_Names._—These dyes have long been made by all of the great firms, although two or three have made more of a specialty of them than the rest. It was soon found that the presence of common (table) salt in the dyestuffs was valuable, as lessening the waste of dyestuff in the dye-liquor, and also increasing the fastness to washing of the dyed goods. For this reason the common name given to this class is that of “Salt Colors.” Owing, however, to the fact that Congo red, the first discovered of the whole class, was derived from the chemical known as benzidine, these salt colors are sometimes referred to, in general, as the “Congo,” or as the “benzidine” dyes. Besides this they are frequently known as “cotton colors,” or “direct cotton colors.” The different manufacturers, however, have assigned certain class names to their own dyestuffs, as follows: Benzo (_Elberfeld_); Diamine (_Cassella_); Dianil (_Metz_); Mikado (_Elberfeld_); Naphthamine (_Kalle_); Oxamine (_Badische_); Phenamine (_Badische_). _Uses._—These colors are chiefly used for dyeing cotton, linen, and paper. They take particularly well on mercerized cotton, and on some varieties of artificial silk. They can also be used to dye wool and silk, and, indeed, in many cases give colors faster, both to light and to washing, on these fibres than on cotton. As a rule they will not dye animal fibres excepting at a high temperature—near the boiling point—and in an acid bath. Whereas cotton and linen are preferably dyed in an alkaline or at least a neutral bath, and, while they must be boiled in the dye-bath for at all permanent results, will take the color as a stain at quite low temperatures. For this reason these dyes are often used for dyeing even shades in one bath, upon mixed goods—that is, wool and cotton, cotton and silk, etc. The goods are first dyed in a lukewarm bath till the cotton is nearly the proper shade, and then, on heating, the wool or silk will take up the color and, before long, catch up with the cotton. It must, however, be remembered that on cotton and linen these dyes are not, as a rule, at all fast to washing, unless they have been well boiled with the goods. When dyed on silk at a boil, they are fast to hot soap and water, a fact which, sometimes, is of much importance. DYEING DIRECTIONS