SULPHATE OF ALUMINA
Year: 1881

page_text: LETTERS PATENT to Alexander Angus Croll, of Coleman Street, in the City of
London, for an Invention of
SULPHATE OF ALUMINA."
$6
IMPROVEMENTS IN THE MANUFACTURE OF
PROVISIONAL SPECIFICATION left by the said Alexander Angus Croll
at the Office of the Commissioners of Patents on the 21st April 1881.
ALEXANDER ANGUS CROLL, of Coleman Street, in the City of London.
IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF ALUMINA."
When manufacturing sulphate of alumina or sulphate of alumina cake by a
process of the character of that described in the Specification of Letters Patent
granted to me, bearing date the 20th day of August 1878, No. 3282, I find greatly
increased advantages are obtained by diluting the mass of sulphate of alumina or
sulphate of alumina cake from the concentrated form in which such sulphate of
alumina so manufactured is obtained before that mass has had time to consolidate
or set.
This dilution I effect by the use of highly heated water or steam, the heat of the
water or steam I employ being about the same as that of the sulphate of alumina
under operation. Thus, for instance, assuming that the temperature of the
sulphate of alumina for the time under operation to be 260° Fahrenheit, then I
prefer that the heat of the steam or water to be used for the purpose of dilution
of that sulphate of alumina should be introduced thereto at about the same
temperature.
The extent of the dilution I prefer to adopt is that by which the mass under
operation may be retained after dilution in a soluble condition at a temperature of
about 200° Fahrenheit.
When it is found desirable to draw off the material acted upon without
settlement it is still desirable to use the hot water or steam to promote the full
chemical action.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Alexander Angus Croll in the Great Seal Patent Office on the
21st October 1881.
ALEXANDER ANGUS CROLL, of Coleman Street, in the City of London.
"IMPROVEMENTS IN THE MANUFACTURE OF SULPHATE OF ALUMINA."
When manufacturing sulphate of alumina or sulphate of alumina cake by a
process of the character of that described in the Specification of Letters Patent
granted to me, bearing date the 20th day of August 1878, No. 3282, I find greatly
increased advantages are obtained by diluting the mass of sulphate of alumina or
sulphate of alumina cake from the concentrated form in which such sulphate of
alumina so manufactured is obtained before that mass has had time to consolidate
or set.
This dilution I effect by the use of highly heated water or steam, the heat of the
water or steam I employ being about the same as that of the sulphate of alumina
under operation. Thus, for instance, assuming that the temperature of the sulphate
of alumina for the time under operation be 260° Fahrenheit, then I prefer that the
heat of the steam or water to be used for the purpose of dilution of that sulphate
of alumina should be introduced thereto at about the same temperature.
In the manufacture of sulphate of alumina according to these improvements, I
find that I obtain the best results by employing equal weights of china clay rich in
alumina and boiling sulphuric acid of about 70 per cent. strength, but good results
may be obtained by the use of other material rich in alumina, and the strength or
quantity of acid employed may be varied depending on the quantity of alumina
contained in the china clay or other aluminous material under operation.
The mixture is best conducted in saturating vessels surrounded with some
non-conducting substance to retain the heat. Before the chemical action has ceased
I cause a stream of superheated steam, which is obtained from a boiler worked at
about 60 lbs. pressure per square inch, to enter this vessel at or near the bottom
thereof, and be continued for about one hour, depending on the mass under operation
and the rapidity of action of the steam.
The mass I then dilute by super-heated water conveyed from a boiler to near
the bottom of this vessel and at a similar pressure or temperature until the whole
is diluted, so that when it is allowed to cool it forms a solid cake.
After the chemical action resulting from the mixture of the clay and. acid, as
before described, any free acid that may remain I neutralize. by adding a sufficient
quantity of soda ash to the mixture.
"
Should it be desired to produce a product to be used as what is known as "alum
cake" the dilution is stopped at a point at which the desired strength, is obtained;
which point is easily ascertained by roughly analizing a sample, and which sample
on analysis will indicate about 40 per cent. of alumina. If, on the other hand, it
is desired to obtain "sulphate of alumina tolerably free from insoluble matter,
the dilution is then stopped at a point at which the clear liquid will on cooling
form a solid cake, and in obtaining this article I have, found it to be desirable to
retain the heat in the mass as long as possible, so that the insoluble matter may
sink to the bottom. I have found also that the separation is accelerated by sinking
a circular or other suitable filtering tube or chamber into the mass, such tube or
chamber being of a weight or loaded with lead, so as to be of a specific weight a
little less than the specific weight of the liquor, so that it may gradually sink into
the mass; the clear liquid as it passes through the filtering medium placed around
and under this filtering vessel is to be drawn off by syphon or other suitable means
so regulated that it may run at or about at the same rate as the filtration
proceeds.

page_text: The remainder of the mass in the saturating vessel may be used as alumina cake
in the manufacture of the coarser qualities of paper.
The pipes conveying the superheated steam and the superheated water should
both be well protected by non-conducting material in order as much as possible to
prevent the escape of heat.
Having thus described my Invention, and means I adopt in carrying the same
into effect, I would have it understood that what I claim is, the improvements in
the manufacture of sulphate of alumina, in manner substantially as described.
In witness whereof, I, the said Alexander Angus Croll, have hereunto set
my hand and seal, this Twenty first day of October, in the year One
thousand eight hundred and eighty one.