Improvements in the Manufacture of Pearl Hardening.
Year: 1890

page_text: Date of Application, 8th Aug., 1890
Complete Specification Left, 6th May, 1891-Accepted, 20th Jure, 1891
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Pearl Hardening.
I JAMES BEVERIDGE Technical Chemist of 4 Kent Road Gravesend in the
County of Kent do hereby declare the nature of this invention to be as follows:-
:-
It relates to the manufacture of crystallized sulphate of lime technically known
as "pearl hardening "a substance extensively used in the manufacture of paper;
and in the treatment of salt cake or crude sulphate of soda for that purpose.
In carrying it out in practice I first prepare an aqueous solution of salt-cake or
crude sulphate of soda by dissolving it in hot or cold water and in order to remove
wholly or in part ferruginous and other impurities I add thereto caustic lime made
into a milk with water or finely ground chalk or an alkaline soda salt such as
carbonate of soda in such excess that the free acid is neutralized and the iron and
alumina salts are decomposed.
After this treatment the liquor is allowed to remain at rest till the suspended or
precipitated matter has subsided. The clear liquor is then run off into a separate
lead lined vessel constructed of wood or iron and provided with a revolving
agitator.
Second I now add to the salt cake or sulphate of soda liquor, thus purified, an
aqueous solution of bisulphite of lime procured by any of the well known methods,
in such quantity that nearly the whole of the sulphate of soda has been converted
into sulphate of lime having the formula CaSO, + 2 H₂O.
The reaction which takes place may be represented by the following chemical
In practice find that for every equivalent or 142 parts of real sulphate of
soda (Na₂SO) existing in the salt cake liquor it is advisable to add somewhat less
than one equivalent or 184 parts of bisulphite of lime (CaSO,SO),
After the addition of the bisulphite of lime liquor the mixture is agitated with
the revolving agitator and if the temperature of the charge does not register
100° Fah. I prefer to heat it to this temperature, although it is not absolutely
necessary to do so, by injecting steam into it. After the lapse of an hour or so, a
sample of the mixture is withdrawn and filtered and the sulphate of soda and
bisulphite of lime estimated in a measured quantity of the filtrate, in order to
ascertain whether or not the right proportion of bisulpite to sulphate liquor has
been used. The amount of sulphate of soda thus found in the whole charge should
be about 10 per cent. of the original amount operated upon. The mixture of
crystallized sulphate of lime or "pearl hardening and bisulphites is then allowed
to remain at perfect rest till the white insoluble sulphate has subsided. The clear
supernatant liquor, consisting substantially of bisulphite of soda is syphoned off,
filtered if necessary and sold as such or it may be used for a variety of purposes in
paper mills.
Third: The white magma remaining in the vessel is first washed by decantation
with successive quantities of fresh water to remove soluble bisulphites and then
treated with a weak and preferably warm aqueous solution of sulphurous acid of
about 1° or 2° Twaddell's hydrometer in order to remove normal sulphite of
lime CaSO, which may have been precipitated along with the sulphate of lime, or
in lieu of such treatment with warm aqueous sulphurous acid, hot water slightly
acidified with sulphuric, hydrochloric or other mineral acid may be employed.
The sulphate of lime is now run off' through a tap or plug hole in the bottom of

page_text: It is
the vessel on to a filter and finally washed with water free from ferruginous and
insoluble impurities until the washings are free from sulphurous acid or compounds
thereof or other mineral acids. The sulphate of lime or pearl hardening" thus
obtained is practically free from iron-compounds and is of a good colour.
allowed to drain and further dried in a hydrotractor or by suction applied beneathı
the filter bed or it may be mixed with water and pumped or otherwise forced into a
receptacle in the beater room of the paper mill for use when required.
Dated this 8th day of August 1890.
JAMES BEVERIDGE.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Pearl Hardening.
1, JAMES BEVERIDGE, of 4 Kent Road, Gravesend, in the County of Kent,
Technical Chemist, 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:-
My invention relates to the manufacture of crystallized sulphate of lime
technically known as "pearl hardening" and extensively used in the manufacture
of paper.
The invention consists in a new and improved process or method of manufacturing
pearl hardening by adding an aqueous solution of salt cake or other sulphate of
soda, from which the ferruginous and other impurities have as much as practicable
been eliminated, to an aqueous solution of bisulphite of lime, or a solution of
sulphite of lime in aqueous sulphurous acid, in such quantity that nearly the whole
of the sulphate of soda will be converted into sulphate of lime having the
formula CaSO, + 2 HO, while bisulphite of soda which is also extensively used m
the manufacture of paper is obtained as a bye product. After separating the
sulphate of lime from the bisulphite of soda, I treat the former with aqueous
sulphurous acid, or other mineral acid or acids in order to remove any normal
sulphite of lime and subsequently wash with water.
In carrying my invention into practice I first prepare an aqueous solution of salt
cake or crude sulphate of soda by dissolving it in hot or cold water, and I remove
as much as practicable the ferruginous and other impurities which it contains.
This can be conveniently effected by adding to the solution caustic lime made into
a milk with water or finely ground chalk, or an alkaline soda salt such as carbonate
of soda, in such excess that the free acid is neutralized and the iron and alumina
salts are decomposed, the liquor after this treatment being allowed to remain at rest
till the suspended or precipitated matter has subsided when the clear liquor, that is
to say, the purified aqueous solution of sulphate of soda can be run off into a
separate lead lined vessel constructed of wood or iron and provided with a revolving
agitator.
I add to the purified salt cake or sulphate of soda liquor an aqueous solution of
bisulphite of lime procured by any of the well known methods in such quantity
that nearly the whole of the sulphate of soda will be converted into sulphate of lime
having the formula CaSO, + 2H,O, while the bisulphite of lime is converted into
bisulphite of soda. The reaction which takes place may be represented by the
following equation riz. :-
CaSO,SO, Na,SO, + 2 H₂O = Na₂SO,SO₂ + CaSO4 + 2 H₂O.
In practice I find that for every equivalent or 142 parts of real sulphate of
soda (Na₂SO) existing in the salt cake liquor it is advisable to add somewhat less
than one equivalent or 184 parts of bisulphite of lime (CaSO,SO,). After the
addition of the bisulphite of lime liquor the mixture is agitated with a revolving
agitator and if the temperature of the charge does not register 100° F. I prefer te

page_text: heat it to this temperature, (although it is not absolutely necessary to do so), by
injecting steam into it.
After the lapse of an hour or so a sample of the mixture
is withdrawn and filtered and the sulphate of soda and bisulphite of lime estimated
in a measured quantity of the filtrate, in order to ascertain whether or not the right
proportion of bisulphite to sulphate liquor has been used. The amount of sulphate
of soda thus found in the whole charge should be about from 5 to 10 per cent. of the
original amount operated upon. If the test shows a considerable variation from
this percentage a proportionate addition of the sulphate of soda solution or of the
bisulphite of lime liquor should be made and the agitation of the mixture be then
renewed for a while.
I have obtained good results when 100 gallons of purified salt cake liquor having
a strength of 26 degrees of Twaddell's hydrometer at a temperature of 113° F. and
containing about 1.65 lbs., more or less, of dry sulphate of soda, Na,So, per gallon,
have been added to about 400 gallons, more or less of bisulphite of lime liquor
having a strength of 10 degrees of Twaddell's hydrometer at 60° F. and having
substantially the following composition, namely:-0.531 lb. of bisulphite of
lime, CaSOSO, per gallon together with a slight excess of sulphurous acid, SO,
(over and above that required to form bisulphite, CaSO,SO, with the lime CaO)
usually occuring in bisulphite of lime liquors.
The mixture of crystallized sulphate of lime or "pearl hardening" and bisulphite
after the agitation has ceased is allowed to remain at perfect rest till the white
insoluble sulphate has subsided. The clear supernatant liquor consisting sub-
stantially of bisulphite of soda is syphoned off, and filtered if necessary; it may be
used for a variety of purposes in paper mills.
The white magma remaining in the vessel is next washed by decantation with
successive quantities of fresh water to remove soluble bisulphites and then treated
with a weak and preferably warm aqueous solution of sulphurous acid of about 1°
or 2° Twaddell's hydrometer in order to remove normal sulphite of lime CaSO,
which may have been precipitated along with the sulphate of lime. Or in lieu of
such treatment with warm aqueous sulphurous acid, hot water slightly acidified
with sulphuric, hydrochloric, or nitric acid may be employed. The sulphate of lime
is now run off through a tap or plug hole in the bottom of the vessel on to a filter
and finally washed with water free from ferruginous and insoluble impurities until
the washings are free from sulphurous acid or compounds thereof or other mineral
acid. The sulphate of lime or "pearl hardening" thus obtained is practically free
from iron compounds and is of a good white colour. It is allowed to drain and
further dried in a hydroextractor, or by suction applied beneath the filter bed, or
it may be mixed with water and pumped or otherwise forced into a receptacle in the
beater room of a paper mill for use when required or into any other suitable
receptacle. Instead of employing sulphate of soda, sulphate of magnesia may be
combined with the bisulphite or sulphite of lime in a manner analogous to that
above described and pearl hardening be manufactured as described and claimed in
the Specification of my Application for Patent No. 7797 of 1891.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what 1
claim is :-
:-
1. The manufacture of pearl hardening by adding together in approximately the
proportions hereinbefore specified, a purified aqueous solution of salt cake or other
sulphate of soda and an aqueous solution of bisulphite of lime, or a solution of
sulphite of lime in an aqueous solution of sulphurous acid, and submitting the
mixture to agitation with or without the application of heat, substantially as
herein before described.
2. The process of manufacturing pearl hardening which consists in first adding
together in approximately the proportions herein before specified, a purified aqueous
solution of salt cake or other sulphate of soda and an aqueous solution of bisulphite
of lime or a solution of sulphite of lime in an aqueous solution of sulphurous acid

page_text: and submitting the mixture to agitation with or without the application of heat,
and secondly, after separating the pearl hardening thereby obtained, treating it
with aqueous sulphurous acid or with water acidulated with sulphuric, hydrochloric
or nitric acid, to remove normal sulphite of lime and subsequently washing with
water, substantially as herein before described.
L
Ma 1901
J. C. MEWBURN,
55 & 56, Chancery Lane, London, Patent Agent.