IMPROVEMENTS IN THE MANUFACTURE OF CERTAIN ACIDS, ALKALI AND ALKALINE SALTS
Year: 1847

page_text: TILGHMAN'S SPECIFICATION
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, RICHARD
ALBERT TILGHMAN, of Scotts Yard, Bush Lane, London, Chemist, send
greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the First day of February
(One thousand eight hundred and forty-seven), in the tenth year of Her reign,
did, lor Herself, Her heirs and successors, give and grant unto me, the said
Richard Albert Tilghman, my exors, admors, and assigns, Her especial licence,
full power, sole privilege and authority, that I, the said Richard Albert Tilghman,
my exors, admors, and assigns, or such others as I, the said Richard Albert
Tilghman, my exors, admors, or 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 in the Islands
of Guernsey, Jersey, Alderney, Sark, and Man, and also in all Her said
Majesty's Colonies and Plantations abroad, iny Invention of "IMPROVEMENTS
IN THE MANUFACTURE OF CERTAIN ACIDS, ALKALI AND ALKALINE SALTS;" in which
said Letters Patent is contained a proviso that I, the said Richard Albert
Tilghman, should cause a particular description of the nature of my said
Invention, and in what manner the same is to be performed, by an instru-
ment in writing under my hand and seal, to be inrolled in Her said Majesty's
High Court Chancery within six calendar months next and innuediately

page_text: after the date of the said in part recited Letters Patent, as in and by the same,
reference being thereunto bad, will more fully and at large appear.
NOW KNOW YE, that in compliance' with the said proviso, I, the said
Richard Albert Tilghman, do hereby declare that the nature of my said Inven-
tion, and the manner in which the same is to be performed, are fully described
and ascertained in and by the following statement theroof, that is to say:-
My Invention consists in a method of obtaining certain acids, alkalies, and
alkaline salts, by exposing at a high temperature certain salts containing such
acids and alkalies to the action of steam or vapour of water, by which the
acid is carried off, and the alkaline base either remains free or enters into
combination with some third substance provided for that purpose. To obtain
sulphuric and sulphurous acids I prefer using sulphate of lime, and I perform
the operation in the following manner:--I have a fire clay cylinder of close
texture, and of any convenient size, placed vertically in a furnace and provided
with openings at the top and bottom for charging and discharging, which open-
ings are capable of being closed air-tight. To the top of this cylinder I adapt an
escape tube of fire clay for conveying off the acid vapor, and to the bottom, for
the admission of the steam, I adapt another clay pipe connected with a steam
boiler by a series of fire clay tubes. In order to diminish the corrosion of the
cylinder by the sulphate of lime, or the lime itself, I line it with a coating of
native carbonate of magnesia, applied in a similar manner to the usual clay
linings of chemical furnaces; 1 fill the cylinder with pieces of sulphate of lime
about one quarter of an inch in diameter, and having luted the openings air-
tight, heat the cylinder and its contents to a high red heat. I then pass
steam from the boiler through the red-hot clay tubes into the bottom of
the cylinder and up through the charge. The heated steam, in its passage
through the pieces of sulphate of lime, carries off the acid in the state of
sulphurous acid and oxygen, with sometimes a little sulphuric acid mixed with
it. The acid vapors pass off by the escape tube at the top of the cylinder, and
I convey them by stoneware tubes into a leaden chamber in order to combine
them into sulphuric acid by the usual means. I take care that the heat is
not raised so high at first as to melt the sulphate of lime in the cylinder, but
I increase it towards the end of the operation, the charge becoming more
infusible when partly decomposed. I have an opening in the tube conveying
off the acid vapors from the top of the cylinder, by means of which I examine
the vapors from time to time. and from the relative acidity of these ascertained
by the usual tests I judge of the progress of the operation. I regulate by a
stopcock the quantity of steam passed through the charge in the cylinder,
maintaining the supply at that point which produces the greatest quantity

page_text: of acid in the vapors. When the vapors cease to contain any notable pro-
portion of acid, the cylinder and its contents being at a high red or low
white heat, I shut off the steam, withdraw the charge from the cylinder by
the lower opening, and put in a fresh one to be treated like the first. The
charge thus operated upon will be found to consist chiefly of caustic lime.
When I wish to obtain the acid and alkaline base from the sulphate of
magnesia. I first drive off by heat all its water; I then introduce it in small
pieces into a cylinder, such as I have before described, and operate upon it in
the manner directed for the sulphate of lime; but I take care to keep the heat
at low redness at first to prevent the fusion of the charge. which would choak
up the cylinder and prevent the passage of the steam. The decomposition of
sulphate of magnesia takes place at a much lower temperature than that of
sulphate of lime (a low red heat is sufficient). and a considerable part of the
acid is given off in the state of sulphuric acid. When the charge has been
treated as directed the residue will be found to consist chiefly of caustic
magnesia. When I wish to decompose the sulphates of baryta and strontia. I
operate upon them in a reverberatory furnace. This mode is less advantageous
for the manufacture of sulphuric acid than the use of the close cylinder
formerly described, but I prefer it for the two last-mentioned salts. because T
consider their bases the more important product of their decomposition, and
the hydrates of these alkalies, and particularly that of baryta, being fusible.
would have much tendency to corrode the interior of the cylinder at the heat
necessary to decompose the salts. I use a common reverberatory furnace
heated by a coke fire, with its hearth covered with a compact bed of native
Several clay steam pipes
carbonate of magnesia three or four inches thick.
The sulphate
are introduced through the roof of the furnace, so as to throw a current of
heated steam over the whole width of the hearth; these pipes are connected
with a steam boiler by a series of fire-clay tubes kept red hot.
broken into pieces of about half an inch in diameter is spread over the lining
of carbonate of magnesia on the hearth of the furnace, and brought to a high
red or low white hent. A current of steam is then admitted from the boiler
through the red-hot tubes upon the charge. The acid of the sulphate is carried
off by the steam; and when I wish to collect it the acid vapors are conveyed
along with the gases of the fire into a leaden chamber to be combined into
sulphuric acid by the usual means. The quantity of steam thrown upon the
charge is kept at the point which produces the most rapid evolution of acid,
and the charge is stirred occasionally so as to expose fresh surfaces to the
action of the steam. As the contact of deoxidizing gases with the sulphate
is injurious, I admit, if necessary, by suitable openings above the fuel, such an

page_text: excess of air as will render the atmosphere in the furnace oxidizing. The
sulphate of strontia requires a higher heat than the sulphate of lime for its
decomposition, and the sulphate of baryta still higher than the sulphate of
strontia. When the sulphate of baryta is partly decomposed the mass melts
and becomes more fusible as the decomposition proceeds: I judge of the pro-
gress of the operation by testing a portion of the charge from time to time:
when it dissolves altogether, or nearly so, in dilute nitric acid, I withdraw the
charge, which now consists chiefly of the hydrate of baryta or strontia.
To obtain muriatic acid and the hydrates of baryta, or of strontia, or caustic
lime, from the muriates of those bases I employ the same process as that above
described for the decomposition of the sulphate of baryta. The sulphates of
potash and soda may. to some extent, be decomposed by being subjected at a
high temperature to the action of a current of heated steam in the manner
directed for the decomposition of the sulphate of haryta; but owing pro-
bably to the volatile nature of the bases of these salts at a high temperature.
no large proportion of them can thus be obtained in a free state.
To aid
therefore the decomposing action of the steam. I employ some substance
capable when mixed with these sulphates, highly heated and exposed to steam,
of forming a combination with their alkaline bases, which shall yet, when
cold, give up the alkali to the action either of water, or of water and carbonic
ncid. Of the large class of substances possessing these properties, which,
for convenience, I will call combining substances. I prefer to use either
alumina or the subphosphate of alumina. The alumina is prepared by
strongly igniting the sulphate of alumina, or by any other well-known process.
The subphosphate of alumina is prepared (as is directed in chemical works)
by mixing solutions of the phosphate of soda and the sulphate of alumina, and
adding to the solution a slight excess of ammonia. I mix the alumina in the
state of powder, with an equal weight of the sulphate of potash or of soda,
also powdered, and spread the mixture upon the hearth of a reverberatory
furnace, such as I have before described for the decomposition of the sulphate
of baryta. The mixture is then heated, exposed to steam, stirred, and the
operation conducted in all respects in the manner described for the treatment
of the sulphate of baryta. When a specimen of the charge shews by the
usual tests that it contains no notable proportion of the sulphate undecomposed
the operation is completed: I then withdraw the charge, lixiviate it with hot
water, and when the clear solution of aluminate of potash or soda thus obtained
has become cold, I pass through it an excess of carbonic acid until no more
precipitate of alumina is formed. The clear solution of carbonate of potash
or soda is then drawn off and evaporated; the alumina thus recovered is again

page_text: I
used as the combining substance. When I wish to obtain the aluminate of
potash or of soda I merely evaporate the solution above described, without
introducing the carbonic acid. The muriate of potash or of soda may also be
decomposed, when in a fused state. by the joint action of alumina, or the sub-
phosphate of alumina and steam. The operation is to be conducted in all
respects in the same manner as that just described for the sulphates of
potash and soda: but owing to the great volatility of the muriates of potash
and soda, when exposed at a high temperature to a current of air or steam, a
large quantity of the muriate will escape with the steam and gases of the fire
in the state of vapor undecomposed, and will be lost, or will be difficult to
condense: I prefer therefore to effect the decomposition of the muriates of
potash and soda by causing their vapors, intimately mixed with highly heated
steam, to pass slowly through a mass of small pieces of alumina kept at a high
red heat. I use for this purpose a vertical fire-clay cylinder lined with a coating
of native carbonate of magnesia to diminish the corrosion of its sides by the
alkali, and made with convenient openings at top and bottom for charging and
discharging, which openings should be capable of being closed air-tight.
arrange a cast-iron retort so that its tube enters directly the cylinder near
its bottom. The retort should have a charging door at the top capable of
being made air-tight, through which is introduced the muriate of potash or
soda to be decomposed. The muriates of potash and soda will not vaporize
freely even when fused and highly heated, unless the atmosphere above them
is continually changed. This may be effected by a current of steam, and I
find that I can sufficiently regulate the quantity of the salt volatilized from
the retort by the amount of steam which I blow over its melted surface; I
therefore insert a small steam pipe into the top of the rotort, so as to
throw a jet of heated steam upon the surface of the melted salt, and thus
force its vapor to enter the cylinder. The quantity of steam thus introduced to
aid the volatilization is not sufficient to decompose all the salt volatilized. The
rest of the steam necessary for this purpose is passed directly into the cylinder
by a fire-clay pipe entering it near the bottom, and connected through a series
of fire-clay tubes kept red hot with a steam boiler. Both steam pipes are
provided with cocks. An escape tube is inserted into the top of the cylinder
to convey the acid vapor, and the vapor of any undecomposed muriate, into
suitable condensers. I have an opening in this tube by which I can withdraw
at times a portion of the vapors in it to examine their saline and acid
character. The cylinder and retort are to be so constructed and arranged as
o allow their contents to be heated to high redness and upwards by any of the
vell-known means. The manner of operating is as follows: --The discharging
oor being closed air-tight. I fill the cylinder with alumina in pieces of about

page_text: one quarter of an inch in diameter, and fill the retort with the muriate of
potash or soda, and then close both the charging door of the cylinder and that
of the retort air-tight. I now bring the cylinder to a high red or white heat,
and the retort to a cherry-red heat, so that the salt in it is melted and ready to
volatilize freely on the admission of the steam upon its surface. Steam is now
passed from the boiler through the red-hot tubes into the cylinder by the pipe
entering near its bottom, so that it is filled with highly heated steam passing
upwards in a slow current through the interstices of the pieces of alumina.
I now admit by degrees a jet of heated steam into the salt retort by the pipe
entering its top, and thus drive a quantity of salt vapor into the cylinder;
where it mixes thoroughly with the current of steam which has entered by the
other pipe, and ascends with it through the column of highly heated alumina.
In its passage the alkaline vase of the muriates combines with the alumina,
forming an aluminate of potash or soda and the muriatic acid, together with
any of the salt vapor which may have escaped decomposition, passes off with
the steam through the escape tube at the top of the cylinder into tho
condensers provided. The progress of the operation can be ascertained by
examining the nature of the vapors which are passing through the escape tube.
When these vapors contain a large quantity of salt, and are strongly acid at
the same time, I admit more steam through the pipe leading directly into the
cylinder, and if this does not have the effect of diminishing the quantity of salt
in the vapors I lessen the quantity of steam thrown into the salt retort, and by
that means decrease the supply of salt vapor driven into the cylinder. When
the escaping vapors contain but little salt and a large quantity of acid, I
consider the operation as proceeding favorably, and I always endeavour to
regulate the quantities of steam passed through the two pipes, and by that
means the proportions of salt vapor and steam thrown into the cylinder, so as to
produce this effect. When the escaping vapors contain a large quantity of
salt of steam, and but little acid, the cylinder and its contents being at a high
red heat. I consider that the decomposition of the salt is no longer effected in
the cylinder, and I then shut off both currents of steam, withdraw the charge
by the lower door, and replace it with fresh alumina. The withdrawn charge
is then lixiviated with hot water, and the solution of aluminate of potash or
soda thus obtained is treated with carbonic acid, as before described. The
lining of the cylinder should be examined occasionally and kept in repair, so
that the fire-clay may not be corroded by the alkali. Provided the charge of
alumina in the cylinder is readily and equally permeable to the current of
steam and salt vapor, the smaller the pieces of which it consists and the
greater the surface they expose to the current, the more rapidly will the
decomposition of the muriate proceed. The steam used need not be of higher

page_text: boiler pressure than will suffice to secure its passage through the charge in the
cylinder. The subphosphate of alumina may be substituted for the alumina in
the processes for the decomposition of the sulphates and muriates of potash
and soda, and its action is even more powerful, but its first cost is greater.
Although to aid the decomposition of the sulphate and muriates of potash and
soda by steam at a high temperature, the use of either alumina or its sub-
phosphate is preferred as the combining substance, yet there are a great
number of substances which also possess the requisite properties, but act with
various degrees of energy. Thus many salts which already contain a certain
proportion of base will yet, when exposed in contact with the sulphates and
muriates of potash and soda at a high heat to the action of steam, form a
combination with the potash or soda, decomposable when cold, by water or
water and carbonic acid. The subphosphates of lime, baryta, and strontia, and
the subsilicates of lime, baryta, and strontia, will, under these circumstances
combine with the alkali, and yield it to the action of water alone when cold.
The sulphates of baryta and strontia, although themselves decomposable by
the action of steam at high temperatures, are still capable of thus aiding in the
decomposition of the sulphates and muriates of potash and soda, and yield the
alkali by the action of water. The neutral phosphates and neutral silicates of
potash and soda when thus treated form basic salts, which are soluble in
water and then decomposable by carbonic acid. The alkalies, lime, and
magnesia will also thus combine with a portion of free potash or soda, which
may be extracted by water. Other materials are capable of being used as
combining substances, but I have named those which I consider preferable.
The decomposition of the muriate of soda by the action of steam at a high
temperature may be applied to the production of soda in another way, videlicit,
by exposing the muriate mixed with sulphate of lime to a high heat and to the
current of steam, and afterwards decomposing the sulphate of soda thus
formed by the usual mode. For this process I use a horizontal cylinder of
close fire ware, protected on the inside from the action of lime and sulphate by
a lining of carbonate of magnesia, and provided with an opening for charging
capable of being made air-tight. Into the top of the cylinder at one end
a steam pipe is introduced, and from the other end at the top an escape pipe
connects with suitable condensers for collecting the vaporized salt and acid.
The cylinder is half filled with a mixture of equal parts by weight of sulphate
of lime and muriate of soda, the opening made tight, and 'the cylinder and its
contents brought to a red heat. A current of heated steam is then admitted
which passes over the surface of the melted mixture and carries off muriatic
When the steam
acid with more or less volatilized salt into the condensers.
escaping from the cylinder ceases to contain any notable quantity of muriatic

page_text: acid the operation is discontinued and the charge is withdrawn; its soluble
salts are extracted by water, and the sulphate of soda separated from any
undecomposed muriate by evaporation and crystallization. In this operation
the heat should not be raised so high as to cause the decomposition by the
steam of the sulphate of soda produced, or of the sulphate of lime itself.
I obtain the chromates of potash and soda by subjecting a mixture of the
muriate or sulphate of either of those bases respectively with chrome ore in
fine powder at a bright read heat to the action of a current of steam and
atmospheric air. The muriatic or sulphuric acid is carried off by the steam,
and the oxide of chromium is oxidized and reacts upon the liberated alkali,
forming a chromate. When the sulphate of potash or soda is to be used I
mix intimately one part by weight of ground chrome ore with two parts of
the sulphate of potash or soda and two parts of lime, and heat the mixture to
bright redness for eighteen or twenty hours on the hearth of a reverberatory
furnace, while currents of heated steam are thrown upon its surface from pipes
coming through the roof of the furnace. The atmosphere in the furnace must
always be kept in an oxidizing state, by the admission of a sufficient quantity
of air through openings above the level of the fuel, and the charge should be
frequently stirred to expose fresh surfaces to the steam and air. The lime is
not absolutely required in the above mixture, but I prefer it as aiding the action
and making the charge more porous. When the charge is found by the usual
tests to contain a sufficient quantity of the alkaline chromate it is withdrawn,
and the soluble parts extracted by water and treated in the usual way.
When I wish to use the muriates of potash and soda for the production of the
chromates of potash and soda, 1 mix the ground chrome ore with twice its
weight of powdered chalk, moisten the mixture with water, and form it into
pieces of about half an inch in diameter, which are well dried. With these I
fill a cylinder having a retort and steam pipes attached, such as are described
for the decomposition of the muriates of potash and soda by means of alumina,
and I proceed exactly as in that operation, except that I insert another pipe near
the bottom of the cylinder through which I force a stream of heated air which
mixes with the ascending current of steam and salt vapor, so as to pass with
them through the charge. When the nature of the vapors escaping from the
top of the cylinder is such as I have before described as indicating that the
decomposition of the muriate ceases to be effected in the cylinder the charge
is withdrawn, and the alkaline chromate extracted by water as usual. Though
1 prefer in all the above-described processes heating the steam highly before
passing it upon the salt to be decomposed, yet the same effect will be produced
whenever the steam and salt are in contact at the proper temperature for the
respective decompositions, whether they have both been previously heated, or

page_text: one alone heated so highly as to be able to raise the other to the requisite
temperature. As has been before stated some of the salts are decomposable
by steam at a much lower temperature than others, but with all the decom-
position proceeds more rapidly in proportion as the heat is increased.
I claim as of my Invention the decomposing the sulphates of baryta, strontia,
lime, and magnesia, and the muriates of baryta, strontia, and lime, by
exposing them at a high temperature to the action of a current of steam,
for the purpose of obtaining the acids and the alkalies of these salts
respectively.
I claim as of my Invention the decomposing the sulphates and muriates of
potash and soda, for the purpose of obtaining the acids and the alkalies of
these salts respectively, by exposing them at a high temperature to the joint
action of a current of steam and of alumina, or other combining substance.
I claim as of my Invention the making sulphate of soda by the combined
action of sulphate of lime and a current of steam upon the muriate of soda at
a red heat.
I claim as of my Invention the making the chromates of potash and soda
by exposing a mixture of chrome ore and sulphates,. or muriates of those
alkalies respectively, at a bright red heat to a current of steam and an
oxidizing atmosphere.
I claim as of my Invention the making aluminate of potash and soda by the
action of a current of steam upon a mixture of alumina, and the sulphate or
muriate of potash or soda at a high red heat.
In witness whereof, I, the said Richard Albert Tilghman, have hereunto
set my hand and seal, this Thirty-first day of July, in the year of our
Lord One thousand eight hundred and forty-seven.
RICHARD A. (L.s.) TILGHMAN.
AND BE IT REMEMBERED, that on the Thirty-first day of July, in the
year of our Lord 1847, the aforesaid Richard Albert Tilghman came before our
said Lady the Queen in Her Chancery, and acknowledged the Specification
aforesaid, and all and every thing therein contained and specified, in form
above written. And also the Specification aforesaid was stamped according to
the tenor of the Statute made for that purpose.
Enrolled the Thirty-first day of July, in the year of our Lord One
thousand eight hundred and forty-seven.