=Permanent Colors on Basketry.=—While for most purposes the straw, raffia chips, willows, etc., dyed with Basic colors will be found satisfactory enough, it is best for craftsmen who are making a specialty of very high-grade baskets, to use some of the fast Acid colors, described and listed in the next chapter, for their reds and yellows, and for all mixed shades in which these two colors play an important part. The Acid dyes are applied in a boiling bath, with the addition of a little acetic acid, and, while not fast to washing, and not imparting their colors as readily as the Basic dyes, can be thoroughly depended upon, even in light and delicate shades, against the action of sunlight. Salt dyes can also be used, in a boiling bath with the addition of some salt, but, excepting in some special cases, are not superior to the Acid dyes, although somewhat faster to washing. CHAPTER VIII THE ACID COLORS The discovery and introduction into commerce of Mauveine and the other Basic dyes, focussed the attention of chemists, all over the world, upon this new and important application of their science. And it was soon noticed that certain organic bodies, of a decidedly _acid_ character, had the power of dyeing wool and silk. These early dyes were so-called “nitro” compounds, formed by the action of strong nitric acid upon derivatives of coal tar, and in most cases they gave strong and brilliant, but rather fugitive, shades of yellow. The most interesting of these, perhaps, was the compound known as “picric acid,” which at one time was considerably used for dyeing silk yellow. Now it has been abandoned for that purpose but is manufactured on an enormous scale for use as an explosive. These original acid dyes were of little importance. But in the early seventies chemists began to make use of a reaction—known as “diazotizing”—for making new organic compounds by the coupling of aniline or bodies similar to aniline, with all sorts and kinds of other compounds derived from coal tar. The number of derivatives of this sort proved enormous, and many of them had more or less valuable dyeing properties. And in a very short time new dyestuffs had been discovered, good, bad, and indifferent, numbering not hundreds, but thousands. A very few of these so-called “Azo” dyes were of the Basic class, like Bismarck Brown, mentioned in the last chapter. Others, discovered ten or fifteen years later, constituted the class of Direct Cotton colors or Salt colors. But the great bulk of these colors belonged to the so-called “Acid” class, forming salts with bases and alkalies, and being liberated from the salts by strong acids.