Improved Method of Hardening or Preserving Gypsum or like Hydrous Rock.
Year: 1897

page_text: Date of Application, 4th Oct., 1897-Accepted, 11th Dec., 1897
COMPLETE SPECIFICATION.
Improved Method of Hardening or Preserving Gypsum or like
Hydrous Rock.
I, ARCHIBALD ANDERSON DICKSON, of Spadina Road, in the City of Toronto, County
of York and Province of Ontario, in the Dominion of Canada, Manufacturer, 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 the treatment of hydrous materials of a rocky character
found in natural deposits, or veins, such as gypsum and the like, for the purpose of
rendering them capable of being readily cut, hardened and polished, and whereby
various useful and ornamental articles and materials may be produced, either plain
or colored to resemble different kinds of marble, chalcedony, or the like, the object
being to perform such work and to produce such articles and materials in a manner
more economically, conveniently and efficiently than by the other methods known in.
the art.
In practice it has been found that one of the chief difficulties has been that during
the process of dehydration the native material has been found to curl and twist to such an
extent as to destroy the form or equality of shape of the article or block under treat-
ment; another fatal objection to all of the old methods with which I am acquainted,
is that in the majority of cases cracking or slacking of the material occurs both
during the dehydrating and cooling processes.
I will now describe my improved method or process, in such detail as will enable
those skilled in the art to put the same into practice, and more particularly point out
the novelty in the claims."
In mining the native material (which for clearness of description I will confine to
gypsum rock,) I use channelling or sawing machines in preference to breaking out,
or blasting, as the rock is thus in no danger of becoming fractured, shattered or
separated in its pores.
The blocks or pieces are now sawn, turned or otherwise worked into the desired
shapes, and then put into clamps, or other holding devices of such character that a
support or slight pressure will be had at the necessary points. (These clamps or holders
may include in their grasp either single articles or pieces, or a number of such, as
may suit the circumstances; their use, however, being specially valuable when used
in connection with pieces of large dimensions.
The next step is that of dehydration, that is to say, I drive off the desired or
necessary proportion or amount of the inherent moisture by subjecting the articles or
pieces to the action of heat-preferably by hot air of the required temperature in a
closed chamber or compartment.
When, according to the quality of the gypsum,-(in which the moisture varies) or
the size of the piece, it has been subjected to a suitable degree of heat, and for the
necessary time, the heating agent is withdrawn from the chamber and a gradual
cooling of the material is thus effected, (or in using a large plant, I may find it
convenient to move the dehydrated material to one or more cooler chambers, thus
keeping up a constant operation with a large quantity of gypsum.)

page_text: The desired degree of coolness having been thus effected, I prepare a bath
containing a solution (preferably of the same temperature as is now possessed by the
gypsum,) of Ammonia Alum (AL, О„—3S, O + (N.H₁)„, 0‚—SO¸ + 24 H₂O) and
iminerse the articles (with their clamps still in place, when such are used) therein,
and let them remain until the pores, are completely filled with this hardening
solution.
Upon their removal from the bath, I allow them to drain and dry, preferably in
the open air, or in a suitably-conditioned apartment, the time now depending solely
upon the size of the article and state of the atmosphere. (I may add any suitable
coloring ingredients to the solution in the bath according to the appearance desired
for the article, but prefer to use the chemical equivalents or affinities of the pure
Ammonia Alum, such as Chrome Alum, and the like.)
The clamps or holders (when used) are now removed, and the blocks, slabs, or
ornamental pieces can be polished by any known or suitable means or methods.
I have found by practical experiment that the above process produces a finished
article of superior hardness, and free from crack or blemish, and the chemicals
employed are such as will not be objectionable or dangerous to the workmen
employed.
I do not claim, nor is it necessary to describe any particular form or arrrangement
of apparatus, as any intelligent person may easily construct and arrange a plant
suitable for carrying out my present improved process.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed, I declare that what I claim is :-
1. The art, method or process of treating a hydrous material (as Gypsum Rock) to
enable it to be hardened and polished, which consists, essentially, in first, dehydrating
the shaped block or piece by the action of heat; second, cooling it gradually;
third, filling the pores of the cooled material with a hardening element by immersing
it in a solution of Ammonia Alum, and finally drying it previous to polishing,
substantially as set forth.
2. The art, method or process of treating a hydrous material (as Gypsum Rock) to
enable it to be hardened and polished, which consists essentially, in first, clamping
the shaped block or piece:-second, dehydrating it by the action of heat: third,
cooling it gradually: fourth, filling the pores of the cooled material with a hardening
element by immersing it in a solution of Ammonia Alum: fifth, drying it by the
action of the atmosphere, and finally removing the clamps previous to polishing,
substantially as set forth.
Dated this hutoanth
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