■ •' ^ ■':! ■ : •■ i' ^avj nvi^ to k^V)^^ ' fe^^v*"^ LIBRARY OF CONGRESS. ' ^M^ '^ rS)V ^<^:^^i^^ Chai)._^__.. Copyrio-ht No. Slielf-..X5 ^' A TEXT BOOK PHYSICS OF AGRICULTURE BY R H. KING Professor of Agricultural Physics in tite University of Wisconsin Author of "The Soil;" "Irrigation and Drainage;" "Principles and Movements of Ground Water" Madison, Wis. PUHLISllKD BY THI-: AUTHOR 1900 All rights reserved .^'\ 91150 L.itDr««r> off Conn » ' *» » | DEC 201900 SECOND COPY OdwwHl to ORDER DIVISION m: 24 1900 COPYKIGHT, 1890 «Y F. H. KING PREFACE. The great need of ai>rieii]tural practices at the present time is a keener a])preciation and a more thorough com- prehension of the principles which underlie them. The facts of agric\ilture are spread through so many and widely different fields, and are so numerous, that no one can hope to grasp them all or nee(1s to do so. But the laws and l^rinciples which control his ])ractice each farmer must know before he can secure his results with the greatest cer- tainty and at the least cost. In these ])ages 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 ni<*re than WHAT^ and it is hoped the student will ]mrsue the vari Their Way into Milk 14 Enter cUu-ing 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. Deodorizi.n'g ]Milk 16 Method, p. 10 ; 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 ov Heat and Cold 25 Temferattre 25 Measurement, p. '2'> ; Accuracy of thermometers, p. 26. Units of Work and KNER(iv 27 Foot-pound and foot-ton, p. 27 ; Horse-power, p. 27 ; Unit of heat, p. 28. Specific and Latent HE.vr 29 Melting of ice, p. 31 ; Evaporation of water, p. 31. PHYSICS OF THE SOIL. CHAPTER I. Nature. Origi.v and Waste of Soil. Soils and Subsoils 49 Uses of Soil 50 Formation of Soil 51 Influence of rock texture, p. 51 ; Rock fissures, p. 53 ; Running water, p. .")4 ; Glaciers, p. 51 ; Humus soil. p. 61 ; Wind-formed, p. 03 ; Animals, p. 64. CHArTRU II. Chemical and Mi.xkkal Xatcke of Soils. PAGE. Essential CoNSTi'rrEXTS of a Fektile Soil 69 Functions of E.ssential Plant Foods 70 Chemical Cojiposition 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 liumus, p. IH : Between clay and loess, p. 73 ; Between arid and humid, j). 7."! : Ijctwecn soil and rock, p. 77. Humus ^ 7G Of arid and liumid climates, p. 70. Plant Food 79 Amount removed from soil by crops, p. 7!) : Amount in soil, p. 79 : Number of crops produced, p. SO : Itotliamstead experiments, p. 81. Nitrogen ix the Sou 82 Amount in Manitoba soils, p. S2 : Forms of occurrence, p. S3 ; Dis- tribution in soil, p. S?> : Amount as nitric acid, p. 84. Sources of Soil Nitkooex 85 Of humic nitrogen, p. 8.5 : Symbiosis, p. 87 : Observations of Wino- gradsky and Berthelot. p. 88. Nitrification 89 Denituificatio.n 89 CHAPTER in. Soi.TBLE .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. !>;'>: Concentration in Zones, n. '.)4 : Origin, p. 94 ; In marsli soils, p. 95. Leaching Necessary to Fertile Soils 95 Correction of alkali lands, p. 9.") : Drainage ultimate remedy, p. 98 ; Tillage helpful, p. 98. Changes in Amount of Solirle 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 whicli 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. 106; On viscosity, p. 106. Vll ClIAl'TKlt IV. I'll vsicAi. Xatiuk ok Soil,. PAGM. Textikk of Sou los Size of soil i.'riiii!s. u. KiS; Sizi^ of soil l^eincls. n. no. Poke Si'aok ix Son Ill Determines ma.vimuni wafer capacity, p. 114: Intluences rate of percolation, p. lir> : Method nieasiiring. p. ]1.">: Lai-gest possi- ble, p. 116. Intkknai, SiKFArE OF Soils 118 Amount per gram and s(|. ft., p. IIM: Iteterminatiim. p. 111). EFFECTIVIC DiAilETEK OF SoIL (JUAIN.S 121 Method of determination, p. 121 ; Flow of fluids computed from, p. 128; surface computed from, p. 124. Wkioht < Root Action. Mechanis.m and Method of Transpiration 142 Breathing of plants and animals, p. 142 : Respiratory organs in plants, p. 142: Breathing pores, p. 148: chlorophyll cells, p. 148: (Juard cells, n. 14:'.: Their action, p. 144: Loss of water through, p. 14."i. Strih'TI'RE and Mode of Root .\ciion 145 Functions of roots, ]). 14."): 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. i). 148; lOx- tent of root develoi)ment. \). ^7,(\ ; Total root of plants, p. 157. ClIAl'TKK VII. MiiVKMKNTS OF SoIL MoISTlIiK. PAGE. OltAVITATlUNAL MdVKME.N'TS 158 I'erc-olation. p. 108 ; Rate through sand, p. 150 ; Through soli, p. 150: Through dry soil. p. ItiO. Capillary Movements 161 Kise in capillary tubes, p. Itil : Rise in soils, p. 163 ; Observed hight in moist soil, p. 165 : Measurement of maximum hight, p. 1(!7 : Rate of rise in wet soil. p. 168 ; In dry soil, p. 168 ; In- fluenced by rain, p. 170; By farmyard manure, p. 172; By mulches, p. 17.S ; By firming the soil, p. 174. Thermal Movement.s 175 Hygroscopic soil moisture, p. 175; ^Movements, p. 175: Relation to size of soil grains, p. 176; Amount a soil may absorb, p. 178; Intei'nal evaiioi'athin. p. 170. CIIAl'TKR Till. <'(iNSKU\.\rio\ or Son. Moistiue. Modes of ('ontkoi.lixc Sou, ;\Ioi.stike 181 Late fall plowing, p. ISl: I>ate tillage for orchards, p. 182: Early fall plowing, p. 182: Early spring plowing, p. 18.3: Ef- fectiveness of mulches, p. 185 : Frequency of cultivation, p. 187: Cultivation after rains, p. 100; Depth of cultivation, p. 101 : Depth and frequency vary with the season, p. 191 : Early harrowing of corn and potatoes, p. 102 : Harrowing and rolling small grain after it is up, p. 102 ; Mulches other than soil. p. 10.",. SiP.s.iii.!.\(; TO Save Moistfre 105 Increases water capacity, p. 108 : decreases cai>illarity. p. 199 ; Favors percolation, p. 199 : More of water available, p. 200. Danger From Grekx Manfrixo 201 Wind-Breaks and Hedges 202 CIIAl'TER 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. 207 : By changes of barometric pressure, p. 208 : By wind suction, p. 208 : By rains, p. 209. Ways of I NFU'ENciNf; Soil Ventilation 2oo Modified by tillage, p. 209 ; Reduced bv rolling, p. 210 ; Increased by drainage, p. 210 ; Modified by vegetation, p. 211. tiiAi-ri:u X. Soil- 'ri:.MrKUA'rruii. PAGE. TK.Mi'KitATriiK AT Which (JiiDwrii ISkcins 212 Best Soil Ti:.Mi'i:uATri;i; 212 Influence on rate of germination, p. Iil4 ; Effect on root pressure, p. 215 : On the formation of nitrates. ii. -\'). ("ONDITIOXS IXFLIEXCIXG Soil. TKMI'KKATfKK 215 Speoiflc lieat of soil, p. 21") : Moisture in soil, p. 216 ; Color of soil, 1). 217 : Topography, p. 218 : Texture of surface, p. 218 ; Tillage, p. 2r.t: Chemical changes, p. 219 : Uains and percolation, p. 21'.> ; Uate of evaporation, p. 220. Mk ANS OF COXTKOI.LlXd SoiL Tempekatlre 221 Kolling, p. 221 : Earl.v thorough tillage, p. 222 ; Thorough drainage, ]). 222. (•1I.\1'T1:K XI. Oh.ikcts, Mi;rnoi>s ami I.mi'i.emexts of Tillage. ()B.ii;(Ts OF Tii.la.;e 223 Tillage to De.sthoy Weeds 223 Best time, p. 224: Best tools, p. 22."! ; For early killing, p. 225; For intertillage, p. 22<). Tillage to Moiufy Textihe 231 Soil texture and tilth, p. 2:'.l : Importance of good tilth, p. 233. IIo-\v Textuhe axi) Tilth are Devkloped 233 The uses of harrows, p. 234; The planker, p. .236 ; The roller, p. 237 ; The plow, p. 238 : How may puddle soil.s. p. 2:i!t ; May correct texture and improve tilth, p. 230. Forms of I' 239 Must be adapted to the soil. p. 24(t : Sod plow, p. 241 ; Pulverizing plow, 1). 242 : Mellow soil plow, p. 242. Draft of I'i.ows 243 English and American trials, p. 243; Draft of sod plow with and without coulter, p. 243 ; Sod compared with stubble plow, p. ::44 : influence of moisture on draft, p. 244 : Draft of sulky plow. p. 245 : Line of draft, p. 240 : Scouring of pJows, p. 247. Care of Plows 247 When not in use. p. 247 : Keeping in form. p. 247. SiBSOiL Plow 250 Ob.tegts, Methods axd Times of Plowixg 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. 25:? : Early fall plowing, p. 254. GROUND WATER, WELLS AND FARM DRAINAGE. CHAI'TKU XII. MdVKME.NTS OF GliOl .\1> W.VTKU. PAGE. AmoT'Nt SroiiKD IN (JiidiMi 2r>5 Ground water surface, p. 258 : Seepage, p. 258 : (irowth of streams, p. 259 : Kise of ground water througli precipitation, i). 260 ; Law of flow tlirougli sands, p. 202 ; Calculation of flow, p. 202 : (Observed and computed flow. p. 204 ; Relation of rate of flow to diameter, p. 200 ; Relation of pressure to flow, p. 20() ; Observed rates of flow in sand and rock, j). 208 ; (leneral movements across wide areas, p. 270. Fluctuations in the Rate op Flow of Gkound Water 270 Due to bai-ometric changes, p. 270 ; In springs, p. 270 : In rate of discharge from tile drains, p. 271 : Change of level in wells. i>. 272; Due to changes in soil temperature, p. 271. CHAPTKR XITI. I'Aiur Wei.i.s. Essential Featiikes of a (Umd Well 275 Capacity, p. 275 ; Best geological conditions, p. 27:e uf tile. p. 2!»!» : rractical illustration of sizes and leniiths. p. .•'.(M : Outlets, p. .■502: Joining laterals with mains, p. 'MV.i : OhstrucI ions. p. :'.():!. LAYIN. :!1.S : Contour map. p. 31.''): I.ocatinu: mains and laterals, p. :'i1.">: Uetermining grade, p. .'UT: ('hangiii.t;- frcun niic j;rade lo anothei'. ]i. 310. L>i(i(;iN(; THE Ditch 321 Ditching tools, p. 321 : Width of ditch, p. 322 : Bringing bottom to grade, p. 322: I'lacing tile. p. 324: Filling the ditch, p. 328. RTT.1AL AROHITECTITRE. fHAI'TKR XVI. Stkength of Materials. 5STKE.N(iTii OK Posts 329 Stress, p. 329 : White pine pillars, p. 330. Transvekse Stuenoth 331 Tensile streDSTth. o. 331 : Principles, u. :'.:'>1 : Proportional to squares of depth, p. 332 : Relation to length, p. 334 : Break- ing constants, p. 33.') : Computing loads, p. 336 ; Rafters, p. 337 : Safe loads for horizontal beams, p. 337 ; Selection of lum- ber, p. 33S. Barn Frame.s 338 Braces, p. 338: Constructing timbers from 2 inch lumber, p. 330: Forms of frames, p. 330; Plank frame, p. .'UO : Balloon frame, p. 340: Cylindrical frame, p. 341. ClIAPTKR XVII. Warmth. Light am. Ventilation. Control ov Tk.mi'Eratire Normal animal temperatures, p. 343 : Best stable temperature, p. 344: Solid masonry walls, p. 346: Hollow masonry walls, p. 347: Brick veneered walls, p. 347: All wood walls, p. 348. 343 PAGE. Lighting Faum Buildings ; 34g Efficiency of windows, p. :!4.S ; I'o.sitioii of windows, p. 349. Ventilation of Farm Buildings 350 Necessity for ventilation, p. 350 ; Carbon dioxide, p. 350 ; Mois- tnre from lungs and skin. p. 350 ; Ammonia and organic mat- ter, p. 3.1J : Micro-organisms and dust. p. 352 : Bad ventila- tion predisposes to disease, p. '.','>'.'. Amount of Air Rrqi;ired 353 Amount respired, p. 353 ; Degree of imiiurity 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 XVIir. Principles of Construction. Relation of Covering rt> Si-ace Enclosed 3 ; 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. 3S5 : Movable halter ties, p. 387. Mangers -"^SS Manure Drops 388 Provisions for Watering 388 Watering in bain, p. 388 ; Storing water in tanks, p. 389 ; Water- ing trough, p. 390. Arrangements for Fvloadini; Hay 391 CHAPTER XIX. Construction of Silcs. CONDITION.S Essential for Preserving Silage 394 Depth, p. 394 ; Rigid walls, p. 394 ; Protection against frost, p. 396. I'AOB. COXSTIUTTION nv SliiMO Sll.dS 397 Laying walls, p. ;->y7 : I'lastering. p. 398 ; Doors, p. 399. COXSTIUTTION Ul'- Buit'K SlLOS 400 Foundation, p. 400; Walls, p. 4(»2 : Tie-rods. p. 402: Making walls air-tight, p. 402 ; Uoors, p. 403. CoxsTinrTiox mf Bkick-Lixku Silos 40.3 Foundation and sill, p. 405 ; Setting studding, p. 40.") : Slieeting, p. 40."> : Siding, p. 406 ; Lining, p. 40(i. Lathed axu I'lasteked Silos 407 coxstrtctiox 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. 41.'^: Ivoof, p. 417: "V'entilation, j). 417: Tainting lining, p. 4 IS. Stave or Taxk Silo 418 Construction, p. 420 : Staves, p. 422 ; Foundation, p. 422 ; Hoops, p. 422 : Doors, p. 423. Pit Silo.s 423 DiMENSiox OF Silos 424 Weight of silage, p. 424: Capacity of silos, p. 424: Horizontal feeding area, p. 42.5. Daxoek IX Fn.i.ixi: Silos 427 FARM MECHANICS. CHAPTER XX. Prixcii'LES of Kraft 428-443 CHAPTKK XXI. CONSTRFC'TIOX AXD ^LilXTEXAXCE OP COUXTRY ROADS. RdAD 1 tRAIXAGE 445 Texti're of Roaii Materiai, 450 Earth Roads 452 Stoxe Roads 461 MAIXTEXANCK DF CofXTRV RO.VDS 480 METEOROLOGY. CH.VPTKU XXII. TiiK Atmusfiieui:. Rki.atiun tu the IvutTii 48(; Interpenetration of the three spheres, p. 4.S7 : Relation of the life ■ zone, p. 4S7. PAGE. ATMOSr-HKKE ^gf^ Depth, p. 48S : ("omposition, p. 4.S1I : Materials iiieehanieally sus- pended, p. 4.S!t. I'AKTS I'LAYED l;Y TIIK DlFFEIiK.N T I XCKKPIEXTS 489 Oxygen, p. 48!): Nitrogen, p. 4!i(i : Water, p. 490; Dust, p. 490: Carlion dioxide, p. 4P0. ATMOSI'HKUIC I'KES.StRE 491 Applications or pressure, p. 491. Temtekatihe of the AriKi.si'HEiiE 492 CIIAI'TKK X.XIII. .MuVEMEXTS (IE THE At.M( tSI'UEHE. I'KI.MAIJV t'AlHE ()'■' WlXIiS 493 GEiNEKAI. ClIfCTEATIOX OK THE AtJIOSPHEUE 494 World system of winds, p. 494 : Wind zones, p. 49.5 : Direction af- fected by form and rotation of tlie eartli, i). 496 : Character of the winds, p. 496 : Weather of the wind zones, p. 497 : Shift- ing of the zones, p. 497. Continental Wi.xds 498 Influence of continents on winds, p. 498 : Winds of .Tanuary. p. 499: Winds of .Julv. ii. 4!>'.> : Mi)nsoons, p. .")02. ( )iiiii xauy Si < iiiM.s .">02 Cyclones, p. ')0'2 : Cause of wind directions, p. ."02 : Progressive movements, p. 504 : Direction of movement, i). 506 ; Rate of progress, p. 506: Diameters, p. 506 : Duration, p. 507: Region of precipitation, p. 507: Origin, j). 508. ciiAi'Tin: \\n'. Weaiheh Chaxiies. PBINCIPEES (IF F(IHE('ASTTN(J WEATHEI! CHAX(iES 510 I'revailing winds of locality, p. 510: I>ocating storm center, p. 511 : Change of wind direction, p. 511 ; Direction of storm cen- ter, p. 511 : Predicting the course of tlie storm track, p. 512 : Temperature changes, p. 512 : Barometric cliaufres. p. 514. COI-P WEAVES 514 Forecasting warm and cold weather, ]>. 515. I.oNf; Warm and Ditv PEUTdps 515 Tropicae Cyclones •''>17 Thunder Storms. Hail Stukms axk T()i;x\p(ies 518 Relations to ordinary storms, p. 518: Tornaoops. p. 518; Schools of tornadoes, p. 520 : Distribution of thunder showers, p. 520 : Conditions of formation, p. 520 ; Formation of tornadoes, p. 521 : Explosive violence of tornadoes, p. 522 : Unsteady move- ment, p. 523 : Character of tornado path. p. 523 : Formation of thunder showers, p. 524 ; Formation of hail, p. 524. INTRODUCTION. 1. Physics. — Briefly defined, pliysies is tlie science of ^latfer and Energy. It aims to nieasnre and investigate the movements of or within any body, whether living or dead, endeavoring to show how the forces of nature operate upon or wifhin the hody 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 Pliijsics. 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 Tevvestrial or Earth Physics. If we were measuring the strength of a horse ; how many ]iounds 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 woidd 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 fhe green <'hloro])hyll, onr ])roblem would become one of Plant Phjjs- vrx. 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 the pressure of the wind, then we are dealing with the PJn/strs of Avcliilcclure. And so we might go on enumer- ating every science and every art to show that there is a physics of each or a necessary treatment of them from the standiDoint of mechanical principles of matter and energy. Physics, therefore, a broad science, is one of wide applica- tion and fundamentally imjwrtant to the nnderstanding of almost any concrete snbject 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 the 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. — AH 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- 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. AVlien this is done the rubl)er 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 tnbe where the amount of change can be read. The bottle is ])laced 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 nnits which have received the name of atoms and the number of these atoms 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-live atoms of three different kinds, carbon, hydrogen and oxygen, and there are many sub- stances having molecules more complex than those of sugar. Fig 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 greater the higher and less the h^wer 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 altliough 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 Avhen 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 9 sun the greater tension which is (h'veloped is due to the fact that the alisorption of heat causes ail the niok'cules to travel faster, and, traveling- faster, they must exert a greater pressure whenever collision occurs and tlieir motion is arrested. It has been computed that tlie mean rate at which the molecules of hydrogen gas travel at ordinary temperature and atmospheric jDressure is some (3,000 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 hanuner 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. — ]\Ioleeul>'s 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. Xobert, for example, ruled parallel lines on glass at the rate of 101,000 per linear inch, })roving that the point of the diamond which jDlowed the furrows must have l)een far less than tdcVoij 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 be as great as 10^^ 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 analine violet in alcohol and distribute it through 500 cu. in. of water in a large glass 10 flask. Pom- out half the colored water and fill to 500 cu. in. again. Eepeat 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 Mdien 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 analine is carried to this extent there will bo in the last 500 cubic inches of water only 5J2 of Jqq = iQ 240 ^^ ^ gram of analine. It is reasonable to suppose that in the last 500 cubic inches of water there was at least one molecule of analine 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 =3 500,000,000 molecules of analine in the last vessel of w^ater. Since at least this number of molecules is found in TXiho of a gram of analine one gram would contain not less than 10, 240 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 ana- line at least must be very small and that a pound of the material would contain an enormous nund)er. 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 tal)lo below are re- quired to weigh one gram. jSTumber of molecules in one gram of Hydrogen Oxygen Carbon dioxide 2,171(10)='^ 1,359(10)2 2 9,881(10)2 1 That is to say, the number of molec\iles is so large in one gram of these three substances that 2,171, 1,359 and 9,881 11 must be multiplied hy 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 strimge fact that iUU to 501) 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 tlir(iugh 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 eifects 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 30,300. The experiment Avith an- aline 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, 1-20, 000^00^000 _ ""36,300X1,728 " «' ' '^^^ We see, then, that a single gram of analine may be di- vided enough to place 81,624 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, NaNOg :2 O :: No. of O molecules : No. of NaNOg molecules or 85:32 :: 1,359(10)" ; x whence x = 51(10)-» ^5,100,000,000,000,000,000,000,000 12 Treating this result as we did tliat of the aiialine wo shall have 5, 100, 000, 000, 000, 000, 000, 000, 000 „, ofi onn ./ 1 U -^ = 81,310,000,000,000,000 as the numher of molecules of sodium nitrate in each cubic inch of water from which the plants may draw their sup- ply of nitrogen. It will be seeu 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 onediundredth of an inch on a side. 8. Molecular Structure in Relation to Poisons. — It is the extremely large nundjer of molecules which may exist in a small space, coupled with the energy which these molecules may carry wdth 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 understood from what has been said regarding the vast number of fertilizer molecules per cubic inch of soil moisture, when oidy 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 molecides enough to charge, the body of the largest animal with) great numbers of the poisonous units. The important i)ractical lesson t<;> be remendjered 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 13 lines as these we must search fur an exphuiation of soniG of the little understood points associated with the nourish- ment of both plants and animals. 9. Ability to Recognize Small Quantities of Matter. — We often marvel at the (h'licacv of the chemical l)ahince and many other instruments of measurement, hut 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 he formed. The sensations of odors result from the disturbances jjroduced on the organs of smell by molecules of different substances moving through the air when brought to the nose. But Avhen the blind lady took the glove of a stranger and, walking up and down the aisles of a large audience room filled with ]ieo]ile, handed the glove to the owner, made known to her only by the likeness of the odor from the glove to that escajiing 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 where many other peojde may have passed along the same course more re- cently than did his master. The readiness with which flow^ers, 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 vast nundjors of mole- cules, while at the same time they prove how sensitive is the animal organization to such minute quantities of ma- terial. 14 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 j)i*otlucing sub- stances are certain to awaken the undesirable impressions,, it is clear that the greatest of care must be exercised in l>roducing, 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 2>lain 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 ju-ice 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. — Auv volatile principle Avhicli 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. N^early 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 15 any of these priiiei])les still reiuain 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 fonnd 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 Avlien 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 of 16 saturation be readied, simply Lecause 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 Eesulting 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 the 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 17 the (i(l(irs rather than favors it and if the milk coukl be ex- ])osc(.l in a vacnuin tlieir escape Avouhl be more e<:)mplete and more rapid. The escape of the odors from the milk depends upon tho rapid motion of the odor molecules in it which forces them to escape whenever they approach the surface with sufti- 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 thev 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 molecidar movement is greater the higher the temperature it follows that the deodorizing process shotdd 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 oi- where there are many ob- jectionable odors it must bo 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 becoino charged with odors from outside, and hence the deodorizer or aerator should be placed where it is surrounded by a current of ])ure air. 19. Cooling Milk. — The cooling of milk innnediately after it is drawn has a ])owerful influence in preventing odors from develoi)ing 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 it is desired to remove tli/e 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-j)ound. 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 work 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. Wlien a larger iniit 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 Avill 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 4X60X10X5,280 _ „__ , . , 9~?jm ^^ ' root-tons. So, too, if the pressure of steam on the head of tlie 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. 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 ean be made to do in coming to rest. If a weight suspended from a string be dra^m 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 imj^art 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 Avinding 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 wath 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^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 Avhich drive the ])iston whenever the valves are opened holding to it. 22. Conservation of Energy. — Xo discovery of modern science is more fundamental than the fact that neither mat- ter nor enerc'v can be destroved or created. One form 20 of energy may be transformed into another, and one kind of snbstance may be decomposed and others made from the components, bnt in these transformations there is neither annihilation nor creation. The small amount of ashes left from the winter's snpply of coal or wood seems to point to a destrnction of matter, bnt their Aveight added to that of the products which pass np the chimney is even greater than that of the original fnel by the amonnt of oxy- gen which was required to bnrn the fnel. So, too, the energy of 10 horses expended in threshing grain seems to be annihilated bnt 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 develoned by the horses. Again we appear to realize in the increase of our domestic ani- mals or in milk jn-oduced 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. — Tlie real source of the eartli'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 hy gravity back to their original level to be raised again and to again re- turn, just as a pendulum rises and falls wdiile 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 condiinations as readily per- mits of their return to other forms, setting free the energy M-hich was consumed in producing them. 24. Solar Energy. — When the sun rises the temperature increases, usually l)ecoming higher and higlier until past 21 noon, then when the sun sets the teni})erature 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 sunnuer 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 J>3,000,000 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 inio heat and thus the person in a small 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 2 22 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 18(3,680 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 so 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 2>er eacli square yard of surface. 23 But 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 ohserved, hut 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 hold the mean temperature even as high as 45° F. which is 273' + 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° 0. above the space in which it moves, the demand for energy needed to maintain the movements of water and of Avinds, 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 ditferent 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 oolor waves there are many other dark waves to which the human eye is not sensitive. Some of these are much shorter than the color wav(>s and are especially powerfnl in breaking down the molecular structure of ditferent sub- stances; that is, in ]iro(lucing cliemical changes such as oc- cur on the photographer's plate when the negative is made and such as take ])lace in the green parts of plants when car- 24 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 w^ater. When bright sunshine is allowed to pass through a large lens the glass is but little w'armed 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 w'ater 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 ocean, lakes and streams, and from the soil and the leaves of vegetation. When these Avaves 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 w^ater not so opaque to the dark Avaves, 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 dark waves fall upon many substances they appear to set 25 iij) vibrations within the molecules themselves, vhich in time may become so intense as to overcome tlu^ force l)y which the components are bound together and the molecule is thrown into parts, setting- them free so tliat when their motion slows down thev may join in new combinations. It is much as if some giant power w-ere 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. — ^Vlien 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 tlie 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 degTces 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 ease with water, which we know as ice, water and steam, or invisible vapor, change from the solid to the liquid forui and from the liquid to the gaseous form when the rate of molecular motion has reached a certain 26 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 is placed under the in- fluence of melting or freezing water, and the place at which the moving jDoint 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 countr}', the degree of the former being equal to y 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 l)y holding the bulb in rapidly boiling soft water. 27 A thcnnoineter may be eorrect at the freezing and boil- ing- points and inaecnrato at most intervening degrees, growing out of the nneqnal 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 gi-avity. 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 tbe 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 force 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-poiver is one of these. The horse-}X)wer used liy English and American engineers is the amount of energy which can do 550 foot-pounds of work per second or 33,000 foot- pounds per minute, equal to 16.5 foot-tons in the same time. To raise grain in an elevator to a liiglit 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 exeTting a steady pull on his traces of 100 pounds then the effective energy he is developing is 100X5,280X2.5 60 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 on(^ form of energy may be converted into another the value of a heat unit may be expressed in foot-pounds. The English scientist, Joul, was tlie 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 is 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 higli in the sauie time. 39. Determination of the Mechanical Equivalent of Heat. — In order to ascertain the value of the heat unit in foot- 29 jMiuiuls, Joul an'aiieratures are not raised through an equal nund>er of degrees. The same amount of heat, for example, which will raise the tempera- ture of one pound of water from S2° 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 ..t 32° F. has heat applied to it its temjierature 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 in doing tlie Avork of melting. The amount of heat re- quired to melt one pound of ice is 142 units when ex- l^ressed 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 1)0 110,518.6 oo- • , 33,000 -3.30 minutes. 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. & heat units. When expressed in foot-pounds it becomes 778.3X966.6 = 752,305 and the time required for one horse-power to do this work is 752,305 „. . , g^P^^^ = 22.8 minutes. When a pound of water at 32° F. becomes ice at 32° F. there reappears as heat tlie 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- 31 they ii»»\v arc, it Mas siqiposcd that tlic licat bceamo hidden 01" latent l)iit that it was heat stilL 42. Measuring the Energy Required to Melt Ice. — This may he deteriniued appruxiinately by taking equal weights of water at 212° E. and of ice at 32° F., putting the two together and noting the temperature at the moment the ice is all melted. When this has been done it will be found that the combined water has a temjx^rature 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 ^ = 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 ease an apparent loss of 161 — 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 jwunds 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 32 212° — 32" = 180° without having its temperature materially lowered. The molecular energy, therefore, which the one pound of steam contained was 180 X 5.37 = 966.6 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 Avhj a burn from steam may be so much more se- vere than that from boiling water. . 49 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 u]) 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 gTains, 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 Avas evajDorated. 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 w^eight 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 tlie term ''dead-furroV has been universally applied to the finishing of a land in plowing where the two furrows are thrown in opposite 50 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 w4ien 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 witli 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 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 jilace their roots in such a numiier 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 l)rinuirily 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 down 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 Rock Texture on Soil Formation. — Xearly 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 chauging it will dissolve away the cementing materials and the faces of the crystals them- selves, making the rock still more open and the gTains may even fall apart as is frequently observed in tliose 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 rocks made up of minerals of different kinds the crystalr* 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. Fig. 8. — Section of limestone hill showing rock changing to soil. (After Cliamberlin.) 69. Formation of Soil From Limestone. — If one will visit any limestone qurarry 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 Cliamberlin.) The mantle of soil seen above gravel beds in railroad cuts and where hills have been graded down on wagon roads has usually most of it originated from the decompositioa 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 53 ])Ovu Id'oki'ii (IdWii ;iii«l the over-lyiiii;' soil de- rived from tlu'iiL 70. Influence of Rock Fissures.— All cxMiniii;!- tioii of aliuiist aiiv (piar- ry where eonsidcrahle surfaces are i xpost-d re- veals the ])reseiK'e of systems of fissures which divide the stone hiyers into lilot'ks of various sizes and at the same time provide easy nvi:- nues for the entranee of surface Avaters. Tht'se features are shown clearly in Fili'S. 10, 11, Fu; H- Fort Danger, Wis., .^liowiair rock lis- 10 rm/l 1 Q .T,wl i,,+^ sures wliich lead to ruck desjiuctiou. (After 1^ ana lo, ana into cuamberlin.) them the roots of trees sometimes make their way where by expansion, (hie to growth, such strong- pressures are devoloped as sometimes to throw down large blocks of stone. Then again, in cold climates these tis- siires may become tilled with water which, when I freezing, overturns and throws down manv frag- ments, thus hastening their ])assage into soil. 71. Soil Removal. — Tt follows from what has been said that the same processes which result in 1" IG. 4— lic(f Hlull', Wis , ^howiiid rock fis.^iirps ^ . , ,. . ■, wliich Icui to rock destruction. (After Soil formation lllUSt alSO Cliainberlin.) , •, , , •, i , contrihute to its destruc- 54 f^3 tion in one place or re- moval to another. All are familiar with the creeping of soils from the broAvs of steep hill- sides toward their bas( and ont npon the mun level ]:)1 a ins which stretch away from them. These downward'move- ments are caused bv sca eral agencies: (1) Tli beating of falling raii drops and the carrying 230wer of the streandet^ wdiich fV)rm as these gather together ; {2) the expansion and contrac tion of the soil due to the alternate wetting and drving, there being Fig. rz.— Giant's ('a.-flcncarCamp Douglas, n„ '• , , Wis., showing cliffs of rock crumbling into less resistance to expan- soil. (After Cliamberlin.; sion dowin\'ard 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 draAV downward because of less resistance in that direction. (3) Then, again, every disturbance of the soil produced by animals burrowing or walking up or doA\ni the hillside, tends usually to work the soil from higher to lower levels. Even the action of the wind is on the whole doAmward. 72. Soils Produced by Running Water. — Eivers and streams are contiiinally at work at this double process of soil building and soil removal. When one watches the bed of a stream as the water rijiples over the uneven surface 55 it is oas^y to note how I'apidly soil and sand grains are be- ing rolled and tiiiid)lcd along the bottom. If it is desired to nieasnre this rate of movement a shallow pan or box may be sunk in the bed of the stream, leaving its rim Hnsh M'ith the surface ovei- Avbieh the water i-olls. After a sufficient in- terval remove the box and dry and weigh the material collected. At each bend in a stream soil is l)eing taken from the con- cave side and carried onward toward the sea, while on the o])- posite side new soil is being formed from that draggXM 1 ah )ng the bottom. In this manner streams change their courses 1 1 J? • 1 Fig I'-i — Pillar Rock, Wi-;.. sliowinff rocliy cliff ana wander irom SUle in tUe last stages of decay. (After Cbamber- to side across the val- ^'"'^ ley, each time making a new soil 03i tlie 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, sucli as are shown in P"'ig. 14. It is in this way, too, that the '^'ox- hows" (if the ^Mississippi below Vicksburg were formed, some of which are re])resented in Fig. 15. These abandoned river channels are at tirst long and narrow lakes hut ultimately, with the rejx'atcnl overflows of the stream, they became filled. Sometimes they remain for long intei'vals de])ressions in which swam]) or humus soils develoj). 56 O ( Fig. 15.— ShowiLg the sliiftin^^ of river chanaels, the formation of "ox-bows' and alluvial soils. 73. Glacial Soils. — In those portions of the world where the temjieratni'c is so low that most of the moisture falls as snow and where these snows do not all melt dnrine; the warm season there come to be sneli vast accnuiiihitions that the areat weii>lit eompresses the snow into ice. So ex- tensive and massive are these snow and ice fields in Green- 58 59 60 land and in parts of Alaska today that tliev move over the face of the eonntry miicli as a broad river would move,, except at a much slower rale. 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 ahraid into soil the rigid rock surfaces over which thev move. ^iiG. 18.— Shovvitiiarrock surface over which glaciers have passed, scratching and polisliing it. In a recent geological epoch the whole of the Xorth American continent north of the Ohio and Missouri rivers and much of northern Europ,e 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 ]dains. Eigs. 16, IT, 18 and 19 are views illustrating different jdiases of soil forma- tion bv j>lacial action. 61 Fig. 19.— Relief Map of Wisconsin, showing the diti'erence in topography of a glaciated and non-glaciated surface. 74. Formation of Humus Soils. — There is a class of soils having their origin in vari<;ns types of swamps or marshes ^vllicll contain an nnnsnal anionnt of organic matter in va- rions stages of decomposition and Avhicli have by some ■writers been given the name of hnmns or swamp soils, the former name referring to the large amonnt of hnmns these soils contain and the latter to the physical conditions iTnder which they have been formed. In many places in the higher latitndcs and at consider- able elevations nearer the eqnator where the snrface is too flat for ready drainage, and where the winter snows re- main so long npon the gronnd that the snmmer is too short 62 to permit the soil to l^eeome dry eiiono'li to allow the air to penetrate deeply and freely, the organic matter accn- nmlates and soils are formed containing a large proportion of hnmus ; even beds of peat may develop. Under other conditions, where rivers ap- proach their outlet across a very flat country t and are no longer able to scour their clian- .5 nels and keep them clean, the moving sedi- I ment finally raises the banks and the bed un- rt til the water is flowing above the surround- ^ ing country. Under these conditions with a a continual seepage and frequent overflows =« swamps are developed in wdiich marsh vege- ^ tation grows luxuriantly and, falling under § conditions where free oxidation cannot oc- J cur, the renuiins only partially deca,j, giving ^ rise to beds of peat and rich humus soils. f In other cases, where a river often shifts 1 its course and especially where the cut-offs o or ox-bows illustrated in Fig. 15 are formed, .2 these places, with the poor drainage which g they must have and with the occasional over- o flows to keep the cut-offs filled Avith water, are maintained wet long and continuously 2 enough to allow humus soils to form. 1 With the final withdrawal of the great ice ^ sheet from the glaciated parts of America •| and Europe there were left large numbers of J shallow lakes whose flat margins were wet j enough to support marsh vegetation and ° 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 winds and washed in 6( from tlio snrvdiiiidiini- liiiilu'r land, became so heavy and so thick as to rest upon the bottom of the lake, converting it into a marsh of peat or hnnins soik On the margins of larger lakes and especially along the seashore, sand bars or reefs are thrown n]) behind which bodies of water are shut off and in 5 these organic matter may accumulate ii in the same manner as that iust de- ' c — scribed, giving rise to the same type of 5 soils. =■ In still other cases, on the margins I of the sea bottom, there flourishes a pe- | culiar type of vegetation known as eel ^ ffrass, which lives alwavs beneath the C water at low tide in a position repre- sented in Fig. 21. These a'l'asses offer ?. a natural obstruction to the incoming ^ and outgoing tidal waters, causing &■ them to throw down their sediments 3 and thus build up the sea floor with :;; silt containing large amounts of or- ■=■ ganic matter under conditions unfav- 2 orable to rapid decay. As the sea floor ^ rises in this way above low tide level % the eel grass dies and another type of 5- swamp vegetation takes its place, as % between a and b in the figure, and here g, again the formation of humus soil is « continued under somewhat dift'erent ^ conditions. 75. Wind-Formed Soils. — The wind moving continuously o\'er the face of the land is now and long has been a potent factor in soil removal and soil Iniilding. Iiid(H-d, it is probable that nowhere can soils be found which do not contain many wind-borne ])articles. Every raindrop which falls and every suowflakc, however white, brings to the field upon j^ 64 Avhicli it falls one or more particles of soil Avliicli has been drifting in tlie higher air from unknown distances. The drifting of dnst from roads during dry times and from fields in 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, wjnd-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 Richthofen as having been formed from dust accumulations drifted by the prevailing winds from the high desert plateaus of Central Asia. In Enrojje, 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. — Tlu re are many animals Avhicli have contributed largely to the forma- tion of soil through a grinding of pebbles and the coarser sand and soil grains into finer materials. 65 Darwiiu tlirouiili a louii; and cai-cful studv, reached the conehision that in inaiiy [)ai'ts of Kiitiland eartlnvorins pass more than 10 tmis of dry earth per acre through their hodies annually and that the grains of sand and hits of flint in these earths are i)artly 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, swallowing the earth, when the point of the head is held fast in the excavation while an enlarged por- tion of the tt'sophagus 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 hirds, 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- ^—'^^^—~ .,= ,=-5-— ^- i-or-+i<^n ■ii'lnV.li in ^.+'.FiG. 23 — A tower-like casting ojected by a spe- Aecrion AMUCII, in (l cies of earthworm, from the Botanic Garden, feet amounts to the Calcutta. India. Natural size from photo. ' ' (After Darwin.) 66 V ^- i". ». . ' *i- T" -' ^% •% K' t:-^^ ^ '. .",> #^-' *•!', \**^ .■^!iu' '^'AV'W^A^Vfi * /"\'i^'/'^^' ' o Fig. 2t.— Section of vegetable mould in a field drained and reclaimed 15 years before: ^iioxMtiK turf, vegetable moiild'. without ^t()ue•-, mould with frag- ments of buiut marl, coal cinders and A- Oxide of Peroxide Residue. Silica. Man- OF Iron. ganese. Sand. Clay. Sand Clay. Sand Clay Sand Clay. Sand Clay. Sand. Clay. 93.630 72.746 1.682 8.926 .060 .112 .102 .106 .761 12 406 1.532 2.473 94.770 73 690 .486 3.370 .069 .004 .156 .146 .706 5.989 .733 7 305 93.362 60.310 1.721 2.000 .018 .119 .220 .196 .941 9.709 1.339 18 066 95.630 73.422 .879 2.709 .064 trace .049 .164 .224 4.054 .473 10.598 92.090 63.444 1.220 11.325 .035 .079 .126 .052 .963 3.894 1.9.59 13.454 90.230 77.860 1.940 1 790 .009 .041 .313 .056 1.927 5.fit6 •Z.141 7.538 90.681 54.565 1.885 13 219 .130 .277 .172 .079 1.837 7.089 1.436 16.071 92.460 51.063 1.550 20.704 .036 .325 .010 .119 .843 5.818 2.649 10.539 94.428 79.580 .529 3.628 .069 .065 .101 .195 .661 3.420 1.195 4.988 94.822 75.350 1.037 7.310 7.498 .022 .2.D8 .020 .038 .930 5.784 1.576 5.567 93.210 68.209 1.293 .051 .128 .130 .115 .979 6.381 1.503 9.660 91.498 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 20 825 4.918 .109 .165 .098 .164 7.010 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 6.998 SUB-SOILS. 90.714 66.290 -i-7.688 2.212 7.446 .064 .085 .080 .125 1.739 6.947 2.276 12.086 -1-2.508 -1.193 -2.412 -H.008 .000 -H.044 -1-.008 -.577 -1.742 -1.131 -5.088 ARID AND HUMID SOILS COMPARED. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. Hu- mid. Arid. Hu- mid, Arid. Hu- mid. Arid, 84.031 70.565 4.212 7.266 .091 .264 .133 .059 3.131 5.752 4.296 7.888 times as much magnesia as do the humid soils with which they have been comj)ared. 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 wall be seen that, excepting potash, lime and magiiesia, 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 ingTedient of fertile soils and is the product of decaying organic matter. In torrid climates where the soil 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. — Tlilgard and Jaffa have made the important dis- covery that the humus of arid soils is relatively richer in nitroffen than is that of humid soils and hence that smaller 77 amounts of it will inoet the needs of niter-fovming 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 8 8 Per cent. .75 .99 3.01 Per cent. 15.87 10.03 5.24 Per cent. .101 .102 .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, wdiich 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 ^vith 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 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 eqnal 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 rocks and residual soils. ^ Trenton Limestone Bermuda Limestone I Gneiss, Granite. DiORITE. Rock Soil. Rock Soil. Rock Soil. Rock SoU. Rock Soil. Silica (Si02) .... Alumina (AI2O3) Ferric oxide. . . . Prct. .44 .042 Prct. 43.07 25.07 15.16 0,63 0.03 2.50 1.20 tr. Prct. .052 54 54 '.496 1.751 0.066 0.252 44.251 Prct. 45.16 15.473 13.898 3.948 0.539 0.133 0.007 2.533 Prct. 60.69 16.89 9.16 4.44 l.Od 4.25 2.42 Prct. 45.31 26 55' 12.18 tr. 40 1.10 0.22 0.00 0.47 13 75 Prct. 69.33 14.33 3.60 3.21 2.44 2.67 2.70 Prct. 65.69 15.23 4.39 2.63 2.64 2.00 2.12 Prct. 46.75 17.61 16.79 9.46 5.12 0.55 2.56 00 0.25 0.92 Prct. 42.44 25.51 19 20 Lime (CaO) Magnesia (MgO; Potash (KjOj ... Soda (NaaO).... Carbon dioxide.. 34.77 tr. not d. notd. 42.72 0.37 0.21 0.49 0.56 0.00 Plios. acidiP.jOs" 0.10 11.22 0.06 4.70 0.29 Water and vola- tile products . . l.OS 12.98 .328 18.265 .62 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, Y5, 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 1 Rocks, Rock Weathering and Soils. Merrill. 79 are dissolved and carried away l)y the water for each 2 pounds of soil formed, the chief materials carried away beinc; the lime, maoiiesia and carhon 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 of amount of plant food in lOOo lbs. of air-dried liroduct. (WOLFF.) Maize. Oats. Wint'e Spring Wint'h Red Wheat Wheat Eye. Clover i a i a i d fe CI i a i d 5; a ca ca 2 ctf f. CS CS ? cfl C8 CS CS ctf CS £ u 7J CiJ 61.6 26.7 46.0 16.8 38.1 18.3 CO ■38 2 17 9 45.9 22 3 m P7 6 O Total ash 45.3 12.4 38 3 Potash (KoO) ... 16.4 3.7 16.3 4.8 6.3 5.2 11.6 5.6 8.6 5,8 10,7 4.7 18,6 13,5 Soda (NaaO) ... .5 0.1 2.0 1.0 0.6 0.3 1.0 0.3 7 3 1.6 0,5 1 1 4 Magnesia (MgO) 2.6 1.9 2.3 1.9 1.1 2.0 0.9 2.2 1.2 2.0 1.2 2.0 6.3 4.9 Lime (CaO) 4.9 0.3 4.3 1.0 2.7 5 2 6 0.5 3,1 5 3 H 6 ?0 1 •,^,5 Phos acidiPjOst ;i8 5.7 2 H 6.S 2.2 7.9 2.0 9.0 2 5 8.5 1.9 7 8 5.6 14 5 Sul. acid CSOa).. 2 4 0.1 2.0 0.5 1.1 0.1 1.2 0.2 1 6 0.2 1.8 0,4 1.9 9 Suipllur 3.9 1.2 1.7 1.7 1.6 1.5 0.9 1.7 1.3 1.4 2 1 Nitrogen 4.8 16.0 5.6 17.6 4.8 20.8 5.6 20.5 4.0 17.6 6.4 16.0 19.7 30 5 From this table it appears that each ton of clover hay withdraws from the soil 30.4 11)S. of nitrogen; 37.3 lbs. of potash ; 12.6 lbs. of magnesia ; -40.2 lbs. of lime ; 11.2 lbs. of phosphoric acid; and 14.2 lbs of sulphuric acid, making an ac'CTco-ate of ash ingredients alone of 154.S lbs. 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 Table giving the tons of essential 2olant food per acre-foot of different types of soil. Potash (KoO) Lime (CaO) Magnesia (MpO) Phosphoric acid (P3O5) Sulphuric acid (SO3 ) . . . Sandy soil, Tons. 2.42 1.70 .96 1.74 1.10 Clay soil. Tons. 6.38 12.34 9.12 2.82 1.50 Loess soil, Tons. 8.70 116.40 73.84 4.00 1.80 Humus soil. Tons, 6.39 37.86 8.68 1.50 1.48 From this table it appears that the amount of plant food per acre-foot of iield soils, not including nitrogen, ranges from abont 2 to S tons of potash, 2 to 11(3 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 Remove the Plant Food of an Acre-foot of Soil. — ^rhc ratio (»f dry weight of the ker- nels to that of the straw and chatf 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 2,1:00 lbs. of grain and 3,600 lbs. 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 crops of wheat yielding 10 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 81 where 6.38 is the tons of potash per acre-foot, 2,000 is the number of lbs. in one ton, 2.4 is the number of 1,000 lbs. of grain in 40 bush, of wheat, 5.2 is the nvimber of lbs. of potash per 1,000 lbs. of grain, 3.6 is the number of 1,000 lbs. of straw with 40 bush, of wheat, 6.3 is the number of pounds of jjotash per 1,000 lbs. of straw, 362.9 is the number of crops of wheat. When the j)robleiii is solved for each of the essential plant foods used bv 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 l^er 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 10 bushels of grain and 3, GOO 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 plaut 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. Laws and his as- sociates regarding the conditions which determine the fer- tility of the soil, have thrown much needed light upon this 82 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 ingTcdients 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 lbs. of nitrogen ^Der acre, the same crop on adjacent and similar land given fertilizers without nitrogen could gather 22.1 lbs. or Q.76 per cent. more. Barley, which, with no fertilizers, during 24: years could gather but 18.3 lbs. per acre per amium, did, when aided with other ash ingredients, remove from the soil 22.4 lbs. of nitrogen per acre. Beans, which gathered from untreated land 31.3 lbs. of nitrogen per acre during 24 years, took off from the land under the other treatment 45.5 lbs. per acre. So, too, in a rotation of crops, 7 courses in 28 years, no fertil- izers gave 36.8 lbs. of nitrogen, while with superphosphate of lime the yield was 45.2 lbs. per acre. Again in the mixed herbage of grass land 20 years without fertilizers gave 33 lbs. of nitrogen per acre, but Avhere mixed mineral fertilizers containing potash were given the yield was 55.6 lbs. of nitrogen per acre. 95. Store of Nitrogen in the Soil. — The mean amount of nitrogen in eleven arable and grass soils at Bothamstead is placed by Laws 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 lbs. 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 83 below gives tlio distribution and amount per acre in each of the upper four feet of four Manitoba soils : Niverville. •• Brandon. Selkirk. Winnipeg. First foot Lbs. 7,308 5,408 2,484 1,520 16,720 8.36 Lbs. 5,236 3,488 2,592 870 12,186 6.093 Lbs, 17,304 8,448 2,736 1,487 Lbs. 11,984 10, 464 Third foot 5,688 4,045 Total 29,975 14.987 32, 181 Tons 16.09 Tlius it is seen that in the upper four feet of these rich soils there was found from to 16 tons per acre of nitrogen. 97. Forms in Which Nitrogen Occurs in the Soil. — JSTitro- gen occurs in the soil in several distinct forms : 1. In humus, deseril)ed in (88), wdiich 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 has 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 1'2 inches, but as already shown in (96) large quan- tities are found as deep as four feet below the surface. 84 Warrington determined the distribution of nitrogen in some of the Rothamstead soils to a depth of 9 feet in 9-inch sections. The resuhs he found are given in the table be- low : Nitrogen in soils at various depths. Arable soils. Old pasture. Lbs. per acre 3,015 1,629 1,461 1,228 1,090 1,131 7,333 4,365 4,559 16,257 Lbs. per acre 5,351 2,313 1,580 1,412 1,301 1,186 10,656 Total 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. Warrington 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 366.6 lbs. of nitric nitrogen and 1,650 lbs. of nitric acid per acre; enough, if it could all be used, to give a yield of 57.5 bushels of 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 85 feet in one-foot sections on May 24 and again on Ang. 22, and the resnlts are given in the table below : JVitric acid in fallow ground in pounds per acre. 1st foot. 2nd foot. 3rd foot. 4th foot. May 24 78.03 293.72 21.43 116.17 8.13 23.50 4.76 August 22 16.72 215.69 94.74 15.37 11.96 These figures are a mean of the ainonnts fonnd in nine different snb-plots, the soil being a clay loam changing into sand in the third foot. It will be seen that the total ainonnt of nitric acid at the close of May was 112.35 lbs., contain- ing 24.97 lbs. of nitrogen, enongh for only abont 14.3 bnshels of Avheat. On the 22nd of Angnst, however, there had been an increase to 450.11 ll)s. per acre, containing 100.02 lbs. of nitrogen, enongh for nearly 60 bnshels of wheat per acre. 101. Source of Soil Nitrogen. — Until recently it was inaintain{' })er cent, the ju'oto- 94 plasmic lining, p, began to shrink away from the cell wall h., as shown at 3, and when the strength of the solution Avas made 10 per cent., the conditions shown in 4 are produced. Wlieji the cells of plants are affected in this w^ay they wilt and growth ceases. A soil containing 20 per cent, of water and also 2,000 lbs. of water soluble salts per million of dry soil would contain 2,000 lbs. in 200,000 lbs. of water or 1 part in 200, which is .5 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 ecpial to that which De Vries found fatal to plants, or 10 per cent. The salts in the surface three inches of soil upon Avhich Hilgard found barley to grow four feet high were 1.2 per cent., wdiile it was 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 ease 12.2 per cent., Avhich 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 M-av become injurious to plants when they would not be so with an abundance of w^ater 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 j)ercolation, 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 95 coiitiniu'd rock deeav under conditions where little or no leaching' has taken place. Rains enongli fall to produce decay, bnt not enongh to carry the salts formed into the drainage channels and ont of the conntry. 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 np and carry away the extremely solubl.e salts not availalde as plant food all soils would in time become "al- kali lands ;" so that while excessive leaching is undesirable, a sufficient amount is indispe-nsable. 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 jn-aetical 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 lbs. 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 Avell 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 Fiu 29.--Sh(>\vinjr the seasonal f)ianj;es in (lie Mimniiits of nitrates in the soil under irrowiuK' corn. 97 l-"l';. 3ii. — SlKiwin.n' liic scnsiiii.il cli.-ii ill tile suil iimh iH'cs ill tile MllHiillits of •1- jiTowinK i-iii-ii. ihible 98 112. Drainage the Ultimate Remedy. — Drainage must be tlie 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 exeessive evaporation of water from the surface wall 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 ->0 ar(^ re|)resented the changes in the nitrates and total soluble salts in the surface four feet under three fields of corn, beginning with Aj^ril and ending with Sept. Re- ferring to th(? nitrate curves it wiM 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 tlie 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 lbs. i>ev mil- lion of the dry soil for the four feet, or 1,968 lbs. 99 115. Variation of Soluble Salts with Different Crops. — There is a marked ditt'ereiiee in the aniount of sohible salts, and es[)ecialJy in the amount of nitrates, in soils under crops like corn and potatoes, where inter-tillage is i)rac- ticed, and nnder such crops as clover and oats, where the ground is not cultivated at any time of the season. This is very clearly siiown in Fig. 82; tlio 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 f<:)ot under the corn and potatoes increased rapidly until July 1st, when they were five times as concentrated as in the fourth foot ; but in oO days more the nitrates had been res. On the clover phjts the start was at 250 ll)s. j)er aci-e in the surface foot, risiiii;' to 21)0 llis. in 12 .1»T to 1 for the clover, alfalfa and oats; and these ratios ai'c wduit would be ex- ])ected it the loi'malioii of nitric aeid destroys the carbon- ates and bi-ea rhonates in the soil water. 117. Closeness of Plant Feeding. — it was pointed <»uf in (7) wlnit small amounts of a fertilizer can he widely dis- tiMbnte(l through an aci'c of soil, and we ma\' now consider liow extremely (dose plants do feed the nitrates of a soil. In the table which follows are i;iven the amounts of ni- trates Avhich wei-e found in each foot of nine field plots, rejiresentec] by the cnrves, between .Inly IS aii!» for potatoes, and yet with these small amonnts of nitr<)i»,en in the soil dnrinc,- the time when the chief i>'rowtli 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 n[)on 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 Oats green. ( June 10 .025 .213 Parts of nitric nitrogen per million of dry .-^oil - (June 11 .027 .297 Th-ese amonnts, when expressed in pounds per acre and •as nitrates, are only .392 lbs. and 3.813 lbs., respectively, for the yellow and green oats. Table showing the amounts of nitric nitrogen under corn rows where leaves are turning yelloiv and tvhere they are yet normal green. Depth. Plot 9. Marsh soil. RandaU field. Yellow. Green. Yellow. Green. Yellow. Green. 1st foot 0.61 0.14 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 P.3C 0.95 2d foot 3d foot 4th foot 0.60 0.37 0.30 103 Small as those amounts of nitric nitrogen are the yield of corn on plot 9 was a mean of 8,000 lbs. of water-free matter per acre. On another plot where the yield was 11,440 lbs. of water-free matter pen* acre the nitric nitro- gen was reduced as low as 1.440 parts per million in the iirst 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 phnits were taking it up almost as rapidly as it could be produced, leaving the amouuts so low, as the figures show. 119. Nitrates of Fallow and Cropped Ground. — In the table whicli follows arc given the amounts of nitrates found under diiferent crops and, at the same time, under immediately adjacent fallow ground which had been cul- tivated and kept free from weeds. 1st foot. 2d foot. 3d foot . 4th foot. l.st foot. 2d foot. 3d foot . 4th foot. 1st foot. 2d foot. 3d foot . 4th foot. Oats. Nitrates. 5.94 8.12 4.73 4.60 Total salts. 70.94 114.6 124.7 39.44 Oat,>< 3.25 3.22 2.95 2.70 80.35 162.1 102.7 58.24 Oats. 2.47 2,46 3.83 3.16 78.56 102.9 72.98 33.99 Fallow . Nitrates. 246.40 26.75 6.50 2.84 Total salts. 199.3 123.5 108.0 42.10 Fallow. 143.05 ;;9.50 8.87 4.10 206.1 254.3 115.0 95.32 Fallow . 129.15 35.60 9.11 4.08 211.3 254 7 117.8 61.92 Barley. Nitrates 2.62 5.10 4 04 3.03 Total salts, 61.72 87,08 112.6 51.76 Peas. 8.38 18.57 6.59 2,66 77.00 197.2 135.8 44,62 Spriiif,' rye. 1.24 2.62 2.07 2.78 77,34 102.1 94.82 48.85 If the mean anionnt of nitrates in the surface foot of the fallow ground and uikKt the crops are expressed in pounds per acre they stand 4T;i.G5 to 10.88. This ditference is enough for 85 bushels of oats per acre, where the ratio of grain to straw stands as 3 to 5. 104 120. Loss of Nitrates from Fallow Ground During: Winter and Spring-. — A lidd wliicli Ims hccn kcjit fallow n^'. iiml tliiil upon wliicli 105 Ix'iiiii' liii;iicr tlic followiiiii' MiiN' Ix'fdI'C. Iinii tlicv were Aiiiiiist 22 121. Nitrates on Fallow Ground in Spring Compared with That not Fallow. — ( 'ompnriiiii the mcnii niiioiint of nitric iiitr()i>,'('ii in iiiiic field plots hen rini;' crops in 1S1)!» with that of the nine fallow plots of the same year, as found in tlu; spriiiii' of 11M)(), I he anion Ills arc as st at CI I in I he laMc Ixdow and rcpi'csc ntcij i;i'aphically in l*'iii'. '■'>'■'>. I'able s/iowtiif/ the diffcrcncjH in the amounts of nitric nitro- gen after the n>inter and earfi/ spring rainn in ground kejyt 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 of 212.00 25.24 56.22 15 08 21.91 10.00 13.11 Plots not fallow, pounds per acre 7.24 Ditt'oronce 186.76 41.14 11 91 5.87 From tin's it is clear that tlie ci'o))s on tlie fallow n-romul start out in the spi-iuii' nnder coiidilions \( ry snpci'ior to those on the ficdds which had not heen fallow, thci'c hciiiju,' 245. (j8 lbs. of nitrates more per acre in the surface four feet. 122. Development of Nitrates Influenced by Depth and Frequency of Cultivation. WIk'ii a series of cylinders lik(^ those i-epi-esentcd in I^'ii;'. 5S, p. jsT, arc mulclied Ity stir- ring' at different depths and the stirrini;,- is repeated at dif- fei'cnt iiit(i'\-als the I'alc of formation of nitrates is ma- terially iiiodilied, as sjiowii in the talde helow : Difference in the amount of nitric nitrogen, after 258 days, due to differences indej)th and frequency of cultivation. Depth of cultivati'n. Cultivated once per week. Cultivated once in two weeks. 1 inch deep 2 inches deep 3 inches deep 4 inches deep Lbs. per acre. 217,69 32:i.44 441.24 387.96 Lbs. per acre. 213.29 199,00 401. (is 245. ;i6 106 It can be seen that the nitric nitrogen has increased in both series to a de])th of '3-incli cultivation and it has in- creased witli tlie fi'ccincncv of the cultivation. 123. Soluble Salts Affect the Movement of Soil Moisture - The varying strengtii 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) by 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 evajtoratioii 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 of Evaporation. — When water has been brought to the surface of the soil by capil- larity it has yet to eva])orate and unless this takes j^lace the surface soil would become cai)illarily saturated with water and remain so. Since salts in solution increase the sur- face tension it will recpiirc a greater energy — a higher temperature — to throw the water molecules oft" 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 sh)\ver than it is from Aveaker ones under other- Avise 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. — 'J'lie internal friction of soil moisture is made greater by 107 the j^resence of salts in solutiuii and the more concentrated the soil solution is the greater is the internal friction, and hence the slower must he the rate of flow, and it may be that the much slower rate of capillary movement in a compara- tivelv 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 Avork 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. — AVhere 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 assistance in conserving soil moisture. C'irAPTKK IV. PHYSICAL NATURE OF SOILS. 128. Texture of Soils.- Tlic size ni' soil ^rniiis iind the way tlicv iii'c i;r(iii|)c(l in cuinixisitc clnstci's foriuiiii;' ker- nels or ci-iiinhs has a \'cry i^i-cat iiilluciicc in (Ictcrmiiiiiig' the })liysi(',al])r()peTti('s ol' soils and their aiiricnltural vahic, and as soils vary (piitc as \\idel\- in tlic size and ;irraiii>'e- inent of their i>i'ains as they do in thcii' chemical composi- tion it is (dear that I his phase of soil prohlcnis must take at least erains are then hroUi;lit into the (dosest possihie arrangement, and. they hecoine nearix' or (piile iiiipei'\ious to hoth water and air, a|)proachinii' the condition .M';uiis on the iKiri' spnci' :imiI upi'U llic iiic>\cinciil oC .-lir mimI walri- llii-(iii^'li a 110 determiue the number in a cubic inch. If a soil were made up entirely of the lai-gest size given in the last table, theiL 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 loAver part of Fig. 34 would be 23=» = 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 nund:)er would be 25,000'' =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 wdiile 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 gToups or kernels of various sizes and it is only by long boiling in water or thorough })estling 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 the 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. Ill 133. The Pore Space of Soils. — When the weight of a cu- bic foot of dry soil is known the amount of pore 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 lbs., a cubic foot of dry soil, if there were no open spaces in it, should be 2.65 X 62.42 = 165.4 lbs. With this value and the data given in (149) the Dore space of those soils may be calculated. Thus, for the surface foot we have Pore space = 165.1 — 79 165.4 = 52.23 per cent. 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." First foot Lbs. 79.0 92.62 104.59 106 21 111.06 111.06 Per cent. 52.23 Second foot 44.00 Third foot 36.76 Fourth foot 35.78 Fifth foot 32.85 Sixth foot 32.85 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 sandv soils and sands the smallest. 134. Pore Space Between Spherical Grains. — It can be shown mathematically that when a space is filled wdth spheres all of one size and these are given the closest pos- sible packing, having the arrangement shown in the upper part of Fig. 34 and Fig. 35, the pore space must be 25.95 per cent. ; but when the spheres are given the closest possi- ble packing and the arrangement rejn-esented in the lower 112 part of Fig. o4 and in Fig. 8G, then the pore space mnst be as large as 47.64 per cent. In the first case the water capacity of such a soil with the pores entirely tilled wonld i'jc. J.j. Sliowiiiu llu- closi'st pacldim ijf splu-rical soil urains. the <■!»■- meiit of volume and tlie direction of lines of flow. Face annles (id ana 120°. (Aftei- Slichter.) be 3.114 acre-inches per acre-foot and with the second ar- rangement the maximnni water capacity would be 5.7108 acre-inches i)er acre-foot. l^either of these arrangements would be likely to occur throughout a mass, and hence the 2,'eneral tendency will be 113 to form a }>orc space between these two extremes, and Fig". 37 shows what the observed pore space is in soils, sand, crushed rock aiul ('nis1ie(l ahiss. Tt will be observed that 1- ic. oti.— Shdwiiitc the cl.iscsl ii.-icUiim' of siilicrii-nl ^T.iiiis. the ficiiiciit of Yohiiue. !Ui(l the (lircctidii nf lines of flow when the face anfjlf"^ arc 90°, W anil 120\ (After Slicliter.) the finest clay soils, and indeed the finest g-rained nniterials, have the largest pore space. It will also be noted that the largest observed pore space exceeds the largest theoretical 114 I^ore 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 obsei'vecl pore space of different liinds of soils and sands and tlieir 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 115 amounts of Avator may be stored in them to drain away gradually in the underflow. 136. Subdivision of Pore Space Determines the Rate of Per- colation and Drainage. — If reference is again made to Fig. 34: it will he clear at a glance that water 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 -l 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 S2>heres 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 Vd where Y 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 detennine the pore space in undisturbed field soil 116 the simplest method is to use a soil tube, represented in Fig. 38, taking a nnml)er of cores of the desired depth, Fii;. 38.— Showing- soil tube for taliing sami)les of soil. drying them, and then c<:iin})nte the pore space with the formnla abo\'e. 138. Largest Possible Pore Space. — The largest possible ])OYC Space in soils will be found in the cases where the com- ponnd or kernel-strnctnre is most marked. Referring again to Fig. 3-4, imagine each sphere there represented to be made njt of other very mnch smaller spheres having the same general arrangement. Were this the case it is clear that in consequence of the compound spheres the soil must have a pore space not less than 25.95 jDer 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 ]iore space would be 2.^.95 + [25.95 per cent, of (100 — 25.95)] = 45.17 and in the second case 47.64 + [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 than 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. Eeferring 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. 117 of pore space avuuKI be occupied to the extent of T-i.OS per cent, in the lirst 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, graA'el, 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 grains ^= Ttd^ >< sp. gr. 6 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 lb. 1 . m. m 720 720,000 720,000,000 720,000,000,000 720,000,000,000,000 326,903 326,903,000 326, H03, 000, 000 .001 m. m 326, 903, 000, 000, 000 .0001 m. m 326, 903, 000, 000, 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 ^3 62,9 0^3 . If the soil were made up of some grains of all the sizes 7 118 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 20 20 20 20 144 144,000 144,000,000 .001 m. m 144,000,000,000 .0001 m. m 144,000,000,000,000 Total 144,144,144,144,144 140. Amount of Soil Surface Possessed by a Gram of Soil. ■ — ]\[uch of the water retained by soils is held there in the form of thin films surrounding the grains and the larger this surface is the more water may be retained. So, too, the solution of plant food from the grains takes place at their surfaces and the larger the amount of surface the more rapidly the solution may take place. The extent of soil-surface in a gram of soil can be found by multi])lying the number of grains by the surface of one grain or by introducing Trd" into the etpuition of (139), thus : Weight X^a^ 6 X weight ^d-* X sp. gr. d X sp. gr. 6 = soil surface expressed in square c. m. Using this formula to compute the surface in one gram of soil grains having the sizes given in the table of (139) the results below are obtained : Diameter in grains. Surface per gram sq. cm. Surface per pound sq. feet. 22.64 226.41 2,264 15 22,641.51 226,415.14 11.05 110.54 .01 m. m 1,105.38 11,053.81 .0001 m. m 110,538.16 119 It will be seen fruiii this table that the internal surface of an ideal soil increases in the same ratio that the diam- eter of the grains decreases, that is, reducing the diameter one-half doubles the surface to which water may adhere and upon which it may act. 141. Difficulties in Determining the Surface of a Soil Accu- rately. — While it is possible to determine accurately the surface in a given weight of sjiheres of known dimensions the case is quite different with true soils. Indeed, it is not practicable to determine with much accuracy the sur- face in a soil. This will be clear from a consideration of a simple problem. Take a soil composed of grains, (a) .009 and (b) .00015 m. m. in diameter and let these be mixed in the propor- tions of A. 90 per cent, of (a) with 10 per cent, of (b). B. 10 per cent, of (a) with 90 per cent, of (b). C. 50 per cent, of (a; with 50 per cent, of (b). Under these conditions the surface of one gram of such mixtures of soil having a specific gravity of 2.65 is For A. Surface. 90 per cent, of grains (a") .009 m. m. diameter 2,264 sq. cm. 10 per cent, of grains (b) .00015 m. m. diameter 15,094 sq. cm. Total surface 17,^58 sq. cm. For B. 10 per cent, of grain.s fa") .009 m. m. diameter 251 .6 sq. cm. 90 per cent, of grains (b) .00015 m. m. diameter 135,848.9 sq.Jcm. Total surface 136,100.5 sq. cm. For C. 50 per cent, of grains fa) .009 m. m. diameter 1,258.0 sq. cm. 50 per cent, of grains (b) .00015 m. m. diameter 75,481.7 .sq. cm. Total surface 76,739.7 sq. cm. 120 The iuinil)er of grains in one gram of each of these mix- tures woiihl be as iiiven below : A. B. C. (a) 889, 75:-!, 061 21,354,187,192,118 98,861,363 192,188,0)3,097,345 494,306,818 (b) 106, 770, 833, 333, :«3 Total 21,353,076,945,r.9 192,188,151,958,708 100,771,327,640,151 It is the custom to find the diameter of soil grains either by direct measurement or else by comiting and weighing a given nnmber of grains and then compnting the diameter of the mean grain from the weight and specific gravity. If the diameter of the mean grain in the above three ]>roblems 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 : Actual surface per gram of soil Surface computed from the grain of meau diameter Surface computed from tiie grain of mean weight.. sq. cm. 17, 358 150, 570 10,053 sq. cm. 136,101 150, 939 145, 734 76, 740 150,902 119,804 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 WM)uld 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 Computed from the true diameters in true proportions. the mean of the two extreme diameters. A. B. C. 4,949sq. cm. 17,358 sq. cm. 136, 101 sq. cm. 76, 740 sq. cm. 121 Here it is seen that the computed sm'face, 4,949, is very far indeed from either of the true values 2,iven nnder A, B and C. 142. Effective Diameter of Soil Grains. — While it is not possible to deteniiiiK' cither the mean diameter of the grains in an ordinai-y 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 fjraiii which, if substituted for the actual ones, would ])eruiit, 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. ^ 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 measureell; B, pressure gauge; C. air meter; D, aspirator tube for samples. Per cent, of pore space. Log. k. d. Per cent, of pore space. Log. k. d. 26 1.9258 1.8695 1 8195 1.7701 1.7199 1.6732 1.6277 i..W47 1.5409 1.4999 1.4592 563 500 490 502 467 455 430 438 410 407 400 37 1.4193 1.3816 1.3445 1.3078 1.2725 1.2374 1.2024 1.1690 1.137C 1.1058 1.0729 377 27 38 371 28 39 367 29 40 353 30 41 351 31 42 345 32 43 339 33 44 320 34 45 312 85 . .. 46 329 36 47 144. Observed Flow of Water Through Sand Compared With That Computed From the Effective Diameter. — The ac- curacy of the method described in (143) is Lest sliown 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 1.808 1.451 1.217 1.095 .9149 .7988 .7146 .6006 .5169 Gms. 2,277 1,132 757 522 453 2 297.5 193 122 80.6 66.8 Gms. 2,298 7 6 1,080 756 hVt 542 5 604.6 4 3i9.2 3 210.0 2 138.6 1 94.8 72.3 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. 124 145. The Effective Diameters of Soil Grains and the Amount of Surface Computed From Them. — We have no means of knowing vet how accnrately the conijnited 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 computrd surface of soil grains in different types of soil. Kind of soil. Finest clay soil. .. . Fine clay soil Fine clay soil Heavy red clay soil Loamy clay soil .. . Clayey loam Loam Loam Sandy loam Sandy soil Sandy soil Coarse sandy soil. , Effective diameter of soil grains. m. m. .004956 .007657 .008612 .01111 .02542 .01810 .02197 .02619 .03035 .07555 .1119 .1432 Per cent. of pore space. 52.94 45.69 48.00 44.15 49.19 47.10 44.15 34.49 38.83 34.45 3i!.49 34.91 Surface of soil grains in one cubic foot. Sq. Ft. 173,700 129, 100 110,500 91,960 70,500 53, 490 46,510 45, 760 36,880 15,870 11,030 8,S18 It Avill 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 Ifi 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 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 ont of Avater 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 ])lace. 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 A 1 of an inch 174,210 " 43,560 or one-half the thickness of the film of a soap bubl)le when it becomes yellow just before appearing black and breaking, from thinning ont. This thickness is also about ^ 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 gV 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 tt 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 difl:"erent 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 aiven. 126 It will be seen from this table that when the grains are so large that 10 of them will s])an a linear inch only 37 seconds are required for a jn-essiire of .1 foot of water to force 5,000 e. e., 5.3 (pnirts, of air throngh a cohmin a foot long and .01 of a scinare foot in cross section; but in the finest clay soil, Avliich makes the best grass land, where 5,125 grains must be set in line to measure a linear inch, then the time reijuired is 2,983,000 seconds for tlic same amonnt of air uiuler the same conditions to be forced throngh, a ratio of 37 seconds to 45 days. Table shotoing the differences in the rate of movement of air through gravel, sand and iest, bnt on account of the differences in dry weiglit of these soils their water contents are more nearly e(|ual than they ajvpear, the sandy loam containing about Hi His., the chiv l(tam IS lbs. and the liuiiius soil 2(> ll)s. |)(M' cnl)ic f(H(t. Kx])rcss('d in inches the amounts stand .■), .')..") and ."> inches nearly. 158. Maximum Capacity of Undisturbed Field Soil. — In the table below are given the amounts of water wjiich com- pletely tilled 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 pcM-forated covers and then placing the cylinders nn- aring these per cents, of moisture with th not able to place themselves in the most favorable relations with the soil to permit, cai)illarity to bring the moisture to the rootlets. It is because the sandy soils and loams seldom d(n'elo]> the structure referred to and because the rootlets and i"oot hairs are- able to secure a more uniform distribniion llii'onglioiU them as well as because of the larger size of their grains that ])lants are able to drain their moisture down to so low a ]Kn" cent. 165. Available Soil-Moisture Increased by Open Structure. — When soils ar(^ in any way left with a loose opim struc- ture, as happens with dee|) ])lowing and especially with good subsoiling, not only is the ability of the loos(^ soil to retain moisture increased but a largi'r proportion of this retained Avater bcH'onu's available to the croj). A larger amount of water is retained because when jierfect cajiillary connection with the unstirred soil below, is broken, surface tension o]>})oses rather than aids gravity in ])roducing per- colation and s])aces too large to remain full of watt'r other- wise are able to retain it. When the soil is open and loose the case is cpiite ditferent from that resulting from shrinkage referred to in (164)^ for in this case the roots and root hairs are better able to enter the sejiarated portions and, as the moisture films are thickei", th(^ moisture is mori' readilv i2,athered. 139 166. Drainage May Increase the Available Soil-Moisture — When tlie siihsuil is too closo 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 })hiiits are forced to develop in so limited an amount of soil that wlieu a dry- ing time comes, and when the deiuands 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, whei-e a field is well drained the roots are extended through much larger volumes of soil ; the lo- cal demands are thus less urgent aud tlie water need not move so far by capillarity before the ])laiit 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 aud capillarity may still add to this supply from below. 167. The Amount of Water Required by Crops.— It has been determined by careful aud extended observations in this country and in Europe that almost any one of the cul- tivated crops withdraws from :'>00 to ."iOO tons of water from the soil for each ton of dry matter produced. Tn Wiscon- sin the amounts of water lost from the soil by evaporation during the growing season and through the jdant are given in the table lielow : Table showing the mean amount of water used hy various ■plants in Wisconsin in producing a ton of dry matter. No. of trials. Water used per ton of dr.v matter. Water used. Dry matter per acre. Acre-in. of water per ton of dry matter. Barley Oats 5 20 52 46 1 14 Tons. 464.1 503.9 270.9 576.6 477. 2 385.1 luches. 20 69 39 53 15.76 22.34 16.89 23.78 Tons. 5.05 8.89 6.59 4.39 4 009 6.995 4.096 4 447 Maize 2 391 Clover 5 089 Peas 4 212 Potatoes 3 3l»9 138 Av. 446.3 23, 165 5.987 3.939 140 From this table it is seen that the amount of water used ranges from 270 tons of water with corn to 570 tons with clover per ton of dry matter; or Avhen expressed in acre- inches from 2.4 to 5.1 inches nearly, the average for the six crops being neai'ly 450 tons or 4 acre-inches per ton of drv mattei-. When the yields jier acre ai'c 2, ;> and 4 tons the nnm- bi'i's gi\'eii al)o\'e must be mult i|ili('(l l)y the same fa(;tors. 168. Amounts of Water Required for Different Yields of Wheat. — 111 order to express the data of the last section in terms which it is more ciistoinarv to use, there is given in the next table the amount of water recpiired by a crop of wheat when the yields ])er acre range from 15 to 40 bnshels. Observations made by Ilellriegel in Germany show that wheat uses about 453 tons or 3. 998 acre-inches of water for a ton of dry matter. TTsing this ratio and one pound of grain to 1.5 ])ounds of straw the water i-ccjuired will stand as below : Table sliowincj the leant amount of water required to produce different yields of wheat per acre when the ratio of grain to straw is t to 1.5. Yield per acre. Number of bushels. Weight of grain. Weight of straw. Total weight Water used. 15 Tons. .45 .60 .73 .90 1.05 1.20 Tons. .675 90 1.125 1.350 1.575 1.800 Tons. 1.125 1.500 1.875 2.',0()() in each square centimeter of surface, an. i area equal to the square shown in Fig. 44. The In the case of a corn leaf 2 1 per cent, of the surface ^ci?io^^^ occupied by the door- Avays to the breathing chambei'S. Fig. 42— Structure of bar]e,v ]eaf. Sorauer) so is a breatiiiug pore ; ni. rophyll cells; i, respiratory cliainbers 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 stai'clies, sugars and most otlicr compounds. 174. Guard Cells. — In order that the loss of water may be as little as ])ossihh' each l)reathing ])ore 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 144 the plant. Tlic chlorophvll <2,riiiiis can hr cft'cctivo in breakiiiii' down the carbon (lioxi(U' only in c()ni])aratively Id 000 Q DC^I B D Fig. 43. — Dhini'.-mi sliowiiiji- the inei-hiuiical iK-tiou of Kn.-ird cells In opoii- ing and closinji- lircitliiuf; poros. Tlit' sqiiiirc shows the wvvw of unt cap is pushed for- 150 "vvarJ and wedged sidewise, setting tlie soil aside and thus making room for itself. The root oa]) does not slide for- Avard j)ast soil grains but is anchored rigidly to them; the tip entering existing cavities is enlarged by growing for- ward under and through the ca]i, the rear cells of which die after the root has grown |)ast them, the root cap being a sort of point continually renewed as tiie 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 45) are shown the amount and distribution of corn roots at two stages of e-rowth. When the corn was 30 inclies hiiih the whole of the soil to a de])tli 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 bad come closer to tbe surface ; and at ma- turity the roots had reacluMl four feet in depth, making their way through a fairly lu avy chiy loam and clay sub- soil, the fourth foot only being sandy. It should be understood that the roots here shown grew in undisturl)ed tield soil and were obtained by going into the held at the stage of growth shown and digging a trench around a block of soil a foot through and the length of the Avidth 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 i)umping water in a hue sju'ay upon the block. Iliree days' work for two men were recpiired to secure the sani])le in Fig. 40. 184. Extent of Root Development of Grain. — In Fig. 50 is represented the depth to which the roots of winter wheats 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 cylin- 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 (lej)th of fully four feet. 151 Fig -Shi)\vin<; .iiiKiiint ;iml ilislrilmtidii of c-m-ii I'outs under natural licld I'liiidil ions. i:.2 Fir,. 49. — Sliowiiii; Miiioiint iind distribution of funi roots timlor natural lield C'onilitiuns. -1 - o 1 .) ■) Wheat. Barley. Oats. Fig. 50.— Showing amount of roots found in tlit^ fit'ld in .-vlindcr of soil one foot in diuDK-tcr, fxteniiny to a depth of four fci-t. 154 Kic. 51.— Slidwiiif; llic t(it;il runt of one hill of cnni. Fig. 52.— Showing total roots of Dat.s. l.-iG Fi<;. .W.-Sliowiiii; lutjil rcKits of mcdhiin clover. 157 The coarse branches sliown with the winter wheat roots are tlie 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 j»innp('(l after it has been gathered. 185. The Total Root of Plants. — In the preceding sections tlie sani2)les simply show the amount of root found in a given volume of field soil. In Fig. 51 is sliown 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 ])hints in cylinders 42 inches deep and 18 inches in diameter, lilled with soil. When the crops were mature the cylinders were cut down and the soil Avaslicd away. In each case the roots ext(;nded to the bottoms of the cylinders, forming a dense mat there, as the engravings show. The roots shown with tlic <'lo\'er, and which gathered the moisture for the top, forccid fi'om tlie soil water enough to cover the si)a('{' to a depth of 29 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 suj^plying 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. 158 CIIArTKK \U. MOVEMENTS OF SOIL MOISTURE. 186. Types of Soil Moisture Movement. — The moisture wliicli is foniitl in the soil above tlie surface of the croiind water is coiitiimally subjected to tliree types of movement : (1) Gravitational,'^ (2)'Capinary and (3) Thermal; the first due to the action of gravity, the second to surface ten- sion and the third to heat. AVhen 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. GRAVITATIONAT. MOVEMENTS. 187. Percolation of Soil Moisture. — The diicet 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 159 impodos percolation oxccpt in those cases where wide shrinkage cheeks and cracks have resulted. Where percolation is influenced chiefly by soil texture it is most raj)id 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 iiUcd 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 wat(M- which percolated from the columns of sand rcfcn'cti to in ( 160). Table (jiving the rate of percohdion frohi aaruhs under the prnvitational head of the inclosed tvater. Geade of Sand. No. 20. . No. 40. . No. 60. . No. 80.. No. 100. Eil'ectivo Per cent Wcierht diameter of pore of sand of grain. space. per 8 cu- bic feet. m. :n. Pounds. 0.474.5 H8.86 809.28 .1848 40.07 793.28 . 1551 40 76 784.00 Aim 40.. 57 786.64 .0826.5 39.73 797.76 Amount of Watee Pbeco- I^ATED IN — First 30 min. Second 30 min. Lbs. .53 3a 39.27 29.99 7.86 6.31 Indies. 10.?.5 7. 549 5 674 1.512 1 213 Lbs. 24. K6 27.35 23 .^2 6.73 4.40 Incbes. 4.683 5.2,58 4.. 522 1.294 .815 It will be seen from the above table that the rate at which the water moved downwai'd thi'ough the coarsest or Xo. 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. — 'llic jK'rcolation of Walter from the sandy loam and from the clay soil, given IGO in tlic hililc (if (160), AvluMi tlio ciglit-foot coluiiiiis M'cre eoiiiplctclv full of Wiitcr at the start, took ])la('C at a much slower rate than from the sands, as indicated in (188)^ the rates beine' SmihI.v loam, iiiclios. Chxy loiuii inciies. First 21 hours. . 2.640 1.958 First 10 difl'ei-ences in the rate of ])ercolation M'hy the sand could not he produ(!tive under ortlinary con- ditions of I'aiiif.ill, no matter how miicli plant food it might contain. It is ch'ar also that tiuencss or closeness of tex- ture is one of the most iui|»ortant qualities of a good soil, for without this \]u) water (.trains away so ra])idly that, Avith tli(^ ordinary intervals between rains, not eiKUigh could be retained for the ne(Mls of crops. 190. Percolation Through Dry Soil.- When soils have 1h^- come relatively dry, as happens especially during the mid- dle and later summer, Avater docs not percolate into them as readily as it does in the spring Avhen the pores are more nearly tilled. AVhen the volume of air in the soil is large, and Avhen the films of Avater surrounding the soil grains are very tliin, the How downward ])ast the air is V(>ry slow. It is on this account, in part, that the lighter rains arc less effectiA'o in midsummer than they are in the spring, the Avater being retained close to the surface Avhere it is quickly lost by evapoi-ation. 161 CAPILLAKY 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 gTOund; 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 vai-ying with the diameter of the 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 Haised in Capillary Tubes. — The reason for the differences 1(1:3 ill li('ii;lit to uliicli \\;itcr m:iv he niiscd in cnpillary liiluvs by siii-fiicc Iciisidii is loiiiid in tlic I'cliilioii cxisliiiii,' Ix'twcen tli(> \(ilniiic of lilt' tnl)(' ;in(l ils iiilcrinil circnin rcrcnco at the lr\cl (if llic wnlcr snrfnci'. (j)nink(' liiis sliowii tliilt the force ol' collision is c\crtc(l o\'ci' a dislancc of non'ooo incli ; so lliat wlicii a i^lass liihc is llinist. into water llio molecules in the surface of llie wall just al)o\c llic water draw upward npon the rows (d mioIccmIcs in IIk^ stirlaco l\ini;' nearest, raisiiii;' llieiii ahoNc llie natural waler l(>V('l. r.iil as I lie edii'c second. Inhe, for then ils load hecoiiies 10 limes as ii,reat, and this is llie limit id' ils power, as expressed in the laMe helow : nianu'tiM- (if tiibo. Rolntivo area <>r (M'OSS- sootioii of til 1)0. H«idit to wliicli \vat(^^ i.-i lift 0(1. Holativo aiiioiiiit of wator liftoil. 1,0 inch. .1 iiicli. .01 inch. .001 iuoh. 1,(HK),0(K) X .O'VtSO inchos - .'i4. 560.00 10,(1(10 N .ru^ii iiidios - 5,466.00 10(1 X 5.456 inchos - 546.00 1 X 51.560 inchos = 61.56 The actual ainoiint itf waler lifled hv the surface" film slrelched across tlu> Inhe and carried iii)ward hv tlio {)ull (d" lli(> ii'iass niolecnles just ahove ils ediic is as fol- lows : Hj'S In the 1.0 inch tube 04285 cubic inch. In the .1 inch tube 004285 cubic inch. In the .01 inch tube 0004285 cubic inch. In the .001 inch tube 00004285 cubic inch. 193. Capillary Rise of "Water in Soils. — U'lie spaces left bc- tweuii tlic soil grains funii more or less triangular capillary tubes whose cross-section, formed b_v four spherical grains, ])lace(l as closely together as possible, is represented at the left in i'ig. 54; and these tnbes extend in all directions tlirongh 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 jDacking, doubling the diameters of the grains would also double the effective diameters of the capillary tubes thronch which the water must bo moved. 'J'hs ai-ea of cross section of the two capillary pores .-;ho\vii 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 tbo 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 = ("/S — ^) X r* = .1613 r« where r is tbo radius of tlie soil gTain. 1G4 Tho capillary pores in nii ideal soil do not have a uni- form diameter but are shaped like the cast shown in Fiff. Via. 55.— SliowiiiL;- a cast of ihc i»or.> spare botwoou siiluu'ical grains, much cnlarfii'd. 55, largest at one place and decreasing in. either direc- tion to the area given bv 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- Avhieh Avould nnike the largest or effective cross section of the ca]>illary pore not far from ( .2118 X 2) — . 161.3 = .2623 r- From this the effective diameter of the capillary tubes may be found, using the formula P^, ^ \2623r^ whore 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. 165 On this basis spherical soil grains of one size and the •closest packing, having diameters of m. m. m. m. m. m. m. m. m. m. 1. .5 .1 .05 .01 wonld form capiUai-y tnbes whose largest cross sections arc nearly ecpiivalcnt in area to circles having diameters of m. lu. m. ru. m. lu. m. m. m. m. .289 .1445 .0289 .01445 .00289 Did such soil grains hav(^ the attractive power of glass for water and w^ere their triangnlar 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 .4 ft. .8 ft. 4 ft. 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 iillod, 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 Avater 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. 10 166 Table showing the loss of water by surface evaporation from, columns of soil 10 feet long, mulched and not mulched. Sandy Loam. Clat Soil. Mulched 3 inches. Not nnulched. Mulched 3 inches. Not mulched. Surface 6 inches. Per cent. 8.83 12 97 14.59 15.25 15.55 15.89 16.22 16.29 16.58 17.07 17.05 17.26 17.56 17.78 17 94 17.96 18.25 18.67 18.. V3 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 J7.43 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 29.33 29.79 30.32 31.15 30.47 31.25 Per cent. 7.79 18 30 21 46 26 26 24 iuche.s to 30 inches 30 inches to 36 inches 26.89 27.16 27 61 42 inches to 48 inches 27.64 27 28 28 23 60 inches to 66 inches 66 inches to 72 inches 72 inches to 78 inches 27.79 28.05 i'8.93 28.31 28.32 90 inclies to 96 inches 96 inches to 102 inches 28.80 29.14 29.16 108 iuclies to 114 inches 29.33 114 inches to 120 inches 29.46 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 qnite 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 diamet-er 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. ; thish would indicate that there might be a capillary rise of 23.6 and 30.8 feet respectively. 10" 195. Capillary Kise of Water in Sand. — In the case of a sorted sand witli grains .4743 m. ni. in diameter, when saturated Avith vrater in an apparatus represented in Fig. ;■)(), it Avas found that water was raised through a col- umn 6.75 inclies above the level of water in the reservoir at the rate of 44.09 inches of water on the level per 24 hours, hut that when the column was made 11.75 inches lone no water was raised to the surface. 1 n. I Fif;. 56. — Apparatus for uicasuriiij;- the iiiAxiuuun rate and lu'ijrht of capillary rise of water in s.-mds. A, evaporatiiin' reservoir; I!, water reservoir; (', rui)l)er tiiV)e. 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 44.0 J) 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 majcimum limit must lie very close to that computed for the glass sand. 1G8 196. Rate of Capillary Rise of Water in Wet Soil. — There is yot no very .satisfiU'torv data, as to just how rapidly wa- ter may Ix^ luoved by ea])ilhirity through wet soils. It is ])robal)l(' that the case cited in (195) represents abont the nia:xiMiuui rato in that coarse cpnirt/ sand, throng'h that lieiglil, nauudy, 41.()!> iucdics in (l(']»tli ]>er 24 'hours. This is an (niornious quantity of water to be raised by capil- larity and was rendered |)ossibl(' only by expanding the column of" sand at the lop, as shown in the figure, so as to increase the rate of cNaporat ion until it exceeded the abil- ity of ca|>illai'ity to bring the water to tli(> surface. Experiments ha\'e shown that with a strong current of air passing aci-oss the wet surface oi the soil, water was lifted by capillarity at the following rates: From a squan^ foot, of soil, water was lifted through the different y a dry (doth or sponge tlian by a similar one when damp. in, the table whicdi f(dlows is given tlic rate at which water I'Utered ,"> cylinders of \vater-fr(H' soil, G inches ill 1G9 diameter and 12 inches loii^i;', staiidiiii;- in one inch of wa- ter and possessing" the nndisturbed Held texture. The cylinders stood in a satnrated atmosphere and the amount of water absoi-hcd was (let(M-mincd by weighing every third day, the samples Ix'iiig tlic siiiiic (»iies nsed in (158) and (159). Table showing the mean daily absorption of cap illavfj ivater by undisturbed field soil. Cylinders 6 inehes in diameter, 12 inches long, standing 11 inches out of water. Pounds pbh Cubic Foot. First foot. Second foot. Third foot. Fourtli foot. Fifth foot. Water absorbed during 1st 3 days Water absorVied durinK- 2ii(l 3 days Water absorbed diiriat,' 3rd 3 days Water absorlx-d during 4tli H days Water absorbed dtiriiit; r)tli 3 days Water absorlx'd diuint,-- til li 3 dax s Water absorbi'il durint,' 71 li 3 days Water absorbed during 8tli 3 days 12.50 2.57 1.74 1.33 .96 .44 .12 .07 12.42 2.18 1.02 .79 .59 .46 .32 .25 9.61 2 33 1..-J6 1.28 1.16 1.00 .69 .48 13.. 50 3.58 1.71 .51 .23 17 .10 .03 10.73 2.93 2.15 .61 .16 .06 .01 .02 19.73 Per ct. 32.2 28.28 3.92 18.03 Per ct. 23.8 20.43 3.37 18.32 Per ct. 24.5 20 39 4.11 19.83 Per ct. 22.6 21.30 1.30 16.67 Per ct. 17.5 15.72 1.78 From this table it is seen that the amount of water absorbed during the first three days was only at the mean daily rate of 4.1 C, 4.K5, 3.20, 4.5 and 3.58 lbs. 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 lbs. per sq. ft. would have been greater had the evaporation only been more rapid. In the case of the sand of (195 ) ihc water was lifted by capillarity at the enormous rat(^ of 22S.(» lbs. ]>er sq. ft. in 24 hours while the sandy loam of (194), jdaced under the conditions of (195), using the same piece of apparatus, lifted water at the rate of 26.02 lbs. per sq. ft. in the same 24 hours. 170 In the case of the G-iiich cylinders of soil above, with their tops only 11 inches ont of water, the length of time reqnired for the surface of the soil to begin to appear damp was 2 days for the fine sand or oth 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 caiiiUary action in a ffiven soil is stroniier when the soil contains a certain amount of moisture than it is when that amount is much reduced. When soils have thcii' water c(»iiteut so much reduced that they begin to h)ok dry, and especially after they become air-dry, they act as efFective mulches and M'ater will neither rise through them so rapidly nor so high the dryer they heeonie, and, if undei' these eonditions, a light siiower 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. Rain May Cause a Capillary Rise of the Deeper Soil Moisture. — It was observed in 1S8U, wdien 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, wdiile 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. Table showing the translocation of soil moisture due to ivetting the surface. Percent, of Water. Difference. Depth. Before After wetting. wetting. In per cent. In pounds per cub. ft. 0-6 inches 14. 15.14 16.23 17.70 16 76 15.51 1 22.23 15.71 15.75 16.92 14.41 15.21 + 8. 23 + .57 - .48 - .7rt - 2.35 - ,30 +2.873 + .199 , — .213 — 347 12 inches to 18 inches 24 inches to 30 inclies 30 inches to 36 inches -1.032 - .132 The amount of water applied to the surface in this ex- periment was 2 lbs. per sq. ft. but when samples of soil were taken 26 hours later there had been an increase of 3.072 lbs. in the surface foot and a loss of 1.Y24 lbs. 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 lbs. per sq. ft. ; and, as' suming that tlie tield soil lost water at the same rate, makes the water to be accounted for 3.072+ .428 = 3.5 lbs., while the total loss from the lower two feet plus the water added was 2 + 1.724 = 3.724 lbs. an amount as nearly equal to the 3.5 lbs. as could be ex- pected. In another trial, adding- 1.33 lbs. of water to the sur- face produced the gain, by translocation upward into the upper four feet, shown in the next table. 1T2 Water Content of the Soil. Depth. Before wetting. After wetting. Change. First foot Pound.s per cu. ft. 11.78 15.79 14.73 14.03 Pounds per cu. ft. 14.06 17.52 15.58 15.40 Pounds per cu. ft. 2.28 1.73 Third foot Fourtli foot .85 1.37 6.23 The interval during- this experiment was one of very little evaporation and the adjacent untreated ground gained 1.21 lbs. 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 4- i-33) = 3.69 lbs. 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 fooL. 2nd foot. 3rd foot. 4th foot. 5th foot. 6th foot. Manured Per cent. of wator. 19 88 18.79 +1.09 Per cent. of water. 19.79 19.33 + .46 Per cent, of water. 18.88 18.60 + 28 Per cent. of water. 17.29 17 32 -.03 Per cent. of watar. 14.35 14.63 -.28 Per cent» of water. 16.98 17.13 -.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. 173 201. Heavy Soil Mulches May Strengthen the Capillary Kise 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 wonld 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 deej>, the distribu- tion of moisture, ou July 16, was found to be as follows: Table showing the effect of mulches in strengthening the cajnl- lary rise of soil moisture. 1st foot . 2nd foot. 3rd foot. 4 th foot. Field No. 1 cultivated 3 inches deep .. Field No. 1 cultivated 1.5 inches deep .... Perct. of water. 11.30 9.92 l.:38~ Per ct. of water. 15.57 15.43 Per ct. of water. 10 54 11.56 Per ct. of water. 11.37 13.99 Difference .14 -1.02 -1.62 Field No. 2 cultivated 3 inches deep Field No. 2 cultivated 1 ,5 inches deep .... 13.96 12.98 22.74 20.44 23.39 24.02 19.47 21.34 Difference .98 2.30 -.63 —1.87 Field No. 3 cultivated 3 inclies deep .... Field No. 3 cultivated 1 . 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 sTound cultivated 3 inches deep, where the up- 174 per two feet of soil eoiitaiiu'd, in spite of the larger crop, much more moisture, but at tho expense of that deeper in the ground, as shown by the fact tliat in every case these soils were drvest in the 8d and 4tli feet. 202. Firming- the Soil May Strengthen the Capillary Rise of Soil Moisture. — When soils have been rendered open and loose by ])lowing or other deep stirring the first ertect is to permit the loose and o]>(ni soil to become dry, because this soil is less perfectly in contact with that below. If, after such soil has beconu' 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 i'oH to saturate the firmed dryer soil. In the table below are shown the changes which occurred in the dec^pcM- and sujierficial soil layers as the result of rollin<>-. Tnhir slioiriug how roJlinq ma}/ strengthen the caplllarii rise of soil moisture. Depth of sample. No. of trials. Rolled ground. Unrolled ground. Change produced. Surface 2 to 18 inclios 62 61 24 Per cent, of water, 15.85 19.49 18.72 Per cent. of water, 15.64 19.85 19.43 Per cent, of water. + .21 36 Surfaco 24 iiiclios Surface 36 to 54 inches ... -.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 sam])le9 are taken deeper than 18 inclies 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, howcvci-, the soil is loft firmed voi-y long then the ^\•h(>h' column, to the surface, becomes dryer, until it has lost so much moisture that it beains to act as a mulch. 175 TIIKK'MAI. MOVKAriONTS OF SOIL MOISTURE. Besides the gravitational and capillary movcuients of soil moisture there are others due to the molecular vibra- tions set uj) in the suil-air and water by the absorbed solar energy. 203. Hygroscopic Soil Moisture. — It is seldom if ever true that any solid surface, e\cu when in the dryest air, can be found which is not invested with a film of inoisturo 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 calh^d liy(]yo.^copic moisture. 204. The Movements of Hygroscopic Moisture. — It Avill bo seen that the movements of hygroscopic moisture are the same as those of evaporation. The same molecular at- traction which causes the ca])inary rise of water in a glass tube tends to collect the water molecules, which may be moving about in the air, n])on solid surfaces. So when a dry sodl is exposed to a damp atmos])here soine 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 atti'acted 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 fartlier removed, and hence there must always be a certain quan- tity of water upon the surfaces of soil grains which neither ova])(>riit('s rcntlih' nor ])('('oiii(>s cnsilv iiviiihihlci lo [)limls, jiiul I his iiinv lu' rciinrdcd ;is I lie li_vj;-r()sc<)|)i(', inoisllii'c. 205. Relation of the Diameter of Soil Grains to the Hyg-roscopic Moisture. || wns shown in (163) ili;ii wilh lh(^ snnic thickness of wnlcr snn-onndina,' ihc soil iiriiins the per ccnl. ni' wjitcr \\;is ncccssiiri I v ninch hii;ii('i* in Ihc soils hnvini;' Ihc sniiiMcsl soil i^rnins. in (192) is liixcn (^)ninckc's ohsci'\;il ion of ihc dishincc nci'oss which the foi'cc (d' cohesion is scnsil)le, or .-.(mi'imm. inch. Sinci^ lliis ;ill nicl ion (d' Ihc soil for wilier is slroni;-cr lh;ni that pr(>scnt. This niav he compnled foi' spherical soil U'raius wilh the tormnla l'(>r ('(Mit. of \v;ili>r ^= TT (d + ^t)-' _ n d" 6 6 ff d" s[). gr. ~ (5 w liiMH* il iliiiiiuMtM" of soil ^rain in c. in. t -• tliickiKvss (if \v;il(>r iilin. sp. gr, = tho spocilic -Jiravity of tht> soil. Takiiii;' a \-crv line siul ha\in<;- grains with a diameter (d" .0(>r>(IS ni. m. and a coarse one with a diamctiM' of .1 m. m., a lilm id" nioislnre on each, haxini:,' the thickness of the rani;t' (d" sensihle cohcsi\(' attraction, as a'iv(Mi hy (»)iiincke, woidd make the p(M' cent, for tlic linest soil !2..'M hnl for tho coai"S(> soil only .1 1. "■).'). \o crop can siir\'ive in soils as dry as these; and air dry soils whose grains rani;'C li(M\vi>cn tlit»si- <;iv(Mi will li-entM'ally contain more than these amounts of moistnre. It follows from these consideva- tions, thcr(d'oi-(\ that what has heen i'(\ii'ard(Nl as the hyi;'ro- scopic moistnre is more than that held within the range 177 ol' scnsildc (•\' the air and its de^ gre(i of saturation. If llie lenipei'ature of a soil could be nniintained eontinually Itdow that of a saturated atmos- |)liere above, it would in lime become so fully charged wilh waler as to resnll nol oiilv in capillary saturati(»n bill in pereolalion as well; and il rre(piently ocKMirs on clear nights ill summer, when dews are heavy, that a. thick, loose, dry \' llie Inilli (d' the stateiiienl made; when it evapo- i-ates wilh the rising of llie sun llu; loss of moisture from tin* blades (d" i^rass may carry the amount all th(! way frHorpfivc poiri r of ,so/7.s spread out in thin lai/ers. KiM) OK Soil. Dark nlliivial loam, Piitali Valloy, Solano county... Satubated Atmosphbre. Tomp. Far.*' I 58 I 59 I 61 I 77 I 88 I 100 Time, lirs. Per cent, of water absorbed. 11.745 ii.s-^e ii,4as i2.oi;i 12.23;< 13.141 ia.48i Half Saturated Atmosphere. Temp. Far." 57 70 77 88 100 Time, hrs. Per cent, of water ab.sorbed 6 547 6.424 6.305 ().3.'i6 6.209 Black adobe soil, Univer- sity Kronnds, Alameda county Calcareous silt soil, Fresno county 55 57 70 80.5 82.5 100 19 19 7 17 7.5 7 7.144 7. two 7.696 8.681 8.948 9.569 61 18 61 7 5 80 6 83 7.5 89.5 7.5 100 7 2.133 2,983 3.396 4.211 59 18 79 6 84 7 95 6 4.008 4 122 4.024 3.926 3.910 3.885 0.987 0.959 0.858 0.821 It will be soon that in the sntiirattMl atmosplun-o the largest amount of nKnstnve was absorbed at the highest temperature, while the rtncrse was true in the half sat- nratetl atmos})hert'. I'nder the high tem]ierature the rate of moleeular movcuu'ut is so ra]ii(l that tlu> rate at whieh the watiM' troiu ihc air falls upon autl enters llu> soil is so mueh iuereascd that nitirc water must have aeeumnlated in the soil hetori' the nnniher ef nidlecnles whieh can leave its surfaee in a unit of time equals that whieh falls upon it. Tn the drver atmosphere, on the other hand. Avhere there iwo less moliH'ules to fall npiui tlu^ soil and iner(\ise its aniouuf, the liigher teuiperaturi' favors ihe rajtid es('n|)e as nuu-h as when the saturation was high and, siuee less water is eondensing, a lower ptn* cent, is finally present when an equilibrium of interehang-e hao been reached. 17!> 208. Internal Evaporation of Soil Moisture. — It is likely that uiK-lcr ccrtaiii c(tii(lil ions llic ihcniial movements of soil moisture may be considei-ahh^ and perliaps of sufficient imjxtrtance to materially inliueiice vegetation, directly or iniiiroctly. When tlu^ jkm- cent, of imoceupied pore space in a soil has been materially increased by the loss of wa- ter and when the moistuni 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 ]iosition. If, for (wample, when the soil has become quite dry, to considci-ablc depths, the surface six inches should become cooler than that below, the tendency to continual difl"usiing 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. 11 182 AVIr'u grouiKl is plowed late in the fall, just before freezing, it then acts during the winter and early spring as a niuleh, 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 the 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 diifereuce represents a rainfall of 1.15 inches and is a very important saving in climates of deficient water sui>])ly 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. — lu 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 Avhere winter grain is not to be sowed, it will often be desirable to plow as early as possible in order to retain 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 tx) develop nitrates and where there is much rain in the late fall and early spring, wliich has led to the sowing of "cover crops" having tVjr their primarv 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 jiercolation and the loss of plant food may some- times make this practice undc^sirable 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), wdiere 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 tlie 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 uppep 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 184 185 C'ii!,-lith <»L' till' rainfall of llic i;r<)\viii^' .season of tliiit lo- cality. JSTorvvastlio saviiii>; of inoistiiro the only advantaiiv ii'ained 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 necossai-y to fit it for planting. In another rxpci'iincnt to slndy tiu^ effectiven(!ss of carl\- as coinpai-cMl with late sjn'ing ])lowiiig in conserving soil nioisture Fig. 57 shows how eN'ideiit the eti'ects were to the eye. 215. Disking- or Harrowing Where There is Not Time to Plow. — It often happens in the H])ring that hot dvy winds come on when there is not o])])ortnnity to get the ground plowed in time to save the needed nioistnre and ])i-event the develoi)nient of clods. In such (;ases the use of tlio disk harrow, or even the ordinary s]dke tooth harrow, will do vei'v nmeh to save iho moisture and ])reserve tlie tilth of the soil, if oidy the fields are gone over with these. The disk harrow is one of the best of tools for early nse in the spring to work the soil and de\'elo]) mulches. 216. Corn and Potato Ground, Orchards and Gardens Plowed Early in the Spring. — (iroiind to be ])lanted to corn or ])otat.oes, as well as the orchard and gai'den, should gen- erally bo plowed (piite eai'ly 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 b(> 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 ])i'actice. 217. Effectiveness of Soil Mulches. — I'lie effectiveness of soil mulches as means for diminishing evaporation variea (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 witli which the soil is 186 stirred. Soils which maintain a strong capiRary rise of water throngh them will, when converted into mnlches^ 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 for 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 w^ater they are able to retain effective in crop production. In Fig. 58 is show^n an apparatus for measuring the relative effectiveness of mulches and in the table which follows are given the 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 100 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 per 100 days. Black marsh soil : 588.0 5.193 355.0 3.12 39.54 270.0 2.384 54.08 256.4 2.265 56.39 252 5 Inches of water Per cent, saved by 2.230 57.06 Sandy loam : 741.5 6.548 373.7 3.300 49.69 339.3 2.996 54 24 287.5 2.539 61.22 315.4 Inches of water . Per cent, saved by 2.785 57.47 Virgin clay loam : Tons per acre . . . inches of water . Per cent, saved by 2,414. 21.31 1.260. 11.13 47.76 979.7 8.652 59.38 889.2 7.852 63.13 883.9 7.805 63.34 From this table it will be seen that the soil mulches have exerted a very great influence in saving 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 w^ell 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 eifect of the stirring; is iH Ji ii lh Fig. 58.— Ai)paratii.-; fcv measui-iiig- the relative efl'er-ti^'eness of mulches. to increase the rate of evaporation from the field, on ac- count of the much larger surface of wet soil w^hich is ex- posed to the air. This gi'eater loss of water, however, is largely from the stirred soil. If dry wdnds 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 togX't.lici- iiiiil iiiiiiin ('()m|.;iclc(l .'iiid I'cmiilcd willi llic im- stirnid soil Ix'low. IT this clinii^c diH'^ l;ikc |t|;ic(' tlic inulcrli is rendered less (dlecliv*' iiiid ;i second slirriiij;' is iieediMJ. li'h!. U'.l Slidwin.; |;ir.<;<> cy liiidci-s I'lir si iid \ i iii;' s,iil prdlili'ius. 'rile rel;ili\-e elleel iveiiess of innlclies stirred Iwiee per \veek, once |)er wi'ek. jind once in I wo weeks, foi' a virgin <'lav loam, in c\lind('rs 52 Indies dee|) and IS inclios in Table Hlioirino the relative effect Iveiienn of noil tnalcheH of er 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 Avilting 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 the chapter on Implements of Tillage. 225. Harrowing and Rolling Small Grain After It Is Up. — It sometimes happens in hunlid 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 irhen the surface soil is dry 193 will break up the crust by crumbling down the ridges and lumps and at the same time develop a true and eliective 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 Ivansas, 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 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 wath 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 j)ractice rests in part u]>on 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 betweeii Jhe 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 savinc: was the cause of the larger vield. 195 Table showing the water content of soil, Sept. 19, wider and between roivs of potatoes hilled and left fiat when laid by. Nos. of sub- plots. Hilled, Flat, Depth of S.\mple. In row. Between row. In row. Between row. ( 1 Per cent, 12.8a 12.01 Per cent. 14.11 13.61 Per cent, 11.85 12.18 Per cent. 14.23 First foot \ 2 13.54 3 Mean 1 13.86 12.42 12.02 13.89 i 16.71 15.84 18.56 17.85 15.38 16.03 17.69 2 17.84 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 Third foot K 2 17.97 3 Mean 1 16.27 17.55 18.08 18.00 ( 15.78 14.41 16.95 13.98 9.79 13.08 11.75 Fourth foot . . . . ■< 2 14.01 3 Mean 11.44 13.86 15.06 15.33 15.46 16.40 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, has 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 10 G creeping. From the siibsoilod area 8 inches of the surface :\vere removed, the snbsoil spaded to a dejjth of 13 inches more, and the soil returned to its place. After taking ntV\' samples from ihc live plaees indicated by the dots, 1.36 inches of water were gradually sprinkled over the two areas on June 11th and they -were allowed to remain cov- ered until the IStli, wdien 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 nubsoilcd ground to hold water against gravity. Snbsoiled. Not subsoiled. Difference. Tlie first foot trained Lbs. 124.6 72.. 57 .•W.22 33.26 2.29 268.65 254.41 Lbs. 102.1 10 34 12.05 3.82 19.5 Lbs. +22.5 4 62.23 426.17 +29.43 17 21 Tlio s(>coiid foot paiiKid Tlie third foot Rained Tho fourth foot pained The fifth foot lost Total water gained 128.31 254.41 Total water added Difference +14.24 —126.1 197 The subsoiled gTOund had therefore not only retained all the water added but it had gained by capillarity 14.24: lbs. more. It is noteworthy too that the fifth foot in both 23laces had lost water upward by capillarity, 2.29 lbs. in the former and 19.5 lbs. 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 <3overed 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 ivater from the deeper soil when no evaporation can take place from the surface. J"-26 j^?^] '^y^ \^^^1^Z\ Change June 26— start July 2— close Change 22.52 23.97 +1.45 On Subsoiled Ground. 1st foot. 2ad foot. 3rd foot. 4th foot. 5th foot. 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 - .63 + .61 - .36 + .31 + .72 On Ground not Subsoiled. 20.67 22.09 +1.32 17.74 18.92 +1.18 15.06 14 62 .44 19.34 18.33 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 lbs., 53.52 lbs. 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 12 198 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 fonnd^ after an interval of 75 days from June until September, that the water content of the soil stood as in the next table. Subsoiled ground. Not subsoiled ground. Difference. Per cent. 17.07 23.29 22.76 16.35 18.14 Per cent. 18.91 19.42 17.78 14.19 19.20 Per cent. —1.84 +3.87 Third foot +4.98 +2.16 Fifth foot —1.06 In this case the surface foot of subsoiled gi-ound 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 1.64 inches. 229. Moisture Effects of Subsoiling. — The results whick have been given in the last section illustrate several very distinct effects produced by subsoiling: (1) Subsoiling increases the jjercentage 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 Avould, 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 199 interior nearly full of water, drainage being largely con- fined to those passageways and cavities which have larger 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, las 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 tha 200 water is tlien free to move rapidly dowiiAvard through tho large n-on-capinary pores, urged by the strong force of gravity. ]^ot only this, bnt, 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 M^ater 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 "svas shown in (161) and (162) that there is a certain ])er 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 wdiere 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 m'oisture, by taking advantage of that which otherwise would be lost by surface evaporation, and enabling his crop to use this in growth. Such timely i)lanting may not only 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 dno diligence should be exercised in timely planting and sowing, tliere 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 bad been plowed and tilled early but left naked, or even if not ])low('(l 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 ahoiv in cf the drying effect upon the soil of a green ma- nure crop. 1 to 6 inches. 12 to 18 inches. 18 to 24 inches. Ground not planted Ground in clover Per cent. 23.33 9.59 13.74 Per cent. 19.13 14.75 Per cent. 16.85 13.75 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 growth of herbage, when plowed under, would so much cut off the capillary connection with tlie deeper soil moisture that 202 it could not readily become available until after the roots had penetrated below this level. ]^or is this all ; any snch cro]) would have locked up in insoluble form, for the time being, a large portion of the soluble plant food, and unless abundant and timely raina were to follow the ]»l()wing speedily to develop a new sup- ply, the next croj) 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. — "Tu""'' 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, -Awd wiiich are lacking in adhesive quality, the fields nuiy suffer greatly at times, not only from excessive less of moisture, but the soil itself may be greatly danmged by drifting caused by the winds. Under such conditions, it is a matter of great importance that the wind velocities clos(^ to the surface should be reduced as much as possible." On the lighter saiuly 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. ]^ot only do trees along line fences and roadsides, un- der these conditions, prevent such direct injuries to soil and * Irrigation and Drainage, p. 168. 203 <3rops l)ut they materially lessen the evaporation of moisture from the soil and thus help to secure a higher yield of crops. *''The A\TLter 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 ISO feet from the hedge-row the evaporation was 12.5 c.c. At 300 feet from the hedge-row tlie 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 9.3c. c. At 150 feet from clover 12.1 c. c. At 300 feet from clover 13 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. 169. 204 CHAPTER IX. RELATION OF AIE TO SOIL. NEKDS OF SOIL VENTILATION. .Vir ill the soil in which crops are to be grown is as es- sential to tlic life (if the plants as the air in a stable is to the life of the animals honsed. Canvful observations and liiies of ex})eriiii(Mitation have proved, in many ways, that when oxygen is eoin})lctely ex- elnded from seeds that are otherwise nnder good conditions for germination they fail to start. It has been found, too, that even after a seed has begnn to grow, if the oxygen snpply is cnt off, it makes no farther progress. Growth does take place in seeds in a very dilnte atmosphere of oxy- gen, bnt aftcM- the amount has been reduced below sV of llie average in the air the jdants advance very slowly and are sickly. A soil in ilio best coiidilion for cro])s must permit of ready cut ranee: of fresh air and an abundant escape of the air once tis(h1 ; in other words, like the stable, it mnst 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 nse of the free- nitrogen-fixing germs. (3) To remove the excess of carl)on-dioxido which is set free in the soil. 238. Needs For Free Oxygen in the Soil. — Free oxygen in the soil is recpiircd not only by the seeds, when they are germinating, but throughont 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, 205 and (.U'caviui:' orgiuiic iiuittcr in llic soil into iiiliMc acid, lai'C'e cUnounts of oxy^'cn arc ncc(|c(|, t'or cacli ol I lie three known forms of niicroscopic life wliieli '!<> this work are iniaMe to live in its absence. 239. A Water-log-ged Soil. — One of tlu; chief reasons for the nnproUnctiveness of a water-h)iii>-e(l soil is the deficiency of free atniosphcric ox_vi>en in it. When the soil ]»ores are filled with water and this water is statitmarv, that is, not changinii', the free oxyiicn which it may contain in the air dissolved in it is soon nsed nj) and then the rate at which oxygen from the air almve the soil is able to make its way downwai-(l thi'onuli the soil-watei- and around and between the soil grains is mnch too slow to meet the s npon floating rafts of logs an- chored in a stream or lake and thinly covered with soil may seem to contradict the statenuMits in the last paragraph regarding a waterdogged soil because, in these cases, the soil is very wet in its lower portion and the roots of the ]dants 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 Avater is chang- ing continually so that a new sn|)ply, charged Avith fresh oxygen, is being continually brought- to the roots or very near them. It is the abundau'co of oxygen Avhich rain water and that nsed for irrigation contains which prevents it from killing crops when the water entering the soil is excessive. As long as the Avafer is moving thronuh the soil, and a 20(3 frcsli «u])ply from above cntei-iiig, an abundance of air is carried with it for the needs of the roots. 241. Excessive Soil Ventilation. — Tlie higher temperature of a pile of open horse manure, as compared with tliat of the ch)ser lieap of cow-dung', ilhistrates 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 measui-c 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 hunnis in these soils up, not only because of its need for plant food, but because it enables tlie sandy soils to hold more water, and this in turn makes them less readily ]ienetrated 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 ])lant life that the vast systems of roots which are develo]>ed in the soil should be broken down, first into humus and then into carbon-dioxide, water and free nitrogen, and all of tlie 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. — Tn the processes of symbiosis discussed in (101), Avhicli load 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 suj^ply both the oxygen and nitrogen of the air which the micro-organisms are obliged to use in carrying on their life ]ux>cesses. 207 PROCESSES OF SOIL VENTILATI02C. Tlio interchange of gases between the soil and atmos- phere is brouglit 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 j for each degree F. or 57? for each degree C. ; so that if 4!>1 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 t^^mperature was raised, and a like amount would enter if the temjH'ratni-e were to fall the same amount. The temperature of the surface three inches of soil often changes as much as 10° to 20° F. and that at 18 inches deep as much as 1.5° F. A soil like the surface foot in (133), coutaiiiiiig 1^ ]H'V cent, of water, would enclose i>()S :il»(Mit. .")..") iicrc-iiiclics of ;iir in llic siirlncc l.T) feel niid, willi ;i (liiininl clKiiiiic of 1(1.1 l'\ in llic ii]i|icr .'5 iiiclics iliid 1..') I'\ ;il ;i (|c|)lli of is inches, llir iinioiinl of soil-ilir M'liicli wonld lie forced onl :ind :ii;nin l;d'('S in S(dl lenipcral nrc will rani;(' fr \o pos- sihlv I'O en. in. per s(|nare fool. 246. Influences of Chang-es in Barometric Pressure on Soil Ventilation. — Anv <*haiif>'c wliicli luav occur in the prcs.sure (if the air al»(i\'e the soil is followed liv a (dniiiii'c in the Volnine of the soil-ail', cansini;- an escajie from the soil, if the pressnre aliii\-e falls, and ihe enli-ance of an extra snp- ]ilv \\lieiie\'er the prcssni'e is inci'eascd. With soil like (hat in (133), liavinj;' IS |)or ccuf, of water in tho first foot, LM) per cent, in the second and 15 ]>er cent, in the third and fonrlli feel, there wonld he 7.8S inches in depth ol soihair containe(| in tli(> fonr fVet and ex'erv chanii'e in atmospheric pi'cssnre amonntinii" to .1 inch wonltl cause the escape oi- entrance of 3.TS cuhic inches J'or each s(piare foot of snrface and 18.0 cnhic inches for each clniniic in pi'cssnre of .."» inches of harometer. It is common in the Unitxnl States for waves of ]iiij:h and low jiressnre to pass a g'ivon locality ahont twice each wook, and the difFcronces in pressure hetween hiuh and low baronietei- ai-e ii'emM-ally not far from .Ti inch, so that the resnils s(ale<| aliox'e i;i\'e a J'air measni'e of this infinonce in soil \-ent.ilation. 247. Wind Suction and Soil Ventilation. — Tt is seldom trne that the wind hlowini;- across a field has a nnifoi-ni velocity, the on 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 widel3^ But all of these effects upon the soil are only the meana which 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 oj)ened 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. ^Vlien 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, tliere are very many and important passageways opened up after the roots decay, Avhich 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 fi-om below. 212 CHAPTER X. SOIL TEMPERATURE. 253. Importance of Soil Temperature. — Xoiic of tlie chem- ical, physical or biological changes essential to the devel- oj)ment 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 tenij^erature. When the tem- perature of the soil falls to 32° F. nearly all the life processes become dormant and for most of the cidtivated 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 Ebermayer growth will not be- gin, with most cultivated crops, until 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 213 f>-ivoii the best soil tein])(M-iitnr(^s and the lowest and ]nif]\- est toinporatnrcs at Avliicli certain seeds have been observed to e'eruiinate. 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 8t 93 79 93 SIT. 83 80 93 4l»F. 41 44.5 48 ■ 49 54 4l»F. 41 44 49 104» F. 104 10-i 115 111 115 99° F. 100 Poas 115 70 89 81 99 42 82 Turnips 10:^ 32 99 The two important facts fixed by tliese ckta 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 those 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, whih^ 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 ditferent depths during the diiferent months of the growing season Avill be of inter- est in connection with the statements nuule 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 countrv and the other in Europe. 1.3 214 Table shoivi.ng the mean monthli/ soil temperatures, at State College, Pa ., by Dr. Frear, and at Munich, Germany, by Eberniayer. At State Collegb, Pennsylvania . Depth. 3 iiiclios.. G iiicliOR.. 12 inclios.. 24 iiiclies.. 5 9 inclios 11.8 inches 'i'A.l inches 35.4 inches April. "F. 4:^.74 4:^ 08 42.69 41,43 May, op- 55.13 54,72 53.83 51.45 June . "F. 67.29 66.34 65.03 61.90 July. >.p 70.16 69.75 68.89 66.42 Aug. -TpT— 6.S.70 68,49 68.66 67.41 Sept. "F. 61 32 61.70 62.73 63.59 At Munich, Germany. 44.65 56.79 61.11 67.26 64 09 44.31 57.51 60.06 66.16 63 61 44.40 53.58 59.11 63.12 63.55 43.56 51.24 .')7.33 62.92 62.26 58.31 57.88 58.82 58.51 It luaj appear tliat tlic temporatures recorded in these tables are too low to be in liannony witli the comparatively high teniperatnres i2,iven n.s llu' best for i;'erinination. It mnst bo understood, bdwcvcr, thai the avcrago must bo lower than wonld be fi)iiiid in the soil dui-ing the warmest portion of the \h\\. In regard to the minininm tempera- ture at which germination takes ]daee it will be clear enough that the April i-ecords for soil t<'ni|H'rat ure are qnite in liarnion\- with thost' iiiN'on for iicrniinat ion. 257. Influence of Soil Temperature on the Rate of Germi- nation. — Tlie more (luickly seeds are |)erniilled to gei'mi- iiate after tlu\v are phieed in the soil the liigher will be the \\vv cent, of seeds growing and, as a rnle, the more \ig- orons will the ])lants be. Indeed, seeds of low vitality placed in too eold a. soil often fail to germinate at all. ITaberlandt found that, when corn would germinate in 3 days at a tein])erature of (>r).-> ' F., it re(|nired 11 days when the soil was as low as 51^ F., and {[(dli'iegel showed that when corn was ])lanted nnd(M- a mean tiMiiperatnre of 48° only 2 ont (d" 10 kernels spi'outed in 42 days; that under the same temperatui'e rye germimite*! in 9 davs, M'intor uiieat in 12 days, and barley and oats in 13 days, Avliilc ciKMunhc'i's did iiot i;crniinat(' in i'2 days. 258. Effect of Soil Temperature on Root Pressure. — The power wliieli sends the soil moisture into the roots of plants and np into the leaves is osmotic pressure, developed, by the warmth of the soil, and nnless the soil temperature is sufKciently liii;li phinis may wilt, as Sachs has shown, where lie demonstrated that ])nmpkin and tobacco plants wilted badly, even at ni<>-lit with an abundance of moisture, as soon as the soil Icuipcrat urc^ fell much Ixdow 55° F., the moisture not risiun- last enough to eomijejisate for even the slow e\ a I MUM I ion dui'iuii" the night. 259. Influence of Soil Temperature on the Formation of Nitrates. — Tlie nitrates in tin; soil do not develop until the tem])erature luis risen above 41 ' F. ; tlie action of the germs is exti-cmely fcn-ble at 54" and they do not attain their maximum actixily until a soil temperature of 98° has been reached ; but if the cai'tli IxH'oines as warm as 113° F. then the action is nearly stopped, it being as weak as at 54°. CONDITIOXS INKiaiKNCING SOIL TKMl'KKATUUE. 260. Specific Heat of Dry Soil. — When the sanu- lunnber of heat units are given to likc^ weights of different kinds of soil their tem])eratui-es are not raised throug4i the same number of degrees and this is because their s])ecific heats (40) arediffer-nt. From the determination of r)endei- it appears that the number of heat units i-ecpiii-ed to raise the temperature of 100 lbs. of water and lOO lbs. of soil of different kinds from 32° to 33° F. is as stated in the table which follows: L' 1 (I I'ablc of Mfii <'i/ir Ih ttl of (Irii soifa. Wat.w Moor iMti't li lllllllllM HmmiI.v Iiiiimiih Liiiiin I'icli ill Iiiiimiih, < 'lil.vn.v lllllllllH I/IIMIII I'lini irliiy HiiikI I'lU'it cliiilk N... ..(• l.iMil iiiiilM vr. ■|'(>iii|i(iriitiiro < •r KHi ■ luil'IMl l<> I'lliMK 1(1(1 ll>H II.H. iiI'dM- (III' III i|ilicii- I'loiii 'M" \'\ lo ICC I''. lion <>r Kil) li«M( llllitH. Iliiiil iiiiils. u],'. 1(M).(KI .s:i.(X) 22,15 :m.M 2(1 W. m.iv II II Hit 07 1(1. (IJ •M.{)Z Ifi.'AI ■MM I4.t)(l HH.CIH III. 7:1 !)l».2S lU.Utt 41. 0i: 18.48 a7.4i 1 1, is clciir iVmii lliis hiMc lli;il. iiiiicli more licnl is fc- (|iiii-('il III niisc llic l('iii|icr;il HIT nl wiilcr I liniiii!,li (Uic dr nrcc llciii 111' :i like wci^lil nf i\\-\ soil, ;iii(l liciicc lliiil, a tirv Sdil will warm in llic smisliiiic iiinrc capidlv lliaii a iimisl, soil can. 261. Specific Heat of Wet Soil. Thr .lill'cicnccs in (lie \\'('ii!;lil per ciihic IikiI oI Ihs. per ciiliic indl and a s;ilid\ soil jUli Ills, and llie Iwo hold '.'>'■'> per ceiil. and IS per cell!, of waler respecl i\ d v, when capillarilv salur- aled, Iheii llic iiiiinltcr of decrees l'\ llial M»0 heal imils will raise llic leiiiperal lire of a ciiliic fool of each soil when salnraleil, Ii;ilf salnralcil and Av\ are i';i\'eii hehtw: Sal uiiidxi. :i 1" \'\ 2. US Half Mill iiialKil. r. ' !■'. l»iy. Hiiixh Moil It. 1)2" F. ( May liiiiiii 02 OMCO DilllM .42 .ni 8.9 Olio llniiisiiiid lioiif. units would i-iiisc {\\o di ITcrciiccs in toiiipcriiturcs to \.'2 \ f). 1 .-iml -'!'.> , iiiid|)(i|',rii|iliy oil S(ul 'l'ciii|i(iiiliirc. Thr (|p^'l'(>(< III ilirl ilijll lull III llir liiliil iiirrniT Mill! llir illri'fli III • if IIk* fi|n|ii', wlirl liri' riiriii;' fii:!, wimI, imrlli i>r mimiIIi, limy I'M'i'l. II llllll'lvcij illlllicili'r ii|iiin llir li'lii|M'i'ill III')' iA' llli^ soil iiihl ji.'irl iriiliii'l \ ii|iiiii il:. iliiirii:il i'iiii,".i'. Tlic l*'iii|ii'ni Illi'Kiil II ilil] I'i'il cliiy Mill, ii|iiiii a IrN'i'l liililr, ami ii|inii ii Hiilllli cSlHillirr :Jii|ii ll;-; alu.illl, is , win rmillil III llic Mill' llir(< llii'rr iii('l|i':i |(» lio IIM rcj il'CMrll I cil m llir laMc lu'ldW: tShiui'inil till inlliifiiii n/' fo/mifniii/i 1/ ii/iini miil ti iii/» riitiirr. ImnD III' Hull,, Dii'i II llinMiw riiM Htiliii'ACli). l>l :ii(l loot. lloil olliy, ftiilll II nl(>lit\, ,, II (III II II III Itixl i>ln,v, Ik vol miiTMOK,, ..i.n. ,< 1 7(1, !l" 1''. 1)7, 'J IW,I" K. lift, 4 (Ill,*" K. ita,(i 2,8 ||lM'(> ll l.'l MI'CII llial llir I'lll'l'l ol 11 JUilllll (AlKiSIII't' IS l<> iiiiikc II ili iTcrt'irM' ill lriii|u'i'al iiic nl' Irdiii a lillli' iimn^ tliaii ;i ' I''., Ill llic iiirrafc In.il, III a lilllc lr:;:i III llic si'ciukI and IliinI I'lvl. 'riic I'ciiuiii Ini' I licM • tlilliTt'iiccs will lie ri'iiilily iiihIci' Mjni.il III. Ill a . hills I'l' l''i<';. (II. Sii|i|ios(' A (1 ;"> I! to r(>|>- iT'.ciil a •('(•! idii of a |>ri;iiii (if ;am,;liiiii' I'alliii.", ii|t«iii III.' Iiill A K II. wli.M-o A l<: \ |M I lie MiMil ll sl(i|M> mimI K H is I lir iii'ii ll. < h\ accoiiiii (if llir 1111 linl licili;', tli irrl l\ \ III iral i'\rr llic hill llir ',.>iilli ■,li.|ii' rcrt-ivos HH KiikTi lull, n..,».Ki.ujl'.v"— I """■'' """'' '"•'' '" " ""''• '•'" """" ,.r liiiK- tliaii III." north slopo lis IIh' liiu> I «'• is loii-'vr than llio lin.' I .'•. 2(M liitluciii<' o( l.odsfucss inul U ucvciimchh o( Surraco on Roil 'IVinixMiilurc. W luii a iirM r Nil \t r\ iiii<\oii. ami L'li> (-(|irciiill\' i I' cdNriTil w i 1 1 1 liii(i|i , IIm' l;ir;'i' iiiiiHiiiil III Miir- fjicc i'\|i.,:;((| 1(1 llii' : ly nml In llir :iii- |mtiiiiI:i IIic liriil, ul llif .iirriii-c, soil III lir Idsl, ni|ii(ll_v in wnniiiii^' llir iiir iilnivn ami llli' I'csilll i llii' (|rr|irl' sciil rrlllilillM ill. II ln\vrr Iclll- |MT,lllirf. Sn, In", il' llii' "nil in InnCC illjil n|)c|l, llic < I l\V siipci'lifiiil liiNir licrniiic;; w'linii aiid Ileal:, llic air, wliili^ |||(< I • ilh'lili;'; caiiacilN nf llic npili nil |.ITVclll;', llic ||(.;i| iVnlll liriliv rnll\c\r(| (|cr|,l\ l.clnw ijic ; lll'larc all'l il luw'cr Iclll |icimI iii'c I (lie null 266. Iiilliiciicf ol Siiirii(;(- Tilli(j;c (»ii Soil 'r«'m|Mi uliirc. Wlicii I'niii ,"rniiii(| w a . cull i\ aliil ;; iiicIk:; (|rc|i a; miii paicil willi |.;i, ill iillcniiilf ;^rnii|i,s. ul' I'mir mwiH, llic iiiciiii |('lll|ii'l'al HITS III' llic Huil ill llir lil'Ml, M nil! IIImI lllil'il Id'l. Iirlnw llic snil ;^lirrc(| WIIH I'nillMJ In lie .Sl{" |«\ Wll I'l I M T ill ihc lir, I Innl ami ..'.H" I''., aii'l .'Wi ' I''. t'<'H|)<'<'l i V<'l.y in llm 'ccniidaml lliinl Iccl nii I Ik' /'iniiml rcccivJM'^' llic. HllllllnWi'l- cull I \ al inn. 2(i(;. IiilliHMicc of Chemical and PhyHusal ChanncH on Soil T«Mii|)crHtiir\' lli' trillcH ill llic ml I'cilll III llli' e\(illlllani and an ad- jacent black marsh S(3il, n()t well drained, the observa- tions being taken simnltaneonsly and the differences in temperature being due largely to differences in the rate of eva])oration in the two cases. MEAXS OF COXTROLLIXG SOIL TEMPEKATURE. 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 gTound, not rolled, and 6.5° at 3 inches below the surface. This dif- ference is due to the better conducting i>ower of the soil, on accoimt of its firmer texture, and is in spite of the loss of heat due to greater evaporation which takes place from the rolled surface. Fli -Shdwini;- tin •t nf nilliui;- nil soil tciiiprriituri'. The average difference in temjierature of soil on eight Wisconsin farms, at the season ^\•hen oats were germinat- ing, was found to lie as given in the table below: 222 Time. 2 to 4 p. m. . Mean air temp. 65.37" F. Mean soil temperature at 1.5 inches deep. Rolled. 71.69» F. Unrolled. 68.57° F. Mean soil temperature at 3 inches deep. Rolled. 67.330 F. Unrolled. 64.39" F. Here is a mean dirt'ereiice of ."J. 1 F. at 1.5 inelies, and 2.9° F. at -'5 inches d(H'p in favor of tlie rolled snrfaee. 270. Influence of Thorough Preparation of the Seed-bed on Soil Temperature. — It follows, from what has been said, in previous ])araiiraphs, that the practice of thoroughly pre- paring the seed-bed before sowing or planting mnst 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, hrst 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 w^eeds to be destroyed before the crop is u]) in the way of cultivation. ITenoe there is much to gain and little to lose in the thoi'ough preparation of the seed-bed before planting. 271. Controlling Soil Temperature by TJnderdraining. — 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 watei- and the lessening of the loss of heat by evaporation. CHAPTER XI. OBJECTS, METHODS AND IMPLEMENTS OF TILLAGE. Tilling the soil is one of the oldest of ag-ricnltural arts, and (hiring 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- uvated crops. The chi(4' objects which tillage aims to secure are : 1. To destroy and pre\-ent tlie growth of weeds and other vegetation not desired ii|)oii the gi'ound. 2. To place beneath the surface manure, stubble and other organic matter whei-e it will not be in the way and where it may be converted rapidly into inimus. 3. To develop various degrees of o})enness 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 change conditions as to make the soil either warmer or colder. TILLAGE TO DESTROY WEEDS. It mu&t 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 Avhatever extent this is permitted, to that extent is 224 tlio possible yield of any crop lessened. No soil can mature a iiiaxiiinun ero]) of eorii when weeds are |)ei"niitted to grow with it. Neither is it possible for an orchard of any kind to eonie iirto beariiii>' as ([uiekly or to ])ro(lneei as viiioi-ons trees wheic the soil between and beneath them is occiipicMl by either weeds or grass. It may be thought that so long as 'the weeds are destroyeid ujxm the ground thiey return to it whatevei' they lia\'e taken out ainl therefore cannot leave the soil pooi'er. 'i'o this it must l)e said 'that whatever moisture is i-emoNcd is a ])ositive loss because it is carried away by the winds; the nitric acid that is taken up and the potash, phos])horic acid and other ash ingredients are also larg'ely a positive loss so far as that season is concerned for they are removed frcmi the soil moisture and converted into dry matter in the tissues of the weeds wIumt the cro]) can- not use them. Kvvw 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 eiiougli to become at once available. 273. The Best Time to Kill Weeds. — The l)est time to kill weeds is just as the se'eds are genninating or while they are yet very small. When this is done but little moistun^ is lost through them and they render but little jdant food insoluble. in the thorough and early ])re])aration of the seedbed many weeds are destroyed by killing them just as they are coming m]). So, too, in the case of a grain field, M'hich is rolled after being seeded and is then harrowed, the rolling hastens the germination of the weed seeds and the harrowing tluni throws i\ivni out into a dry soil which kills them. If such a field is again hai'rowed just aftei' the grain is up a eiecond cro]) of weeds may be destroyed and the yield made gi-(^ater as a consequence. In the case of potatoies and corn it is A-ery easy to destroy at least two cro])s of weeds before the corn or ])otatoes are large enough to cultivate, by harrowing before and just aft('r the plants are up. This is very important because it not only saves plant food for th(> croji but it can ])e done 225 so iiiiicli more clicaplv ami vapidlv with tlic l)roa(l ]]\i;lit harrows and wccmIci's than it can lalcf with the rultivator. 274. Weed Seeds Do not All Germinate at Once. — It must he rcmemherod in ]ian(llini>' soils to kill weei^ls that the seeds do not all o-erininate at onee. The tiivt harrowinii' which is done to kill weeds niav itself hrinji' up from l)elow seeds which were too deep in the i;rounil to i;r()W or it luaj cover some seeds which were Iviiii: upon or too close to the sur- face to g'erminate, hence fre(|ucut cultivations for hoed crops are needful. 275. The Best Tools for Weed Killing. — The tool which Avill do the most t'tfective sei'vicc in killin and tliei'e should be enough of them to 'thoroughly stir the whole soil surface to a depth of two an(l one-half to three inches. Fig. G-t shows a good set of teeth for soils not too heavy, while Fig. 05 shows a t(^ol which should not as a rule find a place in well cared for lields, for the teeth arc too wide and too few for good general work, 'i'hey an^ wasteful of moisture, waste- ful of fei'tility and liable to do too much root i)rnning. 227 Kh;. r>4,-A type <<( ynoil cult ivnlor. ( 'nil ixaloi's willi riii,i(l tcclli like tliosc ol: Fiii,'. <»•> do l)et- teo" work as a rule 'than those of the spring tooth typo rt']> rescntod in Fig'. 04, for the reason tliat the tiTonnd is stirred more couiplctclv and to a more uniform depth. On natnrallv nudlow soils tlic s])i"ini>' tooth is ^'ood ;ind wliere the land is vcrv stonv it is safer a^'ainst breakini:'. liiiiiiiini II iiiiw Fjg. 65.-Ciilliv:il(ir wiili Im. \\u\<- Irclli for -cuitmI use. 228 278. Easy and Quick Movement of Teeth. — A xcrv ini- ]»(irt;iiit fcntiirc of a ridiunor walk iiii;- sulk v cultivator is to liavc I he i;auus of Iciilli so swuuii' fi'oiu the carriaiic 1liat a slii>iit ctVovt will produce a cpiick aud cciiaiu uiovciucut. Tliis is iudisix'usaMc in ordci" lo work (dose to the rows. 279. The Teeth of the Cultivator Adjustable. — Auotlicr ini|)(M'laut t'eatui-c sidkv cultivators should possess is the ]»ossil)ilit V (d' tiltiuii the i;aui;s so as to allow tlicni to work luori^ deeply in the soil toward the ceuttr of tlu' row in llio \i\\v\' staii'es of cnltixalion hecause then the roo'ts near tlu^ rows have developed (dose to the surface, and deeper culti- vation in the centei', where the soil is iiior(> exposed to the sun, is ueeded for etfeet ivcness as a niuKdi. 280. Covering Weeds in the Row. - It soiuetinies lia|)peus with ihe most careful nianau'enieul that weeds will oct suidi a start in the row tlia't elthei' hand lioeiuu' must he resorted to or (dse a tool must he used whicdi will throw euoui;h 229 Fig. 67.— Ciiltiviitoi- which fan Ite usei'rsciits llic l(\liir;il ("Icincnls of u r\n\ Idtiiii ill |ircllv i^nod lillli. 'I'licrc nrc shown seven si/.es of <;riiniiles liiri^c eii()ii>;|i lo Ke reiidily disl ini^iiislied willi llie n;ike(l eve, :iiiil e;ieli si/.e is (•(•ni|»(ise(l of line soil ^■filiiis <■( iiieiiled l(i^cl lier. All ;ire re| ireseiilcd ii:illll':il si/.e iiiid were e;i rein 1 1 v dni wii Iroiii :iii :i<'l inil siiinple I iikeii Iroiil il lliree ilieli iiiilleli iis.lel'l iil'ler llie llie liiri;('sl: porlioii. Tlie liiiesi n'rnde. No. S, is :ilso lar^'(dv e(>iii|»oscd (d' e(>iii|M)iiiid i;r;iins, iininv l;iri:,c enough lo |te el(';il'lv d isl iii^ii islied liv llie niuiided e\(', lull liinilV IlKM-e td llie llllilinile i;i';iilis wliieli \\arl icies. A soil is in ii'ood tilth when its i^rannles are neither loo line nor loo coarse, and when thev are not loo tii'inly <'(;'iii(Uil('j('ct tho changing of the soil 'texture so' that it will become 1st, warmer, ^d, dryer, 3d, better aerated, 4tli, better suited to lessen the raite of evaporation of the deeper soil water, and 5th, to hasten the development of weed seeds so they may be destroyed before the cro]) is in the way of killing tlicni. 287. The Disc Harrow. — (hw 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 ])lowing as this tool. When set to vork deep the draft is heavy but the amoinit of work it is doing 235 is relatively large. To ])ut a [)iece of fall i)lowing in the best shape the harrow should be lapped half and in doing this the furrow between the two sets of discs will he en- tirely filled and the surface left level. O m. f'n,W:Vljni*l ^ irl^l I'm. 72.- Siiriii^;-tootli harrow. Where small gi-ains are to follow corn or potatoes the use of this tool will often make the plow unnecessary. On the upland prairie soils and others natural I v uiellow, ground for corn may bo 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 comutries and where the tields ai'e roniiii and stoiiv the liar- Fio. 73.— Spiko-tootli or sniootliiiig liiirrow. 236 row r(^])r('s(nt('(l in Fi<)-. 7i' docs _i>()0(l work. Tts weight iorcH's it into tlu' soil iiiid tlu^ cliisticit.y of the tcctii prcA'ciit tlicin tVoiii l)('iiii>- hrokcii, hut such tools can ncxcr do tlie (lc_<;i'('c (il |>nl\-ciM/.ini; that the disc hai'i'ow a('co!n])lishcs. 289. Smoothing Harrows. — When the soil has been pnl- A'(M-ized with ihc disc or other tool and it is (h'sii-ed to h'ave th(^ surface iiioi-c neai'lv cncii, or where the* soil is naturally \cry mellow, uiakiuii,' less force necessary to chaniic the surface texture, then the heavier 'wei,i;hts of tiltiui;' har- rows, Fig. 7o, nniy he used to _ii,'reat advantaji'e on aeeoinit (d the iireatcr area whi{di may he co\'ered with them in a dav and their lii-htci- draft. Fi(!. 74.- Tlu' plank. ■!•. 290. The Flanker. — It is sometinu's desirahle to h^ave the Burface ])articulai'ly smooth without finninj;' it and at the same time to crnsh lumps. Tliis may l)e done hy means of a plaid-es ovei'lapi)inii' as repr(>sented in V\ix. 74. The tool is b(\st made of oak j)]ank two inches thick and (Miilit to twelve feet, lon,«i'. Such a. tool cannot lake the place of a I'oller wlier(> it is desired to firm the iinnind. 291. The Use of the Roller.- -'riie roller is used chiefly when it is desired to linn the surfaceaml to hel}) cover seed, especially when sown hroadcasl. In other cases it imav bo used to crush clods or to com])ress the furrow vsliot^s after the sod plow. Agai)i when a orei(>n ciop like; rye or clover has been turned under for manure, or where coni-se litter luis heen plowed undei', a roller is neiMled to c()imi)ress the soil and eslablidi good cai)illai-y connection with the deeper soil water. It is sometinu's used to d(W(dop a mulch where grain is rolled after it is up. 23^ III Jill of llicsc (;;is('s wciiiiit is one of the cssciitiiil iciit- iii'cs of the fool. A I'dllcr t'of tillaiic sliouM li:i\'c a, vvciiilit of about 100 ll)s. to the I'liiiiiiui;' foot and a (liaiiictcr ot alxtuf 2 fecit. Kid. 75. Twi) t.vpcs of i-dUcrs. Two tA'ix's of rollers are represented in V'\'^. T"), tlic one made of bars hein^' desii>ne(l to ernsli clods more cimpletelv and 'to leave the snrfa('<' i-id^ed so as to' be lees likely to be inllnenced bv the wind driflinii' the surface soil. 292. The Harrow Should Follow the Roller. — Tii most cases wlien it has been desii'able to use the rollei' to smooth or firm the surface a liii,ht hai'row shoidd follow it quickly in order to prcNciit uiinecessarv loss of soil moisture, Ix;- cause the iirmiiiii' draws the deeper watei- to the surface, tlie surface temperature becomes higher in the sunshine and the wind veloeity u'ear tlie smooth surface is greater; ea(di of wliicdi favors the rapid loss of water. 293. Danger in the Use of the Roller. — On heavy soils, when they ai'c a little wet, injuiMous i-esuits may i'ollow the use of the roller j\ist after ])lanting or seeding on account {A' the close packing, excluding tlu^ air from the seed, wliieli 238 iiilcrlcrcs willi (|iiick ucrniiiiiiliinii. Tliis diiiimT is i;rc;il('sl: wlifrci fii-jiiii liiis Ix'cii sown willi ;i drill. 'rii(> use of iJic i-()||('i- wlicii llic soil is ;i lit i Ic loo 'acI mnv ;ilso inloi-rcrc willi ilic fonii.'ilidii of iiilric ncid in ihc soil l»v iimkiiii;' il loo (dose :iiid \an wet. In smdi ;i cjisc llic ini- "i('lo\v ns :i lillii,«iv tool is used for (wo disliiicl |)iii-|ios(s, Isl, l(. ;ilt('i' llic Icxhirc, loniiini;' I'Mc. Tti. Sliowllii;- llic |ii'iiicl|i!i' ol III,' |Mil\ rri/lim arlinil oT llic plow. iToiu il conipnriilixcly liard soil ;i dcrp nnd incllow hivcr of ciirlJi ; I'd, lo Imrv Kcncnlli llic surlncc weeds mmI oilier vof>'ot.iil ion ol" niniuire wliere il iiiiiv deciiv riipidlv and bo coiivc'rled inio axailaMci plaiil food. If you will o|icn a hook, i)lii(*in_i;' the iiiiii;ers upon iho lly }oi\[' in froid and the tlninihs uiuKt th(> lly leaf in I ho back and ahnipllv IxmhI iij) llu^ cornei" it. will bo soon that every loaf is slipixMl over its n(>i,i>,libor. What takes place is rep- resented in l*'i_i!,'. TC*. Had ])ins been ])iit throiis2,li the book before attempt inf>' to bond the loaves the bendins>- M'ould 2.'}!) Ii;i\<' tended lo ciil llie |iiiis into ;is iii;ili\ [Heees ;is llici'(! were Iciivcs, jiisl iis seen in h'ii;-. 7, thus dest roviii<;' its tilth b\' pnddliiii;- it. 296. How Plowing May Correct Texture and Improve Tilth. — I I' a soil has i^ot ten onl of tilth, has beeoine cloddy or lias been partly puddled there is a shape of mold board, 51 sla^'c of soil nioisliire, and a depth of fiin'ow slice wliicli will iielp to restore the lillli best ami ipiickesl. When siK'li a soil is the least amoiiiil, loo dry lo puddle the ])low will shear it into the thiiiiiesl- slices ; if si ill drier the layers will be thicker and will form coa rser n'l'a miles. When II inch too di'y no shear iii^' c;i!i I ake place at all, and the furrow slice is siniplv broken into coarse lumps. 1 r \'on bend but a few leaves of the book at- a lime tli(M-e is but, little slippini;, but the thicker the |)ile of leaves ili(! i^'reater is the slidini;' and the greater is the lendeiuiy to sheai'. So it, is in jdowiii^', the deep furrow pulvei'i/es Ik;!.- ter and puddles worse than the tliin slice or shallow furrow. A^'aiii if yon bend the leaves i^'eii I ly there is lilil(! shear- iliji', bill if abruptly llie siidini;' is f^reat. So il you plow with the lo'\- mold Imard if I'iij,'. 77 yoii disturb llie tilth least, puddled the soil least, and leave the Ic.xliirc! coarsest; but if the sleep mold board (d" h'iii'. 7S is used there is tlio ^'i-ealcst, danii'er of piiddlini;' if the soil is too wet and the <;i'ealesl opportiinit-y to piil\eri/.e the soil and iiii|)ro\'e tJi«i tilt li if the moist ui'e is I'i^iil. 297. Forms of Plows. IMows are made with two fiinda- 240 iiK'iitallx- (lilh'rciit shapi's (lejj('ii(liiien tlu^se two extremes. 298. Kind and Condition of Soil and Shape of Plow. — It must be ch-ar from the mechanical action of the })low that its form shonld be adapted to the soil. If the soil has a teoidency to be too open and porotis, and is nam rally coarse grained, like the sandy soils, it shonld be plowed with a steep mold board, a little over wet and as deep as other con- ditions Avill j)ei'mit, so as to break down the grannlation and secure the ch)S(T textnre. If the soil is generally too close in texture, is heavy and soggy, it needs the less steep mold board nsed when the soil is a little dry so as to shear into thicker layers and form grannies of larger size. If ph»wing mnst be done wheu the soil is a little too wet 241 use tlio less stcej) mold bourd and [)l()\v as shallow as other conditions will allow. If a soilhas heconu^ a little too di-yiand is noit pulverizing" fine enough, use the steeper mold board and ])low deej) for this will S])lit it into thinncu- hiyers, make tlu^ 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 hoard hends the furrow slice most and pulverizes most, it is clear that the work done is gi-eatest, and hence that the draft will be most. Since deep plowing |)ulverizes more than shallow ])low- ing the work done is more than in i)roportion to the depth. Since clay soils have more and larger grannies which must be sheared in two in ])lowing 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 ])l()wed decjx'r rather than shallower. This is necessary to pulverize better, to get more moist soil on the surface f<»r the immediate seed bed, and to (piicker moisten and bring into condition the layer which has become too di-y. 300. The Sod Plow. — IMie sod or breaking plow is con- structed so {.s to reduce the draft as much as possible by doing only the work needed to cut and turn over tlie fur- row slice. This is ac('onii)lislied by making the mold board very long and slanting so that the fui-row slic(* is 1 enit and twisted as little as ])ossible, as shown in Fig. 77; the chief work being to cut it and roll it bottom u]). The extremely obliipu^ edge of the share in the breaking ])low reduces the draft in cutting (,if the i-oots by allowing the cutting to be done gradually and with a di'awing cut, just as it is easiei- to cut off a limb by letting tlx' l)la'e nnder tlic best possible conditions, and it is so easy to make it unnecessarily large, that it is important to understand the principles upon which the draft depends. ]\rr. Pusey in Eniiland, in 1S4(), made a series of trials on the draft of plows in soils of different kinds, using 10 different pl(;\vs. We have coanbined his results and give them in the table below: Tabic shoiving the draft of plows in tests made in England and in America. Kind of Soil. Loamy sand Sandy loam Moor soil Strong loam Blue clay Sandy loam f J. C. Morton). Stiff clay loam (N. i'. 1850) . No of plows. Size of Total furrow. draft. Lbs. 5 in. z 9 in. 227 5 in. X 9 in. 250 5 in. X 9 in. 2*50 5 in. X 9 in. 440 5 in. X 9 in. 661 6 in. X 9 in. 566 7 in. X 10 in. 407 Draft per sq. in. of furrow. LbT 5.04 5. ,55 6.22 9.72 14.69 10.48 5.81 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.!>8 lbs. per sq. inch of the cross section of the fun-ow 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 lbs 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. 48, 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 Sod plow with wliool coulter. Sod plow witliout coulter Size of furrow. Total draft. 5.575 in.x 15.08 iu. fiM'if) in. X 14.5 iu. DilTerenco. Lbs. 296.25 343.75 47.50 Draft per sq. in. Lbs. 3.524 4.453 .929 iJcsidcs (loiiiii" the work Ix'llcr tlic (•(Miller (liiiiiiiisli('(l tlio (lr;rl"t. l!(i..'!('> per cent. 305. Draft of Sod Compared With Stubble Plow. — Auotluu- set. of triiils were made al I lie tiiiic of 304 (o ('oiiij);\i"C the stuhhlc tv|>(' of plow, Fig. 7S, willi thai of l^'i_i>'. 77, iuul tlio results uiv given below: Size of furrow. Total draft. Draft per sq. inch. Stubblo plow witliout coultor Sod plow without coultor 5.87-i X 14.31 iu. 5.325 X 14.5 iu DitTerouco Lb.s. 4,52.4 343.75 Lb.s. 5.384 4.453 108.65 .931 In this case itlie sliajx^ of tlie ])low altered the dralt 20.1) per ('('111., and 'lie di nerciicc is prol»al>l\ a iiicasiii'c ol the dill'ereiicc in IIh' ainoiiinl of piiKcri/.ing done liv llic two ])lows. 306. Influence of Difference of Soil Moisture on the Draft of Plows. A iliird .scries of ohserxal ions wias made on a elover sod with the same sod plow proN'ided wi'th a wlieel coulter, hut at a time when the S(»il was drver than when the other measurements were made. The results loiind \V(^re : Size of furrow. Total draft. Draft per sq. in. Clover .sod without coultor 6.47 X 11.61 in. 6.413 X 12.47 iu. DitFeronco Lbs. 714.35 664.82 Lb.«. 10.80 8 616 49.53 2.181 24{ 111 lliis set (if I. rials l\n-, ('(iiillcr lijis reduced, tlu; dral't 25.34 percent. Soil rather dry Soil in best condition. .. DiiTorDiice Sod flow with coulter. Draft i)or n(i. in. 8.616 3.524 5.092 Sod plow witliout coultnr. Draft per s(|. in. 10.80 4.453 6.347 l"'r()iii llii.-. cniiiiiiiilsdii ii is clear 'lliat tlic draft (d" llio ])I()VV' is \-ci'v iiiiicli iiKidilicil |>\- ihc cdiidilidii ol' llic soil. 'J'lie results sIkiw I lie dialt luore tliau douMeel wlieu the soil was drver. 7(t. 'I'.vpc. (,r jiMili|l,i.;in ^^^^. ■^iiili''! I" riicllciu .sdils rc(|iiii-inn- lilllc jiul- vcri/.in;;. 307. The Draft of Sulky Plows— It is gonorally claimed that tli(H draft ef sulkv plows is less 'rliau tlial of tlie frec- swimiiiiuo' iv|.es hecause tlie frictiou of the sole and land- .shle i.s transferred to the well oiled hearings cd' the cari-iage. The f(w records aceessihlc do not show a matfudal gain, when-th(^ influence cf the weight of the carriage and driver arc not(ledu(ted, hut where the draft is no greater on tlio team with the luau ridiug than wheu walkiug, and the plow 15 '^1 L>l(i call !)(• 1i:iimII('(I witli ('(iiuil I'acililv, there is :iii e\i(leiil nd- \iiiil;i;;e ill ridiiii; pluws siicli as I'^ii;'. SO. V'li;. Mi. Sulky 111- liiliii;; pluw. 308. The Line of Draft. It is \crv iiii|i(>rt:iiil in the liaiidliiii;' <'!' a plow I hat the line of dnifl he just riii,lit- and such that a line ediiiieel iiii; the center (d d ra 1 1 A, Fiji'. 81, in I he iindd heard with I he ph-icc (d' at tatdinieiit le I ht phiw hridh' shall also lie in the iilane (d' the traces, as shewn in Km. SI. Dli-cclicni dC llir line of iIimCI U<\- \i\u\\: 247 tlu! cut l)y ihc line A, I!, I). II fni- ;iiiy rciisdii tlic line of (h'jif't l)i"('()iiics ;i lii'dkcii dill' lis A, ( *, I ) (ir I , •'!, .") (,)• 1, 1,5 instead of 1, 2, .") I lie dnifl of I lie plow is iiiii is especially liahle to i^ct into had t'oriii and dull, eausina,' the plow to iff"'''''!iiiiiiiiiiiiiiiiiiiiiiiiiiii^ J''ni. Si. Sliiiwinu liiM'l 1.1' pli'w ill I'liriii fur ilr.\ soil. Avina,' o\'(M' to t]i(^ land ami draw hardei', not oidv IxH'anse it is dnil hti't hecanse a stc^ady ])r(\ssnre ni\ist lic< exerted at tho liandles to pre\'ent the |)low from tippinu' to land. Fig. S5. — .S1iiu\ iiii; liccl ol' plow in I'liriii I'nr iui>ist soil. Tt. is sometimes necessary to tdian^e the form of tiie ])l()w to snit, a harder (H* more mellow coiidil Ion (d' I he soil. W hen 249 tlu;' soil is dry iiiid liiird tlui liccl iiocmIs to be set down, as sliown iit i\ Fi^'. 84, and tUv \Hni\t niiiy need to dip oven luon^ than in Ki^'. 8.'{, but when tlic soil is wot and niollow tlic shape shown in i'ii>-. SH is recpiired to prevent it draw- iiiH' l(i(f (Iccplv into the iii'onnd. In takinjj,' lh(* share to the shop for sharpen iiiu!; or sH,ling tho landsidc; shonhl accompany it in oi'dcr 'that the; bhudc- sniil h may lia\c a i;iii(h' in i;i\in^ it t he proper sh a |)('. 312. The Jointer Attachment. One of the most useful atiiudimenls for a ph»\v is known as a, jointer, repi'esieu'ted in -Fi^'. S(i. This tool is used toi;reat ad\antai;'(' when con- siderabh': material neeils lo he tnriie(| imih-r, such as h)ng stuhbh", course manure or In turiiini;' uu(h'r a i!,i'een crop for manure. When tiiis is iise(| with the (h'ai;' chain in the furrow very loni;' weeds can he completely laid under tin; surface, leax'in"' the lironnd in oNcellcnt sliaix'. Kllo\v is r('|ir('sciilc(| in l''ii;. S7. Il is iiilciidcd lo 1m' used ill llic li(Ht(iiii nf ;iii (ii'di ii;ii'v fiiiTdW, (Hic |il(i\v t'd'llnwiiii; llicdilicr ill dniiij^ llic work. M\l rciiicJ y i;(Hid jiidiiiiiciil is i'c(|iiin'(| in llic use (d llic siilisoil |d(iw l(t ;i\<>id piidd 1 i ii!4', winch is sun • to rcsiill h'oiii iisini;' llir lo(d when llic siilisoil is loo wcl. In liiiiiiid (diiiiiilcs tlic d;iiii;crs ;irc i;rc:ilcsl in llic spriiii;' iiiid Icasl. ill llic r:ill, :iii(| il Miiisl lie kc|)l in mind llnil llic siirhicc soil iiniv lie in i;(>od coiidilion |o plow wIkii llic snlisoil is iiincli loo wcl . (•'li:. > ., S oil plnXN. Ill scini.'iiid (diiinilcs llic dimmers of injuring:, llic soil •h'xlnrc :irc iiMudi less :iiid il is under siudi coiidilioiis llial subsoilini; is likely lo inoxc mosl |iiolil;iMe, leiidiiii; ;is il i)s AM> ri Mi'.s u|.' n.ow i \'(.'. 314. Depth of Plowing. 'rii<> hesi deplli to plow :it a _i;'i\('ii I line, on :i i;i\'cii soil, lor ;i iiiNCii crop iiinsi Itc Av- <'ided on llic spol mI'Ici' cxcrcisinii' i^ood jiideiiH'nl willi il 251 l (Icc|i('r lli.'iii III turn iindies iH' lesM, JIS these lliri\c hesi in ;i sinillow sccillx'd. 315. Best Condition of Soil for Plowing'. Ihere is m ei»ii- ditio'ii of moisture |)ecnli:ir lo cindi ;iiid e\'er_v soil id whicdi it, will he hd't with 'the hcsl le\l lire ;i 1 1 cr plowing', recpiirin^' thl(^ Iciist iiinoiinl. of tinishin^ work l< fui'row slice may iHH'ome too dry for the hcsi gcu'mi- nation. If the j)lowing is for coi'ii, potatoes or the garden and is done some time before the ground is to be ])lant(Hl 'then the surface is better k>ft as it would be for fall plowing, pro- vided tlie soil is in good condition when plow^ed, because it will foi'm a better mid'ch, it will take th(» rains better, be less likely to become too mucdi eompaeted by the rains and will harmw down better when ])lanting time comes, 317. Plowing for Corn in the Fall. — On soils whicli are naturally nu'llow, where large areas are to be plan'ted and the spring's work is crowded it is often best to plow for corn lat(^ in the fall, just before freezing. If such ground is to 1k^ manured ii 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 thie soils are very heavy and hixxo a tend(>iicy tO' run "to- gether -wath the spring rains then there is danger that the disc may not. be able to bring the field inti condition. 318. Plowing Sod. — There are two methods of plowing sod, 1st, skini-])lo\ving, usually in the fall, turning over a thin sod to kill the turf, oxjiocting to cross, plow in the spring deep enough to bury the sod and turn up enough soil to work up lino and form tlic si'cd bod. 2(1. Plowing deep enoiigk at first to provide a sufficient soil to work up with a disc harrow and give the desired depth of seedbed. The latter inctliod usually rexpiires less time but the draft is heavier. It is usually bent 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 i, usually bctlcr lo place it under a deej) fuiTOW because it neieds more moisture to rot it and in heavy soils it will lot the air peiu'trate more deeply into the soil. In such cases it is better to do the ])lowing in tluv fall or as early in the spring as itlic: soil will permit. If the ground is a little too dry when ])lowed and seeding time is at hand the field should be tJKirdughly harrowed and lirmcd, using the heavy roller if necetssary in order to establish good (•a[)illary connection, with the deeper soil. Jf this is not done the soil above is liabh; to become too dry. When the manure is wcdl rotted it may be left nearer the surface to advantage, except in tho sandy soils where the air penetrates so deeply as to cause too rapid docom])osition of the manure. 320. Plowing Under Green Manure. — Where a crop is 'turned under for green nuuuire it is usually best tO' plow deep, 'to use the jointer and the drag-chain if necessary to get everything well and deeply buriecl. ]f a considerable body of material is turned under thorough firming of the soil af'ter ])lowiug will be beneficial. In green manuring good judgment is always required not to let the cro]> turned under exhaust the soil moisture too completely, for when this has occuiTcd 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 uj) with the water by the green ma- nure crop. 254 320. Early Fall Plowing. — in vooious niid at times wlicro there is a (Icticieiicy of I'ain, wliei'c the soil is lioiit and when tlu^ amount of soil Jeaclifiui;' is small it is often de- sirable to ]>lo\v as early in the fall as the et'o)) has been vv- moved Iroiii iheuroiind, in order !(► save soil moisijni'e and to enahie the intrates and other soluMe salts to develoj) in sntlieient (piantity for the next season. Where crops hold the soil moisture low it may eNcii hecMtme neeessary ill dry elinnites to I'aise one only evei-y other year because the |)lant lood and the crop cannol l)e ]»roduce(I l)\' the; availahle moisture of a sini>,le season. But early fallowing in th'(^ fall will often render the full vear unnecessary. GROUND WATER, WELLS AND FARM DRAlNA(iE. CllAPTKIi XII. MOVEMENTS OF GROUND WATER. Of the watcf wliicli I'lills npiMi I lie l:iiiT<>und water which is the sourc-e of sup[)ly for wells and .spriniis and which recpiires removal hy land (Iraiiiau'e when too close to the suiiace. 322. Amount of Water Stored in the Ground. — Tn most localities after |)assinii- a certain distance helow the earth's surface a horizon is rea(died where the ])ore space in the soil, sand and i-ock is tilled with water or nearly so. AVlien these pore sj)aces are lar<;(', so that water can flow through tiuMu readilv, wells sunk heneath the surface till with water to the level oi' the lii'ound water sui'face. In sands and sandstones lyinij,' l)(dt)W drainage outlets the amount of water may be as hi,<;h as 15 to JJS per cent, of the total volume of tlr(> rock so that where a coumtiy is underlaid with broad and thick sheets of sandstone, such as the Potsdam and St. i*etei-s in Wisconsin and further south, or the Dakota formation in the west, there is the equivalent of from in to :>S fVct = -^ ^ ^^ ^ ' i ,=.^ ,, l- I** 1^ s Fig. 92. - Profile .showing increase of the Los Angeles river by seepage in 25,978 feet. 260 no visible s])rini>'s or streams anywhere along the line. Fig. *.)2 shows the increase in 2r),!)78 feet, determined by ganging. 326. Changes in the Level of the Ground Water. — The level of the ground water in a given scH'tion is nsnally sub- ject to changes, the surface rising and falling with the sea- son and with the rainfall of the place. The change may bo as much as 5 or 6 feet in a single season, as represented in Fig. 93, and wdien a series of dry or of wet years follow in Fl«i. 1(3. — Showing cIimjiucs in the level 'if llic >,'r==J^-5=;^=^^^^::=^S^^NS^^g^:ss:g:g^^s=pr^3;,_ : >S=^ Fi(!. SA.— SliowiiiL'- ti>p jinifniut of unocfiipied snacc in complett'ly 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 lbs. of water or .226 inch raised the surface 6.7 inches. In still another trial the withdraw^al of 33.575 lbs. 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- Tahle showing amount of rain necessary to raise level of ground water after thorough drainage. Grade of sand. 1 foot. 2 feet. 3 feet. 4 feet. No. 20 No.40 Inches, 0.874 .433 .579 .370 .242 Inches. 4.379 3.551 2.701 1.592 1.030 Inches, 8.. 5.50 7.795 6.454 4.0-0 2.635 Inches, 12,81 12.19 10.80 7.. 573 5.131 No. 60 No. 80 No. 100 16 262 quired to raise the surface of 'the ground water 1, 2, 3 and 4 feet in the sands of Fig-. 1)4, 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 liow of water through sands and soils is directly proportional to the effective pressure and inversely proportional to the length of the column through ^diich 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 fonnulated for the flow of fluids through capillary tubes and under certain conditi(ms of pressure and dimensions the law has been nearly fultilled, both with sands and capillary tubes. In practical measurements^ 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 P V = k^ 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- and given below: 1 Nineteenth Annual Report, U. S. Geol. Survey, Part II., p. 202. -Nineteenth Annual Report, U. S. Geo!. Survey, Part II., pp. 301-322. 263 q = 10.22 -^-rr— c. c. per second (1) ^ //hk ■\vliere 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 [].009i.] 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 graii^s in mil- limeters the formula is q = .2012 ■ ■ cubic feet per minute. (2) //h k If the floAv of water oceurs under a temperature of 10° C. or 50° F. the formula may be written q = 15.30 - 1— r— cubic feet per minute. (3) Problem. — A cylinder 4 feet long, having a cross sec- tion of 2 sq. ft., is filled with saud whose grains have an effective diameter of .15 nnn. What will be the flow of water through it under an eifective 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. 12x(15)-'x2 . 10.3 — - — r,T-7.f, — = .06532 cu. ft. per minute. 4 X 31. bJ Problem. — AVhat would be the flow in cubic feet })er minute under the same conditions except at a temperature of 68° instead of 50° F, ? In this case use formula (2) and the results are, taking the coefficient of viscosity at 68° F. at .0101 from the table below: 204 \-2 \ ( If))' \ ii -••'^..l..lx.|v:U..;2 •O'Hil.u.n.pM-.ni.u.l. 'I'Aiti.K III. ('()<■ l]ici( Ills of i'isc(,si/i/ J'lir iiudcr far ixtn'oiin tciii- peratureti cen./i(M'II- // coolllcidiil () li'iniMifn- II <'<)olli(Ml^lll llll'O ol' liiro ..r coil tiKi'uilu. viHOoHit.,v. <'t>iit Iki'ikIk. viHCOMity. 0,{)17H Id ().()i:il I (1 (Il7'.i II ()I2M 2 1) linitl VJ, 11 i»i:!.| :i 11 (III!) III (1 OIJO 1 (loiriii UAHWJ, i: IT) (' (1117 II mil II o.oin lit II Hill 7 1) (iii:{ 17 (I IIIIKI H (ii:i.s IM II (iKn; 11 (i(>i:ir. 111 OIlKt 10 1) iii:ii •^0 OOIUI 330. Observed and Computed Flows Compared. Wlion sjiikIs 1iii\i' 1)c('ii soi'Icil into n'rjidrs of iiciirly miil'oi'iii Hi/o :iihI llir rllVcl i\i' d iiiiiirlcr ili'lrniiiiii'il hv I, lie luclhod of (^143) :iii(l llii'ii I III" lldw of Willi'!' llii'oiii;ii lliciu iiiciisiinMl ill such :iii ;i|i|i:ir:i( IIS ;is is ri'pri sciifcil in l^'ii;'. \K> llm oh- sci'Vcil Mini coiiiiinlril llows JUT I'clnfrd ;is nixrn in llic next luhlc. o^ >_ 43 ^« . y ■ / .■^' - 10000 oc ^ ^ ^ ^ M)00 cc // ■y" y^ ^'l.Ji^ ?f.,... 03 ....1 0« ...1.... Oft OS or 1 i"l(). !ir>. Shiiwliin ii|ii';iriil US I'or niciisiirliit; (lie How (if wiilrf llir(Ui;;li siiiids mill llic rcliUliiMs nl' How (o I In- (lliiiiu'lcis of llw siiiiil ;;i-aliis. IjIiics show I lu'urt'lit'iil How; dols, oliscrvi'il llow. L^c.r. >.\ ' HiidSin,, /' •,!..:' Si J 7 5" Kid. OC- SlmwliiK llii' s.-niil uniiiis n.fi.i ri'd lo in hiMc uf (21"J|. .\iiliir;il Hi-/,.'. 26G Table shoKnng observed and computed flow of ivater through simple sands of different diameters under a pressure of 1 a. ni. of water. (irrado of Diainotor of Ob.sorvod Computed sand. Ki-ains. flow. flow. m. m. gms. Rms. 8 2.54 2. 296 2,2!7 7 1.808 1,0811 1,132 6 1.451 756 7.57 .V/j 1.217 542 .5:^2 5 1.(.95 ."JOLe 453.2 4 .9149 829.2 297.5 3 .7988 210.0 193 2 .714G 138.6 122 1 .6006 94.8 80.6 .5169 72.3 66.8 The iliiTcciiicul Ix'twt'cii the ohscrvcd mid ('(iiii|)iit('(l Hows is not as (.'loso as could Ix' wislicd hul when it is observed that tlie How of ail", fVoiii wliieli tlic diauielei's were com- puted, was not iiieasurcd tliroiii>li the same sample as 'the one tliroiigli whieli the llow of walcr was measured, that the pieces of a]i])ai'atiis were not 'tlie same and that the How varies theorcticallv, as the squares of the diaiiK'ters of the soil i>'raiiis, it must he coiu'cded thai there is iiiiudi more tliaii a chance aiii\eiiient. The samples of sand used in these trials are repri'seiited full size in Fio-. <»(;. 331. Relation of Observed Flow to Diameter of Soil Grains. — If tlic s(inares (d' the diaiiieters of the sand j;rains represented in I^'io. <)(; are plotted as abscissas and the ob- served and com})ute(l Hows as ordinates their relations will be as shown in Fii>-. 95, where it is clear that the rates are such as to agree reasonably well with the sipiares of the diameters of the <>-rains. 332. Relation of Pressure to Flow Through Sands.— Most experinienters aloii^,' this line haxc found that wliile 'there is a general teiidencv for the tlcnv 'to increase directly as the pressure there arc^ nevertheless conditions wliitdi prevent 267 tlR'sie relations l)(.'iii^' realized in exj)eriiiieiit, in mjino cases the flow being' systematically too fast and in others too slow. A series of .ibservations by Wclitschkoivvsky and Wollny ; 25cm. - 500 CC. /' -4-00 ♦ / 50cm -300 ♦ / ^ -200 7 y^ ^ ^75cm lOOcm -100 / z^^::^^^ (^'ffTi, , 50 75 lOO 125 ., 1 .... 1 ... 1 1 ... 1 . . 150 . . 1 . . . \75 . 1 , . 200 cm. , . 1 . , , .1 ^ Fig. 97.— Slidwiii;;- .iiiicii-.ii ns (if Wclitschkovvsky mihI the rchilioTi .if pn-s- snic td bv AVelitsclikowskv were 25 :\ m. and 2G8 50 c. III. loiii;' tlic llow iiici'cascd laslcr lliaii llic jircssuve ; Lilt wlien the colniini was 75 c. lu. long the flow increased directly as the ])ressiirc, wliilc when it was made 100 c. m. loiig tlieii the ildw did iml increase as rapidly as llic [)ress- nre. - ' 1 ' — r • [ ■too 1 17 ilOO n — ' • 3 lOOOcm -1600 cc . -liOO • ^ ^2> -800 ' ^ .2 - « ^ii , . -S'S - tOOCC <^ • ' ' ' ^*3 - rV^^ ■ — ^^ ^ ^-^ Fio. 9S.— Shdwiiiu- II W tlu'oli!.'.!! ;;:iiiilsl(iiH'. •veil rcliilioii 111' iHTssun' Ic llow cf water iiic':isiii-imI in llic ,i|i|ki ral lis uf \'"]'^. li'J. 333. Relation of Pressure to Flow Through Sandstone. — AVluiii. the ilow of water is mrasiiriMl itlir(Mii;h sandstones such as constitute most water-lx'aring l)eds it is often tnund tliat here, Jis in the sands, the How may inci-ease in a niiudi liig'hcr ratio than the prckssure. Three series of sncdi obser- vations are ])lotted in V'\iX. OS, and Ihc apparatns used is showji in Fig. 1)1>. Whore the flow does not increase as rapidly as 1 he pres- sure the departure from Ihe theoretical llow has Keen ex- plained hy aasuming thai llie^ cni'rents heiMmie turlinient and tlnis rednco the disehai'gcs hnt no satisfactory reason has yet hcen assigned to the cases where tlie thnv increases fas.ter than the i»ressure. 334. Observed Rates of Flow of Water Through Sands and Sandstones. — ''I'he ohserxcd ratcvS of flow of water through the series of sands rej)resented in Fig. i^O, when expressed 200 ill ciiltic feet per iiiiiiiilc per s(|ii;irc U><>\ of section ;iih1 per foot: of Iciin'tli, iiikIci- ;i ,ii,rii(li('iit of I in 10, is f>ivcn below: No. « 7 6 5!4 5 4 :i 2 1 Cu. ft. per min. 5.23 3.65 1.85 1.30 122 .82 .51 .33 .23 .18 Fhj. 99.— ApparntilH for iiicMsniiii;: Ilif llnw d' \v;iicr 1lir(Mi;;li s;iniii'.s, uiidcr (inicrciil kimwii |)i-cs.sMrc>. AccordiMg to Diii'cv'.s hiw, if tlicsc siiii of those given. In the case of fonr sandstones the rales of flow were so slow that 10 (lavs were i'e<|nii'ed foi- ..!!», .;54, 2.45 and .14 cubic 270 ieH. of water to be (lischargcd luidcr the coiKlitious for the Hand. 335. General Movement of Ground Water Across Wide Areas. — Tlic: waters whicdi supply aitcsiaii wells and many springs, where the discharges take phice 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 (234j and it is clear that nearly the whole movement across long distances must take place ithrough rock fissures and along bedding planes, the water seeping out of the rock into tlu^e 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 diseiiarge of water from s]>rings, artesian wells or lines of tile drains it is seen tliat the tl(nv is not uniform, varying not only with the season, Init often daily and even hourly. Fl(!. 100.— Showiiif;- o1is.tv.m1 l>;ir.iiii.'(i-i.' cliMimcs in tlu- nitc ,it' fl.iw (if water I'rom a spring, an.l tli.' jippjir.i t ns f.ir rccinliiifr it. l..iwfr .-iirve record of sprinjr. In Fig. 100 is shown an autographic record of the dis- charge of water from a spiing during 13 days, together with the changes in barometric pressure as recorded by a baro- graph 45 miles t^. the west of the spring. The method of 271 reeurtliiig' 'the cliaiiiijCs is also re})r('8('nte(l in the saiiu' tiiiiire. The clianges 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. tlif li;ii-ciiH('ti'ic chniijics in llic r;\t< tile ilraiiis. Lower '''-' /I f^ * a/zf-f T, TTTT 1 1 1 l-m-^- m J ^f^^ffl B £^. Rate of Discharge from Tile Drains. — Besides the changes as- --j sociated with changes of baro- HM I / I I \^\y ] r ~~~ nietric pressure referred to in t~2Z^Jz2-\Z^lIiU2M (237) there may also be diurnal changes in the rate of discharge which are due to the diurnal 71 1 I / I 'LU-^^t^id^l I I I I I f'li^i^i^.'P^ which take place in the -^Hm^I m flTTrl I I I I I I soil air above the ground water. As the air expands under the heat reJii^sci^^edSichanS^in al>sorl)ed it prcsses dowirward welistue'^J'^chlnies Z'soCi ^^^n the watcr, causiug it to drain temperature. awav fastcr, whicli niakcs it 272 iimcli ;is it :i rjiiii luid (•cciin'cd :iii(l |>('rco|;ii i(»ii li;i''! shows aiiol lier series of diurnal fluetnalions where the ehanncs in level were measured twice dailv, in the niorninji,' and at niiilit, and Fig'. 104 shows the conditions under which these changes occurred. The lower cni've represents the changes in the inner well M'hile the upper cni'Nc shows those in the outer well where the water ])erc(>lated from above the stratum of claj under the intluence of the air pressure caused by the diuriuil changes in temperature. ti(i. 10;i.-Mu,wiii« (lull tKilclianKcs 111 tlio Fid. IU4. Sliowing the soil con- leviilof the KmuiKi \vat(n- lueasiuod twice ditioiis under which the chanKOs daily in surface woUs. „f Fig. 108 took place. 339. Fluctuations in the Level of Water in Wells.— In all (U'dinarv wells, wluther tlic\- are deep or shallow, the water is seldom at rest, tire surface continually either I'ising or falling througli varving distances, and Fig. lO,"* is a record (done such series (d'changes which it will be seen a I'e nearly Wednesday NQ)ursday f^fiday 10 12 2 4- 6 8 10 M ^ f/f a\o 12 2 4 6 8 /O M 2 4- ^f\j,'es in pressure. 274 (•(liiicitlciil ill |ili;isi' willi (liosc wliicli (icciincd in llic dis- ('hiii'^'c (»l Wilier Irniii ;i spniii;'. ( 'li;iiii;cs iiiiicli iiioic xio- Iciit lliiiM t licsc iiiid (il slioitcr ,' or curbing which is vermin ])roof at the to]) and if ixwsihle \vater-pi'(K>f in its upper JO lo 20 f(«t. 341. The Capacity of a Well. —The capacity of a well should alwitys, if possible, be much gi'(>ater than the prob- able dctuands wliicli will be put upon it, and it should not b(^ jxissiblc in a few lidurs lo pump il Avy witji an ordinary puni]>. In working tlu^ ordinary domestic |)um]) about 20 strokes are uuule per minuter and theise will till a |)ail with 20 to 24 p lbs. wlien it was cold. At this rate the eipiivalent of 40 adult cows M'ould need ;;,4ir> lbs. of water or .■)4.7 cul)ic feet and this Av<»u]d re(piii-e, at the rate assumed above for pumping, 2 hours and 4.") minutes to supply tliem. 270 342. Geological Conditions Which Give the Best Wells "J'lici hiriicsl iiiid Ix'st. supplies of well wnlci- jirc iisii;illv touiul in tli(^ cxtcusivci SiUidstoiU' foniKil ions mid wlicrcNcr tlicsi! arc witliiii ciisy rciu-li the well sliduld Uc sunk iiilo tlicui (lec|> cuoiiuli l(» li;i\(' iM) (ir iiku'c feel dl pcrcohit ini; sand- stone: suri'iU'c. Next to t lie saiidsloiic I'onnalions as sources of water su))ply stand llie liss\ii'ed linu'stones which either ov(M-lie sandst(,iu\s or ai-e S(» i-ehited lo the surface soil that water Ironi the;n can pei'coiate doA'u iiiito the lissures and tliroui;li llieui reach the v\'ell when suid< so as lo connect Wi'tli a sv-teni of these lissnres. Ai^ain heds of sand hetwec n heds ot' (dav often uive lari;t? supplies (d' pure cold water. In nianv localities artesian or llonini;- wvlls can he se- cure(l and some id' the conditions under which these orii^'i- uateare re prescnicd in ViiX. 1(>7. 343. Conditions which Influence the Capacity of a Well. — The rale at which watei- can enter a well depends upon five })riine factors: ( 1 ) The size of the grains of the water- bearing- heds and the pore space. (i2) The depth of the well in the watcr-heariui;' bed. (o) T\\v auiouut the water is lowered in tlu^ well when piinipiiii>'. (4) Tlu^ diameter of the W(dl. (.">) Whether the well is in or near a system of fissures. 344. Influence of Size of Grains and Pore Space on the Capacity of the Well. — JMoni the fact that the How (d" water tlirouiih sands is nearly ])roi)ortional to the stpuires of the dianivters of the scdl urains, and is i^reatiM- tlu* larger the pore space, it is (dear that these are \'er\- inipoi'tant factors in deterniiniui;' die capacity of wells. It has heen conipiitC'd that when all other factors are the same the ca])acities of two wcdls, ill sands haviui*- the diameter of grains of .15 mm. and .25 mm. and pore s])ac(>s of 'M) ])er cent, and 32 per cent., are to each other as 5.2.")4 to IS. 01 or one is over tlire(> times the other. It is thcrefon^ (dc-^ir that when the sand grains and ])orc' space are small th(» other wcdl factors must he made enough larger to compensate. 277 8- Krillrllanilr Fic. 107. — Sliowiii).^ ;,'cii|r)j,'ii-:il I'niiilil inns iiuili'i- wliiih nriosljiii wi'll.s are Ji.niMMl. 17 278 The caj^acity of a G-incli well sunk 100 feet into sand- stone having different sizes of sand grains but with uni- form pore s^^ace of 32 per cent, and a temperature of 50° F. give computed flows under a joressure of four feet as follows : Size of grains in m. m. Cu. ft. per mill .02 .04 .06 .08 .1 .2 .4 .6 .047 .189 .580 .-757 1.C8} 4.73 18.93 57.96 345. Influence of Depth on the Capacity of a WelL — When other conditions are the same the greater the depth of a well in the water-bearing beds the greater will be is capac- ity because this increases the area of the section of the sand or sandstone through which the water mav enter the well. If a ()-inch well is sunk just to the surface of a water- bearing bed the area through which the water can enter it is only 28.27 square inches. So, too, if a G-inch well casing ends in a water-bearing sand only so much water can enter this well as can flow through a circle of sand G incheis in diameter. If the well penetrates the Avater-bearing bed one foot so that water can enter the sides as freely as it enters the bot- tom then the percolation surface will be increased to 28.27 -f 226.2 = 25i.47 sq. in. making the section of flow nine times as great. Leaving the lK)tt(Hn of the well out of consideration it is clear that doubling the depth of the well in the water-bearing beds doubles the area for water to ent(M* and hence it is a matter of the greatest impoi'tance to secure a sufficiently large per- colating surface in the water-bearing beds. This capacity increases in a somewhat slower ratio than the depth, as in- dicated in the table below-. 279 Table showing tlie flow in a 6-inch well sunk different depths into WO feet of loatcr-beai'ing sandstone ivhere tli epore space is 3:3 per cent, and the diameter of Ihe grains .25 m. m. Flow in cubic feet per minute Depth of well in feet. 4. 8. 12. 16. 20. 40. 8('. 100. 200. 1.003 1.818 2.544 3.265 4.08 7.68 14.88 18.49 36.02 346. Influence of Pressure on the Capacity of a Well. — Since the fx()^v of water through sands and sandstone is some- wliat nearly proportional to the effective pressure it is clear that the de])th of water in the well at low water stage should be great enough to permit its surface 'to be lowered until the needed pressure to force the water into the well is der veloped. If, in pumping, the wiatcr in a well is lowered -i feet the pressure developed will be about that of four feet of water and to lower it 8, 12, 1() or 20 feet \Vill increase the pres- sure 2, 3, 4 and 5-fold. This relation being true it is clear that not only sliould tliere be an ample depth of water in the well but the cylinder of the pump should be so placed as to enable the full dcjtth to be lutilized. In the ease of a H-inch well sunk 100 feet into water- bearing sandstone 200 feet thick having a pore space of 32 per cent, and diameter of grains of .25 nun. ithe capacity of the well under different pressures is computed to be as follows : Amount the water is lowered in the well in pumping. Cu. ft. per minute 1 1.8483 2 3.6966 4 7.3932 8 14.7864 12 22.1796 16 29.5728 20 36.966 347. Influence of the Diameter of the Well on its Ca- pacity. — Tlie capacity of wells when they extend any con- siderable de])th into the water-bearing l^eds does not in- crease as rapidly with increase of diameter as might be ex- 280 pected, and Slicliiter computes that three wells 2 inches, 6 inches and 12 inches in diameter respectively, if sunk 100 feet into a bed of sandstone having sand grains ,25 mm. in diameter and a pore space of 32 per cent, will have capaci- ties in cubic feet per minute as follows, when the water is lowered 20 feet: Diameter. 'L iuch. Diameter. B inch. Diameter. 12 inch. Cubic ft. par minute . ... 31.90 36.94 44.45 These amounts are on the ass^umption that the walls of the weJl or casing offer no resistance to the discharge, which of course is not true, and the 2-incli well could not discharge the amount indicated under the pressure of 20 feet akhough that amount could enter the well if it were removed fast enouoh. HARD PAT Mi Fk; 108. — Sliows a j;oo(l fonn of sanfl strainer niailc by sawinj^ sh>ts in brass tubing. It is clear from these results that for most wells there is little gained in making them larger in diameter than is needed to provide accommodation for the pump. 281 348. The Use of Sand Strainers. — Where water must be procured in loose sand, especially if it is line, some form of sand strainer should be used unless the well is an open one and even then a suitable point will often g'reatly increase the capacity. The dilticulty in getting water rapidly from loose sand grows out of its tendency to move with the water, filling up the well or the suction pipe or cutting out the valves. Since the speciiic gravity of sand is only about 3.65 just as soon as a pressure greater than 3 feet is developed to force the water out of the sand the sand must mjove with it unless there is something to prevent it. \ Fig. 109.— Showing ordinary sand strainers and nu'tlidd of measuring their capaeity. The best sand strainer we have seen is represented in Fig, 108 and is made of heavy brass tubing cut as shown in the illustration, the width of the cuts varying for the different degrees of fineness of sand. Made of heavy sitock and of one kind of metal it is not liable to corrode and clog as with the common form represented in Fig. 109. 349. Capacity of Sand Strainers — The capacity of sand strainers varies essentially in the same way as wells of simi- lar dimensions would, made in the same kind of material. The longer the strainer, the coarser the sand and the greater the pressure the larger will be the capacity. 282 III l^'iij,'. lOi* is i"c|trcsciit('(l :i iiiclliud used in iiiciisiiriii^' tlid (•iij)JU'itv dl' tlii'C'Ci (ioiild S;iii(l Si r;iiui'.|-s, ^\os. 50, SO and JM), ciudi IS iiudics loii^', and tlic- tabic below f>'iv('s the rcsiijils sci'iii'cd. Tdhit; n/ioiriii// tin r sand abont the No. .")() sfi-aiiur liad a diauuMci' of .2!» I iiiiii., illial aboiil llic Xn. SO. 172 iiiiii., and about t ho No. !H) .OS,') niiii. 'riic lablc sliows under tliesc eoiidilions about. 2 niinnles (d' steady How, under a pressure; (d" 12 i"(H't, are re(|nired for the Xo. .M) strainei- to snp|)lv sidlicicnt water lor a, sin<;ie cow one dav; (I niinuilcs lor the No. 80 and more than 20 ininnte'S For the No. UO strainer. Il wlonid ill 'ludore be iiccessai'\ to use a strainer .^ 1: iiudies loiiji' in 'the Xo. SO ,' l)ed id' stdlieient tliiekness,l>ut Mir)ariiii7 working gaud HtraifKU' and ou an open woll. 284 ])l;icc tlic! [)iijiij) so as to draw i\w. water from thv. bottom wluvro it is coolest and freshest. JJotli de|)tli of soil, to act as a Hlter, and time to bring- about eliimi;('s in surliice waters, to free them IVom organic mnttc^r, :ire re(|uire(l in order to render tlie watei- t'nllin^j,' li|)oii the i;roiiii(| |Mirc ;ind siiit:d)le lo drink. 352. Temperature of Well Water. — Tlie zone of lowest i>'r<»iiiHl teniiperatnre is _i>-enei-all_v fi-om '20 to 70 I'eet below tlu^ surtiiiee and in this zonc^ the coldest waters are pro- eured., Alxn-i^ :,'() feet. Ilie walei-s will be colder in w^inter and warniei" in, .^nninier and below 7<> to ~^> I'eet ilie water i^cnerallv becomes warmer from llie internal lu il of llie earth. 'The normal lemperalnre of tlie coldest well v\aler in a locality is nsnall\' from 2 to 4 dei;rees liii;iier than tlie inran . annual aii- temperature of the place, and in Wis^'onsiu this rang'os from 4-'^^ in the norlliern portion to abont 50° in the sont liern port ion. 353. Well Casing- or Curbing-. iM-erytliini; consiipe g"al\'ani/,e(l is lu'tter because it. will not rust out so ipiickly. The great advantage of this kind of casing is that it is --.o (*()mi)letely watiM- tight and at the top can be so securely closed as to |»re\'ent insects and Ncrndn tailing in. Next tO' tiiei ste(4 casing is one made (d' cement tile or glazed sewer iilo; with their joints set in cement. Where a vv(dl is to have a bri(4<: oi* stonie curbing the u|)per 10 feet should bei laid in cenu'nt and plastered with the sanu' on tlie back to excdnde surface water and \'crmin. 354. Top of the Well. — in linishing a well the casing should be cai-ried 1 1} lo IS iiudies abo\'e the surronnding sni'face and then earth be i;i-aded up to it so as to secure |)er- fcct and quick removal of all surface water. 285 When' ;i steel Ciisiiia," is used the well |)l;ij t'onii is best iiijulo by serewin^' ii wide Haii^e on the iop and then bolting tlic piun))h(>a(i i features that the excess of rainfall is opportiuu'ly removed by })ere(dation and seepage or surface flow; and this is nature's metluxl ' 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 the-m 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. Tlie water in the soil needs to bo frequently changed or replaced by a. fresh supply containing an abundance of 2ST atni()s])li('i'i(' o\vi;('n hct'ansc the roots of plants and micro- scopic life tend tO' exhaust this suivply. If the soil is not drained 'the water in it becomes stagnant in a sense, the rains wlii(di fall sini})ly nmning' off the surface, leaving the soil water tlie^ same as was there before the rain. .'5. Fai-m lands mnst be drained in order to render them snfhciently tii'ni to pei'mit the farm ojx'rations. 4. Soils mnst he di-aine<| in order to ])rovide room for soil air. (238.) (251.) 5. The excess of water must be removed to ])ennit the soil to become Avarm enough for plant growth. (268.) (271.) 356. Conditions which Require Drainage. — The cases in which it becomes desirable to sui)])lement natural drainage fall into five classes: 1. ( 'om])arativel y Hat lands oi- basins npon whicli the water from the surrounding higher lands collect. 2. Areas adjacent to higher lands where t\\v structure is such as to ])ermit the watei- which sinks into the high land to flow or seep under and up thi-ough tlie low ground, making them welt. 3. Lands inundated regularly by the I'ise of 'tides or fre- quently by the ovei-flow of rivei*s. 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 aj>])lied in excessive (piantities at stated tini(\s and must he removed again quickly. 357. Deep Drainage Increases Root Room. — ISTo plant can utilize the resources of the soil to the^ Ix^st advantage unless there is ])rovided for it an abundance of root room. In all well drained soils the roots of most cultivated crops spread themselves widely and to a de])tli of 2.5 to 4 or more feet. When conditions are such as to permit crops to do this the best growth and lai-gesit yields result. 288 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 waiter in the soil be- low, and Fig. 45, p. 148, shows the apparatus with the corn growing in it. 358. Drainage Increases the Available Moisture. — When the roots of a cro]) are forced to (U'vclop 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 diy 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 moisture. On the other hand if the ground water is lowered the roots are permitted to advance deeper, making it unneces- sary for the water to miove u]) as higli 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 thermometei-s 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 stovei has the temperature of its bottom held constantly near 212° by the evajioration of the boil- ing water, sho'wing the cooling power of w^ater 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°. Tlie differences in the amount of moisture in clayey and sandy soil often cause a diff'erence of 7° F., in the surface 280 Kiii. 111.— SlKiwiiiK' linw llic nulls if <■<<{■][ ;n-i' fm-ccil Id ilcvcldii near the siirfiLiM' \\li('n tile soil is hkI dr.-iiiicil. Set' aiiparatiis. I'"ii;. Ifi. \>. 148. 290 Iddt, when Itdtli arc well diniiicd, and :is iiiiicli ns ."> in the ScxmuhI :iii(I I liird feet. 360. Soil Better Ventilated by Drainage. 'I'lic cliaiio'c of air ill wi I soils allcr llicv have Itccii well drained is very iiiiudi iiioic- i| lioroiiiili and this is perhaps I lie i;r,-|l('sl henc- iit. due to drai iiai;c Tlierc^ are several wavs in wliiidi I lioroiii;li drainaii'e leads lo a more rapid e\(dia!ii;(' of air in tlie soil: 1. Loweriiii;- llie i;roniid water eiiahles hotli the roots (d plants, and aniinals like earthworins and ants, to penetrate tliosoil ui()r('(lee|)lv, lea\iiii; passai;('\\avs lari^cr and freer tlijiii. existed hefoi^e. -. When the (h cper (davs eoine to dry alter heini;' drained sliriiikai;e (dieeks are formed in i;reat nnmhers and liiroui^'h th(\s(s the air iiioncs more IreeK'. '■). W'i'lli tlu'i deeper penetration of soil air nitrates aro more t reely lormed, and witli the lariicr amounts if solnhK' salts the (day is lloeeMlat( d, makiiij^' a more i;raiinlar text- ure, which auaiii admits the air more freely. I. When lines of tile are laid under a H(dd :>() to 100 feet apart they furnish an opporl unity, with {'vrvy (diaiii;-e in atni()S])lierie pressure and (d' soil temperal nre, to force air into and out o( the soil, and so a line of tile laid in the soil hecoines a system lor air circnlat ion. T). With i'Vi'vy liea\y rain wdiicdi causes jtercolat ion, where the water can tlow away, a \olnnie of fresh air is drawn into t he soil after it, coni|iletely (dianuin^ 'I he air. 361. Kinds of Drains.- Ther.' are tw(. types of drawings: (1 ) (dosed and heiieath the surface after the manner of un- derground water channels; and ( iM open, such as (litt'lu"S, wdii(di are in fuiudion like natural ri\('r (dianiuds. 'Idle (do^ed forms ai'c usually iiuvst etl'(vtivo, l(^ast in the way, re(piir(v less expense; in maintenance and are nutst durable and should generally he adopted, Imt I here are cases w here surface ditidies luusif l)e used. I n t he earlier history (d" underdrainini;- (dosed drains wero 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 l^ottoni of tlie ditch or two slabs were laid ('(]*y(' to edge with their i-onnd sides down. 'I'wo Iniai'ds were sonietinies set on (Mlgc X'-shaped, with o))cning d(nvn. Mow |)ci mancnt cIoscmI drains w( i-c niay iilling tl)0 bo'ttom (jf tlie ditcdi with (•ol)hh'stone, by setting Hat stone on edge V-shape, by setting two lines of stone on edge and covering with flat stone and eve-n by using four stone for top, bottom and sides. In other cases brick wCre used in place of svtoiKJ and some even made tile out of blocks of ])eat, 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 im])ro\'eiiients, and have largely gone out of us(\ The modern tile, made of iiai-d bui'ned clay, is cylindrical in form and usually in 1-foot lengths with diametei's rang- ing from 2 to ] 2 or more incdies. 362. Essential Features of Drain Tile. — A good drain tile should be liai'orous. Soft burned tile wdiich give little or no ring when struck are much more liable to crumble down under the action of fi-osit. We have visited one ficdd 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 l)urned are converted into lime. These lumps of lime bedded in the tile slack as soon as wa;ter enough reaches them and by Iheir expansion the tile 292 - are broken. It will often happen that such tile may be laid in place and covered before the slacking occurs. Besides being hard bnmed, strong, giving a clear ring Avhen strnck 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 Avhich 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 Ayater 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 .Tefferson, Wisconsin, tile showed a flow of 8.1 cubic feet per 100 feet of leng-th in 24 hours, under a pressure of 23.5 inches, when surrounded by clear water oidy. 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.G2 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 larc.e enough to slip over tJie joints readily. The use of collars is not ad^dsable, first, on account of the greater cost, and second, becaiise Avlien 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 wat( r 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- 39; age ai'c oiilv t(M» wet (hiring tlie s})riiig it may be best to lav the (li'aiiis only so cleej) as is needful to bring the field into condition for working in due season, and in such eas(^s tile ])laced 2.5 to 8 feet, rather than 3.5 to 4 feet, will usually be found sutticient for general farm crops. AVlun tile are ])laeed needlessly deep not only is the cost greater but, in all of those cases where there is an under- floAV 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. Fk;. 112.— Ht-prosentiii}; an apparatus for demonstrating the slope of the firoiind water surface back from a tile drain and the changes in I)ressure when discharffe is takiiiir place. A. front elevation of tank, with a, b, c, d, faucels from drain tile, and 1, 2, 3 15, i)ressure gauges: H. li, venical scctKiiis Iciiict liwise, with 1, 2, 3, 4, tile and faucets, ;ni. 366. Rise of Ground Water Away from Drainage Outlet. — ■ If reference is made to the contour map of the ground water surface, Fig. 80, p. 257, it will be easy to compute 18 2!)4 tlio gr;i(li('iil, of the groiiiid water surface as it rises back from tlu! lake. In well 2t), 150 feet from the lake, the water hUxhI on a certain date 7.214 feet above the level of the wat(M' in llic lake, tlins slu)winf>' a mean rise or gradient of 1 foot in 2 1.1 feet. J n llu; same locality, but outside the area represented by the unip, a well stands 1,250 feet back from llic lake and in this the waiei- has a level 52 feet above the lake or di'aina_i;(! ontlet, which i;i\'('S a mean g'radient or rise of I foot in 2 1. in V\}2;. 112 is r(\])resente(l an a|)i)aratus for demonstrat- iug the position of the snrface of the <;ro\ind water and the dillcrcni'c ol prcssnrc at ditlci'cnl distiinccs awny from and above a di-ain tile, and l<'ig'. llo shows the observed differ- ences of prcssnrc nn(h'r I wo sets of conditions. In l*'ii;'. Ill is also rcprcscntcil the <;('iicral slope? of the gronnd wati'r surface and 'llic niodilication (»[ it by a line Ji3*'S67BaionJ S 13 1* ^* J \ t X ; _- —"* ^ ^^ ■ Fid. US. -Sliowlufj 1h(> cluuiHOM In ]>n'ssur>> ill (UlVcrciit tlisluiic(>s froiii (lie lilc ilniiii wlicM llic >\i\t('r is llowiiiK. Tlic lower ciirvo sliows (lie in-cssiirt' wlicii (lie (lew Is fi'niii (lie slopcdck n, It'l^'. H'-!. iiiid I lie iipiMT set ol' curves reiircsciM cliinifics wliicli ccciirrcil during ii period of ll.iw Iroiii llie stopcock ., l<'i).v. 312. of inliltration ])ipcs, which is in effcH't a tih^ drain. The rate of rise of the grouud water back from a tile drain is one of tlu^ chief factors in determining- ihe distance apart the drains should be placed in the field. 2on F 3 B E r "^ 39_ G ai 20 19 18 17 16 IS 14 1 iwm nmn ON JNE (VC- 1 \ ,'^ " PRC FILE nrnrrTTi rnrrlm V ~~~i 1 10 ? IS 7 & 5 4 D 3 2l 3 2 1 1 1 '^ 3 'nranffp Vmtm 'tTlTmr -m™ m.^ "TnAnfl wmrm im%, 1 Li^ J6 37 'HIIJIJJT Urn J^ mm. rnimrn mm PR FILE ON JNE AAB ...II ' Kic. 114.— 'I'lic tiiipci- imrti'in is ;i (liiif;r:iiii of lliiiiie (if West Los AiiKuIes AValcr ( 'oiiipiiiiy .mikI vi'Miiil.v. Niiiiilicrcd^ dots sliow wIiitc Icvt'l of ;;rouii(l walt-r was iiicasurcii in wells siuiK for the |)iiri)os(', and cor- respond Willi iniiiilx'rs on lower part. Lower iiart, jirotiles of the surface of the ;iroiind water in tlie ^i(•inil.\■ of the West Los Angeles A\''ater ("ompaiiy. 'I'lie lieavll.\' shadiMl line is the f^rouiul water surface. Kai-li square represeiils ]()() by 10 feet. 29G 367. Distance Between Tile Drains. — Tliero are three j)rini(' factors wliicli (Iclci'iiiiiic llic distance between tile (li-aiiis. I. 'riic crtVctivc siz(! of soil i>'rains and ])oro space of the subsoil tliro.uji>li which the water nnist move to reach the drain. Jf the subsoil has u close fine texture the re- sistance to the flow will 1)(^ lii-eat, and hence the water sur- face will rise fastci- back from the drain, bringing' it near the surface sooner mid inakini;' it necessary to place the lines (doser togetlier. 2. The depth at which the di'ains ai'c |)hieed. It is clear, that when it is desifed to hold the wat(M' midway betwe<'n a line of tile a certain distance below the surface, that the (leei)er the 'tile are placed the fui'ther they may be apart, and Fig. 1 1.") illustrates both this point and the first. '"). 'idle iiiter\;d between lainf'alls sullicientiv heavy to ])i'o(luce percolation. In regions where the rainfall is both hea\-y and frecpient iiles need to be placed nearer together than wliei'e the revei'se coinlilioiis exist. Fl(!. lir.. Show ih.i; I he inlliiciic.. ,,1' ilKl ;iiic.- hrlwccn file ilr:iiiis on llii- rcljilinii ,,( III.' -rdiiiHJ wilier \,< llic siirl'arr .if llic m-.imiil. In general piactice for field crops it is usually siiflicient to place the lines of tile frdni ,')(» |.. loil fed apart. In tav(uable cases tiny may be placed ev< ii fnrlhei- apart than this and in special cases tlie\- nia\' be icipiired as (dose as ;'>() feet. 368. Observed Ground Water Surface in a Tile Drained Field.— in Fig. JKi is represented the observed ground AViitcr sui'1;icc in :i t ilc 'I raiiic(| ticM where (li<' lines arc 33 feet apai't, -'{ to 4 feet Ik'Iow \\n' surface and wlu^re tlu; sub- soil at ') to 4 feet and helow is sand. TIk^ slopes of tlic sur- face was oKtained hy horinii' wells with a 4-ineh au^cr be- tween the lines of 1 i ha iM I I he nieasnrenients were nuide 48 ^ y^ ronni '/ 1 V -S -^ t^ — 1 ^M fi ~ X ^'^'^-^-^-- L^_~^-^^iri' - ^ ~ ..— _ - n^-tL.-^T'— -^ L'.-_— _-_^^-- It if ' « n n 19 ^i> I<'i(;. in;. Show ii]^;- ll I)srr\i i| ciiiirdi-niMl ion <>( llic ni-(iiiiiil w:iIit siir- f-Ai-i- iij :i lili' iliMiiird I'h'lil IS iHJiirs mI'Iit a |-:'iiir:ill (il' ,X7 ilicli. liours after a I'ainfall of .^7 inch May 1-'), when th(! soil was already well saturate (, 7 1 1 IZ |)('r pdilioii, 'llif walcr iii(i\iiii;' :is iii(lic:it('(l hv llic \()\\<^ MlTdWS. 370. Movement of Water where Heavy Clay Soils are Underlaid with Sand. — WIk ii :i lic;i\v, close sdil is midcrhiid Avitli Siiiid (ii- t;'i"i\'('l llic iii(i\ciiiciil ol watci' towiird tlic lilci drjiins will he nliiidsl ciitirrlv 1 lii-()ii_<;li the sand when i\n\ (•(Hidit ions arc like those represented in 1^'ii;'. IIS. In such en.ses I lie rains |terc(dale \'ei'l icall v down iiilo I lie sainl and 'then nioN'e latei'allv to tlie tile di'ains, wlieriv it rises to enter tlieiui, as shown 1)V the arrows. r\N j^— ■ ^ ■— h'ni. UN, Shuwihi;- how lln- main Mow ciC walcr Id lines i.l' lilc may l)i,> llu'ini;;li a snlisiiil nt' saml when lliis is pri'scnl and near Ilif sui'I'arc. It is (deal' I lial under coiid it ions like t liese t he hea\' v (day soil al>o\'(* (lo(>s not deterinine the distance apart, drains should lie placed luit rather the sand stratum l)(dow. 371. Fall orGradient forDrains. — (JeneralK' drainsshonhl be _i;i\('n as niiKdi fall as I he condit i(tns will permit and 'tho _t;,i'adient should not he less than l' iiudies in !(»(> I'eet if this can he secured. ( 'ases will occur where less must bo acccjvtctl and then car(d'nl le\'(dini;' must be doiu' to sccui'O the largest fall a\ailahle. It. will olleii happen that the line (»f lowest i;i'onnd is (piite toi'tiions, iiiakiiiii,- the distance loiii;', and on this ac- (M»nnt niakini;- the fall small. l*'re(puMitl_y in such cases cuts a,crc)ss bends can be made by di^iiini;- deeper, in this way iu- creasiui;' the fall, as is sometimes done in st raiiihtening sti-ea.ms. 372. Uniform Fall Desirable. — Eil^^ort should ho iiiado to .secure lln'onj^liont the couise of a uiain or hitoral drain a uiiiform fall, .iiid iieNcr, whei'e it can well he a\'oidod, 209 change from a steeper to a less steo]) orade^ because if tliis is done there is thiiiiicr that sediiiieirt may lodge where the fall is less and close uj) the drain. The case is different where a change can be made from a small fall to one which is greater, for then whatever sediment is carried by the water along -the flatter slope will be carried down the steeper one. \m}m^^i^<^^^^^\i^^^j\^ ^^ J./'z/'S.-i Fio. 119.— Showing the construction of a silt basin. 373. Silt Basin. — In changing from a steeper gradient to one which is less the danger of clogging the tile can be re- duced by introducing in the line, at the place where the change is made, a silt well. Fig. 119, which provides still water in which sediment falls and from which it may be re- moA-ed as often as necessary. AVhere these silt basins may be small glazed sewer tile of suitable size may be used for the portion above the ground. 374. Size of Tile. — Tju- pnjjxM- size of tile can only be de- fini'tely stated when the: detailed conditions under which, the drain is to work are known, 'i'hey sh(»uld be large enough to remove in 24 to 4S hours the (wcess water of the heaviest rains likely to occur. ;;(>o 1. Wlici'c single (liiiiiis jirc hiid line iiiid llici'c in iii'ci;- llhir oi'dcr Id (liiiiii IdW plnrcs liirij,(M- lilc -.we rc(|iiir('(l illiiiii where ;i wlnde ireii is svsleiiiiit iciil I v tre;ile(|, liec'iiise in llie lornier eiises ;i liir^cr per cenl. of snrfiice wi.ih r IVoni snr- ]'. 'i'he nrens id" cross seetiim ol lile inerciise with ihe squares of I heir dininelers: M' tlieir diiiUK'lers are in 1 he r;il io nt" 2, -5, I, .'., •;, 7, their anuirt will be; iii the ratio (d" 1, !», Ki, lT), 'M\, 4!», hut as the 301 tVictioii on llif walls .if small lllc and tlic (list nrl.anrc dno to eddies set np at llie joints are uri aler in pi'opoi't mii to lli(> ainolint (d' water eairie(l the capacities of tile, rnnnini;' lull, iiu'i-ciise faster llian the s(|nares ni' tlieii' inside diameters. 1. I't is seldom advisahN to use tile smaller than '■'> intdies in diameter because so litl le \ariat ion al)o\-e oi- Ixdow a true <;rad(^ will lill t lu'in with sediment. ■). The size (d' mains niusi varv with the ai'ea tlioy aivto drain, with their fall and their leni;th. ( ". (1. Klli<'tt stales that where drains are laid ■'! feet uv more deep, and on a i-radc not less than :) inches in 100 feet, a 2-incli main not mole than .^00 feet lonu' will drain L* aci'es. A tliroo inch lil(^ will drain 5 acros. A four " ^'^ A flvo " " " " ''^" A six ' *^ A seven " " " " "^ lie speciti(s fnriliei' that a i' in(di main slhtuld not he laid loni;cr than :>(H) feet and a :; in(di ikH loni;ci' than 1,000 feet. 375. A Practical Illustration of Sizes and Distances Apart of Drains. — The sizes of mains and suh mains, the sizes of laterals, the^ len<;tlis of ea(di size used and the distance be- tween drains mav be most (dearly and brieliy slaited by (dtin^ a piactical example. The case selected is an SO acre Held laid out under t hedirect ion of ('.( i. lI<' li;i\r ;i ficc nnll';ill ;is slmwii ;il A, h'ii;'. 121, I'll t lie I' til ill! In end Ix'iH'iilli Wiitcr ns :it II. /f ^ "f -l';.:..i.tMMJ! y^y^ ^. - I I \ ■'•) li'iij. l::i. .\, |ir(i|irr iiiilli'l I'nr ili-alii; 1!, lin|pni|iii' lullri, i , |m..|>i'i n linn III lal'i'iil wllli iiiain; I >, liii|irii|ii'r Juiirllon. 'Ti* moid iiijiirv I'nnii rr('c/.iii<>' in cold el iiii;ilcs ■! lie |;ist H> li> lt'> led (d tlic iiKiin slumld <'iid in i.d;i/.rd sewer jije er in llie i-l;i/ed di';iiii lile; :ind llie onllel slieilld l>e ^iiiirded willi iiKisoniv iind euvcitMJ with w ^i'ii'l ilii; In Lee|» diit nili- inals. 3o;i 377. Connecting- Sub-main with Main. Wlicn-M siil» iiwiiii joins ii iiiiiiii llic' (•(.iiiircl ion should he iii;i(lo :il iin Jiciito iin^lc ns iv|n-csciil('(l at ( !, \^'\^. liil, riiilicr lliiin at rift'lit ;,i,u|,.s ;is a'l I). I f this is not (lone, silt will ••olhct on ae- cinnt (if the ic(lncc(| \clocity canscd hv IIm' nicdini; ol I he two sircanis. It is host in sncli cascH, to use tlio niannlac- 'tui'('(| jnnct ion t ilc 378. Joining- Laterals with Main. The jnnclion of a latci-a! shonld if po.-sihic he iMa. 379. Obstructions to Drains. The d( inand lor water by trees is so gicat that they must not l»e |iermitti'd lo ;j,row within :5 or I r(Mls .pf a line (d' 'I ile whi.di has wat n.'presenis two iMinelies of Muro|)eaii hirch roots tak(ii from (> inch tile whicdi they had complelely (dosed. A small r<»ol let entered ;it t he joint ,wlier(! it ft'rew, branched 304 iiiid cNiiniidcMl until ils tihrils collcrlcd so iiiiicli silt as to coiiiplcitclv close I lie drain. 'I'lie willow, ]>o|»lar, ("liii, larch and soft niajdc arc aiuoni;' tlic trees most likelv 'lo make tronhle in I liis wa v. Fl';. 123.— Udots of l';iir(i|U':iii l.iiili i-cinowd fnnn ;i Ci inch lilc dr.iiii, wliu-U (licv luul crrcclniillv cloiAuvcl. 380. Laying- out Drains. — Careful study slioidd he given to the best inanner ol' hiving out a system of drains; i he aim being to sin-ure the gi'catest talK the least amount of dig- ging, the least (Hit lay fls must he as few as possible and only as large tile used as are needt'd to (h* ihe work. I''l-2:> feel of 1 iiieli main and ;5,0iJ0 feet of 3 inch laterals are rcciiiired ; while hy tlie system B only 550 feet (tf 4 inch and 2,S-'50 feet <»f .") inch tile are ro(|nire(l to coN'er the liround so as to secure cinaldrainaiiv. It '''''' . , '''''^ '' '' ' '''''' 3 3 will he seen that in the sys- 1eni A I h( ■ ends (d' all t he laterals I !'a\-ei-se '>() feel of territory drained hy the }nain. When loiii^ I iiies of tile must he laid, !'e(|nirinu- more than one si/.e, three systems ha\c heen used : 1st, tliat re|)res(iit(>(l at A, Fi^. 124; lM, that at A, 125and :{rd,that at B, 125. In the second case, cover- — s* iui!,' an area 2,000 feet hv i>00 feet, above llie line aa, ''"'- ^^^-'r^o.yst^sU>vh,y infant !J,000 feet of 4 inch and N y„-^ S <"..■• 306 9,000 feet of ;] iiK'li iHo uiv laid 100 feet apart; Imt follow- iiipj tlic third system only 3,000 feet of 4 iiieli and 15,300 feet of .') iiu'li rcMidcr tlie same service M'itli a saving of about $3:5.00 for tile. Usnallv no siiii;l(' sy.'-itciii can l»c followcil hiil I lie sl(»|)e and slia|t(^ of the land will i'c(|uii'c a citiiihiual ion of two or more. 381. Intercepting Surface Drainage. — hi vcrv nianv cases wliei-e drainage is recpiircd the necessity is caused by lie collection of surface \ate!'s from llie snrfiMind- ing higher lands. 1 1 nuiy lien be ])ossil)le iii such cas(>s to avoid a hirge part id" the expense of under- drainagc by inti-rcepting ind controlling the sur- face waters, (collecting hem into surface drains and leading tlu>m away as represented in Yig. 126. 111 this ease the water is Fui. ]26-Motliod.)r intorcoptinsr snrfac><'""*'<'l^^'<^ i"^<> '^ SUrfaCG (Iriiiiiajfo. A, B, siirfiico ditcli. cFi-oin,| jf ,,1, lw>f, ,,•(> if- vciches tliP Irrifjation and Draiiia^'o.) HIH II 01 roU 11 1 ( .U IK S UK. low area and is carried around on tlu^ 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 t(» ])revent the con- struction of underdrains. 382. Construction of Surface Drains.- -Wh(>r(> surface "waters arc lo he handled as in (381) it can nsually best be done by const nicl iiig broad and coinparal ively shallow runways, wliicdi can be kepi in periiianeut gra.SxS, the width an:d slope (d" the ditch heiiig such that a W(agon and mower c:au readily be driven along and across it. Such waterways slu)uld usually be 1 to 2 feet deep and 10 to 15 feet wide r,07 witll .-ides slo|»iii,i;' i;ciill_V 'in ;i ll;i( ImiII(iiii wliicli ciiii carry a coii'si(l(M-:iM('V<»luiii(' ol'walcr slowlv -villKml, Immhi'' eroded. 383. Intercepting the Underflow from Higher Lands. — In a verv lai'iic iiiiiiihei- (d' eases lands rei|iiire drainage he- cause (d' tlie uudei-llow ni' waler t'roiii the adjacent Idiiiier Jand in th(! manner indicated in Yvj;. 1^7. Tu such cases, Kl(!. 127.-SlHiwiim li.iw liiirs ..f lilc in:^\ br |ilai-,.,l ,il A ami 1'. lo iiilci-- <-,'pl llic iiiHlcrMiiw I'mhii tlic hi^licr ImihI, when (h'ains are hiid ahmi;' the Idu't el" tlie hili hehiw t ho ground water surface, as I'epresentecl :it A and I!, nnudi ol tlio see|)a^c \v'a''-'-'MiiMk,,iiuijui;»-^ *^}^ I'll.. l:^N. Mclhoil ,,r (liMiiiiiij; sinks. leadin;^' to a coUeetini;- hasiii, I), whicdi is eonneetod with th(^ well I rem wliieli the water is dischariicd thi'oui;h tUo, pump into t he drain ( '. I I' the area is snndl or the ea|)a('ity of the pnnip lari^e the watei' may diseliai'uc direetly into (he well, \liieh ma\' he pro\'il' Ininls nf llic Illinois Anl'if'lll iiriil < 'oiiiii:iiiy, Kdiiliiiil. llliiiiMs lAfltT .1. (). l!;il miles (d' main ditch ;'>(> to CO feet wide at the top and S to 11 feet deep. Leading into these mains there are live laterals 30 feet \vide and 7 to ',> feet deep, the wliolo system (Mnhvaciug 70 miles of op(Mi diteh for the purpose of pro\-iding outlets for nnder- drains. 311 CllAl'TKii XV. PRACTICE OF UNDEEDRAINAGE. Tlic I)cs1 work ill iiimIcimI r.-iiiiliia' '"in <'iil_\' Ix' done l>y \\\c iiiiiii. who lijis ;i t lioroii<;li ,i!,riis|) ol llic principles ol 'llic iirl, iin and of what coiisl il ulcs I lioroiii;lily nond dclail |n'iicl ice. "K!. i:!l. Slinwinu' rnniis III' (lr:iiM,-inc ti 386. Means for Determinimg Levels. — As a gxMieral rule I lie laviiiii' out (if a svMlcin ot diains should oidv \)v ai- tcuiptcd with i;'oo(l iust runiculs, two of \vlii(di arc rcpi'c- scutcd in l^'ii;'. i;!!. Where a i^ood drainai^c levcd cannot be had the: best, sul)^|^it utx' is tlu^ water le\'el, one forui of which is i-e|)i-esente'd iu Fig'. 131 and auotlier in Fig. 132; wlii(di consists cd' a piece (d' gas |)ipei ahoul ;! teet long nionnted on a standard and pi'o\-i(le(l with two ellvows into nhich ai'c cenie:ited I ,\'o pieces (d wal er gauge* glass. When th(^ instrument is filled with watei- the suidaees in the two tubes stand on a level and can he used to sight across. To nio\(' 't li(^ iust run lent (dose the ends (d" t he t uhes with cin'ks. As a. sul)Sititiite f(U- the gas pi|)e a piece (d" riihher luhiug may bci nsed or a piece of garden hose. A less i-eliablcj levcd can he iinproxised hv {irrauging an arm upon a standard upon which a car|»eiiter's Ie\'(d may be set. ()r a still more crude le\(d iiia\" lie made Irom a r,i3 I'Ki. i:--. Show in^; orjc form of waler lovol. (•iii'|)ciili'rV s(|iiai'c iiioiiiitcd (»ii ;i liori/oiilal arm on wliieh a pliiiiil) hul) is suspended, witli w'hicli to set the S(]iiai-<' with its long ariii' level. 387. leveling a Field. — In (letcniiiiiiiig I lid dilTci'- ences of level, in ditfere-nt parts of a field it is desired to drain, tlu; simplest method for the inexper- ienecd person is to lay out the field into squares of 100 or more feet, driving short stakes at tin; corners. Set the iiisl niment at a, Fig. I'i.'j, midway between the stations I-l and and i-ecord I lie ; cad in; tluf targel placi'il iipun i he stake at J-1 in the tahic in llie eolinnn heaon stake 1-2, when its distance below the level is found lo be :',.H feet and is entere(l in the column headed "fore-siglit." This shows that the ground at 1-2 is 4 ft. — 38 ft. = .2 ft. higliei" t hail slat ion 1- 1 . Ill the column headed "Klevaticni" the fiist stalion is given arhil rai-iiy a higlit of 10 feet al)(,\'e an assumed da'hiin |)laiie to a\did minus signs. I he le\(l i-< now trans- ferred to It and llie dislance of \-2 heloiv the inslniiiKMlt found to he l.l' feel which is entered in t he cnj iniiii "back- sight" as b(d'ore. 'riirniiig now upon I .'!, its reading is found to be 4 feet ami this is enlere(| in the column "fore- sight." 'J^he difference in level between the l)ack sight and fore sight shows the difference in level between the two stations 314 ;iii(l is placed in the ('(iliiiiiu licadcd "dilVcrciu'c." 'V\\c first diff('i-('iK'(^ added '(o the dahiiii, 10, oives 10.2, the hif^lit (if stati(iii 1-2 ah(i\-e Ihe (hilniii, phiiie. The seeoiid differ- VI V IV III II I l'"l>:. l:;o. SlidwhiK iiicIIkmI (iT li'Nclhi;; ;i lid ence, .2, added to the eU'vaitiou of station 1-2 f;ives 10.4, tho oloA'ation of station T-3 above da t inn. In this manner the h'\('I is nidA'ed from station to s'lation nnlii e is ii'aehed when it. is transferred to I" and ha(dv sia,'hts and fore sii^hts taken as l)(^fore, and entered in Ihe 'tahh' to connect the first lino of observations with the new one just be^un. Proeeedinii' as Ix'fore tlie hn'el is nio\('d from f to <;• and then thi'ouuli h, i, j, k and I '((» ni and so on nntil tlie tiehl is all e()ni|)leled. When |)roceedin<;' from hi^i»,her to lower leviil;if a slojx- as this hut the |)i'iii('i j)l(' is Jio less 'tnu'i for ])oinf2,' so siiiiplv stale*!. VI V rv m II 1 l<"jii. ];!:>.- Slli)winj4- :i syslclii <>( lilr (li-:iilis Inid oul (Hi llic leveled field of ViH. V.'l. (I'"niin I rrii;.-! I hni and I )raiii:i,i;e. i If siu'li a field is to be di-aiiied by ])laeiii,i>- bilevals 100 feet apart about the maximum fall for tliem, and the mini- mum amount of tih; anlMin;i.uc. I 390. Laying^ Out Drains. — W'jicn the positions of the mains and laterals have been decided the next stc]) is to mark tlie-n. with "i>rade ])ei>-s" and ''tinders.''' 'I'lie g'rade pegs ai'e shoi-t, dri\'en secnrcjv into IJie oi'omid jnst 'to one side of the intended ditch, and are placed at regular inter- vals apart. To one side of the grade ])r'gs ai'c placed longer ■ones called "finders" ii|>(iii which is to be recoi'de<| the dejitli liclow the gray llic ticid level iiili', the I'esiills heiiii;- recorded in ;i 'l;iMe eiilliiii;' for two more coliimns when worked out than M'cre needed in th(> field work. 'Idiese are indicated in 'the table below: Tabic s/ioivi/ig Field JS'utea fur ) .11 10.5 7.48 3.02 250 3.87 3.82 .13 1(1 i;3 7.f) 3.03 H(M) 4 3.t>9 .18 10 81 7,72 3.09 950 4.25 3.83 .17 10 98 7.81 3.14 400 4 OS 4 1 .15 11 13 7.96 3.17 450 4.0.) 3.9fi .12 11.25 8.08 3.17 500 3 97 3 95 .1 11 35 8.2 3.15 550 3.75 3 97 — 11.35 8.02 3.03 600 3.74 1 11.3(5 ».44 2.92 III 1^'ii;'. !.")T, whicli is a |»roliie of the data in the tabl(i showiiii;- the outlet of the drain at A, the tirst. stake at () and the second al .M), etc., up to (iOO, both the lines (d' i;i'a(lean(l tliC'daluin plane arc shown. ()ii each niiinbered stake is <;i\-en the de|)tli of the ditch below the lop of the i^rade pci;', and below the peii' has been set the lii<;lit of tlu^ botfoin (d the ditch aboxc the datiiin plane. Since the oiiilet in this case is 7 feet abo\'e dattini and the surface at COO feet is 1 I.IU; feet the total fall is 11.30 feet — 7 feet 4.30. lint if it he depth (d' tlic ditidi at tlici up|»er cud is made 2.!)2 feet the available fall will IIh^u be 4.30 feet — 2 92 feet== 1.44. SiIlc(^ the dit(di is 12 times 50 feet loui;- the fall will bo J 44 -y^ -- .12 feet i)(>r fiO feet. or .24 feet per 100 feet. At eacdi 50 foot station tlien the bottom of tlu^ ditcdi abovo datum plane will be found by 310 acldiiii;- .12 fool, lo 7 I'cct, wliidi is the Iiciiilit of t lie oiitlot, for tliJli of the .-ccoikI sliilinii; llicii . 1 1! feet iiddf d In this jiiiN'cs tlic tliii'd station and so on, 'thus: 7, 7.1i', 7.24, 7:M, 7.4S, T.CU), 7.72, 7.S4, 7.U(\, 8.08, 8.20, S.;52, 8.44. 200 250 ^^ 50 100 "0 350 *^ 150 500 650 «00 £^--'="^'-^ 2-s^^-^--.;^ VS^ y^ ' V'-'OAtOmCplane"/ t; ^^'■'^'-Ssz^-^"-^ ^'s iriJ-^ ' Fn;. 137.— rnililc (if diicli sliik.'il rcidy fur ili^rKiii;,', witli dcpllis for the (lilcli ;il llic scvci-.-il sliilioiis. If these (Miinihcrs arc suhtractcd froMi the hiiihts oi tlie surface of the ground ai tho respective ])hices tlie differ- ence will he the de])th flu* ditch nnist he du£>' at those places, and the figures which are placed upon the finders for the instniclion of the men in diiiiiinii'. These fi<2,'ures are given in tlie tahh' in the colnnin "(h pth of dit(di." The ex])erienced (h-ainage engineer with acciwate tele- scojx* level makes the details of lev(ding, es'tahlishing the grade and mai-kinii' the gr^wle pegs simph'i- than here given hut it is not safe for a farmer with a (dieap h v(d to follow liis methods. 392. Changing from One Grade to Another. — It may liap- ]ten in hiving on! the ditch that it is impracticable to fol- low a single grade on acconnt of ha\'ing to dig too deep in some ])lacers or of leaving the lih' too close to tlu^ surface in others. Suppose in the last profile (391) the ditch was to he ;")()() fet^t loiii-cr and that in this 500 feet there had been »20 321 it rise (if lull ', l."Il>. \\ \\c\-{' llic ditch lillisl lie l.."> to Ti feel :iiid icceivc a (i inch lilc, as shown in l<'ii;-. I I I, il iniisl have a wiihli al- I he lo|i of I .'i |o IS inches. 'Idle dilcher i^ trained lo cut the walls slraii^hl vvilli an ('\'cii slope lo. llin lioilldin so as to^ lea\'e a slrai^'lil liin^ aloiiii' Ihc hotloin lo reccixc I he I ih'. In I'^ij;'. NO it will he seen llial loiir iiieii arc workinj^' in line to coinplclc. Ilii; dcplh of the (lit(di w lii.di is !.:• feel at llic place. 395. Shaping- the Bottom and Bringing- It to Grade. In I^'i.i;'. I I I the man in llic forc^TouiK] is iisin^' th(^ tile hoc to (dean out llic last loose earlli and lo hrinii' ihc holluin to }i,'r'ad(^ and proper shape to rccci\'c ihc tile. The uradc is sccnrcd hv stretching;' Ihc dihdicr's line tiii'lit, and on (ho slant the holtoin ol' llio dilcli is to ho i^'ivon, and ;it a known liii^hl. aliovc it. It is then oiilv neccssarv for I Ik c\pcr- iciK'cd mail to nsc a mo.'isnriiii;- rod to secure the depth and ;;rade desired. '.\<-)'\ r>24 W'lifii llic i'('(|iiisilc skill :iii(l jii(ii;iii('iit li;i\(' luil been :ic(|iiiic(l l(ir lliis work llic 111:111 is proNidcd willi ;i. iiicas- iiriiif;' stick willi ;i slidiiiii;- iinm wliicli c.xIcikIs jiI, iMi;-lil, iUl|j,"l('S to tile itid :iiid loiii;' ("ii(iili;li li> rciudi the li'mdc line. It. is llicii (iidv iicccssnrv to liold llic Vi^A n\- "ditclicr's s(|ii:ii'c" |iJiiiiil) Id kiKiW" wlicl lici' llic ditch li;is the (l('|»th desired. 396. Placing- the Tile. When llic dilcli lias boon fiiiislied Ihe lih' ;ire laid with the tile hook, ns vc])i'<'S(nit('(l in Fi^. I I'J. With the aid n\' ijiis t()(d lliev are placed ra])idly and acciiralclv withdiil er e(|o(.^ thev slio\dd lit s(|iiartdv and (di.scdv lhr(Mii;ii the ciilire circiini Ici'cncc and it nccessarv tile tee inucdi \\ai|tc(| jo |ieriiiil ol lliis must he discarded. Sdiiie |n(dcr to place the tile with llic hand, standing;,' in the ditch npon lla 111, cii\-eriiii;' llieiii as rapidl_\' as laid with ■I to (') inelics (d' earlli, lakiiii^' care Id' ^cl il I lidrdni;iil_\' pa(d jnnclidii should he made and lile ciKaiuii laid in I he latci'al to pcr- niil the iiiain Id he parllv lilled. The main inav then he, carried on iinlil the next lateral is reached, when tllis should he coiiimciieed as hiderc. ('are should he cx( rcisi d not, to lca\'e the upper end (d an untinished lim* of lile opiMi tor lica\' V rains to wash mud into it . 1 I' I he line cannot 1)0 linished lud'ore the rain the end iiiav he iiuai'tled hv t losinii; it with a heard, hri(d< er hiiiudi (d t^rass. 'Jt 320 n^: >« 028 397. Filling the Ditch.— After the tile have been placed and covered with the first hiyer of earth the balance may be put in bv any convenient niethod. A common and ex- peditions way is re]n'esented in Fii>-. 143 where a plow is drawn by a team at'tachcd to a Inuix evener. For tlu^ finish- ing the ordinary road grader makes an efficient tdol. Still another ii eth()(l is to iisi- a light board scra))er pro- vided Avith handles to l)e held against the bank of earth, which is drawn into the (Hteh by a team on the opposite side drawing from a ro])^ and l»ackiiig when the scraper is emptied. 329 EURAL ARCHITECTLEE. C'lIAPTER XVI. STRENGTH OF MATERIALS. A knowledge of tlic ])iiiK'i])les ooveriiing the strength of materials is helpful jilong uuiny line,'^ of farm practice and particularly in the construction of farm buildings. 398. A Stress. — When a })ost is jilaced upon a foundation and a load of two thousand pounds set u]>on it the post is nndergoing or oi)j)osing a stress of two thousand pounds. AVheii a rope is supporting a load of one thousand pounds in a condition of rnst it is subjeoii to a .sfr(s:< of one thou- sand i>(;unds. The ioists under a mow of liav are subjected to a .str< .ss measnied 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 strevss is great enough. I'hcse are: 1. A crushing stress, where the load tends to crowd the molecides closer together, as ndien kernels of corn are crushed between the teeth of an animal. 2. A stretching stress, as wdiere a coi'd is broken by a load hung upon it. ■K A twisting stress, as where a screu' is l)roken by trving to foi-cc i! into h;ir(l wo-id with a screw-driver. 400. Strength of Moderately Seasoned White and Yellow Pine Pillars. — Ah', ('has. Shaler Smith has (h^duced, from experiments c(jnducted by himself, the following nde for :];50 etreiigiih of iiKHii'iatcly .-ca-oued wliito and vcllow pine pillars : Eule. — J)ir/i/<' III,' siiiifirc of (he length in inches In/ the square of the least thickness in indies; multipty t lie quo- tient 1)1/ .004 and to fhis product add 1; then divide 5,000 hy this sum and llie rcsull is llie strenqth in pounds per square iiirli <>f aira nf llir cud of llie post. Multiply this result hy the . If the boaid in ipiestion is 4M iiudies long and *I inclics wide, it will, in breaking, tend to re\dl\c about ,lic center (d the line, .")-'», and the upper lliree iiudies will be put under the longitudinal strain, bnt according to (402), is capable of withstanding 3 K 10,000 lbs. = :50,000 lbs. without l)i-eaking; bnt in carrying I he h ad at the end as shown, this cohesi\'e pi wer is acting at the sIku'I end of a hciit lever whose mean lenglh of power arm is one-half of 4-5 or 1.5 iuidies, while the weight arm is forty-eight iiiolios in length. It should therefore only be able to Indd at W lt;)7.5 jionnds, for as P P A = W K W A, we have 30, 000 X 1-5 = W v 48. whence W = 1^1^ = 937.5 jbs. A\'hen a l)oard, in cNci'y respect like the one in A, Fig. 144, is placed under the conditions re])resented in either B or (\ Fig. 144, it shonhl recpiire just four times the h^ad to })reak it, because the board is ])ractically converted into two levers Avhose jiower-arms renniin the same, but wliose w( ight-arms are only one-half as long each. 405. The Transverse Strength of Timbers Proportional to the Squares of their Vertical Thicknesses. — ( 'ommon ex])eri- ence demonstrates that a icu'st restini!' on ediic is able to ciiri'v ;i imicli iiTcnt*'!' load tliaii wlicii l\iii_s hecome ])owers acting through theii" res))ective power-arms V, P, whose mean lengths are, in the 2x4 joist, one in(di, and in the 2x8 joist, two inches. .\ow we ]ia\'e PXP A = WX W A, and sul).v siiltsi i'l 111 iii<^' iiiiiii('ii(-:il \;ilii(s in I lie ciiHO III" I lid L'.\.S j((isl we i^c\. H l(»,()(l() ti VV 10, or It; 10, 0(10 10 W, iiiiil W 10, 000. I I. I liiis ;i|i|)r;irs I li;il I lie londs I lie I wo ji li-'l s will cjiitn' iirci lo ciicli oilier ;is l,(»(l() is lo M;,(HM), or iih 1 is lo I; l>iil, S(|ii;iriiii;' llic \ciiic;il lliickin'ss of llic I, wo joisis in (picH- I ion we i;c|, for I lie ■J,\ I joisi I I 10, ,'1111 1 fur llir '1 ,- H joisI, H H <;i; l)nl. \i\ is to (II IIS I is lo I, which shows Ihiil. t.h(^ iriuisvcrsc! sl.i'cni^l lis of siini I.I r I i in Iters jire proporl ioiiiil lo I he S(|lliU'C8 ol I Ik 'I r \ crl iciil d iiiinelei's. 406. The Traiisvcr.se Strenjith of Materials Diminishes Di- rectly as the Leiij^'tli Increases. Ii \ ilMie rejidilv seen froin ;in illS|iee| i I lie oilier (lillieiisions reiii;iin 'llie s;iiiic, lenuilielis llie loiii;' ;irili of llie lever, while llie sliorl ;iriii re Jii.'iiiis niicli!iiii;('(l ; iind since llie lorce (d' cohesion reiii;iiiis ninillel'ed, llie |o;(d iiecess;ir\- |o (.\ercoiiie || iiiiisi he less ill proptu'lioii ;is llie lever iii'iii upon which il ;icls is incrciised. 'IMiiis, if llie l'\S in l^'ii;. I 1.') is nuide 20 iiiclies lon^', wo sJiiill li;i\'e, I* l'.\ W W.\ Mild hv siihsl il III iiii;' llie iiniiieric.il \;iliies we n'cl, HO, 000 "J W '20 W H,0()0 iiislriid of Mi, 000, ;is found in (405). 407. The Constants of the Transverse Brcakinf^- Streiifith of Wood. Since llir l;i\vs >/i\i-\\ ill 404, 405, imd 406 ;i|.))ly l,o iill kinds ol niiilcriiils, il rullows lli:il, llic ;i<'1iinl l)rc;ikiii^ •strcn^lli (il ils |»rc;i(|||i, nriill i |)l icy j^r;i(ln;illy ;i(ic( n ilcteiiiiiiic(| hy ex|K'riiiietil, iin breadth in inches - Constant in inches ) Length in feet. What is the center breaking load of a white pine 2x1^ joists 12 feet long^ Dill 12X12X2X450 ir>onniK Breaking load = — -(^-^ = 10, 800 lbs. What is tlic l)icakiiii:' lna- tlu- jois-its, laying the in- liereutly weak nieces in 2)lac(»s wiiere little strain can come upon tlieni, juuch saving of Inniher may be made. a Span 10 feet. Span 12 feet. Span 14 feet. Span 16 feet. Breadth. Breadth . Breadth. Breadth. fl-9 2 in. 4 in. 6 in. 2 in. 4 in. 6 in. 2 in. 4 in. 6 in. 2 in. 4 in. lbs. 6 in. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. 4.... 210 4>>0 720 200 400 600 IV 344 516 1.50 300 450 6.... 510 l.O'-O 1,620 450 800 1,350! 386 772 1.158 336 672 1,008 8.... 9(50 1,920 2,8S0 8(J0 1,600 2,400 686 1,372 2,0.58 600 1,200 1,800 10.... 1,500 3,000 4,500 1,250 2,,')0i) 3, 750 1,072 2,144 3,216 936 1,872 2,808 12.... 2, 160 1, 320 6,480 1,800 3,600 5,400 1,544 3,088 4,63: 1,350 2, 700 4,050 Breadth. Breadth. Breadth . Breadth. 4 in. 10 in. 12 in . lbs. 8 in. 10 in. lbs. 12 in . Ib"^ Siu. 10 in. 12 in. lb.s. Sin. 10 in. 12 in. lbs. lbs. lb..-. lbs. lbs. lbs. lbs. lbs. 4.... 960 1,200 1,440 800 1,000 1,200 688 660 1,032 600 750 900 6.... 2, 160 2,701) 3,240 1,800 2,2.50 2,700 1,5U 1,930 2,316 1,314 1,680 2,016 8.... S,S40 4, SOD 5, 760 3, 200 4,000 4, too 2, 744 3,430 4,116 2,40U 3,000 3, 600 10.... 6, 000 7,500 9,000 5,000 6,250 7,500 4,28^ 5, 360 6,432 3,744 4,680 5,616 1<5.... 8,640 10,800 12,960 7,200 9,000 10,800 6, 176 7,720 9,264 5,400 6,750 8,100 413. Selection of Lumber to Increase Carrying Capacity. — It is ])().-y giving attention to the luinher u^vi], selecting tlie e\i(lently strongest pieces for use where it is known tlie heaviest strains will come. Some- times a joist sh(»ul(l he reversed or turned the other side up in oi'(hM' to eiiahh' the j»iece to render its highest service. In the arrangement of joists under a hay bay or granaiy, where hea^■y loads are to be carried, the cross-grained pieces and those Avith exce})tionally large knots shouhl l)e well dis- tributed among thei stronger ones, making the evidently weak come Ik twecn those evidently al)o\'i' the aveiage in s4renuth. 414. Braces. — There are two princi])les iniderlying the use of hraces to give greater strength to lumber, 1. That of equalizing the load, making it fall more heavily upon the 339 S'tro'iiger iiiciiiIk'I's. -2. 'I'hnt of sli(irl(iiiii^- t lie tree span. The first l-i\sli is illusti;it('(l in tlic- rows of bridging used between tlie joists in a floor. In these eases Avheii a weak inembi'r is hridi^cd between t >.vo stronger ones a pcrtion of its h)ad, beeanise it viebis soonest, is tbrown by tbe bridging upon file stronger, and stiff'tr lloois are tbus secured and the breaking of intUvichial })ieees ))revente(l. Jhaees in nearly ;dl eases are, in prinei])le, either posts ov else tliey are si'spcnsion rods wliicb allo.v tbe strength of 'thei nniterial to be utilized unafl'ected by tbe ]»rinei})le of leverage, tbe strei-s Ix'ing a direct ])nll or a ])nsb, bimging into ])lay tbe fnll tensile or cinsbing strengib of the nia- teiial. To sboi'ten ibe fi'ce span of an iS-fViot joist or timber two feet at eatdi end by means of suital)le braces is in- creasing its cari'ving |)(iwer '2X.~> ])vv cent. it is nincb more inipoitant to pay strict attention tO' these nnitters of strength at the })resen'r time than in former years both becanse bunber is higher and often (d' mncli inferior ([nality. 415. Constructing Timbers from Two-inch Lumber. — It is often not oidy .'lieaper bnt better to construct SxfO or 8x12 heanis by pntting togetbcr I'xlO oi' l^\12 ]dank, the timber 1 bus const 1 nctedcften being stroiigci- tban a solid ine would be beicause weak places are; more likely -to be distributed so as to give a greater nu>an strength, it is of coui'se not true that a fOxlO so madc! would b(^ stronger than a solid timher (d the same dimensions if jxitli were (d' hiubest erade 416. Form of Barn Frame. — During ])ione(r days, when saw mills were none or few, it was mucli easier to secure the needed stabili'ty for a barn by hewing a few heavy timbers of suitable length and putting them together with I)races than it was to use the 2 inch bunber now so comnmn in the frames of dwelling houses. Since tbe old type ui' bai-n fi'anie was de|)ended upon to 340 liivc the ii('('(l('(l ^tahility, little ov im sii]>|)(irt (-(.ii/inif tVoin the sidiiiii' in- shcctinii', it \v;is iicccssnrv to use lai'iic timbers ^^'^V^C^,.^^ Vu:. 1-17 and to fVaiiic llieiiL toiicther and hracc tlicui vcvy securely iiiakiiiu' a stnictme eostlv both in material and labor. 417. Plank Frame. — The hii;li j)riee of hnnber has led to an etioi't to imitate the coiistriietion of the old lie'vii timber frame barn in the eoiistniction of essentially the same type of frame but iisino' plank spiked together instead of' tim- bers. This type of frame is represented in Fig'. l-iT. The frame so made is strong and not as ex])i:'nsive as ono of heavy timbers at the ])resent ])riees but it is neither as sim])l(^ in eonstnu'tion nor as (dieap as a frame for most barns can be made. Now that the eonditi()ns .\iii:'li made the heavy timber frame a neet'ssity ha\'e disaj)]>eart'd there is no need of imitating it by splicing Inmber. 418. Balloon or House Frame. — The reason for not ad- hering to the ^)ld ty|)e (d' barn frame is beeanse ir j)ermits of no advantau'e beini>- taken of the inherent strenuth oi the 341 \\ I'fii the .r\v.. incli Imiil,,.,- used in il,,. m|.,„1- f ;""-'«■ >". i-.» ..».i" ,,:';,;,":; J''';;';<'^l<-Ha.lsa>HlK>sJal.orarom,„ire(l '"^'"^'^■^^ \\ liciv I he l)iiii(iino- is |,Mio. .,11,1 |)i-,,.,,| s.. .. . r • 1 419. The Round Barn Framp 'V\, 21 :542 will Ml I li(* hiirii i-i iii;i. Ill lliis Ivpc ..f li;ii-|i iKil oiilv is lli(> .siiiiillcsl iiiiinlx r of sIikMiiiv ii'(|ii i red lo forin llic (Milcr I'm; I I!i .Sliciwliiu rrniiic ninl yciii'riil |>laii «\ ii <■> iliiilrirjil l):irn. A, ili-lvrwiivM licliliiil ciiillr- n, r I iill.'.v; ( '. |p|,i H'.pnus I'.ir rnillc. |):irl of Ihr rr:iiiic lull siii;illrr si/.cs ciin Iw used, lor llu! I'cjisoii lliiil cNcrv Ixcird in llir sidiiii; is ;i |H)rli t :i li()(>|> wliicli iiiiikrs s|)r<'!idiiii;' iiii|M)ssilil(', wliilc :il I lie s;ini»' tini(? \\\('\ Jirc iircliccl iii^ninsl llir wind :iiid l;ikc ils |>ccssnre willi 11 cnisliiii^' si rcss. Willi l)!inis uf lliis lv|»(' L*\l slnddiiii;' scl li feci jip.irt, li;i\r !iiii|>lf slrcni;lli I'nr :il| diiiinclrrs n|> lo 1<> feci :ind li\(> sl.ilddini;' is l;iruv cnoiiiili for Iciriis |(> lo 100 feci in diaiii- vlvv. , : , .1 un ciiAi'Ti-;!; xvii. WARMTH, LIGHT AND VENTILATION. CO.N'rii'ol, (>]■ risM I'lsKATIlKK. Tlic life ;icli\ilics iiiiiiii fcslcd in llic ;iiiiiii;il Ixxly involve I lie. <-i)n!l innons ni;ii nl< niinrc ul ;i liiiin ul clicniKMl <'ii:in^'('S wliif'li ^'i\'<' ri-'" \<> <.i' )ii;iinl;iin llnni. I ln' c cln'mic;!! cliiin^'cs, like ;ill oilier-, r;in only licf^in ;il- ;i cfrliiin Icni |K'r,'il nrc ; Itclow I hi-, I licv crjisr; wi'l liiii ;i ccrl;! i n i';in;_'<; I Imy p> torwiinl ;il n(irni;il i;itt'.-,; iihuN'c llii-, Iciii)hi';i hire itmc- lions occur wliidi in|(||Vrc willi llic lilc ;ic'l i\ il ic-, ni;ikiii/^ tlicni :ilinoi'ni;i I or c;ni-in^' llicni lo cciisc. 420. Automatic Control of Temperature. 'I'lic ;uiiin!il l)0(|\' is so consi ihilfil 1 1 nil wil Inn ccrlii i n I i mils I lie nornnii lcni|icr;il N n • of llic l)o iiies; d| ihe liodily rnnelions resiill in the iicnei'a- tidii (d more or less liea! and since the leiiiipei'al lire must he k< pt held A KM) td !(»."» it is clear ihal no aeti\-e animal shdiild he surrdnnded hy lemperalnres as hi_i;h as rlie n-or- mal lemperatiire of the hdd\. ()ne of the main oh)ects of the circniatioii ~>( the hli.od tliron^h the skin is to Idwer its teinperal III e Ixdere it reliirns td the interior, so I li.rl those parts may he codjed. In diii' case we hecdiiie niicdni fdftahle in a. siirroiindinii' tempeialnri miudi ahoxc Ti! ' and I he same is line ot onr domestic animals. Slahles should then as a rule liaxc a temperature lower than 7-' \'\ hill how niiudi innst depend upon cii'cnm- stanees. The rii^lil surroiiiidinii' temperature is that which will permit the necessary loss of lie;it from the hod\- with (Uily the normal rate vine, steers or ^heep, as wtdl as in^ilch co .vs, will do helter in somewhal co(der (piarters hecanse ( 1 ) the lariicr activity necessary to |ti'odnce the extra assimilalion desire or hiiildiiii:- can he so constructed that all I h(^ iK'ut it con- tains will he pre\'eiited from escaping. If it ]H ko.pt above froozin^ through c(d(l winters tliciH^ must be within \\\(i on- c'losnrc a source of heat. So, too, no (enclosure or hiiildiii<; can be so tlioronf:,hly made as to cxcdnde all heat anv I lie licjil which ♦'liters il. thr(»ii^h ithc hothMii. 'V\h' saiiici c'cMiir iliirin^' tlui suiiiiiicr <;i"<»\\s j;rii(lii;illv wiiniicr :is thci season jkIvjiju'cb iiiid is (iiilv i'('hili\cl V codl Ix't-ausc pari of I he heat ciilerillg aboN'c is ('<»ii\'c_v('(l through the lK)(t(tm into the cartli, to re- sl(»l•l^ that whii'h k('|)t the ('('Ihir Irdiii frcczini;' dnnii/i,' tho ^\"illt('l•. The '\';i)'iii slaMc which (hies iml Ircc/.c is kept s<) by thci heat of the aiiiinats sheltered, and the waciidy coil- stnictcHl ir'itabh' (Hily makes h'ss aiiiiiial iicat ueech'd to main- tain the teiii:pei-al iii-e ; I he >.\alls ill I heiiiseh'es :ire iml warm. So, too, no li tiie sani(> walls, but from the opposito' direction. To secni'o either (d' theses (mkIs 'two essentials (d" constrnc- tion innsl. be obser\e(l. The walls iimst be as nearly air tiji,lit and as |)o(ii- conductors of heal as |»ossible. In the conHtnu'tioii (d" a warm house, a. warm stable, a cool i('(i house or a, cool curin^i,' room lor (dieese t he ,i;reatest at teiition should be ])aid 'to securin*;- air ti^lit walls because, no mat- ter how ])oor condni'tors are ]nit into tlu^ walls, if there are craeks ahont doors and windows or open joints in the wall, the effect of wind ]n*essnre and wind suction will be 'to change 'the air in the room so rapitlly that it will be diffi- vult to keep il either warm or cold. 425. Solid Masonry Walls. — Stone basements with solid walls are sniliciently warm f(U' stables but they are too good conductors (d" heat tside teni])eraiture must be mamlained at 72° V. Hollow brick walls, wlien plastered with a close textured mortal-, throui;h wdiicli air cannot ])ass readily, are 347 Keller lliiiii s(]|i.| iii;iMiiii'\ liiil ;ii'e iKil ;is wjiriii ;is lliese Well (MUiwti'ueted of jtll wood ;tiii' a hriek wall plastered with (•(larse liiii'( iiiorlar (inl\\ is one of I lie pooi-est wliicli (nill be used eillier to relaiii or exclmle lieat. Its porewi are so upon lliat the siiiall("it wind pressure (»r wind siic-tioii causes a ready ilow of air lliioiii:li cNcry porlion of I lie wall, (dian^iiiii tlu^ air ol 'I lie room (|iiickly. l^'or cheese ciiri Hi;' rooms, wlieie llie lemperat lire is to bo held down by 'iieaiis of cold air diuMs, masonry walls, (weu when iiiiade air liulil, are not snitajile because^ they ar(i such od conductors of liea'l and so massive that they tend to maintain a nnirorm tem]»eraliire in siiimner somewhat hitiher than the mean ol the air outside. 426. Hollow Masonry Walls.-- -When stone or brick walls are miide liolldw they beeoiiie miieli wanner in winter and cooler in suninier than vvdien built solid because; the air is a niiudi p(MH'er con or 1 feet of the wall hollow for the reason that the cellar will be warmer and hence the lloors under the living rooms al)o\'e. 427. Brick Veneered Walls. — Wlum; brick arc 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 paints ing are avoided. It do'Cs not do 'to (le|H iid u|)on the bri(d< for wai'inth, how- :U8 cA'cr; llicv siiiiplv Inkf the phicc ol the ^i(lill^• :iii(l |Kiint. WluM'ci llic li(»iis('i is simply sheeted (nilside willi ('(umiioii boards and \'eiieei'ed with hi'icU, and then hillu^'d and })h>st(M'e(l insi(h", the hnildinii,' will he very cold because the wind will iz.'O' easily 1 lii'(iiii;li lire brick ami the cracks in the sheetini;'. 428. All Wood Walls.— Koi- tjie constrnctiou of dwelling honses, cdierse ciirini;- rooms abo\'e i;ro\iiid and ice houses thei'e is no t\|te ol wall so etlective and so cliea]) in iirst covst as the all wood \\:dl w here ij^dod biiildini;' paper is used with th'C' hnnber. I'or a dwelliiiii lionse a reasonably warm wall is secured >>lien the studding' are sheeted ouiside and in with one layer ol toni;ne'li, and a brii;ht (dieerfnl nmiii has uiiudi the samei etiect upon those who (H'cn|)y it. 429. Efficiency of Windows. — 'Plu^re are many conditions which atf(xit tlici ettici(Mic.y of windows in lighting a build- 340 iiij;'. Ticcs or l)iiil(liiii;s iic;ir hv, wliicli coxcf ;i (•(Uisitlcr- ilh\o |W)i'li()ii <»l' I lie sky, iiiiiv i-cdiicc I lie lii;lil (■iilvriii<4- ji window Very iiiiicli. Alncli more li;^lit coincs iVoiii tlu; sky liii^li ;il)o\c I lie liori/oii tli:iii fiom low down :iiid lumco a ]>()i'('h <)\-{ r ;i, wiii(K)w cirls out ;i \cry laiiic sliiirc of tlio li' tlie winter, when.tlio sun is low, the advantage wliieli comes from its heating effect as well as the lio-ht is very considerahle. 350 VENTILATION OF FAEM BUILDINGS. Ill tlu' physiological sense air is as iiulispensable to tbo cow ami horse as is water, grain, hay or gitiss; so, too, is it as essential to the developiui-nit of power ^n the steam engine as is the Avater and the fneh It is so abinnknt abont ns and we procnre it nsnally so unconsciously that its necessity does not occur to us. But when large numbei-s of animals are housed together in close stables ample pro- A-ision must be made for th'e ingress and egress of air. 431. Necessity for Ventilation. — The need of ventilating dwellings and stables grows out of several conditions: (1) Tke consumption of the oxygen which is die essential in- gredient; (2) the exhalation from the lungs of carbon dioxide, moisture, ammonia, marsh gas ((' II4) and organic matter; (8) 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. — Tliis gas is given off from the lung's with each respiration in nearly the same ratio that the oxygen is i-einoved, hence air once breathed is not only depriveirotl air and injct-tod 1.") ct,'. ol" k. into a rabbit wliii'h (Hei(l from tlio offci'ts. Urown StHpianl couisideired tlit^ substjini'i'i a volatilv alkaloid scH'rotod b_v \\\v Inno-s. Water standing over night in a jHutrlv viMitilaitcd room or sta.blo comos to lia\H' a Ncrv disagrt'cabU^ taslo fruin tlio absorption of impurities from the air and ihis is oiui of the luotst serious objections to keoi)ing water standing in the stable for cows or o'th'er animals. 435. Micro-organisms and Dust in the Air. — It has long l)(HMi reeogni/ed that th(> air of old and pooidv \'eirtilat(Hl liouses, espeoially if they are not ke|)t tdean, contains many mo'rc>< dust pai'tiides, spores and nui-ro-orgunisms than newer and bettcn* ventilated housi's do. The' same must bo tru(> also oi' stables but in a higher degree. 'Idio anunmt of (\\\>t and of organisms as well is almost always morei abundant in oeeujvied rooms than in the optMi air. This W(ndd bo ex])eeted both beeause of the slowing down of air uu)vemH'nts after entering tlu' honse, whiidi acts exaeitly like a silt basin in a. line ni' tile, and beeanse (d' their |)rodnetion there from \ai'ions eanses. Strong ventihition tends to remoxc these organisms and duiit ])a,rtieles with tiu^' aii* from the eomjvartmients and this is the rational basis t'or airing a txMlroom or any other after sweeping. Tlu^ air has Ixn-n tilled with l)oth sets o( im})nritieis and opening 'the windows or using any other means (d" prodneing a strong euncnt will help to eh'iar tho room. 436. Bad Ventilation Predisposes to Disease.— The most helpful health rule whieh man am adopt for himself or for his donu\stic animals is to avoid whatevcM- tendi^ to wealcen the system and to take a.lvantage of whatever tends to greaiter vigor. 353 It hluiiiM l)c clciiilv icicofiTiizcd tiiiit tlic gcnriK of dipli- llicria. (/t t iilicrciilosis, \\<}<^ cliolci'ii and other (;ty lious<'s and stables jxjorly venti- lated and eared for are not in tlieniselves a source of dan- ger, tlic I'lin-down, weakened condition which poor ventila- tion is sure to engender will certainly tend to start a case of contagious disease and tlien, witli greater nujnbers of gerins in the air to be introduce*] into the system, animals of greater vigor niu.-t sueeund) to the-e irn'isible^ fow be- cause of th;ii- vast nuinhei-. Ain]>l( vent ilal ion then -lionld a'.\a_\-s lie seeui'e(l, jirst, as an indispensible condition f(»i- maintaining flie power to resist disease, and second, in case of disease, to botli clear file ail- and to give '|-he animals an o|»j)()irtiinity to defend tli( tn-('l\'('s against, this type of foe. 437. Amount of Air Respired. -'J'he amount of air ordi- narily taken into and put out of the lungs by man. witli eaeli respiration is gi\'en by different observers as follows: "«i"l)st 20 - HO cubic iricties Valentin 14 - 92 cubic inches Vierordt 10 - 42 cubic inclies Coatlinpf! 16 cubic incites llntcliin.son 16 - 20 cubic inches A vcraKP 15.'i _ 46 cubic inches or an a\-eiage of about .".0 cidiic inidies. Tlie auKMint oi pure air whicdi must be breathed in order to supply It he (hxvgcn needed by different animals, (h'duced ironi ('olin's table, is given below: 354 Air Breathed in 24 Hours. Oxygen Consumed in 24 BOURS. Animal. Per 1,900 lbs. of \vt>ight. Per lie'>d. Per 1,000 lbs. of weight. Per head. cu. ft. 2,833 3,401 2,601 7,353 7,259 8,278 cu. ft. 425 3,101 2,804 1,103 726 21.84 lbs. 12.207 13.272 11.01 29.698 29.314 21.84 lbs. 1.831 13.272 Cow 11.04 4.4!>6 2 931 Hen .075 438. Amount of Air Used Compared with Feed and Water. — A 1,000-pound cow requires daily tlie equivalent of about 30 lbs. oi liav and iirain and 70 ll>s. of water or, in round nunibei's, 100 1K<. })or head and per day of solid and liquid food. A cubic foot of air weii;lis about .OS lbs. lieiiee, from the table in (437) , avc have 2804 X -08 lbs. = 22i.32 lbs. which shows that a cow needs to be sup]>lied with twiee the wedg'hit of pure air that she chiew of food and water eoin- bined. 439. Degree of Impurity of Air Permissible. — We are yet "Without sutheiontly exaet (hita. t(^ permit this problem to be concisely stated for stables used for doinestic animals. In absence of exact data and in view of the unavoidable leakag'e of air through the walls and about windows and dooi-s we have arbitrarily assumed that if the air is ch.inged in the stable ait such a rate that it at all times contains no more than 3.3 per cent, of air once breatherovided. 440. Rate of Supply of Air to Stablas. — On the basis of (439) the number of cubic feet of air per head and per 355 hour, iisiuu' tlic (l;it;i in rlic r.-iMc of (437), wonld ])e as sfated helow: For liorses 4,296 cii. ft. per liour per head. For cows 3,542 cu. ft. per liour per head. For swine 1,:-I92 cu. ft. per hour per head. For sheep .... 917 cu. ft. per hour per liead. For hens HI .4 cu. ft. j)Pr hour t)er liead. Fifi. I30. — Simph'st method of takiuff air into .'() cous llii'cc; SO COW'S t'diii' ;iii(l 100 ('(iws li\(\ If'lt!. ir>l.— M()(ll(\fiill('ii of KIk. ino wlicri' 111! tln> rl^lit :i notch Is left In tlic Willi wluMl luilldliif;, so lluil the line rises llnsli with the Inside of the Willi. While on the iel'l side the line is shown l>nllt In llie wiill. Tills niji.v be done by biilldinn iiroiiiid :> inch driiln llie or iironiid n Iio\ iiKlde (it tciu-ilij;-. 442. Cubic Feet of Space in Stable per Animal. — Tt has Ih'cii iMisjiiiiiiii'v Willi s;iiiil;iiv cniiinccrs in jilannini;' liospi- liils, pi'isins. sciauil rcuiins. ('(c, to all(.\\" so niaiiv ciiliic i'cvi of spare |iei' (U'eii|iaiil , ImiI llie nniiilier ('liosen lias not Kju. ir>2.-Melhod of liiktnjr iilr Into a lumk burn on the np-hlll or bank side. 'riu> iilr line Is niiide In llie siinie wiiy iis descrlbi'd In I'Mji's. 150 1111(1 LM, lint oil (lie outside has its end covered as reiiresented at A on the lelt with a leiii,'lli of (I or S Inch sewer tile witli Us top cov- ered with a cap of coarse wire screen, Praln tile wonid not answer f(M- the outside e\|iisiire at the surface \<( the ground as trosi woiihl cause it to cruiiiblc. Wood could lie used and replacei- aiiioiint of air Itiit ratiuT to axoid (Iratls loo elt (' K represenls liow ;, li;i.\ sliool nui.v lie nsed also for veiilllalin;? line. Ill eaeli of tlM^se eases (lie veiil llallni,' fine would laki" llie jilaee ol one cow. 'I'his method would -ive llie I.esI vent ila I ion linl has thi- olMcelloii (d oeeiiiiyiii};- valuable s|)aee. ( ', In llie Iced shoot, is a door wlii(di swiiius oiil wIk'Ii hay is I.eiiiK thrown down, hnl is elosed when used as a venlllalor. the door not rea(diiiiK (iiilte Ir) the lloor. lo take air into this slal.li. iC il is liiiill of wood wll h slnddlliir o|'«'iilMKS wonid he lell at A aooni 1x12 in.'lies •■very tw(dve to six- leeii leel. and the air wonhl enhr and rise l.et wi'on the she.diiiL' ol he insi.le and the siding; on Hie oiiiside, .Mil .m-Iiik at I', as renr.- seiiled l,y I he arrows. If llie harn is a lusenient or stoii<. stnietun; the air inl.-ilies eoiild be such .-.s .lescribed in (i;;nres KH, Ifd and 152 1 weiitv cows sliould not lie lioiised in a space iniicli less tliaii 2Sx:{:} feet, Avilli cci linos S feet in tlie clear. Tti warm (dimates there is no ohjcctioii, exce|)t tin; mutter of cost, lo hio-h stahles, hut whei-e it is cold liioji ceilings pcr- 22 358 luit the warm aiv to rise so far ahovo tlio animnk as to leave tlio 8t<)l)le eoh! at tlie tloor. 443. Forces Which Produce Ventilation. 'V\w iiiovemeut ot" air (Mirrciiis into ami fi'oiii a xciit ilaled sialilc^ is caused 1. .l)_v the wind pri'ssurc ai;aiiisi \\\v huiltliiii;' teiulini:; to foree air into the stahh'. •2. \\y wiiul siu'ticii i>ii the leeward side of the stable teiuliiiii' ti> draw air (Uil. ->. H_v as]>iratiou aeross ihc idp ot" the Ncniilator. 1. \\\ the ditVereiiee in h'liiiu'rature hi'twei'U the air in the stahle and t hat oul-idc. When llic wind i< iilnwini; auainst a Iniildinu' ihere is an increase of pressuri' al>o\i' that inside which forces air into the stable throuiih any available oj^eninii' and then out aiiain on the o[)|>osite side or np the ventilating tltie. At the same time theie is a low pressnie on the lee side which tends to draw air ihionuh any (i|)( nings on that side. Where the ventilator i i of the expansion making the air in the stabh^ relatividy lighter than that outside; anil the hmger the chimney or veutihiting flue tlie stronger Avill l>e the draft, b(^th froui difference of tiMup(>rature and the aspi- ration across the to]i of the chimney. 444. Essential Features of a Ventilating- Flue. — A i>ood ventilating line must have all of the characteristics ])os- sessod by a good chimney. it should be constructed with air-tiglit walls s(» that no air can enter except from the stable. It should rise abovi' the highest porticui of the roof so as to get the full force of the wind. It should be as mnirly straight as ])racticable and should havi' an ample eross section. Stronger currents through the ventilators 359 will 1)0 secured Uy iiiakiiii:' one ir. but in itliiii^ would be needed exceiit perhaps an occasional the li;'y from <-nishiiitf it in. If it is not desired 'S through the ro;isses straight down to the lh>or lictween the cows, as r.'prcsciiicd iu l''ii;. l.'ui, not it niav hv loeatod in varions placc-s, as indicated in Fiiis. J:>;!"to IGO. 446. Openings to the Ventilator. — The ventilator should reach to the stable lioor so that air may enter tlie shaft frtnn that level. This is very important because: (1) The animals not only st-and and lie Ioav doAvn but are so consti- tnt(Ml as to breathe the impurities directly to the floor where 361 the carbon dioxide tends to remain, because it is heavier than the rest of tli(3 air in the staljlo, oven althoufich its h'inporatnro is hi<2,hor. I'm;. 156".— Ucprcseiiis a inethoil of carrying the flues up the sides ami then along under the roof between the rafters, so as to reach the ridge either under tiic cupola, or at otlier phices on either side. Such a flue couhl lie made very tight, ]>y nailing the light galvanized iron on the outside' and inside of studding, and rafters, having a suflicienf width to give tlie proper capacity for the ventiliiting flues, .•ind siu-h a system of veniilalion would v^'orl< fairly well l)Ut could not b(! expected to do as efl'ectlve service as the methods shown in Figs. J.5.S, 154, 158 and 159. (2) The cohlest air is at the floor and the warmest at the ceiling and it is the cold air which should be removed during- tlic vvint<'r rather 'than the warm. There should be an ojxjning 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 be provided with regu- lating valves so that either or boith may be partly or com- pletely closed. :k»2 447. Entrance for Fresh Air. — WIumi a sliihlc has been iiiiidc close and warm, rciiiiiiiiii; altciilKHi to \fiil ilat ioii, |>r(i\isi(iii iiiiisit lie matic ItH' air to ciilcr I lie stable as well as to lea\c it. Tliis iii;iv best be doiK' as represeiltecl in Fiiis. I. Ml i:.;; Mud ms ic.o. 11. I,')?. — Slu)WS iinMllod oC vciil lliidii;'' nil s l)iilll bclwccn llic sHi..(liiif; iin(i_ I't'i wcfii till' .jdisls of llu> f'.illii);, llic iilr IIh'ii rlsinu, lliri>ii};li vi'iii lint liiK slml'ts, iiiiulc iiKiil'i^'l <>r iis n |i!\r( of one or more uf llic inirl'iiio posts, 'riic air outers Jil A A 1111(1 li. followiiin- llie arrows ami passing- out aloiij; Hie Hues (' 1> K. These ventilators, if do- slred, eaii lie earrled out slralKli' tl)roii;;li the roof, or may he tor- lillii.'lled Inside under the purllne iilale. or iis represeiitcMl In tlio lljrure. The I'ross seellon at the rl};lit shows how L'xlL'"s and I'xii's may bo nailed tou'ether and placed so as to eonstltute a pnrllne post, and at th(> same time a ventilating lliu>. The two sides of the pnrllne post or \ out Hat In;; line are represtMiled closed with sheets of yah itiil'/.ed iron. 'I'liey may also ho closed with well seasoned in.'itchtMl lloorln;^-. The nninher of lieiids nect'ssarv In this plan is ;in object ion. as tlu'v Interfere with the drjifl miliiii>'. Tliis is I'oi- the purpose of iiiiiii;linii it with the wanuesl air (d' the stable so as to I'aist' its f(>iii ;;i;:; ]i('i'!il lire iHfdic il fulls lo llic lluor. Ill lliifl vviiy IIm' li<';it, wliicli i-. w.isliiiii ;il I lie cciliiiL' i-; s;i\<'il iiiid liii" iiiiliiifils •.[Vi- |H(\ciiI(m| fidiii jviiij^- ill cidd ;iir. I 'ro\isi(iii is rnrllicr iii;ii|f Inr llic ;iir lo cuter llici iiiliikcs (ill'lsis dill ilircrllv ;is il woiilil il llicv (jpciicd dircc'l l\' I lii'iiii;j II llic \\;il Is. Tlicsc ii|ic!iiliiis slidlllil lie phici'd (III ;ill sides .S. .McIIkiiI of vciillliilliiK II Iciinld Htiililc. 'I'llc iilr i'IiIHi'iilc(l h.v IIk- MiTdWH III \ V, mill jiiimmch mil IIicoukIi n Hue liiilll Mil llii- liiHiil*- of iiH> ii)hIkIiI or iiiiilii liiini. Tills Miic iniiv iIhc ill rcclly lliidiiKli Ilii- roiil. or II iiiiiy ciiij iil !■; iih hIiovmi In ilic IlKiin-, lli<> iilr piiMHiiiK lliriiiiKli II ciiiiolii. II llic ii|(iIkIiI liiiiii liiiH II lull Nioii rniiiic, llii'ii III)- Hiincc hflwi'iMi llic hI iidilliii; roiilij he hhi-iI ilH VCllllllllllll,' IlllCM III ||||> HilllK' IIIIIMIK'I- IIM (IcK.ll llOll III I'"Ik. IM. 'I'llI'MC lll'CH < Irl I,,, liiiolr lltihtrr Im .•oM'IIIK IiimI.I.' mill oiil on Hit; Hliidillnt,'. Willi till- ll).-lil<-Hl -!iImiiiI/,.'(| iron. ^CA r(i|>c((S(Mil('(l in I'^ii;'. IT)?, wlicrc tlic sides iii'c iilso jiiiidc of ^iilviiiii/cd iron. As a subslitnlc I'oi- ,i;alv:ini/.cd ii'oii in lliis fofiii (v|' \(>n- tilatin^' fhu> a pxxl roolini; papci' may l»o used, h\w\\ as tlic riihci'oid i-oofinn' made I)v lli(>. Slandnrd Paint Coinj)any. 449. Ventilation of Basement Stables. Tlioro is a jjjcnoral ini|H'('ssi(in tliat hascincn'r slnMcs nrc necessarily nnlicallh- ful. 'I'liis idea lias le In niak'(^ these slahles nineh closer and wanner lliaii ordinary over i^ronnd foi-nis, and wIk re ample \-ent.i- la,ti(»M. has nol heen proxided they have heen dam|) and cliKst^ Kia. I.W. Mcllmd of vciil llnlliit; a Imrn wlicro n silo or ;rraiiiir.v occupies llic cciilnil iMirlloii. 'riic nil- ciilcrs jil A I! iiikI IIic vciililjitliif;' lines lin> I lie spiiccs l.clwccii (In- sludilinj; wlilcll I'onii (lie wiills of llio silo, or ollit-r siniiliirc. 'I'lic iilr ciil crliij; ,il (" In i.|ifiilii«s Icl'l nil liroUIKl tin- silo. Mini piissiim out Ml 1» Ml till' |o|l. Where hasemeiit slahles are well liohicd and propcM'ly venlilalcd there is no ohject ion to them on sanitary ^i'(Hinds and they have many points in their favor wliero tlio (H)iidifions admit of their heini!,' easily constrnct(Hl. M(^tli(>ds of introdiicino' the ;iir into these stahles are repro- soiited in I'^ius. I.")!) to 1,')!*. 365 Cic. 1(W.- Is ji section iiC I he cow stiihlc of I lie dairy li:irii ill llic Wis- consin lO.vpcrinicnl Slalioii. A sinulc vcnl ilal iii^' line I) I-: rises al)ovL' the root' of till- main liarn. and is divided Ixdow tlie roof into two iirnis A M I>, wiiicli terminate at or m'ar liie ievel ClIAPTKR Win. PRINCIPLES OF CONSTRUCTION. KKI.ATIO.X Ol' ('(i\ i:i;l .\(|iiiii(' willi tlic oMdiii;' l)iiildinroviding nearly idcnticjij accoanniodations. The longer one is 105 feet 10 inch(;s in length, 30 feet wide with 18 foot poHts. The second is 75 feet 10 incliet^ x 44 feet and re- • piircH over S p( r cent, less wall and over )K'r cicnt. less Hoor spacx."'. 451. Relation of Hight to Capacity. — In the building of barns, silos, ic(^ houses, giain bins and root cellars the more depth or higlut which can be secured the larger will 368 1>(> the cjipiicity ill pi'dportiinii to rdnt, cciliiii; or tloor. The Muitcrial for lloorin^' luid rootini;' ii low l)iiil(liii<;- is usuiilly no l(>ss tli'iiii is i"('/r// OnlM(l( Snrfaas. LAcess of floor ywc Jboire J "mX87 D IGOA^ B ZOZiO C 3.)83/< loUd FloornSpace J 5U63g/l B 66 /C J\lon C C /I/34 3ll9X3i9 1)13300 ■ ^^ Hound Baf/i Abo\r> B ^0150 10 A CZ) 40/35 /4 5Gxmm^ Ig \5omii^ 18 18 /4 96 X5A 10 30X30 zo 40X4(Ji ZO ^C li'id. 1 ? I»in>;niiii nIiowIii^' llic (•(iiiipnrsil lvt> otitsldo surface and amoiiiil of kl»M)r space in four sets of barns represented in l'M;rs. 1(>4. Itlfi, It;*', an ' U>i. 369 ^0 452. Combined and Separate Construction. — The amount of capital required to build and inaiutaiu in repair a large number of small buildings, is gioater tlian that required for a single consolidated structure providing like accommo- dations. This is clearly illuetratod by the conqiarative 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 US c(t\vs 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 261) ft ct more than the group of buildings in Fig. 165, which shelters only 37 cows and 15 horses, has no sib>, no tool house and not enough s})ace for liav. Fio. 16G.— Gi-oiip nf luiildiiiss wlii-h shclW'j- 114 and S li()i> Comparing with the 1)uildings of Fig. 166, their aggre^ gate outside surface exceeds that of the standard l)v an o i i area ()4.\<)4 tVn-t and yet they j)r(ivi(l(' ciMiiijx'il (juarters for (tnlv 114 cows ami S hdrs-es. Kic. Iti" — 'liDiiji ol" ImiMiiiiis ^\lli(•ll sliclicr 1^4 cows and 14 Ikh-scs Avith ti)oI liuusi- aiid granary. In the group of buildings shown in Fig. IGT, there is an aggregaite 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 exitreme wastefulness of lumber. ta 168.^ f Iiani .-■Iiowiim- ili-i\. 111(1 and 372 453. 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 wliere they are scattered through many buildings and Figs. 164, 168, 169, lYO and 171 rep- resent a consolidated type of barn with composite func- tions, where all of the stock are brought together under one roof. Fl(i. ItiV). — Coiisolidalcd 1 vpc of l>;irii showini;- (trivcw:! v t" tirst and second tlour. Economy in labor is of much greiatci' moment than economy in material because the material simply repre- sents money invested in this case while the (wtra labor re- quired is a continual expense^ of a high order. 454. Distribution of Animals in Stables. — The ge-neral arrangement of animals in stables must vaiy in detail in almost endless variety, and individual circumstances must determine just what is Ixist. Three types of arrangement for cows are illustrated in cross-section in Figs. 150 to 159 undei' the chapter on ventilation, and Fie. 162 rcTDresents two convenient groupings for horses. While Fig. 170 shows one ])lan of division and arrangement of space in a cvlindrieal barn. 373 Fig. 171.— Showiiif; l-jss r-onsolidated typo of barn witli silo partly out side :3 374 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 potr^sible tO' c^irry the floor npon the uprights used to fonn the stalls or ties for the cows and in this wa.v save lundver bv making the same ^^^ nnrsi ciose \ rlOf>S£ STABLC rr\ rr\ r\\ feCrO ALL£ B\0* SrjILLS ■^ rerco alle^ 5 i; A i. A CLEANING ALLCr \ MANURC onoP I* 1 1 MAN&rR 2< -J rcco AiiCr U ■ MANGER \ 1 1 MANUfIC: OflOP It 1 „ CLCAf^trve ALL£Y Fir as])halt. The asphalt is supi'iinr t(t rlic Pdithind c(»ucr('t( in beiui>- a poorer con- ductor of hear wliilc tlic ccnicnt has the advau'tage of less fil-st CSt. 457. Cold and Warm Floors. — It is urged against the con- crete as couipauMl with wood Hoors that they are cold. The meaning is that they aie Ix-ttcr coiKhu-tors of heat and so sei've to carry the heat away from 'the body of the animal raj)i(lly. It is true that they do c(mvey heat fa.ster than wood and when usimI in cohl (diniates without bedding are worse than wood from this stand])oiMt. They are not as ])ad in rliis i-e^peet, however, as many imagiire. In the first ])\<\i-i- the stable ought not to fall Ixdow 40 F., and when 376 this is tvwo the floor will only have this temperature and will not lead to inconvenience if other conditions are righ't. In the second place no animal should be required to lie 174. i;.'cl!iii-ul-ii- I I'll w i I li (!'■'' US I'i ti|oiic(| :iii(| oi'(I(i\(mI llnoriliu-. 461. Stone Floors. 'rii(.r(Mi,i;iil,v diirjiMc tloors lor cow .'111(1 lioi'sc sl.'ihlcs ;ii(" iii.'kIc 1>v hcildiiii; ill id;iv rounded coMdc sloiK", I or .") in(di('.-> in di;iiii('t ii , niid iisiiii; iipmi this :in jihniidiincc of licddini;-. 'I'lic iiiicNcii siii fjicc holds |,h(^ l)('i(hlini;- so well 'I hii.l I he :iiiiiii;ils jirc I'nirlv com forinhh' iliid neither wc:ir lun- (h'c;iv will d( -;lrov lliem. Idle inost, sefions ol)jecl loll lies in I he dilhi'iill v in iii;iinl;iiniiiii' (de;in- liness. Where a i^ood onttci- is nnide ix'hiiid the cows mid a row of" ciil sitone 10 *>v I:.' inches wide are set I'or I he hind t"eet. to stand npoii a (hiialde and (|iiili' satisfactoiN' thior is se- cured. 462. Macadam Stable Floors. A Ihior i,i.>re i'\'eii in sur- lace than (461) cnn he made out ol" cartd'iilly constrncted niacadam work, siudi as is used in makiiia,' stone ro^ads, i^ivin^- it, a thickness n[' 't or (i inches. \\'li(>re this is used th('i'(v shonhl he pidvidi'd cement jj,ntters and maiii^'ers as re|)resente(I in \'\iX. 1 T.'>. Vut. ITfi. Shows iiM'llind ,il' iiKikiim :i inM.'aieres of rock and -and with i'oitlami eeinent. 'I'Ik; cement is iton expensi\'e to he nse(| hy itself for ordiiiarv work and the makini;' (d cenieii' concrete aims to |)rodiice the lar^-est hulk of stronii' lock with the ii-e of the least ]H)S- sib](< amount. ) :i clciiii, Co; I rse, slmi'p s;ind le li II I lie |>()res jtcl ween I li(> I r:ii;inciils ol i^rnvcl or line scrccniniis; ( I) cnonuii i'oii land ccincnl lo lill llie s|i,ice liclwcen llie siind and Itind llu^ whole loi^'clhcr; ( ."> ) :ind liiinllv. \\:iler enoni!,ii lo wet all siirlaccs, lill the |iore spncc o|' the ceiiu'iit ;iiid nnike lli(> liloll;li- pl.'isl ic. 467. Presence of Earth, Loam or Dnst. It is (d' I lie great- est. ini|)oi'l;ince lh;i! ;dl of I he ni;iteri;ils \\sv^\ he pcrtectly tdeaii ;iiid I I'cc li'oiu diil or other line i;r;iined ni;iteri;d lia\'inu- I he l<"\l lire vil' 'I he ccnicnl ilsclf. 1 I' ;i line dnst is prrscMl in the roi'k, i;r:i\('l oi' s;ind il will lend lo form a l;iv( r over the sni'liiees ol' the I r;iij;iuenls wliieli prexcnts 'the e( ineiil lidiii eondii^ in eonl;iet with I he jiieees whicdi ar(* to lie eeiiieiitetl toi^elher ;ind ;i we:ik eoiierele rcisnlts. The Iniidiiinenhil is |o h;i\(' iioihiiij^' lull li;ird roek t r;iii'- nieiits hiroc ciionuli lo lie eeiiu irleil tou'elher ;iiid inMhing line preseiil luil t he eeniriit iiii;- iii:ileri;il itself. In I he eoiierete |i;i\ eiiienls used on t he si| reels el London, ;iiid which li;i\i' :i iiincli longer life tli;in the Itest ])aving blocks, t;re;i>t tMiv is taken lo wash onl (\{' the cnished iiraiii'lc ;iiid its scrceninus ;dl dnsi |i;ii'li(des before \isini2; tlieiii, idlhonuh the dnst m;iv he iVoiii ihcL'rnnitc itself. 468. Wettiuj;- the Crushed Rock Before Use. There are I wo iin|ioit;int reasons wliv cnished vovk [H' coarse screened li'raNcI, lo he nsed as tlu> hodv of concr(>t(\ should be wet ho- fi>re niixinii' with the cement. Thesi* are (1) to dis|)la('0 as much adherinu' air as |tossible, and ( iM so as not to draw ;{Hi (Hit (Vmii llic (•(•iiiciit llii' \\;it(i' ii((''lc(l Id iii:i!iil:iin ils |)liist icil \ ;ili(l In ;is-isl ill I I K • S( 'I 1 i 111;'. If llic (•(i;ii'-i' iii;il('ii;i Is iiic mixed wrlli llic (•ciiiciil ilrv ;i l;iri;(' niiKiiiiil ;ic(s Itciiii;' lillcd, Iml llic »'lli( r ilillicilltv (•(lines iVdiil llie ;iil' pi e\'eni| i lli;- the cenielil. lloiii ;i(llieriiiu' lo llie ■^iii'hices. S( i slrdii^'iv (|(ies ;iir ;i(lliere !<► cdiii'se siiiid I lull il iiiii-l I le Ik n l( d sniiiei I iiiic ii iider wilier li( lore il is ;il I renid\ cd. 469. Ratio of Ingredients for Concrete. 'I'lie .iinoiiiils of (';icli iiiiiredieni ic(|iiii'e(| Id iii:ilse :i solid cdiieicle willi :ill spiices lilled depi'iids ii|idii llie |idfe) spiice in llie di ll'eircilil iii;ileii;il-. 'i"i';i ill w' i lie ;issiiiiies lli:il. I'di' e;icli i iiij rc( I ieirl llie \'. ( f lav el or scHMMiinnH, Coiirsc hiiikI. ('iiiiniil. •^7cii n. i:!ri<-M n. (i '.iricu. n. :i ri.'i cu, n This rill id jdi- pdi'e splice iscerhiiiilv hir^cr ih.'iii is likelv Id dcciir iiiid Idr hiriii piirpdses il will he s;ile eiidiii^h Id f;ikei I he i;il idS id' ("rusllcd .Kick, ( J|•MV(^I in- MTIM^IlillKS. .Sllllll ('llnilll 27cii.ri. i'ioii CM. II. ri-'ihi cii n. z.i'.i'.icii. n. 'rii(s(' lii;iircs iissuiiie llie pdrc' ,s|iiic(' nl I hci I'ocds to \)\' 47 ])(•!• cciil., (if llic <:,rii\('l 11 per c(Mit. 5111(1 of tlio Hiuid .']8 per <^('iil. 470. Ratio of Ingredients for Finishing. Wlicic ^ood pljl.slcrili^' s;iiid is used I'di- iii;ikiii^; IIk lliiisliiii<;- siirlMce llic ]rdi"ci sp;icc Id he Idled will lie iilidiil, ."..'"i per ceiil. :iiid lliis Wdllld rcipiirc ;i little nioic tli:ili dlie dl ceinellt tdilhrccidl sjiiid, iiiid unless there is sonic ^I'Jivcl or scrcciiiir^s to use with tlic sjiiid id will he siifcr to iiuikc llici i'iiciii^' 2 of sjiiid lo I dl ccinciil. 382 471. Thickness of Floor — For most stables wlun-e the ground has l>p- ment, in th'e ratio of one to one. 472. Making the Concrete. — The cement, sand and gravel are put together drv on a mi.\in<2,' board and thoi'oughly worked over, then enough water added to make a stitt' paste. The right amount of crushed rock is thoroughly drenched with water and the whole mixed bv shoveling nntil the rock is thoroughly incor]iorated with the cement. 473. Laying the Concrete. — The floor of the stable should first be given the ]iro]>er form and very thoi'onghly tamped so that no settling shall occur after the floor is laid. The concrete slnmld be laid in blocks foiir or five feet square, bnildinc,- alternate blocks first, Fig. 170, so as to give time for setting and prevent a strong union of the blocks. If the floor is not laid in this mannei- shrinkage cracks will occur. The concrete should be nnide oidv as fast as used 183 and sliould 1.;' tlioi-ouiiiily raiiiiii('(l uulil the tine ('('incut shows as a layer on the surfact'i. Af'k'r staiidiui; a slujrt time, but hefon^ tiie concrete has set, tin finishiuo- surface should he ajjplied and thoroug'hlj trowelcHl until it is even and smooth. Fig. 177 is a cross section of floor and manners. Fls. ISO, 181, 182, and 183 are designed to give the cows the maxinmm amount of freedom of head movement but to force tliem to stand close enongh to the gutter to preveu't the platform being soih'(l. The manger or the head of the Htall is made aii(.:'d to se- cure clcauliiuss ill spite of this habit. Tn the !N^ewton tie it is cxjx'c'tcd that wliilc the cow is stand inc; the yoke to wliich slie is tied ^vill force her hack siiffici(Mdly to prevent the (lillicully. In ])racticc. liowcvcr, tlicre is necessarily SO Fi(i. 18J.-Halcrr tie. Fig. 18.'). — Newton ti(*, niucli frccdiiiii al the lu'ck tlial 'tlic dhjcct is luit scu'urcd. 'I'lic ''.Mixicl I ic" |)i'()\i(lcs a har on tlic lloor, just in front of whcr(^ tlu'i cow's feet are forced to lie while standinii,- and fVedini;', and Avhich is so nnich of an ohstruction that in order to lie in ('(inifoit she steps forward enouiili to lie on t Ik (dean heddinii-. Fifi. 186. Kiii»pv> tie Fic. 187.-"Model tie. 387 477. Movable Halter Ties.— Anothrr class of tics repre- sented in Fii;s. IS I, ISS, ntteni])! to eoiititie tlie cow in movenieiitw forward aiul hackwaid hy iisiui;' a short cliaiii which slides at the other end in siudi a iiiaiinei' as to per- mit freedoiu of iiioition up and (l from the mangei*. Wliei'c sn(di ])rovisions arc insisted ni)oii it shonhl he kcjit in mind that anything whicdi tends to enchise the eow, especially her head, in a tiglut box tends in a high degree to defeat the ])nr])oses of good ventilation by confining the air once bicathed about the ainmal, hence such arrangements should be shittecl oi' else (,pen at the level of the flo'Oi'. So, to(N \vlier(ver box stalls are used thewe should be slatted or o|)en at the bottom and not "boxes" as they too often are. 479. Tying for Feeding Only. — For calves, yonng cattle and feeding steoii*s 'there is ])erha])s no mode of confining the animals in the stable so good as to- give them complete freedom except at the time of feeding, using ]denty of bed- ding on a cemenil^ floor \vhi(di is (deancd as often as needful. 388 111 siicli cases the staueliioii tie is the best as eA'erythiug" 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 nnmbers of animals are to bo handled with the greatest economv. The manger should have an inside Avidth of at least 2 feet, a depth of S inches and should have its bottom o or 4 inches abuve the plat- form upon which the coavs ^itaiid. 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 C 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 <> inches next to the cows and 6 inches in the rear is best; and where a wagon is driven behind itlie animals to clean the stable a depth her hind of onlv 1 inches cives k\ss hiuht to lift the manure. PKOVISIONS FOR WATEEII^G. 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 ^vith expensive storage tanks. In case the power is pumping waiter faster than is needed it is a simple matter to ju'ovide an overflow, returning the water to the well. 482. Watering in the Barn. — In climates having severe winters it. is best, if practicable, to wat.er the animals in the barn, and where a good fresh running stream can be 389 inaintiiiiicd the idciil \v;iv is to Iinxc tlic water before the cows all the time so tlia'f it can Ix- taken when desired. It. is not (h'siial)h' to keep watei- standing' before the oows continuously as it is certain to become foul; but it may be maintained dm iiiii- the uveatf r part of the day if the drink- ing- basins or trouiihs arc em])tie(l chan each evening'. 483. Methods of Watering in the Stable. — We have seen but 'two r('asonal)ly satisfactory methods of watering a large nnnd)er of catth' in the stabU', and these are either to clean the maiiiicr ami luu the watei' into 'that or else to have a special liiiiii' wateiiiiii' tiough us'.'d for that alone. Fin. ]i)0.-Siini)l incut for wjitcriiij;- <•' in stal)le. The sim])l(st airangement of s])ecial trough is repre- sented in Fig. 100, and extends the full length of the stable, the wat( r cduiin^ to it from above so tliat the supply pipe is entirely above gidund 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 driidsing, letting it fall when .she is through. 484. Storing: Water in Tanks.— Where there Is a basement barn the heM. ai'raiigement for a storage water tank is a 24 390 cement lined cistern benea.tk the surface in the hill above ■the barn. {Such a cistern is Ictss expensive, is a pennanent improvement and will keep the water warm and clean. We have seen cases where a satisfactory cement lined cistern is built entirely abo\'e ground and then covered in by grading- a mound of caith about and o^'er it sufficient to make it frost proof. Such a cistern should be provided with a man-hole so that it may l)e entered if necessary. 485. Watering Trough. — Where stock is watered in the yard a good arrangemeu't for \\'inter, where the ground is porous, is represented in Fig. 101. 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 em]:>ty the tank the plug can be removed and the w^ater al- lowed to drain into the dry well. Fig. 191.— Representing a sti>r:i.ue rescrvnir .ind drinking tant; 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. 301 AKRANGEMENTS FOR UA^LOADIiN'G HAY. 486. Unloading Direct from Wagon. — Where the hay is not to be lifT('(l and can Itc rolled directly from the wagon with the fork into the bay, there is no simpler and more ex- peditions way ; and where the load can be driven to the top of the Larn, as re]>reserited in Figs. 168, 171 and 173, there is little need of other mechanical arrangements. Fig. 192.— Curved track aud hay carrier for use in cylindiifal baiu 487. Unloading Hay in Cylindrical Barns. — Where the cylindrical type of barn is used there arc 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 re])resented 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- Tantage of the princijde illustrated in Fig. 193 for distrib- 392 Fig. 153.— Ordinary hay carrier and revolvinfr platform for distributing Iiay in (\\iindrieal barn. Fig. Iit4.— Kepreseuting a movable, tilting platform for distributing hay in rectangular l)arn. 393 iiting hay in ordinary rectanoular barns, Avliose timbers are not in the way. Fig. lU-t represents a tilting platform, which rocks upon two bars carried bv four cables secured to pulleys which roll along tracks or cables secured to rafters, as shown in the cut. With this arrangement hay may be drop])ed at either side or in the center of the bay, as desired. ;;i>i ('ii.\rTi<:ij XIX. CONSTRUCTION OF SILOS. 489. Conditions Essential (or Preserving Silage. Tho (tiilv ('oiidil ions IK rcssii I'v l of inatiir- ily. W'liatcN'cr nicaiis ni:iv lie :i(lo|tte(l lo e\clno HJionld bo ni;ide as i^rciil :is |tr;iel ienhle ( \) heciinse in lliis way tllG hu'iicst nniouiil (d feed |»erenhie fool m:iv he slored. (2) There is less loss r(lali\'ely ;d I he siiid'iice. (-'!) The si ronj; hilcnd |»i'essnre forces llie silage :i,i;ainst llui walls so tdoselv lli:il less ;iir cnlers :ind hence lliere is less loss. 491. Silo Walls Must be Rigid and Strong.^ The oidward pressure (d' cnl corn sihii^c when selllin«;', nt the iinio of lillinti'. increases will; (lie deplli id llie r:ile (d" 11 lbs. per K(piai{^ I'eel for eiudi fool (d' deplli. A I ;i deplli (d 10 ftH'ifc (Jie laleral pressure is 1 10 Ihs. per s(pi;ire fool, al L*0 f(>et it is ^20 Ills, ami :il .".O feel ;'>;;0 Ihs. ilcciin-i' (d' ihis i;re;il picssiirv silo \\;ills iiiiisl lie mado v'ci'V si roiiii,' when llie\' li;i\(' :i deplli (d "_'0 or nun'c led. It- is (lillicnll lo in.'ike deep !'ecl;iiijj,iil:i r silos whose wnlls will M<»l spread as i-epreseidcd in V\'j;. ll^T), and wlicre (bis takes place the Willis iire i-rowded iiwiiy from (lie sihiiid so iniich (hill iiir ciiii circiil.'ile up :iiid down nexl lo llie Wiills timl (his rrsiills in lie;i\ \ losses. ,".'>r. Ill t'ii'ciihii' silos llic prcissiirr is siisliiiiKMl hy iflic Icnsilci stnMJ^'di of I. lie iii;il(ii:ils in I lie walls, wliicli i;i\'cK lliciii Ijic, jiTCJitcsl [xissiUlc ii(l\:iiil:i^('i. m. I'lt; 1:1.",. llhisl i:il ill;; liipw Ihc liiil;;lii;^ iiT reef 1 n„iil 11 wooil silo Wiills illlipws iiii' Id (■(line down llic siilr'^ liclwccii I lie Willis :illnsilv he scciuhmI. PLaeiiig' llui silo dec]) saves t'l('\;itiii<;' I lie silage so liioji Avlu'ii lilliiiiiand a lai'uc |)(»rti(iii ol" it is hrlow tVost. Flc. l!i*i. -Slio\\iiii; !iii nil stone silo with roiiiciil roof ,iucroid roolini;-. 493. Protection Against Frost. — Tt is not iiocossary to build a. silo so as to he ciitifcly frost proof in cold (dimatt^s, but it will pay in hiiild tliciii rcasonaMy warm whcroi they ai'O to 1h' fed froiii diiriiiii' cold wcatlicr. The iVo'O/ing" of silage dtx's not injure it seriously but it is uct wcdl to fe(>id it wlicu frozen. If a siloi is not to bo o]>eiu^d until warm woathior no s]>oeial atteutiion need b(> oiven lo warinth. If a silo is 10 to II) foot in the ii'round and onlv iM) feet above 897 ground, tlic scttJiiii;' mu\ the early feeding' before s(>vere cold wealthier will usually have carried tlie surface of the silag'c so low that little iiiconN'cuiencc I'roin tr(tst will b(; experienced c \-en in stone silos. In all the Wdixlen silow, ex- cept the (luestional)le staves tv|)es, 'Hie const rucTioii neerled for streiiiith and to ke(q> the air fi'oni the sila,i;(; will usually be a ^snfi^cient pi-oteclion a<;ainst frost. OOA'STIlUfl'ITOX OF STONE SIT.OS. Whenever stone can he liad on the farm suitable for l)uildinii- pui])oses these may be u^^i'd in silo c(jnstniction, thus coTLvertin^- idh"; into active cai)i'tal. So far as the silo itself is concerned no bettn- oi' moi'c dui'able material can be used, an or l' of (dean ^^harp sand. If I he uiortar is not rich and troweled smooth, the acids of the silage will act upon it nnudi move rai)idly, dissolving out the lime and leaving it open and ])orous. It Avill usually b(^ pnident also to whitewash these linings every twO' or thrxH'i years, espcndally the lower portion wdicre the sihige is longest in c(Uitact with the cement, in order to proA'ent softening, using cciment to make the ^\•ilitewash. 80 !> 496. Doors. — Doors for filling and feeding should be ar- ranged as re])rcsented in A, Fig. 196, and if the lower one is long, cntting out a good deal of the wall, an iron rod shonld be bedded in the wall above it to prevent cracking between the doors. The rod shonld be of f inch ronnd iron l)ent to the curve of the circle and about 12 feet long. The two ends shonld be turned sliort at right angles, so as to anchor better in tli(' mortar. In deep stone silos, which rise more than 18 feet above •the surface of the ground, it Avill be safest to strengthen the wall betwe(^n tb(' two Idwci- doors with iron tie rods and, if such a. silo, is built of lioulders, it will be well to use rods enough to make a t'oiiii)letc line or hoop around the silo about two feet above the ground, as represented in Fig. 198. Fia lOS.-SlM.wiiiK iiH^thod ut iHMldiHfi iron rods in stone '"'i'-k "'• con- ;-ivt(- silo walls to incrensf. tlu- str(.ni.'lli. The li.-avy lines with ends bent represent the iron rods. The door jambs for the stone silo are best made of -lrx4'8 framed together and set far enough apart to give a depth four inches less than the t.hickne^'w of the wall. This will allow mortar to be filled in between the 4x4's to make an 400 air-tig'lit joint. A (Much board inav he fitted around the outside of the inner side of the door jand)s to form the rab- bet for the daois, or the jambs may be made as rejiresented in Fig. 19G. There will be slight shoulders left in the round stone silo above and below the doors when these are made flat^ and these should be filled out with mortar when plastering, giving a long, gentle slope back to the wall. The door is beet made of two layers of 6-inch flooring, tongued and grooved, ciossing at right angles, nailed or screwed together, Avitli a layer of good acid- and water- proof paper between, as shown at E, Fig. 196. To make the door fit j)erfectlj air-tight there should be tacked to the face of the door jamb, all around, a wide strij) of thick roof paper or strips of old woan out rubber belting, and the door drawn u]) against this wirli tour ^A^^ ineli lag bolts })ro- vided with washers. If one prefers to do sO' the door may be made small enough so as to leave a half-inch s])ace between it and the jamb all around, and this space filled with puddled clay after the door is ]uit in ])lace. Either of these methods is better than to tack striji.-i of tar paper oA-er the joints. CONSTRUCTIOlSr OF BRICK SILOS. Very excellent silos may be made of l)rick, as repre- sented in Fig. 199, and where brick of a good quality can. be obtained at $4.25 to $7.00 per thousand a silo Avhich will last indefinitely may be made at a moderate cost. 497. Foundation. — The foundation of the brick silo is beet made of stone, wherever these may be had, canwing the stone work u]) at least a foot above the gTound and be- ginning below frost line. The l)rick work will then be set with its inner face flush with the inner surface of the stone work. If the silo is to be carried 20 or more feet above the stone wall it will be desirable to bed a f-incli round iron hoop 401 into the n])pf r surface of 'the stone work in order to guard against eiaeking- tlu^ wall \>y the pn^v^nre of tli^ first tilling before the mortar has liacated every two or three years as the acid of tlie silag'e: dissolves it away. 2. The face of the brick wall mav be iiiven a good, rich 403 coat of cciiu'iit })lastor, oiic-fduitli to (iuc-lialt' an inch thick, and tlien this he k(>])'t whiti waslxyl so as to nculfali/.c: the acid and prevent it ficiii softening' the cement. 8. Tlif^ wall, or at least the inner portion, may he laid in rich cement mortal', makini; the horizontal joints ahont one- fonrth of an incdi tliick and the A'crticai ones a half inch thick, takinii' gicat care to get all joints of the inner 'tier of biick thoionghly filled with mortar. This method will place 'the cement where it will not be as readily affected by the acids and fVost and does away with the necessity ol" plastering, care being taken to lay the brick smoothly and to point the pints carefully. Milwaukee cement will answer for this work. AVhitewashing the inner face of such a lining will be sufficient for smoothness aud tightness. 4. The very best possible lining which could be made wo'uld b(^ secured by using the small, thin size of viitrified pa^dng brick. These may be set on edge, to. reduce botli the cost and the number of cement joints. It will be nec- essary to tie tliis course occasionally to the main wall by turning a brick endwise. Kicdi cement mortar should bo used and the joints made tliin but tlioroiighly filled with the mortar. Such a lining Avould give a surface like a stone jug, thoroughly air-tight and indefinitely ]X'rmanent. 502. Boors. — The jand)s may best be made of 3x6's or 3xilos; (.'5) l)ii(d< lined silos; (4) lathed and plastered silo.-. Fir!. 200.— Sliowiiii;- a brick liiicil rciniKl silo witli hficks scl oii (■iti'\iction will he (l(\scrihele to ohtaiii the material for it. Upon this should first be laid the sill made of :ix4's cut in two-foot leii,i;tlis with the ends beveled so that th( v iiuiy be toe-nailed togethei' and bedded in cement nmrtar \i|iiin the wall in the manner represented in Fig. 201. The sill is set just far enough back from the in^iide of tjie wall so 'that when the bnck an; laid they come Hush with the inside (if th<' silo wall. I'Ui. 201.— Sliowiiijr iiii'llu"! oi nijikiiitr the sill of lu-ick lined mmiI of round wiK.d silos. 15. pinii (1 slmld.ii;; for .-lU-wood. Ip]-jck liiiod or lathed iind pl.islered sin. 504. Setting Studding, — The 2x4 studding are next sc^ np and to<'-nailed to the sill. A stud is linst set at each angle of the sill, pliunbed and staved from a post set in the center of the silo. After four or five of these are set and plumbed from the center they shoidd be stayed from side to side by tacking to them a sti-ij) of half-inch sheeiting bent around the outside ac- high up as a man can reach, taking care to get each stud pliunb in this dii-cctioii before staying. After the alternate stiuU have been lace, toe-nailed to the sill and staved to the rib holding the others in place. 505. Sheeting.— l^ji,- next step should be to put on the outside ]ay( r of .sheeting which, for all of the sihjs Ichk than 25 406 30 feet ill diaiuoiter, should hr tlir(>e-ei_i2,'li!tlis inch luiiiIxT made by bm'iiii>' a iiood »|uality of fciiciiii;' and takiiiii; it to the mill to liavo it clawed in two. 'i'lic usual })i-ic(' for irawing foneiui'' in two in this way is $1.00 pen- thousand. The reason for i>"('ttinii,' fcncinii' and havinii' it sawed in this manner is to sa\'o expruse. It is the custoui of dealei's to eliarge the same jnieo for half inch a^ foi- iiudi lund»t'r, and hence buying g'O'od fenc'ina,- and ha\iii,u' it sawctl reduces the cost just omvhalf, lees the cost of sawinii'. The studding' should be covered iiiside and out with this sheeting-, nailing thoroughly with S-pciiny nails, two nails in each bo^ard at. every stud. The object of the boards is to act as hreviously wet. Tlie most rigid lining will be secured by laying the l)rick Hatwise, making the lay(M' 4 inches thick, but with onedialf the anioiint of hi'ick tluy may be set on edge, thus considerably leissening the cost. If set on edge, as represented in Fig. 200, a row of sj^ikes should be driven into the studding through the joints of every fourth course to h(dd the brick more ^ecnrclv in i»lac(! until the cement has had time to season. The mortar should not be niaih' more than one-fourth (d* an inch thick and great care shoidd he taken to leave no O'pen sjmce anywhere. The necessity of {dastering the wall may be avoided by hlling behind each brick wi'th onedialf an inch of mortar, wdiich will kee]) out the air as well as if on the front .side and there will be the a- in diix^ct contact with tho silage jnices. If care is taken in sicttin*;- the l)rick so aH to secure a smooth face, pointing the joints carefully, it will not be nec- essary to even whitewash the wall and a permanent lining requiring no attention will thns he secured. In tliis form of silo the brick may have one face tilled with coal tar, or the vitritied paving brick may be used, giving a lining wholly air tight and jK-rmancn't. Kor.Xn PLASTERKD SILO. AVhere l)!i(d< are high, luniher low, and clean, sharp sand may be readily obtained, a cemenr plastered lining may be made to take the ])lace of the brick lining, nsing the Mil- waukee, Akron, Kosendale or Louisville cement in making the mortar. The first coat is usually made with hair and a little lime to make it hang to the wall better. There are a good many of these lathed and })lastered cylindrical silos in Kacine and Kenosha counties in this state, and across the line in Illinois. Some of these have been in use since 1S,S!) and have given good satisfaction. 508. Construction. — The frame work of the silo should be made exactly like that of the silo ^vilth brick lining ex- cept that there should be two layers of half-inch sheeting on the inside with a layer of -J-ply (^iant P. and B. pa})er between, or other of as good quality. After the woodwork of the silo has been completed it should be lathed and ])laytei'ed wi'th a cement mortar made of 1 of cement to '1 of sand. If wood lath are used there should l)e furring strips of lath nailed to ea(di stud u)> and down and rhe lath nailed through the-e. If iiietal lath is used this may be nailed directly to furring !-tri])s of lath nailed to the studding over the lining and the plastering then done. It should be understood that it wouhl not do to lath and plaster a lectangular wood silo because the springing of the 408 walla wcmld crack the ceaneiit. It sliould be iinderetood further that on account of the fact that the layer of ceinent is so thin it is a niaibter of greater importance to keep the d^" tM' jrW' H Pui. 202. — Sbowiiiji' an all-wdud round silo on stone foundation. H rep- resents a method of sa\Yini; boards for the conical roof. surface whitewashed to prevent the acid from softening the cement and rendering it porous. It is because of this alsf> that two layers of lining with paper between are recom- mended. 409 CONSTRICTION OF ALL WOOD SILOS. T'j) to the urcsent 'tiiiK- iiKirc silos have be?n built of wood than of any other niatenal, and since 181)1, the niajority of wood silos hnilt have been after the model represented in Yig. 20'2. Very few silos of the rectangular type are now bnilt nnle.;. 2()-'> \j. Ill boil), iviHCS tlic Willi sliniijd lie linislicd sldpiiiii' ;is sliowii in tlu' di'iiwiiiiis. 510. Cementing- the Bottom. A tier the silo has been (•(►inpleted the j;riiiind loiinini; llie Imlildiii slmidd he thoi'- (Mij^hlv lain|H' sidid and then covered with, two d()d ednt'retci made of I of (•( nienit to li oi" 4 ot sand and t;ra\'el. The anioiint of silage wlii(di will s|)oil on a liaid clav lloor will nol lie lai'iic, ImiI enou^i;h to ]r,\.y a. i;' (d I he wall in some wav. If the woodwork rises from I he outer cdac of lire wall, tlien luiildiiiii' the wall n|> willi <•( incnl so as to coAcr the sill and lining' as represented in i^'iii'. 2()T will givo the needed slreiiiilh, hccansc the wodd-work will act as Ji lioo]); hut if I he silo stands a't the inner face (d' the wall, it will he he^t to lav pieces (vf irou rod in I he wall near t he top to act as a hoop. \\'liei-e I he s'tone |H)rtion 'li wall hclweieii the toj) and tile sill to allow a lie ro(l (d' iron to he heddrd in 'tliis portiou. So, too, the lower door in the woodwork of tlu' sil<) should lea\'e a full foot in width helow it (d' liiiiilii' and siding uncnl to act as a hooj), wliei-e the pressure is strongest. 512. Sills and Studding. The sill in the all-wood silo uiav he made (d' a single L'xl, cut in 2-foot l(.ngths, in the nianiier represented in Fig. 201 and deserilved under the hrick lined silo. 411 I lie ^t IhMkiJJ- oI IIiC nil \\(M|(| |(Ullnl mI() I'ect, liiil, tiu'V slHttild he set ;is close to^ctjier }is omk' fooi froiri (u-uicr to center, :i- re)ireseiilc(| in Fig, 201, I!. 'i'liis nniiilter of studs is not re(|nii-e(| Jor slrengtli hut tli(;y nn-. )i(^(;de,d in order to lirin;^ tlie two hiy''i*s ol' iitiinji- very close tf)get,}i(!r so }is io j)rcss the |)}i|»er rdosely iind |ire\cnt iiir Irom c]\\ca'- iii^' \vher(! tlie paper 1}||)H. A . ^ •^ . O . Kl<;. JJfM.- Sliowllij.' the (•(.liKliirflioM .,(■ Ilic il>iii|- (or tlii' iill worxl bIIo. l.v nilnToid i-ooUnu iiiid lidfl III pliici- with rmir lilt.' lioltM iiiiil ikiihIii'I'm, (Ik- i|iir>r opi'iiliiK on tli<- liiMlOr-. !•' Ik ;i Ironl vli-w of III.- (lour iriiidc of two lii.v hold in phic<. the alt<-rniitr -tiids nntil the lower 5 feet of outside shicct.iiii;' li;is Ix cii piil (Hi. 'I'lic -IikUsIkhiM h" set lir.-l ;il, tlio iiii^'lns I'oriiicd in tlic sill ;iii('d, (HI the side towiird llic cciiler. Wli.cii ;i miinlMT ol" llicsc liiivc Ix'cii scl llicv should he lied l(>i;( 'I hi'l' h_V hctidiiiii- ii' slri|» i>\' hidl' Iiudi sliciil iiii!, aioiiiid the outside.' as Jil<;li up as a luau can reacdi, lakina,' care to |)linnl» eatdi stud on tJu^ side l)(>:fore nailiuf;-. When I he altrrnate s'luds have IxH'ii set ill this way the halance may he placed and toe- nailed to the sill and stayi'd lo'llic I'ih, iii'st phnnhiui^' them sideways and to\\ai'( the thick edo-e do!("|) -enoujiii to receiixc the ihin e(li;i' n\ ihe hmii'd hehnv, will he all that is ahsolutely neeessary on the outside toi* streuiith and pi'otection ai;ainsl weather. This statement is made on the supposition llial the lininii' is made (d two layei's (d" fencinii' split in two, the three layers const it lit iui;' t hie hoops. If the silo is larger than IS feel inside diameler, there should h(^ a layer id half iiitdi sheeliiii;- oirtside, under the. sidiiii;'. If hasswood is used lor sidiiiii eare should he. taken to paint it at once, otherwise it will warp hadly if it ••'ets wet before > paiiitini;-. Ill applyinii,' the sheeting' heiiiii at the hotl(Uii, carrvinf» the work upward until staiiiii*;" is needed, f(dlowin ill. cjicli liojii'd ill cN-crv shid, ;iiiil !(► prcNciil tlic \v;ills from iictt iiii;' "out ol roiiiKr' I lie siicccccling i-ourscs of Ixjurd.s sliouifi Ix'iiiii oil the next -hill, fliiirt iiiakiii«i' tlic ciuU of tho boards hi'icak joiiifs. When tine staf;iiii;s arc put ii|) ik'W >l;iys slioiiM \\r 'lacked to the studs alutx'c, lakiiii;' ciiK to pliiiiih ciudi one Iroiii sid(» to side; tlic siding' itself will l)riii<;' 'tlieiii into |)laex! and kcc)) tliciii pliiiiil) the, otlier \va_v if caic is taken to start iiiew coiii'-es ;is deseiilted al)o\'( . 514. Forming the Plate.- -When the last sta«>,ino- is up the jdate should l»(^ foniied Ivv spiking' :^x4's, cut in two-foot leiifiths, in the iiiaiiincr ol" the sill, and as i"e|)resent.ed in. Fig'. 205, down upon the to])s of the studs, usini;' two courses, inakinu' the -second hiejik joints with the liist. l-'li;. 2Msiriictliiii ol' coiih-mI i-imr of roiinil sIId wlicrc riil'lcrs arc iiDl iisrace be- tween three or four studs. Headers, should be pul in every 8 feet to nail the ends of the sheets to between the studs, and these are best when sawed to the curve of the silo. The inetial should be put on with roofiug nails, nailing close so as to make the joints tight. After the metal is in place it should be given a heavy coat of asphalt paint, taking special care to make it heavy where the nails and laps come so as to shut out the air. When the metal is in place and painted it should be covered with a layer of sheeting made the same as that used outside, by splitting good fencing in two. The object of this layer of sheeting is, first to take the pressure of the silage; second, to act as a hoop for strength, and third, to kee]) the silage from softening and wi])iug the ]iaiut from the metal lining. Were it not for the fact that the heat of the silage tends to soften the paint, and its settling to wipe it off, it would be better to let the metal come next to the silage. Where the silo is more than IS feet in diameter it will be best to use two layers of fencing split in two, placing the galvanized iron between the two layers. In these cases the sheets of metal may be put on horizontally, using those 36 inches wide. All Wood Lining of 4-inch Flooring — If one is willing to permit a loss of 10 to 12 per cent, of the silage by heat- ing, then a lining of tongued and grooved ordinary 4-incli white pine flooring may be made in the manner repre- sented in Fig. 206, where the flooring runs up and down. 415 When this hiiiihcr is |)ut on in the seasoned condition a single hiyer wouhl make tighter walls than can he secured with the stave silo wliere the staves are neither heveled nor tongued and grooved. In the silos smalk-r than IS feet in- side diameter the two layers of boards outside will give the needed strength, but when the silo is larger than this and deep there would ])e needed a layer of the split fencing on the inside for strength ; and if in addition to this there is added a layer of 3-ply Giant P. and B. paper, a lining of very su- perior quality would be thus secured. Lining of Half-inch Boards and Paper. — Where paper is used to make the joints between boards air tight, as represented in Fig. 207, it is ex- tremely important that a quality which will not decay and which is both acid and water-jn-oof be used. .V paper wdiich is not acid and water- proof will disintegrate at the joints in a very shoi't time and thus leave the lining very defective. Great care should be taken to have the two layers of boards break joints at their centers, and the paper should lap not less than 8 to 1 2 inches. The great danger with this tvpe of silo where tiie lining is made ^. . -Ti 1 T 1 1 ofordiuary tour inch noor- lining W'lll be that the boards maV not ins running up and down, , , „ '^' and nailed to girts cut in press tne tw^O layers OI paper together between the studding every close enough so but that some air may rise between the two sheets where they overlap and thus gain access to the silage. It w^ould be an pxcellent precaution to tack down the edges of the paper Fig. 206. — Showing the construe' ion of the all-wood I 1 closclv witli small carix't tiK'ks wiici'c tlicv oNcrlap, and if this is (loiic a lai» of 2 iiiclics will he snilicicnt. Fii!. 3)7. I>. Sliowiiiii' iiu'llioil or isl riicliiij:- Ihc !ill-\vo(iil roiiinl silo iiiul cDiiiiccliiiK i( with Ihc \v;ill llnsli wilh Ihc onlsiilc. This t\)i\\ro sliuws Ihc iiiosi siilistiiiil iiil I'nriii nl' ciiiisl ruclloii with three liiycM's (if li;ill-iiiili liiinlpcr Mil. I two l.MVci-s ol' I lircc ply jicid Mini water lirool' I'. iV- r>. |iM|)er iielwcen llieiu. A very excellent silo is iiiMile al'tei- this jilMii oiniltini;- ihc inner iMyer of liiiiiin mikI paper and tlie layer of pMpcr on Ihc oulsiile. With siiiMll silos Ifi I'eet in diaiii- elcr (inly 1 lie siding >>ii Hie oiiiside is neccssMry I'or slrcn};ih Mini lirotcctiiin a!;Minsl weather. I'l. Showinu' method of const rnel ion for venlilalinj; the spaces hctween tlie stnddiiii;- in all-wood and lathed Mild piMstered silos. The tower portion shows the intakes of fresh air fron; the oiitsid(» at the lioltoin. and the npper portion shows wliert> Hie air enters tli" silo at the plate to pass out at the ventilator ill I fie roof. Siicli a liiiino' as this will he very iliirahlc' hci'ansri tlio pajMT will kc('|> all \\\r liiiiihcr drv except tlir inner layer of lialt'-inch hoards, and this will he kept W( 4. hy the paper and silaii,(i until eini)ty and then the small thi(d' to s(>t in. A still iiionp substantial lining- of the same type may be secured by using- two layr between iln'ee layei'S of boards, as roprosented in Fig. "207, and if the climate is 417 not, oxtreriicly s»v(-i'c, or if the -ilo i- only to ]>■ f< (| from in tlio KuinnuT, it would Ik- l.ctici t the undf-rside of rhe roof dry and in tln^ case of wood silos, to prevent tin- walls and lining from rotting. One of the nio.st sei-ious mistake- in the early con.stniction of wcxwl filcjs was the making of the walls with dearl-air spaces which, on accrumt of the dampnes- from the ~ilage, lead to rapid "dry rot" of the lining. In the \v(H)<\ -ilo aiid in the brick lined silo it is irnfx^rtant to provifle ample ventilation for the spaces lK;twrif?n the .studs, as w(dl as for the roof and the inside of the silo, and a g(Kjd method of doing this is n^jresented in Fig. 207, E, where the lower portion represents the sill and the upper the plate of the silo, lietween each pair of stnds, where needled, a one and one-fourth inch auger hoh^ to admit air is hored through the siding and slx-eting and covere kf^ep out m'loa and ratH. Ai the t/jp of the silo on the inside the lining is only r^overed to within, two inchfis of the plate and this sparse is covered "with wire netting to prevent silage from })eing thrown over when filling, 'i'his arrangement jyarmitH dry air from outside to enter at tho bottom between each pair f/f sturls and to pass 418 u)) and into the silo, thus k('{'])iiii;- th<' liiiiiiii' and studding' dry and at, the same time drving the undrr side of the root" and the inside of the lining avS fast as exposed. In those c^S'es where the sill is mach^ of 2x4\s eut in 2-foot lengths there will be sj)are enough left between the curved edge of the siding and sheeting and the sill for air to enter, so that no ho[es need be bored as (h'scribed above and re])re- sented in Fig. 207 E. The ojienings at the plate shonld al- ways be provided and the silo should have some sort of ven- tilator in the roof. This ventilator nia_y take the form of a cupola to serve for an ornament as well, or it may he a simple galvanized iron pipe 12 to 24 inches in diameter, rising a foot ov two through the ])eak of the r stave silos and liave made a careful study of the unavoidable losses in one ol" these. We have also studied tire unavoid- able losvses in two kinds (d" small stave silos. .\s a result of these obvservations it Ims heen demonstrated that there ai"e several very senious objections to stav(> silos intended as ])er- manent huildings out of dooi-s. Some of these are stated below: 1. When the: silo is empty the staves sliriid< and loosen the lioojis and in this condition the wind racks the building, getting it out (^f round, out (d" ])lumb, and out of ])lace u])on the foundation. It is nuudi more easil\- blown down tlian 410 o-tluM' fdiiiis of silos. 'I'wo of the foui-tci'ii oirf-of-(|()or nilos visitt'U had \>vvi\ Mown down; one (»f these was abandoned and the hoops sohl to aiiotlier farniei-; the other was set up aiiain at the expense o-f a (Uiy's (h'ive for new staverf and j»(^t- tiiiii' the carpenters to set it np, tlie aceich'iit ha]>peiniii>' just as they weie ready to till 'the sil<» last fall. A third silo of the fourteen out-of-doors we visited liud moved on the founut, by a fortunate coincidence, two of the ten hoops remained intact to hold the silo u]), assisted by some half-inch boards Avhich had been bent around the inside of the silo at the top to prevent the staves from falling in. In another silo where 4x4 oak ])ieces had been used as lugs, the i;-iii(di iron washers had been crusheil their full dejrth of one-half inch into the hard wood and tw'o of the ])ieces of wood lia; to ciiui'o.ss tlic nt- tciitioii of i;,"lit or to loose. 3. Staves do not eoiitain the same ainomit of ©apwood in all parts and for tliis reason shriidc nnecpially, with the re- sult that after -'5 o^r 4 years' use there are places which do not clone up tig,'htly on swellinii; and whicdi oi>eii again on 'the sunny side of the silo, and thus admit air, even where the silagie is in contact Avith them. Three of the silos visited showed these jiecidiarities, and in one of tlieni visited last winter we couhl see thVouiU,h be- tween several stax'cs on the south side (d' the sih» close to the silage surface, on the inside. 4. The expansion and conti'action of the staves duriui;;^ wetting by the silage and drying when the silo is einpty makes it dithcult to securely anchor a ])erinan.ent roof and impossible t(> connect the staA'cs permanently with the foun- dation, so as to be air-tight. Something must be done each season to ceinent the joints Ix'tween the staves and fonn- dation or air will enter. 5. There is no reason to hope thai good silage with snudl losses ,in dry nuilter can he made in the stave silos which are not cai-efully constructed (d good IuiuIkm- Avith the staves both beveled, aiul tongued and grooveil. It is I'eally more difhcult to make a stave silo air tight than it is to make a tank water-tight, and we have found by carefni tefttsthat the unavoidable losses in a new stave silo next to the walls were: as high as 24 to 2cS |)cr cent. 519. Construction of Stave Silos, 'idiere ar(^ three meth- ods adoj)ted in the construction cd" these silos. The; best and only one which should be used in the ]h rnuinent siK> is that represented in Fig. 208, where the staves are both beveled and tongued-and-grooved; the second is where the staves are beveled so that the Hat surfaces Hi together ac- curately as water tanks are nmde; the third ])laji us(\s the lumber without, either lievc'ling or tonguing-and-grooving, and this both observation and principles of construction in- 421 (licatc slioiild lie ;i(l'ardino- fhoir perma- nent {■tiicicucv. I'"n;. 20JS. — SiKiwiiif;- ilic ci.iisrrui lidii nC ilic sliivc silo. A sliows Hit- sili> oimiplftc on stdiic f()iii!e a trasicet of tlii-eeiily rulieroid rooting,'. 'IMie door slionld also lie laii ha.s hccu rceouiniendcd he(^au!-ti the first cost is relati\( ly hiw and because it is assumed that the pres- 2G 422 siiro duo to tlio swclliiii;' (if the wooil iind tlic liiiiditv of tlu; HoQps will result in criisliiiiii' the cdiids (d" tlu' t^taveis to- gether so as to uiakc a sutliciciitly tiolit ji>iiit to pivscrve the silage. 520. Lumber for Staves.- -T lie linuLer s(dectod for the staves of this t\})e of silo should he (d' the <>Tade knowu coui- luereially as "tank stiitf," and luiidtci' fircst from knots and steaightest giaincd is host. Wood is (piite air-tight undei' low ])re^ss^l^('s in directions aci'oss tlic giain Invt along the grain tlu^ air passrs nioie oi less freely. The \Va.shing- ton eedar appears to he an excellent wood for this ])uri)(xse, as it shrinks nnudi hss than the pine attcr the silage is re- moved and, ftn'this rcasdii, tlic hnilding will he nnudi more stable when cmpt\' and U'ss jiahlc to hurst tlic hoops when tilled. Where the silo is to he deepc r than can readily he secured with singh' lengths of lund)cr thc! staves may he spliced in the manner represented at ( ■, Fig. 208, where a saw-cut is made in the ends of the two staves and a })ieee (d' galvanized iron, a little wider than the stax'c is sli[)ped into it. Thi^ ernshes into 'tlu' wood dii the sides and forms a water tight joint. 521. Foundation of Stave Silo. — Ou account of the ten- •deney of the sta\'e i I'l (iciirc ill pi.sts set up al;ain-^t the sih) outsi(K' or sha|)('d to act a< a part of the slaxcs as has hrcii reeoni mended. In \isitiiii: o\( v 100 sihis in istM it was found tluit whcicvci a sih) liniuii had a hca\v tindicf hack of it, the holding ot danipncss cansid totting there in three or four years, and il i- ipiil.' <'eilai!i thai the use df iion lugs is the; safest way to a\oid ihi- danger in sta\'e silos. 523. Doors for Stave Silos. — A good method of construct- ing d(^(>rs for the stave silo is represented in Fig. 208. Two inch hiniher is holtcfl to the staves on the outside, pro- jecting two in<'iies into the doorway all around, thus form- ing a rahliet against which the door may rest. A strip of thick rtdx'roid rooting shonhl he nse<| on the rahhet under the door and the door drawn down tight with four lag holts and wa.shers. A common way |)lasitered with a tliick coat of puddled (day and the duor i'nvm] lightl\- into this a fairly ilage to i\ i(\. If the soil is of such a charactei- that it will not cave in tlie i)it may he ma'e.>^. .V silo oO feet dec]) will .-tore nearly ."> times llio anioTint of feed that one 12 feet deep will. l)onl)lin<;' the diameter of a silo increases its eapacitv more than fonifold and a silo :')() feet in diameter will hold more than S) times as mn(di as one 10 feet in diami ter and of the same d(>])th. It is (deai' from this that small silos must he I'elativelv mor<' eostiv that those of larii'ei- diameter. Table giving the approximate capacAtij of cijlindrical silos for well matured corn silage, in tons. Depth, Inside Diameter in Feet. Feet. 15 16 17 18 19 94.41 ICO. 9 107.9 115.1 122.1 129.3 1.H7.1 144.7 15;i 4 160.3 168.4 176.2 184.6 20 21 22 23 138.3 147.9 1.58.1 168.7 179.0 1S9.5 200.9 21i.0 223.3 234.9 246.8 258.2 270.5 24 25 163.4 174.7 186.8 199.3 ill. 5 .'23.9 •37.4 :;n0.5 63.9 !77.6 91.6 05.1 319.6 26 20 21 22 23 24 25 26 27 28 29... 30 31 32 58.84 62.90 67.:^5 71.73 76.12 80.6^ 85.45 90.17 91.99 99.92 105.0 109.8 115.1 66.95 71. 56 76. 5i 81.61 86.61 89 61 97. 23 102.6 108.1 113.7 119.4 121.9 135.9 75.58 80.79 86.38 92.14 97. ?8 103.6 109.8 115.8 li2.0 128.3 134.8 141.1 147.8 84.74 bO.57 96.84 103.3 109 6 116.1 123.0 129.8 i:-;6.8 143.9 i51.1 1.58.2 165.7 101.6 111.8 119 6 1V7.5 135.3 143.3 151.9 160.3 168.9 177.6 186.6 195.2 204.6 115.3 123.3 131.8 140 6 119.2 158.0 167.5 176.7 186 2 19.1.8 20.) 7 215.3 225.5 126.6 135 3 144.7 1.54.3 163.7 173.4 183.8 194.0 i!01.3 214.9 •^25. 8 236.3 247.5 1.50.6 161.0 172 2 183.6 191.9 208.4 218 8 230.8 243.2 255.8 268.7 281.8 291.0 176.8 189,0 202.1 ifl5.5 2' ex]>osed or feeding sur- face. It is also important to have the horizontal dimensions as large as jiosyihle Ix'cause the larger the silo is the less it costs in ])roportion to the feed it stores. Then, too, nan'ow, small silos (lo not alloAv the silage to settle as well, and hence in them the necessary losses are proportionally greater than in the larger ones. 426 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 np})er half of the silo than in the lower half l)ut it will be ]n-udent to have 'the silo of such a diameter as to lower the surface more rapidly in feeding than is nece^saiy rathei- than less rajndly. A silo 30 feet deep will allow 1.5 inches in de]irh of silage 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 will be seen that the mean weight of silage per cubic foot for a silo 30 feet deep is 39.0 lbs., and allowing 40 lbs. of silage per cow per day it is seen that a cubic foot of silage on the average will feed a co^v one day. But from the same table it will 1)e seen that if the silo is 24 feet deep there will l)e required 1.1 14 cnbic feet of silage to give the desired weiffht. Table giviuf/ the inside diameter of silos £4 feet and SO feet deep luhich will permit the surface to he lowered in feeding at the mean rate of 1.2 tolii inches per day, assuming 40 lbs. of sil- age to be fed to each coiv daily. Feed for 240 Days. Feed for 180 Days. No. OF Cows. Silo 2U feet deep. Silo 30 feet deep. Silo iUfeet deep. Silo SO feet deep. Rate 1.2 in. daily. Rate 1.5 in. daily. 1 Kate 1.6 in. daily. Rate 2 in. daily. Tons. Inside diameter. Tons. Inside diameter. Tons. Inside diameter. Tons. Inside diameter. f^. in. ft. in. ft. in. ft. in. 10. .. 48 11 11 48 10 2 36 10 4 36 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 \m 15 2 35 168 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 5 162 21 11 162 18 7 50 240 26 8 240 22 7 180 23 1 180 19 7 60 288 29 2 288 24 9 216 25 3 216 21 5 70 336 31 6 336 26 9 252 27 4 252 23 2 80 384 33 8 384 28 7 288 29 2 288 24 9 90 432 35 9 432 30 4 324 30 11 324 26 3 100.... 480 37 8 480 31 11 360 32 8 360 i,7 8 Using these data tlic iii>i(l(' (liaincrcr of cvliiidi'ical silos 24 feet and 30 feet deep which will hold feed enoiiii'li for diif(n*ent nnnibers of cows may he coniputed and sncdi re- sults are given in the preceding' table. 528. Danger in Filling Silos. — It never should be forgot- ten in connection with the lilling of silos, that carbon diox- ide is generated very rapidly the first few days after sil- age is pnt 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 accuninlates in sufficient quantity over the silage 'to make it impossible for a man to live in it. (Jases ao-'e 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 Avill 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 injunous. In causes where the silage is below any opening far enough to leave a man's head below tlu^ o]>ening 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 cuiTcnts 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 accunmla- lation to take place. 428 FARM MECHANICS. CHAPTER XX. PRINCIPLES OF DRAFT. Tt" it wero jxtssihlc to constnict ;i pci'tcct road its leiigtli would be the shortest distance between the places con- nected, and it would offer no resistance to movement over it. A pair of ])arallel, level, smooth and rigid steel rails, well bedded, constitut(^s tlie nearest approach to the perfect road yet devised, and how vastly superior the steel track of the railroad is to the best ])aved street is shown by the enoniious loads moved and liii;li speed attained over them. 529. How the Draft Increases With the Grade.— A ])ull of 2,000 lbs. 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 ofte foot in 100 feet it is said to have a one per cent, grade, and this anionnt of slope will increase the draft one ]>er cent, of the weight of tlu^ 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 fe(4 and will increase the draft of a ton 200 lbs. over what it is on a level road of the same char- acter. The heavier the loads to be moved, then^fore, the 429 more ohjcctioiiiihic bccoiiics any . Weight Distance P. X P- D- = W. < W. D. Suppose the road-bed in Fig. 209 has a lengtli 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 lun-e passed over a distance of 100, acting parallel with the road bed, but, leaving friction out of consideration, the Avork done is to lift the load vertically through a distance of only 10, and since the distance which the weight is raised is only A of that over which the power has acted it is only neces- sary that the pttwer shall be "/» of the weight or P. X P. D. = W. X W. D. P. X 100 = 60 X 10 whence 100 P. = 600 and Power = 6 lbs. 532. The Steepest Grade Admissible. — When it is asked what is the steep)est grade which should be permitted on a given road there are many factors which must Ix; consid- ered, but the most general rule is to make the grade as small as practicabki on roads where horses are expected to carry all they can well handle on good, nearly level roads, and 431 the better the level ])art of the r(»a(l, the longer the haul and the more teams to ])ass over it, the less steep should the grade he. On all well designed roads a great effort is usnally made to keej) l)el()\v a rise of seven feet in 100 feet. Just M'hy low grades are so necessary will he readily understood from the following considerations: About the maxinnim walking draft of a horse on a good level road is measured hy onedialf his weight. Trials have shown that a l,(i.'>ldb. horse can excn't a steady pull of 800 lbs. Avhile walking 100 feet, and that an 83G-lb. horse may maintain through the same distance a steady draft of 400 lbs. It would not be safe, however, to repeat such strains often nor maintain them long. Even a draft equal to oue-fourth the Aveight of the animal is a heavy and ex- haustive pull. Indeed a steady pull eipud to one-tenth of the. weight of the horse for a tendiour daily service at the Avalking pace of 2.5 miles per hour is an average of effect- ive service and the work of a l,0'00-]iouud horse Avould equal 5,280X2.5X100 _ . h 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 lbs. ; he may pull over hills at the rate of 200 lbs. and in emergencies 400 lbs. A l,600-})ound horse at the same rating may pull steadilv ir)0 lbs., up hills 400 lbs. and in an emeTgency 800 lbs. It has been found that to move a gross ton over a good level dirt road requires a traction of about 140 lbs. A team of 800-pound horses may therefore come to a hill with a load of .j-tt; tons = 2,2855 pounds. 140 Up how steep a grade may such a team carry this load with a steady exertion of 200 lbs. jier horse? To over- 432 come the resistance the road bed offers to the h^ad requires a steady pull of and this leaves the reserve draft to go np the grade (200 :■: 2) —160 = 210 The load to he carried up the grade is the weight of the team plus that of the load or (800 v; 2) + 2,2855 = 3,885f lbs. Up how steep a grade will 240 lbs. carry 3,885f lbs.? Solving this problem by applying the principle of (531) we shall have P. X P. D. ^-- W. W. D. or 240 X 100 -= 3, 885f X W. D. , „- „ 24,000 „_,. whence W. I). = = b.lib or o, oo52 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 lbs. Proceeding as in the other case we shall have P. X P. D- = W. X W. D. and 640 X 100 = 3,885? x W. D. 6,4000 _ .^ whence W. D. = = 16.4 < O, OoOS 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- 433 pected to carry tlio load over wliicli it was able to briug over a level dirt road to it. These results have been computed from the standpoint of an SOO-jxiund 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 -^ = 2^ t\mes as much or 4,666| lbs. = 2^ tons. on the level macadam road. Since it requires but 60 lbs. to move a ton on a macadam road it will require 60 ;<; 21 = 140 lbs. to draM' the 2-t tons on the level road, hence the effective power of the team will be 4(X) — 140 = 260 lbs. Up how steep a grade will 2(>0 ll)s. carry the team and 21/^ tons ( Solving this as we did the other we get 260 X 100 = 6,266| X W. D. , .„ ^ 26,000 , ,,„ whence W. D. = _ ' „ = 4.149 b, 2od| or a little more than a 4 per cent, grade. That is to say, when a dirt road is improved so as to reduce the draft from 140 lbs. per ton to 60 lbs. per ton then, in order to utilize this improved road with equal effectiveness under the con- ditions assumed, the 6.2 per cent, grade should be reduced to 4 per cent. ; and the highest grade could not exceed 10.53 }>er cent. 434 DKAFT or UA'ioXS OX THE LEVEL. There are many factors Avliich modify the draft of a wagon over a h'vel road and some of the most important oi these are: 1. Smoothness of the road-bed. 2. Rigiditv of the road-bed. 3. Width of the tire. 4. Diameter of the wheel. 5. Dis'tribntion of the h)ad on the carriaiic 6. Direction of the line of draft. 7. ]\ig'idity ot' the t-arviaiic 534. The Smoothness of the Road-bed. — "When the road- bed is not smooth and has nnmerons I'nts, stones or other obstructions npon its surface, the draft of the h>ad is in- creased and the wear on the vehicle and on the road-bed is also greater so that much effort and care shoidil bi- ex- ercised to have the road smooth. The increase iu the mean draft of the load is not so great, howt'ver, as rlu' other dilficulties 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 tt'nds always to give back a ))ortion of the energy ex}>ended in I'aisiug the load upon the ol)- struction or out of the rut. 535. Rigidity of the Road-bed. — A yielding road-bed is perha})s the most serious defect of roads, and the one which inci^eases the draft more than any other. If a wheel is steadily cutting into its road-bed it is continmdly tending to rise over an obstruction ov 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. 200 is represented a method of measuring the in- crease in draft due to the wheel rising over an obstruction whose hight is a stated ytov cent, of tlu' radius of the wheel. The arraiiii'eniPiit at (' is provided witli a screw and iii-adn- ated so that tlio hl<»ek may l)e raised or lowered al will, setting it so as to re pi-esciit rlie wiiecl passinu' (>\-er an oh- struction, 3, 4, 5, etc., per cent, of the i-adius (»f the wheel. By setting- the road-hed indiiKMl ;is shown in the tignre, the draft is first noted and then the thumh sercnv at 1) is turned until the wlund rises upon the hloek and the diffei'ence be- tween the two j-eadings of the scale exjjresses the increased draft due to the ohsri-uctioii. When the ohstrnetion is oidy four [lei- cent, of the radius of the wheel the di-aft is increased inore than two-fold. That is to say, if a wheel is 4S inches in dianietei'. an ob- struction of four ])er cent, would lie oidy .IXi of an inch, and yet the draft is nuide by it more than twice as heavy. When the wheel cuts in one inch the draft would not in- crease quite so much becaust' the wheel never rises quite out of the rut, but the diiference between the draft on the macadam and dii-t road is diu^ nu)stly to the ditference in the yielding, oi* cu.tting in of the wheels. An experiment conducted by the I'nited States Depart- ment of Agriculture, testing the draft of ordinary wagons on a steel wagon road, showed that a single small horse 436 oiiHily drew 11 tons, <>v ii2 (iiiicH ilic- woiglit of the animal, and it is Htutcd in tlu^ report tliat tlic lioi'Bo could readily liii\'(' lianlcd r»0 times his own weight. Tliis would he, for a |,()()0-p(innd liovse, LT) tons, hnt ol' course wilh such a. h>ad thi(^ i'o;id nuisl h(< pr;icl i<';dlv h'Vel, tor :i <;r;i(le (d one per cent, woidd increase ils(h';ill r>(»0 pounds. 536. Draft of Wagon Shown by English Trials. — The powi^r re(|iiire(| lo draw ;i Innr wliee|e(| \\';ijL;on oNcr roads of ditl'erent chai'aclers has l)een lesled :ind ihe tullowing (!X|)i'esses the results in. pounSO j)ounds respecl ively, when the wa:;(iiis were tree from mud. 'r\w following' are his residts: On niai-adani Htrents, wide tire 2G per cent, less than narrow tire. On gravel road, wide tire 24.1 per cent, les.s than narrow tire. On (iirt roaiJH, dry, smooth, free from dust, wide tire 26.8 per cent, less tiian narrow tire On clay road, with nuid deep, and drying on topand spongy ixmeath, wide tire 52 to (il per ct^nt. less than narrow tire. On meatlow, pastin(\ Htul)ljle, corn ground and f)lowed ground from dry to wet, wide tire 17 to 120 p(fr cent, less than narrow tire. On ihe oIImi- liaud hi' touud that when the roads were eoveretl wilh a deep dusi, i>v wilh a Ihin mud Iml hard he- low, the narrow I i red wa^on ga\'e the liiihiesi dratl. .\lso when ihe mud was lliick and so slicky as to roll up on ihe vvhe<'l, loading' it down, ami a^ain when narrow tired wagons had made dee|> ruts in the road which the wide > Bull. No. ;{'J, Missouri Agr. K.xp. Station. 43T tired wagon tended to fill up, tlic narrow wheeled wagon gave the lightest draft. 538. Size of the Carriage Wheel, — It is plain from what lias 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 Avheels 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- nnnits 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. Station, Colnnd)ia, ^lo. 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 wheels and 28 inch hind wheels, all having tires 6 inches wide. The total load including the wagon was: For 1, 3,762 ; for 2, 3,580, and for 3," 3,362 pounds. The drafts in his trials are stated in the table below : Description of Conditions. Dry gravel road: sand 1 inch deep; some small, loose stones Gravel road up grade 1 in 44; covered with one-half inch wet sand ; frozen beneath Dirt road frozen; thavping oue-half inch; rather rougli ; mud sticky Timothy and blue grass sod, dry, grass cut Timothy and blue grass sod, wet and spongy. .. — Cornfield, flat culture, with spring-tooth cultiva- tor ; across rows ; dry on top Plowed ground not harrowed, dry and cloddy 27 High wheels. Medium wheels. Lbs per ton. Lbs. per ton. 84.48 90.45 123.0 132.1 100.6 119 2 131.9 145 2 172.9 202 6 178.5 201.2 252.5 302.8 Low wheels. Lbs. per ton. 110.2 173.1 139.1 178.8 281.1 265.1 373.6 438 For uso on the I'ariii the advaiitiiiic^ of truck or low wheels comes in the saving' of lal)or in liiiili lifts in placing manure and other materials upon tlu^ wagcm, and here a sacrifiee of strength of the horse may advantageously be made to save that of the man. A lighter draft and lower life in handling loads are seeiire(| by nsing the low (h)wn carriage hed in the nppei- part of Fig. 211, than are possi- ble with the \'ery low whe( led wagons shown in the same ent. 539. Distribution of Load on the Carriage. — When there is nothing to prevent doing so, the load carried l)y the wagon should he so (listribnte(l npon the wheels as to be di- vided ])ro))ortionately to the surface the wdiecds present to the ground, and when the front wheels are' smaller they should carrv a snuiller load. When care is not exercised Firations of the next paragraph. 440 541. Direction of the Line of Draft. — lu 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, wiiere the apparatus may be used to clearly dem- onstrate this princi])le. It will he seen that as the spring balance is moved u}) upon its arc the line of draft is such that it tends partly to lift the load oif the road and so much that if it were pushed around until the direction Fig. 2l2.^A!H)ar;itn>i fur demonstratins the influence of the direction o£ tlie line ot draff iin tlie draft nf 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 do\vnward wpon 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 Mdiole effect would be lost in pro- ducing pressure. In the movement of cars by the locomotive over the 441 smooth nil vicl'liiiii '»<',raplL may appear to be contradieled by the general practice of having the traces nearly always slope decidedly backward and downwai'd. The former state- ments, liowever, are not incorrect, neither is the common practice fnndamentally wrong. The apparent contradic- tion grows ont of the fact that the road is seldom either smooth or rigid so that the wheels on the average are in effect continnally 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 Fi<;. 21S. — Apjii'r.it IIS fm- dcnioiistriitiiiji the iiifliK'Ucc, iiixiii the draft, of the rtirertioii (if the line cf the draft nf ;i wafioii when the wheels ;ire passing' over an ohstrnctiou or cuttiiifi into the road or jji-onnd. 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 stnietioii, it Avill be found that tlie draft dt-creases until this direction is reached, but that passing beyond it again increases. In other M'ords, the draft is least when the di- rection of tlie traces is parallel with the effective road-bed. It is clear, tlierefore, that in teaming with wagons on the Held and on any but rigid, smooth roads the least draft is secured when th(> traces incline more or less downward, the amonnt increasing the more yielding and the more un- even the road. In regard to the di\'ision of the load between the front and hind wheels it is clear that the hind wheels are drawn bj the reach from the king-l);dt, the line of draft being nearly horizontal, and, this being true, it may fairly be concluded that on ordinai-y roads and upon the Held 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. Rigidity of the Carriage. — Where the road is notper- 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, diminisb the strain upon the car- riage, and permit less injury to the road. 443 544. Results of General Morin's Experiments in France General JMorin. after a series of experiments carried on nnder the French government, reached the following- con- clnsions regarding the draft of carriages on roads: 1. The traction is directlv proportional to the load, and inversely ])roj)ortional to the diameter of the wheel. '2. I ])oii ])aved or hard macadam roads the traction is independent of the width of the tire when this exceeds three or fonr inclies. .';. At a walking pace tlu^ ti-action is the same for car- riages with springs as for those withont springs. 4. rpon a macadam or paved road the traction increases Avitli the s])eed ahove a velocity of 2.25 miles ])er honr. 5. Upon soft roads of earth or sand the traction is inde- pendent of the velocity. 6. The destrnction of the road is in all cases greater as the diameter of the wheels is less, and it is greater by the nse of carriages withont springs than of carriages with them. 444 CHAPTER XXI. 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-])ed 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 an mud them, but when the hill is both long and high then it may be best to reduce the grade by j)assing obliquely up the hill, or in mountainous countries where ranges are crossed through I^asses 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 gi-ade, it will not be as important to cut other hills down as much as a more level country would warrant. 445 The better the more level portions of the i'<»a(l are, where heavy teaming is done, the more important it i« to reduce the grade to a low per cent, because it is important to be able to go over any hill readily wliicli can In^ ap])i'oached with the largest hiad 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 roah'tel\ li Hed with water the iiulividual soil gTains are iuvestiHl hv wati r and tend to float in it so that there is the ii'reatest freedom of motion of the jKirtieles. On the other liaiid h't all water he removed troni the soil and the j:,round, whih' hard. I'asilv frets into tini-, loosi', si'jiarate dust partieles, which not only increase the draft hut ai'e easily drifted away hy the wind, thu> injnrini:- the road much as it would he were llie top waslunl away hy running water. There is a meilium condition or amount of water in the soil which gives it pt)wer to withstand the eroding tendency <»f the tramp of the horses' feet and the rolling of thi' wheels. When sand is just wet enough its surface is hard and will carry a hea\y load, th.e grains heing hound tii- gether hy tln' surface ti'usion <,»f the water films. So, too, with the clay roads and th;ise of the host of loam, tln' right amount of water always ju'csent, so as to keep the sur- face dam]) and dark without making them soft, greatly improves the ipuility and lengthens their lite. So \alua- ble is the right amoiuit of watt'r on earth roads thai spi'ink- ling tlu'iu in arid and semi-arid (dinuites and in di-y times in liumid clinuitcs. is one (d' the most t'tlectixc means ot uniintenauce. 548. Depth of Under Drainage. — AVherc under drainage is n{H>ded the drain shoidd not he less than three t(» four feet deep, and this is I'specially true if heavy trathc is to ho maintained over it. No one thiid\s of walking on th(> yielding surface of the water of a lake t)r stream, hut let it lie coveri'd with a sutfi- ciently thick layer of ice ami it then makes the host kind of a road-bed. The drained iiroiind heneath the road surface 447 Jiitist lie siiHi<'i(iitlv tliick i<> riii;it. !i <', because; this M'ill not be injured bv i'reezini;' uor b(^ easily broken. There should be a I'va' fall at the end of the drain, and it is better that the openiiii; shouhl be protected bv some sort of metal g'ratini;' or screen to pi'e\'eiil aninnds from running' in in drv t imcs. 552. Size of Tile. Tile thi'ce inches in diauu'tcr is the bi'st to use lor the reason that, in case the i;ra\' the road and the I'oaihhed hcneath it can he kej)t with only a small i>ei- cent, of eapillarv water in them the danjifr of irijni-y lieni frost is i:i-eat!y lesscne(l and the liahility to soften dnrinii,' wet pei-iods is idsu lamely removed. Water shonhl under no conditions he permitted to stand either upon the surface nor alonj;' the side of the; I'oad, the Kha|)e heiiiii' snthciently i"(ninde(| to thi'ow the rains cpiickly to either side, and the snrfa<'e dit.ches deep eiioniih, clean enon^h and possessina snllicient ciipacity to cai-ry id; water rapidly away. 555. Slope of the Road Surface. — In order to luive quick, comj)lete surface drainage it is uecessary to so ai'ch the face, as to make a road twelve feet wide thi-ee inches hiyher in the center than at eithei' mai'iiin, a slope of ahont four per cent, or foiii- inches in 100 inches. Dnt if the road has itself a considerahle j^rade, then the slo])e must be made (nuiu^h greater than four per cent, to force the water to the side ditches i-ather than to permit it to How down the center of tiie road. ihif (^'(jnness or smoothness of surface is the most im| across them. \\'liene\'er it hecdines necessary to cari'\' water across a road on a hill from one i^nttei' to the other it is mneh better to cai'ry it nnder the road than ahoxc it, as is so often done with the aid ol waterdtreaks. A cnKcrt is of course necessai'X' bnt it shonld he \\>('d. 'I'K.XrrU'K <)K IJOAI) AlATKUIAl-S. Closeness of texture is necessary to the building' of a solid road, 'i'lie more complet(dy all ])ores can be obliter- ated ami the road iii\-en the close texture (d' iron the bettei- and more dnrable will it l)e. Fi(dd soil in its natnral con' each layer hcdore th<' next is l)Ut in plaec ; the thickness of these iayei's should he 2 ijiches ami less, rather than more. 558. Uniformity of Size of Material Used. — It is impossi- hle to ci'ush reach gravels and sands cannot be held rigidly by any ordinary cementing nuiterial because, with the round, smooth snrfaces, there is little o])]>ortunity for any locking. 560. Cleanness of Material. — Where crushed rock is used in the buihiing of roads it is important that these nniterials 1)0 clean and tree fi'om dirt, chiy and rnbbish of any sort. So with gravel or sand, when these are called for they should be clean. Tn general, anything which works against uniforniitv of material should be avoided. EARTH ROADS. In the country in most parts of the Tnited States the gr(;atest nund)er of miles of travel for a long time to come must be nuule over eai'th roads. It is therefore of gTeat imjiortance that they should be built in the best possible nuinner. The projier construction of earth roads is made tli'e more important through the fact that when well built and well nuuntained there is no road easier on the team, the carriage or the ])arties riding, where speed is an im- ])ortant c,iv('T) the f(ti'iii and width dcsircid by a road inacliiiic sutdi as represented in Fig. 215, or by other means. Tlie ro'Ai] itself shoidd liave a width of IG or IS feet bor- dered (111 eillier side by ;i slrip of grass three feet wide, out- side of which shoidd lie the surface (]rains, wherc^ needed, five feet \vi(h' at the top, two feet at tlie ])ottoin and 24 inches (K'C]), making a total width' of .'52 oi' 34 feet as rep- resentee] ill I'^ig. 2 14. Fig Jit — Show ui^ tios-, '•t c tioii ol 111 ( iillii 1(1 1> fi I t \\ i(l( boi'dcreii on each Hide with .i ti>(it ot Kiass, oiit^nio til winch aru placo.! tlin surlaco (Jrains when needed. Tlic center of thi^ road is three iiiciies luKlior than the sides at the srass. The ceiitei- of the roaddn'd shoidd be thoroughly rolled with as heavy a I'oJhT as practicable in order to compact it and to discover in it any soft jilaces. Jf soft places are found these should be filled and brought to tlu? projier lev(d. Jf the soft jilace is due to a different kind of ma- terial this should be removed and replaced liy other and better. The center (d' the finished road sh(tuld be two to six inches higher than the margins at the grass boi'der, vary- ing with the width of the track, in onh'r to give quick, com- ])lete surface^ drainage, and tiiis should be built up in thin successive^ layers of as uniform material as possible. If eartli is brought in Irom the sides and ditches gi'cat care shonld lie exercised in distributing it evenly, and thor- oughly harrowing it ahead of tlu^ roller, so as to secure the necessary nniformity of textnre. 'Idiis is of the utmost im- ])ortance in order to ])revent tlu^ formation of ruts. Thor- ough rolling should follow tlK' addition of each layer of ma- terial and shonld be kejit nj* until a hard, even surface has been secured. ' • 28 In iiiiikiiii;' (Mi'lli I'oiHls il is pjirl iciihirl v iiii|i-|i|y packed with the roller, the use (d which is iiecessai'y cvoii where no leNcliiiii, is nccdcil, in order to disco\'er any soft s|>ots, (piitc certain to exist, and in oilier to <^\vc the foun- dation a more ihoronvdi packini:' than the wauoiis lia\'e se- Clll'Cll. 563. Preparing' the Road-bed a Year or More in Advance.— It will generally he round arties in the sand when dry. If there were any cheap method of keej)- ing the surface wet, sand W)nld 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, nudving but little im- pression upon it. The water, however, drains away so rapidly from the coarse clean I'ounded 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 ]:)articles 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 457 may be too great to jx-nnit 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 (day retaining too much for tight l:)inding. With this principle to direct practice it is clear that if the right amount of finer soil particles can be ol)taine(l to in- corporate with the sand of sandy roads their firmness will be increased. It is unfortunately too often true that in districts whei-e sandy roads prevail there is no clayey or loamy material avaihible, 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 im]>rovement is that stated in the last paragraph; that is, in the power they have of maintaining a higher ])er cent, of water in the sand, Avhich is necessary in order to bind lhe 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 C(uiverted into soluble salts and gaseous products which finally leave the sand as if notliing had been added. 569. Road Gravel. — It occasionally happens that natural gravel beds are found Avhicli possess the right characteris- tics for making roads, and when the gravel is just right ex- cellent roads mav l)e made from it. 458 Tliere are several ini^xirtaut features wliicli a good road gravel must possess : 1. There must be one prevailing size of pebble in suffi- cient quantitv so that when tlioroughly rolled they press against one another. '2. There must be enough of the liner sizes of coarse sand and fine gravel to fill the voids between the coarser gravel. ?). There must be enough of tine loam to till 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 iine 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 levssen 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 (Uice that the several chnraeteristics which have been point(Ml out are not likely often to occur together in just the right ratios; and so tliere 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 Avhen this is true it is useless to try to nudvc a road with it. Such nmterials can only be used to temi)er 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. AVhen this is true much better qualities may be secured by using either the crusher or the screen or both together, one form of which is represented in Fig. 210. It will be at once apparent that where much of the 459 gravel is too odiii'sc. to v\ui it thrduiili the cnislicr so as to re- (liico the material t(» a more uniform size and at tlio same time to increase the aiiiiiilai-itv of the fraiiments will make a miicli hetter road material to nse ( itlier hy itself, or as a tempei'iiiii' material. Ficj. 216.— Champion lock ci usher and i>cieeu. 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 priuciple must be kept always in mind that too much of a too fine uuiterial will take in and retain so much water that the l)inding quality of the Avater is lost. These gravelly clays occur in many of the hills of the glaciated portions of the United States and throtiiih 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 suitalde 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. 4(10 111 t'lR' rolling it will \)c iiii|)(irt;iiir ro tinii the outer edg-es of the gravel first in order that r'ue rolling may not force it outward and destroy the slope. Should the gravel be too dry to pack it nmst be moistened or the work he suspended to take advantage of the rains. To make a good road there sliould lu' iiut less tliaii three 3-incli layers, and usually four will he hctter. Of course a road 6 inches thick will he a great iniprovenieut, and often where the travel is light and the road-bed thoroughly made, thre(> inches of good gravel, well ])laced, will make a great improvement in tli(> road, serving as a wearing sur- face. Wlier(^ the gravel must he crushed and screened to secure the ])ro[)er sizes the revolving screen represented in Fig. 210 should be used and should have two sizes of holes 1.5 to 2 inch and .'> to 4 inch in diameter. The coarsi-r size of gravel will form the body of ihc rojul while tlu> Huer will have to be discarded unless it happens to he of the right quality to use as a binding material or in making a bicycle path along oiu' side of the road. 574. Koads in Swampy Places. — it occasionally happens that roads must be built in ])laces which cannot be drained and which are too soft to peruiit of the construction of a solid earth foundation. A co, union way to meet this ty])e of coiulitions is to lay a fi)iiiidatiou (if logs, poles or even brush, having the desired width ol rh,' road and of suifi- cient body to enable an earth or gravel road to be built u})on it. When such roads are built iu situations where the wood is kept constantly beneath the water it e, bnil(liiii>' the earth or liravcl roaTeat roads the paved portion had a width of f-waT8 Ciich ciiiht tcct \\i(h', Jiiul the |):i\('(| \v;iv soiiic- tiiiies had an a<>,iii"c French eni;ineer 'rresatiuel appears to ha\'e inti'o'. 2lSj consistini;' (d' a stone ]>avement co\'ered with two or three Indies of ernslied rock as a facinu'inateriah Alter being' intro(hieed into Fnghind and Scothmd, where the (U'- tails were modilied and perfecled hv TcMoi'd ahont lSj>(), tliis tvpe of stone constrnclion came to he known as tlic '^l\dford roaih Fig. 218.— T.vp3 (if road iiitroducod into Fimiicp by Trcsatrupt about 17t)4. CAftiu- Sliiiler.) Maca(hinrs work '.legan somewhal eai'lier ihan '[".dtord's in iS'Ji, and to him apparent Iv is (hie ihe i(h-a thai when any r(tad-hed is thoronghlv mnh'r (lraine(l, so as to remain ]iermaneiitl_v har, hetweeii which the r(»a(hhe(| is co\-eri(l with i\ Uiyer of crushed voi-k as nearly one size as i)ossihh' and three or four inches thick. This layer is next thoronghly roHed and then coNcred with eiiongli of tinely crushed rock to fil] the voids between the hirger fragments. This ma- terial is worked in with the roller and water until a solid bed has been foriiu(h 403 After llic fii'st l;i\ci- li;is l)cc;i plnccd llic scccikI is jip- jilied ill the siiiiic iiuiiiiici-, ritllcd, jiiid llic hiiidirio- matcriai jif)j)li('d {iiid aiiiiiii ndlcd, until thorough coiiscdidatioii has been secured. Fig. 210.— View showing the road bed, in the foioKround. shai)C'' touches. After the shoulders have been roughly foruied and before the tiuishiug' touches are given the roller should go over the road-bed to make sure that it is properly tirnuMl and that there :ire 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 hirge bouhh^rs 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 sucli that it holds the nccdi'd amount of moisture to nudvc it l)ind together well, and consequently a road built from these fragments sets sooner than almost any other crystalline rock and hence is subject tr) less in- ternal wear. Next to the trap r(jck in value foi- road building purposes stand the closer grained liond)lend-liearing sycuiites and gneisses which are species of granite where bornl)h'ud takes the place of mica of the true gi-anites. It is the class of dark minerals allied to hornblend conii)osiiig much of the trap rock referred to above which makes that the best road stone. Next in order stand the true granites nuule uji of quartz, feldspar and mica, and tlieii- gnt'issoid varieties. The best of this class of rocks are the close fine-grained varieties having the least tendency to l)reak 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 alacial drift. 465 Tlio ('liiof (litticiiltv 'vvitli syenites luid iiriniites for road inetal is their brittle, iiiiyieldiiiii (jujility and coarse crystal- line structure which makes theui i^riud and pound up into a coarse sand without a sutheient amount of the tinest dust to i>ive it the needed water-liohliuii- ])ower to permit it to |»roper]j hind the pieces together. The road-bed fails to Fig. 220— View showing where four inchc.'; of cru.'^hed rock for wearing surface is bsin'j; built upoa f.jur inciies of roail-^r.ivel as founiritiun la^er. set quickly and the internal wear is larger while there is a greater tendenc^y 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 4G() whicli break into hard, clean blocks and fragments with sharp edges and little material which will rnb oif under the fingers. Any reck which crnshes rcndily into an earth- like or sandy material will not answci- for road work. When a good road limestone wears down under the wheels, the horses' feet or the rollci-, a loamdike jvowder is formed which holds the riglit aiiiouiit oi water for good binding, and besides this it ajjpcars more quickly to pass into that cementing stage which in nature cements beds of loose fragments into rock. The chief objecti reat advaiitag-c as a hinding material to hold the harder rocks nmre securely in place. This practice would be C'speeially desirable for the foundation layer where it could not be converted into dust. But in localities where both limestone and the harder i-ock are availal)le, but where the limestone can be obtained at much the less cost, this may be used alone for the foundation and as a liinding nui- terial for the surface layer. 583. Roads Made Without Binding Material. — It was ]\[a- cadam's practice in road buihling to strictly forbid the use of all binding material whatsoever. He preferred to wait for the general traffic over the road to develop from the 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 hliing and binding material was be- ing sh»\vly ]iro(hiced thei'e was brought upon the road with the wheels ami hoi'ses' feet a considerable amount of earth "which slowly A\'orked downward and united with the rock flour to com])lete the consolidiition. .Macadam certainly secured in the end a better road by this nielhod than was usually secured with the use of the then available binding material. It must be rememl>ere(b lio\ve\-er, that in his time rock were crushed by hand and little fine matcM'ial was made to use for binding, Avhereas with the modern rock crushers a large amount of this nnitei-ial is produci'd whicli must be a dead loss if it cannot be nsed for l)inding and surfacing, and it is (|uite certain that had .Macadam \\:^i'(\ our modern rock crushers he would have availed himself of the screen- ings. 584. Use of Sand for Binding. — The great readiness with Avhich clean dvy sand works into and fills the \-oids between the stone of a road, the ease with which it mav be handled 408 and the readiness with which it may < if ten he obtained, leads to its occasional use as a binding material in macadam road. The coarse silicions sands, however, have very little cementing quality, they do not retain water well enough either to make the road shed the rains nor give the surface tension of water much ojvportunity to bind the grains to- ^/. Fig. 221. — View .sliowin<3: tlio binHini; matprLal or screenings being applied to tlie found iiiou layer of crushdd rock. getlier firmly; consequently the l)est 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 4(>!) the bottom so as to coinplctclv lill tlic \'(M(1s. There' is the still further dauiier that it will work in hetween the flat surfaces of the crushed rock, hol(liu<>- tlieui a])art vo such au extent that liea\'v loads A\ill produce too iimch rocking of the pieces and quicklv lead to tlie fornnition of ruts. If the loam c(,iild \\:' li;i(iii-I(i;i(l of s', one is all (Iiiiii]K'(I, ill (iiic |ilacc. Iciviiiii,- il tnr a man to spread, it is cerlaiii tu (K'cur tliat all ot* tlr/ drsl ami iinr iiiatcria.ls not ronioved hy the scrc:'ii will Ave.]} into ili- voids at tlif jjlaeo where Fic. 2il.— V'Knv of siiificitii; cnis!ie'1 r.)ck as Ipft, by tlio di^tributinir cart on the roail. 'tiir w.itcli. 1 mcliea in (Jiainetjr, f:e.V(is as a scale to show the size of til 3 lock fiairiutiii.-. the loa' at a slow and nniforni pace. Fii>'. 224 is a view showiiiosiTio]is of the most stable equilibrium; that is, in positions such' as to make certain that they shall not tip oi' turn when the stress of the wagon or team is l)ronght u[u' n roller of .')..") tu ,').,") tdus, wliil;' otlicrs Iwtld that oiily one of 15 to 20 tons wcuilil will s"i'v.' t'lK- jMirpuse. Others advocate a Huht Avciuht 1o ]);'iii!i with and a lu'avior one at the close. Fig. 226.— View bhowii irse I'dlliT at work coniparl iuK the road metal. 590. Amount of Rolling'. — Tlic only "cneral rnle which can be given in regard to tlu^ amount of rollini;' a given layer slunild receive is that the work should h;' continued until the stone cease to move in front of the roller o^- un- til the roller no longer sensibly dej)resses the bed and it has become hard and smooth. It should be kept in mind, however, that the i-(»ad neay be rolled too much, or until 475 the stone a^aiii briiiii to iiioxc. 'I'liis is most likely to oc- cur wlu'ii the stone is too di'v. 591. Manner of Rolling. — 'I'W rollini; should heoiu at the outer sides of the road, paekiug tlu^ stone first aiiainst the shoulder. If this is not done the fact that the road-bed is hii>hest in the center Avill 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 Eoller. — Inhere are three methods of consol- idating the layers of stnne put into a road. The flrst, now largely abandoned as being too expensiye and too uncertain, is to allow it to be done by the natural traffic. The second, also being abandoned as too (>x])ensiy(\ is the use ci a 3.5 to 5-ton horse roller; and the third, which is regarded the cheapest and best, is with tlie aid of an S to 20 ton steam roller. The safest indications seem to jxiint to ihe use on coun- try roads of an .S to l()-tt)n steam roller as most satisfactory; although good work eau be dune wilh the horse roller of half this weight which nuiy be made heavier or lighter by taking on and laying off weights Such a roller as this is represented in Fig. 22() 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 ini})ortant 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. — lh\t\] recently all rock crushing for road work has been done by hand and hammer, and in the days of slave labor Avhen the man was a machine which managed, fed, cared for and i'e]>r(i(!uced itself, it is clear 470 ho-A' siK'li I Icrruk';!!! tasks as rlic aiiricnt liuinan roads could be accomplished. But happily, the use of steel aud iuani- inate forces is freeiug uuiu from such drudgerv ; aud in Figs. 227 aud 228 are two views of a rock crusher at work, })reaking stone, sorting it and delivering it into hins where it may easily he dro])]icar»est jjrade of brolien stone. At the time these vievvs were taken the ciMislu r was be- ing driven hy a 22 II. 1*. tra.ctiou eiigiue aud 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 weariui>' surface and the finest as binding aud 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. 594. Eevolving Screen. — 'I'lu- rcvc.lviiio- screen is an indis- pensable attaehnient to ;i rock ci'iisliei-, because a yood read cannot, be nnid(> \vith the niisdrted material, fnr with this method of putting- the (tusIkmI rock upnn the road the fine materials are ccrtiiiii to work (h)Wiiwar(l niid the coarser frag'ments to couk" to the surface. It sliouhl he th(n"ouglily nnderstood too that the cluite screen will not do the Avork. Fh;. 228. - Side view of No. 3 Austin ('rusher ami \vat,'oii loadiiitt screeiiiugs. 595. Earth and Stone Road Combined. — Where it is de- sired to chea])en the construction of stone roads it is ]irac- 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 widtli of 1() or 24 foet to the margin of grass and ;»() feet to the side ditches. The most serious objection to this condjineil jilan is the securing at all times of sufficient and (piick surface drainage. The chief difficnlty which will arise in the carrying out 1 7S of lliis |il;iii will cniiic iVdiii ihc iciKJciicv of siiiiiiiicr Irnllic oil llic liiii'i'dW (■.■irlli i'(i;i(| Id i;() sii |iri'sisli'iil I V In niic I I'lurk ;is If) (|c\cl(i|( wliri'l :iihI IimiI wjivs (Ici'j) cimii;;!! In pfcvciil surrjicc (Iniiiiii^c. Tlic I'licl lli;il iIu'sImih' i-diid iiinv (toiiu; into sci'N'icc wlicn Ihc ^rniind is wtI will niilv Ic^scii llic IcikIciicv III (lc\"li)|» llir evil |iniii|c<| oill liiil iiol [irrvcMl il. I''(ir wiiilcr ,'.('i'\'ic;' in cnM cliiinilcs il srs'ins cli'iir llinl llic ciirlli l'ii;i(l will II ' likcl\' In (risiiri' li'lli'i' .slciiiliiiiii'. L..B^^ flAMI^ "V "TI ^.>--" I DIICH I ■->*- efT a r T --^ •• bTONL* -;riniis s'lmwlii^' |irulllcs i<\' cmi'IIi .•iimI sfdiic i":itl coiiihliicil. 596. Telford Foundation. W'licn il is ncccssiirv lo l»iiil(l Ihr r(i;iil wlirrc ill!' i^niund is snl'l llicii il ni;iv li!' I)i'sl lo iii V il found ill ion ol' liiriicr si one iis wiis I lie pMicnil |)riU'l ice willi llio Ivoiiiiins iiiid willi llic iMi'^lisli cni^inccr, Telford, M'li(>sc niinic is now iill;iclird lo lliis lypc oxct'Cfl 10 inclics ill lciii;lli, Ci iiiclics wide on tlic Koltoiii and 4 inclics at the to|), tlic tliickncss 1i('iiii]K- (ir <»f stone. \\'(i' a cross-section of more than S scpiare feet is necessary and where stone are avaih^hle, it will be chea])est to make it of arched masonry. Where the culverts ai'e of sewer pipe there should be not less than J!S inches of earth in tlie I'oad al)ove them to prevent erushini;'. The cast iron pi])e is the safest tf» use and cliea])er than either sewer or cement tile whi'n diameters above 10 inches are required. VIAlXrKAAACK OF CorNTIiV liOAOS. Important as the matter of construction of ^^ood roads is, it is, or should \n\ secondary to that of maiiitenance; when a i>()od tiling' has bet u made which is designed for permanent service it is clearly a matter of sound business policy to ]U'ovide whatever economic iueans is ])racticable for keepinu it in order. 598. Section Men Necessary. — In the maintenance of railroads it was early leiwiied that two oi' uku'c men pro- vided with propel' tools must he employed by the year, per- manently or as long as they i-enderi'd ethcient 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 ovei- their section and kvc]) it in iirst class re])air and their tenure of office is only conditional upon their (hn'ug this satisfac- torily. It is self-evident that good country roatls can only be maintained by adojiting and kee])ing in force a system wliieh is equivalent to that found indis])ensable in railroad maintenance. That is, men competent to do the work, 481 provided with tlie ncccssarv imtlioriTv, tools ami iiiaterials, must have C(jnstaiit eui[)h Anient at a price wliieh will per- mit them to devote tlieii- time to it, and thev must be made responsible for llie maintenance of a cei-tain inunber of miles of road ''>()") davs in a vear. Fig. 231.— View of country stone road with foot path on one side, near Maybole, Ayrsliire, Scotland. From pliuto iu l.'9.i. 599. Road Master. — in the conntrv road service it will be necessary to liav(^ one man who correspoiids in duties and responsibilities to the "Section I>oss" of tlu' railroad. He must be com])etent, tenii)eratc and in every way relia- ble and trustworthy. He mnst have a practical knowl- edge of the princi])les ae.d details underlying the main- tenance of o()od r(»ads and at his coniniand the necessary authority, assistance and appliances foi' doing the work re- quired. 600. Width of Tires Controlled. — When we come to have a svstem of ^ood roads an. ISO inch tires. Carts with more than four iiiid wagons with more than eiglit horses are not allowed to nse th(^ roach' without a special ])erniit from tlie aulhorities. Other countries of the Old W'oi-ld have found similar ordinances necessary and it is clearly rational and just tJuit su.ch matters should he r(^i>ulated, for othei'wise one man nuiy easily ])ut in jeop;!rdy the interests of a whole community. 601. Maintenance and Repairs. — A sharp distinction should ahvays he luiide hetween the nniintenancc? of a road and its re])airs. it is only when some accident has oc- curred to seriously injure a road or when, from long neglect, it has become well nigh Avorn out that re])airs are needed, but the daily touching up of slight defects and places of evident wear constitutes maintenance. 602. Good Maintenance. — (lood maintenance will con- sist in daily attention to all the details wliicli are necessary to keep a section of road up to the standard of ])erfection practicable to its tyjie, influenced hy 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; (8) in kee])ing the road surface and drainage channels clean ; (4) in keeping the road sides 483 free from weeds inid o'.iierwise neat; (.")) in cariuii' for and maintaining' road trees if tliev are grown; (G) m main- taining the jjroper conditions in winter in regard to snow. 603. Maintenance of Earth and Gravel Roads. — The first reqnisite for the n'aiiit;'n;inee of any road is the knowledge which can he gained hy going over the road whiki or im- mediately after it rain-. Ohservations at this time will show the road master wliere the most serions defects exist jind he slumld iiia!-:e careful note of them to use in directing his etl'orts a.s so(in as the weather permits. It shonhl therefore he ihe hnsiness of the road master to study his roads in wet weal her and he should he equipped with clothing, etc., in a way which will ])ermit him to do this witliont idsk of injurv to heahli. Fig. 232.-; View of French country road 20 fePt wide, showing piles of crushed limestone used in luaiutenance. PLoio. in lt9j, near (irignon. Whenever ruts or saucers begin to show in the road they should be corrected immediately, provided the moisture 484 conditions permit of doing t^n, l)nr mi the earth roads the soil may he either too wet or too drv to aUow tliis to he done well, and the hiiiliest success will he nttaincd when the road mastei' comes to know and understand his conditions and tlien is alert to uionc ;it just the I'iulit time. The rnts will he formed chiefly in hotli the \-ery wet and the \-ery dry weatlier, and in I he c Mint r\- wle're spriiikliuii- the roads cannot he ail'or(le(l, cNcrythini:- must i)e );lanned to take ad- vantage of every shower heavy ('noiigh to hriiig the road into condition for working with grader, shovel, rake and roller. Fig. 233. - View oil tlie same road showiiis: the tool housi- where ajipliauces for carins for the road are kept. Photo, in 1895, near Grignou. The intelligent use (d' the grader and rolh'r at the right time after the rains of n 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 proverh- iallv had. 485 We cannot too strongly eni|)li;i.siz(' tliat to di-ivo up one side of the road with a road machine and l)ack on the other, scraping a lot of loose, heterogeneous rnl)l)ish and earth into the middle of th(i road, to he traui])ed out again by the ti'atiic, is neithei- re])airing nor maintaining the road. The material hrought upnn the road should he well dis- tributed and hari-owcil until an cs'cn, iinit'oi'iii layei* has been seciii'ed and tlicn the rdlei- should he thoroughly aj)- plicd when the earth is in jnst the I'iglit ('(mdition to ])ack well. AVork of this soi-t will count and will l)e appreciated. :30 486 METEOROLOGY. CHAPTEK XXII. THE ATMOSPHERE. As the life jn-ocesses of all ])lants and animals are de- pendent npon the air, and are greatly inflneneed by changes in it, it is eminently jtroper that the atmosphere and its changes slionld be considered in their relations to agricul- ture. From the standpoint of food su])ply the clover crop, for example, containing at maturity 70 per cent, of water, has — directly or indirectly — obtained all but its ash in- gredients from the atmosphere. The water is brought to the soil as rain, tlie carbon comes from the carbon dioxide and the nitrogen is obtained from the soil air by the free- nitrogen-tixing bacteria. Tlu^ rehitions stand Water from the atmosphere us rain 70 percent. Nitrogen from the soil-air 70 per cent. Carbon and oxygen Ironi liic atiiiosplierc a.s rain and carbon dioxide 26.57 per cent. Ash ingredient.s from the . ) and outside of all is the ojus or air sphere. These have been named — 1. Geospliere. 2. Hydrosphere. 3. Atniesphere. 605. Interpenetration of the Three Spheres. — The mate- rials of the three spheres are neitlier entirely separated from one another nor stationary. Beneath the oceans and be- neath the surface of the continents the solid earth is per- meated by water. Even nnder desert skies there may be wells and the soil contains moistnre. With the water, too, ii'oes more or less of aii" from the atmos])here; the fishes of the oceans and lakes hnd air to breathe Avherever they go and the spaces in rock and soil not occupied by water are tilled with air. Floating' in the water and drifting in the atmosphere even at great hights are solid })articles of silt and dust broken fi'oni the earth-sphere, and nowhere is air 9o dry that it contains no moisture. Drifted by the currents of air and water on land and at sea solid jiarticles are continually being moved from place to place. The ^\'ater of the ocean, of the lakes or of the at- mosphere is never at rest, neither is that which has pene- trated the solid crust of the earth. So, too, the air of the atmos])here, of the water and of the soil is continually changing and upon the rate of these changes depends the well being of plant and animal life. 608. Relation of the Life Zone to the Three Spheres. — The living forms of the earth make their homes in the bottom of the atmosphere and in the top of the water sphere or of the earth sphere. This relation is necessitated by the fact that all living forms derive their food from the air, from the water, and either from the earth or from other forms which take their ash ingredients from the earth. This re- lation is further necessitated by the fact that all living f(U-ms must dwell where they can have a certain amount of direct sunshine or else where they can live upon other 488 forms which depend upon it, for this is the moving power of the world and all life implies motion. Deep in the solid earth no life exists. In the greatest depths of the ocean, where the air changes are slow and where little or no light can come, life is nearly absent ; and high in the atmos- phere only latent forms of life, like the spores and germs of niierosco])ic forms are drifted by the winds. In brief the life zone is that portion of the three spheres where the largest aiiu)unt of suusliinc is transformed into heat motion and therefore Avhere there is tbe largest amonnt of energy available for the use of plants and ani- mals. 607. Depth of the Atmosphere. — We are living at the bot- tom of an ocean of air whose de2)th is at present unknown. Judging from the rate of decrease of pressure, as measured by the barometer, its de])th woidd be placed at something less than 50 miles, for at 30 miles, could an instrument be placed at that level, it is calculated that its reading would be only .005 of an inch of mercury. Observations which have been made upon the hight at which shooting stars or meteors become visible shows that this is even more than 100 miles and it is believed that these bodies become visible only after they have traversed enough of our atmosphere to develop sufficient heat by friction and compression to make them white-hot; and although the velocity of these- bodies is very great yet the upjier air is so rarified they must pass through great depths before sufficient heat can be developed to make them white-hot. From these consid- erations it appears likely that air may be found at hights even exceeding 500 miles. (608. Composition of the Atmosphere. — The air at differ- ent times and in different jdaces contains a great variety of gases and volatile products but there are certain con- stituents which are found everywhere in the explored reg- ions and in pretty constant ratios. These are, for dry air : 1. Nitrogen, forming about 77.18 per cent, by volume. 489 2. Oxviieii, forming about 20.61 per cent, by volume. -'». Water vapor, foruiiiiii' :ibont 1.40 per cent, by vol- lllllC. 4. Ariion, foriiiinii,' about .78 per cent, by volume. r>. ('arl)(>u dioxide, foniiiui;' about .03 per cent, by vol- ume, i Jlesides tliese iuiiredicuts there are usually present in the air small amounts of ammonia and of nitric acid, which are brought down with the rains to the extent of 3.37 pounds ])er acre per annum at llothamatead, England; 1.74 pounds at Lincoln, ISTew Zealand; and 3.77 pounds in the Barbadoes Islands. Oxygen often occurs in the allotropic form of ozone, which is much more active as an oxidizing agent than the ordinary condition. 609. Materials Mechanically Suspended in the Atmos- phere. — In the gaseous body of the atmosphere there are always mechanically suspended varying amounts of solid and liquid particles and bodies. These are: 1. Inorganic dust grains or soil particles. 2. Organic dust fragments. 3. ]\licroscopic geTms and spores. 4. Pollen grains from various plants. .5. Snow or water crystals. 6. Water particles in cloud forms. PARTS I'LAYKD I'.V Til t DIFFKKEiXT INGREDIENTS. The atmosphere as a whole, in its relation to living forms, plays the important function of an equalizer of tem- perature, preventing the occurrence of such excessively high and extremely low degrees as would otherwise be pro- duced when the sun is above or below the horizon. 610. Oxygen — Oxygen is essential to both plants and animals, it l)eing indispensable to the activities of the proto- 41) plasm of living cells, wlic'tlier tliis be in tlie root, stem or leaf of ])lants ov in the tissnes of animals, in the develop- ment of mnsoular and nerv(Mis energy large quantities are used by the animal kingdom, and other large volumes are used by man with fuel as a source of ]iower and heat. 611. Nitrogen. — The nitrogen of the atmosphere is pri- marily the sonrce of all nitrogen com])ounds of living forms; and by its dilution ot" nil the other ingredients it modifies their phvsiological eflccts. 612. Water. — Moisture in the ntuiosphere greatly influ- ences th(! tem])C'rature of the eartlTs surface, as it is very opaque to dark heat waves radiated back into space. The frosts forming under clear skies and the absence of them when the air is dani]) are evidence of this influence. But the chief function of water is found in its large movement to the land in the form of rain and snow and its return from the fields through springs and rivers to the seas. As it falls it is food for i)lants and drink for aninuils, as it re- turns it carries away soluble salts which, if left, would de- velop st(n-ile "alkiili" hinds. 613. Dust. — The dust ])articles give to the skv its blue color and by their radiation of heat into space become cold centers u])on which moisture condenses and snow flakes form. In this wav they greatly influence the ])recipita- tion, making it less violent than it might othei'wise be. 614. Carbon Dioxide.^ ('a rbon dioxide is the source of all the carb(»n entering into the constitution of the tissues of both ])lants and animals, and it is a constituent of the great majority of feeding stuffs and of most organic com- pounds. Froni recent investigations it is held that carbon dioxide plays an im])ortant ])art, with water, in lessening the transparency of the atmosphere to dark heat rays radiating from the earth into space, and in this way holds our tem- 491 peratiire much higher than it coiihl he with this gas absent; and Chamberlin has proposed tlie working hypothesis that long period changes in the amount of carbon dioxide in the atmosphere may be the cause of the recurrent glacial periods to which the earth has been subjected. 615. Pressure of the Atmosphere. — The air, like all other substances, has weight, and this weight causes it to exert pressure proportional to the amount above a place. Its mean pressure at sea level is equal to 14.73 pounds per square incli. A cubic foot of air at this pressure and at a temperature of 62° F. weighs about .08 pounds, 100 cubic feet would weigh 8 i^ounds, and 10,000 cubic feet 807.28 pounds. Tlie air of a stable 40x40 feet, 10 feet high, weighs a ton. As the hight increases above sea level tlie amount of air to exert pressure is less, the weight of a cubic foot becomes less and it is necessary to breathe a larger volume to supply the system witli the same amount of oxygen. In the next table are given in round nundjers the bights al)Ove the sea at which the pressure w^oukl fall from 30 to 16 inches and the higlit to which these pressures would sustain a column of water, could a perfect vacuum be maintained. Hifclit above sea level. Barometric pressure. Hight of water column. 30 inches. 34.0 feet. l,80()feet. 28 " HI 7 " 3,MJ0 " 26 " Sti.4 " .'),9TO " 24 " 27.2 " 8,200 " 22 ' ' 24.9 '• 10, fiOO ' ' 20 ' ' 22.6 " 13, 200 ' ' 18 " 20.4 " 16,000 " 16 " 18.1 " 616. Applications of Atmospheric Pressure. — The most general application of atmospheric pressure by the animal world is in bringing air into their respiratory organs. Where animals are constituted so as to take advantage of this, a reduction of pressure is made about the luiigs, as in raising the ribs and lowering the dia[)hragm, and throi the greater pressure of the air outside expands them and causes a fresh supply to enter and fill the space. 402 111 (Iriiikiiiii, Jiiid in sucking- ;iii!iii:ils hike adviintugo of the nil' pressure !<• |)erl'(»riii these ()|K'ral i<»iis, wliicli would he iiiipossihh' without the prtvssure, and dillicult wlierc the pressure is siiialk lu'cii ill eatiiiii', aiiiiiials witli lips mid cheeks take ad- vaiitaii;e ol" air pressui-e to I'orce the food from hetweon the teeth after it has heeii iiiastit^ateil, and a man would make awkward work ealiiiii for the tirst lime in a vacuum. In the einiiiiioii suction piiiiip and the siphon air [)rcs- 811 re is an esseiit iai lactor, as it is in I he hiw pressure steam eniiine. All (tf the iiiacliines inxciited for niilkinji; cows develop a vaeuiini and (h peiid upon atmospheric pressure to force the milk from I he ii(hh'r. 617. Temperature of the Atmosphere. Tlie air is warnuKl in three wavs: lirsl, and chiellv, hv coiilaci with the earth's surface and with solid ohjects upon it, tliis lieatiup; ii'iving rise to ascendiiii;- currents , rci'i'<'-<'iit(''l in I'iii'. 2.'{4. In tlio lower .......\. m Vh.. '"A. I ii;i;.'|-:iiri ^ho \\ j ii lt I In- (iiiLrin nf wiiiil i]io\ I'lii'-fjl s. part <»f the fieni'f tlic white portion represents a region where the air is ex])andin^-. When thi.s oeenr.s the lower and heavier air is carried upward and hrought alongside 494 that which is lighter ; then because of the resulting unbal- anced pressure the air above flows over outward, as repre- sented by the upper arrows. But as soon as some air has left the expanding area the whole column is made lighter, while the shaded areas become heavier from the added amount, and there is an unbalanced condition through the whole hight. At the center there is an area of low pres- sure and around it one of high, hence the winds set inward from all sides at the surface and outward above, as shown by the arrows in the diagram, and we have what is called a cyclonic system of winds, where the currents are mov- ing inward toward a low pressure area below and outward above toward one that is higher. If the central area is one where the air is contracting and becoming denser then air will flow in upon it from above, as shown in the upper part of the diagram of Fig. 234. But as soon as air moves from the surrounding area upon the central one the inner region becomes a liigh area, where the greater pressure forces the air outward below and in- ward above. Such a wind system as this lias been named an anticyclone. GENERAL CIRCULATIOIN" OF THE ATMOSPHERE. 619. The World System of Winds. — In the region of the equator, wliere the lioat is greatest, the air is continually expanding, and flowing toward the poles above ; this makes the pressure greater on either side, resulting in surface winds setting toward the equator, as represented in ver- tical section in Fig. 235, Avhicli it will be seen is essentially the cyclonic system of Fig. 234. Farther toward the poles on either side, where the overflowing air from the equator accumulates, a high pressure belt is developed, from under which part of the air flows toward the equator below and another toward the poles ; these are the tropical high pres- sure belts. At the poles, where the air is continually cooling, it is 495 steadily (Icsc'eiuliiin' and tlowino (Mitwanl hclow, maintain- ing an anti-evclonic svsteni of winds ]iko that of the upper part of Fig. 284. Between the high area at the poles and the tro|)i(*;iI high ])ressure belts, where the two systems of ■<=5^->-t"^--., surface winds mci r, there is, in the judgment of Ferrel, a tendency to develop a third or ]jolar calm belt, over which the air rises to return as an upj^er current to the tropical per winds of the same zones have the reverse direction. In the temperate zones the winds are southwest or northwest at the surface and northeast or southeast above, according as they are north or south of the equator. 622. Character of the Winds. — Winds blowing toward the ('(juator or descending from the upper regions have a tendency to be dry and to maintain a clear sky. On the other hand winds moving toward the poles, or rising to greater altitudes, tend to become more and more nearly sat- urated with moisture and hence to produce cloudy skies and precii)itation. The reasons for these relations are found in the fact that 41)7 air rising' or moving toward tiie j)oles is i^assing to^vard a colder region. Lowering the temperature of the air, with- out changing the amount of moisture in it makes it more nearly saturated, while raising the temperature without changing the amount of moisture makes the air dryer. Besides this, air is cooled by expansion and warmed by compression, and on these accounts ascending currents tend, to heconic (huii]) and descending aii' more dry. 623. Weather of the Wind Zones. — It will l)e evident from 622 that, so far as tlie worhl system of winds are not interfered with by local conditions, they must give to the countries over which they blow characteristic types of weather. Fnder the tro])ical high pressure calm belts, where the aii- is descending, and for a long distance to the south and a shorter one to the north, there must be a region of clear skies and dry weather, and it is under these two zones that the deserts of the world are found. In the polar regions also the cloudiness and ])recipita- tion are relatively small for the same reason. But at the equator, where large volumes of air are ris- ing into the upjier regions and after doing so pass toward the poles, the air having become very moist before rising, quickly becomes saturated and throws l)ack to the earth large amounts of rain. The heaviest rainfalls of the v.'orld ar(' mnU'r the equatorial calm belt of ascending cur- rents. In the two temperate zones also, where tlie winds cool as they move northward, frequent rains and showers and much cloudy weather are the rule. There is thus a tendency for the systems of world winds to develop three rainy or cloudy zones and four clear weather or dry zones. Tlie dry zones are under the tropics and about the ])oles ; the wet and cloudy zones are under the equator and l)etween the tropical and polar circles of both hemispheres. 624. Shifting of the Zones. — Because the vertical rays 498 of the sun fall alternately 23^/2 degrees north and south of the equator, the regions of greatest heating must also move north and south with the aj)parent shifting of the sun, and this causes the equatorial and tropical calm belts to move north and south. As a result of this shifting there is a tendency to develop two rainy and two dry seasons each year in the regions over wliich tlie calm belts travel twice. CONTINENTAL WINDS. 625. Continents Disturb the World System of Winds and Weather. — Tlie small s})ecitic lieat of the land, its opaque nature and the absence of currents of all kinds in it cause the land surface to warm rapidly in the day and during summer, and to cool rapidly at night and during the win- ter. On the other hand the transparency of the oceans, which allows the sunshine to be distributed through a great depth of water ; their high specitic heat and the horizontal and vertical currents to which they are subject, all con- spire to make the oceans, relative to the lands in the same latitude, wariu in winter and cool in summer. During the huig days of summer and short nights, in high latitudes, the land becomes much warmer than the water and tends to develop ascending currents and a low air pressure, causing the winds to tend to blow toward the land at the surface and away from the land above in sum- mer ; but in winter, when the nights are long and the days short, the ground becomes very cold and the air contracts, causing the upper air to blow in over the continents above, thus developing high pressure, which forces the surface Avinds to move from the land toward the ocean in winter. There is therefore a tendency for the weather of conti- nents to be rainy and cloudy in summer and dry and sunny in winter, and for the oceans to be dry and sunny in sum- mer and wet and cloudy in winter. This is a very for- tunate relation, because it diminishes the evaporation on the land and increases that on the ocean and thus makes 490 the rainfall heaviest at just the season when crops need most water. 626. The World Winds of January. — The prevailing winds of the worhl, as tliey arc observed during the month of January, are represented in Fig. 236, the lines of black circles showing where the modified tropical high pressure calm belts are situateil, and the light circles showing wheTC the equatorial calm belt and other low pressure areas are. In the southern liemis]iliere, where it is summer, and where the amount of land is small compared with the watei", the tropical high pressure calm belt is crowded to- ward the ])ole on the land and the air is liea]3ed up on the water, and the arrows show that the wind blows toward the land ; l)ut in the northern hemisphere, Avhere it is win- ter, and where the amount of land is much larger, it is also drawn toward the poles by the extreme cold of the land, while a low area is formed over each of the northern oceans. The wind blows oif both continents onto the two oceans and there are ui)per currents tending toward the land from the low areas. The equatorial calm belt is farther south everywhere, but esjiecially so over South America and over Africa and Australia, where the land becomes warmest. 627. World Winds in July. — At this time of the year, when the northern hemisphere has the vertical rays of the sun and the longest days, the large masses of laud have be- come over-heated, the equatorial calm belt has been drawn northward and expanded into wide continental low areas, <'row(ling the high pressure belt of the Tropic of Cancer upon the Atlantic and Pacific oceans, as represented in Fig. 237. The warm air rising over the continents and flowing over upon the oceans makes high pressure there and low pressure over the land, and this brings surface winds and moisture from the sea, giving rains to the land in the summer season. 500 501 502 South of the equator, where it is winter, the high pres- sure cabn belt has moved nearer the equator so that the air is bhiwing- olf the three continents and they are exjierienc- ing: their dry season. 628. Monsoon "Winds. — Where the world syste-m of winds is so strongly influenced by the land areas as is the case notably in the region of the Indian Ocean they have been given the special name of monsoons, and these give to In- dia its rainy season, when they blow from the ocean, and its drv season, when thev blow fi'om the land. ORDINARY STORMS. Besides the world system of winds, wdiich have been de- scribed, and the continental winds with their intensified forms called monsoons, which change with the seasons, there are others of smaller magnitude and shorter duration which give rise to our ordinary storms and the still more local tornadoes and thunder storms which are associated with them. These are technically called cyclones or cy- clonic storms. 629. Cyclones. — Most of the rainfall of temperate climates and much of that which falls between the tropics and the eqnatorial calm belt, occurs during the passage of these cyclonic systems of wind movement, represented in Figs. 288 and 239. In these winds the surface air moves sjjirally about a center, going to the east as it passes toward the poles and to the west of the center when it comes toward the equator. Air coming from the eastward of a cyclonic center always passes to the polar side, while that coming from the west always passes to the equatorial side. 630. Cause of Wind Directions in Ordinary Storms. — The cause of the wind directions in ordinary storms is the same 503 as tliat of fho direction of tlic iiciu ral cartli ciirrents, that is,— the form and rotatiou of the eartli. As the air leaves the ecpiator it passes over land niovini;- eastward slower than it and hence ontruns, appearing to blow from the Fig. 23S. — DiM^T.-iin dl' surface winds in a typical cjcloiiy. (After Ferrel.> S. AV. toward the X. E. in the northern hemisphere, and from the X. W. toward the S. E. in the southern hemi- sphere. If it approaches the eqnator it travels over land moving eastward faster than it does and hence appears to come from the jST. E. in th(^ northern hemisphere and from the S. E. in the southern. Where the wind approaches the center from the east it can only do so by having its eastward motion with the earth made slower than the earth's surface in the same latitude; 504: while if it upp roaches the center from the A\'est it can only do so by traveling eastward faster than the earth itself and these changes in velocity canse winds from the west to move toward the eqnator side of the storm center, while those from the east always go to the polar side. The effect is the same as would resnlt from checkinc; or increasing TTiG. 239. — T)in!ir.nu of ujipcr a\ iiulf; in :i i.\iiic;il (•ycloiic. (After Ferri'l.t the rate of rotation of the earth npon its axis. Making it rotate faster wonld throw the air and water also toward the equator, while slackening its speed would permit both air and water to move toward the poles. 631. Progressive Movements of Storms. — Cyclonic storms in all parts of the woj-ld liaxc a progressive movement 505 500 across the earth's surfjicc iiiid I lie licncriil dii-cction is that of tlu^ prcx'jiilini;- winds of the part of the earth in wliich they arc. Tliat is, in tlic Icniix-ratc zones lliev tend to move awaj from the ecpiator and towai'd the east, wliile in tlie tropical zones tliev tend to move toward the ecjuator and toward the west. 632. Direction of Storms in the United States. In tlio great majoritv <»f cases the storms ol' the I'nited States travel fi'om some westerly towai'd some castci'ly ])oint and iho mean direction is a litth' noi'th of east. \'ery many of tliese storms t ra\cl lor a time I roni the nortliwest toward tlie southeast until they near the lon_i;t it nde of the Missis- sip|)i riv(M% when they scry ot'teii turn their course strouii,ly to tlie northeast, and Fig. 240 re|)resents the- courses of the storm cenlers as they traversed tli(> country duriiiii; IMarch, 1900, there being 1 :'. of them in all. Wherever the storms of tli(^ United States originate or enter the territory tliey nearly all h^avc it by crossing the New Kngland states. 633. Rate of Travel of Storms in the United States.— There is a x'cry wide range in tlie rate at which the storm centers progi'css across the I'nitfd States, hut the ax'crage is from 2(i to ;>0 miles ])er hour. The circdes in the paths of the scu'era! storm tracks in Kig. I'tO inarh the positions of the storm centers at intervals ol 1 2 hours. 634. Diameters of Storms. — The diameter of thes(> cy- clonic wind systems in the I'liited States is generally from 1,500 to 2,000 miles, the longest diameter being usually from the southwest to the northeast. A typical one of these storms is re])resente(l in Fig. 241, where the heavy lines are drawn through |)laces having the same weight of air above thc'On, while the dotted lines are lines of e(|iial tenip(M-ature. It will be seen that this wind system reaches from north of the Great Lakes to well into T'exas and from North Dakota to Tenncsssee. 507 635. Duration of Ordinary Storms. — Tlxi loiiofli of time one of the ovdiiinrv cvcliniic storms of IIk; atmosplierc lasts is very varisiMc In some cases tin v arc of l)iit a few days duration; at other times tiiey last I'oi- weeks toi^ctlicr and in that time travel lon<;' distances. It is common for them to cross tlie United States, the !N^orth Atlantic and the wiiole of Murope; and one, nnnsnal at least in the comph'teness of its iion o\'ei- which rain or snow falls dni'ing 508 the ])as:*ai;'(' of cyclones across the I7iiite('iu'ral rule is that with the approach of a storm the temperature rises above the normal for the place and season, if it is the cold part of the year, but after the storm passes the temperature falls below the avcrai>'e. The rise in temjierature is due to three causes: (1) The warming of the air l)v the heat due to the condensation of moisture ; ( 2 ) the checking of radiation by the moisture in the air ; ( :>) the imj)ortation of warmer air from farther south under the influence of the storm center. It was shown in (41) and (42) that the formation of a pound of water at i^l^*^ from a pound of steam at 212° is associated with the development of IMjO heat units, and the freezing of a pound of water is also associated with the ap- pearance of 142 heat units. When, therefore, a pound of snow forms in the air from a 2:)ound of water vai:)or there is imparted to the air in which this occurs 9Gi; -h 142 = 1108 heat units and if snow enough falls to represent an inch of rain the heat produced in the air is at the rate of about 62 4 1,108 -— = 5701. G heat units per square foot of the surface upon which the snow falls. The warming of tlie atmosphere Avhen it snows heavily must be very considerable and this is why it is seldom more than a few degrees Ixdow freezing when a heavy snow is in progress. The low temperature following a storm is due to three chief causes : (1) The rapid loss of heat by radiation from the ground under the clear sky; (2) the descent of cold air from high altitudes; auei'ature of 514 only 17° F., 42° colder. In the northwest HIGH there is a temperatnre of — 10° F., while to the east of the LOW, above 60°, or a difference of 70° F., and while a part of this difference is dne to difference of hititude, most of it is dne to the effect of the storm. 644. Barometric Changes Connected with Storms. — Dnr- ing the progress of a storm across a given station the bar- ometer falls more or less gradually until the center has reached the place and then it begins to rise, and may con- tinue to do so nntil a pressure greater than is normal has been attained. The changes of tlie barometer, therefore, become indices of the approach, progress and passage of a storm, and so, too, in a less degree, may temperature changes also, during the winter. If the barometer falls faster than usual, if the wind velocity increases rapidly and rapid changes in the wind direction occur, the indica- tions are either that the storm center is approaching at a high rate of speed or that its diameter is small and he-nce that it is likely to arrive sooner after indications have de- velo])ed. 645. Cold Waves. — Cold waves in the United States are usually the result of a strongly developed storm which has traversed somewhat slowly the southern and eastern states. When these conditions prevail a HIGH area with clear sky and descending cold air from above forms over Mani- toba, or the northern boundary of the United States, and the strongly developed LOW area, traveling slowly, sets this body of cold air in motion toward it, which often at- tains a velocity of 25 to 40 miles ])er hour. Under these conditions intense cold is rapidly transported southward and eastward with the speed of an express train, and occa- sionally temperatures even below zero are transported as far south as northern Alabama. Besides the extremely cold waves just referred to there are others more common, which are due principally to the first two causes named, and are usually coincident with the 515 IlKill areas, following tlicin in their course across tbe count rv. 646. Forecasting^ Warm and Cold Weather. — Since stronii'lv developed storms tend to draw the air into them- selves across long distances, it is clear that when they pass to the south during the cold months of the year cold waves are likely to follow their passage. On the other hand, if the low area has passed to the north it can only bring air from the south northward, im])orting but little cold with it. To be able to forecast the path of a storm then is also lo Ix' al)le to forecast the tein]ierature changes which axe likcdy to follow. 647. Long Warm and Dry Periods. — It frequently hap- }»ens that a series of storms follow along a single track, one after another for several w^eeks together, and Fig. 243 rep- Kkj. 240. — Clinrt showing; coiiiliiioiis which deteniiiue dry weather in the eastern I'nited States. resents one of these sets of conditions. During the montli of October, 18J)5, all but four of the fifteen low areas re- 516 corded by tlie Weatlier Bureau, moved along axes within the northern belt marked "axis of low areas." It is clear that so long as such conditions as these pre- vail but little rain could fall in the United States, and all the northern portion must have unusually warm weather. The weather must be clear and dry because along the axis of high pressure the air is descending from the higher al- titudes where it is already dry, and in descending must become still dryer because of increasing temperature due to compression. As this is the air which must be drawn toward the low areas on either side of the axis it could con- tribute but little moisture for rainfall in either system of lows, and the map shows that but little fell. Fii;. 244.— I'atli of the West Indian JUu-rii-uie of Sept. 1-11, 1900. So long as a high pressure occupies the Gulf and At- lantic states, this effectually shuts off the moist gulf and ocean air and forces the storm centers to maintain a high •northerly course. Then, too, as long as storms pursue a 51' course oif the Atlantic honler tliey also must shut oii* the moisture from the northern states and tend to inaiutaiu warm, dry weather there. Whether in this case the two systems of h)\v areas were the cause of the belt of hii>h ])ressure which ])revaile'd, or whether the high pressni-e belt simply nuirks the place where, for some reason, the upper air from the general wind system was falling to the earth, the outcome, so far as the weather is concerned, must be essentially the same. 648. Tropical Cyclones. — During the latter part of Aug- ust, September and the fore part of October it frequently hap])ens that storms of unusual magnitude, intensity and destructiveness originate in the north tropical zone of trade winds, somewhere in or to the east of the Carribean Isl- ands and, after traveling westward with the prevailing Ki<;. 245. — I'ath nl' West IihIkiii llurricaiic of Aim'. 7 -H. 1.S99. winds of that zone, they tiiially make their way northward across the tropical calm l)elt and break into the zone of j!outhwest winds, making their way northward and east- ward, as represented by the two storm tracks in Figs. 244 and 24.5, the former being the storm which ])roduced the terrible destructi(m of life and ])ropertv at Galv(^ston on 32 518 September 8, 1900, when more than 5,000 human lives and $20,000,000 of property were lost. The severe cold winds which are designated as the "Northers of Texas" owe their origin to storm centers of iinusnal intensity off the Gulf coast, which set large bodies of air in motion from the nortliward, drawing it into them- selves as thev pass along to the southward and eastward. TIIUiSrUER STORMS, HAIL STORMS AND TORNADOES. Associated witli the ordinary storms which have been described in a preceding section there are others much more local in their character, shorter in duration, but often more violent in wind movement and precipitation. These are thunder storms, hail storms and tornadoes. 649. Relation of Tornadoes and Thunder Showers to Ordi- nary Storms. — ( 'areful study of the time of occurrence and distribution of these storms has shown that they are almost always associated in a definite way with some cyclonic wind movement, and that they usually originate to the southeast, south or west of south of a storm center, in the region designated })v the cumulus clouds in the diagram, rig. 242. 650. Tornadoes. — I'ornadoes are whirling winds of ex- treme violence which last but a short time, progressing al- most always from the southwest toward the northeast, often at the rate of a mile per minute, sweeping a belt 40 to 80 rods wide and several miles long. Sometimes the width of the zone of destructive winds may reach a full mile. At the center of the tornado the moisture is swept together by the revolving winds into a dark funnel-shaped cloud, "where the velocity of the whirling air may be so great that few structures can withstand the enormous pressure they develop. 519 Fr.:. v4i,._i,i..,.,,,,„ .|,„wi,.^ ,1m. . ri^u, m , nrn,-i.lu,.s .-n,,! ilnunl.T stonii* 520 651. Schools of Tornadoes. — When the conditions are ex- tremely f;i\'ora!)]e for the formation of tornadoes they often appear in scliools, originatinii,' (uie after another or simul- taneonsly, as tlie main storm center progresses across the country, and Fig. 240 sliows how tliese local but violent storms are ndated 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 ])atlis of toi-nadocs which devel- oped during its course. 652. Distribution of Thunder Showers. — Thunder show- ers, like tornadoes, originate in the gi'cat majority of cases to the southeast and south of a well develo]ied storm center and often large numbers of tlirin, scattered over consider- able areas, form as the storm progresses, much as is the case with tornadoes, and Fig. 247 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. 1-lS. On May 3 a long low area had advanced from the south and west and at 8 P. M. its lowest portion w^as central north of Lake Huron. The front of the thunder shower line had reached the east end of Lake Frie at 2 P. M. of the same date and showers Avere in jU'ogress along the line marked 2 P. M. in Fig. 247. 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. 653. Conditions Under Which Thunder Showers and Tor- nadoes Originate. — In the diagram (»f Fig. 24G 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 southerlv winds to the south and east of the low area 521 and anotlior rciiidii of decidedly colder winds blowing fiMiii the west and nortli of west; and it is along the meet- ing of these two systems of winds that thnndeT showers tend specially to form, and in advance of it that the tor- nadoes have their birth. /^"\ i\ ^^si^^:') ) '^ )y ^--^-—''^ i '^: /-;/ z vi^Jl 12 ti Fic. -DiMfil-.-llll sli(i\\ili;i- tile (lc\cli)|illirlll (if thllllilrr 654. Formation of Tornadoes. — The most satisfactory ex- }danation of the formation of tornadoes is represented in the lower portion of Fig. 246, which is a cross-section of the lower ])ortion 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, nnder these conditions, the cold west and northwest winds at times over-rnn th(' moist warm and lighter sontherly stratum, thus producing a condition of unstable e(jnilibrium. When snch conditions have been developed the wai-ni air, at some point, is supposed to l)reak ^^) thi-ongh the over-rnnning colder layer, as shown in the lower rightdiand corner of the diaG:ram, and in do- 522 ing so is thrown into a rapidly wliirlino; niovenient in the same niamier that water rnns into whirls in discharging throngh the l)ottom of a wash-bowl. When the volumes of air w^hich 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. Fig. 24ti.— IHiifii-aiii nl' the p.-itli of a toi-iiado. 655. 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 vacuvmi 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. 523 656. Unsteady Action of Tornadoes. — A tornado seldom displays a uniformly destrnetivc j)ow('r and oft(uitimes tlu:' point of the funnel fails to i-eaeli tlu; 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 tlie rotary motion in the cloud due to the great fric- tion developed at the ground. .Vftcr 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 rt-aches the surface it does not always describe a straight path along the ground, but tends to cross and recross the main axis of movement. T7OT mmnrm mrnt +2 FEET ,NOTT0ai^. •i Oowr^oowN BUT 'NOTroi^ : 30 '2.* I DOWN . 76 f f CT.FetT^FEe: |fTUB8lSH lOOwH ,30UT H 3*De wira iouTiH SIOeI Fig. 2-49. — Diiigraiii slidwiiiii ilic rx])ansion and by mixing with the cold air, thus giving rise to the heavy preci]>itation so often observed. The horizontal r<:>ning movement shown in the diagram is often \i<»lent enough and involves so great a hight in the atmosphere, that often raindro])s 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 hail stones, in the most violent storms, are often ■carried around Avitli 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. iA 'l^ ^^ .^: .> £ ^^ '-'/^