AN IMPROVEMENT IN PREPARING INDIGO FOR DYEING AND OTHER PURPOSES
Year: 1859

page_text: LETTERS PATENT to William Watson, of Leeds, in the County of York,
Manufacturing Chemist, for the Invention of "AN IMPROVEMENT IN
PREPARING INDIGO FOR DYEING AND OTHER PURPOSES."
Sealed the 12th June 1860, and dated the 14th December 1859.
PROVISIONAL SPECIFICATION left by the said William Watson at the
Office of the Commissioners of Patents, with his Petition, on the
14th December 1859.
I, WILLIAM WATSON, of Leeds, in the County of York, Manufacturing
Chemist, do hereby declare the nature of the Invention for "AN IMPROVE-
MENT IN PREPARING INDIGO FOR DYEING AND OTHER PURPOSES," to be а5
follows:-
My improvement consists in forming a solution of indigo in sulphuric acid,
and after diluting the solution with water, adding a salt or earth having the
property of forming an insoluble compound with sulphuric acid; for which
purpose I prefer the carbonate of barytes, by which the free sulphuric acid, or
so much thereof as will unite with and decompose the salt of barytes, forms an
insoluble compound; I then separate the sulphate of barytes by subsidence or

page_text: filtration, and I prefer that the solution be kept hot during the addition of the
carbonate of barytes and during such subsidence or filtration; the sulphate
of barytes being separated, the solution is allowed to cool, and an extract or
compound of indigo is deposited on cooling, which may then be reduced to a
dry state by evaporation or other convenient mode.
The compound or extract of indigo prepared according to my improvement
may be used for dyeing or other purposes for which what is now known in com-
merce as extract of indigo, is applied. The liquid from which the extract or
compound has been deposited still contains a portion of the compound of
indigo, which may be separated by evaporation, or precipitated by the addition
of chloride of barium or other salt, or may be used in succeeding operations.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said William Watson in the Great Seal Patent Office on the
14th June 1860.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
WATSON, of Leeds, in the County of York, Manufacturing Chemist, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Fourteenth day of December, One thousand eight
hundred and fifty-nine, in the twenty-third year of Her reign, did, for
Herself, Her heirs and successors, give and grant unto me, the said William
Watson, Her special license that I, the said William Watson, my execu-
tors, administrators, and assigns, or such others as I, the said William
Watson, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times hereafter during the
term therein expressed, should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "AN IMPROVEMENT IN PREPARING
INDIGO FOR DYEING AND OTHER PURPOSES," upon the condition (amongst others)
that I, the said William Watson, my executors or administrators, by an
instrument in writing under my hand and seal, should particularly describe
and ascertain the nature of the said Invention, and in what manner the
Isame was to be performed, and cause the same to be filed in the Great
Seal Patent Office within six calendar months next and immediately after
the date of the said Letters Patent.

page_text: NOW KNOW YE, that I, the said William Watson, do hereby declare the
nature of the said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement thereof (that is to say):-
My improvement consists in forming a solution of indigo in sulphuric acid,
and after diluting the solution with water, adding a salt or earth having the
property of forming an insoluble compound with sulphuric acid; for which
purpose I prefer the carbonate of barytes, by which the free sulphuric acid, or
so much thereof as will unite with and decompose the salt of barytes, forms an
insoluble compound; I then separate the sulphate of barytes by subsidence or
filtration, and I prefer that the solution be kept hot during the addition of the
carbonate of barytes, and during such subsidence or filtration, the sulphate
of barytes being separated, the solution is allowed to cool, and an extract or
compound of indigo is deposited on cooling, which may then be reduced to a
dry state by evaporation or other convenient mode.
The compound or extract of indigo prepared according to my improvement
may be used for dyeing or other purposes for which what is now known in
commerce as extract of indigo, is applied. The liquid from which the extract
or compound has been deposited still contains a portion of the compound of
indigo, which may be separated by evaporation, or precipitated by the addition
of chloride of barium or other salt, or may be used in succeeding operations.
Having thus stated the nature of my Invention, I will proceed more fully
to describe the manner of performing the same.
One part of indigo by weight is to be dissolved in four parts by weight of
concentrated sulphuric acid, as is well understood, and after diluting the
solution with twenty-five parts of water by weight, twelve parts of carbonate
of barytes by weight is to be added in fine powder at intervals, and heat
applied to the solution, so that it may be kept boiling. When the neutra-
lization of the acid is effected, which may be ascertained by litmus paper, as
is well understood, fifty parts more of boiling water are to be added, in order
to dissolve and separate the compound of indigo from the insoluble sulphate
and excess of carbonate of barytes, and after allowing the salts of barytes to
subside, the solution of coloring matter is to be. separated by decantation,
and successive portions of hot water used to wash out more of the soluble
compound, as is well understood in regard to washing precipitates. The com-
pound or solution of indigo, prepared in the manner described, is then to be
allowed to cool, when a portion of the coloring matter subsides, and may be
separated from the supernatant liquor by filtration, and the coloring matter.

page_text: remaining in solution may be afterwards precipitated by the addition of
chloride of barium in small quantities at intervals, until the coloring matter is
precipitated, when it is to be separated from the liquor by filtration, as before;
(a small quantity of chloride of barium is sufficient, but the quantity varies
according to temperature and the purity of the water and materials used).
The compound of indigo which has been precipitated by cooling or by addition
of chloride of barium, is to be dried and reduced to a solid state by the application
of heat, as is well known in drying precipitates.
The process which I have now described is such as I prefer to adopt, but I
do not confine myself thereto, as each part of the process may be greatly varied.
Thus, in place of using carbonate of barytes, as above directed, other suitable
salts of barium may be applied, such as the oxide or sulphuret of barium; the
process of neutralizing the sulphuric acid may also be varied, as the carbonate
of barytes, instead of being added to the solution of indigo in sulphuric acid
after it has been diluted with water, may be added to the solution without water.
The method of separating the compound of indigo from the sulphate and
carbonate of barytes may be also varied, as the compound of indigo may be
dissolved in a large quantity of cold water, and precipitated by the addition of
a salt of barium or other suitable salt; and I have found that the addition of
other cheap salts, such as the sulphate of soda, the chloride of sodium, or the
sulphate of magnesia, may be used instead of the chloride of barium for
effecting the precipitation of the coloring matter. Lastly, the process of
separating the compound of indigo from its solution in hot water after being
separated from the sulphate and carbonate of barytes, may be also varied, as
instead of allowing it to cool and deposit a portion of the coloring matter and
precipitating the remaining portion of coloring matter by the addition of a salt
of barium or other salt, as before mentioned, the salt may be added to the
solution while it is hot, and the whole of the coloring matter precipitated at
once. The compound may be also commercially applied in several stages; thus
the solution of coloring matter left after the precipitation of the sulphate of
barytes may be at once used in dyeing, or a portion of the coloring matter may
be allowed to precipitate by cooling, or be precipitated by chloride of barium
or other salt, and the precipitate, after separation by filtration or other such
suitable means as are well known, being reduced to the form of a paste may be
used in dyeing, or may be more completely dried, according to the circumstances
under which it is intended to be used.
Having thus described the nature of my Invention, and the manner of
performing the same, I would have it understood that what I claim is, the

page_text: manufacture of a preparation of indigo, made by adding a salt of barium to a
solution of indigo in sulphuric acid, as herein described.
In witness whereof, I, the said William Watson, have hereunto set my
band and seal, this Seventh day of June, in the year of our Lord One
thousand eight bundred and sixty.
Witness,
WILLIAM STEAD,
Clerk to Mr. W. S. Ward, Sol.,
Leeds.
WM. WATSON. (L.S.)