A New Yellow Dye.

Scientific American 39, 12.6.1852

M. Guinon, an eminent dyer of Lyons, France, has succeeded in dyeing silk light yellow by means of "picric acid." His attention was first directed to the subject by noticing the yellow color which it imparted to the skin. The acid is made by him in the following manner: - Int a good stone-ware vessel, able to contain three times the quantity employed, are put three parts by measure of commercial nitric acid, which is heated to 140° Fah. The vessel is then removed from the fire and 1 part by measure of coal oil is added through an earthenware tube, tapering at its lower end, and dipping into the acid. Each portion of oil, on entering the acid, causes a violent re-action, heat being generated, and carbonic acid and nitric oxide given off; should the liquor threaten to run over, the addition of oil must be suspended, and the whole cooled with a little nitric acid. The oil is the all poured in, and when this is done the rgeater part is already converted into picric acid, but a portion yet remains as a reddish resinous mass. Three parts more of nitric acid are then added, and the liwuid is boiled to a syrup. It must not be suffered to dry, or it will ignite with violence. The syrup thus formed solidifies into a yellow paste when cooling. This is then boiled in water for 20 minutes, and suffered to cool, when the picric acid form in crystals on cooling, and the residue is nitric acid and some resin. It can be purified like all salts by repeated crystallization. To purify it perfectly it must be mixed with ammonia, and precipitated with hydrochloric acid, but this is not required for dyeing. Silk mordanted with alum and tartar takes a fine straw color by being handled in a weak solution of picric acid. It can be washed severel times, but it does not stand alkalies or acids, but it is a valuable color, as it endured the sun and air; it is well known that tumeric, which is used to color a number of yellows, cannot stand the sun at all - it fades in a few minutes. - Wool, if prepared with alum and tartar, takes a fine citron yellow. It stands washing very well, and also the sun and air. This acid does not give any color to cotton. It is an improvement in the use of nitric acid whichhas often been used to give a kind of faint yellow to a white silk.

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