r 51C5 \qriculture T' '^^ m I > f + X . .'jlti XH*.> iS^i* -:<: r '-< - BIO-AGRICULTURAL LIBRARY UNIVERSITY OF CALIFORNIA RIVERSIDE, CALIFORNIA 92502 tm/ _ *- i P i>< , M rj :^ &.fm A TEXT BOOK PHYSICS OF AGRICULTURE BY F. H. KING Formtrly Professor of Agricultural. PhysL in/fffJlMverslty of Wisconsin Author of "The Soil;" "Irrigation and Drainage;" "Principles and Atovemedts of Ground Water" THIRD EDITION LIBRARY UNIVERSITY OF CALIFORNIA CITRUS EXPdMENT STATION MADISON, Wis. PUBLISHED BY THE AUTHOR 1904 All rights reserved CorrEiGHT, 1899 Bx F. H. KING PREFACE. The great need of agricultural practices at the present time is a keener appreciation and a more thorough com- prehension of the principles which underlie them. The facts of agriculture are spread through so many and widely different fields, and are so numerous, that no one can hope to grasp them all or needs to do so. But the laws and principles which control Ms practice each farmer must know before he can secure his re-suits with the greatest cer- tainty and at the least cost. In these pages the aim has been to present to the student who expects to be a farmer, some of the fundamental prin- ciples he must understand to become successful. They are presented from the standpoint of physics rather than of chemistry or of biology, and in dealing with the physical side of the problems the burden of effort has been to lead the student to see WHY he should practice more than WHAT, and it is hoped the student will pursue the various subjects treated in this spirit, not only in his study, but above all on the farm and in the field. The book has been written from the standpoint of the general student and farmer rather than that of more tech- nical scientific agriculture and only so much of laboratory methods and specific data of observation are given as may serve to demonstrate the fundamental principles treated. F. H. KING. University of Wisconsin, Madison, Wis., May, 1901. CONTENTS. INTRODUCTION. rum. MATTER AND FORCB 6 MOLECULAR CONSTITUTION OF BODIES 6 Distance between molecules, p. 7 ; Motions, p. 8 ; Size, p. 9 ; Rela- tion to fertilizers, p. 11 ; to poisons, p. 12 ; to odors, p. 13. How ODORS AND FLAVORS FIND THEIR WAY INTO MILK 14 Enter during secretion of milk, p. 14 ; Influenced by feed, p. 15 ; From the air. p. 15 ; Introduced with solids, p. 16 ; Developed after drawn, p. 16. DEODORIZING MILK 16 Method, p. 16 ; Place, p. 17 ; Cooling, p. 17. WORK - 18 ENERGY 19 Conservation, p. 19 ; Source of the earth's energy, p. 20 ; Solar energy, p. 20 ; How it reaches the earth, p. 21 ; Amount, p. 22 ; Rate of transmission, p. 23 ; Kinds of waves, p. 23 ; Evapora- tion of water, p. 24 ; Chemical changes produced, p. 24. NATURE OK HEAT AND COLD 25 TEMPERATURE 25 Measurement, p. 25 ; Accuracy of thermometers, p. 26. UNITS OF WORK AND ENERGY 27 Foot-pound and foot-ton, p. 27 ; Horse-power, p. 27 ; Unit of heat, p. 28. SPECIFIC AND LATENT HEAT 29 Melting of ice, p. 31 ; Evaporation of water, p. 31 ; Cooling by evaporation, p. 32 ; Effect of rain and snow on domestic ani- mals, p. 33 ; Cooling milk, p. 34 ; Heat used in melting and evaporating, p. 35. SUBFACH TENSION, SOLUTION AND OSMOSIS 36 Rise of water in capillary tubes, p. 37 ; Evaporation and solution, p. 38 ; Diffusion, p. 40 ; Osmosis, p. 41 ; Osmotic pressure, p. 42 ; Osmosis In plant feeding, p. 46 ; Dissociation of salts in solu- tion, p. 48. PHYSICS OF THE SOIL. CHAPTER I. NATURE, ORIGIN AND WASTE OF SOIL. BOILS AND SUBSOILS 49 USES OF SOIL 50 FORMATION OF SOIL 51 Influence of rock texture, p. 51 ; Rock fissures, p. 53 ; Running water, p. 54 ; Glaciers, p. 57 ; Humus soil, p. 61 ; Wind-formed, p. 63 ; Animals, p. 64. Contents. v CHAPTER IL CHEMICAL AND MINERAL NATURE OF SOILS. PAGH. ESSENTIAL CONSTITUENTS OF A FERTILE SOIL 69 FUNCTIONS OF ESSENTIAL PLANT POODS 70 CHEMICAL COMPOSITION OF SOILS 71 Difference between clayey and sandy, p. 71 ; Differences due to texture, p. 72 ; Between soils and subsoils, p. 72 ; Between clay and humus, p. 73 ; Between clay and loess, p. 73 ; Between arid and humid, p. 73 ; between soil and rock, p. 77. HUMUS , 76 Of arid and humid climates, p. 7C. PLANT FOOD 79 Amount removed from soil by crops, p. 79 ; Amount in soil, p. 79 ; Number of crops produced, p. 80 ; Rothamstead experiments, p. 81. NITROGEN IN THE SOIL 82 Amount in Manitoba soils, p. 82 ; Forms of occurrence, p. 83 ; Dis- tribution in soil, p. 83 ; Amount as nitric acid, p. 84. SOURCES OF SOIL NITROGEN 85 Of humic nitrogen, p. 85 ; Symbiosis, p. 87 ; Observations of Wlno- gradsky and Berthelot, p. 88. NITRIFICATION 89 DHNITUIFICATION 89 CHAPTER III. SOLUBLE SALTS IN FIELD SOILS. SOLUBLE SALTS IN FIELD SOILS 92 Amount, p. 92 ; Amount limiting plant growth, p. 93 ; Mode of action on plants, p. 93 ; Concentration in Zones, p. 94 ; Origin, p. 94 ; In marsh soils, p. 95. LEACHING NECESSARY TO FERTILE SOILS 95 Correction of alkali lands, p. 95 ; Drainage ultimate remedy, p. 98 ; Tillage helpful, p. 98. CHANGES IN AMOUNT OF SOLUBLE SALTS 98 With season, p. 98 ; with different crops, p. 99. NITRATES 101 Relation to total salts, p. 101 ; Closeness of plant feeding, p. 101 ; Limits at which plants turn yellow, p. 102 ; In fallow and cropped ground, p. 103 ; Loss during winter, p. 104 ; Influenced by cultivation, p. 105. PHYSICAL EFFECTS OF SOLUBLE SALTS 106 On movements of soil moisture, p. 106 ; On surface tension, p. 106 ; On evaporation, p. 100 ; On viscosity, p. 106. ri Contents. CHAPTER IV. PHYSICAL NATURE OF SOIL. PAGE. TBXTURB OF Son, 108 Size of soil grains, p. 108 ; Size of soil kernels, p. 110. POKE SPACE IN SOIL Ill Determines maximum water capacity, p. 114 ; Influences rate of percolation, p. 115 ; Method of measuring, p. 115 ; Largest possi- ble, p. 116. INTERNAL SURFACE OF SOILS 118 Amount per gram and sq. ft., p. 118 ; Determination, p. 115). EFFECTIVE DIAMETER OF SOIL GRAINS 121 Method of determination, p. 121 ; Flow of fluids computed from, p. 123 ; surface computed from, p. 124. WEIGHT OF SOILS 127 CHAPTER V. SOIL MOISTURE. CONDITIONS OF SOIL MOISTURE 129 Gravitational, p. 329; Capillary, p. 130; Hygroscopic, p. 130. WATER CONTENT OF SOILS 131 Ways of expressing, p. 131 ; Maximum capacity of field soils, p. 131; Capillary capacity, p. 132; Influence of distance above standing water on capacity, p. 134. SOIL MOISTURE AVAILABLE TO CROPS 135 Soils which yield moisture most completely, p. 13G ; Relation of thickness of moisture film to per cent, of water, p. 137 ; Af- fected by jointed structure, p. 138 ; Increased by open struc- ture, p. 138 ; By drainage, p. 139. AMOUNT OF WATEB REQUIRED BY CROPS 13 For different yields of wheat, p. 140 ; Least amount for different crops, p. 141. CHAPTER VL PHYSICS OF PLANT BREATHING AND ROOT ACTION. MECHANISM AND METHOD OF TRANSPIRATION 112 Breathing of plants and animals, p. 142 ; Respiratory organs In plants, p. 142 ; Breathing pores, p. 143 ; chlorophyll cells, p. 143 ; Guard cells, p. 143 ; Their action, p. 144 ; Loss of water through, p. 145. STRUCTURE AND MODE OF ROOT ACTION 145 Functions of roots, p. 145 ; Absorbing portion, p. 146 ; structure of root hairs, p. 147 ; Relation to soil grains, p. 147 ; Method of gathering water, p. 147 ; Advance through soil, p. 148 ; Ex- tent of root development, p. 150 ; Total root of plants, p. 157. Contents. vii CHAPTER VII. MOVEMENTS OF SOIL MOISTURE. PAQH. GRAVITATIONAL MOVEMENTS 158 Percolation, p. 158 ; Rate through sand, p. 159 ; Through scil, p. 159 ; Through dry soil, p. l(iO. CAPILLARY MOVEMENTS 161 Rise in capillary tubes, p. 161 ; Rise in soils, p. 163 ; Observed bight in moist soil, p. 165 ; Measurement of maximum liight, p. 167 ; Rate of rise in wet soil, p. 168 ; In dry soil, p. 168 ; In- fluenced by rain, p. 170 : L>y farmyard manure, p. 172 ; By mulches, p. 173 ; By firming the soil, p. 174. THERMAL MOVEMENTS 175 Hygroscopic soil moisture, p. 175 ; Movements, p. 175 ; Relation to size of soil grains, p. 176 ; Amount a soil may absorb, p. 178 ; Internal evaporation, p. 179. CHAPTER VIII. CONSERVATION OF SOIL MOISTURE. MODES OF CONTROLLING SOIL MOISTURE 181 Late fall plowing, p. 181 : Late tillage for orchards, p. 182 ; Early fall plowing, p. 182 ; Early spring plowing, p. 183 ; Ef- fectiveness of mulches, p. 185 ; Frequency of cultivation, p. 187 ; Cultivation after rains, p. 190 ; Depth of cultivation, p. 191 ; Depth and frequency vary with the season, p. 191 ; Early harrowing of corn and potatoes, p. 192 ; Harrowing and rolling small grain after it is up, p. 192 ; Mulches other than soil, p. 193. SUBSOILING TO SAVE MOISTURE 195 Increases water capacity, p. 198 ; decreases capillarity, p. 199 ; Favors percolation, p. 199 ; More of water available, p. 200. DANGER FROM GREEN MANURING 201 WIND-BREAKS AND HEDGES 202 CHAPTER IX. RELATION OF AIR TO SOIL. NEEDS OF SOIL VENTILATION 204 Needs of free oxygen, p. 204 ; Fixing of free nitrogen, p. 206. PROCESSES OF SOIL VENTILATION 207 By diffusion, p. 207 ; By changes of soil temperature, p. 2^7 : Pr changes of barometric pressure, p. 208 ; By wind suction, p. 208 ; By rains, p. 209. WAYS OF INFLUENCING SOIL VENTILATION 209 Modified by tillage, p. 209 ; Reduced by rolling, p. 210 ; Increased by drainage, p. 210 ; Modified by vegetation, p. 211. Contents. CHAPTER X. SOIL TEMPERATURE. PAGE. TEMPERATURE AT WHICH GROWTH BEGINS 212 BEST SOIL TEMPERATURE 212 Influence on rate of germination, p. 214 ; Effect on root pressure, p. 215 ; On the formation of nitrates, p. 215. CONDITIONS INFLUENCING SOIL TEMPERATURE 215 Specific heat of soil, p. 215 ; Moisture In soli, p. 216 ; Color of soil, p. 217 ; Topography, p. 218 : Texture of surface, p. 218 ; Tillage, p. 219 : Chemical changes, p. 219 ; Rains and percolation, p. 219 ; Rate of evaporation, p. 220. MEANS OF CONTROLLING SOIL TEMPERATURE 221 Rolling, p. 221 ; Early thorough tillage, p. 222 ; Thorough drainage, p. 222. CHAPTER XI. OBJECTS, METHODS AND IMPLEMENTS OF TILLAGE. OBJECTS OF TILLAGE 223 TILLAGE TO DESTROY WEEDS 223 Best time, p. 224; Best tools, p. 225; For early killing, p. 225; For Intertillage. p. 226. TILLAGE TO MODIFY TEXTUBE 231 Soil texture and tilth, p. 231 ; Importance of good tilth, p. 233. I low TEXTURE AND TILTH ABB DEVELOPED 233 The uses of harrows, p. 234 ; The planker. p. 236 ; The roller, p. 237 ; The plow, p. 238 ; How may puddle soils, p. 239 ; May correct texture and improve tilth, p. 239. FOBMS OF PLOWS 239 Must be adapted to the soil, p. 240 ; Sod plow, p. 241 ; Pulverizing plow, p. 242 ; Mellow soil plow, p. 242. DBAFT OF PLOWS. . .- 243 English and American trials, p. 243 ; Draft of sod plow with and without coulter, p. 243 ; Sod compared with stubble plow, p. 244 : Influence of moisture on draft, p. 244 ; Draft of sulky plow, p. 245 ; Line of draft, p. 246 ; Scouring of plows, p. 247. CARE OF PLOWS 247 When not in use, p. 247 ; Keeping in form, p. 247. SUBSOIL PLOW 250 OBJECTS, METHODS AND TIMES OF PLOWING 250 Depth of plowing, p. 250 ; Best condition of soil for, p. 251 ; Treat- ment after plowing, p. 252 ; Plowing for corn in the fall, p. 252 ; Plowing sod, p. 252 ; Plowing under manure, p. 253 : Plow- Ing under green manure, p. 253 ; Early fall plowing, p. 254. Contents. ix GROUND WATER, WELLS AND FARM DRAINAGE. CHAPTER XII. MOVEMENTS OF GROUND WATER. PAGB. AMOUNT STORED IN GROUND 255 Ground water surface, p. 258 : Seepage, p. 258 ; Growth of streams, p. 259 : Rise of ground water through precipitation, p. 260 ; Law of flow through sands, p. 262 ; Calculation of flow, p. 262 ; Observed and computed flow, p. 264 ; Relation of rate of flow to diameter, p. 266 ; Relation of pressure to flow, p. 266 ; Observed rates of flow in sand and rock. p. 268 ; General movements across wide areas, p. 270. FLUCTUATIONS IN THE RATE OF FLOW OF GROUND WATER 270 Due to barometric changes, p. 270 ; In springs, p. 270 : In rate of discharge from tile drains, p. 271 ; Change of level In wells, p. 272 ; Due to changes in soil temperature, p. 271. CHAPTER XIII. FARM WELLS. ESSENTIAL FEATURES OF A GOOD WELL 275 Capacity, p. 275 ; Best geological conditions, p. 276 ; Depth, p. 283. CONDITIONS INFLUENCING CAPACITY 276 Size of grains and pore space, p. 276 : Depth in water-bearing beds, p. 278 ; Pressure, p. 279 ; Diameter of well, p. 279. USB OF SAND STRAINERS 281 Capacity, p. 281 ; Compared with open well, p. 282. TEMPERATURE OF WELL WATER 284 WELL CASINO AND TOP 284 CHAPTER XIV. PRINCIPLES OF FARM DRAINAGE. NECESSITY FOR DRAINAGE 28b CONDITIONS REQUIRING DRAINAGE 287 ADVANTAGE OF DRAINAGE 287 Increases root room. p. 287 : Increases available moisture, p. 288 ; Makes soil warmer, p. 288 ; Better ventilation, p. 290. TILE DRAINS 290 Essential features of drain tile, p. 291 ; How water enters tile, p. 292 ; Collars, p. 292 ; Depth laid, p. 292 ; Distance between tile drains, p. 296. CONFORMATION OF GROUND WATER ABOUT DRAINS 294 Rise away from drains, p. 293 ; Observed ground water surface, p. 296 ; Rate of change of surface, p. 297. Contents. PAGE. MOVEMENT OP DRAINAGE WATER 298 Heavy clay underlaid with sand, p. 298 ; Gradient, p. 298 ; Silt basin, p. 299 ; size of tile, p. 299 ; Practical illustration of sizes and lengths, p. 301 ; Outlets, p. 302 ; Joining laterals with mains, p. 303 ; Obstructions, p. 303. LAYING OUT DRAINS 304 SURFACE DRAINAGE 306 Construction, p. 306 ; Intercepting underflow, p. 307 : Basins with- out outlets, p. 307. Lands requiring surface drainage, p. 309. CHAPTER XV. PRACTICE OF UNDERDRAINAGB. DETERMINING LEVELS 312 Instruments, p. 312 ; Method of leveling, p. 313 ; Contour map, p. 315 ; Locating mains and laterals, p. 315 ; Determining grade, p. 317 ; Changing from one grade to another, p. 319. DIGGING THE DITCH 321 Ditching tools, p. 321 ; Width of ditch, p. 322 ; Bringing bottom to grade, p. 322; Placing tile, p. 324; Filling the ditch, p. 328. PRINCIPLES OF RURAL ARCHITECTURE. CHAPTER XVI. STRENGTH OF MATERIALS. STRENGTH OF POSTS 329 Stress, p. 329 ; White pine pillars, p. 330. TBANSVERSE STRENGTH 331 Tensile strength, p. 331 : Principles, p. 331 : Proportional to squares of depth, p. 332 ; Relation to length, p. 334 ; Break- Ing constants, p. 335 ; Computing loads, p. 336 ; Rafters, p. 337 ; Safe loads for horizontal beams, p. 337 ; Selection of lum- ber, p. 338. BARN FRAMES 338 Braces, p. 338 : Constructing timbers from 2-inch lumber, p. 339 ; Forms of frames, p. 339 ; Plank frame, p. 340 ; Balloon frame, p. 340 ; Cylindrical frame, p. 341. CHAPTER XVII. WARMTH, LIGHT AND VENTILATION. CONTROL OF TEMPERATURE 343 Normal animal temperatures, p. 343 : Best stable temperature, p. 344; Solid masonry walls, p. 346; Hollow masonry walls, p. 347; Brick veneered \\alls, p. 347; All wood walls, p. 348. Contents. xi PAGE. LIGHTING FARM. BUILDINGS 348 Efficiency of windows, p. 348 ; Position of windows, p. 349. VENTILATION OF FARM BUILDINGS 350 Necessity for ventilation, p. 350 ; Carbon dioxide, p. 350 ; Mois- ture from lungs and skin, p. 350 ; Ammonia and organic mat- ter, p. 351 ; Micro-organisms and dust, p. 352 ; Bad ventila- tion predisposes to disease, p. 352. AMOUNT OF AIK REQUIRED 353 Amount respired, p. 353 ; Degree of impurity permissible, p. 354 ; Rate of supply, p. 354. CONSTRUCTION OF VENTILATORS 355 Capacity of flues, p. 355 ; Forces producing ventilation, p. 358 ; es- sential features, p. 358: Location, p. 359; Place of openings, p. 360 ; Introduction of fresh air, p. 362 ; Construction, p. 363 ; Ventilation of basement stables, p. 364. CHAPTER XVIII. PRINCIPLES OF CONSTRUCTION. RELATION OF COVERING TO SPACE ENCLOSED 366 Relation of walls to floor space, p. 366; Relation of bight to ca- pacity, p. 367 ; Combined and separate construction, p. 370 ; Saving of labor, p. 372. STABLE FLOORS 374 Essential features, p. 374 ; Cold and warm floors, p. 375 ; Use of bedding, p. 376 ; Wood floors, p. 377 ; Making wood floors water- tight, p. 377 ; Stone floors, p. 378 ; Macadam floors, p. 378 ; Macadam for barn yard, p. 379. CONSTRUCTION OF CEMENT FLOORS AND WALKS 379 Kinds of cement, p. 379: Cement concrete, p. 379; Materials, p. 380 ; Wetting crushed rock. p. 380 ; Ratio of ingredients for concrete, p. 381 ; For finishing, p. 381 ; Thickness, p. 382 ; Making and laying, p. 382. CATTLE TIES 384 Stanchions, p. 384; Adjustable stalls, p. 385; Movable halter ties, p. 387. MANGERS 388 MANURE DROPS 3SS PROVISIONS FOR WATERING 388 Watering in bain, p. 388 ; Storing water in tanks, p. 389 ; Water- ing trough, p. 390. ARRANGEMENTS FOB UNLOADING HAT 391 CHAPTER XIX. CONSTRUCTION OF SILOS. CONDITIONS ESSENTIAL FOR PRESERVING SILAGE 394 Depth, p. 394 ; Rigid walls, p. 394 ; Protection against frost, p. 396. xii Contents. PAG*. CONSTRUCTION OF STONE SILOS 397 Laying walls, p. 397 ; Plastering, p. 398 ; Doors, p. 309. CONSTRUCTION OF BRICK SILOS 400 Foundation, p. 400 ; Walls, p. 402 ; Tie- rods, p. 402 ; Making walla air-tight, p. 402 ; Doors, p. 403. CONSTRUCTION OF BRICK-LINED SILOS 403 Foundation and sill, p. 405 ; Setting studding, p. 405 ; Sheeting, p. 405; Siding, p. 406; Lining, p. 406. LATHED AND PLASTERED SILOS 407 CONSTRUCTION OF ALL WOOD SILOS 409 Foundation, p. 409 ; Cementing bottom, p. 410 ; Sills and studding, p. 410; Sheeting and siding, p. 412; Plate, p. 413; Lining, p. 413; Roof, p. 417; Ventilation, p. 417; Painting lining, p. 418. STAVE OR TANK SILO 418 Construction, p. 420 ; Staves, p. 422 ; Foundation, p. 422 ; Hoops, p. 422 ; Doors, p. 423. PIT SILOS 423 DIMENSION OF SILOS 424 Weight of silage, p. 424 ; Capacity of silos, p. 424 ; Horizontal feeding area, p. 425. DANGER IN FILLING SILOS 427 FARM MECHANICS. CHAPTER XX. PRINCIPLES OF DRAFT. How THB DRAFT INCREASES WITH THE GRADE 428 Experimental demonstration of influence of grade on draft, 429. THE MECHANICAL PRINCIPLE INVOLVED IN THE RELATION OF DRAFT TO GRADE 430 THE STEEPEST GRADE ADMISSIBLE 430 GOOD ROADS MAKE HIGH GRADES MORE OBJECTIONABLE 433 DRAFT OF WAGONS ON THE LEVEL 434 The smoothness of the road-bed, p. 434 ; Rigidity of the road-bed, p. 434 ; Draft of wagons shown by English trials, p. 436 ; Draft with different widths of tire, p. 436 ; Size of the carriage wheel, p. 437 ; Distribution of load on the carriage, p. 438 ; Heaviest load on the hind wheels, p. 439 ; Direction of the line of draft, p. 440 ; Line of draft on road wagon, p. 441 ; Rigidity of the carriage, p. 442 ; Results of Gen. Morin's experiments in France, p. 443. CHAPTER XXI. CONSTRUCTION AND MAINTENANCE OF COUNTRY ROADS. ESTABLISHING THE GRADE 444 FACTORS TO BE CONSIDERED IN ESTABLISHING THE GRADE 444 Contents. xiii PAOK. EOAD DRAIN-AGE 445 The relation of water to roads, p. 446 ; Depth of under-drainage, p. 446 ; Place for the drain, p. 447 ; Fall of the drain, p. 447 ; Outlet of the drain, p. 448; Size of tile p. 448; Kind of tile, p. 448 ; Surface drainage, p. 448 ; Slope of the road surface, p. 449 ; Water-breaks, p. 449. TEXTURE OF ROAD MATERIALS 450 Roads should be built in layers, p. 450 ; Uniformity of size of ma- terial used, p. 451 ; Shape of fragment, p. 451 ; Cleanness of material, p. 452. EARTH ROADS 452 Forming the road-bed, p. 452 ; Utilizing the old road as a road bed, p. 455 ; Preparing the road-bed a year or more in advance, p. 455 ; Roads on gravelly loam, p. 455 ; Roads in fine clay soil, p. 455 ; Clay roads surfaced with gravel, p. 456 ; Sandy roads, p. 456 ; The use of straw, saw dust and tan bank on sandy roads, p. .457 ; Road gravel, p. 457 ; Clean white gravel not suit- able, p. 458 ; Texture of gravel altered by crushing and screen- ing, p. 458 ; Some gravels contain too much clay, p. 459 ; Gravel roads, p. 459 ; Roads in swainpy places, p. 460. STONE ROADS 461 Macadam roads, p. 462 ; Construction of macadam roads, p. 462; Fitting the road-bed, p. 463; Forming the shoulders, p. 463; Kinds of rock for the road, p. 464 ; Foundation and surfacing stone may be different, p. 466 ; Sorting boulders before crush- Ing, p. 466 ; Using limestone for binding, p. 466 ; Roads made without binding material, p. 467 ; Use of sand for binding, p. 467 ; Limestone for stone roads, p. 469 ; Spreading the rock on the road-bed, p. 470 ; Thickness of layer, p. 473 ; Rolling, p. 473 ; Size and weight of roller, p. 473 ; Amount of rolling, p. 474 ; Manner of rolling, p. 475 ; Kind of roller, p. 475 , Rock crusher, p. 475 ; Revolving screen, p. 477 ; Earth and stone roads combined, p. 477 ; Telford foundation, p. 478 ; Cul- verts, p. 479. MAINTENANCE OF COUNTRY ROADS 480 Section men necessary, p. 480 ; Road master, p. 481 ; Width of tires controlled, p. 481 ; Maintenance and repairs, p. 482 ; Good maintenance, p. 482 ; Maintenance of earth and gravel roads, p. 483. CHAPTER XXII. FARM MOTORS. FARM MOTORS 486 ANIMALS AS MOTORS 487 The horse as a motor, p. 487 ; Muscles are motors, p. 487 ; Strength of muscles, p. 488 ; Need of great muscular strength, p. 489 ; Rate at which a horse can generate energy, p. 489 ; Horse power required to haul loads on a wagon, p. 490 ; horse power re- quired to plow, p. 491 ; Increased speed diminishes the traction power, p. 491 ; Diminishing the number of hours per day in- creases the power of traction, p. 492. xiv Contents. PAOK. PRINCIPLES UNDERLYING THE DRAFT OF THE HORSE 492 Direction of the line of draft, p. 492 ; Influence of weight on the draft of the horse, p. 493 ; Influence of the distribution of weight on the draft of a horse, 494 ; Influence of the strength of the hock muscle on the draft of a horse, p. 494 ; Influence of the width of the hock on the draft of the horse, p. 495 ; Attachment of the traces to the hames at the shoulder, p. 496 ; Two-horse evener, p. 49ti ; Giving one horse tne advantage, p. 498 ; Three-horse equalizer, p. 499. THE TREAD POWER 499 Working the horse in the tread power, p. 500. THE SWEEP POWEB 501 STEASI ENGINES 502 Principle of action in the steam engine, p. 502 ; Efficiency of the steam engine, p. 503 ; Pressure of steam at different tempera- tures, p. 504 ; Dry and wet steam, p. 504 : Causes of water in the cylinder of an engine, p. 505 ; Wetness of steam from the boiler, p. 505 ; Wetness due to condensation in steam pipes and valve chest, p. 506 ; Initial condensation, p. 506 ; Condensation due to work during expansion, p. 507 ; Engine boilers, p. 508 ; Construction of steam boilers, p. 509 ; Gage cocks, p. 510 ; Gage glass, p. 510; Pressure gage, p. 511; Safety valve, p. 511; Care of the boiler, p. 512; Firing, p. 513; Foaming, p. 513; Low water in the boiler, p. 514 ; Soft plug, p. 514 ; Water sup- ply, p. 515 ; Cross-head pump, p. 515 ; The injector, p. 515 ; Boiler incrustation, p. 517 ; The engine, p. 518 ; Governor, p. 521; Lubricator, p. 521; Fly wheel, p. 522. GASOLINE ENGINES 522 Gasoline and steam engines contrasted, p. 523 ; Principal parts of a gasoline engine, p. 523 ; The working cycle, p. 523 ; Arrange- ments to prevent over-heating, p. 524 : Types of gasoline en- gines, p. 524 ; Cylinder, p. 525 ; Pumping mechanism, p. 525 ; Governor, p. 526 ; Valve mechanism, p. 528 ; Igniting the charge, p. 529 ; Lubrication, p. 529 ; Gasoline, p. 530 ; Size of engine, p. 530. WINDMILL 530 Work to which the wind mill is adapted, p. 531 ; Wind pressure, p. 532 ; Relation of wind pressure to wind velocity, p. 532 ; Ability of wind to do work, p. 533 ; Relation of diameter of wheel to Its efficiency, p. 533 ; Unsteadiness of wind velocity, p. 534 ; Hight of towers, p. 534 ; Observed amount of work done by a windmill in pumping water, p. 535 ; Observed amount of work done by a windmill In grinding feed, p. 536. Contents. xv CHAPTER XXIIL FARM MACHINES*. PAGE. FRICTION , -. 538 Friction between solids, p. 538 ; Friction of rest or static friction between solids, p. 539 ; Friction of motion between solids, p. 539 ; Rolling friction, p. 540 ; Friction between liquids, p. 540 ; The action of lubricants, p. 541 ; Adaptation of lubricant to place of service, p. 541 ; Scrupulous cleanliness of bearings, p. 542 ; Hot boxes, p. 543. BELTI NG 543 Action of belting, p. 543 ; Efficiency of belting, p. 543 ; Size of belt for transmission of given horse power, p. 544 ; Condition of belt, p. 544 ; Pulley and shaft, p. 545 ; Lacing a belt, p. 545 ; Calculating the lengths of belts, p. 546. FARM PUMPS 546 Suction pump, p. 546 ; Size of piston, p. 547 ; Rate of pumping, p. 548 ; Relation of size of suction and discharge pipe and pis- ton to power required to work the pump, p. 548 ; Influence of elbows on the power required to work a pump, p. 550 ; Double- acting suction pumps, p. 550 ; Proper place for the cylinder in the well, p. 551. HYDRAULIC RAM . 552 PRINCIPLES OF WEATHER FORECASTING. CHAPTER XXIV, THE ATMOSPHERE. RELATION TO THE EARTH 554 Interpenetration of the three spheres, p. 555 : Relation of the life zone, p. 555. ATMOSPHERE 556 Depth, p. 556 ; Composition, p. 556 ; Materials mechanically sus- pended, p. 557. PARTS PLAYED EY THE DIFFERENT INGREDIENTS. ? 557 Oxygen, p. 557 ; Nitrogen, p. 558 ; Water, p. 558 ; Dust, p. 558 ; Carbon dioxide, p. 558. ATMOSPHERIC PRESSURE 559 Applications of pressure, p. 559. TEMPERATURE OF THE ATMOSPHERE . , 560 CHAPTER XXV. MOVEMENTS OF THE ATMOSPHERE. PRIMARY CAUSE OF WINDS 561 Contents. PAGE. GENERAL CIRCULATION OP THE ATMOSPHERE 562 World system of winds, p. 562 ; Wind zones, p. 563 ; Direction af- fected by form and rotation of the earth, p. 564 : Character of the winds, p. 564 ; Weather of the wind zones, p. 565 ; Shift- ing of the zones, p. 565. CONTINENTAL WINDS 568 Influence of continents on winds, p. 566 ; Winds of January, p. 567 ; Winds of July, p. 567 ; Monsoons, p. 570. OBDINARY STORMS 570 Cyclones, p. 570 ; Cause of wind directions, p. 570 ; Progressive movements, p. 572 ; Direction of movement, p. 574 ; Rate of progress, p. 574 ; Diameters, p. 574 ; Duration, p. 575 ; Region of precipitation, p. 575 ; Origin, p. 576. CHAPTER XXVL WEATHEB CHANGES. PBINCIPLES OF FORECASTING WEATHER CHANGES 578 Prevailing winds of locality, p. 578 ; Locating storm center, p. 579 ; Change of wind direction, p. 579 ; Direction of storm cen- ter, p. 579 ; Predicting the course of the storm track, p. 580 ; Temperature changes, p. 580 ; Barometric changes, p. 582. COLD WAVES 582 Forecasting warm and cold weather, p. 583. LONG WARM AND DRY PERIODS 583 TBOPICAL CYCLONES 585 THUNDER STORMS, HAIL STORMS AND TORNADOES 586 Relations to ordinary storms, p. 586 ; Tornadoes, p. 586 ; Schools of tornadoes, p. 588 ; Distribution of thunder showers, p. 588 ; Conditions of formation, p. 588 ; Formation of tornadoes, p. 589 ; Explosive violence of tornadoes, p. 590 ; Unsteady move- ment, p. 591 ; Character of tornado path, p. 591 ; Formation of thunder showers, p. 592 ; Formation of hail, p. 592. INTRODUCTION, 1. Physics. Briefly defined, physics is the science of Matter and Energy. It aims to measure and investigate the movements of or within any body, whether living or dead, endeavoring to show how the forces of nature operate upon or within the body to produce the phenomena associ- ated with it. If we were endeavoring to ascertain how much the sun weighs, how much energy in the form of heat and light is being sent out from it daily, or how this energy is pro- duced, our study would be one of Solar Physics. If we were measuring the diameter of the earth, or the volume of water in the oceans ; if we were endeavoring to ascertain how the forces have operated to uplift mountain ranges or to cut out deep canons or broad valleys, then our problem would be one of Terrestrial or Earth Physics. If we were measuring the strength of a horse; how many pounds of feed he must use to plow 10 acres of ground ; or endeavor- ing to show how the oxygen he breathes and the food he eats give rise to the energy of his muscles, our problem would be one of Animal Physics. If we were studying how the root forces its way through the soil ; how water is forced into and through the roots to the leaves on the tree or how the sunshine breaks down the carbon dioxide in the green chlorophyll, our problem would become one of Plant Phys- ics. If we are endeavoring to determine the dimensions of beams to use in a barn ; how heavy a rod to use in a truss or how to brace a building so that it may safely withstand tho pressure of the wind, then we are dealing with the Physics of Architecture. And so we might go on enumcr- 6 Introduction. ating every science and every art to show that there is a physics of each or a necessary treatment of them from the standpoint of mechanical principles of matter and energy. Physics, therefore, a broad science, is one of wide applica- tion and fundamentally important to the understanding of almost any concrete subject when treated from the stand- point of cause and effect. 2. Matter and Force. So far as we are at present able to comprehend, the various phenomena of nature are mani- festations of two classes of agencies, matter and force. The river flowing steadily toward the sea is a mass of matter urged continually onward by the force of gravitation. Coal and oxygen burning in the firebox of the locomotive are two forms of matter urged into motion by the force chemical affinity. The time-keeping watch is a mechanism of brass and steel kept in uniform motion by the force cohesion un- coiling the wound-up spring; and tLe capillary rise of oil in the lamp wick and of water through the soil are other movements of matter actuated by the same force. 3. Constitution of Bodies. All bodies or masses of mat- ter with which we are acquainted possess such properties as to make it appear that there is room in them not occu- pied by the essential material which makes up the body. They are made out of definite units which have been named molecules much as a bank of sand is composed of grains or as a sack of shot is filled with spheres of lead. The openness of structure of all bodies is a very impor- tant conception to have clearly in mind. It is this open- ness of structure which makes it possible for foul odors to be absorbed by milk or drinking water; for moisture to enter sprouting seeds ; for the food we eat to pass through the walls of the alimentary canal to enter the blood vessels and out of these again to the muscles and nerve centers. It is the openness of structure of the lung lining which per- mits the oxygen of the air to enter the system and the car- bonic oxide to escape from it ; and were it not for this struc- Constitution of Bodies. ture we could neither smell nor taste, for substances must penetrate these sense organs before the sensations are awakened. That there is unoccupied space in bodies which appear to have a close structure may be demonstrated with the ap- paratus represented in Fig. 1. The bottle is filled with water and into this is dropped a large crystal of some salt, as potassium ni- trate or sulfate, or 4 teaspoonfuls of granu- lated sugar. When this is done the rubber cork carrying the graduated glass tube is in- serted and crowded down until the water rises in the tube and stands at one of the graduation marks. If any change in volume occurs with the solution of the salt it will be shown by a rise or fall of the water in the tube where the amount of change can be read. The bottle is placed in a large vessel of water for the purpose of maintaining a con- stant temperature during the experiment. The molecules themselves are made up of smaller units which have received the name of atoms and the number of these atoms Fm ' 1- which enter into the construction of the molecule varies with the substance. In some substances the molecule con- sists of two atoms, as common salt, one of sodium and one of chlorine, while the water molecule contains three atoms, two of hydrogen and one of oxygen. In molecules of cane sugar there are forty-five atoms of three different kinds, carbon, hydrogen and oxygen, and there are many sub- stances having molecules more complex than those of sugar. 4. Distances Between Molecules Change With the Tem- perature of the Body. A bar of iron lengthens and shortens as its temperature rises and falls, and the wheelwright takes advantage of the fact to set the tires of the wagon. This change of volume with temperature is due to the fact that the mean distance between the molecules becomes 8 Introduction. greater the higher and less the lower the temperature is. From this it follows that ordinarily molecules are not in contact and that there is room in the interior of bodies, however compact they appear to be, not occupied by them. Observations with the ordinary mercurial thermometer prove the same general fact. As the temperature rises a portion of the mercury is forced out of the bulb into the stem showing that there is not room enough there for all of the mercury although the bulb has actually become larger. So, too, when the temperature falls the mercury again returns to the bulb although the bulb has itself be- come smaller than before. 5. Molecules of Bodies Always in Motion. It follows from what has been said in the last section that with every change of temperature in bodies their molecules move. The general fact is that the molecules of all bodies whose temperature is not absolute zero are in rapid" motion no matter whether the body be a solid, a liquid or a gas. The higher the temperature of the body the more rapidly do the molecules in it vibrate, the greater is their rebound after each collision and so the greater is the mean distance between them ; this is why most bodies expand with in- crease of temperature and contract when cooling. It is the fact of movement among molecules which causes the diffusion of sugar or salt through water after solution takes place, which causes the perfume of flowers to be constantly moving away from them, which gives solid camphor its odor and which causes snow and ice to evapo- rate at temperatures even below freezing. The elastic power of air in the bicycle tire is due to the rapid movement of the molecules and their frequent and hard collision against the walls. It is the same fact which gives the steam its power to drive the engine. The larger the amount of air which is pumped into the tire of the bicycle the greater is the number of collisions per square inch of surface per second and so the harder the tire be- comes. Then, again, when the wheel is left in the hot Size of Molecules. 9 sun the greater tension which is developed is due to the fact that the absorption of heat causes all the molecules to travel faster, and, traveling faster, they must exert a greater pressure whenever collision occurs and their motion is arrested. It has been computed that the mean rate at which the molecules of hydrogen gas travel at ordinary temperature and atmospheric pressure is some 6,000 feet per second. Under the same conditions molecules of oxygen gas which are 16 times as heavy travel only one-fourth as rapidly. If it is difficult to think of a body like a horse-shoe or a hammer maintaining its form against great strains when the molecules composing it are neither at rest nor in con- tact it may be helpful to recall the conditions which exist in the solar system. Here we have the sun with all its planets and their satellites, together with asteroids, comets and meteors, each in rapid motion but separated by im- mense distances, and yet the whole system constitutes one gigantic body maintaining persistently its form as it moves through space. 6. The Size of Molecules. Molecules are so very small that it is extremely difficult to form any just conception of them, yet there are many experiments and observations which prove them very minute. Nobcrt, for example, ruled parallel lines on glass at the rate of 101,600 per linear inch, proving that the point of the diamond which plowed the furrows must have been far less than roVo&ff of an inch in diameter. Lord Kelvin has computed that the number of molecules in a cubic inch of any perfect gas under a temperature of 32 F. and a pressure of 30 inches of mercury must bo as great as 10 23 or ten sextillions. This is an enormous number, but that, there is a proba- bility of truth in it may be demonstrated by a simple ex- periment Dissolve .05 of a gram of aniline violet in alcohol and distribute it through 500 cu. in. of water in a large glass 10 Introduction. flask. Pour out half the colored water and fill to 500 cu. in. again. Repeat this operation as long as the eye can with certainty detect the color in the water. As many as nine divisions may be made and the eye detect the color when looking down through 12 inches of the water poured into a long glass tube held over white paper, using a sim- ilar tube with clear water as a standard for comparison. If the division of the aniline is carried to this extent there will be in the last 500 cubic inches of water only 5l2 of 100 = 107210 of a S ram of aniline - It is reasonable to suppose that in the last 500 cubic inches of water there was at least one molecule of aniline in each cube of water .01 of an inch on a side, and if this is true there must have been at least 100 X 100 X 100 X 500 = 500,000,000 molecules of aniline in the last vessel of water. Since at least this number of molecules is found in Tsku of a gram of aniline one gram would contain not less than 10, 210 X 500, 000, 000 = 5, 120, 000, 000, 000 molecules. It is plain, therefore, from this straightforward line of observation and simple calculation that molecules of ani- line at least must be very small and that a pound of tho material would contain an enormous number. From another line of observation Maxwell has computed that the molecules of hydrogen, oxygen and carbon dioxide are so small that the numbers in the table below are re- quired to weigh one gram. Number of molecules in one gram of Hydrogen Oxygen Carbon dioxido 2,174(10) !!3 l,359(10) ss 9,881(10) 3 ' That is to say, the number of molecules is so large in ono gram of these three substances that 2,174, 1,359 and 9,881 ^Divisibility of Matter. 11 must be .multiplied by 10 used as a factor 23, 22 and 21 times respectively in order to express them. 7. Molecules and Commercial Fertilizers. It is a very strange fact that 100 to 500 pounds of commercial fertil- izers applied to a poor soil will produce such marked ef- fects upon the growth of plants when these small amounts are spread over an acre of ground and then dissolved in and distributed through the soil water of perhaps the en- tire surface four feet. To know, however, that the mole- cules of these fertilizers are so extremely small and that there are such immense numbers of them in a single pound enables the mind to better comprehend how such marked effects are possible. The surface four feet of good field soil when well supplied with moisture may contain the equivalent of 10 inches of water on the level. This amount of water expressed in cubic feet per acre is 3G,300. The experiment with an- iline indicates that a single gram has been divided into not less than 5,120,000,000,000 parts. Let us compute how many parts this number would give to each cubic inch of the 36,300 cubic feet of soil- water in the upper four feet of an acre. 5, 120, 000, 000, 000_ _ fi1 , 36,300X1,728 ' We see, thm, that a single gram of aniline may be di- vided enough to place 81,C24 parts in every cubic inch of moisture of an entire acre of good soil to a depth of four feet. But one gram of sodium nitrate would contain, accord- ing to Maxwell's results, NaNO 3 :2 O :: No. of O molecules : No. of NaNO 3 molecules or 85:32 :: ],359(10) aa : x whence x = 51(10) 2 - =5,100,000,000,000,000,000,000,000 12 Introduction. Treating this result as we did that of the aniline we shall have 5^00.000(000000,000,000 as the number of molecules of sodium nitrate iu each cubic inch of water from which the plants may draw their sup- ply of nitrogen. It will be seen that this number is so large that even a cube of water .01 inch on a side will contain 81,310,000,000, a number far too large for com- prehension, and yet if 200 pounds of sodium nitrate were applied to the acre this number would have to be multiplied by the number of grams in 200 pounds to express the num- ber of molecules there would be for each cube of soil-water one-hundredth of an inch on a side. 8. Molecular Structure in Relation to Poisons. It is the extremely large number of molecules which may exist in a small space, coupled with the energy which these molecules may carry with them in their movements, which makes possible the violent disturbances in the life processes of animals and plants associated with the introduction into the system of such small quantities of substances known as poisons. It will be easily undei stood from what has been said regarding the vast number of fertilizer molecules per cubic inch of soil moisture, when only a single gram has been disseminated throughout the surface four feet of a full acre, that extremely small quantities of any poison, like strychnine, will contain molecules enough to charge the body of 4,lie largest animal with great numbers of the poisonous units. The important practical lesson to be remembered in this connection is that, since such extremely small quan- tities of matter, when introduced into the plant or animal body, are sometimes capable of producing such profound disturbances as to cause death, extremely small quantities of other substances may have very important beneficial effects ; and it is quite possible that it may be along such Odors and Flavors. 13 lines as these we must search for an explanation of some of the little understood points associated with the nourish- ment of both plants and animals. 9. Ability to Recognize Small Quantities of Matter. \Ve often marvel at the delicacy of the chemical balance and many other instruments of measurement, but the delicacy of the sense organs of men and animals, and particularly the sense of smell, is so extreme that it is difficult to form a just conception of the minuteness of the quantity of matter or of energy to which they will respond with the degree of intensity which permits accurate judgments to be formed. The sensations of odors result from the disturbances produced on the organs of smell by molecules of different substances moving through the air when brought to the nose. But when the blind lady took the glove of a stranger and, walking up and down the aisles of a large audience room filled with people, handed the glove to the owner, made known to her only by the likeness of the odor from the glove to that escaping from the stranger, who will say what fraction of a gram of that volatile principle it was which produced so marked a sensation ? The weight of volatile substance rising into the air from a man's track, made by a shoe rather than his bare foot, must be very small indeed, and yet the sense of smell in the dog is so keen that he will follow his master at a rapid run even when the tracks are two hours old and w r here many other people may have passed along the same course more re- cently than did his master. The readiness with which flowers, fruits and vegetables may be identified by their odors alone, often at consider- able distances, and with which animals scent their enemies or their food, are all of them concrete demonstrations at once of the extreme minuteness and Hast numbers of mole- cules, while at the same time they prove how sensitive is the animal organization to such minute quantities of ma- terial. 14: Introduction. 10. Foul Odors and Flavors in Dairy Products. Since the commercial value of dairy products is determined in a high degree by their flavors and odors and since these qualities are judged through the sense of smell, which we have seen is so extremely delicate and keen, and since such minute quantities of the odor or flavor producing sub- stances are certain to awaken the undesirable impressions, it is clear that the greatest of care must be exercised in producing, handling and caring for them through all the steps preceding the delivery to the consumer. Since we have seen that so little fertilizer may be disseminated through so much soil moisture and since so little may be de- tected by the organs of smell, it is plain that too great care cannot be taken in keeping the milk clean and that only those who do this can hope to secure the custom of people willing to pay a high price for the milk, cream, butter or cheese which just suits them. 11. How Odors and Flavors Find Their Way Into Milk. . The substances producing these qualities in milk make their entrance there in three different ways: (1) from the blood at the time the milk is secreted ; (2) from the outside after the milk is drawn; and (3) they are produced within the milk after it has been secreted before or after it is drawn. 12. Odors Entering Milk During Secretion. Any volatile principle which may chance to be present in the blood of the animal at the time the milk is being drawn will find its way into the milk and will impart a quality to it, the intensity of the flavor or odor depending upon the amount of the volatile principle present and the readiness with which it evaporates. Nearly all food stuffs contain substances which produce odors and if these substances are not destroyed during the processes of digestion they will again escape from the body of the animal through the channels of excretion ; that is, through the skin, kidneys, lungs, rectum or udder, and if Odors in Milk. 15 any of these principles still remain in the blood at the time the milk is being drawn they will appear in it. It follows, therefore, that the longer the interval of time be- tween the taking of food into the body and the drawing of the milk the less danger there will be of the milk be- ing tainted by it. The reason for this is found in the fact that the milk is excreted during the time of milking while the blood is coursing through the udder, carrying whatever odor producing substances may then be present. 13. Time to Feed Odor Producing Foods. It is clear from what has been said that if it is desired not to have the milk charged with the undigestible odor-principles of food while it is being drawn these foods should be fed as soon as possible after milking and never just before in order that time enough may have elapsed to permit the odor principles to have been eliminated from the blood by the other organs. On the other hand, if the food contains a principle whose odor is desired in the milk, then the re- verse rule as regards time of feeding should be practiced, namely, to feed these just before milking. 14. Introduction of Odors Into Milk From the Air. It is the fact that the molecules of substances are not in contact and that they are in motion which makes it possible for milk when in an atmosphere containing odors to become charged with them. If the odors of manure, of urine, of ammonia, or any of those associated with the decay of organic matter are in the air above the milk the rapid motion of these molecules will cause some of them to plunge into the milk and accumulate there until they be- come so numerous that just as many tend to escape per minute as tend to enter. The milk is then saturated with the odor in question. The warmer the air surrounding the milk and the warmer the milk the more quickly will the condition oi 16 Introduction. saturation be reached, simply because the rapidity of mo- lecular motion increases with the temperature, for when the molecules of foul odor are once inside the warm milk they travel or diffuse downward more rapidly because it is warm. 15. Odors and Flavors Resulting From the Introduction of Solids Into Milk. It must be clear from what was demon- strated in (6) that when great care is not taken both in keeping the stable and cows clean and free from dust tho fine particles of dirt falling into the milk, even though the amount is small, may readily dissolve and impart a strong flavor to it, and one careless milker may easily greatly injure the quality of that from the whole herd where all of the milk is pooled. The fundamental point to be kept ever in mind is that a very little dirt is capable of being divided to an extreme degree and that through the senses of taste and smell extremely small amounts may readily be detected. 16. Odors and Flavors Developed in Milk After It is Drawn. Milk is a very nutritive fluid and for this rea- son great care must be exercised not only to keep dirt out but also to prevent those germs from entering it which have the power of developing rapidly there, producing un- desirable odors and flavors and thus injuring the quality of the milk. These objectionable germs are liable to be introduced into the milk through the dust from the sta- ble and the cow as well as from the lack of proper cleanli- ness of the vessels in which the milk is handled. 17. Deodorizing Milk. The removal of odors from milk may be accomplished by greatly increasing its surface in a space containing none of the odors which the milk con- tains. The method known as the "Aeration of Milk" has for its purpose this rather than the exposure of the milk to the air, as the presence of the air hinders the escape of Deodorizing Milk. 17 the odors rather than favors it and if the milk could be ex- posed in a vacuum their escape would be more complete and more rapid. The escape of the odors from the milk depends upon the rapid motion of the odor molecules in it which forces them to escape whenever they approach the surface with suffi- cient velocity to overcome the surface attraction, and the division of the milk into a large number of small streams increases the chances for the odors to escape in proportion to the increase of the surface. The finer the milk streams, the farther they are apart and the longer the stream is in falling the more complete will the removal of the odors be. Where there can be a movement of air over the milk surface or among the streams of milk this will favor the removal by carrying the odor molecules away and thus preventing them from re-entering the streams. Since the molecular movement is greater the higher the temperature it follows that the deodorizing process should be applied as soon after the drawing of the milk as possi- ble before it has had time to cool and the molecular motion to slow down. 18. Place For Using the Deodorizer If the aerator or deodorizer is used in the barn or where there are many ob- jectionable odors it must be remembered that exactly the same conditions which favor the escape of the odors which the milk contains when drawn are the best conditions to permit it to become charged with odors from outside, and hence the deodorizer or aerator should be placed where it is surrounded by a current of pure air. 19. Cooling Milk. The cooling of milk immediately after it is drawn has a powerful influence in preventing odors from developing in it as a result of the growth of any germs which may have found their way into the milk because the low temperature makes their growth much slower. Cooling, then, is not a deodorizing process but one which prevents the formation of new odors. If, then, 18 Introduction. it is desired to remove the animal odors this if possible should be done first and then the milk cooled to prevent the formation of other odors. 20. Work. Whenever any body is moved under the ac- tion of a force work is done and the amount of this work is measured by the intensity of the force and the distance through which it has acted. When a body weighing one pound is lifted one foot against the attraction of the earth the amount of work done is one foot-pound. The same weight lifted 10 feet represents 10 foot-pounds and 10 pounds raised one foot has the same value. A team hauling a load over a road under a mean pull of 200 pounds is doing 200 foot-pounds of effective \vork for every foot traveled and in traveling 10 miles the total work done is 10 X 5,280 X 200= 10,560,000 foot-pounds. When a larger unit than the foot-pound is desired that of the foot-ton may be employed and its value is 2,000 pounds lifted one foot high or 2,000 foot-pounds. If a wagon with its load weighing 4,000 pounds is moved along the road the work done will not be measured by the product of the load into the distance traveled but by the intensity of the pull necessary to pull the load into the distance trav- eled. On a good level macadam road 60 pounds will move a ton and 120 pounds two tons. To draw four tons over 10 miles of such level road means the doing of 4 X COX IPX 5,280 R oofi fnnt t , ~ 27000" =6, 336 foot-tons. So, too, if the pressure of steam on the head of the piston in a steam engine is 80 pounds per square inch and the area of the piston is 100 square inches the amount of work it can do per foot of stroke is 80 X 100 = 8,000 foot-pounds. Conservation of Energy. 19 If this engine makes 200 strokes per minute, then the work it does per minute will be 200 X 8,000 = 1,600,000 foot-pounds. 21. Energy. Energy is the ability of a moving body to do work and the amount of energy the moving body has is measured by the amount of work it can be made to do in coming to rest. If a weight suspended from a string be drawn to one side and then released it will begin fall- ing and acquiring velocity, and on reaching the lowest level it will possess the ability of doing a certain amount of work. That amount will be enough to raise its own weight through the height from which it fell in the same time. If a bow is bent and the string is released against the arrow it will recover its form of rest but in doing so will impart to the arrow an amount of motion equal to that which the bow acquired in straightening out. When work is done in winding the clock the distorted spring has the power to develop an amount of energy equal to that expended in winding it up. In chopping wood the action of the woodsman's muscles increases the amount of motion in the ax until it falls upon the wood, when the energy which has been imparted to it does the work of cut- ting. We cannot exert pressure enough with the hand alone to force the nail into the board, but by giving the muscles an opportunity to act gradually upon the hammer it is a simple matter to store in it enough energy to easily drive the nail into the wood. W T hen coal or wood is burned in the fire-box of the engine and the heat developed converts water into steam under high pressure in the boiler we have still another case where energy is developed and accumu- lated in the rapidly moving molecules of steam which drive the piston whenever the valves are opened leading to it. 22. Conservation of Energy No discovery of modern science is more fundamental than the fact that neither mat- ter nor energy can be destroyed or created. One form 20 Introduction. of energy may be transformed into another, and one kind of substance may be decomposed and others made from the components, but in these transformations there is neither annihilation nor creation. The small amount of ashes left from the winter's supply of coal or wood seems to point to a destruction of matter, but their weight added to that of the products which pass up the chimney is even greater than that of the original fuel by the amount of oxy- gen which was required to burn the fuel. So, too, the energy of 10 horses expended in threshing grain seems to be annihilated but it is only transformed. Heat of fric- tion and concussion, sound and material raised into new positions, from which it may fall, when added together will make a sum equal to that developed by the horses. Again we appear to realize in the increase of our domestic ani- mals or in milk produced much less weight than has been used by them in feed and drink but this is because such large quantities of the materials eaten, breathed and drank escape in an invisible form through the skin and lungs. 23. The Source of the Earth's Energy. The real source of tha earth's energy is the sun. All the rivers of the world flowing to the sea and the rush of the winds swaying the tree-tops and lashing the ocean into billows represent so much water and air lifted from a lower to a higher level by the sun's heat and now being pulled by gravity back to their original level to be raised again and to again re- turn, just as a pendulum rises and falls while swinging through its arc. The wood burned in the stove, the coal burned in the en- gine and the food consumed by the horse are all the prod- uct of sunshine which lifted the constituents of soil, moisture and air into such combinations as readily per- mits of their return to other forms, setting free the energy which was consumed in producing them. 24. Solar Energy. When the sun rises the temperature increases, usually becoming higher and higher until past Solar Energy. 2 1 noon, then when the sun sets the temperature falls again, continuing to do so until once more the sun is above the horizon. So, too, as our days grow longer and longer with the approach of summer in the middle and higher lati- tudes, making more hours of sunshine in every twenty- four, the mean daily temperature increases but falls away again when the nights became longer than the days. Such and many other facts prove the sun to be a. source of energy which in some manner is being transferred to our earth. More than this, since the earth travels entirely around the sun once each year and yet each day receives heat and light from it, it follows that solar energy is con- tinually leaving the sun in all directions, so that the amount arrested by the earth forms a very small portion of the whole. 25. How Solar Energy Reaches the Earth. To under- stand how the energy of the sun reaches us, coming across 93,000,000 of miles we must learn that the energy travels in the form of waves through some medium filling space, which has been named ether, but whose real nature is not yet understood. Something similar to the process in question would be represented by a man at the center of a pond throwing its water into waves. These waves would spread in all directions and when reaching the beach a portion of the energy of the waves would be absorbed or transferred to whatever body they chanced to strike. The energy, therefore, generated in the muscles, is changed first into wave energy in the water and conveyed away from the man in all directions, but afterward when arrested at the beach, the waves may move the pebbles, making them grind upon one another, wearing themselves into sand, or their sliding may change a portion of the wave energy into heat and thus the person in a sjnall degree may warm the pebbles lying on the distant margin of the lake, not di- rectly by the heat of his body, but by the waves set up in 3 22 Introduction. the water, and much as the earth is warmed by waves sent out through the ether of space from the surface of the sun. The rapid and intense molecular motion at the surface of the sun is transformed into wave motions in the sur- rounding ether of space, as the motions of the imaginary man were changed into waves in the water, and these ether waves travel away from the sun's surface in all directions at the rate of 186,680 miles per second. So many of these waves as the size of the earth permits it to stop are arrested and transformed into the various forms of motion which are manifested at its surface. 26. Amount of Energy Developed at the Sun's Surface. Careful measurements and calculations have shown that the energy developed second by second at the -sun's surface, amounts, according to Lord Kelvin, to not less than 133,000 horse power on each square meter or 1.09 square yards of its surface. 27. Rate at Which Solar Energy Reaches the Earth's Surface. As the intense energy developed at the surface of the sun spreads away from it, it becomes weaker and weaker in the ratio that the square of the distance of the waves from the sun increases, as represented in Fig. 2, and \ \ \ \ \ \ \ FIG. 2. BO at the earth's surface the amount of energy has become so much reduced that Lord Kelvin places it at only a little more than 1.3 horse power per each square yard of surface. Solar Energy. 23 Cut small as this amount of energy is when compared with that leaving a like area at the sun's surface it is neverthe- less very large. It may seem strange that so much energy falling upon the earth does not keep its surface at a higher temperature than is observed, but when it is stated that the temperature of the space which surrounds the earth outside its atmos- phere is 273 C. and that only the thin atmosphere shields the surface from this intense cold, it is plain that a large amount of heat must be required to held the mean temperature even as high as 45 F. which is 273 -f 7 = 280 C above absolute zero. If we add to the necessity of holding the earth's surface at a temperature 280 C. to 300 C. above the space in which it moves, the demand for energy needed to maintain the movements of water and of winds, together with that em- bodied in activities of animal and plant life, then 1.3 horse power per square yard of surface does not appear so much too large. 28. Kinds of Ether Waves. The energy reaching the earth from the sun in the form of wave motion is not all alike in that the waves have different lengths, or, what is the same thing, greater numbers of one kind reach the earth in a unit of time. Waves which are so frequent that from 392 to 757 billions reach us per second produce the sensation of light when falling upon the eye; the slower ones producing red light and the more rapid ones the ex- treme violet colors of the rainbow. Associated with these color waves there are many other dark waves to which the human eye is not sensitive. Some of these are much shorter than the color waves and are especially powerful in breaking down the molecular structure of different sub- stances; that is, in producing chemical changes such as oc- cur on the photographer's plate when the negative is made and such as take place in the green parts of plants when car- 24 Introduction. bon dioxide is broken down and the chemical changes are produced which result in building the sugars, starches and cellulose of plants. Others of these waves are much longer than the light waves and these have a wonderful power in producing heating effects when they fall upon certain sub- stances, one of which is water. When bright sunshine is allowed to pass through a large lens the glass is but little warmed by the passage, but if paper is held at the light focus it is quickly set on fire by the dark or invisible rays. That it is the dark rays may be proved by allowing the light to pass first through a solution of iodine in bisulphide of carbon which permits the dark waves to easily pass while it cuts down or stops the light waves. When these dark waves are brought to a focus in water it is made to boil quickly under their in- fluence. On the other hand if sunlight is first passed through a solution of alum in water, which stops the dark waves but allows the light waves to pass, then when they are focused upon water but little heating effect is noted. 29. How Water is Evaporated. It is the fact that water does not allow the long dark waves from the sun to pass readily through it which causes it to evaporate so rapidly from t>cean, lakes and streams, and from the soil and the leaves of vegetation. When these waves fall upon water they set its molecules in such rapid vibration that the sur- face tension, or force of cohesion, is overcome and many of the water molecules are thrown out into the air in the form of invisible vapor. Were the water not so opaque to the dark waves, neither snow nor ice would be as rapidly melted in the spring nor would there be so much evapora- tion from the ocean as we now have, hence rains would be less frequent and the land less productive. 30. How Chemical Changes Are Produced by Ether Waves. When the light waves and especially the shorter dnrk waves fall upon many substances they appear to set Heat and Temperature. 25 up vibrations within the molecules themselves, which in time may become so intense as to overcome the force by which the components are bound together and the molecule is thrown into parts, setting them free so that when their motion slows down they may join in new combinations. It is much as if some giant power were to seize upon a steel chain, throwing it into such intense vibrations that its sev- eral links are broken. 31. Nature of Heat and Cold. When a body becomes warm the rate of vibration of the molecules which compose it is increased and the path through which they move becomes longer. If the body becomes cold the rate of movement of the molecules becomes less rapid and the dis- tance through which they move less. The higher the rate of molecular motion within a given body the warmer that body is and vice versa. If the molecular motion of a body could be completely brought to rest its temperature would be absolute zero. Under this condition it is supposed that any body would have its smallest volume; and all liquids and gases would become solid. 32. Temperature. When the temperature of a body is given it is intended to state the degree of molecular vibra- tion within it. The temperature at which a Fahrenheit thermometer marks zero is not that of no molecular motion but simply 32 degrees of that scale slower than the rate at which pure water becomes a solid; while zero indicated by a Centigrade thermometer is the rate of molecular motion which permits water to become solid and is a temperature 273 degrees above what is assumed to be absolute zero or the condition of absolute rest. 33. How Temperature is Measured. It is a general law that those substances which may exist as solids, as liquids or as gases, as is the case with water, which we know as ice, water and steam, or invisible vapor, change from the solid to the liquid form and from the liquid to the gaseous form when the rate of molecular motion has reached a certain 26 Introduction. degree, and this being true the freezing and boiling points of various substances may be taken as standards of tem- perature. Water being a common substance which changes its state at convenient and common rates of molecular motion has been selected to fix two degrees of temperature called the freezing and boiling points of water. When a thermom- eter scale is to be graduated its bulb js placed under the in- fluence of melting or freezing water, and the place at which the moving point comes to rest marked ; then it is placed under the conditions of boiling water and the new point also marked. The space between these two points on the scale is then divided into 80, 100 or 180 divisions, accord- ing to the system which it is designed to follow. Since this range in molecular vibration is divided into 180 degrees on the Fahrenheit scale its degrees are the shortest, while those of the Reaumer scale are the longest because the same range is divided into but 80 divisions. The Centigrade and the Fahrenheit scales are the two commonly used in this country, the degree gf the former being equal to I of the latter. 34. Accuracy of Thermometers. The bulbs of most ther- mometers shrink after they are blown and if they have not been permitted to stand for a number of years to season before fixing the zero and boiling points of the scale, these points will change and the thermometer will give incorrect readings in time and the cheaper grades of thermometers are liable to be subject to this error. The accuracy of the freezing point may be approxi- mately tested by surrounding the bulb with snow or crushed ice out of which the melted water may drain, al- lowing the thermometer to remain until the temperature becomes stationary. The accuracy of the boiling point may also be approxi- mately determined by holding the bulb in rapidly boiling soft water. Foot-Pound and Horse-Power. 27 A thermometer may be correct at the freezing and boil- ing points and inaccurate at most intervening degrees, growing out of the unequal diameter of the tube in differ- ent portions and the fact that all degree marks may be made of the same length. Errors of this sort can be de- tected only by comparing the thermometer with a standard. 35. Units of Work and Energy. It has been found neces- sary in dealing with the numerical relations of work and energy to adopt standards of measurement just as has been done for lengths, volumes, surfaces and mass, and various units are in use. 36. Foot-pound and Foot-ton. A common unit of work is the foot-pound, which is a mass or weight of one pound lifted vertically against or in opposition to the force of gravity. If a body is moved one foot in any other direction than against the force of gravity and the intensity of the pull or push necessary to do this is equal to that required to lift one pound, then in this case the work done is one foot-', pound. If 2,000 pounds is lifted one foot high then 2,000 foot-pounds of work have been done, and this is sometimes designated a foot-ton. The same intensity of pull in any other direction may be expressed in the same terms. Time is not a factor taken into account in simply ex- pressing the amount of work done for the reason that a very small force when permitted to act for a very long time may raise the same weight through one foot, which would require a very intense force if permitted to act but a very short time. 37. Horse-power. When the rate- at which work is done and the intensity of the fagee required to do the work at the stated rate are to be expressed quantitively, then a unit involving time must be chosen and the horse-power is one of these. The horse-power used by English and^ American engineers is -the amount of energy which can do 550 foot-pounds of work per second or 33,000 foot- 28 Introduction. pounds per minute, equal to 16.5 foot-tons in the same time. To raise grain in an elevator to a hight of 20 feet at the rate of 16.5 tons per minute would require 20 horse- power. If a horse is walking 2.5 miles per hour and exerting a steady pull on his traces of 100 pounds then the effective energy he is devdoping is 100 X 5. 280 X 2.5 _ GO X 60 X 550 and this for a well fed horse weighing 1,000 pounds, work- ing 10 hours per day at the rate of 2.5 miles per hour, is called a fair day's work. If a 1,500-pound horse could do work in proportion to his weight then his ability to de- velop energy would be equal to the standard English horse- power of 550 foot-pounds per second. Gen. Morin, how- ever, has placed the ability of the average horse to do work at the rate of 435.8 foot-pounds per second. 38. Heat Unit In the steam engine the energy of heat is converted into work, and since heat is a form of molecu- lar motion its quantity must have a fixed relation to the temperature of a given amount of material. The English and American heat unit is the amount of heat energy which is required to raise the temperature of one pound of pure water from 32 F. to 33 F., and since one form of energy may be converted into another the value of a heat unit may be expressed in foot-pounds. The English scientist, Joule, was the first to measure the number of foot-pounds of work which one heat unit could do and found it to be 772, which when corrected for the mercurial thermometer became at 15 C. 775 foot-pounds. Rowland obtained the value 778.3 foot-pounds. This means that the source of heat which ia able to raise the temperature of one pound of water one degree every second would also be able to raise 778.3 pounds one foot high in the same time. 39. Determination of the Mechanical Equivalent of Heat. In order to ascertain the value of the heat unit in foot- Specific and Latent Heat. 29 pounds, Joule arranged a vessel containing water in such a way that by means of nicely adjusted weights he could cause them to drive a set of paddles in the water and by the mechanical agitation warm it. By knowing the number of pounds in his weights, the distance they were allowed to fall and the rise in temperature which was observed in a given weight of water, he found the relation to be that stated in (38). 40. Specific Heat. We have learned (32) that tempera- ture is a measure of the rate of molecular motion within a given body ; it is not, however, a measure of the amount of work which must be done upon that body to change its temperature through a given number of degrees ; neither is it a measure of the amount of work which may be secured from that body \vhen its temperature falls a given amount. When the same number of heat units is imparted to like weights of different substances their temperatures are not raised through an equal number of degrees. The same amount of heat, for example, which will raise the tempera- ture of one pound of water from 32 F. to 33 F. will raise a pound of sand from 32 F. to 37.23 F. For some reason more work must be done on water than on the sand to secure the same change of temperature, but, true to the law of the conservation of energy, when the water again cools down it gives out as much more heat in doing so as was required to produce the rise in temperature. It is this fact which causes large bodies of water to make the winters of adjacent lands warmer and the summers cooler. Soils change in temperature more rapidly than would be the case were their specific heats higher, and for this rea- son in part a wet soil is cooler than the same soil when dryer. 41. Latent Heat. When ice at 32 F. has heat applied to it its temperature does not rise so long as there is still ice to melt, the whole of the energy given to it being con- sumed in changing the solid ice into liquid water, that is, 30 Introduction. in doing the work of melting. The amount of heat re- quired to melt one pound of ice is 142 units when ex- pressed in round numbers ; or if the work done is expressed in foot-pounds it will be 142 X 778.3 = 110,518.6 foot-pounds and the time required for one horse power to do the work would be 110,518.6 When crushed ice and salt are mixed in the ice-cream freezer the changing of the two solids to a liquid requires so much energy, and it is used so rapidly, that the cream is quickly frozen, its molecular motion being used in doing the work. When water has been brought to the boiling tempera- ture it ceases to become warmer so long as boiling contin- ues, all of the heat energy entering from the fire being re- quired to do the work of changing liquid water into steam. The amount of heat required to change one pound of water at 212 F. into steam at the same temperature is 966.6 hoat units. When expressed in foot-pounds it becomes 778.3X960.6 = 752,305 p.nd the time required for one horse-power to do this work ia 752,305 _ 00 =22.8 minutes. 60 X When a pound of water at 32 F. becomes ice at 32 F. there reappears as heat the 142 heat units which were re- quired to melt it, and so too when one pound of steam con- denses into water there reappears 966.6 heat units. Be- fore the nature of these changes were as well understood as Latent Heat of Water and Ice. 31 they now arc, it was supposed that the heat became hidden or latent but that it was heat still. 42. Measuring the Energy Required to Melt Ice. This may be determined approximately by taking equal weights of water at 212 F and of ice at 32 F., putting the two together and noting the temperature at the moment the ico is all melted. When this has been done it will be found that the combined water has a temperature of about 51 F. If, however, equal weights of water at 32 and 212 are mixed there will be found a temperature of 212 + 32 -2~ =122 one volume of water having lost as much as the other gained. . In the first case, however, the water lost 212 51 = 161 while the ice gained only 51 - 32 = 19. There was therefore in this case an apparent loss of 1G1 19 = 142 If a pound of. water and of ice had been taken for these ex- periments it is plain from (38) that the 142 would also represent 142 heat units. 43; Measuring the Energy Required to Evaporate Water. " If a pound of steam at 212 F. be condensed within 5.37 pounds of water at 32 F. there will result 6.37 pounds of water having a temperature very close to 212 F. The one pound of steam has therefore raised the temperature of 5.37 pounds of water through 212 3 32 p =iSO 32 Introduction. 212> 32 = 180 without having its temperature materially lowered. The molecular energy, therefore, which the one pound of steam contained was 180 X 5.37 = CC3.6 units. This large amount of energy in steam explains how it is able to do so much work when acting upon the engine pis- ton and why a burn from steam may be so much more se- vere than that from boiling water. 44. Evaporation Cools the Soil. We have seen that one pound of steam in condensing into water generates Ofifi.C heat units, and that the reverse statement is also true, namely, to convert a pound of water into the gaseous state, under the mean atmospheric pressure, requires the absorp- tion by that pound of 9GG.G heat units. When one pound of water disappears from a cubic foot of soil by evapora- tion, it carries with it heat enough to lower its tempera- ture, if saturated sand, 32.8 F. ; and if saturated clay loam, 28.8 F. To dry saturated sandy soil until it contains one-half of its maximum amount of water requires the evaporation of about 9.5 pounds to the square foot of soil surface when this drying extends to a depth of one foot, while the simi- lar drying of clay loam requires the evaporation of 11.5 pounds, and 11.5-9.5 = 21bs. or the amount of evaporation which must take place in the clay loam to bring it to the same degree of dryness as the sandy soil. But to evaporate two pounds of water re- quires 9G6.6 X 2 = 1933.2 heat units. and this, if withdrawn directly from a cubic foot of satur- ated clay loam, would lower its temperature 57.6 F. Here is one of the chief reasons why a wet soil is cold. Latent Heat. 33 Tlir.t the evaporation of water from a body does lower its temperature may be easily proved by covering the bulb of a thermometer with a close fitting layer of dry muslin, not- ing the temperature. If the muslin be now wet, with water having the temperature noted, and the thermomotcr rapidly whirled in a drying atmosphere its temperature will quickly fall, owing to the withdrawal of heat from the bulb by the evaporation of water from the muslin. 45. Regulation of Animal Temperatures. All of our do- mestic animals require the internal temperature of their bodies to be maintained constantly at a point varying only a little from 100 F., and this necessity requires provi- sions both for heating the body and cooling it. The cool- ing of the body is accomplished by the evaporation of per- spiration from the skin, and the amount of perspiration is under the control of the nervous system. When the tem- perature becomes too high, because of increased action on the part cf the animal, or in consequence of a high ex- ternal temperature, the sweat glands are stimulated to greater action and water is poured out upon the evaporat- ing surfaces and the surplus heat is rapidly carried away ; each pound evaporated by heat from the animal withdraw- ing about 966. 6 heat units. 46. Bad Effects of Cold Rains and Wet Snows on Domestic Animals. When cattle, horses and sheep are left out in the cold rains of our climate the evaporation of the largo amount of water which lodges upon the bodies, and espe- cially in the long wool of sheep, creates a great demand upon the animab to evaporate this water. The theoretical fuel value of one pound of beef fat is 16,331 heat units, and that of average milk is 1,148 heat units. A pound of beef fat may therefore evaporate 16, 331 (> R = 16.8 Ibs. of water 9C6.6 and a pound of average cow's milk 1118 ',. ,. = 1.13 103. of water 34 Introduction. On this basis, if a cow evaporates from her body four pounds of rain she must expend the equivalent of the solids of 3.39 pounds of milk. A wet snow-storm is often worse for animals to be out in than a rain-storm, because in this case the snow requires melting as well as evaporating, and the number of heat units per pound of snow is 142. C5 + 906. 6 = 1109.25 heat units, and the heat value of a pound of milk is barely sufficient to melt and evaporate a pound of snow. 47. Cooling Milk with Ice and Cold Water. If it is de- sired to cool one hundred pounds of milk from 80 F. down to 40 F. it is practically impossible to do so with water in the summer season in Wisconsin. It is difficult even to cool it as low as 48 F. for most of the well and spring water has a temperature above 45 F. and much of it is. above 50 F. If lower temperatures than 48 F. are desired during the warm season some other means must be resorted to. Since it requires 142 heat units to melt a pound of ice, one pound is capable of cooling from 80 to 40 F. 3.751bs. of milk, supposing the specific heat of milk to be the same as that of water, which is not quite true. To cool 100 pound? of milk from 80 F. to 40 F. will require, therefore, about 100 -=26 1 Ibs. of ice, 3.75 supposing it to be used wholly in cooling the milk. If the water has a temperature above 40 F. before the milk and ice are placed in it, there will be required enough more ice to cool the water down to the temperature desired for the milk. The greatest economy in the use of ice will be secured, therefore, when the creamer contains just as little water as will cover the cans and give the needed space for the ice, Latent Heat. 35 and when the walls of the creamer are made of so poor a conductor of heat as to admit as little as possible from without. 48. Washing with Snow or Ice. When ice or snow are used in winter for washing purposes there is a large loss of heat incurred in simply melting the ice and raising the temperature of the water from 32 F. up to 45 F., the temperature it may have in any well protected cistern. To melt a pound of ice and raise its temperature to 45 F. will require 142 -f 13 = 155 heat units, If 300 pounds of water are required for a washing then the lost heat will be 300 X 155 = 46,500 heat units. The fuel value of one pound of water-free, non-resinous wood, such as oak or maple, has been found to be 15,873 heat units; that of ordinary dry wood, not sheltered, con- taining 20 per cent, of water, is 12,272 heat units. At this latter value it will require, supposing 50 per cent, of the fuel value to be utilized in melting the ice and heating the water, 2X46,500 ~^o OTO ' = 7.53 Iks. of wood I - . ( more than would be needed to do the same washing with water at 45 F., to say nothing of the expense of getting the snow or ice and the unhealthfulness of handling it. 48a. Burning Green or Wet Wood. Whatever water wood or other fuel may contain when it is placed in the stove, so much of the fuel as is required to evaporate this water must be so expended and is prevented from doing work outside of the stove. We have seen (48) that when wood contains 20 per cent, of water there is required 15,873 12,272 = 3,601 heat units per pound of wood to evaporate the water contained, which is 22.7 per cent, of the total value. Wood, after being in CO Introduction. a rain of several days, contains more water than this and green wood much more, sometimes as high as 50 per cent., while well seasoned sheltered wood may contain less than half that amount. It is frequently urged that when some green or wet wood is burned with that which is dry there is a saving of fuel. There is some truth in this, especially in stoves having too strong a draft and too direct a connection with the chim- ney and if the radiating surface is small or poor. The evaporation of the water prevents so high a temperature from occurring in the stove, which makes the draft less strong, and this gives more time for the heat to escape from the stove before reaching the chimney, and hence less is lost in this way. Then as the fire burns more slowly there is not the overheating of the stove, at times, which may occur with lack of care when very dry wood is used, and a considerable saving occurs in this way. These statements apply more particularly to heating stoves than to cooking stoves. Dry wood is best for the kitchen stove under most circumstances, the slower fire being secured when needed by using larger sticks and by controlling the draft. SURFACE TENSION,, SOLUTION AND OSMOSIS. 49. Surface Tension. The free surface of any liquid be- haves much as though it were covered by an elastic mem- brane and it is this surface action which draws the rain- drop into the form of a sphere as it falls through the air. It is surface tension that causes water to form into spheres on a dusty floor, on a hot stove or on cabbage leaves. The dewdrop owes its shape to surface tension, and it is this which is employed to mould the melted lead into perfect spheres as it falls from high towers, cooling into solid shot before reaching the bottom. The cause of surface tension is the cohesive attraction of the molecules for one another. This attraction extends Surface Tension. action ' throughout the liquid and is very strong; but only the molecules at the surface show | its influence because it is only these which are not pulled evenly in all directions by water molecules on every side, thus leaving the interior ones free to move in any direction, while those on the surface are only pulled toward the sides and to- ward the interior. In Fig. 3 is illustrated one method of show- ' ing the action of surface ten- sion. Here the dry camel's ' 3 '~~ I hair brush at the left shows the individual hairs standing apart, and when the brush is placed in the water they still stand apart, but Avhen it is removed, as shown on the right, the whole are closely com- pacted by the pull of the surface film. 50. Rise of Water in Capillary Tubes. It is surface ten- sion which causes the rise of water in capillary tubes, as represented in Fig. 4, above the level of the water in the open vessel in which they are placed, when the water wets the glass tube that is when the attraction of the glass for the water is stronger than the attraction of the water, as explained in (191) and (192). The rows of molecules of glass just above the water level attract and lift the water closest to them but, as these are moved upward, they draw after themselves more water also. This attraction is felt over a distance which Quinke estimates at not far from nnfffjnr of an inch. The first lifting of the water by the glass brings it near enough to other glass FIG. 4. Rise of water m cap- , , , , , , iiiary tubes, molecules next above and the water is drawn still higher; in this way 3 38 Introduction. the column rises higher and higher until the strength of the pull is balanced by the weight of the water column so lifted. 51. Evaporation. Very many substances, when they have a free surface exposed, change in weight by evapora- tion. The action of heat causes the molecules to vibrate rapidly and by colliding with one another near the free sur- face some are thrown out by the force and direction of the blows. It is in this way that clothes dry rapidly on a warm day, and that water evaporates from the surface of the soil, from the leaves of plants and from the bodies of animals. Even snow and ice evaporate, as camphor does, without first becoming liquid, but the process and the cause are the same as the evaporation of water, namely, rapid vibration and collision at the surface due to the absorption of heat energy from outside. It is often said that the air takes up the moisture and the more rapidly the dryer it is or the stronger the wind blows. The air itself is not the cause of the more rapid evaporation observed, neither does evaporation stop when the air becomes saturated with moisture. Evaporation may be even more rapid in a vacuum and in rarefied air than where the air is dense and the pressure heavy ; and when the air is saturated with water vapor and evaporation appears to stop, it may be going on just as rapidly, only condensation may be taking place at the same rate, that is, just as many molecules of water return from the space above the surface as leave it in a unit of time. 52. Solution of Solids. The solution of solids, like sugar or salt in water, is not fundamentally different, either in cause or in manner, from the evaporation of water or of camphor referred to in (51), and is due to the absorption of heat from without which causes some of the surface molecules to be thrown into such rapid motion that the attractive force which draws them toward the center is no longer able to retain them in place and they are thrown out. Solution of Solids. 39 When a lump of salt is dropped into water its surface molecules are drawn outward by the surrounding water so that the effective pull upon them toward the center is made less by it. It is therefore easier for a given temperature to throw out into the water some of the molecules in the surface layer of the salt. Stated in another way the water surrounding the salt so weakens the surface tension of the solid lump of salt that solution takes place at a lower tem- perature. 53. Influence of Temperature on Solution Since it is the absorption of heat which causes solution it is clear that the higher the temperature the more rapid will the solution be. .It is even true that any solid will evaporate or dissolve if only it is given a high enough temperature, provided its molecules are not decomposed at a lower temperature than that, which is required to overcome the force of cohesion which makes them solid. It is a matter of common ob- servation that substances dissolve more rapidly in warm than in cold water and it is equally true that the soluble salts in the soil will form more rapidly when the soil is warm than when it is cold and it is because of this fact, in part, that crops grow better under the higher temperature. 54. A Saturated Solution. When conditions are favor- able for the solution of a solid in water there comes a time when there is no increase in the concentration of the solu- tion. A condition is reached which is analogous to the air saturated with moisture, when as many molecules pass from the solution and become fixed upon the face of the solid as are thrown by heat from the face of the solid into the solution. When a solution reaches this condition it is said to be saturated. In the case of the soil water, where the roots of plants are brought in contact with it, if the roots are removing the materials which are dissolved, their action hastens the rate of solution, for they prevent it from becoming satur- ated and thus prevent the return to the soil grains of par- ticles once removed. 40 Introduction. 55. Diffusion When water has evaporated into the air ; when a salt has dissolved in water, there is a tendency for these separated molecules to travel in any and all direc- tions until the whole body of the liquid in which the solu- tion is taking place contains the same number of the dis- solved molocules per cubic inch. A lump of sugar placed in the bottom of a cup of tea dissolves in time and be- comes scattered uniformly through the whole mass, making all parts equally sweet. This scattering of molecules is called diffusion and the rate varies with the temperature and the individual velocities of the molecules dissolved. B A Fro. 5. Illustrating the difference in Iho rate of diffusion in soil and ia liquids The rate of diffusion of salts in a vessel of water is much more rapid at the same temperature than it could be if the water were filled with sand. This will be under- stood from a study of Fig. 5, where A is supposed to be a place from which salts are diffusing through the water surrounding a set of soil grains, while B is a correspond- ing point from which diffusion is taking place in direc- tions indicated by the arrows of that figure. Where the diffusion must take place through the films surrounding the soil moisture not only is there less water to travel in but the course of the molecules must be many times ar- rested by the soil grains themselves. 56. Gaseous Pressure The pressure which is exerted Osmosis. 41 by gaseous bodies like air or steam, upon the walls of confining' chambers or vessels, is due to the combined energy of the blows of the molecules against these walls. The greater the number of molecules in a given space and the more rapidly they move the greater is the pressure they exert. If the temperature of a gas is increased, leaving the volume the same, the pressure is increased in the same ratio, because the velocity with which the mole- cules are moving is increased. So, too, if the number of molecules of a given gas in a given space is increased the pressure is increased in a like ratio, if the temperature remains the same, because then there are more molecules to strike a unit area in a given time. To double the pressure on a gas will reduce its volume one-half and to double the volume of a gas will reduce its pressure one-half. So, too, will doubling the absolute tem- perature of a gas double its pressure if it is not allowed to expand. It is on these accounts that the higher the steam pressure in a boiler the hotter it is and the more work it is capable of doing. 57. Osmosis. Abbe Nollet, who lived between 1700 and 1770, appears to have been the first to record that, if a glass vessel be filled with wine and covered with a bladder and then immersed in water, the contents of the vessel would increase and sometimes to such an extent as to rupture the membrane. Such a phenomenon has been named osmosis, and there are many familiar phe- nomena of every day experience which are of the same nature. When dry beans, peas or grain of any kind are put into water they swell, increasing in volume as the wine in Collet's covered dish did when placed in water. So, too, if dried raisins, prunes or apples are placed in water they increase in size, thus exhibiting the process of osmosis. On the other hand if fresh fruit of almost any kind ia placed in a strong solution of sugar it at once begins to shrivel and decrease in size; this again is due to osmosis, 4:2 Introduction. the juices being forced from the fruit by the pressure of the dissolved sugar as will be explained in the next section. 58. Osmotic Pressure. The power which causes the swell- ing of the dried grains and fruits and that which causes the shrinkage of the fresh fruit, in the cases cited in (57), is known as osmotic pressure and is caused in fundamental- ly the same manner as that of gaseous or steam pressure, but in this case by molecules of substances in solution moving in the same manner as the molecules of gas move when developing gaseous pressure. 59. Conditions \Jnder "Which Osmotic Pressure Becomes Manifest. In order that the molecules of a dissolved sub- stance may exert pressure analogous to gases they must be dilute solutions, so that the individual molecules of the kind manifesting the pressure are too far from one another to be influenced by their individual attractions; besides this, in order that the pressure may become mani- fest, the dissolving substance and the substance dissolved must be separated by a membrane through which the mole- cules of one of the fluids pass more readily than the other, as represented in Fig. G. FIG. 6. lllustrat ing the principle of osmotic pressure. Osmosis. 43 The diagram on the left may represent a raisin, dry bean or other dry seed placed in water, the upper circle showing the conditions just as placed in the water, and the larger one after the water has diffused through the wall, dissolving the substances on the inside, which pro- duce the osmotic pressure. In this diagram it is supposed that the surrounding membrane is porous enough to let the molecules of water pass readily through by the or- dinary laws of diffusion, but the molecules of the sub- stance inside, which is dissolved by the entering water, are too large to be able to pass out into the water by diffusion, and the result is they simply strike against the membrane, distending it in exactly the same way that the molecules of air in a rubber ball or rubber bicycle tire distend that. In the diagram on the right in Fig. 6, the reverse con- ditions are represented. A green or fresh fruit is sup- posed to be placed in a solution of sugar, whose molecules are too large to readily pass into the fruit through its wall, while the contained sap of the fruit readily diffuses outward into the sweetened water. Under these con- ditions the molecules of sugar, striking against the fruit on all sides at once, develop so much pressure that the juices of the berry are squeezed out of it as water might be forced out of a sponge, and its volume is reduced from the large size in the upper part of the diagram to the smaller one in the lower portion. 60. Measurement of Osmotic Pressure. It was a long time after the discovery of osmotic pressure before satis- factory means for measuring its full intensity were de- vised. The parchment and animal or vegetable mem- branes which were first used in such studies were either not sufficiently impervious to the pressure producing mole- cules or else their strength was not great enough to allow the full measure of pressure to develop and the result was the early experiments failed to show how powerful osmotic pressure may become when the conditions are all favor- able. 44 Introduction. Tranbe discovered the possibility of producing mem- branes by chemical precipitation, at the plane of contact between two solutions, which could be used instead of or- ganic membranes to study osmotic pressure, and later Pfeffer devised the apparatus represented in Fig. 7, with FIG. 7. Pfeffer's apparatus for measuring osmotic pressure. which he was able to measure osmotic pressures of very high intensity and with a fair degree of accuracy. He used a porous porcelain cell Z, with three glass pieces, t, v, r, put together with sealing wax in the manner represented in section in the left of the figure, where the method and arrangements for measuring the pressure are also shown at a, m. The complete apparatus, in working order, is represented at the right in the same figure. Osmosis. 45 To secure the manifestation of osmotic pressure with this apparatus there is developed, on the inner wall of the porous porcelain cell, a precipitation membrane which is impervious to the solution whose pressure is to be measured but which is readily permeable by water, placed in the outer vessel. The function of the porous cell is to act as a strong framework capable of permitting the precipitation membrane to withstand the pressure de- veloped without a sensible increase in the volume of the cell taking place. When the pressure-producing fluid is placed on the inside and the apparatus is placed in water the case becomes analogous to the left diagram of Fig. 6, except that the wall is now incapable of expansion and the pressure becomes manifest through the rise of mercury in the pressure gage.* 61. Osmotic Pressure of Cane Sugar. Pfeffer, working with his apparatus and different strengths of cane sugar in solution on the inside, was able to show that pressures were developed having the intensities indicated in the table below : Table shoiving osmotic pressure of solutions of cane sugar of different degrees of concentration. Strength of solution. Pressure in m.m. of mercury. Pressure per sq. inch. Height of colrmn of water susti iued, in feet. 535 Ibs. 10 36 23.9 2 per cent 1,016 19 68 45.4 2.74 per cent 1,518 29.41 67.8 4 per cent 2.0S2 40 34 93.0 6 per cent .. 3 075 59 57 137.4 From this table it appears that Pfeffer was able to secure pressures ranging from about 10 to 60 pounds per square inch, or enough to sustain a column of water from 24 to 137 feet high. * Detailed descriptions of the method of forming the membrane and setting up the apparatus can be found in Gray's Botanical Text Book, 6th Ed., Vol. II, p. 5:27, and in Jones' The Modern Theory cf Solutions, p. 3. 4:6 Introduction. Using a 3.3 per cent, solution of potassium nitrate in his apparatus Pfeffer secured a pressure of nearly 85 pounds per square inch or enough to sustain a column of water 195 feet high. This force has been looked upon as the cause of the movement of sap in plants and it was a search for a cause for this movement which led Pfeffer to make the observations here referred to. 62. Influence of Temperature on Osmotic Pressure. Pfeffer extended his observations so as to measure the influence of different temperatures on the osmotic pressure of the same solution in the same piece of apparatus and some of the results he obtained are given in the next table. * Table showing the influence of temperature on the in- tensity of osmotic pressure. 1 With temp. 14.2C. pressure=51 c. m. but with temp. 32C.pressure= 54.4 c. m. 2 " " 6.8 " 50.5 " " " 13.7 " = 52.5 " 3 " " 15.5 " =52. " " " 36.0 " =56.7 " In order to understand the relation of osmotic pressure to temperature it is necessary to state them in terms of degrees above absolute zero (32) rather than above the temperature at which water freezes. When the results are stated with reference to the absolute zero of temperature they stand as below: 1 With temp. 287.92C pressure=51 c. m. but with temp. 305.72C pressure- 54.4 c.m. 2 " " 280.52 " =50.5 " <' " 287.42 " =52.5 " 3 " " 289.22 ' =52. " " " 309.92 " =56.7 " These observations are in harmony with others regard- ing plant growth which show that a low soil temperature may cause plants to wilt even in the night when evapora- tion from the leaf surface is small, while a high soil tem- perature may increase the root pressure to such an extent as to cause drops of water to form at the tips of leaves in a bright day. 62a. Osmosis and Diffusion in Plant Feeding. If in a plant cell water is being used in the production of some substance such as starch, sugar or cellulose, the water Osmosis. 47 molecules will be removed from solution and prevented from exercising pressure, thus causing a reduction of the osmotic water pressure in that cell; this will permit more water from the adjacent cells to be driven in to make good the loss. So, too, if water is being lost by evaporation from the leaves, this loss will result in a reduced osmotic water pressure in the leaf cells which will permit the heavier pressure in the cells extending backward toward and to the root hair in the soil to force more water onward toward the leaves and thus maintain the flow of water by powerful osmotic pressure toward the leaves as long as evaporation continues. When nourishment is being stored in the seed the sub- stances in solution in the sap are being taken out and laid down in solid form, thus tending to maintain at that place a reduced osmotic pressure which permits the sub- stance of that sort to be forced continually toward the place where the formation is going on. In this way the starch and other products are supposed to be brought from the leaves and stems to the seeds or places in stems, like the potato, where food products are. being stored. In the gathering of nitrogen from the nitrates in the soil water, too, the process would be the same. Wherever the nitrate is being transformed there its osmotic pres- sure would be falling and this permits more to be forced to the same point. The so-called selective power of plants, whereby they obtain those substances dissolved in the soil water which they need, is thus explained. It should be understood that unless the mole-cules of a substance in solution are too large to pass from cell to cell through the walls these substances will do so until the solution inside the plant has a strength equal to that outside, but if this substance chances to be one which the plant does not use there will be no further concentration of that substance in the plant unless it be at places where evaporation is taking place. If a poisonous principle exists in the soil water os- 48 Introduction. motic pressure will tend to force this substance into the plant tissues and the plant is helpless to prevent this en- trance. 63. Dissociation of Salts in Solution. There is a large class of substances which, when they go into solution in water, increase its electrical conductivity. It is also true that the osmotic pressure which they may develop is greater than can be explained on the basis of the number of molecules which were contained in the salt before its solution occurred. To account for both the greater electric conductivity and the higher osmotic pressure in such cases it has been assumed that, at the time of solution, more or less of the molecules dissolved separate into two groups, each of which may take part in developing osmotic press- ure, making it greater than it could otherwise be. When a very dilute solution of potassium nitrate, for ex- ample, is made, it is supposed that the molecules are broken into two groups, each of which may absorb heat energy and so strike a greater number of blows per unit of time against the confining membrane, and in this way produce a higher pressure. The two ions, as they are called, act like two hammers and each is able to absorb and deliver more energy when moving separately than when combined as a single but heavier hammer. PHYSICS OF THE SOIL, CHAPTER I. NATURE, ORIGIN AND WASTE OF SOIL. 64. Nature of the Soil. The great bulk of most soils is made up of small fragments of rock of various kinds, but nearly always there is associated with these varying amounts of organic matter derived from the breaking down of plant and animal tissue. On the surface of the soil grains, too, there is always ad- hering more or less of substances which have been dis- solved in the soil-water but which have been deposited again when the water was evaporated. In most soils, but chiefly in the clayey types, there oc- curs some aluminium silicate having water combined with it, which is regarded as giving to them their sticky, plastic quality when wet. The amount of this material in a good soil is always small, seldom reaching more than 1.5 per cent., but the particles are so extremely minute that very little by weight has a marked effect upon its character. 65. Soils and Sub-soils. In climates where the rainfall is sufficient for large crops it is common to speak of the sur- face few inches of rock fragments as the soil while that below is known as the sub-soil. The fundamental reason for making this distinction is found in the fact that the latter is less productive than the surface soil. So general is this difference in fertility that the term "dead-furrow" has been universally applied to the finishing of a land in plowing where the two furrows are thrown in opposite 50 Physics of the Soil. directions, leaving the sub-soil exposed, and where crops are always smaller. On the other hand, where two fur- rows are thrown together to form the "back-furrow" and the depth of soil increased crops are notably more vigorous. We do not yet know just why a sub-soil , when exposed to the surface is less productive than the true soil, but the difference seems in some way to be associated with the larger per cent, of the extremely minute particles which sub-soils contain. In arid regions where the rainfall is not sufficient for crop production it seldom occurs that the deeper soil is markedly different in productiveness from that at the sur- face. Soil taken from the bottom of cellars and even from depths as great as 30 feet is found quite as productive when placed upon the surface as the top soil. So gener- ally true is this that when it is desirable to level fields for purposes of irrigation in arid climates the soil from the higher places may be scraped to the lower levels without fear of lessening the productiveness of the fields. 66. Uses of Soil. In the agricultural sense the most im- portant use of soil is to act as a storehouse of moisture for the use of plants; and the productiveness of any soil is in a very large degree determined by the amount it can hold, by the manner in which it is held and by the readiness and completeness with which the plant growing in it is able to withdraw that water for its use as needed. In the second place, the soil is a storehouse from which plants derive the ash ingredients of their food, the lime, the potash, phosphoric acid and other materials of this class, all of which are derived from the slow decay and solution of the soil grains. Besides these the soil is a laboratory in which a great variety of microscopic forms of life are at work during the warm portions of the year, breaking down the dead organic matter of the soil, converting it into nitric acid and other forms available to higher plants, and the student must never forget that the magnitude of the crop taken Formation of Soil. 51 from the field is always in proportion to the size of the crop developed by the micro-organisms in the soil. Then again ; the soil is a medium in which plants may place their roots in such a manner as to enable them to stand erect in the open sunshine and moving air currents above. Finally, the soil is a means whereby the sunshine is changed into forms of energy available to the needs of soil organisms and the roots of plants and without which this life could not exist ; for all of its movements must originate primarily from the sunshine altered in the soil or in the tis- sues of the plant above the soil. 67. Formation of Soil There are many agencies at work in the formation of soils and the processes of soil growth are in continuous operation day and night, winter and sum- mer. Since all soil material originates from the breaking dow y n of the various rock structures which make up the earth's surface all of the agencies which are operative in rock destruction may also contribute to soil formation. 68. Influence of Hock Texture on Soil Formation. Nearly all kinds of rock are made up of fragments or crystals of various sizes and shapes and these are held together by in- terlocking, by some cementing material, or else by direct cohesion when extreme pressure has brought the grains close enough together to make this possible. It is seldom true, however, that the structure is so close or the cement- ing so complete as to make the rock impervious to water and the closest granite or the finest marble may absorb as much as .1 to .4 of a pound of water to 100 pounds of rock. If this water is changing it will dissolve away the cementing materials and the faces of the crystals them- selves, making the rock still more open and the grains may even fall apart as is frequently observed in those cases known as "rotten stones." The water may freeze in the stone and by its expansion cause it to crumble. Or again, when the sun shines on 52 Physics of the Soil. rocks made up of minerals of different kinds the crystal? do not all expand at the same rate and this unequal expan- sion and contraction tends to loosen crystals and fragments, breaking the rock down, and thus form soil. FlQ. 8. Section of limestone hill showing rock changing to soil. (After Chamberlin.) 69. Formation of Soil From Limestone If one will visit any limestone quarry where the soil and rock are exposed in section as represented in Figs. 8 and 9 it will be clearly seen how the rock is slowly converted into soil. In such cases as these, the water containing carbonic or other acids dissolves away the lime and magnesia, leaving the more insoluble portions of the lime rock to form the soil mantle which is left. These more insoluble portions are usually clay and very fine sand so that soils formed in this way are oftenest clayey soils, sometimes containing even less lime than other soils not derived from limestone. FIG. 9. Section of flat limestone surface showing rock changing to soil. (After Chamberlin.) The mantle of soil seen above gravel beds in railroad cuts and \vhere hills have been graded down on wagon roads has usually most of it originated from the decomposition of the gravel in place in the same manner as a soil from the limestone itself. So, too, in countries where granite and other crystalline rocks lie beneath the soil, these have Formation of Soil. 53 been broken down and - the over-lying soil de- rived from them. 70. Influence of Rock Fissures. An examina- tion of almost any quar- ry where considerable surfaces are exposed re- veals the presence of systems of fissures which divide the stone layers into blocks of various sizes and at the same time provide easy ave- nues for the entrance of surface waters. These features are shown clearly in FlgS. 10, 11, FIG 10. Fort Danger, Wis., showing rock fls- 19, iiirl 13 nnrl intn fcures which lead to rock destruction. L0 > (After Chamberliu.) them the roots of trees sometimes make their way where by expansion, due to growth, such strong pressures are developed as sometimes to throw down large blocks of stone. Then again, in cold climates these fis- sures may become filled with water which, when freezing, overturns and throws down many frag- ments, thus hastening their passage into soil. 71. Soil Removal. It follows from what has been said that the same processes which result in FIG. 11. -Bee Bluff, Wis., showing rock fis.=nre? * ., _ . , which lead to rock destruction. (After SOll lOrmatlOn niUSt alSO chamberiin.) contribute to its destruc- 4 54 Physics of the Soil. tion in one place or re- moval to another. All are familiar with the creeping of soils from the brows of steep hill- sides toward their bases and out upon the more level plains which stretch away from them. These downward move- ments are caused by sev- eral agencies: (1) The beating of falling rain- drops and the carrying power of the streamlets which form as these gather together ; ( 2 ) the expansion and contrac- tion of the soil due to the alternate wetting and drying, there being FIG. 12. Giant's Castle, near Camp Douplas, , . , Wis., showing cliff's of rock crumbling into less resistance to expan- soil. (After Cbamberlin.) sion downward than upward against gravity. These movements are analogous to those of the steel rails of the railroad which tend to creep down grade under the influence of changing temperature, which causes them to first lengthen and push down hill and then shorten and again draw downward because of less resistance in that direction. (3) Then, again, every disturbance of the soil produced by animals burrowing or walking up or down the hillside, tends usually to work the soil from higher to lower levels. Even the action of the wind is on the whole downward. 72. Soils Produced by Running Water. Rivers and streams are continually at work at this double process of soil building and soil removal. When one watches the bed of a stream as the water ripples over the uneven surface Formation of Soil. 55 it is easy to note how rapidly soil and sand grains are be- ing rolled and tumbled along the bottom. If it is desired to measure this rate of movement a shallow pan or box may be sunk in the bed of the stream, leaving its rim flush with the surface over which the water rolls. After a sufficient in- terval remove the box and dry and weigh the material collected. At each bend in a stream soil is being taken from the con- cave side and carried onward toward the sea, while on the op- posite side new soil is being formed from that dragged along the bottom. In this manlier streams change their courses QTirl -nTQTnrloT. -f oiVl FlG - 13 -~ Pillar Rock, Wis., showhu? rocky cliff ana^vanaer irom Side in the last stages of decay. (After Chamber- tO side across the val- lm> ) ley, each time making a new soil on the side from which they are retreating and carrying away an older soil from the encroaching side. It is in this way that broad and flat river valleys are formed, with their terraces, such as are shown in Fig. 14. It is in this way, too, that the "ox- bows" of the Mississippi below Vicksburg were formed, some of which are represented in Fig. 15. These abandoned river channels are at first long and narrow lakes but ultimately, with the repeated overflows of the stream, they become lilled. Sometimes they remain for long intervals depressions in which swamp or humus soils develop. 56 Physics of the Soil. I tc Formation of Soil. FIG. 15. Showing the shifting of river channels, the formation of "ox-bows" and alluvial soils. 73. Glacial Soils. In those portions of the world where the temperature is so low that most of the moisture falls as snow and where these snows do not all melt during the warm season there come to be such vast accumulations that the great weight compresses the snow into ice. So ex- tensive and massive are these snow and ice fields in Green- 58 Physics of the Soil. Formation of Soil. 60 Physics of the Soil. land and in parts of Alaska today that they move over the face of the country much as a broad river would move, except at a much slower rate. The same type of phenom- ena occur, too, in the elevated mountain districts of Europe and in the Sierras of this country, the ice streams con- verging and flowing into the lower valleys in the form of glaciers. As these ice streams move over the uneven sur- face of their valleys and crowd against their sides, the rocks, gravel and sand taken up by the moving ice act with great effectiveness to abraid into soil the rigid rock surfaces over which they move. FIG. 18. Showing rock surface over which glaciers have passed, scratching and polishing it. In a recent geological epoch the whole of the Xorth American continent north of the Ohio and Missouri rivers and much of northern Europe and Siberia were under enor- mous moving ice sheets which resulted in the formation of the extensive glacial soils of these countries ; consisting largely of a rock flour ground to varying degrees of fine- ness, and naturally very fertile where the materials have not been sorted by the waters from the melting ice in such a way as to form siliceous sandy plains. Figs. 16, 17, 18 and i9 are views illustrating different phases of soil forma- tion by glacial action. Formation of Soil. 61 FIG. 19. Relief Map of Wisconsin, showing the difference in topography be- tween glaciated and non-glaciated surfaces. 74. Formation of Humus Soils. There is a class of soils having their origin in various types of swamps or marshes which contain an unusual amount of organic matter in va- rious stages of decomposition and which have by some writers been given the name of humus or swamp soils, the former name referring to the large amount of humus these soils contain and the latter to the physical conditions under which they have been formed. In many places in the higher latitudes and at consider- able elevations nearer the equator where the surface is too flat for ready drainage, and where the winter snows re- main so long upon the ground that the summer is too short 62 Physics of the Soil. to permit the soil to become dry enough to allow the air to penetrate deeply and freely, the organic matter accu- mulates and soils are formed containing a large proportion of humus ; even beds of peat may develop. Under other conditions, where rivers ap- proach their outlet across a very flat country g and are no longer able to scour their chan- .2 nels and keep them clean, the moving sedi- | ment finally raises the banks and the bed un- * til the water is flowing above the surround- = ing country. Under these conditions with a a continual seepage and frequent overflows a swamps are developed in which marsh vege- ^ tation grows luxuriantly and, falling under % conditions where free oxidation cannot oc- | cur, the remains only partially decay, giving 1 rise to beds of peat and rich humus soils. In other cases, where a river often shifts | its course and especially where the cut-offs "S or ox-bows illustrated in Fig. 15 are formed, | these places, with the poor drainage which | they must have and with the occasional over- o flows to keep the cut-offs filled with water, "S are maintained wet long and continuously j enough to allow humus soils to form. | With the final withdrawal of the great ice * sheet from the glaciated parts of America S and Europe there were left large numbers of J5 shallow lakes whose flat margins were wet \ enough to support marsh vegetation and S very often this vegetation came to form a 2 floating fringe steadily encroaching upon the lake in the manner represented in Fig. 20. As the vegetation continued to grow and die the fringe became heavier and sank more deeply in the water until finally the whole lake was overgrown and until the organic matter, together with the sediments brought down by the rains and the w'inds and washed in Formation of Soil. 63 from the surrounding higher land, became so heavy and so thick as to rest upon the bottom of the lake, converting it into a marsh of peat or humus soil. On the margins of larger lakes and especially along the seashore, sand bars or reefs are thrown up behind which bodies of water are shut off and in 5 these organic matter may accumulate ti in the same manner as that just de- ^ scribed, giving rise to the same type of -f soils. In still other cases, on the margins of the sea bottom, there flourishes a pe- 1 culiar type of vegetation known as eel grass, which lives always beneath the water at low tide in a position repre- g sented in Fig. 21. These grasses offer ?. a natural obstruction to the incoming g and outgoing tidal waters, causing them to throw down their sediments B and thus build up the sea floor with silt containing large amounts of or- & ganic matter under conditions unfav- g orable to rapid decay. As the sea floor ? rises in this way above low tide level g* the eel grass dies and another type of g- swamp vegetation takes its place, as between a and b in the figure, and here j* again the formation of humus soil is continued under somewhat different conditions. 75. Wind-Formed Soils. The wind moving continuously over the face of the land is now and long has been a potent factor in soil removal and soil building. Indeed, it is probable that nowhere can soils be found which do not contain many wind-borne particles. Every raindrop which falls and every snowflake, however white, brings to the field upon 64 Physics of the Soil. which it falls one or more particles of soil which has been drifting in the higher air from unknown distances. The drifting of dust from roads during dry times and from fields iii the spring are strong reminders of the po- tency of wind action at times, but it is the less evident but continuous action that counts most in the long run and, were it not for the steady wearing away and rearrangement of the soil surface, wind-formed soils would be much more evident and general than they are. On the leeward margins of arid regions and on sandy coasts the building and eroding power of the wind becomes most evident, and the most extensive deposits which have been assigned to this cause are the loess beds of China which have great horizontal extent and in some places depths reaching even 1,200 and 2,000 feet. These depos- its have been described by llichthofen as having been formed from dust accumulations drifted by the prevailing winds from the high desert plateaus of Central Asia. In Europe, and in this country in the Mississippi val- ley, there are deposits of a similar character. They are distributed along the border of a former ice sheet of the glacial period and from thence they spread down the main streams, along the Mississippi from Minnesota to near the Gulf, along the Missouri from Dakota to its mouth, and along both the Illinois and the Wabash. These deposits are thickest, most typical and coarsest along the bluffs nearest 'to the streams and they thin out and become finer as the distance back increases. It is thought that the fine silts borne along by the waters of the glacial streams in times of high water were spread out over broad flats and as the ^.waters withdrew they were left to dry in the sun and then -picked up by the winds and drifted away. The loess soils are almost always extremely fertile and very en- during. 76. The Work of Animals as Soil Producers Thci'e are ninny animals which have contributed largely to the forma- tion of soil through a grinding of pebbles and the coarser sand and soil grains into finer materials. Formation of Soil. 65 Darwin, through a long and careful study, reached the conclusion that in many parts of England earthworms pass more than 10 tons of dry earth per acre through their bodies annually and that the grains of sand and bits of flint in these earths are partly worn to fine silt by the muscu- lar action of the gizzards of these animals. Their method of action in moving through the soil is this : They eat a narrow hole, s\vallowing the earth, when the point of the head is held fast in the excavation while an enlarged por- tion of the oesophagus or swallow is drawn forward, forc- ing the cheeks outward in all directions, thus crowding the soil aside and making the opening wider, when more dirt is eaten and the operation repeated, allowing the animal to advance through the soil. Domestic fowls and all seed-eating birds, in picking up pebbles for service in grinding their food, do the same sort of work as the earth- worms in producing fine soil, as every housewife can testify from the worn condi- tion of bits of glass and pottery taken from the gizzard of the chicken. 77. Soil Convection There is another very important line of work done by earthworms, ants and all burrowing animals, in bringing the sub-soil to the sur- face and carrying the surface soil into the ground, thus maintain- ing a sort of soil-con- , i i f FIG. 22. A tower-liko casting ."ejected by a spo- VeCtlOn WniCn, in CI- cies of earthworm, from the Botanic Garden, ,^4-n 4-^ amounts to Calcutta, India. Natural size from photo. ( After Darwin.) 66 Physics of the Soil. . 23 Showimg the work of the common earth worm during a single night after a heavy rain. Formation of Soil. 67 same thing as plowing except that its influence extends much deeper. Both earthworms and ants often burrow in the ground to a depth of four feet, and in some cases more than nine, bringing the material to the surface and forming passage- ways down which the rains may wash the finer surface soil. Fig. 22 shows a single pile of earth cast up by an earthworm in the Botanic Gardens of Calcutta, and Fig. 23 shows the work of our common earthworm during a single night in bringing up soil after a rain. FIG. 21. Section of vegetable mould in a field drained and reclaimed 15 years before; showing turf, vegetable moulds without stones, mould with frag- ments of burnt marl, coal cinders and quartz pebbles buried under the influence of earthworms. Ono-third' natural size. (After Darwin.) This frequent bringing of earth to the surface tends to bury objects and gradually to lower them into the ground, and Fig. 24 represents the results of one of Darwin's studies, showing the amount of soil which has accumu- 08 Physics of ike Soil. lated above bits of burnt marl, cinders and pebbles dur- ing 15 years, largely through this action of earthworms and ants in bringing to the surface portions of the sub- soil. It will be seen that the amount accumulated is more than three inches, or at the rate of an inch in 5 years. CHAPTER II. CHEMICAL AND MINERAL NATURE OF SOILS. 73. Unsatisfactory State of Present Knowledge. It is now pretty generally conceded that the capacity of a soil to feed crops of a given kind cannot be foretold with much certainty from the results of chemical analyses as it has been the custom to make and present them. It has been found, for example, in the arid west, that soils nota- bly deficient in humic nitrogen and which for this reason should be comparatively unproductive, have, nevertheless, been found capable of giving large yields when irrigated. Then again, in moist climates there are types of soil ex- ceptionally rich in both humic and nitric nitrogen which are comparatively unproductive until they are given dressings of coarse farmyard manure. The analyst would place them among the richest of soils and yet they are among the poorest until given farmyard manure; and, what appears stranger still, straw and coarse litter may be much more beneficial to them than liquids from the sta- ble cistern. 79. Essential Constituents of a Fertile Soil. While it is true that our chemical knowledge of soils is very unsatis- factory, it has nevertheless been thoroughly established that a fertile soil must contain certain substances in order to permit any crop to come to maturity upon it and these are potassium, calcium, magnesium, phosphorus, sulphur, iron, nitrogen and probably chlorine. Let any one of these ele- ments be absent from a soil, or its moisture, and crops fail to develop upon it. It has not, however, been established yet in what form of combination these elements must or may exist nor in what proportions to give the best results. It is known that they do not exist in the soil in the elementary form and that they are combined in a great variety of ways. 5 70 Physics of the Soil. Furthermore, from these combinations, under favorable conditions, plants are able to supply their needs. 80. Functions of the Essential Plant Foods. From the standpoint of plant physiology it is again unfortunate that little has yet been positively demonstrated regarding the part played by each of the essential elements of plant food taken through the soil and soil moisture. It is known that nitrogen is an essential constituent of the protein com- pounds of living tissues, and that to most of the cultivated crops it becomes available in the form of nitric acid or of a nitrate of lime, magnesia, potash or some other base. Po- tassium does not appear as an essential ingredient of plant tissues or of its storage products like starch or gluten, but Nobbe, Schroeder and Erdmann have shown that when Japanese buckwheat, placed in nutritive solutions en- tirely free from potash salts, after a few weeks' growth came to a standstill and that all organs of the plant came to be nearly or quite free from starch ; but when a potas- sium salt was added to the solution starch began to develop and growth became normal. In regard to phosphorus the clearest indications go to suggest that it is usually taken into the plant in the form of phosphates and, because its compounds are often asso- ciated with the soluble albuminoids, that it assists in some way in the transfer of these from place to place in the plant. Some compound of iron must exist in soil solutions and must enter the plant before the normal development of the green coloring matter, chlorophyll, can take place; so ex- tremely small quantities, however, are needed that no soil is ever lacking in sufficient available forms. Sulphur is apparently largely if not wholly taken into the plant in the form of sulphates, and these are thought to be decomposed by the oxalic acid, setting the sulphuric acid free, which is then broken down and the sulphur appro- priated to enter as an essential constituent of the albumin- oid compounds. But little is known of the part played in plant life by Chemical Nature of Soils. 71 the salts of magnesium except that they must be present in the seed. The action of lime is held to be medicinal, its function being to neutralize the poisonous oxalic acid liberated a3 an intermediate product in the oxidation of carbohydrates. Largo amounts of silica and alumina and smaller amounts of many other substances are found in the ash of plants but their presence there is regarded as accidental, growing out of the simple fact that they chanced to be dis- solved in the soil-water and passed into the tissues with it during growth. 81. Chemical Composition of Soils. From what has been said regarding the origin of soils and the manner in which their particles have been moved from place to place, it is evident that there must necessarily be a strong similarity among them, of both chemical and mineral composition, wherever found. It has been customary in analyzing soils to digest a certain weight of dry soil for a stated time in a certain strength of hot hydrochloric acid and to examine the solution for the compounds it might contain, calling the part not dissolved the insoluble residue. The tables on pages 74-75 show the results of some of these analyses, taken from the papers of Hilgard in the Tenth Census of the United States. 82. Chemical Difference Between Clayey and Sandy Soils. Studying the table of clayey and sandy soils it will be noted that out of every 100 pounds of the clayey soil there were, as an average, 31.791 pounds which dissolved in hot hydrochloric acid, while only G.79 pounds were soluble in like weight of the. sandy soil. In other words, a quarter of the weight of the clayey soils more than of the sandy soils is soluble in a unit of time in hot hydrochloric acid. There is about 2.5 times as much potash and organic matter, nearly twice as much phosphoric acid, 7 times as much lime, 9 times as much magnesia and 1.4 times as much sulphuric acid in the clayey as in the sandy soil, which may be dissolved out in equal times by the solvent used. These ratios, however, are sometimes a long ways from 72 Physics of tlie Soil. true when single cases are compared, and this is shown in a striking manner in the single case of clay soil given below the line of averages in the table of sandy and clayey soils. This is described by Hilgard as a fair upland soil yielding 700 to 800 pounds of cotton per acre, gray in color, not heavy, 6 to 8 inches deep, and underlaid by a subsoil quite heavy in tillage and dark orange in color ; and yet its in- soluble residue is about 91 per cent, and there are two of the sandy soils where the per cents, are 90 and 92 respec- tively, showing that the two are more nearly alike chemi- cally than they are physically. 83. Observed Chemical Differences, Partly Due to Differ- ences in Amount of Soil Surface. It is a common experience that the more finely a substance is subdivided the more rapidly will it dissolve. Fine salt and powdered sugar, for example, dissolve much more rapidly in water than the coarser grained varieties do. In the clay soils the particles have a much smaller diameter than they do in the sandy soils and hence the number of grains in a given weight of soil will be much larger, but the number of grains cannot be increased without also increasing the surface upon which the solvent may act, and hence with the same strength and amount of acid, for equal weights of the coarse and fine grained soil, having exactly the same chemical composition, there should be dissolved in equal times a larger per cent, of the soil having the largest amount of sur- face. The sandy soils therefore are not likely to be as dif- ferent from the clayey ones as the table of analyses indi- cate. 84. The Chemical Differences Between Soils and Their Subsoils. In humid climates there is usually a marked dif- ference in the producing capacity of the soils and their sub- soils as was pointed out in (65), and a study of the table of subsoils, pp. 74, 75, will show that there is a chemical difference also. It will be seen that the surface soils con- tain more lime, phosphoric acid and organic matter, less soluble silica, alumina and iron and about the same amounts of potash, magnesia and sulphuric acid. Chemical Nature of Soils. 73 85. Comparison Between Clay Soils and Swamp Soils. If a comparison is made between the clayey soils, which are generally productive naturally, and the humus soils it will be seen that the latter contain about twice as much potash, magnesia, sulphuric acid and organic matter, six times as much lime and a little more phosphoric acid, and yet for some reason the humus soils, when well drained, may not naturally be as productive as the clay soils are and here is where the present methods of soil analysis fail to tell the whole truth. 86. Comparison Between Clayey Soils and Loess Soils. The loess soils do not show a much larger percentage amount of the essential ingredients of plant food than do the clayey ones. Indeed there is less of organic matter and only a little more of potash, phosphoric and sulphuric acids. The chief and great difference lies in the large amount of lime and magnesia which they contain, the first being more than 9, and the latter more than 8 times as large. If it is true that these soils are largely wind-formed it is to be ex- pected that these A wo substances would appear at the sur- face to be taken up by the winds more than any other of the essential ingredients, first, because they are comparatively soluble and bence likely to be brought up by the capillary waters and left after evaporation where the wind has free access to them ; and second, because they are not so soluble as to be completely dissolved by the heavy rains and car- ried back into the ground again. 87. Difference Between Arid and Humid Soils. The soils which have accumulated in the arid climates of the world are quite markedly different from those of the more humid portions, both in physical and chemical properties. The per cents, given in the table of arid and humid soils are those of Hilgard and are averages of 466 analyses from hu- mid climates and 313 from arid. It will bp seen that the arid soils contain more than 3 times as much potash, nearly 13 times as much lime and 6 Physics of the Soil. Chemical composition of soils. Essential ingredients in per cent of dry soil. POTASH. LlUE. MAGNESIA. PHOSPHOR- IC ACID. SULPHURIC ACID. WATEB AND ORGANIC MATTER. Sand. Clay. Sand Clay. Sand. Clay. Sand. Clay. Sand. Clay. Sand. Clay. .100 .416 .120 .080 .040 .691 .051 .103 .028 .061 2.055 1.006 .156 .176 .081 090 .069 .112 .101 .071 .Or7 .055 2.642 8.891 .015 .186 .064 .071 .005 .065 .066 .204 .091 .285 2. 422 8.9S3 .117 .134 .058 .219 .042 .289 .092 .069 .058 .035 1.807 8.309 .110 .242 .090 .387 .025 .508 .191 .071 .105 .055 3.477 6.843 .067 .092 .119 .036 .090 .070 .111 .082 .054 .054 2.881 6.167 .275 .431 .055 .540 .048 .836 .105 .187 .001 .009 3.682 6.922 .095 1.104 .076 1.349 .083 1.665 .0.(9 .304 .045 .024 2.354 7.369 .209 .150 .141 3.054 .031 .0:29 .103 .24i .046 .089 3.113 4.962 .034 .255 .045 .340 .013 .296 .014 .079 .035 .079 1.636 4.962 .121 .319 .085 .617 .048 .456 .037 .141 .055 .075 2.607 6.528 .137 .173 .203 .038 3.394 SWAMP AND LOESS SOILS. Hu- mus Loess Hu- mus. Loess Hu- mus Looss Hu- mus. Loess Hu- mus. Loess. Hu- mus. Loess. .639 .435 3.786 5.820 .886 3.C02 .150 .203 .148 .090 13.943 1.205 SOILS COMPARED WITH THEIR SUG-SOILS. SOILS. Sand. Clay. Sand Clay. Sand Clay. Sand Clay Sand. Clay. Sand. Clay. 6.014 .157 .214 .115 1.761 .076 .182 .128 .207 052 .030 2.853 SUB-SOILS. .143 .314 .096 1.481 .073 .240 .058 .124 .150 .060 .071 1.9J3 4.780 }-. 014 -.130 + 019 + .280 +.003 +.004 + .018 -.008 +.019 +.910 +1.234 ARID AND HUMID SOILS COMPARED. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. Hu- mid, Arid. .216 .729 .103 1.362 .225 1.411 .113 .117 .052 .041 3.644 4.945 Chemical Nature of Soils. Chemical composition of noils. Inert ingredients in per cent, of dry soil. BROWN INSOLUBLE RESIDUE. SOLUBLE SILICA. SODA. OXIDE OF MAN- PEROXIDE or IEON. ALUMINA. GANESE. Sand. Clay. Sand Clay. Sand Clay. Sand Clay. Sand Clay. Sand. Clay 93.630 72.746 1.682 8.9:!6 .000 .112 .102 .106 .761 12 406 1.532 2.473 94 770 73 690 .488 3.370 .069 .004 .156 .146 .706 5.939 .7*3 7 305 93.882 60.3-0 1.721 2.000 .018 .119 .220 .196 .941 9.709 1.33;) IS 0*16 05.690 73.422 .879 2.70) .OS4 trace .4)49 .164 .224 4.054 .473 10.598 92.0UO 63.444 1.220 11.325 .035 .079 .126 .052 .963 3.894 1.959 13.454 90 230 77.880 1.940 1 790 .009 .041 .313 .056 1.927 5.646 1 2.141 7. 538 90. CM 54 565 1.8X5 13 219 .130 .277 .172 .079 1.837 7.089 1.436 1C. 071 9^ 460 51.0(53 1.650 20 701 .036 .325 .040 .119 .843 5.818 2.649 10.539 94. 4 'is 79 5.HO .529 3.628 .069 .065 .101 .195 .661 3.4-20 1.185 4.9N-* 94.822 75.350 1.03J 7.310 .022 .258 .020 .038 .930 5.784 1.576 5.567 93.210 68.203 1.293 7.498 .051 .128 .130 .115 .979 6.381 1.503 9.660 91.49S 1.722 .054 .066 1.372 1.522 SWAMP AND LOESS SOILS. Hu- mus. Loess. Hu- mus. Loess. Hu- mus. Loess Hu- mus. Loess Hu- mus. Loess Hu- mus. Loess 35.886 68.853 20825 4.913 .109 .165 .098 .164 7.040 3.569 14.476 2.812 SOILS COMPARED WITH THEIR SUB-SOILS. SOILS. Sand. Clay. Sand Clay. Sand Clay, Sand Clay. Sand Clay. Sand. Clay. 93.222 73.978 1.019 5.034 .072 .085 .124 .133 1.162 5.205 1.145 6.993 SUB-SOILS. 90.714 66.290 2.212 7.446 .061 .085 .080 .125 1.739 6.947 2.276 12.036 +2.508 +7.688 -1.193 -2.412 + .003 .000 +.014 +.003 .577 -1.742 1.131 -5.083 ARID AND HUMID SOILS COMPARED. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. S4.031 70.565 4.212 7.266 .091 .264 .133 .059 3.131 5.752 4.296 7.883 76 Physics of the Soil. times as much magnesia as do the humid soils with which they have been compared. They also contain some more of each of the other essential plant foods except sulphur, the sulphuric acid being less. If, however, a comparison is made between the arid soils and the mean of the 10 clay soils given in the first table, it will be seen that, excepting potash, lime and magnesia, these contain more of the essential ingredients of plant food than do the arid soils, and so, too, there is more solu- ble silica. 88. Humus. It is this product in the soil which gives to it usually its dark color, but so far as its chemical composi- tion is concerned its nature is not yet well understood. It is a very important ingredient of fertile soils and is the product of decaying organic matter, In torrid climates where the scil is warm the whole year and in arid regions where the soil is more open on account of deficient moisture as well as on sandy soils wherever found, the rate of complete decay is so rapid that the amount of humus is generally relatively small ; but in tem- perate climates, where the soil is damp, its texture close and rains frequent, the organic matter decays more slowly and the amount of humus in the soil is relatively greater. The great importance of humus in agricultural soils is found in the fact that it is relatively insoluble under good field conditions and does not leach away and in this form becomes the food of niter-forming germs which convert it by degrees into nitric acid, as one of their waste products, but the essential form of nitrogen for the food of most higher plants. A soil entirely devoid of humus must neces- sarily be manured or given nitrogen in some other form in order to make it fertile. 89. Difference Between the Humus of Arid and Humid Cli- mates. Hilgard and Jaffa have made the important dis- covery that the humus of arid soils is relatively richer in nitrogen than is that of humid soils and hence that smaller Chemical Nature of Soils. 77 amounts of it will meet the needs of niter-forming germs and thus allow large crops to be produced where, with a poor form of humus, this would be impossible. The results of their studies in this line are stated in the table below : No. of samples. Humus in soil. Nitrogen in humus. Humic nitrogen in soil. 18 Per cent. .75 Per cent. 15 87 Per cent. 101 g .99 10 03 .102 8 3.0t 5 24 .132 In speaking of these results they say, "It thus appears that, on the average, the humus of the arid soils contains three times as much nitrogen as that of the humid, that in the extreme cases the nitrogen percentages in the arid hu- mus actually exceeds that of the albuminoid group, the flesh-forming substances." "It thus becomes intelligible that in the arid region a humus percentage, which, under humid conditions, would justly be considered entirely inadequate for the success of normal crops, may, nevertheless, suffice even for the more exacting crops. This is more clearly seen on inspection of the figures in the third column, which represent the product resulting from the multiplication of the humus percentages of the soil into the nitrogen of the humus." 90. Chemical Composition of Soils Compared With the Rock from Which They Are Derived. When a soil accumu- lates in place from slow decomposition of the underlying rock there is sometimes a close resemblance in chemical composition between the rock and the derived soil, but in other cases there is little resemblance between them. If the rock is made up of a large percentage of relatively solu- ble materials, as is the case with most limestones, then the solvent power of water, combined with the effects of leach- ing, tend to cause a concentration of the relatively insoluble 78 Physics of the Soil, ingredients, thus giving rise to a soil very different in chem- ical composition from the parent rock. If, on the other hand, the rock is made up of minerals of nearly equal solubilities, or if in any way the soil results from a mechanical breaking up of the rock, then the soil may have much the same relative amounts of ingredients as the parent rock shows. In the table which follows are given the composition of some rocks and of soils derived directly from them: Composition of rocJcs and residual soils. ] 'TRENTON LIMESTONE BERMUDA LIMESTONE GNEISS, GRANITE. DlOBITB. Rock Soil. Rock Soil. Rock Soil. Rock Soil. Rook Soil. Prct. Prct. Prct. Pr ct Prct. Prct. Prct. Prct. Prct. Prct. Silica (SiO 2 ) .... .44 43.07 .052 45.16 60.69 45.31 69.33 65.69 46.75) 42.44 Alumina (A^Os) .042 25.07 .54 15 473 16.89 26 55 14.33 15.23 17.fi! 25.51 Ferric oxide 15.16 13.898 9.16 12.18 3.60J 4.39 16.79 19.20 Lirno (CaO) ti'.ii' 0.63 54 '496 3.948 4.41 tr. 3.211 2.63 9.46 0.37 Magnesia (MgO) tr. 0.03 1.751 0.539 1.06 0.40 2.44 2.64 5.12 21 Potash (KzO) ... notd. 2.50 0.06S 0.133 4.25 1.10 2.67 2.00 0.55 0.49 Soda (Na2t>) notd. 1.20 0.252 0.007 2.42 0.22 2.70 2.12 2.56 56 Carbon dioxide.. 42.72 tr. 44.251 2.533 0.00 0.00 0.00 Phos. acid (PaOs) 0.47 '6!io 6!66 0.25 0.29 Water and vola- tile products .. 1.03 12.98 .32* 18.265 .62 13.75 11.22 4.70 0.92 10.92 The two limestones, it will be seen, have given rise to a soil containing almost as much silica, alumina and iron oxide combined as is contained in the three soils from the other three kinds of rock, the per cents, standing, in round numbers, 83, 75, 84, 85 and 87. In other words there is a strong tendency to bring all soils approximately to one composition. Indeed it may be said that in any soil the essential ingredients of plant food make up but from 3 to 8 per cent, of the total dry weight. It will be observed that in the case of the soil derived from the Bermuda lime- stone, not less than 98 pounds of every 100 pounds of rock i Rocks, Rock Weathering and Soils. Merrill. Chemical Food in Soils. 79 arc dissolved and carried away by the water for each 2 pounds of soil formed, the chief materials carried away being the lime, magnesia and carbon dioxide. 91. Amount of Essential Plant Food Removed from the Soil by Crops. It is very important, in the management of soils, to know something of the draught upon them which crops of different kinds make, and in the table which fol- lows is given the amount of materials removed from the soil in 1,000 pounds of fresh or air-dried product. Table showing Ibs. of plant food in 1000 Ibs. oj air-dried product. (WOLFF.) MAIZE. OATS. WTNT'E WHEAT SPRING WHEAT WINT'B RYE. BARLEY BED CLOVEB It id E O & C3 fa 03 a S 3 Total ash Potash (K 8 O) ... Soda (Na a O) ... Magnesia (MgO) Lime (CaO) Fhos acid iPgOs) Sul. acid (SOs).. Sulphur Nitrogen 45.3 16.4 .5 2.6 4.9 3.8 2.4 3.9 4.8 12.4 3.7 0.1 1.9 0.3 5.7 0.1 1.2 16.0 61.6 16.3 2.0 2.3 4.3 28 2.0 1.7 5.6 26.7 4.8 1.0 1.9 1.0 6.8 0.5 1.7 17.6 46.0 6.3 0.6 1.1 2.7 2.2 1.1 1.6 4 X 16.8 5.2 0.3 2.0 5 7.9 0.1 1.5 20.8 ..! 11.6 1.0 0.9 2 6 2.0 1.2 '.V6 18.3 5.6 0.31 2.2 0.5 9.0 0.2 20'5 38.2 8.6 0.7 1.2 3.1 2.5 1.6 0.9 4.0 17.!) 5.8 03 2.0 5 8.5 0.2 1.7 17.6 45.9 10.7 1.6 1.2 3 * 1.9 1.8 1.3 6.4 22.3 4.7 0.5 2.0 0.6 7.8 0.4 1.4 16.0 57.6 18.6 1 1 6.3 20.1 5.6 1.6 2.1 19.7 38.3 13.5 0.4 4.9 2.5 14.5 0.9 30 '.5 From this table it appears that each ton of clover hay withdraws from the soil 39.4 Ibs. of nitrogen; 37.2 Ibs. of potash ; 12.6 Ibs. of magnesia ; 40.2 Ibs. of lime ; 11.2 Ibs. of phosphoric acid ; and 14.2 Ibs of sulphuric acid, making an aggregate of ash ingredients alone of 154.8 Ibs. 92. Amount of Plant Food in an Acre-foot of Soil. If we take 4,000,000 pounds as the dry weight of an acre-foot of all soils, except the humus and that at 2,000.000 (149), and the percentages of essential plant food given in the tables on pages 74 and 75, the amount of plant food per acre-foot may then be computed, giving the results in the table below: 80 Physics of the Soil. Table giving the tons of essential plant food per acre-foot of different types of soil. Sandy soil. Clay soil. Loess soil. Humus soil. Potash (KgO) Tons. 2 42 Tons. 6 38 Tons. 8 70 Tons. 6 39 Lime (CaO) 1.70 12 at 116 40 37 86 Magnesia (MgO) .96 9.12 73.84 8 68 Phosphoric acid (PvOs) 1.74 2.82 4.00 1 M3 Sulphuric acid (SOj) 1.10 1.50 1.80 1 48 From this table it appears that the amount of plant food per acre-foot of field soils, not including nitrogen, ranges from about 2 to 8 tons of potash, 2 to 116 tons of lime, 1 to 73 tons of magnesia, 2 to 4 tons of phosphoric acid, and 1 to 2 tons of sulphuric acid. 93. Number of Crops Required to Kemove the Plant Food of an Acre-foot of Soil. The ratio of dry weight of the ker- nels to that of the straw and chaff in a crop of wheat has been found to be as 1 to 1.1 in a dry season, but to be as high as 1 to 1.5 when there has not been an undesirable stimulation to the growth of straw. Taking this ratio of 1 to 1.5, a yield of 40 bushels of wheat per acre would mean a crop of 2,400 Ibs. of grain and 3,600 Ibs. of straw. From these two figures, the data in the table of (91) and that of (92), it is possible to compute the number of ci-ops of wheat yielding 40 bushels per acre which would remove the amount of plant food in an acre-foot of one of the sev- eral types of soil represented in the table of (92). Solv- ing the problem for the potash in the clay soil the case would be 6.38 X 2,000 (2.4X5.2) + (3.6X6.3) = 362.9 Plant Food in Soils. 81 where 6.38 is the tons of potash per acre-foot, 2,000 is the number of Ibs. in one ton, 2.4 is the number of 1,000 Ibs. of grain in 40 bush, of wheat, 5.2 is the number of Ibs. of potash per 1,000 Ibs. of grain, 3.6 is the number of 1,000 Ibs. of straw with 40 bush, of wheat 6.3 is the number of pounds of potash per 1,000 Ibs. of straw, 362.9 is the number of crops of wheat. When the problem is solved for each of the essential plant foods used by the wheat crop, the results will stand for the clay soil as given below : Potash enough for 363 crops of wheat of 40 bush, per acre. Magnesia enough for 2,082 crops of wheat of 40 bush, per acre. Lime enough for 2,260 crops of wheat of 40 bush, per acre. Phosphoric acid enough for 210 crops of wheat of 40 bush, per acre. Sulphuric acid enough for 108 crops of wheat of 40 bush, per acre. Nitrogen enough for 78.5 crops of wheat of 40 bush, per acre. In computing the nitrogen in the soil for this table .132 per cent, from the table in (89), was taken and the same weight of soil, 4,000,000 pounds per acre-foot as used for the other plant foods. It has been assumed that 40 bushels of grain and 3,600 pounds of straw per acre are taken from the ground each crop and that nothing is returned to the soil, and yet chem- ical analyses would indicate that there is enough of every- thing but nitrogen for more than a century of cropping, and this is saying nothing regarding the plant food which is known to exist in the second, third and fourth feet of soil in which the roots of plants regularly feed. Plainly we have very important knowledge yet to discover regarding the feeding of plants from the soil. 94. Experiments at Rothamstead The classic experi- ments which have been made by Sir J. B. Lawes and his as- sociates regarding the conditions which determine the fer- tility of the soil, have thrown much needed light upon this 82 Physics of the Soil. problem. By growing the same crop year after year on the same ground to which, no nitrogen-bearing manures were applied, they learned that when fertilizers containing the essential ash ingredients of the plant were added to the soil larger yields and more nitrogen could be taken from the ground. They found that when wheat grown continuously for 32 years on the same soil without manure of any sort could obtain but 20.7 Ibs. of nitrogen per acre, the same crop on adjacent and similar land given fertilizers without nitrogen could gather 22.1 Ibs. or 6.76 per cent. more. Barley, which, with no fertilizers, during 24 years could gather but 18.3 Ibs. per acre per annum, did, when aided with other ash ingredients, remove from the soil 22.4 Ibs. of nitrogen per acre. Beans, which gathered from untreated land 31.3 Ibs. of nitrogen per acre during 24 years, took off from the land under the other treatment 45.5 Ibs. per acre. So, too, in a rotation of crops, 7 courses in 28 years, no fertil- izers gave 36.8 Ibs. of nitrogen, while with superphosphate of lime the yield was 45.2 Ibs. per acre. Again in the mixed herbage of grass land 20 years without fertilizers gave 33 Ibs. of nitrogen per acre, but where mixed mineral fertilizers containing potash were given the yield was 55.6 Ibs. of nitrogen per acre. 95. Store of Nitrogen in the Soil. The mean amount of nitrogen in eleven arable and grass soils at Rothamstead is placed by Lawes and Gilbert at .149 per cent, and for eight other Great Britain soils at .166 per cent. Voelcker found in four Illinois prairie soils .308 per cent., and C. Schmidt gives for seven rich Russian soils .341 per cent. The mean of these 30 analyses is .219 per cent, and yet a soil containing but .1 per cent, will carry 4,000 Ibs. or enough for nearly 60 40-bushel crops. 96. Amount of Nitrogen in Four Manitoba Soils. As an example of soils exceptionally rich in nitrogen the table Nitrogen in Soils. below gives the distribution and amount per acre in each of the upper four feet of four Manitoba soils: Niverville. firandon. Selkirk. Winnipeg. First foot Lbs. 7,308 Lbs. 5 236 Lbs. 17 304 Lbs. 1] 984 5,408 3.48S 8,448 10,464 Third foot 2,484 2, 592 2,736 5,fiM8 Fourth foot 1,520 870 1,47 4 045 Total 16, 720 12, 186 29, 975 3^,181 Tons 8 36 6 093 14 987 16 09 Thus it is seen that in the upper four feet of these rich soils there was found from 6 to 16 tons per acre of nitrogen. 97. Forms in Which Nitrogen Occurs in the Soil. Nitro- gen occurs in the soil in several distinct forms : 1. In humus, described in (88) ; which is by far the most important form and the substance which carries the largest proportion of that which the soil contains. 2. In organic matter in the form of roots, stubble and farmyard manure, which by slow degrees is converted into humus to make good that which bus been used. 3. As free nitrogen in soil-air which is seized upon by some forms of microscopic life described in (101) and con- verted into organic form for their use. 4. As nitrates of lime, magnesia, potash and soda, and this is the form from which most of the higher plants get their supply. 5. As ammonia, nitrous acid and nitric acid, which are transition stages to one of the nitrates named above and which are formed either from the humus or organic matter or are brought down with the rain. 98. Distribution of Nitrogen in the Soil In humid cli- mates the largest amount, of nitrogen is found in the surface 6 to 12 inches, but as already shown in (96) large quan- tities are found as deep as four feet below the surface. fi4 Physics of the Soil. Warington determined the distribution of nitrogen in some of the Rothamstead soils to a depth of 9 feet in 9-inch sections. The results he found are given in the table be- low: Nitrogen in soils at various depths. Arable soils. Old pasture. Lbs. per acre 3,015 Lbs. per acre 5,351 1,629 2,313 1,461 1,580 1/228 1,412 1,090 1,301 1,131 1,186 7, 333 10, 656 4,305 4,559 Total 16,257 In these two cases the nitrogen decreases downward until about four feet and below this depth to nine feet the amount remains nearly constant. It will be seen that the amount is very large in the aggregate. Enough for more than 240 crops of wheat, 40 bushels per acre, could it all be used. 99. Amount of Nitric Acid in Soils. The amount of the available nitrogen in soils, or nitric acid, is seldom a large quantity and while crops are growing the quantity is still smaller. Warington states that the nitric nitrogen in the soil seldom reaches 5 per cent, of the total amount present, and in the surface three feet of the arable soil referred to in (98) this would represent 36G.6 Ibs. of nitric nitrogen and 1,650 Ibs. of nitric acid per acre; enough, if it could all be used, to give a yield of 211.4 bushels of spring wheat per acre. 100. Nitric Acid in Fallow Ground. The amount of ni- tric acid in fallow ground was determined to a depth of 4 Nitrogen in Soils. 85 feet in one-foot sections on May 24 and again on Aug. 22, and the results are given in the table below : Nitric acid in fallow ground in pounds per acre. 1st foot. 2nd foot. 3rd foot. 4th foot. If ay 24 78.03 21 43 8.13 4 76 293.72 116.17 23 50 16 72 215.69 9*. 74 15 37 11 96 These figures are a mean of the amounts found in nine different sub-plots, the soil being a clay loam changing into sand in the third foot. It will be seen that the total amount of nitric acid at the close of May was 112.35 Ibs., contain- ing 24.97 Ibs. of nitrogen, enough for only about 14.3 bushels of wheat. On the 22nd of August, however, there had been an increase to 450.11 Ibs. per acre, containing 100.02 Ibs. of nitrogen, enough for nearly 60 bushels of wheat per acre. 101. Source of Soil Nitrogen Until recently it was maintained that the nitrogen for the growth of all plants was derived from the humus of the soil and from the small amount of ammonia and nitrous and nitric acids brought down by the rains. It is now known that the free nitrogen of the atmosphere is the ultimate source of soil-nitrogen, and that the soil-nitrogen is being continually returned to the air again just as was long ago recognized to be the case with the carbon of living forms. 1. The immediate source of humic nitrogen is the slow decay of organic matter, whether this be the roots, stems or leaves of plants or the tissues and waste products of ani- mals, and a large part of the life processes of the world take place between the conversion of humus into living tis- sues and dead tissues back into humus again. 2. The formation of nitrous and nitric acids through an oxidation of the nitrogen of the air by electrical discharges 86 Physics of the Soil. such as occur during thunder storms is generally conceded. It is also thought that a part of these combinations may be brought about through the action of ozone upon ammonia. Warington is also of the opinion that the peroxide of hy- drogen in the air causes the conversion of some atmospheric ammonia into nitric acid, and hence that not all the nitric acid brought down by the rains was formed as new ma- terials in the atmosphere from direct union of oxygen and nitrogen gases. The amount of nitrogen brought to the soil with the rains seldom equals 5 Ibs. per acre per annum in the open coun- try, as shown by the following table : Nitrogen as ammonia and nitric acid, in pounds per acre per annum, in rain. Rothamsted. 8 years. Lincoln, New Zealand. 3 years. Barbadoes. 3 years. Lbs. 2.53 Lbs. 0.74 Lbs. 93 Nitrogen as nitric acid 0.84 1 00 2.84 3.37 1.74 3.77 f It FIG. 25 Showing the influence of free-nitrogen-fixing perms on the growth of peas. The large plants all grew in sand containing the nitrogen -fixing bac- teria, while the small plants grew in soils identically the same except that all bacteria were excluded from them. After Hellriegel Nitrogen in Soils. 87 These amounts, it will be seen, are far too small to be of great importance to plant life. 3. The process of symbiosis is a third method by which the nitrogen supply of the soil is maintained and next to the decay of organic matter is the most important of any yet well understood. It was in 1888 that Hellriegel pub- lished the results of his studies, which thoroughly estab- lished the fact that great numbers of microscopic forms of life inhabit the roots of leguminous plants, forming upon FIG. 26. Showing the growth of rye, oats, peas, wheat, flax and buckwheat in soils fertile in all elements of plant food except nitrogen, and illustrating the power of the pea, through its root tubercles, to procure nitrogen from the air. After P. Wagner. them tubercles in which these organisms live and withdraw free nitrogen from the soil-air for their needs. It had long been known to farmers that in some way clover in rotation with other crops left the soil richer in nitrogen, and it is now known that the bacterium which lives on the clover roots, deriving a part of its food from the clover plant, at the same time increases the nitrogen supply available to the clover crop and so we have two forms of life living together Physics of the Soil. in what has been named symbiotic relations. There are other forms of bacteria which live upon the bean, pea, lu- pine and other members of this family, also having the power of fixing free nitrogen from the soil-air in forms available to higher plants. It is known that other forms of bacteria live in symbiotic relation with soil algae and in this way increase the sup- ply of soil nitrogen as shown by Frank, Schlosing, Jr., and Laurent in 1891, followed by Kosswitsch in 1894; and the great demands for the fixing of free nitrogen to make good the rapid return of it to the air and loss in drainage waters appears to call for other agencies than those named. i Mi lit' FIG. 27. Showing oats growing under conditions identical with those of Fig. 26, except that the several pots received Chile saltpetre, 1, 2 and 3 grams respectively, thus enforcing the immense importance to such plants of nitric nitrogen. After P. Wagner. 4. Winogradsky has shown that there is a form of bacil- lus in the soil which, when supplied with sugar and iso- lated from the influence of oxygen, is capable of thriving and fixing free nitrogen from the air, and this discovery may lead to a knowledge of still a fourth mode of increas- ing the world's supply of nitrogen. Nitrification in Soils. 89 Some of Berthelot's experiments are thought by him to show that soils destitute of all visible vegetation may gain large quantities of nitrogen when simply exposed to the air, and he thinks he has realized gains as large as 70 to 130 Ibs. of nitrogen per acre in 11 weeks. Such conclusions, how- ever, require careful verification as they are at least ap- parently contradicted by field practice. 102. Nitrification. The formation of nitrates in the soil involves at least four distinct phases or stages : (1 } llio ain- monia stage,- (2) the nitrous acid stage, (3) the nitric acid stage and (4) the nitrate forming stage. When humus or dead organic matter is placed under the right conditions of temperature, moisture and air in the pres- ence of ammonia-forming germs, these organisms feed upon portions of it and throw off ammonia as a waste prod- uct. Ammonia is extremely soluble in water and is re- tained by it in large volumes. Even dry soil has the power of condensing and retaining it. In a fertile soil where ammonia has been formed there are also present nitrous acid germs which are able to use ammonia in their life processes but throwing off nitrous acid as a waste prod- uct. The niter germs or "mother of petre" utilize the nitrous acid in their work and throw off as a by-product nitric acid. This nitric acid readily attacks any of the bases in the soil which are held by carbonic and other weak acids, displacing them and forming nitrate of lime, mag- nesia, potash or soda, as the case may be. In the old days of "niter farming," when nitrate of potash for gunpowder was obtained from the soil, great pains were taken to form a soil rich in organic matter and to keep it warm, well supplied with moisture and thor- oughly aerated. These, too, are the points to be secured in the best management of soil for farm and garden crops. 103. Denitrification. Pitted against the processes of fix- ing free nitrogen from the air, which have been described, 90 Physics of the Soil. there are other processes which reverse these operations and set free again the nitrogen of organic compounds and of ni- trates so that it is again returned to the atmosphere as free nitrogen gas. (1) Dr. Angus Smith showed in 1867 that nitrates in sewage waters are decomposed and the nitrogen set free as a gas. (2) Scblosing showed that when moist humus- bearing soils are placed in an atmosphere free from oxygen they quickly lose all traces of nitrates. (3) Warington demonstrated that sodium nitrate in a water-logged soil is decomposed and the nitrogen liberated as a gas. (4) So great is the demand for oxygen in rich water-logged soils that according to the experiments of Mtintz even such compounds as chlorates, iodates and bromates are deprived of their oxygen, leaving iodides, chlorides and bromides in their place. (5) When black marsh soils are stirred up with water and allowed to stand Prof. J. A. Jeffery and the writer have shown that the nitrates rapidly disappear and nitrogen gas is set free. In all of these cases there are microscopic organisms in the soil and water whose needs for oxygen are so great that when that which is free in the soil-air or water-air is not sufficient they have the power of decomposing nitrates and even some organic compounds for the oxygen they contain and in this way liberate free nitrogen. (6) There is still another condition under which denitri- fication takes place in which the loss is large, rapid and nearly complete. It is when human excrements are covered with pulverized dry soil, as is done in the dry-earth closets. The late Colonel Waring kept two tons of dry earth for a number of years, having it used over and over again in or- der to see how long it might be used without losing its effi- ciency. The closets were filled with the dry earth and excre- ment about 6 times each year, and when they were emptied the material was thrown in a heap on a floor of a well venti- lated cellar to dry. After the same soil had been used over not less than 10 times it was analyzed for the amount of nitrogen it contained, and in 4,000 Ibs. of the soil was found Denitrifi cation of Soils, 91 no more than 11 Ibs. of nitrogen and yet not less than 230 Ibs. had been added to it and the soil at the start contained at least 3 Ibs. There had been set free therefore 230 8 = 222 Ibs. of nitrogen. Nor was this all, for so completely had all the carbonaceous materials been oxidized that even the paper used had en- tirely disappeared. How far these processes take place under field condi- tions when farmyard manure is applied we have yet to learn. CHAPTER III. SOLUBLE SALTS IN FIELD SOILS. All the food of plants is taken by them in the form of liquids or of gases, and hence the fertility of a soil must be determined by the rate at which plant food may be dis- solved in the soil water and carried to them at the time the crops are growing. If the ash ingredients and the nitro- gen used by plants while growing are supplied in the soil water as rapidly as the crop can use them, then maximum yields will be certain if the temperature and sunshine are nlso right. 1C4. Amount of Soluble Salts in Field Soils. There is a very wide difference in the amount of salts dissolved in soil water under different conditions. In arid regions, where there is little soil leaching, the salts become in places so abundant that plants are unable to grow and alkali lands are the result. In humid climates, especially where the soils are sandy, the salts may be so small in amount that plants starve. In the table below these differences are shown for the surface foot. Watersolnble salts in soils of arid climates. Water soluble salts in soils of humid climates. Where bar- ley will not grow. Whore bar- ley prows 4ft. hili. Fertile clay loam. Poor sandy soil. 21 81 Lbs. per million of dry soil LJv. per acre of 4,000,000 Ibs 8,585 34,340 4.877 15,503 272 1,088 These figures show a range of total salts soluble in water from 17 tons per acre foot to less than .05 tons. Soluble Salts in Soils. 93 105. Maximum Amount of Water Soluble Salts Which Limit Plant Growth. Hilgard concludes from his studies that the maximum amount of soluble alkali salts which are consistent with a full crop of barley hay is 25,000 to 32,000 Ibs. per acre in the surface four feet of soil, pro- vided this is not more than one-half its weight sodium car- bonate. Whitney places the limit of possible plant production in the soils of the Yellowstone Park at 15,000 Ibs. per acre in the surface foot, where the black alkali or sodium carbonate is absent. Grapes grow in Algeria in alkali soils containing 600 Ibs. per million of dry soil but die when it reaches 1,YOO Ibs. per million in the surface soil and 3,700 in the sub- soil ; but grain crops grow normally when the soil contains 2,000 Ibs. per million. 106. Why too Much Soluble Salt in Soil Kills Plants. De Vries found, as represented in Fig. 28, that when the liv- Fto. 28. Showing the effect of too strong solution of salts on the proto- plasm of plant cells. ing cells of a plant were immersed in a 4 per cent, solution of potassium nitrate, there was first a shrinkage in volume through a loss of water, as shown between 1 and 2. When the solution was given a strength of 6 per cent, the proto- 94 Physics of the Soil. plasmic lining, p, began to shrink away from the cell wall h, as shown at 3, and when the strength of the solution was made 10 per cent., the conditions shown in 4 are produced. When the cells of plants are affected in this way they wilt and growth ceases. A soil containing 20 per cent, of water and also 2,000 Ibs. of water soluble salts per million of dry soil would contain 2,000 Ibs. in 200,000 Ibs. of water, or 1 part in 100, which is 1 per cent. If the soluble salts constitute 2 per cent, of the dry weight of the soil then with 20 per cent, of moisture present the strength of the soil solution would be equal to that which De Vries found fatal to plants, or 10 per cent. The salts in the surface three inches of soil upon which Hilgard found barley to grow four feet high were 1.2 per cent, while they were 2. 44 per cent, in the same level where the barley died. With 20 per cent, of moisture in the soil, and all the salts dissolved, the soil solution in the first case would represent a strength of 6 per cent, and in the second case 12.2 per cent., which is larger than the amount De Vries found fatal. 107. Concentration of Salts in Zones. Where long contin- ued drought has occurred in soils rich in soluble salts the tendency is for the salts to collect in the surface two or three inches and in this way become injurious to plants when they would not be so with an abundance of water in the soil. When heavy rains follow such a concentration of salts at the surface, or if the land is irrigated so as to produce percolation, the result is to wash the salts down in a body to the depth reached by percolation, and hence it may hap- pen that a layer of soil very rich in salts may occur at the surface at one time and later at a distance of 12, 18, 24 or 30 or more inches below, determined by the depth of per- colation. 108. Origin of Soluble Salts The excessive amounts of salts found in alkali lands are usually the result of long Soluble Salts in Soils. 95 continued rock decay under conditions where little or no leaching has taken place. Rains enough fall to produce decay, but not enough to carry the salts formed into the drainage channels and out of the country. This is why alkali lands are largely peculiar to desert or semi-arid climates. 109. Leaching Necessary to Fertile Soils. It is clear from 106 and 108 that if there was not some leaching to take up and carry away the extremely soluble salts not available as plant food all soils would in time become "al- kali lands ;" so that while excessive leaching is undesirable, a sufficient amount is indispensable. The prevention of the accumulation of undesirable solu- ble salts in the soil of irrigated lands in dry climates is one of the most serious of practical problems. 110. Soluble Salts in Marsh Soils. The black marsh soils of humid climates often contain unusually large amounts of soluble salts, sometimes reaching 2,366 parts per mil- lion of the dry soil in the surface 6 inches after maturing a crop. This would make the water contain 1.18 per cent, of salts if the water content of the soil was 20 Ibs. per 100 of dry soil. Many of these soils behave much like alkali lands, being unproductive, the crops often dying when there is no evident reason for it. 111. Correction for Alkali Lands. It has been found that when a soil is unproductive from too high a per cent, of sodium carbonate or black alkali and there is not enough of other soluble salts to be injurious, this may be corrected in part by the use of gypsum, or land plaster, which has the effect of converting the carbonate into the sulphate or "white alkali," like amounts of which are less harmful. It often happens that waters which must be used in irri- gation contain black alkali, and where this is the case it is well to correct the water by using land plaster in the reser- voirs or distributing canals, for the water to run over or through, before reaching the field. 96 Physics of the Soil. FIG, 29. Showing the seasonal changes in tho amounts of nitrates in each of the surface four feet of .soil under growing corn. Soluble Salts in Soils. 97 FIG. 30. Showing the seasonal chnnges In the amounts of soluble salts in the soil under growing corn. 98 Physics of the Soil. 112. Drainage the Ultimate Remedy. Drainage must be the ultimate remedy for any alkali land, as it can be only a matter of time when any fertile soil will develop enough undesirable soluble salts to render it sterile or less produc- tive, unless the soluble salts not needed are removed, and only drainage can do this. 113. Deep and Frequent Tillage Helpful. It is clear that whatever means will prevent the excessive evaporation of water from the surface will in so far lessen the concentra- tion of salts there, and hence frequent and deep cultiva- tion, to form effective mulches, will lessen the rise of water, and therefore of salts, to the surface and in this way permit crops to be grown on soils which are critically near the limit of sterility on account of the high salt content. 114. Change in Soluble Salts with Season. In Figs. 29 and 30 are represented the changes in the nitrates and total soluble salts in the surface four feet under three fields of corn, beginning with April and ending with Sept. Re- ferring to the nitrate curves it will be seen that the nitrates start in April nearly equal in the four feet, but increase rapidly in the first foot until the middle of June, when the corn begins to draw on the supply. From this time they decrease rapidly until the middle of July, when they are less than in April and less than in the second foot. By the middle of August, when the crop has ceased to draw much but water from the soil, there is a slow increase again and then one more rapid after the corn is cut, Sept. 1. The change in the total salts is much less marked, but evident, there being a general decrease. The mean amount of salts at the beginning and at the end of the season are : April 18. Sept. 1. Total salts 540 363 Nitrates 86 32 Difference 454 331 From these figures it appears that the salts, other than nitrates, have decreased during the season 123 Ibs. per mil- lion of the dry soil for the four feet, or 1,968 lb$, Soluble Salts in Soils. 99 115. Variation of Soluble Salts with Different Crops. . There is a marked difference in the amount of soluble salts, and especially in the amount of nitrates, in soils under crops like corn and potatoes, where inter-tillage is prac- ticed, and under such crops as clover and oats, where the ground is not cultivated at any time of the season. This is very clearly shown in Fig. 32 ; the nitrates are plotted in the lower two sets of curves and the total soluble salts in the upper two sets. The nitrates in the first foot under the corn and potatoes increased rapidly until July 1st, when they were five times as concentrated as in the fourth foot ; but in 30 days more the nitrates had been reduced from over 400 Ibs. to 40 Ibs. per acre. PARTS PER MILLION < DRY SOIL. FIG. 31. Sliows the menu amount of nitrates and total soluble salts in the surface four feet of soil under cultivated and not cultivated crops. Heavy shading is uncultivated ground. In the case of the uncultivated crops the fields started with about 40 Ibs. per acre and increased to only 70, June 1st, when they were highest; from this date they fell to little more than 10 Ibs. per acre in the surface foot, but rose again to 60 Ibs. at the end of August. With the total soluble salts there was at first a more Physics of the Soil. GROuND NOT CULTIVATED GROUND CULTIVATED CORN AND POTATOES Fin. 32. Showing the difference between the amounts of nitrates and of total soluble salts in the soil under cultivated and not cultivated crops. Closeness of Plant Feeding. 101 rapid rise, from nearly 300 Ibs. per acre in the surface foot on the cultivated ground April 18, to about 500 Ibs. per acre, but falling again on August 1st to 250 Ibs. On the clover plots the start was at 250 Jbs. per acre in the surface foot, rising to 290 Ibs. in 12 days. From this date there was a slow decrease, falling to 220 Ibs. on the date when the cultivated grounds were highest, at GOO Ibs. per acre. 116. Relation Between Nitrates and Total Soluble Salts . As a general rule when the nitric nitrogen in clay loams is very high the total soluble salts, as indicated by the electrical method, are very low. It will even happen that the electrical resistance will show but little more salts than are required to account for the nitrates, and this is perhaps what should be expected for, if nitric acid is being formed in the presence of carbonates, these would be decomposed to form nitrates, and if the rate of nitrification were suf- ficiently rapid, it might be that all the carbonates would be decomposed and little else but nitrates left. The ratio of total soluble salts to nitrates in the surface foot of the five cultivated fields represented by the curves was a mean for the season of 2.14 to 1, while in the surface foot of the clover fields it was 4.8 to 1. For the second, third and fourth feet the ratio is Y.29 to 1 for the corn and potatoes, and 9.97 to 1 for the clover, alfalfa and oats ; and these ratios are what would be ex- pected if the formation of nitric acid destroys the carbon- ates and bi-carbonates in the soil water. 117. Closeness of Plant Feeding It was pointed out. in (7) what small amounts of a fertilizer can be widely dis- tributed through an acre of soil, and we may now consider how extremely close plants do feed the nitrates of a soil. In the table which follows are given the amounts of ni- trates which were found in each foot of nine field plots, represented by the curves, between July 18 and Sept. 1. 7 BIO-AGRICULTURAL LIBRA! UNIVERSITY OF CALIFORNI 102 Physics of the Soil. Tablet showing mean amounts of nitrates under different crops between July 18 and Sept. 1, in Ibs. per acre of dry soil. Plotl. Plot 2. PlotG. Plot 4. PlotS. Plot 6. Plot 7. Plot 8. Plot 9. Corn. Clover. Corn. Oats and clover. Pota toes. Pota- toes. Clover. Alfalfa Corn. 1st foot.. 2nd foot. 3rd foot.. 4t!i i.M.t-. Lbs. 50.94 127.35 83.52 40.83 Lbs. 58.32 23.74 10.2-5 14.80 Lbs. 24.11 4X.81 59.44 64.82 Lbs. 15.07 It. 42 18.81 27.05 Lbs. 130.21 155 ! 5 49.65 21.08 Lbs. 10V32 172 62 50. f 6 59.82 Lbs. 44.91 15 63 1.75 4.59 Lbs. 18 t-4 10.6.1 9.53 9.73 Lbs. 10.85 8 S3 10.79 12 51 \Vhen these amounts are expressed as parts per million of the dry soil in the form of nitrogen, they stand 3.38, 1.61, 0.72 for corn; 3.87, 2.98, 1.00 for clover; 1.25 for alfalfa and 6.99 for potatoes, and yet with these small amounts of nitrogen in the soil during the time when the chief growth was being made, large yields were produced. 118. Limits of Nitric Nitrogen at Which Corn and Oats Turn Yellow. Taking samples of soil from the surface foot upon which oats were turning yellow and under adja- cent areas where the plants were normal green it was found that two sets of duplicate determinations gave Oats yellow Oatj green. ( June 10 .025 .213 Parts of nitric nitrogen per million of dry soil < (June 11 .027 .297 These amounts, when expressed in pounds per acre and as nitrates, are only .392 Ibs. and 3.843 Ibs., respectively, for the yellow and green oats. Table showing the amounts of nitric nitrogen under corn row* where leaves are turning yellow and where they are yet normal green. Depth. Plot 9. Marsh soil. Randall field. Yellow. Green. Yellow. Green. Yellow. Green. 1st foot 0.61 14 0.41 0.42 0.92 1.70 2.95 1.82 0.95 0.40 0.07 0.00 3.62 1.41 0.52 0.00 0.10 0.06 0.25 0.30 0.95 0.60 0.37 0.30 2nd foot 3rd foot 4tb foot \Nitrales in Soils. 103 Small as these amounts of nitric nitrogen are the yield of corn on plot 9 was a mean of 8,000 Ibs. of water-free matter per acre. On another plot where the yield was 11,440 Ibs. of water-free matter per acre the nitric nitro- gen was reduced as low as 1.44G parts per million in the first foot and .726 parts in the second foot. It must be understood that^in these cases the demands for nitrogen were so urgent that the plants were taking it up almost as rapidly as it could be produced, leaving the amounts so low, as the figures show. 119. Nitrates of Fallow and Cropped Ground. In the table which follows are given the amounts of nitrates found under different crops and, at the same time, under immediately adjacent fallow ground which had been cul- tivated and kept free from weeds. - Oats. Fallow. Barley. Nitrates. Total salts. Nitrates. Total salts. Nitrates Total salts. 1st foot 5.94 8.12 4.73 4.60 Oa 3.25 3.22 2 Ho 70.94 114.6 124.7 39.44 ts. 80.35 162.1 102.7 58.24 ts. 78.56 10*. 9 72.98 33.99 246.40 26.75 6.50 2.84 Fal 143.05 *9.50 8.87 4.10 Fall 129.15 35.60 9.11 4.08 199.3 123.5 108.0 42.10 ow. 206.1 254.3 115.0 95.32 ow. 211.3 254 7 117.8 61.92 2.62 5.10 4 04 3.03 Pe 8.38 18.57 6.59 2.66 Sprin 1.24 2.62 2.07 2.78 61.72 87.08 112.6 51.76 as. 77.00 197.2 135.8 44.62 ? rye. 77.34 102.1 94.82 48.85 2d foot 3d foot 4th foot 1st foot 2d foot 3d foot 4th foot 2.70 Oa 2.47 2.46 3. S3 3.16 1st foot 2d foot 3d foot 4th foot If the mean amount of nitrates in the surface foot of the fallow ground and under the crops are expressed in pounds per acre they stand 473.65 to 10.88. This difference is enough for 85 bushels of oats per acre, where the ratio of grain to straw stands as 3 to 5. 104: Physics of the Soil. 120. Loss of Nitrates from Fallow Ground During Winter and Spring. A field which has been kept fallow during a whole season and cultivated either once per week or once in two weeks had the nitrates determined in it on August 25 and again the next spring, April 30. The field was di- vided into nine plots and the nitric nitrogen was deter- mined in each one to a depth of four feet on both dates. The results are given in the next table. Table showing the amount of nitric nitrogen found in fallow ground after the leaching of winter and early spring. Pounds per million of dry soil. No. of plot. I. 2. 3. 4-. 5. 6. 7. 8. 9. Apr. 30, 1900 ( 75.90 58.31 58.05 55.22 51 68 51.25 38.02 44.34 48.26 Aug. 22, l-9.fi 16.81 13.58 26.67 26. M) 19.0.4 16.82 5.50 24 07 19.60 2d foot \ Apr. 30, 190.) \ 15.81 16.75 7.97 6.51 13 06 15.66 17.33 18.56 14.85 Aug. 22, 18'.->9 I 4.34 7.75 1.81 9.07 5.74 2.76 1.43 6.06 6.61 8d footj Apr. 30, ItOO ( Aug. 22, 1S99 ( 2.46 .70 4.75 .54 4.93 2.4i 4.89 .80 3.94 0.54 7.35 1.37 6.04 0.95 8.24 0.54 6.71 3 01 4thfoot ] Apr. 30, 1900 ] Aug. 22, 1S99 1 2.95 2.37 3.05 1 04 2.35 2.01 1 P5 2.36 52 3.65 26 5.60 53 5.08 't 51 It is clear from this table that however large the leach- ing may have been it was not enough to prevent the nitrates FIG. 33. Showing the difference in the amount of nitrates in the surfnco four feet of fallow ground, the succeeding spring, aiid that upon which crops had been grown. Nitrates in Soils. 105 being higher the following May than they were August 22 before. 121. Nitrates on Fallow Ground in Spring Compared with That not Fallow. Comparing the mean amount of nitric nitrogen in nine field plots bearing crops in 1899 with that of the nine fallow plots of the same year, as found in the spring of 1900, the amounts are as stated in the table below and represented graphically in Fig. 33. Table showing the difference* in the amounts of nitric nitro- gen after the winter and early spring rains in ground kept fallow and free from iveeds the previous season and that bearing crops. Depth. 1st foot. 2d foot. 3rd foot. 4th foot. Fallow plots, pounds per acre.. 212.00 56.22 21.91 13.11 Plots not fallow, pounds per acre 25.24 1503 10.00 7.24 Difference 183.76 41 14 11 91 5.87 From this it is clear that the crops on the fallow ground start out in the spring under conditions very superior to those on the fields which had not been fallow, there being 245.68 Ibs. of nitrates more per acre in the surface four feet. 122. Development of Nitrates Influenced by Depth and Frequency of Cultivation. When a series of cylinders like those represented in Fig. 58, p. 187, are mulched by stir- ring at different depths and the stirring is repeated at dif- ferent intervals the rate of formation of nitrates is ma- terially modified, as shown in the table below: Difference in the amount of nitric nitrogen, after 258 days, due . to differences in depth and frequency of cultivation. Depth of cultivati'n. Cultivated once per week. Cultivated once in two weeks. 1 inch deep Lbs. per acre. 217.69 Lbs. per acre. 213 29 2 inches deep 323.44 199 00 3 inches deep 441.24 401.68 4 inches deep... 3b7.96 245.26 106 Physics of the Soil. It can be seen that the nitric nitrogen has increased in both series to a depth of 3-inch cultivation and it has in- creased with the frequency of the cultivation. 123. Soluble Salts Affect the Movement of Soil Moisture The varying strength of salt solutions in soil moisture mod- ify both the movement of moisture in the soil and its rate of loss from the surface. These movements are influenced (1) by changes in the intensity of surface tension; (2) l>y changes in the internal friction of the soil moisture or its viscosity; and (3) by modifications of the surface of the soil due to deposits of salts upon and within it, where evaporation is taking place. 124. Modification of Surface Tension by Soluble Salts. As a general rule the surface tension of a strong soil solu- tion is greater than that of a weaker one, or of pure water, and in so far as this influence is operative it tends to in- crease the rate of capillary movement toward the surface or toward the roots of plants. 125. Salts in Solution Lessen Rate cf Evaporation. When water has been brought to the surface of the soil by capil- larity it has yet to evaporate and unless this takes place the surface soil would become capillarily saturated with water and remain so. Since salts in solution increase the sur- face tension it will require a greater energy a higher temperature to throw the water molecules off into the air than would be required to do so from the surface of pure water and hence the evaporation from soil solutions rich in salts is slower than it is from weaker ones under other- wise like conditions. As the salts become concentrated at the surface by evaporation the moisture becomes a stronger and stronger solution and hence the rate of evaporation be- comes less and less so far as it can be influenced by this factor, in this way. 126. Viscosity of Soil Water Modified by Soluble Salts. The internal friction of soil moisture is made greater by Physical Effects of Soluble Salts. 107 the presence of salts in solution and the more concentrated the soil solution is the greater is the internal friction, and hence the slower must be the rate of flow, and it may be that the much slower rate of capillary movement in a compara- tively dry soil is to a considerable extent due to this in- creased viscosity or internal friction. But as one effect of the salt in solution is to increase the surface tension, while the other decreases the flow by increasing the friction, the two influences work against each other, making the com- bined result less than it would be could either act alone. 127. Deposits of Salts after Evaporation May Lessen Loss of Soil Moisture Where water rich in salts is being evap- orated from a soil these salts may accumulate upon the sur- face and form a sort of mulch more or less effective accord- ing to its texture ; or they may be deposited as a crust upon, over and between the soil grains, which may nearly close the capillary pores and in this way lessen the loss of water by evaporation. Such a closing of the pores is likely to be more harmful in shutting out the air and in lessening the freedom of entrance of water after rains than it can render resistance in conserving soil moisture. CHAPTER IV. PHYSICAL NATURE OF SOILS. 128. Texture of Soils. The size of soil grains and the way they are grouped in composite clusters forming ker- nels or crumbs has a very great influence in determining the physical properties of soils and their agricultural value, and as soils vary quite as widely in the size and arrange- ment of their grains as they do in their chemical composi- tion it is clear that this phase of soil problems must take at least equal rank with those considered in the last chapter. In all agricultural soils except the very coarse and sandy ones there is a composite granular structure which renders them much more open and porous than they could otherwise be, and when a soil is puddled this structure or texture is destroyed in a large measure and the separate grains are then brought into the closest possible arrangement, and they become nearly or quite impervious to both water and air, approaching the condition of brick and potter's clays. 129. Size of Soil Grains. When the fragments of rock are so coarse that very few are smaller than .01 of an inch in diameter we have a sand rather than a soil. Most plas- tering sands are made up of grains ranging from .01 up to .08 of an inch in diameter. In the table which follows is given the mechanical anal- yses of three types of soil : It will be seen from this table that only .8 per cent, of either soil is made up of grains having diameters so great that only 23 are required to span a linear inch, while the heavy clay soil has nearly one-half of its weight made up Texture of Soils. 109 of grains so small that 25,000 of them must be placed side by side to span a linear inch. SANDY SOIL. LOESS SOIL. HEAVY CLAY SOIL. Number of Number of Number of Diana. m. m. grains per linear inch. Per cent. Diam. m. m. grains per linear inch. Per cent. Diam. m. m. grains per linear inch. Per cent. Ito3 23.1 .4 Ito3 23.1? Ito3 23.1 .8 .5tol 31.7 3.0 .5tol 31.7) .5tol 31.7 1.2 .4 63.5 6.9 .4 63.5 .4 .4 63.5 2.0 .3 84.7 8.1 .3 84.7 .6 .3 84.7 1.6 .16 163.9 3.0 .16 163.9 .9 .16 163.9 .9 .12 211.9 1.6 12 211.9 1.7 .12 211.9 .3 .072 353.4 1.2 .072 353.4 2.0 .072 358.4 .2 .047 510.1 3.6 .047 540.1 14.3 .047 240.1 2 5 .036 704.3 6.8 .036 704.3 16.2 .036 704.3 3.7 .025 1,020. 14.6 025 1,020. 20.1 .025 1,020. 5.6 .015 1,695. 14.8 .015 1,695. 5.6 .015 1,695. 10.6 .808 3,226. 30.7 .008 3,226. 33.6 .008 3,226. 24.7 .0001 25,000. 4.6 .0001 25,000. 2 5 .0001 25,000. 48.0 130. Number of Grains of Soil in a Cubic Inch If soil grains were perfect spheres like shot and in a given soil they were all of a single size it would be a simple matter to FIG. 34. Showing the effect of size and arrangement of soil grains on the pore space and upon the movement of air and water through a soil. 110 Physics of the Soil. determine the number in a cubic inch. If a soil were made up entirely of the largest size given in the last table, then 23 would build one edge of a cube an inch on a side and the number in a cubic inch arranged in the manner repre- sented in the upper part of Fig. 34 would be 23 3 = 23 X 23 X 23 = 12, 167. On the other hand, if they were all the size of the smallest grain in the table then the number would be 25.000 3 =15,625,000,000,000, or enough to form three and a third continuous lines of grains in contact from Boston to San Francisco. 131. The Size of Soil Kernels. It must be kept in mind that while it is true that the heavy clay soils are made up largely of soil grains of the extremely small size considered .in (130) these minute grains are generally bound together in groups or kernels of various sizes and it is only by long boiling in water or thorough pestling that these can be broken down. The writer has found that when air-dry samples of the heaviest clay soils are thoroughly pestled in the dry condition it is difficult to reduce their texture to a finer degree than kernels averaging .01 to .005 m. m. in diameter or such that from 2,500 to 5,000 are required to span a linear inch; but even this degree of closeness of texture is too fine to allow of proper drainage and soil ven- tilation and to permit roots to make their way through tho soil with the freedom required for good crops. 132. Specific Gravity of Soil Grains. The specific gravity of soil grains, or the number of times they are heavier than an equal volume of water, varies somewhat, as does that of the minerals which compose them. As there are not many common minerals more than three times as heavy as water and not many lighter than 2.5 times as heavy, the specific gravity of soil grains will lie between these two figures and it is usually found to be near 2.65. Texture of Soils. Ill 133. The Pore Space of Soils When the weight of a cu- bic foot of dry soil is known the amount of pors space or space not occupied by the soil grains may be computed from the specific gravity. Taking the weight of a cubic foot of water at 62.42 Ibs., a cubic foot of dry soil, if there were no open spaces in it, should be 2.65 X 62.42 = 165.4 Ibs. With this value and the data given in (149) the pore space of those soils may be calculated. Thus, for the surface foot we have 165.4 79 Pore space = = 52.23 per cent. -Lou . 4- That is, in this soil the surface foot is more than half open space. The pore space for the six feet will be as given be- low: Weight of soil. Pore space. Firstfoot Lbs. 79 Per cent. 52 23 92 62 44 ('<) Third foot 104.59 36 76 Fourth foot 10(5 21 35 78 Fifth foot 111.06 32 85 111 06 31 85 Thus it is seen that the unoccupied space in a soil varies from more than half to less than one-third of its volume, the finest grained soils having the largest pore space and the sandy soils and sands the smallest. 134. Pore Space Between Spherical Grains. It can be shown mathematically that when a space is filled with spheres all of one size and these are given the closest pos- sible packing, having the arrangement shown in the lower part of Fig. 34 and in Fig. 35, the pore space must be 25.95 per cent. ; but when the spheres are given the closest possible packing and the arrangement represented in 112 Physics of the Soil. the tipper part of Fig. 34, then the pore space must be as large as 47.64 per cent. In the first case the water capacity of such a soil with the pores entirely filled would FIG. 35. Showing the closest packing of spherical soil grains, the ele- ment of volume and the direction of lines Of flow. Face angles 60 and 120. (After Slichter.) be 3.114 acre-inches per acre-foot and with the second ar- rangement the maximum water capacity would be 5.7168 acre-inches per acre-foot. Neither of these arrangements would be likely to occur throughout a mass, and hence the general tendency will be Texture of Soils. 113 to form a pore space between these two extremes, and Fig. 37 shows what the observed pore space is in soils, sand, crushed rock and crushed glass. It will be observed that FIG. 36. Showing the closest packing of spherical grains, the element of volume, and the direction of lines of flow when the face angles are 90, 60 and 120. (After Slichter.) the finest clay soils, and indeed the finest grained materials, have the largest pore space. It will also be noted that the largest observed pore space exceeds the largest theoretical 114 Physics of the Soil. pore space and that the smallest observed pore space also falls below the smallest theoretical limit for spherical grains of a single size. FIG. 37. Showing the observed pore space of different kinds of soils and sands and their relation to the theoretical pore space of spheres of a simple diameter. 135. Amount of Pore Space Determines Maximum Water Capacity of Soil. The amount of water a soil may contain when below the level of the ground water surface is meas- ured by the pore space. So too in the case of heavy and protracted rains the pore space determines the number of inches of water which may enter the ground before it be- comes so filled that surface drainage must carry away that which is falling, and it will be readily understood that in the clay soils, where the pore space is so high, very large Texture of Soils. 115 amounts of water may be stored in them to drain away gradually in the underflow. 136. Subdivision of Fore Space Determines the Rate of Per- colation and Drainage. If reference is again made to Fig. 34 it will be clear at a glance that Avater must flow through spaces filled with these different sizes of spheres at very different rates. Where the spheres are largest there are 16 passage-ways for the movement of air or of water ; but in the middle section where the spheres have one-half the diameter, the number of passages is 4 times as great, while in the last section with spheres of one-quarter the size the number of passages is 16 times as great. The aggregate area of the cross-sections of the pores is exactly the same in the three cases, and from this it follows that the areas of the cross-sections of single pores are to each other as 16 : 4 : 1. The coarse spheres divide the column of water into 16 streams, the medium ones divide it into 64 streams, while the smallest spheres divide the column into 256 streams, each having only one-sixteenth the sectional area of the first. But to subdivide the column into 256 streams in- stead of 16 means that the friction must be much greater in the aggregate on the smaller streams, and hence that the flow must be slower. 137. Method of Determining the Pore Space of Soil The simplest method of determining the pore space of soil is to pack the dry material into a cylindrical vessel containing 100 c. c. until it is even full, and then weigh and compute the per cent, of pore space from the volume, weight and specific gravity, using the formula Vd W _ p Vd where V is the volume of the vessel in c. c., d is the specific gravity and W is the weight of the soil in grams. To determine the pore space in undisturbed field soil 116 Physics of the Soil. the simplest method is to use a soil tube, represented in Fig. 38, taking a number of cores of the desired depth, FIG. 38. Showing soil tube for taking samples of soil. drying them, and then compute the pore space with the formula above. 138. Largest Possible Pore Space. The largest possible pore space in soils will be found in the cases where the com- pound or kernel-structure is most marked. Referring again to Fig. 34, imagine each sphere there represented to be made up of other very much smaller spheres having the same general arrangement. Were this the cass it is clear that in consequence of the compound spheres the soil must have a pore space not less than 25.95 per cent, with one arrangement and 47.64 per cent, with the other. But in addition to this pore space there must be a like pore space within each compound sphere so that in the first case the total pore space would be 25.95 -f [25.95 per cent, of (100 25.95)] = 45.17 and in the second case 47.64 4- [47.64 per cent, of (100 47.64)] = 72 58 per cent. The first pore space, 45.17, it will be seen, lies close to that possessed by the finer soils but the latter is larger r.han anything ever found except it be in the loose mulches. The smallest pore spaces result when grains of different sizes are so related that the small ones fall into the pores formed by the large ones without at the same time crowd- ing them farther apart. Referring again to Fig. 34, it will be seen that if small spheres are packed into the pores there shown, with the same arrangement that the large ones have, the original 25.95 per cent, and 47.64 per cent. Texture of Soils. 117 of pore space would be occupied to the extent of 74.05 per cent, in the first case and of 52.36 per cent, in the second case. Such a condition would leave only about 6.73 per cent, of pore space for the closest packing. Such arrangements as this are not likely of course to occur in nature but in the construction of macadam roads and in all concrete work a definite effort is made to reduce the pore space to the smallest possible limit by using crushed rock, gravel, sand and finally cement to fill all pores as completely as possible. 139. Number of Soil Grains per Unit Weight. If soil grains were all spheres and in a given case they were all of the same size the number in a gram could be found by the equation Weight of soil No. of grams = where the weight of the soil is in grams and the diameter of the soil grains, d, is in c. m. In the table below are given in round numbers the num- ber of grains in one gram and in one pound of soil, sup- posing the grains all spheres and to have a specific gravity of 2.65. Diameter. No. of grains in one gram. No. of grains in one Ib. 720 3 9 6 90S 720,000 36 90M 000 720,000,000 3 9 6 ^03 000 OUO 001 m m 720,000 OOo 000 3?6 90.1 000 000 000 . 0001 m. m. ... 720, OU),000, 000, OUO 3 9 6 903 000 OOO' 000,000 That is to say, 720 multiplied by 10 used as a factor 3, 6, 9 and 12 times gives the number of grains in a gram of soil in round numbers and the number in a pound may be found by using 10 as a factor in the same way and the number 326,903. If the soil were made up of some grains of all the sizes 118 Physics of the Soil. in the table, then to find the total number in a gram or pound it would be necessary to multiply those numbers by the per cent, of each size found in a gram of the soil and add the several products. If the soil were made up of 20 per cent, of each size in the table the number would be as follows: Diameter. Per cent. No. of grains per gram. 20 144 20 141 20 1-14, OMI. (MO 001 m. m 20 144,0>>,t 945,l l i9 192,188,151,958,708 106,771,327,610,151 It is the custom to find the diameter of soil grains cither by direct measurement or else by counting and weighing a given number of grains and then computing the diameter of the mean grain from the weight and specific gravity. If the diameter of the mean grain in the above three problems is computed by each of these methods the results will be as below: If the surface of a gram of soil is computed from each of these diameters the results given below will be found : A. B. c. Actual surface per gram of soil sq. cm. 17,358 sq. cm. 136,101 sq. cm. 76,740 Surface computed from the grain of mean diameter Surface computed from the grain of mean weight.. 150, 570 10,053 150,9.i9 145,734 150,902 119,804 These results are very different and differ so much from the actual as to make them of little value in determining the actual surface a given soil may possess. It has been the practice to take as the mean diameter of the soil grain the average between the diameter of the largest grain in the group and the smallest, which in the above problem w r ould give .004575 as the mean value. But to use this to compute the surface in a gram of soil would give the results below : Computed from the mean of the two eAireine diameters. A. B. C. 4,949 sq. cm. 17,358sq. cm. 138,101 sq. cm. 7G,"40sq. cm. Internal Surface of Soils. 121 Here it is seen that the computed surface, 4,949, is very far indeed from either of the true values given under A, B and C. 142. Effective Diameter of Soil Grains. While it is not possible to determine either the mean diameter of the grains in an ordinary soil or the amount of surface a given weight of soil may possess with even approximate accu- racy, it is possible for the simple sands, at least, to deter- mine the diameter of a grain which, if substituted for the actual ones, would permit, under like conditions, the same amount of air or of water to flow through. The method is based upon the laws of flow of fluids through capillary tubes and aims to compute from the ob- served rate of flow of air through a given column of soil the effective diameter of the capillary pores and from this the size of spherical grains which would be required to form such capillary tubes as those computed. The theory of the method is fully set forth in Prof. C. S. Slichter's paper. 1 143. Description of the Method. The apparatus used to determine the effective size of soil grains is represented in Fig. 39, and consists of a cylinder in which a sample of soil is carefully packed and weighed to determine the per cent, of pore space. When this has been done the tube is connected with the aspirator and the rate at which air will flow through it under a measured tempera- ture and pressure found. When these data have been ob- tained, then the formula below, used with the table given, enables the effective diameter to be computed when the flow has been measured at the temperature of 20 C. 1 Nineteenth Annual Report of the U. S. Geol. Survey, Part II. 122 Physics of the Soil. spt [8.9434 10] where d = diameter of grain in c. m. h = length of sand column in c. m. 8 = area of cross-section of sand column in sq. c. m. p = pressure in c. m. of water at 20 C. t = time in sec. for 5,000 c. c. of air to flow through at a torn perature of 20 C. [8.9434 10] is a logarithm of a constant k is a constant taken from the following table. FIG. 39. Showing aspirator for determining the mean effective diameter of soil grains. A, aspirator bell; B, pressure gauge; C, air meter; D, aspirator tube for samples. Movements of Fluids Through Soils. 123 Per cent, of pore space. Log. k. d. Per cent, of pore space. Log. k. d. 26 1 958 563 37... 4193 377 27 1.8695 500 38 .3816 71 28 1 8195 490 39 3445 367 29 1.7701 502 40 .3u.~8 353 JO .7199 467 41 2725 351 31 .67*2 455 42 1.2374 345 32 .6277 430 43 1.2024 339 33 .5*47 438 n 1 1690 320 34 5109 410 45 1 1370 312 35 .4999 407 46... 1 1058 329 S6 .4592 400 47 1 0729 144. Observed Flow of Water Through Sand Compared With That Computed From the Effective Diameter. The ac- curacy of the method described in (143) is best shown by computing from the effective diameter of the soil grains what the flow of water ought to be and then measuring the flow of water to see how it corresponds. This has been done and the results are given in the table below : Grade of sand. Effective diameter of grain. Computed flow of water. Observed flow of water 8... m. m. 2.54 Gms. 2,277 Gms. 2,296 7 1 808 1,132 1,080 6 1.451 757 756 f,H 1.217 522 542 5 1.095 453 2 504 6 4 .9149 297.5 3^9.2 3 .7988 193 210 2 .7146 122 138 6 1 .6006 80.6 94.8 .5169 66.8 T2.3 When it is observed that the effective diameter of the grains in these sands was found by measuring the flow of air through one sample in one piece of apparatus and the flow of water was measured through another sample and in another piece of apparatus-, and that the flow varies as the squares of the diameters of the soil grains, it is clear that the effective diameter has a very exact value so far as the flow of fluids is concerned. 124 Physics of the Soil. 145. The Effective Diameters of Soil Grains and the Amount of Surface Computed From Them We have no means of knowing yet how accurately the computed sur- face of soil grains in a given weight of sample compares with that which is possessed by it. We do know, however, that the comparison is accurate enough to furnish a valua- ble basis for comparing different types of soils, and in the table which follows is given the effective diameters of sev- eral kinds of soils, together with the pore space and the computed amount of soil surface per cubic foot of dry soil. Table of computed surface of soil grains in different types of soil. Kind of soil. Effective diameter of soil grains. Per cent. of pore space. Surface of soil grains in one cubic foot. Finest clay soil m. m. .004956 52 94 Sq. Ft. 173 700 Fine clay soil .007657 45 69 129 100 Fine clay soil .008612 48 00 110, 500 Heavy red clay soil .01111 44 15 91 960 Loamy clay soil .02542 49 19 70 500 Clayey loam 01810 47 10 53 490 Loam 02197 44 15 46 510 .02619 34 49 45 760 .03035 38 83 36,880 Sandy soil .07555 34 45 15 870 Sandy soil .1119 32 49 11 030 Coarse sandy soil 1432 34 91 8 818 It will be seen from this table that the amount of surface in the true soils is indeed very great, ranging from a little less than a quarter to more than a third of an acre in the sandy soils, through more than an acre in the loams to as much as four acres per cubic foot in the finest clay soils. The amount of soil surface in the upper four feet of every cultivated field ranges from not less than one acre to more than 16 acres per each square foot of surface cultivated. 146. Relation of the Surface of Soil Grains to the Water Capacity A large portion of the water held by a soil is spread out as a thin film surrounding the soil grains and it Movements of Fluids Through Soils. 125 is generally true that the larger the surface of the soil grains the more water the soil will retain. If a marble is lifted out of water it retains a film sur- rounding it and its surface is wet; so if rains fall upon a sand or soil surface until percolation takes place, there is held back upon the grains a certain amount of water which is characteristic of or peculiar to each type. It is clear that a soil whose internal surface is 4 acres per cubic foot may contain a large amount of water even though the film is extremely thin. In an acre there are 43,560 sq. ft. and in four acres 174,240 sq. ft. The thickness of a water film on this surface sufficient to equal 4 inches on the level per square foot of soil would be 17172*0 = 13^60 ofaninch or one-half the thickness of the film of a soap bubble when it becomes yellow just before appearing black and breaking, from thinning out. This thickness is also about -J the di- ameter of the soil grain itself. In the case of a fine sand having grains .08188 m. m., which retains, after complete drainage 8 feet above stand- ing water, 3.44 per cent, of water, the film would have to have a thickness of only about *Y of the diameter of the grain, and when containing 20 per cent, of its dry weight then the film need have a thickness of only about & of the diameter of the sand grains, that is, .0072 m. m. It is clear, therefore, from these considerations that the surface of soil grains has much to do in determining the water-holding power of a soil and that the films may be very thin and yet on account of their great extent represent a high per cent, of the soil itself. 147. Movement of Air Through Soil. There is perhaps nothing which shows how physically different the fine and the coarse grained soils are as clearly as the rates at which air will pass through them when dry, and in the next table some of these are given. 126 Physics of the Soil. It will be seen from this table that when the grains are so large that 10 of them will span a linear inch only 37 seconds are required for a pressure of .1 foot of water to force 5,000 c. c., 5.3 quarts, of air through a column a foot long and .01 of a square foot in cross section ; but in the finest clay soil, which makes the best grass land, where 5,125 grains must be set in line to measure a linear inch, then the time required is 2,933,000 seconds for the same amount of air under the same conditions to be forced through, a ratio of 37 seconds to nearly 34 days. Table showing the differences in the rate of movement of air through gravel, sand and soils of different types when the columns are 1 foot long, .01 ft. in cross section and under a pressure of .1 ft. of water. Description of material. No. of grains per linear inch. Per cent. of pore space. No. of seconds for 5,000 c. c. of air to tiow through. 10. 37 60 37 14.0 38.44 67 17.5 38.85 99 20 6 39.26 138 24.3 39.88 184 27.8 38.53 260 31.8 36.26 418 35.5 34.66 6)2 Medium saiid, grade No. 1 42.3 34.43 869 49 1 34.42 1,178 Fine sand, grade No 60 143 34.20 10,370 Fine sand, grade No. 100 310 35.32 44,310 177 34.91 14,580 227 32.49 30,460 336 34.45 54,910 837 38.83 227, 400 970 34.49 45,750 1,156 44.15 2^2,200 1,403 47 10 476,600 1,647 40.19 804,600 2,286.0 44.15 1,129,000 2,949.0 48.00 1,412,000 3, 310.0 45 96 2,057,000 5,125.0 52.94 2,933,000 It should be understood that this slow rate of movement of air through the finest clay soils was observed when the air-dry soil had been pulverized in a mortar and made as fine as practicable before packing into the aspirator. Un- Movements of Fluids Through Soils. 127 der field conditions, as has been pointed out, a good clay soil has its clusters of various sizes and there are passage- ways of various sizes and forms which allow both air and water to move much more freely than has been recorded in the table and if it were not so plants could not thrive in them. 148. Permeability to Air of Undisturbed Field Soils. The rate at which air may flow through soils in their natural condition, in place In the field, may be readily studied with an apparatus such as is shown in Fig. 40. When the soil tube A is driven into the ground to near the depth at which the flow of air is to be measured it is recovered, the core of soil re- moved and the tube returned to its place, when the aspirator is connected as shown in the cut, and the time required for a given volume of air to be drawn F i G . 40- showing apparatus for MirrmrrVi r\r>tf>rrr\\nf*r\ Tn tlipcp measuring the permeability to nilOllgn C .Q. in tnese a jrof soils in the field. A core of field Studies it will be found soil is removed to the (le.-ired depth and the soil tube replaced. that the dryer the soils are the more freely air passes through them but that when they are saturated with water, as just after heavy rains, little or no air will pass through them even under a pressure of 12 inches of water. 149. Weight of a Cubic Foot of Dry Soil. A cubic foot of undisturbed air-dry soil varies in weight between quite wide limits, the humus soils being the lightest, and the coarse sandy soils the heaviest. The writer has found a dry soil to have the weight per cubic foot given in the table be- low: 128 Physics of the Soil. 1st foot. 2d foot. 3d foot. 4th foot. 5th foot. 6th foot. Pounds per cubic foot Pounds per acre 79 2,740,000 92.6;; 4,034,000 104.59 4,557,000 106.21 4,637,000 111.06 4,840,000 111.06 4,840,000 Shubler gives the weight of a cubic foot of dry soil as follows : Dry calareous or siliceous sand 110 Ibs. Half sand and half clay 96 Ibg. Common arable soil 80 to 90 Ibg. Heavy clay 75 Ibs. Garden mould rich in vegetable matter 70 Ibs. Peat soil 30 to 50 Ibs. As a number easy to remember it may be taken as a safe figure that the mean weight of the surface four feet of field soils is, in round numbers, 4,000,000 Ibs. per acre- foot. 150. Heavy and Light Soils. These terms are used more with reference to the ease with which soils may be worked than to their weight per cubic foot. A soil that is nat- urally mellow and easily stirred is called a light soil, while one that becomes hard when dry and which tends to form clods is often called heavy. Sandy soils, as shown in (149) are among the heaviest we have while the clayey va- rieties are the lightest by weight except the humus types. The prairie loams which contain much humus and the black swamp soils when drained are among the most mellow of all soils, the large amount of humus preventing the soil grains from adhering and baking. CHAPTEK V. SOIL MOISTURE. 151. Occurrence of Moisture in the Soil. For purposes of discussing the cultural relations of soil moisture water may be said to occur in the soil under three conditions : (1) That which fills the pore spaces between the soil grains and is free to move under gravitational or hydro- static pressure and may be called gravitational or hydro- static water. (2) That which adheres to the surfaces of soil grains and to the roots of plants in films thick enough to allow surface tension to move it slowly from place to place, and which may be called capillary water. (3) That still retained on the surfaces of soil grains when they become air-dry; whose chief movements are those of evaporation and condensation and which has been designated hygroscopic moisture. 152. Gravitational Water. When water in a soil in- .creases in quantity sufficiently to move readily under the pull of gravity it may be harmful in three ways: (1) by washing out the soluble plant foods, thus leaving the soil poor ; (2) by excluding the air and thus causing suffocation of the roots of plants and micro-organisms living in the soil; (3) by preventing surface tension and by dissolving cementing materials, thus destroying or reducing the gran- ulation of soils, injuring their texture. It may be helpful in two ways : ( 1 ) by replenishing the capillary moisture when this has become too small to enable crops to supply themselves, and (2) by washing out and carrying away sol- uble substances w y liich, if allowed to accumulate, become in- 130 Physics of the Soil. jurious, such as black alkalies and possibly toxic principles developed by the roots of plants or soil organisms or during their decay. 153. Capillary Water. It is in this condition or quantity in the soil from which crops and soil organisms chiefly de- rive their supply of water, and the right amount at all times is therefore very important. It is in the capillary water, too, that most of the plant foods derived from the soil are held in solution and with it moved to the plants as needed. When the texture of the soil is right the capillary water simply surrounds the soil grains and soil granules as a thin sheet which is continuous where the grains are nearly or quite in contact, but there are always open spaces through which the air may circulate and supply the needs of roots and soil bacteria. If the soil is puddled and the granules broken down then the surface films on the smaller soil grains come so nearly in complete contact that there is insufficient room for air to diffuse and plants cannot thrive in it. 154. Hygroscopic Water Moisture in this form possibly plays an important part in the actual solution of plant food from the soil and fertilizer grains because it is this portion which lies in immediate contact where the action must take place; but if this is true it can only do its work rapidly when capillary water is also present to carry away from the dissolving surfaces the products which are being formed. Polished surfaces do not as readily rust as those which have become tarnished or otherwise roughened. When a steel knife blade has become a little rusty the rusting then goes on much more rapidly, possibly because each particle of rust becomes invested with its film of hygroscopic mois- ture, and when these lie against the fresh metal the water can have a greater thickness and permit a more rapid move- ment of the compounds formed, away from the corroding surface. Water Capacity of Soils. 131 It is not probable, however, that the hygroscopic mois- ture of a soil can in any direct way aid plant growth. 155. Ways of Expressing the Water Content of Soils. The amount of water a soil will or may contain has been ex- pressed in different ways: (1) As a per cent, of the wet weight of the soil, (2) as a per cent, of the dry weight of the soil, (3) as a per cent, of the volume of the soil, (4) in pounds per cubic foot, (5) in inches per cubic foot. The amount of moisture a soil does contain may be most readily and precisely stated as per cents, of the wet or dry weight, but for agricultural purposes it is best to state the amount in per cent, of the volume or in inches per cubic foot. 156. The Maximum Water Capacity of Soils. The largest amount of water a soil may contain is expressed by its per cent, of pore space and if reference is made to the table in ( 145) it will be seen that this ranges from about 32 to more than 52 per cent, that is from 4 to 6 acre-inches per acre- foot of soil, and from 20 to 32 Ibs. per cubic foot. These amounts of water, however, are never found in soils under field conditions. 157. Water Capacity of Soils Under Field Conditions The amount of water which may be retained by soils under field conditions is extremely variable and depends upon a number of factors. In the table below are given the amounts of water which were found in three types of soil with the undisturbed field texture, when they contained as much as they would retain after a few days of drainage fol- lowing heavy rains. Capacity of field soils for moisture. Depth. Sandy loam. Clay loam. Humus soil. First foot Per cent. 17 65 Per cent. 22.67 Per cent. 44 72 14 59 19 78 31 24 Third foot 10 67 18 16 21 29 132 Physics of the Soil. In this table the third foot in each case is more or less sandy and for this reason shows percentagely less water than the soil above. It will be seen that the surface foot of sandy loam contains the smallest per cent, of water and the humus soil the largest, but on account of the differences in dry weight of these soils their water contents are more nearly equal than they appear, the sandy loam containing about 16 Ibs., the clay loam 18 Ibs. and the humus soil 26 Ibs. per cubic foot. Expressed in inches the amounts stand 3, 3.5 and 5 inches nearly. 158. Maximum Capacity of Undisturbed Field Soil. In the table below are given the amounts of water which com- pletely filled the first five feet of undisturbed field soil^ as determined by driving 6-inch metal cylinders one foot long into the soil and, recovering them, covering the bottoms with perforated covers and then placing the cylinders un- der water until the pores became completely filled. Table showing maximum capacity of undisturbed field soil for water. Kind of soil. Depth. Per cent. of water. Inches of water. 1st foot 41.3 5 88 2d foot 28 1 5.03 3d foot 28.4 5.07 Clay with sand 4th foot 5th foot 24.8 17.4 4.67 3.76 Total 24.41 In this case it is seen that two feet out of five feet of the soil was open space which could be occupied with water. 159. Maximum Capillary Capacity of Soils for Wp.ter. The amount of water which may be retained in soils by capillarity is greatly influenced by the distance of the soil above standing water in the ground and by the frequency and amount of rainfall. The cylinders of soil referred to \[Valcr Capacity of Soils. 133 in (158) when thoroughly dried and then placed in one inch of water in a chamber where no evaporation could take place, took up and retained by capillarity the follow- ing amounts of water : Table showing the maximum capillary capacity for water of field soils ruith the surface 11 inches above standing water. Per cent. of water. Lbs. of water per cu. ft. Inches of water. 32 2 23 9 4 59 Second foot of reddish clay contained 23 8 2 2 4 26 24 5 22 7 4 37 Fourth foot of clay and sand contained 22 6 22 ! 4 9 5 Fifth foot of fine sand contained 17.5 19 6 3 77 Total... 110.5 21.24 FIG. 41. Apparatus for measuring the capillary capacity of long columns of sand. It is clear from this table and the last that much of the pore space in the clayey soils cannot be maintained full of water by capillarity even when the surface is only 11 inches above standing water. 134 Physics of ike Soil. 160. Influence of Distance Above Standing Water on the Water Capacity of Soils. When the distance to the ground- water is considerable the force of surface tension is not great enough to maintain as much water in the soil as when the distance is less, and the table which follows shows how the amount of water retained varies with the distance. The sands and soils were placed in an apparatus represented in Fig. 41, arranged so as to permit free percolation but allow- ing very little evaporation from the surface. The sand columns were 8 feet long and percolation was allowed to continue nearly 2.5 years. The soil columns were 7 feet long and percolation from them was continued during 60 days, at the end of which time the tubes were cut into short sections and the amount of water still retained determined by drying. Percentage distribution of water left in columns of sand, sandy loam and clay loam after percolation had continued two and one-half years with the sand and 60 days with the soils. Height of section above ground water. Sand No. 20 Sand No. 40 Sand No. 60 Sand No. 80 Sand No. 100 Sandy loam. Clny 1 am Inches. 96-93... Pr. ct. 27 Pr. ct 17 Pr. ct 22 Pr. ct. 1 26 Pr. ct 3 44 Pr. ct Pr. ct. 93-90 .22 .17 .23 1.16 3 41 90-87 23 16 29 1 34 3 82 87-84 .22 .15 .32 1 61 3>3 84-81 23 18 61 1 98 3 93 16.16 21 . 18 81-78... .29 .19 1 07 2 32 4.19 78-75 44 26 1 33 2 61 4 38 16.08 30 TO 75-72 89 58 1 57 2 90 4.92 72-9 1 18 16 1 80 3 12 4 94 16.55 31.05 69 66 1 48 45 1 85 3 36 5.70 66-63 1 71 67 2 03 3 56 5 91 16.97 31.11 63-60... 1 80 80 2 18 3 92 6 43 60-57 1.83 86 2.26 4.22 6.77 17.59 31.21 57-54 1 93 87 2 27 4 53 7 72 54-51 1.98 98 2 30 4 88 8.59 17.99 31. 4 51-43 2 02 9 3 38 5 42 9 42 48-4.i 2 03 2 12 2 46 6 03 10.50 18.70 31.99 4542 2 02 2 07 2 71 6 99 11 34 42-39 2.06 2 18 3 08 7 47 12.68 19.44 32.18 39-36 2 17 2 29 3 46 8 71 13 00 36-33 2 31 2 48 4 10 10 54 14.95 20.90 32.45 33-30 2 36 2 65 ?.09 11 77 15 90 30-27 2 63 3.14 6.36 12.95 17.20 21.71 33.31 27-24 2 86 3 63 X 74 15 05 17.96 2t-2I 3 42 4 71 13 52 17 24 18 92 21.46 34.40 21-18 4 26 6 76 23 57 19 08 20 49 18-15 6 41 9 38 27 93 19 37 21 34 22.17 35.51 15 12 .. 9 77 14 66 23 61 21 44 21 63 12- 9 16 08 21 31 22 46 22 69 22 68 22.68 35.97 9- 6 19 33 22 39 22 76 2.1 20 23 39 6- 3 20 96 23 52 22 88 24 22 30 28 27.69 37.19 3- Q.. n 21 58 24 61 23 54 25 07 21 08 Water Capacity of Soils. 135 This table shows very clearly that the amount of water a soil can retain by capillarity is very materially influenced by the distance it is above the zone of complete saturation or of standing water in the ground. The decrease of water upward is most rapid in the coarsest sand and it is least rapid in the finest soil. It is remarkable that in sands so coarse as those used water should continue to drain away during more than two years from so short a vertical column and that so small an amount of water was retained in the upper sections of the columns. It is not probable that drainage had become complete from the two soils although it may possibly have been, as there was no percolation during the last five days of the trial. 161. Proportion of Soil- Water Available to Crops. Not all the water which soils will retain is available to plants. A certain amount must be left overspreading the soil grains which the roots of plants are unable to use. The amount found in one field soil, when corn and clover ceased to grow and when the leaves curled early in the day, is given in the table below. In the same table is also given the moisture of adjacent fallow ground determined at the same time and which contains the least amount of water which, for this soil, will permit maximum crops. Soil moisture relations when growth /.s brought to a standstill. Depth of samp" . Clover. Maize. Fallow ground. Per cent. 8.39 Per cent. 6 97 Per cent. 16.28 8.48 7.8 17.74 12-18 inch reddish clay.......... 12.42 11.6 19.88 13.27 11.98 19.81 13.52 10.84 18.56 9.53 4.17 15.9 The moisture contained in the fallow ground shows how much this type of soil may retain, against evaporation and percolation, during a dry season, and it happens to stand 136 Physics of the Soil. just at the under limit for most vigorous growth while the upper limit is given in the next table. Showing upper and lower limits of best amount of soil moist' ure for one type of soil. Kind and depth of soil. Lower limit of soil moisture. Upper limit of soil moisture. Available soil moisture. Clay loam, first foot Per cent. 17 01 Per cent. 23 77 Los. per cu. ft. 6 92 Reddish clay, second foot 19 86 24 3 4.112 Sandy clav, third foot 18.55 24.03 5 722 Sand, fourth foot 15.9 22.29 6.786 Total 23.54 It will be seen from this table that, to bring the surface four feet of soil from the lower limit of the best productive stage of water content to the upper limit, requires an ap- plication of 23.54 pounds per square foot, or a depth of rainfall equal to 4.527 inches. This therefore represents the available moisture in this type of soil and is about one- third of its full capillary capacity. 162. Kinds of Soil Which Yield Their Moisture to Crops Most Completely. When the roots of plants come to draw upon the supply of soil-water those soils yield their mois- ture to the plant most completely whose grains have the largest diameter or, more precisely, which have the smallest internal surface to which the moisture may adhere and over which it is spread. Referring to the table in (161), giving the per cents, of moisture which were too low to permit the plants to supply their needs, it will be seen that under the corn the water in the sand had been drawn down to about 4 per cent. ; in the surface loam to 7 and 8 per cent. ; while in the intervening more clayey portion only to 11 and 12 per cent. The fun- damental truth which should be grasped here is that all these soils are equally dry so far as the needs of the corn crop are concerned, and one of the reasons why they are Water Capacity of Soils. 137 so is because the thickness of the water film surrounding the grains is nearly the same in all the cases. The truth of this statement will be evident if we com- pute the per cent, of moisture in a soil which a given thick- ness of film surrounding the grains will produce. 163. Relation of Thickness of Moisture Films to Per Cent. of Soil Moisture. If the data in the table of (145) is used the per cent, of soil moisture a given thickness of film will produce may be computed approximately from the formula where P = the per cent, of moisture in the soil. K= a factor, Log. 5.497532 = .0314355 S = surface of soil per cu. ft. taken from (145) T = thickness of film of moisture Q = per cent, of dry soil obtained by subtracting the pore space in (145) from 100. Using this formula and the data in (145) it will be found that the per cents, of moisture stand as given below : With thickness of film nroVsW inch the per cent, of water will be, in the Heavy red clay .......................... 14 .24 per cent. Loamy clay .............................. 12.00 per cent. Loamy clay .............................. 8. 74 percent. Loam .................................... 7.20 per cent. Sandy loam .............................. 5.21 percent. Sandy soil ............................... 2.09 per cent. Sandy soil ......... ...................... 1.41 per cent. Coarse sandy soil ........................ 1 . 11 per cent . From this table it will be seen that the coarse sandy soil contains only 1.1 per cent, of its dry weight of moisture when the heavy red clay contains 14 per cent, with the same thickness of film surrounding the soil grains. Comparing these per cents, of moisture with ihose con- tained in the soil in which the corn wilted, it will be seen that the sand of that soil was really the wettest soil there, so far as the available moisture is concerned, there being at 138 Physics of the Soil. least 2 per cent, of moisture yet available. The loamy clay of (145), and given in the table, has about the same texture as that of the reddish clay in the table of (161) and it will be seen that its per cent, of moisture under the corn was also about the same as that computed. 164. Available Soil-Moisture Affected by Jointed Structure in Clay Subsoils. The tendency of clay subsoils to shrink and become divided into small cube-like blocks greatly di- minishes the available moisture in them. This shrinkage not only often i-esults in breaking rootlets in two but when new rootlets form they advance most readily through the fissure planes and are not able to place themselves in the most favorable relations with the soil to permit capillarity to bring the moisture to the rootlets. It is because the sandy soils and loams seldom develop the structure referred to and because the rootlets and root hairs are able to secure a more uniform distribution throughout them as well as because of the larger size of their grains that plants are able to drain their moisture down to so low a per cent. 165. Available Soil-Moisture Increased by Open Structure. When soils are in any way left with a loose open struc- ture, as happens with deep plowing and especially with good subsoiling, not only is the ability of the loose soil to retain moisture increased but a larger proportion of this retained water becomes available to the crop. A larger amount of water is retained because when perfect capillary connection with the unstirred soil below, is broken, surface tension opposes rather than aids gravity in producing per- colation and spaces too large to remain full of water other- wise are able to retain it. When the soil is open and loose the case is quite different from that resulting from shrinkage referred to in (164), for in this case the roots and root hairs are better able to enter the separated portions and, as the moisture films are thicker, the moisture is more readily gathered. Amount of Water Required by Crops. 139 166. Drainage May Increase the Available Soil-Moisture. When the subsoil is too close and too fully saturated with water to permit the roots of crops to penetrate it, as is the case where drainage is needed, the roots of plants are forced to develop in so limited an amount of soil that when a dry- ing time conies, and when the demands of the crops for moisture are large because of rapid growth, capillarity from below is not able to supply the moisture as fast as needed, and the result is the zone of soil occupied by the roots becomes so dry that growth is impeded. On the other hand, where a field is well drained the roots are extended through much larger volumes of soil ; the lo- cal demands are thus less urgent and the water need not move so far by capillarity before the plant comes in pos- session of it. Under these conditions the moisture of the surface four feet of soil is in close reach of the roots and capillarity may still add to this supply from below. 167. The Amount of Water Required by Crops. It has been determined by careful and extended observations in this country and in Europe that almost any one of the cul- tivated crops withdraws from 300 to 500 tons of water from the soil for each ton of dry matter produced. In Wiscon- sin the amounts of water lost from the soil by evaporation during the growing season and through the plant are given in the table below : Table showing the mean amount of water used by various plants in Wisconsin in producing a ton of dry matter. Water Acre-in. of No. of trials. used per ton of dry Water used. Dry matter per acre. water per ton of dry matter. matter. Tons. Inches. Tons. Barley 5 464.1 20 69 5 05 4 096 Oats 20 503.9 39 53 8.89 4.447 Maize 52 270.9 15 76 6 59 2 391 Clover 46 576.6 22 34 4.39 5.089 1 477.2 16 89 4 009 4 212 Potatoes 14 385.1 23.78 6 995 138 Av. 446.3 23,165 5.987 3.939 140 Physics of the Soil. From this table it is seen that the amount of water used ranges from 270 tons of water with corn to 576 tons with clover per ton of dry matter ; or when expressed in acre- inches from 2.4 to 5.1 inches nearly, the average for the six crops being nearly 450 tons or 4 acre-inches per ton of dry matter. When the yields per acre are 2, 3 and 4 tons the num- bers given above must be multiplied by the same factors. 168. Amounts of Water Required for Different Yields of Wheat. In order to express the data of the last section in terms which it is more customary to use, there is given in the next table the amount of water required by a crop of wheat when the yields per acre range from 15 to 40 bushels. Observations made by Hellriegel in Germany show that wheat uses about 453 tons or 3.998 acre-inches of water for a ton of dry matter. Using this ratio and one pound of grain to 1.5 pounds of straw the water required will *f and as below : Table showing the least amount of water required to produce different yields of wheat per acre when the ratio of grain to straw is I to 1.5. YIELD PEE ACRE. Water used. Number of bushels. . Weight of grain. Weight of straw. Total weight 15... Tons. .45 .60 .75 .90 1.05 1.20 Tons. .675 90 1 125 1.350 1.575 1.800 Tons. 1.125 1.500 1.575 2.*50 2.625 3. Acre- inch. 4 498 5.998 7.497 8.997 10.495 12. 20... 25 ao... 85... 40 This table shows that 12 inches of effective rain during the growing season of wheat, starting with the soil moisture in good condition, should enable a yield of 40 bushels per acre to be produced. Amount of Water Required by Crops. 141 1G9. least Amount of Water Which Will Permit Yields of Different Amounts. In the next table there is given the least amount of water taken from the soil which can be ex- pected to give the yields for the different crops there stated : This table must be regarded as showing the minimum amounts of water which will bring the crops named to full maturity so as to produce the yields specified under conditions of absolutely no loss by surface or under-drain- age, and where the evaporation from the soil itself is aa small as it can well be. It must be farther understood that the soil at seeding time already possesses the needful amount of water for the best conditions, and that at the end of the growing season it is yet so moist that no check to vigorous, normal growth has occurred. Table showing the highest probable duty of water for differ- ent yields per acre of different crops. Bushels per acre 15 20 30 40 50 60 70 80 100 200 300 400 Name of crop. Least number of acre-inches of water. Wheat 4.5 3.21 2.35 2. 52 6 4 28 3.136 3.36 .41 9 6.42 5 701 5.31 .62 12 8.56 6.27J 6.72 .83 15 10.7 7 81 8.4 1.03 18 12.84 9.40 10.08 1.24 19 98 10.98 11.75 1.45 Oats 12.54 13.43 1.65 15.6J- 16.77 2.07 Maize I'.U '6.2 '8"27 Tons per acre. .. 1 2 3 4 6 8 10 12 14 16 18 Least number of acre-inches of water. Clover hay, 15 per cent, water Corn with ears, 15 perct. water Corn silage, 70 percent, water 4.43 2.08 1.41 8.85 4.16 2.82 13.28 6.24 4.23 17.7 8.32 5.64 26.55 12.47 8.46 35.4 16.61 11.23 14.25 20.72 14.1 24.95 16.92 29.1 19.74 33.26 22.56 37.42 25.38 41.58 28.2 CHAPTER VI. PHYSICS OF PLANT BREATHING AND ROOT ACTION. MECHANISM AND METHOD OF TRANSPIRATION IN PLANTS. 170. Breathing of Plants and Animals. The transpira- tion of plants and the respiration of animals are processes which have much in common. Both plants and animals are provided with internal cavities into which air may en- ter. They both breath air. While breathing air both give off large quantities of moisture. The primary object of the lungs is to supply the body of the animal with oxygen and to remove carbon dioxide. The corresponding structure in the leaves of plants is to supply it with carbon dioxide and to throw off oxygen. In both cases the breathing surface has a very delicate texture and is situated where it can al- ways be kept wet; the chief function of the water escaping from the breathing surface is to keep it moist. If the lining of the lungs were to become dry and parched the gases would not as readily pass through and there would be like difficulty in the case of leaves, if their breathing surfaces were not kept moist. In both plants and animals the breathing surfaces are carefully guarded from the intense sun and strong drying winds. 171. Respiratory Organs in Plants. The air passages or breathing chambers of plants are chiefly located in the leaves, but they are also found to greater or less extent in all the green parts. They are simply irregular chambers left between the cellular tissue and are represented in the Respiration and Transpiration of Plants. 143 lower portion of Fig. 42, which shows a section of barley leaf with the epidermis removed and much magnified. 172. Breathing Pores. Leading into the air chambers are many breathing pores through which the air enters. Eight of these are repre- sented in Fig. 42. They are most numerous on the under sides of leaves where evaporation may be least. The breathing pores or stomata are very small and numerous, Weiss es- timating, from an average of 40 plants, as many as 209,000 in each square centimeter of surface, an area equal to the square shown in Fig. 43. In the case of a corn leaf 21 per cefit. of the surface FIG. 42 Structure of barley leaf. fAfteria nr>r>iTmprl Kv flip rlnnr- Sorauer; sp is a breathing pore ; m, chlo- 1S "J ] rophyll cells ; i, respiratory chambers, ways to the breathing chambers. 173. Chlorophyll Cells. Surrounding the air chambers in every leaf there are multitudes of tender, thin-walled cells in which are found the green chlorophyll grains, giv- ing color to the leaf, which absorb the sunshine and use it in breaking down the carbon dioxide for the carbon, which is one of the chief constituents of plant tissues, and of the starches, sugars and most other compounds. 174. Guard Cells. In order that the loss of water may be as little as possible each breathing pore is surrounded by a pair of guard cells, represented in Fig. 42, and on a much larger scale in Fig. 43. These guard cells have for their function the regulation of the amount of evaporation from Physics of the Soil. the plant. The chlorophyll grains can be effective in breaking down the carbon dioxide only in comparatively FIG. 43. Diagram showing the mechanical action or guard cells In open ing and closing breathing pores. The square shows the area of under side of leaf containing an average of 209,000 breathing pores or stomata. (From Irrigation and Drainage.) bright light and so, during cloudy days and at night, the guard cells automatically change their form and close the doors, reducing evaporation. Indeed they remain open only when there is light enough to utilize it in decomposing the carbon dioxide. 175. Action of the Guard Cells. The opening and closing of the guard cells is brought about by their peculiar shape and changes in the amount of material they contain. Unlike the other cells in the epidermis of the leaf these contain chlorophyll grains and are thus able to carry on the process of developing plant food. The advantage of hav-- ing this work done here is to increase the osmotic pressure through the rendering of the sap denser when the sun is shining, thus distending the cells and changing their shape BO as to open the doors widest when the sun shines brightest, as represented at A, Fig. 43. When night comes or it is cloudy then the osmotic pressure forces the assimilated ma- terial out of the guard cells faster than it is produced and the walls collapse, taking the attitude represented at C and in cross section at D, closing the opening. B and D are cross sections of a pair of guard cells along the lines 1-2 and B shows how a full cell must pull the edges apart while Root Action in Plants. 145 D shows how the limp condition will permit the walls to fall together. 176. loss of Water Through the Guard Cells. The epi- dermis of the leaf is so close in texture and often so water- proofed that when the guard cells close there is but little loss of moisture. But when the sun shines and there is moisture enough in the soil to keep the leaves from wilting the guard cells open wide and great evaporation may take place even in a saturated atmosphere. By admitting live steam into our plant house on bright sunny days, keeping the air highly saturated, we have found corn to lose nearly as much moisture as in the dryer condition of the air with the sun also shining. The reason this is possible is that the epidermis acts like the glass of the hot bed, permitting the sunshine to enter but preventing the longer dark heat waves from escaping. In this way the air saturated outside is not so inside on account of the higher temperature. This remarkable provision of the plant to save moisture should teach how important it is to assist, in every way practicable, the conservation of soil moisture. STRUCTURE AND MODE OF ROOT ACTION". There is scarcely a better illustration anywhere in Nature of the adaptation of living organisms to their en- vironments than is furnished by the mechanism by which the higher land plants supply themselves with moisture; and one of the most remarkable of remarkable tasks is that of a corn plant pumping into its stem and leaves, from a comparatively dry soil, 2.896 pounds of water daily for 13 consecutive days. 177. Functions of Roots The roots of ordinary land plants have three distinct functions to perform: First, to gather from the soil its moisture and the salts dissolved in it for the use of the plant; second, to convey and deliver 146 Physics of the Soil. into the stem and leaves the water absorbed ; and third, to act as an anchor or support, holding the plant upright in the soil, air and sunshine. Fid. 44. A, Root-hairs of mustard plants, with soil adhering, and with soil removed. B. root-lmirs of wheat, when very young, and four weeks later. (After Sachs.) 178. The Absorbing Portion of Roots It is the general belief of plant physiologists that the active portion of roots that which is immediately concerned in gathering the water from the soil is what are known as root hairs, rep- resented at the left of A, Fig. 44, and at A buried in the soil grains in the same figure. In Fig. 46 is a much en- larged view of a single root hair which has worked its way in among the soil grains where it is in place to absorb soil moisture and soluble salts. The appearance of root hairs in relation to soil grains can be clearly demonstrated by growing plants in rather coarse sand between glass plates as represented in the apparatus shown in Fig. 45. Root Action in Plants. 147 179. Structure of Root Hairs. Boot hairs are extremely thin walled and greatly lengthened single cells, having lengths ranging up to an eighth or quarter of an inch and a diameter of TOU of an inch. They stand out about the main root like the pile of velvet, forming a brush-like appearance as shown in Fig. 44. The object of this form is to secure a large area around which surface tension may force the water in the same way that it does about the soil grains. In- deed root hairs have forms adapted to drawing upon themselves a portion of the water film invest- ing the soil grains. 180. Relation of Root Hairs to Soil Grains. The manner in which root . , hairs place themselves Fio.45. Apparatus for observing the growth f. ., of roots and their relation to soil grains. amonST tne SOli grains 13 The sides of the apparatus are two panes n i T 7i / of glass, 1.5 inches apart. cleariy shown in the form of a diagram in Fig. 46 where h h is a root hair ; e is the main root, 2 a soil granule, and 1 an air space; while the concentric lines represent the films of capillary moisture which surround both the granules and the root hairs. In Fig. 47 is represented the tip of a young growing root ad- vancing into fresh soil and having five root hairs developed in place among the soil grains ready for work. 181. Method by which Root Hairs Gather Water As the root hairs force their way through the pore spaces among the soil granules they bring their walls into close touch with 148 Physics of the Soil. them in such a way that in form and position they make up a part of the soil mass. In this relation the force of adhesion draws the capillary water out over their walls so FIG. 46. Distribution of water on the surfaces of soil grains and of root-hairs, e, main root: 1, air space; 2, soil grain; 3, nlni of water; h h, root-hairs. (After Sachs.) as to leave them and the soil granules surrounded by the water film. Each root hair is or should be in a sense under water, that is invested in a film of greater or less thickness. When a portion of this water enters the root hair and passes on into the root and up to the leaves, the water layer surrounding the root hair is left thinner; but no sooner does this thinning out occur than the equilibrium is de- stroyed and surface tension at once squeezes more water onto the surface from the surrounding soil. In this way capillarity keeps the water moving to the root hairs as they pass it on to the plant. 182. Advance of Eoots through the Soil. Until the method by which roots advance through the soil is under- stood it is difficult to realize how it is possible for such deli- cate structures to set the heavy soil aside sufficiently to reach the great depths they do. Nature's method of over- coming the difficulty is simple enough and it is as effective as it is simple. The large amount of open space there is in the surface four to six feet of soil makes it easier to set the Root Action in Plants. 149 soil aside, and the setting of fence posts proves how large this space is. A 6-inch post set in the hole dug for it seldom occupies so much of tho space but that all of the soil re- moved may be returned by thorough ramming. It is the existence of such large amounts of open space in the soil which makes the movements of water, air and roots through it possible and the absence of it which makes a puddled soil so uncongenial to plant growth. FIG. 47. Methc jy which root-hairs advan< (Adapted from Sachs.) jugh the solL In Fig. 47 is represented a section of the tip of a root growing and advancing through the soil. It has been found that at 1, a short way back from the tip, there is a center of growth. Here new cells are forming by division and subsequent enlargement. On the forward side of this cell the new ones build the root cap, which acts as a shield and wedge, while those in the rear are finally transformed to make the various structures found in the root. At the center of growth new cells are forming and ex- panding under the intense power of osmotic pressure and, as the root is anchored behind, the root cap is pushed for- 10 150 Physics of the SoiL ward and wedged sidewise, setting the soil aside and tlni3 making room for itself. The root cap does not slide for- ward past soil grains but is anchored rigidly to them ; the tip entering existing cavities is enlarged by growing for- ward under and through the cap, the rear cells of which die after the root has grown past them, the root cap being a sor of point continually renewed as the root advances. 183. The Extent of Root Development of Corn. It is only by careful study that the extent of root development in a soil can be learned. In Figs. 48 and 49 are shown the amount and distribution of corn roots at two stages of growth. When the corn was 30 inches high the whole of the soil to a depth of two feet was as full of roots as the engraving shows between the two hills ; when the corn was coming into tassel the roots had penetrated to a depth of three feet and had come closer to the surface ; and at ma- turity the roots had reached four feet in depth, making their way through a fairly heavy clay loam and clay sub- soil, the fourth foot only being sandy. It should be understood that the roots here shown grew in undisturbed field soil and were obtained by going into the field at the stage of growth shown and digging a trench around a block of soil a foot through and the length of the width of the row. The cage was then set down over the block ; wires run through the block of soil to hold the roots in place and then the soil washed away by pumping water in a fine spray upon the block. Three days' work for two men were required to secure the sample in Fig. 49. 184. Extent of Root Development of Grain. In Fig. 50 is represented the depth to which the roots of winter wheat, barley and oats penetrated a heavy clay soil and subsoil. The roots are what were found in a cylinder of soil just one foot in diameter and were obtained by driving a cylii. der of metal four feet long its full depth into the soil and then washing the dirt out of it. It will be seen that in each case the roots have reached a depth of fully four feet. Hoot Action in Plants. 151 FIG. 48. Showing amount and distribution of corn roots under natural field conditions. 152 Physics of the Soil. FIG. 49. Showing amount and distribution of corn roots under natural field conditions. Root Action in Plants. 153 Wheat. Barley. Oats. FIG. 50. Showing amount of roots found in the field in cylinder of soil one loot in diameter, extending to a depth of four feet. 154 Physics of the Soil. FIG. 51. Showing the total root of one hill of corn. Root Action in Plants. 155 PIG. B2. Showing total roots of oats. 15.6 Physics o iltie Soil. FIG. 53. Showing total roots of medium clover. Extent of Root Growth. 157 The coarse branches shown with the winter wheat roots are the roots of a red oak tree which was growing in a pasture 33 feet away, and they serve to show how far forest trees send their roots foraging through the soil for water and food, and through ,what long lines the water must be pumped after it has been gathered. 185. The Total Root of Plants. In the preceding sections the samples simply show the amount of root found in a given volume of field soil. In Fig. 51 is shown the total root of four stalks of corn, while Figs. 52 and 53 show the same thing for oats and medium clover. These were se- cured by growing the plants in cylinders 42 inches deep and 18 inches in diameter, filled with soil. When the crops were mature the cylinders were cut down and the soil washed away. In each case the roots extended to the bottoms of the cylinders, forming a dense mat there, as the engravings show. The roots shown with the clover, and which gathered the moisture for the top, forced from the soil water enough to cover the space to a depth of 2-9 inches. It will be seen that the stand of clover is very close, fully three times as heavy as a good clover crop in the field; This was made possible by having a rich soil and supplying all the water the plant could use at just the right time. The length of all these roots is less than it would have been had the cylinders been deeper, as proven by the mat- ting at the bottom. CHAPTEK VIL MOVEMENTS OF SOIL MOISTTTEE, 186. Types of Soil Moisture Movement. The moisture which is found in the soil above the surface of the ground water is continually subjected to three types of movement: (1) Gravitational," (2) Capillary and (3) Thermal; the, first due to the action of gravity^ the second to surface ten- sion and the third to heat. When rain falls upon the soil one portion of it begins to flow vertically downward through the pore spaces, urged to do so by the pull of gravity ; a second portion increases the thickness of the water film surrounding the soil grains and root hairs and is made to do so by surface tension; while a third portion is returned to the atmosphere through evaporation, caused by heat. GRAVITATIONAL MOVEMENTS. 187. Percolation of Soil Moisture. The direct gravita- tional flow of soil moisture, which occurs during and after rains, is nearly always vertically downward until the ground-water surface is reached. The movement takes place chiefly through the shrinkage cracks and passage- ways left by the decay of roots and the burrowing of ani- mals, but also through the capillary pores formed by the grains of the coarser soils and by the granules of the finer types. The rate of movement is most rapid following heavy rains when the soil is already well saturated. After pro- longed periods of drought, when the soil has become very dry, there is so much air in the pore spaces that it greatly Rate of Percolation of Soil Water. 159 impedes percolation except in those cases where wide shrinkage checks and cracks have resulted. Where percolation is influenced chiefly by soil texture it is most rapid through the sandy soils and the more granu- lated clay types. It is least rapid through the puddled clays. 188. Rate of Percolation Through Sands. When the sim- ple sands are once completely filled with water the perco- lation from them is quite rapid but decreases with the size of the sand grains. In the table below is given the amount of water which percolated from the columns of sand referred to in (160). Table giving the rate of percolation from sands under the gravitational head of the inclosed water. GRADE OF SAND. Effective diameter of grain. Per cent of pore space. Weight of sand per 8 cu- bic feet. AMOUNT OF WATEE PKRCO- LATtD IN First 30 min. Second 30 min. No. 20..., ra. m. 0.4745 .1818 .1551 .1183 .08265 38.83 40.07 40 76 40.57 39.73 Pounds. 809.28 79.J.28 784.00 786.61 797.76 Lbs. 53 33 30.27 29.99 7.86 6.31 Inches. 10.95 7.519 5 671 1.512 1 213 Lbs. 21. ?6 27. H5 23 f2 6.73 4.40 Inches. 46S3 5.2.iS 4.W2 l.'JtU .815 No. 40 No. ft) No. fcO No. 100 It will be seen from the above table that the rate at which the water moved downward through the coarsest or No. 20 sand was such as to average during the first thirty minutes 492 inches per twenty-four hours, while for the finest or No. 100 sand the mean rate was 58.16 inches, the flow from the first being nearly 8.5 times as fast, with grains not quite 6 times as large. After the end of the first nine days of percolation these coarse sands lost about 1.7 per cent, of their dry weight in each case, or only about .33 of an inch. 189. Rate of Percolation from Soils. The percolation of water from the sandy loam and from the clay soil, given 160 Physics of the Soil. in the table of (160), when the eight-foot columns were completely full of water at the start, took place at a much slower rate than from the sands, as indicated in (188), the rates being Sandy loam, inches. Clay loam inches. First 21 hours 2.640 First 23 hours 1 953 First 10 davs following the above 5.072 2.111 .905 .493 Total in about 21 days 8.617 4.562 The rates in these cases were such that more water per- colated from the three coarsest sands during the first 30 minutes than from the clay loam in as many days ; and yet the loam contained at the start the largest amount of water. It is clear from these differences in the rate of percolation why the sand could not be productive under ordinary con- ditions of rainfall, no matter how much plant food it might contain. It is clear also that fineness or closeness of tex- ture is one of the most important qualities of a good soil, for without this the water drains away so rapidly that, with the ordinary intervals between rains, not enough could be retained for the needs of crops. 190. Percolation Through Dry Soil. When soils have be- come relatively dry, as happens especially during the mid- dle and later summer, water does not percolate into them as readily as it does in the spring when the pores are more nearly filled. When the volume of air in the soil is large, and when the films of water surrounding the soil grains are very thin, the flow downward past the air is very slow. It is on this account, in part, that the lighter rains are less effective in midsummer than they are in the spring, the water being retained close to the surface where it is quickly lost by evaporation. Capillary Movements of Soil Moisture. 161 CAPILLARY MOVEMENTS OF SOIL MOISTURE. The capillary movements of soil moisture are relatively slow, when compared with those of percolation, and are slower in dry than in wet soil. The general tendency of capillarity is to bring water to the surface from varying depths, but its movements may occur in any other direction, the flow being always from a soil where the water films are relatively thick toward those where they are thinner, or from the wetter toward the dryer soils. If the roots of plants have made the soil dryer in their immediate neighborhood capillarity may carry water to them from below, above or from either side. When heavy rains follow a dry spell then capillarity will assist gravity in carrying the water more deeply into the ground ; and when water is applied by the furrow method in irrigation capillarity carries it laterally away from the furrows. 191. The Rise of Water in Capillary Tubes. When a. clean glass tube whose bore is small and wet is held verti- cally in water the liquid rises to a certain height above the level outside, the amount varying with the diameter of tho tube, as given in the table below : In a tube 1. inch in diameter the water raises .054 inches. In a tube .1 inch in diameter the water raises .545 inches. In a tube .01 inch in diameter the water raises 5.456 inches. In a tube .001 inch in diameter the water raises 54.56 inches. That is to say, reducing the diameter of the tube one-half doubles the height the water may be raised by capillarity, and reducing the diameter to one-hundredth enables the water to rise 100 times as high. The results in the table above will be true only when the walls of the tube are very clean, the water pure and the temperature 32 F. 192. Cause of the Variation in Height to Which Water Is Raised in Capillary Tubes. The reason for the differences 1G2 Physics of the Soil. in height to which water may be raised in capillary tubes by surface tension is found in the relation existing between the volume of the tube and its internal circumference at the level of the water surface. Quinke has shown that the force of cohesion is exerted over a distance of sWoo^ inch; so that when a glass tube is thrust into water the molecules in the surface of the wall just above the water draw upward upon the rows of molecules in the surface lying nearest, raising them above the naiural water level. But as the edge of the surface film is raised the whole water column is carried upward also until the weight lifted above the hydrostatic level is equal to the cohesive attraction be- tween the glass and the water. As each molecule of glass has a fixed power to pull, the tube of large diameter will be able to lift as much more water than the small one, as the number of molecules in its circumference is greater. But the circumferences of tubes increase in the same ratio as their diameters, and hence a tube whose diameter is .1 inch will lift above the water level 10 times as much w r ater as the one .01 inch in diameter. But, as the weight of water lifted increases as the squares of the diameters of the tubes, the first tube will only lift its column one-tenth as high as the second tube, for then its load becomes 10 times as great, and this is the limit of its power, as expressed in the table below: Diameter of tube. Relative area of cross- sect ion of tube. Heieht to which water is lifted. Relative amount of water lifted. 1.0 .1 .01 .001 inch 1,000,000 X -05456 inches 10,000 X .5456 inches 100 X 5.456 inches 1 X 54.560 inches 54,. VO 00 inch = 5.45fi.OO 546 00 5tt5 50 The actual amount of water lifted by the surface film stretched across the tube and carried upward by the pull of the glass molecules just above its edge is as fol- lows , Capillary Movements of Soil Moisture. 1G3 In the 1.0 inch tube 01285 cubic inch. In the .1 inch tube 0012S5 cubic inch. In the .01 inch tube 0001285 cubic in<;h. In the .001 inch tube 00001285 cubic inch. 193. Capillary Rise of Water in Soils. The spaces left be- tween the soil grains form more or less triangular capillary tubes whose cross-section, formed by four spherical grains, placed as closely together as possible, is represented at the left in Fig. 54; and these tubes extend in all directions through a soil. The effective diameters of these capillary tubes are somewhat nearly proportional to the diameters of the soil grains so that for soils with spherical grains having the closest pcickiug, doubling the diameters of the grains would also double the effective diameters of the capillary tubes through which the water must be moved. FIG. 54. Showing the shape of cross-sections of the pore space between soil grains. Tli3 area of cross section of the two capillary pores shown in Fig. 54 is equal to the area of the rhombus con- necting the centers of the four grains minus the area of a circle having the diameter of the soil grains, so that divid- ing this area by two gives the area of the section of the pore. Where the pore has the smallest section its area is given by the equation Area = (v3 -^J X r 8 = .1613 r 8 where r is the radius of the soil grain, 164 Physics of the Soil. .The capillary pores in an ideal soil do not have a uni- form diameter but are shaped like the cast shown in Fig. FIG. 55. Showing a cast of the pore space between spherical grains, much enlarged. 55, largest at one place and decreasing in either direc- tion to the area given by the equation above. The mean area of the section of the pore, is given by Slichter,* as mean area of section of pore = 0.2118 r 2 which would make the largest or effective cross section of the capillary pore not far from (.2118 X 2) .1613 = .2623 r 2 From this the effective diameter of the capillary tubes may be found, using the formula D = 2 -/- 2623r8 where r is the radius of the soil grain and D is the diameter of the capillary pore. * Theoretical Investigation of the Motion of Ground Waters, 19th annual report of the Geological Survey, part II, p. 316, Capillary Movements of Soil Moisture. 165 On this basis spherical soil grains of one size and the closest packing, having diameters of m. m. m. m. m. m. ru. m. m. m. 1. .5 .1 .05 .01 would form capillary tubes whose largest cross sections are nearly equivalent in area to circles having diameters of m. m. m. m. m. m. m. m. m. m. .289 .1445 .0289 .01445 .00289 Did such soil grains have the attractive power of glass for water and were their triangular pores capable of rais- ing water to the height of circular tubes of equivalent cross sections they should be able to lift water at 32 F. to very nearly the height of .4ft. .8ft. 4ft. 8 ft. and 40 ft. respectively. 194. Observed Height of Capillary Rise of Soil Moisture To measure the rise of water by capillarity in ordinary soils four cylinders, 10 feet long and .04611 sq. ft, in sec- tion, were filled, two with a sandy loam and two with a clay loam, the first containing 18.88 per cent., and the second 32.63 per cent, of water uniformly distributed throughout the columns. On one of each set of tubes a soil mulch was developed 3 inches deep, when they were all placed in front of a ventilator where a current of air was maintained across their tops during 314 days. At the end of this time the tubes were cut into 6-inch sec- tions and the water content of the soil determined, with the results given in the table which follows: It is clear from this table that there has been an up- ward movement of water and loss through the surface even from the bottom layers of soil in the case -of the medium clay, and probably also from the sandy loam. This follows from the fact that the clay soil contained, when put into the cylinders, 32.63 per cent., whereas the lower six inches is 1.38 per cent, drier in the mulched cyl- inder and 3.17 per cent, drier in the cylinder not mulched. 1G6 Physics of the Soil. Table showing the loss of water by surface evaporation from columns of soil 10 feet long, mulched and not mulched. SAND? LOAM. CLAY SOIL. Mulched 3 inches. Not mulched. Mulched 3 inches. Not mulched. Per cent. 8.33 12 97 14.59 15.25 15.55 15.89 16.22 16.29 16.58 17.07 17.05 17.26 17.56 17.73 17.94 17.96 18.25 18.67 18.53 19.21 Per cent. 7.41 14.48 14.70 14.96 15.53 16.17 16.33 16. 33 16.10 16.76 17.31 17.43 17.79 17 88 17.85 17.67 18.05 18.09 18.63 19.95 Per cent. 17 66 24.59 26.58 26.95 27.45 27.92 27.94 28.24 28.46 28.47 28.87 28.70 29.24 29.28 29. 35 29.79 30.32 31.15 30.47 31.25 Per cent 7.79 18 30 21 46 26 26 26. S9 27 . 16 27 61 27.64 27.28 28.23 27.79 28.05 28.93 28.31 28.32 28.80 29.14 29.16 29.33 29.46 6 inches to 12 inches 12 inches to 18 inches 24 inches to 30 inches 36 inches to 42 inches 48 inches to 54 inches 54 inches to 60 inches 60 inches to 86 inches 66 inches to 72 inches 72 inches to 78 inches 78 inches to 84 inches 90 inches to 96 inches... 102 inches to 108 inches 108 inches to 114 inches Hi inches to 120 inches . .. In the case of the sandy loam the lower six inches in each case is wetter than when it went in, showing that at first percolation downward had taken place, and as this soil when allowed to drain freely only retained 19.44 per cent. of water at a depth of 36-42 inches, it is quite probable that at some time the lower soil 10 feet below the sur- face may have been wetter than found at the end of the trials, and if this is true then even the sandy loam has lost water upward from a depth of ten feet below the sur- face. It is quite certain that a drying of these soils has taken place through a depth of ten feet, and hence that moisture ten feet below the surface of the ground may become available for vegetation purposes at or near the surface. The effective diameter of the soil grains in these two cases was found to be, for the sandy loam, about .01635 m. m., and for the medium clay loam, .01254 m. m. ; this would indicate that there might be a capillary rise of 23.6 and 30.8 feet respectively. Capillary Movements of Soil Moisture. 167 195. Capillary Rise of Water in Sand. In the case of a sorted sand with grains .4743 m. m. in diameter, when saturated with water in an apparatus represented in Fig. 56, it was found that water was raised through a col- umn 6.75 inches above the level of water in the reservoir at the rate of 44.09 inches of water on the level per 24 hours, but that when the column was made 11.75 inches long no water was raised to the surface. ill FIG. 56. Apparatus for measuring the maximum rate and height of capillary rise of water in sands. A, evaporating reservoir; B, water reservoir; C, rubber tube. From the formula in (193) a glass sand with grains the size of this one should be able to lift water by capillarity to a height of 10.11 inches and, since the quartz sand used did lift water at the rate of 44.09 inches in depth in 24 hours through a height of 6.75 inches, and failed to lift any water to a height of 11.75 inches, it is clear that its maximum limit must lie very close to that computed for the glass sand. 168 Physics of the Soil. 196. Rate of Capillary Rise of Water in Wet Soil. There is yet no very satisfactory data as to just how rapidly wa- ter may be moved by capillarity through wet soils. It is probable that the case cited in (195) represents about the maximum rate in that coarse quartz sand, through that height, namely, 44.09 inches in depth per 24 hours. This is an enormous quantity of water to be raised by capil- larity and was rendered possible only by expanding the column of sand at the top, as shown in the figure, so as to increase the rate of evaporation until it exceeded the abil- ity of capillarity to bring the water to the surface. Experiments have shown that with a strong current of air passing across the wet surface of the soil, water was lifted by capillarity in a square foot of soil, through the different distances and at the rates given in the table be- low: 1 foot. 2 feet. ' 3 feet. 4 feet. Fine quartz sand Ibs. per day 2.37 ibs. per day. 2.07 Ibs. per day. 1 . 23 Ibs. per day. .91 2 05 1.G2 1.00 .00 It is quite certain that these figures do not represent the maximum rate of capillary rise through these soils; be- cause, as the surface of the soil had no greater area than the section of the soil column, the rate of rise could not exceed the rate of evaporation. 197. Rate cf Capillary Movement of Water in Dry Soil The movement of water through a thoroughly dry soil, by capillarity, is not as rapid as it is through the same soil when wet; the case being analogous to the much slower absorption of water by a dry cloth or sponge than by a similar one when damp. In the table which follows is given the rate at which water entered 5 cvlinders of water-free soil, 6 inches in Capillary Movements of Soil Moisture. 169 diameter and 12 inches long, standing in one inch of wa- ter and possessing the undisturbed field texture. The cylinders stood in a saturated atmosphere and the amount of water absorbed was determined by weighing every third day, the samples being the same ones used in (158) and (159). Table showing the mean daily absorption of capillary water by undisturbed field soil. Cylinders 6 inches in diameter, 12 inches long, standing 11 inches out of water. POUNDS PEE CUBIC FOOT. First foot. Second foot. Third foot. Fourth foot. Fifth foot. Water absorbed dur ng 1st 3 days Water absorbed rlui tig 2nd 3 days 12.50 2.57 1.74 1 33 .96 .44 .It .07 19.73 Per ct. 32 2 28.28 3.92 12.42 2 18 1.02 .79 .59 .46 .32 .25 18 03 Per ct. 23.8 20.43 3.37 9 61 2 33 1.56 1.28 1.16 1.00 .69 .48 18.32 Per ct. 24.5 20 39 4.11 13 50 3.f'8 1.71 .51 .-3 17 .10 .03 19 83 Per ct. 22 6 21.30 1.30 10.73 2 9:i 2.15 .61 .16 .Oo .01 .02 16.67 Per ct. 17 5 15.72 1.78 Water absorbed dur iisf 4th 3 days Water absorbed dur ng 5th 3 days., Water absorbed dur ng tith 3 days Water absorbed dur ng 7th 3 days Water absorbed dur ng Sth 3 days Water absorbed during 24 days Complete saturation Degree of saturation attained Difference 'rom this table it is seen that the amount of water absorbed during the first three days, was only at the mean daily rate of 4.16, 4.13, 3.20, 4.5 and 3.58 Ibs. respective- ly; after the first period the rate of rise was much less rapid and did not equal the rate at which an almost iden- tical soil (196) raised water through 4 feet as measured by the daily evaporation ; and yet the daily rise of water of .91 and .90 Ibs. per sq. ft, would have been greater had the evaporation only been more rapid. In the case of the sand of (195) the water was lifted by capillarity at the enormous rate of 228.6 Ibs. per sq. ft. in 24 hours while the sandy loam of (194), placed under the conditions of (195), using the same piece of apparatus, lifted water at the rate of 26.62 Ibs. per sq. ft. in the same 24 hours. 170 Physics of the Soil. In the case of the 6-inch cylinders of soil above, with their tope only 11 inches out of water, the length of time required for the surface of the soil to begin, to appear damp was 2 days for the fine sand or 5th foot. 6 days for the sand and clay or 4th foot. 6 days for the clay loam or 1st foot. 18 days for the reddish clay or 3rd foot. 22 days for the reddish clay or 2nd foot It is clear from the data presented that the rate of cap- illary movement of soil moisture is greatly influenced by the water content of the soil. 198. Capillarity Is Stronger in Wet than in Dry Soils. It follows from (196) and (197) that capillary action in a given soil is stronger when the soil contains a certain amount of moisture than it is when that amount is much reduced. When soils have their water content so much reduced that they begin to look dry, and especially after they become air-dry, they act as effective mulches and water will neither rise through them so rapidly nor so high the dryer they become, and if, under these conditions, a light shower should fall it might have the effect of leaving the surface soil with a greater increase of moisture than is represented by the rain which fell. 199. Kain May Cause a Capillary Kise of the Deeper Soil Moisture. It was observed in 1889, when determining the water content of soils at different, depths in the field, just before and immediately after rains, that frequently the lower soil showed a smaller amount of moisture than it had before the rain, while the surface layers had gained in water more than that represented by the rainfall. It was later shown that, by applying a known amount of water to a section of a field, the lower soil became dryer while the surface layers had gained more water than was added, as shown in the table. Capillary Movements of Soil Moisture. 171 Table showing the translocation of soil moisture due to welting the surface. DEPTH. PERCENT. OF WATER. DIFFERENCE. Befr.re wetting. After wetting. In per cent In pounds per cub. ft. 0-6 inches 14. 15 14 16.23 17.70 16.76 15.51 22.23 15 71 15.75 16 92 14 41 15.21 + 8.23 + .57 - .48 - .78 2.35 .30 +2.873 -f .199 - .213 .347 I.I '32 .132 6 inches to 12 inches 18 inches to 24 inches 30 inches to 36 inches The amount of water applied to the surface in this ex- periment was 2 Ibs. per sq. ft. but when samples of soil were taken 26 hours later there had been an increase of 3.072 Ibs. in the surface foot and a loss of 1.724- Ibs. from the second and third feet. Observation showed that a tray of soil, on a pair of scales at the place, lost, by evapora- tion during the same time, .428 Ibs. per sq. ft. ; and, as- 1 suming that the field soil lost water at the same rate, makes the water to be accounted for 3.072+ .428 = 3. 5 Ibs., while the total loss from the lower two feet plus the water added was .721 = 3.7241b3. an amount as nearly equal to the 3.5 Ibs. as could be ex- pected. In another trial, adding 1.33 Ibs. of water to the sur- face produced the gain, by translocation upward into the upper four feet, shown in the next table. 172 Physics of the Soil. DEPTH. WATEB CONTENT OF THE SOIL. Before wetting. After wettiug. Change. Pounds per cu. ft. 11.78 15 79 11 7:! 14.02 Pounds per cu. ft. 14 06 17 52 15.53 15.40 Pounds per cu. ft. 2.28 1.73 .85 1.37 Third foot Fourth foot 6.23 The interval during this experiment was one of very little evaporation and the adjacent untreated ground gained 1.21 Ibs. per sq. ft. in the same depth. This amount and the water added deducted from the gain in the treated area leaves the translocation 6.23 (1.21+ 1.33) = 3. 69 Ibs. per sq. ft. 200. Farmyard Manure May Strengthen Capillary Rise of Soil Moisture. When a soil is treated with farmyard ma- nure which has become well incorporated with it, it has the effect of causing a stronger rise of the deeper soil moisture into the surface three feet, where it is most needed in the production of crops. The table which fol- lows shows the mean results of experiments aiming to measure this effect during three years. Table showing effect of farmyard manure in strengthening the capillary rise of soil moisture. 1st foot. 2nd foot. 3rd foor. 4th foot. 5th foot. 6th foot. Manured Per cent, of watar. ly 88 18.79 Per cent, of water. 19.79 19.33 Per cent, of water. 18.88 18.60 Per cent, of water. 17.29 17 32 Per cent, of watpr. 14.35 14.63 Per cent, of water. 16. 9 17.13 Not manured Difference +1.09 + .46 + 28 .03 -.28 -.15 It is seen here that the surface three feet have in some way been maintained more moist, and apparently by the manure, at the expense of moisture from below. Capillary Movements of Soil Moisture. 201. Heavy Soil Mulches May Strengthen the Capillary Rise of Soil Moisture. Since capillary action is not as strong in a dry as in a well moistened soil it should be anticipated that any condition which would maintain a fair degree of saturation in the surface one to three feet of soil would permit it to bring up from below, for the use of crops, a larger supply of capillary water. On three different kinds of soil, where the ground had been cultivated during the season in alternate groups of four rows 3 inches deep and 1.5 inches deep, the distribu- tion of moisture, on July 16, was found to be as follows: Table showing the effect of mulches in strengthening the capil- lary rise of soil moisture. 1st foot. 2nd foot. 3rd foot. 4th foot. Field No. 1 cultivated 3 Field No. 1 cultivated 1 Difference inches deep 5 inches deep Perct. of water. 11.30 9.92 Per ct. of water. 15.57 15.43 Per ct. of watfr. 10 54 11.56 Per ct. of water. 11.37 13.99 1.88 .14 1.02 -1.62 Field No. 2 cultivated 3 Field No. 2 cultivated 1 Difference inches deep 5 inches deep 13 96 12.98 22.74 20.44 2339 24 02 19.47 21.31 .93 2.30 -.03 -1.87 Field No. 3 cultivated 3 Field No. 3 cultivated 1 Difference inches deep 5 inches deep 11.65 10.65 17.47 16.85 16.44 17.81 13.03 13.32 1.00 .62 -1.37 -.29 This table indicates that the 3-inch mulch, by main- taining the surface soil more moist, enabled capillarity to bring up from below a larger supply of water; that is, the maintaining of a relatively high per cent, of moisture in the upper two feet of soil makes it possible, through capillarity, for crops to utilize a larger amount of the soil moisture which is stored in the deeper layers. This view is confirmed by the fact that, in the fields of the ta- ble above, the largest yields of corn were in all cases taken from the ground cultivated 3 inches deep, where the up- m Pliysics of the Soil. per two feet of soil contained, in spite of the larger crop, much more moisture, but at the expense of that deeper in the ground, as shown by the fact that in every case these soils were dryest in the 3d and 4th feet 202. Firming the Soil May Strengthen the Capillary Rise of Soil Moisture. When soils have been rendered open and loose by plowing or other deep stirring the first effect is to permit the loose and open soil to become dry, because this soil is less perfectly in contact with that below. If, after such soil has become dry, it is firmed again the moist- ure films will then increase in thickness over the surface of the soil grains and, as a result of this, moisture will be raised from depths as great as four feet to saturate the firmed dryer soil. In the table below are shown tho changes which occurred in the deeper and superficial soil layers as the result of rolling. Table showing how rolling may strengthen the capillary rise of soil moisture. Depth of sample. No. of trials. Rolled ground. Unrolled ground. Change produced. Surface 2 to 18 inches 62 Per cent. of water. 15.85 Per cent, of water. 15 t>4 Per cent, of water. + .21 Surface 24 inches 61 19.49 19.85 .36 Surtace 36 to 54 inches .. - 24 18 72 19.43 .71 From this table it is seen that the first effect of rolling is to increase the amount of moisture in the upper 18 inches of soil, but that when samples are taken deeper than 18 inches the total amount in the soil is decreased. In other words, the first effect is to concentrate the deeper soil moisture toward the surface. If, however, the soil is left firmed very long then the whole column, to the surface, becomes dryer, until it has lost so much moisture that it beg-ins to act as a mulch. Thermal Movements of Soil Moisture. 175 THERMAL MOVEMENTS OF SOIL MOISTURE. Besides the gravitational and capillary movements of soil moisture there are others due to the molecular vibra- tions set up in the soil-air and water by the absorbed solar energy. 203. Hygroscopic Soil Moisture It is seldom if ever true that any solid surface, even when in the dryest air, can be found which is not invested with a film of moist uro of greater or less thickness. It is also true that even when all moisture has been driven from the surface of a solid by drying at the high heat of 200 C., the same body will again become coated with moisture when exposed to a moisture-bearing atmosphere. Water thus collected on the surface of solids is called hygroscopic moisture. 204. The Movements of Hygroscopic Moisture. It will be seen that the movements of hygroscopic moisture are the same as those of evaporation. The same molecular at- traction which causes the capillary rise of water in a glass tube tends to collect the water molecules, which may be moving about in the air, upon solid surfaces. So when a dry soil is exposed to a damp atmosphere some of the moving water molecules are brought in contact with, and retained by, the surfaces of the soil grains. The moisture will go on accumulating upon the soil grains until the rate of evaporation from them equals the rate of condensation. Since the water molecules are attracted to the soil grains more strongly than they are attracted to one another the water in immediate contact with the soil grains cannot evaporate as readily as that which is further removed when the water films are thick, as they are in a well saturated soil. Neither can the innermost layers of molecules adhering to the soil grains escape to enter the root hairs of plants by osmotic pressure as readily as those from the layers farther removed, and hence there must always be a certain quan- tity of water upon the surfaces of soil grains which neither 176 Physics of the Soil. evaporates readily nor becomes easily available to plants, and this may be regarded as the hygroscopic moisture. 205. Relation of the Diameter of Soil Grains to the Hygroscopic Moisture. It was shown in (163) that with the same thickness of water surrounding the soil grains the per cent, of water was necessarily much higher in the soils having the smallest soil grains. In (192) is given Quincke's observation of the distance across which the force of cohesion is sensible, or CT^OTT inch. Since this attraction of the soil for water is stronger than that of the water for the water it appears likely that a layer of water surrounding the soil grains, at least as thick as this, would not be as free to evaporate or to otherwise move about as that much farther removed from this cohesive attraction, and if so it is important to know what per cents of soil moisture a water-film of such a thickness would represent. This may be computed for spherical soil grains with the formula jf (d + 2t) 3 n d 8 Per cent, of water = , it d s sp. gr. 6 where d = diameter of soil grain in c. m. t = thickness of water film, sp. gr. the specific gravity of the soil. Taking a very fine soil having grains with a diameter of .00508 m. m. and a coarse one with a diameter of .1 m. m., a film of moisture on each, having the thickness of the range of sensible cohesive attraction, as given by Quincke, would make the per cent, for the finest soil 2.31 but for the coarse soil only .1153. No crop can survive in soils as dry as these; and air-dry soils whose grains range between those given will generally contain more than these amounts of moisture. It follows from these considera- tions, therefore, that what has been regarded as the hygro- scopic moisture is more than that held within the range Thermal Movements of Soil Moisture. 177 of sensible cohesive attraction. It appears clear also that no hard and fast line can be drawn between capillary and hygroscopic moisture, nor indeed between cither of these and the gravitational water; each must shade by insensi- ble decrees into the other. to' 206. The Amount of Moisture a Soil May Absorb from the Air. The amount of so-called hygroscopic moisture a given soil may absorb from the air depends primarily upon ihr relative temperature of the soil and of the air and its de j gree of saturation. If the temperature of a soil could be maintained continually below that of a saturated atmos- phere above, it would in time become so fully charged with water as to result not only in capillary saturation but in percolation as well ; and it frequently occurs on clear nights in summer, when dews are heavy, that a thick, loose, dry dust blanket will cool down so much that moisture condenses upon it in sufficient quantity to make it appear damp. Indeed dew, wherever it forms, is a demonstra- tion of the truth of the statement made; when it evapo- rates with the rising of the sun the loss of moisture from the blades of grass may carry the amount all the way from the drops, too heavy to be retained upon the blades, through the thick adhering films, to those which become invisible and are called hygroscopic. 207. Observed Absorption of Moisture from the Air. The rate and amount of moisture which may be absorbed from the air is influenced by many factors. Hilgard has studied the rate and amount of absorption of moisture by soils when spread out in layers* about 1 m. m. thick in a fully saturated and a half saturated atmosphere, maintained at a uniform temperature. He finds that fully 7 hours are required for an equilibrium to be reached in so thin a layer. In the table which follows are given some of his observations. 178 Physics of the Soil. Table showing the absorptive power of soils spread out in thin layers. SATURATED ATMOSPHERE HALF SATURATED ATMOSPHERE. KIND OF SOIL. Temp. Far." Time, hrs. Per cent, of water absorbed. Temp. Far." Time, hrs. Per cont. of water absorbed [ 58 19 11.745 57 43 6 547 59 19 11.8^6 Dark alluvial loam, Putah Valley, Solano county... 61 ! 72 77 18 7 7 11.40H 12. OH 12.2*J 70 77 7 7.5 6.424 6.305 88 7 13.141 88 7 6.H56 I 100 6 13.481 100 6 6.209 r 55 19 7.144 61 18 4.008 Black adobe soil, Univer- sity grounds, Alameda county 57 ! 70 | 80.5 82.5 19 7 17 7.5 7.880 7.696 8.681 8.948 61 80 83 89.5 7 5 6 7.5 7.5 4 122 4.024 3 92S 3.910 I 100 7 9.569 100 7 3. 885 r ei 18 2.133 59 18 987 Calcareous silt soil, Fresno J 79 6 2.983 79 6 O.i-59 county 84 7 3.396 84 7 818 I 95 6 4.211 95 6 0.821 It will be seen that in the saturated atmosphere the largest amount of moisture was absorbed at the highest temperature, while the reverse was true in the half sat- urated atmosphere. Under the high temperature the rate of molecular movement is so rapid that the rate at which the water from the air falls upon and enters the soil is so much increased that more water must have accumulated in the soil before the number of molecules which can leave its surface in a unit of time equals that which falls upon it. In the dryer atmosphere,- on the other hand, where there are less molecules to fall upon the soil and increase its amount, the higher temperature favors the rapid escape as much as when the saturation was high and, since less water is condensing, a lower per cent, is finally present when an equilibrium of interchange has been reached. Thermal Movements of Soil Moisture. 179 208. Internal Evaporation of Soil Moisture. It is likely that under certain conditions the thermal movements of soil moisture may be considerable and perhaps of sufficient importance to materially influence vegetation, directly or indirectly. When the per cent, of unoccupied pore space in a soil has been materially increased by the loss of wa- ter and when the moisture films have become so thin that capillarity is much enfeebled it is possible that internal evaporation of soil moisture may result in a considerable change of its position. If, for example, when the soil has become quite dry, to considerable depths, the surface six inches should become cooler than that below, the tendency to continual diffusion of water vapor under the impulse of heat would produce more internal evaporation of moist- ure where the soil is warmest and most moist, and a larger condensation of moisture where the soil is dryer and cool- er. Even where there is little difference in temperature be- tween adjacent layers of soil there must be, if they are not equally saturated, a tendency for diffusion to take place more rapidly from the wettest layer of soil toward that which is least moist. It is possible that during dry times and in dry climates during the dry season some moisture, too far below the root zone to be made available through capillarity, may be carried upward by these thermal or evaporation movements so as to become helpful to crops in a measure. We are yet lacking in experimental data to form any just conception as to the magnitude of such a movement. 209. Temperature Influence of Hygroscopic Moisture. It is Hilgard's view that, in dry climates and during droughty periods in humid climates, the moisture still retained by soils when capillarity has become very feeble may exert an important influence in preventing the soil from becom- ing overheated during dry soil conditions, by the cooling effect of internal evaporation. It must be observed, how- ever, that in order that this influence may become effective the moisture evaporated must have left the soil and not ISO Physics of the Soil have been replaced by an equal amount through, condensa- tion from some other place. It appears to the writer possible that the ability of such soils to withstand drought may perhaps be partly due to a more rapid evaporation from the soil grains and con- densation of moisture on the root hairs, the thermal move- ment, in this way, tending to supplement the enfeebled capillarity. CHAPTER VIII. CONSERVATION OF SOIL MOISTURE. There are very few fields upon which crops of any kind, in any climate, can be brought to maturity with the max- imum yields the soils are capable of producing without adopting means of saving the soil moisture. There are fields, it is true, where, at times, the moisture in the soil is too great, and drainage becomes necessary; but even un- der these conditions it will usually be found advisable to adopt measures for conserving the water not so removed. 210. Modes of Controlling Soil Moisture. In aiming to control soil moisture three distinct lines of operation are followed, based upon as many different aims. These are: (1) To conserve the moisture already in the soil (a) by different modes, times and frequencies of tillage, (b) by the application of mulches, and (c) by establishing wind breaks. (2) To reduce the quantity of water in a soil (a) by frequent stirring, (b) by ridging or firming the surface, (c) by decreasing the water capacity, and (d) by surface or under drainage. (3) To increase the amount of water in a soil (a) by increasing its water capacity, (b) by strengthening the capillary movement upward and (c) by irrigation. 211. Late Fall Plowing to Conserve Moisture There is no method of developing so effective a soil mulch as that furnished by a tool which, like the plow, completely cuts off a layer of surface soil and returns it loosely, bottom up, to place again. 182 Physics of the Soil. When ground is plowed late in the fall, just before freezing, it then acts during the winter and early spring as a mulch, diminishing the loss of water by surface evapo- ration, and at the same time the roughened surface tends to hold the snows and to permit winter and early spring rains to penetrate more deeply into the soil, leaving tho ground more moist at seeding time than would be the case if it were left unplowed. Determinations of the moisture in the spring, as late as May 14, have proved that late fall plowed ground may contain fully 6 pounds per square foot more water in the upper four feet than similar adja- cent ground not plowed. This difference represents a rainfall of 1.15 inches and is a very important saving in climates of deficient water supply for crops. 212. Late Tillage for Orchards and Small Fruits. Late fall plowing and deep cultivation in orchards of fruit trees and in vineyards of small fruits, after the wood is fully matured and growth arrested by the cold weather, will do very much toward giving the soil better moisture relations the next spring, tending to secure such results as are cited in (211). In cases where injury from deep freezing is liable to occur the late plowing will lessen this danger because the loose soil blanket will help to retain the heat in the ground as well as the soil moisture. In the late plowing and deep tillage, advised in this and the last section, there is little danger of increasing the loss of plant food by leaching because the season is too late and the temperature of the soil too low to stimulate the formation of nitrates. 213. Early Fall Plowing to Save Soil Moisture. In those cases where winter grain is to be sowed, the early plowing of the ground, or plowing as soon as the field has been freed from the preceding crop, is in the direction of econ- omy of soil moisture. So too in sub-humid climates, even where winter grain is not to be sowed, it will often be desirable to plow as early as possible in order to retain Conserving Soil Moisture. 183 soil moisture and to facilitate the entrance of the fall rains more deeply into the ground. The early plowing or disk- ing in these cases may also be helpful in hastening nitrifi- cation in the soil. It is the strong tendency of early fall plowing, in cli- mates where there is plenty of soil moisture to develop nitrates and where there is much rain in the late fall and early spring, Which has led to the sowing of "cover crops" having for their primary object the locking up of the solu- ble plant foods to prevent them from being lost by soil leaching ; and the tendency of early fall plowing to dimin- ish surface evaporation and thus, in wet climates, to in- crease percolation and the loss of plant food may some- times make this practice undesirable in such cases. 214. Early Spring Plowing to Save Soil Moisture In all climates where there is a tendency of the soil to become too dry the earliest stirring in the spring, which is prac- ticable without injuring the soil texture, is in the direc- tion of economy in most cases because, at this season of the year, the effectiveness of tillage in conserving soil moisture is greater than at almost any other time. This statement follows from (198), where it is shown that a wet soil car- ries water to the surface much more rapidly and from a greater depth than a dry soil can. In the spring the soil at the surface is usually not only wet but also well com- pacted, two of the most important conditions for the rapid movement of water to the surface, and it is because of these that early and deep spring tillage is so important as a means of saving soil moisture. In one instance, where two immediately adjacent pieces of ground, in every way alike, were plowed in the spring, 7 days apart, it was found that the earliest plowed ground contained, at the time the second piece was plowed, a lit- tle more moisture in the upper four feet than it had 7 days before, while the ground which had not been plowed had lost, in the same interval of time, an amount of moisture from the surface four feet equal to 1.75 inches, a full 184 Physics of the Soil. Conserving Soil Moisture. 185 eighth of the rainfall of the growing season of that lo- cality. Norwasthe saving of moisture the only advantage gained by the early plowing, for the soil plowed last had dried so extensively as to become very hard and lumpy, thus great- ly increasing the labor necessary to fit it for planting. In another experiment to study the effectiveness of early as compared with late spring plowing in conserving soil moisture Fig. 57 shows how evident the effects were to the eye. 215. Disking or Harrowing Where There is Not Time to Plow. It often happens in the spring that hot dry winds come on when there is not opportunity to get the ground plowed in time to save the needed moisture and prevent the development of clods. In such cases the use of tho disk harrow, or even 'the ordinary spike tooth harrow, will do very much to save the moisture and preserve the tiltli of the soil, if only the fields are gone over with these. The disk harrow is one of the best of tools for early use in the spring to work the soil and develop mulches. 216. Corn and Potato Ground, Orchards and Gardens Plowed Early in the Spring. Ground to be planted to corn or potatoes, as well as the orchard and garden, should gen- erally be plowed quite early in the spring and a consid- erable time before it is intended to plant them. By doing this, not only will moisture be saved but the development of nitrates in the soil will be hastened and thus larger crops secured on this account. It is only in the event of long, frequent and heavy rains, following such early tillage, that loss can result from such a practice. 217. Effectiveness of Soil Mulches. The effectiveness of soil mulches as means for diminishing evaporation varies (1) with the size of the soil grains, (2) with the coarse- ness of the crumb structure, (3) with the thickness of the mulch and (4) with the frequency with which the soil is 186 Physics of the Soil. stirred. Soils which maintain a strong capillary rise of water through them will, when converted into mulches, still permit the water to waste through their mulches faster than it will be lost through the mulches of soils which permit only slow capillary movements. That is, the sandy soils form more effective mulches than do the clayey ones and this greater effectiveness of the sandy soils, as mulches, goes a long way toward making the smaller amount of water they are able to retain effective in crop production. In Fig. 58 is shown an apparatus for measuring the relative effectiveness of mulches and in the table which follows are given ths results of a series of trials with three types of soil. The cylinders in this series, however, stood out in the open air of the field rather than in the case shown in the cut. Table showing the effectiveness of soil mulches of different kinds and different thicknesses. No mulch, water lost per 1UO days. Mulch 1 in. deep, water lost per 100 days. Mulch 2 in. deep, water lost per 100 days. Mulch 3 in. deep, water lost per 100 days. Mulch 4 in. deep, water lost por 100 days. Black marsh soil: Tons per acre 588.0 355.0 270.0 256.4 252 5 Inches of water Per cent, saved by 5.193 3.12 39.54 2.381 51.08 2.265 56 39 2.230 57 06 Sandy loam : Tons pur acre 741.5 373.7 339.3 287.5 315 4 Inches of water Per cent, saved by mulches 6.548 3.300 49.69 2.996 54 24 2.539 61.22 2.785 57.47 Virgin clay loam : Tons per acre 2,414. 1.260. 979.7 889.2 883 9 Inches of water Per cent, saved by mulches 21.31 11.13 47.76 8.652 59.38 7.852 63.13 7. SOS 63.34 From this table it will be seen that the soil mulches have exerted a*very great influence in saving soil moisture. Conserving Soil Moisture. 187 It should be understood, however, that if the water reservoirs had been much farther below the surface of the soil, and below the mulch, the mulches would have been more effective as well as less water would have been lost from the unmulched cylinders. 218. Frequency of Cultivation May Make Mulches More Effective. When a fresh mulch is formed upon the surface of a well moistened soil the first effect of the stirring is k ':- ] 1 [ :;:v | a FIG. 58. Apparatus for measuring the relative effectiveness of mulches. to increase the rate of evaporation from the field, on ac- count of the much larger surface of wet soil which is ex- posed to the air. This greater loss of water, however, is largely from the stirred soil. If dry winds and sunny weather follow the formation of the soil mulch it soon becomes so dry that but a relatively small amount of wa- ter can pass up through it On the other hand if a series of cloudy days follow, when the rate of evaporation must be small even from firm wet soil, and if at the same time the soil below the mulch is quite moist, so much water may pass up into the mulch as to nearly saturate the lower portion of it and to cause the kernels to be drawn 188 Physics of the Soil. together and again compacted and reunited with the un- stirred soil below. If this change does take place the mulch is rendered less effective and a second stirring is needed. FIG. 59. Showing large cylinders for studying soil problems. The relative effectiveness of mulches stirred twice per week, once per week, and once in two weeks, for a virgin clay loam, in cylinders 52 inches deep and 18 inches in diameter, standing in our plant house, as shown in Fig. 59, is given in the table which follows. Conserving Soil Moisture. 189 Table showing the relative effectiveness of soil mulches of dif- ferent depths and different frequencies of cultivation. Not culti- vated. Per acre. Once in 2 woi'ks. Per acre. Oncrc per week Per acre. Twice per week. Per aero. Cultivated one inch deep: The loss in tons per 100 days was The loss in inches per 100 days was 724.1 6 304 551.2 4 867 545.0 4 812 527.8 4 662 The percentage of water saved was 23 88 24 73 27 10 Cultivated two inches deep : The loss in tons per 10U days was The loss in inches per 10U days was 724.1 6.394 609.2 5.380 552.1 4 875 515.4 4.552 The percentage of water saved was 15.88 23.76 28.81 Cultivated three inches deep: The loss in tons per 100 days was The loss in inches per 100 days was 724.1 6.394 612.0 5.402 531 5 4.B94 495.0 4.371 The percentage of water saved was 15.49 26 60 31.64 It will be seen that with each of the three depths of cul- tivation the percentage of moisture saved, over that which was lost from the ground not cultivated, increased with the frequency of cultivation. 219. Too Frequent Cultivation "Undesirable. When a soil mulch is well loosened and thoroughly separated from the firm ground beneath, and especially after the mulch has become quite dry, little can be gained by stirring the soil. Indeed it must ever be kept in mind that it costs to cul- tivate a field and when this is done without need the work is a dead loss. Further than this, late in the season, when the surface of the ground has become relatively dry, posi- tive harm may bo done by unnecessary cultivation because at this season many plants have put up, very close to the surface, great numbers of fine roots in order to avail themselves of the moisture from light showers and from the dew which may be condensed in the surface layer 190 Physics of the Soil. of soil on the coolest nights. To destroy these roots will, in most cases, cause a greater loss by root pruning than can be gained by saving moisture. It is possible also, by too frequent tillage, to make the texture of the mulch so fine that its effectiveness is decreased. 220. Cultivations Should Be Most Frequent in the Spring. In the early part of the season when the aeration of the soil, the warming of it and the killing of weeds are other important objects to be attained it is more important to cultivate frequently. This is the season of the year when the effectiveness of mulches decreases most rapidly, it is the season when there is least danger of destroying the roots of the crop, and it is the time when cultivation is needed to help develop plant food. 221. Cultivation After Heavy Rains Whenever a rain has occurred which has thoroughly united the soil crumbs to one another, and with the soil below, it is time to cul- tivate again if this can possibly be done without too heavy root pruning, and the cultivation should be done just a3 quickly as the soil will permit. In the early part of the season there is little danger of root pruning if the culti- vator teeth do not go too close to the plants and not more than 3 inches deep. A rain which does not wet down more than 3 inches cannot be saved by cultivation; all that can be done in this case is to permit the surface roots to get as much of it as possible and to stir, if it appears expedient, when the wetting is likely to strengthen the upward movement too much. It must be remembered in this connection, however, that if, late in the season, the roots of the crop have spread horizontally through the whole soil, anything which strengthens the rise of the deeper water, causing it to come nearer the surface, at the same time brings it to the roots where it is needed, and hence it will seldom happen that a crop like corn or potatoes can be helped by Conserving Soil Moisture. 191 cultivation after the corn is in tassel or the vines begin to well cover the ground. 222. Depth of Cultivation to Save Moisture. In regard to this point it must be kept in mind that the soils out of which mulches are made are the richest on the farm and that when they are converted into perfect mulches they are prac- tically useless so far as direct pknt feeding is concerned. The general rule must then be to make the mulch just as thin as it can be and not permit too heavy a waste oi the deeper soil water. On the lighter and coarser grained soils the mulches may be shallower than on those of the clayey type. In Wisconsin we have found that with the ordinary narrow pointed tooth cultivators a depth of about three inches saves more moisture and permits larger yields of corn in about 15 cases out of 20 than less depth of culti- vation. Where the tool is of such a character that it shaves off the whole surface of the ground and leaves the stirred soil spread in a blanket of uniform thickness the stirring iriay be shallower than if the surface of the ground is left in either narrow or wide ridges. 223. Depth and Frequency of Cultivation Should Vary With the Season and Crop. From what has been said in the preceding paragraphs it follows that the soil may to ad- vantage be cultivated more deeply and more frequently during the early part of the season when the soil tem- peratures tend to be low, when the moisture may be over- abundant, and when weed seeds are germinating. Later in the season, however, when there is not as great need to encourage the development of nitrates by tillage, when the roots have come closer to the surface, and the main- tenance of a soil mulch is the chief or only object, the cultivation may evidently be less deep and not so fre- quent. The general practice then should be to gradually make the cultivation both less deep and less frequent. It should also be kept in mind that cultivation may gener- 192 Physics of the SoiL. ally be a little deeper in the middle of the space between rows, than close to the hills, because of less danger of root pruning. 224. Best Time to Cultivate Corn and Potatoes The best time to till land for corn, potatoes and similar crops, where intertillage is practiced, is before the ground is planted and just as the crop is coming up. When the ground is plowed two or three weeks before the crop is to be planted there is opportunity to develop the nitrates, to kill one or two crops of weeds, and to store in the upper five feet of soil the largest reserve of soil moisture from the spring rains. Besides these advantages there is no period in the growth of the crop when the ground can be stirred so rapidly and so cheaply. Before planting the disk or spring-tooth harrow may be used and afterward the dif- ferent weights of spike-tooth harrows, which enable a larger area of ground to be covered in a day by a man and team. The harrowing of corn and potatoes should be continued until the plants are well out of the ground and if care is taken to do the work during the hot por- tion of the day, when from slight wilting the plants do not break off readily, there need be but little serious in- jury to them. The different types of mulch producing tools are dis- cussed in Chapter XL 225. Harrowing and Rolling Small Grain After It Is Up. It sometimes happens in humid climates, when drying weather follows a wet period, that a crust forms on the surface of fields sowed to the small grains, which may be injurious to the plants by preventing sufficient aera- tion and increasing the loss of moisture. In such cases the difficulties may be partly corrected by using either the roller or the light harrow with teeth sloping backward. If the grain is large, and especially if the surface of the field has been left narrowly ridged and somewhat lumpy, the use of the roller when the surface soil is dry Conserving Soil Moisture. 193 will break up the crust by crumbling down the ridges and lumps and at the same time develop a true and effective mulch. The light harrow, when driven across the ridges, may be effective in breaking up the crust and in develop- ing a mulch. In sub-humid climates, such as that of western Kansas, fields seeded permanently to alfalfa have been, in the very early spring, gone over with the disk harrow and then crossed with the spike-tooth harrow, thus developing a very effective mulch which materially increases the yield. 226. Mulches Not Made From Soil While it is true that most conservation of moisture must be through earth mulches it should be understood that all vegetation growing upon the ground, whether it completely covers the surface or not, exerts a protective influence and diminishes the loss of moisture directly from the soil itself. This pro- tection comes partly from shading, partly from diminish- ing the wind velocity and partly from the saturation of the air with moisture by the transpiration from the grow- ing plants. Even in pastures where the grass is short, but close, the mulching effect is strong and hence it is not in the direc- tion of economy to allow the feeding to be too close, not only because the growth of the grass is slower from too severe destruction of the foliage, but because there is a greater loss of soil moisture besides that passing through the grass. The surface dressing of meadows with farmyard manure, thoroughly harrowed to spread it evenly over the ground, is extremely beneficial through its mulching effect as well as in the plant food it brings to the soil. When such dressings are applied in the winter and early spring and spread over the surface while the soil is yet wet beneath, the saving in soil moisture is greatest and in the case of meadows where the clover has disappeared, for any rea- son, such a dressing may make it possible to get a new seeding, by sowing the clover broadcast before the frost 194 Physics of the Soil. is out in the spring, so that the thawing and freezing will tend to cover the seed and the thin mulch protect the ground from too rapid drying until the young plants are well rooted. The use of straw and other coarse litter and coarse sand for mulching will generally only be practicable in gardens and orchards and for the protection of shade trees and the like. 227. Ridged and Flat Cultivation. It used to be a com- mon practice to "lay by" the corn and potato crop with a strong hilling of the rows. This practice, however, ex- cept for potatoes, is now generally abandoned unless in localities where surface drainage is needed. The general abandonment of the practice rests in part upon the be- lief that the evaporation from the soil is appreciably in- creased by this process on account of the greater amount of surface exposed to the air. In making a practical test during the season of 1899 the results recorded in the following table were secured. These plots, each seven rows wide, alternated across a field of nearly uniform soil and samples were taken under and between every row. It will be seen that the soil re- ceiving the flat cultivation contained at the end of the growing season a little less water than the ridged plots, which is contrary to the accepted belief. Since the ridges are all shaded by the potato vines and since the wind cur- rents may be supposed, to be less strong between the fur- rows, perhaps this is as should be expected. It is true, however, that the plots cultivated flat produced a little larger yield per acre and on this account the soil should have lost more moisture. It may be that the flat cul- tivation did really make a larger saving of water and that this saving was the cause of the larger yield. Conserving Soil Moisture. 195 Table showing the water content of soil, Sept. 19, under and between rows of potatoes hilled and left flat when laid by. DEPTH OF SAMPLE. Nos. of sub- plots. HILLED. FLAT. In row. Between row. In row. Between row. Firstfoot \ 1.. . Per cent. 12.83 12.01 Per cent. 14 11 13.61 Per cent. 11.85 12.18 Per cent. 14.23 13.54 2 3 ... Mean 1 .. 12.42 13.86 12.02 13.89 16.71 15.84 IN. 56 17.85 15. H8 16.03 17.69 17.84 2 Third foot j 3 Mean 1... 16.28 18.21 15.71 17.77 18.00 17.09 18.61 17.55 16.41 16.13 18.03 17.97 2 Fourth foot ] Mean of four feet 3 Mean 1 .. 17.55 18.03 16.27 18 00 15.78 14.41 16.95 13.98 9.79 13.08 11.75 14.01 2 3 Mean 15.06 15.33 15.46 16.40 11.44 13.86 12.88 15.64 228. Subsoiling to Save Soil Moisture. The deep -plowing or stirring of the soil, to which this name has been applied, lias the effect of making a larger per cent, of the rainfall available in producing crops, but it will never have the wide applicability that is possible for surface tillage. In sub-humid climates where the subsoils are less liable to be puddled and where there is the greatest need of economy this method of conserving soil moisture will find its widest usefulness. A piece of ground when subsoiled, as represented in Fig. 60 and given, with an adjacent area, a like amount of water, and protected from surface evaporation, was found to have retained not only the water given it but to have gained an additional supply through capillarity from below- while the ground not subsoiled lost a large per cent, of that given to it through percolation and capillary 190 Physics of the Soil. creeping. From the subsoiled area 8 inches of the surface were removed, the subsoil spaded to a depth of 13 inches more, and the soil returned to its place. After taking FIG. 60. Alethod of demonstrating the influence of subsoiling on soil moisture. samples from the five places indicated by the dots, 1.36 inches of water \vere gradually sprinkled over the two areas on June llth and they were allowed to remain cov- ered until the 15th, when samples were again taken. The changes in the water content of the soil in the two areas are shown in the table which follows: Table showing the ability of subsoiled ground to hold water against gravity. Subsoiled. Not subsoiled. Difference. The first foot gained Lbs. 124.6 Lbs. 102.1 Lbs. + 9 2 5 12 57 10 34 +62 23 The third foot sained 38.22 12.05 +26 17 33 26 3 82 +29 43 The fifth foot lost 2.29 19.5 17 21 26S 65 128 31 254.41 251 41 Difference +14.24 126 1 Conserving Soil Moisture. 197 The subsoiled ground had therefore not only retained all the water added but it had gained by capillarity 14.24 Ibs. more. It is noteworthy too that the fifth foot in both places had lost water upward by capillarity, 2.29 Ibs. in the former and 19.5 Ibs. in the latter case. The effect of subsoiling on the capillary rise of water from below was demonstrated by using the same piece of apparatus in the same way except that the two areas were covered to prevent evaporation, without adding any water, the experiment extending from June 26 until July 2, giv- ing the results shown in the next table. Table showing the effect of subsoiling on the capillary rise of water from the deeper soil when no evaporation can take place from the surface. ON SUBSOILED GROUND. 1st foot. 2nd foot. 3rd foot. 4th foot. 5th foot. June 26 (Moisture ( Per ct. 23.29 22.66 Per ct. 21.89 22.50 Per ct. 17.85 17.49 Per ct. 14.14 14.45 Per ct. 19.55 20.27 ? at start ( July 2 I Moisture ( ( at close. < Change .63 + .61 .36 + .31 + .72 June 26 start ON GEOUND NOT SUBSOILED . 22.52 ^3 97 2C.67 22.09 17.74 18.92 15.06 14 62 19.34 18.33 July 2 close +1.45 +1.32 +1.18 - .44 It will be seen that in the subsoiled area there had been but little change in the water condition while the ground not subsoiled had gained a very material amount of water in the surface three feet at the expense of that deeper in the ground, the gain in the upper three feet amounting, on the 36 square feet, to 129.69 Ibs., 53.52 Ibs. having come from the fourth and fifth feet and the balance prob- ably partly from the sides and partly from the sixth foot. When the ground was subsoiled in the same manner as 13 198 'Physics of the Soil. before and allowed to stand exposed under natural condi- tions, and the surface kept free from weeds by shaving them off close to the surface with a sharp hoe, it was found, after an interval of 75 days from June until September, that the water content of the soil stood as in the next table. In this case the surface foot of subsoiled ground is dryer than that not so treated, but the second, third and fourth have gained in moisture, over and above that lost from the other two feet, enough to represent a rainfall of 1.G4 inches. Subsoiled ground Not subsoiled ground. Difference. Firstfoot Per cent. 17.07 Per cent. 18 91 Per cent. 1.84 S -cond foot 23.29 19.42 +3.87 Third foot 22.76 17.78 +4.98 Fourth foot 16 35 14.19 +2.16 Fifth foot 18.14 19.20 1.06 229. Moisture Effects of Subsoiling. The results which have been given in the last section illustrate several verj distinct effects produced by subsoiling: (1) Subsoiling increases the percentage capacity of the soils stirred for moisture. ("2) Subsoiling decreases the capillary conducting power of the soil stirred. (3) Subsoiling increases percolation through the soil stirred or its gravitational conducting capacity. 230. How Subsoiling Increases the Water Capacity of the Soil Stirred. When a soil is broken into lumps lying loosely together, and these become filled with water, each one behaves in a measure much as if it were standing by it- self and much as a lump of sugar would, plunged into water and then withdrawn, coming forth with its pores practically filled with water. In short columns of soil, like the lumps, the surface films of water which span their capillary pores are strong enough to maintain their whole Conserving Soil Moisture. 199 interior nearly full of water, drainage being largely con- fined to those passageways a"nd cavities which have largei than capillary dimensions. If a dozen strands of candle-wicking, two feet long, are twisted loosely together, saturated in a basin of water, and then held horizontally from the two ends to drain, more water will be retained than if it is allowed to sag into a loop and drainage from it will be still more complete when hanging from one end. So it is with long continuous col- umns of soil; from them the drainage is more complete than from shorter ones. 231. How Subsoiling Decreases the Capillary Conducting Power. When large open spaces have been formed in a soil, by any means, as is the case in subsoiling, every such cavity cuts off the capillary connection with the unstirred soil below and above and in this way reduces the number of capillary passageways by which water may rise to the surface. This being true, when rains fall upon subsoiled ground, water travels downward quite slowly until after it has become capillarily saturated and, if the rain is not enough to over-saturate the layer, the whole will be retained. On the other hand, when the subsoiled layer has once become dry, the poor connection with the firmer ground below and its open texture makes it impossible for the moisture to rise through it to the surface as rapidly as it could through a more compact layer. It is clear, from these relations, that when the root system of a crop once develops through the subsoiled layer it may then act as a mulch of great thickness and increase the yield ; but should a crop fail to get its roots below the subsoiled layer before the moisture becomes too scanty then a diminished yield might be the result even with an abundance of water below. 232. How Subsoiling Favors Percolation When rain enough has fallen upon an earth mulch or upon subsoiled ground to completely saturate the soil the balance of the 200 Physics of the Soil. water is then free to move rapidly downward through the large non-capillary pores, urged by the strong force of gravity. Not only this, but, since the pores are many of them too large to be filled by the percolating streams, there is left an easy egress for the soil-air, which must escape upward before the water can enter, and this does not re- tard percolation as it does in a compact soil. 233. A larger Percentage of the Moisture of Subsoiled Ground Available to Crops. When a soil has been made more open by subsoiling, and its capacity for holding water thereby increased, this extra amount of water retained be- comes wholly available to crops. It was shown in (161) and (162) that there is a certain per cent, of water in a soil which the roots of plants are unable to remove with sufficient rapidity to meet their needs and as this amount depends upon the size of the soil grains, which subsoiling does not alter, the increased percentage held becomes a clear gain to the crop. 234. Dangers From Subsoiling One of the most serious difficulties associated with subsoiling, aside from the ex- pense, is the danger of puddling, and this is particularly great in humid climates where the subsoil, especially in the spring, is liable to be too wet. The danger is intensi- fied on account of the fact that the surface soil may be in good condition for plowing when that below is much too wet. If this work is attempted when the ground is not in condition very great harm may be done and so it is gen- erally much safer to subsoil late in the fall in humid cli- mates, when the deeper ground is generally dryest. 235. Early Seeding When the crop is started to grow- ing upon the ground as early as the temperature of the soil and of the air will permit the farmer is conserving soil moisture, by taking advantage of that which otherwise would be lost by surface evaporation, and enabling his crop to use this in growth. Such timely planting may not only Conserving Soil Moisture. 201 save moisture from going to waste, both by evaporation and by percolation, but it may save plant food from loss in the drainage waters. Yet, while due diligence should be exercised in timely planting and sowing, there is danger of too great haste and it will generally be better to make the mistake of getting the crop in a little late rather than too early. The soil should by all means be warm enough and dry enough to make germination prompt and vigorous, for otherwise weak and sickly plants will result, if the seed does not rot in the ground. 236. Danger From Green Manuring. In the practice of growing cover-crops, and in green manuring, attention must always be given to the effect these have upon the soil moisture, as related to the crop which is to follow. When either rye or clover is used in green manuring, and the plants are allowed to make a heavy growth before plowing under, the soil will be found very much dryer than if the field had been plowed and tilled early but left naked, or even if not plowed at all. The next table demonstrates the truth of this statement, showing, as it does, the strong drying effect of clover as early as May 13. Table showing the drying effect upon the soil of a green ma- nure crop. 1 to 6 inches. n to 18 inches. 18 to 21 inches. Per cent. 23 33 Per cent. 19 13 Per cent. 16 85 Ground in clover. .................. 9 59 14.75 13 75 13 74 4.38 3 10 In such a case as this, with the soil as dry when plowed as that under the clover, not only would there be danger of the seed not germinating properly but the large growtli of herbage, when plowed under, would so much cut off the capillary connection with the deeper soil moisture that 202 Physics of the Soil. it could not readily become available until after the roots had penetrated below this level. Nor is this all ; any such crop would have locked up in insoluble form, for the time being, a large portion of the soluble plant food, and unless abundant and timely rains were to follow the plowing speedily to develop a new sup- ply, the next crop would suffer for lack of nitrates and other plant foods. On soils naturally too wet and in wet seasons the dan- gers referred to will of course not be so great and the green manure crop might even be an advantage from the soil moisture side by making the over-wet soil more open, thus favoring stronger root action and more rapid nitri- fication. 237. Wind-breaks and Hedges. "In* sub-humid climates, especially like those of our western prairies, where there is a high mean wind velocity, and in the level districts of humid climates, where the soils are light and sandy, with a small water capacity, and which are lacking in adhesive quality, the fields may suffer greatly at times, not only from excessive less of moisture, but the soil itself may be greatly damaged by drifting caused by the winds. Under such conditions, it is a matter of great importance that the wind velocities close to the surface should be reduced as much as possible." On the lighter sandy lands, wherever broad fields lie unsheltered by any wind-break, strong dry winds frequent- ly sweep entirely away crops of grain after they are four inches high, and at the same time drift away even as much as three or four inches of the surface soil, the best in the field. In such cases wind-breaks and hedge-rows exert a very strong protective influence and greatly lessen such dis- astrous results. Not only do trees along line fences and roadsides, un- der these conditions, prevent such direct injuries to soil and Irrigation and Drainage, p. 163. Conserving Soil Moisture. 203 crops but they materially lessen the evaporation of moisture from the soil and thus help to secure a higher yield of crops. *"The writer has observed that, when the rate of evaporation at 20, 40, and 60 feet to the leeward of a grove of black oak 15 to 20 feet high was 11.5 c. c., 11.6 c. c., and 11.9 c. c., respectively, from a wet surface of 27 square inches, it was 14.5, 14.2 and 14.7 c. c., at 280, 300 and 320 feet distant, or 24 per cent, greater at the three outer stations than at the nearer ones. So, too, a scanty hedge-row produced observed differences in the rate of evaporation as follows, during an interval of one hour ; At 20 feet from the hedge-row the evaporation was 10.3 c. c. At 350 feet from the hedge-row the evaporation was 12.5 c. c. At 300 feet from the hedge-row the evaporation was 13.4 c. c. Here the drying effect of the wind at 300 feet was 30 per cent, greater than at 20 feet, and 7 per cent, greater than at 150 feet from the hedge. Then, too, when the air came across a clover field 780 feet wide the observed rates of evaporation were : At 20 feet from clover 9.3 c. c. At 150 feet from clover 12.1 c. c. At 300 feet from clover 18 c. c. Or 40 per cent greater at 300 feet away than at 20 feet, and 7.4 per cent, greater than at 150 feet" * Irrigation and Drainage, p- 109. CHAPTER BELATION OF AIR TO SOIL. NEEDS OF SOIL VENTILATION. . Air in the soil in which crops are to be grown is as es- sential to the life of the plants as the air in a stable is to the life of the animals housed. Careful observations and lines of experimentation have proved, in many ways, that when oxygen is completely ex- cluded from seeds that are otherwise under good conditions for germination they fail to start. It has been found, too, that even after a seed has begun to grow, if the oxygen supply is cut off, it makes no farther progress. Growth does take place in seeds in a very dilute atmosphere of oxy- gen, but after the amount has been reduced below L 2 of the average in the air the plants advance very slowly and are sickly. A soil in the best condition for crops must permit of ready entrance of fresh air and an abundant escape of the air once used; in other words, like the stable, it must be well ventilated. This ventilation is needed : (1) To supply free oxygen to be consumed in the soil. (2) To supply free nitrogen for the use of the free- nitrogen-fixing germs. (3) To remove the excess of carbon-dioxide which is set free in the soil. 238. Needs For Free Oxygen in the Soil. Free oxygen in the soil is required not only by the seeds, when they are germinating, but throughout the active life of the plant in order to permit the roots to live, for they, too, must breathe. Then in the conversion of the nitrogen of humus, manure, Needs of Soil Ventilation. 205 and decaying organic matter in the soil into nitric acid, large amounts of oxygen are needed, for each of the three known forms of microscopic life which do this work are unable to live in its absence. 239. A Water-logged Sott One of the chief reasons for the unproductiveness of a water-logged soil is the deficiency of free atmospheric oxygen in it. When the soil pores are filled with water and this water is stationary, that is, not changing, the free oxygen which it may contain in the air dissolved in it is soon used up and then the rate at which oxygen from the air above the soil is able to make its way downward through the soil-water and around and between the soil grains is much too slow to meet the ordinary needs of the roots of any crop. Not only this, but, as pointed out in (103), even the microscopic organisms in the soil find so scanty a supply that they are obliged to decompose the nitric acid for the oxygen it contains in order to supply their needs. The chief need of draining wet lands, then, is to secure to the soil a more rapid change of air. 240. Floating Gardens. The instances where the Chinese and Mexicans grow crops upon floating rafts of logs an- chored in a stream or lake and thinly covered with soil may seem to contradict the statements in the last paragraph regarding a water-logged soil because, in these cases, the soil is very wet in its lower portion and the roots of the plants are continually immersed in a saturated soil or in the water itself beneath. A little reflection, however, will make it clear that the two cases are very different. Both in the lake and in the running stream the water is chang- ing continually so that a new supply, charged with fresh \ oxygen, is being continually brought to the roots or very near them. It is the abundance of oxygen which rain water and that used for irrigation contains which prevents it from killing crops when the water entering the soil is excessive. As long as the water is moving through the soil, and a 206 Physics of the Soil. fresh supply from above entering, an abundance of air is carried with it for the needs of the roots. 241. Excessive Soil Ventilation. The higher temperature of a pile of open horse manure, as compared with that of the closer heap of cow-dung, illustrates how important the free and rapid access of air to the interior is to the forma- tion of the ammonia, for the difference in temperature in the two cases is largely due to a difference in the rate of fermentation, and this to the too rapid entrance of air. In these cases the air is entering too rapidly and a loss of nitrogen is the result. And the same thing may occur in a too open soil. Indeed, the small amount of humus in the sandy soils is in a large measure due to the freer ac- cess of air to the interior. It is for this reason that unusual care must be exercised to keep the supply of humus in these soils up, not only because of its need for plant food, but because it enables the sandy soils to hold more water, and this in turn makes them less readily penetrated by the air and the humus does not waste as rapidly. 242. Return of Carbon-Dioxide to the Air It is of course necessary to the continuance of plant life that the vast systems of roots which are developed in the soil should be broken down, first into humus and then into carbon-dioxide, water and free nitrogen, and all of the processes concerned in these changes demand free oxygen taken from the air and the escape of the carbon-dioxide and nitrogen gas set free, and here again is ample soil ventilation necessary. 243. The Fixing of Free Nitrogen In the processes of symbiosis discussed in (101), which lead to the removal of the free nitrogen of the air in the soil and soil moisture, and the conversion of it into organic compounds suitable for the food of higher plants, soil ventilation is necessary in order to supply both the oxygen and nitrogen of the air which the micro-organisms are obliged to use in carrying on their life processes. Processes of Soil Ventilation,. 207 PROCESSES OF SOIL VENTILATION. The interchange of gases between the soil and atmos- phere is brought about in several ways and by different agencies. Among these are (1) the slow process of diffu- sion described in (5) and (14). (2) The expansion and contraction of soil-air due to changes in temperature. (3) The expansion and compression of the air due to changes in barometric pressure. (4) The suctional effect of the wind, especially when it is gusty. (5) The air absorbed by rainwater is carried into the soil when percolation takes place. (6) When water drains away from a soil or is carried upward and out by capillarity or root action it acts by suction to draw into the soil a volume of air equal to that of the water which flows out. 244. Ventilation of Soil by Diffusion. The exchange of air between that in the soil and the atmosphere above by diffusion is a very slow process but, because it is all the time taking place, the total exchange during the growing season is considerable. The more open the texture of the soil is and the higher the soil temperature the more rap- idly will the interchange by this process take place. 245. Soil Ventilation Due to Changes in Soil Tempera- ture. When the temperature of air is changed its volume is also altered and in the ratio of rer for each degree F. or -STS for each degree C. ; so that if 491 cubic feet of soil-air were to have its temperature changed 1 F. this would result in one cubic foot of air being forced out of the soil, if the temperature was raised, and a like amount would enter if the temperature were to fall the same amount. The temperature of the surface three inches of soil often changes as much as 16 to 20 F. and that at 18 inches deep as much as 1.5 F. A soil like the surface foot in (133), containing 18 per cent, of water, would enclose 208 Physics of the Soil about 5.3 acre-inches of air in the surface 1.5 feet and, with a diurnal change of 16.4 F. in the upper '3 inches and 1.5 F. at a depth of 18 inches, the amount of soil-air which would be forced out and again taken in each 24 hours would be about 14 cubic inches for each square foot of surface. So that the soil ventilation due to diurnal changes in soil temperature will range from up to pos- sibly 20 cu. in. per square foot. 246. Influences of Changes in Barometric Pressure on Soil Ventilation. Any change which may occur in the pressure of the air above the soil is followed by a change in the volume of the soil-air, causing an escape from the soil, if the pressure above falls, and the entrance of an extra sup- ply whenever the pressure is increased. With soil like that in (133), having 18 per cent, of water in the first foot, 20 per cent, in the second and 15 per cent, in the third and fourth feet, there would be 7.88 inches in depth of soil-air contained in the four feet and every change in atmospheric pressure amounting to .1 incli would cause the escape or entrance of 3.78 cubic inches for each square foot of surface and 18.9 cubic inches for each change in pressure of .5 inches of barometer. It is common in the United States for waves of high and low pressure to pass a given locality about twice each week, and the differences in pressure between high and low barometer are generally not far from .5 inch, so that the results stated above give a fair measure of this influence in soil ventilation. 247. Wind Suction and Soil Ventilation. It is seldom true that the wind blowing across a field has a uniform velocity, the general tendency being for it to blow in gusts. This unsteady action tends at times to increase the pres- sure on the soil-air and at other times to decrease that pressure and, as a result, there is a nearly constant ten- dency for air to leave or enter the soil on this account, and it is possible that this factor in soil ventilation may Ways of Influencing Soil Ventilation. 209 be stronger than any other, on account of the great fre- quency with which the changes recur. 248. Movements of Water and Soil Ventilation. The water which enters the soil as rain must displace a volume of air equal to the rainfall which penetrates the soil and then, when this water is again lost by the soil, whether by percolation or by capillary or root action, the same vol- ume of air must again be returned. In a climate where the rainfall, which penetrates the soil, is 24 inches dur- ing the growing season, two cubic feet of air per square foot of surface enters the soil in consequence. WAYS OF INFLUENCING SOIL VENTILATION. There are important means and methods of controlling and modifying the rate and extent of soil ventilation, which are under the control of the farmer. 249. Soil Ventilation Modified by Tillage. Nearly all of the operations of surface tillage modify the rate of entrance or escape of air from the soil. Plowing effects a sudden and complete change of air in the soil to the depth stirred and in the spring, when nitrates are deficient, and the pores largely closed with water, this breaking up of the soil may be very beneficial. The thorough preparation of the seedbed before plant- ing, so strenuously insisted upon by the best practical men, has a portion of its rational basis in the need of soil ven- tilation ; and deep subsoiling, when done at such a time as not to puddle the soil, must always profoundly affect the relation of air to soil, as well as of moisture. Indeed, all of the operations of soil loosening serve, not only to admit air more freely to the soil stirred, but the undis- turbed portions beneath will also be better ventilated be- cause of the surface loosening. 210 Physics of the Soil. 250. Rolling and Harrowing For Soil Ventilation. It fre- quently happens, especially with small grains in the spring, when the season has been unusually wet and evaporation large, that a crust forms upon the surface, partly by shrink- age, partly by the crumb-structure breaking down and partly by the deposit of soluble salts between the soil grains, thus closing up the pores and greatly impeding the en- trance of air. Under such conditions the harrowing or rolling of small grains after they are up owes its advan- tages in part to the better soil breathing it secures, by breaking the crust. But it will sometimes happen, when small grains are rolled immediately after seeding, if the ground chances to be a little too moist, that soil ventilation will be so much hindered by the packing as to result in defective germina- tion and sickly plants. In one case a crop of barley was so much affected in this way that a serious reduction of yield was the result and the plants, even when mature, were so evidently influenced, that the rolled strip, between two adjacent areas not rolled, but in other respects the same, snowed in strong contrast on account of the smaller plants. 251. TJnderdraining For Soil Ventilation. When heavy soils are underdrained they are so much more deeply and better aerated that this is one of the chief advantages of that method of land improvement. In such cases the roots of plants penetrate the subsoil so much farther, and earth- worms and ants burrow so much deeper, that with the decay of the roots the more or less vertical galleries formed by these agencies permit much freer and deeper soil ven- tilation. Then when the under clays dry out, as they do after draining, great numbers of shrinkage checks form and in- to these both the roots of plants and the free soil-air pene- trate and are brought together. After this last stage of soil improvement has taken place the bringing in of carbonic acid with the air leads, through Ways of Influencing Soil Ventilation. 211 its action upon the lime, to the flocculation of the minuter soil particles and thus to a more extensive granulation of the whole subsoil, which in turn extends the soil ventilation still more widely. But all of these effects upon the soil are only the means \vbich permit the underdrains to render their greatest serv- ice in permitting a strong and extensive movement of air into and from the soil ; for once the soil is opened up in this way, the air, through the action of the wind, changes in barometric pressure and changes in soil temperature, read- ily enters the soil, not only through the surface above but throughout the whole length of the underdrains. When it is seen that changes in soil temperature and in atmospheric pressure make such marked changes in the flow of water from springs and from tile drains as are shown in (337) and (338) it becomes clear that the move- ments of soil-air into and out of tile drains must be even more marked than the movements of ground water. 252. Influence of Vegetation on Soil Ventilation. In the case of such crops as clover, which send long and somewhat fleshy roots down deeply into the subsoil, there are very many and important passageways opened up after the roots decay, which greatly facilitate the deeper and more rapid change of soil-air, and, as has been pointed out, the re- moval of water by the- living roots must also draw into the soil a volume of air equal to the amount of water used, except in so far as this is made good by the rise of capil- lary water from below. CHAPTER X. SOIL TEMPERATUEE. 253. Importance of Soil Temperature. None of the chem- ical, physical or biological changes essential to the devel- opment of plant food in the soil and to the action of roots, can. take place in the absence of the energy stored up in the soil and indicated by its temperature. When the tem- perature of the soil falls to 32 F. nearly all the life processes become dormant and for most of the cultivated crops and higher plants these cannot begin until a tem- perature above 40 F. has been reached. All living bodies must have their temperature maintained between certain limits in order to have growth take place. 254. Soil Temperature at Which Growth Begins. Accord- ing to the observations of Ebermayor growth will not be- gin, with most cultivated cropsTtmtil the soil has attained a temperature of 45 to 48 F. and it does not take place most vigorously until after it has reached 68 to 70 F. Neither do the niter germs begin the formation of nitric acid from humus until a temperature above 41 F has been reached and its greatest activity is not attained until the soil temperature has risen to 98 F. 255. Best Soil Temperature for Germination There is, for most seeds, a certain range of soil temperature under which germination is most rapid, under which the plants become most vigorous, and which ensures the highest per- centage of plants from the seed. This general truth should never be overlooked in the spring when it is possible to plant in a too cold soil. In the table which follows are Soil Temperatures. 213 given the best soil temperatures and the lowest and high- est temperatures at which certain seeds have been observed to germinate. NAME OF PLANT. BEST SOIL TEMP. LOWEST SOIL TEMP. HIGHEST SOIL. TEMP. Sachs. Van Tiegham. Sachs. Van Tiegham. Sachs. Van Tiegham. Wheat 84 F. 84 84 93 79 93 81 F. 83 80 93 41F. 41 44.5 48 49 54 41" F. 41 44 49 104 F. 104 102 115 111 115 99 F. 100 Barley 115 70 89 81 99 42 82 108 99 32 The two important facts fixed by these data are: (1) The soil temperatures at which the seeds of most cultivated crops germinate best, lie between 70 and 100 F., with an average of about 85 F. (2) The soil temperatures below which germination does not take place are between 41 and 54 F. From these it is clear that seeding should not begin until the thermometer will show the temperature of the soil at the depth of planting, well up toward 70 F. during the warmest portion of the day. These state- ments should not be understood as advising against the sowing of clover seed early in the spring, while the frost is yet on the ground, under conditions where it might not be possible to get a stand otherwise. 256. Observed Soil Temperatures The temperatures which the soil does attain at different depths during the different months of the growing season will be of inter- est in connection with the statements made in the last two sections. In the two tables which follow are given the mean seasonal variations of soil temperature at two sta- tions, one in this country and the other in Europe. 14 214 Physics of the Soil. Table showing the mean monthly soil temperatures, at State College, Pa., by Dr. Frear, and at Munich, Germany, by Ebermayer. AT STATE COLLEGE, PENNSYLVANIA. Depth. April. May. June July. Aug. Sept. 3 inches F. 43.74 F. 55 13 F. 67 29 "F. 70 16 "F. 68 70 op 01 32 6 laches 43 08 5t 72 63 34 69.75 68 49 61 70 12 inches 42.69 53 83 65 03 68 89 68 66 62.73 24 inches 41 43 51 45 61 90 66 42 67 41 63 5'J AT MUNICH, GERMANY. 44 65 56 79 61 11 67 2ti 61 09 5S.21 11.8 inches 23 7 inches 44.31 44 40 57.51 53 58 60.06 59 11 66.16 63 12 6.5 61 63 55 57. S8 58 82 35.4 inches 43.56 51.24 57.33 62.92 62.26 ftfc.ol It may appear that the temperatures recorded in these tables are too low to be in harmony with the comparatively high temperatures given as the best for germination. It must be understood, however, that the average must bo lower than would be found in the soil during the warmest portion of the day. In regard to the minimum tempera- ture at which germination takes place it will be clear enough that the April records for soil temperature are quite in harmony with those given for germination. 257. Influence of Soil Temperature on the Rate of Germi- nation. The more quickly seeds are permitted to germi- nate after they are placed in the soil the higher will be the per cent, of seeds growing and, as a rule, the more vig- orous will the plants be. Indeed, seeds of low vitality placed in too cold a soil often fail to germinate at all. Haberlandt found that, when corn would germinate in 3 days at a temperature of 65.3 F., it required 11 days when the soil was as low as 51 F., and Hellriegel showed that when corn was planted under a mean temperature of 48 only 2 out of 10 kernels sprouted in 42 days; that Vinder the same temperature rye germinated in 9 days, Conditions Influencing Soil Temperatures. 215 winter wheat in 12 days, and barley and oats in 13 days, while cucumbers did not germinate in 42 days. 258. Effect of Soil Temperature on Root Pressure. The power which sends the soil moisture into the roots of plants and up into the leaves is osmotic pressure, developed by the warmth of the soil, and unless the soil temperature is sufficiently high plants may wilt, as Sachs has shown, where he demonstrated that pumpkin and tobacco plants wilted badly, even at night with an abundance of moisture, as soon as the soil temperature fell much below 55 F., the moisture not rising fast enough to compensate for even the slow evaporation during the night. 2C9. Influence of Soil Temperature on the Formation of Nitrates. The nitrates in the soil do not develop until the temperature has risen above 41 F. ; the action of the germs is extremely feeble at 54 and they do not attain their maximum activity until a soil temperature of 98 has been reached ; but if the earth Becomes as warm as 113 F. then the action is nearly stopped, it being as weak as at 54. CONDITIONS INFLUENCING SOIL TEMPEKATUKE. 260. Specific Heat of Dry Soil. When the same number of heat units are given to like weights of different kinds of soil their temperatures are not raised through the same number of degrees and this is because their specific heats (40) are different. From the determination of Oemler it appears that the number of heat units required to raise the temperature of 100 Ibs. of water and 100 Ibs. of soil of different kinds from 32 to 33 F. is as stated in the table which follows: 216 Physics of the Soil. Table of specific heat of dry soils. No. of heat units re- quired to raise 100 Ibs. from 32? F. to 33" F. Temperature of 100 Ibs. after the applica- tion of 100 heat units. Water Heat units. 100 00 F. 83 00 22.15 36.51 20.86 36 '79 Sandy humus 14.14 39 07 16.62 38 02 Clayey hum us 15.79 38 53 14.95 38 68 Pure clay 13.73 39 28 Sand . 10 08 41 92 18.48 37 41 It is clear from this table that much more heat is re- quired to raise the temperature of water through one de- gree than of a like weight of dry soil, and hence that a dry soil will warm in the sunshine more rapidly than a moist soil can. 261. Specific Heat of Wet Soil. The differences m the weight per cubic foot of dry soils and the differences in their water content greatly affect the specific heat or the rate at which the surface temperatures will rise under the same conditions. Sand has a small capacity for water and on this account is naturally warm, but its greater weight per cubic foot acts as an offset, tending to make it colder. If a loosely packed clay loam weighs 70 Ibs. per cubic foot and a sandy soil 106 Ibs. and the two hold 33 per cent, and 18 per cent, of water respectively, when capillarily satur- ated, then the number of degrees F. that 100 heat units will raise the temperature of a cubic foot of each soil when saturated, half saturated and dry are given below: Saturated. Half saturated. Dry. Sandy soil 3 4F. 5.F. 9.92 F. 2.98 4.49 6 02 .42 .51 3.9 Conditions Influencing Soil Temperatures. 217 One thousand heat units would raise the differences in temperatures to 4.2, 5.1 and 39, making it clear that the differences in weight and in water content greatly in- fluence the degree of warmth. 262. Influence of Color on Soil Temperature. The color of a soil, especially when dry, so that the rate of evapora- iton from its surface is small, has a marked influence on the temperature, even at considerable depths. Wollny made a series of experiments to note the effect of color, using white marble dust and lampblack in different pro- portions, to secure different shades from light grey to black, in which he placed two thermometers, one with the bulb just beneath the surface and the other 4 inches below. The temperatures were taken every two hours of the 24 and the results are given in the table below, together with those of a similar trial using yellow ocher. Table showing the influence of color on the temperature of soil. AT THE StJBFACB. AT FOUB INCHES DBEP. Black. Dark grey. Med'm grey. Light grey. Black. Dark grey. Med'm grey. Light grey. Mean temp.. Variations... "P. 32.82 31.55 P. 32 39 32.90 31.98 32.45 T7 30.94 30.10 F. 28.33 15.20 28.46 14.25 o F 27. 83 12.50 "F. 27.20 11.85 Dark brown. Medium brown. Light brown. Faint brown. Dark brown. Medium brown. Light brown. Faint brown. Mean temp Variations . F. 31.76 81.95 F. 81.65 31.75 F. 30.93 29.90 F. 30.70 27.65 W F. 27.29 12.30 27.19 12.15 27.34 11. iO F, ST. 40 10.75 From this table it appears that the darkest soil, whether black or brown, was more than a degree warmer than the light soil at four inches deep ; and that the black soil had a daily variation in temperature at four inches more than 3 F. greater than the light soil, and the dark brown soil one of 1.55 F. 218 Physics of the Soil. 263. Influence of Topography on Soil Temperature. The degree of inclination of the land surface and the direction of the slope, whether facing east, west, north or south, may exert a marked influence upon the temperature of the soil and particularly upon its diurnal range. The tempera- ture of a stiff red clay soil, upon a level table, and upon a south exposure sloping about 18, was found in the sur- face three feet to be as represent CM! in the table below : Showing the influence of topography upon soil temperature. KIND OF SOIL. DEPTH BELOW THE SURFACE. 1st foot. 2nd foot. 3rd foot. Red clay, Red clay, south slope 70. 3 F. C7.2 3.1 68.1F. 65.4 2.7 66.4 F. 63.6 2.8 level surface , Here it is seen that the effect of a south exposure is to make a difference in temperature of from a little more than 3 F., in the surface foot, to a little less in the second and third feet. The reason for these differences will be readily under- stood from a study of Fig. 61. Suppose A 6 5 Bte rep- resent a section of a prism of sunshine falling upon the hill A E B, where A E is the south slope and .E B is the north. On account of the sun not being di- rectly vertical over the hill the south slope receives as ., much more heat in a unit FIG. 61. Influence of topography on soil , T.I temperature. oi time than the nortn elope as the line 4-6 is longer than the line 4-5. 264. Influence of Looseness and TJnevenness of Surface on Soil Temperature. When a field is left very uneven, and Conditions Influencing Soil Temperatures. 219 especially if covered with lumps, the large amount of sur- face exposed to the sky and to the air permits the heat of the surface soil to be lost rapidly in warming the air above and the result is the deeper soil remains at a lower tem- perature. So, too, if the soil is loose and open, the dry superficial layer becomes warm and heats the air, while the poor conducting capacity of the open soil prevents the heat from being conveyed deeply below the surface and a lower temperature is the result. 265. Influence of Surface Tillage on Soil Temperature. When corn rround was cultivated 3 inches deep as com- pared with 1.5, in alternate groups of four rows, the mean temperatures of the soil ifi the first, second and third feet below the soil stirred was found to be .82 F. warmer in the first foot and .59 F., and .36 F. respectively in the second and third feet on the ground receiving the shallower cultivation. 266. Influence of Chemical and Physical Changes on Soil Temperature. When heavy dressings of farmyard manure are plowed in, and when heavy crops are turned under for green manure, the fermentation which is set up in these materials results in a measure of heat which warms the soil in the same way that a manure heap heats when fer- menting. Indeed all of the steps in the formation of ni- trates in the soil result in the evolution of some heat. Again, when the surfaces of dry soil grains become mois- tened with %vater, whether by "rain or by capillary move- ments, surface tension in forcing the water to surround the soil grains generates a small amount of heat, which affects, in so far, the soil temperature. 267. Influence of Rains on Soil Temperature. Heavy rains which fall upon fields and penetrate the soil may ex- ert very marked effects upon its temperature on account of the relatively high specific heat of the water as compared with that of the soil. If the atmosphere is wanner than the deeper soil, as 220 Physics of the Soil. may be the case in the spring, and if rains fall which re- sult in heavy percolation, a large amount of heat is con- veyed rapidly and deeply into the soil with the water and the temperature of the ground, two to four feet below the surface, may thus be very materially raised. 268. Influence of Evaporation on Soil Temperature. There is no factor, except the direct sunshine and the direct radiation of heat away from the earth into space, which exerts so strong an influence on the temperature of the soil as the evaporation of moisture from its surface; and the chief reason why an undrained clay soil is colder than ono well drained is the cooling effect associated with the larger evaporation of soil moisture. To evaporate a pound of water from the surface of a square foot of soil, by means of the heat contained in the soil, makes it imperative that 966.6 heat units be expended to do the work and this, if withdrawn from a cubic foot of saturated clay soil, would lower its temperature some 10.3 F. The difference in temperature shown by the wet and dry bulb thermometers measures, in one way, the cooling effect of evaporation ; the wet bulb often reading as much as 15 or even 20 degrees lower than the dry one, under otherwise identical conditions. Table showing the influence of rapid evaporation upon the temperature of the soil. Date. Time. Condition of weather. Temp, of air. Temp, of drained soil. Temp, of un- drained soil. Differ- ence. April 24^ 3. 30 to 4pm. Cloudy, with brisk east wind. 5j |eo.5 QJJI 66.5 F. 54 00 "F. 12.50 April 25J 3 to 3.30 p. in. Cloady, with brisk east wind. '-64.0 70.0 58.00 12.03 April 26] 1.30 to 2 p. m. Cloudy, rain all the forenoon. [45.0 50.0 44.00 6.00 April 27] l.POto 2 p. m. Cloudy and sunshine, wind S. W. brisk. ^530 55.0 50.75 4.23 April 2SJ 7 to 8.SO a. m. Cloudy and sunshine, wind N. W. brisk. [45.0 47.0 44.50 2.50 . Means of Controlling Soil Temperature. 221 In the table above are given the observed differences in temperature of a well drained sandy loam and an ad- jacent black marsh soil, not well drained, the observa- tions being taken simultaneously and the differences in temperature being due largely to differences in the rate of evaporation in the two cases. MEANS OF CONTROLLING SOIL TEMPERATURE. 269. Effect of Rolling on Soil Temperature. In the spring of the year, when the soil is naturally cold, the first effect of rolling is to cause the soil to warm deeply at a more rapid rate, and Fig. 62 shows how strong this influence may be. In extreme cases the soil temperature, at 1.5 inches below the surface, has been found as much as 10 F. higher than on entirely similar and adjacent ground, not rolled, and 6.5 at 3 inches below the surface. This dif- ference is due to the better conducting power of the soil, on account of its firmer texture, and is in spite of the loss of heat due to greater evaporation which takes place from the rolled surface. FIG. 62. Showing the effect of rolling on soil temperature. The average difference in temperature of soil on eight Wisconsin farms, at the season when oats were germinat- ing, was found to be as given in the table below: 222 Physics of the Soil. Time. Mean air temp. Mean soil temperature at 1.5 inches deep. Mean soil temperature at 3 inches deep. ' 2 to 4 p. in... 65.37 F. Rolled. 71.69F. Unrolled. 68.57F. Rolled. 67.33T. Unrolled. 64.39" F- Here is a mean difference of 3.1 I\ at 1.5 inches, arid 2.9 F. at 3 inches deep in favor of the rolled surface. 270. Influence of Thorough Preparation of the Seed-bed on Soil Temperature. It follows, from what has been said in previous paragraphs, that the practice of thoroughly pre- paring the seed-bed before sowing or planting must have the effect of decreasing the capillary rise of cold water from below and its loss by evaporation from the soil. This then would tend to concentrate the sun's heat in the seed- bed itself, first by lessening its rate of conduction down- ward, and second by diminishing its loss, by lessening the evaporation. In the spring, then, early and thorough preparation of the seed-bed tends to make the seed-bed warmer ; it diminishes the loss of soil moisture ; it increases the formation of nitrates, thus making the soil richer; it hastens and makes stronger the germination and it enables one or more crops of weeds to be destroyed before the crop is up in the way of cultivation. Hence there is much to gain and little to lose in the thorough preparation of tho seed-bed before planting. 271. Controlling Soil Temperature by TTnderdraining. When land naturally too wet for tillage early in the spring has been thoroughly underdrained, the soil is brought into fit condition for seeding much earlier than would be pos- sible without this improvement, and one of the great points gained is the warming of the soil to a greater depth, on account of the removal of the water and tlie lessening of the loss of heat by evaporation. CHAPTER XL OBJECTS, METHODS AND IMPLEMENTS OF TILLAGE. Tilling the soil is one of the oldest of agricultural arts, and during its long practice very many methods have been adopted and tools devised for securing the ends sought. 272. Objects of Tillage. The term "tillage" has been applied to the different methods of working the soil in or- der to secure the conditions needful for the growth of cul- tivated crops. The chief objects which tillage aims to secure are: 1. To destroy and prevent the growth of weeds and other vegetation not desired upon the ground. 2. To place beneath the surface manure, stubble and other organic matter where it will not be in the way and where it may be converted rapidly into humus. 3. To develop various degrees of openness of texture and uniformity of soil conditions suitable to the planting of seeds and the setting of plants. 4. In still other cases the object of tillage may be to so modify the movements of soil moisture and of soil air. 5. In still other cases the objects of tillage may be to so chang'e conditions as to make the soil either warmer or colder. TILLAGE TO DESTROY WEEDS. It must ever be kept in mind that wherever weeds are al- lowed to grow they are removing from the soil both avail- able moisture and plant food in the form of soluble salts and, to whatever extent this is permitted, to that extent is 224: Physics of the Soil. the possible yield of any crop lessened. No soil can mature a maximum crop of corn when weeds are permitted to grow with it. Neither is it possible for an orchard of any kind to come into hearing as quickly or to produce as vigorous trees where the soil between and beneath them is occupied by either weeds or grass. It may be thought that so long as the weeds are destroyed upon the ground they return to it whatever they have taken out and therefore cannot leave the soil poorer. To this it must be said that whatever moisture is removed is a positive loss because it is carried away by the winds; the nitric acid that is taken up and the potash, phosphoric acid and other ash ingredients are also largely a positive loss so far as that season is concerned for they are removed from the soil moisture and converted into dry matter in the tissues of the weeds where the crop can- not use them. Even if the weeds are killed while the crop is yet on the ground they cannot furnish food for it for they are likely not to decay soon enough to become at once available. 273. The Best Time to Kill Weeds. The best time to kill weeds is just as the seeds are germinating or while they are yet very small. When this is done but little moisture is lost through them and they render but little plant food insoluble. In the thorough and early preparation of the seed-bed many weeds are destroyed by killing them just as they are coming up. So, too, in the case of a grain field, which is rolled after being seeded and is then harrowed, the rolling hastens the germination of the weed seeds and the harrowing then throws them out into a dry soil which kills them. If such a field is again harrowed just after the grain is up a second crop of weeds may be destroyed and the yield made greater as a consequence. In the case of potatoes and corn it is very easy to destroy at least two crops of weeds before the corn or potatoes are large enough to cultivate, by harrowing before and just after the plants are up. This is very important because it not only saves plant food for the crop but it can be done Tillage to Destroy Weeds. 225 so much, more cheaply and rapidly with the broad light harrows and weeders than it can later with the cultivator. 274. Weed Seeds Do not All Germinate at Once It must be remembered in handling soils to kill weeds that the seeds do not all germinate at once. The first harrowing which is done to kill weeds may itself bring up from below seeda whioh were too deep in the ground to grow or it may cover some seeds which were lying upon or too close to the sur- face to germinate, hence frequent cultivations for hoed crops are needful. 275. The Best Tools for Weed Killing. The tool which will do the most effective service in killing weeds depends upon the character and condition of the soil and the size of the weeds. When they are not yet fairly out of the ground or are just coming up and before a root system has been de veloped there is no tool equal to a medium weight or light spike-toothed harrow represented in Fig. 6 2 a. The stiffer and more compact the soil is the heavier should be the har- row or rather the deeper it should be run in the ground. FIG. 62a. Tilting harrow, best tool for killing young weeds. The tilting harrow, constructed so that the teeth may be inclined forward or backward, is one of the best forms a?, with this arrangement, it may be made to run deep or shal- low as desired. On sandy soils and other soils when very loose the form of tool represented in Fig. 63 may be used to kill very 226 Physics of the Soil. young weeds before they are well rooted ; but this is not an effective tool when weeds have a start nor where the soil is at all hard or heavy. FIG. 63. Weeder. 276. Cultivation After the Harrowing Stage. When plants have become too large to permit the harrow or weeder to be used to advantage a tool with broader teeth is needed. Cultivation or intertillage should begin as soon as the first fresh weeds start and great pains should be taken to work so close to the row that all the soil is either stirred or covered with a thin layer of fresh soil. Few realize how close it is possible to work to a row without either covering the plants or seriously injuring the roots, until they have learned to do it. It is early and frequent harrowing and careful close first cultivation that insures scrupulously clean fields and the largest yields the season's rainfall will permit. 277. Cultivators for Intertillage. When harrowing has been properly practiced intertillage may begin with a tool \vhose teeth are about 2 inches wide and there should be enough of them to thoroughly stir the whole soil surface to a depth of two and one-half to three inches. Fig. 64 shows a good set of teeth for soils not too heavy, while Fig. 65 shows a tool which should not as a rule find a place in well cared for fields, for the teeth are too wide and too few for good general work. They are wasteful of moisture, waste- ful of fertility and liable to do too much root pruning. Tillage to Destroy Weeds. 22^ FIG. 64. A type of good cultivator. Cultivators with rigid teeth like those of Fig. 66 do bet- ter work as a rule than those of the spring tooth type rep resented in Fig. 64, for the reason that the ground is stirred more completely and to a more uniform depth. On naturally mellow soils the spring tooth is good and where the land is very stony it is safer against breaking. FIG. 65. Cultivator with too wide teeth for general use. 228 Physics of the Soil. 278. Easy and Quick Movement of Teeth. A very im- portant feature of a riding or walking sulky cultivator is to have the gangs of teeth so swung from the carriage that a slight effort will produce a quick and certain movement. This is indispensable in order to work close to the rows. FIG. 66. Cultivator with rigid teeth; best where soil is heavy and not stony. 279. The Teeth of the Cultivator Adjustable. Another important feature sulky cultivators should possess is the possibility of tilting the gangs so as to allow them to work more deeply in the soil toward the center of the row in the later stages of cultivation because then the roots near the rows have developed close to the surface, and deeper culti- vation in the center, where the soil is more exposed to the sun, is needed for effectiveness as a mulch. 280. Covering Weeds in the Row. It sometimes happens with the most careful management that weeds will get such a start in the row that either hand hoeing must be resorted to or else a tool must be used which will throw enough Tillage to Destroy Weeds. 229 JANESVlLLE T DISK CULTIVATOR *' FIG. 67. Cultivator which can be used to cover weeds in row. 15 FIG. 68. Tool for shallow surface cultivation. 230 Physics of the Soil. earth to cover the weeds in the row. A good cultivator for this kind of work is represented in Fig. 67. The levelers represented in the rear of the discs are intended to throw FIG. 69. Two good garden cultivators. the earth back to prevent ridging when the tool is used for ordinary cultivation and ridging is not desired. 281. Garden Cultivators. Two good forms of garden cul- tivators are represented in Fig. 69, where the upper one is to be used early, when the plants and weeds are small, and the lower one when the harrow-stage has passed. In the garden as in the field the best time to kill weeds is just aa Tillage to Modify Soil Texture. 231 the seeds are germinating and emerging from the soil and the harrow-soothed cultivator is very effective in doing this. It stirs the surface thoroughly enough to throw the young weeds out and cause the soil close to the surface to dry sufficiently to kill them. Much worry and hard work will be saved by the timely use of this or a similar tool. TILLAGE TO MODIFY SOIL TEXTUEE. 282. Soil Texture and Tilth. Texture of soil, like the texture of cloth has reference to the size of the elements which give it its evident structure; and just as the threads of a piece of cotton, a piece of woolen or a piece of silk are FIG. 70. Showing the granular character of a soil in good tilth after cultivation. made by twisting together varying numbers of small fibers, making the threads coarse or fine, so is it with soils ; they are composed of granules of varying sizes formed out of ultimate soil grains which are cemented together more or 232 Physics of the Soil. less firmly. Fig. 70 represents the textural elements of a clay loam in pretty good tilth. There are shown seven sizes of granules large enough to be readily distinguished with the naked eye, and each size is composed of fine soil grains cemented together. All are represented natural size and were carefully drawn from an actual sample taken from a three inch mulch as left after the cultivator. The granules were sorted by means of a series of sieves and the relative amount of each size of granules is repre- sented by the shading in the vials where it is seen that the largest size constitutes the smallest part of this soil, and No. 5 the largest portion. The finest grade, No. 8, is also largely composed of compound grains, many large enough to be clearly distinguished by the unaided eye, but many more of the ultimate grains which were rubbed off from the larger grains by cultivating and during the process of screening. Just as woolen cloths differ when the threads are of the same size because some are twisted from finer and others from coarser wool, so soils differ in having their granules made of coarser or finer soil particles cemented together. Then, too, just as one cloth may differ from another in having its threads loosely twisted^ while another is hard twisted, so one soil may differ from another in the degree of firmness with which the soil particles are cemented to- gether. Still again, just as one fabric may be loosely woven while another is firm, so one soil may have its granules more strongly cemented together than another, making it hard to work and heavy while the other is light and mellow. A sand differs from a soil in being composed of simple separate grains, usually of rather large size, while a clay is composed very largely of extremely fine granules made from the finest of particles. A soil is in good tilth when its granules are neither too fine nor too coarse, and when they are not too firmly cemented together. Tillage to Modify Soil Texture. 233 283. Why Good Tilth and Good Tillage Are Important It is clear from the rounded form of the granules of soil shown in Fig. 70, that when they are massed together with- out being crushed a very large amount of unoccupied space must exist ; this unoccupied space in a soil is needed for the movement of air and of water; for the spreading out of the root fibers and root hairs, and for the home of micro- organisms which develop the available nitrogen used by all the higher plants. If the granules are too large and too loosely packed the soil lets the rains fall through it too freely and does not bring it back rapidly enough by capillarity to meet the needs of crops. If the granules are too small and too close then the water moves too slowly, too much is retained by capillarity and there is too little air. If the granules are bound together too strongly, the soil is too hard and the roots are unable to set it aside in making their advance and this lack of freedom reduces the yield. 284. How Texture and Tilth Are Developed. The soil particles are drawn together into the rounded granules by the tension of the soil water in the same way that water forms itself into spheres when sprinkled on a dust covered floor. As long as there are large open spaces in the soil not filled with water the water is all the time drawing itself to- gether, tending to form spheres, and in this system of pulls the soil particles become involved and are drawn together also. As the water is lost by evaporation and the salts dis- solved become too strong to remain in solution they are de- posited upon and between the grains and granules tending to cement them together. 285. Difference Between Soil and Potter's Clay. When the granules of a fine soil are all broken down and separated into their ultimate grains we have the puddled condition so fatal to crops, but the one the potter strives to secure to make his wares close in texture and strong. In the pud- dled soil and potter's clay enough of the granules have been 234 Physics of the Soil. broken down to fill the spaces between the larger simple grains and finer granules not yet broken down to make a close textured, impervious material in which no plant can thrive, and through which neither water nor air can move. 286. Early Spring Tillage The early stirring of the soil in the spring preparatory to seeding has for its main object the changing of the soil "texture so that it will become 1st, warmer, 2d, dryer, 3d, better aerated, 4th, better suited to lessen the rate of evaporation of the deeper soil water, and 5th, to hasten the development of weed seeds so they may be destroyed before the crop is in the way of killing them. mj iS FIG. 71. The disc harrow. 287. The Disc Harrow. One of the best tillage tools yet devised is the disc harrow represented in Fig. 71. There is no harrow which so thoroughly pulverizes a soil in the spring after fall plowing as this tool. When set to work deep the draft is heavy but the amount of work it is doing Tillage to Modify Soil Texture. 235 is relatively large. To put a piece of fall plowing in the best shape the harrow should be lapped half and in doing this the furrow between the two sets of discs will be en- tirely filled and the surface left level. FIG. 72. Spring-tooth harrow. Where small grains are to follow corn or potatoes the use of this tool will often make the plow unnecessary. On the upland prairie soils and others naturally mellow, ground for corn njay be plowed in the fall and fitted in the spring with the disc harrow with good results. 288. The Spring Tooth Harrow. On new land in wooded countries and where the fields are rough and stony the har- FIG. 73. Spike-tooth or smoothing harrow. 236 Physics of the Soil. row represented in Fig. 72 does good work. Its weight forces it into the soil and the elasticity of the teeth prevent them from being broken, but such tools can never do the degree of pulverizing that the disc harrow accomplishes. 289. Smoothing Harrows When the soil has been pul- verized with the disc or other tool and it is desired to leave the surface more nearly even, or where the soil is naturally very mellow, making less force necessary to change the surface texture, then the heavier weights of tilting har- rows, Fig. 73, may be used to great advantage on account of the greater area which may be covered with them in a day and their lighter draft. FIG. 74. The planker. 290. The Planker. It is sometimes desirable to leave the surface particularly smooth without firming it and at the same time to crush lumps. This may be done by means of a planker made of three to five 8- or 10-inch plank bolted together with their edges overlapping as represented in Fig. 74. The tool is best made of oak plank two inches thick and eight to twelve feet long. Such a tool cannot take the place of a roller where it is desired to firm the ground. 291. The Use of the Roller The roller is used chiefly when it is desired to firm the surf ace and to help cover seed, especially when sown broadcast. In other cases it may be used to crush clods or to compress the furrow slices after the sod plow. Again when a green crop like rye or clover has been turned under for manure, or where coarse litter has been plowed under, a roller is needed to compress the soil and establish good capillary connection with the deeper Boil water. It is sometimes used to develop a mulch where grain is rolled after it is up. Tillage to Modify Soil Texture. 237 In all of these cases weight is one of the essential feat- ures of the tool. A roller for tillage should have a weight of about 100 Ibs. to the running foot and a diameter of about 2 feet. FIG. 75. Two types of rollers. Two types of rollers are represented in Fig. 75, the one made of bars being designed to crush clods more completely and to leave the surface ridged so as to be less likely to be influenced by the wind drifting the surface soil. 292. The Harrow Should Follow the Roller. In most cases when it has been desirable to use the roller to smooth or firm the surface a light harrow should follow it quickly in order to prevent unnecessary loss of soil moisture, be- cause the firming draws the deeper water to the surface, the surface temperature becomes higher in the sunshine and the wind velocity near the smooth surface is greater; each of which favors the rapid loss of water. 293. Danger in the Use of the Roller. On heavy soils, when they are a little wet, injurious results may follow the use of the roller just after planting or seeding on account of the close packing, excluding the air from the seed, which 238 Plvysics of the Soil. interferes with quick germination. This danger is greatest where grain has been sown with a drill. The use of the roller when the soil is a little too wet may also interfere with the formation of nitric acid in the soil by making it too close and too wet. In such a case the im- mediate use of a light harrow would only retain the moist- ure and make the rate of nitrification slower. 294. The Plow. The plow as a tillage tool is usorl for two distinct purposes, 1st, to alter the texture, forming FIG. 76. Showing the principle of the pulverizing action of the plow. from a comparatively hard soil a deep and mellow layer of earth; 2d, to bury beneath the surface weeds and other vegetation or manure where it may decay rapidly and be converted into available plant food. If you will open a book, placing the fingers upon the fly leaf in front and the thumbs under the fly leaf in the back and abruptly bend up the corner it will be seen that every leaf is slipped over its neighbor. What takes place is rep- resented in Fig. 76. Had pins been put through the book before attempting to bend the leaves the bending would Tillage to Modify Soil Texture. 239 have tended to cut the pins into as many pieces as there were leaves, just as seen in Fig. 76. Now the plow has exactly this kind of effect upon the furrow slice; it tends to make it divide into thin layers which slide over one another just as the leaves of the book did, and it is because of this sort of action that a plow pul- verizes a soil as no other tool can. 295. How Plowing May Puddle Soils. When a soil is too wet its granules are so easily broken that the plow is liable to shear all the coarser ones into two, three, or more slices just as the pin has been sliced in Fig. 76, thus destroying its tilth by puddling it. 296. How Plowing May Correct Texture and Improve Tilth. If a soil has gotten out of tilth, has become cloddy or has been partly puddled there is a shape of mold board, a stage of soil moisture, and a depth of furrow slice which will help to restore the tilth best and quickest. When such a soil is the least amount too dry to puddle the plow will shear it into the thinnest slices ; if still drier the layers will be thicker and will form coarser granules. When much too dry no shearing can take place at all, and the furrow slice is simply broken into coarse lumps. If you bend but a few leaves of the book at a time there is but little slipping, but the thicker the pile of leaves the greater is the sliding and the greater is the tendency to shear. So it is in plowing, the deep furrow pulverizes bet- ter and puddles worse than the thin slice or shallow furrow. Again if you bend the leaves gently there is little shear- ing, but if abruptly the sliding is great. So if you plow with the low mold board of Fig. 77 you disturb the tilth least, puddled the soil least, and leave the texture coarsest ; but if the steep mold board of Fig. 78 is used there is the greatest danger of puddling if the soil is too wet and the greatest opportunity to pulverize the soil and improve the ti 1 th if the moisture is right. 297. Forms of Plows. Plows are made with two funda- 240 Physics of the Soil. mentally different shapes depending upon the character of the work which they are expected to do. If the chief object of the plow is to cut a clean furrow slice and turn it over so as to completely cover whatever may be upon the surface a shape represented in Fig. Y7 is used. FIG. 77. Typo of sod plow, \vhicb pulverizes but little. If on the other hand the primary object of the plow is to thoroughly pulverize the soil, making it deep and mellow, a form represented in Fig. 78 must be used. Then accord- ing as one or the other of these two chief objects vary in importance shapes of plows will be chosen which are in- termediate between these two extremes. 298. Kind and Condition of Soil and Shape of Plow. It must be clear from the mechanical action of the plow that its form should be adapted to the soil. If the soil has a tendency to be too open and porous, and is naturally coarse grained, like the sandy soils, it should be plowed with a steep mold board, a little over wet and as deep as other con- ditions will permit, so as to break down the granulation and secure the closer texture. If the soil is generally too close in texture, is heavy and soggy, it needs the less steep mold board used when the soil is a little dry so as to shear into thicker layers and form granules of larger size. If plowing must be done when the soil is a little too wet Forms of Plows. 241 use the less steep mold board and plow as shallow as other conditions will allow. If a soil has become a little too dry and is not pulverizing fine enough, use the steeper mold board and plow deep for this will split it into thinner layers, make the soil finer, and the tilth better. 299. The Kind of Soil, the Shape of the Mold Board, and the Draft of the Plow. Since the steepest mold board bends the furrow slice most and pulverizes most, it is clear that the work done is greatest, and hence that the draft will be most. Since deep plowing pulverizes more than shallow plow- ing the work done is more than in proportion to the depth. Since clay soils have more and larger granules which must be sheared in two in plowing than sandy soils do, the labor of plowing must be greater. Since the granules of the soil are not as strong when the soil is moist as when dry it plows much easier, when in good condition. But if the soil has become too dry and yet must be plowed, it should be plowed deeper rather than shallower. This is necessary to pulverize better, to get more moist soil on the surface for the immediate seed bed, and to quicker moisten and bring into condition the layer which has become too dry. 300. The Sod Plow The sod or breaking plow is con- structed so as to reduce the draft as much as possible by doing only the work needed to cut and turn over the fur- row slice. This is accomplished by making the mold board very long and slanting so that the furrow slice is bent and twisted as little as possible, as shown in Fig. 77 ; the chief work being to cut it and roll it bottom up. The extremely oblique edge of the share in the breaking plow reduces the draft in cutting off the roots by allowing the cutting to be done gradually and with a drawing cut, just as it is easier to cut off a limb by letting the blade of the knife slant backward, drawing it across. 242 Physics of the Soil. The extremely oblique construction of this plow too, makes it easier to hold it steady when passing and cutting oif strong roots or other obstruction. FIG. 78. Type of pulverizing plow with steep moldboard. 301, The Pulverizing or Stubble Plow. It will be seen from Fig. 78 that this plow has a much steeper mold board and much less oblique plowshare, the object being to bend the furrow slice as abruptly as possible before it is turned over, for this is what pulverizes the soil, giving it the loose, fine, open texture sought. 302. Mellow Soil Plows. Soils which are sandy and naturally very mellow may be plowed with "a plow having the mold board less steep and more like that of Fig. 79 in shape. With such a form as this the team may cut a wider furrow, and thus cover the ground more rapidly, because the draft is less. When soils are very heavy and stiff it may also be de- sirable to use this type of plow, simply because the draft would be too heavy for the team with the type which pul- verized the soil more. Again very loose soils which have an extremely fine tex- ture and tend to clog will often clear better from the less steep mold board because the pressure comes more obliquely against the surface. Draft of Plows. 243 303. Draft of Stubble Plows The amount of labor in- volved in plowing a field is so large under the best possible conditions, and it is so easy to make it unnecessarily large, that it is important to understand the principles upon \7hich the draft depends. Mr. Pusey in England, in 1840, made a series of trials on the draft of plows in soils of different kinds, using 10 different plows. We have combined his results and give them in the table below: Table showing the draft of plows in tests made in England and in America. Kind of soil. No. of plows. Size of furrow. Total draft. Draft per sq. in. of furrow 10 5 in. x 9 in. Lbs. 227 Lbs. 5.04 10 5 in. x 9 in. 250 5.55 10 5 in. x 9 in. 280 6 22 10 5 in. x 9 in. 440 9.72 Blue clay 10 5 in. x 9 in. 661 14.69 Sandy loam C.T. C. Morton) 5 6 in. x 9 in. 566 10.48 Stiff clay loam (N. Y. 1850) 14 1 in. x 10 in. 407 5.bl Prof. J. "W. Sanborn made an extended series of trials in 1890 in Missouri and later in Utah and the average of all his trials gives a draft of 5.98 Ibs. per sq. inch of the cross section of the furrow slice. Separating these trials historic- ally, omitting those in the blue clay in England, the re- sults stand: English trials 1840, mean draft 7.41 Ibs per sq. Inch. American trials 1850, " " 5.81 " " " " " " 1890, " " 5.98 " " " 304. Draft of Sod Plow With and Without Coulter 'A set of trials with a sod plow near the type of Fig. 77, in clover sod 2 years old, when the moisture present was about as high as it is prudent to work the soil, gave results as fol- lows: 244 Physics of the Soil. Size of farrow. Total draft. Draft per sg. in. Sod plow with wheel coulter 5.575 in.x 15.08 in. 5.325 in. x 14.5 in. Lbs. 296.25 313 75 Lbs. 3 524 4.453 Difference 47.50 .929 Besides doing the work better the coulter diminished the draft 20.86 percent. A later series of observations was made on a clover sod with the same sod plow provided with a wheel coulter, but at a time when the soil was dryer than when the other measurements were made. The results found were: Size of furrow. Total draft. Draft por sq. in. Clover sod without coulter .......... 6.47 x 11.61 in. Lbs. 714 35 Lbs. 10 80 6.413x 12 47 in. G61 82 8 616 Difference.... 49.53 2.184 In this set of trials the coulter has reduced the draft 25.34 per cent. 305. Draft of Sod Compared With Stubble Plow. Another set of trials were made at the time of (304) to compare the stubble type of plow, Fig. 78, with that of Fig. 77, and the results are given below: Size of furrow. Total draft. Draft per sq. inch. 5.872 x 14.31 in. Lbs. 452 4 Lbs. 5 384 Sod plow without coulter 5.325 x 14.5 in. 313.75 4.453 Difference 108.65 .931 In this case the shape of the plow altered the draft 20.9 per cent., and the difference is probably a measure of the difference in the amount of pulverizing done by the two plows. Draft of Plows. 245 306. Influence of Difference of Soil Moisture on the Draft of Plows By combining the data in the two tables of (304) with reference to the degree of moisture in the soil when the trials were made we have the results given below. Sod plow with coulter. Draft per sq. in. Sod plow without coulter. Draft per sq. in. Soil rather dry 8.616 10.80 Soil in best condition. .. 3.524 4.453 5.092 6.347 From this comparison it is clear that the draft of the plow is very much modified by the condition of the soil. The results show the draft more than doubled when the soil was dryer. FIG. 79. Type of moldboard suited to mellow soils requiring little pul verizing. 307. The Draft of Sulky Plows It is generally claimed that the draft of sulky plows is less than that of the free- swimming types because the friction of the sole and land- side is transferred to the well oiled bearings of the carriage. The few records accessible do not show a material gain, when the influence of the weight of the carriage and driver are not deducted, but where the draft is no greater on the team with the man riding than when walking, and the plow 16 246 Physics of the Soil. can be handled with equal facility, there is an evident ad- vantage in riding plows such as Fig. 80. FIG. 80. Sulky or riding plow. 308. The Line of Draft. It is very important in the handling of a plow that the line of draft be just right and such that a line connecting the center. of draft A, Fig. 81, in the mold board with the place of attachment to the plow bridle shall also lie in the plane of the traces, as shown in PIG. 81. Direction of the Mne of draft for plows. Care of Plows. 247 the cut. by the line A, B, D. If for any reason the line of draft becomes a broken one as A, C, D or 1, 3, 5 or 1, 4, 5 instead of 1, 2, 5 the draft of the plow is made heavier. The greatest care should be exercised to have the length of the traces, or the hitch at the plow bridle such that the plow "swims free," requiring little or no pressure at the handles to guide it. If a steady pressure in any direction is required at the handles something is wrong and the team is doing more work than is necessary as well as the man holding the plow. 309. The Securing of Plows. There are certain soils, whose texture is such that the most perfect plow surface fails to shed them completely and in such cases tlie shapes approaching the sod-plow are more successful. But it is a matter of greatest moment that the mold board possess not only an extremely hard finish, so as not to be scratched by stone or grit in the soil, but it must also possess an ex- tremely close texture so as to be susceptible of a very high polish. If the metal itself is coarse grained there will be inequalities even in the bright surface in which the fine soil particles may lodge and thus clog the plow. 310. Care of the Plow. Too great pains cannot be taken to maintain a bright clean surface on all polished parts of the plow and the necessary care to do this will always pay; this caution is doubly important where the soils are in- clined to clog. Whenever a plow is laid by, even for a few weeks, its bright surfaces should be thoroughly cleaned, wiped dry and coated with a layer of the thick mineral lubricant used for journal bearings, to prevent rusting. A little rusting may practically ruin a plow for use in a soil which tends to clog and a single winter of rusting may injure a plow more than a full season of heavy service in the field. 311. Keeping the Plow in Form. A plow cannot render heavy and long continued service without getting out of proper form. The point becomes dull, too short and as- 248 Physics of, the Soil. sumes the form shown in Fig. 82, instead of that in Fig. 83. In this worn condition the inclination of the mold FIG. 82. Showing point of plow worn into bad form. board to the furrow slice is changed, the plow tends to run on its point, is more difficult to hold, the draft becomes heavier and poorer work is done with it. FIG. 83. Showing point of plow in good form. The heel of the share C in Figs. 84 and 85 is especially liable to get into bad form and dull, causing the plow to FIG. 84. Showing heel of plow in form for dry soil. wing over to the land and draw harder, not only because it is dull but because a steady pressure must be exerted at the handles to prevent the plow from tipping to land. FIG. 85. Showing heel of plow in form for moist soil. It is sometimes necessary to change the form of the plow to suit a harder or more mellow condition of the soil. When Jointer Attachment of Plows. 249 the soil is dry and hard the heel needs to be set down, as shown at C, Fig. 84, and the point may need to dip even more than in Fig. 83, but when the soil is wet and mellow the shape shown in Fig. 85 is required to prevent it draw- ing too deeply into the ground. In taking the share to the shop for sharpening or setting the landside should accompany it in order that the black- smith may have a guide in giving it the proper shape. 312. The Jointer Attachment. One of the most useful attachments for a plow is known as a jointer, represented in Fig. 86. This tool is used to great advantage when con- siderable material needs to be turned under, such as long stubble, coarse manure or in turning under a green crop for manure. When this is used with the drag chain in the furrow very long weeds can be completely laid under the surface, leaving the ground in excellent shape. FIG. 86. Plow with jointer. When sod ground is to be plowed deep and left in shape for immediate pulverizing to fit it for crops this tool will often render excellent service by cutting out a section of the sod, turning it into the bottom of the furrow, where it will be completely covered, at the same time leaving the upper edge of the furrow slice composed only of compara- tively loose earth. 250 Physics of the Soil. 313. Subsoil Plow. One of the most widely used forms of sub-soil plow is represented in Fig. 87. It is intended to be used in the bottom of an ordinary furrow, one plow following the other in doing the work. Extremely good judgment is required in the use of the subsoil plow to avoid puddling, which is sure to result from using the tool when the subsoil is too wet. In humid climates the dangers are greatest in the spring and least in the fall, and it must be kept in mind that the surface soil may be in good condition to plow when the subsoil is much too wet. FIG. 87. Sub-soil plow. In semi-arid climates the dangers of injuring the soil texture are much less and it is under such conditions that subsoiling is likely to prove most profitable, tending as it does to increase the available moisture for crop production. OBJECTS, METHODS AND TIMES OF PLOWING. 314. Depth of Plowing. The best depth to plow at a given time, on a given soil, for a given crop must be de- cided on the spot after exercising good judgment with a Best Conditions o/ Soil for Plowing. 251 knowledge of the needs and conditions. There can be no "rule of thumb" for plowing. As a general rule in humid climates the plow never should go deeper than to turn over the surface or dark colored layer of weathered soil. If deeper plowing is done, turning up the unweathered subsoil, the productiveness of the field will be reduced. It is very desirable to develop and maintain a deep soil; this is clearly proved by the heavier crops which always grow upon "back furrows" and the scanty ones which grow in "dead furrows" as compared with the rest of the field. When a soil is thin and the subsoil is close and heavy it is only safe to deepen it gradually by plowing a little deeper each year or two, turning under as far as possible coarse manure, stubble and green crops to make the soil open and form humus in it. Fall plowing may usually be as deep as the soil will per- mit, down to 6, 7 or even 8 inches, but the cases are rela- tively few where it is important to plow deeper than 6 or 7 inches. Where plowing is for small grains to be sowed at onoe the depth may usually be shallow, 5 inches or less, as these thrive best in a shallow seedbed. 315. Best Condition of Soil for Plowing. There is a con- dition of moisture peculiar to each and every soil at which it will be left with the best texture after plowing, requiring the least amount of finishing work to put it in final condi- tion. If the soil is too wet the crumb structure so essen- tial to a clay soil will be partly destroyed and the soil puddled; if too dry the furrow slice will not shear in thin layers and the soil will not be pulverized fine. The water content should be such that the damp soil squeezed in the hand will hold its form but will easily crumble to pieces and not be at all pasty. Sod ground can always be plowed a little wetter than corn, potato or stubble ground because the roots lessen the danger of puddling and the shearing effect of the plow is less. 252 Physics of the Soil. 316. Treatment of Ground After Plowing. Ground plowed late in the fall, to act as a mulch, to allow the moisture to penetiate deeply and to have its texture altered by thawing and freezing, should be left with the natural furrow surface rough and uneven. If plowed in the spring when the ground is a little over wet and the turned furrow shows large polished surfaces the ground should be gone over with a harrow but not im- mediately, for if the soil is a little too wet it should be al- lowed to dry just enough so as to crumble perfectly. If the soil is already a little too dry and a crop is to be put on at once then the harrow should follow the plow olosely, otherwise the soil will become lumpy and the whole furrow slice may become too dry for the best germi- nation. If the plowing is for corn, potatoes or the garden and is done some time before the ground is to be planted then the surface is better left as it would be for fall plowing, pro- vided the soil is in good condition when plowed, because it will form a better mulch, it will take the rains better, be less likely to become too much compacted by the rains and will harrow down better when planting time comes. 317. Plowing for Corn in the Fall On soils which are naturally mellow, where large areas are to be planted and the spring's work is crowded it is often best to plow for corn late in the fall, just before freezing. If such ground is to be manured it can be plowed in then to advantage or if the manure is not too coarse it may be applied as a sur- face dressing during the winter and disked in the spring. If the soils are very heavy and have a tendency to run to- gether with the spring rains then there is danger that the disc may not be able to bring the field into condition. 318. Plowing Sod. There are two methods of plowing sod, 1st, skim-plowing, usually in the fall, turning over a thin sod to kill the turf, expecting to cross plow in the spring deep enough to bury the sod and turn up enough Plowing Under Manure. 253 soil to work up fine and form the seed bed. 2d. Plowing deep enough at first to provide a sufficient soil to work up with a disc harrow and give the desired depth of seed-bed. The latter method usually requires less time but the draft is heavier. It is usually best in such cases to go over the surface with a heavy roller to press the sod home and lessen the danger of the disc turning them over. 319. Plowing Under Manure. If manure is coarse or the soil light it is usually better to place it under a deep furrow because it needs more moisture to rot it and in heavy soils it will let the air penetrate more deeply into the soil. In such cases it is better to do the plowing in the fall or as early in the spring as the soil will permit. If the ground is a little too dry when plowed and seeding time is at hand the field should be thoroughly harrowed and firmed, using the heavy roller if necessary in order to 'establish good capillary connection with the deeper soil. If this is not done the soil above is liable to become too dry. When the manure is well rotted it may be left nearer the surface to advantage, except in the sandy soils where the air penetrates so deeply as to cause too rapid decomposition of the manure. 320. Plowing Under Green Manure Where a crop is turned under for green manure it is usually best to plow deep, to use the jointer and the drag-chain if necessary to get everything well and deeply buried. If a considerable body of material is turned under thorough firming of the soil after plowing will be beneficial. In green manuring good judgment is always required not to let the crop turned under exhaust the soil moisture too completely, for when this has occurred a new crop starts under very unfavorable conditions, both because of lack of -water and immediately available plant food, for the soluble salts are used up with the water by the green ma- nure crop. 2 54: Physics of the Soil. 320. Early Fall Plowing In regions and at times where there is a deficiency of rain, where the soil is light and when the amount of soil leaching is small it is often de- sirable to plow as early in the fall as the crop has been re- moved from the ground, in order to save soil moisture and to enable the nitrates and other soluble salts to develop in sufficient quantity for the next season. Where crops hold the soil moisture low it may even become necessary in dry climates to raise one only every other year because the plant food and the crop cannot be produced by the available moisture of a single season. But early fallowing in the fall will often render the full year unnecessary. GROUND WATER, WELLS AND FARM DRAINAGE. CHAPTEK XII. MOVEMENTS OF GROUND WATER. Of the water which falls upon the land one portion finds its way at once, by surface flow, into drainage channels; a second portion is evaporated where it fell, while a third enters the ground. That portion which enters the ground and is not returned by capillarity or root action constitutes the body of ground water which is the source of supply for wells and springs and which requires removal by land drainage when too close to the surface. 322. Amount of Water Stored in the Ground. In most localities after passing a certain distance below the earth's surface a horizon is reached where the pore space in the soil, sand and rock is filled with water or nearly so. When these pore spaces are large, so that water can flow through them readily, wells sunk beneath the surface fill with water to the level of the ground water surface. In sands and sandstones lying below drainage outlets the amount of water may be as high as 15 to 38 per cent, of the total volume of the rock so that where a country is underlaid with broad and thick sheets of sandstone, such as the Potsdam and St. Peters in Wisconsin and further south, or the Dakota formation in the west, there is the equivalent of from 15 to 38 feet of water on the level for every 100 feet in thickness of the rock formation, and 256 Ground Water, Wells and Farm Drainage. abundant supplies of water can always be found in such places. The loose sands and gravels have a pore space of 20 to Fio. 88. Contour map of a field, one portion of which has been tile drained. 38 per cent, of their volume so that where these lie below the ground water surface and their volume is large an abundance of water exists. Ground Waier Surface. 257 In the soils and clays the pore space is even larger than it is in the sands and this too may be filled with water but here the texture is usually so close that a well sunk in such FIG 89. Contour map of the ground water surface under the field of Fig. 88. material fills with water so slowly that they cannot serve as sources of water supply. Even in the hard crystalline rock, like marble anc( 258 Ground Water, Wells and Farm Drainage. granite, there may be as much as A of a pound of water in each cubic foot, but here again the texture is too close to permit such water to become available in wells. 323. The Ground Water Surface. As the rains which fall in a given locality percolate beneath the surface they fill the pore spaces between the soil grains and raise the level of the ground water. If none of this water drained away and none of it were lost by evaporation the whole soil would have its pore spaces filled with water and the surface of the ground water would coincide with the surface of the land. As it is, as soon as the surface of the ground water ceases to be level drainage begins and the water under the higher land is lowered until a condition is reached when the rate of drainage laterally exactly equals the rate of ac- cumulation of water from the rains. In Figs. 88 and 89 are shown the contours of the surface of a section of land and of the ground water beneath, both sets of contours being referred to the same datum plane, Lake Mendota, into which the water is draining. Here, it will be seen, the ground water stands highest where the surface is highest and lowest where the land is lowest. The arrows show the lines of flow and make it clear why the tile drained area needed that treatment. FIG. 90. Showing lines of flow of ground water during seepage into a stream. 324. Seepage Almost everywhere under the land areas there is a slow movement of the ground water from higher to lower levels destined ultimately to reach some drainage outlet. This movement is known as seepage and Fig. 90 13 Ground Water Surface. 259 a cross-section showing how the water flows from the ad- jacent higher lands and enters the channels of streams, the beds of lakes and even the ocean itself. l'iu 91. Showing contours' of ground water surface in the vicinity of Los Angeles River, Cal. 325. Growth of Streams The water which maintains the low stage flow of streams finds its way into channels all along the banks and bot- toms rather than at isolated places in the form of springs, entering in the manner stated in (324). In Fig. 91 is represented the ground ater surface in the valley of the Los Angeles river, Cali- fornia, where it is seen to rise back from the stream and up the valley. This river must be draining the seepage in 25,978 feet. adjacent higher land and it was found by actual measurement that the growth of this stream in 11 miles was 60 cubic feet of water per second; the water all entering by slow general seepage, there being r 260 Ground Water, Wells, and Farm Drainage no visible springs or streams anywhere along the line. Fig. 92 shows the increase in 25,978 feet, determined by gauging. 326. Changes in the Level of the Ground Water. The level of the ground water in a given section is usually sub- ject to changes, the surface rising and falling with the sea- son and with the rainfall of the place. The change may be as much as 5 or 6 feet in a single season, as represented in Fig. 93, and when a series of dry or of wet years follow in \ VMLl2 9 3 9 J I J i. } J J 4. 3 r. J f J r Jf Feet. = *" . ^^ JlLllti ^-" I "^ JuritSJL- f- J 1 Vf' i / / Lak* Mtndot i June ?/, U9Z. - FIG 93. Sliowiug changes in the level of the ground water surface during the season. succession the changes may be larger than this. It is clear from these facts that in digging wells whose water comes from near the surface of the ground water the bottom should be carried deep enough into the water bearing beds to leave it below the lowest stages of the ground water. 327. Elevation of the Ground Water through Precipitation and Percolation. In Fig. 94 is represented the unoccupied space in eight feet of five grades of sand, above standing water, after 2.5 years had been allowed for percolation under conditions where no evaporation could take place from the surface. The unshaded portions of this figure represent the relative amounts of space into which rains may percolate for each grade of sand, as compared with the whole area of the diagram; that is to say, if an inch of rain were to fall upon the whole surface of the diagram and it were occupied with the ISTo. 1-00 sand the space into which the rain could descend is measured by the un- shaded area under 100; so for each of the other sands, Ground Water Surface. 261 It will be seen from the diagram that up to 12 inches above the ground water surface the space into which water can settle in either sand is very small and hence that a small amount of percolation will produce a relatively large elevation of the ground water surface at first. FIG. S3. Showing the aniouut of unoccupied snace in completely drained sands. Space between long rules, one foot. In a tank filled with rather coarse sand and provided with glass gauge tubes, as represented in Fig. 112, p. 293, to show the level of the ground water surface, a single pound of water added to the 14 square feet of surface raised the level of the ground water .31 inch. In another trial 16.435 Ibs. of water or .226 inch raised the surface 6.7 inches. In still another trial the withdrawal of 33.575 Ibs. of water from the tank, or .461 inch, lowered the ground water 9.05 inches. In the table below are given the amounts of water re- Tdble showing amount of rain necessary to raise level of ground water after thorough drainage. Grade of sand. Ifoot. 2 feet. 3 feet. 4 feet. No. 20 Inche. 0.874 Inches. 4.379 Inches. 8 550 Inches. 12.81 No. 40 .4:i3 3.551 7.795 12 19 No. 60 .579 2.701 6.454 10 80 No 80. .370 1.592 4 080 7.573 No. 100 .242 1.030 2.635 5.131 17 262 Ground Water, Wells, and Farm Drainage quired to raise the surface of the ground water 1, 2, 3 and i feet in the sands of Fig. 94, after thorough drainage has taken place. 328. Law of Flow of Water Through Sands and Soils. It has been generally claimed that the velocity of flow of water through sands and soils is directly proportional to the effective pressure and inversely proportional to the length of the column through which the flow is taking place. This means that to double the pressure will double the rate of flow but to double the length through which the water must flow will decrease the rate one half. A law analogous is formulated for the flow of fluids through capillary tubes and under certain conditions of pressure and dimensions the law has been nearly fulfilled, both with sands and capillary tubes. In practical measurements 1 of flow it is found that the flow through some sands and some capillary tubes increases faster than the pressure while in others it does not increase so rapidly. The law of flow here referred to has been designated "Darcy's Law" and has been expressed by the formula where V is the velocity, P is the difference in pressure at the ends of the column, h is the length of the column. k is a constant depending upon the size of the soil grains, the amount of pore space and the viscosity of the fluid. 329. To Compute Flow of Water Through a Column of Sand, Soil or Rock. Under the conditions where Darcy's law may be fulfilled the amount of discharge may be com- puted by means of the formula derived by Slichter 2 and given below: 1 Nineteenth Annual Report, U. S. Geol. Survey, Part II., p. 202. 'Nineteenth Annual Report, U. S. Geol. Survey, Part II., pp. 301-322. Flow of Ground Water. 263 T)cl^ S q = 10.22 c. c. per second (1) where p is the pressure in c. m. of water at 4 C. d is the diameter of the soil grains in millimeters. s is the area of the cross-section in sq. c. m. // is the coefficient of viscosity. h is the length of the column. k is a constant whose log. is taken from the table, p. 123. and 10.22 is a constant whose log. is [1.0094.] If the pressure is measured in feet of water at 4 C., the length in feet, the area of cross section in square feet, the time in minutes and the diameter of the soil grains in mil- limeters the formula is T)(12 g q = .2012 , . cubic feet per minute. (2) juh k If the flow of water occurs under a temperature of 10 C. or 50 F. the formula may be written q = 15.30 , . cubic feet per minute. (3) Jl K. Problem. A cylinder 4 feet long, having a cross sec- tion of 2 sq. ft., is filled with sand whose grains have an effective diameter of .15 mm. What will be the flow of water through it under an effective pressure of 12 feet, when the temperature is 50 F. and the pore space is 35 per cent. ? Substituting these values in equation (3) we get, taking the value of k from the table, page 123. 15.3 4X 3 1 6 2 = -0 65 32 cu. ft. per minute. Problem. What would be the flow in cubic feet per iminute under the same conditions except at a temperature df 68 instead of 50 F. ? In this case use formula (2) and the results are, taking the coefficient of viscosity at 08 F. at .0101 from the table below: 264: Ground Water, Wells, and Farm Drainage. ft - TABLE III. Coefficients of viscosity for tvater for various tem- peratures centigrade. 0=tempera- ture /^coefficient of 0=tempera- ture //^coefficient of centigrade. viscosity. centigrade. viscosity. 0.0178 10 0.0131 1 0.0172 11 0.0128 2 0.0166 12 0.0124 3 0.0161 13 0.0120 4 0.0156 14 C.0117 5 0.0152 15 0.0114 6 0.0147 16 0.0111 7 0.0143 17 0.0109 8 0.0138 18 0.0106 9 0.0135 19 0.0103 10 0.0131 20 0.0101 330. Observed and Computed Flows Compared When sands have bee.n sorted into grades of nearly uniform size and the effective diameter determined by the method of (143) and then the flow of water through them measured in such an apparatus as is represented in Fig. 95 the ob- served and computed flows are related as given in the next table. FIG. 95. Showing apparatus for measuring the flow of water through sands and the relations of flow to the diameters of the sand grains. Lines show theoretical flow; dots, observed flow. Flow of Ground Water. 265 -1- '"^T -^ f ._,. FIG. 96. Showing the sand grains referred to In table on p. 266. Natural size. 266 Ground Water, Wells and Farm Drainage. Table showing observed and computed flow of water through simple sands of different diameters under a pressure of I c. m. of water. Grade of sand. Diameter of grains. Observed flow. Computed flow. m. m. gms. gms. 8 2.54 2,296 2,277 7 1.808 1,080 1,132 6 1.451 756 757 Mi 1.217 542 522 5 1.095 504.6 453.2 4 .9149 329.2 297.5 3 .7988 210.0 193 2 .7146 138.6 122 1 .6006 94.8 80.6 .5169 72.3 66.8 The agreement between the observed and computed flows is not as close as could be wished but when it is observed that the flow of air, from which the diameters were com- puted, was not measured through the same sample as the one through which the flow of water was measured, that the pieces of apparatus were not the same and that the flow varies, theoretically, as the squares of the diameters of the soil grains, it must be conceded that there is much more than a chance agreement. The samples of sand used in these trials are represented full size in Fig. 96. 331. Relation of Observed Flow to Diameter of Soil Grains. If the squares of the diameters of the sand grains represented in Fig. 96 are plotted as abscissas and the ob- served and computed flows as ordinates their relations will be as shown in Fig. 95, where it is clear that the rates are such as to agree reasonably well with the squares of the diameters of the grains. 332. Relation of Pressure to Flow Through Sands. Most experimenters along this line have found that while there is a general tendency for the flow to increase directly as the pressure there are nevertheless conditions which prevent Flow of Ground Water. 267 these relations being realized in experiment, in some cases the flow being systematically too fast and in others too slow. A series of observations by Welitsdhkowsky and Wollny FIG. 97. Showing apparatus of Welitschkowsky and the relation of pres- sure to flow of water observed by him. and the apparatus with which they were secured are repre- sented in Fig. 97. It will be observed that where the col- umns of sand used by Welitschkowsky were 25 c. m. and 2 08 Ground Water, Wells, and Farm Drainage. 50 c. m. long the flow increased faster than the pressure ; but when the column was 75 c. m. long the flow increased directly as the pressure, while when it was made 100 c. m. long then the flow did not increase as rapidly as the pres- sure. zoo cm 100 eoo aoo o tooocm FIG. 98. Showing the observed relation of pressure to flow of water through sandstone, as measured in the apparatus of Fig. 99. 333. Relation of Pressure to Flow Through Sandstone. When the flow of water is measured through sandstones such as constitute most water-bearing beds it is often found that here, as in the sands, the flow may increase in a much higher ratio than the pressure. Three series of such obser- vations are plotted in Fig. 98, and the apparatus used is shown in Fig. 99. Where the'flow does not increase as rapidly as the pres- sure the departure from the theoretical flow has been ex- plained by assuming that the currents become turbulent and thus reduce the discharge; but no satisfactory reason has yet been assigned to the cases where the flow increases faster than the pressure. 334. Observed Hates of Flow of Water Through Sands and Sandstones. The observed rates of flow of water throuHi the series of sands represented in Fig. 96, when expressed Flow of Ground Water. 269 in cubic feet per minute per square foot of section and per foot of length, under a gradient of 1 in 10, is given below: No. 8 7 6 5 l /j 5 Cn. ft. per min. 5.23 3.65 1.85 1.36 1.22 4 .82 3 .51 210 .33 .23 .18 Fio. 99. Apparatus for measuring the flow of water through sandstones, under different known pressures. According to Darcy's law, if these sand columns had their lengths increased 10, 100 and 1,000 times the discharges observed would be only A, TOTT and ToW of those given. In the case of four sandstones the rates of flow were so slow that 10 days were required for .29, .34, 2.45 and .14 cubic 270 Ground Water, Wells, and Farm Drainage feet of water to be discharged under the conditions for the eand. 335. General Movement of Ground Water Across Wide Areas. The waters which supply artesian wells and many springs, where the discharges take place through openings in overlying impervious beds, are often obliged to travel long distances, even 100 or more miles, before reaching their outlets. But this cannot occur with such low rates of flow as those observed in (334) and it is clear that nearly the whole movement across long distances must take place through rock fissures and along bedding planes, the water seeping out of the rock into these as it does into river chan- nels and lines of tile drains. 336. Fluctuations in the Rate of Flow of Ground Water. When arrangements are made to automatically record the rate of discharge of water from springs, artesian wells or lines of tile drains it is seen that the flow is not uniform, varying not only with the season, but often daily and even hourly. i * I ! i . . J_J- . j!i j [rP T ,, 1 I- . ' , . ..... ] '' ' j , ,|. . ., . i :...., L 1 . ....rf-... 1 i '? <:'-c: :::! ii: ;:;i!i::i, *.: i . i! !::. ( ( . --^^ V i i (. - i I- : ^===4=1 ) r :: ;::: : :::.. iN^ 1 : _-} . ' PSfe-nJ v '.''-*' - - .?&&:& j , ' T ',"?. mm ... ':^:.-^ ; :-:i-:-:<>'v:-..-.--:.-':>-.v/ j m , : ::?' ':, .:.'..' ! i! Via. 100. Showing observed barometric changes in the rate of flow of water from a spring, and the apparatus for recording it. Lower curve, record of spring. In Fig. 100 is shown an autographic record of the dis- charge of water from a spring during 13 days, together with the changes in barometric pressure as recorded by a baro- graph 45 miles to the west of the spring. The method of Fluctuations of Ground Water. 271 recording the changes is also represented in the same figure. The changes in the rate of discharge from the spring, which are associated with changes in the pressure of the atmos- phere, amount to as much as 8 per cent, of the total nor- mal flow. AtfMOAY TuesofY nrfowfjour rnu#soAr rmoAr SATURCAY SUNDAY XII M XII M XII M XII M XII M XII M XII --/- -1 '-'-I-- 1 ; -y-/- C_ -/- -/-: M- -f p- k-s* "in [3 C= K - A s. ^ T o L| \, ^ ,, -4 *.' 5 f- 0^ V ft" - J ' - iB , ~ t -i . o. 5j 23 \ screwing a wide flange on the top and then bolting the pumphead directly to this, having first drilled holes through both to receive the bolts. This arrangement secures a very solid and perfectly tight platform. Around this plank may be laid, or better still, a block of cement. CHAPTER XIV. PRINCIPLES OF FARM DRAINAGE. Both irrigation and drainage are usually looked upon as arts whose application to agriculture are required only in special cases; but a broader and more helpful conception is that all fertile fields must be both well irrigated and thor- oughly drained. It is true that over much the larger portion of the earth's surface the water required for the growth of crops is sup- plied by the natural rainfall, and when this is timely and sufficient it is the best and ideal irrigation, done by nature's hand. It is again fortunately true that most land areas have ac- quired such surface features that the excess of rainfall is opportunely removed by percolation and seepage or surface flow; and this is nature's method of land drainage. The fundamental fact is that all lands must be irrigated or watered and drained and in special cases nature's efforts need to be supplemented. 355. Necessity for Drainage. There are several impera- tive demands for the drainage of farm lands: 1. The removal of the more soluble salts formed by the decay of rock and organic matters, because when the soil water becomes too strong in soluble salts it either poisons the plant or renders the root hairs inactive by causing them to shrivel. If these soluble salts which plants cannot use are not removed the soil comes into the condition known as alkali lands, upon which little vegetation can grow. 2. The water in the soil needs to be frequently changed or replaced by a fresh supply containing an abundance of ' . Conditions Requiring Drainage. 287 atmospheric oxygen because the roots of plants and micro- scopic life tend to exhaust this supply. If the soil is not drained "the water in it becomes stagnant in a sense, the rains which fall simply running off the surface, leaving the soil water the same as was there before the rain. 3. Farm lands must be drained in order to render them sufficiently firm to permit the farm operations. 4. Soils must be drained in order to provide room for soil air. (238.) (251.) 5. The excess of water must be removed to permit the soil to become warm enough for plant growth. (268.) (271.) 356. Conditions which Require Drainage The cases in which it becomes desirable to supplement natural drainage fall into five classes: 1. Comparatively flat lands or basins upon which the water from the surrounding higher lands collect. 2. Areas adjacent to higher lands where the structure is such as to permit the water which sinks into the high land to flow or seep under and up through the low ground, making them wet. 3. Lands inundated regularly by the rise of tides or fre- quently by the overflow of rivers. 4. Extremely flat lands in wide areas which are under- laid near the surface by a thick, close, nearly impervious stratum of clay, such as were formerly old lake bottoms. 5. Lands like rice-fields, water-meadows and cranberry marshes where water is applied in excessive quantities at stated times and must be removed again quickly. 357. Deep Drainage Increases Root Room. No plant can utilize the resources of the soil to the best advantage unless there is provided for it an abundance of root room. In all well drained soils the roots of most cultivated crops spread themselves widely and to a depth of 2.5 to 4 or more feet. When conditions are such as to permit crops to do this the beet growth and largest yields result. 288 Ground Water, Wells and Farm Drainage. Proper drainage so lowers the ground water surface that roots are able to penetrate to their normal depth, and Fig. Ill shows how the roots of corn have been massed together near the surface because of too much water in the soil be- low, and Fig. 45, p. 147, shows the apparatus with the corn growing in it. 358. Drainage Increases the Available Moisture. When the roots of a crop are forced to develop so close to the sur- face as shown in (357) the first effect is to exhaust the soil of its moisture so much as to leave it too dry and so lessen the capillary rise that, although there is an abundance of water in the soil below, it cannot be brought to the roots and the soil below is too wet to permit the roots to go to the moistura OB the other hand if the ground water is lowered the roots are permitted to advance deeper, making it unneces- sary for the water to move up as high and leaving the soil more moist, and so capillary action stronger and capable of lifting water higher and faster. (198.) (199.) 359. Soil Made Warmer by Drainage. Whenever soils are kept continuously wet, so that large amounts of water evaporate from their surfaces, the temperature is low. Two thermometers having their bulbs side by side, one left naked and the other covered with a close fitting layer of wet mus- lin, will often show temperatures as much as 20 different, the wet one colder, made so by the evaporation of water. The teakettle on the stove has the temperature of its bottom held constantly near 212 by the evaporation of the boil- ing water, showing the cooling power of water when evapo- rating. During early spring differences in soil temperature at the surface, due to differences in drainage, may often be as great as 12. The differences in the amount of moisture in clayey and sandy soil often cause a difference of 7 F., in the surface CoriSUions Requiring Drainage, 2.8.9 PIG. 111. Showing how the roots of corn are forced to develop near the surface when the soil i not drained. See apparatus, Fig. 45, p 147 290 Ground Water, Wells and Farm Drainage. foot, when both are well drained, and as much as 5 in the second and third feet. 360. Soil Better Ventilated by Drainage The change of air in wet soils after they have been well drained is very much more thorough and this is perhaps the greatest bene- fit due to drainage. There are several ways in which thorough drainage leads to a more rapid exchange of air in the soil: 1. Lowering the ground water enables both the roots of plants, and animals like earthworms and ants, to penetrate the soil more deeply, leaving passageways larger and freer than existed before. 2. When the deeper clays come to dry after being drained shrinkage checks are formed in great numbers and through these the air moves more freely. 3. With the deeper penetration of soil air nitrates are more freely formed, and with the larger amounts of soluble salts the clay is flocculated, making a more granular text- ure, which again admits the air more freely. 4. When lines of tile are laid under a field 50 to 100 feet apart they furnish an opportunity, with every change in atmospheric pressure and of soil temperature, to force air into and out of the soil, and so a line of tile laid in the soil becomes a system for air circulation. 5. With every heavy rain which causes percolation, where the water can flow away, a volume of fresh air is drawn into the soil after it, completely changing the air. 361. Kinds of Drains. There are two types of drains: (1) closed and beneath the surface after the manner of un- derground water channels; and (2) open, such as ditches, which are in function like natural river channels. The closed forms are usually most effective, least in the way, require less expense in maintenance and are most durable and should generally be adopted, but there are cases where surface ditches must be used. Jn the earlier history of underdraining closed drains were Kinds of Drains. 291 made by laying bundles of twigs in the bottom of the ditch and covering them, expecting the water to trickle through the passageways left. In other cases two or three round poles were covered in the bottom, of the ditch or two slabs were laid edge to edge with their round sides down. Two boards were sometimes set on edge V-shaped, with opening down. More permanent closed drains were made by filling the bottom of the ditch with cobblestone, by setting flat stone on edge V-shape, by setting two lines of stone on edge and covering with flat stone and even by using four stone for top, bottom and sides. In other cases brick were used in place of stone and some even made tile out of blocks of peat, cutting semi-cylindrical cavities in the faces of square blocks of peat, then laying these together to form the water- way. Most of these devices, however, must be looked upon as makeshifts rather than as permanent improvements, and have largely gone out of use. The modern tile, made of hard burned clay, is cylindrical in form and usually in 1-foot lengths with diameters rang- ing from 2 to 12 or more inches. 362. Essential Features of Drain Tile A good drain tile should be hard burned, giving a clear ring when struck. It is much more important to have them hard burned and strong than it is to have them open and porous. Soft burned tile which give little or no ring when struck are much more liable to crumble down under the action of frost. "We have visited one field drained with soft burned tile laid 2.5 to 3.5 feet deep and, in less than five years after laying, holes appeared in the field in many places. On digging in these places it was found that the tile had crumbled into small chips, caused by freezing. Tile are sometimes made from clay containing pebbles of limestone which when burned are converted into lime. These lumps of lime bedded in the tile slack as soon as epoujgh reaches theni and by their expansion the tjle 292 Ground Water, Wells and Farm Drainage. are broken. It will often happen that such tile may be laid in place and covered before the slacking occurs. Besides being hard burned, strong, giving a clear ring when struck and free from lime the tile should be smooth and straight, with square cut ends and true circular outline so that they may be laid with close joints which will ex- clude silt, 363. How Water Enters Tile The texture of a tile is like that of common brick and will allow water to flow readily through the walls, but even were the walls water tight the water could still find access to the tile through the joints formed by the abutting sections as rapidly as it can be brought by ordinary soils requiring drainage. Measurements made of the rate of percolation through 2-inch Jefferson, Wisconsin, tile showed a flow of 8. 1 cubic feet per 100 feet of length in 24 hours, under a pressure of 23.5 inches, when surrounded by clear water only. When the same tile were bedded in a fine clay loam, so that the water had to percolate through the soil, the discharge was reduced to 1.62 cubic feet per 24 hours and per 100 feet, 364. The Use of Collars. It has sometimes been the custom to use collars to slip over the joints formed by the meeting of the sections of the tile, with the idea of better excluding the silt and of holding a better alignment. The collars are short sections of a size of the tile large enough to slip over the joints readily. The use of collars is not advisable, first, on account of the greater cost, and second, because when good tile are prop- erly laid they are not needed. 365. Depth at which Drains Should be Laid. It is seldom necessary to lower the ground water more than four feet below the surface and except in very springy places a depth of 3 feet will answer most purposes. Since the level of the ground water changes with the season and since many lands which are benefited by drain- Depth of Drains. 293 age are only too wet during the spring it may be best to lay the drains only so deep as is needful to bring the field into condition for working in due season, and in such cases tile placed 2.5 to 3 feet, rather than 3.5 to 4 feet, will usually be found sufficient for general farm crops. When tile are placed needlessly deep not only is the cost greater but, in all of those cases where there is an under- flow of water from the higher land, the level of the ground water is drawn down earlier in the season to such a depth that the crop will get less advantage by the subirrigation resulting from the capillary rise of the underflowing water into the root zone. .__. D C B i i 3 - ' : - -Or * k fib '"i 55"" "*" 'H , /e ....-* ""* i tf , lnpQ tlip Irrigation and Drainage.) low area and is carried around on the higher ground. It is specially important to use this method in cases where low areas are surrounded on all sides by a rim of land high enough to prevent the con- struction of underdrains. 382. Construction of Surface Drains. Where surface waters are to be handled as in (381) it can usually best be done by constructing broad and comparatively shallow runways, which can be kept in permanent grass, the widtli and slope of the ditch being such that a wagon and mower can readily be driven along and across it. Such waterways should usually be 1 to 2 feet deep and 10 to 15 feet wide \ \ ^Draining Basins. 307, with sides sloping gently, to a flat bottom which can carry a considerablevolume of water slowly without being eroded. 383. Intercepting the Underflow from Higher Lands In a very large number of cases lands require drainage be- cause of the underflow of water from the adjacent higher Jand in the manner indicated in Fig. 127. In such cases, FIG. 127. Showing how lines of tile may be placed at A and B to inter cept the underflow from the higher land. when drains are laid along the foot of the hill below the ground water surface, as represented at A and B, much of the seepage water will rise into the drain and be conveyed away rather than flow on under the flat land beyond. When such corrections as these are made it may even be unneces- sary to underdrain the flat land or when the drains at the foot of the hill do not fully correct the evil the cost is made relatively less. 384. Draining Basins Without Outlets. There frequently occur sinks or ponds entirely surrounded by rims too high to permit drainage outlets to be constructed across them. Such cases must be met in special ways. 1. Occasionally such basins are underlaid with gravel or sand which is well drained and the water is retained on the surface only by a comparatively thin stratum of clay subsoil. When tiiis is true, one or more wells may be sunk through the clay into the sand or gravel, as represented in Fig. 128, and filled with cobblestone and gravel. Into this underdrains may be led from various directions to collect the water and bring it to the subterranean outlet thus provided. 2. Where several acres must be drained the above method would hardly be practicable even if the under- drainage conditions were favorable. It is possible, how- 308 Ground Water, Wells and Farm Drainage. ever, to arrange in such a manner that a good windmill will drain a considerable bckly of land, where only the underflow must be dealt .with and the lift is less than 20 feet. One method of draining by wind power is illustrated in Fig. 129 where A is one of a number of closed drains FIG. 128. Method of draining sinks. leading to a collecting basin, D, which is connected with the well from which the water is discharged through the pump into the drain C. If the area is small or the capacity of the pump large the water may discharge directly into the well, which may be provided with a float to throw the FIG. 129. Method of draining sinks by wind power. (From Irrigation and Drainage.) mill out of gear when the water is getting too low for the pump. The object of the well is to permit the mill to work during the winter. 3. In still other cases it may be practicable to lay the sink off into lands separated by broad, open "and rather deep ditches, into which the water from the lands could drain and where evaporation would be much more rapid than from the soil. To increase the rate of evaporation of water from the ditches lines of water loving trees, like the willow, could be planted, but these would interfere with Surface Drainage. 309 cropping. The better plan would be to utilize the ground with a crop which would endure the shallow drainage. 385. Lands Requiring Surface Drainage. There are many wide stretches of very flat land which can only be drained through surface channels. Such are the districts which in recent geologic times were lake bottoms, over which a heavy sheet of close textured clay was deposited. Soils like these have subsoils so close that were there plenty of fall and good opportunity to find outlets for drains the rains could riot reach the drains freely enough to meet the needs of crops. FIG. 130. Plan for drainage of lands of the Illinois Agricultural Company, Rontoul, Illinois. (After J. O. Baker.) The smallest squares are 40 acres; double lines show open ditches; single lines are tile drains. Such fields must be plowed in narrow lands with the dead furrows in the direction of greatest fall in order to provide a quick removal of the surplus rains. Other districts are so flat that the rains have not yet been able to cut sufficiently deep river channels to dram the fields enough for agricultural purposes. The soil may be porous enough, even a coarse sand, and yet for lack of natural drainage channels remain too wet to till. 310 Ground Water, Wells and Farm Drainage. In such cases deep open ditches must be provided to con- vey the water out of the country, serving as outlets for underdrains laid in the adjoining fields. A district of this type of land drainage is represented in Fig. 130, covering nearly six square miles. The double lines represent deep open ditches and the single lines underdrains. Another drainage system of .this sort in Mason and Tazvvell counties, 111., has 17.5 miles of main ditch 30 to 60 feet wide at the top and 8 to 11 feet deep. Leading into these mains there are five laterals 30 feet wide and Y to 9 feet deep, the whole system embracing TO miles of open ditch for the purpose of providing outlets for under- drains. CHAPTER XV. PRACTICE OF ITNDEEDRAINAGE. The best work in underdraining can only be done by tlie man who has a thorough grasp of the principles of the art and who has had enough practical experience to make him perfectly familiar with the essential details as they vary with soil, topography, climate and crop conditions. There are many cases of local drainage where the area and expense involved are small, where the farmer having a fair knowledge of the principles of drainage can super- vise or do his own work, but when large areas are to be underdrained, where the fall is small and the surface con- ditions complex, it will be safest 'to entrust the leveling and staking out of the mains and laterals ready for the ditcher to a competent and thoroughly reliable drainage engineer. Indeed it will generally be best and more economical to let the whole job if it is large and difficult to a man of ex- perience who has established a reputation for reliable work. Even in the matter of digging the ditch, raid particularly in giving it its finish, as well as in placing the tile, drainage engineers find it difficult to find men who have the pa- tience, the feeling of responsibility and the practical skill to do it well. A man who has the right frame of mind and the skill to do this finishing and most important work we 1 .! is much more to be trusted than the farmer himself who has so many duties to distract his attention and tempt him to rush the job. But while the general farmer should not be encouraged to attempt the draining of large and difficult areas on his 312 Ground Water, Wells and Farm Drainage. own place it is quite important for him. to have a clear con- ception of the general principles of drainage and of what constitutes thoroughly good detail practice. FIG. 131. Showing forms of drainage tools. 38G. Means for Determining levels. As a general rule the laying out of a system of drains should only be at- tempted with good instruments, two of which are repre- sented in Fig. 131. Where a good drainage level cannot be had the best substitute is the water level, one form of which is represented in Fig. 131 and another in Fig. 132 ; which consists of a piece of gas pipe about 3 feet long mounted on a standard and provided with two elbows into which are cemented two pieces of water gauge glass. When the instrument is filled with water the surfaces in the two tubes stand on a level and can be used to sight across. To move the instrument close the ends of the tubes with corks. As a substitute for the gas pipe a piece of rubber tubing may be used or a piece of garden hose. A less reliable level can be improvised by arranging an arm upon a standard upon which a carpenter's level may be set. Or a still more crude level may be made from a Means for Leveling. carpenter's square mounted on a horizontal arm on which a plumb bob is suspended, with which to set the square with its long arm level. 387. Leveling a Field. . In determining the differ- ences of level, in different parts of a field it is desired to drain, the simplest method for the inexper- ienced person is to lay out the field into squares of 100 or more feet, driving short stakes at the corners. Set the instrument at a, Fig. 133, midway between V the stations 1-1 and 1-? j i ,1 T ,H' IG. 132. -Showing cue form of water level. and record the reading oi the target placed upon the stake at 1-1 in the table in the column headed "back-sight" which is assumed for illustration to be 4 feet. Next turn the instrument upon stake 1-2, when its distance below the level is found to be 3.8 feet and is entered in the column headed "fore-sight." This shows that the ground at 1-2 is 4ft. 3.8ft. =.2 ft. higher than station 1-1. In the column headed "Elevation" the first station is given arbitrarily a hight of 10 feet above an assumed da'tum plane to avoid minus signs. The level is now trans- ferred to b and the distance of 1-2 below the instrument found to be 4.2 feet which is entered in the column "back- sight" as before. Turning now upon 1-3, its reading is found to be 4 feet and this is entered in th* 1 column "fore- sight." The difference in level between the back sight and fore sight shows the difference in level between the two stations 314 Ground Water, Wells and Farm Drainage. and is placed in the column headed "difference." The first difference added to the datum, 10, gives 10.2, the hight of station 1-2 above the datum plane. The second differ- VI V IV III II I FIG. 133. Showiijg method of leveling a field. ence, .2, added to the elevation of station 1-2 gives 10.4, the elevation of station 1-3 above datum. In this manner the level is moved from station to station until e is reached when it is transferred to f and back sights r.nd fore sights taken as before, and entered in the table to connect the first line of observations with the new one jr.st begun. Proceeding as before the level is moved from, f to g and then through h, i, j, k and 1 to m and so on until the field is all completed. When proceeding from higher to lower levels the differences must be subtracted rather than added to obtain the elevation of the lower station. Fig. 104 shows the relation of the level to the target 'rod along a single line of stations shown in profile. Location of Drains. 315 Table giving data obtained in leveling field of Pig. 133. Station. Back-sight. Fore-sight. Difference. Elevation 1-1 4 10 1-2 4.2 3.8 .2 10.2 1-3 3.8 4 .2 10.4 1-4 4 3.6 .2 10.6 1-5 3.9 38 .2 10.8 1-6 4 3.7 .2 11 II-6 38 3.98 .02 11.02 11-5 3.9 3.995 .195 10.825 II-4 4 4.095 .195 10 63 II-3 4.1 4.19 .19 10.44 11-2 3.9 4.26 .16 10.28 II-l 3.8 3.98 .08 10.2 1II-1 4 3.6 _o 10.4 III-3 3.9 3.96 .'04 10.44 III-3 4.2 3.775 .125 10 5G5 III 4 4.1 4.045 .155 10.72 1II-5 3.8 3 93 .17 10. "9 111-6 4.1 3.625 .185 11.075 IV-6 4 4.185 .085 11.16 1V-5 3.84 .16 11 388. Contour Map of Field. When the field has been laid out as represented in Fig. 133, and the elevations of the several stations transferred to the map, the figures show at - . FIG. 134. Showing method of leveling. a glance where the field k high and where it is low. If now lines are drawn upon the map through all places hav- ing the same elevation the topography of the field becomes still more evident to the eye. Such lines are called con- tours or contour lines, and such are the dotted lines in the map. 389. location of Mains and laterals. It is clear from the contour map that the highest station in the field is VI 6 and the lowest 1-1. If then we are seeking the steepest fall or gradient for the main it will be found along a straight 316 Ground Water, Wells and Farm Drainage. line connecting these two stations. Of course no field will be found with so regular a slope as this but the principle is no less true for being so simply stated. vi v rv m n i ^10. 135. Showing a system of tile drains laid out on the leveled field of Fig. 133. (From Irrigation and Drainage.) If such a field is to be drained by placing laterals 100 feet apart about the maximum fall for them, and the mini- mum amount of tile and ditching, will be secured by placing the laterals along the lines of leveling, in which case the lines I, II, III, IV, V, VI will constitute the laterals on one side of the main and the lines 1, 2, 3, 4, 5, 6 the laterals on the other side, as represented in Fig. 135, Since the lines I and 1 are both radii of the same circle and have the same elevation at their outer extremities the fall or gradient will be the same or .2 of a foot per 100 feet, as shown on the contour map, but along the lines Y and 5 the gradient will be .15 feet per 100 feet or 1.8 inches instead of 2.4 inches per 100 feet along the lines I and 1. The fall Location of Drains. 317 is therefore not uniform for all the laterals nor can it be when they are placed along parallel lines. If the field required drains every 50 feet then a greater mean fall could be secured and less tile would be required if a system like that of Fig. 136 were adopted. FIG. 136. Showing a second system ot drains laid out on the field of Fig. 133. (From Irrigation and Drainage.) 390. Laying Out Drains When the positions of the mains and laterals have been decided the next step is to mark them with "grade pegs" and "finders." The grade pegs are short, driven securely into the ground just to one side of the intended ditch, and are placed at regular inter- vals apart. To one side of the grade pegs are placed longer ones called "finders" upon which is to be recorded the depth below the grade peg the ditch is to be dug. 391. Determining the Grade and Depth of the Ditch. In doing this work the leveling begins at the outlet and the 318 Ground Water, Wells and Farm Drainage. steps are the same as those already described for the field leveling, the results being recorded in a table calling for two more columns when worked out than were needed in the field work. These are indicated in the table below : Table showing Field Notes for determining depth of ditch and grade of drain. Station Back-sight Fore-sight. Difference. Elevations Grade -line Depth of ditch. Outlet 7 7 7 4 3 10 7 3 50 3.97 3.87 .13 10.13 7.12 3.01 100 4.2 3.83 .14 10.27 7.24 3.03 150 4.1 4.08 .12 10.39 7.36 3,03 200 3.95 3.99 .11 10.5 7.48 3.02 250 3.87 3.82 .13 10.63 7.6 3.02 300 4 3.69 .18 10.81 7.72 3.09 350 4.25 3.83 .17 10.98 7.84 3.14 400 4.08 4.1 .15 11.13 7.96 3.17 450 4.05 3.96 .12 11.25 8.08 3.17 500 3.97 395 .1 11.35 8.2. 3.15 550 3.75 3.97 __ 11.35 841 3.03 600 3.74 0.1 11.36 8.14 2.93 In "Fig. 13T, which is a profile of the data in the table showing the outlet of the drain at A, the first stake at O and the second at 50, etc., up to 600, both the lines of grade and the datum plane are shown. On each numbered stake is given the depth of the ditch below the top of the grade peg, and below the peg has been set the hight of the bottom of the ditch above the datum plane. Since the outlet in this case is 7 feet above datum and the s'urface at 600 feet is 11.36 feet the total fall is 11.36 feet 7 feet = 4.36. But if the depth of the ditch at the upper end is made 2.92 feet the available fall will then be 4.36 feet 2.92 feet = 1.44. Since the ditch is 12 times 50 feet long the fall will be ~~ = .12 feet per 50 feet. or .24 feet per 100 feet. At each 50 foot station then the bottom of the ditch above datum plane will be found by Determining Grade. 119 adding .12 foot, to 7 feet, which is the height of the outlet, for that of the second station; then .12 feet added to this gives the third station and so on, thus: 7, 7.12, 7.24, 7.36, 7.48, 7.60, 7.72, 7.84, 7.96, 8.08, 8.20, 8.32, 8.44. o so IN "? r 800 850 SOO > *?0 450 500 550 600 FiQ. 137. Profile of ditch staked ready for digging, with depths for the ditch at the several stations. If these numbers are subtracted from the hights of the surface of the ground at the respective places the differ- ence will be the depth the ditch must be dug at those places, and the figures which are placed upon the finders for the instruction of the men in digging. These figures are. given in the table in the column "depth of ditch." The experienced drainage engineer with accurate tele- scope level makes the details of leveling, establishing the gra'de and marking the grade pegs simpler than here given but it is not safe for a fanner with a cheap level to follow his methods. 392. Changing from One Grade to Another It may hap- pen in laying out the ditch that it is impracticable to fol- low a single grade on account of having to dig too deep in some places or of leaving the tile too close to the surface in others. Suppose in the last profile (391) the ditch was to be 500' feet longer and that in this 500 feet there had been 320 Ground Water, Wells and Farm Drainage. Digging Ditches. 321 a rise of but 6 inches. It is clear that to hold a single grade, making the upper end of the ditch 2.92 feet deep, would require a greater depth in other portions than necessary. But if the grade is changed at the 600 foot station so as to give a fall of 5 - ft " = .1 ft. per 100 ft. o a sufficient depth will be secured and labor in digging saved. FIG. f3y. Showing the ditching line and the commencement of digging. 393. Ditching Tools In digging a ditch it is a matter of first importance to have suitable tools ; and whatever else is 322 Ground Water, Wells and Farm Drainage. chosen the men should be provided with first class spades, kept sharp and free from rust. The spade which gives the best satisfaction has a long, thin, narrow and curved blade. The curvature is of first importance in giving greater stiff- ness and allowing the blade to be made thinner and lighter. The spade should be narrow and thin to enable the user to force it full length into the soil with the pressure of the foot and so as to be able to leave the bottom of the ditch narrow, removing as little earth as possible. In Fig. 131 are shown two forms of spades, four tile hoes, which are used in finishing the bottom of the ditch and removing the loose earth, and a tile hook, used in plac- ing the tile. The series of half tones shows these different tools in use. 394. Making the Ditch Narrow and Straight. To make the ditch straight a strong light line is stretched taut near the surface and 4 inches back from the edge. If the ditcb is to be only 2.5 to 3 feet deep it need be no wider at the top than one foot, as shown by the length of tile in Fig. 139. Where the ditch must be 4.5 to 5 feet and receive a 6 inch tile, as shown in Fig. 141, it must have a width at the top of 15 to 18 inches. The ditcher is trained to cut the walls straight with an even slope to the bottom so as to leave a straight line along the bottom to receive the tile. In Fig. 140 it will be seen that four men are working in line to complete the depth of the ditch which is 4.5 feet at the place. 395. Shaping the Bottom and Bringing It to Grade. In Fig. 141 the man in the foreground is using the tile hoe to clean out the last loose earth and to bring the bottom to grade and proper shape to receive the tile. The grade is secured by stretching the ditcher's line tight, and on the slant the bottom of the ditch is to be given, and at a known hight above it. It is then only necessary for the exper- ienced man to use a measuring rod to secure the depth and grade desired. Digging Ditches. 323 324 Ground Water, Wells and Farm Drainage. When the requisite skill and judgment have not been acquired for this work the man is provided with a meas- uring stick with a sliding arm which extends at right angles to the rod and long enough to reach the grade line. It is then only necessary to hold the rod or "ditcher's square" plumb to know whether the ditch has the depth desired. 396. Placing the Tile. When the ditch has been finished the tile are laid with the tile hook, as represented in Fig. 142. With the aid of this tool they are placed rapidly and accurately without getting into the ditch. Great care should always be taken to turn and shift the tile until a perfectly close joint is made all around. It does not do to simply have them meet on the upper edge, they should fit squarely and closely through the entire circumference and if necessary tile too much warped to permit of this must be discarded. Some prefer to place the tile with the hand, standing in the ditch upon them, covering them as rapidly as laid with 4 to 6 inches of earth, taking care to get it thoroughly packed and not to get the tile out of alignment. The greatest care should be exercised to pack the earth thoroughly about the joints so as to avoid large open cavities through which the water may rush during heavy rains, washing dirt into the tile. Tile laying should begin at the outlet of the main r pro- ceeding upward to the first lateral, where the junction should be made and tile enough laid in the lateral to per- mit the main to be partly filled. The main may then be carried on until the next lateral is reached, when this should be commenced as before. Care should be exercised not to leave the upper end of an unfinished line of tile open for heavy rains to wash mud into it. If the line cannot be finished before the rain the end may be guarded by closing it with a board, brick or bunch of grass. Digging Ditches. 325 21 326 Ground Water, Wells and Farm Drainage. Digging Ditches. 327 328 Ground Water, Wells and Farm Drainage. 397. Filling the Ditch After the tile have heen placed and covered with the first layer of earth the balance may be put in by any convenient method. A common and ex- peditious way is represented in Fig. 143 where a plow is drawn by a team attached to a long evener. For the finish- ing the ordinary road grader makes an efficient tool. Still another method is to use a light board scraper pro- vided with handles to be held against the bank of earth, which is drawn into the ditch by a team on the opposite side drawing from a rope and backing when the scraper is emptied. PRINCIPLES OF RURAL ARCHITECTURE, CHAPTER XVI. STRENGTH OF MATERIALS. A knowledge of the principles governing the strength of materials is helpful along many lines of farm practice and particularly in the construction of farm buildings. 398. A Stress. When a post is placed upon a foundation and a load of two thousand pounds set upon it the post is undergoing or opposing a stress of two thousand pounds. When a rope is supporting a load of one thousand pounds in a condition of rest it is subject to a stress of one thou- sand pounds. The joists under a mow of hay are subjected to a stress measured by the tons of hay which they carry. 399. Kinds of Stress Solid bodies may be subjected to three kinds of stress which tend to break them and will do so if the stress is great enough. These are : 1. A crushing stress, where the load tends to crowd the molecules closer together, as when kernels of corn are crushed between the teeth of an animal. 2. A stretching stress, as where a cord is broken by a load hung upon it. 3. A twisting stress, as where a screw is broken by trying to force it into hard wood with a screw-driver. 400. Strength of Moderately Seasoned White and Yellow Pine Pillars. Mr. Chas. Shaler Smith has deduced, from experiments conducted by himself, the following rule for 330 Rural Architecture. strength of moderately seasoned white and yellow pine pillars: Rule. Divide the square of the length in inches by the square of the least thickness in inches; multiply the quo- tient by .00 4 and to this product add 1; then divide 5,000 by this sum and the result is the strength in pounds per square inch of area of the end of the post. Multiply this result by the area of the end of the post in inches, and the answer is the strength of the post in pounds. In applying this rule in the construction of farm build- ings the timbers should not be trusted with more than one- fourth to one-sixth of the theoretical load they are com- puted to carry, because the theoretical results are based upon averages, and there is a wide variation in the strength of individual pieces. Table of breaking load in tons, of rectangular pillars of half seasoned white or yellow pine firmly fixed and equally loaded, computed from C. S. Smith's formula. si g-8 AS Dimensions of rectangular pine pillars in inches. 4x4 4x6 4x8 4x10 4x12 6x6 6x8 6x10 6x12 8x8 8x10 8x12 10x10 10x12 8. 10. . 12. . 14. . 16. . 18... tons 12 1 8.7 65 5.0 3.9 tons 18.1 13.0 9.7 7.4 5.9 tons 24.2 17.4 12.9 9.9 7.8 tons 30.2 21.7 16.1 12.4 9.8 tons 36.3 26.1 19.4 14.9 11.7 tons 44.5 31.6 27.2 21.7 17.7 14.6 12 2 10.3 8.8 tons 59.3 46.2 S6.3 29.0 23.5 19.4 16.2 13.7 11.7 tons 74.1 57.7 45.4 36.2 29.4 24.3 20. 3 17.2 14.7 tons 88.9 69 2 54 4 43.5 35.3 29.1 24.3 20.6 17.6 tons 101.7 84.2 69.7 57.9 48.4 40.8 34.8 29.9 25.9 tons 126.9 105.3 87.1 72 3 60.6 51.0 43.4 37.4 32.3 tons 152.3 126.3 104.5 86.8 72.7 61.2 52.1 44.8 38.8 tons 182.7 158.6 136.7 117.4 101.0 87.2 75.7 65.8 57.9 tons 219.2 190.3 164.0 140.9 121.2 102.6 90.8 79.0 69.4 20 22. 24.... In the application of the rule for the crushing load for posts in barn building the length referred to is the greatest distance between any supports which prevent the post from bending. 401. Bearings for Posts. In order that a post may carry its maximum load it is important that it rests squarely upon its support and that the load carried presses squarely upon the post. If the ends of the post are not square or if Strength of Materials. 331 the bearing is out of true so that the strain comes upon one edge the carrying power is greatly lessened. 402. Tensile or Stretching'strength of Timber. The ten- sile strength of materials is measured by the least weight which will break a vertical rod one inch square firmly and squarely fixed at its upper end, the load hanging from the lower end. Below are given the results of experiments with different varieties of wood, but the strengths vary greatly with the age of the trees, with the part of the tree from which the piece comes, the degree of seasoning, etc. Elm 6,000 Ibs American hickory 11, 000 Ibs Maple 10, 000 Ibs Oak, white aud rod 10, 000 Ibs Poplar 7, 000 Ibs White pine 10,000 Ibs per square inch, per square inch, per square inch, per square inch, per square inch, per square inch. 403. Tensile or Cohesive Strength of Other Materials. American cast iron 16, 000 to 28,000 Ibs. per sq. Wrought iron wire, annealed 30,000 to 60,000 Ibs. per sq. Wrought iron wire, hard 50,000 to 100, 000 Ibs. per sq. Wrought iron wire ropes, per sq. in. of ropo 38,000 Ibs. per sq. Leather belts, 1,500 to 5,0'JO, good 3,000 Ibs. per sq. Rope, manila, best 12, COO Ibs. per sq. Rope, hemp, bott 15,000 Ibs. per sq. neb. nch. nch. nch. nch. nch. nch. 404. Transverse Strength of Materials. When a board is placed upon edge and fixed at one end as represented at A, Fig. 144, a load acting at W puts the upper edge under a stretching stress. We know from experience that in case the board breaks under its load when so situated the fracture will occur 332 'Rural Architecture. somewhere near 5-6. Now in order that this may take place there must be, with white pine, according to (402) a tensile stress at the upper edge of ten thousand pounds to the square inch, and if the board is one inch thick the upper inch should resist a stress of 10,000 pounds at any point from 5 to 1; but we know that no such load will be carried at W. The reason for this, and also for its breaking at 5 rather than at any other point, is found in the fact that the load acts upon a lever arm whose length is the distance from the point of attachment of the load to the breaking point, wherever that may be, and this being true the great- est stress comes necessarily at 5. If the board in question is 48 inches long and 6 inches wide, it will, in breaking, tend to revolve about the center of the line, 5-6, and the upper three inches will be put under the longitudinal strain but, according to (402), ia capable of withstanding 3 X 10,000 Ibs. = 30,000 Ibs. without breaking; but in carrying the load at the end as shown, this cohesive power is acting at the short end of a bent lever whose mean length of power arm is one-half of 4-5 or 1.5 inches, while the weight arm is forty-eight inches in length. It should therefore only be able to hold at W 937.5 pounds, for we have 30, 000 X 1.5 = W X 48. whence W = ^^ = 937.5 Ibs. When a board, in every respect like the one in A, Fig. 144, is placed under the conditions represented in either B or C, Fig. 144, it should require just four times the load to break it, because the board is practically converted into two levers whose power-arms remain the same, but whose weight-arms are only one-half as long each. 405. The Transverse Strength of Timbers Proportional to the Squares of their Vertical Thicknesses. Common experi- ence demonstrates that a joist resting on edge is able to Strength of Materials. 333 carry a much greater load than when lying flat-wise. If we place a 2x4 and a 2x8, which differ only in thickness, on edge their relative strengths are to each other as the squares of 4 and 8, or as 16 to 64. That is the 2x8, containing only twice the amount of lumber as the 2x4 will, under the con- ditions named, sustain four times the load. The reason for this is as follows : In Fig. 145 let A represent a 2x4 and B a 2x8. In each of these cases the load draws lengthwise upon the upper half of the joist, acting through a weight- FIG. 145. arm F, W, ten inches in length, to overcome the force of co- hesion at the fixed ends, whose strength, according to (402) is ten thousand pounds per square inch, or a total of 2 X 2 X 10, 000 Ibs. = 40, 000 Ibs. in the 2 X * Joist, and of 2 X 4 XlO, 000 Ibs. = 80, 000 Ibs. in the 2 X 8 joist, These two total strengths become powers acting through their respective power-arms F, P, whose mean lengths are, in the 2x4 joist, one inch, and in the 2x8 joist, two inches. Now we have (531) PXPA = WXWA, and substituting the numerical values, in the 2x4 joist, we get 4X10,000X1 = or 4X10, 000 = 10W, and W = 4,000. 334 .Rural Architecture. Similarly, by substituting numerical values in the case of the 2x8 joist we get 8X10,000X2 = WX10, or 16X 10,000 = 10W, and W= 16,000. It thus appears that the loads the two joists will carry are to each other as 4,000 is to 16,000, or as 1 is to 4; but squaring the vertical thickness of the two joists in ques- tion we get, for the 2x4 joist and for the 2x8 joist 8X8 = 64; but 16 is to 64 as 1 is to 4, which shows that the transverse strengths of similar timbers are proportional to the squares of their vertical diameters. 406. The Transverse Strength of Materials Diminishes Di- rectly as the Length Increases. It will be readily seen from an inspection of Fig. 145, that lengthening the pieces of joists, while the other dimensions remain the same, lengthens the long arm of the lever, while the short arm re- mains unchanged; and since the force of cohesion remains unaltered, the load necessary to overcome it must be less in proportion as the lever arm upon which it acts is increased. Thus, if the 2x8 in Fig. 145 is made 20 inches long, we shall have, i PXPA = WXWA and by substituting the numerical values we get 80,000X2 = WX20 W = 8,000 instead of 16 ; 000 ; as found in (405). Strength of Materials. 335 C7. The Constants of the Transverse Breaking Strength of Wood. Since the laws given in 404, 405, and 406 apply to all kinds of materials, it follows that the actual breaking strength of different kinds of materials will depend upon the cohesive power of the molecules as well as upon the form and dimensions of the body which they constitute. The breaking strength of a beam of any material is always in proportion to its breadth, multiplied by the square of its depth, divided by its length, or Breadth X the square of the depth length and if the breadth of a piece of white pine in inches is 4, its depth in inches 10, and its length in feet 10, we shall have, taking the length in feet, 10 Now if we find by actual trial, by gradually adding weights to the center of such a beam, that it breaks at 18,000 pounds, including half its own weight, the ratio be- tween this and forty will be 18,000 -40- = 45 ' and as this ratio is always found for white pine, when the breadth and depth are taken in inches and the length in feet, no matter what the dimensions of the timbers may be, 450 is called its breaking constant for a center load. For other materials this constant is different, and has been determined by experiment and given in tables in various works relating to such subjects. The following are taken from Trautwine. 330 Rural Architecture. 408. Breaking Constants of Transverse Strength of Differ- ent Materials. WOODS. American White Ash 650 Ibs. Black Ash 600 Ibs. American Yellow Birch 850 Ibs. American Hickory and Bitter-nut 800 Ibs. Larch and Tamarack 400 Ibs. Soft Maple., 7:.0 Ibs. American White Pine 4.",0 Ibs. American Yellow Pino '.... 500 Ibs. Poplar S50 Ibs. American White Oak GOO Ibs. American Red Oak 8107 Ibs. METALS. Cast iron 1,5^0 to 2,700 Ihs. Wrought iron, bends at 1, COO to 2,000 Ibs. Brass Sodlbs. 409. To Find the Quiescent Center Breaking Load of Mater- ials having Rectangular Cross-sections, when Placed Hori- zontally and Supported at Both Ends. In placing joists and beams in barns it is important to know the breaking load of the timbers used. This may be determined with the aid of the following rule and the table of constants given in (408) : Rule. Multiply the square of the depth in inches by the breadth in inches and this by the breaking constant given in (408) divide the result by the clear length in feet and the result is the load in pounds. But in the case of long heavy timbers and iron beams one-half of the clear weight of the beam must be deducted because they must always carry their own weight. Square of ) depth [ X breadth in inches X Constant Breaking load = "inches) ^- r - T Length in feet. What is the center breaking load of a white pine 2x1 "2 joist 12 feet long? Strength of Materials. 337 Breaking -load = Yo ~ 10,8001bs. Da What is the breaking load for the same 10 feet long? 14 feet long? 16 feet long? 18 feet long? Solve the same prob- lems for other woods. 410. General Statements regarding the Quiescent Breaking loads of Uniform Horizontal Beams. If the center quiescent breaking load be taken as 1, then, when all dimensions are the same, to find the breaking load: (1) When the beam is fixed at both ends and evenly loaded throughout its whole length, multiply the result found by (409) by two. (2) When fixed at only one end and loaded at the other, divide the result obtained by (409) by four. (3) When fixed only at one end and the load evenly distributed divide the result obtained by (409) by two. (4) To find the breaking load of a cylindrical beam, first find the breaking load of a square beam having a thickness equal to the diameter of the log and multiply the result by the decimal .589. 411. Breaking load of Rafters. In finding the breaking load of timbers placed in an oblique posi- tion, as shown in Fig. 146, take the length of tl rafter equal to the hori- u FIG. 146. zontal span A, C, and pro- ceed as in (409) and (410). 412. Table of Safe Quiescent Center Loads for Horizontal Beams of White Pine Supported at Both Ends. In this table the safe load is taken at one-sixth of the theoretical break- ing load. This large reduction is made necessary on account of the cross-grain of timbers and joists and the large knots 338 Rural Architecture. which weaken very materially the pieces. Where a judi- cious selection is made in placing the joists, laying the in- herently weak pieces in places where little strain can come upon them, much saving of lumber may be made. KOOOOJ*. Depth in inches. Span 10 feet. Breadth. Span 12 feet. Breadth. Span 14 feet. Breadth. Span 16 feet. Breadth. 2 in. 4 in. 6 in. 2 in. 4 in. 6 in. 2 in. 4 in. 6 in. 2 in. 4 in. 6 in. Ibs. 450 1,008 1,800 2,808 4,050 Ibs. 240 540 960 1,500 2,160 Ibs. 1,0*0 1,920 3,000 4,320 Ibs. 720 1,620 2,880 4,500 6,480 Ibs. 200 450 800 1,250 1,800 Ibs. 400 900 1,600 2.50J 3,600 Ibs. 600 1,350 2,400 3,750 5,400 Ibs. 17;? 386 686 1,072 1,544 Ibs. 344 772 1,372 2,144 3,088 Ibs. 516 1,158 2,058 3,216 4.63J Ibs. 150 336 600 S36 1,350 Ibs. 300 672 1,200 1,872 2,700 fc 8.. 10.. Breadth. Breadth. Breadth. Breadth. 4 in. 10 in. 12 in. 8 in. 10 in. Ibs. 1,000 2,250 4,000 6,250 9,000 12 in. Ibs. 1,200 2,700 4,{;00 7,500 10,800 Sin. 10 in. 12 in. Sin. 10 in. 12 in. Ibs. 960 2,160 3,840 6,000 8,640 Ibs. 1,200 2.70U 4,800 7,500 10,800 Ibs. 1,440 3,240 5,760 9,000 12,960 Ibs. 800 1,800 3,200 5,000 7,200 Ibs. 688 1,544 2, 744 4,288 6,176 Ibs. 860 1,930 3,430 5,360 7,720 Ibs. 1,032 2,316 4,116 6, 432 9,264 Ibs. 600 1.3J4 2,400 5^400 Ibs. 750 l,6fcO 3,000 e!750 Ibs. 900 2,000 3,610 5,601 8,166 413. Selection of Lumber to Increase Carrying Capacity. It is possible to greatly increase the carrying capacity of a lot of joists or of a set of beams by giving attention to the lumber used, selecting the evidently strongest pieces for use where it is known the heaviest strains will come. Some- times a joist should be reversed or turned the other side up in order to enable the piece to render its highest service. In the arrangement of joists under a hay bay or granary, where heavy loads are to be carried, the cross-grained pieces and those with exceptionally large knots should be well dis- tributed among the stronger ones, making the evidently weak come between those evidently above the average in strength. 414. Braces There are two principles underlying the use of braces to give greater strength to lumber. (1) That of equalizing the load, making it fall more heavily upon Construction of Barn Frames. 339 the stronger members. (2) That of shortening the free span. The first case is illustrated in the rows of bridging used between the joists in a floor. In these cases when a weak member is bridged between two stronger ones a portion of its load, because it yields soonest, is thrown by the bridging upon the stronger, and stiffer floors are thus secured and the breaking of individual pieces prevented. Braces in nearly all cases are, in principle, either posts or else they are suspension rods which allow the strength of the material to be utilized unaffected by the principle of leverage, the stress being a direct pull or a push, bringing into play the full tensile or crushing strength of the ma- terial. To shorten the free span of an 18-foot joist or timber two feet at each end by means of suitable braces is in- creasing its carrying power 28.5 per cent. It is much more important to pay strict attention to these matters of strength at the present time than in former years both because lumber is higher and often of much inferior quality. 415. Constructing Timbers from Two-inch Lumber. It is often not only cheaper but better to construct 8x10 or 8x12 beams by putting together 2x10 or 2x12 plank, the timber thus constructed often being stronger than a solid one would be because weak places are more likely to be distributed so as to give a greater mean strength. It is of course not true that a 10x10 so made would be stronger than a solid timber of the same dimensions if both were of highest grade lumber. 416. Form of Barn Frame. During pioneer days, when, saw mills were none or few, it was much easier to secure the needed stability for a barn by hewing a few heavy timbers of suitable length and putting them together with braces than it was to use the 2 inch lumber now so common in the frames of dwelling houses. Since the old type of barn frame was depended upon to 340 Rural Architecture. give the needed stability, little or no support coming from the siding or sheeting, it was necessary to use large timbers FIG. 147. and to frame them, together and brace them very securely making a structure costly both in material and labor. 417. Plank Frame The high price of lumber has led to an effort to imitate the construction of the old hewn timber frame barn in the construction of essentially the same type of frame but using plank spiked together instead of tim- bers. This type of frame is represented in Fig. 147. The frame so made is strong and not as expensive as one of heavy timbers at the present prices but it is neither aa simple in construction nor as cheap as a frame for most barns can be made. Now that the conditions which made the heavy timber frame a necessity have disappeared there is no need of imitating it by splicing lumber. 418. Balloon or House Frame The reason for not ad- hering to the old type of barn frame is because it permits of no advantage being taken of the inherent strength of the Construction of Barn Frames. 341 siding and sheeting to give the barn its needed ability to withstand wind pressure. When the -two inch lumber used in the plank frame is treated as studding and the siding and sheeting are put on horizontally, and securely nailed, the whole covering of the barn then braces it from all sides and does double duty by largely dispensing with braces. To distribute the plank, using them as studding rather than building them into timbers forming bents, does not give them less power to withstand pressure from within or without and much less lumber, less nails and less labor are required. Where the building is long and broad so as to require the sides to be tied, bents may be used and made in the ordinary way except that less lumber need be used at the walls. 419. The Eound Barn Frame The strongest possible structure for a barn, with the least amount of lumber in its frame and the least special attention to bracing, is secured FIG. 148. Showing frame and general plan for a cylindrical barn. A. barn floor extending around the silo; B, hay bay; C, granary; and T, tool room. 22 842 Rural Architecture. when the barn is made cylindrical in form and the studding set upon the circumference of a circle as represented in Figs 148 and 149. In this type of barn not only is the smallest number of studding required to form the outer FIG. 149. Showing frame and general plan of a cylindrical barn. A, driveways behind cattle; B, feed alley; C, platforms for cattle. part of the frame but smaller sizes can be used, for the reason that every board in the siding is a portion of a hoop which makes spreading impossible, while at the same time they are arched against the wind and take its pressure with a crushing stress. With barns of this type 2x4 studding set 2 feet apart have ample strength for all diameters up to 40 feet and 2x6 studding is large enough for barns 40 to 100 feet in diam- eter. CHAPTER XVII. WARMTH, LIGHT AND VENTILATION. CONTROL OF TEMPEBATUBE. The life activities manifested in the animal body involve the continuous maintenance of a train of chemical changes which give rise to or maintain them. These chemical changes, like all others, can only begin at a certain tem- perature; below this they cease; within a certain range they go forward at normal rates; above this temperature reac- tions occur which interfere with the life activities, making them abnormal or causing them to cease. 420. Automatic Control of Temperature. The animal body is so constituted that within certain limits the normal temperature of the body may be maintained automatically, if only sufficient food is supplied. If outside conditions are such as to lower the temperature of the body the nervous system reacts, setting in operation a train of changes which evolve heat fast enough to meet the greater loss. If on the other hand the surrounding temperatures are too high and the body is becoming too warm the heat producing reac- tions are inhibited or perspiration is stimulated to reduce the too high temperature by bringing the blood to the skin, where the temperature may be lowered by the evaporation of water in the same manner that the wet bulb of a ther- mometer is cooled by the loss of heat which does the work of evaporation. 421. Normal Animal Temperatures. The normal temper- atures which must be maintained within the animal body 344 Rural Architecture. vary with different species of animals but among the warm blooded forms the range is not wide, as indicated in the table below. Horse 100.4F. tol00.8F. ) Cattle 101.8 to 102 Sheep 101.3 to 105.8 probably 103.8 to 104.4 Swine 100.9 to 105.4 Dog 99.5 tol01.7 Any marked departure from these temperatures in the animal body, either up or down, results in physiological disturbances which injure the health of the animal. 422. Best Stable Temperature. The data for a rational practice with reference to this point have yet to be de- termined experimentally. At present rules can be formu- lated only from general considerations. Since most of the bodily functions result in the genera- tion of more or less heat and since the temperature must be kept below 100 to 105 it is clear that no active animal should be surrounded by temperatures as high as the nor- mal temperature of the body. One of the main objects of .the circulation of the blood through the skin is to lower its temperature before it returns to the interior, so that those parts may be cooled. In our case we become uncomfortable in a surrounding temperature much above 72 and the same is true of our domestic animals. Stables should then as a rule have a temperature lower than 72 F. but how much must depend upon circum- stances. The right surrounding temperature is that which will permit the necessary loss of heat from the body with only the normal rate of perspiration. Reasoning from general principles it is to be anticipated that animals which are being fed heavily, like fattening swine, steers or sheep, as well as milch cows, will do better in somewhat cooler quarters because (1) the larger activity necessary to produce the extra assimilation desired would develop more heat which must be removed from the body, and (2) because the aim is to induce such animals to eat as Control of Temperature. 345 f ' much as they can convert economically into flesh and milk and warm quarters must make the demand for food less. It has been found with man that when fasting and at rest under a temperature of 90 F. he consumed 1,465 cubic inches of oxygen per hour, but under the same conditions except a temperature of 59 F. the amount of oxygen was 13 per cen^. greater and the amountof carbon dioxide given off also 13 per cent, greater, showing that a higher rate of consumption of food in the body was maintained and hence that the man would be required to eat more. " It is with the cow and fattening animals as it is with a threshing machine, it requires a higher rate of waste of energy, to run the machine rapidly than it does to run it slower, but the saving in time of all employed to manage the machine more than pays for the greater waste. So the cow may require an extra amount of food for temperature maintenance to overcome the cooler quarters but she is likely to eat enough more food to enable her to make more milk and a higher profit when all items of expense are taken into account. With animals on simply a maintenance ration the aim is to carry them with the least amount of food and hence in as warm quarters as will be healthful. It seems likely that the best temperature surroundings for animals being crowded will be found between 40 and 50 F. and for animals upon maintenance rations from 50 to 65 or even 70 F. 423. Heat-Proof Construction Impossible, To enclosure or building can be so constructed that all the heat it con- tains will be prevented from escaping. If it is kept above freezing through cold winters there must be within the en- closure a source of heat. So, too, no enclosure or building can be so thoroughly made as to exclude all heat and hence it is impossible to build a "cool room" which will not get warmer during the summer unless it contains some means of removing the heat which enters. The out-door root cellar which does not freeze during 346 Rural Architecture. the winter is prevented from doing so by the heat which enters it through the bottom. The same cellar during the summer grows gradually warmer as the season advances and is only relatively cool because part of the heat entering above is conveyed through the bottom into the earth, to re- store that which kept the cellar from freezing during the winter. The warm stable which does not freeze is kept so by the heat of the animals sheltered, and the warmly con- structed stable only makes less animal heat needed to main- tain the temperature ; the walls in themselves are not warm. So, too, no garment however made is in itself warm. We call it warm when the loss of heat through it is slow. 424. Means of Controlling Temperature. When it is de- sired to construct a room which will be warm in winter or one which will be cool in summer the same principles must be employed in each. In the first case it is desired to re- tain the heat produced in the room; in the second ca^e to prevent heat coming through the same walls, but from the opposite direction. To secure either of these ends two essentials of construc- tion must be observed. The walls must be as nearly air tight and as poor conductors of heat as possible. In i.. construction of a warm house, a warm stable, a cool ice house or a cool curing room for cheese the greatest attention should be paid to securing air tight walls because, no mat- ter how poor conductors are put into the walls, if there are cracks about doors and windows or open joints in the wall, the effect of wind pressure and wind suction will be tc change the air in the room so rapidly that it will be (diffi- cult to keep it either warm or cold. 425. Solid Masonry Walls. Stone basements with solid walls are sufficiently warm for stables but they are too good conductors of heat to be suitable for dwelling houses in cold climates where the inside temperature must be maintained at 72 F. Hollow brick walls, when plastered with a close textured mortar, through which air cannot pass readily, are Control of Temperature. 347 better than solid masonry but are not as warm as those well constructed of all wood and good building paper. An unplastered brick wall, or a brick wall plastered with coarse limie mortar only, is one of the poorest which can be used either to retain or exclude heat. Its pores are so open that the smallest wind pressure or wind suction causes a ready flow of air through every portion of the wall, changing the air of the room quickly. For cheese curing rooms, where the temperature is to be held down by means of cold air ducts, masonry walls, even when made air tight, are not suitable because they are such good conductors of heat and so massive that they tend to maintain a uniform temperature in summer somewhat higher than the mean of the air outside. 426. Hollow Masonry Walls. When stone or brick walla are made hollow they become much warmer in winter and cooler in summer than when built solid because the air is a much poorer conductor of heat. The thickness of the air space is not important and one-half an inch thick is prac- tically as serviceable as one of 6 inches. Where basement or semi-basement curing rooms for cheese are constructed the upper four feet of the wall should be made with a dead air space to prevent the heat of the warm soil as readily reaching the interior. So, too, in the case of dwelling houses in cold climates, whether they have cellars under them or not, it is important to make the upper 3 or 4 feet of the wall hollow for the reason that the cellar will be warmer and hence the floors under the living rooms above. 427. Brick Veneered Walls. Where brick are cheap and lumber high, walls made of 2x4 studding sheeted inside and outside with matched fencing and then veneered with brick make a very durable and warm building. The brick will not decay and the expense of nails and frequent paint- ing are avoided. It does not do to depend upon the brick for warmth, how- 34:8 Rural Architecture. ever; they simply take the place of the siding and paint. "Where the house is simply sheeted outside with common boards and veneered with brick, and then lathed and plastered inside, the building will be very cold because the wind will go easily through the brick and the cracks in the sheeting. i 428. All Wood Walls. For the construction of dwelling houses, cheese curing rooms above ground and ice houses there is no type of wall so effective and so cheap in first cost as the all wood wall where good building paper is used with the lumber. For a dwelling house a reasonably warm : wall is secured when the studding are sheeted outside and in with one layer of tongued and grooved fencing, covered outside with 2-ply acid and waterproof paper and lathed and plastered inside. The inside sheeting is warmer than back plastering and better because it gives a more solid wall, and lath may be used on it for furring. LIGHTING FAEM BUILDINGS. The lighting of farm buildings is required to secure three important objects: (1) facility in doing work; (2) needs of the animals housed, and (3) healthful conditions. In the dwelling house much care should be exercised to secure an ample amount of light in the kitchen, in the dining room and especially in the main living rooms. An abundance; of light is needed in the kitchen not only to facilitate the work but to make the best intentions and efforts toward cleanliness more certain. It requires an effort to be gloomy and feel ugly in the face of a hearty laugh, and a bright cheerful room has much the same effect upon those who occupy it. 429. Efficiency of Windows. There are many conditions which affect the efficiency of windows in lighting a build- Lighting of Farm Buildings. 349 ing. Trees or buildings near by, which cover a consider- able portion, of. the sky, may reduce the light entering a window very much. Much more light comes from the sky high- above the horizon than from low down and hence a porch over a window cuts out a very large share of the light which might enter it. Buildings which have thick walls require larger win- dows to- admit the same amount of light as would enter through windows in thin walls. Basement stables with heavy stone walls require larger windows because the walls are thick, and so with a brick or stone house. Windows long up and down admit much more light thafr windows of the same dimensions with their long axis horizontal because much more light comes from the upper portion of the sky. So, too, windows extending from near the ceiling toward the floor light the room better than when extending from near the floor up. 430. Position of Windows Living rooms and stables should if possible be arranged so that the body of light may come from the south side where the direct sunshine may enter the windows. In. a dwelling house in the win- ter this is very important because then the amount of light is smallest at best and the family must be more closely confined and therefore need the direct sun then most. For poultry and for swine south windows are specially de- sirable. Large windows at the south are not as objec- tionable for heat in summer as might at first be thought because the sun is so high that a large portion of the direct sunshine is reflected from the glass and prevented from entering the house ; but during the winter, when the sun is low, the advantage which comes from its heating effect as Well as the light is very considerable^ 50 Rural Architecture. VENTILATION OF FARM BUILDINGS. In the physiological sense air is as indispensable to the cow and horse as is water, grain, hay or grass] so, too, is it as essential to the development of power in the steam engine as is the water and the fuel. It is so abundant about us and we procure it usually so unconsciously that its necessity does not occur to us. But when large numbers of animals are housed together in close stables ample pro- vision must be made for the ingress and egress of air. 431. Necessity for Ventilation. The need of ventilating dwellings and stables grows out of several conditions: (1) The consumption of the oxygen which is the essential in- gredient; (2) the exhalation from the lungs of carbon dioxide, moisture, ammonia, marsh gas (C H 4 ) and organic matter; (3) the accumulation in the air of occupied stables and dwellings of bacteria and other micro-organisms as well as solid dust particles. 432. Carbon Dioxide in the Air. This gas is given off from the lungs with each respiration in nearly the same ratio that the oxygen is removed, hence air once breathed is not only deprived of a portion of its oxygen but it is di- luted with an equal volume of carbon dioxide and is there- fore rendered doubly unfit for use again. That air once breathed from the lungs is not suited to further use can be clearly and forcibly proved by filling a quart Mason jar with air from the lungs, by blowing through a rubber tube, and then quickly lowering a lighted taper into it, which is quickly extinguished, showing that the air has lost so much oxygen and gained so much carbon dioxide that the taper cannot burn in it. 433. Moisture from the Lungs and Skin. The moisture taken with the food and as drink must be again removed Ventilation of Farm Buildings. 351 from the body and a large portion of it leaves through the lungs and skin in the form of invisible vapor. If the air of a stable or dwelling is not changed with sufficient fre- quency it becomes so damp as to interfere with the proper action of the lungs and skin in this respect, and it is im- portant that the ventilation should be strong enough to prevent the air becoming too damp. One of the surest indications of an improperly venti- lated stable is the condensation of moisture on the walls, ceiling and floors. It is sometimes remarked that cement floors, and stone basements are objectionable because they "draw moisture," making the air damp. The truth is the stables are insufficiently ventilated and the moisture from the animals condenses upon the cement floor and stone walls simply because these happen to be colder. Instead of "drawing" moisture and making the air damp they have exerted exactly the opposite effect by condensing the moisture from the air, leaving it dryer than if the con- densation had not occurred. 434. Ammonia and Organic Matter Removed from the Lungs. When one passes from the fresh air into an occu- pied stable or room where the air has been rendered im- pure from imperfect ventilation a depressed feeling and offensive odor are recognized and sometimes this effect may be so strong as to produce nausea. When these odors and the odor of ammonia can be detected it is positive proof that the air needs changing more rapidly. Some of the organic matter given off from the lungs is strictly poisonous and so much so as to produce death in a few moments. If a live mouse is kept in a sealed pint fruit jar until it is nearly suffocated, as shown by its action, another mouse introduced into this jar will die at once, while the one which vitiated the air may be removed and it will apparently recover. It appears as if the organic principle eliminated from one animal is more poisonous when breathed by another, even of the same kind. 352 Rural Architecture. So poisonous is the organic principle removed from the lungs that Brown-Sequard in 1887 condensed the vapor of expired air and injected 15 cc. of it into a rabbit which died from the effects. Brown-Sequard considered the substance a volatile alkaloid secreted by the lungs. Water standing over night in a poorly ventilated room or stable comes to have a very disagreeable taste from the absorption of impurities from the air and this is one of the most serious objections to keeping water standing in the Btable for cows or other animals. 435. Micro-organisms and Dust in the Air It has long been recognized that the air of old and poorly ventilated houses, especially if they are not kept clean, contains many more dust particles, spores and micro-organisms than newer and better ventilated houses do. The same must be true also of stables but in a higher degree. The amount of dust and of organisms as well is almost always more abundant in occupied rooms than in the open air. This would be expected both because of the slowing down of air movements after entering the house, which acts exactly like a silt basin in a line of tile, and because of their production there from various causes. Strong ventilation tends to remove these organisms and dust particles with the air from the compartments and this is the rational basis for airing a bedroom or any other after sweeping. The air has been filled with both sets of impurities and opening the windows or using any other means of producing a strong current will help to clear the room. 436. Bad Ventilation Predisposes to Disease The most helpful health rule which man can adopt for himself or for his domestic animals is to avoid whatever tends to weaken the system and to take advantage of whatever tends to greater vigor. Ventilation of Farm Buildings. 353 It should be cleaily recognized that the germs of diph- rtheria, of tuberculosis, hog cholera and other contagious diseases are liable to be met with almost any day and in any place and that wherever a proper breeding place may be found the disease is liable to start and from it spread by force of greater numbers of germs. While therefore the micro-organisms usually found in greatest numbers in dusty houses and stables poorly venti- lated and cared for are not in themselves a source of dan- ger, the run-down, weakened condition which poor ventila- tion is sure to engender will certainly tend to start a case of contagious disease and then, with greater numbers of germs in the air to be introduced into the system, animals of greater vigor must succumb to these invisible foes be- cause of their vast numbers. Ample ventilation then should always be secured, first, as an indispensible condition for maintaining the power to resist disease, and second, in case of disease, to both clear the air and to give the animals an opportunity to defend themselves against this type of foe. 437. Amount of Air Respired. The amount of air ordi- narily taken into and put out of the lungs by man with each respiration is given by different observers as follows: Herbst 20 30 cubic nches Valentin 14 92 cubic Vierordt 10 42 cubic Coathupe 16 cubic nchea nches nchos Ilutchinson 16 20 cubic inches Average 15.2 46 cubic inches or an average of about 30 cubic inches. The amount of pure air which must be breathed in order to supply the oxygen needed by different animals, deduced from Colin's table, is given below: 154: Rural Architecture. ANIMAL. AIR BREATHED IN 24 HOURS. OXYGEN CONSUMED IN 24 HOURS. Per 1,000 Ibs. of weight. Per head. cu. ft. 425 3,401 2,*04 1, 10.J 726 24.84 Per 1,000 Ibs. of weight. Per head. Man cu. ft. 2,833 3,401 2, C0t 7,353 Ibs. 12.207 13.272 11 04 29.65)8 29.314 24.84 Ibs. 1 Ml 13 ^72 11 01 4.456 2.931 .075 Cow. 7,259 8,278 Hen. 438. Amount of Air Used Compared with Feed and Water. A 1,000-pound cow requires daily the equivalent of about 30 Ibs. of hay and grain and 70 Ibs. of water or, in round numbers, 100 Ibs. per head and per day of solid and liquid food. A cubic foot of air weighs about .08 Ibs. hence, from the table in (437), we have 2804 X -08 Ibs. = 224.32 Ibs. which shows that a cow needs to be supplied with twice the weight of pure air that she does of food and water com- bined. 439. Degree of Impurity of Air Permissible We are yet without sufficiently exact data to permit this problem to be concisely stated for stables used for domestic animals. In absence of exact data and in view of the unavoidable leakage of air through the walls and about windows and doors we have arbitrarily assumed that if the air is changed in the stable ait such a rate that it at all times contains no more than 3.3 per cent, of air once breathed fairly good ventilation would be provided. 440. Rate of Supply of Air to Stables. On the basis of (439) the number of cubic feet of air per head and per Ventilation of Farm Buildings. 355 hour, using the data in the table of (437), would be as stated below: For horses 4, 296 en. ft. per hour per head. For cows 3,542 cu. ft. per hour per head. For swine 1,392 cu. ft. per hour per head. For sheep 917 cu. ft. per hour per head. For hens 31.4 cu. ft. per hour per head. PIG. ISO. Simplest method of taking air into stone or basement stable. A B and A B show where the air enters. These flues may be made out of ordinary 5 or 6 inch stove pipe with elbow, or galvanized Iron conductor pipe, or the pipe through wall may be ordinary 5 inch drain tile, with stove pipe and elbow on inside, or the flue may be made of 6 inch fencing. The weights here assumed are 1,000 Ibs. for the horse and cow, 150 Ibs. for the hog, 100 Ibs. for sheep and 3 Ibs. for the hen. With different weights the amounts would change somewhat in proportion to the size of the animals. 441. Capacity of Ventilating Flues With the data in the last section, and the number of animals to be provided with air, the capacity of ventilating flues should be such as to ensure an air movement equal the rate given in the table of (440). It is practicable to construct ventilating flues through which the air from stables will travel at the rate of 200 to 500 feet per minute without mechanical forcing or the aid of heat, other than that derived from the ani- mals in the stable. With a ventilating flue 2x2 feet inside measure 20 cows would be supplied when the current in the flue was at the rate of 295 feet per minute. At this rate 40 cows would 356 Rural Architecture. need two flues 2x2 feet inside measure; 60 cows three; 80 cows four and 100 cows five. FIG. 151. Modification, of Fig. 150 where on the right a notch is left In the wall when building, so that the flue rises flush with tke inside of the wall. While on the left side the flue is shown built in the wall. This may be done by building around 5-inch drain tile or around a box made of fencing. 442. Cubic Feet of Space in Stable per Animal It haa been customary with sanitary engineers in planning hospi- tals, prisons, school rooms, etc., to allow so many cubic feet of space per occupant, but the number chosen has not FIG. 152. Method of taking air into a bank barn on the up-hill or bank sfde. The air flue is made In the same way as described in Figs. 150 and 151. but on the outside has its end covered as represented at A on the right with a length of 6 or 8 inch sewer tile with its top cov- ered with a cap of coarse wire screen. Drain tile would not answer for the outside exposure at the surface of the ground as frost would cause it to crumble. Wood could be used and replaced after rotting has occurred. been to supply the proper amount of air but rather to avoid drafts too strong for health and comfort. It should be distinctly stated that in matters of rentila- Ventilation of Farm Buildings. 357 tion it is cubic feet of air rather than cubic feet of space which should be provided, and in the construction of stables the amount of space need be only so much as is required to permit ample room and freedom to care for the animals. FIG. 15?. Two methods of ventilating a dairy barn. On the right the ven- tilating flue D F rises straight from the floor, passing out through the roof and rising above the ridge. One, two, or three of these would be used according to number of cattle. The flues should be at one or the other side of the cupola rather than behind it. On the left C E represents how a hay shoot may be used also for ventilating flue. In each of these cases the ventilating flue would take the place of one cow. This method would give the best ventilation but has the objection of occupying valuable space. C, in the feed shoot, Is a door which swings out when hay is being thrown down, but is closed when used as a ventilator, the door not reaching quite to the floor. To take air into this stable if it is built of wood with studding, openings would be left at A about 4x12 inches every twelve to six- teen feet, and the air would enter and rise between the sheeting of the inside and the siding on the outside, entering at B as repre- sented by the arrows. If the barn is a basement or stone structure the air intakes could be such as described in figures 150, 151. and 152. Twenty cows should not be housed in a space much less than 28x33 feet, with ceilings 8 feet in the clear. In warm climates there is no objection, except the matter of cost, to high stables, but where it is cold high ceilings per- 23 358 Rural Architecture. mit the warm air to rise so far above the animals as to leave the stable cold at the floor. 443. Forces Which Produce Ventilation. The movement of air currents into and from a ventilated stable is caused 1. By the wind pressure against the building tending to force air into the stable. 2. By wind suction on the leeward side of the stable tending to draw air out. 3. By aspiration across the top of the ventilator. 4. By the difference in temperature between the air in the stable and that outside. When the wind is blowing against a building there is an increase of precsure above that inside which forces air into the stable through any available opening and then out again on the opposite side or up the ventilating flue. At the same time there is a low pressure on the lee side which tends to draw air through any openings on that side. Where the ventilator rises above the roof as a chimney does the movement of air across its top produces a di- minished pressure and the air is aspirated out on the prin- ciple of the aspirator used on perfumery bottles. The difference of temperature causes a difference of pressure because of the expansion making the air in the stable relatively lighter than that outside; and the longer the chimney or ventilating flue the stronger will be the draft, both from difference of temperature and the aspi- ration across the top of the chimney. 444. Essential Features of a Ventilating Flue. A good ventilating flue must have all of the characteristics pos- sessed by a good chimney. It should be constructed with air-tight walls so that no air can enter except from the stable. It should rise above the highest portion of the roof so as to get the full force of the wind. It should be as nearly straight as practicable and should have an ample cross section. Stronger currents through the ventilators Ventilation of Farm Buildings. 359 will be secured by making one or a few large ones than where many small ones are provided, and it is usually best FIG. 154. Second best method of ventilating an ordinary barn. The air comes in as described in the other figures, and passes out through one or more ventilators rising against the side of the barn and pass- ing out through the roof, as represented at A C E. To make these flues if the barn is a balloon frame, the best method would be to secure the lightest galvanized iron in eight or ten foot lengths, and place the studding where the flues are to be, the right distance apart, so that a width of the metal covers the space between two studs. Sheets of this metal nailed on opposite faces of the stud would make an air-tight flue. On the outside, this metal would be covered with the siding. On the inside in the stable, with the sheeting, but in the barn above nothing would be needed except perhaps an occasional shield to prevent the hay from crushing it in. If it is not desired to carry the flues through the roof, they may end just below the plate, and the air pass out through the cupola. The method repre- sented, however, would give the strongest draft. The width of stud- ding used for the flue would vary with the number of animals to be provided for. to have as few as practicable and not leave the air impure in distant parts of the stable. 445. location of Ventilator. The best location for the ventilating shaft is near the center of the stable where 360 Rural Architecture. such a position will not interfere with the work. It is not of ten. that this position can be utilized, and when it can- FIG. 155. Modification of Fig. 157, where the air passes straight out through the 1'oof, instead of being carried in and out through the ridge of the roof. This method would give a stronger current, un- less the ventilator passes straight down to the floor between the cows, as represented in Fig. 153. not it may .be located in various places, as indicated in Figs. 153 to 160. 446. Openings to the Ventilator.- The ventilator should reach to the stable floor so that air may enter the shaft from that level. This is very important because: (1) The animals not only stand and lie low down but are so consti- tuted as to breathe the impurities directly to the floor where Ventilation of Farm B.iildings. 361 the carbon dioxide tends to remain, because it, is heavier than the rest of the air in the stable, even although its temperature is higher. FIG. 155. Represents a method of carrying the flues up the sides and then along undor the roof between the rafters, so as to reach the ridge either under the cupola, or at other places on either side. Such^a flue could be made very tight, by nailing the light galvanized Iron on the outside and inside of studding, and rafters, haying a sufficient width to give the proper capacity for the ventilating flues, and such a system of ventilation would work fairly well but could not be expected to do as effective service as the methods shown in Figs. 153, 154, 158 and 159. (2) The coldest air is at the floor and the warmest at the ceiling and it is the cold air which should be removed during the winter rather than the warm. There should be an opening provided at the ceiling for warm air to escape when the stable is too warm and when it is desired to force the ventilation at the expense of the heat developed by the animals. -'Both of these openings should bo provided with regu- lating valves so that either or both may be partly or com- pletely closed. 362 Rural Architecture. 447. Entrance for Fresh Air. When a stable has been made close and warm, requiring attention to ventilation, provision must be made for air to enter the stable as well as to leave it. This may best be done as represented in Figs. 150-153 and 158-1GO. IPlo. 157. Shows method of ventilating an ordinary barn, where the air is taken out of the stable through flues built between the studding and between the joists of the ceiling, the air then rising, through ventilating shafts, made against or as a part of one or more of the purliue posts. The air enters at A A and B, following the arrows and passing out along the lines C D E. These ventilators, if de- sired, can be carried out straight through the roof, or may be ter- minated inside under the purline plate, or as represented in the figure.' The cross section at the right shows how 2xl2's and 2x6's may be nailed together and placed so as to constitute a purline post, and at the same time a ventilating flue. The two sides of the purline post or ventilating flue are represented closed with sheets oZ galvanized iron. They may also be closed with well seasoned matched flooring. The number of bends necessary in this plan is an objection, as they interfere with the draft more or less. In all of these cases it will be noted that the fresh air enters at the ceiling. This is for the purpose of mingling it with the warmest air of the stable so as to raise its tern- Ventilation of Farm Buildings. 3G3 perature before it falls to the floor. In this way the heat which is wasting at the ceiling is saved and the animals are prevented from lying in cold air. Provision is further made for the air to enter the intakes outside at a distance of 3 or more feet below the ceiling so as to prevent the warm air being drawn out at these places by suction or to pass out directly as it would if they opened directly through the walls. These openings should be placed on all sides of the stable if possible so as to take advantage of the wind pres- sure at all times in increasing the draft. It is better to have many small openings than a few large ones because the cold air is better distributed, lessening drafts. 448. Construction of the Ventilators. The best form of ventilating flue is that represented in Fig. 160, made of galvanized iron in cylindrical form. Another good form is FIG. 158. Method of ventilating a lean-to stable. The air enters as rep- resented bv the arrows at A B and passes out through a flue built ou the inside of the upright or main barn. This flue may rise di- rectly through the roof or it may end at E as shown in the figure, the air passing through a cupola. If the upright barn has a bal- loon frame, then the space between the studding could be used as ventilating flues in the same manner as described in Fig. 154. These flues could be made tighter by covering inside and out on the studding, with the lightest galvanized iron. 3G4: Rural Architecture. represented in Fig. 157, where the sides are also made of galvanized iron. As a substitute for galvanized iron in this form of ven- tilating flue a good roofing paper may he used, such as the ruberoid roofing made by the Standard Paint Company. 449. Ventilation of Basement Stables. There is a general impression that basement stables are necessarily unhealth- ful. This idea has grown out of the fact that it has been possible to make these stables much closer and warmer than ordinary over-ground forms, and where ample venti- lation has not been provided they have been damp and close. FIG. 159. Method of ventilating a barn where a silo or granary occupies the central portion. The air enters at A B and the ventilating Hues are the spaces between the studding which form the walls of the silo, or other structure. The air entering at C in openings left all around the silo, and passing out at D at the top. Where basement stables are well lighted and properly ventilated there is no objection to them on sanitary grounds and they have many points in their favor where the conditions admit of their being easily constructed. Methods of introducing the air into these stables are repre- sented in Figs. 150 to 152. Ventilation of Farm Buildings. 365 ( 1 FIG. 160. Is a section of the cow stable of the dairy barn at the Wis- consin Experiment Station. A single ventilating flue D E rises above the roof of the main barn, and is divided below the roof into two arms A B D, which terminate at or near the level of the stable floor at A A. These openings are provided with ordinary registers, with valves, to be opened and closed when desired. Two other ventilators are placed at B B, to be used when the stable is too warm, but are provided with valves to be closed at other times. C is a di- rect 12-inch ventilator leading into the main shaft, and opening from the ceiling, so as to admit a current of warm air at all times to the main shaft to help force the draft. This ventilating shaft ia made of galvanized iron, the upper portion being 3 feet in diameter. The covering on the outside is simply for architectural effect. CHAPTEK XVIII. PRINCIPLES OF CONSTRUCTION. DELATION OF COVERING TO SPACE ENCLOSED. The first cost of a building, when expressed in terms of cubic feet enclosed, is influenced much by its relative di- mensions. 450. Relation of Walls to Floor Space. The form of floor space which can be enclosed by the smallest amount of wall is a circle, and Fig. 161 represents equal amounts of floor space enclosed by the circle, the square and the oblong. If the circle encloses a floor space of 1,600 square feet the length of the outside wall will be about 143.7 feet; the square would then be 40x40 feet and have 160 feet of out- side wall; w r hile the oblong would be 20x80 feet and have an outside wall of 200 feet. 144 ft. 100 ft 200 ft. FIG. 1C1. Shows equal areas enclosed by three types of walls. The square which encloses the same floor space as a circle requires 11.44 per cent, more wall, while the oblong whose length is twice the breadth requires nearly 40 per cent, more wall. This means that 40 per cent, more siding, more nails and more paint would be required to cover an Relation of Covering to Space Inclosed. 367 oblong building, where the length is twice the width, than would be required for a circular one enclosing the same floor space. Comparing the square with the oblong building it re- quires 25 per cent, less wall to enclose it. From these rela- tions it is clear that wherever it is practicable to avoid long narrow buildings there will be not only a saving in mater- ials but the buildings may more easily be kept warm in winter and cool in summer, and in the case of silos there will be less loss of silage. 1 COURT WALK tn 3*^3^ sTT TT MSSAfiC CUTTER S*" IT D^ GUTTER M Ul 1 < STALLS *&- STALLS 6KIO I STALLS ~B tad 9xi6 10 : 3X STALLS 12 FEED PASSAGE V D HARNESS Cf s SHOOTS M. HrORAKTS NAMES! GUTTER fr CUTTER S 51MLLS STALLS I 5* xbo BXIO I FEED PASSAGE UJ 1 - L 81 >X STALL (0 12 X 10 luo 2XIO 6|ciO| HA mas CUTTER PASSA&E -, FIG. 162. Showing the same conveniences in two types of horse barns. In Fig. 162 are represented two plans for horse barns providing nearly identical accommodations. The longer one is 105 feet 10 inches in length, 30 feet wide with 18 foot posts. The second is 75 feet 10 inches x 44 feet and re- quires over 8 per cent, less wall and over 6 per cent, less floor space. 451. Relation of Hight to Capacity In the building of barns, silos, ice houses, grain bins and root cellars the more depth or hight which can be secured the larger will 368 'Rural Architecture. be the capacity in proportion to roof, ceiling or floor. Tlio material for flooring and roofing a low building is usually no less than is required for a high building and yet the cubic contents are in the ratio of their depth. In the case of hay barns and silos the capacities increase much faster than the hight because with greater depth of material it is compressed and on this account greater stor- age capacity is secured. Total Ouhid( Surfaces. Excess of floor- space 15 789 SQ ft covered bu the' if n * n * ' -*_ no and Jjarn D ./6048 B. Z0210 C. Total floor-Space J\ 57365gfl; B 66/6 - * C 11732 - - D 1 3300 - '' JboveB 96 X 5 A 20 40X40 ZO C \/8X30 $0X30 ZO Fro. 163. Diagram showing the comparative outside snrfnce and_amonnt of floor space in four sets of barns represented in Figs. 1(51, 105, Ititi and 107. Relation of Covering to Space Inclosed. 369 FIG. 164. Cylindrical barn \vhicli accommodates 98 cows and 10 horses, contains a granary and tool house, each equivalent to a floor space 16x40 feet, aiid a 400-ton silo. FIG. 165. Buildings which shelter 37 cows and 15 horses. Eural Architecture. 452. Combined and Separate Construction. The amount of capital required to build and maintain in repair a large number of small buildings is greater than that required for a single consolidated structure providing like accommo- dations. This is clearly illustrated by the comparative chart, Fig. 163, which represents the relations of build- ings shown in Figs. 164, 165, 166, 167. Taking the cylindrical barn as a standard of compari- son, it provides shelter for 98 cows and 10 horses, contains a 400 ton silo, a granary 16x40 feet, a tool space 16x40 and storage capacity for all the hay needed; and yet its roof and side area is only 269 feet more than the group of buildings in Fig. 165, which shelters only 37 cows and 15 horses, has no silo, no tool house and not enough space for hay. FIG. 166. Group of buildings which shelter 114 cows and 8 horses. Comparing with the buildings of Fig. 166, their aggre- gate outside surface exceeds that of the standard by an Combined and Separate Construction, 371 area 64x64 feet and yet they provide cramped quarters for only 114 cows and 8 horses. FIG. 167. Group of buildings which shelter 144 cows and 14 horses with tool house and granary. In the group of buildings shown in Fig. 167, there is an aggregate outside surface exceeding that of the round barn by 140x140 feet, or more than twice, and they have less floor space by an area of nearly 40x40 feet, and the group of buildings shelters but 36 more cows and 4 more horses. In this last group the buildings are both low and narrow, causing extreme wastefulness of lumber. FIG. 168. Consolidated type of barn showing driveway to second and third floor. 372 Rural Architecture. 453. Saving of Labor. It is possible to care for animals with less labor and time where all are brought together under one roof than it is where they are scattered through many buildings and Figs. 164, 168, 169, 170 and^L71 rep- resent a consolidated type of barn with composite func- tions, where all of the stock are brought together under one roof. FIG. 169. Consolidated type of barn showing driveway to first and second floor. Economy in labor is of much greater moment than economy in material because the material simply repre- sents money invested in this case while the extra labor re- quired is a continual expense of a high order. 454. Distribution of Animals in Stables. The general arrangement of animals in stables must vary in detail in almost endless variety, and individual circumstances must determine just what is best. Three types of arrangement for cows are illustrated in cross-section in Figs. 150 to 159 under the chapter on ventilation, and Fig. 162 represents two convenient groupings for horses. While Fig. 170 shows one plan of division and arrangement of space in a cylindrical barn. Combined and Separate Construction. !73 ?' ' *V^ FIG. 170. Showing plan of the three floors of Figs. 168 and 169. FIQ. 171. Showing less consolidated type of barn with silo partly outside. 24 374 Rural Architecture. A combined cow and horse barn with silo outside has the arrangement shown in Fig. 172 and permits the work being easily done. 455. Avoiding the Use of Posts. In cow stables having a second story it will often be possible to carry the floor upon the uprights used to form the stalls or ties for the cows and in this way save lumber by making the same I j 1 1 ' i i i : ; HAY BAY \ 5 i i n 8Af>N FLOOR |_J-Avir enure f< i i *T3=t-* Aff/vrss r/osfrtr OS, ' HORSE STABLE A r^ r^ A '' rE ED ALLEY - | % r* 3 OX STALLS I f~E:CO ALLEY ,4 -. *f- ^ CLEANING ALLC1 MAfJURf 0/tOP 1 MAHG1 H n - rCO ALiCY E iMAMefft H FIG. 172. Plan of combined cow and horse barn with silo outside. pieces render double duty, and at the same time avoid the inconvenience of the posts and save the space they would occupy. This plan is illustrated in the various figures showing methods of ventilation. STABLE FLOCKS. 456. Essential Features The essential features of a good stable floor are: (1) Imperviousness to water and 'Stable Floors. 375 urine. (2) A surface sufficiently even to be readily and thoroughly cleaned with a small amount of labor. (3) A durability approximating that of the building itself. (4) FIG. 173. Rectangular barn showing driveways to second and third floors. A reasonably low first cost. There are two materials which have been used in the construction of stable floors which fulfill these requirements; they are concretes made either with Portland cement or asphalt. The asphalt is superior to the Portland concrete in being a poorer con- ductor of heat while the cement has the advantage of less first cost. 457. Cold and Warm Floors. It is urged against the con- crete as compared with wood floors that they are cold. The meaning is that they are better conductors of heat and so serve to carry the heat away from the body of the animal rapidly. It is true that they do convey heat faster than wood and when used in cold climates without bedding are worse than wood from this standpoint. They are not as bad in this respect, however, as many imagine. In the first place the stable ought not to fall below 40 F., and when 376 Rural Architecture. this is true the floor will only have this temperature and will not lead to inconvenience if other conditions are right. In the second place no animal should be required to lie FIG. 174. Rectangular barn with driveway to first and third floors. Same as Fig. 173. even upon a naked wood floor and when plenty of bedding is provided the cement floor is not too cold for warm stables kept clean. 458. The Use of Bedding. No farmer who is attempting to maintain the fertility of his land at the standard of best yield can afford to use no bedding or even a scanty supply. He can better afford to overfeed with hay so that the least nutritious portions are rejected and use this for bedding, than go without, because the extra amount of manure made and the greater comfort and cleanliness of his animals will pay a good return for it. The waste roughage of the farm, when used as bedding and mixed with the manure, in- creases the value of both because it increases the total quantity of manure so much that the fields can be dressed more frequently, thus holding the humus content higher Stable Floors. 377 and the soil in better tilth, both essential conditions for large yields. The liability of animals -to kick the bedding off from the floor is not a sufficient reason against cement floors. It is only when too little bedding is used or it has not' the right texture that the floor is left seriously exposed. 459. All Wood Floors. These floors are generally laid in one of two ways, either close upon the ground, nailed to stringers bedded in the earth; or else upon joists with an air space between the floor and the earth. When laid in either of these ways they are certain to wear out through the tramping of the animals and 'the use of the tools in cleaning the stables, but if conditions are favorable so that rotting does not occur they may last as long as 6 to 12 years. It is oftener true that wood floors give out from decay before they do from wear. Where the floor is kept con- tinually saturated with, moisture it will not decay; and when kept continually dry it gives out only through wear, but when it contains the right amount of moisture the growth, of moulds, causing the decay, takes place. When the floor is bedded in a close textured clay soil, where the subsoil is close and all the time saturated with water, decay will go on very slowly; but where the soil is dry and open, and especially if this is the character of the subsoil, decay may destroy the floor in 3 to 5 years. So, too, where the floors are laid upon joists on the ground and a dead air space left, beneath, decay is certain to occur in 3 to 5 years, but if the joists are so arranged that there is free circulation of air beneath, destruction from decay is not likely to occur. 460. Making Wood Floors Water Tight Wood floors are made so as: to prevent water from running through them by using more than one layer with some waterproof com- position between them. For heavy floors matched plank are laid and coated with a layer of coal tar roofing com- 378 Rural Architecture. position and then upon this a second layer of plank is laid, painting the joints with the same composition before drawing them together. Lighter floors are made in the same way, using tongued and grooved flooring. 461. Stone Floors. Thoroughly durable floors for cow and horse stables are made by bedding in clay rounded cobble stone, 4 or 5 inches in diameter, and using upon this an abundance of bedding. The uneven surface holds the bedding so well that the animals are fairly comfortable and neither wear nor decay will destroy them. The most serious objection lies in the difficulty in maintaining clean- liness. Where a good gutter is made behind the cows and a row of cut stone 10 or 12 inches wide are set for the hind feet to stand upon a durable and quite satisfactory floor is se- cured. 462. Macadam Stable Floors A floor more even in sur- face than (461) can be made out of carefully constructed macadam work, such as is used in making stone roads, giving it a thickness of 5 or 6 inches. Where this is used there should be provided cement gutters and mangers as represented in Fig. 175. FIG. 175. Shows method of making a macadam stable floor with cement mangers and gutters. Before laying such a floor the ground should be shaped and made thoroughly hard by tramping or ramming. The crushed stone should be put on in two layers, thoroughly compacting the first layer and filling the voids with screen- Cement Floors and Walks. 379 ings before the surface layer is made. Indeed the method should be the same as that followed in making a good stone road. 463. Macadam Surface for Barnyard The paving or flooring the barnyard with macadam surface is perhaps the best solution of the difficult problem of maintaining a hard dry yard. On account of the puddling of the soil by the tramping of feet, surface drainage is all thai: can be adopted and hence even when the yard has been macadamized it is necessary to scrape the manure into piles so that the water may flow away. CONSTRUCTION OF CEMENT FLOORS AND WALKS. 464. Kinds of Cement. There are two classes of cement on the market, Common and Portland. Of the common cements in the United States familiar brands are Akron, Louisville and Milwaukee. They are suitable for laying walls below ground and plastering cisterns but will not answer for stable, cellar or creamery floors, nor for walks, because they do not make a hard enough stone. For walks and floors some brand of Portland cement should be used. These are American, English or German according to the country in which they are manufactured. American brands are Vulcanite, Alpha, Atlas and Wol- verine. 465. Cement Concrete The making of cement concrete is in effect the production of artificial stone by binding to- gether pieces of rock and sand with Portland cement. The cement is too expensive to be used by itself for ordinary work and the making of cement concrete aims to produce the largest bulk of strong rock with the use of the least pos- sible amount, of the more costly cement. This is secured when only so much space is left between the materials bound together as will leave room for the cement to form 380 Rural Architecture. a thin laye,r between the faces of the fragments to be joined together. 466. Materials for Concrete Floors The materials used for cement walks and floors should be (1) as large, clean fragments of hard rock as can be readily mixed and worked into the forms and thickness of layer desired; (2) a finer grade of crushed rock or coarse clean gravel which will readily pack into the voids between the larger fragments ; (3) a clean, coarse, sharp sand to fill the pores between the fragments of gravel or fine screenings ; (4) enough Port- land cement to fill the space between the sand and bind the whole together; (5) and finally, water enough to wet all surfaces, fill the pore space of the cement and make the mortar plastic. 467. Presence of Earth, Loam or Dust. It is of the great- est importance that all of tli'e materials used be perfectly clean and free from dirt or other fine grained material having the texture of the cement itself. If a fine dust is present in the rock, gravel or sand it will tend to form a layer over the surfaces of the fragments which prevents the cement from coming in contact with the pieces which are to be cemented together and a weak concrete results. The fundamental is to have nothing but hard rock frag- ments large enough to be cemented together and nothing fine present but the cementing material itself. In the concrete pavements used on the streets of London, and which have a much longer life than the best paving blocks, great car"e is taken to wash out of the crushed granite and its screenings all dust particles before using them, although the dust may be from the granite itself. 468. Wetting the Crushed Rock Before Use. There are two important reasons why crushed rock or coarse screened gravel, to be used as the body of concrete, should be wet be- fore mixing with the cement. These are (1) to displnco as much adhering air as possible, and (2) so as not to draw Cement Floors and Walks. 381- out from the cement the water needed to maintain its plasticity and to assist in the setting. If the coarse materials are mixed with the cement dry a large amount of air will be set free and entangled in the concrete, which will prevent all spaces being filled, but the chief difficulty conies from the air preventing the cement from adhering to the surfaces. So strongly does air adhere to coarse sand that it must be boiled some time under water before it is all removed. 469. Ratio of Ingredients for Concrete. The amounts of each ingredient required to make a solid concrete with all spaces filled depends upon the pore space in the different materials. Trautwine assumes that for each ingredient the voids are near enough to 50 per cent, so that as a safe work- ing basis this should be taken. To make a cubic yard of concrete it would be necessary to use, on Trautwine's basis, Crushed rock. Gravel or screenings. Coarse sand. Cement. 27 cu. ft. 13.5 cu. ft. 6.75 cu. ft. 3.375 cu. ft . This ratio for pore space is certainly larger than is likely to occur and for farm purposes it will be safe enough to take the ratios of Crushed rock. Gravel or screenings. Sand. Cement. 27 cu. ft. 12.69 cu. ft. 5. 584 cu ft. 2. 122 cu. ft. These figures assume the pore space of the rock to be 47 per cent., of the gravel 44 per cent, and of the sand 38 per cent. 470. Ratio of Ingredients for Finishing. Where good plastering sand is used for making the finishing surface the pore space to be filled will be about 35 per cent, and this would require a little more than one of cement to two of sand, and unless there is some gravel or screenings to use with the sand it will be safer to make the facing 2 of sand to 1 of cement. 382 Rural Architecture. 471. Thickness of Floor. For most stables where the ground has been well firmed and shaped a thickness of 4 inches of concrete and one-half inch of facing will be enough; for house cellars and for the bottoms of silos 3 inches of concrete and one-fourth inch of facing will do. For creameries and milk rooms the concrete better be 4 inches and the facing a full half inch, made richer in ce- ment, in the ratio of one to one. 472. Making the Concrete The cement, sand and gravel are put together dry on a mixing board and thoroughly worked over, then enough water added to make a stiff paste. The right amount of crushed rock is thoroughly drenched with water and the whole mixed by shoveling until the rock is thoroughly incorporated with the cement. 473. laying the Concrete. The floor of the stable should first be given the proper form and very thoroughly tamped so that no settling shall occur after the floor is laid. The concrete should be laid in blocks four or five feet square, building alternate blocks first, Fig. 1Y6, so as to give time -.."-r^_- ^y*~*:~ _; " _,--_ ..-.rc\' FIG. 176. Shows method of laying cement floors in blocks to prevent cracking. for setting and prevent a strong union of the blocks. If the floor is not laid in this manner shrinkage cracks will occur. The concrete should be made only as fast as used Cement Floors and Walks. 383 and should be thoroughly rammed until the fine cement shows as a layer on the surface. After standing a short time, but before the concrete has set, the finisliing surface should be applied and thoroughly troweled until it is even and smooth. Fig. 1Y7 is- a cross section of floor and mangers. FIG. 177. Shows cross-section of cement stable floor with mangers and gutters. For a cellar or creamery floor, where it is desired to have a fine smooth surface, easily cleaned, after troweling, it may be wet with a whitewash brush and some pure dry ce- ment sprinkled over, which is troweled until it is hard, smooth and glossy. When the second series of blocks in a given, tier is made and the surface finished it is necessary to cut through the finishing layer exactly above the joint in the concrete, to prevent cracking, and then neatly round the joint. 474. Cost of Materials for Cement Floor. Taking mater- ials at the prices given and the concrete 4 inches thick, made in the proportions of (469) the cost per 100 square feet of floor, and the amount of materials will be as given in the table below : The floor made of wood 2 inches thick, laid upon 2x6's, 16 inches from center to center, would cost $4.12 or $4.95 per 100 square feet when the price is $15 or $18 per thou- sand. This makes the concrete 99 cents per 100 square feet more than the lumber, comparing the lowest prices in each case, and $1.72 more, comparing the higher prices. 384 Rural Architecture. Material required for 100 square feet of concrete floor 4 inches thick with one -half inch of facing. Material. Amount. Cost per 100 sq. ft. 1 23 cu. yds $ 80 per cu. yd $ 9S4 Sand and gravel Cement .73 cu. yds 3.76 cwt .50 per cu. yd. .365 1.00 per cwt. 3.760 Total 5.109 Crushed rock Sand and gravel 1.23cu. yds .73 cu. yds 3.76 cwt . . 1.00 percu. yd. 1.23 .75 per cu. yd. .55 1 30 per cwt. 4 89 Total $6.67 Where crushed rock cannot be had, but coarse gravel and plastering sand are available, a good floor can be made, but more cement must be used, usually 4 of sand and gravel to 1 of cement. TIES FOE CATTLE. The methods of tying cattle must vary widely with the taste and objects of the owner. The essential objects to be secured are: (1) comfort for the animals. This is neces- sary whether the main object is milk, breeding or beef ; (2) cleanliness, and (3) economy of time in tying and of space. 3E FIG. 17& Wilder swinging stanchion. FIG. 179. Scott self-closing swinging stanchion. 475. The Stanchion. There is no tie for cows, if we ex- cept -the plain halter or rope, which has been so universally Ties for Cattle. 385 used as one of the forms of stanchions represented in Figs. 178, 179 and 186. It is the simplest, cheapest and most expeditious tie invented and the swinging forms which per- mit the yoke to turn and to move a little back and forth provide a reasonable amount of comfort; and where the width of the platform is adapted to the size of the animal they secure as high a degree of cleanliness as is practicable. FIG. 180. Thorp stall. FIG. 181. Drown stall. 476. Adjustable Stalls. The four stalls represented in Figs. 180, 181, 182, and 183 are designed to give the cows the maximum amount of freedom of head movement but to force them to stand close enough to the gutter to prevent the platform being soiled. The manger or the head of the stall is made adjustable so as to crowd the cow back against the chain in the rear which confines her. Practically there is no form of tie which can prevent the cow from soiling the platform upon which she stands on account of the un- changable habit of shortening the body by humping the back when the evacuations occur. FIG. 182. Roberts stall. FIG. 183. Bidwell stall. 386 Rural Architecture. The two stalls, Figs. 184, 185, have been designed to se- cure cleanliness in spite of this habit. In the Newton tie it is expected that while the cow is standing the yoke to which she is tied will force her back sufficiently to prevent the difficulty. In practice, however, there is necessarily so FIG. 184. Knapp tie FIG. 185. Newton tie. much freedom at the neck that the object is not secured. The "Model tie" provides a bar on the floor, just in front of where the cow's feet are forced to be while standing and feeding, and which is so much of an obstruction that in order to lie in comfort she steps forward enough to He on the clean bedding. Fig. 186. Rigid stanchion. FIG. 187. "Model tie. Ties for Cattle. 387 477. Movable Halter Ties Another class of ties repre- sented in Figs. 188, 189, attempt to confine the cow in movements forward and backward by using a short chain which slides at the other end in such a manner as to per- mit freedom of motion up and down. FIG. 133. Chain tie. Fid. 189. Baker tie. 478. Tight Side Partitions. There is an effort among some feeders to prevent the animal from moving sidewise so as to interfere with the neighbor, either by stepping upon the feet or teats of the cow lying down or of taking the food from the manger. Where such provisions are insisted upon it should be kept in mind that anything which tends to enclose the cow, especially her head, in a tight box tends in a high degree to defeat the purposes of good ventilation by confining the air once breathed about the animal, hence such arrangements should be slatted or else open at the level of the floor. So, too, wherever box stalls are used these should be slatted or open at the bottom and not "boxes" as they too often are. 479. Tying for Feeding Only For calves, young cattle and feeding steers there is perhaps no mode of confining the animals in the stable so good as to give them complete freedom except at the time of feeding, using plenty of bed- ding on a cement floor which is cleaned as often as needful. 388 Rural Architecture. In such cases the stanchion 'tie is the best as everything is then reduced to the simplest conditions. 480. Mangers. One of the simplest mangers for feeding cows is represented in Fig. 177, and when made of cement as represented in the cut it is the best for feeding, cleaning and watering, where large numbers of animals are to be handled with the greatest economy. The manger should have an inside width of at least 2 feet, a depth of 8 inches and should have its bottom 3 or 4 inches above the plat- form upon which the cows stand. 481. The Manure Drop. This should have a width for adult cows not less than 18 inches and not more than 20 inches. Its depth next to the animals may be 8 inches and on the rear side 6 inches. These dimensions give ample capacity to prevent the walk behind from being soiled and make it easily cleaned. On some accounts a depth of 6 inches next to the cows and 6 inches in the rear is best; and where a wagon is driven behind "the animals to clean the stable a depth be- hind of only 4 inches gives less hight to lift the manure. PEOVISIONS FOK WATERING. Where there is a well of ample capacity, and 30 or more cows are kept, the best arrangement, everything considered is to pump the water from the well at the time it is needed. This plan provides water that is both fresh and natural temperature, and does away with expensive storage tanks. In case the power is pumping waiter faster than is needed it is a simple matter to provide an overflow, returning the water to the well. 482. Watering in the Barn. In climates having severe winters it is best, if practicable, to water the animals in the barn, and where a good fresh running stream can be Provisions for Watering. 389 maintained the ideal way is to have the water before the cows all the time so that it can be taken when desired. It is not desirable to keep water standing before the cows continuously as it is certain to become foul ; but it may be maintained during the greater part of the day if the drink- ing basins or troughs are emptied clean each evening. 483. Methods of Watering in the Stable. We have seen but two reasonably satisfactory methods of watering a large number of cattle in the stable, and these are either to clean the manger and run the water into that or else to have a special long watering trough used for that alone. FIG. 190. Simple arraiigement for watering cows in stable. The simplest arrangement of special trough is repre- sented in Fig. 190, and extends the full length of the stable, the water coming to it from above so that the supply pipe is entirely above ground where it can be gotten at and can be emptied at once after using. The trough is covered its entire length with a hinged lid, but in front of each cow the lid is cut so the cow can raise a section with her nose when drinking, letting it fall when she is through. 484. Storing Water in Tanks Where there is a basement barn the best arrangement for a storage water tank is a 25 390 Rural Architecture. cement lined cistern beneath the surface in the hill above the barn. Such a cistern is less expensive, is a permanent improvement and will keep the water warm and clean. We have seen cases where a satisfactory cement lined cistern is built entirely above ground and then covered in by grading a mound of earth about and over it sufficient to make it frost proof. Such a cistern should be provided with a man-hole so that it may be entered if necessary. 485. Watering Trough. Where stock is watered in the yard a good arrangement for winter, where the ground is porous, is represented in Fig. 191. The tank is a galvan- ized cylinder 3 or more feet in diameter and 5 feet deep which stands in a dry well 15 or more feet deep and so ar- ranged that the warm air from the bottom of the well all the time surrounds the tank and keeps it from freezing. Water may be pumped into this direct or it may be sup- plied from the bank cistern. When it is necessary to empty the tank the plug can be removed and the water al- lowed to drain into the dry well. FIG. 191. Representing a storage reservoir and drinking tank arranged to avoid freezing. It is of course important to provide a warm jacket about the tank and cover, as represented, so as to assist in keeping the water warm. Arrangements for Unloading Hay. 391 ARRANGEMENTS FOR UNLOADING HAY. 486. Unloading Direct from Wagon. Where the hay is not to be lifted and can be rolled directly from the wagon with the fork into the bay, there is no simpler and more ex- peditious way ; and where the load can be driven to the top of the barn, as represented in Figs. 168, 171 and 173, there is little need of other mechanical arrangements. Fio. 192. Curved track and hay carrier for use in cylindrical barn. 487. Unloading Hay in Cylindrical Barns. Where the cylindrical type of barn is used there are two methods of distributing the hay; (1) that represented in Fig. 192, where an ordinary hay carrier is moved over a curved track and (2) that represented in Fig. 193, where an ordinary hay carrier delivers the hay upon a central inclined plat- form, which is turned about by the operator in the bay so as to deliver the hay at any desired point. 488. Tilting Hay Distributor. It is possible to take ad- vantage of the principle illustrated in Fig. 193 for distrib- 392 Rural Architecture* FIG. 193. Ordinary hay r-nrrier nn.64 97.23 102.6 108.1 113 7 119.4 124.9 135.9 103.6 109.8 115.8 122.0 128.3 134.8 141.1 147.8 116.1 123.0 129 8 136.8 143.9 151 1 158.2 165.7 129.3 137.1 144.7 152.4 160.3 168.4 176.2 184.6 143.3 151.9 160.3 168.9 177.6 186.6 195.2 201.6 158.0 167.5 176.7 186.2 195.8 205.7 215.3 225.5 173.4 183.8 194 201.3 214.9 225.8 236.3 247.5 189.5 200.9 212.0 223.3 234.9 246.8 258.2 270.5 206.4 218.8 230.8 243.2 255.8 268.7 281.8 294.6 223.9 237.4 250 5 263.9 277.6 291.6 305.1 319.6 242.2 256.7 270.9 285.4 300.2 315.3 330.0 345.7 In this table the horizontal lines give the number of tons of silage held by a silo having the depth given at the left of the column. 527. Horizontal Feeding Area In the construction of silos it is very important to have the horizontal dimensions such that the rate of feeding shall be rapid enough not to permit moulding to occur on the exposed or feeding sur- face. It is also important to have the horizontal dimensions as large as possible because the larger the silo is the less it costs in proportion to the feed it stores. Then, too, narrow, small silos do not allow the silage to settle as well, and hence in them the necessary losses are proportionally greater than in the larger ones. 426 Rural Architecture. Observations indicate that if silage is fed down at a rate slower than 1.2 inches daily, moulding is liable to set in. This is more likely to be true in the upper half of the silo than in the lower half but it will be prudent to have the silo of such a diameter as to lower the surface more rapidly in feeding than is necessary rather than less rapidly. A silo 30 feet deep will allow 1.5 inches in depth of silnge per day for 240 days, and one 24 feet deep will allow 1.2 inches for the same time. From the table on page 424 it v/ill be seen that the mean weight of silage per cubic foot for a silo 30 feet deep is 39.6 Ibs., and allowing 40 Ibs. of silage per cow per day it is seen that a cubic foot of silage on the average will feed a cow one day. But from the same table it will be seen that if the silo is 24 feet deep there will be required 1.114 cubic feet of silage to give the desired weight. Table giving the inside diameter of silos 24 feet and 30 feet deep which will permit the surface to be lowered in feeding at the mean rate of 1.2 to 2 inches per day, assuming 40 Ibs. of sil- age to be fed to each cow daily. FEED FOR 240 DATS. FEED FOR 180 DATS. Silo %lt feet deep. Silo SO feet deep. Silo Ufeet deep. Silo SO feet deep. No. OP Cowa. Rate 1.2 in. daily. Rate 1.5 in. daily. Kate 1.6 in. daily. Rate 2 in. daily. Tons. Inside diameter. Tons. Inside diameter. Tons. Inside diameter. Tons. Inside diameter. 10. 48 ft. in. 11 11 48 ft. in. 10 2 36 ft. in, 10 4 36 ft. in. 8 9 15. 72 14 7 72 12 5 34 12 8 54 10 9 20. 96 16 10 96 14 4 72 14 7 72 12 5 25. 120 18 10 120 16 90 16 4 90 13 10 30. 144 20 8 144 17 6 108 17 10 108 15 2 33. 188 22 4 168 18 11 126 19 4 126 16 4 40. 192 23 10 192 20 3 144 20 8 144 17 6 45. ' 216 25 7 216 21 5 16i 21 11 162 18 7 50. 240 26 8 210 22 7 IfO 23 1 JM) 19 7 60. 2S8 29 2 tea 24 9 216 25 3 216 21 5 70. auj al 6 3H6 26 9 w 27 4 252 23 2 80. Ml 33 8 3M 28 7 288 29 2 '288 24 9 90. cn 35 9 * 30 4 324 30 11 324 26 3 100. 480 37 8 460 31 11 3CO 32 8 2CO 27 8 Danger in Filling Silos. 427 Using these data the inside diameter of cylindrical silos 24 feet and 30 feet deep which will hold feed enough for different numbers of cows may be computed and such re- sults are given in the preceding table. 528. Danger in Filling Silos. It never should be forgot- ten in connection with the filling of silos, that carbon diox- ide is generated very rapidly the first few days after sil- age is put into the silo, and it sometimes happens if the air is very still over night, and if the surface of the silage is a considerable distance below any door, that carbonic acid accumulates in sufficient quantity over the silage to make it impossible for a man to live in it. Cases are on record where people have been suffocated by going into a silo under these conditions. If the doors in a silo are so close together that a man standing on the silage will have his head above an open door the carbonic acid gas will flow out of the door and not accumulate to such an extent as to be injurious. In cases where the silage is below any opening far enough to leave a man's head below the opening care should be taken not to go into the silo in the morning after filling has begun until after the machinery has been started. After the silage has been dropping into the silo for a few minutes it will stir the air up sufficiently to render it pure enough for a man to work in it without danger. Ordinarily the air currents outside are sufficiently strong to prevent the car- bonic acid from accumulating, but it should be kept in mind that it is possible on still nights for this accumula- lation to take place. PARM MECHANICS. CHAPTEE XX. PRINCIPLES OF DRAFT. If it were possible to construct a perfect road its length would be the shortest distance between the places con- nected, and it would offer no resistance to movement over it. A pair of parallel, level, smooth and rigid steel rails, well bedded, constitutes the nearest approach to the perfect road yet devised, and how vastly superior the steel track of the railroad is to the best paved street is shown by the enormous loads moved and high speed attained over them. 529. How the Draft Increases With the Grade. A pull of 2,000 Ibs. is required to lift a ton vertically, but to simply move it horizontally only the friction of the carriage and the resistance of the air need be overcome. The more nearly level that roads are built, therefore, the heavier and the faster may loads be moved over them. If the road- bed rises one foot in 100 feet it is said to have a one per cent, grade, and this amount of slope will increase the draft one per cent, of the weight of the load over what it would be on the same road-bed level. A two per cent, grade rises two feet in every 100 feet and the draft is increased by it two per cent, of the load ; a ten per cent, grade rises ten feet in every 100 feet and will increase the draft of a ton 200 Ibs. over what it is on a level road of the same char- acter. The heavier the loads to be moved, therefore, the Influence of Grade on Draft. 429 more objectionable becomes any grade in the road. This is why with all railroads the heavier their freight the more they overhaul their tracks and lower the grade. FiU. 200. Apparatus for demonstrating the Influence of different grades and of obstructions on the draft of wagons on roads. 530. Experimental Demonstration of Influence of Grade on Draft. In Fig. 209 the steel bar may be set so that it represents any grade from one to twenty per cent., and by setting the road-bed at these different grades the spring balance shows the force necessary to sustain the load in the several cases. If the load with the carriage is made equal to 60 Ibs. then the scales will read .6, 1.2, 1.8, 2.4, etc., up to 12 Ibs. for the 20 per cent, grade. If now the 430 Farm Mechanics. road-bed is set for a 10 per cent, grade and then the load, including the carriage, varied it will be found that the draft on the scale will be always 10 per cent, of the load. 531. The Mechanical Principle Involved in the Relation of Draft to Grade It is a general truth or principle in over- coming any resistance or in doing work of any kind that the force or power doing the work, when multiplied by the distance through which it moves, is always equal to the re- sistance or work multiplied by the distance through which it is moved. Stated mathematically the equation stands Power X Power Distance = Weight X Weight Distance or P. X P. D. = W. X W. D. Suppose the road-bed in Fig. 209 has a length of 100 and the grade is 10 per cent., then if a load of 60 is drawn along the length of the road the power will have passed over a distance of 100, acting parallel with the road-bed, but, leaving friction out of consideration, the work done is to lift the load vertically through a. distance of only 10, and since the distance which the weight is raised is only i^of that over which the power has acted it is only neces- sary that the power shall be A of the weight or P. X P. D. = W. X W. D. P. X 100 = 60 X10 whence 100 P. = 600 and Power = 6 Ibs. 532. The Steepest Grade Admissible When it is asked what is the steepest grade which should be permitted on a given road there are many factors which must be consid- ered, but the most general rule is to make the grade as small as practicable on roads where horses are expected to carry all they can well handle on good, nearly level roads, and Influence of Grade on Draft. 431 the better the level part of the road, the longer the haul and the more teams to pass over it, the less steep should the grade be. On all well designed roads a great effort is usually made to keep below a rise of seven feet in 100 feet. Just why low grades are so necessary will be readily understood from the following considerations : About the maximum walking draft of a horse on a good level road is measured by one-half his weight. Trials have shown that a 1,634-lb. horse can exert a steady pull of 800 Ibs. while walking 100 feet, and that an 836-lb. horse may maintain through the same distance a steady draft of 400 Ibs. It would not be safe, however, to repeat such strains often nor maintain them long. Even a draft equal to one-fourth the weight of the animal is a heavy and ex- haustive pull. Indeed a steady pull equal to one-tenth of the weight of the horse for a ten-hour daily service at the walking pace of 2.5 miles per hour is an average of effect- ive service and the work of a 1,000-pound horse would equal _ 2TT p 60X33,000 Taking this as the safe rate of work for a team on the road an 800-pound horse may pull steadily 80 Ibs. ; he may pull over hills at the rate of 200 Ibs. and in emergencies 400 Ibs. A 1,600-pound horse at the same rating may pull steadily 160 Ibs., up hills 400 Ibs. and in an emergency 800 Ibs. It has been found that to move a gross ton over a good level dirt road requires a traction of about 140 Ibs. A team of 800-pound horses may therefore come to a hill with a load of 160 r-Tjr tons = 2, 285f pounds. LiU Up how steep a grade may such a team carry this load with a steady exertion of 200 Ibs. per horse? To over- 432 Farm Mechanics. come the resistance the road-bed offers to the load requires a steady pull of and this leaves the reserve draft to go up the grade (200 X 2) 160 = 240 The load to be carried up the grade is the weight of the team plus that of the load or (800 X 2) + 2, 285f = 3, 885f Ibs. Up how steep a grade will 240 Ibs. carry 3, 8851 Ibs.? Solving this problem by applying the principle of (531) we shall have P. X P. D. = W. X W. D. or 240 X 100 = 3, 885f X W. D. t\A 000 whence W. D. = -^ = 6.176 or Oj OOOrj.- a rise of about 6.2 feet per 100 feet, which is a 6.2 per cent. grade. By taxing the team to its utmost capacity its effective power to ascend the grade would be (400 X 2) 160 = 640 Ibs. Proceeding as in the other case we shall have P. X P. D. = W. X W. D. and 640 X 100 = 3, 885f X W. D. whence W. D. = = 16 - 47 or about a 16.5 per cent, grade. That is, a grade of 16.5 feet in 100 feet is the steepest dirt road a team can be ex- Influence of Grade on Draft. 433 pected to carry the load over which it was able to bring over a level dirt road to it. These results have been computed from the standpoint of an 800-pound horse, but since the ability of a team to work is in a general way proportional to its weight the same results would have obtained had we taken the 1,600- pound horse with a proportional load. 533. Good Roads Make High Grades More Objectionable. When the good macadam road-bed is substituted for the common dirt road then the same draft, 140 pounds, which draws a ton on the dirt road will draw 140 -?-- = 2J times as much or 4, 666| Ibs. = 2 tons. on the level macadam road. Since it requires but 60 Ibs. to move a ton on a macadam road the team may come to the hill with a load of 1RO ~ = 2f tons = 6,9331 iba. \J\) The effective power of the team will be 400 160 = 240 Ibs. Up how steep a grade will 240 Ibs. carry the team and 2f tons? Solving this as we did the other we get 240 X 100 = 6,9331 X W. D. 94 000 whence W. D. = = 3.46 or a little less than a 3.5 per cent, grade. That is to say, when a dirt road is improved so as to reduce the draft from 140 Ibs. per ton to 60 Ibs. per ton then, in order to utilize this improved road with equal effectiveness under the con- ditions assumed, the 6.2 percent, grade should be reduced to 4 per cent. ; and the highest grade could not exceed 9.23 per cent. 434 Farm Mechanics. DKAFT OF W4GONS ON THE LEVEL. There are many factors which modify the draft of a wagon over a level road and some of the most important of these are : 1. Smoothness of the road-bed. 2. Rigidity of the road-bed. 3. Width of the tire. 4. Diameter of the wheel. 5. Distribution of the load on the^carriage. 6. Direction of the line of draft. 7. Rigidity of the carriage. 534. The Smoothness of the Road-bed. When the road- bed is not smooth and has numerous ruts, stones or other obstructions upon its surface, the draft of the load is in- creased and the wear on the vehicle and on the road-bed is also greater so that much effort and care should be ex- ercised to have the road smooth. The increase in the mean draft of the load is not so great, however, as the other difficulties which result for the reason that when the wheel enters a rut or passes down off from an obstruction there is a push forward which tends always to give back a portion of the energy expended in raising the load upon the ob- struction or out of the rut. 535. Rigidity of the Road-bed. A yielding road-bed ia perhaps the most serious defect of roads, and the one which increases the draft more than any other. If a wheel is steadily cutting into its road-bed it is continually tending to rise over an obstruction or out of a rut, or it is doing what is in effect all the time passing up a grade, as repre- sented in Fig. 210, the hill being steeper in proportion as the wheels are smaller. In Fig. 209 is represented a method of measuring the in- crease in draft due to the wheel rising over an obstruction who'se hight is a stated per cent, of the radius of the wheel. Draft of Wagons. 435 The arrangement at C is provided with a screw and gradu- ated so that the block may be raised or lowered at will, setting it so as to represent the wheel passing over an ob- struction, 3, 4, 5, etc., per cent, of the radius of the wheel. By setting the road-bed inclined as shown in the figure, the draft is first noted and then the thumb screw at D is turned until the wheel rises upon the block and the difference be- tween the two readings of the scale expresses the increased draft due to the obstruction. FIG. 210. When the obstruction is only four per cent, of the radius of the wheel the draft is increased more than two-fold. That is to say, if a wheel is 48 inches in diameter, an ob- struction of four per cent, would be only .96 of an inch, and yet the draft is made by it more than twice as heavy. When the wheel cuts in one inch the draft would not in- crease quite so much because the wheel never rises quite out of the rut, but the difference between the draft on the macadam and dirt road is due mostly to the difference in the yielding, or cutting in of the wheels. An experiment conducted by the United States Depart- ment of Agriculture, testing the draft of ordinary wagons on a steel wagon road, showed that a single small horse 43 G Farm Mechanics. easily drew 11 tons, or 22 times the weight of the- animal, and it is stated in the report that the horse could readily have hauled 50 times his own weight. This would be, for a 1,000-pound horse, 25 tons, but of course with such a load the road must be practically level, for a grade of one per cent, would increase its draft 500 pounds. 536. Draft of Wagon Shown by English Trials The power required to draw a four-wheeled wagon over roads of different characters has been tested and the following expresses the results in pounds per 2,000 Ibs. of gross load: On cubical block pavement 28 to 44 Ibs. per ton On macadam road 55 to 67 Ibs. p( r ton On gravel road 75 to 140 Ibs. per ton On plank road 25 to 44 Ibs. per ton On common dirt road 75 to 224 Ibs. per ton 537. Draft With Different Widths of Tire Prof. J. H. Waters 1 has made an extended series of trials to test the effect of the width of tires on the draft of loads under dif- ferent conditions of road. He used always a net load of one ton, but the 6-inch tired wagon was 245 pounds haavier than. the 1.5 inch, making the gross loads 3,225 and 2,980 pounds respectively, when the wagons were free from mud. The following are his results: On macadam streets, wide tire 26 per cent, less than narrow tire. On gravel road, wide tire 24.1 per cent, less than narrow tire. On dirt roads, dry, smooth, free from dust, wide tire 26.8 per cent, less than narrow tire. On clay road, with mud deep, and drying on top and spongy beneath, wide tire 52 to 61 per cent, less than narrow tire. On meadow, pasture, stubble, corn ground and plowed ground from dry to wet, wide tire 17 to 120 per cent, less than narrow tire. On the other hand he found that when the roads were covered with a deep dust, or with a thin mud but hard be- low, the narrow tired wagon gave the lightest draft. Also when the mud was thick and so sticky as to roll up on the wheel, loading it down, and again when narrow tired wagons had made deep ruts in the road which the wide iBull. No. 39, Missouri Agr. Exp. Station. Draft of Wagons. 437 wagon tired wagon tended to fill up, the narrow wheeled gave the lightest draft. 538. Size of the Carriage Wheel It is plain from what has been said, that on yielding road-beds the draft must necessarily be heavier, other things being the same, the smaller the wheels of the vehicle. This must be so both because small wheels present less surface to the road-bed to sustain the load, and because when the wheel has de- pressed the surface it must move its load up a steeper grade than the large wheel. It follows also from these state- ments that wagons with small wheels must be more de- structive to the road itself, whether this be of dirt, gravel, stone or iron. Some unpublished data bearing upon this point are given here by permission of Prof. T. J. Mairs of the Agr. Exp. Staflon, Columbia, Mo. Wagons with three sizes of wheels were used in these experiments : 1. High, 44 inch front wheels and 56 inch hind wheels. 2. Medium, 36 inch front wheels and 40 inch hind wheels. 3. Low, 24 inch front whesls and 28 inch hin J wheels, all having tires 6 inches wide. The total load including the wagon was : For 1, 3,T62 ; for 2, 3,580, and for 3, 3,362 pounds. The drafts in his trials are stated in the table below : Description of Conditions. High wheels. Medium wheels. Low wheels. Dry gravel road; sand 1 inch deep; some small, loose stones Lbs per ton. 34.48 Lbs. per ton. 90.45 Lbs. per ton. 110.2 Gravel road up grade 1 in 44 ; covered with one-half inch wet sand ; frozen beneath 123.0 132.1 173 1 Dirt road frozen ; thawing one-half inch ; rather rou^h ; mud sticky 100.6 119.2 139.1 Timothy and blue grass sod, dry, grass cut 131.9 145.2 178 8 Timothy and blue grass sod, wet and spongy 172.9 202 6 281.1 Cornfield, flat culture, with spring-tooth cultiva- 178 5 201 2 265 ' Plowed ground not harrowed, dry and cloddy 252.5 302.8 373.6 .28 438 Farm Mechanics. For use on the farm the advantage of truck or low wheels comes in the saving of labor in high lifts in placing manure and other materials upon the wagon, and here a sacrifice of strength of the horse may advantageously be made to save that of the man. A lighter draft and lower lift in handling loads are secured by using the low down carriage bed in the upper part of Fig. 211, than are possi- ble with the very low wheeled wagons shown in the same cut. 539. Distribution of Load on the Carriage. When there is nothing to prevent doing so, the load carried by the wagon should be so distributed upon the wheels as to be di- vided proportionately to the surface the wheels present to the ground, and when the front wheels are smaller they should carry a smaller load. When care is not exercised FIG. 211. in this matter there is danger, especially on soft roads and in the field generally, of very materially increasing the labor of hauling. When the load is heaviest on one side the wheels of that side are unduly depressed, thus increas- ing the draft. The tilting of the wagon in this way throws Draft of Wagons. 43< the center of the load to one side still further and to a very serious degree if the load is high, as is the case in hauling hay or cord-wood. 540. Heaviest Load on the Hind Wheels. In loading the ordinary wagon the heaviest load should be placed on the hind wheels for three important reasons: First, because they are larger and will not depress the road-bed so much and will draw easier if they do; second, when the wheels track, the front wheels make a road, by firming the ground, over which the balance of the load may be more easily- drawn; third, when the axle of the front wheel is free to be turned, as in the common wagon, the slight inequalities of the road-bed tend all the time to keep the tongue vibrat- ing, so that there is a strong tendency, by this to and fro swinging, to cause the front wheels to cut more deeply into the ground and thus increase the draft. On a very rigid road-bed this matter is not as important as in doing field work, but the differences are large enough on earth roads so that they should never be overlooked. In the following table some observed differences are re- corded : Dry sheep pasture. Dry meadow. Lbs. per ton. 110.4 Lbs. per ton. 174.0 120.0 187.5 129.3 229.9 101 8 190 9 These statements may appear to contradict the common practice of hauling logs butt end forward and the general tendency of placing the heaviest portion of the load for- ward. The conditions, however, are quite different from those where there is a real advantage in placing the heav- iest load forward. The reason for this will be better un- derstood from the considerations of the next paragraph. 440 Farm Mechanics. 541. Direction of the Line of Draft. In drawing a load over a plane surface which remains unchanged during the movement the least draft is required when the line of draft is maintained parallel with the road as shown at A. B., Fig. 212, where the apparatus may be used to clearly dem- onstrate this principle. It will be seen that as the spring balance is moved up upon its arc the line of draft is such that it tends partly to lift the load off the road and so much that if it were pushed around until the direction t'io. 212. Apparatus for demonstrating tlie influence of tlie direuuuii oi " the line of draft on the draft of wagons. became vertical the whole weight of the load would come upon the spring balance. Then, too, if the line of draft is carried below a parallel to the road-bed the draft must increase because then it is partly downward upon the bed, tending to practically increase the weight of the load by the lost portion of the force of traction, for it is clear that were the scales carried downward until the draft became vertical to the road the whole effect would be lost in pro- ducing pressure. In the movement of cars by the locomotive ove,r the Draft of Wagons. 441 smooth unyielding bed of the steel. rail the line of draft is always parallel with the rail. 542. Line of Draft on E,oad Wagon. The statements of the last paragraph may appear to be contradicted by the general practice of having the traces nearly always slope decidedly backward and downward. The former state- ments, however, are not incorrect, neither is the common practice fundamentally wrong. The apparent contradic- tion grows out of the fact that the road is seldom either smooth or rigid so that the wheels on the average are in effect continually rolling up an inclined plane. The principle is clearly shown in Fig. 213 where the wheel is rising over the obstruction which in effect makes FIG. 213. Apparatus for demonstrating the Influence, upon the draft, of the direction of the line of the draft of a wagon when the wheels are passing over an obstruction or cutting into the road or ground. an inclined road upon the general road-bed. If now the draft required to bring this load upon the obstruc- tion is measured when the line of draft is parallel with the general road-bed and then the line of draft is made more and more slanting until the direction finally be- comes parallel with the secondary road made by the ob- 442 Farm Mechanics. struction, it will be found that the draft decreases until this direction is reached, but that passing beyond it again increases. In other words, the draft is least when the di- rection of the traces is parallel with the effective road-bed. It is clear, therefore, that in teaming with wagons on the field and on any but rigid, smooth roads the least draft is secured when the traces incline more or less downward, the amount increasing the more yielding and the more un- even the road. In regard to the division of the load between the front and hind wheels it is clear that the hind wheels are drawn by the reach from the king-bolt, the line of draft being nearly horizontal, and, this being true, it may fairly be concluded that on ordinary roads and upcn the field the load must draw harder if the heaviest portion is not placed upon the front wheels where the line of draft can be more inclined. It is quite possible and even probable that when the unevenness of the road is considerable the least draft may be secured when the front wheels are carrying more than half the load. More observations, however, are re- quired along this line to establish the whole truth. 543. Kigidity of the Carriage. Where the road is not per- fectly smooth and where the speed is faster than a medium walk, springs under the load diminish the draft and the ad- vantage of elasticity increases with the roughness of the road and with the speed. For small and rigid inequalities in the road the maximum advantage is secured in the use of the elastic tire, and especially with the pneumatic form, where the load is not too heavy, because in these cases the energy which would be lost by concussion is prevented, the tire quickly and effectually conforming to the road. Where the loads must* be heavy, and where the inequalities are larger, then springs under the load carried by the axles respond in rapid transit and relieve the concussions and thus lessen the draft, diminish the strain upon the car- riage, and permit less injury to the road. Draft of Wagons. 443 544. Results of General Morin's Experiments in France. General Morin, after a series of experiments carried on under the French government, reached the following con- clusions regarding the draft of carriages on roads : 1. The traction is directly proportional to the load, and inversely proportional to the diameter of the wheel. 2. Upon paved or hard macadam roads the traction is independent of the width of the tire when this exceeds three or four inches. 3. At a walking pace the traction is the same for car- riages with springs as for those without springs. 4. Upon a macadam or paved road the traction increases with the speed above a velocity of 2.25 miles per hour. 5. Upon soft roads of earth or sand the traction is inde- pendent of the velocity. 6. The destruction of the road is in all cases greater as the diameter of the wheels is less, and it is greater by the xise Q carriages without springs than of carriages with them. OHAPTEK XXL CONSTRUCTION AND MAINTENANCE OF COUNTRY ROADS. Having outlined the principles underlying the draft of wagons on roads the next consideration should be how to make and maintain the road for the given locality which, everything considered, is the most economical. 545. Establishing the Grade. For ordinary country roads the road-bed will generally conform with the natural slope of the surface over which it passes ; steep hills, how- ever, should, if possible, always be avoided either by turn- ing to one side or by grading and filling. Where the hills are short and steep they may usually be graded down to better advantage than to pass around them, but when the hill is both long and high then it may be best to reduce the grade by passing obliquely up the hill, or in mountainous countries where ranges are crossed through passes it often becomes necessary to pass down the long steep slopes by a series of zigzags, having short and steep rounded turns. 546. Factors to Be Considered in Establishing the Grade. There are many factors which must be considered in de- ciding the particular grade a road over a given hill may be permitted to have. If the road for the main travel is generally excellent and level, with a good deal of traffic over it, then it is important to keep the grade as low as practicable. Where the country is generally rolling, so that there are many hills which must in any event have a high grade, it will not be as important to cut other hills down as much as a more level country would warrant. Eoad Drainage. 445 The better the more level portions of the road are, where heavy teaming is done, the more important it is to reduce the grade -to a low per cent, because it is important to be able to go over any hill readily which can be approached with the largest load the team is able to handle without in- jury to itself. The great importance of this point will be readily understood when it is stated that the steepest grade admissible on an average macadam road is 10.5 per cent., and on a dirt road in good condition 16 per cent But as these grades will tax the team to its utmost the hills should not be permitted to rise if practicable faster than 4 feet in 100 feet for the ordinary macadam and 6.2 feet in 100 feet for the earth road in good condition. In thinly settled sections people must be content to im- prove the roads gradually, but if the end finally to be reached is kept in mind all the time it will usually be pos- sible to make each year's work count as permanent im- provement and avoid tearing down one year the work of the years preceding. EOAD DRAINAGE. The keeping of the road dry, both above and below, ia the most fundamental necessity of a good permanent high- way. Fill any soil, however hard and firm, completely with water, and a child walking over it will mire ; and to completely drain and dry any soft and marshy place will leave it so that heavy loads may be moved across it readily and safely. Drainage is one of the first requisites of a good road. In some places only surface drainage requires attention. Where the surface is more or less rolling and underlaid with coarse porous materials, so that standing water in. the ground does not occur within 10 to 20 feet of the sur- face, under drainage will not be necessary; but wherever the adjacent fields would be improved by drainage, wher- ever the ground is springy, and wherever the ground war 446 Farm, Mechanics. \ ter at any season of the year rises to within three or four feet of the surface there the road-bed should be drained. In humid climates provisions should be made to surface drain every road. 547. The Relation of Water to Koads. When a soil is completely filled with water the individual soil grains are invested by water and tend to float in it so that there is the greatest freedom of motion of the particles. On the other hand let all water be removed from the soil and the ground, while hard, easily frets into fine, loose, separate dust particles, which not only increase the draft but are easily drifted away by the wind, thus injuring the road much as it would be were the top washed away by running water. There is a medium condition or amount of water in the soil which gives it power to withstand the eroding tendency of the tramp of the horses' feet and the rolling of the wheels. When sand is just wet enough its surface is hard and will carry a heavy load, the grains being bound to- gether by the surface tension of the water films. So, too, with the clay roads and those of the best of loam^ the right amount of water always present, so as to keep the sur- face damp and dark without making them soft, greatly improves the quality and lengthens their life. So valua- ble is the right amount of water on earth roads that sprink- ling them in arid and semi-arid climates and in dry times in humid climates, is one of the most effective means of maintenance. 548. Depth of Under Drainage. Where under drainage is needed the drain should not be less than three to four feet deep, and this is especially true if heavy traffic is to be maintained over it. No one thinks of walking on the yielding surface of the water of a lake or stream, but let it be covered with a suffi- ciently thick layer of ice and it then makes the best kind of a road-bed. The drained ground beneath the road surface Road Drainage. 447 must be sufficiently thick to float, on the soft soil beneath, any load which may be driven along it, just as the ice floats its burden. 549. Place For the Drain In the narrow roads of eight to sixteen feet, where the water to be removed is that which may be raised by hydrostatic pressure vertically upward beneath the road-bed, the best place for the drain is di- rectly beneath the center of the drive-way. Where the main source of the water causing the trouble is an underflow through sands and gravels from adjacent higher lands then the drain should be placed upon the side of the road from which the water comes. Where the ground is marshy on all sides, and particu- larly if the road is wide, it may then be necessary to lay two lines of tile, one on each side. If springy places occur under or near the road-bed drains must be connected with the spring itself, so as to effectually remove the excess of water. 550. Fall of the Drain. The fall of the drain will usu- ally conform somewhat nearly to the grade of the road-bed, but should not be less than two inches in 100 feet, if this can be secured. It will, however, be necessary sometimes to lay the drain on a slope less than this, even as low as -J an inch in 100 feet. In all cases care should be exercised to lay the tile on a true grade, not allowing them to drop anywhere below or rise above a rigidly maintained grade line. If they are not laid in this manner water will stand in the sags and behind the bends, and in these places the tile may become filled with silt. It may sometimes occur that the road is so nearly level that there is no fall for the drain. In such cases it may be necessary to lay the beginning end of the drain nearer the surface of the ground by as much as six or even twelve inches. In this way there could be given a fall of one inch in 100 feet over a distance of 1,200 feet, but of course 448 Farm Mechanics. the upper portion of the road could not be as well drained and the plan should be followed only where there is no other alternative. 551. Outlet of the Drain. The drain should be turned out to the side of the road whenever there is an opportunity for doing so, that is, whenever there is a natural line of drainage leading across the road which will answer for the purpose. The free end of the drain is best made of one length of cast iron sewer pipe eight feet long, because this will not be injured by freezing nor be easily broken. There should.be a free fall at the end of the drain, and it is better that the opening should be protected by some sort of metal grating or screen to prevent animals from running in in dry times. * 552. Size of Tile. Tile three inches in diameter is the best to use for ihe reason that, in case the grade is very small, slight errors -in laying the line cannot carry the en- tire opening of the tile above or below the grade line and hence permit the drain to be entirely closed by silt. 553. Kind of Tile Where the tile can be laid two feet or more below the surface of the road ordinary drain tile which are well burned, straight, smooth inside and having the ends cut squarely off so that they may fit closely to- gether are best. Great care should be taken in placing the tile to turn them until the ends fit very closely all the way around, and then to fix them rigidly there. This care is needed in order to prevent silt from being washed in at the joints. Where the tile must come less than two feet below the surface it will be safer either to use the vitrified drain tile or else second quality sewer tile not likely to be disinte- grated by frost. 554. Surface Drainage The quick removal of water from the surface of a road and the prevention of seepage Eoad Drainage. 449 down through the road-bed are the most important points to be secured in the matter of maintenance. The surface of every road, therefore, should be so shaped as to act like a roof in throwing all rains quickly and completely off, permitting only a little moisture to be drawn downward by capillary attraction to moisten the material and lessen the formation of dust. If the compacted material of the road and the road-bed beneath it can be kept with only a small per cent, of capillary water in them the danger of injury from frost is greatly lessened and the liability to soften during wet periods is also largely removed. Water should under no conditions be permitted to stand either upon the surface nor along the side of the road, the shape being sufficiently rounded to throw the rains quickly to either side, and the surface ditches deep enough, clean enough and possessing sufficient capacity to carry all water rapidly away* - . 555. Slope of the Eoad Surface. [n order to have quick, complete surface drainage it is necessary to so arch the face as to make a road twelve feet wide three inches higher ,in the center than at either margin, a slope of about four per cent, or four inches in 100 inches. But if the road has itself a considerable grade, then the slope must be made enough greater than four per cent, to force the water to the side ditches rather than to permit it to flow down the center of the road. But evenness or smoothness of surface is the most important condition to be secured and maintained in order to afford perfect drainage. If the road surface is left uneven, or is permitted to become so, no amount of slope which can be tolerated will secure the drainage. The road must not be made too rounding or sloping for the reason that then teams all drive in one place on the surface and wear it into ruts and this prevents drainage. 556. Water-Breaks. On steep grades where the hill is long it is a common practice to throw a ridge obliquely 450 'Farm Mechanics. across the road at intervals to turn the water to the side. This is a bad practice and should be avoided wherever possible, and in all but the steepest grades this may be done by making the slope of the road higher than the grade. If the water cannot be turned off in this way it is bet- ter to make two paved gutters meeting V-shaped in the cen- ter of the road with the point up the grade. The paving will prevent washing and making the gutters meet in the cen- ter does not tip the wagon in passing across them. Whenever it becomes necessary to carry water across a road on a hill from one gutter to the other it is much better to carry it under the road than above it, as is so often done with the aid of water-breaks. A culvert is of course necessary but it should be used. TEXTUEE OF ROAD MATERIALS. Closeness of texture is necessary to the building of a solid road. The more completely all pores can be obliter- ated and the road given the close texture of iron the better and more durable will it be. Field soil in its natural condition may have from 30 to 50 per cent, of space unoccupied by anything but water and air, and in this condition it cannot form a good road. It is too yielding to pressure and water percolates through it too rapidly. When it is properly rolled and tamped the pore space is very greatly reduced, giving it so close a texture that water does not enter it readily, and so large a portion of the grains are in actual contact that it ap- proaches the character of a rock. Of whatever material a road is built it should permit the parts to pack so closely as to resemble a solid rock. 557. Hoads Should Be Built in Layers. Whether a road is to be built of crushed rock or earth it is indispensable that the materials used shall be put on in layers. The thickness of the layers will depend primarily upon the Texture of Road Materials. 451 size of the pieces of material used, the layers being thicker the coarser the material. With crushed rock having pieces 2 to 2 1-2 inches in diameter the layers will need to be 3 to 4 inches thick ; with smaller pieces the layers should be thinner. If thicker layers than these are made the ef- fect will be the formation of a closely packed crust, a lit- tle thicker than the diameter of the material used, over a loose and open structure below. The hardest and best earth road can be built only by spreading the material on very uniformly in thin layers and thoroughly compacting each layer before the next is put in place; the thickness of these layers should be 2 inches and less, rather than more. 558. Uniformity of Size of Material Used. It is impossi- ble to crush rock into sizes varying all the way from fine dust to pieces 1.5 inches in diameter and then use this ma- terial unsorted to make a solid, unyielding road. The materials when laid down at once with all sizes mixed will not pack so as not to work up loose with the travel upon it ; and this is the main reason why more solid roads cannot be built from earth. Crushed rock must be carefully separated into nearly uniform sizes by means of screens and the different grades applied to the road in layers. When a layer is made of only a single size of pieces these may be brought together by packing so that all touch and press firmly against one another. If now a grade is used of smaller pieces such as will work readily into the pores left between the angles of the larger ones, pressing hard upon all sides, a still more stable layer will be formed. If it were practicable to follow this method step by step there would be reproduced a nearly solid rock from the fragments made and the most substantial of roads built. 559. Shape of Fragments. The shape of the materials used in road building has important bearings on the quality pf the road. The best form is that which approaches most 452 'Farm 'Mechanics. closely to the cube with broad, flat faces, sharp angles and having the same diameter in three directions. Fragments of this form pack most readily and, as the broad, flat faces set against each other, the fragments do not so readily turn under the wheel or horses' feet and withstand a heavier load without crushing. Where sands and gravels are used in road building those of glacial origin which are much sharper and more angular than water worn types are much to be preferred, for the simple reason that when packed together they give a more rigid body and stronger binding. Beach gravels and sands cannot be held rigidly by any ordinary cementing material because, with the round, smooth surfaces, there is little opportunity for any locking. 560. Cleanness of Material. Where crushed rock is used in the building of roads it is important that these materials be clean and free from dirt, clay and rubbish of any sort. So with gravel or sand, when these are called for they should be clean. In general, anything which works against uniformity of material should be avoided. EARTH EOADS. In the country in most parts of the United States the greatest number of miles of travel for a long time to come must be made over earth roads. It is therefore of great importance that they should be built in the best possible manner. The proper construction of earth roads is made the more important through the fact that when well built and well maintained there is no road easier on the team, the carriage or the parties riding, where speed is an im- portant consideration, than an earth road. 561. Forming the Road-bed. After the grade has been established and under-drainage provided where necessary, all organic material and stone should be cleared out of the Earth Roads. 453 war and the road given the form and width desired by a road machine such as represented in Fig. 215, or by other means. The road itself should have a width of 1C or 18 feet bor- dered on either side by a strip of grass three feet wide, out- side of which should be the surface drains, where needed, five feet wide at the top, two feet at the bottom and 24 inches deep, making a total width of 32 or 34 feet as rep- resented in Fig. 214. The center of the road-bed should be thoroughly rolled with as heavy a roller as practicable in order to compact it and to discover in it any soft places. If soft places are found these should be filled and brought to the proper level. If the soft place is due to a different kind of ma- terial this should be removed and replaced by other and better. The center of the finished road should be two to six inches higher than the margins at the grass border, vary- ing with the width of the track, in order to give quick, com- plete surface drainage, and this should be built up in thin successive layers of as uniform material as possible. If earth is brought in from the sides and ditches great care should be exercised in distributing it evenly, and thor- oughly harrowing it ahead of the roller, so as to secure the necessary uniformity of texture. This is of the utmost im- portance in order to prevent the formation of ruts. Thor- ough rolling should follow the addition of each layer of ma- terial and should be kept up until a hard, even surface has been secured. 29 454 Farm Mechanics. In making earth roads it is particularly important not to make them wider than necessary because the narrow roi>d is always more quickly and better drained and lack of drainage more than anything else will destroy the earth road. FIG. 215. View of one type of road machine, Champion road grader. If the soil contains cobble stones everything larger than one inch in diameter should be thrown out, otherwise they will form ruts. If, in establishing the necessary grades on the earth roads, fills must be made, this filling should be done sys- tematically, distributing the earth in uniform layers which are thoroughly firmed with the roller as the work pro- gresses. Earth Roads. 455 562. Utilizing the Old Road as a Road-bed. In cases where the grade does not require changing' and where nat- ural under-drainage is adequate the old road-bed may be utilized in its already tramped and packed condition upon which to build the new road. This may be fitted with the road machine by throwing the loose and uneven portion of the surface outward to form the shoulders. Then if there are still low places these should be filled in and thoroughly packed with the roller, the use of which is necessary even where no leveling is needed, in order to discover any soft spots, quite certain to exist, and in order to give the foun- dation a more thorough packing than the wagons have se- cured. 563. Preparing the Road-bed a Year or More in Advance. It will generally be found advantageous to get the road-bed into proper shape to receive the surfacing material, whether this be gravel or crushed rock, a year or more in advance, utilizing the weathering of rains, the frost of winter and the traffic to settle the road-bed, but directing and assisting these agencies by a timely and judicious use of the harrow, road machine and roller. It is particularly important to allow time to intervene where there has been much filling necessary. 564. Roads on Gravelly Loam. Where the soils are a gravelly loam the best earth roads are possible. The reason for this is found in the fact that a gravelly loam is made up of large and small grains in such proportions that when they are thoroughly worked and compacted the coarser sand particles work in between the gravel, and the fine clay par- ticles between those of sand, in such a way that there is left almost no open space ; under these conditions the water is shed the most rapidly and completely so that the road is less liable to soften under the travel over it and it is less liable to be injured by frost. 565. Roads in Fine Clay Soil. Where the soil is a fine ad- hesive clay it is hardly possible to make a good road with- 456 Farm Mechanics. out the aid of foreign material. Of course by grading it into proper form so as to secure the needed drainage the road will be good when it is not wet, and under these con- ditions it will remain fair much longer than if not so pre- pared because, when this soil has been once thoroughly com- pacted and dry, water enters it very slowly, so that it is only during long wet spells and when the frost is going out that the most serious injury* to the road comes. 566. Clay Roads Surfaced With Gravel. Where gravel of suitable quality is available a covering of three or four inches, thoroughly rolled and packed, will very greatly improve the surface of a clay road, preventing it from soft- ening so readily with every rain and with the action of frost. Even sand and good loam, where nothing better is available, will improve the quality. In some cases burning the clay has been practiced so as to render it less plastic and sticky, but this practice will be one of the last to be resorted to at this time of cheap trans- portation and high price of fuel. 587. Sandy Roads. The making of good roads in a coun- try of very sandy soil is extremely difficult on account of the nearly complete absence of binding properties in the sand when dry. If there were any cheap method of keep- ing the surface wet, sand would make an excellent road. Even the rounded grains of beach sand for a short time after the waves have withdrawn are so tightly bonded that a horse may canter along the beach, making but little im- pression upon it. The water, however, drains away so rapidly from the coarse clean rounded grains that there is no longer anything to bind them together, and the foot or wheel easily sets them aside. When, however, there are a sufficient number of much finer particles commingled with the coarse sand grains a loam is the result whose water holding power is increased so that for a longer time the grains are bonded together by it, enabling the loam to form the better road. On the other hand, the amount of water Earth Roads. 457 may be too great to permit it to act as a binding material and as the water-holding power of the clays is greater than the loams, they more quickly come into the condition of over saturation during long rains and so the loam which is intermediate between the two extremes makes the best earth road, sand tending most of the time to retain too little water and the clay retaining too much for tight binding. With this principle to direct practice it is clear that if the right amount of finer soil particles can be obtained to in- corporate with the sand of sandy roads their firmness will be increased. It is unfortunately too often true that in districts where sandy roads prevail there is no clayey or loamy material available, either to incorporate with the sand or to place above it. 568. The Use of Straw, Sawdust and Tan Bark on Sandy Roads. It is well known that these materials when applied to sandy roads have temporarily a beneficial effect. The fundamental principle underlying this improvement is that stated in the last paragraph ; that is, in the power they have of maintaining a higher per cent, of water in the sand, which is necessary in order to bind the grains together. The sawdust, tan bark and straw act in two ways to main- tain the needed amount of water in the sand. At first they act as a mulch, lessening the rate of evaporation from the surface. Later, when they begin to disintegrate, they form a humus-like material, in its physical effects, which increases the capillary power and diminishes the rate of percolation downward after rains. The reason why these materials are only temporary in their effect is because they rapidly decay, being converted into soluble salts and gaseous products which finally leave the sand as if nothing had been added. 569. Road Gravel. It occasionally happens that natural gravel beds are found which possess the right characteris- tics for making roads, and when the gravel is just right ex- cellent roads may be made from it. 458 Farm Mechanics. There are several important features which a good road gravel must possess: 1. There must be one prevailing size of pebble in suffi- cient quantity so that when thoroughly rolled they press against one another. 2. There must be enough of the finer sizes of coarse sand and fine gravel to fill the voids between the coarser gravel. 3. There must be enough of fine loam to fill the voids between the coarse sand and fine gravel and retain a suffi- cient amount of water to bind the sand grains together and prevent their rolling. 4. The coarse and fine gravel and the sand must be made up of more or less angular fragments in order that flat faces of rock may set together and thus lessen the danger of rolling and of crushing under the weight of the load. It is not possible to give specific, concise directions for identifying a good road gravel, but a man who has seen and worked with it readily recognizes it. 570. Clean White Gravel Not Suitable. It will be appar- ent at once that the several characteristics which have been pointed out are not likely often to occur together in just the right ratios ; and so there will be all possible gradations from the ideal gravels to those which will not answer at all. Indeed it must be said that most gravel beds have had the finer materials so completely washed out that only clean sand and gravel remains ; and when this is true it is useless to try to make a road with it. Such materials can only be used to temper a road which is too clayey in its texture, by reducing its water capacity. 571. Texture of Gravels Altered by Crushing and Screen- ing. It happens in the majority of cases that much of the gravel is too large and too rounded to permit close packing and fast binding. When this is true much better qualities may be secured by using either the crusher or the screen oi' both together, one form of which is represented in Fig. 216. It will be at once apparent that where much of the Earth Roads. 459 gravel is too coarse, to run it through the crusher so as to re- duce the material to a more uniform size and at the same time to increase the angularity of the fragments will make a much better road material to use either by itself or as a tempering material. FIG. 216. Champion rock crusher and screen. 572. Some Gravels Contain Too Much Clay. There are many deposits of gravelly clay which it might appear would make a good road material, but the principle must be kept always in mind that too much of a too fine material will take in and retain so much water that the binding quality of the water is lost. These gravelly clays occur in many of the hills of the glaciated portions of the United States and through which roads are often cut. 573. Gravel Roads. In the construction of a gravel road, as in that of a stone road, it is of prime importance to se- cure first of all a properly shaped and thoroughly rolled and firmed road-bed before any gravel is laid on. When this has been done, and a suitable gravel has been found, the next step is to spread evenly over the surface and thor- oughly roll a layer which, when finished, will measure three inches thick. 460 Farm Mechanics. In the rolling it will be important to firm the outer edges of the gravel first in order that the rolling may not force it outward and destroy the slope. Should the gravel be too dry to pack it must be moistened or the work be suspended to take advantage of the rains. To make a good road there should be not less than three 3-inch layers, and usually four will be better. Of course a road 6 inches thick will be a great improvement, and often where the travel is light and the road-bed thoroughly made, three inches of good gravel, well placed, will make a great improvement in the road, serving as a wearing sur- face. Where the gravel must be crushed and screened to secure the proper sizes the revolving screen represented in Fig. 216 should be used and should have two sizes of holes 1.5 to 2 inch and 3 to 4 inch in diameter. The coarser size of gravel will form the body of the road while the finer will have to be discarded unless it happens to be of the right quality to use as a binding material or in making a bicycle path along one side of the road. 574. Roads in Swampy Places. It occasionally happens that roads must be built in places which cannot be drained and which are too soft to permit of the construction of a solid earth foundation. A common way to meet this type of conditions is to lay a foundation of logs, poles or even brush, having the desired width of the road and of suffi- cient body to enable an earth or gravel road to be built upon it. When such roads are built in situations where the wood is kept constantly beneath the water it does not decay and a road of considerable permanence and solidity is secured. Where logs are used care is taken to arrange them at right angles to the direction of the road, parallel with one another and like sizes side by side. The depressions be- tween the logs are filled with smaller logs or poles, whole or split, while these in turn may be covered with twigs and limbs forming a mat upon which the earth or gravel road is built. Upon this mat of wood is usually first thrown Stone Roads. 461 the material taken from ditches on either side made for drainage, building 1 the earth or gravel road upon this after it has first been well spread and firmed. STONE KOADS. Stone roads of one form or another date back to and pos- sibly beyond Roman times; and Fig. 217 represents two types of the extremely massive and substantial roads which were built ten or fifteen centuries ago, some of which still survive. These roads had a width of 30 feet and pavements of heavy stone at the bottom and often one or more layers of stone bedded in cement to make the road water proof. One type of construction which they fol- lowed made the road consist of four layers : FIG. 217. Two types of Ancient Roman stone roads. (After Shaler.) 1. Two or three courses of flat stone or, if these were not obtainable, of other stone, generally laid in mortar. 2. A layer of rubble masonry or coarse concrete. 3. A finer concrete upon which was laid 4. A layer of paving blocks jointed with the greatest nicety. It is stated that with many of the great roads the paved portion had a width of 16 feet bordered by raised stone 462 Farm Mechanics. causeways *outside of which, on each side, were unpaved side-ways each eight feet wide, and the paved way some- times had an aggregate thickness of three feet. 575. Macadam Roads. The use of crushed rock in road building is at least as old as Roman history ; but as, during the dark ages, little road building of a permanent character was practiced, the art had to be revived in modern times and about 1764 the French engineer Tresaguet appears to have introduced into France the type of road represented in Fig. 218, consisting of a stone pavement covered with two or three inches of crushed rock as a facing material. After being introduced into England and Scotland, where the de- tails were modified and perfected by Telford about 1820, this type of stone construction came to be known as the Telford road. FIG. 218. Type of road introduced into France by Tresaguet about 1764. (After Shaler.) Macadam's work began somewhat earlier than Telford's in 1816, and to him apparently is due the idea that when any road-bed is thoroughly under- drained, so as to remain permanently hard, then crushed stone alone may be used, the pavement of Roman practice becoming unnecessary. 576. Construction of Macadam Roads. After the founda- tion for the stone road has been completed the border is left with a shoulder of earth on each side as represented in Fig. 219, between which the road-bed is covered with a layer of crushed rock as nearly one size as possible and three or four inches thick. This layer is next thoroughly rolled and then covered with enough of finely crushed rock to fill the voids between the larger fragments. This ma- terial is worked in with the roller and water until a solid bed has been formed. Stone Roads. 463 After the first layer has been placed the second is ap- plied in the same manner, rolled, and the binding material applied and again rolled, until thorough consolidation has been secured. FIG. 219. View showing the road-bed, in the foreground, shaped with road grader and receiving the foundation layer of crushed rock 4 inches thick. 577. .Fitting the Road-bed. It is of the utmost impor- tance to have a thoroughly firmed and seasoned road-bed put into proper form and well drained before the stone sur- face is to be applied, and to do this most economically it is well to do all of this preliminary work a year or more ahead so that traffic, rains and frosts shall have an opportunity to do the work of consolidation, and to discover the soft places which may exist. In short, the formation of a good earth road to be used for a number of years as such will generally be found the best and most economical preparation for the stone road. 578. Forming the Shoulders. The formation of the shoul- ders represented in the foreground of Fig. 219 is best done 464 Farm Mechanics. with a road grader or road machine. With this tool the surface of the road-bed is prepared at the same time and the shoulders left in such shape that very little hand labor will be required for the finishing touches. After the shoulders have been roughly formed and before the finishing touches are given the roller should go over the road-bed to make sure that it is properly firmed and that there are no soft places. 579. Kinds of Rock for the Road. Practical experience has demonstrated that the best rocks for road making are the dark green, black and dark gray trap or igneous rock such as are known in common language as "nigger heads" in glaciated countries where large boulders are common in the fields and cuts of roads. They are tough, fine grained rock, much less brittle than most others, which yield when grinding upon themselves and under the wheel a fine rock flour whose texture is such that it holds the needed amount of moisture to make it bind together well, and consequently a road built from these fragments sets sooner than almost any other crystalline rock and hence is subject to less in- ternal wear. Next to the trap rock in value for road building purposes stand the closer grained hornblend-bearing syenites and gneisses which are species of granite where hornblend takes the place of mica of the true granites. It is the class of dark minerals allied to hornblend composing much of the trap rock referred to above which makes that the best road stone. Next in order stand the true granites made up of quartz, feldspar and mica, and their gncissoid varieties. The best of this class of rocks are the close fine-grained varieties having the least tendency to break into thin layers, giving flat instead of cubical blocks. To the granites and syenites with their banded or gneiss- oid varieties belong the lighter colored and flesh colored boulders which are usually associated with the "nigger heads" of glacial drift. Stone Roads. 465 The chief difficulty with syenites and granites for road metal is their brittle, unyielding quality and coarse crystal- line structure which makes them grind and pound up into a coarse sand without a sufficient amount of the finest dust to give it the needed water-holding power to permit it to properly bind the pieces together. The road-bed fails to FIG. 220. View showing where four inches of crashed rock for wearing surface is being built upon four inches of road-gravel as foundation layer. set quickly and the internal wear is larger while there is a greater tendency for ruts to form in wet weather and for the surface to ravel or throw out loose pieces in a dry time. Next to the syenites and granites in general availability for road metal stand the close grained hard limestones 466 Farm Mechanics. which break into hard, clean blocks and fragments with sharp edges and little material which will rub off under the fingers. Any rock which crushes readily into an earth- like or sandy material will not answer for road work. When a good road limestone wears down under the wheels, the horses' feet or the roller, a loam-like powder is formed which holds the right amount of water for good binding, and besides this it appears more quickly to pass into that cementing stage which in nature cements beds of loose fragments into rock. The chief objection to limestone as a road metal is its softness, which permits it to wear away rapidly, leaving the surface dusty in dry and muddy in wet weather. The extremely hard and brittle quartzite which throws off angular bits under the blows of horses' feet and the roll- ing of wheels makes one of the poorest road materials be- cause it too nearly possesses glass-like brittleness and the dust is too coarse and sand-like to hold the needed water for binding. 580. Foundation and Surfacing Stone May be Different Where there is in the locality a rock which does not make a good wearing surface but which binds well, like limestone, this may be used to advantage for the foundation of coun- try roads, thus making it necessary to import only the wear- ing surface layer. 581. Sorting Boulders Before Crushing. In localities where there are many boulders available for road work it will often be practicable to sort these when hauling them to the crusher in such manner as to use the lighter colored varieties for the foundation, reserving all of the "nigger heads" for the surface layer, and in this way increase the efficiency of the material. 582. TJsing Limestone for Binding. Where only granitic rock and quartzite are available for road work and these do not bind well, it will often happen that the limestone of Stone Roads. 467 the locality may be crushed fine to form screenings and used to great advantage as a binding material to hold the harder rocks more securely in place. This practice would be especially desirable for the foundation layer where it could not be converted into dust. But in localities where both limestone and the harder rock are available, but where the limestone can be obtained at much the less cost, this may be used alone for the foundation and as a binding ma- terial for the surface layer. 583. Roads Made Without Binding Material. It was Ma- cadam's practice in road building to strictly forbid the use of all binding material whatsoever. He preferred to wait for the general traffic over the road to develop from tho wear of the crushed stone, both superficial and internal, the necessary amount of rock flour to do the work of filling and cementing. While this work was in progress the road was given constant supervision to keep it in proper form. At the same time the filling and binding material was be- ing slowly produced there was brought upon the road with the wheels and horses' feet a considerable amount of earth which slowly worked downward and united with the rock flour to complete the consolidation. Macadam certainly secured in the end a better road by this method than was usually secured with the use of the then available binding material. It must be remembered, however, that in his time rock were crushed by hand and little fine material was made to use for binding, whereas with the modern rock crushers a large amount of this material is produced which must be a dead loss if it cannot be used for binding and surfacing, and it is quite certain that had Macadam used our modern rock crushers he would have availed himself of the screen- ings. 584. Use of Sand for Binding. The great readiness with which clean dry sand works into and fills the voids between the stone of a road, the ease with which it may be handled 468 Farm Mechanics. and the readiness with which it may often be obtained, leads to its occasional use as a binding material in macadam road. The coarse silicious sands, however, have very little cementing quality, they do not retain water well enough cither to make the road shed the rains nor give the surface tension of water much opportunity to bind the grains to- FIG. 221. View showing the binding material or screenings being applied to the foundation layer of crushed rock. gether firmly; consequently the best results cannot be se- cured when it is used. If loam is used there is danger that it will pack in the upper surface of the layer of stone and prevent even the combined use of water and the roller from working it to Stone Roads. 469 the bottom so as to completely fill the voids. There is the still further danger that it will work in between the tlat surfaces of the crushed rock, holding them apart to such an extent that heavy loads will produce too much rocking of the pieces and quickly lead to the formation of ruts. It the loam could be had in a dry condition, such as is usually the case with the screenings and the sand, it would be possi- ble with dry rolling to nearly completely fill the voids so that the subsequent use of water would, with the roller, lead to good results. 585. Limestone for Stone Roads. There is no doubt that crushed limestone although a soft rock will make an excel- FIG. 222. View of distributing cart being raised to spread crushed rock. lent country road where the traffic is not heavy and the use of it should be encouraged wherever suitable quality of rock is available. There is no rock which breaks in better 30 470 Farm Mechanics. form or which binds as well and sets as quickly. It is readily quarried and put in shape for the crusher ; and the power required for crushing being small makes it less bur- densome for towns to invest in the necessary machinery. It is true that the road wears rapidly under heavy traffic and the surface becomes dusty in a dry time, but not more so than clay roads do. It is true that careful road engi- neers advise against its use, but it is usually from the stand- point of city and suburban traffic rather than from that of the purely country road. FIG. 223. View of distributing cart spreading crushed rock on the road. 586. Spreading the Rock on the Road-bed. It is import- ant that the crushed rock should be laid down on the road- bed in a sheet both of uniform thickness and uniform den- sity and where this is not done the road is quite certain to roll to an uneven surface which will make it necessary to add more material in some places and remove it in others. But this will unnecessarily add to the cost of the road. Stone Roads. 471 Not only this, but when a wagon-load of stone is all dumped in one place, leaving it for a man to spread, it is certain to occur that all of the dust and fine materials not removed by the screen will drop into the voids at the place where FIG. 224. View of surfacing crushed rock as left by the distributing cart on the road. The watch, 2 inches in diameter, serves as a scale to show the size of the rock fragments. the load was left and this will give rise to a spot more com- pacted than the balance of the road and hence when it cornea into service two ruts or depressions are liable to form one on either side of the harder spot. 472 Farm Mechanics. To avoid these difficulties and to save time in spreading the material the distributing cart represented in Figs. 222 and 223 has been devised. In it can be placed two cubic yards of rock, and after tilting the box as shown in Fig. 222 the end board may be opened to such a width as to deposit FIG. 225. View of the surfacing rock after it has been packed by the roller. a uniform layer of any desired thickness while the team travels along at a slow and uniform pace. Fig. 224 is a view showing how the surface was left by the distributing Stone Roads. 473 cart and the watch is a scale by which the size of the pieces may be judged, its diameter being a trifle less than two inches. 587. Thickness of Layer. The thickness of a layer placed at one time should vary somewhat with the size of the pieces, the depth being greater with the larger frag- ments. With pieces of the size shown in Fig. 224 the layer when packed should not be greater than four inches and three inches will pack more quickly and closely than four inches. A too thick layer tends to form a crust on the sur- face, making it difficult to fill all the voids below com- pletely. 588. Rolling. The function of rolling is to arrange the fragments in the positions of the greatest stability with ref- erence to the rolling of wheels and the tramping of horses. The first effect of the roller is to bring the pieces nearer together and to reduce the size of the voids. This is clearly brought out by the two photo-engravings, Figs. 224 and 225. There is one other important thing which rolling should secure and that is to put the several pieces of stone together in the positions of the most stable equilibrium ; that is, in positions such as to make certain that they shall not tip or turn when the stress of the wagon or team is brought upon them. 589. Size and Weight of Roller. The diameter of the roller should be large to prevent it from shoving the stone forward as it moves and in order that the thrust may be as nearly directly downward as possible. It will be observed that even the front wheel of a loaded wagon often slides rather than rolls when coming upon the unpacked layer of rock on the road, and such movement cannot do proper packing. There appears to be a lack of agreement between prac- tical men regarding the proper weight of the roller, some 474 Farm Mechanics. advocating a roller of 3.5 to 5.5 tons, while others hold that only one of 15 to 20 tons weight will serve the purpose. Others advocate a light weight to begin with and a heavier one at the close. FIG. 226. View showing horse roller at work compacting the road metal. 590. Amount of Rolling. The only general rule which can be given in regard to the amount of rolling a given layer should receive is that the work should be continued until the stones cease to move in front of the roller or un- til the roller no longer sensibly depresses the bed and it has become hard and smooth. It should be kept in mind, however, that the road may be rolled too much, or until Stone Roads. 475 the stone again begin to move. This is most likely to oc- cur when the stone is too dry. 591. Manner of Rolling. The rolling should begin at the outer sides of the road, packing the stone first against the shoulder. If this is not done the fact that the road-bed is highest in the center will lead to flattening the slope and thinning out the rock in the center through a side creeping of the material from under the roller. 592. Kind of Roller. There are three methods of consol- idating the layers of stone put into a road. The first, now largely abandoned as being too expensive and too uncertain, is to allow it to be done by the natural traffic. The second, also being abandoned as too expensive, is the use of a 3.5 to 5-ton horse roller ; and the third, which is regarded the cheapest and best, is with the aid of an 8 to 20-ton steam roller. The safest indications seem to point to the use on coun- try roads of an 8 to 10-ton steam roller as most satisfactory ; although good work can be done with the horse roller of half this weight which may be made heavier or lighter by taking on and laying off weights Such a roller as this is represented in Fig. 226 which, naked, weighs 3.5 tons, but by the addition of castings to the inside of the roller may be increased to 5.5 tons. This roller has the frame and tongue so constructed that the team may be turned without reversing the roller, a very important feature. It will be readily seen that the use of two men and two teams must make the service of this roller very expensive, and when the disturbing effects of the horses' feet are re- called it becomes clear that the steam roller easily managed by one man is much better. 593. Rock Crushers. Until recently all rock crushing for road work has been done by hand and hammer, and in the days of slave labor when the man was a machine which managed, fed, cared for and reproduced itself, it is clear 476 Farm Mechanics. how such Herculean tasks as the ancient Roman roads could be accomplished. But happily, the use of steel and iriani- mate forces is freeing man from such drudgery ; and in Figs. 227 and 228 are two views of a rock crusher at work, breaking stone, sorting it and delivering it into bins where it may easily be dropped into wagons for delivery upon the road. FIG. 227. View of No. 3 Austin Crusher, with revolving soreon bronklng boulders for road; and wagon loading coarsest grade of broken stone. At the time these views were taken the crusher was be- ing driven by a 22 H. P. traction engine and was crushing rock at the rate of 100 wagon loads per day. The material is separated into three sizes, the coarsest used for the foun- dation, the intermediate for the wearing surface and the finest as binding and surfacing material, and Fig. 227 shows a wagon loading with the foundation size, and Fig. 228 with the screenings or binding material. There are various forms of crushers on the market and Fig. 216 represents another type. Stone Roads. 477 594. Revolving Screen. The revolving screen is an indis- pensable attachment to a rock crusher, because a good road cannot be made with the unsorted material, for with this method of putting the crushed rock upon the road the fine materials are certain to work downward and the coarser fragments to come to the surface. It should be thoroughly understood too that the chute screen will not do the work. FIG. 228. Side view of No. 3 Austin Crusher and wagon loading screenings. 595. Earth and Stone Road Combined. Where it is de- sired to cheapen the construction of stone roads it is prac- ticable to make the central portion 8 feet wide of this ma- terial and then have on one or both sides an earth road of eight feet, giving a total width of 16 or 24 feet to the margin of grass and 30 feet to the side ditches. The most serious objection to this combined plan is the securing at all times of sufficient and quick surface drainage. The chief difficulty which will arise in the carrying out 478 Farm Mechanics. of this plan will come from the tendency of summer traffic on the narrow earth road to go so persistently in one track as to develop wheel and foot ways deep enough to prevent surface drainage. The fact that the stone road may come into service when the ground is wet will only lessen the tendency to develop the evil pointed out but riot prevent it. For winter service in cold climates it seems clear that the earth road will be likely to ensure better sleighing. 0TT. FIQ. 229. Diagrams showing profiles of earth and stone road combined. 596. Telford Foundation When it is necessary to build the road where the ground is soft then it may be best to lay a foundation of larger stone as was the general practice with the Komans and with the English engineer, Telford, whose name is now attached to this type of road founda- tion. The paving blocks should be uniform in size, laid in rows across the road after it has been given the proper slope, the pieces breaking joints. The stones should not Stone Roads. 479 exceed 10 inches in length, 6 inches wide on the bottom and 4 inches at the top, the thickness being 4 or 5 inches for a road 8 inches thick. The surface of the pavement foundation should be as even as practicable and the voids filled with broken stone. It is necessary to have each piece thoroughly bedded before the macadam material is added so as not to be tilted on the surface. PIG. 230. View showing road with the stone portion in the foreground nearly completed. 597. Culverts. Culverts are necessary for carrying un- der a road the water from adjacent fields which collects as surface drainage in times of heavy rains and melting snows. The permanent forms are made of sewer tile, cement tile, 480 Farm Mechanics. cast iron sewer pipe or of stone. Wood should only be used as a temporary expedient. Where the amount of water to be conveyed is small so as to demand only one, two or three 12-inch sewer, or ce- ment tile, it will usually be cheapest to use these, but where a water-way demanding a cross-section of more than 8 square feet is necessary and where stone are available, it will be cheapest to make it of arched masonry. Where the culverts are of sewer pipe there should be not less than 18 inches of earth in the road above them to prevent crushing. The cast iron pipe is the safest to use and cheaper than either sewer or cement tile when diameters above 16 inches are required. MAINTENANCE OF COUNTEY EOADS. Important as the matter of construction of good roads is, it is, or should be, secondary to that of maintenance; when a good thing has been made which is designed for permanent service it is clearly a matter of sound business policy to provide whatever economic means is practicable for keeping it in order. 598. Section Men Necessary. In the maintenance of railroads it was early learned that two or more men pro- vided with proper tools must be employed by the year, per- manently or as long as they rendered efficient service, to care for and keep in order a certain number of miles of road. It is the business of these men to daily go over their section and keep it in first class repair and their tenure of office is only conditional upon their doing this satisfac- torily. It is self-evident that good country roads can only be maintained by adopting and keeping in force a system which is equivalent to that found indispensable in railroad maintenance. That is, men competent to do the work, Maintenance of Country Roads. 481 provided with the necessary authority, tools and materials, must have constant employment at a price which will per- mit them to devote their time to it, and they must be made responsible for the maintenance of a certain number of miles of road 365 days in a year. FIG. 231. View of country stone road with foot path on one side, near Maybole, Ayrshire, Scotland. From photo in 195. 599. Road Master. In the country road service it will be necessary to have one man who corresponds in duties and responsibilities to the "Section Boss" of the railroad. He must be competent, temperate and in every way relia- ble and trustworthy. He must have a practical knowl- edge of the principles and details underlying the main- tenance of good roads and at his command the necessary authority, assistance and appliances for doing the work re- quired. 600. Width of Tires Controlled When we come to have a system of good roads and the means for maintaining them 482 Farm Mechanics. it will be necessary to have ordinances regulating the width of tire and diameter of wheel which may be used on the roads when carrying specified loads. In Europe, where better roads are found and a better system for maintenance exists, there are ordinances which fix the width of tire to be used with given loads. In Bavaria the regulations are as follows : Two wheel carts with two horses, 4.133 inch tires. Two wheel carts with four horses, 6.180 inch tires. Four wheel carts with two horses, 2.596 inch tires. Four wheel carts with four horses, 4.133 inch tires. Four wheel carts with five to eight horses, 6.180 inch tires. Carts with more than four and wagons with more than eight horses are not allowed to use the roads without a special permit from the authorities. Other countries of the Old World have found similar ordinances necessary and it is clearly rational and just that such matters should be regulated, for otherwise one man may easily put in jeopardy the interests of a whole community. 601. Maintenance and Repairs. A sharp distinction should always be made between the maintenance of a road and its repairs. It is only when some accident has oc- curred to seriously injure a road or when, from long neglect, it has become well nigh worn out that repairs are needed, but the daily touching up of slight defects and places of evident wear constitutes maintenance. 602. Good Maintenance. Good maintenance will con- sist in daily attention to all the details which are necessary to keep a section of road up to the standard of perfection practicable to its type, influenced by its local surroundings and conditions. It must consist in (1) keeping the road in proper form; (2) in adding materials to the wearing surface where needed; (3) in keeping the road surface and drainage channels clean ; (4) in keeping the road sides Maintenance of Country Roads. 483 free from weeds and otherwise neat; (5) in caring for and maintaining road trees if they are grown; (G) in main- taining the proper conditions in winter in regard to snow. 603. Maintenance of Earth and Gravel Roads. The first requisite for the maintenance of any road is the knowledge which can be gained by going over the road while or im- mediately after it rains. Observations at this time will show the road master where the most serious defects exist and he should make careful note of them to use in directing his efforts as soon as the weather permits. It should therefore be the business of the road master to study his roads in wet weather and he should be equipped with clothing, etc., in a way which will permit him to do this without risk of injury to health. FIG. 232. View of French country road 20 feet wide, showing piles of crushed limestone used in maintenance. 1'uoto. in 1895, near Grfgnon. Whenever ruts or saucers begin to show in the road they should be corrected immediately, provided the moisture 484 Farm Mechanics. conditions permit of doing so, but on the earth roads the soil may be either too Avct or too dry to allow this to be done well, and the highest success will be attained when the road master comes to know and understand his conditions and then is alert to move at just the right time. The ruts will be formed chiefly in both the very wet and the very dry weather, and in the country where sprinkling the roads cannot be afforded, everything must be planned to take ad- vantage of every shower heavy enough to bring the road into condition for working with grader, shovel, rake and roller. FIG. 233. View on the same road showing the tool house where appliances for caring for the road are kept. Photo, in 1895, near Griguon. The intelligent use of the grader and roller at the right time after the rains of a wet period and after a dry period will make marvelous changes in the character of earth roads of all classes and particularly in those which are proverb- ially bad. Maintenance of Country Roads. 485 We cannot too strongly emphasize that to drive up one side of the road with a road machine and back on the other, scraping a lot of loose, heterogeneous rubbish and earth into the middle of the road, to be tramped out again by the traffic, is neither repairing nor maintaining the road. The material brought upon the road should be well dis- tributed and harrowed until an even, uniform layer has been secured and then the roller should be thoroughly ap- plied when the earth is in just the right condition to pack well. Work of this sort will count and will be appreciated. 31 CHAPTER XXII. FARM MOTORS. The tendency of modern civilization is toward the adop- tion of methods and appliances which free man from the necessity of expending his strength in developing mere mechanical power such as a horse, a windmill or an engine may create, and thus to leave him greater freedom to devote a larger share of his time and energies to lines of mental activity, the necessity for which becomes greater and greater as competition becomes wider and more intense. As a result of this tendency farm machines are steadily in- creasing, becoming more complicated and demanding more and more the employment of one or another form of motor or engine to drive them. This in turn makes it necessary for the farmer to know more of mechanical principles, and how to handle and care for machinery than was formerly necessary. 604. Farm Motors. The sources of energy which are used on the farm to drive machinery are (1) animal motors, (2) wind motors, (3) water motors, (4) steam motors, (5) oil motors and (6) electric motors. All of these motors are machines designed to utilize the energy of (1) chemical action, (2) moving air and (3) running water. The horse, the steam engine and the oil engine each derives its power from the chemical action of the fuel consumed or food eaten and may therefore be called chemical engines ; the windmill and the water wheel get their power by arresting the motion of wind or water, actuated by the force of gravity, and these may be called gravitation engines. The chemical engines use the energy (Animals as Motors. 487 derived from the collision of molecules and atoms, while the gravitation engines use the energy derived from the movement of streams of air or water traveling as a body. ANIMALS AS MOTOES. When animals are viewed from the standpoint of ma- chines they are wonderful mechanisms. Xot only are they self-feeding, self-controlling, self-maintaining and self-re- producing, but they are far more economical in the energy they are able to develop from a given weight of fuel ma- terial, than any other existing form of motor. While they are like the steam engine in requiring car- bonaceous fuel, oxygen and water for use in developing energy these are made to combine in the animal body at a much lower temperature than is possible in the steam en- gine, and a much smaller proportion of the fuel value is lost in the form of heat, when work is being done. 605. The Horse as a Motor. The essential elements which constitute the horse a machine for developing power are (1) a system of rigid levers united by ligaments and capsules at the joints which are automatically lubricated by a synovial fluid; (2) a system of muscles, each one of which is a motor, corresponding in function to the piston and cylinder of a steam engine; (3) a fuel supplying and waste removing system, consisting of the digestive, excre- tory and respiratory organs ; (4) a co-ordinating and reg- ulating mechanism, consisting of the nervous system, which throws the different motors or muscles into and out of action at the times needful to secure the results; (5) a protecting and insulating system, consisting of the skin and hair, which keeps all of the working parts free from dust and reduces the waste of heat. 606. Muscles Are Motors. Muscles are made up of bun- dles of fibers which can be stimulated by the nervous sys- tem and made to shorten, thus exerting a pull of greater or less intensity as desired. All muscles do their work by 488 Farm Mechanics. shortening and a pull and they are arranged in systems of pairs designed to produce movements in opposite direc- tions, as illustrated by the biceps and triceps muscles which move the fore arm as represented in Fig. 234. Just how the shortening of the muscle fibers is accomplished under the nervous stimulus sent to it is not clearly understood, but it is known that, while in action, the muscle fibers are in a state of vibration which gives rise to sounds known as the muscular murmur. When muscles are in action and are producing mechan- ical movements their temperature changes but little, but if the muscles are held in a state of rigid contraction with- out producing motion as the result, then the temperature rises, showing that the energy which normally would be changed into mechanical motion is changed into heat ; this is exactly what occurs in a steam engine. When it is working hard a large portion of the heat energy of the steam is transformed into mechanical work and the heat generated in the fire box thus disappears but the moment the engine is stopped and the steam is held so that it is unable to produce motion of the piston the temperature rapidly rises. 607. Strength of Muscles. The strength of individual muscles is often very great and more than at first seems possible. Taking the case of the biceps and triceps mus- cles in the arm, represented in Fig. 234, it is possible to measure their power with a spring balance. If a loop of strong cord is fastened to each end of a spring balance and the foot put through one, while the hand is put through the other, the strength of the muscle can be measured by lift- ing against the balance, bending the fore arm so as to make a right angle with the arm and holding it horizontal with the elbow against the edge of the desk. A man of average strength will exert a pull of 50 pounds in this way ; and as the lever arm upon which the muscle acts is only one-sixth of the length of the weight arm the pull of the muscle must have been 300 pounds. When 'Animals as Motors. 489 the strength of the triceps muscle is measured in a similar way it is found to be able to exert a pull of 25 to 30 pounds ; and as the lengths of the lever arms in this case are in the ratio of 1 to 20 or 1 to 24 the power of the mus- cle must equal 500 to 600 pounds. f> FIG. 231. Showing the mechanical action of muscles. It is clear from these measurements that the power of the larger muscle^ in a horse must be very great indeed. 608. Need of Great Muscular Strength. It is because the rate at which muscles are able to change their length is relatively quite slow and because they are only able to con- tract through short distances, that it is necessary to have them act upon the short ends of levers in order to secure the rapid movements through long distances which ani- mals are obliged to make. The horse as an engine consists of a large number of very powerful motors acting through a system of levers. 609. Rate at Which a Horse Can Generate Energy. It is recorded in (532) that about the maximum walking draft of a horse is one-half his own weight ; pulling with this in- tensity and traveling at the rate of 2.5 miles per hour the ability of a 1,600-pound horse would be 2.5X 5280 X 800 60 X 60 X 550 = 5 horse power. 490 Farm Mechanics. It is not safe, however, to have a horse repeat such strains as this often nor maintain them long at a time. Even when a horse is pulling with an intensity of one- fourth its weight this is too heavy for steady work and rep- resents For a 1,600-lb. horse, 2f H. P. Foral,200-lb. horse, 2 H. P. For a 1,000-lb. horse, If H. P. For an 800-lb. horse, 1 H. P. Indeed, it is commonly allowed that for steady and con- tinuous work 10 hours per day at the rate of 2.5 miles per hour a horse should not be asked to pull more than \ to tV of its own weight. At this rate the work of horses of different weights would be For a 1,600-pound horse, 1.06 to 1.33 H. P. For a 1,400-pound horse, .93 to 1.17 H. P. For a 1,200-pound horse, .80 to 1.00 H. P. For a 1,000-pound horse, .67 to .83 H. P. For an 800-pound horse, .53 to .67 H. P. 610. Horse Power Required to Haul Loads on a Wagon Taking 1 H. P. equal to 550 foot-pounds per second and the data in the table of (538), the number of horse power required to haul two tons, including the weight of the wagon, under the conditions there stated, are given in the table below : Table giving the number of H. P. required to haul 2 tons on wagons under different conditions, when the rate of travel is 2.5 miles per hour. Conditions. High wheels. Medium wheels. Low wheels. Dry gravel road; sand 1 inch deep; some small, loose stones 1.13 1.21 1.47 Gravel road up grade i in 44; covered with one-half inch wet sand ; frozen beneath Dirt road frozen; thawing one-half inch; rather rough ; mud sticky 1.64 1.34 1.76 1.59 2.31 1 85 Timothy and blue grass sod, dry, grass cut.... Timothy and blue grass sod, wet and spongy.. Cornfield, flat culture, with spring-tooth cul- tivator ; across rows dry on top 1 76 2.30 2 38 1.94 2.70 2 68 2.38 3.75 3 55 Plowed ground not harrowed, dry and cloddy. 3 37 4.23 4.98 Animals as Motors. 491 From this table it appears that the hauling of two tons on a wagon, at the rate of 2.5 miles per hour, under the varying conditions of the farm, requires a team to develop energy at a rate ranging from 1.13 H. P. to as high as 4.98 H. P. of 550 foot-pounds per second. 611. Horse Power Required to Plow. Taking the draft of the stubble plow as given in (305) and the mean rate of travel for tli:: team 2.5 miles per hour, the mean H. P. required t<. do the work, for furrows of different widths and depth, is as given in the table which follows : Table giving the H. P. required to draw the stubble plow when the soil is in medium condition. Depth of furrow 4 inches. 5 inches. 6 inches. 7 inches. 8 inches. Width of furrow 10 inches. 10 inches. 10 inches. 10 inches. 10 inches. Horse power 1.44 1.79 2.15 2.51 2.87 Wid th of furrow 12 inches. 12 inches. 12 inches 12 inches. 12 inches. Horse power 1.72 2 14 2.58 3.02 3.45 Width of furrow 14 inches. 14 inches. 14 inches. 14 inches. 14 inches. 2.01 2,51 3.02 3.52 4.02 From this table and the one of (609) it appears that two 1,600-pound horses find their full capacity for work taxed by the 14-inch plow cutting 4 to 5 inches deep ; by the 12- inch plow running 5 to 6 inches deep and by the 10-inch plow running 6 to 7 inches deep. The team of 1,200- pound horses finds its full ability taxed by the plow cut- ting a 12-inch furrow 4 to 5 inches deep and a 10-inch fur- row 5 to G inches deep. 612. Increased Speed Diminishes the Traction Power. If the horse walks more rapidly than 2.5 miles per hour, or at a slower pace, the force which he can exert changes also and is less or greater than 100 pounds. Experience seems to indicate that at speeds between | of a mile and 4 miles per hour, and continued 10 hours per day, the traction will be given by the following equation : 492 Farm Mechanics. 2.5 miles X 100 = n miles X Traction. Thus at two miles per hour the traction would be: 2.5 X 100 = 2 X Traction, whence Traction = 2 | Q or 125 Ibs. 613. Diminishing the Number of Hours Per Day Increases the Power of Traction. When the speed remains the same experience has shown that, between 5 and 10 hours per day, diminishing the time increases the possible traction in about the same ratio, or 10 hours X 100 = n hours X. Traction. Thus, if the horse is to be worked only 5 hours the trac- tion he may exert will be 10 X 100 = 5 X Traction, whence Traction = *** = 200 Ibs. PRINCIPLES UNDERLYING THE DRAFT OF THE HORSE. The principles governing the draft of a wagon have been discussed in Chapter XXj there are others affecting the horse as a- motor which need to be considered here. 614. Direction of the Line of Draft. When a horse has a muscular development and a type of skeleton which per- mits him to utilize his full weight in hauling then the di- rection of the line of draft, or of the traces in pulling, ex- erts an important influence upon how much the horse can draw. In Fig. 235 is represented an apparatus for dem- onstrating this and other principles underlying the draft of the horse. When the line of draft is horizontal, as represented in the figure, the spring balance will register a tension on the traces nearly equal to the weight of the model when the Principles Underlying tlic Draft of Hie Horse. 49 ?> fore feet are raised from the ground, and this is the limit of its power to draw under these conditions. If the traces are moved downward it is clear that there will he less ten- dency to tip the horse up, and hence the greater the slope of the traces the more will be required to raise the horse from his front feet ; and at an angle of 18 to 20 degrees the weight of the horse will permit him to draw double what he can with the traces horizontal. If the traces are carried above the horizontal then the horse is raised from his front feet more easily and his draft will be decreased. Pro. 235. Apparatus for demonstrating the principles of draft in the horse. It is difficult to get a living horse to demonstrate its full ability to draw in a standing pull, because it is accus- tomed to pull against loads which move. In the case of a horse weighing 1,645 Ibs. a measured standing draft of 1,250 Ibs. has been recorded when the traces slanted at an angle of 22, and of 1,120 Ibs. with them horizontal. It is doubtful if any of the heavy draft horses are able to utilize their full weight in hauling except when the line of draft is above the horizontal. 615. Influence of Weight on the Draft of the Horse. Weight in a draft horse is as important a factor to his ser- 494 Farm Mechanics. vice as it is in a locomotive ; there must be weight enough to make a secure footing. It can be demonstrated with the apparatus in Fig. 235 that two pounds at the place of the center weight in the figure increases the ability of the model to draw an equal amount when the traces are hori- zontal and, with the same added weight and the traces given a slant of 20 degrees, the ability to draw is increased 4 pounds. These results mean that of two horses, each having a muscular power capable of utilizing its full weight, the heavier one will exert the stronger pull. The 1,200- pound horse may pull about 200 pounds more than the 1,000-pound horse of like build when the traces are hori- zontal and 400 pounds more when the traces slope at an angle of 20 degrees. 616. Influence of the Distribution of Weight on the Draft of a Horse. It will be clear from an inspection of the model represented in Fig. 235 that to transfer the weight from the center ring to the forward one, giving what is in effect a horse with heavier shoulders, will make the weight count for more in preventing the horse being raised off his feet ; so, too, will it be evident that if the weight is shifted to the hind quarters it must have much less influence on the draft. Indeed, most horses in heavy draft, when given the free- dom of the head, show that they understand this principle in practice, by both lowering the neck and extending the nose forward, thus giving this portion of their weight a longer leverage to hold the body down on the hind feet which are acting as a fulcrum. 617. Influence of the Strength of the Hock Muscle on the Draft of a Horse. When a horse is drawing a heavy load a tremendous strain is brought upon the muscles which straighten the hock joint so as to force the body forward, and the load after it, in walking; and it is a deficiency of ability at this point oftener tha-n at any other which limits the power of the horse as a draft animal. Principles Underlying the Draft of the Horse. 495 With the spring balance represented above the back of the model in Fig. 235, which controls the hinged hock joint through a rod, it is possible to vary the tension which holds it rigid and thus demonstrate the ratio of muscular tension to the draft on the load and show that with too weak muscles only a portion of the weight of the body can be utilized in draft. In the model the tension of the hock muscle is about double the draft and while this is not in- tended to demonstrate the relation of strength of muscle to intensity of draft in any horse it illustrates the funda- mental principle and shows how extremely powerful the muscles of the horse must be to permit him to make the draft he does. 618. Influence of the Width of the Hock on the Draft of the Horse. JSTot less important than the strength of the hock muscle, in determining the qualities of a draft ani- mal, is the "width of the hock joint" itself; or, stated in the language of mechanics, the ratio between the two arms of the lever upon which the hock muscle acts. If the pro- jection of the heel bone backward, which forms the point of the hock, is long in comparison with the distance to the hoof, as represented in the diagram, Fig. 236, at the left, instead of short as shown at the right, then it is clear that FIG. 233. Diagram showing difference between wide and narrow hock. with a given strength of hock muscle it will be possible to straighten the limb under a greater pull and the ability of the horse to draw is thereby increased. In the model rep- 496 Farm Mechanics. resented in Fig. 235 the attachment at the hock joint is ar- ranged so as to lengthen the power arm of the hock muscle lever different amounts and thus demonstrate an increas- ing draft when the strength of the muscle is maintained constant. In fixing the attention upon the hock joint as influenc- ing the draft of a horse it is not intended to convey the idea that other features are not important or that they do not vary in a marked degree in the different types ; for it is true that the make-up of the whole body of the draft ani- mal is notably different from that of the one built primar- ily for speed, but the type of variation shown at the hock joint runs through the whole framework. 619. Attachment of the Traces to the Hames at the Shoul- der. To enable a horse to utilize his full weight to the best advantage in draft it is important that the attachment of the traces at the collar should be as low as the comfort of the animal and other conditions will permit. When the traces are low at the shoulder there is less leverage for the draft to raise the horse off his front feet and hence his weight counts for more. For the same reason a horse low on his feet and with a relatively long body has greater lev- erage for his weight in draft. It will not do to so lengthen the hame strap above and shorten that below as to bring the attachment of the traces down upon the point of the shoulder, for then the heavy pressure of the collar will irritate the shoulder and make it sore. 620. Two-Horse Evener. There are three types of two- horse equalizers or eveners in use on the farm : ( 1 ) where the holes for the whiffletrees are in a line back of the hole for the draft pin; (2) where the holes for the whiffletrees are in a line in front of the draft pin; and (3) where all three holes are in the same straight line. Each of these types of evener divide the work equally Principles Underlying the Draft of the Horse. 497 between the two horses so long as the evener crosses the line of draft at a right angle, but as soon as one horse falls behind the other then only the third type remains a just equalizer. The truth of this statement can be readily demonstrated with the apparatus represented in Fig. 237, where the three types of eveners are combined in one piece. FIG. 237. -Apparatus for demonstrating the principle'of eveners. Referring to the figure it will be seen that as the clevises for the whiffletrees are there set the evener may be made to form various angles with the line of draft and the in- equality of draft resulting may be measured with the pair of scales. With a 4-foot evener where the holes for the clevises are 4 inches behind the draft pin the horse which is ahead may have an advantage greater than 25 per cent., if the angle formed is as much as 20. 498 Farm Mechanics. Even in an equalizer where the three holes are only one inch out of line an angle of 20 for the evener with tbe line of draft may give the horse ahead nearly as much ad- vantage as would result by setting the clevis of the other horse in toward the center one inch. When the holes for the clevis pins are in front of the draft pin a similar inequality of division of labor occurs, but in this case the horse which is in front must pull the most, the differences measuring as great as with the other type. When the three pins are placed in a straight line there is nearly a true division of labor between the horses, even when the angle formed by the evener is large. This statement, however, is only true when the clevis pins and the draft pin fit the holes closely. 621. Giving One Horse the Advantage. When it is de- sired that one horse shall do more work than the other this is accomplished by shortening the lever arm of the horse which it is intended shall do the larger share of the work. If it is desired that the off horse shall do 60 per cent and the near horse 40 per cent of the work then the clevis pin of the off horse must be set in until the two ends of the evener are in the reverse ratio, or as 40 to 60. If the evener is 48 inches long the two arms would be each 24 inches. From the equation of the lever we have PX P A = WX W A and 60 X P A = 100 X 24 whence 30 X P A = 2, 400 and PA- 40 From this is appears that the clevis must be set in 48 40 = 8 inches, which leaves the off horse with a weight arm of 16 inches and the near horse with one of 24 inches. Principles Underlying the Draft of the Horse. 499 i,, -mm M PLOW EVENERS. flv HORSE A8REAST ' FIG. 238. Equalizers for horses. 622. Three-Horse Equalizer. There have been many forms of 3-horse equalizers devised, but the straight bar in which one horse pulls against two others is the simplest and gener- ally the most effective. To make this evener the holes should all be as nearly in the same straight line as possible, and if the work is to be divided equally the hole for the draft pin should be placed at of the length of the evener from one end. Fig. 238 represents a set of three, four and five-horse equal- izers, and Fig. 239 represents a method of driving four horses abreast. nnn nn m j -n mi FIG. 239. Ananpcment of lines 623. The Tread Power. The for driving four horses abreast. tread power is a rolling end- less inclined plane so arranged that its motion is trans- ferred to a shaft which is made to revolve and drive a belt. One form is represented in the upper portion of Fig. 240, and in the lower portion of the same figure are represented two forms of treads, the level at the right and the inclined at the left. The level tread has the advantage of permit- ting the horse to travel with its feet more nearly in the 500 Farm Mechanics. normal attitude to its limbs and on this account the fatigue is supposed to be and probably is less. FIG. 240. The tread power. In order that a large per cent of the labor expended by the horse, when working on the tread power, shall become available it is very important to have all of the bearings clean, free from dust and grit and well oiled. There are so many of these bearings and they are of such a character that great care is required in running this power to avoid heavy loss of efficiency due to friction. 624. Working the Horse in the Tread Power When a horse is put into a tread power to work he accomplishes the result by lifting his own weight against the force of gravity and the more steeply the power is inclined and the faster the horses walk the more work they do. Inclin- ing the power so that the bed rises 2 feet in 8 feet requires the horse to lift i of his own weight, thus producing a pull equal to that on the belt when it travels at the same rate. This for a 1,600-pound horse represents a pull of 400 Ibs. ; for a 1,200-pound horse, 300 pounds ; and for an 800-pound horse, 200 pounds. If, under these conditions, the horse walks at the rate of 2 miles per hour, the work done will be 2.13 H. P. for the 1,600-pound horse, 1.6 Sweep Power. 501 H. P. for the 1,200, and 1.07 H. P. for the 800-pound horse. These results are about double the horse power for corresponding weights where the draft is A that of the weight of the horse, as given in the table of (609). It is a common practice to set the tread power as steep as 2 feet in 8 feet and when this is done it is clear that the horse is called upon to develop power faster than he is able to do and follow it day after day. It is clear also how a horse may be made to do more work in a tread power than when drawing on the sweep power, and why this form of power may appear more effective, when the chief differ- ence is due to the fact that the horse is working harder, and horses are often overworked in a tread power without knowing it or intending to do so. FIG. 241. The sweep power. 625. The Sweep Power When horses are worked on a sweep power such as is represented in Fig. 241 it is im- 32 502 Farm Mechanics. portant that the line of draft be as nearly as possible at right angles to the sweep, for it is this angle .which renders the highest per cent, of the draft available. It will be clear from the upper portion of the figure, representing a plan of a 14-horse sweep, that the line of draft there can- not be at right angles to the sweeps and that it is impossi- ble for it to be so in any sweep power. On this account, there is a considerable portion of the draft lost in produc- ing pressure on the bull-wheel and this is greater the shorter the sweeps are and the longer the hitch is between the horses and the sweep. If the line of draft made an angle of 45 degrees with the sweep, one-half of the power would be lost in pressure on the bull-wheel and in increas- ing the friction. STEAM ENGINES. The steam engine is one of the earliest of man's inven- tions designed to utilize or transform molecular motion, in the form of heat, into useful work. The intense vibra- tions which are caused by the burning fuel in the combus- tion chamber are imparted to the water, converting it into steam capable of exerting greater or less pressure, accord- ing as its temperature is high or low. 626. Principle of Action in the Steam Engine. It was shown in (43) that 966.6 heat units are required to convert one pound of water at 212 F. into steam at 212 under a pressure of one atmosphere; and in (41) it is shown that these heat units are equivalent to 752,305 foot-pounds of work. The fuel value of one pound of coal is 14,000 heat units which, expressed in foot-pounds, is 14,000 X 778.3 = 10,896,200 foot-pounds. The steam engine aims to utilize the power of coal or other fuel by transforming its enormous potential energy into Steam Engines. 503 that of confined steam, and if it were only possible to util- ize 80 or 90 per cent, of this power the steam engine would be a very inexpensive motor. 627. Efficiency of the Steam Engine. It is unfortunately true of the steam engine as a source of power, that in prac- tical experience it is only able to render available from 2.5 to 20 per cent, of the full heat value of the fuel burned in the fire box, and it is still more unfortunate that there seems to be little hope that its efficiency can ever be made to much exceed 31.5 per cent. The reason this is so is be- cause it has not been found practicable to use steam at very high temperatures nor to cool it much below that of the ordinary air conditions. To enable a water wheel to util- ize the highest per cent, of the power of a falling stream it must be so arranged as to be able to take the water at the highest possible level and not to release it until it has reached the lowest possible level, and the principle is the same with the steam engine. If the steam could be taken into the cylinder at a temperature of 1,000 F. and re- leased from it only after its temperature had fallen to 60 F. it is clear that much more work could be performed than when the temperature is only permitted to fall be- tween 300 F. and 212 F. Where heat is converted into work the efficiency is al- ways equal to the quantity of heat taken into the engine minus the quantity given out divided by the quantity taken in; thus, if the steam entering the cylinder carries 100 heat units and it escapes from the cylinder with 90 heat units after moving the piston the efficiency of the en- gine has been only 100 90 JQQ = 10 per cent. So, too, if steam enters a cylinder at a temperature of 300 F. and escapes at 212 F., the maximum efficiency would be only (461 + 300) - (461 + 212) 461 + 300 = 11 . 5 per cent. 504 Farm Mechanics. In this equation 461 is the number of degrees F. which the zero of the Fahrenheit scale is above absolute zero, and in such problems as these it is necessary to express the tem- perature in absolute degrees. When this is done 300 F. becomes 761 F and 212 F. becomes 673 F., and the above equation becomes 761 - 673 sgj = 11.5 per cent. From the results of this problem it is clear why it is not possible for the steam engine to utilize a very large per cent, of the total energy which the steam carries with it into the cylinder. Even if the steam could be carried into the cylinder at 1,000 F. and could do work on the piston until its temperature fell to 100, the maximum efficiency would only be (1000 + 461) (100 + 461) 1000 + 461 61 ' 6 per cent< 628. Pressure of Steam at Different Temperatures. The temperature at which water is changed from a liquid into steam or invisible vapor varies with the pressure to which the water is subjected as stated in the table below: Table showing the pressure of steam or water vapor at differ- ent temperatures. Temperature of water. Pressure of steam. 102 F 1 Ib. per sq. inch. 162 5 Ib. per sq. inch. 194 lOlb. persq. inch. 212 14.73 persq. inch. 228 20 Ib. per sq. inch. 328 1(X) Ib. per sq. inch. 432 350 )b. per sq. inch. 546 1000 Ib. persq. inch. 629. Dry and Wet Steam. When steam contains no water held mechanically in suspension it is known as dry steam, but it is seldom possible to develop absolutely dry steam because as it escapes from the surface of the water in the boiler there is a tendency to carry away with it Steam Engines. 505 more or less water in the form of tiny drops, such, as form the white cloud. Steam carrying much water in suspen- sion is called wet steam. It is important to keep this property of steam in mind when comparing the efficiency both of boilers and of en- gines. If, for example, the evaporating surface of the water in the boiler is small, and steam is forming rapidly, so that large quantities of water are carried over not evap- orated, the boiler may be credited with evaporating a large amount of water with a comparatively small amount of fuel, when it is only carrying it away mechanically sus- pended in the steam. Then, too, if an engine is being worked with wet instead of dry steam, and the fact is not known, it will appear that it is using much more steam for a given amount of work than it really is, because the water carried over in this way is not effective in developing power. 630. Causes of Water in the Cylinder of an Engine. There are several causes for the presence of water in the cylinder of an engine, and these may be stated as 1. Wetness of the steam coming from the boiler. 2. Wetness due to cooling of the steam when passing through pipes and steam chest on its way from the boiler to the cylinder. 3. Condensation of steam in the cylinder when the en- gine is first started, before the walls become heated to the temperature of the steam. 4. Condensation due to the work done by the piston after the cut-off has occurred. 5. Condensation due to cooling of the walls of the cylin- der itself. . ... ^ ... ^ 631. Wetness of Steam from the Boiler. The wetness of the steam as it comes from the boiler is modified in several ways: (1) If the steam is generated rapidly the amount of water carried over is larger than when the generation is slow, because there is greater mechanical agitation. (2) 506 Farm Mechanics. If the area of the water surface at the water level in the boiler is small in proportion to the pounds of steam deliv- ered the water carried over will be large and for this rea- son the horizontal boilers of a given H. P. tend to supply dryer steam than the vertical boilers do because there is more surface from which the steam may escape and the agitation is less. (3) If the volume of steam space above the water is large there is more opportunity for the sus- pended water to fall back and leave the steam dryer, hence one means of preventing "priming," as carrying over water is called, is to work with the water level low in the gage glass. (4) If the size of the boiler compared with the amount of steam required for each stroke of the piston is small the tendency will be to cause the pressure in the boiler to vary and this variation will agitate the water and cause "priming." When this is the case prim- ing may be lessened by throttling down the steam supply at the stop valve. 632. Wetness Due to Condensation in Steam Pipes and Valve Chest. When the steam pipes are long, lead- ing from the boiler to the steam chest, and when they are not jacketed and are exposed to the cold, priming is pro- duced. Jacketing the steam pipes and the steam chest reduces the priming from this cause very materially be- cause the loss of steam from uncovered iron steam pipes, per degree of difference of temperature between steam and outside air, is about 2.4 heat units per square foot of out- side surface of the pipe per hour, while covering the pipe with wool felt one-half an inch thick reduces the loss to .7 heat units in the same time. 633. Initial Condensation The temperature of the walls of the cylinder is always, in practice, colder than the entering steam as it comes from the boiler and so there must be a greater or less condensation as it enters until both are brought to the same temperature. So great is tlio condensation of steam when the engine is first started Steam Engines. 507 that it is necessary to provide the cylinder with relief cocks at each end, shown at 8 in Fig. 250, which must be opened at the start to allow the water to escape. If these are not opened at the start enough water may collect in the cylinder to cause the piston to drive out the head of the cylinder or do some other injury. As the temperature of the cylinder gradually increases less and less water is deposited and then the relief cocks may be closed, the water which is condensed afterward being so Jittle that it is re-evaporated after the cut-off takes place and during the exhaust stroke because, as the piston travels, the space for the steam increases and this reduces the pressure so that at the lower pressure the heat in the walls of the cylinder is able to re-evaporate the water which had been condensed. In this way a well protected cylinder keeps itself empty after it has become heated. 634. Condensation Due to Work During Expansion.- When the steam expands and expends its energy in driv- FIG. 243. Horizontal boiler. ing the piston forward its temperature is lowered in pro- portion to the amount of work which it does and on this 508 Farm Mechanics. account more or less of water tends to condense in the cylinder which, like the rest, must be removed by re- evaporation. It should be clear from this and the preceding para- graphs that the cylinder should be well jacketed so as to reduce as far as possible all tendency to condense the steam in the cylinder before it escapes through the ex- haust. 635. Engine Boilers The boilers of farm engines are commonly one or the other of two types, horizontal or up- right, represented in Figs. 243 and 244. The horizontal boilers are best adapted to the engines of the larger sizes "and are as a rule the most economical forms ; but where a small engine is desired, and especially one which is compact and which occupies but little space, then the up- right types may be used, such as represented in Fig. 244. FIG. 244. Vertical hotter and engine.' Steam Engines. 509 636. Construction of Steam Boilers. Steam boilers are usually made of strong sheet steel f i or & inches thick which are rolled into cylindrical forms, securely riveted and often braced as represented in Fig. 245. The fire-box is placed in one end and is entirely surrounded by water so as to lessen the loss of heat. The boiler repre- sented in Fig. 245 is designed specially for burning straw as fuel, which is introduced into the fire-box A, from which the flame passes forward through the main large flue B into the combustion chamber C. From the combustion chamber the flame is sub-divided, returning to the smoke FIG. 245. Construction of steam boiler. staek E through the small flues D. In the same figure FF and FF represent the steam dome from which the dry steam is taken by the supply pipe G to the steam chest at H, not represented. At the bottom of the boiler at KK and -K.KKK are represented hand holes to be used in clean- ing it out. The construction of the valve for closing the hand hole is shown at A in Fig. 243 and also the relation of the flues to the water being heated by them. In the arrangement of the flues in the boilers, particular- ly in the horizontal forms, it is important to have them placed in vertical rows rather than one flue above the space between the two below, in order that there may be as free and rapid a circulation of water as possible. It is 510 Farm Mechanics. very important in the construction and management of a boiler to so arrange conditions as to have as little difference of temperature in all parts of the boiler as possible; be- cause unequal temperature tends to develop strains in the metal and to tear or loosen rivets and cause leaks. 637. Gage Cocks. Boilers are commonly provided with three gage cocks, represented at 13,13 in Fig. 244 and at 13 in Fig. 249. These are for the purpose of showing where the upper surface of the water is in the boiler at any time. The lower gage cock is placed about two inches above the upper surface of the upper flues in the horizontal boiler. When the engine is running the water is held in the boiler near the level of the middle gage cock and is fed into the boiler so as to reach the upper gage cock only when the engine is to be shut down to stand for some time without allowing the fire to go out. 638. Gage Glass. The object of the gage glass is to show at a glance just what the water level in the boiler is at any moment and its position is represented in Figs. 244 and 249 at 3. It should always be kept in mind that it is not safe to rely entirely upon the indications of the gage glass be- cause it is peculiarly liable to become clogged with sedi- ment from the boiler ; on this account the lower cock should be frequently opened to blow it off and clear out any sediment, and the water level in the boiler should fre- quently be tested by means of the gage cocks. When the engine is to be stopped to stand with the fire on for any length of time the gage glass should be closed, shutting off the water first and then the steam ; this is to lessen evaporation and to prevent escape of water from the boiler in case the gage glass should break. When opening the gage again the steam should be turned on first, the water last, and the pet cock opened to blow off any sedi- ment and show that the gage is in proper working order Steam Engines. 511 In case a gage glass should be broken when the pressure is on the water should be shut off first and then the steam, after which a new glass may be put in. 639. Pressure Gage. The pressure gage is intended to show the number of pounds per square inch of steam pressure there is on the boiler at any moment and to serve as an indicator to the fire- man of the condition of his fire. It is represented at 4 in Fig. 244 and the interior construction of this gage is shown in Pig. 246. As the steam enters the hollow spring shown in the figure its pressure tends to straighten it be- cause the pressure on the longer circumference is greater than that On the FIG. 246. Constmctioifof steam gage. shorter one. The motion thus produced is communicated, through a segment lever and pinion, to the index which is made to revolve over a dial upon which the pressure may be read. It should be remembered that a steam gage may get out of order and fail to show the true pressure. In such cases the operator must be guided by the safety valve. (640). Some pressure gages are provided with a siphon placed between the boiler and the gage, which prevents the dry steam entering the spring at too high a tempera- ture and also automatically drains out the water, thus preventing injury from freezing. 640. Safety Valve. The safety valve is connected with the steam chamber of the boiler where, when the pressure reaches a point as high as the boiler is intended to carry, it may be opened by the pressure and the steam be allowed 512 Farm Mechanics. to escape, thus relieving the pressure and at the same time warning the engineer by the sound of the escaping steam. The position of the safety valve is represented at 5, Fig. 244. Care should he taken hy the operator to see that this valve is in good working or- der by raising it gently at times to see that it has not be- come set in some way. The weight which has been pro- vided by the manufacturers to hold the valve against the steam pressure should never be made heavier by loading or so set that it will oppose a greater pressure than the maximum intended for the boiler. In Fig. 247 is represented the Kunkle lockup pop safety valve operated by a spring instead of a lever and weight. 641. Care of the Boiler. In order to get the best results from a boiler it is necessary that the flues be often cleaned in order that there may be no soot or ashes to prevent the heat coming in direct contact with the metal. How often this should be done must depend entirely upon circum- stances. Oftentimes it should be done daily, at any rate the flues should be kept clean and the draft perfect. Periodically it is necessary to clean the interior of the boiler to remove the scale and sediment which accumulates from the water used in making the steam; (649). How often this must be done will depend entirely upon the character of the water. In some cases it must be done once a week but with clean soft water it may not be required oftener than once in six months. FIG. 247. Kunkle lockup pop safety valve. Steam Engines. 513 When cleaning is to be done it is important to make sure that the fire is all out and the steam should be permitted to fall to as low as 10 pounds before the blow-off is opened. If the fire is not all out the flues may be made to leak and if the steam is too hot the mud will be caked on the flues so that it cannot be readily removed. In replacing the plates for the hand holes it is important to see that they are clean and that no scale or dirt is on the seat. Sheet lead makes the best packing for these places. The nuts should be turned up tight at first and after steam is up and the metal expanded they may need tightening a little more. 642. Firing Care and skill are required to do good firing, whether with wood or coal. In firing with wood it is necessary to keep the fire-box nearly full all the time and it will occasionally require "knocking down" but it is a good plan not to use the poker more than neces- sary. The wood should be placed in the fire-box as closely as practicable. In firing with coal the grates should be kept as evenly covered as possible with a thin fire, avoiding throwing on large lumps of coal or putting on large quantities at a time. If the coal forms clinkers these must be removed from the grate through the door but it is desirable not to use the poker when it can be avoided. The ashes must be kept removed form under the grate or the bars will be warped or melted. It is well to allow the safety valve to blow off once a day to note how this and the pressure gage agree, but good firing will not permit this to occur unless the engine is stopped. When the fire is too strong it may be controlled by open- ing the door to the fire-box an inch or less or leaving the damper open. It is not a good plan to open the fire door and close the damper at the same time when the engine is running. 643, Foaming. Foaming in the boiler is a dangerous 514: Farm Mechanics. symptom and should be avoided. The fact is indicated by the water in the gage glass becoming muddy and un- steady, rising sometimes very high and then falling again as quickly. It is often caused by dirty water, es- pecially when it contains alkali or grease. When foaming occurs it is difficult to tell just where the water stands in the boiler and here is where the danger lies. The tendency with foaming is to cause the heated surfaces of the boiler to become uncovered and become excessively hot so that when the water returns steam may be suddenly generated with explosive violence. 644. Low Water in the Boiler If by any chance the water should become too low in the boiler, cool judgment and quick action are called for, because if the crown sheet has become exposed it is liable to be weakened by over- heating. In short, an explosion is imminent. The thing to do first is to cover at once the fire in the fire-box with three or four inches of wet ashes or earth so as to shut off the heat. Do not under any circumstances undertake to rake out the fire, as stirring it up fresh only makes the heat more intense for the moment. At such a time the safety valve should not be opened as the sudden release of pressure which this would permit may cause an explosion by the agitation throwing water onto the overheated crown plate. The thing to do is to allow the engine to cool down and when cool enough to refill the boiler. 645. Soft Plug. Boilers are provided with a "soft plug" which screws into the crown plate and is fitted with an alloy which melts at a low heat to allow the water to be forced upon the fire and extinguish it before the crown sheet could be injured. Such a plug, however, is not al- ways reliable as the top of it may become coated with lime and thus rendered ineffective. On this account the plug should be removed and scraped occasionally and it is prudent to put in a new one each year or refill it. Steam Engines. 515 If a soft plug blows out in the field it may be tem- porarily refilled with lead or Babbitt metal but the melt- ing point of these is too high to prevent the plate from being injured. The soft metal is an alloy made by melting together equal weights of lead and tin, having a melting point of 420 F., that of lead being 610 and Babbitt metal 650 F. 646. Water Supply. The water supply to the boiler must always be adequate and under complete control. The greatest care and vigilance should be exercised by the engineer and he should know that his pump and in- jector are in prime condition at all times. In the first place the cleanest water which can be had should always be used and if necessary the water should be strained when it is put into the supply tank. Be sure that the suction hose and connections are free from leaks. It sometimes happens that the nipples screwed into the boiler through which the injector and pump feed, lime up and these should be examined occasionally to see that they are free. There are two methods of supplying the boiler with water (1) with a pump and (2) with an injector. Pumps are either driven by the engine when that is running or directly by steam pressure. 647. Cross-head Pump. A common form of pump for supplying the boiler with water is known as the cross- head because it is driven from the cross-head of the engine. This being true it is of course only available when the engine is running and an engine with this sort of pump should also be provided with an injector. The independent boiler feed pumps are some one of the steam types and are practically small steam engines which drive the pump cylinder. 648. The Injector. The principle by which steam from the boiler is able to force water back into the same boiler against the same pressure and the action of the injector 516 Farm Mechanics. is as follows: When steam is issuing from the boiler under a pressure of eighty pounds and entering the in- jector at V, Fig. 248, it may have a velocity of nearly 1,800 feet per second; as this passes through E into S it produces a strong suction in through the suppl-y pipe and when the steam strikes the cold water it is at once condensed. But when the steam is condensed into water it still has its high initial velocity and, striking the incom- ing water, drives a portion of it directly into the mouth Y through into the chamber O and from thence into the boiler. FIG. 248. Penberthy injector. When the injector is used at a steam pressure of 65 pounds the water supply valve is opened one turn, then the steam valve wide. If the injector does not start at once, and water runs from the overflow, throttle the water supply slowly until it picks up ; but if hot steam and water issue from the overflow open the water supply valve farther. Steam Engines. 517 649. Boiler Incrustation The use of hard water for making steam results in the precipitation of the carbonates of lime and magnesia, and their sulphates also, when these are present, on the flues and walls of the boiler in the form of a more or less resistant scale which may be harmful in several ways: (1) The incrustation on the boiler is not a good conductor of heat and both the capacity and effi- ciency of the boiler are decreased. (2) When a heavy crust forms on the boiler which prevents perfect contact of the water the boiler may become overheated and the scale thus weaken it by allowing it to "burn out." (3) It is thought that even boiler explosions may sometimes orig- inate from the thick scale suddenly flaking off when the boiler underneath is overheated and thus letting the hot water come suddenly in contact with the hot surface, which results in the sudden evolution of a large volume of steam. To prevent the formation of scale on boilers and to, re- move it when formed many methods have been proposed. A common one is to use the simple sodium carbonate or sal soda of commerce, dissolving a quantity in water and letting it be fed into the boiler with the water. Its action is to cause the carbonates to be precipitated in a more or less powdery form which does not adhere to the flues so firmly. It is possible that the influence of the sodium carbonate, besides taking up the excess of carbon dioxide from the bicarbonates of lime and magnesia, is to floc- culate the lime and magnesium carbonates and sul- phates, causing them to fall in larger granules which have not the power of adhering to the walls of the boiler and flues as the molecules do. Sometimes ammoni- um chloride is used and in this case the carbonates are converted into chlorides, which are very soluble in the water, while the ammonium carbonate is volatile and passes off with the steam. Where the steam is not to be used for any other purpose than driving the engine, kero- sene is sometimes employed but its method of action is not clearly understood. 33 518 Farm Mechanics. 650. The Engine. Most farm engines are mounted upon their boilers as represented in Fig. 244, at the left, and in Figs. 249 and 250. Its chief parts are the cylinder, 5 ; the steam chest with sliding valve, 4; the fly-wheel, 2; the eccentric ; the governor, 6 ; and the throttle valve, 7. The construction of the cylinder of the compound en- gine is shown in Fig. 252, where A is the high pressure cyl- inder, B the low pressure cylinder and 1, 1, 1, 1, 1, 1, 1, 1, the sliding valve which regulates the entrance and exit of FIG. 249. Portable steam engine . the steam. As the steam from the boiler comes to the steam chest at E it first enters the compartment D of the slide valve by a port not shown in the section and from there is conveyed into the cylinder A along the passage O where it forces the piston toward G. While this is being done the steam on the other side of the piston at A, which has spent only a part of its energy, passes out through the passage 2,2, into the steam chest C from which it enters the large cylinder B on the side of the piston at 3 and Steam Engines. 519 FIG. 250. Portable steam engine. in this position assists the high pressure steam in driving the piston toward G. On the opposite side of the large piston, in the low pressure cylinder B, is the steam which has spent its available energy in driving the large piston in the opposite direction and this is being forced out through the passage 4,4 into the exhaust 5. At the proper time, when the pistons are nearing the ends of the cylinders toward G, the eccentric reverses the action of the rod F and pushes the slide valve until 6 stands over 4 and 7 over 2, which permits the high pressure steam to enter A' through 2,2 and the 811 partly expanded steam to enter B by way of O to C and from thence through 4,4 to B, when the direction of motion of the pis- ton is reversed. mi .,.,, FIG. 251. Piston head Ihe construction of the piston head with metal packing, with its self adjusting metal packing rings are shown in Fig. 251. 520 'Farm Mechanics. Steam Engines. 521 FIG. 253. Governor of steam engine. 651. Governor. In order that the speed of the engine may be controlled it is necessary that the amount of steam admitted to the cylinder should vary with the work before the engine. To main- tain a uniform speed there is provided a governor, one form of which is represented in Fig. 253, whose action is as follows : At the point 2 in the pipe 1 leading from the boiler there is a valve which can be opened and closed by the ac- tion of the balls 4, which are made to revolve by the belt working on the pulley 3. As the speed of the en- gine increases the balls of the governor are made to revolve more rapidly and by their centrifugal force bend the strips of elastic metal to which they are attached outward, and this draws the upper end of the spindle downward, partly closing the valve at 2. By means of the spring at 5 the resistance the governor must overcome to close the valve may be varied and in this way the governor may be set so as to cause the engine to run steadily at different speeds. 652. Lubricator. To keep the valves in the steam chest and the cylinder well oiled, a special form of lubricator is required, and one of these is represented in Fig. 254 and is seen in place on the engine at 10, Fig. 249. This is screwed into the steam pipe leading to the steam chest at the threaded end H. The oil receptical is the cylinder above I which must be filled bv removing F, but first clos- ing E and G and removing I so as to drain out the water. After returning I the oil cup is filled entirely full above the level of the sight-feed D, when F is again closed and E and G opened. 522 Farm Mechanics. The action of the lubricator is caused by steam rising into the bend B and condensing in the left leg. The water being heavier than oil flows through G across the glass face D and falls to the bottom of the oil reser- voir, thus forcing a like amount of oil up and out through valve E and on into the steam pipe where the steam carries it into the steam chest and cylinders. When the oil is all out of the cup the water shows through the face D, and the lubricator must be refilled. D I FIG. 254. Swift sight feed lubricator. 653. FlyWheel. In all single crank engines it is very important to have a well designed and ample fly wheel in order to en- sure steady running of the engine. It will be clear that as the piston rod passes through the course of its stroke its efficiency must rise and fall as it approaches and recedes from the dead centers. The fly wheel, repre- sented at 2 in Figs. 244, 249 and 250, enables energy to be stored in its heavy fast-moving rim when the crank shaft has the greatest efficiency and this may be given out again to maintain the speed when the dead centers are being ap- proached and passed. GASOLINE ENGINES. Within the past ten years there has been a strong move- ment to place upon the market for farm use motors of the internal combustion type and many kinds of gasoline en- Gasoline Engines. 523 gines^ ranging from' 1 to 15 and 20 horse-power, are now offered for sale by manufacturers. While it cannot be said that these motors have in general earned for them- selves the reputation for reliability that steam engines pos- sess, it is now acknowledged that there are upon the mar- ket gasoline engines which are efficient and quite satisfac- tory for farm purposes. 654. Gasoline and Steam Engines Contrasted. Gasoline engines are widely different from the steam types de- scribed in the last section. In those the power is derived from a steadily burning fire converting water into steam, which transmits the power to the working parts of the en- gine; in these the fire is an intermittent one which is al- most instantaneous in duration and which begins and ends like an explosion. Indeed, the gasoline engine may be likened to a cannon which loads and fires itself at deter- mined intervals and where the ball is a piston whose mo- tion is arrested by a crank shaft and transformed into rot- ary motion in the fly wheels of the engine, to be used as a source of power. After the first charge has been fired a portion of its energy is used to reload the piece again, making it ready for a second explosion, to be repeated as often as needed. 655. Principal Parts of a Gasoline Engine. The gasoline engine, like the steam engine, has its cylinder and piston, and its fly wheel and governor, but it has no boiler or fire- box and is much more simple in its construction and man- agement. There are provisions for supplying the engine with gasoline and air as needed for the explosions, for ig- niting the charge when ready and for disposing of the waste products after the explosion has taken place. 656. The Working Cycle. The working cycle of moat gasoline engines consists of five operations : 1. Charging the cylinder with the explosive mixture of air and gasoline vapor. 624 Farm Mechanics. 2. Compressing the charge preparatory to explosion. 3. Igniting the compressed charge. 4. Expansion of the charge after its explosion. 5. Expulsion of the waste products of the explosion. 657. Arrangements to Prevent Over-heating. The con- tinual repetition of the explosions in the cylinder of the engine results in so much heating of the parts, where any considerable work is done, that it is found necessary to provide means for absorbing the heat not changed into me- chanical motion. This is usually done by providing the working parts which come in contact with the heat with water jackets in which water or oil is kept circulating to absorb the heat imparted to them. Where water is used to cool with it is necessary in freez- ing weather to draw it off when the engine is shut down to avoid injury, but where a lubricating oil is used as the cir- culating medium there is no danger of this sort. FIG. 255. Horizontal gasoline engine . 658. Types of Gasoline Engines. Gasoline engines, like the boilers of steam engines, are spoken of as vertical or horizontal according as the cylinder is upright or horizon- tal. It is possible to make the floor space occupied by the upright engines less than with the horizontal forms, but with few exceptions all the larger engines belong to the Construction of the Gasoline Engine. 525 horizontal type. These two types of engines are repre- sented in Figs. 255 and 256. CONSTRUCTION OF THE GASOLINE ENGINE. 659. Cylinder The cylinder of the ordinary gasoline engine with its piston is not widely different from that of the steam engine, except that here there is nothing which corresponds to the steam chest and the slide valve, and the cylinder has a double jacket through which water is kept circulating to prevent over-heating. In Fig. 255 A repre- sents the cylinder and the opening on the side is the ex- haust port. The piston has essentially the same construction as that of the steam engine represented in Fig. 251, using similar elastic metallic packing rings. There being no head in one end of the cylinder the piston can usually be seen. 660. Pumping Mechanism Formally it was the practice to arrange the gasoline supply tank so that the oil would How by gravity to the engine, but this practical experience has proved to be unsafe on account of the tendency for leaks to develop and flood the engine room with the explo- sive oil. The plan now generally followed is to use an automatic pump, represented in connection with the en- gine in Fig. 257, where D is the plunger and A, B, C parts for working it when it is desired to throw a charge into the reservoir H. The gasoline comes from a tank outside the building through the valve F, and is discharged from the pump through the pipe E into H. The disk with the hand wheel J is used to regulate the amount of oil going to the engine and when the pointer I is over the letter O the valve is wide open, but the proper amount of oil is supplied when the pointer is at R in this engine. The air is drawn in through the same chamber H by means of a pipe not shown in the cut, which ends un- der the base of the engine where as little dust as possible will be sucked in. 526 Farm Mechanics. 661. Governor. The governing mechanism for gaso- line engines varies in detail, but is usually a device by FIG. 256. Vertical gasoline engine showing governing mechanism. which the pump is made to supply a charge of gasoline whenever an explosion is desired and the essential parts of the mechanism are represented in Fig. 256, where E E are a pair of governing balls which revolve with the fly- Construction of the Gasoline Engine. 527 wheel and operate a finger in such a way as to prevent a charge being given to the engine whenever its speed is running too high. As the speed runs up the balls fly apart and this brings the finger C down upon the catch B FIG. 257. Pumping mechanism for supplying gasoline to gasoline engine. which holds the exhaust valve open and prevents the pump being worked. The catch and finger are more clearly seen 528 Farm Mechanics. at M in Fig. 257 where the upper K is the valve stem which also works the gasoline pump. 662. Valve Mechanism. The supply and exhaust valves for the engine of Fig. 256 are represented in Fig. 258 and FIG. 258. Valve mechanism of gasoline engine. are located in the chamber A of Fig. 256. The upper valve A is the exhaust and is represented forced down so as to open the port, allowing the burnt charge to escape up- Construction of the Gasoline Engine. 529 ward to reach the opening E in Fig. 258, which is the same as F in Fig. 256. When this valve is closed it is at H and is always controlled by the stem C worked by the revolutions of the fly-wheels. The supply valve B is represented closed and is held down by the spring K, which can be regulated by the ten- sion given through the jamb-nut L. This valve is lifted by the suction produced by the up-stroke of the engine pis- ton. The opening G is a water jacket around the valves to keep them cool. 663. Igniting the Charge. There are two methods of ig- niting the charge at the proper time, in these engines : one is by means of an electric spark which is produced at just the right time by means of a devise worked by the engine ; the other is by means of a hot tube which rises out of the chamber A, of Fig. 256, into the curved chimney standing just to the left of C B. This tube is kept at the proper temperature by means of a Bunsen burner fed through the cock shown above F and at L, Fig. 257. After the charge has been draw r n in and the piston is coming down in the cylinder so as to compress the gas, this compression forces a part of the explosive mixture up into this hot tube and when this is done the gas ignites and an explosion follows. If this tube becomes too hot the tendency will be for it to explode the charge too soon and either lessen the power of the engine or reverse its motion. If it is too cold the ex- plosion will be too late. After the tube has been used for some time a scale may form over it which prevents the in- ner wall from taking the proper temperature and it is then necessary to replace it with a new one. In replacing this tube it is necessary to use one which is adapted specially to the engine because if it is too large or too small, or too long or too short, its capacity will affect the time of the explosion and it will not be correct. 664. Lubrication Cleanliness of all working parts of the engine and proper oiling are matters of prime impor- 530 Farm Mechanics. tance and should receive the most careful attention. It requires a special lubricating oil for gasoline engines and only this oil should be used. It is known on the market as gas or gasoline engine oil. All parts should be care- fully wiped clean at frequent intervals to free them from grit or gummy products and the operator should uhvavs have an ear to the sounds of his engine and should know what are normal and what are not in order that he may the quicker discover when anything is getting out of order and remedy it in time. 665. Gasoline. Only the best quality of gasoline should be used with these engines, that known, as the "74 test gasoline." 666. Size of Engine In purchasing a motor of any kind it should be remembered that it is much better to get one which has a little greater capacity than will be needed than one which is a little too small ; and this caution ap- plies with special force to the gasoline engines, for the rea- son that their capacity cannot be increased above the nor- mal. With the steam engine it is possible to increase the steam pressure and the rate of firing, and the horse may for a short time develop two, three or even four horse- power, but if you overload a gasoline engine it must stop. If, therefore, it is desired to use steadily two full horse- power from a gasoline engine it should be not less than a three horse actual to do at all times perfectly satisfactory work. It should be said in this connection, however, that it is never economical of fuel to use a large engine to develop a small horse-power. A 10 H. P. engine could not be eco- nomically used when it is desired to simply pump water from an ordinary well or to run a small separator which a man can turn. There should be a rational relation be- tween the engine and the amount of work it is expected to perform, Windmill 531 WINDMILL. If we except horse-power and that of cattle there is no form of motor which has been so generally or so widely used on the farm as the windmill and its use is daily in- creasing, especially now since all parts are made of steel well galvanized to protect them from rust, and their rela- tive efficiency has been increased. 667. Work to Which the Windmill Is Adapted. It must not be understood that a windmill is well suited to furnish power for any and all kinds of farm work if only it is made large enough. On the contrary it is only adapted to certain lines where the work done can be accumulated at times when the wind is favorable. The windmill is peculiarly well adapted to pumping water for stock and for the supply of the house if only a suitably placed reservoir of sufficient capacity is provided. It must be remembered, however, that in many localities there may be periods of calm of three or even occasionally of seven days' duration when there will not be wind enough to permit the mill to do any work. For grinding grain for farm stock the windmill is pecu- liarly well suited, provided arrangements are made so that the grinder is automatically fed and the meal "allowed to drop into a bin where it may accumulate without personal attention. Arrangements of this sort may easily be made but it requires a special form of grinder which is not only automatic in its feed, but in the rate at which it feeds as well, supplying the mill heavily when the wind is strong and leaving the burrs empty whenever the wind falls so that no work can be done. Where an abundance of water is available, with a lift of only 10 to 20 feet, the windmill may be used to advantage in irrigating small areas of two to five acres, but in such cases it will usually be necessary to provide a reservoir of suitable size into which the water may be pumped and stored. 532 Farm Mechanics. For wood sawing also the windmill may often be used to advantage, bj getting everything in readiness to do the work on those days when the wind shall be strong, but for this kind of work mills as large as 12 to 16 feet in diameter are required. 668. Wind Pressure The pressure which the wind may exert upon a surface depends primarily upon (1) its weight per cubic foot, (2) its velocity, and (3) the angle at which it strikes the surface. The weight of the wind per cubic foot is greater when the air temperature is low and when the barometric pressure is high ; this being true, the capacity of a windmill in a given place varies with the season, being greatest in winter and least in summer, for like wind velocities. As the weight of a cubic foot of air decreases with alti- tude windmills at sea level can do more work than those at bights of 1,000, 2,000 or 3,000 feet, when the air tem- peratures and wind velocities are equal. 669. Relation of Wind Pressure to Wind Velocity. When conditions are similar wind pressures increase as the squares of the wind velocity. Thus, if the wind pres- sure at 5 miles per hour is taken as 1, then at 10, 15, 20, 25, 30, 35 and 40 miles per hour the wind pressure will increase in the ratio of the squares of the numbers 2, 3, 4, 5, 6, T, 8 ; that is to say, a 10 mile wind may exert 4 times the pressure that a 5 mile wind does, and a 40 mile wind a pressure 64 times as great. Taking the air at a pressure of 2,116.5 Ibs. per sq. ft. the wind pressures at different velocities and temperatures will be as stated in the table below : Table giving the pressure of the wind per sq.ft. at different velocities and temperatures when the barometric pressure remains the same. ( Wolff.) Wind velocity, miles per hour.. 5 10 15 20 25 30 35 40 Pressure at temperature of H0 F .126 .505 1.135 2.0l?< 3.156 4.548 6.195 8.099 Pressure at temperature of 60 F .1187 .475 i.o jy 1.902 2.973 4.284 5.836 7.628 Windmill. WO. Ability of Wind to Do Work. The work which wind can do depends upon the amount which passes through a given windmill per minute and the pressure which it exerts, But as the pressure varies with the square of the velocity, and the quantity passing the mill varies di- rectly as the velocity, the theoretic working capacity of the wind must increase as the cubes of the wind velocity. Thus with miles per hour of 5 10 15 20 25 30 35 40 Or, taniiiK 5 = to 1 they are as . 1 2 3 4 5 6 7 8 The relative horse-powers are as- 1 8 27 64 125 2lf 34H 512 Theoretical horse-power is .025 .2 .675 1.6 3.125 5.4 8.575 12.8 Perry regards it approximately correct to state that a 12 ft. windmill in a 5 mile wind may develop ^ of a horse-power and the figures in the last line in the table above are his. 671. Relation of Diameter of Wheel to Its Efficiency. In increasing the horse-power of an engine it is not usually necessary to increase its weight and strength much more than in proportion to the increase of power which is to be developed, but in the case of two wind wheels, having the same type of construction, the one which is to develop double the horse-power must have a strength of resistance practically 8 times as great in order to withstand the high- est wind pressures to which it is liable to be subjected. This is so because doubling the diameter of the wheel not only makes the surface of wind pressure four-fold, but at the same time carries the center of pressure farther from the axis of the wheel, causing it to act upon a longer lever arm. But to increase the strength of resistance of the wheel 8-fold makes it necessary to build it much heavier and this detracts from its relative efficiency. Besides this, with wheels of large diameter there are much greater differences in the wind pressure on the dif- ferent parts of the wind sails because the actual velocity 534: Farm Mechanics. of the sails increases with the distance of their points from the center of the wheel. But the angular velocity must be the same in all parts of the sail, and this causes the wind sail to be forced around away from the wind passing through the wheel with very different velocities, and this difference reduces the relative efficiency so that large wind- mills of like pattern do not increase the available horse- power as much as the size is increased. 672. Unsteadiness of Wind Velocity. It should be under- stood that the wind rarely blows with anything like uni- form velocity for even a single minute, and an anemometer which gives the total number of miles of wind in an hour furnishes no sufficiently reliable data from which to cal- culate the work which the windmill should be expected to do. It very often happens that a wind which is registered as 10 miles per hour may have been blowing during a con- siderable portion of the time at the rate of 20 miles per hour and these high velocities are very much more effective than the mean 10-mile wind, and this would cause the wheel to show a relatively high efficiency in such a case. 673. Hight of Towers. The wind velocity near the earth's surface is not only less than at higher elevations at the same time, but near the ground it is very much less uniform, so that for both of these reasons mills should be placed upon as high towers as practicable when the great- est efficiency is desired. If there are obstructions to the wind movement even within 1,000 feet of the windmill the tower should carry it several feet higher than these. Observations indicate that, taking the velocity of the wind at a hight of 50 feet as 1, at 25 feet its velocity would be nearly .8 ; at 75 feet it would be 1.2 and at 100 feet it would be nearly 1.4. These are deduced from Steven- son's formula,* which is H+72 V = v ~122~ Journal of the Scottish Meteorological Society, 1881, Windmill. 535 where V is the velocity at the hight of the tower, v the ve- locity at 50 feet, and H the hight of the windmill. Taking the efficiency of the wind as increasing with the cube of the velocity, the relative efficiency of the same mill at the four hights would be at 25 feet .51, at 50 feet 1, at 75 feet 1.73 and at 100 feet 2.74, from which it appears that a mill placed on a 100-foot tower may have more than 5 times the efficiency of one placed at 25 feet, and a mill on a 75 foot tower is likely to do three-fourths more work than one on a 50-foot tower. 674. Observed Amount of Work Done by a Windmill in Pumping Water. We have measured the amount of water which was pumped during one entire year by the 16-foot geared windmill represented on the cover of this book.* This mill was provided with three pumps arranged so as to lift water 12.85 feet whenever there was wind enough to enable it to do any work. When the wind was lightest it was given the pump of smallest capacity, when stronger the one of next size, when still stronger both pumps to- gether, the third pump being used only in the very high- est winds. The water was pumped into a large tank holding 141.2 cu. ft., so arranged that when full it emptied itself auto- matically in f of a second, and at the same time recorded the time of emptying. In connection with this an auto- matic U. S. Weather Bureau anemometer made a continu- ous record of the miles of wind passing through the mill each hour of the day for a whole year and the amount of water pumped during the same intervals. The amount of work done by this windmill during 10- day periods for the whole year is computed in acre-inches of water lifted to a hight of 10 feet and expressed in the table below: Bulletin 68, Wisconsin Agricultural Experiment Station. 536 Farm Mechanics. Table showing computed amount of water lifted 10 feet high during consecutive 10-day periods for one full year, ex- pressed in acre-inches. Date. Water pumped. Date. Water pumped. Date. Water pumped. Feb. 28-Mch. 10 Acre- in. 33.f4 July 8-18... A ere- in. 21.53 Nov. 15-25 Acre-in. 53.77 Mch. 10-20 3 r^ A ^-::-^:':'^ y^ - V" ^^^^^^^'''^'^i t ^ ^^^ummmii ^Q , ^ >~-SMS^SlSS >^/^faifeteliiiii FIG. 273. Diagram showing the origin of tornadoes and thunder storms. 588 Principles of Weather Forecasting. 747. Schools of Tornadoes When the conditions are ex- tremely favorable for the formation of tornadoes they often appear in schools, originating one after another or simul- taneously, as the main storm center progresses across the country, and Fig. 273 shows how these local but violent storms are related to a storm center and how many may develop in the southeast quadrant as it travels along. In this figure the short, heavy straight lines to the southeast of the center represent the paths of tornadoes which devel- oped during its course. 748. Distribution of Thunder Showers. Thunder show- ers, like tornadoes, originate in the great majority of cases to the southeast and south of a well developed storm center and often large numbers of them, scattered over consider- able areas, form as the storm progresses, much as is the case with tornadoes, and Fig. 274 is a diagram showing the advance of the front along which thunder showers orig- inated in a storm of early May, 1892, as recorded in the Monthly Weather Review of that month, p. 138. On May 3 a long low area had advanced from the south and west and at 8 P. M. its lowest portion was central north of Lake Huron. The front of the thunder shower line had reached the east end of Lake Erie at 2 P. M. of the same date and showers were in progress along the line marked 2 P. M. in Fig. 274. As the storm center ad- vanced the thunder-shower-front also moved forward and swept across the state, as shown by the curves on the dia- gram, reaching Long Island at 2 A. M. on the morning of May 4th, the front thus progressing from 20 to 30 miles per hour. 749. Conditions Tinder Which Thunder Showers and Tor- nadoes Originate. In the diagram of Fig. 273 are repre- sented the wind directions and temperature relations which exist when conditions are favorable for the formation of both of these classes of storms. There is a region of warm moist southerly winds to the south and east of the low area Formation of Thunder Storms. 589 and another region of decidedly colder winds blowing from the west and north of west ; and it is along the meet- ing of these two systems of winds that thunder showers tend specially to form, and in advance of it that the tor- nadoes have their birth. FIG. 274. Diagram showing the progressive development of thunder storms. 750. Formation of Tornadoes. The most satisfactory ex- planation of the formation of tornadoes is represented in the lower portion of Fig. 273, which is a cross-section of the lower portion of the atmosphere at right angles to the line dividing the two systems of winds shown in the upper portion of the same diagram. It is supposed that, under these conditions, the cold west and northwest winds at times over-run the moist warm and lighter southerly stratum, thus producing a condition of unstable equilibrium. When such conditions have been developed the warm air, at some point, is supposed to break up through the over-running colder layer, as shown in the lower right-hand corner of the diagram, and in do- 590 Principles of Weather Forecasting. ing so is thrown into a rapidly whirling movement in the same manner that water runs into whirls in discharging through the bottom of a wash-bowl. When the volumes of air which must change places are large and the stratum of cold air deep, there comes ultimately to be developed an enormous rotary velocity which gives to the air an ex- tremely destructive power. V FIG. 275. Diagram of the path of a tornado. 751. Explosive Violence of Tornadoes. At the center of a tornado cloud the rapidly whirling motion reduces the air pressure at the center of the funnel so much as to pro- duce a high vacuum, and when a building lies in the path of the funnel the vacuum surrounds it so suddenly that often the great pressure of air within the building will throw the walls outward or lift the roof off before the air has time to escape into the vacuum formed by the tornado. Formation of Tornadoes. 591 752. Unsteady Action of Tornadoes. A tornado seldom displays a uniformly destructive power and oftentimes the point of the funnel fails to reach the ground and con- siderable gaps are passed in the path where little damage is done. This unsteady action is often due to the slowing up of the rotary motion in the cloud due to the great fric- tion developed at the ground. After withdrawing to the upper air the speed increases sufficiently to allow the fun- nel to grow to the surface again and resume the destructive work. When the funnel reaches the surface it does not always describe a straight path along the ground, but tends to cross and recross the main axis of movement. FIG. 276. Diagram showing the rotary movement of winds in a tornado. 753. Character of the Tornado Path. It is usually true that the path of a destructive tornado is not symmetrical, one side being wider than the other, as represented in Fig. 275, where it will be seen that the northwest side is nar- rower than the southeast side. Not only is the zone of de- structive winds wider on the south side but that of the sensible winds is also. On account of this character of the tornado track it is clear that if one has an occasion to escape from an ordinary tornado, the shortest path would 592 Principles of Weather Forecasting. lie to the northwest, at right angles to the line of progress. The evidences of a rotary motion of the air in a tornado are abundant and conclusive, and in Fig. 276 are repre- sented some of these. 754. Formation of Thunder Showers. Thunder showers appear to have an origin similar to that of tornadoes, but evidently occur where there is less air to change places, and probably also where the depth of the overlying stratum is less. Indeed, it appears very often, if not generally, true that a volume of cold heavy air has dropped directly to the ground and is moving bodily against the warmer moist air, which it is forcing upward, as represented in the lower left-hand corner of Fig. 273. The rapidly ascending warm moist air is cooled by expansion and by mixing with the cold air, thus giving rise to the heavy precipitation so often observed. The rolling movement shown in the diagram is often violent enough and involves so great a hight in the at- mosphere, that often raindrops are carried round and round until they become very large before they are able to fall. If the vertical circulation reaches above the zone of freezing temperature the raindrops freeze, forming hail. These hailstones, in the most violent storms, are often carried around with such force and so many times that they become very large before they are able to overcome, by their weight, the velocity of the air ; and fall to the ground. INDEX, Air, movements through soil, 125 ; elas- ticity of, 8 ; moisture absorbed from by soils, 177 ; need for in soil, 204 ; volume changes with temperature, 207 ; volume of in soil, 208 : composition of respired, 350 ; micro-organisms In, 3t>2 ; amount respired, 355 : depth of, 556 : com- position of, 556 ; materials suspended In, 557 : functions of ingredients, 557 ; pressure, 559 : temperature of, 560 ; movements of, 561 ; general circula- tion, 562, 564. Atoms, 7. B Babbitt metal, 515. Baker, J. O., drainage system of Ron- toul, III., 309. Balloon frame, 340. Barley, nitrogen used by, 62 ; alkali salts limiting growth of, 94 : water used by, 143 : root development of, 150, 153 ; germination temperature. 212. Barn frames, forms of, 339; plank, 340; balloon, 340; round, 341. Barns, frames of, 339, 340, 341 ; best temperature for, 344 ; relation of hight to capacity, 367 : separate or consolidated, 370 ; avoiding posts in, 374 ; stable floors, 374 ; watering in, 388 ; unloading hay in, 391 ; ventila- tion of. 350. Barometric pressure, 559, 568, 569 : changes influence' soil' ventilation, 208 ; causes change of level of water in wells, 173 ; of rate of discharge from springs, 273 ; of rate of dis- charge from tiled drains, 271 ; changes of in storms, 575, 582. Basement stables, ventilation of, 355, 356, 364 ; may be sanitary, 364. Beams, strength of, 331, 332, 334 : com- puting loads for, 336 ; table of safe loads, 338. Beans, nitrogen used by, 82 ; germina- tion temperature, 212. Bedding, use of, 376. Beef fat, fuel value of, 33. Belting, 543 ; action of, 543 ; efficiency. 543 ; computing size, 544 ; care of. 544 ; management of. 545 ; lacing of, 545 : computing length of, 546. Berthelot, on soil nitrogen, 89. Tlidwell, stall, 385. Boiler, 508 : construction of. 509 : care of, 512 ; cleaning, 512: firlne. 51:{; foaming, 513 ; low water in, 514 ; ex- plosion of, 514 : soft plug, 51 1 ; water for, 515, 517. Boiler scale, 512, 517. Box stall, ventilation of, 387. Braces, uses of, 338. Brick, walls of, 347, 402 ; vitrified, 403. 594 Index. Brick-lined silos, construction of, 403 ; lining for, 406. Brick silos, construction of, 400 ; strengthening walls of, 401, 402. Brown-Sequard, on respiration, 352. Building paper, for walls, 348 ; for silos, 41o. Calcium, essential plant food, 69 ; func- tion of, 71. Calm belts, .jUo to <'.'.>. Capillarity, modified l>y dissolved salts, 106 ; principle of, .'57. Capillary capacity, innxinnim of soils for water, 182 ; of sands for water, 134 ; influenced by distance above standing water, 134. Capillary rise, in glnss tubes. 37. Ifil : of water in soils, 103 ; in sandy loam, 165 : in clay loam. 10.> ; in sand. 107 ; in wet soil, 1G8 ; in dry soil 168: in- fluenced by rain. 170, 190 ; by farm yard manure. 172, by soil mulches, 173. by firming the soil, 174, by sub- soiling. 199. Carbon dioxide, mode of escane from lungs, 6 ; number of molecules in one gram, 10 : removed by soil ventilation 206 : causes flocculation of clay, 210 inexpired air, 350 : heavier than air 361 : danger from in filling silos, 427 source of carbon in plants. 554 : per cent, of in atmosphere, 557 ; influ- ence of on temperature, 558. Cattle, normal temperature of. 344 ; ties for. 384 : tying for feeding, 387. Cement, kinds of, 379 ; for silo walls 398, 402, 406, 407. Cement floors, 379 : condensation of moisture on, 351 ; temperature of, 375 ; construction of, 379 : materials for. 380 : ratio of ingredients for, 381 : laying. 382 : cost, 383 ; for cel- lar or creamery. 383; for silos, 410. Chamberiin, cause of glacial periods, 559. Cheese curing rooms, masonry walls for, 347 : construction of. 347. 348. Chemical changes produced by ether waves, 24 : influence of on soil tem- perature. 219 ; source of power in en- gir.ps. 486. Chemical nature of soils, 69, 74, 75. Chlorine, essential to fertile soil, 69. Chloronlivll. requires iron In soil, 70: cells. 143. Clay, difference between puddled, and soil. 233 : shrinkage checks when drained, 290. Clay soil, aluminum silicate In, 49 ; com- pared with sandy. 71, 74, 75, with others, 73 : amount of plant food per acre foot, 80 : flocculation by carbonic acid, 210. 290. Clover, plant food contained In 79 ; sowing seed before frost is out, 193 ; germination temperature, 213 ; water used by, 141 ; extent of root develop- ment, 150, 156. Coal, fuel value of, 502. Coal tar, use on floors, 377 ; use on silo linings, 407. Coathupe, amount of air respired, 353. Cohesion, 6. Cold, nature of, 25. Cold waves, 582. Colin, amount of air breathed, 354. Collars, for tile drains, 292. Color, influence on soil temperature, 217 ; waves of, 23. Conservation of energy, 19. Contour maps, of surface, 256 ; of ground water, 257, 259. Corn, variation of soluble salts in soil under with season, 96 ; water used by. 141; root development of, 150, 152. 154, 157 ; early fitting of ground for. 185; danger in late cultivation, 189. 190; best time to cultivate, 192; hill- ing 194 ; plowing for in fall, 252 : grinding by windmill, 536. Coulter, effect of on draft of plow, 243 Cover crops, object of, 183 ; danger of, 201. Cows, normal temperature of, 344 : stable temperature for, 344 ; amount of air respired, 354 ; supply of air for. 355 ; cubic feet of space for, 357 ; ties for, 384. Crops, amount of water required by, 139: proportion of soil water avai- lable to, 135 ; soils which yield moist- ure most completely, 136. Cultivation after heavy rains, 190 depth of to save moisture, 191 ; fre- quency of, 187 : frequency vary with season, 191 ; influence of frequency on mulches, 189; influence of depth on effectiveness of soil mulches 189 ridged and flat, 194 ; too great fre- quency undesirable, 189. Cultivators, for intertillage, 226- spring tooth, 227; with wiae shovels' 227; with rigid teeth, 228; teeth of adjustable, 228 ; disk form, 229 for surface cultivation, 229 ; garden types, Culverts, 479. Cyclone, 562, 570, 571, 572, 576; trop- ical, 585. Cylinder of pump, in well. 546, 551 ; of steam engine, 518, 520; water jacket for in gasoline engine, 524 ; o* double acting pump, 550. D. Darcy's law, 262, 269. Darwfn formation of soil, 65 ; soil con- Index. 595 Denltrifleatlon, process of, In dry earth closet, 90 ; ill sewage water, 90 ; in water-logged soils. 90. 205 : in marsh soil, 90. Deodorizing milk, 16. Deodorizer, 17. Deserts, relation to wind zones, 565. DeVries, alkali salts, limiting plan growth, 93. Diffusion, principles of, 40 ; influence o temperature on, 40 ; slow rate in soi 40 ; in plant feeding, 46 ; in soil ven tilation, 207. Disease, caused by lack of ventilation 352. Disk harrow, 234 : use in early spring to develop mulch, 185 ; to fit seed bee 234. Distributing cart, 469, 470. Ditch digging, 322 ; shaping and eradin bottom, 322 ; placing tile in, 324 ; fil ing, 328. Dog, normal temperature, 344. Doors, construction of for silos, 396 399, 403, 411, 421, 423 ; strengthen ing wall between, 399, 402, 410, 423 Draft on macadam road, 18 ; of plow 241, 243 ; influence of soil moisture on draft of plows, 244 ; line of in plow, 246 ; principles of, 428 ; rela tion to grade, 430 ; of wagons, 434 436, 490 ; relation of width of tire to 436 ; of size of wheel, 437 ; of dis tribution of load. 438 ; of line draft, 440, 492, 497 ; of rigidity of carriage, 442 ; of speed, 491 ; of hours work per day, 492 ; of weight horse, 493 ; of distribution of weight in the horse, 494 ; of strength of hock muscle, 494 ; of width of hock, 495 ; line of in sweep power, 502. Drainage, remedy for alkali lands, 98 ; rate of, determined by pore space, 115 ; may increase available soil moisture, 139, 288 ; influence on soil ventilation, 210, 290 ; influence on soil tempera- ture, 222, 228 ; necessity for, 286 ; in- creases root room, 287 ; conditions re- quiring, 287 : interception of surface, 306; of basins without outlets, 307; of flat areas, 309 ; intercepting under- flow, 307 ; practice of, 311 ; tools for, 312, 321 ; determining levels for 312 ; of roads 445, 448, 449 ; water-breaks, 449. Drains, fluctuations in rate of flow from. 270 ; barometric changes in rate of flow from. 271 ; temperature changes in rate of flow from. 271 : kinds of, 290: depth of. 292: distance be- tween, 296 ; surface of ground watei between, 297 : rate of change of ground water between, 297 : gradient for, 298 : uniform fall for important, 298 : outlet for, 302, 303 : connection of sub-main with main, 303 : joining lateraf with main, 303 ; obstructions to, 303 ; laying out systems of, 304 ; construction of surface, 30(J ; levoMin? for, 312 ; locating mains and laterals, 315 ; determining grade and depth, 317 ; changes in grade. 310. Drown, cow stall, 385. Dry earth closets, denitriflcation in, 90. Dust in soil formation. ti4 : micro-organ- isms, in of houses and stables, 352 ; avoiding in concrete, 380 ; of atmos- phere, 557, 558. E. Ebermayer, best temperature for growth, 212 ; observed soil temperatures, 314. Eel grass, 63. Elbows, resistance to flow of water, 550. Elliott, C. G., size of tile, 301, 302. Energy, 19 ; conservation of, 19 ; trans- formation of, 20 ; solar, 20, 22 : unita of, 27 ; amount required to melt ice, 30 ; to evaporate water, 31. Engine. 518 ; steam, 502 ; gasoline, 522 ; see steam and gasoline. Erdmann, function of potash, 70. Ether waves, 21 ; velocity of, 22 ; kinds of, 23 ; transparency to, 24 : produce evaporation and chemical changes, 24. Evaporation, 24, 30 : heat required for, 30 ; rate of influenced by dissolved salts, 106 ; influence of on soil tem- perature, 32, 220. Evener, kinds, 496 ; principles of, 497 ; giving one horse the advantage, 498 ; more than two horse, 499. Fallow ground, nitric acid In, 84 ; ni- trates in, 103 ; loss of nitrates from, 104. Farm buildings, frames, 340 ; means of controlling temperature, 346 ; lighting of, 348 : ventilation of, 350. 'arm machinery, 538. Farm motors, kinds, 486 ; tread power, 499 ; sweep power, 501 : steam engine, 502 ; gasoline engine, 522 ; windmill, 5oT. Fattening animals, best temperature for. 344. 'eeding, of odor producing foods, 15. errel. world system of winds. 563. ertility, of soils in arid regions, 50 ; conditions essential to. 69. "ertilizers, diffusion of through soil. 11; influence of, on amount of nitrogen removed from soil, 82. 'ield soils, permeability of to air, 127 ; weight of dry, per cu. ft., 127 ; heavy and light, 128. issures in rock, 53. lavors, in dairy products. 14 : how they are absorbed, 14 ; removal of. Iti"; time to feed odor-producing foods, 1. 596 Index. Floors, stable, 374 ; temperature of, 375 ; wood, 377 ; stone, 378 ; cement, 379 ; comparative cost, 383 ; manure drop, 388. Foaming, in boiler, 513. Foot-pound 18, 27 ; equivalent in beat units, 28. Foot-ton, 18, 27. Frank, symbiosis, 88. Frear, Dr., soil temperatures, 214. Freezing, with ice and salt, 30. Friction, 538 ; kinds, 538 ; between sol- ids, 539; rolling, 540; of fluids, 540; lubricants, 541 ; influence of grit on, 542. Furrows, dead and back, 49. G Gage, cocks, 510 ; glass, 510 ; pressure, Galvanized iron, silo lining, 414. Gardens, early plowing of to save moist- ure, 185 ; floating, 205 ; cultivators for, 230. Gasoline engine. 522 : parts, 523 ; work- ing cycle, 523: cooling of parts, 524; types of, 524 ; construction, 525, cylinder, 525, pumping mechanism, 525, governor, 526. -valve mechan- ism, 528 ; igniting charge, 529 ; lubri- cation, 529 ; gasoline for, 530. Gasoline, for engine, 530. Germination, interfered with by green manure, 201 : retarded by too early seeding, 201 ; oxygen needed for, 204 ; temperatures for, 213 ; rate of in- fluenced by soil temperature, 214 ; of weed seeds, 225. Glacial soils. 57. Governor. 521, 526. Grade, 428 ; effect on draft, 429 ; steep- est admissible, 430 ; conditions which determine, 433. Grain, ratio of to straw, 80 ; harrowing after up. 192, 224 ; rolling after up, 192, 224 : fitting seed bed with disk harrow, 235. Grapes, affected by alkalies, 93. Gravel, 457 ; for road surface, 456 ; char- acter, 458, 459 ; altering texture, 458. Gravel roads, 459. Green manures, danger from, 201 ; plow- ing under, 253. Grinding, by wind mill, 531, 536. Ground water, movements of, 255 ; con- tours of surface of. 257, 259 ; changes in level of, 260 ; elevation of through percolation, 260 ; changes with season, 260 : general movement of across wide areas. 270 ; fluctuations in rate of flow of, 270 ; changes in rate of flow due to barometric changes, 271 : diurnal changes in rate of flow of, 271, 272 ; rise of away from drainage outlets. 203. 285 : observed surface In tile-drained field, 297 : rate of change in level between tile drains, 297. Guard cells, 143 ; action of, 144 ; loss of water through, 145. Haberlandt, temperature of germination, 214. Hail, formation of, 524. Harrow, spike-tooth, to save moisture, 185 ; disk harrow to save moisture, 185; for small grain after it is up, 192 ; for corn and potatoes after they are up, 192 ; tilting, 225 ; use in kill- ing weeds, 224, 225 ; spring tooth, 233 ; smoothing type, 236 ; should follow roller, 237. Harrowing, influence of on soil ventila- tion. 210 ; after plowing. 252. Hay, arrangements for unloading, 391. Heat, 25 ; mechanical equivalent. 28 ; specific, 29 : latent. 29. 5N1 : froin green and wet woods, 35 ; control of in animals, 343 ; normal for animals, 343 ; construction to prevent change, 345 ; produced by muscular action, 488 ; loss from engines 506. Heat unit, 28 ; number of consumed In melting and in evaporation, 30. 220 ; number of, In one pound of beef fat, and one pound of milk, 33; value of wood in, 35 ; value of coal In, 502. Hedges, as wind breaks, 202. Hellriegel, on symbiosis, 87 ; effect of temperature on rate of germination, 214. Hens, air breathed by, 354, 355. Herbst, respiration, 353. Hilgard, soil analyses, 71, 74, 75 ; humus of arid climates, 76 ; alkali salts limiting plant growth. 93 ; on hygroscopic moisture, 177, 179. Hock joint, 495. Hoops, for silos, 399, 422. Horse, normal temperature of, 344 ; air respired by, 354 ; supply of air for, 355 : as a motor, 487 : generation of energy by, 489, expended in hauling loads, 490, in plowing, 491 ; trac- tion of 491 ; principles of draft of, 493, 494, 495, 496 ; equalizers for, 496, 499 ; in tread power. 500. Horse power, 27 ; measure of solar en- ergy, 22 ; equivalent of, consumed In melting ice and in evaporating water, 30 : of horses, 490, in hauling loads, 490, in plowing, 491 ; in tread power, 500 : of engine. 530 ; trans- mission of by belts, 544. Hot box, 542. Hot tube, 529. Humus. 76 ; of arid and humid climates, 76 : loss from and need for in sandy soils, 206 ; on sandy roads, 457. Index. 597 Humus soil, formation of, 55, 61 ; plant food per acre foot, 80. Hurricane, West Indian, 584, 585. Hutchinson, respiration, 353. Hydraulic ram, 552. Hydrogen, rate of molecular vibration, 9 ; size of molecules, 10. Hygroscopic moisture, 175 ; movements 'of, 175 ; relation of to diameter of soil grains, 176 ; amount absorbed by soil, 177 ; influence of temperature on, 179. Ice, melting of, 29 ; In soil formation, 57 ; for cooling milk, 34 ; melting for water, 35. Illinois soils, nitrogen in, 82. Injector, 516. Infiltration pipes, lowering ground water, 295. Ions, 48. Iron, essential to fertile soil, 69 ; func- tion of, 70. Irrigation, by windmill, 531, 536. Isobars, 568, 569, 575, 584, 585. Jaffa, humus of arid climates, 76. January, winds of world, 567, 568. Jeffery, denitrification, 90. Jointer, attachment for plow, 249 ; use in plowing under green manure, 253. Joule, heat unit, 28. July, winds of the world, 567, 569. Kelvin, Lord, size of molecules, 9 ; solar energy, 22. Kosswitch. symbiosis, 88. Kuhn, Julius, connection of lateral with main drain, 303. Kunkle, safety valve, 512. Lacing, belts, 545. Lakes, in formation of humus soil, 62. Laurent, symbiosis, 88. Lawes, Sir J. B., Rothamstead experi- ments, 81. Lawes and Gilbert, nitrogen in soil, 82. Leaching, effect of in soil formation, 77 ; a correction for alkali lands, 95. Leveling a field, methods of, 314 : con- tour map. 315 : locating mains and laterals, 315 ; laying out drains, 317 ; determining grade and depth, 318 ; changing grade, 319. Levers, of arm, 489 ; mechanical prin- ciple of, 498. 38 Lighting, farm buildings. 348 ; efficiency of windows, 349. Lime, function of in plant life, 71 ; amount removed by crops, 79 ; amount in soil, 80. Limestone, formation of soil from, 52. 78 ; source of water supply, 276 ; for road metal, 466, 469 ; for binding, 466. Line of draft, in plow, 246 ; in wagons. 440, 441. Lining, for silos, 413 ; brick, 402, 406, 403 ; galvanized iron, 414 ; 4-inch flooring, 414 ; half-inch boards and paper, 415 ; painting, 418. Loam, effectiveness of as mulches, 186. Loess, 64, 73, 74, 75 ; amount of plant food in acre foot, 80. Los Angeles Water Company, diagram of flume, 295. Low area, 494, 507 ; course of, 505 : re-i latlon of to cold waves, 514'; to warm dry periods, 515. Lubricator, Swift, 521. Lubricants, 541 ; reduction of friction by, 541 : selection of, 541 ; for gaso- line engines, 529. M Macadam, Engineer, 462, 467 ; roads, 462 ; road-bed for, 463 ; rock for, 46'4, 466 ; without binding material, 467 ; thickness of, 473 ; rolling of, 473 ; for stable floor, 378 ; for barn yard, 379. Magnesia, as plant food, 69 ; function of, 71 ; amount removed by crops. 7J> ; amount in an acre foot of soil, 80. Mairs, T. J., draft of wagons, 437. Man, oxygen consumed, influenced by temperature, 345 ; air respired by, 353, 354. Mangers, 388. Manitoba soils, nitrogen in, 82. Manure, effect of capillarity, 172 ; as mulch for meadows, 193 ; green. 201 ; ventilation hastens fermentation, 206; plowing under, 253. Manure drop, 388. Maple, fuel value of, 35. Maps, contour of ground water, 257, 259 ; of surface, 256. Marsh soils, formation of, 62 ; analyses of, 73, 74, 75 : as mulches, 186 ; tem- perature of, 220. Masonry walls, relation to temperature, 347 ; for silos, 397, 400. 405, 409, 422. Maxwell, size of molecules. 10. Melon, temperature for germination, 212. Melting of ice, 30, 35. Micro-organisms, in soil, 50 : convert humus into nitric acid, 76 ; soil al- gae, 88 ; nitrifying germs, 89 ; de- nitrifying germs, 90 ; require air, 205 : in air of unventilated buildings. 352, dangers from, 353 ; in the atmosphere, 557. 598 . Index. Milk, odors and flavors in, 14 ; deodoriz- ing of, 16; cooling of, 17, 34; value : of, in neat units, 33. Mixed herbage, nitrogen used by, 82. Molecules, 6 ; composed of atoms, 7 ; .' not in contact, 8; movements of, 8, 13 ; diffusion of, 8 ; relation to elastic- ity, 8 ; velocities of, 9 ; number of per . gram, 10, 11 ; size of, 9 ; relation of to steam pressure, 19 ; movements in evaporation, 24; dissociation of in so- lution, 48. Monsoons, 570. Morin Gen., draft of wagons, 443 ; fric- tion, 540. Motors, farm, 486. Mulches, effectiveness of, in marsh soil, 186 ; sandy loam, 186 ; clay loam, 186 ; character influenced by frequency of cultivation, 187 ; depth of. 189, f 191 ; depth and frequency of stirring should vary with season, 191 ; de- veloped by rolling, 193 : other than soil, 193 ; for alfalfa fields, 193 ; for meadows. 193. Miintz. denitriflcation, 90. Muscles, as motors, .487 ; temperature of in action, 488 ; power of, 488 ; of hock, .494. Mustard, temperature of germinatioa. 212 N Nitrates, seasonal changes under corn, 96 : in cultivated and uncultivated ground, 100 ; relation of to total sol- uble salts, 101 ; closeness of removal of by plants, 101 ; in fallow and crop- ped ground compared. 103. 105 ; loss of during wintej, 104 ; development influenced by. cultivation, 105 ; by late . ,fall plowing, 182 ; loss of lessened by cover crops, 183 ; developed by early tillage. 185 ; air required for develop- ment 206; temperature for formation, 212, 215. Nitric acid, amount of in soils, 84 ; in . fallow ground^. 84 ; action of ozone and 'peroxide of hydrogen in formation of, , 86 ; formation, of, 89 : formed by niter 'germs, 89; in' atmosphere, 557. Nitric nitrogen, in soil, 84 ; limiting amount for corn and oats, 102, Nitrification, process of, 89 ; tempera- ture for, 212. Niter germs, forming nitric acid, 89; temperature for growth of, 212. Nitrogen, . essential to plant life, 69; form . of used by plants, 70 ; from humus, 76 ; amount removed by crops, 79, 82 ; amount stored in soils, 82 ; forms of occurrence in soil, 82 ; dis- tribution of in soil. 83 ; source of in ' Boil, 85 ; accumulated by ' symbiosis, 87 ; increased in soil, by ventilation, 206 ; of plants derived from air. 554 ; amount In air, 556 ; functions of, 558. Nobbe, function of potash, 70. Nobert, ruling of glass by, 9. Nollet, Abb6, 41. Northers, of Texas, 586. Oak value of one pound of in heat units, 35. Oats, water used by, 141 ; nitric nitrogen limiting growth, 102 ; extent of root development, 150, 155. Odors, 8, 13; in dairy products, 14; accumulation of in dairy products, 14 ; removal of, 16. Oemler, specific heat of soils, 215. Orchards, late tillage of to conserve moisture, 182; early plowing for, 185. Osmosis, phenomena of, 41; principles of, 42; measurement of pressure, 43; in plant feeding. 46. Osmotic pressure, 42; influence of tem- perature on, 46; increased by dissocia- tion of salts, 48. Oxalic acid, action in plant growth, 70, 71. . Ox-bows. .55, 57, 62. Oxygen, absorption of in breathing, 6 ; rate of molecular motion, 9 ; size of molecules, 10 ; essential to germina- tion, 204 : uses in soil. 204 ; essential to plant breathing, 204 ; amount con- sumed by man varies with tempera- ture, 345 ; demand for necessitates ventilation, 350 ; amount in air, 557 ; functions of, 557. Ozone action of in forming nitric acid, 86 ; in atmosphere, 557. Paper, function of in walls, 348 ; es- sential qualities. 348 : for ventilators, 364 ; for silos, 400, 407, 415. Peas, temperature for germination, 212. Peat, formation 1 of, 62. Percolation, rate influenced by pore space, 115; of teoil moisture, 158; rate of through sand and soil, 159 ; through dry . sojl. 160 : rate of in- creased by sub-soiling, 199 : influence of on soil ventilation. 209 ; rise of ground water due to,' 260. Pfeffer. osmotic pressure. 44, 4fi. Peroxide of hydrogen, action of in form- ing nitric acid, 86. Perspiration controls body tempera- ture, 33. Phosphoric acid, in soil, 74, 78, 80; amoiint removed by crops. 79. Phosphorus essential to plant life, 69; function of, 70. Pillars;' strength of, 330; bearings for, 330. Piston, of steam engine. 519 : of gasoline engine, 525 ; size of for pumps, 547. Index. 599 Pit silos, 423. Plank frame, 340. Flanker, use of, 236. Plant food, essential constituents, 69 ; functions of, 70 ; proportion of total soil, 78 ; amount removed by crops, 79 ; in an acre-foot of soil, 79, 81 ; con- served by early seeding, 201 ; Impor- tance of temperature in development of, 212 ; loss of through weeds, 224 ; manner of supply to plants, 46 ; de- rived from the air, 554. Plants, growth of limited by soluble salts, 93 : breathing of, 142 ; respira- tory organs of, 142. Plastering, silo walls, 398, 402, 403, 406, 407. Plow, 238 ; as a tool to develop texture, 238; forms of, 239; for sod, 240, 241 ; soil and function determine form, 240 ; for pulverizing soil, 242 ; for mellow soil, 242 ; draft of, 243, 244. 245 ; draft influenced by soil moisture, 244 ; line of draft in, 246 ; scouring of, 247 ; care of, 247 ; jointer attachment for, 249 ; sub-soil form, 250. Plowing, to conserve soil moisture, 181, 182, IS'! ; early for corn and potatoes, 185 ; may puddle soils, 239 : to cor- rect texture. 239; depth of, 250; con dition of soil for, 251 ; treatment ef ground after, 252 ; for corn in the fall, 252 : sod, 252 ; covering manure, 253; green manure, 253: early fall, 254 ; horse power required for, 491. Poisons, 12. Pore space, of soils, 111, 233 ; maximum and minimum for spherical grains, 109, 111. 114 : influence on water ca- pacity, 114 ; of different kinds of soil, 114 ; iiiJluence of suu-uivision of on rate of percolation, 115 ; method of de- termination, 115 ; maximum in soils, 116 ; shape of, 163. 164 ; necessary for roots, 233 ; in sands and gravels, 256 ; in soil and clay, 257 : unoccupied in drained sands, 261 ; influence of on capacity of wells, 276 ; for materials for concrete, 381. Posts, strength of, 330 ; avoiding use of in barns, 374. Potash, essential to plant growth, 69 ; function of, 70 ; amount removed by crops, 79 ; amount in soil, 80 ; in wheat crop, 81. Potatoes, amount of water used by, 141 ; early plowing for, 185 ; best time to cultivate, 192 ; ridged and flat cul- tivation for, 194. Precipitation, rise of ground water due to, 260. Pressure, relation of to flow of water, 262. 268 : influence of on capacity of wells. 279: of gases, 40; osmotic, 42; relation of to volume of gases, 41 ; measurement of osmotic, 43 ; of silage, 394 ; of atmosphere, 559 ; of steam, 504 ; gage, 511 ; on piston in pumping, 547, 548. Priming, in engine, 506. Pulley, relation to belts, 545. 1'urnp, capacity of on sand point com- pared with open suction pipe, 282 ; cross-head, 575 ; in gasoline engine, 525 ; suction, 546 ; size of piston, 547 ; rate of discharge, 548 ; relation ct size to discharge pipe, 548 ; double- acting, 550 ; place for cylinder, 551. Pumping, by windmill, 531, 535 ; rate of. 536 ; power for influenced by size of discharge pipe, 548. Pusey, draft of plows, 243 Q Quincke, distance over which cohesive attraction becomes sensible, 37. It Rain, bad effect of on animals, 33 ; evaporation of, 33 ; ammonia and ni- tric acid in, 86 ; cultivation after, 190; influence of 9n soil temperature, 219 ; effect of on rise of ground water, 261. Rainfall, relation to storm center, 575; conditions unfavorable for, 584. Ram, hydraulic, 552. Respiration, products of, 350, 351 ; amount of air breathed, 353. Richthoffen, formation of loess, 64. Rivers, formation of soil by, 54, 55, 56, 57. Roads. 428 ; grade of, 428 ; effect of grade on draft, 428 ; steepest grade admissible, 430 ; conditions modifying grade. 433 ; draft on different kinds, 436. 437, 443 ; establishing grade, 444 ; drainage of, 445, relation of water to, 446, depth of, 446, place for drains, 447,, fall of drains, 447, outlet of drains, 448, size of tile, 448, sur- face, 448 ; slope, 449 ; water-breaks, 449 ; texture of road metal, 450, size of material, 451, shape of material, 451. cleanness. 452 : earth, 452, 477. forming road-bed, 452, 455, util- izing old road-bed, 455 ; on' grav- elly loam, 455 : on clay soil, 455 ; on sandy soil, 456 ; use of straw, saw- dust and tan bark, 457 ; gravel for, 457 ; in swampy places. 460 ; stone, 461 ; ancient types, 461 ; macadam, 462, construction. 462, 463, road metal for, 464, 465, 466. 467, , 468, 469, spreading rock, 470. thickness of layers, 473, rolling, 473, 474, 475 ; roller, kind, 475 ; rock crusher, 459, 475 : rock screens, 459, 477 ; com- bined roads, 477 : Telford foundation, 478 ; culverts, 479 ; maintenance, 480. 600 Index. Headmaster, 481. Roberts, stall, 385. Rocks, formation of soil from, 50 ; In- fluence of fissures on soil formation, 53 ; composition of compared with soil 77 ; composition of, 78 ; flow of water through 262 ; kinds for roads, 464. Rock crushers, 459, 475. Roller, uses of, 236 ; weight of for farm use, 237 ; types of, 237 ; danger in uses of, 237 ; should be followed by harrow, 237 ; may strengthen capil- lary rise of soil moisture, 174 ; as a tool for producing mulch, 192 ; in- ' fluence of on soil temperature. 221 ; 'for roads, 473, 475, 484, size, 473. Rolling, grain after up, 192 ; influence of on soil ventilation, 210 ; influence of on soil temperature, 221 ; influence of on capillary rise of water, 174 ; of roads, 474 . Roman roads, 461. 478 : roads, 474. Root hairs, structure of, 147 ; relation of to soil grains, 147, 148 ; method of gathering water, 147 : conditions for Improved by proper tilth, 233. Root pressure, influence of soil tempera- ture on, 215. Roots, functions of, 145 ; absorbing por- tion of, 146 ; structure of root hairs, 147 ; advance of through soil, 148 ; ex- tent of development of in corn, 150, 151, 152, 154 ; in grain, 150, 153, 155 ; total system, 154, 155. 156, 157: near surface late in season, 189 ; Influence of on soil ventilation, 210 ; room for increased by drainage, 287 ; obstruct tile drains, 303. Rothamstead, experiments at, 81 ; nitro- gen in soil at, 82. Round barn, frame. 341 ; consolidated type, 371 ; handling hay in, 391. Rowland, heat unit, 28. Ruberoid roofing, for ventilators, 364 ; for silo doors, 411, 423. Russia, nitrogen In soils of, 82. Salt used with Ice as freezing mixture, 30 ; solution of, 7. Sal-soda, for boiler scale, 517. Sanborn, J. W.. draft of plows, 243. Sand, specific heat of. 29, 32, 216 ; flow of water through, 123 ; rate of percola- tion through, 159 ; water reservoir, 255 ; law of dow of water through, 262 ; method of measuring flow of water throneh. 264. 267 : relation of pressure to flow through, 266 ; observed rates of flow through, 268 ; sandstone, capacity for water, 255 ; rate of Uow of wate'r through, 268 : apparatus for measur- ing flow of water through. 269 ; as source of water for wells, 276. Sandy soil, compared with clay, 71, 74, 75 ; amount of plant food in, 80 ; wind breaks to protect, 202 ; rapid decomposition of humus in, 206. Sand strainers, uses, 280 ; capacity of compared with open suction, 281. Scale, in boilers. 517. Schlosing, denitrification, 90. Schlosing, Jr., symbiosis, 88. Schmidt, C., nitrogen in soils, 82. Schroeder, function of potash, 70. Scouring of plows, 247. Screen rock, 451, 459. 477. Seed" bed. thorough nreparation for. 222. Seeds, absorption of moisture by, 6. 60 ; require magnesia, 71 ; germination, 213, 225. Seepage, growth of streams due to, 258. Sheep, bad effect of cold rains on, 33, amount of air breathed, 354. Sheeting, silos, 405, 412, 414. Showers, thunder, 586 ; relation to low areas, 576, 588 : formation of, 592. Shubler, weight of soils, 128. Silage, conditions for preserving, 394 ; lateral pressure. 394 ; loss of in stave silo, 420 ; weight per cu. ft., 424 : proper feeding area, 425 ; generation of carbon dioxide in, 427. Silos, relation of depth to capacity. 367 : importance of depth, 394 : rigidity of walls, 394 : depth of in ground, 395 ; construction against free/ing, 396 ; stone, 397; laying wall, 397. 402; plastering, 398 ; doors, 396, 399, 403, 411 423 ; strengthening walls, 399, 401. 402. 410 : brick ; 400 ; brick- lined, 403; sill, 405, 410 : setting^ stud- ding, 405. 411 : sheeting, 405, 412, 414; siding, 406. 412; lining. 403, 40fi. 413: round plastered. 407: wood. 409 ; foundation, 400, 405, 409 ; ce- menting bottom, 382. 410 : plate, 413 ; roof, 417 ; ventilation. 417 : decay of, 417; painting lining, 418: stave, 418; hoops for, 422 ; pit silo, 423 ; capacity of. 424 : feeding area, 425 ; danger in filling, 427. Silt basin, construction and use, 299. Slichter, C. S., formula for computing effective diameter of soil grains, 121 ; formula for flow of water through soil, 262 ; computed capacity of wells, 280. Smell, sense, delicacy of, 13. Smith, Angus, denitrification, 90. Smith, C. S., strength of pillars, 329. Snow, latent heat of, 34 ; melting for washing, 35. Snow storm, chilling effect from heat lost in melting, 34. Sod plow, form, 241, draft of, 243. 244 ; dralt compared with stubble, 244. Sodium nitrate, number of molecules per gram, 11. Soft plug, 514. Index. 601 Soil, temperature low when wet, 29 ; cooled by evaporation. 32 ; nature of. 49 ; compared with subsoils, 49, 72, 74, 75 ; clayey types, 49, 71, 74, 75 ; uses of, 50 ; micro-organisms in, 50 ; forma- tion of, 51 ; rock texture in formation, 51 ; conversion of limestone into, 52 ; influence of rock fissures on soil forma- tion, 53 ; removal of, 53 ; produced by running water, 54, originating through glaciers, 57, 58, 59, 60, formation of humus type, 61, 62, 63 ; formed by wind action, 63 ; loess, 64 ; produced by animals, 64 ; convection, 65, ac- tion of earth worms, 66, 67 : chemical nature of, 69, 71 ; chemical composi- tion, 69, 71, 74, 75, 78, 81; constitu- ents of essential to fertility, 69 ; com- parison of kinds, 72, 74, 75 ; of arid and humid regions, 73, 76 ; chemical nature compared with parent rock, 77 ; plant food removed from by crops, 79, plant food in acre foot, 79 ; nitrogen in, 82 ; forms in which nitrogen oc- curs in, 83 ; distribution of nitrogen In, 83 ; amount of nitric acid iu, 84 : sources of nitrogen in, 85 ; soluble salts in field, 92 ; physical nature of, 108 ; texture of, 108 ; number of grains per cubic inch, 109 ; pore space of, 111 ; surface of per gram, 118, per pound, 118, per cubic foot, 124 ; movement of air through. 125 ; heavy and light, 128 ; weight per cubic foot, 127 ; capacity of for water, 131, 134 ; kinds yielding moisture to crops most completely, 136 ; advance of roots through, 148 ; rate of percola- tion from, 159, 160; capillary rise of water in, 163 ; mulches, 185 : changes in temperature of, 207 ; im- portance of right temperature of, 212 ; observed temperatures, 213 ; specific heat of. 215. 21 fi: temperature In fluenced by color, 217, by texture, 218. by topography, 218, by tillage, 219, by chemical changes, 219 ; by rain, 219, by evaporation, 32. 212 ; best condition of for plowing, 251. Soil grains, number per cubic inch, 109, per gram, 118, per pound, 117 ; specific gravity of, 110 ; effective diam- eter, 121, 124 ; method of determining effective diameter, 121 : computed sur- face of, 124 ; relation of water capacity to, 124 ; relation of root hairs to. 147 ; relation of diameter of to flow, 266. Soil kernels, size, 110 : relation to tex- ture, 231 ; "destruction of In puddled soil, 239 : illustration of, 231. Soil moisture. 129 ; movements of Influ- enced by soluble salts. 106 : loss of. lessened by soluble salts, 107 ; relation of per cent, of to thickness of water film, 137 ; amount of, affected by jointed, structure, 138; amount in-j creased by open texture. 138 ; amount 1 available Increased by drainage, 139, by subsoilmg, 200 ; types of move- ment, 158; percolation of, 158; grav- itational movements of, 158 ; capil- lary movements of, 161 ; observed hight of capillary rise of, 165, influ- enced by rain, 170, 190, by farm yard manure, 172, by mulches, 173, by firming the soil, 174 ; thermal movements of, 175 ; hygroscopic, 175 ; conserved by early fall plowing, 182, early spring plowing, 183 ; by sub- soiling, 195, by early seeding, 200, by wind breaks, 202 ; possible waste through untimely cultivation,- 189; movement of, affected by subsoiling, 197 ; danger of loss of through! green manuring, 201 ; loss through action of weeds, 224 ; Influence of on draft of plows, 244. Soil mulches, effectiveness of, 185 ; method of demonstrating influence of, 187. Soil surface, Influence of, on chemi- cal analyses, 72 : amount per gram, 118, per pound, 118, per cubic foot, 124 ; difficulty of determination, 119. Soil temperature, 212 ; importance of to life forms, 212 ; at which growth be- gins, 212 ; best for germination, 212 ; influence of on rate of germination, 214 ; effect of on root pressure, 215 ; influence of color on, '217, of to- pography on, 218, of unevenness of surface on, 218,- of looseness of sur- face on, 219, of tillage on, 219, of physical and chemical changes on, 219, ^i rams on, 219, of evaporation, 220, of rolling on, 221, of prepara- tion of seed bed on, 222, of under draining on, 222, 287 ; means for con- trolling, 221. Soil-tube, 116. Soil water, viscosity of modified by salts, 106 ; proportion of available to crops, 161 ; internal evaporation of, 179 ; conservation of, 181 ; modes of controlling, 181, late fall plowing to conserve, 181. Solar energy, 20 ; rate of transmission, 22, amount of, 22. Soluble salts, amount In field soils, 92 ; amount of limiting plant growth, 93, in Yellowstone Park, 93; In Algeria, 93; why injurious to plants, 93 ^con- centration of in zones, 94 ; origin of, 94; removal of by leaching, 95; In marsh soils, 95 ; change in amount of with season, 98 ; variation of with dif- ferent crops, 99 ; influence of on move- ments of soil moisture, 106 : modifica- tion of surface tension by, 106 : lessen the loss of soil moisture. 107 : influence in cementing soil granules. 233 ; drain- age of to remove excess, 286. Solution, 38 ; Influence of temperature on, 39 ; saturated. 39. 602 Index. Specific gravity, of soil grains, 110. Specific heat, 29 ; of dry soil, 215 : o wet soils, 216 : of water, 216 : of moor earth, 216 ; of humus, 216 ; of loam 216 ; of clay, 216 ; of sand, 216 ; chalk 216. Springs, fluctuations In rate of flow. 270 Squash, germination temperature, 213. Stables, temperature for, 344 ; ventila tion of, 355 to 365 ; floors for, 374 to 384. Stalls, for cows, 384 to 387. Stanchions, 384, 386, 388. Starch, potassium required for formation of. 70. Stave silo, 418 to 423. Steam, pressure of. 504 : dry and wet, 504 ; condensation of, 506 ; water for, 517 Steam engine, 502 principle of 502 ; ef- ficiency of, 503 ; dry and wet steam, 504 : priming, 505 to 508 : relief cocks, 507 ; boiler, 508 ; construction, 509, 518 ; gage cocks, 510 ; gage glass, 510 ; pressure gage, 511 ; safety valve, 511 ; care of boiler, 512 ; firing, 513 ; foaming. 513 ; low water in, 514 ; water for, 515 ; fly-wheel, 522 ; governor, 521. Stone roads, 401. Stone silos, 397. Storm center, 575. Storms, 570 ; wind directions in, 570 to 572 : progressive movements of, 572 to 574 ; rate of travel, 574 ; diameter of, 574 ; duration of, 575 ; region of precipitation, 575 ; prediction of, 578 to 580 ; temperature changes of, 580 ; barometric changes of, 582 ; thunder and hail, 586. Strength of materials, 329 ; of pillars, 330 ; tensile, 331 ; transverse, 331 to 336 : breaking constants, 336 ; comput- ing breaking loads, 336 ; safe quiescent center loads. 337. Stress, kinds, 329. Stubble plow. 242 ; draft of, 243, 491. Studding, use in balloon barn frame, 341 ; in round barn, 242 ; in silo, 405, 411. Suction pump, 546 : double-acting. 550. Subsoils, jointed structure in, 138 ; in arid regions. 50 ; chemical composi- tion. 74 : differ from soils, 72 ; should not *"> turned UD by plow. 251. Subsoiling to save moisture, 195 ; meth- od of demonstrating effect of on soil moisture, 196 : moisture effects of, 198 : how water capacity is Increased by. 198 ; decreases capillary rise, 199 ; Influence of on percolation, 199 : in- creases per cent, of available moisture, 200 ; dangers from, 200 ; influence of t on soil ventilation, 209 ; plow for, 250 ; ventilation. 209. Subsoil plow, 250. Sugar, osmotic pressure, 45. Sulky plow, 245. Sulphur, essential to fertile soil, 69 ; function of, 70. Sulphuric acid, in soils, 74, 80 : removed by crops, 79. Sun, source of earth's energy, 20. Surface drainage, where needed, 306, 309. Surface drains, construction of, 306. Surface tension. 36 : overcome in evap- oration, 24 ; in solution, 38 : modified by dissolved salts, 106 ; effect of on soil texture, 233. Sweep power, 501. Swine, normal temperature of, 344 ; amount of air breathed, 354. Symbiosis, source of soil nitrogen, 87; need of soil ventilation for, 206. Tanks, for watering stock, 389, 390. Telford, road construction, 462, 478. Temperature, 25 ; expansion due to, 7 ; of interplanitary space, 23 ; measure- ment of, 25 ; for cooling milk, 34 ; regulation of in animal body, 33 ; in- fluence of hygroscopic moisture on, 179;effect of changes in onsoil ventila- tion, 207 ; importance of right for soil, 212 ; of water in wells, 284 : see soil temperature ; control of, 343, 346 ; normal for animals, 343 ; for stables, 344, 345 ; force in ventilation, 359 ; construction for control of 345 to 348, 367 ; atmospheric, 560 : influ- enced by storms, 575, 580, 582, 583; effect on wind power, 532 ; of muscles, 488 ; of steam, 504. Terraces, of river valleys, 55. Texture, of rock in soil formation. 51 ; of soil, 108, 231 ; influence on loss of soil moisture, 183 ; changed in sub- soiling, 199 : influence of on soil tem- perature, 218 ; modified by tillage, 232 : Importance of, 233, development of, 233 ; difference of in soil and in Potter's clay, 233 ; of puddled soil, 233 : developed by plow, 238 ; effect of after-treatment on. 252 : of road ma- terial, 450, 451, 456, 458. 459. Thermometer, 8, 26 ; accuracy of, 26 ; wet and dry bulb, 33, 220. Thorp, stall, 385. Thunder storms, associated with changes of level of water in wells, 274 : rela- tion to ordinary storms, 586, 588, origin of, 588, 592 ; progressive move- ment of, 589. Thurston, friction. 539. Ties, for cattle, 384. Tile, essential features of, 291 ; how water enters. 292 ; rate of percolation into. 292 : Injured by frost. 291 : clay suited to manufacture of. 291 : use of collars for, 292 ; size of, 299, 301. Index. 603 Tile drains, Influence soil ventilation, 211 ; fluctuations In rate of flow from, 270 ; leveling for, 312 ; lor ix.au drainage, 448. Tillage, checks concentration of alkali, 98 ; influence of on development of nitrates, 105 ; to conserve soil mois- ture, 182 ; effectiveness of increased by frequency, 187 ; too great frequency undesirable, 189 ; disadvantages of late, 189 : should be most frequent in spring, 19 ; following rains, 190, should vary with season, 191 : best time for, 192 ; subsoil ing, 195 : in- fluence of on soil ventilation, 209 ; in- fluence of on soil temperature, 219, 222 ; objects of, 223, tools for earliest, 225, 234 ; for later cultivation, 226 ; to cover weed In row, 228 ; garden cultivators for, 230 ; to modify soil texture, 231 ; plow as a tool for, 238. Tilth, importance of good, 233 ; how de- veloped, 233 ; modified by plowing, 239. Timber, strength of, 330 to 334 ; safe center loads, 338 ; selection of, 338 ; construction of from 2-inch lumber, 339. Tires, effect of width on draft, 436 ; con- trol of width, 481. Topography, influence of on soil tempera- ture. 218. Tornadoes, 586 ; relation to storms, 586; origin, 589. Towers, hight for windmills, 534. Traces, influence of slope on draft, 440, 441, 492. 496. Traction, see draft. Trautwine, 332. 381. Tread power, 499. Tresaguet, type of road. 462. Triceps muscle, measuring strength of, 489. Traube, precipitation membranes, 44. Tubes, capillary rise of water in, 37, cause of variation of hight of water in, 161 ; flow of water through, 300. Turnip, temperature for germination of, 213. Under drainage, Influence of on sol! ven- tilation, 210 ; practice of, 311 ; tools for, 312 ; determining levels for, 312 ; for roads, 445 to 448. Units, of energy, 27 ; of heat. 28 ; of work, 18, 27. Valentin, respiration, 353. Valve, slide, of steam engine, 518 ; of gasoline, engine, 528. Vegetation, influence of on soil ventila- tion, 211. Ventilation of soil, lessened by rolling 192 ; needs for, 204 ; imperfect in water logged soil, 205 : may be exces- sive, 206 ; processes of, 207 ; due to changes in temperature, 207 ; influ- enced by changes in barometric pressure, 208 : influenced by wind suc- tion, 208 ; influenced by percolation, 209 ; modified by tillage, 209 : by underdraining, 210, 287, 290; influ- enced by vegetation, 211. Ventilation of farm buildings, 350 ; ma- terials to be removed by, 350 to 353 ; lack of predisposes to disease, 352 ; amount of air required for. 353 to 355 ; forces producing, 358 ; types of, 355 to 365 ; of silos, 417 ; of box stalls, 387. Ventilating flues, capacity of, 355 ; es- sential features of, 358 ; location of, 359 ; for basement stables, 355, 356, 364 ; openings into, 360 ; for fresb air, 362 ; construction of, 363. Vierordt, respiration, 353. Viscosity, modified by dissolved salts, 106 ; table of coefficients of, 264. Voelcker, nitrogen In soil, 82. W Wagner, Illustration of symbiosis, 87, ef- fect of Chile saltpeter, 88. Wagon, draft of, 434 to 443, 490. Walls, solid masonry, 346 ; hollow ma- sonry, 347 ; brick veneered, 347 ; wood, 348 ; relation of to floor space, 366 ; rigidity of for silos, 394. Waring, denitriflcation, 90. Warington, distribution of nitrogen In soil, 84 ; amount of nitric acid in soil, 84 ; formation of nitric acid in the at- mosphere, 86 ; denitriflcation 90. Water, specific heat of, 29 ; influence of on climate, 29 ; use in cooling iniik, 34 : amount stored in rock, 51, 257 ; work of in soil formation, 54, 78 ; flow of through sand, 123 : conditions of In soil, 129, 130: amount of required by crops, 139, 140 ; least amount re- quired by different yields, 141 ; trans- piration of, 145 : absorption of by roots, 147 ; capillary rise of in tubes, 161, in soils, 163 ; amount and move- ment of influenced by subsoil ing, 197 ; influence of movements of on soil ven- tilation, 209 ; amount of stored in soil and rock, 255 ; seepage of 258, 259 ; laws of flow through porous media, 262, 264 ; measurements of flow of through sands and sandstone, 264, 266, 268 ; fluctuations in rate of flr-w of from springs. 270, 271 ; rise and fn'.l of in wells, 272 ; temperature of In wells, 284: how it enters ti'e drains. 292 ; movement of toward tile drains, 604 Index. 298. See ground water ; In expired air, 350 ; relation of to roads, 446 ; in atmosphere, 558 ; for steam boilers, 517. Water breaks, 449. Watering stock in barn, 388 ; trough, 390; tank, 390. Waters, J. H., draft of wagons, 436. Water capacity, of soils, 114, 131, 132, 134 ; relation of to surface of soil grains, 124 ; increased by subsoiling, 199. Waves, of solar energy, 21 ; kinds of, 23 ; transparency to, 24 ; produce chemical changes, 24. Weather, forecasting, 554, 583 ; of dif- ferent wind zones, 565, changes, 578 ; influenced by storms, 580, 582. Weeder, 226. Weeds, best time to kill, 192, 224 ; till- age to destroy, 223, loss of plant food through, 224 ; do not all germinate at once, 225 ; best tools for killing, 225 ; covering in row, 228 ; jointer for plowing under, 249. Wells, level of water in, 255 ; soils and clay supply water too slowly for, 257 ; fluctuations in flow from, 270 ; fluctu- ations in level of water in, 272 ; es- sential features of, 275 ; capacity of, 275 : geological conditions best suited to, 276 : depth of, 283. Wheat, exhaustion of soil by, 80 ; Roth- amstead experiments with, 82 : water used by, 140, 141 : extent of root de- velopment of, 150, 153 ; temperature for germination of, 213. Wheels, effect of size on draft, 437, 490 ; width of tire, 436, 481. Whitewashing, silo linings, 393, 402, 403, 408. Whitney, alkali salts limiting plant growth, 93. Winds, formation of soils by, 63 ; soil ventilation influenced by, 208 ; prim- ary cause of, 561 ; of the globe, 562 ; zones of, 563 ; influence of earth's ro- tation on, 564 ; character of, 564 ; con- tinental, 566 ; of January, 567, 568 ; of July, 567, 569 ; monsoon, 570 ; cy- clonic, 570 ; anticyclonic, 572 ; direc- tion of in forecasting, 579, 580 ; rela- tion to cold waves, 582 ; relation of pressure to velocity, 532 ; working power of, 533 ; unsteady character of, 534. Wind-breaks, to conserve soil moisture, 202. Windmill, 531; pumping by, 531, 535; grinding by, 531, 536 ; relation of di- ameter to efficiency, 533 ; towers for, 534. Wind pressure, force in ventilation, 346, 358 ; relation to velocity, 532 ; rela- tion to altitude, 532, 534 ; relation to temperature. 532. Wind zones, 563 ; weather of, 565 ; shift- ing of, 565. Windows, efficiency of, 348 ; position of, 349. Winogradsky, symbiosis, 88. Wollny, influence of color on soil tem- perature, 217. Wolff, ash of crops, 79. Wolff, A. R., wind pressure, 532. Wood floors, for stables, 377. Work, 18 ; units of, 27. Z. Zero, absolute, 23 ; of thermometers, 25. - Date Due ! AUG28'* v*y Life SEP 2 -64 ^ ' AUG 5 '65 1 SEP 2 \ 96$ ;* / T^ j-jZax ^F? : ~ V , -.' .-' 5 -lpf\ B/' /*g^ J/ JTV ^ 1 K^r^' ^^T . ^ Demco 293-5 ^PSt?,^o