IMPROVEMENTS IN THE MANUFACTURE OF BICHROMATE OF SODA
Year: 1884

page_text: We; THOMAS CARLILE, Chemical Manufacturer, and JAMES PARK, Chemist, both
of the Millburn Chemical Works, Glasgow, in the County of Lanark, North
Britain do hereby declare the nature of our said Invention for "IMPROVEMENTS IN
THE MANUFACTURE OF BICHROMATE OF SODA," to be as follows:-
Our said Invention has for its object to obtain bichromate of soda in an
anhydrous crystalline form, a result which has been long desiderated and sought
for in many ways without practical success.
In carrying out our said Invention we adopt any well known or suitable process
so far as to obtain the bichromate of soda in the form of a concentrated solution,
or in the form of hydrated crystals. We take the concentrated solution or the
solution obtained by heating the hydrated crystals until the salt becomes dissolved
in its water of crystallisation, and subject the same to heat in any suitable vessel
fitted. with mechanical agitating or stirring apparatus. We prefer to apply the
heat by means of steam admitted to a jacket encasing or surrounding the vessel;
but the heat may be applied, in any other convenient way, care being taken to
have it uniform at all parts of the vessel, and to keep the temperature below the
fusing point of anhydrous bichromate of soda. Whilst the heat is being applied
constant agitation is kept up; and as the water evaporates small anhydrous
crystals are formed, the entire mass being ultimately converted into an anhydrous
crystalline powder.
Dated hi h 1
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1007
EDMUND HUNT,
Applicants' Agent.

page_text: We, THOMAS CARLILE, Chemical Manufacturer, and JAMES PARK, Chemist,
both of the Millburn Chemical Works, Glasgow, in the County of Lanark, North
Britain, do hereby declare the nature of our said Invention for "IMPROVEMENTS
IN THE MANUFACTURE OF BICHROMATE OF SODA," and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement:-
Our said Invention has for its object to manufacture bichromate of soda in such
a form and by means of such processes and apparatus as to be a new commercial
product different from anything hitherto brought into the market, and much more
suitable for being packed for conveyance from place to place and for being applied
in various important chemical manufactures. It is well known to chemists that
very many attempts have been made to obtain bichromate of soda in a dry
crystalline form, but these attempts have hitherto not been successful; and even if
hydrated crystals or a ground powder have been recently obtained these products
have been objectionable on account of their extremely deliquescent nature. By
the present Invention the bichromate of soda is obtained in an anhydrous crystalline
forin, in which form it is not only less deliquescent than in other forms, but it is
also less bulky and weighty for a given strength.
In carrying out our Invention any known process may be used to the extent of
obtaining the bichromate of soda in the form of a concentrated solution or in the
form of hydrated crystals. This concentrated solution or the solution obtained by
heating the hydrated crystals until the salt becomes dissolved in its water
of crystallisation is put into a vessel of the kind shown in the accompanying
Drawings; Figure, 1, being an elevation and Figure, 2, a vertical section. The
vessel, A, is of a shallow cylindrical form, and made with a double shell so as to
have a steam jacket space, B, round the sides and under the bottom. The steam
enters the jacket space by a pipe, C, and water of condensation passes off by a
pipe, D, connected to a steam trap. The vessel, A, is supported on pillars, E; and
has fixed to it a framing, F, G, to carry gearing for driving a central vertical
shaft, H, which has fixed to it a horizontal cross bar, J, fitted with stirring blades, K.
The bottoms of these stirring blades, K, are made with inclined parts to act like
ploughs as shown in Figure, 3, which is a view of one of the blades as at right
angles to Figure, 2. A discharge hole is provided in the bottom of the vessel, A,
being closed by a plug, L, connected to a lever, M.
Bi
In order to obtain the bichromate of soda as anhydrous as possible and in a
crystalline form, the concentrated solution is kept constantly stirred whilst the
heat is applied to it by means of the steam admitted to the jacket space, and
the heat is by preference applied by means of a steam jacket in this way in order
that the heat may be as uniform as possible at all parts of the vessel, A. The
beat may be applied in any other way provided care is taken to secure this
uniformity in its action which is necessary to obtain good results. The constant
stirring combined with the uniform action of the heat causes the water vapor to
escape regularly and equally from all parts of the thickening mass; and as the
bichromate of soda becomes anhydrous it crystallises in small grains. It is known
when the operation is finished by the entire mass being converted into a crystalline
powder the heat being maintained throughout. It is important that the heat
applied should not be as high as the fusing point of the anhydrous bichromate of
soda, because if portions became fused they would prevent the complete dehydration

page_text: of other portions. The heat of steam of about 30 pounds pressure per square inch
is in practice found to be sufficient; this heat may however be exceeded if a
greater heat can be applied conveniently and in a uniform manner, and if it is
desired to conduct the process more rapidly; but a greater heat. than 200 degrees
Centigrade must not be used. The vertical shaft, H, may be driven at the rate of
about fifteen turns per minute.
The distinctive feature of our Invention is the making of bichromate of soda in
the form of anhydrous crystals by the action of a moderate and uniform heat upon
the concentrated solution, combined with mechanical stirring or agitation in a
suitable vessel and continued until the mass is converted into a crystalline
powder.
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:-
Making bichromate of soda in the form of anhydrous crystals by the action of
a moderate and uniform heat upon the concentrated solution, combined with
mechanical stirring or agitation in a suitable vessel and continued until the mass
is converted into a crystalline powder.
EDMUND HUNT,
Applicants' Agent.