Improvements in the Manufacture of Artificial Stone.
Year: 1895

page_text: Date of Application, 24th June, 1895
Complete Specification Left, 23rd Mar., 1896-Accepted, 25th Apr., 1896
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Artificial Stone.
We, ERNST MORITZ ARNDT, Doctor of Philosophy, or 53, Frauen Strasse,
Stettin, Chemist, and GUSTAV DE BRUYN, of 48, Hirschgraben, Hamburg,
Architect, both in the German Empire, do hereby declare the nature of this
invention to be as follows:-
This invention relates to an improved process for the manufacture of artificial
stone suitable for use as slabs and in building walls, ceilings, arches and the like,
the stone not being affected by moisture nor undergoing any chemical alteration
in structure thereby ensuring that the solidity, elasticity and durability of the same
remain unchanged.
It has already been proposed to convert a mass containing gypsum and caustic
lime into a crystallized solid mass by means of sulphuric acid.
It was found, however, by experience that such a process did not produce the
results desired because the formation of sulphate of lime from the lime and
sulphuric acid takes place rapidly and for this reason the conversion of the lime to
the crystalline condition is not sufficiently regular and does not extend through the
whole mass.
According to our invention we obviate this difficulty by causing the formation of
the crystallized gypsum to proceed more slowly but at the same time sufficiently
quickly to prevent any injurious. reaction or change in the mass which would
produce an injurious change in the structure of the stone.
In carrying our invention we employ sulphurous acid or a sulphite instead of
sulphuric acid in order to first cause the formation of calcium sulphite which is
converted by oxidation into crystallized gypsum. This crystallized gypsum
formed quickly through the whole mass, as the calcium sulphite is finely divided,
so that an injurious change in the material is avoided, the process being,
however, sufficiently slow to enable the reaction to take place regularly through
the whole mass and to penetrate thoroughly through the same and render it
homogeneous, compact and solid.
The reactions which take place in the above described process differ essentially
from those which take place when a sulphite solution acts on gypsum already set,
in which case the sulphite solution acts chiefly as a liquid for hardening the already
set gypsum, whilst in our process calcium sulphite is produced in the mass and is
converted into crystallized gypsum.
The chemical changes in the mass, formed of gypsum, lime and a sulphite or
sulphurous acid and water, can be also aided by the treatment of the same with hot
water; by this means oxidation is hastened and any soluble substances which may
be present are removed.
We advantageously stir up the mixed gypsum and lime with an aqueous solution
of sulphurous acid the amount of which is so calculated that the whole of the lime
is used up in the formation of the calcium sulphite.
The aqueous sulphurous acid can also be advantageously produced by treating a
solution of a sulphite with sulphuric acid.
It is obvious that other materials, such as cinders, sand, slag and infusorial earth
can be added to the mass. In such cases, in which silicic acid is added, the amount
of caustic lime can be increased so that a quantity of the same remains, after the

page_text: above described reaction, and forms a double silicate with the silicic acid and with
the base set free by the lime from the sulphite employed, which may be, for
instance, aluminium sulphite. In this case also the above described treatment with
hot water would be advantageous. To carry out this process cinders or sand, slag
and gypsum are stirred up with water and a mixture consisting either of milk or
paste of lime and of aluminium sulphite with sulphuric acid or a mixture obtained
from milk of lime and free sulphurous acid is added.
The mass after being well stirred up is then moulded to the desired form and
after hardening (which occurs in about a day's time) is treated by having hot water
poured on it or by being dipped into the same.
We advantageously replace from 10 to 30 per cent. of the gypsum by hydraulic
lime and we take a quantity of the acid aluminium sulphite sufficient to convert one
third to two thirds of the lime into sulphate of lime. One third of the slaked lime
serves for the formation of silicate of calcium. For the manufacture of slabs I
advantageously employ from 5 to 8 per cent. of lime and for arched structures as
much as 10 per cent.
The amount of sulphurous acid added depends on the amount of lime present and
this amount is smaller when silicic acid is added to the mixture. The amount of
sulphurous acid or of sulphite can therefore be so regulated that instead of
converting from one to two thirds of the lime into sulphite of lime as above stated
this amount is equivalent to the whole mass of lime up to a tenth per cent. of
slaked lime.
The order in which materials are added to one another is not of importance so
that the process can take place as follows:-
A prepared mixture of gypsum lime and infusorial earth is stirred up with water,
and then cirders or sand and the calculated quantity of acid aluminium sulphite
dissolved in water are added.
The proportion of gypsum and cinders or sand is 1 : 2 to 3.
Instead of cinders, which must always be free from white ash and which should
preferably be not lixiviated, I can employ fragments of slag or coarse lumps of
iron slag.
In the mauufacture of plaster and stucco also the mass is treated with the
addition of sand.
The cinders do not act in any way on the other constituents of the mass but
serve only as a filling material. The sand which is used in the manufacture of
arched structures does, however, act on the other constituents and this action is
greater according as the amount of slaked lime increases in quantity.
Dated the 24th day of June 1895.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.
Improvements in the Manufacture of Artificial Stone.
We, ERNST MORITZ ARNDT, Doctor of Philosophy, of 53, Frauen Strasse,
Stettin, Chemist, and GUSTAV DE BRUYN, formerly of 48, Hirschgraben,
Hamburg, now. of Saarbrücken, Alsace-Lorraine, Architect, both in the German
Empire, 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 :-
This invention relates to an improved process for the manufacture of artificial
stone suitable for use as slabs and in building walls, ceilings, arches and the like,
the stone not being affected by moisture nor undergoing any chemical alteration in

page_text: structure thereby ensuring that the solidity, elasticity and durability of the same
remain unchanged.
It has already been proposed to convert a mass containing gypsum and caustic
lime into a crystallized solid mass by means of sulphuric acid.
It was found, however, by experience that such a process did not produce the
results desired because the formation of sulphate of lime from the lime and sulphuric
acid takes place rapidly and for this reason the conversion of the lime to the
crystalline condition is not sufficiently regular and does not extend through the
whole mass.
According to our invention we obviate this difficulty by causing the formation of
the crystallized gypsum to proceed more slowly but at the same time sufficiently
quickly to prevent any injurious reaction or change in the mass which would
produce an injurious change in the structure of the stone.
In carrying out our invention we employ sulphurous acid or a sulphite instead of
sulphuric acid in order to first cause the formation of calcium sulphite which is
converted by oxidation into crystallized gypsum. This crystallized gypsum is
formed quickly through the whole mass, as the calcium sulphite is finely divided,
so that an injurious change in the material is avoided, the process being, however,
sufficiently slow to enable the reaction to take place regularly through the whole
mass and to penetrate thoroughly through the same and render it homogeneous,
compact and solid.
The reactions which take place in the above described process differ essentially
from those which take place when a sulphite solution acts on gypsum already
set, in which case the sulphite solution acts chiefly as a liquid for hardening the
already set gypsum, whilst in our process calcium sulphite is produced in the mass
and is converted into crystallized gypsum.
The chemical changes in the mass, formed of gypsum, lime and a sulphite or
sulphurous acid and water, can be also aided by the treatment of the same with hot
water by this means oxidation is hastened and any soluble substances which may
be present are removed.
We advantageously stir up the mixed gypsum and lime with an aqueous solution
of sulphurous acid the amount of which is so calculated that the whole of the lime
isused up in the formation of the calcium sulphite.
The aqueous sulphurous acid can also be advantageously produced by treating a
solution of a sulphite with sulphuric acid.
It is obvious that other materials, such as cinders, sand, slag and infusorial earth
can be added to the mass. In such cases, in which silicic acid is added, the amount
of caustic lime can be increased so that a quantity of the same remains, after the
above described reaction and forms a double silicate with the silicic acid and with
the base set free by the lime from the sulphite employed, which may be, for
instance, aluminium sulphite. In this case also the above described treatment with
hot water would be advantageous. To carry out this process cinders or sand, zlag
and gypsum are stirred up with water and a mixture consisting either of milk or
paste of lime and of aluminium sulphite with sulphuric acid or a mixture obtained
from milk of lime and free sulphurous acid is added.
The mass after being well stirred up is then moulded to the desired form and
after hardening (which occurs in about a day's time) is treated by having hot water
poured on it or by being dipped into the same.
We advantageously replace from 10 to 30 per cent. of the gypsum by hydraulic
lime and we take a quantity of the acid aluminium sulphite sufficient to convert
one third to two thirds of the lime into sulphate of lime. One third of the slaked
lime serves for the formation of silicate of calcium. For the manufacture of slabs
we advantageously employ from 5 to 8 per cent. of lime and for arched structures
as much as 10 per cent.
The amount of sulphurous acid added depends on the amount of lime present
and this amount is smaller when silicic acid is added to the mixture. The amount
of sulphurous acid or of sulphite can therefore be so regulated that instead of

page_text: converting from one to two thirds of the lime into sulphite of lime as above stated
this amount is equivalent to the whole mass of lime up to a teuth per cent. of
slaked lime.
The order in which materials are added to one another is not of importance so
that the process can take place as follows:-
A prepared mixture of gypsum lime and infusorial earth is stirred up with water,
and then cinders or sand and the calculated quantity of acid aluminium sulphite
dissolved in water are added.
The proportion of gypsum and cinders or sand is 1 : 2 to 3.
Instead of cinders, which must always be free from white ash and which should
preferably be not lixiviated, we can employ fragments of slag or coarse lumps of
iron slag.
In the manufacture of plaster and stucco also the mass is treated with the
addition of sand.
The cinders do not act in any way on the other constituents of the mass but
serve only as a filling material. The sand which is used in the manufacture of
arched structures does, however, act on the other constituents and this action is
greater according as the amount of slaked lime increases in quantity.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. A process for the manufacture of artificial stone such process consisting in
treating a mixture of gypsum and lime, before it is set, with sulphurous acid or a
sulphite for the purpose of converting the lime into sulphite of lime, calcium
sulphite being first formed substantially as described.
2. In a process of the kind described in Claim 1 assisting the mutual reaction of
the cement constituents by treating the mass, after it has hardened or set, with
hot water substantially as described.
Dated the 23rd day of March 1896.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.