Year: 1883

page_text: We EDMUND PEEL POTTER and WILLIAM HENRY HIGOIN both of Hall Chemical
Works Little Lever near Bolton in the County of Lancaster seek leave to amend
the specification of Letters Patent, No. 3229 of 1883, as shown in red ink in the
copy of the original specification hereunto annexed, namely by transposing the
words "adding the requisite amount of acid" from line 2 of page 6 between tho
words "Salts" and "filtering" to line 1 of the same page 6 between the words
"latter" and "concontrating."
Our reasons for making this amendment are as follows That the words proposed
to be transposed were inserted in their present position by a clerical error and do
not agree so well with the detailed description of the process given in the
preceding part of the specification as they will when transposed in the specification
amended in the manner proposed.

page_text: LETTERS PATENT to Edmund Peel Potter and William Henry Higgin both of
Bolton in the county of Lancaster for an Invention of "IMPROVEMENTS
IN THE MANUFACTURE OF CHROMATES OF SODA AND IN
THERETO
"
RELATION
PROVISIONAL SPECIFICATION left by the said Edmund Peol Potter and
William Henry Higgin at the Office of the Commissioners of Patents on the
29th June 1883.
EDMUND PEEL POTTER and WILLIAM HENRY HIGGIN both of Bolton in the
county of Lancaster "IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES OF
SODA AND IN RELATION THERETO
"
This invention relates to improvements on our patented.invention No 587 of
this year; the following is a description of the process as thus improved :—Sodium
being a very much cheaper base and having a lower combining equivalent than
Potassium, we reasoned that Sodium bichromate would be a cheaper and better
oxydizing agent than Potassium bichromate, but on wishing to try the experiment
we were unable to procure the compound anywhere, or find any published method
of isolating it. The ordinary process of manufacturing bichromate of. Potash.
utterly failed when applied to the production of its sister compound the Sodic Salt,
at least in producing it in an isolated condition.
We have however .succeeded in isolating. it so as to obtain it in a
commercially useful form by the following process, and have found it, when
used pure, a much more powerful oxydizer than the Potassium Salt.
We furnace Chrome ore with lime or carbonate of lime and a suitable Sodium
Salt, but preferably the Sulphate, using in some cases a certain proportion of the
recovered Sodium Sulphate.
The furnacing is done in substantially the same manner as in the Potassium
bichromate manufacture whero lime and Sulphate of Potash are used; it is
therefore needless to describo it further as that process is well known.
The resulting material is lixiviated with water in the ordinary manner, and the
liquor obtained is treated with hydrochloric or other acid and in such quantity as
to exactly neutralize it; we have found that other acids may be used, but
hydrochloric is much preferred to sulphuric or any other.
On neutralization the Silica and alumina are entirely precipitated and we
carefully remove the same by settling and filtration..
We now proceed to concentrate the neutralized and purified liquor in underfired
pans of suitable construction and find as the boiling solution foses its water, the
chloride and residual Sulphate of Soda contained therein are thrown out in the
crystalline form, but that the Chromates of Soda remain in solution. The crystals
are removed by mechanical means either by ordinary hand fishing, or by other
means and after draining are washed with neutralized vat liquor before concen-
tration. This liquor containing a considerable quantity of these salts already, fails
to dissolve them but being far from saturated with Chromates takes up nearly all
the latter.
The washings resulting are then concentrated as above, and practically little or
no neutralised liquor will go straight to the pans, but will all previously be used
to wash Salts as above,

page_text: It will thus be scen that the action is an accumulative one by which gradually
all the Chromates are left in solution in the pan and all the other Salts are obtained
in a washed state nearly free from Chromatos, when Sulphuric acid has been used
to neutralize the vat liquor.
These washed fished Salts containing a trace of Chromates, are then used again
after drying in place of an equivalent quantity of fresh Salt-cake as above
mentioned, but when, as we prefer, Hydrochloric acid is used to neutralize the vat
liquor, then the washed fished Salts which consist in this case mainly of Sodium
Chloride with traces of Chromates, are converted into Sulphates by the ordinary
Salt-Cake process, and then used again in place of an equivalent quantity of fresh
Salt Cake as above, thus recovering and utilizing the last remaining Chromium
compounds. The strong solution remaining in the pan is filtered or otherwiso
freed from the last Crystals of Chloride and Sulphate of Soda floating in it, and
is then boiled down to dryness and the Salt perfectly dried but not fused in a
top-fired mechanical pan or by other means, care being takon to keep the
temperature low, and an excess of oxygen always in the gases in contact with
bichrome Salts.
The bichromate of Soda obtained by the process. as above fully described
contains monochromate, but as the reactions of the Salt are identical, this is of no
importance. In cases however where a pure specimen of bichromate is wanted for
a special purpose, the neutralised and purified vat liquor obtained as above is after
removal of Alumina and Silica, treated with a further quantity of acid (preferably
hydrochloric), in exactly the quantity required to convert the whole of the
Monochromate Salt into bichromate as calculated from analysis of the vat liquor
before treatment with acid, and the process is then conducted as above, but in
this case the pans used would have to be of special material to avoid contami-
nating the acid liquor, for which purpose lead would probably be the most
available.
In practice however we find the manufacture of the pure Salt not so advan-
tageous as an impure article composed of about two thirds bichromate and one
third monochromate, with a very small but variable quantity of neutral Salts of
Soda, as at this point it has a neutral reaction and the same amount of oxidizing
power as the Potassium Salt, and can consequently be substituted for it in whole
or in part in equal quantities, weight for weight, a practical advantage. Whether
pure or impure as above described the action is the same only the quantity required
differing.
Finally we believe that the reason why no one has hitherto succeeded in
obtaining commercially useful Bichromate of Soda are thesc,-First, Sulphuric
acid has been experimented with instead of hydrochloric acid; now the Sulphate
of Soda formed unites with a great quantity of water on Crystallizing in the cold,
and hitherto the separation as far as wo know has been attempted in the cold, and
hence the crystals of Sulphate of Soda enclosed and carried with them a very
large proportion of the bichromate present in the Solution, on the other hand
hydrochloric acid forms Common Salt, which separates in the anhydrous condition
and we find practically carries with it a much less considerable fraction of the
Chromic Salts present, and moreover is much more easily washed, pressed, et cetera,
owing to the form of the crystals which are square and hard whilst, the sulphate
forms a softer closer mass much more difficult to deal with. Secondly, The whole
separation was attempted at one crystallization the crystals not being fished out as
formed and the "accumulating principle" was not applied. Thirdly, the Crystals
obtained were useless for ordinary purposes and it does not appear to havo
occurred to the experimenters to use them after drying in the furnace in lieu of
fresh sulphate, this would however be impracticable in this case owing to the
extreme richness the mixing would arrive at when as is well known decomposition
is apt to take place at the elovated temperatures of the furnace.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed ·
by the. said Edmund Peel Potter and William Henry Higgin in the Great
Seal Patent Office on the 27th December 1883.
EDMUND PEEL POTTER and WILLIAM HENRY HIGGIN both of Bolton in the
county of Lancaster "IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES OF
SODA AND IN RELATION THERETO."
Sodium being a very much cheaper base and having a lower combining
equivalent than potassium we reasoned that sodium bichromate would be a
cheaper and better oxydizing agent than potassium bichromate, but on wishing
to try the experiment we were unable to procure the compound anywhere or find
any published method of isolating it. The ordinary process of manufacturing
bichromate of potash utterly failed when applied to production of its sister
compound the sodic salt at least in producing it in an isolated condition.
We have however succeeded in isolating it so as to obtain it in a commercially
useful form by the following process and have found it, when used pure, a much
more powerful oxidiser than the potassium salt.
.
We furnace chrome oro with lime or carbonate of lime, and a suitable sodium.
salt, but preferably the sulphate, using in some cases a certain proportion of the
recovered sodium sulphate.
The furnacing is done in substantially the same manner as in the potassium,
bichromate manufacture where lime and sulphate of potash are used; it is
therefore needless to describe it further as that process is well known.
The resulting material is lixiviated with water in the ordinary manner, and the
liquor obtained is treated with hydrochloric or other acid in such quantity as to
exactly neutralize it; we have found that other acids may be used but hydrochloric,
is much preferred to sulphuric or any other.
On neutralization the silica and alumina are entirely precipitated and wo
carefully remove the same by settling and filtration.
We now proceed to concentrate the neutralized. and purified liquor in under
fired pans of suitable construction and find that as the boiling solution loses its,
water the chloride and residual sulphate of soda contained therein aro thrown out
in the crystalline form but that the chromates of soda remain in solution. The
crystals are removed by mechanical means either by ordinary hand fishing or by:
other means, and after draining are washed with neutralised vat liquor before
concentration. This liquor containing a considerable quantity of these salts
already, fails to dissolve them but being far from saturated with chromates takes
up nearly all the latter.
The washings resulting are then concentrated as above, and practically little or
no neutralized liquor will go straight to the pan, but will all previously be used.
to wash salts as above. It will thus be seen that the action is an accumulating
one by which gradually all the chromates are left in solution in the pan and all
the other salts are obtained in a washed state nearly free from chromates.
When sulphuric acid has been used to neutralize the vat liquor these washed.
fished salts containing a trace of chromates are then used again after drying in
place of an equivalent quantity of fresh salt, cake,as above mentioned..
:

page_text: But when, as we prefer, hydrochloric acid is used to neutralize the vat liquor
then the washed fished salts, which consist in this case mainly of sodium chlorido
with traces of chromates, are converted into sulphates by the ordinary salt-cake
process and then used again in place of an equivalent quantity of fresh salt-cake
as above, thus recovering and utilizing the last remaining chromium compounds.
The strong solution remaining in the pan is filtered or otherwise freed from the
last crystals of chloride and sulphate of soda floating in it, and is then boiled down
to dryness and the salt perfectly dried but not fused in a top fired mechanical pan,
or by other means, care being taken to keep the temperature low and an excess of
oxygen always in the gases in contact with the bichrome salt. The bichromate of
soda obtained by the process as fully described above contains monochromate but
as the reactions of the salt are identical this is of no importance. In cases however
where a pure specimen of bichromate is wanted for a special purpose the neutralised
and purified vat liquor obtained as above is after removal of alumina and silica
treated with a further quantity of acid (preferably hydrochloric) in exactly the
quantity required to convert the whole of the monochromate salt into bichromate
as calculated from analysis of the vat liquor before treatment with acid, and the
process is then conducted as above, but in this case the pans used would have to be
of special material to avoid contaminating the acid liquor, for which purpose lead
would probably be the most available.
In practice however we find the manufacture of the pure salt not so advantageous
as an impure article composed of about two thirds of bichromate, and one third
monochromate, with a very small but variable quantity of neutral salt of soda as
at this point it has a neutral reaction and the same amount of oxidising power as
the potassium salt and can consequently be substituted for it in whole or in part
in equal quantities weight for weight, a practical advantage. Whether pure or
impure as above described the action is the same only the quantity required.
differing.
Finally we believe. that the reasons why no one has succeeded in obtaining
commercially useful bichromate of soda are these. First,-sulphuric acid has been
experimented with instead of hydrochloric acid, now the sulphate of soda formed
unites with a great quantity of water on crystallizing in the cold and hitherto the
Beparation as far as we know has been attempted in the cold and hence the crystals
of sulphate of soda enclosed and carried with them a very large proportion of the
bichromate present in the solution, on the other hand hydrochloric acid forms
common salt which separates in the anhydrous condition and we find practically
carries with it a much less considerable fraction of the chromic salts present, and
moreover is much more easily washed, pressed, et-cetera owing to the form of the
crystals which are square and hard, whilst the sulphate forms a softer closer ass
much more difficult to deal with; Secondly,-The whole separation was attempted at
one crystallization the crystals not being fished out as formed and the "accumulating
principle" was not applied.
Finally. The crystals obtained were useless for ordinary purposes and it does not
appear to have occurred to the experimenters to use then after drying in the furnace
in lieu of fresh sulphate, this would howover be impracticable in their case owing
to the extreme richness in chromates the mixing would arrive at when as is well
known decomposition is apt to take place at the elevated temperature of the
furnace.
Having now described our invention and the best mode known to us of carrying
it into effect we wish it to be understood that what we claim as new under the
Letters patent is the improved process for the manufacture of chromates of soda
substantially as herein described, and also the following parts of the invention taken
separately, each substantially as and for the purposes described.
1st. The adding of just sufficient acid to the crude monochromate solution to
neutralize it and thereby precipitate the silica and alumina present in the liquid.

page_text: 2nd. The manufacture of a neutral chromate of soda or combination or mixture
of mono-chromate and bichromate of soda, in such proportions that its aqueous
solution shall be neither alkaline nor acid to litmus paper.
3rd. The manufacture of pure or nearly pure bichromate of soda from mono-
chromate solution, by first neutralizing the latter to precipitate the silica and
alumina, separating the latter, adding the requisite amount of acid, concentrating
the solution with separation of foreign Salts, filtering out the crystals, and.
concentrating the solution at a low heat in an oxydizing atmosphere.
In witness whereof we the said Edmund Peel Potter and William Henry
Higgin have hereunto set our hands and seals this twenty sixth day of
December in the year of our Lord, one thousand eight hundred and eighty
three.

page_text: LETTERS PATENT to Edmund Peel Potter and William Henry Higgin both of
Bolton in the county of Lancaster for an Invention of "IMPROVEMENTS
IN THE MANUFACTURE OF CHROMATES
OF SODA AND IN
RELATION
THERETO
J
PROVISIONAL SPECIFICATION left by the said Edmund Peel Potter and
William Henry Higgin at the Office of the Commissioners of Patents on the
29th June 1883.
EDMUND PEEL POTTER and WILLIAM HENRY HIGGIN both of Bolton in the
"IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES OF
county of Lancaster
SODA AND IN RELATION THERETO
This invention relates to improvements on our patented invention N° 587 of
this year; the following is a description of the process as thus improved :-Sodium
being a very much cheaper base and having a lower combining equivalent than
Potassium, wo reasoned that Sodium bichromate would be a cheaper and better
oxydizing agent than Potassium bichromate, but on wishing to try the experiment
we were unable to procure the compound anywhere, or find any published method
of isolating it. The ordinary process of manufacturing bichromate of Potash
utterly failed when applied to the production of its sister compound the Sodic Salt,
at least in producing it in an isolated condition.
as to obtain it in a
We have however succeeded in isolating it so
commercially useful form by the following process, and have found it, when
used pure, a much more powerful oxydizer than the Potassium Salt.
We furnace Chrome ore with lime or carbonate of lime and a suitable Sodium
Salt, but preferably the Sulphate, using in some cases a certain proportion of the
recovered Sodium Sulphate.
The furnacing is done in substantially the same manner as in the Potassium
bichromate manufacture where lime and Sulphate of Potash are used; it is
therefore needless to describe it further as that process is well known.
The resulting material is lixiviated with water in the ordinary manner, and the

page_text: liquor obtained is treated with hydrochloric or other acid and in such quantity as
to exactly neutralize it; we have found that other acids may be used, but
hydrochloric is much preferred to sulphuric or any other.
"
On neutralization the Silica and alumina are entirely precipitated and we
carefully remove the same by settling and filtration.
We now proceed to concentrate the neutralized and purified liquor in underfired
pans of suitable construction and find as the boiling solution loses its water, the
chloride and residual Sulphate of Soda contained therein are thrown out in the
crystalline form, but that the Chromates of Soda remain in solution. The crystals
are removed by mechanical means either by ordinary hand fishing, or by other
means and after draining are washed with neutralized vat liquor before concen-
tration. This liquor containing a considerable quantity of these salts already, fails
to dissolve them but being far from saturated with Chromates takes up nearly all
the latter.
The washings resulting are then concentrated as above, and practically little or
no neutralised liquor will go straight to the pans, but will all previously be used
to wash Salts as above.
It will thus be seen that the action is an accumulative one by which gradually
all the Chromates are left in solution in the pan and all the other Salts are obtained
in a washed state nearly free from Chromates, when Sulphuric acid has been used
to neutralize the vat liquor.
These washed fished Salts containing a trace of Chromates, are then used again
after drying in place of an equivalent quantity of fresh Salt-cake as above
mentioned, but when, as we prefer, Hydrochloric acid is used to neutralize the vat
liquor, then the washed fished Salts which consist in this case mainly of Sodium
Chloride with traces of Chromates, are converted into Sulphates by the ordinary
Salt-Cake process, and then used again in place of an equivalent quantity of fresh
Salt Cake as above, thus recovering and utilizing the last remaining Chromium
compounds. The strong solution remaining in the pan is filtered or otherwise
freed from the last Crystals of Chloride and Sulphate of Soda floating in it, and
is then.boiled down to dryness and the Salt perfectly dried but not fused in a
top-fired mechanical pan or by other means, care being taken to keep the
temperature low, and an excess of oxygen always in the gases in contact with
bichrome Salts.
The bichromate of Soda obtained by the process as above fully described
contains monochromate, but as the reactions of the Salt are identical, this is of no
importance. In cases however where a pure specimen of bichromate is wanted for
a special purpose, the neutralised and purified vat liquor obtained as above is after
removal of Alumina and Silica, treated with a further quantity of acid (preferably
hydrochloric), in exactly the quantity required to convert the whole of the
Monochromate Salt into bichromate as calculated from analysis of the vat liquor
before treatment with acid, and the process is then conducted as above, but in
this case the pans used would have to be of special material to avoid contami-
nating the acid liquor, for which purpose lead would probably be the most
available.
In practice however wo find the manufacture of the pure Salt not so advan-
tageous as an impure article composed of about two thirds bichromate and one
third monochromate, with a very small but variable quantity of neutral Salts of
Soda, as at this point it has a neutral reaction and the same amount of oxidizing
power as the Potassium Salt, and can consequently be substituted for it in whole
or in part in equal quantities, weight for weight, a practical advantage. Whether
pure or impure as above described the action is the same only the quantity required
differing.
Finally we believe that the reason why no one has hitherto succeeded in
obtaining commercially useful Bichromate of Soda are these,-First, Sulphuric
acid has been experimented with instead of hydrochloric acid; now the Sulphato
of Soda formed unites with a great quantity of water on Crystallizing in the cold,

page_text: and hitherto the separation as far as we know has been attempted in the cold, and
hence the crystals of Sulphate of Soda enclosed and carried with them a very
large proportion of the bichromate present in the Solution, on the other hand
hydrochloric acid forms Common Salt, which separates in the anhydrous condition
and we find practically carries with it a much less considerable fraction of the
Chromic Salts present, and moreover is much more easily washed, pressed, et cetera,
owing to the form of the crystals which are square and hard whilst, the sulphate
forms a softer closer mass much more difficult to deal with. Secondly, The wholo
separation was attempted at one crystallization the crystals not being fished out as
formed and the "accumulating principle" was not applied. Thirdly, the Crystals
obtained were useless for ordinary purposes and it does not appear to have
occurred to the experimenters to use them after drying in the furnace in lieu of
fresh sulphate, this would however be impracticable in this case owing to the
extreme richness the mixing would arrive at when as is well known decomposition
is apt to take place at the elevated temperatures of the furnace.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Edmund Peel Potter and William Henry Higgin in the Great
Seal Patent Office on the 27th December 1883.
EDMUND PEEL POTTER and WILLIAM HENRY HIGGIN both of Bolton in the
county of Lancaster "IMPROVEMENTS IN THE MANUFACTURE OF CHROMATES OF
SODA AND IN RELATION THERETO.'
"
Sodium being a very much cheaper base and having a lower combining
equivalent than potassium we reasoned that sodium bichromato would be a
cheaper and better oxydizing agent than potassium bichromate, but on wishing
to try the experiment wo were unable to procure the compound anywhere or find
any published method of isolating it. The ordinary process of manufacturing
bichromate of potash utterly failed when applied to production of its sister
compound the sodic salt at least in producing it in an isolated condition.
We have however succeeded in isolating it so as to obtain it in a commercially
useful form by the following process and have found it, when used pure, a much
more powerful oxidiser than the potassium salt.
We furnace chrome ore with lime or carbonate of limo, and a suitable sodium
salt, but preferably the sulphate, using in some cases a certain proportion of the
recovered sodium sulphate.
The furnacing is done in substantially the same manner as in the potassium
bichromate manufacture where lime and sulphate of potash are used; it is
therefore needless to describe it further as that process is well known.
The resulting material is lixiviated with water in the ordinary manner, and the
liquor obtained is treated with hydrochloric or other acid in such quantity as to
exactly neutralize it; we havo found that other acids may be used but bydrochloric
is much preferred to sulphuric or any other.
On neutralization the silica and alumina are entirely precipitated and we
carefully remove the same by sottling and filtration.
We now proceed to concentrate the neutralized and purified liquor in under
fired pans of suitable construction and find that as the boiling solution loses its
water the chloride and residual sulphate of soda contained therein are thrown out
in the crystalline form but that the chromates of soda remain in solution. Tho
crystals are removed by mechanical means either by ordinary hand fishing or by
other means, and after draining are washed with neutralised yat liquor before
concentration. This liquor containing a considerable quantity of these salts
already, fails to dissolve them but being far from saturated with chromates takes
up nearly all the latter.
The washings resulting are then concentrated as above, and practically little or
no neutralized liquor will go straight to the pan, but will all previously be used
to wash salts as above. It will thus be seen that the action is an accumulating
one by which gradually all the chromates are left in solution in the pan and all
the other salts are obtained in a washed state carly free from chromates.
When sulphuric acid has been used to neutralize the vat liquor these washed
fished salts containing a trace of chromates are then used again after drying in
place of an equivalent quantity of fresh salt cake as above mentioned.
But when, as we prefer, hydrochloric acid is used to neutralize the vat liquor
then the washed fished salts, which consist in this case mainly of sodium chlorido
with traces of chromates, are converted into sulphates by the ordinary salt-cako
process and then used again in place of an equivalent quantity of fresh salt-cake

page_text: as above, thus recovering and utilizing the last remaining chromium compounds.
The strong solution remaining in the pan is filtered or otherwise freed from the
last crystals of chloride and sulphate of soda floating in it, and is then boiled down
to dryness and the salt perfectly dried but not fused in a top fired mechanical pan,
or by other means, care being taken to keep the temperature low and an excess of
oxygen always in the gases in contact with the bichrome salt. The bichromate of
soda.obtained by the process as fully described above contains monochromate but
as the reactions of the salt are identical this is of no importance. In cases however
where a pure specimen of bichromate is wanted for a special purpose the neutralised
and purified vat liquor obtained as above is after removal of alumina and silica
treated with a further quantity of acid (preferably hydrochloric) in exactly the
quantity required to convert the whole of the monochromate salt into bichromate
as calculated from analysis of the vat liquor before treatment with acid, and the
process is then conducted as above, but in this case the pans used would have to be
of special material to avoid contaminating the acid liquor, for which purpose lead
would probably be the most available.
In practice however we find the manufacture of the pure salt not so advantageous
as an impure article composed of about two thirds of bichromate, and one third
monochromate, with a very small but variable quantity of neutral salt of soda as
at this point it has a neutral reaction and the same amount of oxidising power as
the potassium salt and can consequently be substituted for it in whole or in part
in equal quantities weight for weight, a practical advantage. Whether pure or
impure as above described the action is the same only the quantity required
differing.
Finally wo believe that the reasons why no one has succeeded in obtaining
commercially useful bichromate of soda are these. First,-sulphuric acid has been
experimented with instead of hydrochloric acid, now the sulphate of soda formed
unites with a great quantity of water on crystallizing in the cold and hitherto the
separation as far as we know has been attempted in the cold and hence the crystals
of sulphate of soda enclosed and carried with them a very large proportion of the
bichromate present in the solution, on the other hand hydrochloric acid forms
common salt which separates in the anhydrous condition and we find practically
carries with it a much less considerable fraction of the chromic salts present, and
moreover is much more casily washed, pressed, et-cetera owing to the form of the
crystals which are square and hard, whilst the sulphate forms a softer closer mass
much more difficult to deal with; Secondly,-The whole separation was attempted at
one crystallization the crystals not being fished out as formed and the "accumulating
principle" was not applied.
Finally. The crystals obtained were useless for ordinary purposes and it does not
appear to have occurred to the experimenters to use them after drying in the furnace
in lieu of fresh sulphate, this would however be impracticable in their case owing
to the extreme richness in chromates the mixing would arrive at when as is well
known decomposition is apt to take place at the elevated temperature of the
furnace.
Having now described our invention and the best mode known to us of carrying
it into effect we wish it to be understood that what we claim as new under the
Letters patent is the improved process for the manufacture of chromates of soda
substantially as herein described, and also the following parts of the invention taken
separately, each substantially as and for the purposes described.
1st. The adding of just sufficient acid to the crude monochromate solution to
neutralize it and thereby precipitate the silica and alumina present in the liquid.
2nd. The manufacture of a neutral chromate of soda or combination or mixture
of mono-chromate and bichromate of soda, in such proportions that its aqueous
solution shall be neither alkaline nor acid to litmus paper.
3rd. The manufacture of pure or nearly pure bichromate of soda from mono-
chromate solution, by first neutralizing the latter to precipitate the silica and

page_text: alumina, separating the latter, concentrating the solution with separation of
foreign Salts, adding the requisite amount of acid, filtering out the crystals, and
concentrating the solution at a low heat in an oxydizing atmosphere.
In witness whercof we the said Edmund Peel Potter and William Henry
Higgin have hereunto set our hands and scals this twenty sixth day of December
in the year of our Lord, one thousand eight hundred and eighty three.
EDMUND. PEEL. POTTER.
(L.S.)