, 333-335;
a compound of, an essential in explosives, 347.

Pancakes, made from sour milk, 362.

Paper, carbon and hydrogen in, 315.

Paraffine, production of, 114.

Parallel circuits, 221-223*.

Peat, carbon and hydrogen in, 315.

Pencils, making arc light with, 233*-234*.

Periscope experiment, 134-135*.

Petroleum, gasoline and kerosene distilled from, 114.

Phonograph, working of, 177-178*.

Phosphorescence, cause of, 341-342.

Phosphorus, an element, 300;
meaning of name, 341.

Photographs, process of making, 327-332*.

Pitch of sound, explanation of, 185-188*.

Plants, light and the manufacture of food in, 332-333;
how oxygen is supplied by, 333-335.

Plating of metals, 336-339*.

Platinum, an element, 300.

Poles, positive and negative, 206-207.

Porcelain, used as insulator, 215.

Positive charges of electricity, 198-200.

Potassium, experiment with, 304.

Potassium chlorate, an essential in
explosives, 347.

Precious stones, formation of, 263-264.

Prism, refraction of light by, 136-140*;
separation of light into rainbow colors by, 162-163*.

Quicksilver. _See_ Mercury.

Radiation of heat and light, 122*-128.

Radium, an element, 300.

Rain, 275;
cause of, 278-280.

Rainbow, making a, on wall, 162*-163;
how formed, 170-171.

Reading glasses, 144*;
convex lens in, 150.

Red color of sky at sunset, reason for, 170.

Reflecting telescopes, 157.

Reflection of light, 129-135*.

Refraction of light, 136-141*.

Resistance, electrical, 229-232.

Retina of eye, 151*, 153.

Reverberation of sound, 183-185.

Ring around moon, cause of, 131.

Rock candy, how made, 267.

Rubber, used as insulator, 215.

Rusting of iron, 349.

Safety valves on steam boilers, 347.

Salt, reason for, in sea, 104-105*;
a compound, 308;
elements of, 310-311;
formed by hydrochloric acid and zinc, 351;
iron, formed by lemon juice on steel, 353;
acids and bases turned to water and, by combining, 361-362.

Salt water, litmus test of, 359.

Samson cells, 204.

Scattering of light (diffusion), 158-161*.

Seesaw, example of a lever, 57-58*.

Seltzer siphon, working of, 17.

Ships, reason for floating, 24*-26.

Shock, electrical, 214-215.

Short circuits and fuses, 240-245.

Silver, an element, 300;
plating of, 33