Soap cannot be used in the presence of so much salt for fear of its depositing on the fibre in spots and so causing trouble. For medium shades, however, where it is well to use soap in the dye-bath so as to have the color go on the fibre evenly, a little phosphate of soda is often employed instead of salt, one or two tablespoonfuls to the gallon, to diminish the waste of color, without making the soap insoluble. For the darker shades it is particularly important to thoroughly boil the goods for half an hour or more, before taking them out of the dye-bath. Otherwise the dyestuff will not penetrate the fibre, but will simply stain the surface, and will not only be easily washed off, with very mild soaping, but, when dry, will be apt to crack and rub. _Finishing._—After the materials have been dyed as just described, they should be taken out of the dye-bath, rinsed with water to wash off the excess of dye-liquor, and then shaken out and dried. When used in this way the best dyes of this class, such as those listed a little further on, will give, on cotton and linen, shades that are very fast to light, and fairly fast to washing. On wool and silk the shades are fast to both light and washing. For purposes of comparison it may be stated here what is generally meant by these terms. _Fastness to Light._—The test for light-fastness is usually made by partially covering a dyed skein with a piece of wood, or heavy piece of blotting paper, and exposing it to direct sunlight, back of a window with southern exposure. At intervals the skein is taken out and the color studied, and it is then easy to see whether any change has taken place in the portion of the goods exposed to the light. If the goods have faded appreciably in the space of one week, the dyestuff is considered _not fast_. If the color changes after two weeks’ exposure, but not after one week, it is to be considered _fairly fast_. If it stands for two weeks but fades in four weeks it is to be called _fast_. And if it resists, without appreciable change, the action of the summer sunlight for full four weeks, it is called _very fast_.