 100 parts of —

Carbonate of potassa 915

Carbonate of soda 55

Chloride of potassium and sulphate of potassa 30

1000
The carbonate of soda possessing a strength of 80 to 85 alkalimetrical degrees is
refined by being washed with a very concentrated aqueous solution of sodic carbonate,
and thus brought to a strength of fully 90 alkalimetrical degrees.

The sulphate of potassa, chloride of potassium, and the double salt of the two
carbonates, are purified and re-crystallised. The following analyses exhibit the com-
position of refined potash obtained firom beet-root sugar molasses : —

a.

Carbonate of potassa 8873

Carbonate of soda 644

Sulphate of potassa 227

Chloride of potassium 100

Iodide of potassium 002

Water 1*39

Insoluble substances 012 — . —

a and b are firom Waghausel in Baden ; is doubly refined French potash. The
crude potash firom beet-root sugar works, a product not to be confused with salin,
is composed as follows : —

Carbonate of potassa ...
Carbonate of soda
Sulphate of potassa
Chloride of potassium ...

a is French product ; 6, firom Valenciennes : c. fi'om Paris ; d, Belgian ; e, firom
Magdeburg, Prussia.

^"^'SmSkT^ ^^- Potassa salts are obtained in large quantities from various sea-
weeds, as a by-product of the manufacture of bromine and iodine. The three
following methods are employed for this purpose : —

a. The old calcination method, consisting in a complete reduction of tlie weeds to
ash, and the methodical lixiviation of that product, so as to obtain various salts
by crystallisation.

b. The carbonisation, or Stanford's method, consisting in the dry distillation of the
weeds to convert them into a carbonaceous mass, afterwards lixiviated, whOe



6.


c.


94*39


893


Ijraces


5-6


028


22


240


15


oil





176






a. b.


c.


d. e.


539 790


760


430 329


231 I4'3


163


170 iJ8'5


2'9 3 9


119


47 '4-°


19-6 2*8


416


180 160


1 Valenciennes;


c, firom Paris ;


d, Belgian ; e, \



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X30 CHEMICAL TECHNOLOGY,

products are Edmultaneously obtained, the sale of which considerably lessens the cost



Online LibraryJohannes Rudolf WagnerA handbook of chemical technology → online text (page 22 of 109)