75*.

Automobile tires, reason for wearing of, 80;
blow-outs of, 348.

Baking powder, chemical change by solution shown by, 349-350;
elements of which made, 367-368.

Baking soda, a common base, 356;
testing with litmus paper, 359;
neutralization of sour milk by, in cooking, 362;
carbon dioxid in, 366-367.

Ball bearings, used to diminish friction, 54-55.

Balloon, expansion of, 17-18, 109*;
reason for rising of, 26;
filling of, with hydrogen, 301-304*.

Barometer, use of, 280-285*.

Bases, substances called, 355-358;
litmus test for distinguishing from acids, 358-359;
neutralization of, by acids, 360-364.

Batteries, electric, 203-205*;
different kinds of, 205*-207*;
general principle of all, 206.

Bell, electric battery for ringing, 204-205*;
working of electric, 255*.

Bending of light (refraction), 136-141*.

Black, the absence of light, 164.

Bleaching, process of, 326-327.

Blow-out of tire, a real explosion, 348.

Blue-flame heaters, 319.

Blueness of sky, reason for, 169.

Blueprints, making of, 330-331.

Boiling and condensing, 107-115*.

Borax bead test, 371*-372*.

Brass, an alloy, 310.

Bread making, chemical action in, 365.

Breath, cause of visibility of, on cold days, 288, 289*.

Bronze, an alloy, 310.

Burning, explanation of, 308, 312-313.

Calcium chlorid, 114.

Camera, lens of, 143, 148;
human eye as a small, 151*-153;
explanation of, 327-332.

Capillary attraction, 36*-40;
difference between adhesion, cohesion, and, 47.

Carbon, in electric battery, 203-206;
resistance of, to electric current, 231;
an element, 293, 299;
one of chief elements in fuel, 315-316.

Carbon dioxid, in seltzer siphon, 17;
produced by joining of carbon with oxygen, 315;
combining of water and, by plants, 332-333;
releasing of, in baking powder, 349-350;
bubbling of, in effervescence, 365-366;
in soda water, springs, and baking soda, 366-367;
limewater test for, 375-376.

Carbonic acid gas, commercial name for pure carbon dioxid, 365-366.

Cat's hairs, static electricity in, 201.

Caustic soda, a common base, 356.

Center of weight, 30-33*.

Centrifugal force, 5, 72-74;
law of, 74-75.

Charcoal, production of, 316.

Charging water with carbon dioxid, 366.

Chemical analysis, 370-376.

Chemi