IMPROVE- MENTS IN DECOMPOSING SULPHATE OF IRON AND IN THE OBTAINING SULPHUROUS ACID, AND RED OXIDE OF IRON THEREBY
Year: 1884

page_text: COMPLETE SPECIFICATION.
I, THOMAS TERRELL, of New Court, Temple, in the County of Middlesex,
Barrister-at-Law, do hereby declare the nature of my Invention for "IMPROVE-
MENTS IN DECOMPOSING SULPHATE OF IRON AND IN THE OBTAINING SULPHUROUS
ACID, AND RED OXIDE OF IRON THEREBY " and in what manner the same is to
be. performed, to be particularly described and ascertained in and by the following
statement:-
Sulphate of iron, commonly known as green copperas, has hitherto been
submitted to destructive distillation and the result has been that the sulphuric
acid present has been partly decomposed a portion passing off as sulphurous acid
and a portion as fuming sulphuric acid the residue in the furnace or retort being
red oxide of iron. This process of destructive distillation is very costly by reason
of the difficulty experienced in driving off the heavy fumes of the sulphuric acid it
being necessary to maintain the sulphate of iron for many hours at a temperature
bordering upon a white heat and even then it frequently happens that the oxide of
iron, when withdrawn, from the retort or furnace contains large quantities of
undecomposed sulphate of iron and of free sulphuric acid.
My Invention consists in mixing the sulphate of iron with free sulphur in the
proportion of about one part of free sulphur to ten parts of hydrated sulphate of
iron or crystal copperas.
I use the sulphur in the condition either of sublimed sulphur or as ground
brimstone. I throw the mixture either upon a drying floor of cast iron or tiles or
into a cast iron pan and by the aid of fire drive off the water of crystallisation and
by constant stirring whilst the drying process is proceeding I reduce the mixture
to a pulverulent dry mass.
I then place this dry substance, in the form of powder, into a furnace constructed
upon the plan of a burner similar to those commonly used for converting sulphur
into sulphurous acid for the purpose of manufacturing sulphuric acid with this
exception that under the floor of the burner I place a furnace capable of rendering
the floor of the burner red hot. At the further end of the furnace I have a cast
iron flue leading into an ordinary vitriol chamber in this flue I have a door to
which access can be obtained and in the flue I place the nitre pots necessary to
convert the sulphurous acid into sulphuric acid. The fumes of sulphurous acid are
converted into sulphuric acid in the ordinary way.

page_text: I first place a fire in the furnace under the floor of the burner and having heated
the said floor to a dull red heat I throw in the dry powder above described. So
soon as the heat has penetrated, which, as a rule, takes from five minutes to
twenty minutes, the excess of sulphur burns out forming sulphurous acid which
passes into the chamber. The remaining sulphur reduces the sulphuric acid in the
sulphate of iron to sulphurous acid and in this condition a rapid decomposition
takes place and before the whole mass has become red hot the whole of the
sulphuric acid in the sulphate of iron passes off into the chamber as sulphurous
acid leaving behind oxide of iron in a brilliant red form which is valuable as a
pigment. The oxide of iron may be drawn out in from an hour to an hour and a
half according to the temperature attained or so soon as fumes of sulphurous acid
are no longer emitted.
The accompanying Drawing is a longitudinal section of a furnace and parts
connected therewith constructed and arranged as hereinbefore described. A. is the
furnace, B. the flue thereof, C, is the floor for supporting the dry powdered mixture
of sulphate of iron and sulphur. D. is a nitre pot, E an opening for inserting the
same, F. is the flue for conducting the fumes to the chamber G., H. and I. aro
respectively the doors of the burning chamber and the furnace, and, J. is the
ash pit.
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-
The admixture of sulphur with sulphate of iron for the purpose of assisting the
decomposition of the latter by the process of destructive distillation.