Textile Mercury, 27.4.1889
Indophenol is a blue colouring matter discovered in 1881 by Horace Koechlin and O.N. Witt, and it is prepared by the action of nitrosodimethylanilin on α-napthol.
When first sent out it was hoped that it would form an efficient substitute for indigo, but it was found that it did not possess that fastness to light and washing so characteristic of indigo, and so of last years it has gone out of use among dyers, although a limited application has been found for it among calico printers. Like indigo, indophenol is capable of forming a white soluble reduction product, and hence was used chiefly as a vat dye the same as indigo.
Recently, the Koechlins have taken out a patent for the combined use, as a vat dye, of indigo and indophenol. For this purpose they take 44lbs. of indigo and 14lbs. 9oz. indophenol, and grind the two most thoroughly together into a paste with water, so that there will be 16 gallons of paste produced; this is then mixed with 212lbs. bisulphite of soda, 70°Tw.; 29lbs. 2oz. tin crystals, 35lbs. 7oz. zinc dust, and 146 gallons of water; these are all mixed and thoroughly agitated together for one hour, and then 114 gallons of caustic soda, 67°Tw. are added, and after mixing the whole is allowed to stand for one day. This constitutes what is called the mother vat A; after standing, the clear liquor is mixed with 1,210 gallons of water and 74 gallons of a hydrosulphite liquor, made by mixing 110 gallons of water, 44lbs. of zinc dust, 27½ gallons bisulphite of soda at 70°Tw., and 55lbs. tin crystals; when these are all dissolved, 17½ gallons caustic soda at 67°Tw. are added. The dye vat thus made is stirred and the goods dyed in the same manner as with indigo.
As indophenol is a much stronger colouring matter than indigo fewer dips are necessary to produce the same depth of colour on the yarns or cloth dyed in the vat.
The shades obtained are rather redder, but on first washing they bleed and the shade becomes more indigo blue, and they stand further washings. It resists dilute acids and alkalies. Strong nitric acid gives the characteristic yellow stain of indigo. It is said that the combined blue is fast to light and air as indigo blue, but whether such is really the case time only can tell; if so then the combination of indophenol with indigo must alter in some way the properties of the former colour. The combined shade can be produced at a much cheaper rate than pure indigo shades of the same depth.
Messrs. Durand and Huguenin, of Basle, hold the patent rights in connection with this colour.
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