IMPROVED PROCESS OR MEANS OF RESTORING SPENT INDIGO BO AS TO ENABLE IT TO BE USED OR UTILIZED TO ADVANTAGE
Year: 1871

page_text: PROVISIONAL SPECIFICATION left by Francis Asbury Sawyer at the
Office of the Commissioners of Patents, with his Petition, on
the 15th November 1871.
I, FRANCIS ASBURY SAWYER, 2nd, of the State of Massachusetts, of
the United States of America, do hereby declare the nature of my
Invention of "IMPROVED PROCESS OR MEANS OF RESTORING SPENT INDIGO BO AS
TO ENABLE IT TO BE USED OR UTILIZED TO ADVANTAGE," to be fully described
as follows:-
:-
From the nature of indigo it is only possible to employ it as a coloring
agent while it is in a reduced state, that is to say, while deprived by
some chemical reducing agent of an atom of its oxygen; then the
indigo becomes soluble in an alkali, and can be used to color. Now in
the process of printing particularly what are termed "China blues" the
reduced indigo is exposed to the atmosphere, and having a great
affinity for oxygen becomes more or less oxydized, (that is returned to
its former insoluble blue state,) and after a time can no longer be used
either to color or print to advantage.

page_text: Owing to the fact that the coloring matter has been thickened or
requires to be mixed with gum or starch to render the printing with it
on cloth possible by a printing machine, a second reduction of the indigo
as in the first instance is found impracticable; hence the spent or
oxydized indigo becomes in most print works a waste. It is this
mixture of gum reducing agents, (as orpiment, tin, etc.,) alkali (as
soda), and indigo, that I propose to treat to separate from it the indigo
in a state fit for use in dyeing, coloring, or printing; and the process I
have discovered, and which I adopt for the accomplishment of such
result, I will now proceed to describe.
To thirty gallons of the waste liquor add about twelve times the
amount of water. Next the solution is to be heated until the gummy
matter may have become thoroughly incorporated with or diffused in
the water. Next I add to the solution one or more oxydizable materials
(such as sulphate of copper, bichromate of potash, or hydrochloric acid, 1
for instance;) the quantity to be added may be of sulphate of copper, say
about six pounds, or four pounds of the bichromate of potash, or when
bydrochloric acid is employed about two pounds or enough to sufficiently
acidify the solution. Next the solution should be well stirred, after
which it should be allowed to stand still for about two days when it will 2
be found that the indigo will have been separated from the foreign
matters in solution and have settled at the bottom of the liquid. Next
the supernatent liquid is to be drawn off or separated from the indigo,
or the latter abstracted from it by any proper means, after which there
should be added to the indigo a suitable amount of alkali to neutralize 2
the acid remaining therein. The indigo will then be found to be in a
restored state fit for use as a coloring agent.
I do not confine my Invention to the precise proportions of the liquid
and chemicals as herein-before set forth as used with the amount of
waste indigo liquor as stated, as such may be considerably varied and be 3
productive of good results.
I claim as my Invention the process substantially as described of