IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF LIME OR PLASTER OF PARIS
Year: 1883

page_text: LETTERS PATENT to John Henry Johnson of 47 Lincolns Inn Fields in
"
com-
the County of Middlesex, Gentleman, for an Invention of "IMPROVEMENTS
IN THE MANUFACTURE OF SULPHATE OF LIME OR PLASTER OF PARIS'
municated to him from Philippe Gabriel Journet a person resident at Paris
in the Republic of France
PROVISIONAL SPECIFICATION left by the said John Henry Johnson at the
Office of the Commissioners of Patents on the 22nd May 1883.
JOHN HENRY JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex
Gentleman "IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF LIME OR
PLASTER OF PARIS " a communication to me from Philippe Gabriel Journet a
person resident at Paris in the Republic of France
This Invention relates to the manufacture of an improved product or plaster
obtained by completely or partially converting lime into plaster or Sulphate of
lime by the process hereinafter described
In carrying out this Invention the Lime is first slaked by ordinary means with
water alone or with water acidulated with Sulphuric Acid and then preferably
allowed to dry; the powder thus obtained is moistened with Sulphuric Acid diluted
with water and worked up into a paste-After partial desiccation this paste is
exposed to an elevated temperature in a kiln or furnace and anhydrous plaster or
an anhydrous mixture of plaster and lime is thus obtained-This product may be
subsequently crushed and sifted and is capable of being employed for the same
purposes as ordinary plaster
The quantity or proportion of Sulphuric Acid to be added to the water varies
according to the quality of the product and the purposes to which the latter is to
be applied
Between the quantity of acid requisite to convert the whole of the lime into
plaster and that which is sufficient to barely acidulate the water and yield a small
proportion of Sulphate a considerable difference will be found to exist and the
intermediate quantities are capable of producing a large variety of products of

page_text: similar nature but differing in respect of hardness and rate of setting. In certain
cases especially when concentrated Sulphuric Acid is employed the exposure to an
elevated temperature as hereinbefore described may be dispensed with
As a modification of the process hereinbefore described the lime instead of being
slaked in the first place with water alone as hereinbefore described may be slaked
with water acidulated with Sulphuric Acid.
The Sulphate of Lime obtained by means of this Invention sets in the same
manner as plaster but in general is much harder than ordinary plaster of Paris
and admits of acquiring a polish-These products may be applied with advantage
to all building purposes in the same manner as ordinary plaster and may be
employed as a coating which may be caused to present any desired colour or veins
of colour by incorporating suitable coloring matter with the mass, when preparing
it for use or they may be moulded into blocks or articles of any form-The
hardness of these moulded articles may be increased by immersing them repeatedly
in water slightly acidulated with Sulphuric Acid and allowing them to dry after
each immersion
Lime has been mixed with plaster in order to increase the hardness of the latter
but however intimate the mixture the result is not equal to that obtained by this
improved process in which the Sulphate is formed in the body of the mass of Lime
in such a manner as to ensure the absolute homogeneity of the product.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Henry Johnson in the Great Seal Patent Office on the
15th November 1883..
JOHN HENRY JOHNSON of 47 Lincoln's Inn Fields in the County of Middlesex
Gentleman "IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF LIME OR
PLASTER OF PARIS " a communication to me from Philippe Gabriel Journet a
person resident at Paris in the Republic of France
This Invention relates to the manufacture of sulphate of lime or Plaster of Paris
by completely or partially converting lime into Sulphate of Lime or Plaster of
Paris by means of sulphuric acid as hereinafter described.
According to the said invention the lime is first slaked by water alone or by
water acidulated with sulphuric acid and is then preferably allowed to dry: the
powder thus obtained is moistened with sulphuric acid diluted with water and
worked up into a paste. After partial drying this paste is desiccated by exposure
to an elevated temperature in a kiln or furnace and anhydrous plaster or an
anhydrous mixture of plasture and lime is thus obtained. This product may be
subsequently crushed and sifted and is capable of being employed for the same
purposes as ordinary plaster.
The quantity or proportion of sulphuric acid to be added to the water varies
according te
the quality of the plaster to be produced and the purposes to which it
is to be applied.
Between the quantity of acid requisite to convert the whole of the lime into
plaster and that which is sufficient to barely acidulate the water and yield a small
proportion of Sulphate a considerable difference will be found to exist and the
intermediate quantities are capable of producing a large variety of products of
similar nature but differing in degree of hardness and in the time they require for
setting. In certain cases especially when strong solutions of sulphuric acid are
employed the exposure to an elevated temperature as hereinbefore described may
be dispensed with
The sulphate of lime obtained by means of this Invention sets in the same
manner as plaster but in general is much harder than ordinary plaster of Paris and
admits of being polished with pumice stone for example. The said Sulphate of
lime may be applied with advantage to building purposes in the same manner as
ordinary plaster and it may be employed as a coating which may be caused to
present any desired colour or veins of colour by incorporating suitable colouring
matter with the mass when preparing it for use or it may be moulded or formed
into blocks or articles of any required shape and size. The hardness of these
moulded articles may be increased by immersing them repeatedly in water slightly
acidulated with sulphuric acid and allowing them to dry after each immersion.
Lime has been mixed with plaster in order to increase the hardness of the latter
but however intimate the mixture the result is not equal to that obtained by this
improved process in which the sulphate is formed in the body of the mass of lime
in such a manner as to ensure the absolute homogeneity of the product.
Having now described and particularly ascertained the nature of the said
Invention and the manner in which the same is or may be used or carried into
effect I would observe in conclusion that I do not claim the production of a
mixture of Plaster and lime generally but what I consider to be novel and original

page_text: and therefore elaim as the invention secured to me by the hereinbefore in part
recited Letters Patent is :-
The improvements in the manufacture of Sulphate of lime, or Plaster of Paris,
consisting in treating lime with a solution of sulphuric acid so as to wholly or
partially convert the lime into sulphate, substantially as hereinbefore described.
In witness whereof I the said John Henry Johnson have to this my
Specification set my hand and seal this Seventh day of November One thousand
eight hundred and eighty three.
.