Oil the sweeper regularly about once a month by putting one drop of oil on the ball bearing on the hub of each wheel. Failure to oil carpet sweepers causes them to wear out quickly, to squeak, and to run hard. More oil than is needed only gathers dust and gums the sweeper. Empty the sweeper (Fig. 102) each time it is used, even during the sweeping if necessary. Don't fill it to overflowing. Always open the pans by pressing on the dump levers, not by taking hold of the pans. Don't let the brush get tangled with hair, ravelings, etc. Take it out occasionally and clean it (Figs. 103 and 103-_a_). Cut along between the spiral rows of bristles with a sharp knife or shears, and the ravelings and hairs can be picked or combed out easily without injuring the brush (Fig. 104). Never try to pull them off whole. Also remove any accumulation of dirt or ravelings which catch in the wheels or bearings. Don't let dirt collect in any part of the machine. Keep it clean. Good sweepers work best without extreme pressure on the handle. Never put oil, water or any liquid on the bristles. Don't keep a sweeper on a warm-air register--it takes the life out of the bristles. [Illustration: FIG. 102. Emptying sweeper.] [Illustration: FIG. 103. Releasing brush in sweeper.] [Illustration: FIG. 103-_a_. Details of construction of carpet sweeper.] [Illustration: FIG. 104. Cut ravelings from brush.] [Illustration: FIG. 105. Mop wringer.] [Illustration: FIG. 106. Another type of mop wringer.] =191. Mop Wringers.= There are two kinds of mop wringers to attach to pails. One is made of two flat surfaces which, when pressed together with the mop between (Fig. 105), squeeze the water out of it, and the other is made of two wringer rollers which, when brought together by a lever after the mop is put between them, rotate as the mop is pulled upward and wring out the water (Fig. 106). QUESTIONS FOR PART VII 1. How do vacuum cleaners pick up dust? 2. Describe some type of vacuum cleaner. 3. What care should be given a vacuum cleaner? 4. Tell how to clean a carpet sweeper. PART VIII DEVICES FOR PREPARATION AND CONSERVATION OF FOOD CHAPTER XXVII POTS, PANS, AND OTHER DEVICES =192. Materials from Which Utensils Are Made.= Since there is considerable choice in utensils made from different materials, the housekeeper may like to know something about these materials and about their care, and the effect of acids and alkalis upon them. Russia iron is one of the older materials for pots and pans, and it still holds a place in cookery, for it makes bread, loaf cake and cooky pans, which give to the food a thin, brown crust, due, undoubtedly, to the way in which it conducts heat. (See tables on page 158.)