IMPROVEMENTS IN THE MANUFACTURE OF CERTAIN CHROMATES AND ACID CHROMATES
Year: 1885

page_text: 1
We, JOHN BROCK of the British Alkali Works, Widnes, Lancashire, Chemical
Manufacturer and WILLIAM AUGUSTUS ROWELL of the British Alkali Works,
Widnes Lancashire Chemist do hereby declare the nature of our invention for
"IMPROVEMENTS IN THE MANUFACTURE OF CERTAIN CHROMATES AND ACID
CHROMATES " to be as follows:-
This Invention has for its object the manufacture of the normal and acid
chromates of the following bases, viz soda, potash, ammonia, and alumina, either
more cheaply, or in a state of greater purity than by existing processes.
"
In most of the processes at present in use for the manufacture of bichromate of
soda or potash; the neutral chromate which is formed by furnacing chrome iron ore
with lime, and some suitable soda or potash salt, is decomposed with sulphuric or
hydrochloric acid, and the resulting sulphate or chloride of the base operated on
separated more or less completely.
In the case of soda, owing to the high solubility of both bichromate of soda,, and,
sulphate of soda, it appears to be difficult to obtain a complete separation, as most
of the bichromate of soda of commerce contains sulphate of soda. In the case of
potash the bichromate appears to be very much purer in this respect, but the
process suffers from the disadvantage of furnacing an expensive alkali, and one
whose salts, which act most readily on chrome iron ore, are rather volatile at high
temperatures.
In the case also of the chromates and acid chromates of ammonia and alumina
room for improvement exist on present processes.
Whichever of the bases specified it is desired to operate on, chromate of soda"
is first manufactured in the usual manner by furnacing chrome iron ore, with lime,
and a suitable soda salt, so that even if potassium chomate is required the intro-
duction of pottasium. salts into the furnace is avoided. This crude chromate of
soda is lixiviated and the solution, which may contain as well some chromate of
lime, is treated with some suitable strontium salt so as to obtain chromate,
of strontia, in a similar manner to that described in an application for Patent
No 12834 in the past year made by one of the present applicants..

page_text: This chromate of strontia, a nearly insoluble body, is treated with, preferably
boiled with solution of, bisulphate of ammonia or bisulphate of soda, or bisulphate
of potash or sulphate or bisulphate of alumina accordingly as it is desired to
produce, bichromate of ammonia, or bichromate of soda, or bichromate of potash
or chromate or bichromate of alumina in the same manner for each base, and we
find that when this is properly carried out and the chromate of strontia thoroughly
boiled with solution of any of the bisulphates mentioned, or sulphate of alumina,
that practically the whole of the chromate of strontia is decomposed, when
bisulphate of the alkalies named, or sulphate or bisulphate of alumina, is present
in such quantity that there is an equivalent of sulphuric acid present in the
bisulphate or sulphate above mentioned, for every equivalent of chromic acid in
the chromate of strontia.
Since this decomposition can be got to 98% and even with care to 99% of
the chromate of strontia present, it follows that alkaline bichromates or chromate
of alumina can be made of very great purity by this process, and in only one
necessary operation.
The result of the action of the bisulphates and sulphates specified is, that the
chromate of strontia is almost entirely converted into sulphate of strontia, and
the base previously combined with the sulphuric acid into chromate or bichromate.
As the sulphate of strontia is insoluble and the chromates and bichromates
named are soluble these two bodies are easily separated, and the chromate or
bichromate solution treated as is customary. If said solution contains any small
quantity of sulphate of strontia, it will be found that it is deposited, considerably
on concentration and completely on boiling to dryness, and the soluble chromate
may be separated by redissolving settling etc.
We wish to point out that this process is applicable to the purification from
sulphuric acid or sulphates of solutions of the chromates of the bases named, or
their bichromates, or acid chromates made by other processes.
If we desire to manufacture neutral chromates of soda, potash or ammonia by.
this process we boil the chromate of strontia with sulphate of the base whose
chromate we require, but as the normal sulphates of soda, ammonia' and potash do
not completely decompose the chromate of strontia with equivalent proportions we
prefer to boil the chromate of strontia with a sulphate of soda potash or ammonia
containing some free acid, and afterwards neutralize the corresponding quantity of
free chromic acid existing in the solution.
When we talk of "treating" chromate of strontia with the various sulphates
particularized, we wish it to be understood that we prefer to thoroughly boil the
chromate of strontia in as fine a state of division as possible, with solution of the
particular sulphate or acid sulphate whose base we wish to obtain as chromate or
acid chromate of that base. More or less perfect reactions can be obtained without
actually boiling, but to ensure good results the process should be conducted as
described.
Chromates of any of the specified bases of any degree of acidity required can
be obtained by this process, care being taken firstly that the sulphate of the base
has that or nearly that acidity itself as regards the sulphuric acid it contains before
use, and secondly that it is used in the proportion or nearly in the proportion of
one chemical equivalent of sulphuric acid free and combined for one such equivalent.
of chromic acid combined with the strontia.
In prescribing chemical equivalents as the quantities of the respective bodies to
be used to react on each other, we wish to remark that this is all that is necessary
in the case of acid chromates of the alkalies and chromate and acid chromate of
alumina, and that departure from this proportion has a tendency to render the
resulting chromates impure or to lead to loss of chromate, nevertheless this process
can be conducted by the method of successive boilings with successive quantities
but to no advantage if the processes described be adhered to. In the case only.
of the neutral chromates of soda, potash or ammonia this might be advantageous
г

page_text: as the neutral sulphates of these bases do not completely decompose chromate of
strontia to the extent of 98%. Nevertheless we prefer to boil chromate of
strontia with a sulphate to some extent acid, and afterwards neutralise, as
previously mentioned to prepare these neutral chromates, and thus decompose the
chromate of strontia in one operation only.
We have further to state that we find strontia possesses various advantageous
properties which make it extremely suitable for the purpose to which we apply it,
and that it is very superior to any other cheap base, from the fact, that its chromate
is nearly insoluble and yet easily decomposed and its sulphate very insoluble.
Neither Baryta nor lime possess such properties when existing as chromates.
Dated thin 2012

page_text: Improvements in the Manufacture of Certain Chromates and
Acid Chromates.
We JOHN BROCK of the British Alkali Works, Widnes, Lancashire, Chemical
Manufacturer and WILLIAM AUGUSTUS ROWELL of the British Alkali Works
Widnes Lancashire 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 :-
This invention has for its object the manufacture of the normal and acid
chromates of the following bases, viz soda, potash, ammonia and alumina, either
more cheaply, or in a state of greater purity than by existing processes.
In most of the processes at present in use for the manufacture of bichromate of
soda or potash, the neutral chromate which is formed by furnacing chrome iron
ore with lime, and some suitable soda or potash salt, is decomposed with sulphuric
or hydrochloric acid, and the resulting sulphate or chloride of the base operated on
separated more or less completely.
In the case of soda, owing to the high solubility of both bichromate of soda and
sulphate of soda, it appears to be difficult to obtain a complete separation, as most
of the bichromate of soda of commerce contains sulphate of soda. In the case of
potash the bichromate appears to be very much purer in this respect, but the
process suffers from the disadvantage of furnacing an expensive alkali, and one
whose salts, which act most readily on chrome iron ore, are rather volatile at high
temperatures.
In the case also of the chromates and acid chromates of ammonia and alumina
room for improvement exists on present processes.
We proceed as follows:-
Whichever of the bases specified it is desired to operate on, chromate of soda is
first manufactured in the usual manner by furnacing chrome iron ore, with lime
and a suitable soda salt, so that even if potassium chromate is required the intro-
duction of potassium salts into the furnace is avoided. This crude chromate of
soda is lixiviated and the solution, which may contain as well some chromate of
lime, is treated with some suitable strontium salt so as to obtain chromate
of strontia in a similar manner to that described in an application for Patent
No 12,834 in the past year made by one of the present applicants.
This chromate of strontia, a nearly insoluble body, is treated with, preferably
boiled with solution of bisulphate of ammonia, or bisulphate of soda or bisulphate
of potash or sulphate or bisulphate of alumina accordingly as it is desired to
produce bichromate of ammonia or bichromate of soda or bichromate of potash or
chromate or bichromate of alumina in the same manner for each base and we find
that when this is properly carried out and the chromate of strontia thoroughly
boiled with solution of any of the bisulphates mentioned or sulphate of alumina,
that practically the whole of the chromate of strontia is decomposed, when
bisulphate of the alkalies named or sulphate or bisulphate of alumina is present

page_text: in such quantity that there is an equivalent of sulphuric acid present in the
bisulphate or sulphate above mentioned for every equivalent of chromic acid in the
chromate of strontia.
Since this decomposition can be got to 98% and even with care to 991% of
the chromate of strontia present, it follows that alkaline bichromates or chromate
of alumina can be made of very great purity by this process, and in only one
necessary operation.
The result of the action of the bisulphates and sulphates specified is that the
chromate of strontia is almost entirely converted into sulphate of strontia and
the base previously combined with the sulphuric acid into chromate or bichromate.
As the sulphate of strontia is insoluble and the chromates and bichromates
named are soluble these two bodies are easily separated, and the chromate or
bichromate solution treated as is customary. If said solution contains any small
quantity of sulphate of strontia, it will be found that it is deposited, considerably
on concentration and completely on boiling to dryness, and the soluble chromate
may be separated by redissolving settling etc.
We wish to point out that this process is applicable to the purification from
sulphuric acid or sulphates of solutions of the chromates of the bases named or
their bichromates or acid chromates, made by other processes.
If we desire to manufacture neutral chromates of soda potash or ammonia by
this process we boil the chromate of strontia with sulphate of the base whose
chromate we require, but as the normal sulphates of soda, ammonia and potash do
not completly decompose the chromate of strontia with equivalent proportions we
prefer to boil the chromate of strontia with a sulphate of soda potash or ammonia
containing some free acid, and afterwards neutralize the corresponding quantity of
free chromic acid existing in the solution,
When we talk of "treating" chromate of strontia with the various sulphates
particularized, we wish it to be understood that we prefer to thoroughly boil the
chromate of strontia in as fine a state of division as possible with solution of the
particular sulphate or acid sulphate who base we wish to obtain as chromate or
acid chromate of that base. More or less perfect reactions can be obtained without
actually boiling, but to ensure good results the process should be conducted as
described.
Chromates of any of the specified bases, of any degree of acidity required can be
obtained by this process, care being taken firstly that the sulphate of the base has
that or nearly that acidity itself as regards the sulphuric acid it contains before
use, and secondly that it is used in the proportion or nearly in the proportion of
one chemical equivalent of sulphuric acid free and combined for one such equivalent
of chromic acid combined with the strontia.
In prescribing chemical equivalents as the quantities of the respective bodies to
be used to react on each other, we wish to remark that this is all that is necessary
in the case of acid chromates of the alkalies and chromate and acid chromate of
alumina, and that departure from this proportion has a tendency to render the
resulting chromates impure or to lead to loss of chromate, nevertheless this process
can be conducted by the method of successive boilings with successive quantities
but to no advantage if the processes described be adhered to. In the case only of
the neutral chromates of soda, potash or ammonia this might be advantageous as
the neutral sulphates of these bases do not completely decompose chromate of
strontia to the extent of 98%. Nevertheless we prefer to boil chromate of strontia
with a sulphate to some extent acid, and afterwards neutralise as previously
mentioned, to prepare these neutral chromates, and thus decompose the chromate
of strontia in one operation only.
We have further to state that we find strontia possesses various advantageous
properties which make it extremely suitable for the purpose to which we apply it,
and that it is very superior to any other cheap base, from the fact that its chromate
is nearly insoluble and yet easily decomposed and its sulphate very insoluble.
Neither baryta nor lime possess such properties when existing as chromates.

page_text: :
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is
(1.) The manufacture of bichromate of ammonia, soda, potash or alumina by
treating the chromate of strontia with the bisulphate of the corresponding base.
(2.) The manufacture of chromate of alumina by treating the chromate of
strontia with the sulphate of alumina.
(3.) The manufacture of chromate of soda, potash or ammonia by treating
chromate of strontia with the sulphate of the corresponding base and some free
sulphuric acid and afterwards neutralising free acid with the base corresponding to
the salt in process of manufacture.
(4.) The purification from sulphuric acid and sulphates of solutions of the
chromates, bichromates or acid chromates of soda, potash, ammonia, or alumina by
treating the same with chromate of strontia.