On the other hand, weighted silk, especially when the added mineral matter amounts to 25% or over, is quite hard to burn. If it catches fire at all, it just flashes up for a moment and then the flame dies right out. And when persistently heated, until the organic matter is all burnt away, it still leaves a very considerable residue of ash. When this test is to be made on unwoven or skein silk, it is enough to take two or three threads, five or six inches long, and to light them in the flame of a match. For piece goods it is best to pick out the threads carefully, with a pin or fine knife blade, separating the tram from the organzine, and then, with a match, to test each of these in turn. A very little practice will enable the most inexperienced student to make this test satisfactorily. Of course, for an accurate determination of the percentage of weighting contained in a given sample of silk, it is necessary to resort to delicate chemical analyses. But for all ordinary purposes this simple flame test is quite sufficient. DYEING SILK WITH COLORS FAST TO WASHING As a rule the method previously described of dyeing silk with Acid dyes in a broken bath of soap, or better, of boiled-off liquor, will be found perfectly satisfactory. The shades are easily obtained, the colors are brilliant, and, if the right dyes are used, exceedingly fast to light, and the material, if properly rinsed, suffers no deterioration. On the other hand these colors are not, in the slightest degree, fast to washing. The dyed goods can be cleaned with gasoline and the like, but when passed through a lukewarm bath of soap and water they bleed badly, and in boiling soapsuds the color can be completely stripped from them. In most cases this is not a serious objection, for a person who will send a handsome hand-dyed silk scarf or piece of embroidery to the family washtub is entitled to scant sympathy if the results are disastrous. But occasionally it is important to have colors on silk which can be guaranteed against moderate or even against, severe, washing. _Fast Colors on Silk._—There are two grades of fastness known to the dyers—“fast” and “embroidery fast.” “Fast” means simply that the silk is to be dyed fast to ordinary, careful handling so that the colors will not bleed or run in a warm or even hot soap bath, but does not guarantee them against every possible maltreatment. The best way of doing this is by the use of the Direct Cotton or Salt dyes, described in Chapter III, which, it will be remembered, only dye wool or silk at a high temperature, at or near the boiling point and, preferably, in an acid bath, but, when once on, are very hard to dislodge. The selected ones are very fast to light and present a great range of bright, attractive colors, which are nearly, if not quite, as brilliant as those produced by the Acid dyes.