Ions, iv, 382, vii, 370, viii, 378; in electric batteries, vi, 133, vii, 247; number in air, i, 142-3; of solutions, viii, 120-4, 286-90; origin of name, 124; positive and negative, i, 142, vii, 247, 370 Iowa, glacial deposits, iii, 241; gypsum deposits, 376; loess deposits, xiv, 72; porous rocks beneath, iii, 114; soil of, xiv, 383; wells, iii, 118, 119, 125 Ireland, Alpine invasion, xvi, 49; coast formations, xiv, 24, 47, 249, 251, 257; continental island in character, 273; "Emerald Isle," 352; eskers and drumlins, 59, 60; former volcanoes, 318; Ice Age in, xv, 74; lakes of, xiv, 200; lava plateau of, 104; potato in, xiii, 218; rainfall in, xiv, 41, 352; scurvy and potato crop, x, 266; snakes in, xii, 217 Iridescence, cause of, xii, 245 Iridium, viii, 173, 383 Iridocytes, xii, 135 Iris, xiii, 22-3, 57 (fig.) Iris Family, xiii, 189 Irish, pre-Nordic, xvi, 49 Irish Language, xv, 162 Irish Potato, xiii, 218, 219 Irish School, of Medicine, x, 112 Irish Wakes, xv, 336 Iron, affinity strength, viii, 128; antiquity of use, v, 314-15; atomic weight of, viii, 180, 383; body use of, ix, 184, x, 256; cast and wrought, v, 316-17; cast and wrought, viii, 157, 158, 159; castings of, iv, 150; density of, 111; electrical conductivity, 283, vi, 77; electrical positiveness, 59; electrolytic refining, vii, 320; expansion on solidifying, iv, 150; expansion rate, 145-6; extraction from ores, viii, 271; fusibility, 384; galvanized, vii, 318-19, viii, 155-6, 273; heat conduction by, iv, 179; importance, v, 314, viii, 156; in blood, 354; in chlorophyll, xiii, 79-80; in earth's crust, iii, 308, viii, 19, 129, 192; in earth's interior, xiv, 11; magnetic, iv, 242, 243 (fig.); magnetization, 243, 245, 251, 287-8, vi, 35-6; melting point and requirements, iv, 162, 163; metallography of, viii, 273-4; meteoric, ii, 292; meteoric, in deep sea, iii, 55; ores and occurrence, 355-9, viii, 47, 130, 148, 156, 198; ores, profitable, 197; plant needs of, 337, 341; properties of, 126-7, 154; rusting, iii, 25, viii, 9, 13, 155-6; sheet tin, 161; shortness, hot and cold, iii, 356; sound velocity in, iv, 201; specific gravity of, 109, viii, 384; specific heat, 308; symbol, 383; test for, 287, 288-9; valences, 161, 189 Iron Age, xvi, 51; tools of, 47 Iron Compounds, viii, 160-1 Iron Industry, history, xvi, 174-6; processes in, v, 315-18, viii, 157-9, 273, 345 Ironing Machines, Electric, vii, 82-3 Iron Oxides, viii, 13, 156, 157; in pigments, 265; in rock decay, iii, 25, 27; in soils, iii, 28; removal in steel-making, v, 320; rock coloring due to, iii, 25-6, 27, 44 Iron Pyrites, iii, 335, viii, 156, 198; in wireless detectors, vii, 269