Year: 1885

page_text: I JOHN JAMES HOOD of 21 Shepherds Bush Road in the County of Middlesex
Doctor of Science do hereby declare the nature of this invention to be as
follows:-
These improvements relate to the manufacture of ammonic bichromate from
sodic or potassic chromates and are for the utilization of the crude ammonia salts
such as the sulphate chloride etc, or the crude ammonical liquors from gas works
or other such sources and which contain organic matters. Employing such
materials in their crude impure state for the manufacture of the ammonic
bichromate the organic matter they contain reduces part of the chromic oxide
of the sodic or potassic chromates when mixed and evaporated down together for
separation of the ammonic bichromate and so occasions loss. The difficulty is
overcome in the following manner.
To make the ammonic bichromate from sodic chromate or bichromate the chrome
ore is furnaced in the customary manner with soda salts for the fabrication of sodic
chromate and the resulting mass lixiviated. To the solution of sodic chromate so
obtained two equivalents of acid, sulphuric hydrochloric or other acid, are added
instead of one equivalent as is the case when sodic bichromate is to be made or in
other words double the amount of acid requisite to convert the sodic monochromate
into the bichromate.
The crude ammoniacal salts, or liquors containing free ammonia and ammoniacal
compounds, are decomposed in a separate closed vessel by means of carbonate of
calcium or the oxide or hydrate of calcium or by other cheap material so as to
cause the evolution of ammoniacal gas or a carbonate of ammonia. Through this
mixture contained in the chamber a current of air or steam is forced which carries
off the ammoniacal gas and which is conducted by a suitable pipe or pipes into the
chrome solution.
The current of ammoniacal gas is passed in just till the free hydrochloric or
sulphuric acid is neutralised. The solution now contains a bichromate and a
sulphate or chloride and on evaporating down first allowing any silica or other
sediment to settle and running off the clear solution the sodic sulphate or chloride
which separates is fished out and on the liquor being allowed to cool ammonic
bichromate more or less pure crystallizes out.

page_text: The liquor from the latter is further concentrated and fished to separate more of
the Bodic sulphate or chloride and again allowed to cool for a fresh crop of ammonic
bichromate crystals.
If the chrome ore has been furnished with potash salts as for the fabrication of
potassic bichromate two equivalents of sulphuric acid are added to the solution
obtained by lixiviating the fritted mass, and the ammoniacal gas is blown or
drawn through the solution as before described but the current of gas is continued
till the two equivalents of acid are neutralised and the solution contains a neutral
or mono-chromate and the chromate solution itself smells of ammonia-on allowing
to cool the potassic sulphate in great part separates out being but comparatively
little soluble in presence of ammonia-and the solution of ammonic mono-chromate
is boiled to decompose it into bichromate, the ammonia that is given off being
collected and allowed to crystallize.
The Bodic or potassic salts chlorides or sulphates obtained by the above processes
may be utilised for furnacing more chrome ore.

page_text: improvements in the manufacture of Ammonic Bichromate.
I JOHN JAMES HOOD of 21 Shepherds Bush Road in the County of Middlesex
Doctor of Science 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 :-
These improvements relate to the manufacture of ammonic bichromate from
sodium or potassium chromates and are for the utilization of the crude ammonium
salts such as the sulphate; chloride etc. or the crude ammoniacal liquors from
gas-works and other such sources and which contain organic matters or other
impurities.
If such crude salts are employed for the manufacture of ammonic bichromate
the organic matters or sulphuretted compounds they may contain tend to reduce
part of the chromic acid of the sodic or potassic chromates when mixed and boiled
together for the formation of ammonic bichromate and so cause loss.
To make ammonic bichromate from sodic chromate the chrome ore is furnaced in
the customary manner with soda salts for the formation of sodic chromate and the
mass lixiviated.
To the solution of sodic chromate so obtained two equivalents of acid are added,
either sulphuric, hydrochloric or nitric acid instead of one equivalent as is the case
when sodic bichromate is manufactured; in other words, an amount of acid is
added sufficient to convert the monochromate of soda into the bichromate together
with such a quantity as when combined with ammonium will yield ammonic
bichromate and sulphate chloride or nitrate of soda by double decomposition.
The crude ammoniacal salts, or liquors containing free ammonia and ammonia
Balte, are decomposed in a separate close vessel by means of carbonate or hydrate
of calcium, or by other cheap suitable material so as to evolve ammonia carbonate
or ammonia gas.
The ammonia gas so evolved is, if necessary, passed over or through a layer of
oxide of iron or other suitable material in order to decompose the sulphuretted
compounds which might otherwise act upon the chromate solution.
The stream of ammonia gas is conducted by a suitable pipe or pipes into the
chromate mixture in amount sufficient to saturate one equivalent of the sulphuric
hydrochloric or nitric acid.
The solution now contains a bichromate and a sulphate chloride or nitrate and
on evaporating down, first allowing any silica or other sediment to settle and
running off the clear solution, the sodic sulphate or chloride which separates is
fished out and on allowing the liquor to cool ammonic bichromate crystallizes out.
Instead of starting with sodic monochromate and adding two equivalents of acid
and then passing in the ammonia gas, sodic bichromate is first formed in the
customary manner and to the solution of this salt one equivalent of either sulphuric,
bydrochloric or nitric acid is added, the ammoniacal gas conducted into the solution
as before and the salts separated by fishing and crystallizing.
If the chrome ore has been furnaced with potassium salts as for the fabrication
of potassic chromates two equivalents of acid are added, by preference sulphurio

page_text: acid, to the monochromate solution and the ammoniacal gas passed into the
solution as before described but the current of gas is continued till the acid is
neutralized and the solution contains a monochromate and some free ammonia. On
allowing to cool the potassic sulphate separates in great part being comparatively
little soluble in presence of free ammonia.
The potassic sulphate is allowed to crystallize, the liquor run off and evaporated
down the ammonia given off owing to the decomposition of ammonic mono-
chromate into bichromate being collected by suitable means and the ammonic
bichromate crystallized.
.
In the above operations instead of passing the ammoniacal gas direct to the
acidulated solutions of sodium or potassium chromates the gas may be first
absorbed in water and the aqueous solution so obtained employed by adding to
the chrome solution.
The sodium or potassium salts obtained in the above processes are to be
utilized by fusing with fresh quantities of chrome ore, in particular the sodic
nitrate.
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 manufacture of ammonium bichromate by decomposing ammoniacal
salts or liquors and passing the ammonia gas into an acidulated solution of sodic
monochromate, or the addition of an aqueous solution of ammonia gas to such a
chrome mixture.
(2.) The manufacture of ammonium bichromate from an acidulated solution of
sodic bichromate by passing into it ammonia gas or an aqueous solution of
this gas..
(3.) The manufacture of ammonium bichromate from potassium monochromate
by employing ammonia gas or an aqueous solution of this gas in quantity sufficient
to produce the monochromate and then by heat driving off ammonia until the
bichromate is obtained.
(4.) In the manufacture of ammonium chromate, the addition of two equivalents
of sulphuric, hydrochloric or nitric acid, to sodic or potassic monochromate solution
and passing ammonia gas or adding an aqueous solution of this gas to such a
mixture.
(5.) The manufacture of bichromate of ammonia by means substantially as herein
described.