Silk is often weighted in the finishing process with sugar and some with dyes and metals. This is because silk has a property which enables it to absorb a great deal of moisture without changing its quality. The manufacturer can buy salts and dyes for less than silk, and so he often uses a large per cent of dye or metal in place of the gum washed out of the silk in manufacture. One can seldom find to-day silks like our grandmothers used to use. This is because people wish cheap silks; the manufacturer cannot produce silks for little money, as the raw fiber is so high; and so he uses other things with silk to weight it. Materials are also adulterated by _combination_ with other materials. Did you ever buy a handkerchief marked "pure linen" and discover it was a mixture of cotton and linen? Cotton is also used to adulterate woolen materials, and sometimes silk materials; "pure silk" so called, is often artificial silk. [Illustration: FIG. 143.--One can sometimes test materials by burning.] Adulteration is also practiced when made-over materials or waste is used to cheapen the cost. We learned about this in studying about wool. Wool materials should be labeled so that the purchaser will know. It is not fair to pay the price for an all-new wool material if shoddy and mungo and flocks, which are all old wool and waste, have been used. The per cent of new wool should be told and the price made accordingly. Silk is sometimes sold as reeled silk when waste from cocoons which is called spun silk has been used for the woof or filling thread. In _finishing_ of materials, adulteration is sometimes practiced. In pressing cotton or linen, a luster is given to the surface. Cotton can be made to appear like silk or like linen, and is often sold for those fibers. Cotton can be napped in finishing and made to look woolly as in blankets or outing flannel, but it is still only cotton. [Illustration: FIG. 144.--The microscope reveals many things.] =How can clothing material be tested?= These are the simple tests which the Pleasant Valley girls learned: =For sizing.= This is easy to identify. Pick at the surface with your nail, and the starch or sizing will easily come off. Hang a wet piece in the air and see how the gloss looks then. This sizing often conceals defects in the cloth. These can be seen if the material is thin, by holding it against the light. [Illustration: FIG. 145.--The test for fading.] =Burning tests.= The girls unraveled the fibers which Miss James gave them and tested wool, silk, cotton, and linen. They tried both warp and filling threads. They burned them with a taper. The animal threads (which are they?) burned slowly, charred, and smelled like burned feathers. Silk burns to an ash, except when weighted. Then it burns more slowly. When very heavily weighted, the flame does not burn readily and the form of the silk will remain. The vegetable fibers, cotton and linen, burn quickly and with a flame.