434 



INDEX 



Osborne, grades of particles, 124 

 Osmosis, temperature for, 298 

 Osmotic pressure, sugar solution, 



131 



Ox-bow lakes, 28 

 Oxidation, 20 



expansion caused by, 21 

 loss of organic matter by, 152 

 Oxygen, combustion in, determina- 

 tion of organic matter, 154 



Packing, subsurface in dry farming, 



247 



Pacific Coast Region, 107 

 Particles, colloid, size of, 130 



soil, and their separation, 123 

 arrangement of, 179 

 number of, 178 

 shape of, 178 

 size of, affecting hygroscopic 



moisture, 194 



Pastures, accumulations in, aid in 

 maintaining organic-matter 

 content, 160 



hold soil against erosion, 361 

 Patten, H. E., specific heat of soils, 



300 

 effect of moisture on specific 



heat, 300 

 Pearce, J. R., size of particles, 124 



chromic acid method, 154 

 Peat, filling lake, 29 



method of formation, 28 

 Peats, 114 

 Peaty loams, 114 

 Peorian interglacial stage, 48 

 Percolation, affected by atmospheric 



pressure, 219 

 by granulation, 218 

 by organic matter, 218 

 by physical composition of soil, 



217 



by roots of plants, 219 

 by shrinkage cracks, 219 

 by viscosity of water, 219 

 defined, 217 

 evaporation, rainfall, Rotham- 



sted, 220 

 large and small, effect of, on 



yield of wheat, 153 

 loss of, by water, in dry farming, 



242 



source of loss of water, 232 

 Pfeffer, osmotic pressure, sugar 

 solution, 131 



Phosphate, rock, and limestone, ef- 

 fect on growth of clo- 

 ver, 159 

 on wheat, 401 



Phosphorus, application of, aid in 

 producing organic matter, 159 

 forms of, acid phosphate, 402 

 basic slag, 402 

 bone meal, 400 

 compared, 402 

 rock phosphate, 400 

 in fertilizing materials, 405 

 Physical agencies of weathering, 12 

 analyses of loess and dust, 64 

 analysis, methods of, 124 

 aspirator. King's, 128 

 centrifugal, Bureau of 



Soils, 127 



elutriator, Yoder's, 128 

 churn elutriator, Hilgard's, 



126 



elutriator, Schone, 124 

 sieve, 124 

 subsidence, 124 

 systems of, 124 

 changes, source of soil heat, 294 

 character of soil changed by ero- 

 sion, 360 

 of water, 186 

 composition of soil in relation 



to bacteria, 321 

 affecting percolation, 217 

 of soils, varied, effect of, on 



porosity, 184 



condition of soil, effect of al- 

 kali on, 280 



or mechanical analysis, 123 

 properties of soils, chapter on, 



175 

 apparent specific gravity, 



175 

 arrangement of particles, 



179 



color, 176 

 internal area or surface, 



181 



odor, 177. 



number of particles, 178 

 porosity, 182 

 real specific gravity, 175 

 shape of particles, 178 

 weight, 1 76 



Pines growing on sand, 60 

 Placing of soil material, chapter 

 on, 27 . 



