CERTAIN IMPROVEMENTS IN THE MANUFACTURE OF PRUSSIAN BLUE, PRUSSIATE OF POTASH, AND PLASTER OF PARIS
Year: 1836

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, PETER
SPENCE, of Henry Street, Commercial Road, in the County of Middlesex,
Chemist, send greeting.
WHEREAS His present most Excellent Majesty King William the Fourth,
by His Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Twenty-seventh day of July, in the seventh year of His
reign, did, for Himself, His heirs and successors, give and grant unto me, the
said Peter Spence, His especial licence, full power, sole privilege and authority,
that I, the said Peter Spence, my exors, adññors, and assigns, or such others
as I, the said Peter Spence, 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, my Invention of "CERTAIN IMPROVEMENTS IN THE MANUFACTURE OF
PRUSSIAN BLUE, PRUSSIATE OF POTASH, AND PLASTER OF PARIS;" in which said
Letters Patent is contained a proviso, that I, the said Peter Spence, shall
cause a particular description of the nature of my said Invention, and in what
manner the same is to be performed, to be inrolled in His said Majesty's
High Court of Chancery within six calendar months next and immediately
after the date of the said in part recited Letters Patent, as in and by the
same, reference being thereunto had, will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Peter Spence, do hereby declare the nature of my Invention, and in what.

page_text: manner the same is to be performed, are fully described and ascertained in
and by the following statement thereof, that is to say :-
My improvements consist in the following modes or manners of manufac-
turing the aforesaid articles, in which I particularly state the various processes
that I adopt, and the various materials that I use in my aforesaid manufacture;
and first, with regard to the materials from which I produce my aforesaid
articles of manufacture:-Be it known that I use for this purpose the refuse
lime liquor of the gas works, being the bright liquor that swims on the top of
the muddy impure lime after they have been emptyed out of the purifying
vessels of those gas works which purify their gas by the wet lime or cream of
Jime process, which liquor is named in many of the aforesaid works, Blue Billy
liquor. I also use for my aforesaid manufacture the refuse dry lime of those
works which use the dry lime mode of purifying, being the aforesaid dry lime
after it is taken out of the purifying vessels. I also use various secondary
articles, which I shall name when I come to specify the processes in which
they are used.
From the aforesaid lime liquor I manufacture prussian blue,
prussiate of potash, and plaster of Paris, and from the aforesaid dry lime, I
manufacture prussian blue and prussiate of potash.
With regard to my modes or manners of operation in my aforesaid manu-
facture, they are as follows:-As I find that the liquors which I receive from
the different works, and also those procured at different times from the
same works, vary very much in strength, so I find it most profitable to separate
the liquors into two distinct classes according to their strengths, and to adopt
two different modes of operation with them; the mode of operation with the
dry lime is also different from the other two modes with the two classes of
liquors, so that altogether I have three different modes of operation, which I
shall now make known in the order in which I have stated them, that is to
say, the two modes of operation with the two classes of liquors, and then the
mode of operation with the dry lime. But first, I shall state my mode of
classing the liquors. In the first class of liquors, I place all the weak liquors,
being those which require less than one pound of oil of vitriol for the saturation
of an imperial gallon, and in the second class I place all the strong liquors,
being those which require one pound and upwards of oil of vitriol for the
saturation of an imperial gallon. My mode of testing, to which class any liquor
which I may procure belongs, is the following:-I measure off an exact gallon
of the liquor to be tested, and pour it into an earthen jar that will contain
from three to four gallons, I then weigh off in a bottle of any convenient
shape two pounds of oil of vitriol or sulphuric acid of the strength 1:845; I

page_text: then pour from this bottle a quantity of the acid into the liquor, adding it
gradually until the effervecense begins to grow weak; I then take a slip of
litmus testing paper, and when I find that on dipping it into the liquor the
paper is coloured red, I stop adding the acid; I then weigh the acid that
remains, and the difference in weight is what is required to saturate a gallon
of the liquor under trial, if it is less than one pound, then the liquor will belong
to the first class, or the class of weak liquors; if it is one pound or more, then
the liquor will belong to the second class, or the class of strong liquors. I
shall now describe my mode of operating upon the first class of liquors, being
the class of weak liquors.. These I receive into large wooden tanks or vats,
containing from four to five thousand gallons; in these tanks or vats when
nearly full I put the liquor through the first or preparatory process; the
liquor as I receive it from the works contains in solution hydrosulphuret of
lime and hydrocyanate of lime or prussiate of lime, the real quantity of these
being of course in proportion to the strength of the liquor, the relative
quantities being in most liquors nearly fourteen parts hydrosulphuret of lime
to one part hydrocyanate or prussiate of lime.
The object of my first or preparatory process is to convert the hydrocyanate
or prussiate of lime into ferrohydrocyanate or ferroprussiate of lime to prevent
its decomposition in the second or saturating process, and this I effect in the
following manner: -For every one hundred gallons of the liquor, I take ten
pounds of green copperas or sulphate of iron, and five pounds of newly slacked
quicklime. I dissolve the copperas in water in one vessel, and mix the quick-
lime with water in another, till it is about the consistence of cream; I then add
the solution of copperas to the lime, and after stirring them for a few minutes,
pour them into the tank or vat of liquor to be operated upon; the the whole body
of the liquor must then be stirred for a quarter of an hour, and then be left for
twelve hours, when it is ready for the saturating process. The saturating pro-
cess I perform in the following manner :-The vessel in which I perform this
operation is an air-tight cask, containing three hundred gallons; on the top of
this cask I place a stoneware receiver, containing sulphuric acid, and having
a stoneware cock fitted into it near the bottom; below this cock is a funnel
of sheet lead which is soldered to a leaden pipe of one half inch internal
diameter, and bent in the form of the letter S. The other end of this pipe is
inserted into the top of the saturating vessel, which stands on end, and through
this funnel and pipe the acid is conveyed into the liquor. I also insert through
the top of the saturating vessel another tube of three inches internal diameter
being of tin plate. This tube rises up one foot from the top of the saturating

page_text: vessel, and then bends off at a right angle, and is carried along horizontally.
This tube is for the purpose of conveying away the sulphuretted hydrogen gas,
which is thrown off in the saturating process, which sulphuretted hydrogen
gas I make use of in a way that I shall afterwards describe. Into the side of
the saturating vessel I also insert a cock to draw off a little of the liquor to
ascertain when it is saturated; in the top of the saturating vessel I also make
a round hole of three inches diameter, into which I fit a wooden plug
moveable at pleasure; this hole is for the filling of the saturating vessel with
the liquor to be saturated. In the side of the saturating vessel close to the
bottom, I make another hole of similar dimensions, into which a plug is also
fitted; this hole is for the purpose of emptying the saturating vessel after the
liquor is saturated; when I proceed with the saturating process, I draw off
the bright liquor free from any of the sediment from the first process vat by
means of a syphon, the saturating vessel being placed on a lower level; by
this means I fill the saturating vessel three-fourths full; I then stop the syphon,
put in the top plug into the saturating vessel, and open the cock of the stone-
ware receiver, allowing the sulphuric acid or oil of vitrol to flow in a stream
the size of a goose quill. After allowing it to flow for about ten minutes, I
draw off a wine glass full of the liquor from the cock in the side of the
saturating vessel for the purpose of testing it to ascertain if it is saturated.
The test I apply is the following:-I dissolve a small quantity of green
copperas or sulphate of iron in a wine glass full of water; I then pour a small
quantity of this solution into the wine glass full of liquor to be tested; if it is
not saturated the liquor immediately assumes a black color, but if it is saturated
it immediately assumes a light green color. When by this means I find that
the saturating process is complete, I immediately stop the cock through
which the acid flows; I now draw the plug which is close by the bottom of the
saturating vessel, when the whole of the liquor flows out, conveying along
with it the sulphate of lime which the acid has precipitated or thrown down
from the liquor. This stream of saturated liquor and sulphate of lime that
flows from the plug hole I receive upon a filter of coarse cloth in a frame
five feet square, and suspended over a sunken wooden tank. The clear liquid
passes through the filter, and the sulphate of lime remains upon it; when it
has ceased flowing from the saturating vessel, I immediately replace the plug,
and the saturating vessel is then ready for another operation. I then pour
three or four pails full of water upon the mass of sulphate of lime on the filter
to drain through any liquor that remains among it. The sulphate of lime is
then removed, and from it I manufacture my plaster of Paris in the following

page_text: manner-After making a large bed of it about three feet in thickness on
any convenient piece of ground, I allow it to remain there for about six
months to drain thoroughly through the action of the rain. I then take it up,
and after being burnt or boiled in the ordinary way of manufacturing plaster
of Paris from native gypsum, it is then fit for the market.
The saturated liquor, after it passes through the aforesaid filter, is then
pumped up into wooden tanks or vats containing one thousand gallons each.
When one of these is filled I add to it a solution in water of sixty pounds
green copperas or sulphate of iron, a precipitate of a light green colour in a
short time falls down from the liquor. The clear liquor is drawn off from
this and run away; fresh water is added, is allowed to settle, and again drawn
off, and this is continued till the water comes off tasteless. The precipitate is
then thrown on filters, when it is brought to the consistence of a pulp or paste;
this I call my coarse blue, and from it in this state I make fine prussian blue
and prussiate of potash. To make prussian blue, I proceed in the following
manner: For every one hundred pounds of the pasty coarse blue, I take
fourteen pounds of soda of commerce, or an equivalent quantity of other alkali.
I dissolve it in ten gallons of water; this solution I bring to a boiling heat"
and pour it upon the pulpy coarse blue; I then stir it at intervals for three
hours; I then allow it to settle, then draw off the clear liquor and throw the
sediment on a filter, that what remains may drain from it; to every gallon of
this liquor I add a solution of one pound green copperas or sulphate of iron,
which throws down a dark green precipitate; to this I add muriatic acid
or spirit of salt till it assumes a deep blue colour; it is then washed till
the water comes off tasteless, thrown upon filters, from them placed on chalk
stones in a drying house, and then dried off on iron plates exposed to the
temperature of from one hundred and fifty to two hundred degrees of Fahren-
heit.
In making my prussiate of potash from the pulpy coarse blue I pro-
ceed in the following manner :-For every one hundred pounds of the pulpy
coarse blue I take nine pounds of the potash of commerce and dissolve.
it in two gallons of water; I then add to it the pulpy blue, and bring up
the whole to a heat of one hundred and fifty degrees of Fahrenheit; I keep it
at this for three hours with frequent stirring; I then allow it to settle, draw off
the clear liquor, throw the sediment upon a filter, and wash out what remains.
with a little water; I then evaporate the whole of this clear solution till.
a pelicle forms upon its surface, when I draw it off to crystallize the suk-
phuretted hydrogen gas, which I described before as being carried off in

page_text: a tube of three inches diameter. I make use of in the following manner :—I
carry it onwards to a leaden chamber constructed upon the ordinary plan of
manufacturing sulphuric acid or oil of vitriol; when within ten feet of the
furnace of the chamber I bend the pipe into an air-tight cask three-fourths
filled with water, the pipe opening two inches below the surface of the water;
the use of this is to prevent explosions of the gas when it gets mixed with air.
Another pipe of the same size that does not enter the water conveys the gas to
the furnace, when, being lighted, it burns with a large blue flame, and is
converted into sulphurous acid gas and watery vapour; these are conveyed by
a large pipe into the chamber, when the sulphurous acid gas is converted into
sulphuric acid by the same means as when it is obtained by the burning
of brimstone; my sulphuric acid thus produced I use in my saturating
process.
I shall now describe my method of operating upon the second class of
liquids, being the class of strong liquors; in operating upon them I proceed
upon the principle of converting the hydrosulphuret of lime into a sulphuret of
lime, at the same time converting the hydro-cyanate of lime or prussiate of
lime into a ferro-hydrocyanate or ferro-prussiate to prevent its decomposition;
This I effect by the following method:-For every one hundred gallons of the
liquor to be operated upon I take six pounds of green copperas or sulphate of
iron and dissolve it in sixteen gallons of water; to this I add two gallons
of the ammoniacal liquor of the gas works; I then allow the precipitate to
settle, pour off the water and put on fresh water, repeating this till the water
comes off tasteless; I then put the sediment among the liquor to be operated
upon, then put the whole into an evaporating vessel and evaporate it down to
perfect dryness, taking care that the heat be so moderated in the last stage of
the process as not in the least degree to burn it. I then take the residual
substance out of the evaporating vessel and reduce it to a coarse powder, and
from this powder I produce prussian blue and prussiate of potash in the
following manner :-To make prussian blue, for every one hundred pounds of
the coarse powder I take fourteen pounds of the soda of commerce, or
an equivalent quantity of other suitable alkali, and dissolve it in sixteen
gallons of water; this I bring to a heat of one hundred and fifty degrees
of Fahrenheit; I then pour it on the powder, and stir every quarter of an hour
for three hours; I then allow it to settle, draw off the clear liquor, throw the
sediment upon a filter, and pour over it six gallons of water at one hundred
and fifty degrees of Fahrenheit. I add the liquor that comes through the
filter to that which was poured off; I then put the whole into a pan, and bring

page_text: it to a boil. I now add to it a substance that will abstract a quantity of
sulphur which the soda has dissolved and holds in solution; for this purpose I
can use the black oxide of manganese or the yellow oxide of lead named
litharge, but I prefer using as cheaper the red oxide of iron obtained from the
decomposition of pyrites by heat; this I reduce to powder and wash thoroughly
to separate any sulphate of iron that might cling to it; for the quantity
of liquor to be operated upon as aforesaid I take a quantity of this oxide of
iron, equal to six pounds of it in a dry state, and put it into the boiling liquid,
stirring till it be thoroughly mixed, and then boil for ten minutes, and then
empty it into a settling vessel; when the liquor brightens it is drawn off, the
sediment thrown upon a filter, and any that may remain among it is washed
out with two or three gallons of water; to this clear solution I now add
eight pounds green copperas or sulphate of iron dissolved in water, which
throws down a dark green precipitate; on this I pour muriatic acid or spirit
of salt till it assumes a deep blue colour, it is then washed, filtered, and dried
in the same way as the prussian blue from the first class of colours.
To make prussiate of potash from my aforesaid coarse powder I proceed
as follows:-For every one hundred pounds of the coarse powder I take
eight pounds of the potash, or nine pounds and a half of the pearlash of
commerce, and dissolve it in twelve gallons of water, bring the solution
to a heat of two hundred degrees of Fahrenheit, and then pour it on the
coarse powder; I stir it frequently for two hours, and then add eight gallons
of water at a boiling heat, stir, and then allow it to settle. I draw off
the clear liquid, throw the sediment on a filter to drain, and then wash
it through with six gallons of water at two hundred degrees of Fahren-
heit;
the liquor passed through the filter I add to that drawn off. I put the
whole into a pan, and bring it to boil; I then add eight pounds of the afore-
said oxide of iron, and boil for ten minutes; it is then drawn to separate the
sediment, after which the bright liquor is returned into the evaporating pan,
and boiled down till a pellicle forms on its surface, when it is drawn into the
crystalizing vessels to crystalize.
I now come to describe my process with the refuse dry lime of those
gas works which use the dry lime mode of purification, being the aforesaid
refuse dry lime after it is taken out of the purifiers; this I find to contain
chiefly sulphuret of lime (or calcium), carbonate of lime and cyanide of lime (or
calcium), carbonate of lime, and cyanide of lime (or calcium), and the two
former not being soluble to any great extent, while the latter is converted into
hydro-cyanate and dissolved when it comes into contact with water. In

page_text: accordance with these statements I proceed in the following manner:-Having
put a quantity of the dry lime into a large wooden vat, I let in water heated-
to about one hundred and fifty degrees of Fahrenheit, till the lime is
thoroughly soaked, and the water stands about a foot above the mass,
and then it is beaten about till well broke; it is then allowed to remain
with occasional stirring for eight hours, when it is allowed to filtrate out by a
cock at the bottom of the vat; this liquor is set aside for using at once; more
water is then added to the mass, is allowed to filtrate through, and is then used:
for another quantity of dry lime..
To make prussian blue from the aforesaid liquor first run off, I proceed as
follows: I bring the liquor to boil; for every one hundred gallons I use-
twenty pounds of the dry oxide of iron, allow it to boil for ten minutes, and
withdraw it into a settling vessel; when settled the liquor is drawn off; to this
liquor I then add a solution of muriate of iron as long as any precipitate is
thrown down; muriatic acid or spirit of salt is then added until it assumes
a deep blue colour; it is washed, filtered, and dried in the same manner
as before specified.
To make prussiate of potash from the before-mentioned liquor, I dissolve a
quantity of the potash or pearl ash of commerce in as small a quantity of.
water as will dissolve it; I then add it to the liquor as long as a white precipi-
tate is thrown down; I then allow this precipitate to settle, and draw off the
clear liquor, bring it to boil, and for every pound of alkali used I take a
pound of the red oxide of iron, boil it ten minutes, then withdraw it to
separate the oxide; I then return the liquor into the evaporating pan, and boil
down till a pellicle forms on its surface, when it is run into the crystalizing
vessels to crystalize.
Having thus described the nature of my Invention, and the manner of
carrying the same into effect, I would remark that I lay no claim to the pro-
ducing sulphuric acid from the sulphuretted hydrogen evolved in what I have
called the saturating process, and I have only mentioned it for the purpose of
pointing out the most advantageous mode of carrying on the other processes;
nor do I claim the production of prussiate of potash from prussian blue
generally; and I am aware that prussian blue admixed with sulphate of lime
has been proposed to be obtained from lime liquor; I do not therefore claim
the manufacture of a product so combined, or in a state of admixture, the one
with the other; but what I do claim as my Invention is,-
First, the production of the three separate products, prussian blue,
prussiate of potash, and plaster of Paris, or either of them, uncombined with

page_text: other matter, from what I have called weak liquors, being the refuse lime
liquors of the gas works, as above described.
Secondly, the producing the two separate products, prussian blue and
prussiate of potash, or either of them, uncombined with other matter, from
what I have called strong liquors, being the refuse lime liquors of gas works,
as above described.
And thirdly, I claim the production of prussian blue and prussiate of potash,
or either of them uncombined with other matter, from the refuse lime after it
has been employed for the dry lime process of gas works, as above described.
In witness whereof, I, the said Peter Spence, have hereunto set my
hand and seal the Twenty-first day of January, in the year of our Lord
One thousand eight hundred and thirty-seven.