IMPROVEMENTS IN THE MANUFACTURE OF CUPELS IN THE METALS AND IN THE PRODUCTION OF OTHER REFRACTORY MATERIALS ass
Year: 1885

page_text: The Title of this Specification was, upon the 10th day of November 1886, amended
under Sections 18 to 21 of the Patents, Designs, and Trade Marks Act, 1883.
I FARNHAM MAXWELL-LYTE of Cotford, Putney, in the
Analytical Chemist do hereby declare the nature of the
"IMPROVEMENTS IN THE MANUFACTURE OF CUPELS IN THE
METALS AND IN THE PRODUCTION OF OTHER REFRACTORY
MATERIALS to be as follows:-
"
County of Surrey,
said invention for.
CUPELLATION OF
APPARATUS AND
My invention relates to the manufacture of cupels from magnesia or compounds
containing magnesia, preferably by any one of the methods set forth in the
specifications of my previous Patents Nos. 48895 and 663985.
I have found that magnesia and magnesian compounds possess, besides valuable
refractory qualities (as also those of improving the quality of steel and other metals
when fused in magnesia crucibles) a remarkable power of absorption for those
oxides of metals which fuse at high temperatures, the basic nature of the magnesia
moreover powerfully promoting such oxidation and thus rendering it specially
suitable for the cupellation of metals.
I find the most satisfactory results in the manufacture of these cupels are
arrived at by calcining magnesite or magnesia at a very high temperature, say that
of melting steel, and then grinding, while the powder thus obtained may with
advantage be recalcined at a temperature exceeding if anything the first calcination.
To the powder thus obtained add the wet hydroxide of magnesium, drained as
dry as possible without pressure, (say about 60% to 10%,) and I work up or pug
the whole to the consistence of moist sand, adding water if necessary, so that it
agglomerates when squeezed in the hand, or I make the same more plastic if
required for throwing. This is now ready for moulding or throwing, which may
be done by any of the usual methods.
The hydroxide above referred to may be made by adding to a boiling solution
of any salt of magnesia a boiling solution of some caustic alkali, such as caustic
soda for instance, in calculated and known proportions sufficient to precipitate the
hydroxide, and then the free soluble salt washed out.

page_text: Such cupels can be used for cupellation when simply dried, but I find it best to
burn them in, say, an ordinary crucible kiln or a muffle.
Although by preference I adopt this method of manufacture, I do not limit
myself thereto nor to any of the proportions of the ingredients. Any of the
compounds and methods of manufacture mentioned in my previous above named
Patents are applicable also to the manufacture of cupels: I also find it advan-
tageous to employ a small portion of finely powdered but less highly calcined
magnesia which I dilute with the hydroxide or other solution to be used. This
magnesia commercially known as "heavy" may be made either by moderately
calcining magnesite or magnesia, or it may be the ordinary heavy magnesia as
commercially sold and it may be ground up into a cream with the hydroxide or
other solution employed.
Cupels may also be made by mixing with the above 25 to 50° or any desired
quantity of bone ash or other powdered calcium phosphate and moulding with or
without pressure, preferably the former.
This mode of preparing magnesia for throwing or moulding extends to its
preparation for other refractory apparatus such as bricks, crucibles, &c described in
my above named previous Patents, No. 488985 and 663985.
Under certain conditions I have also found it to be not disadvantageous to add
in small quantities certain infusible oxides of the other metals.

page_text: I, FARNHAM MAXWELL-LYTE of Cotford, Oakhill Road, Putney in the County
of Surrey Analytical Chemist do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
My Invention relates to the manufacture of cupels for assaying, and tests for
refining precious metals; and to the preparation of materials suitable for the
manufacture thereof from magnesia and from bone-ash and from a mixture: of
the two.
I have found that magnesia and magnesian compounds [with the exception of
those magnesian earths such as dolomites and certain marls which contain limė
(other than phosphate of lime) in considerable quantities] possess a remarkable
power of absorbing certain fusible metallic oxides. Magnesia is, therefore, especially
suitable for the manufacture of cupels for assaying purposes, the cupelling power
being not so much dependent on the refractory nature as on the porous and
absorbent qualities of the magnesia, which promote the dissipation of the fusible
oxides.
"
:
In carrying out my Invention, I calcine at a high white heat magnesium oxidė
or carbonate, the latter as found in its natural form and known as magnesite "
answering very well. One calcination is generally insufficient to cause the desired
contraction, and it is therefore necessary to repeat the calcination at the same, or
preferably at a higher temperature after grinding and sifting the product of the
first calcination. The recalcined product should then be again ground and sifted!
By the second calcination a further and very marked contraction will be produced.
It is sometimes, however, necessary to submit the magnesia to more than two
successive calcinations before the desired degree of contraction is arrived at, but in-
general two calcinations appear to be sufficient When thus calcined the magnesia
is ready for use.
Some forms of magnesia, such as magnesite though nearly pure contain lime in
sufficient quantity to prove deleterious, the lime appearing amongst other things to
cause disintegration. When these forms of magnesia are used I find it advan
tageous to wash the calcined magnesia with a sufficiency of some acid (other than
sulphuric or phosphoric) such as dilute hydrochloric acid or a solution of magnesium
chloride or some magnesian salt to take up, or dissolve and wash away the-lime;
the magnesia being then again calcined if further contraction be required. Another
method which I bave found to answer though not so satisfactorily is to mix with
the water with which the magnesia is made up (as hereafter described) a sufficiency-

page_text: of phosphoric acid or acid phosphate of lime in order to convert the lime into
phosphate of lime. I also find that this conversion process may with advantage be
applied to bone ash which generally contains a certain proportion of lime other
than phosphate of lime.
In making the cupels and tests, I take the highly calcined and ground magnesia
and merely moisten it with water sufficient to cause it to agglomerate and "set"
after being moulded under pressure.
Or, in lieu of one quality of magnesia I may mix highly calcined and lightly
calcined magnesia (in the (proportions of say about-20 per cent of the latter to
80 per cent of the former) and moisten as before, the "setting" being thus
accelerated and increased and this "setting" may be promoted by the addition of
a little acid-such as hydrochloric acid-or some salt of magnesium (such as the
chloride) to the water with which the magnesia is made up Or, again, for this
purpose I may employ magnesium hydroxide of the heavy kind. "
Magnesia which has been burnt at a low heat (i.e. lightly calcined) having
merely disengaged its carbonic acid gas will set hard when mixed with water
alone, and this setting will take place though more slowly in the case of hard
burnt (i.e. highly calcined) and even trebly calcined magnesia; but articles made
in this manner with hard burnt and more than once calcined ground and sifted
magnesia are liable to crack both before and after being fired. This tendency to
crack though diminished by the addition of the ingredients mentioned above,
i.e: the magnesium hydroxide, the acids etc, is further prevented by keeping the
manufactured articles wet until sufficiently set before drying, a trough or "seggar'
of freshly made clay covered with a damp cloth, or a moist sand bath or wet saw-
dust carefully covered with damp sacking answering very well for this purpose.
The time during. which the article should be kept, in a damp condition depends
much upon the degree to which the calcination of the magnesia has been carried so
that no definite time can be given. 24 hours may, however, be taken as an average
period.
"
Cupels or tests made of magnesia according to this Invention may be fired, but
they answer very well when merely. dried that is used " "green".
When increased porosity is desirable, as in cupels for assaying purposes, it may
be obtained by the addition to the calcined magnesia of a suitable quantity of
finely powdered tan, wood pulp, sawdust, flour, starch, bran, or any suitable organic
matter. Bran has the advantage of assisting the plasticity if the starch globules
contained therein be burst by the addition of boiling water, but this object may
also be attained by the addition of flour, starch, glue, or even albumen. Cupels
will, however, be found. to be too friable after firing when thus rendered extra
porous but this difficulty may be overcome by the addition of a small portion (say
10 per cent) of clay or the compounds of some metallic oxides, such as Stourbridge
Clay, Ball Clay, or the other silicates of alumina. But I find as a rule that pure
magnesia is sufficiently porous for cupels used for assaying. As regards the larger
cupels or tests used for refining. purposes 'porosity per se being objectionable,
I would not use any organic matter but would render the body of the cupel or test
more dense and prevent liability of cracking by the addition of some of the
.metallic oxides above referred to.
. "
I find it generally advantageous to coat the bowl of the cupel or test interiorly
with a layer of bone ash, which compound of lime is not injurious; or with
magnesia of a finer grade than that of which the cupel is made; or with a mixture
of magnesia and bone ash. This may be done by sprinkling the face of the cupel with
the bone ash or the magnesia (or with the mixture of the two) previous to final
pressure or previous to setting or drying as the case may be, a superficial admixture
of the bone ash or finer magnesia with the body of the cupel being thus effected.
Bone-Ash may also be mixed with the magnesia in the body of the cupel, its
addition being often advantageous in modifying the contractile powers. I further
find that the cohesive property of cupels or tests whether made of magnesia or
bone ash, or of a mixture, of the two is increased by adding silica or silicates

page_text: (preferably in the form of an alkaline silicate) to the materials previous to
moulding in not too large a quantity-say in sufficient quantity to produce
agglomeration under pressure.
Having now particularly described and ascertained the nature of the said
Invention, and in what manner the same is to be performed; I would observe
that I do not here claim washing out the lime with hydrochloric acid, nor
converting it by phosphoric acid, nor the addition of silicates as last referred to,
these methods formning the subject of another application for Letters Patent but
that what I claim is;
1st. The manufacture of cupels and tests, and of materials suitable for the
manufacture of same, of a mixture of highly calcined and lightly calcined magnesia,
substantially as specified.
2nd. The manufacture of cupels and tests, and the preparation of materials
suitable for the manufacture of same, of a mixture of calcined magnesia and bone
ash substantially as specified.
3rd. In the manufacture of cupels and tests of calcined and ground magnesia,
the addition to the magnesia of an, acid, or of a salt of magnesia, or of magnesium-
hydroxide substantially as and for the purpose specified.
4th. In the preparation of materials for the manufacture of cupels and tests of
calcined and ground magnesia, the addition to the magnesia of metallic oxides
substantially as specified.
5th. A cupel or test of calcined and ground magnesia or of a mixture of magnesia
and bone ash having a superficial admixture or coating of bone ash or finer
magnesia or a mixture of the two, substantially as specified.
6th. The herein-described method of manufacturing cupels and tests from
magnesia or magnesia and bone ash, which method consists in calcining and
grinding the magnesia as berein described, moulding the magnesia or the mixture
of magnesia and bone ash to the required forn, and then maintaining the moulded
article in a moist state until the magnesia has set, substantially as specified.
7th. The hercin described method of preparing magnesia for the manufacture of
cupels and tests, which method consists in alternately calcining and disintegrating
the magnesia two or more times, substantially as specified.
8th. Lastly in the manufacture of cupels and tests of magnesia or bone-ash or of
a mixture of the two, I claim "firing" the cupels, and tests previous to use,
substantially as specified.

page_text: Improvements in the Manufacture of Cupels in the Cupellation
of Metals and in the Production of other Refractory Apparatus
and Materials.
I FARNHAM MAXWELL LYTE of Cotford, Putney, in the County of Surrey,
Analytical Chemist do hereby declare the nature of the said invention for
IMPROVEMENTS IN THE MANUFACTURE OF CUPELS IN THE CUPELLATION OF
METALS AND IN THE PRODUCTION OF OTHER REFRACTORY
MATERIALS to be as follows:-
"
APPARATUS AND
My invention relates to the manufacture of cupels from magnesia or compounds
containing magnesia, preferably by any one of the methods set forth in the
specifications of my previous Patents No 488955 and 663985.
I have found that magnesia and magnesian compounds possess, besides valuable
refractory qualities (as also those of improving the quality of steel and other metals
when fused in magnesia crucibles) a remarkable power of absorption for those
oxides of metals which fuse at high temperatures, the basic nature of the magnesia
moreover powerfully promoting such oxidation and thus rendering it specially
suitable for the cupellation of metals.
I find the most satisfactory results in the manufacture of these cupels are arrived
at by calcining magnesite or magnesia at a very high temperature, say that of
melting steel, and then grinding, while the powder thus obtained may with
advantage be recalcined at a temperature exceeding if anything the first calcination.
To the powder thus obtained I add the wet hydroxide of magnesium, drained as
dry as possible without pressure, (say about 60% to 10%,) and I work up or pug
the whole to the consistence of moist sand, adding water if necessary, so that it
agglomerates when squeezed in the hand, or I make the same more plastic if
required for throwing. This is now ready for moulding or throwing, which may
be done by any of the usual methods.
The hydroxide above referred to may be made by adding to a boiling solution
of any salt of magnesia a boiling solution of some caustic alkali, such as caustic
soda for instance, in calculated and known proportions sufficient to precipitate the
hydroxide, and then the free soluble salt washed out.
Such cupels can be used for cupellation when simply dried, but I find it best to
burn them in, say, an ordinary crucible kiln or a muffle.

page_text: do not limit
Although by preference I adopt this method of manufacture,
myself thereto nor to any of the proportions of the ingredients. Any of the
compounds and methods of manufacture mentioned in my previous above named
Patents are applicable also to the manufacture of cupels. I also find it advantageous
to employ a small portion of finely powdered but less highly calcined magnesia
which I dilute with the hydroxide or other solution to be used. This magnesia com-
mercially known as "heavy" may be made either by moderately calcining magnesite
or magnesia, or it may be the ordinary heavy magnesia as commercially sold and
it may be ground up into a cream with the hydroxide or other solution employed.
Cupels may also be made by mixing with the above 25 to 50% or any desired
quantity of bone ash or other powdered calcium phosphate and moulding with or
without pressure, preferably the former.
This mode of preparing magnesia for throwing or moulding extends to its
preparation for other refractory apparatus such as bricks, crucibles, &c described
in my above named previous Patents, No 48895 and 663985.
Under certain conditions I have also found it to be not disadvantageous to add
in small quantities certain infusible oxides of the other metals.

page_text: Improvements in the Manufacture of Cupels in the Cupellation
of Metals and in the Production of other Refractory. Apparatus
and Materials.
I, FARNHAM MAXWELL-LYTE of Cotford, Oakhill Road, Putney in the County
of Surrey Analytical Chemist do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement:-
My Invention relates to the manufacture of cupels for assaying, and tests for
refining precious metals; and to the preparation of materials suitable for the
manufacture thereof from magnesia and from bone-ash and from a mixture of
the two.
I have found that magnesia and magnesian compounds [with the exception of
those magnesian earths such as dolomites and certain marls which contain lime
(other than phosphate of lime) in considerable quantities] possess a remarkable
power of absorbing certain fusible metallic oxides. Magnesia is, therefore,
especially suitable for the manufacture of cupels for assaying purposes, the cupelling
power being not so much dependent on the refractory nature as on the porous and
absorbent qualities of the magnesia, which promote the dissipation of the fusible
oxides.
"
In carrying out my Invention, I calcine at a high white heat magnesium oxide
or carbonate, the latter as found in its natural form and known as magnesite
answering very well. One calcination is generally insufficient to cause the desired
contraction, and it is therefore necessary to repeat the calcination at the same, or
preferably at a higher temperature after grinding and sifting the product of the first
calcination. The recalcined product should then be again ground and sifted. By
the second calcination a further and very marked contraction will be produced. It
is sometimes, however, necessary to submit the magnesia to more than two successive
calcinations before the desired degree of contraction is arrived at, but in general
two calcinations appear to be sufficient When thus calcined the magnesia is ready
for use.
Some forms of magnesia, such as magnesite though nearly pure contain lime in
sufficient quantity to prove deleterious, the lime appearing amongst other things
to cause disintegration. When these forms of magnesia are used I find it
advantageous to wash the calcined magnesia with a sufficiency of some acid (other
than sulphuric or phosphoric) such as dilute bydrochloric acid or a solution of
magnesiu:n chloride or some magnesian salt to take up, or dissolve and wash away
the lime, the magnesia being then again calcined if further contraction be required:
Another method which I have found to answer though not so satisfactorily is to
mix with the water with which the magnesia is made up (as hereafter described)
a sufficiency of phosphoric acid or acid phosphate of lime in order to convert, the
lime into phosphate of lime. I also find that this conversion process may with
advantage be applied to bone ash which generally contains a certain proportion of
lime other than phosphate of lime.

page_text: In making the cupels and tests, I take the highly calcined and ground magnesia
and merely moisten it with water sufficient to cause it to agglomerate and "set"
after being moulded under pressure.
Or, in lieu of one quality of magnesia I may mix highly calcined and lightly
calcined magnesia (in the proportions of say about 20 per cent of the latter to
SO per cent of the former) and moisten as before, the "setting" being thus
accelerated and increased and this "setting" may be promoted by the addition of
a little acid-such as hydrochloric acid-or some salt of magnesium (such as the
chloride) to the water with which the magnesia is made up Or, again, for this
purpose I may employ magnesium hydroxide of the heavy kind.
Magnesia which has been burnt at a low heat (i.e. lightly calcined) having
merely disengaged its carbonic acid gas will set hard when mixed with water
alone, and this setting will take place though more slowly in the case of hard
burnt (ie highly calcined) and even trebly calcined magnesia; but articles made
in this manner with hard burnt and more than once calcined ground and sifted
magnesia are liable to crack both before and after being fired. This tendency
to crack though diminished by the addition of the ingredients mentioned above,
ie the magnesium hydroxide, the acids etc, is further prevented by keeping the
manufactured articles wet until sufficiently set before drying, a trough or
«< seggar
of freshly made clay covered with a damp cloth, or a moist sand bath or wet saw-
dust carefully covered with damp sacking answering very well for this purpose.
The time during which the article should be kept in a damp condition depends
much upon the degree to which the calcination of the magnesia has been carried
so that no definite time can be given. 24 hours may, however, be taken as an
average period.
"
Cupels or tests made of magnesia according to this Invention may be fired, but
they answer very well when merely dried that is used "green."
When increased porosity is desirable, as in cupels for assaying purposes, it may
be obtained by the addition to the calcined magnesia of a suitable quantity of finely
powdered. tan, wood pulp, sawdust, four, starch, bran, or any suitable organic
matter. Bran has the advantage of assisting the plasticity if the starch globules
contained therein be burst by the addition of boiling water, but this object may
also be attained by the addition-of flour, starch, glue, or even albumen. Cupels
will, however, be found to be too friable after firing when thus rendered extra
porous but this difficulty may be overcome by the addition of a small portion (say
10 per cent) of clay or the compounds of some metallic oxides, such as Stourbridge
Clay, Ball Clay, or the other silicates of alumina. But I find as a rule that pure
magnesia is sufficiently porous for cupels used for assaying. As regards the larger
cupels or tests used for refining purposes porosity per se being objectionable,
I would not use any organic matter but would render the body of the cupel or
test more dense and prevent liability of cracking by the addition of some of the
metallic oxides above referred to.
I find it generally advantageous to coat the bowl of the cupel or test interiorly
with a layer of bone ash, which compound of lime is not injurious; or with
magnesia of a finer grade than that of which the cupel is made; or with a mixture
of magnesia and bone ash. This may be done by sprinkling the face of the cupel
with the bone ash or the magnesia (or with the mixture of the two) previous to
final pressure or previous to setting or drying as the case may be, a superficial
admixture of the bone ash or fiuer magnesia with the body of the cupel being thus
effected. Bone-ash may also be mixed with the magnesia in the body of the.
cupel, its addition being often advantageous in modifying the contractile powers.
I further find that the cohesive property of cupels or tests whether made of
magnesia or bone ash, or of a mixture of the two is increased by adding silica or
silicates (preferably in the form of an alkaline silicate) to the materials previous
to moulding in not too large a quantity-say in sufficient quantity to produce
agglomeration under pressure,

page_text: Having now particularly described and ascertained the nature of the said
Invention, and in what manner the same is to be performed; I would observe
that I do not here claim washing out the lime with bydrochloric acid, nor
converting it by phosphoric acid, nor the addition of silicates as last referred to,
these methods forming the subject of another application for Letters Patent but
that what I claim is ;-
1st The manufacture of cupels and tests, and of materials suitable for the
manufacture of same, of a mixture of highly calcined and lightly calcined magnesia,
substantially as specified.
2nd The manufacture of cupels and tests, and the preparation of materials
suitable for the manufacture of same, of a mixture-of calcined magnesia and bone
ash substantially as specified.
3rd In the manufacture of cupels and tests of calcined and ground magnesia, the
addition to the magnesia of an acid, or of a salt of magnesia, or of magnesium-
hydroxide substantially as and for the purpose specified.
4th In the preparation of materials for the manufacture of cupels and tests of
calcined and ground magnesia, the addition to the magnesia of metallic oxides,
substantially as specified.
5th A cupel or test of calcined and ground magnesia or of a mixture of magnesia
and bone ash having a superficial admixture or coating of bone ash or finer magnesia
or a mixture of the two, substantially as specified.
6th The herein-described method of manufacturing cupels and tests from magnesia
or magnesia and bone ash, which method consists in calcining and grinding the
magnesia as herein described, moulding the magnesia or the mixture of magnesia
and bone ash to the required form, and then maintaining the moulded article in a
moist state until the magnesia has set, substantially as specified.
7th The herein described method of preparing magnesia for the manufacture of
cupels and tests, which method consists in alternately calcining and disintegrating
the magnesia two or more times, substantially as specified.
8th Lastly in the manufacture of cupels and tests of magnesia or bone-ash or
of a mixture of the two, I claim "firing" the cupels and tests previous to use,
substantially as specified.

page_text: The Title of this Specification was, upon the 10th day of November 1886, amended
under Sections 18 to 21 of the Patents, Designs, and Trade Marks Act, 1883.
I FARNHAM MAXWELL-LYTE of Cotford, Putney, in the County of Surrey,
Analytical Chemist do hereby declare the nature of the said invention for
"IMPROVEMENTS IN THE MANUFACTURE OF CUPELS IN THE CUPELLATION OF
METALS AND IN THE PRODUCTION OF OTHER REFRACTORY APPARATUS AND
MATERIALS" to be as follows:
=
My invention relates to the manufacture of cupels from magnesia or compounds
containing magnesia, preferably by any one of the methods set forth in the
specifications of my previous Patents Nos. 488935 and 663985.
I have found that magnesia and magnesian compounds possess, besides valuable
refractory qualities (as also those of improving the quality of steel and other metals
when fused in magnesia crucibles) a remarkable power of absorption for those
oxides of metals which fuse at high temperatures, the basic nature of the magnesia
moreover powerfully promoting such oxidation and thus rendering it specially
suitable for the cupellation of metals.
I find the most satisfactory results in the manufacture of these cupels are
arrived at by calcining magnesite or magnesia at a very high temperature, say that
of melting steel, and then grinding, while the powder thus obtained may with
advantage be recalcined at a temperature exceeding if anything the first calcination.
To the powder thus obtained I add the wet hydroxide of magnesium, drained as
dry as possible without pressure, (say about 6° to 10%,) and I work up or pug
the whole to the consistence of moist sand, adding water if necessary, so that it
agglomerates when squeezed in the hand, or I make the same more plastic if
required for throwing. This is now ready for moulding or throwing, which may
be done by any of the usual methods.
.
The hydroxide above referred to may be made by adding to a boiling solution
of any salt of magnesia a boiling solution of some caustic alkali, such as caustic
soda for instance, in calculated and known proportions sufficient to precipitate the
hydroxide, and then the free soluble salt washed out.

page_text: Such cupels can be used for cupellation when simply dried, but I find it best to
burn them in, say, an ordinary crucible kiln or a muffle.
Although by preference I adopt this method of manufacture, I do not limit
myself thereto nor to any of the proportions of the ingredients. Any of the
compounds and methods of manufacture mentioned in my previous above named
Patents are applicable also to the manufacture of cupels. I also find it advan-
tageous to employ a small portion of finely powdered but less highly ealcined
magnesia which I dilute with the hydroxide or other solution to be used. This
magnesia commercially known as heavy" may be made either by moderately
calcining magnesite or magnesia, or it may be the ordinary. heavy magnesia as
commercially sold and it may be ground up into a cream with the hydroxide or
other solution employed.
"
°
Cupels may also be made by mixing with the above 25 to 50% or any desired
quantity of bone ash or other powdered calcium phosphate and moulding with or
without pressure, preferably the former.
This mode of preparing magnesia for throwing or moulding extends to its
preparation. for other. refractory apparatus such as bricks, crucibles, &c described in
my above named previous Patents, No. 488985 and 663985.
Under certain conditions I have also found it to be not disadvantageous to add
in small quantities certain infusible oxides of the other metals.

page_text: I, FARNHAM MAXWELL-LYTE of Cotford, Oakhill Road, Putney in the County
of Surrey Analytical Chemist do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
My Invention rolates to the manufacture of cupels for assaying, and tests for
refining precious metals; and to the preparation of materials suitable for the
manufacture thereof from magnesia and from bone-ash and from a mixture of
the two.
:
I have found that magnesia and magnesian compounds [with the exception of
those magnesian earths such as dolomites and certain marls which contain lime
(other than phosphate of lime) in considerable quantities] possess a remarkable
power of absorbing certain fusible metallic oxides. Magnesia is, therefore, especially
suitable for the inanufacture of cupels for assaying purposes, the cupelling power
being not so much dependent on the refractory nature as on the porous and
absorbent qualities of the magnesia, which promote the dissipation of the fusible
oxides.
In carrying out my Invention, I calcine at a high white heat magnesium oxide
or carbonate, the latter as found in its natural form and known as." magnesite
answering very well. One calcination is generally insufficient to cause the desired
contraction, and it is therefore necessary to repeat the calcination at the same, or
preferably at a higher temperature after grinding and sifting the product of the
first calcination. The recalcined product should then be again ground and sifted:
By the second calcination a further and very marked contraction will be produced.
It is sometimes, bowever, necessary to submit the magnesia to more than two
successive calcinations before the desired degree of contraction is arrived at; but in
general two calcinations appear to be sufficient When thus calcined the magnesia
is ready for use.
Some forms of magnesia, such as magnesite though nearly pure contain lime in
sufficient quantity to prove deleterious, the lime appearing amongst other things to
cause disintegration. When these forms of magnesia are used I-find it advan
tageous to wash the calcined magnesia with a sufficiency of some acid, (other than
sulphuric or phosphoric) such as dilute hydrochloric acid or a solution of magnesiumn
chloride.or some magnesian,salt to take up, or dissolve and wash away.the lime,
the magnesia being then-again calcined if further contraction be required. Another
method which I have found to answer though not so satisfactorily is to mix with
the water with which the magnesia is made up (as hereafter described) a sufficiency.

page_text: of phosphoric acid or acid phosphate of lime in order to convert the lime into
phosphate of lime. I also find that this conversion process may with advantage be
applied to bone ash which generally contains a certain proportion of lime other
than phosphate of lime.
"
In making the cupels and tests, I take the highly calcined and ground magnesia
and merely moisten it with water sufficient to cause it to agglomerate and "
after being moulded under pressure.
set
Or, in lieu of one quality of magnesia I may mix highly calcined and lightly
calcined magnesia (in the proportions of say about 20 per cent of the latter to
80 per cent of the former) and moisten as before, the "setting" being thus
accelerated and increased and this "setting" may be promoted by the addition of
a little acid-such as hydrochloric acid-or some salt of magnesium (such as the
chloride) to the water with which the magnesia is made up Or, again, for this
purpose may employ magnesium hydroxide of the heavy kind.
Magnesia which has been burnt at a low heat (i.e. lightly calcined) having
merely disengaged its carbonic acid gas will set hard when mixed with water
alone, and this setting will take place though more slowly in the case of hard
burnt (i.e. highly calcined) and even trebly calcined magnesia; but articles made
in this manner with hard burnt and more than once calcined ground and sifted
magnesia are liable to crack both before and after being fired. This tendency to
crack though diminished by the addition of the ingredients mentioned above,
i.e. the magnesium hydroxide, the acids etc, is further prevented by keeping the
manufactured articles wet until sufficiently set before drying, a trough or "seggar
of freshly made clay covered with a damp cloth, or a moist sand bath or wet saw-
dust carefully covered with damp sacking answering very well for this purpose.
The time during which the article should be kept in a damp condition depends
much upon the degree to which the calcination of the magnesia has been carried so
that no definite time can be given. 24 hours may, however, be taken as an average
period.
و"
Cupėls or tests made of magnesia according to this Invention may be fired, but
they answer very well when merely dried that is used "green."
.
When increased porosity is desirable, as in cupels for assaying purposes, it may
be obtained by the addition to the calcined magnesia of a suitable quantity of
finely powdered tan,. wood pulp, sawdust, flour, starch, bran, or any suitable organic
matter. Bran has the advantage of assisting the plasticity if the starch globules
contained-therein be burst by the addition of boiling water, but this object may
also be attained by the addition of flour; starch, glue, or even albumen. Cupels
will, however, be found to be too friable after firing when thus rendered extra
porous but this difficulty may be overcome by the addition of a small portion (say
10 per cent) of clay or the compounds of some metallic oxides, such as Stourbridge
Clay, Ball Clay, or the other silicates of alumina. But I find as a rule that pure
magnesia is sufficiently porous for cupels used for assaying. As regards the larger
cupels or tests used for refining purposes porosity per se being objectionable,
I would not use any organic matter but would render the body of the cupel or test
more dense and prevent liability of cracking by the addition of some of the
metallic oxides above referred to.
"
I find it generally advantageous to coat the bowl of the cupel or test interiorly
with a layer of bone ash, which compound of lime is not injurious;
or with
magnesia of a finer grade than that of which the cupel is made; or with a mixture
of magnesia and bone ash. This may be done by sprinkling the face of the cupel with
the bone ash or the magnesia (or with the mixture of the two) previous to final
pressure or previous to setting or drying as the case may be, a superficial admixture
of the bone ash or finer magnesia with the body of the cupel being thus effected.
Bone-Ash may also be mixed with the magnesia in the body of the cupel, its
addition being often advantageous in modifying the contractile powers. I further
find that the cohesive property of cupels or tests whether made of magnesia or
bone ash, or of a mixture of the two is increased by adding silica or silicates

page_text: (preferably in the form of an alkaline silicate) to the materials previous to
moulding in not too large a quantity-say in sufficient quantity to produce
agglomeration under pressure.
Having now particularly described and ascertained the nature of the said
Invention, and in what manner the same is to be performed; I would observe
that I do not here claim washing out the lime with hydrochloric acid, nor
converting it by phosphoric acid, nor the addition of silicates as last referred to,
these methods forming the subject of another application for Letters Patent but
that what I claim is;
1st. The manufacture of cupels and tests, and of materials suitable for the
manufacture of same, of a mixture of highly calcined and lightly calcined magnesia,
substantially as specified.
2nd. The manufacture of cupels and tests, and the preparation of materials
suitable for the manufacture of same, of a mixture of calcined magnesia and bone
ash substantially as specified.
3rd. In the manufacture of cupels and tests of calcined and ground magnesia,
the addition to the magnesia of an acid, or of a salt of magnesia, or of magnesium-
hydroxide substantially as and for the purpose specified.
4th. In the preparation of materials for the manufacture of cupels and tests of
calcined and ground magnesia, the addition to the magnesia of metallic oxides
substantially as specified.
5th. A cupel or test of calcined and ground magnesia or of a mixture of magnesia
and bone ash having a superficial admixture or coating of bone ash or finer
magnesia or a mixture of the two, substantially as specified.
6th. The herein-described method of manufacturing cupels and tests from
magnesia or magnesia and bone ash, which method consists in calcining and
grinding the magnesia as herein described, moulding the magnesia or the mixture
of magnesia and bone ash to the required form, and then maintaining the moulded
article in a moist state until the magnesia has set, substantially as specified.
7th. The herein described method of preparing magnesia for the manufacture of
cupels and tests, which method consists in alternately calcining and disintegrating
the magnesia two or more times, substantially as specified.
8th. Lastly in the manufacture of cupels and tests of magnesia or bone-ash or of
a mixture of the two, I claim "firing" the cupels, and tests previous to use,
substantially as specified.