Improvements in the Manufacture of Artificial Stone or of Articles Formed of the same.
Year: 1889

page_text: Improvements in the Manufacture of Artificial Stone or of Articles
Formed of the same.
A communication from abroad by CARL KOHN, of Teschen; Bohemia, in the Empire
of Austria.
T, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 6, Lord Street, Liverpool, and 6, Bank Street, Manchester, both
in the County of Lancaster, and 323, High Holborn in the County of Middlesex
Civil Engineer, 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 improvements in the manufacture of artificial stones, and
articles such as plates, blocks and moulded pieces formed of the same..
In the manufacture, as hitherto practised, of a solid mass. resembling and having
the qualities of native stone, such stony matter being preferably made of magnesite,
it has usually been considered sufficient to form the basic salts of magnesia by treating
the calcined magnesite with chloride of magnesium, hydrochloric acid or similar
agents. The artificial stone or stony mass thus obtained when first used is satisfactory
as regards hardness and solidity, but it never attains the desired weather-proof quality,
as the particles of chloride of magnesium, etcetera, which have remained uncombined
in the mass, and formed fine microscopic crystals, especially at or near the
surface, are still soluble and by attracting moisture soon impair the solidity of the
stone.
With the simple mixtures of magnesite and sand, saw-dust, wood-dust, peat-dust,
glycerine and the like, which have been employed to form artificial stones, an effective
and uniform carbonating effect cannot be obtained, nor will a simple addition of
carbonic acid be sufficient to effect the same.
All these difficulties will be overcome by the improvements of this invention.
The improved method of manufacturing artificial stones consists in mixing equivalent
parts of powdered quartz and calcined magnesia or a double portion of quartz and one
portion of calcined magnesia with diluted soluble potash-glass; the mass is well
stirred and intimately mixed to form a stiff paste. The addition of soluble potash
glass is variable according to the degree of calcination of the magnesia employed and
the proportion, which, by experience, has been found to give satisfactory results is
from 1 to 10 per cent. of the calcinated magnesia. The said paste, then, is either
divided into blocks or stones of the desired shape by suitable cutters and press, or it
may be cast into moulds lined with oil, which moulds are brought into a drying
apparatus where the mass is dehydrated and freed from the superfluous amount of
water at a temperature of about 15 degrees Centigrade. From the said drying
apparatus the moulds, filled as described, are brought into another apparatus, provided
with a vacuum gauge and pressure manometer. Within the said apparatus, hermetically
closed, the moulds are, first, submitted to a more or less perfect vacuum to extract all
air contained in the blocks of paste, and immediately afterwards to carbonic acid under
high pressure, said carbonic acid being supplied from a suitable gas-holder or reservoir
from which it is taken and forced into the apparatus by a pump. The pressure of the
carbonic acid applied may be, according to the requirements, from one to ten atmo-
spheres, which is kept about constant till no further decrease of pressure is observed at
the manometer; the process of carbonating is then completed. The real and final
result of the treatment with carbonic acid under high pressure is this, that the hydrate
of oxide of magnesium, is completely converted into carbonate of magnesium, which,
in its turn, combines with the quartz to form carbo-silicate of magnesium. The latter
product consists of a stony mass of extreme hardness which has the advantage of a

page_text: strength of compression not usually heretofore attained, and also of being perfectly
weather-proof for any length of time.
In the same manner, as before described, similar mixtures of calcined magnesia and
powdered quartz, or sand and water, may be successively submitted to the operation
of the vacuum and pressure of carbonic acid.
In all cases, whether the carbonic acid is obtained from the atmosphere, or whether
it is supplied from any other source, the hydrate of oxide of magnesium is not the
passive but the active absorbing part. In both cases a superficial formation of carbonate
of magnesium is indeed obtained, but in the course of successive carbonating,
especially in the treatment with water, and in consequence of the development of heat
thereby occasioned, a molecular dislocation is produced, and a mass results of inferior
quality, being fragile and of brittle structure. A uniform and penetrating carbonisa-
tion and a corresponding hardness and solidity of the stone thereby obtained can only
be produced by the application of carbonic acid under high pressure.
The method, before described, of treating the substance of artificial stone in course
of manufacture, can be employed with good result on stones or other objects which
exist in a complete state and have been made according to the known method by
treating calcined magnesia with hydrochloric acid or sulphate of magnesia or chloride
of magnesium, the weather-proof quality of which stones or objects is not reliable
owing to the free hydroscopic chlorates or sulphates remaining in the mass.
stones or objects can be rendered thoroughly weather-proof by submitting the same,
subsequent to a preparing lixiviation, to the described operation.
Such
As has been mentioned before, artificial stones and articles formed of the same,
acquire, through the improved method of manufacture or treatment, a superior hard-
ness and solidity, and they become perfectly weather-proof. Their resistance to heat
is relatively strong, but, by exposure to very intense heat, said resistance might, in
some cases, be found insufficient, which resistance is of particular importance for
building-stones and pieces employed in buildings.
Accordingly, means have been provided to attain, for the artificial stones manu-
factured according to this invention, the complete resistance to the effects of heat,
where it may be desired.
The treatinent or operation, above described, remains essentially the same, and the
nodification consists only in providing inside the stone or stony mass, a core or cores
of fire-proof material, such as a textile fabric or net-work of asbestos or cords crossing
each other, or perforated sheet or sheets of the same or similar fire-proof material.
The said core or cores of fire-proof material, as described, is or are incorporated with
the body of the stone while filling the moulds with the paste, as described. The
said moulds are not filled up at once with paste, but only the botton is covered with
the mass, which, being well flattened down and spread, receives the fabric or fire-
proof material forced into the surface of the paste by a suitable implement, where-
upon the mould is filled up with the paste. The operation under the vacuum and
carbonic acid pump then proceeds in the manner described.
Mr. Kohn is aware that textile fabrics of vegetable matter such as jute, cotton,
linen and the like, as also metallic wire-gauze or wire-work, have been provided
inside the body of artificial stones to increase their solidity and elasticity, the vegetable
matter, however, is subject to carbonization and the metal to melting or extension by
heat, while, with the asbestos, not the least alteration will be produced that might
affect the solidity of the stone. Plates and blocks of artificial stone provided with
an interior core or cores of asbestos may be divided by saws and other suitable imple-
ments, which cannot readily be performed where metallic work is arranged in the
body of the plate or stone.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is :-
1. The method of manufacturing weather-proof artificial stones, plates and articles
of stone, from quartz, calcined magnesia and soluble potash-glass, by submitting the

page_text: mixture of said substances first to vacuum and subsequently to carbonic acid under a
high pressure of from one to ten atmospheres, substantially as described.
2. The method of manufacturing weather-proof and fire-proof artificial stones,
plates and articles of stone, from quartz, calcined magnesia and soluble potash-glass,
by arranging within the paste or mixture of said materials a core or cores of asbestos,
preferably in the form of textile fabric, net-work, perforated board or cords, and sub-
mitting the mass first to vacuum, and subsequently to carbonic acid under a high
pressure of from one to ten atmospheres, substantially as and for the purpose
described.
WM. P. THOMPSON & Co.,
Agents for the Applicant.