AN IMPROVED GYPSUM CEMENT
Year: 1872

page_text: PROVISIONAL SPECIFICATION left by William Robert Lake at the
Office of the Commissioners of Patents, with his Petition, on the
30th January 1872.-A communication from abroad by Emile
Friedrich August Schott, of Seesen, Germany, Chemist.
I, WILLIAM ROBERT LAKE, of the Firm of Haseltine, Lake, & Co.,
Patent Agents, Southampton Buildings, London, do hereby declare
the nature of the said Invention for "AN IMPROVED GYPSUM CEMENT,"
a communication, to be as follows:-
I reduce natural anhydrite by any known mechanism to a coarse
grained powder or a finer one, and mix it with 73, 5% of limestone
powder or chalk. The mixture thus obtained is heated on the body
of a puddling furnace so that it becomes liquid, and then it is crutched
by means of iron tools through a side opening and cooled. The furnace
is then again filled up. To melt. the mixture I use the well-known
furnace of Siemens as it is employed to puddle pig iron, or any other
furnace, by which a temperature of 2000° C. can be obtained; the
melting of the mixture being only obtained at full white heat. This
operation can be also performed by other and various manipulations
which all are within the reach of my Invention.

page_text: If the limestone is aimficult to pulverize it may be better
and reduce it by slacking to powder. The further operation is quite the
same.
Where anhydrite is not to be bad other material can be employed,
consisting chemically of sulphate of lime. The operation is the same,
but the proportion of the mixture must be calculated from the chemical
component of the raw material in such way that the mixture contains
40 parts of sulphurous anhydrite and 56 parts of lime (oxide of
calcium), whatever the other ingredients may be.
The mass melted in
the puddling furnace contains basic sulphate of lime, a chemical
combination of two equivalents of lime and one equivalent of sulphate`
of anhydrite, which has the property to harden when powdered-
(pulverized) and mixed with water to stone.
The mass smelted is reduced by machinery to a powder of
different size, which forms the cement ready for usc.
The coarser,
of which the grains are of the size of gunpowder, is principally used as
cement for hydraulic work, whereas the fine powder is applied to stucco
work, the latter is mixed with a slight quantity of water and the wetting
and hardening of the mass is finished in 10-20 hours. A piece of the
coarse grained powder caked in water becomes hard in a month; of
fine powdered mass in 8-14 days. The coarse grained mass thrown
into water sinks to the ground, and hardens very slowly but very
well.
The neutral sulphate of lime heated alone sinters in a white heat
to a crystalline mass whereby it loses some sulphuric acid, but becomes
not soft and all the less liquid (as is indicated falsely in several scientific
works). The oxide of calcium is a fireproof body.
It is well known that combinations of weakly burnt gypsum and lime
are used for building purposes as mortar, but they are quite unfit as
hydraulic cement and have never been used as such. All those
mixtures rapidly moisten by the action of the burned gypsum, and
harden afterwards in the air by taking up carbonic acid, but put into
water pieces made of such combinations become soft and lose all
consistency. Combinations of anhydrite or outburnt gypsum with lime
do not at all harden in water, and differ from my gypsum cement in
the same way as a mixture of argillaceous earth (clay) and lime differs
from Portland cement.

page_text: My gypsum cement is a basic sulphate of lime in the same way as
Portland cement is chiefly a basic silicate of lime. The chemical
combination is (Ca O₂,) SO,, and it will combine with 7 parts of water,
whereas a mixture of equal parts of sulphate of lime and oxide of
calcium takes only up 3 parts of water, which is effected under great
heat, whereas gypsum cement becomes not at all warm in water.
It is clear that this Invention is of greatest importance, great
quantities of anhydrite nearly worthless being stored up in the
mountains, and infinite masses of gypsum being by it made profitable
for commercial purposes and changed into a product of which can be
made use everywhere to the profit of men.
The gypsum cement takes up water slowly, but beside this it has the
same qualities as Portland' cement, of which it may take the place in
perhaps all cases. It is distinguished from almost all other cements
by the light colour it has, and can be used in more cases, as it can be dyed
wholly and applied to stucco work and the manufacture of artificial
marble.
.
The cost of manufacture is lower than that of Portland cement
because the raw material is very cheap and mixed in a dry state; the
mixture need not be made very carefully, the mass melting wholly;
the effect of fuel is much greater in puddling furnaces than in
intermitting blast furnaces, as used generally in the manufacture of
Portland cement. The moment when the gypsum cement is burned
can be easily recognised by the beginning melting of the mass by any
workman, and no loss is ensued by unfit or overburnt products.