572. If you take the handle off a faucet, it is almost impossible to turn the valve with your fingers. 573. Sparks fly from a grindstone when you are sharpening a knife. 574. Violin strings are spoiled by getting wet. 575. The oxygen of the air gets into the blood from the lungs, although there are no holes from the blood vessels into the lungs. 576. You push a button or turn a key switch and an electric lamp lights. 577. A rubber comb, rubbed on a piece of wool cloth, will attract bits of paper to it. 578. People whose eyes no longer adjust themselves have to have "reading glasses" and "distance glasses" to see clearly. 579. When you look through a triangular glass prism, things appear to be where they are not. 580. Lye and hot water poured down a clogged kitchen drainpipe clear out the grease. 581. You can draw on rough paper with charcoal. 582. When little children get new shoes, the soles should be scratched and made rough. 583. You can get your face very clean by rubbing cold cream into it, then wiping the cold cream off on a towel or cloth. 584. Soft paper blurs writing when you use ink. 585. Water will flow over the side of a pan through a siphon, if the outer end of the siphon is lower than the surface of the water in the pan. 586. There is a loud noise when a gun is fired. 587. Colored cloths should be matched in daylight, not in artificial light. 588. Lamp chimneys are made of _thin_ glass. 589. When you sweep oiled floors, no dust flies around the room. 590. The ocean is salty, while lakes are usually fresh. 591. A glass gauge on the side of a water tank shows how high the Water in the tank is. 592. You burn your hand when you touch a hot stove. 593. Pounding a piece of steel held horizontally over the earth and pointing north and south will make it become a magnet. 594. When only one side of a sponge is in water, the sponge gradually gets soft all over. 595. If we breathe on a cold mirror, a fine mist collects on it. 596. Butter is kept in cool places. 597. Water will boil more quickly in a covered pan than in an open one. 598. Mucilage, glue, and paste all become hard and dry after being spread out on a surface for a while. 599. You cannot see things clearly through a dusty window. 600. In making fire grates it is necessary to have the bars free to move a little. APPENDIX A. THE ELECTRICAL APPARATUS