IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHORIC ACID
Year: 1886

page_text: We, WILLIAM BRANTINGHAM GILES of 76 St. Paul's Rd. Canonbury, N. in the
County of Middlesex, and ARTHUR SHEARER of 8 Hamfrith Road, Stratford,
in the County of Essex, Chemists, do hereby declare the nature of our Inven-
tion for "IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHORIC ACID," to be as
follows:-
Whereas up to the present time all the Phosphoric Acid of commerce has been
produced either by the oxydation of Phosphorous or by treating various phosphates
with sulphuric acid or other bodies for the purpose of setting free the phosphoric
acid, or by heating Ammonia Phosphate; and as on the one hand in the former
process (that is to say the oxydation of Phosphorous) there is the trouble and
expense of preparing the phosphorous, in addition to the considerable labour and
outlay which are entailed in thoroughly oxydising it and freeing the resulting acid
from arsenic and other impurities which largely increases the cost of manufacture.
On the other hand the acid which is prepared from bone ashes, various forms of
phosphate of lime and other phosphates by means of sulphuric acid or other
re-agents, always contains certain impurities, such as magnesia, soda, ammonia,
iron, etc, which differ in amount and kind according to the source of the phosphate
employed, and the mode of treatment adopted.
These impurities render the acid so made unfit for use where a pure acid is
required as in Pharmacy for instance.
Now we have found that at an elevated temperature, say about dull redness,
phosphoric acid distils freely in a current of steam and this affords a most effectual
means whereby impure phosphoric acid may be freed from all impurities, such as
lime, magnesia, iron and other bases or their compounds and also from all volatile
and fixed acids.
In carrying out the above mentioned invention we take any suitable phosphatic
material, preferably some form of phosphate of lime, and having treated it by any
of the well known processes so as to obtain an impure phosphoric acid or acid
phosphate as is well understood by chemists, we concentrate the acid or the acid
phosphate by evaporation to a syrupy or pasty condition and then in a retort
cylinder or other suitable vessel we pass over it a current of steam (superheated or
not) while the temperature of the material in the operating vessel is maintained at
an elevated temperature by means of a fire preferably at a moderate red heat.

page_text: The vessels employed may be constructed either of platinum, fireclay or iron, or
fire-clay ovens or towers packed with suitable acid and heat resisting material may
be used.
We have successfully used both platinum and fire-clay.
Under these circumstances we have found that phosphoric acid of perfect
chemical purity distils over of a specific gravity as high as 1,250 to 1,300 or more,
should there be any volatile impurities such as hydrochloric acid, hydrofluoric acid,
or sulphuric acid present, these bodies come over with the first portions of the
distillate, and are caught separately, the magnesia, lime iron and all other fixed
impurities or residues remaining in the distilling vessels.

page_text: We WILLIAM BRANTINGHAM GILES of 76 Saint Paul's Road Canonbury, N. in
the County of Middlesex; and ARTHUR SHEARER of 8 Hamfrith Road, Stratford,
in the County of Essex; do hereby declare the nature of our invention for
"IMPROVEMENTS IN THE MANUFACTURE OF PHOSPHORIC ACID" and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :—
Whereas up to the present time all the Phosphoric Acid of commerce has been
produced either by the oxidation of Phosphorus, or by treating various phosphates
with sulphuric acid or other bodies for the purpose of setting free the phosphoric
acid, or by heating Phosphate of Ammonium, and as on the one hand in the former
process (that is to say, the oxidation of phosphorus) there is the trouble and
expense of preparing the phosphorus, in addition to the considerable labour and
outlay which are entailed in thoroughly oxidising it and freeing the resulting acid
from arsenic, and other impurities which greatly enhance the cost of the
phosphoric acid, on the other hand the acid which is prepared from bone ashes,
various forms of phosphates of lime or other phosphates by means of sulphuric
acid, or other re-agents always contains certain impurities such as magnesia, soda,
ammonia, iron, alumina, and the like, which differ in amount and kind according to
the source of the phosphate employed and the mode of treatment adopted.
These impurities render the acid so made unfit for use where a pure acid is
required as in Pharmacy for instance.
Now we have discovered that at an elevated temperature, i.e. from a dull red
heat to bright redness, phosphoric acid distils freely in presence of a current of
steam or of hydrochloric acid, and that this affords a most effectual means whereby
impure phosphoric acid or highly acid phosphates may be freed from all impurities,
such as lime, magnesia, iron or other bases, or their compounds, and also from all
foreign volatile and fixed acids.
In carrying out the said invention we take any suitable phosphatic material,
such as phosphate of lime in any form, phosphate of lead or phosphate of alumina,
or iron, or the phosphoric slag which is produced in iron or steel making, and
having treated any of these materials so as to separate the greater part of the bases
so as to obtain an impure phosphoric or a highly acid phosphate as is understood
by chemists, we concentrate the acid or the acid phosphate by evaporation to a
syrupy or pasty condition, and then placing it in a retort, cylinder oven or other
suitable vessel we pass over it a current of steam (superheated or not) or a current
of hydrochloric acid, preferring however to use steam, while at the same time the
material in the operating vessel is maintained at an elevated temperature by means
of a fire, usually employing a fair red heat.
A partial or perfect vacuum may be created in the condensers to facilitate the
distillation.
We also claim as a part of our invention that it is not absolutely necessary that
the phosphoric acid should be previously separated as above described from the
bases with which it is combined,

page_text: In working this modification of our invention we place in a retort oven, cylinder
or other vessel the phosphoric material mixed with silica, sand, silicious matter,
sulphuric acid or with any other material that will set the phosphoric acid free,
under the joint influence of a high temperature and the presence of steam or
hydrochloric acid, and having raised the temperature to the required degree we
distil off the phosphoric acid in a current of steam or hydrochloric acid, assisting
the operation if necessary by forming a partial or perfect vacuum in the condensing
arrangement.
The vessels employed may be constructed either of platinum, fireclay or of iron,
or may consist of firebrick ovens or towers, and the steam required may be generated
in the same vessel as is used for the distillation, i.e. the syrupy or pasty material
may be dropped, injected or sprayed into a highly heated oven or chamber packed
with suitable acid and heat resisting materials, either alone or mixed with water
or steam.
We have successfully employed vessels both of platinum and fireclay on the
large scale, but we do not claim any particular form of apparatus.
Under these circumstances we have found that phosphoric acid of perfect purity
distils over, having a specific gravity varying from 1.060 to 1.080; we prefer
however to work so that an acid of about 1.500 specific gravity is obtained.
Should any volatile impurities such as hydrochloric acid, hydrofluoric acid or
sulphuric acid be present, these bodies distil over before the phosphoric acid, and
are caught in a separate condenser, the magnesia, lime, iron alumina and all other
fixed impurities or residues remaining in the distilling vessels.
Having now described the nature and the means of carrying out our above
mentioned invention, what we particularly claim as novel in it is
The discovery and application of the fact that phosphoric acid although almost
fixed and non-volatile when treated in close vessels per se, is easily distilled in
a current of steam or hydrochloric acid at an elevated temperature and that this
affords a novel and ready means of procuring pure phosphoric acid from cheap and
easily accessible materials, whereas this could only up to the present time be
prepared from phosphorus.