Improvements in the Manufacture of Soda Alum.
Year: 1889

page_text: Date of Application, 22nd Oct.. 1889
Complete Specification Left. 15th Jan. 1890-Accepted. 8th Mar. 1890
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Soda Alum.
I EUGÈNE AUGÉ of 6 rue Barralerie Montpellier (Herault) in the Republic of
France Chemist do hereby declare the nature of this Invention to be as follows:-
This Invention relates to improvements in the manufacture of soda alum and in
order that the nature of these improvements may be properly understood it is necessary
in the first place to refer to certain views generally held by chemists with regard to
this substance but which I believe to be incorrect. It does not appear to be a fact that
soda alum is efflorescent to such a degree as to fall to dust after a few days as
generally supposed; its solubility at the ordinary temperature is about three times
less than that indicated in the text books (Wurtz's dictionary) nor is it correct to say
that a solution of soda alum which has reached the temperature of ebullition loses
the crystallising property as alleged by German chemists (Muspratt Wagner and
others).
Now by conducting the process of manufacture as hereinafter described I obtain
soda alum in crystals which can be kept in a cool place not exposed to the light for
at least three months without efflorescing.
Description of the process :-To a solution of ordinary sulphate of alumina I add
a corresponding quantity of sulphate of soda preferably anhydrous and in a solid state
as there is thus less water to be evaporated.
I apply heat by means of a steam pipe or worm or other suitable arrangement
without producing ebullition and I evaporate the solution until it attains, at the
temperature of ebullition a density of between about 138 and 1.45 (or 40 to 45
Baumé). In practice I prefer a density of about 1:40 (41 Baumé).
Directly this density is attained I pour out the hot solution onto a plate of I ad
polished marble or limestone or other suitable material in such a manner as to form
a thin layer. After a certain time the length of which is in proportion to the thickness
of the layer (about 3 hours are required for a layer two inches thick) the solution
acquires in cooling a pasty consistency. This paste is transferred to lead tables
inclined longitudinally and transversely to the extent of about one inch in twelve and
provided along the lower edge with a trough or gutter by which the mother liquors
produced during the transformation of the paste into crystals are conducted to a
suitable receptacle.
The thickness of this layer of paste requires attention, if too thin, the crystals
formed are too small; if too thick, the crystallisation proceeds too slowly and may even
be incomplete. A thickness of about 3 inches or say 8 centimeters has been found to
give a good result.
The paste thus arranged is left to itself and after a certain time depending on the
thickness of the layer (about two and a half days for a layer 2 inches thick) a radical
change takes place. The paste is transformed into crystals at the same time gradually
discharging a certain quantity of mother liquors which carry with them almost the
whole of the iron and other impurities.
The greater the density of the solution at the moment when it is poured out the
less is the quantity of mother liquor but on the other hand a low degree of density
or concentration produces a proportionately purer alum. With a density of 1.42 the
mother liquors represent in weight from one fifth to ono fourth of the initial or
original solution.
The crystallised alum is washed preferably in a centrifugal machine. The mother
liquors are concentrated afresh poured out on the plates and treated as hereinbefore
described so as to obtain another quantity of crystallised alum.

page_text: The soda alum may be purified in the same way as potash alum by subjecting it to
one or more refining processes. With this object it suffices to dissolve the alum to
he purified in a steam jet and when the solution is at a suitable degree of concentration
to pour it out onto the plates and treat it as herein before described.
Delhi 201 J
than 1000
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C., Agents.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Soda Alum.
I, EUGENE AUGE of 6 rue Barralerie Montpellier (Herault) in the Republic of
France, Chemist do hereby declare the nature of this Invention and in what manner
the same is to be performed to be particularly described and ascertained in and by
the following statement :-
Chemical treatises contain in connection with Soda alum a very great number of
errors. Thus contrary to the statements heretofore accepted, it is incorrect to say
that this alum is efflorescent to such a degree as to fall to dust at the end of a few
days. Its solubility is about three times less than it has been stated to be (Wurtz's
Dictionary). Lastly, the fact mentioned by the German authors (Muspratt, Wagner
and others) that a solution of soda alum which has attained the temperature of
cbullition loses the property of crystallising is no less erroneous.
Some manufacturers had however mentioned the fact that when a hot and
sufficiently concentrated solution of soda alum is left to cool it sets or forms an
amorphous pasts and this paste at the end of an undetermined period passes into the
the crystallised state. But the mere knowledge of this fact was not sufficient to
derive therefrom a commercial process of manufacture so that prior to the discovery
of my process hereinafter set forth no person had ever manufactured crystallised soda
alum for commercial purposes. It was in fact indispensable to discover the physical
and mechanical conditions of the transformation of the paste into crystals in order to
derive therefrom a practical process of manufacture.
In the first place the temperature of the surrounding atmosphere plays an
important part in this transformation.
When the ambiant temperature is above 82 degrees Fahrenheit the transformation
of the paste into crystals does not take place or takes place so slowly that it ceases
to be commercially practicable.
When the surrounding temperature is on the contrary about 32 degrees Fahrenheit
the transformation into crystals is very rapid but the crystals obtained are
exceedingly small moreover (and this is great importance) their percentage of alumina
is considerably diminished.
It is necessary in order to obtain crystals of regular composition and dimensions
to maintain during the transformation of the paste into crystals an ambiant or
surrounding temperature of between 45 and 75 degrees Fahrenheit. For my part
I prefer to work with a temperature as near 60 degrees Fahrenheit as possible.
The thickness of the layer of paste has considerable influence on the time occupied
by the transformation. For a thickness of 2 inches (5 centimeters) and with a
surrounding temperature of 60 degrees Fahrenheit the time occupied is from two
and a half to three days. With the same temperature and a thickness of about
39 inches or one metre (which is the average depth of the crystallising basins for
potash alum) the time required would be over two months and the operation would
be commercially impracticable.
Having thus explained the conditions under which the crystallisation takes
place will now proceed to describe the practical manufacture according to my
invention.

page_text: To a solution of sulphate of alumina I add the corresponding quantity of sulphate
of soda (177 calculated parts of anhydrous sulphate of soda to 720 parts of sulphate
of alumina with 18 equivalents of water). I apply heat by means of a steam pipe
or worm or any other suitable arrangement without producing ebullition and I
concentrate the solution until it attains (at the temperature of ebullition) a density
comprised between 1.32 and 1-43 (from 64 to 86 degrees Twaddle). In practice I
prefer a density of about 1.39 or 78 degrees Twaddle.
Directly this degree of concentration is attained I pour out the hot solution into
basins or vessels or preferably on to a plate of lead, marble, or limestone or any other
suitable material. After a certain time the length of which is in proportion to the
thickness of the layer the solution passes into a pasty condition. This paste is
transferred and spread before it is cold in a thin regular or even layer on tables of
lead or other suitable material sloping or inclined transversely and longitudinally and
provided along the lower edge with a gutter for conducting to a suitable basin or
receptacle the mother liquors, produced during the transformation of the paste into
crystals. An inclination or slope of about one in twenty (5 centimetres per metre)
transversely and one in a hundred (one centimetre per metre) longitudinally are
found to give good results.
The thickness of the layer of paste must not be too great, I prefer a thickness of
about 2 inches (5 to 6 centimetres).
The inclined tables must be situated in a room which can be heated in winter in
order to maintain the temperature at about 60 degrees Fahrenheit.
In place of the inclined tables horizontal iroughs with sides about 2 inches from
4 to 6 centimetres in height may be employed into which the hot solution is poured
but this method of operating is less practical. These troughs require to be perfectly
horizontal or level, the filling is a delicate operation, lastly after the conversion into
crystals it is necessary in order to separate the mother liquors to tilt or incline the
troughs and this tends to affect their shape. I consequently prefer to employ
inclined tables.
Whether working with the inclined tables or with the level troughs a layer of two
inches in thickness of paste poured out at 78 degrees Twaddle with a temperature of
the surrounding atmosphere standing at about 60 degrees Fahrenheit from two and a
half to three days are required to complete the transformation.
It is advantageous in view of accelerating the transformation into crystals to turn
over the paste and form small transversal furrows in it in order to facilitate the
escape of the mother liquors.
The mother liquors produced represent about one fifth of the weight of the paste.
They carry away almost the whole of the iron and other impurities. They are
collected, concentrated to 78 degrees Twaddle, run out and transferred to the inclined
plates to produce a fresh quantity of soda alum less pure than the first but nevertheless
of commercial value.
The alum crystals remaining on the tables are washed preferably in a centrifugal
machine and kept in the shade in a cool place, by taking these precautions they may
be kept for several months without becoming efflorescent.
I have found by experience that it is advantageous to have in the proportion
between the two sulphates a slight excess of sulphate of alumina.
Where it is desired to obtain, in the first pouring, an alum free or almost free from
iron it is necessary to employ a sulphate of soda from which the iron has been
previously precipitated by carbonate of soda, lime or any other suitable means and a
sulphate of alumina containing as little iron as possible.
Soda alum may be obtained by means of the bisulphate and even by means of the
chloride of sodium but it is preferable to employ the neutral sulphate.
Having now particularly described and ascertained the nature of my said Inven-
tion and in what manner the same is to be performed I declare what I claim is.
The process hereinbefore set forth consisting in treating (at a temperature

page_text: maintained between 45 and 75 degrees Fahrenheit) the paste obtained by the
concentration of the two sulphates, sulphate of alumina and sulphate of soda, upon
inclined tables or flat horizontal troughs substantially as hereinbefore described.
Dated th. 15ih dan of Innu- 1900
J. H. JOHNSON & Co.,
Agents.