CERTAIN IM- PROVEMENTS IN THE MANUFACTURE OF SULPHATE OF MAGNESIA, COMMONLY CALLED EPSOM SALT
Year: 1816

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM.
HENRY, of Manchester, in the County, of Lancaster, Doctor of Physic, send-
greeting.
WHEREAS His most Excellent Majesty King George the Third did, by
His Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the Third day of August,
in the fifty-sixth year of His reign, give and grant unto me, the said William
Henry, my executors, administrators, and assigns, His especial licence, full
power, sole privilege and authority, that I, the said William Henry, my
executors, administrators, and assigns, and every of them, by myself and
themselves, or by my and their deputy or deputies, servants.or agents, or
such others as I, the said William Henry, my executors, administrators, and;
assigns, should at any time agree with, and no others, from time to time and
at all times thereafter during the term of years therein expressed, should and
lawfully might make, use, exercise, and vend, within that part of the United
Kingdom of Great Britain and Ireland called England, the Dominion of
Wales, and Town of Berwick-upon-Tweed, my Invention of "CERTAIN IM-
PROVEMENTS IN THE MANUFACTURE OF SULPHATE OF MAGNESIA, COMMONLY CALLED
EPSOM SALT," in such manner as to me, the said William Henry, my
Cexecutors, administrators, and assigns, or any of them, shall in my or their
discretion seem meet; in which Letters Patent there is contained a proviso,
obliging me, the said William Henry, particularly to describe and ascertain
the nature of my said Iuvention, and in what manner the same is to be
performed, by an instrument in writing under my hand and seal, and to cause

page_text: the same to be inrolled in His Majesty's High Court of Chancery within two
calendar months next and immediately after the date of the said Letters
Patent, as in and by the said Letters Patent, relation being thereunto had,
may more fully and at large appear.
NOW KNOW YE, that I, the said William Henry, in compliance with the
said proviso, do hereby declare that the nature of my said Invention, and
the manner in which the same is to be performed, are as herein-after is
mentioned, that is to say:-
I first expose the caustic magnesian lime, prepared by burning or calcining
the stone called magnesian limestone, to the action of certain acids, either
combined with water only, or with certain alkaline or earthy bases, which
acids have a stronger attraction for lime than for magnesia, and at the
same time form with lime compounds that are readily soluble by cold water.
By the action of the said acids applied to the same magnesian lime in such
proportion as will be herein-after specified, I dissolve the greater part of
the lime, and leave undissolved the greater part of the magnesia, which
magnesia I afterwards apply in the manner herein-after described to the
preparation of sulphate of magnesia; or otherwise I dissolve the whole of
a given portion either of magnesian limestone or else of caustic magnesian
lime in such a quantity of one of the said acids as is barely sufficient for the
purpose, and I afterwards precipitate the magnesia by a due proportion either
of common quick lime or magnesian lime, as will be more particularly
described in a subsequent part of this Specification. And I do hereby
declare that my said Invention consists in applying the magnesia which has
been separated from magnesian limestone or magnesian lime by any of the
methods herein-after described to the preparation of sulphate of magnesia by
means of sulphuric acid or sulphate of iron, and that I do not claim any
exclusive right to the manufacture of sulphate of magnesia by directly acting
with sulphuric acid on the entire magnesian limestone, or with sulphuric acid
or sulphate of iron, on the entire magnesian lime, obtained by burning the said
limestone. The acids by means of which I dissolve the lime of the caustic
magnesian lime, leaving the magnesia undissolved, are the following: the
acetous acid, either in the form of vinegar or of pyroligneous acid, obtained
by the distillation of wood or tar; the nitric acid; the muriatic acid, either
combined with water only, or as it exists in muriate of magnesia; or in
muriate of ammonia, and the oxymuriatic acid or chlorine, either in a gaseous
state or in a state of watery solution. The first step which it is necessary to
take as a preliminary to any of those processes in which the caustic magnesian
lime is to be employed is to reduce the said lime to powder, either by

page_text: mechanical means, or (which I greatly prefer) by converting it into what is
called in chemical language a hydrate, which last object is effected by adding
barely as much water to the fresh burnt magnesian lime as will cause it to
fall into a powder, or else by leaving it exposed to the atmosphere till it has
spontaneously acquired water enough for that purpose. This powder is to
be passed through a fine wire sieve. When the acetous or pyroligneous acid is
employed, I first ascertain how much of the said magnesian lime or else of
its hydrate is sufficient to saturate a gallon of the same acid which I am about
to employ, and to any number of gallons of the said acid I then add twice as
much of the said magnesian lime or else of its hydrate as is necessary for the
saturation of the number of gallons of the said acid, which are actually used.
For example, if one hundred gallons of the said acid require for saturation
forty pounds of the hydrate of the magnesian lime, I add to one hundred
gallons of the said acid eighty pounds of the said hydrate, and I keep the
said quantities of acid and hydrate in a state of mixture by mechanical
agitation for a space of time not less than half an hour, and in preference
for two, three, or four hours; I then allow the insoluble part to fall to the
bottom of the vessel, and I decant the supernatant liquor, and apply it to any
of the purposes to which acetate of lime (which is the substance held in
solution in the said liquor) is adapted. The undissolved portion, which is
chiefly magnesia, I collect on linen drainers, dry in any convenient manner,
and when dry I calcine it at a low red heat, with free access of air (stirring
it frequently), either in earthen or iron pots, or in a furnace, which may be of
any shape adapted to the purpose. The object of this calcination is to burn
away completely the tarry, resinous, and vegetable colouring matter with
which the said undissolved portion is contaminated. On any quantity of the
calcined product last-mentioned, reduced to a fine powder and diffused through
water of the temperature of the atmosphere, in the proportion of half a
pound to each gallon of water or thereabouts, I then pour sulphuric acid of
commerce diluted with five or six times its weight of water, until the acid
begins to be in slight excess. This excess of acid I neutralize, by adding
in successive portions as long as is necessary more of the said calcined product,
after which I add a still further quantity of the said calcined product, in the
proportion of about a pound to every one hundred pounds by weight of
sulphuric acid which have been used, (reckoning the said acid in the concen-
trated state in which it is commonly sold, and I keep the mixture in a state
of agitation for an hour or two before allowing it to remain at rest; or I
unite the sulphuric acid to the said calcined product by using sulphate of
iron in the following manner :-I dissolve any known weight of sulphate of

page_text: iron in seven or eight times its weight of water at or near the boiling tem-
perature, and to the solution while hot, I add a quantity of the said
calcined product finely pulverized, and equal in weight to about one-third
part of the said sulphate of iron, and I keep the inaterials in a state of
agitation for half an hour or longer. Or I dissolve a known weight of
sulphate of iron in seven or eight times its weight of water of the tem-
perature of the atmosphere, and after adding a quantity of the said calcined
product equal in weight to about one-third part of the said sulphate of
iron, I agitate the mixture at intervals for about 'half an hour each time
during one, two, or more days. In either case I assay by means of any
of the known chemical tests for iron a portion of the liquor first filtered
through paper or cleared by standing, and if the whole of the said
sulphate of iron proves not to be decomposed, I mix in successive portions
more of the said calcined product with the said liquor (examining the
liquor by the proper tests for iron after every such addition) until the
decomposition of the said sulphate of iron is complete. By any of these
processes (of which, however, I greatly prefer that in which diluted sul-
phuric acid is used.) I obtain a solution of sulphate of magnesia, which
solution I suffer to clear itself by standing. I then draw off the clear liquor
into a shallow boiler or evaporating vessel of iron or copper, and I wash the
sediment repeatedly with water, adding the washings to the liquor in the afore-
said boiler. After reducing the liquor by evaporation to about one-third of its
original bulk, I allow it to cool, during which cooling it deposits a quantity of
sulphate of lime. I then transfer the clear liquor into another boiler, and
having heated it to nearly two hundred and twelve degrees of Fahrenheit's
thermometer, I add to it either 'carbonate of magnesia, in the proportion of
about one ounce to every five wine gallons of the liquor, or otherwise I add to
it calcined magnesia, in the proportion of about an ounce to every ten wine
gallons of the said liquor, which liquor after such addition I keep heated for at
least half an hour, stirring it frequently. I then allow the impurities to settle,
and when the liquor has become clear I either draw it off into a shallow iron
or copper boiler, in which I again evaporate it to a sufficient density to crystal-
lize, or otherwise I apply it to the preparation of carbonate of magnesia by
commonly known processes. In like manner, when I use the nitric or muriatic
acid, I first determine by a previous experiment how much of either of the
said acids of the strength which I am about to use is sufficient for the satura-
tion of the given weight of the hydrate of magnesian lime. In the next place,
I mix any number of pounds of either of the said acids, previously diluted with
ten or twelve times its weight of water, with twice as much of the hydrate of

page_text: magnesian lime as is necessary to saturate the quantity of acid actually in use.
These materials I agitate together during at least half an hour; I then suffer
the liquor to clear itself by standing, and when clear I draw off the solution
of lime from the sediment, which sediment (consisting chiefly of magnesia) 1
wash repeatedly with water till the water comes off tasteless, and I afterwards
slightly supersaturate the said sediment with dilute sulphuric acid in the
manner which has been already described. The slight excess of sulphuric acid
existing in this case I then neutralize by the addition of a sufficient quantity of
carbonate of magnesia; or I unite the sulphuric acid to the said sediment by
using sulphate of iron in the manner already specified,' in which case I estimate
the weight of the sediment at the rate of thirty-four parts from every one hun-
dred parts of hydrate of magnesian lime that have been used, and I add
to the said sediment a solution of three times its estimated weight of sulphate
of iron. Should the sulphate of iron be proved by the application of the proper
tests to be in excess, I decompose such excess by adding a sufficient quantity
either of carbonate of magnesia, or of magnesia separated by any of the before-
mentioned processes, from magnesian lime; and I continue to make these addi-
tions till the use of any of the tests for iron shews that such additions are no
longer necessary. To decompose magnesian lime by means of muriate of mag-
nesia, I either take any quantity of the said muriate in a solid form, (which is
best obtained by evaporating to dryness the liquor well known under the name
of bittern, that remains after the muriate of soda and sulphate of magnesia
have been separated from sea water by processes generally known and prac-
tised,) and I add to the said solid muriate of magnesia such a quantity of
water that every gallon of the solution may contain about two pounds of the
salt; or, if the muriate of magnesia is already in a liquid state, I ascertain the
strength of the solution by evaporating an aliquot part of a gallon and weighing
the dry salt. In either case I add to a quantity of the solution containing a known
weight of muriate of magnesia an equal weight of the hydrate of magnesian
lime, and I stir the materials together for at least half an hour, but in prefer.
ence for two, three, or four hours; I then allow the undissolved part to
subside, and I decant the supernatant muriate of lime, after which I wash the
sediment repeatedly with water till the water comes off tasteless; I then add
dilute sulphuric acid to the said sediment till there is a slight excess of acid,
which excess I saturate as aforesaid by carbonate of magnesia, or else by mag-
nesia which has been separated from magnesian lime by any of the methods
described this Specification. The remaining operations I conduct in the
manner already described; or I employ the sulphate of iron in the proportion of
three parts to one part of the sediment, in which case I reckon the weight of

page_text: the sediment to be about seventy parts for every one hundred parts of hydrate of
magnesian lime that have been employed, and I proceed in the remainder
of the
e process exactly in the manner which has been already described. By the
use of muriate of magnesia, I obtain not only the magnesia which formed a
constituent part of the magnesian lime, but also a further quantity of magnesia
precipitated from the muriate of magnesia by the calcareous part of the said
magnesian lime. To remove the lime from magnesian lime by means of
muriate of ammonia, I dissolve any quantity of solid muriate of ammonia in
eight or ten times its weight of hot water, and I then add as much of the
hydrate of magnesian lime as is equal to the weight of the said solid muriate
of ammonia. These materials I stir together for at least half an hour. After
allowing them to remain a sufficient time at rest, I then decant the clear liquor,
and submit it to distillation for the purpose of obtaining solution of ammonia.
The sediment from which the said liquor has been decanted I wash repeatedly
with water, and either act upon it with dilute sulphuric acid or with sulphate
of iron, as aforesaid, reckoning the weight of the said sediment in the latter
case at thirty-four parts from every one hundred parts which I have used of
the said hydrate. When I employ oxymuriatic acid or chlorine to remove
the lime from magnesian lime, I regulate the proportion of oxymuriatic acid or
chlorine to the hydrate of magnesian lime, by adjusting the quantity of mate-
rials which are used to afford the said gas to the quantity of magnesian lime
employed to condense the gas. These proportions must necessarily vary with the
purity of the materials from which the gas is obtained, and with the proportion
of the said materials to each other, which is variously regulated by different
persons. The proportions which I prefer for every bushel of common salt are
fifty-six pounds of sulphuric acid of commerce, of the density of one thousand
eight hundred and fifty, water being taken as one thousand, forty wine pints.of
water, and forty pounds of finely-ground manganese; and (as a general rule)
for every bushel of common salt or muriate of soda put along with the aforesaid
ingredients into the still (which still may be of any of the forms usually employed
by bleachers), I allow at least twenty-eight pounds of the hydrate of magnesian
lime, which may either be placed in a dry state in a proper receiver, or be kept
suspended in water by mechanical agitation in the way commonly practised by
bleachers. When the combination has been made in the dry way, I add water
in order to wash off the oxymuriate of lime; but when water has been put at
first into the receiver, I allow the materials therein contained to remain at rest
for some time after the gas has ceased to come over, and I then draw off the
liquid oxymuriatic of lime. In either case I wash the insoluble part repeatedly
with water, and I afterwards act upon it in manner already specified, either with

page_text: dilute sulphuric acid or with sulphate of iron. In these cases, however, I prefer
the dilute sulphuric acid, because to use sulphate of iron to advantage it would
be necessary to estimate the weight of the undissolved portion with greater
accuracy than can be conveniently attained. Indeed, I consider dilute
sulphuric acid, whenever it can be obtained conveniently, and at a reasonable
price, to be much more fit than sulphate of iron for the purpose of pre-
paring sulphate of magnesia. I sometimes find it advantageous to apply more
than one of the said acids in succession. For example, when the oxymuriatic
acid has been used in a proportion not sufficient to take out the whole of the
lime from a quantity of magnesian lime, I afterwards mix the undissolved
part of the said quantity of magnesian lime with a due proportion of acetous,
nitric, or muriatic acid, or of muriate of magnesia, or muriate of ammonia, in
the manner already described. When two acids are thus applied in succession
to the same quantity of magnesian lime, I take care that no more of the second
acid is used than is required to dissolve the calcareous part only of the said
magnesian lime. To insure this, I add the second acid in successive portions,
and after every such addition I ascertain, by an experiment on a sinall sample
of the mixture, whether the undissolved part be soluble or nearly soluble in a
sufficient quantity of dilute sulphuric acid. As soon as this solubility is
attained, I discontinue adding more of the second acid to the mixture from
which the sample was taken, and after decanting the fluid part I wash the
sediment repeatedly with water, and then apply either dilute sulphuric acid or
sulphate of iron, proceeding for the rest of the process as already mentioned.
I occasionally effect the separation of the lime from the magnesia, which
together constitute magnesian lime, in the following manner :-I first com-
pletely saturate any quantity either of the acetous, nitric, or muriatic acids (the
two last being diluted respectively with from ten to twenty times their weight
of water) by adding thereto either a sufficient quantity of pulverized mag-
nesian limestone, or such a quantity of hydrate of magnesian lime as is barely
sufficient for the purpose; I next precipitate the magnesia from the compound
solution of lime and magnesia thus obtained, by adding either as much hydrate
of common lime, finely sifted, as I have learned by an experiment made for the
purpose, is sufficient to saturate one-half only of the acid which the whole of
the said solution contains, or by adding as much hydrate of magnesian lime as is
sufficient to saturate the whole of the acid which the said solution holds in combi-
nation. In either case I stir the materials together for at least half an hour,
and then allow the liquor to clear itself by standing. When cleared, I decant
the fluid and wash the undissolved part repeatedly with water, and I after-
wards apply the said undissolved part to the manufacture of sulphate of mag-

page_text: nesia, by adding thereto either dilute sulphuric acid or sulphate of iron, in the
manner before mentioned. In general the magnesian lime contains in every
ten parts about five parts by weight of carbonic acid, three parts of lime, and
two of magnesia, with small portions of aluminous earth and metallic oxides,
and consequently the caustic magnesian lime consists in every ten parts of about
six parts of lime and, four of magnesia. In this case the acid employed to
saturate the magnesian lime is almost equally divided between those two
earths; and therefore to dissolve only the calcareous earth, half the quantity
of acid must be used, which would be required to dissolve the whole of any
given quantity of the said magnesian lime. But for any variety of magnesian lime
containing in ten parts more than six parts by weight of lime, a proportionally
greater quantity of any of the said acids must be used to take out the lime,
and for any variety of magnesian lime containing in ten parts less than six
parts of lime, a proportionably less quantity of acid will suffice to take out the
lime. The precise quantities to be employed in these cases will be readily
ascertained experimentally by any person who is even moderately versed in the
management of chemical processes.
In witness whereof, I, the said William Henry, have hereunto set my
hand and seal, the Twenty-third day of September, in the year of our
Lord One thousand eight hundred and sixteen.
Inrolled the Twenty-fifth day of September, in the year above written.