IMPROVEMENTS IN THE MANUFACTURE OF PLUMBAGO CRUCIBLES AND OTHER VESSELS IN PLUMBAGO, SUITABLE FOR CHEMICAL AND METALLURGICAL PURPOSES
Year: 1878

page_text: LETTERS PATENT to Samuel Arthur Peto, of South Kensington, in the County
of Middlesex, Gentleman, for the Invention of "IMPROVEMENTS IN THE
MANUFACTURE OF PLUMBAGO CRUCIBLES AND OTHER VESSELS IN PLUMBAGO,
SUITABLE FOR CHEMICAL AND METALLURGICAL PURPOSES."
Sealed the 13th December 1878, and dated the 9th October 1878.
PROVISIONAL SPECIFICATION left by the said Samuel Arthur Peto at
the Office of the Commissioners of Patents on the 9th October 1878.
"
SAMUEL ARTHUR PETO, of South Kensington, in the County of Middlesex,
Gentleman. IMPROVEMENTS IN THE MANUFACTURE OF PLUMBAGO CRUCIBLES,
AND OTHER VESSELS IN PLUMBAGO, SUITABLE FOR CHEMICAL AND METALLURGICAL
PURPOSES."
Plumbago crucibles, as hitherto manufactured, require to be annealed or "got
up" before they can be used, in consequence of the porous nature of the material
of which they are composed, which allows them to absorb a quantity of moisture
from the atmosphere, which, if not expelled by the annealing process, causes them
to "fly," "blow," "bump," or burst when first put in the furnace, thereby causing
the loss of the crucible and, in some cases, of the metal. Further, if the annealing
process be not skilfully and carefully performed, the 'crucible is liable to injury
during the annealing process.
Now the object of my Invention is to dispense with the ordinary annealing
process and to improve the crucible by affording protection to the plumbago and
preventing the crucible from absorbing moisture.
My improvements consist in coating or covering plumbago crucibles, when
manufactured in the ordinary manner, but preferably before they are baked, with
a compound such as is herein-after described. The crucible covered with the
compound is then burned, and at the proper temperature is "salted," and there-
upon the said compound will form with the salt a glaze over the crucible impervious

page_text: to moisture and which will allow of the crucible being placed in a white fire
without previously being annealed in the ordinary way.
The compound I find it advantageous to employ in order to form the glaze or
impervious coating is the following, videlicet About twelve parts by weight of
ball clay, two parts of Cornish stone, four parts of burnt clay, one and a half parts
of red clay ground and mixed with water so as to form a creamy paste, one half
part of manganese or its equivalent being added.
The above proportions may be varied without materially affecting the required
result; in all cases, however, the proportions must be so arranged that the shrink-
age of the covering shall correspond with the shrinkage of the crucible.
I sometimes dispense with the salt, in which case the compound must be so com-
posed that it will vitrify in the kiln; or in lieu of the salt I use a suitable glaze of
materials similar to those used by potters.
In some cases it may be desirable, for the sake of economy, to omit the pre-
liminary coating of the crucible and cover it, either before or after biscuiting, with
any suitable glaze or impervious coating, but I do not recommend this method.
My improvements are applicable to the manufacture of other plumbago vessels
than crucibles, such as vessels for the manufacture and treatment of acids, for which
glazed plumbago would be suitable, from its power of resisting great variations of
temperature.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Samuel Arthur Peto in the Great Seal Patent Office on the 8th April
1879.
"
SAMUEL ARTHUR PETO, of South Kensington, in the County of Middlesex,
Gentleman. IMPROVEMENTS IN THE MANUFACTURE OF PLUMBAGO CRUCIBLES
AND OTHER VESSELS IN PLUMBAGO, SUITABLE FOR CHEMICAL AND METALLURGICAL
PURPOSES."
Plumbago crucibles, as hitherto manufactured, require to be annealed or "got
up" before they can be used, in consequence of the porous nature of the material
of which they are composed, which allows them to absorb a quantity of moisture
from the atmosphere, which, if not expelled by the annealing process, causes them
to "fly," "blow," "bump," or burst when first put in the furnace, thereby causing
the loss of the crucible and, in some cases, of the metal. Further, if the annealing
process be not skillfully and carefully performed, the crucible is liable to injury
during the annealing process.
Now the object of my Invention is to dispense with the ordinary annealing
process and to improve the crucible by affording protection to the plumbago, and
preventing the crucible from absorbing moisture.
4
My improvements consist in coating or covering plumbago crucibles when they
have been manufactured, which may be in the ordinary manner, with a suitable
compound, such as is herein-after described; the compound may, with advantage,
be applied before the crucibles are baked, although, in some cases, it can be applied
after the baking operation, in which case a second burning or baking will be
necessary. The crucible, when it has been coated or covered with the compound,
is burned and at the proper temperature is "salted," and thereupon the compound
employed will form with the salt a glaze over the crucible, impervious to moisture
and which will allow of the crucible being placed in a white hot fire without
previously being annealed in the ordinary way.
The compounds which I have found it specially advantageous to employ in order
to form the slip or coating are the following, videlicet :-About twelve parts by weight
of ball clay, two parts of Cornish stone, four parts of burnt clay, one and a half
parts of red clay ground and mixed with water so as to form a creamy paste, one
half part of manganese or its equivalent being added. Or about twelve parts of
French clay, two and a half parts of Cornish stone, one half part of manganese, one
quart of slip composed of three hundred parts of china clay, two hundred and fifty
parts of ball clay, and one hundred parts of flint. Other analogous compounds,
which, when heated, will take or combine with the salt so as to form a glaze or
coating impervious to moisture may be employed. It follows therefore that some
of the above proportions and constituents may be varied without materially affecting
the required result; in all cases, however, the proportions must be so arranged that
the shrinkage of the covering shall correspond with the shrinkage of the crucible.
I sometimes dispense with the salt, in which case the compound must be so
composed that it will vitrify in the kiln; or, in lieu of the salt, I use a suitable
glaze of materials similar to those used by potters.
In some cases it may be found convenient or economical to omit the preliminary
coating of the crucible and cover it, either before or after biscuiting, with any
suitable glaze or impervious coating, but I do not recommend this method as it may
sometimes be found to fail in practice.
My improvements are applicable to the manufacture of other plumbago vessels
than crucibles, such as vessels made of plumbago and used for the manufacture and
treatment of acids, alkalies, and other chemical compounds for which glazed plum-
bago would be suitable from its power of resisting great variations of temperature.
The glaze, in this case, would of course be such as is ordinarily used for chemical
ware, and capable of resisting such acids, alkalies, and other chemical compounds.

page_text: Having thus described my said Invention and the best means with which I am
acquainted for carrying the same into effect, I wish it to be understood that I do
not confine myself to the precise details herein laid down, as the same may be
varied with departing from the principlé of my Invention, but what I do claim
is,―
Firstly. The manufacture of plumbago crucibles and other vessels of plumbago,
which are rendered damp-proof and non-porous by applying a suitable impervious
coating, as and for the purposes herein-before described.
Secondly. The methods herein-before described of rendering plumbago crucibles
and other vessels of plumbago damp-proof and non-porous, and thereby obviating
the necessity of annealing such vessels.
In witness whereof, I, the said Samuel Arthur Peto, have hereto set my
hand and seal, this Eighth day of April, in the year of our Lord One thou-
sand eight hundred and seventy-nine.
Witness,
G. F. REDFERN,
4, South Street,
Finsbury, London.
SAMUEL ARTHUR PETO. (L.S.)