AND IMPROVEMENT IN THE MAKING OR MANUFACTURING OF ALUM
Year: 1828

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
STRACHAN, of Avon Eitha, in the Parish of Ruabon, in the County of Denbigh,
Manufacturer, send greeting.
WHEREAS His most Excellent Majesty King George the Fourth, by His
Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Twelfth day of June, in the ninth year of His reign, did,
for Himself, His heirs and successors, give and grant unto me, the said
William Strachan, His especial licence and authority, that I, the said William
Strachan, my exors, adiñors, and assigns, or such others as I, the said William
Strachan, my exors, admors, and assigns, should at any time agree with, and
no others, from time to time and at all times during the term of years therein
expressed, should and lawfully might make, use, exercise, and vend, within
England, Wales, and the Town of Berwick-upon-Tweed, and also within
all His Majesty's Colonies and Plantations abroad, my Invention of "AND
IMPROVEMENT IN THE MAKING OR MANUFACTURING OF ALUM;" in which said
Letters Patent there is contained a proviso obliging me, the said William
Strachan, by an instrument in writing under my hand and seal, particularly
to describe and ascertain the nature of my said Invention, and in what
manner the same is to performed, and to cause the same to be enrolled
in His Majesty's High Court of Chancery within four months next and
immediately after the date of the said recited Letters Patent, as in
and by the same, reference being thereunto had, will more fully and at large
appear.

page_text: NOW KNOW YE, that, in compliance with the said proviso, I, the said
William Strachan, do hereby declare that the nature of my said Invention,
and the manner in which the same is to be performed, is described and ascer-
tained as follows (that is to say) :-
It is a well-known fact that the "alum" of commerce has hitherto in this
and other countries been principally if not wholly manufactured from sub-
stances which contain combined naturally two of the constituents of that salt,
namely, the sulphuric acid and the alumine. It is also equally well known
that the green sulphate of iron (the copperas of commerce) is manufactured
from the decomposeable sulphurets of iron, commonly called pyrites, and
that this is effected by exposing these sulphurets to the action of the air in a
heap (called by the copperas manufacturers a "bed"), by which means a
decomposition takes place, which being encouraged by rain and the throwing
on of water, a liquid sulphate of iron is produced, which after evaporation to
a certain point and saturation with iron, is allowed to crystallize, and forms
the green sulphate of iron or copperas. Now my Invention and improvement
consists in the making available for the manufacture of alum the sulphate of
iron, whether in the state of the raw liquid sulphate of iron so used hitherto
for the making of copperas, or of the crystallized sulphate of iron, or copperas
of commerce. Before I proceed to describe how I effect this, I will, for the
benefit of those persons, if such there be, who are not acquainted with what
is by the copperas makers called a "bed," describe what I consider the best
mode of forming one. The ground on which it is intended to stand should,
in the first place, have a low wall built round it about eighteen inches high.
Into this must be puddled and and rammed such a covering of clay as will be
sufficient to form a water-tight bottom. The bed should have a considerable
inclination or slope in order that the liquor may run from it as quickly as it
attains the bottom.. The clay should be covered with bricks, flags, tiles, lead,
or other substance capable of resisting the action of sulphuric acid, and the
top of this last covering being even with the top of the wall, the whole forms
a sloping even-surfaced platform. Upon this platform the pyrites are, to be
piled up or deposited; but I consider that it is adviseable, before depositing
the pyrites, to lay a course of good-sized round pebble stones, in order by
raising the pyrites from the bottom to admit air under, and consequently
through the pyrites, by which the decomposition will be greatly expedited.
Water being from time to time thrown over the pyrites, the liquid sulphate.
will be given out and must be received in a cistern or other convenient
receptacle at the bottom. The thicker the pyrites are heaped up, of course,
the stronger will this liquor will run from the bed, which bed should however.

page_text: be six feet thick at the least. The size or superficial surface of the bed
must, of course, be proportioned to the wants of the manufactory. The shape
I do not consider a matter of much moment, though I prefer an oblong
parallelogram, the slope falling to one of the longer sides over the bottom
of a "bed," of which shape the liquor will have a shorter distance to run
and consequently the chances of loss be diminished. I must here state that
I do not claim the "bed" or the above method of forming one as any part
of my Invention, for the purposes of which the pyrites may be placed in
any other plan, manner, or form, as may be considered best and most
convenient for effecting their decomposition, the foregoing instructions being
only given as a description of what I consider the best mode of exposing
the pyrites for decomposition, and obtaining the greatest quantity of the
resulting liquid sulphate of iron. Supposing, therefore, a supply of liquid
sulphate of iron arising from the decomposition of the martial pyrites of iron,
however placed for the purpose of decomposition, or (if from any circum-
stances it shall be deemed preferrable to use it) the crystallized sulphate of
iron or copperas of commerce to be at hand, I proceed in this order to make
the sulphate of iron (in either state) available in the manufacture of alum.
I procure a quantity of aluminous clay or earth, or other substance containing
alumine, as white and as free from iron as possible, and also as clear from
gravel and other contaminating matter as is to be had. I have from expe-
rience found the light gray colored clay shale, found among the coal measures,
answer the purpose extremely well. Whatever aluminous substance
may be
used it is adviseable by grinding with rollers, pounding, or some other such
method, to reduce it to an even degree of fineness, but this is not absolutely
necessary, and I practise it only as a means of making lighter the labor in
the next part of the process. This aluminous matter I intimately mix and
impregnate with a quantity of the liquid sulphate arising from the decompo-
sition of the martial pyrites of iron, or of the crystallized sulphate or copperas
of commerce, and submits the mass or matter so impregnated to the action of
heat. This may be done in a furnace, kiln, oven, or other convenient
contrivance, by putting the aluminous matter therein, and when there, and
while under the action of heat, throwing in or otherwise applying the liquid
sulphate of iron; or the aluminous matter may first be mixed and impregnated
with the liquid sulphate of iron, and then thrown into the furnace, kiln,
oven, or other contrivance, and there subjected to the action of heat until
it is thouroughly dried and calcined. I should observe, that when the
crystallized sulphate of iron or copperas of commerce is used, it may
be employed either in the state of crystals, or it may first be dissolved

page_text: in water. If in the state of crystals, I should recommend a small
quantity of water to be thrown upon the mixed clay and crystals when in
the furnace, in order to assist the water of crystallization of the copperas
in disseminating the sulphate more evenly through the mass. When the
impregnated clay is sufficiently calcined it will have assumed a pale red
color, and is to be raked or drawn out, and in a cistern or other
couvenient receptacle lixiviated by being covered with water, and from
time to time stirred or plunged up. When the water has extracted from
the impregnated matter or substance all its available strength, which it
will have done in about three days, it will be formed into a liquid
sulphate of alumine, varying in strength in proportion to the strength
of the liquid sulphate of iron and the quantity of it employed to impreg-
nate the aluminous matter, and the quantity of water used to lixiviate
the calcined aluminous substance. After it has been so impregnated this
liquid sulphate of alumine is now ready to be converted into the alum of
commerce by being combined with the alkali and treated in the usual mode
adopted by the manufactures of alum from the materials in common use.
The effect of this process of impregnation, calcination, and lixiviation is this:—
The iron being by the heat so far oxidized as to have become insoluble, the
sulphuric acid, the other constituent of the sulphate of iron, seizes on the
alumine contained in the matter or substance with which it was mixed, and
forms the sulphate of alumine, which is dissolved, taken up, or rendered liquid
by the water with which the impregnated mass is lixiviated.
Having thus stated the combination of which my Invention consists, I shall
proceed to describe the apparatus and method I have adopted for applying
those principles to practice. I pass the clay, earth, or other aluminous matter
I intend using through iron rollers, and when sufficiently crushed and prepared
I throw about thirty hundredweight into the furnace. This consists of a
common arched reverberatory oven, about nine feet long by six feet wide,
having at one end a fireplace extending the whole breadth, and separated from
the floor on which the matter to be acted upon is placed by a bridge or mid-
feather; at the other end is the chimney. In front are three openings with
sliding iron doors for charging and discharging the furnace and stirring the
contents during the operation. The fire I keep at a moderate heat until the
clay, earth, or other aluminous matter is dry, when I proceed to throw in the
sulphate of iron upon the aluminous matter, stirring the mass up with rakes.
This is continued until the whole dose of sulphate (which may be from four
to five hundredweight if the crystallized be used, or from one to two hundred
gallons of the liquid), is thrown in, when the fire is urged higher, the raking

page_text: being continued, adding from time to time water when the crystallized sulphate
is used until the impregnated clay, earth, or other aluminous matter is quite
dry, and so calcined as that the iron which was contained in the sulphate of
iron is so far oxidized as to have become insoluble. When this is effected,
which may be known by the mass having assumed a slightly reddish color, it
is ready for lixiviation. For this purpose I have a row of stone cisterns about
two feet deep, and each of sufficient capacity to contain one charge of the
oven or furnace and as much water as will cover it well. I have also one
general receiving cistern so placed as to receive the liquor from all the
extracting cisterns. The impregnated and calcined clay, earth, or other
aluminous matter, is, when sufficiently calcined, raked out of the oven or
furnace, and put into one of the extracting cisterns and covered with water;
after remaining for two or three days, being stirred and plunged up frequently,
it is let off into the receiving cistern, and is now ready for evaporation.
Instead, however, of immediately running this liquor (which is the liquid
sulphate of alumine) into the evaporator, I think it desirable, in case the
strength should be less than fifteen per cent. above water (which will depend
upon the strength and quantity of the sulphate of iron used), that the liquor
should be returned over freshly impregnated matter until it has attained that
strength. The boiler I use for evaporation, and which I have found very
effective, is an arched chamber twenty-two feet long, seven feet broad, and
three feet deep from the spring of the arch, formed of stone and arched with
brick, having at one end a fireplace extending the whole breadth, separated
from the body of the chamber or cistern by a water-tight bridge or mid-feather.
This boiler, chamber or cistern being filled with the liquid sulphate of alumine
to within a few inches of the top of the bridge or mid-feather, the flame or
heat radiates down from the arch, and sweeps over the whole surface of the
liquor, taking the steam produced with it up the chimney in a continued
stream, the evaporator being supplied with fresh liquor as the water is thrown
off. This is the contrivance I use, but of course any other method may be
pursued as thought best; during the concentration the alkali (the other con-
stituent of alum) is to be added. This may be either the muriate of potash,
the sulphate of potash, potash itself, or any other salt usually employed by
allum makers, though I prefer the first. I consider it best to allow the
evaporation to proceed until the liquor is concentrated to from thirty to thirty-
three per cent. above water before adding the alkali, the preparation of which
will be the same as commonly used by alum makers, and must of course
depend on the quality of the alkaline salts employed; when the alkali has
been added the concentration is to be carried on till the liquor has attained the

page_text: strength of from thirty-five to thirty-eight per cent. above water; it is then to
be let or drawn off into coolers for crystallization. At the end of about ten
days the mothers may be drawn off, when the alum will be found in crystals in
the cooler. These crystals are to be washed, redissolved in clean water, and
again crystallized, and this repeated until, in dissolving a few grains in clean
water, the solution shews no indication of iron on being tested with a few
drops of any Prussian salt. It is now pure alum and fit for all uses to which
alum can be applied, but as alum is generally sold in large masses (the process
of forming which is called "rocking ") it may for this purpose be again dis-
solved in a small quantity of water as will, at the greatest degree of heat
which can be communicated to it, take it up in solution, and run it into casks
or tubs so constructed as to be easily taken to pieces and again set up. In
these it should remain from ten to fourteen days, when the mothers may be let
off, the casks taken to pieces, and the alum broken or cut up into pieces for
sale. I must here observe that the clay, earth, or other aluminous substance,
which has been impregnated with the liquid sulphate of iron, may, after being
lixiviated, serve for the same purpose for a considerable number of times
(varying with the quantity of alumine contained therein originally) until the
whole alumine has been taken up by the successive applications of the sulphate
of iron, and also that the mothers of the first and all the subsequent crystalli-
zations may be used over again without limit. I must also observe that all
the vessels and apparatus used in this manufacture must be composed of
materials capable of resisting the action of sulphuric acid.
After having thus fully described the whole course of my mode of manu-
facturing alum, using for the purpose of such manufacture the sulphate of
iron, I must here, to prevent mistake or misconception, explicitly state and
declare of what my invention and improvement consists. I do not claim as
my Invention the "bed," or the mode of forming one, I have pointed out; nor
do I claim as my Invention any part of the apparatus or process by which the
liquid sulphate of alumine is converted into the crystallized alum of commerce.
What I do claim as my Invention and an improvement in the manufacture
of alum is, the new combination in making available in the manufacture of
of alum the sulphate of iron, whether in the state of the liquid sulphate
resulting from the decomposition by exposure to air and water, however they
may be placed for that purpose, of the decomposable sulphurets of iron, com-
monly called pyrites, or of the crystallized sulphate of iron or copperas of
commerce, by producing from the same, combined with clay, earth, or other
substance containing alumine, a liquid sulphate of alumine, which, being
treated with the usual mode adopted by alum makers, may be formed into

page_text: allum for the purpose of forming this liquid sulphate of alumine. I do not
intend to confine myself to the apparatus or mode of using the apparatus I
have before described, or to any other one particular apparatus or process, but
do for this purpose claim and assert my right to extend to all and every
apparatus by which may be effected the object required, namely, the mixing
or impregnating aluminous clay, earth, or other substance containing alumine,
with the sulphate of iron, in either state exposing the clay, earth, or other
substance so impregnated to the action of a heat sufficient so far to oxidize
the iron as to render it insoluable, and by means of water, dissolving, taking up,
and forming the liquid sulphate of alumine.
In witness whereof, I, the said William Strachan, have hereunto set my
hand and seal, the Fourth day of October, in the year of our Lord
One thousand eight hundred and twenty-eight.
Inrolled the Sixth day of October, in the year of our Lord One thousand
eight hundred and twenty-eight.