ANCIENTand modern ENGINEERING AND mE ISTHMIAN CANAL IJRR (JJornell UtttuEtHity 2Ii&ratry atliata. Neuj fork- THE LIBRARY OF EMIL KUICHLING, C. E. ROCHESTER. NEW YORK THE GIFT OF SARAH L. KUICHLING 1919 The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924005020734 Cornell University Library TA 145.B96 Ancient and modern engineering, and the 3 1924 005 020 734 ,,. ANCIENT AND MODERN ENGINEERING AND THE ISTHMIAN CANAL. WILLIAM H. BURR, C.E., Professor of Civil Engineering in Columbia University: Member of tiie American Society of Civil Engineers and 0/ the Institution of Civil Engineers of Great Britain. Flltsr EDITION. FIRST THOUSAND. NEW YORK: JOHN WILEY & SONS. London: CHAPjMAN & HALL, Limited. 1902. Copyright, 1902, BY WILLIAM H. BURR. EOBERT DRITMMOND, PRINTER, NEW YORK, INTRODUCTION. This book is the outcome of a course of six lectures delivered at the Cooper Union in the city of New York in February and ilarch, 1902, under the auspices of Columbia University. It. seemed desirable by the President of the University that the subject-matter of the lectures should be prepared for ultimate publication. The six Parts of the book, therefore, comprise the substance of the six lectures, suitably expanded for tlie purposes of publication. It may be interesting to state that the half-tone illustrations have, with scarcely an exception, been prepared from photo- graphs of the actual subjects illustrated. ^Vll such illustrations in Parts A' and VI deA'Oted to the Nicaragua and Panama Canal routes are made from photographs at the various locations by members of the force of the Isthmian Canal Commission ; they are, therefore, absolutely true representations of the actual local- ities to which they apply. For other illustrations the author wishes to express his in- debtedness to ilessrs. G. P. Putnam's Sons, ilessrs. Turneaure and Russell, John AViley & Sons, The Morrison-Jewell Filtration Company, J\Ir. H. M. Sperry, Signal Engineer, The Engviecring News, Tlie Railroad Ga:^ette, The American Society of Civil Engineers, The Standard Switch and Signal Company, The IV INTRODUCTION. Baldwin Locomotive Works, The American Locomotive Works, and the International Pump Company, and to others from -whom the author has received courtesies which he deeply appreciates. The classification or division of the matter of the text, and the table of contents, have been made so complete, with a view to conA'cnience even of the desultory reader in seeking any par- ticular subject or paragraph, that no index has been prepared, .as it is believed that the table of contents, as arranged, practi- cally supplies the information ordinarily given bj' a comprehen- ■ sive index. Complete and detailed treatments of the purely technical Tnatters covered by Part II will be found in the author's "Elasticity and Resistance of Materials" and in his " Stresses in Bridge and Roof Trusses, Arched Ribs and Suspension Bridges." W. H. B. CoLUMBi.A. University, Oct(jbcr 24, igo2. CONTENTS. PART I. ANCIENT CIVIL-ENGINEERING WORKS. CHAPTER I. ART. ,.AGE 1. Introductory I 2. H_vdrauUc Works of L'haldea and Et,'}pt 2 3. Structural Works iu Chaldea and Egypt ^ 4. Ancient Maritime Commerce y 5. The L'hanj^e of the Nile CItannel at Mcmpliis . S 6. The I'yranuds S 7. Obelisks, Labyrinths, and Temples 12 S. Nile Irrigation 13 9. Prehistoric Bridgedniilding I^. 10. Ancient Brick-m,daily Consumption in the City of New Vork I(i7 157. Daih' Domestic Consum[>tii.ai 19S 15S. Incurable and Curable Wastes 100 1^0. Needless and Inctirable Waste in Cit}" of N\\\" York 200 160. Increase in Poptilation 2(-X) 101. Sources of Public ^^'ater-sup]dies 202 n.>2. Rain-^aui^es and their Records 204 163. Elements of .Vniuial and Ahmtldy RaiidVill 204 164. Hourly or Less Rates of Rainfall 207 165. E.xtent of Heavy Rain-storms 207 luo. Provisi<.)n fi.>r Low Rainfall Years 208 107. -Vvailable Portion of Rainfall or Run-off of Watersheds 200 loS. Run-oft' of Sudbury Watershed 211 161 1. Run-oft" of Croton Watershed 211 170. Evaj^oration from Reservoirs 213 171. Evaporation from the l-'arth's Surlace 215 CHAPTER XVI. 172. Application of Fitztjerald's Results to the Croton Watershed 2l6 173. The Capacity of the Cmton Watershed 217 /74. Necessarv Storage for New York Supply to Compensate for Ilehciency 21S 175. No E.\act Rule for Storage Capacity 220 1 76. The Color of Water 221 177. Stripping Reservoir Sites 222 X CONTENTS. ART. PAGE 178. Average Depth of Reservoirs should be as Great as Practicable 224 179. Overturn of Contents of Reservoirs Due to Seasonal Changes of Temperature. . 224 180. The Construction of Reservoirs 225 181. Gate-houses, and Pipe-lines in Embankments 229 182. High Masonry Dams 230 CHAPTER XVH. 183. Gravity Supplies 234 184. Masonry Conduits 234 185. Metal Conduits • • • 236 186. General Formula for Discharge of Conduits — Chezy's Formula 237 187. Kutter's Formula 239 188. Hydraulic Gradient 241 189. Flow of Water in Large Masonry Conduits 244 190. Flow of Water through Large Closed Pipes 245 191. Change of Hydraulic Gradient by Changing Diameter of Pipe 250 192. Control of Flow by Gates at Upper End of Pipe-line 251 193. Flow in Old and New Cast-iron Pipes — Tubercles 25 1 194. Timber-stave Pipes 253 CHAPTER XVIII. 195. Pumping and Pumps 254 196. Resistances of Pumps and Main — Dynamic Head 258 197. Duty of Pumping-engines 260 198. Data to be Observed in Pumping-engine Tests 261 199. Basis of Computations for Duty 262 200. Heat-units and Ash in 100 Pounds of Coal, and Amount of Work Equivalent to a Heat-unit 262 201. Three Methods of Estimating Dut)' 265 202. Trial Test and Duty of Allis Pumping-engine 265 203. Conditions Affecting Duty of Pumping-engines 266 204. Speeds and Duties of Modern Pumping-engines 266 CHAPTER XIX. 205. Distributing-reservoirs and their Capacities , 267 206. System of Distributing Mains and Pipes 268 207. Diameters of and Velocities in Distributing Mains and Pipes 269 208. Required Pressures in Mains and Pipes 270 209. Fire-hydrants 270 210. Elements of Distributing Systems 270 CHAPTER XX. 211. Sanitary Improvement of Public Water-supplies 276 212. Improvement by Sedimentation 277 213. Sedimentation Aided by Chemicals 270 214. Amount of Solid Matter Removed by Sedimentation 279 215. Two Methods of Operating Sedimentation-basins 279 CONTENTS. xi AKT. PAGE 216. Sizes and Construction of Settling-basins 2S0 217. Two Methods of Filtration 2S1 218. Conditions Necessary for Reduction of Organic Matter 2S2 219. Slow Filtration through Sand — Intermittent Filtration 2S3 220. Removal of Bacteria in the Filter 2S6 221. Preliminary Treatment — Sizes of Sand Grains 2S6 222. Most Eftective Sizes of Sand Grains 2SS 223. Air and Water Capacities 2SS 224. Bacterial Efficiency and Purification — flygienic Etticienc}' 290 225. Bacterial Activit)' near Top of Filter 290 226. Rate of Filtration 291 227. Efi'ective Head on Filter 291 22S. Constant Rate of Filtration Necessary 292 229. Scraping of Filters 293 230. Introduction of Water to Intermittent Filters 294 231. Effect of Low Temperature 294 2j2. ChL>ice of Intermittent or Continuous Filtration 294 233. Size and Arrangement of Slow Sand Filters 295 234. Design of Filter-beds 296 235. Covered Filters 299 236. Clear-water Drain-pipes of Filters 299 237. Arrangement of the Sand at Lawrence and Albany 300 238. \'elocitv of Flow^ through Sand 302 2:;9. Frequence" of Scraping and Amount Filtered bet\\'een Scrapings 303 240. Cleaning the Clogged Sand 303 241. Controlling or Regulating Apparatus 305 242. Cost of Slow Sand Filters 307 243. Cost of Operation of Albany Filter 30S 244. Operation'and Cost of Operation of Lawrence Filter 309 245. Sanitary Results of Operation of Lawrence and Albany Filters 310 246. Rapid Filtration with Coagulants 311 247. Operation of Coagulants 312 24S. Principal Parts of Mechanical Filter-plant — Coagulation and Subsidence 313 249. Amount of Coagulant — Advantageous Effect of Alum on Organic Matter 314 250. High Heads and Rates for Rapid Filtration 315 2 51. T-ypes and General Arrangement of Mechanical Filters 316 252. Cost of Mechanical Filters 318 253. Relative Features of Slow and Rapid Filtration 318 PART IV. SOJfE FEATURES OF RAILROAD EXGIXEERIXG. CHAPTER XXI. 254. Introductory 320 255. Train Resistances 322 2^6. Grades 3^2 xii CONTENTS. ART. '■AGK 257. Curves 324- 258. Resistance of Curves and Compensation in Grades 3^4 259. Transition Curves 3^5 260. Road-bed, including Ties 3^7 261. Mountain Locations of Railroad Lines 32S 262. The Georgetown Loop 331 263. Tunnel-loop Location, Rhretian Railways, Switzerland 331 CHAPTER XXIL 264. Railroad Signalling 335 265. The Pilot Guard 335 266. The Train Staff. 335 267. First Basis of Railroad Signalling 336 268. Code of American Railway Association 337 26Sa. The Block 338 269. Three Classes of Railroad Signals 338 270. The Banner Signal 338 271. The Semaphore 340 272. Colors for Signalling 340 273. Indications of the .Semaphore 341 274. General Character of Block System 342 275. Block Systems in Use 343 276. Locations of Signals 344 277. Home, Distant, and Advance Signals 344 27S. Typical Working of Auto-controlled Manual S\"stem 345 279. General Results. 348 2S0. Distant Signals 349 281. Function of Advance Signals 349 282. Signalling at a Single-track Crossing 350 283. Signalling at a Double-track Crossing 352 254. Signalling for iJoulile-track Junctitjn and Cross-over 352 285. General Observations 353 286. Interlocking-machines 3^4 2S7. Methods of Applying Power in .S\'stems of Signalling 357 255. Train-staff Signalling 338 CHAPTER XXHL 289. Evolution of the Locomotive 363 290. Increase of Locomotive Weight and Rate of Ci imbustion of Fuel 365 291. Principal Parts of a Modern Locomotive 366 292. The Wootten Fire-box and Boiler 367 293. Locomotives with Wootten BoiK-rs 370 294. Recent Improvements in Locomotive Design 372 295. Compound Locomotives with Tandem Cylinders ^73 296. Evaporative Efficiency of Different Rates of Combustion :;75 296a. Tractive Force of a Ixjcomotive ^^5 297. Central Atlantic Type of Locomotive lyg 298. Consolidation Engine, N. Y. C. & H. R. R. R \.jfy CONTENTS. xiii PAGE ART. 299. r., B. & L. E. Consolidation Engine 380 300. L. S. & M. S, East Pissenger Engine 331 301. Nortliern Pacific Tandem Compound Locomotive 3S2 302. Union Pacific Vauclain Compomid Locomotive 3S4 303. Southern Pacific Mogul witli Vandcrbilt Boiler 3S4. 304. The *■ Soo " Decapod Locomotive 3SC 305. The A.. T. & S. E. Decapod, the Heaviest Locomotive yet Built 3S6 306. Comparison of Some of the Heaviest Locomotives in Use 3S9 PART V. THE NICAl^AGUA KOUTE FOR A SHIP-CANAL. 2oy. Feasibility of Nicaragua Route -^qo 30S. Disctivery of Lake Nicaragua 31,0 309. Early Maritime Commerce with Lake Nicaragua 3rii 310. Earlv Examination of NicaraguLi Route 302 311. English Invasion of Nicaragua 352 312. Atlantic and Pacific Ship -canal Ctmipany -^r^z 313. Survey and Project of Col. U. \V. Childs 303 314. The Project of the iNIaritime Canal Compaii}" y^j 315. The Work of the Ludlow and Nicaragua Canal Commissions ^94 316. The Route of the Isthmian Canal (.'onimission 3c,3 317. Standard Dimensions of Canal Pri^ui yjf^ 31S. The San Juan Deha 3^7 319. The San Carlos and Serapicjui Rivers 3r,8 320. Tlie R.ipids and Castillo \'iejo 3^9 321. The Upper San Juan - 3qg 322. The Rainfall from Grevtown to the L.dce 399 323. Lake-surface Elevation and Slope of the River 400 324. Discharges of the San Juan, San Carlos. Serapirjui 401 321;. N.ivigation on the San Juan 401 326. The Canal Line through the Lake and Across the West Side 402 327. Character of the Country West of the Lake 40:; 325. Granada to Managua, thence to Corinto 404 329. (rcneral Eeatures of the Route 404 ;}^.,o. Artificial Harbor at Gre\-town 40c; 331. Artificial Harbor at Brito 407 332. Erom Greytown Harbor to Lock No. 2 40S 333. Erom Lock No. 2 to the Lake 409 334. Fort San Carlos to Brito. 410 3^=;. Examinations by Borings , 411 ^;^6. Cl.issification and Estimate of (^>uantities 412 337. Classification and Unit Prices 413 335. Curvature of the Route 413 XIV CONTENTS. ART. PAGE 339. The Conchuda Dam and Wasteway 4^4 340. Regulation of the Lake Level 41? 341. Kvaporation and Lockage 4' ^ 342. The Required Skjpe of the Canalized River Surface 419 343. All Surplus Water to be Discharged over the Conchuda Dam 419 344. Control of the Surface Elevation of the Lake 420 345. Greatest Velocities in Canalized River 425 346. Wasteways or Overflows 4-7 347. Temporary Harbors and Service Railroad 427 348. Itemized Statement of Length and Cost 427 PART VI. THE PANAMA ROUTE FOR A SHIP CAXAL. 349. The First Panama Transit Line 4.29 350. Harbor of Porto Bello Established in 1597 429 351. First Traffic along the Chagres River, and the Importance of the Isthmian Commerce 431 352. First Survey for Isthmian Canal Ordered in 1520 431 353. Old Panama Sacked by Morgan and the Present City Founded 431 354. The Beginnings of the French Enterprise 432 355. The Wyse Concession and the International Congress of 1870 432 356. The Plan without Locks of the Old Panama Canal Company ^^n 357. The Control of the Floods in the Chagres 434 358. Estimate of Time and Cost — Appointment of Liquidators 43c 359. The "Commission d'Etude" 4.35 360. Extensions of Time for Completion 436 361. Organization of the New Panama Canal Company, 1S94 437 362. Priority of the Panama Railroad Concession 437 363. Resumption of Work by the New Company — The Engineering Commission and the Comite Technique 43g 364. Plan of the New Company j^^o 365. Alternative Plan of the New Panama Canal Company 440 366. The Isthmian Canal Commission and its Work 441 367. The Route of the Isthmian Canal Commission that of the New Panama Canal Company ^I 368. Plan for a Sea-level Canal 443 369. Colon Harbor and Canal Entrance 443 370. Panama Flarbor and Entrance to Canal 444 371. The Route from Colon to Bohio 4^5 372. The Bohio Dam j^ ig 373. Variation in Surface Elevation of Lake 448 374. The Extent of Lake Bohio and the Canal Line in It 448 375. The Floods of the Chagres ^n CONTEXTS. 376. The Gigante Spillway or Waste-wcir 450 377. Storage in Lake Bohio for Driest Dry Season 451 37S. Lake Bohio as a Flood Controller 452 379. Kffeet ol Highest Floods on Current in Channel in Lake Bohio 453 380. Alhajuela Reservoir not Needed at Opening of Canal 453 381. Locks on Panama Route 454 382. The Bohio Lucks 454 383. The Pedro Miguel and Miraflores Locks 454 384. Guard-gates near Obisp( > 455 3S5. Character and Stability of the Culebra Cut 455 386. Length and Curvature 45*5 387. Small Diversion-channels 457 3S8. Principal Items of Work to be Performed 457 389. Lengths of Sections and Elements of Total Cost 45^ 300. The Twenty Per Cent Allowances for Exigencies 45'i V)i. Value of Plant. Pniperty, and Rights on the Isthmus 4&0 392. Offer of New Panama Coal Company to Sell for $40,000,000 461 393. Annual Costs of Operation and ^Luntenance 4''- 394. Volcanoes and Earthquakes 4^3 305. Hygienic Conditions on the Two Routes 4o4 306. Time of Passage Through the Canal. 4^5 307. Time for Completion on the Two Routes 46^1 30S. Industrial and Commercial Value of the Canal 469 399. Comparison of Routes • 47' PART I. ANCIENT CiyiL-ENGINEERING IVORKS. CHAPTER I. I. Introductory. — It is a common impression eA'en among civil engineers that their profession is of modern origin, and it is frequently called the youngest of the professions. That impres- sion is erroneous from every point of vieAv. Many engineering works of magnitude and of great importance to the peoi^le whom they served were executed in the very dawn of history, and they have been followed by many other works of at least equal mag- nitude and under circumstances scarcely less noteworthy, of Avhich \vc have either remains or records. During the lapse of the arts and of almost every process of ciA'ilization throughout the darkness i;)f the Middle Ages there Avas little if anv progress made in the art of the engineer, and Avhat little was done Avas executed almost entirely under the name of architecture. With the rcA'ival of intellectual actiA-itA" and A^-ith the deA'clopment of science the A-alue of its practical application to the groAving nations of the ciA'ilized world caused the modem profession of ciA'il engineering to take definite shape and to be knoAAii Iaa' the name Avhich it noAV carries, but Avhich Avas not knoAAii to ancient peoples. Unfortunately the beginnings of engineering cannot be traced ; there is no historical record running back far enough to render account of the earliest engineering Avorks AA^hose ruins remain as endiudng eA'idence of what A\'as then accomplished. 2 ANCIEXT ClVlL-EXaiNEERIXG WORKS. It is probably correct to state that the material progress of any people has always been concurrent with the development of the art of civil engineering, and, hence, that the practice of ■civil engineering began among the people who made the earliest progress in ci\-ilization, to whom ' ' the art of directing the Great Sources of Power in Nature for the use and convenience of mian" became an early and imperative necessity. Indeed that con- clusion is confirmed by the most ancient ruins of what may be termed public works that arch2:ological investigations have revealed to us, among which are those to be found in the Chal- dean region, in India, and in Egypt. Obviously, anything hke a detailed account of the structural and other works of such ancient character must be lacking, as some of them were built before even the beginnings of history. Our onty data, therefore, are the remains of such works, and unfortunately they have too fre- quently been subject to the destructive operations of both man and nature. 2. Hydraulic Works of Chaldea and Egypt. — It is absolutely certain that the populous centres of prehistoric times could not have existed nor have been served with those means of com- munication imperatively necessary to their welfare without the practice of the art of engineering, under whatever name they may haA'c apphed to it. It is known beyond any doubt that the anciently populous and prosperous countr^^ at the head of the Persian Gulf and watered by the Euphrates and the Tigris was irrigated and served by a most complete system of canals, and the same observation can be made in reference to the A'alley of the Nile. It is not possible at this period of that country's historA^ to determine to what extent irrigation was practised or how extensi\'ely the former countn^ was served by water trans- portation conducted along artificial channels; but hA-draulic works, including dams and sluices with other regulating appliances designed to bring waters from the rivers on to the land, were certainly among the earliest executed for the benefit of the com- munities inhabiting those regions. The remains of those works, spread over a large territory in the vicinity of ancient Babylon, Nippur, and other centres of population, show beyond the slight- est doubt that there existed a network of water communication HYDRAULIC M-QRKS OF CHALDEA AXD EGYPT. 3 throughout what was in those days a country rich in agricultural products and which supported the operations of a most pros- CHALDEA AND NEIGHBORING COUNTRIES perous commerce. These canals were of ample dimensions to float boats of no mean size, although much smaller than those occupied in our larger systems of canal transportation. They * ANCIENT CIVIL-ENGINEERING WORKS. were many miles in length, frequently interlacing among them- selves and intersecting both the Tigris and the Euphrates. The remains of these canals, some of them still containing water, show that they must originally have been filled to depths vary- ing from five or six to fifteen or twenty feet, and that their widths may haA-e been twenty-five or thirty feet or more. Another curious feature is their occasional arrangement in twos and threes alongside of each other with embankments only between. The entire Euphrates-Tigris valley from the head of the I-'ersian Gulf at least to modern Baghdad (i.e., Babylonia) and possibly to ancient Nineveh was served by these artificial Avaterways. Later, when Alexander the Great made one of his A'ictorious expeditions through the Assyrian country, he found in the Tigris obstructions to the passage of his ships down-stream in the shape of masonry dams. This was between 356 and 322 i-s.c. These substantial dams were built across the river for the purpose of intakes to irrigating-canals for the benefit of the adjacent country. These canals, like those of Egypt, were fitted with all the necessary regulating-devices of sluices or gates, both of a crude character, but evidently sufficients^ eft'ective for their purpose. It is known that there were in those early days interchanges of large amounts and varieties of commodities, and it is almost if not quite certain that the countries tributary to the Persian Gulf not only produced sufficient grain for their own needs, but also carried on considerable commerce with the Asiatic coast. We have no means of ascertaining either the volume or the pre- cise character of the traffic, but there is little or no doubt of its existence. It is established also that the waters of the Red Sea and the Nile were connected by a canal about 1450 b.c. Recent investigations about Nippur and other sites of ancient cities in that region confirm other indications that the practice of some branches of hydraulic engineering had received material develop- ment from possibly two to four thousand years before the Chris- tian era. 3. Structural Works in Chaldea and Egypt. — The ruins of ancient buildings which haA'e been unearthed bv excavations in the same vicinity show with the same degree of certainty that the art of constructing buildings of considerable dimensions had STIWCTUHAL WORKS IN CHALDEA AND EGYPT. 5 also made material progress at the same time, and in many cases must ha\-e involved engineering considerations of a decided character both as t(.> structural materuds and to ftjundations. Bricks were manufactured and used. Stones were quarried and dressed for building purj^jscs and apphed so as to produce structural results of consiileraldc excellence. Even the arch was probably used to some extent in that locality in those early days, but stone and timber beams were constantly employed. In the prehistoric masonry constructions of lioth the Egyptians and Chaldeans and jirobaldy other prehistoric peoples, lime, or cement mortar was not employed, but came into use at a sub- sequent pcri(.)d wlicn the projx'rtics of lime and cement as cement- ing materials began to be recognized. The first cementing material i^roliably used in Egypt W'as a sticky clay, or possibly a calcarecuis cla)' or earth. The same material was also used in the \-alley of the Eujihrates, but in the latter country there are springs of bitumen, where tliat material exudes from tlic earth in large quantities. The use of this asphaltic cement at times possibly in\'olvcd that of sand or grax'cl in some of the early constructions. Later, lime mortar and possibly a A\'eak hx'draulic cement came to be em]doyetl, although there is little if any exd- dencc of the latter material. Iron was manufactured and used at least in small quantities, and for some structural iiuiqioses, e\-en though in a ci"ude manner. Bituminous or other asphaltic material was found as a natural jiroduct at \'arious points, and its value for certain structural puiqioscs was well known; it was used botli for waterjjroofing and for cement. It is practically certain that the construction of engineering works wIkisc interesting iiiins still remain in\-ol\-ed a considerable number of affiliated engineering o]:)erations of whicli no e\'idence has yet been f(iund, and of the emplovment of tools and appliances (^f which we have no record. So far as these works were of a public character they were constructed by the aid of a verA' different labor svstem from that now existing. The kings or ruling potentates of those early times were clothed with the most arbitrarv authoritx', sometimes exercised wiselv in the best interests of their people, but at other times the ruling motive was selfishness actuated bv the most intense egotism ANCIENT CIVIL-ENGINEERING WORKS. and brutal tyranny. Hence all public works were executed practically as royal enterprises and chiefly by forced labor, per- haps generally without compensation except mere sustenance. Under such conditions it was possible to construct works on a scale out of all proportion to national usefulness and without structural economy. When it is remembered that these con- ditions existed without even the shadow of engineering science, it is obvious that structural economy or the adaptation of well- considered means to an end will not be found to characterize engineering operations of prehistoric times. Nevertheless there are ex'idences of good judgment and reasonable engineering design found in connection with some of these works, particularly with those of an hydraulic character. A¥ater was lifted or pumped by spiral or screw machines and by water-wheels, and it is not improbable that other appliances of power served the purposes of many industrial and crude manufacturing opera- tions \\'hich it is now impossible for us to determine. Fig. I. — Home Built on Piles in the Lund ol Punt. It is an interesting fact that while many ancient works were exceedingly massive, like the pyramids, the largest of those of which the ruins have been preserved seldom seem to show little or any evidence of serious settlement. Whether the ancients had unusually sound ideas as to the design of foundation works, or whether those only have come down to us that were founded directly upon rock, we have scarcely any means of deciding. Nor can we determine at this time what special recourses were available for foundation work on soft ground. Probably one ANCIENT MATUTIME COMMERCE. 7 of the earliest reeot;'nized instanees, if not the earliest, of the building t>f structures on ])iles is that given fjy vSir Lieorge J-iaw- linson, when he states that a fleet i if merehant \-essels sent down the northeast African coast by the Egyjjlian (jucen Idatasu, ]~irobal:)ly 1700 B.C. or 1600 B.C., found a pe(.)ple whose huts were su]iported on piles in order to raise them alxn-e the marshy ground anil ])ossibly for additional safety. A re])resentation (Fig. i) of (.inc o[ these native homes on jjiles is found among iigyptian hierogh'])hies of the period of (Jueen Hatasu. 4. Ancient Maritime Commerce. -It is well known that both the Chaldean region and the Nile valley and delta, at least from Ethio]")ia to the Mediterranean Sea, were densely i)opulated dur- ing the ]")eriod of two to four or fi\'e thousand years before the Christian era. By means of the irrigation works to which refer- ence has already been made both lands became highly productive, and it is also well known that those peoples carried on a consider- able commerce Avith other countries, as did the Phoenicians also, at least between the innumerable wars which seemed to be the main business of states in those days. These commercial operations required not only the construction of fleets of what seem to us small \'essels for such purposes, but also harbor works at least suitable to the vessels then in use. The marine activity of the Phoenicians is undoubted, and there is strong reason to believe that there was also similar activity between Babylonian ports and those east (^)f them along the shores of the Indian Ocean, perliaps e\'en as far as ancient Cathay, and possibly also to the eastern coast of Africa. In\'estigations in the early history of Egypt have shown that a I'hixnician fleet, constiticted at some EgA'ptian port on the Red Sea, undoubtedly made the complete circuit of Africa and returned to Egj-pt through the Mediterranean Sea the third year after setting out, over 2100 years (about 600 b.c.) before the historic fleet of the Portuguese explorer \'asco da Gama sailed the same circuit in the opposite direction. It is therefore probable, in view of these facts, that at least simple harbor works of sufficient efficiency for those early davs found place in the public works of the ancient kingdoms bordering upon the Medi- terranean and Red seas and the Persian Gulf. 8 ANCIENT CIVIL-ENOINEERINO WORKS. 5. The Change of the Nile Channel at Memphis.^Although such obscure accounts as can be gathered in connection with the founding of the city of Memphis are so shadowy as to be largely legendary, it has been established beyond much if any doubt that prior to its building the reigning Egyptian monarch deter- mined to change the course of the Nile so as to make it flow on the easterly side of the valley instead of the westerly. This was for the purpose of securing ample space for his city on the west of the river, and, also, that the latter might furnish a defence towards the east, from which direction invading enemies usually approached. He accordingly formed an immense dam or dike across the Nile as it then existed, and compelled it to change its course near the foot of the Libyan Hills on the west and seek a new channel nearer the easterly side of the valley. This must have been an engineering work of almost appalling magnitude in those early times, yet even with the crude means and limited resources of that early period, possibly, if not proba- bly, at least 5000 b.c, the work was successfully accomplished. 6. The Pyramids. — ^Vmong the most prominent ancient structural ^^•orks are the pyramids of Egypt, those royal tombs of which so much has been written. These are found chiefly in the immediate vicinity of Memphis on the Nile. There are sixty or sevent}' of them in all, the first of which was built by the Egyptian king Khufu and is known as the ' ' Great Pyramid" or the ' ' First Pyramid of Ghizeh." They have been called ' ' the most prodigious of all human constructions." Their ages are uncertain, but they probably date from about 4000 B.C. to about 2500 B.C. These are antedated, however, by two Eg\^ptian pyramidal constructions of still more ancient character whose ages cannot be determined, one at Meydoum and the other at Saccarah. The pyramids at Memphis are constructed of limestone and granite, the latter being the prominent material and used entirely for certain portions of the pyramids where the stone would be subjected to severe duty. The great mass of most of the pyra- mids consists of roughly hewn or squared blocks with little of any material properly considered mortar. The interior portions, especially of the later pyramids, were sometimes partially com- THE PYRAMIDS. posed of chips, rough stones, mud bricks, or even mud, cellular retaining-walls being used in the latter cases for the main struc- A Corner of the Great Pyramid. fCopyripht by S. S. McClure Co., IQ02. Courtesy of McChirc^s Magazine^ tural features. In all pyramids, however, the outer or exposed surfaces and the walls and roofs of all interior chambers were finished with finely jointed large stones, perhaps usually polished. 10 ANCIENT CIVIL-ENGINEERING WORKS. 2. — Section of the Great Pyramid. The Great Pyramid has a square base, which was originally 764. feet on a side, with a height of apex above the surface of the ground of over 480 feet. This great mass of masonry contains about 3,500,000 cubic yards and weighs nearly 7,000,000 tons. The area of its base is 13.4 acres. The Greek historian Herodotus states that its construction re- quired the labor of 100,000 men for twenty years. An enormous quantity of gran- ite was required to be trans- ported about 500 miles down the Nile from the quarries at Syene. Some of the blocks at the base are 30 feet long with a cross-section of 5 feet by 4 or 5 feet. The bulk of the entire mass is of comparatively small stones, although so squared and dressed as to fit closely together. Familiar descrip- tions of this work have told us that the small passages leading from the exterior to the sepulchral chambers are placed nearly in a vertical plane through the apex. The highest or king's chamber, as it is called, measures 34 feet by 17 feet and is 19 feet high, and in it is placed the sarcophagus of King Khufu. It is composed entirely of granite most exactly cut and fitted and beautifully polished KING'S CHAMBER AND CHAMBERS OF CONSTRUCTION GREAT PYRAMID. Fig. 3. The construction of the roof is remarkable, as it is composed of nine great blocks ' ' each nearly 19 feet long and 4 feet wide, which are laid side by side upon the walls so as to form a complete ceiling. ' ' There is a singular feature THE PYR^^[fDS. 11 of construction of this ceiling designed to remoAT all pressure from It and consisting of five alternate ojien spaces and blocks of granite placed m A-crtical series, the highest open s])aee being m^^^^-L^^^^ Entrance to the Great Pyramid. roofed OA-er with inclined granite slabs leaning or strutted against each other like the letter V inverted. This arrangement relieA-es the ceiling of the sepulchral chamber from all pressure ; indeed 12 ANCIENT CIVIL-ENGINEERING WORKS. only the inclined highest set of granite blocks or slabs carry any load besides their own weight. There are two small ^'entilating- or air-shafts running in about equally inclined directions upward from the king's chamber to the north and south faces of the, pyra- mid. These air-shafts are square and vary between 6 and 9 inches on a side. The age of this pyramid is probably not far from 5000 years. The second pyramid is not much inferior in size to the Great Pyramid, its base being a square of about 707 feet on a side, and its height about 454 feet. The remaining pyramids are much inferior in size, diminishing to comparatively small dimensions, and of materials much inferior to those used in the earlier and larger pyramids. 7. Obelisks, Labyrinths, and Temples. — Among other con- structions of the Eg}'ptians which may be called engineering in character, as well as architectural, are the obelisks, the ' ' Laby- rinth" so called, on the shore of Lake Moeris, and the magnificent temples at the ancient capital Thebes, which are the most remark- able architectural creations probably that the world has ever known. These latter were not completed by one king, as was each of the pyramids. They were sometimes despoiled and largely wrecked by invading hosts from Assyria, and then recon- structed in following periods by successive Egyptian kings and again added to by still subsequent monarchs, whose reigns were characterized by statesmanship, success in war, and prosperity in the country. Their construction conclusivelv indicates laborious operations and transportation of great blocks of stone characteristic of engineering development of the highest order for the days in which they took place. The dates of these con- structions are by no means well defined, but they extend over the period running from probably about 2500 b.c. to about 400 B.C., with the summit of excellence about midway between. Another class of ancient structures which can receiA-e but a passing notice, although it deserves more, is the elaborate rock tombs of some of the old Eg^^ptian monarchs in the rocks of the Libyan Hills. They w^ere very extensive co.nstructions and contained numerous successions of ' ' passages, chambers, cor- ridors, staircases, and pillared halls, each further removed from NILE IRRIGA TION. 13 the entrance than the last, and all covered with an infinite number of brilliant paintings." These tombs really constituted rock tunnels with complicated ramifications which must ha\'e added much to the difficulty of the work and required the exercise of engineering skill and resources of a high order. 8. Nile Irrigation. — The value of the Avaters of the Nile for irrigation and fertilization were fully appreciated by the ancient Egyptians. They also apparently realized the national value of some means of ecjualizing the overflow, although the annual regimen of the Nile was unusually unife determined, but it mi^x have been as earh- as 2000 B.C., or jicrhafis earlier. 9. Prehistoric Bridge-building. — The de\-elo])ment of the art of liridgedjiiilding seems to ha\-e lagged some\\-hat in the prehistoric period. The use of rafts anst as far. Fortunately it was frequentlv a custom of the ancient brick-makers tc) stamp proprietar^• marks ujion their bricks, and we knciw bv these marks that Itricks were made in the t'haldean regions certainly from 3000 to _iooo A'cars before the Christian era. In Egypt alseT the manufacture of brick dates back nearly or quite as far. Some of these tdialdean bricks, as Avell as those m other parts of the ancient world, were of poor qualit\', readib- destroyed Iiy water or ca'cii a hea^-y storm of rain when dri\-ing upon them. Other bricks, howcA'cr, were manufactured of ginid quality' of material and bA' such methods as tci produce results which com- pare fa\'oral)b- Acitl: emr modern building-bricks. The ruins cif cities, at least in AssA'ria and Chaldea, show that enciriririus buildings, many of them palaces of kings, were constructed largely of these bricks, although they were elalu irately deeoratdi Acith other material. The walls Ayere hea\"y, indeed so massi\-e that many of the ruin-mounds are frequently formed almost entirely of the disintegrated briek of poorer qualit}'. These old builders not only executed their work on a large scale, but did not hesitate to pile up practiealh- an artificial mountain of earth, or idher suitable material, on Achich to ci instruct a palace or temple. Tlie danger of water ti3 tliese nati\e bricks Acas so Acell knoAyn and recognized that elaborate and A^ery excellent SA'stems of subsurface drains or sewers were frequently con- structed to caiTA' eiff the storm-Ayater as fast as it fell. IG AXCIEXT CIVIL-EKGIXEERIXG WORKS. II. Ancient Arches. — In the practice of these building operatii>ns it liecamc necessary to f(jrm many openings and to construct roots for the sewers or drains, and the arch, both true and false, came to be used m the Euphrates valley, in tliat of the Xile, and in other portions of the ancient world. Pi.iinted sewer-arches i if brick ]ia\-e been found in what is supposed to be the palace of Nimrod on the Tigris Ri\-er, possibly of the date aliout 1,^00 B.C. Excavations at Xippur have revealed a muddirick pointed arch supposed to date back tri possibly 4000 B.C. Also semicircular voussoir arches have been discovered at the ruins i>f Khorsabad near XincA-eh with spans of 12 to 15 feet. These arches are supposed to belong to the reign of Sargon, an Assvrian king who flourished abr)ut 705 to 722 B.C. Again, the ancient so-called treasur}' of Atreus at Alycense in Greece, although a dome, exhibits an excellent example of the method of forming the false arch, the date of the construction being probably about 1000 b.c. The main portion of this struc- ture consists of a pointed dome, the diameter of the base being VAULTED DRAIN, KHORSABAD AULTED DRAl^S, KHO SABAD. F'G. 4 Fig. 5. 48 feet and the interior central height 49 feet. A central section shoAvs a beehive shape, as in Fig. 6. The exterior approach is between two walls 20 feet apart, the intermediate entrance to the dome or main chamber being a passage 9 feet 6 inches wirle at the l^ttom and 7 feet 10 inches at the top and about iq feet high. At riglit angle- to the en- trance there is a chamber 27 feet by 20 feet cut int.. the a.liacent AXCIEXT AIK'IIES. 17 rock, entered through a dc.jrway aliout 4 feet 6 melies wide and 9 feet 6 inehes high. I^oth the main entrance to the dome and the doorway t(3 tlie adjacent ehamlier are coA-ered (ir m, ,fed with large flat lintel-stones, over which are the triangular relie\-- ing (false) arches, so cunimon in ancient eonstructiim, li\' which the lintels are relie\-e(l uf load, the triangular dpenings being closed liy smgle, great u]n-ight flat st, doorway; C. approach. . Section of the above: />. doorway; O, approach filled up with eanli: P, slope of tlie ^^round; £, wall on n^irth side of approach; J-', lintel stone, wei£,dlt 1^3 tons; t/, door to rock-cut chamber. and beautiful breccia" from the neighboring hills and Mount Eubora near by. The courses of stone are about two feet thick and closely fitted without cement. The great majority, or perhaps all, of the Assyrian true arches, so far discovered, are formed of wedge-shaped bricks, most of them 18 A^'C•IEXT CIVIL-EXGIXEERI.XG WORKS. being semicircular, although some are pointed, the span being not over about 1 5 feet. The most of the arches found at XincA'eh and Babylon belong to a period reaching possibly from 1300 to 800 B.C., but some of the Egyptian arches are still older. Eg^^p- tians, Assyrians, Greeks, and other ancient people used false arches formed by projecting each horizontal course of stones or bricks over that below it on either side of an opening. The repetition of this procedure at last brings both sides of the opening together at the top of the arch, and they are surmounted at that point with a single flat stone, brick, or tile. It has been supposed by some that these false arches, whose sides may be formed either straight or curved, exhibit the oldest form of the arch, and that the true arch with its ring or rings of wedge- shaped voussoirs was a subsequent development. It is possible that this is true, but the complete proof certainh' is lacking. In Egypt and Chaldea both styles of arches were used concur- rently, and it is probably impossible to determine which preceded the other. Again, some engineers ha^-e contended that two flat slabs of stone leaning against each other, each inclined like the rafters of a roof, was the original form of the arch, as found in the pyramids of Egypt ; but it is probable that the true arch was used in Chaldea prior to the time of the pyramids. Indeed crude arches of brick have been found at Thebes in Egypt dating back possibly to 2500 B.C., or still earlier. Aside from that, however, such an arrangement of two stones is not an arch at all, either true or false. The arrangement is simply a com- bination of two beams. A condition of stress characteristic of that in the true arch is lacking. The ancient character of the engineering works whose ruins are found in Chaldea and Assyria is shown by the simple facts that Babylon was destroyed about the year 690 e.g. and Nineveh about the year 606 b.c. CHAPTER II. 12. The Beginnings of Engineering Works of Record. — In a later period of the \\-orkrs history we reaeh a stage in the devel- opment of engineering works of whieh we huxe both reeonls and remains in snch well-dehned shape that the eharaeteristics of the profession may be realized in a definite manner. This is partieularh' tiaie of the ei\'il-engineeriiig works of the Romans. Ill their sturdy and unyielding charaeter, with their limitless energy and resolution, the eonditions requisite for the execution of engineering works of great magnitude are found. An effemi- nate or generally aesthetic nation like the Greeks would furnish but inditlerent opportunity for the ineeption and de^•elopment of great engineering works, but tlie resolute and Aagorous Roman nation ottered precisely the eonditions needed. They appre- ciated among other things the absolute neeessitvof the freest pos- sible communication with the countries whieh they conquered and made part of their own empire. They recognized water transportation as the most economical and eft'ective, and used it wherever possible. They also realized the advantages of roads of the highest degree of solidity and excellence. No other roads have ever been constructed so direct, so solid, and so admirably adapted to their puiq:ioses as those built by the Romans. They ^"irtuall^■ ignored all obstacles and built their highwavs in the most direct line practicable, making deep cuts and fills with apparentlv little regard for those features whicli we consider obstacles of sufficient magnitude to be aA'oided. They regarded this svstem of land communication so higlily that they made it radiate from the Golden ilile-stone in the Roman Forum. The point from which radiated these roads was therefore in the very centre of Roman life and authority, and it fitly indicated tlie importance which tlie Roman government gave to the system 19 30 ANCIENT CIVIL-ENGINEERING WORKS. of communication that bound together with the strongest bonds all parts of the republic and of the empire. The design and construction of these roads must have been a matter to which their constructors gave the most careful atten- tion and study. They were works involving principles deduced from the most careful thought and extended experience. There were incorporated in them the most effective materials of con- struction then known, and it was evidently the purpose of their constructors that they should possess indefinite endurance. The existence of sume of them at the present time, with no other attention given h ■ them than required frir i)rdinar\- maintenance, demonstrates that the confidence of the builders was not mis- placed. Street Fountain and Waterintj-trouph in Pompeii. Called the Fountain of Plentv. from tlie figure with Horn of Pleuty on the iicrforaled upright post. 13. The Appian Way and other Roman Roads. — Probably the oldest and most celebrated of these old Roman roads is the Appian AVay. It was the most substantially built, and the breadth of roadway varied from 14 to 18 feet exclusive of the footwalks. Statins called it the Queen of Roads. It was begun by Appius Claudius Cfficus, 312 years before the Christian era. He carried THE APPIAX ir.n -WD OTHER ROM AX ROADS. :il its eonsti'uction fnmi the Roman gate ealled Ti irta Capena io Capua, but it \\'as nut entirely eumjileted till ab(jut the year 30 i;!.C. Its tutal length was three hundred and fifty miles, and it formed a perfeet highway from Rome to Brundisium, an important piort on what may be ealled the southeastern point of Italv. It was built in sueh an enduring manner that it appears to have been in perfeet re])air as late as 500 to 505 a.d. The plan of ecmstruetn >n of these roads was so \'aried as to suit loeal eonditions, Imt only as retiuired by sound engineering iudement. Thev wisely emplo\'ed loeal materiids wherexer p)OSsible, but did ne.t hesitate to transport proper material from distant points wherexx-r necessary. This seemed to be one of their fundamental prmeiides of road eonstruetion. In this respect the old Romans exhibited more engineering and business wisdom than some of the Ameru-an states in the beginnings of improved road construction in this countr)'. An examination of the remains of some Roman roads now existing a]ipcars to indicate that m earth the bottom of the requisite cxcaAation was first suitably compacted, ai^parently I>y ramming, although rohers may have been used. On this compacted subgrade were laid txvo or three courses of flat stones on tlieir lieds and generally in mortar. The second layer jdaced on the iireeeding was rubl ile masonry of small stones or of coarse concrete. ( )n tlie latter was placed the third layer of finer concrete. The fourth or surface course, consisting of close and nieeh' jointed poh'gonal blocks, was then put in place, and formed an exeehent unyielding pavement. This resulted in a most substantial roachvay, some- times exceeding 3 feet in total thickness. It is difticult tf) con- ceiyeof a more substantial and enduring type of nxid construction. The two lower layers were omitted when the road was ci.m- structed in rock. Obviously the finer concrete constituting the second layer from the top surface was a binder between the pavement surface and the foundation of the roadway structure. ^ The paved part of a great road xvas usually about 16 feet m width, and raised stone causeways or walls separated it from an unpaved way on each side haAung half the width of the mam or paved portion. This seemed to be the type of the great or main Roman roads. Other highways of less important character 22 ANCIENT CIVIL-ENGINEERING WORKS. were constructed of inferior materials, earth or clay sometimes being used instead of mortar; but in such cases greater crown- ing was employed, and the road was more elevated, possibly for better drain- age. Then, as now, adequate drainage was considered one of the first features of good road design. City streets were paved with the nicely jointed pol}'gonal blocks to which reference has already been made, while the footways were paved with rectangular slabs much like our modem sidewalks. The smooth polygonal pavements of the old Romans put to the keenest shame the barbarous cobblestone street people of American cities have been :!'l(> — ^^ 3 1 ^^ H 5 10 Ft. EXAMPLE OF EARLY BASALT ROAD. BV THE TEMPLE OF SATURN ON THE CLIVUS CAPITOLINUS. Fig. 7- surfaces with which the and are still so tortured. The beneficial influence of these old Roman highways has extended down even to the present time in France, where some of them were built. The unnecessarily elaborate construction has not been followed, but the recognition of the public bene- fits of excellent roads has been maintained. The lower course of the foundation-stones apparently began to be set on edge toward the latter part of the eighteenth century, the French engineer Tresaguet having adopted that practice in 1764. At the same time he reduced the thickness of the upper layers. His methods were but modifications of the old Roman system, and they prevailed in France until the influence of the English engi- neers Macadam and Telford began to be felt. 14. Natural Advantages of Rome in Structural Stones. — Although the ancient Romans were born engineers, possessing the mental qualities and sturdy character requisite for the analytic treatment and execution of engineering problems, it is doubtful whether they would have attained to such an advanced position in structural matters had not the city of Rome been so favorably located. The geological character of the great Roman plain and the Roman hills certainly contributed most materially to the early iV.lT[/7?.lL ADVANTAGES OF ROME IN STRUCTURAL STONES. 23 development of some of the most prominent of the Roman engineering works. The plain sun-ounduig the city of Rome is composed largely of alkn-ial and sandy deposits, or of the emis- sions of neighboring volcanoes, of which the Alban Hills form a group. AVhile these and other volcanic hills in the \-icinity are, and have been for a long period, cjuiescent, they were formerly in a veryactn-e state. The scoria', or matter emitted m \-()lcanic eruptions, is f(jund there in all possible degrees of coherence or solidity, from pul\-erulent masses to hard rock. The charac- teristic Roman material called tufa is a mixture < if volcanic ash and sand, loose and friable, as dropped from the eruptions in large quantities or again compressed into masses with all degrees of hardness. The hard varieties of yellow or Ijrown tufa form building material much used, although a considerable percentage of it would not be considered fit building material for structures of even moderate height at the present time. The most of it weathers easily, but forms a fairly good building-stone when protected by a coating of plaster or stucco. Another class of building-stones found at or in the vicinity of Rome is the so-called " peperino, " consisting chiefly of two varieties of conglomerate of ash, gravel, broken pieces of lava, and pieces of limestone, some possessing good weathering quali- ties, while others do not. Ancient quarries of these stones exist whence millions of cubic yards haA'e been removed, and are still being worked. The better varieties of ''peperino" possess good resisting qualities, and were much used in those portions of masonry construction where high resistance was needed, as in the ring-stones of arches, heavily loaded points of f(.)undations, and other similar situations. Some of the prehistoric masonrv remains of the Romans show that their earliest constructors appreciated intelligently the qualities of this stone for portions of works where tlie duty was most se\'ere. Lava from the extinct A-olcanoes of the All^an Hills called "silex" was used for paving roads and for making concrete. It was hard and of gray color. At times considerable cjuantities of this stone were employed. A species of pure limestone called ' ' travertine," of a creamy white color, was quamed at Tibur or 24 AXCIEXT ClVIL^EXGIXEEIilXG WORKS. Ti\'oli, and Ijegan to be used about the second century B.C. A'ltian-ius speaks of its ha\-ing good weathering qualities, but naturalh- it is easily calcined. Its structure is crystalline, and it is str(jng in conseciuence of that quality only when it is laid on its bed. 15. Pozzuolana Hydraulic Cement. — The most valualde of all building materials of old Rome was the "pozzuolana," as it furnished the basis of a strong, enduring, and economic con- crete, and permitted almost an indefinite develoj.iment of masonry construction. Had there not been at Rome the materials ready at hand to be manufactured into an excellent cementing product, it is highly probable that neither the structural advance nor the commercial supremacy of the Roman people could ha^x- been attained. It is at least certain that the majority of the great masrjnrv works constructed by tlie Romans could not have been faiilt without the hydraulic cementing material produced with so little diilicultv and in such large quantities from the volcanic earth called pozzuolana. The name is believed to have its origin from the large masses of tliis material at Pozzuoli near Naples. Great beds are also found at and near Rome. The earliest date of its use cannot be determined, but it has given that strong and durable character to I-loman concrete which has enabled Roman masonry to stand throughout centuries, to the admiration of engineers. It is a volcanic ash, generally puh'erulent, of a reddish color, but differs somewhat in appearance and texture according to the locality from which it is taken. It consists chiefly of silicate of alumina, but contains a little oxide of iron, alkali, and possibly other components. The Romans therefore pulverized the poz- zuolana and mixed it with lime to make hydraulic cement. This in turn was mixed with sand and gravel and broken stone to form mortar and concrete, and that process is carried on to this day. The concrete was hand-mixed, and treated about as it is at present. After having been well mixed the Romans frequently deposited it in layers of 6 to 9 or 10 inches thick, and subjected it to ramming. In connection with this matter of mortar and concrete production, Vitruvius observes that pit sand is preferable to either sea or river sand. ROMAN BRICKS AND MASONRY ■e i6. Roman Bricks and Masonry. — The J-iomans produced bricks both liy sundjakmg and Ijy burning, ahhougli there an now remaining apparently no specimens of tlie former in liome. Bricks were used very largely for facing ])urposes, such as a veneer for concrete work. Tlie failure to recognize this fact has led some in\'estigators and writers into error. As matter ( if fact bricks were used as a coA'cring for concrete w( >rk, tlie latter per- forming all the structural functions. The old Roman ariueducts were frec[uently lined witli ci m- crete, made of a mixture of pozztiolana, lime, and cruslied (pounded) liricks or ]>otshcrds. The same material Avas also used for floors under tlie fine mortar in which the mijsaics were imbedded. ilarlile came into use in Rome about loo b.c, from Luna, near modern Carrara, Alt. Hymcttus, and Mt. Pentelieus, near iVthens and the Isle of Paros, ncarh' all being for sculpture purposes. Colored and structural marljlcs were brouglit from quarries in various parts of Italy, Creecc, Phrygia, Egyjit, near Thebes (oriental alabaster or " onyx"), Arabia, and near Damascus. From the latter part of the first century b.c. the hard building- stones like granites and basalts were Ijrought to Rome in large quantities. Most of the granites came from Phike cm tlie Nile. The basalts came both from Lacedsmonia and Egypt. Both emery (from the island of Naxos in the .-Egean Sea) and diamond- dust drills were used in ciuarrying or working these stones. Ships among the largest, if not the largest, of those days, were built to transport obehsks and other large monolitlis. The quality of ancient Roman mortar varies considerably as it is now found. That of the first and second centuries is remarkably hard, and made with red pozzuolana. In the third century it began to be inferior in quality, brown pozzuolana sometimes being used. The reason for this difference in quahty cannot be confidently assigned. The deterioration noted in the third-century work may be due to the introduction of bad ma- terials, or to the wrong manipulation of material intrinsically good, or it is not unlikely the deterioration is due to a combina- tion of these two influences. The use of mortar indicates a class 26 ANCIENT CIVIL-ENGINEERING WCJRKS. of early construction; it is found in the Servian wall on the Aventine, of date 700 B.C., or possibly earlier. Under the empire (27 e.g. to a.d. 475) large blocks of tufa, Dovetail Wooden Tenon. W.oden Dowel. Fig. 8. limestone (travertine), or marble were set with ver^^ close joints, with either no mortar or, if any, as thin as paper; end, top, and bottom clamps of iron were used to bond such stones together. It was also customary, in laying such large, nicely finished blocks of stone without mortar, to use double dove- tailed wooden ties, or, as in the case of columns, a continuous central dowel of wood, as shown in the figures. The joints were frequently so close as to give the impression that the stones might have been fitted by grinding together. In rectangular dimension stonework (ashlar) great care was taken, as at present, to secure a good bond by the use of judi- ciously proportioned headers and stretchers. Foundation courses were made thicker than the body of the superincumbent wall, apparently to distribute foundation weights precisely as done at present. Weaker stone was used in thicker portions of walls, and strong stone in thinner portions. Also at points of con- centrated loading, piers or columns of strong stone are found built into the bodies of walls of softer or weaker stone. Quarry chips, broken la^-a, broken bricks, or other suitable refuse frag- ments were used for concrete in the interest of economy, the broken material always being so chosen as to possess a sharp surface to which the cement would attach itself in the strongest possible bond. At the quarries where the stones were cut the latter were marked apparently to identify their places in the complete ROMAN BRICKS AND MASONRY 27 Structure, or for other purposes. The remains of the quarries themselves as seen at present are remarkable both for their enormous extent and for the S3'stem on which the ciuarrjdng was conducted. It appears that the systems cmi)l(-)yed were admirably adapted to the character of the stone \v<-)rkefl, and that the quarrying operations were executed as efficiently and with as sound engineering judgment as those empfiyed in great modem quarries. 17. Roman Building Laws. — So much depended upon the excellence of the building in Rome, and upon the materials and methods employed, that building laws or municipal regulations were enacted in the ancient city, prescrilsing kind and quality of material, thickness of walls, maximum height of buildings, minimum width of streets, and many other proA-isions quite similar to those enacted in our modem cities. Tlie differences appear to arise from the different local conditions to be dealt with, rather than from any failure on the part of the old Romans to reach an adequate conception of the general plans suitable for the masses of buildings in a great city. Prior to the great fire A.D. 64 in Nero's reign, an act prescribing fire-proof exterior coverings of buildings was under consideration, and subsequently to that conflagration it was enacted into law. Many of the city roads or streets were paved with closely fitting irregular polyg- onal blocks of basalt, laid on concrete foundations, and with limestone (travertine) curbs and gutters, producing an effect not unlike our modern streets. 18. Old Roman Walls. — In no class of Avorks did the ancient Romans show greater engineering skill or development than in the massive masonry structures that were built not only in and about the city of Rome, but also in distant provinces under Roman jurisdiction. Among the home structures various walls, constituting strong defences against the attacks of enemies, stand in particular prominence. Some of these great structures had their origin prior even to historic times. The so-called ' ' Wall of Romulus, " around the famous Roma Ouadrata of the Palentine, is among the latter. It is supposed by many that this wall formed the primitive circuit of the legendary city of Romulus. That, however, is an archseological and not an engineering ques- 28 ANCIENT CIVIL-ENGINEERING WORKS. tion, and, whatever its correct answer may be, the Avah itself is a great engineering work; it demonstrates that the early Romans, whate\'er may have been their origin, had attamed no little skill m quarrying and in the building of dry masonry, no mortar being used m this ancient wall. Portions of it 40 feet high and 10 feet thick at bottom, built against a rocky hill, are still standing. The courses are 22 to 24 inches thick, and they are laid as alternate headers and stretchers; the lengths of the blocks being 3 to 5 feet, and the Avidth from 19 to 22 inches. The ends of the blocks are carefully Avorked and true, as are the verti- cal joints in much of the wall, although some of the latter, on the other hand, are left as much as 2 inclies open. Civil engineers, Avho are familiar with the difficulties fre- quently experienced in laying up dry walls of considerable height, as evidenced liy many instances of failure probabl)' \\dthin the knoAvledge of every experienced engineer, will realize that this great dry -masonry structure must ha^-e been put in place b}- men of no little engineering capacity. The rock is soft tufa, and marks on the blocks indicate that chisels from -} to -J inch in width were used, as Avell as sharp-pointed pricks. In all cases the faces of the blocks Avere left undressed, i.e., in modern terms they were ' 'quarry -faced." 19. The Servian Wall. — Later in the history of Rome the great Servian Wall, built chiefly by SerAdus Tullius to enclose the seven hills of Rome, occupies a most prominent position as an engineering AA'ork. Part of the wall, all of Avhich belongs to the regal period (753 to 509 b.c), is supposed to be earlier than SerAdus, and may haA-e been planned and executed b}' Tarquinius Priscus. A part only of the stones of this AA-all Avere laid in cement mortar, and concrete was used, to some extent at least, in its foundation and backing. The presence of cement mortar in this structure differentiates it radically from the Avail of Rom- ulus. Probably the discoA^ery of pozzuolana cement, and the fabrication of mortar and concrete from it, had been made in the intervening period betAveen the tAvo constructions. Tufa, usually the softer varieties but of varying degrees of hardness, was mostly used in this Avail, and the blocks Avere placed, as in the previous instance, as alternate headers and stretchers in OLD UOMAX SEWERS. -uj courses about two feet thick. Portions of the wah ,, feet lu^h ^"^^ '"^f"^. ^= ''■''' tl"^!^ l^ave heen uneoverech At r'ant^ t w;' as embrasures tor eatapults or other engines of war Tli^up,.. ^Lt ^P--"g«.,^-e eireular arehes with tlie iLual ^ ge-hke „ng_s ,,nes. the ^-oussoirs were eut from pepenno ''""":, ^^^^^ ;^-^'ll: ^'^'^- that Mf Romulus, was eonstrAe^d as a mihtarA- work of detenee, and at some points it was built up . Fig. 0. -r;irtof Sr uli Avinti A-i:ni W;lU F[C. lo.- -Wall and A!,'t;e )f Sci-viu-. from the bottom of a wide foss 30 feet deep. At such places it was eounterforted or buttressed, a portion of wall u feet b inches long being found between two C(junterf()rts, each of the latter being 9 feet wide and projecting 7 feet 9 inches out from the wall. 20. Old Roman Sewers. — It is demonstrable bv the writings of \'itiaivius and others that the old Romans, or at any rate the better educated of them, possessed a correct general idea of some portions of the science of Sanitary Engineering, so far as any- thing of the nature of science could then be known. Their sani- tary views were certainly abreast of the scientific knowledge of that early day. The existence of the ' ' cloaca, " or great sewers, of the ancient city of Rome showed that its people, or at least its rulers, not only appreciated the value of draining and sewering their city, but also that they knew how to secure the construction of efficient and enduring sewers or drains. It has been stated, and it is probably true, that this system of cloacae, or sewers, was so complete that e\'ery street of the ancient city was drained through 30 ANCIEXT CIVIL-ENGINEERING ]VORKS. its members into the Tiber. ThiSy were undoubtedly the result of a gradual growth in sewer construction and did not spring at once into existence, but they date back certainly to the beginning of the period of the kings (753 B.C.). The famous Cloaca Max- ima, as great as any sewer in the system, and certainly the most noted, is still in use, much of it being in gocid order. The mouth of the latter where it discharges into the Tiber is 11 feet wide and 12 feet high, constituting a large arch opening with three rings of A'oussoirs of pcperino stone. Many other sewers of this system are also built with arch tops of the same stone, with neatly cut and closely fitting voussoirs. We do not find, unfor- tunately, any detailed accounts of the procedures involved in the design of these sewers, yet it is altogether probable that the old Roman ci^dl engineers formed the cross-sections, grades, and other physical features of their sewer system by rational processes, although they would doubtless appear crude and elementar}- at the present time. It would not be strange if they made many failures in the course of their structural experiences, but they certainly left in the old Roman sewers examples of enduring work of its kind. Some portions of this ancient sewer S3^stem are built with tops that are not true arches, and it is not im]:>ossihjle that they antedate the regal period. These tops are false arches formed of horizontal cotirses of tufa or peperino, each projecting over that below until the two sides thus formed meet at the top. The outline of the crowns of such sewers may therefore be triangular, curved, or polygonal; they were usually triangular. Smaller drains forming feeders to the larger members of the system were formed with tops composed of two flat stones laid with equal inclination to a vertical line so as to lean against each other at their upper edges and over the axis of the sewer. This method of forming the tops of the drains by two inclined flat stones was a crude but effective way of accomplishing the desired purpose. The main members of this great sewer system seem to have followed the meandering courses of small rivers or streams, con- stituting the natural drainage -courses of the site of the city. The Cloaca Maxima has an exceedingly crooked course and it, alono- with others, was probably first formed by walling up the sides EARLY ROMAN liRIDGKS. 31 of a stream and subsequently closing in the top. ^Modern engi- neers know that such an alignment for a sewer is vicioush' liad, and while this complicated system of drains is admirably con- structed in many ways for its date, it cannot be considered a perfect piece of engineering work in the light of present engineer- ing knowledge. It is probable that the walling in ier l^etween the other two arches. This structure is di\ddecl into two jiarts b\- the island ijf .diseulapius. It is known that a wooden bridge must ha\-e joined that island with the left liank of the Tiber as early as 192 k.c, and a similar structure on the (^ther side of the island is suj.iposecl tci haA'e com]">leted the structure. AAdiile Lucius Fabricius was Commis- sioner of Roads in the \'ear 62 k.c. he reconstructed the first- named portion into a masonrA- structmx' cif arclies. An cngra\-ecl inscription below the ]iara]">ets shoA\-s tliat the A\-ork Avas dulv and satisfactorily completed, and further that it A\'as the custom to require the constructors or luiilders of liridges to guarantee their work for the period of forty years. Possession of the last deposit. 34 ANCIENT CIVIL-ENGINEERING WORKS. made in advance as a guarantee of the satisfactory fulfilment of the contract, could not be regained until the forty-first year after completion. The Pons Cestius is a bridge since known as the Pons Gra- tianus and Ponte di S. Bartolomeo. Its first construction is Fii; -Trajan'^ Bridge. supposed to have been completed in or about 46 B.C., and it was rebuilt for the first time in a.d. 365. A third restoration took place in the eleventh century. The modern reconstruction in 1886-89 was so complete that only the middle arch remains as an ancient portion of the structure. The island divides the bridge into two parts, the Ship of ^^sculapius lying between the two, but it is not known when or by whom the island was turned into that form. Another old Roman bridge, of which but a small portion is now standing, is Pons .^-Lmilius, the piers of which were founded in 181 B.C., fjut the arches were added and the bridge completed only in 143 B.C. It was badly placed, so that the current of the river in times of higli water exerted a heavy pressure upon the piers, and in consequence it was at least four times earned away by floods, the first time in the year a.d. 2S0. The discovery of what appears to be a row of three or four ruins of piers nearly 340 feet up-stream from the Ponte Sisto seems to indicate that a bridge was once located at that point, although little or nothing is known of it as a bridge structure. Some suppose it to be the bridge of Agrippa. The most historical of all the old Roman bridges is that which was called Pons ^4ilius, now known as Ponte S. Angelo, built by Hadrian a.d. 136. Before the reconstruction of the bridge in BHlDdE OF ALCAXTAHA. 35 1892 six masonry arches were visible, and the discovery of two more since that date makes a total of eight, of which it is supposed that only three were nectled m a dry season. The pa\-ement of the approach to this liridge as it existed in 1892 was the ancient roadway surface. Its condition at that time was an evidence of the substantial character of the old Roman pa\-emcnt. Below the latter bridge remains of another can be seen at low water. It is supposed that this structure \\'as the work of Nero, although its name is not known. The modern Ponte Sisto is a reconstruction of the old Pons Valentinianus or briilge of Valentinian I. The latter was an old Roman bridge, and it was regarded as one of the most impressiA'c of all the structures crossing the river. It was rebuilt in a.d. 366-67. The most of these bridges were built of masonry and are nf the usual substantial type characteristic of the earh^ Romans. They were ornamented by masonry features in the main portions and by ornate balustrades along either side of the roadway and sidewalks. The roadway pavements Avere of the usual irregular polygonal old Roman type, the sidewalk surfaces being com- posed of the large slabs or stones commonly used in the earh' daj's of Rome for that purpose. 22. Bridge of Alcantara. — .Vmong the old Roman bridges should be mentioned that constructed at .Vlcantara in Spain, supposedlv bv Trajan, about a.d. 105. It is 670 feet long and its greatest height is 210 feet. C)ne of its sjians is partiallv de- stroyed. The structure is built of blocks of stone without cementing material. In this case the number of arches is e\'en, there being six in all, the central two ha\-ing larger spans than those which flank them. It is a bridge of no little impressiveness and beautv and is a most successful design. 23. Military Bridges of the Romans. — In the old Roman mih- tar}' expeditions the art of constmcting temporary timber struc- tures along lines of communication was well known and practised with a high degree of abilitv. Just what system of construction was employed cannot be determined, but piles were constantly used. At least some of these timber military bridges, and possi- bly all, were constructed with comparatively short spans, the 3G ANCIENT CIVIL-ENGINEERING WOEK.':i. trusses being composed of such braces and beams as might be put in place between bents of piles. As already observed, some of the sticks of these bridges have been found in the beds of German rivers, and at other places, perfectly preserved after an immersion of about two thousand years. These instances furnish conclusi\-e e\-idence ui the enduring ciualities of timber always saturated with water. 24. The Roman Arch. —The Romans developed the semicir- cular arcli to a high degree of excellence, and used it most exten- sively in manv sewers, roads, and ac^ueducts. AVhile the aque- duct spans Avere usually made A\-ith a length of about 18 or 20 feet, thev built arches with span lengths as much as 120 feet or more, comparing faA'orably with our modern arch-bridge AA'ork. They seldom used any other curve for their arches than the cir- cular, and when they built bridges an odd number of spans was usually employed, Avith the central opening the largest, possibly in obedience to the well-known esthetic law that an odd number of openings is more agreeable to the eye than an even number. Apparently they were apprehensive of the safety of the piers from which their arches sprang, and it was not an uncommon rule to make the thickness of the piers one third of the clear span. Nearly one fourth of the entire length of the structure would thus be occupied by the pier thicknesses. Although the use of mortar, both lime and cement, early came into use with the Romans, they usually laid up the ring-stones of their arches dry, i.e., with out the interposition of mortar joints. CHAPTER ITI. 25. The Roman Water-supply. —There is no stronger evidence of engineernig ile\-elopment m ancient Rome, nor of the ad- vanced state of ci\-iHzation whicli characterized its people, than its famous system of water-supply, which was remarkaljle both for the volume oi water daily sujjplied to the city and for the extensive acjueducts, many of whose ruins still stand, as impres- sive monuments of the vast pul.lic W()rks completed by the Romans. These ruins, and those of many other works, would of themselves assure us of the elaborate system of supply, but fortunately there has been preserved a most admirable descrip- tion of it, the laws regulating consumption, the manner of ad- ministering the water department of the government of the ancient city, and much other collateral informati(jn of a most interesting character. In the work entitled, in English, "The Two Books on the AA'ater-supply of the Citv of Rome," Ijy (Sextus) Julius ErontinusJ"an eminent old Roman citizen, whn, besides ha\'ing filled the office of vater commissioner* of the citv, was g(i\-emor of Britain and three times consul, as well as having enjoA'cd the dignity of being augur. He may properly be called a Roman engineer, although he evidently was a man of many public aft'airs, and so esteemed by the emperors who ruled during his time that he accompanied them in various wars as a militarv man of high rank. He wrote seven books at least, viz., "A Treatise on Surveying," "Art of War," " Strategemat- ics," " Essavs on Farming," "Treatise on Boundaries, Roads, etc.," "A AYork on Roman Colonies," and his account of the water-works of Rome, entitled " De Aquis." It is the latter * The first permaiimt w.iti-r commissioner in Rome was M. A'.::rippa, son-in-law of Csesar Augustus, wlio to(.k oft'ice B.C. 34. Tie was ..ne ..f the greatest Roman engineers and constructors, if imlee.l he wa's not the first in rank. 37 f Arry,, J.-..M ^0 h, di-:} .../.,' \o2' Ai: 38 ANCIENT CIVIL-ENGINEERING WORKS. book in which engineers are particularly interested. The trans- lation of this book from the original Latin is made from what is termed the " ]\Iontecassino ^Manuscript," an account of which with the translation is given by ]\Ir. Clemens Herschel in his en- tertaining work, ' ' Frontinus, and the Water-supply of the City of Rome." As near as can be determined Frontinus liA'ed from about A.B. 35 to A.D. 103 or 104. Judging from the offices which Fronti- nus held and the honors which he enj< lyed throughout his life, it W(juld appear that he was a patrician; he was certainly a man of excellent executive capacity, of intellectual Adgor and refined taste, and a conscientious public sen^ant. The AA-ater-supply of the city was held by the Romans to be one of the most impor- tant of all its public works, and its administration during the life of Frontinus was entrusted to what we should call a water commissioner, appointed by the emperor. It was considered to be an office of dignity and honor, and the proper discharge of its responsibilities was a public duty which required a high order of talent, as well as great integrity of character. 26. The Roman Aqueducts. — Frontinus states that from the foundation of the city of Rome until 313 b.c, i.e., for a period of 441 years, the only water-supply was that drawn either from the river Tiber or from wells or springs. The veneration of the Romans for springs is a well-known feature of their religious tenets. They were preser\-ed with the greatest care, and hedged about with careful safeguards against irreverent treat- ment or polluting conditions. Apparently after this date the people of Rome began to feel the need of a public water-supply adequate to meet the requirements of a great city. At anv rate, in the year 313 b.c. the first aqueduct, called' the Appia, for bringing public water into the city of Rome was attempted by Censors Appius Claudius, Crassus, and C. Plautius, the former having constructed the aqueduct, and the latter having found the springs. Appius must have been an engineer of no mean capacity, for it was he who constructed the first portion of the Appian Way. The origin of this water-supply is some springs about 10 miles from Rome, and they may now be seen at the bottom of stone quarries in the valley of the Anio River. This A MO VETVS. o'.) aqueduct, Aqua Appia, is mostly an underground waterway, only al>)ut ,:;oo L'eet of it being earried on masdnry arches. At the point where it enters the city it was o\-er 50 feet hcl. iw the surface; its clear cross-section is gu'en as zi feet wide by 5 feet .-Ti.,. "*-^-,.^, :^-'?5fcj?j^.^^ Claudia, of dimension stone, and Anio Novus. of brick ami ci'ncrete, on top of it. high. The elevation of its water-surface in Rome was probably under 60 feet above sea -level. 27. Anio Vetus. — The next aqueduct built fcir the water- supply of Rome was called Anio A'etus. It was built 272-269 B.C., and is about 43 miles long; it took its water from the river Anio. About iioo feet of its length was carried above ground on an artificial structure. It also was a low-level aque- duct, the elevation at which it delivered water at Rome being about 150 feet above sea-level. It was built of heavy blocks of masonry, laid in cement, and the cross-section of its channel was about 3.7 feet wide by 8 feet high. In the year 144 b.c. the Roman senate made an appropriation equal to about $400,000 of our money to repair the two aqueducts already constructed, and to construct a new one called Aqua ;\Iarcia, to dehver Avater to the city at an elevation of about 195 feet above seadevel. This aqueduct was finished 140 b.c; it is nearly 58 miles long, and carried water of most excellent quality through a channel which, at the head of the aqueduct, was 5 J feet wide 40 ANCIENT CIVIL-ENGINEERING WORKS. by 8-i\ feet high, but farther down the structure was reduced to 3 feet wide by St\ feet high. The excellent water of these springs is used for the present supply of Rome, and is brought in the Aqua Pia, built in 1869, as a reconstruction of the old Aqua Marcia. This aqueduct, like its two predecessors, is built of dimension stone, 18 inches Ijy 18 inches by 42 inches, or larger, laid in cement; but concrete and brick were used m the later aqueducts, with the exception of Claudia. 28. Tepula. — The aqueduct called Aqua Tepula, about 11 miles in length, and completed 125 B.C., was constructed to bring into the city of Rome a slightly warm water from the vol- canic springs situated on the hill called ilonte Albani (Alban Hills) southeast of Rome. The temperature of these springs is about 63° Fahr. In the year b.c. 2,0 -^grippa caused the water from some springs high up the same valley to be brought in over the aqueduct Ac^ua Julia, 14 miles long. This latter water was considerably colder than that of the Tepula Springs. The two waters were united before reaching Rome and allowed to flow together far enough to be thoroughly mixed. They were then divided and carried into Rome in two conduits. The vol- ume of water carried in the Aqua Julia w^as about three times that taken from the Tepula Springs, the cross-section of the latter being only 2.7 feet wide by 3.3 feet high, while that of Julia was 2.3 feet by 4.6 feet. The water from Aqua Julia entered Rome at an elevation of about 2 1 2 feet above sea-level, and that from Aqua Tepula about 1 1 feet lower. 2g. Virgo. — The sixth aqueduct in chronological order was called Virgo, and it Avas completed 19 b.c. It takes water from springs about 8 miles from Rome and only about 80 feet above sea-level, but the length of the aciueduct is about 13 miles. Tlie delivery of water in the city bj^ this aqueduct is about 67 feet above that level. The cross-section of this channel is about 1.6 feet wide and 6.6 feet high. 30. Alsietina.— The preceding aqueducts are all located on the left or easterly bank of the TiV.cr, but one early structure was located on the right bank of the Tiber to supply what was called the Trans-Tiberine section of the city, and it was known as Aqua Alsietina. The emperor Augustus had this aqueduct CLAUDIA. 41 constmcted clurino; his reign, and it ^^'as finished in tlie year A.D. lo. Its souree is a small lake of the same name witli itself, about 20 miles from Rome. The elevation of this lake is about 6S0 feet above seadevel, while the water was delivered at an elevation of atiout 55 feet ab<_n-e the scmie level. The water earned by this aquetluet was ..if sueh a poor quahty that I-nmti- nus eould not " eoneeu'e why sueh a wise prince as Augustus should ha\-e brought to Komc such a discreditalde and unwhole- some water as the Alsietina, unless it was for tlie use of Xau- machia." The latter was a small artificial lake or pond m which sham naval fights were conducted. 31. Claudia.~The eighth aqueduct described bv Frontinus is the Aqua Claudia, built of dimension stone, winch he calls a Sand and Pehhie Catch-tanks near Tivoli. 'Dimen^ion-stnne aqueducts of Marcia at eitlier end >>{ the tank Imik of ^mall bt..ine; o/^iis iinr,/iiiir The arches are chambers of tlie tanks. magnificent work on account of the large volume of water which it supplied, its good quality, and the im]iressi\'e character of considerable portions of the aqueduct itself, between 9 and 10 miles being carried on arches. It was built in 38-52 a.d. and is fortv-three miles long. The sources of its supplv are found in the valley of the Anio, and consequently it belongs to the svstem on the left bank of the Tiber. The cross-section 42 ANCIENT CIVIL-ENGINEERING WORKS. of its channel was about ^.t, feet wide by 6.6 feet high. It was a work greatly admired by the Roman people, as is evidenced by the praise ' ' gi^'en to it by Roman authors who wrote at that time." It delivered water at the Palatine 185 feet above sea- level. According to Pliny, the combined cost of it and the Aqua AnioNovuswas 55,500,000 sestertii, or nearly $3,000,000. This aqueduct probably belongs to the highest type of R(jman hy- draulic engineering. It follows closely the locaticjn i.>f the ^Vqua JMarcia, although its alignment noAV includes a cut-r)ff tunnel about 3 miles long, the latter having been constructed about thirty-six years after the aqueduct was opened, ilr. Clemens Herschel observes that the total sum expended for these two aqueducts makes a cost of about $6 per lineal foot for the two. The arches of this aqueduct and those of the Anio Novus have clear spans of 18 to 20 feet, with a. thickness at the crown of about 3 feet. 32. Anio Novus. — The ninth aqueduct described by Frontinus is called Anio Noa'us. It was also constructed in the years a.d. 38-52. This aqueduct has a length of about 54 miles and takes its supply from artificial reservoirs constructed by Nero at his country-seat in the A^alley of the Anio near modern Subiaco. This structure is built of brick masonry lined with concrete. That portion of the Aqua Claudia which is located on the Campagna carries for 7 miles the Anio Novus, and it forms the long line of acjueduct ruins near Roma Vecchia. The upper surface of the arch ring at the crown forms the bottom of the channel of the aqueduct. The cross-section of the channel of the Anio Novus was 3.3 feet wide by 9 feet high. The elevation of the water in this, as in the Claudia, when it reached the Palatine was about 185 feet aboA-e sea-level. The Anio Noa'us in some respects would seem to be a scarcely less notable Avork than the Claudia. About 8 miles of its length is carried on arches, some of them reaching a height of about 105 feet from the ground. 33. Lengths and Dates of Aqueducts. — These nine aqueducts constituted all those described by Frontinus, as no others were completed prior to his time. Five others were, however, sub- sequently completed between the years 109 a.d. and 306 a.d., but enough has already been shown in connection with the older lA'TAKES AXD SETTIJXG-IJ.{i;Lys. 43 Structures to sho\v tlie character of tlie watcr-supnly of ancient Komc. M "^r" !v"T''" *''^'''^'"' statement is a part of that £^i^■en bv Mr. J^ \\. l>lackl<;.rsc built u]. to the end of the I miles and that of the arch j^, ,rti< .ns 44 miles. The figures A-arv a little fr, ,m those given by Lanciani and others, but they arc essentially accurate. 34. Intakes and Settling-basins. — The preceding brief de- scriptions of the old Roman aqueducts give but a sujierficial idea of the real features of those great works and of the svstera of water-supply of which they were such essential portions. Enough has been shown, however, to demonstrate conclusively that the engineers and constructors of old Rome were men who, on the one hand, possessed a high order of engineering talent anch on the other, ability to put in place great structures whose proportions and physical characteristics have commanded the admiration of engineers and others from the time of their com- pletion to the present day. If a detailed statement were to be 44 ANCIEXT CIVIL-EXGIXEERING WORKS. made in regard to the water-supply of ancient Rome, it would appear that much care was taken to insure wholesome and potable water. At the intakes of a number of the aqueducts, reservoirs or basins were constructed in which the waters were first received and which acted as setthng-basins, so that as much sedimentation as possible might take place. Similar basins (picinae) were also constructed at different points along the aque- ducts for the same purpose and for such other purposes as the preservation of the water in a portion of the aqueduct in case another portion had to be repaired or met with an accident which for the time being might put it out of use. These basins were usualljr constructed of a number of apartments, the water flowing from one to the other, very much as sewage in some sewage-disposal works flows at the present time through a series of settling-basins. The object of these picinte was the clear- ing of the water by sedimentation. Indeed there was in some cases a use of salt in the water to aid in clarifying it. This is an early type of the modern process of clarifving water by chemical precipitatiijn, not the best of potable-water practice, but one that is sometimes permissible. 35. Delivery-tanks. — The aqueducts brought the water to cas- tella; or delivery-tanks, i.e., small reservoirs, both inside the city and outside of it, and from these users were obliged by law to take their supplies; that is, for baths, for fountains, for public uses, for irrigation, and for private uses. When Frontinus wrote his "De Aquis" a little less than three tenths of all the Avater brought to Rome by the aqueducts was used outside of the city. The remainder was distributed in the city from 247 delivery- tanks or small reservoirs, about one sixth of it being consumed by 39 ornamental fountains and 591 water-basins. 36. Leakage and Lining of Aqueducts. — These aqueducts were by no means Avater-tight. Indeed they were subject to serious leakage, and Frontinus shows that forces of laborers were constantly employed in maintaining and repairing them. As has been stated, the older aqueducts were built of dimension stones, while the later were constructed of concrete or bricks and concrete. The channels of these aqueducts, as well as reser- voirs and other similar structures, were made as nearly water- CRADE OF AQVEDCCT CJ/ANXELS. 45 tight as possible by lining them with a concrete in «-hich potterA- broken into fine b-agments, was mixe.l with mortar. Cl;iu in luit kw.uk and in a c■.Jmpo^ite id ccncrcLe and l)riLl-.\\ lalv. 37. Grade of Aqueduct Channels. -The fall of the water-sur- face in these acjueduets cannot be exactly determined. The 46 ANCIENT CIVIL-ENGINEERING WORKS. levelling-instruments used by the Romans were simple and, as we should regard them, crude, although they served fairly well the purposes to which they were applied. They were not suffi- ciently accurate to determine closely the slope or grade of the water-surface in the aqueduct channels. The deposition of the lime from the water along the water-surface on the sides of the channels in many cases would enable that slope to be deter- mined at the present time, but sufficiently careful examinations have not yet been made for that purpose. Lanciani states that the slopes in the Aqua Anio Vetus vary from about one in one thousand to four in one thousand. An examination of the in- crustation on the sides of the Aqua Marcia near its intake makes it appear that the slope of the surface was about .06 foot per 100 feet, which would produce a velocity, according to the formula of Darcy, of about 3.3 feet per second. In some aqueducts built in Roman provinces it would appear that slopes have been found ranging from one in six hundred to one in three thousand. 38. Qualities of Roman Waters. — The chief characteristic in most of the old Roman waters was their extreme hardness. They range from 11° to 48° of hardness, the latter belonging to the water of the Anio, while the potable waters in this country scarcely reach 5°. The old Romans recognized these character- istics of their waters and, as has been intimated, used the best of them for table purposes, while the less wholesome were em- plo3^ed for fountains, flushing sewers, and other purposes not affected by undesirable qualities. The water from Claudia, for instance, was used frir the imperial table. The water from the Aqua Marcia was also of excellent quality, while that brought in by the Aqua Alsietina was probably not used for potable pur- poses at all. 39. Combined Aqueducts. — In several cases a number of aqueduct channels were carried in one aqueduct. A marked instance of this kind was that of Julia, Tepula, and Marcia, all being carried in vertical series in one structure. Numerous instances of this sort occurred. 40. Property Rights in Roman Waters.— In reading the two books of Frontinus one will be impressed by the property values which the old Romans created in water rights. The laws of A.IUTAGEH AND UNIT OF MEASUREMENT. 47 Rome were exceedingly explicit as to the rights of water-users and as to the manner in which water should be taken from the aqueducts and from the pipes leadnig from the reservcjirs m and about the city. The proper methods for taking the water and using it were carefully set forth, and penalties were prescribed for violations of the laws pertaining to the use of water. There were many abuses in old Rome in the administration of the public water-supply, and one of the most troublesome duties winch Frontinus had to perform lay in reforming those abuses and pre- venting the stealing of water. The unit of use of water (a "quinaria," whose value is not now determinable) was the vol- ume which would flow from an orifice .907 inch in diameter and having an area of about .63 of a square inch. Mr. Herschcl shows that in consequence of the failure of the Romans to under- stand the laws of the discharge of water under A'arving heads, the quinaria may have ranged from .0143 cubic foot to .0044 cubic foot per second or between even wider limits. 41. Ajutages and Unit of Measurement. — Frontinus describes twenty-fiA-e ajutages of different diameter, ofticially approved in connection with the Roman system of public water-supply; but only fifteen of these were actually used in his day. All of these were circular in form, although tAvo others had been used prior to that time. They varied in diameter from .go; t(.i 8. 964 English inches and were originally made of lead, but tliat soft metal lent itself too easily to the efforts of unscrupulous water- users to enlarge them by thinning the metal. In his time they were made of bronze, which \-\'as a hard metal and cr)uld not be tampered with so as to enlarge its cross-section. The discharge through the smallest of these ajutages was the quinaria, the unit in the scale of water rights. The largest of the above ajutages had a capacity of a little over 97 quinaria;. This unit fthe quinaria) was based Avholly on superficial area, and had no relation whatCA'cr to the head over the orifice or to the velocity corresponding to that head. Although Frontinus refers in several cases to the fact that the deeper the ajutage is placed below the water- surface the greater will be the discharge through it, also to the fact that a channel or pipe of a given area of cross- section will pass more water when the latter flows thnjugh it 48 ANCIENT CIVIL-ENGINEERING WORKS. with a high A'elocity, he and other Roman engineers seem to have failed completely to connect the idea of volume of discharge to the product of area of section by velocity. In the Roman mind of his day, and for perhaps several hundred years after that, the area of the cross-section of the prism of water in motion was the only measure of the volume of discharge. This seems actually preposterous at the present time, and yet, as observed by Mr. Herschel, possibly a majority of people now living haA'e no clearer idea of the volume of water flowing in either a closed or open channel. Existing statutes even respecting water rights bear out this statement, improbable as it may at first sight appear. This early Roman A'iew of the discharge is, howe\-er, in sijme respects inexplicable, for Hero of Alexandria wrote, probably in the period 100-50 B.C., that the section of flow only was not suffi- cient to determine the quantity of Avater furnished bv a spring. He proceeded to set forth that it was also necessary to know the velocity of the current, and further explained that by forming a reservoir into which a stream would discharge for an hour the flow or discharge of that stream for the same length of time would be equal to the A'olume of Avater received by the reservoir. His ideas as to the discharge of a stream of water Avere apparently as clear as those of a hydraulic engineer of the present time. Indeed the method AA'hich he outlines is one AA'hich is noAV used Avhere\-er practicable. It has been a question AA'ith some AA^hether Frontinus and other Roman engineers Avere acquainted with the fact that a flaring or outAA-ard ajutage Avould increase the fli )W or discharge througli the orifice. The cAddence seems insufficient to estaldish completely that degree of knoAAdedge on their part. At the same time, in the CXII. chapter of Frontinus' book on the ' AVater- supply of the City of Rome," he states that in some cases pijies of greater diameter than that of the orifice Avere impnipcrlv attached to legal ajutages. He then states : "As a consequence the Avater, not being held together for the laAvful distance, and being on the contrary forced through the short restricted dis- tance, easily filled the adjoining larger pipe." He Avas conAdnced that the use of a pipe Avith increased diameter under such cir- cumstances Avould giA-e the user of the Avater a larger supplv than THE STEALIXa OF WATER. 49 that to which he was entitled, ami he was certainly right in at least most cases. The actual unit orifice through Avhich the unit volume of water called the quinaria was discliarged was usualh' of bronze stamped by a proper official, thus makiiig its use legal for a gi^'cn amount of water. Tlie Roman engineers understoijd that such an orifice should be inserted accurately at right angles to the side of the \'cssel or orifice, and that was the nnly legal way to make the insertion. Furthermore, the laAv recjuired that there should be no change in the dianaeter vi the pij'c '\\-ithin 50 feet of the orifice. It was well known that a flaring i)ipe of increased diameter a])]ilied immediately at the orifice would largely increase the discharge, and unscrupulous jieople resorted to that means for increasing the amount of water to be obtained fur a given price. 42. The Stealing of "Water. — It appears also that Frontinus experienced much trouble from clandestine abstraction of water from reservoirs and water-pipes. The administration of the water commissioner's office had been exceedingly corrupt prior to his induction into office, and some of his most troublesome official work arose from his efforts to detect Avater-thieves, and to guard the supply system from being tapped irregularly or illegally. We occasionally hear of similar instances of water- stealing at the present time, vd-iich shows that human nature has not altogether changed smce the time of Frontinus. 43. Aqueduct Alignment and Design of Siphons.— The align- ment of some of the Roman aqueducts foll< )wed closely the con- tours of the hills around the heads of vallcA-s, while others took a more direct line across the valleys on suitable stractures, fre- quently series of arches. Judging from our cwn point of view it may not be clear at first sight why such extensive masonry constructions were used when the aqueduct could have been kept in excavation bv foll.wving more closely the topography of the countrv- There is little doubt that the Romans knew perfectly well what they were about. Indeed it is definitely stated m some of the old Roman writings that the structures were built across valleys for the specific pur]i(-.se of saving distance Avhich, in most instances at least, meant saving m cost. 50 AXCIEXT CIVIL-EXGIXEEKIXG WORKS. These masonry structures, it must be remembered, were built of material immediately at hand. Furthermore, these aqueducts were generall}- only made of sufficient width for the purpose of carrying Avater-channels. They were not wide structures. In some cases they were not more than 8 feet or 9 feet wide for a height of ncarh' 100 feet. The cost of construction was thus largely reduced below that of wide structures. Wtt^^" ' "Uk I^^B^^^^^Sfi B^MpBlfeflilf^^^^ S^BJ '^^ 111 "^^^^^^hhSHESI^L^V^W ^^B-j-jil E^*?i j* ^^^SSnS w^^^^ ^.^jj^^^^^f^l^ ^^^^^^m ^I^S^^^tf^lB^^^^^^- ^^ Old Roman Lead and Terra-cotta Pipe. The Romans were perfectly familiar with the construction of inverted siphons. As a matter of fact \'itru^■ius, m Chapter VII of his Eighth book, decribes in detail how they should be designed. His specific descriptions relate to lead pipes, but it is clear from what he states at other points that he considered earthenware pipes equally a^-ailable. He sets forth how the pipes should be carried down one slope, along the bottom of the valley, and up the other slope, the lowest portion being called the "venter." He realized the necessitv of guarding all elbows m the pipe by using a single piece of stone as a detail for the AQUEDUCT ALiaXMEXT ASD DESIGN OF SIPHOXS. 51 elbow, a hule beingj cut in it in each direction in Avhicli the adjoin- ini;' sections of pii^c sliould V)C inscrteih tlie sections of lead pipe being lo feet long, and c\'en goes so far as todescrilie the stand- pipes that should be inserted for the purpose of allowing air to escape. A'itru\"ius also adAascs that the water sh(:)uld not only be admitted tr.) in\-crted siphons in a gradual manner, but that ashes should be thrown into the water Avhen the sijihon is first used in order that thev ma}- settle into tlic joints or o-|:)en places so as to close anv existmg leaks. Lead-pipe si])hons, 12 to iS inches in diameter, with i inch thickness of metal undcr 200 feet head, Iniilt in ancient times, have been found at Lyons in France. Also a drain-]")ipc sijihon with masonry reinforcement was built at Alatri m Italv 125 B.C. to carry water under a hcail of about 340 feet. There are .ifhcr notable instances of inverted siphons consti-ucted and used during the ancient Roman period, some of them being of lead pipe imbedded in concrete. CHAPTER IV. 44. Antiquity of Masonry Aqueducts. — Masonry aqueducts, either solid or with open arches, were not first constructed by the city of Rome ; their origin was much farther back in antiquity than that. The Greeks at least used them before the Roman engineers, and it is not unlikely that the latter drew their original ideas from the former, if indeed they were not instructed by them. Nor during the times of the Romans was the construction of aqueducts confined to Rome. Wherever Roman colonies were created it would appear that vast sums were expended in the construction of aqueducts for the purpose of suitably supplying cities with water. Such constructions are found at many points in Spain, France, and other countries which were in ancient times Roman colonies. It is probable that there are not less than one hundred, and perhaps many more, of such structures in existence at the present time. 45. Pont du Gard. — Among the more prominent aqueducts constructed during the old Roman period and outside of Italy were the Pont du Gard at Nismes in the south of France, and those at Segovia and Tarragona in Spain. The Pont du Gard has three tiers of arches with a single channel at the top. The greatest height above the river Gardon is about 180 feet, and the length of the structure along the second tier of arches is 885 feet. The arches in the lowest tier are 51 feet, 63 feet, and 80.5 feet in span, while the arches in the highest tier are uniformly 1 5 feet 9 inches in span. The thickness of the masonry at the top of the structure from face to face is 11 feet 9 inches, and 20 feet 9 inches at the lower tier of arches, the thickness at the intermediate tier being 1 5 feet. The largest arch has a depth of keystone of 5 feet 3 inches, while the other arches of the lower tier have a depth of keystone AQUEDUCTS AT SEGOVIA, METZ, AND OTHER PLACES. 53 of 5 feet. The depth of the ring-stones of the small upper arches IS 2 feet 7 mehes. This structure forms a sort of composite construction, the lower arches constituting four separate arch rings placed side by side, making a total thickness of .q feet n inches. The intermediate arches consist of three similar series ot narrow arches placed side by side, but the masonry < .f the upper tier IS continuous throughout from face to face The three anuntry-]daces ( if the wealthy Romans that it was no longer possilde for the peasantry to culti- vate sufficient ground to yield the grain required by the home market of the Romans. I^arge fleets were consequently engao-ed in the foreign grain- trade of Rome. The ^\•heat and other grain required in great quantities was grr.wn mosth' in Egvpt, although Carthage and other countries supplied large amounts. The great fleets occupied in tins trade made ancient Ostia their OSTIA, THE HARBOR OF ROME. 57 Roman port. At the present time it has no inhabitants, but is a group of complete ruins, with its streets of tombs, batlis. ; '-^ «.. ,--'4=- — Iris p Sale ^farh. M E D I T ERnAN E AN S~^:^ Fig. ij. — Plan uf Ostia and Porto. palaces, and temples, deeph' coA^ered with the accimiulatinns of many centuries. Enough excaA'atinns ha\-e been made ali^ng the shores of the Tiber at this point to sIk^w that the ri^-er was bordered with continu(^us and substantial mast^nry quays, flanked 58 ANCIENT CIVIL-ENGINEERING WORKS. on the land side by successions of great warehouses, obviously designed to receive grain, vine, oil, and other products of the time. The entrance to this harbor was difficult, as the mouth of the river was shallow, with bars apparently obstructing its approach. There were no jetties, or other seaward works for the protection of vessels desiring to make the harbor. It is stated that during one storm nearly or quite two hundred vessels were destroyed while they were actually in the harbor. 4g. Harbors of Claudius and Trajan. — The difficulty in enter- ing the mouth of the Tiber prompted the emperor Claudius to construct another harbor to accommodate the vast commerce then centring at the port of Rome. Instead of increasing the capacity of (Jstia and opening the mouth of the riA'er by deepen- ing it, he constructed a new harbor on what was then the sea- shore, a short distance from (Jstia, and connected it with the Tiber by a canal, the extension of which by the natural forces of the river has become the Fiumicino, the only present na\'igable entrance to the river. This harbor was enclosed by two walls stretching out from the shore, and converging on the sea side to a suitable opening left for the entrance of ships. The superficial area of this harbor was about 175 acres, but it became insufficient during the time of Trajan. He then proceeded to excavate inland a hexagonal harbor with a superficial area of about 100 acres, which was connected both with the harbor of Claudius and the canal connecting the latter with the Tiber. These harbor- works were elaborate in their fittings for the accommodation of ships, and were built most substantiallv of masonry. They showed that at least in some branches of harbor-work the old Romans were as good engineers as in the construction of aque- ducts, bridges, and other internal public works. The harbors. at ancient Ostia, including those of Claudius and Trajan, were not the only works of their class constructed by the Romans, but they are sufficient to show as great advancement in harbor and dock work as in other lines of engineering. These harbors were practically defenceless and exposed to the incursions of pirates, which came to be frequently and suc- cessfully made in the days of the declining power of Rome. It was therefore rather early in the Christian era that these attacks HARBORS OF CLAUDIUS AND TRAJAN. 5'.) discouraged, and ultimately dro^'e away, first, the maritime business of the Romans and, subsequentlv, all tlie inhabitants of tliese ports, leaving the piUaged remnants of the vast liarhor- works, Avarehouses, pahiees, tem]des, and otlier buildings in the ruined condition in wliich they are now found. CHAPTER V. 50. Ancient Engineering Science. — The state of what may be called the philosophy or science of engineering construction m ancient Rome is admirably illustrated by the work on Archi- tecture by ]\Iarcus Vitruvius PoUio, who is ordinarily known as Vitruvius, and who wrote probably a little more than two thou- sand years ago. He calls himself an architect, and his work is a classic in that profession of which he claims to be a member. Although much of his work was purely architectural, a great portion of it, on the other hand, was not architecture as we now know it, but civil engineering in the best sense of the term. It must be remembered, therefore, that what is here written applies to that large portion of his work which is purely civil engineering. It wil^be seen that although he understood reahy httle or nothing about the science of ci\dl engineering as we noAV com- prehend it, he perceived many of the general and fundamental principles of the best practice f>i that profession and frequently applied them in a manner which would do credit to a modern civil engineer. He not onh' laid down axioms to govern the design of civil-engineering stinictures and machinery for the transmission of power, but he also set forth many considerations bearing upon public and private health and the practice of sani- tary engineering in a way that was highly creditable to the state of scientific knowledge in his day. Speaking of the general qualifications of an architect, remembering that that word as he understood it includes the ci\-il engineer, he states : ' ' An archi- tect should be ingenious, and apt in the acquisition of knowledge; ... he should be a good writer, a skilful draughtsman, versed in geometry and optics, expert at figures, acquainted with history, informed on the principles of natural and moral philosophy, somewhat of a musician, not ignorant of the sciences both of 60 ,.(AyD (-v^C VIEWS OF THE PHYSICAL PROPERTIES OF MATERIALS. fessional life. The need of a general education for a ci\dl engineer is greater now exen than in his day, although musical accomplishments need not be considered as essential in modern engineering practice. That qualification, it is inter- esting to observe in passing, was inserted by Vitru\'ius in order to illustrate the wide range of engineering practice in those days when the architect-engineer was called upon, among other things, to construct catapults and other engines of Avar, in which a nice adjustment of gut ropes was determined by the musical tones emitted under the desired tension. 51. Ancient Views of the Physical Properties of Materials. — \Adien it is remembered that the chemical constitution of mate- rials used in engineering was absolutely unknown, that no quanti- tative determination of physical qualities had been made, and that the first correct conception of engineering science had yet to be acquired, it is a matter of wonder that there had been attained the engineering development cA'idenced b< >th by ancient writings like those of"" A'itruvius and great engineering works like those of Rome, in the Babvlonian Plain and in EgA'pt. In discussing the problem of water-supplv, he mentions that certain learned ancients, "physiologists and philosophers, maintained that there are four elements— air, fire. Avater, and earth— and that their mixture, according to the dift'erence of the species. 62 ANCIENT CIVIL ENGINEERING WORKS. formed a natural mode of different qualities. AVe must recollect that not only from these elements are all things generated, but that thev can neither be nourished nor grow without their assist- ance. ' ' This A'icw of the construction of material things was not conducive to a clear comprehension of those physical laws AA'hich lie at the foundation of engineering science, and it is abso- lutely essential that these elementary considerations be kept constantly in A'iew in considering the engineering attainments of the Romans and other ancient peoples. 52. Roman Civil Engineers Searching for Water. — In ancient times, as at present, it was very important in manv cases to know where to look for water, and how to make what might promise to be a successful search for it. Vitruvius states that the sources of water for a supply may easilv be found ' ' if the springs are open and flowing above ground." If the sources are not so evident, but are more obscure, he recommends that ' ' before sunrise one must lie down prostrate in the spot where he seeks to find it, and, Avith his chin placed on the ground and fixed, look around the place ; for, the chin being fixed, the eye cannot range upAA-ards further than it ought and is confined to the IcA-el of the place. Then where the vapors are seen curling together and rising into the air, there dig, because those appearances are not discovered in dry places." This method of discovering water- supply would be considered by modern engineers at least some- what awkward as well as damp and disagreeal^le in the early morning hours. It is not more fantastic, however, or less philo- sophical than the use of the divining-rod, which lias been prac- tised in modern times as well as ancient, and is used even in some country districts at the present time. Vitruvius does not forget that the local features, including both those of soil and of an artificial character, may aft'ect the qual- ity of the Avater and possibly make it dangerous. He, therefore, sets forth general directions by which good potable water may be found and that of a dangerous nature avoided. The necessity of distinguishing between good and bad water was as present to his mind and to the minds of the old Roman engineers as to civil engineers of the present day, but the means for making a successful discrimination were crude and obviously faulty, and LOCATIXG AXD DESIOXIXd COXDVITS. G3 very often unsuccessful. He set forth, what is wch known, that rain-water Avlien cohectccl fnjni an uncontaminatcd atmospliere is most wholesome, but ])roceeds to gi\'c reasons wliicli would not now be considered in the hit^hest degree scientific. In (.dia]iter A' of liis Eiglith B( lok there are descriljcd some ''means of judging water" so Cjuaint and amusing that tliev mav now \\'ell lie cjuiited cx'cn thuugli no ci\'il engineer would be bold enough to cite theni in modern h\'dratdic jiractice. He saA^s: ' ' If it be of an o]ien and running stream, lieforc we la\- it on, the shape of the limits of the inhal)itants of the neighliorliood should be looked to and considered. If the^' are strongh- formed, of fresh color, with sound legs and «-ithout lilear ca'cs, the su])])ly is of goi^d c^ualitN'." At another ])oint he comes rather closely to our modern requirements which look to the exclusion of minute and elementary \-egetalde gn AA'ths, when he says: ' ' ilore- OA'cr, if tlie water itself, when in the s]iring, is lim]nd anrl trans- parent, and the ]daces n\Qv which it nms do not generate moss, nor reeds, nor other filth be near it, eA'er)-lhing about it ha\-ing a clean appearance, it \\'ill Vie manifest by these signs that such water is light lukI exceedmgly wholesome." 53. Locating and Designing Conduits. — In treating of the manner of comlucting water in ]iipcs or other conduits, he adverts to the necessity of accurate levelling and the instruments that Avere used for tlnit pur]iose. The three instruments which he mentions as being used are called the dioptra, the level {libra aquaria), and the chorobates, the latter consisting of a rod about 20 feet m lengtli, having two legs at its extremities of eciual length and at right angles to it. Cross-pieces were fastened between the rod and the legs with vertical lines accurately marked on them. These A-ertical lines were placed in a truly vertical position bv means of idumb-lines so that the top of the riMi was perfceth' level, and the work could thus be made level in reference t(3 it. In Rome the water was generally conducted either by means of open channels, usually luult m masonry for the ]iur]-)ose, or in lead pipes, or in "earthen tubes." VitruA-ius states tliat the open channels should be as solid as possible, and ha\-e a fall of not less than one half a foot in 100 feet. The open channels 64 ANCIENT CIVIL-ENGINEERING WORKS. were covered with an arch top, so that the sun might be kept from striking the water. After bringing the water to the city it was divided into three parts. One was for the supply of pools and fountains, another for the supply of baths, and a third for tlie supply of private houses. A charge was made for the use of water for the pools, fountains, and baths, and in this way a yearly revenue was obtained. A further charge was also made for the water used in private houses, the revenue from which was applied for the maintenance of the aqueduct which supplied the water. The treatment to be given to the different soils, rocks, and other materials through which the conduit was built which brought the supply to Rome is duly set forth by \'itru- vius, and he describes the conditions under which tunnels were constructed. He also described the methods of classifying the lead pipes through which water was conducted from the reser- A'oirs to the various points in the city after stating that they must be made in lengths of not less than lo feet. The sheets of lead employed in the manufacture of the pipes he describes as ranging in width from 5 inches to 100 inches. The diameter of the pipe would obviously equal \-ery closely the width of the sheet divided by the ratio between the circumference and the diameter of the corresponding circle. 54. Siphons. — He speaks of passing valleys in the construc- tion of the conduits by means of what we now call siphons, and prescribes a method for relieA'ing it of the accumulated air. In speaking of earthen tubes or pipes he says that they are to be provided not less than 2 inches thick and ' ' tongued at one end so that they may fit into one another," the joints being coated with quicklime and oil. He further observes that water con- ducted through earthen pipes is more wholesome than that through lead, and that water conveyed in lead must be injurious because from it white lead is obtained, which is said to be injuri- ous to the human system. Indeed the effects of lead-poisoning were recognized in those early days, and its avoidance was at- tempted. In the digging of wells he wisely states that "the utmost ingenuity and discrimination " must be used in the exami- nation of the conditions under which wells were to be dug. He also appreciated the advantage of sedimentation, for he advises HEALTHFUL SITES FOR CFTIES. 65 that reservoirs be made in compartments so that, as the water flows from one to another, sedimentation may take place and the water be made mc>re wholesome. 55. Healthful Sites for Cities. — In the location of cities, as well as of in-i\-ate residences, Vitruvius lays down the general principle that the greatest care should be taken to select sites which are healthy and subject only to clean and sanitary sur- roundings, Marshy places and those subject to fogs, esj.iecially those "charged with the exhalations oi the fenny animals," are t(.^ be avoided. Apparently this reference to " fcnnv animals" may have beneath it the fundamental idea of liacteria, but that is not certain. The main point of all these directions fijr the securing of sanitary conditions of living is that, so far as his technical knowledge permitted him to go, he insists on the same class of wholesome conditions that would be prescribed by a modern sanitary engineer. 56. Foundations of Structures. — Similarly in Chapter V of his First Book, on "Foundations of Walls and Towers," \dtru- vius shows a realization of the principal conditions needful and requisite for the suitable founding of heavy buildings. After a sanitary site for a city is determined and one that can be put in communication with other people ' ' by good roads, and river or sea navigation for the transportation of merchandise," he proceeds to state that ' ' foundations should be carried down to solid bottom, if such can be found, and that they should be built thereon of such thickness as may be necessary for the proper support of that part of the wall standing above the natural level of the ground. They should be of the soundest workman- ship, and materials of greater thickness than the waUs aboA'e." Again, in speaking of the foundations supporting columns, he states: "The intervals between the foundations brought up under the columns should be either rammed down hard, or arched, so as to prevent the foundation-piers from swerving. If sohd ground cannot be come to, and the ground be loose or marshv, the place must be excavated, cleared, and either alder, olive, or oak piles, previously charred, must be driven with a machine as close to each other as possible and the intervals between the piles filled with ashes. The heaviest foundations 66 AA'CIENT CIVIL-ENGL\EERI\G WORKS. may be laid on such a base." It is thus seen that pile foundations were used by the Romans, and that the piles were driven with a machine. It would be difficult to give sounder general rules of practice even after more than two thousand years' additional ■experience. 57. Pozzuolana and Sand. — Of all the materials which were useful to the Romans in their various classes of construction, including the foundations of roads, "pozzuolana" must have been the most useful, and that which contributed more to the development of successful construction in Rome than any other single agent. Vitruvius speaks of it frequently and gives rules not only for the use of it in the production of mortar and con- crete, but also lays down at considerable length the treatment which should be given to lime in order to produce the best re- sults. It was common, according to his statements, to use two measures of ' ' pozzuolana ' ' with one of lime in order to obtain a suitable cementing material. This mixture was used in vary- ing proportions with sand and gravel or broken stone to produce concrete. He describes the various grades of sands to be found about Rome and the manner of using them. The statement is made that sand should be free of earth and that the best of it was sucli as to yield a ' ' grating sound " when ' ' rubbed between the fingers." This is certainly a good engineering test of sand. He prefers pit-sand to either ri\-er- or sea-sand ; indeed through- out all his directions regarding this particular class of construc- tion his rules might be used at the present time with perfect pro- priety. 58. Lime Mortar.— Tlie old Romans had also discovered the ad\'isability of allowing lime to stand for a considerable period of time after slaking. This insured the slaking ( )f all tlif«e small portions which were possibly a little hydraulic and therefore slaked very slowly. He prescribes as a good proportion two parts of sand to one of lime, and also mentions the proportion of three to one. He attempts to explain the setting, as we term it, of lime, but his explanation in obscure terms, involving quali- ties of the elements of fire and air, is not very satisfactorv. 59. Roman Bricks according to Vitruvius. — As is wcU known, the Romans were good brick-makers, and they were well aware ROM AX TIMBER. 67 that bricks made from "ductile and cohesive" "red or white chalky " earth were far preferable to those made of more gravelly or sandy clay. The Roman bricks were both smi-dried and kiln- burned. 60. Roman Timber. — Timber was a material much used by the Romans, and the greater part of that which they used proba- bly was grown in Italy, although considerable quantities were imported from other localities. Vitruvius writes in consider- able detail concerning the selection of timber while standing, as well as in reference to its treatment before being used in structures. Like e\'ery material used by the old Romans in construction, the various kinds and qualities of timber recei\X'd careful study from them, and they were by no means novices in the art of producing the best results from those kinds of timber with which tlicy were familiar. 61. The Rules of Vitruvius for Harbors. — In Chapter XII of his Fifth Book \'itiai\-ius lays down certain general rules for the selection and formation of harbors, and it is known that the Romans were familiar with elaborate and effecti\-e harbor con- struction, as is shown bN' that at Ostia. He appreciates that a natural harbor is one which has ' ' rocks or long promontories juttmg out, Avhich from the shape of the place form cur\-es or angles," and that m such places "niithing more is necessarj^ than to constract portices and arsenals arotmd them, or passages t( > the markets." He then ]irocceds to state that if such a natural formation is not to be found, and that if "on one side there is a more proper sh(-ire than on the other, Viy means t^f buildmg or of heaps of stones, a proiection is rim out, and in this the enclosures of harbors are formed." He then proceeds to explain how ' ' poz- zuolana" and lime, in the proportion of two of tlie former to one of the latter, are used in subaqueous constructiiin. He also pre- scribed a mode of building a masonry waU u]i from the bottom of an excavation made witliin what we should call a coffer-dam, fonned, among other things, "of oaken piles tied together with chain pieces." The Romans knew well how to select harbors and how to construct in an ettecti\-e manner the artificial works connected with them, although it ap]iears that the effects of tidal and river currents in estuaries were neither well understO(ui m 68 ANCIENT CIVIL-ENGINEERING WORKS. themselves nor in their transporting power of the solid material which those currents eroded. 62. The Thrusts of Arches and Earth ; Retaining- walls and Pavements.— Although the Romans possessed little or no knowl- edge of analytical mechanics they attained to some good quali- tative mechanical conceptions. Among other thmgs they under- stood fairly well the general character of the thrust of an arch and the tendency of the earth to overthrow a retarning-wall. They knew that a massive abutment was needed to receive safely the thrust of an arch, and they counterforted or buttressed re- taining-walls in order to hold them firmly in place. They also- realized the danger of wet earth pressing against a retaining- wall, and even made a series of offsets or teeth on the inside of the wall on which the earth rested in order to aid in holding the wall in place. Vitruvius recommends as a safeguard against the pressure of earth wet by winter rains that ' ' the thickness of the wall must be proportioned to the weight of earth against it," and that counterforts or buttresses be employed " at a distance from each other equal to the height of the foundations, and of the same width as the foundations," the projections at the bot- tom being equal in thickne s to that of the wall, and diminishing toward the top. He gives in considerable detail instructions for the forming of pavements and stucco work, so many examples of which are still existing in Rome. These rules are in many respects pre- cisely the same as would govern the construction of similar work at the present time. There are also described in a general way the methods of producing white and red lead, as pigments of paints, and a considerable number of other pigments of differ- ent colors. 63. The Professional Spirit of Vitruvius. — It is evident, from many passages in the writings of this Roman architect-engineer, that the ways of the professional men in old Rome were not always such as led to his peace of mind. Vitruvius utters bitter complaints which show that he did not consider purely pro- fessional knowledge and service to be adequately recognized or appreciated by his countrymen. He writes that in the city of Ephesus an ancient law provided that if the cost of a given MECHANICAL APPLIAXCES OF THE AXCIENTS. Oi) work completed under the pkins and specificati( )ns of an archi- tect did not exceed tlie estimate, he was commended ' ' with decrees and honors," but if the cost exceeded the estimate with 2 5 per cent added thereto, he ' ' was required to pay that excess out of his own pocket." Then he exckums, "Would to God that such a law existed among the Roman people, not only in rcs]iect to their puldic but also to their pri\'ate buildings, for then the unskilful could not commit their depredations with impunity, and those who were the most skilful in the intricacies of the art would follow the profession! " 64. Mechanical Appliances of the Ancients. — It is well known that the ancients |)ossessed at least sonie simple tvpes of machines, for the reason that they raised many great stones to a consider- able height in completed works after lia\'ing transported them great distances from the quarries whence thev were taken. Undoubtedly these machines were of a simple and crude char- acter and were made effectix'e largely by the power of great numbers of men. We are not acquainted with all the details of these machines, although the general types are fairly well known. The elementary machines, including the le\'er, the inclined plane, the pulley, and the screw, which is only an appli- cation of the inclined plane, were all used nc)t only by the Fiomans, but probably by CA'cry ci\'ilized ancient nation. \'itru\'ius describes a considerable number of these machines, and from his descriptions it is clear that they had wide application in the structural works of the Romans. The block and fall, as we term the pulley at the present time, was a common machine in the plant of a Roman constructor, as were also yarious modifica- tions and applications of the leyer, the rciller, and the inclined plane. 65. Unlimited Forces and Time. — It is neither surprising n( ir yery remarkable that with the use of these simple machines, aided by a practicall)- unlimited number of men, the necessary raising or other moyement of hea^-y Ayeights Ayas accomplished by the Romans and other ancient peoples. It is to be bonie in mind that the element of time was of far less consequence in those days than at present, and that the rate of pro- o-ress made in the consti-uction of most if not all ancient cn- o-ineerino- A\-orks was what we should consider intolerabh- slow. PART II. BRIDGES. CHAPTER VI. 66. Introductory. — Although the bridge structures of to-day serve the same general purposes as those served by the most ancient structures, they are very different engineering products. It is not long, in comparison with the historic and prehistoric periods during which bridges have been built, since the science of mechanics has been sufficiently developed to make bridge design a rational procedure ; and it is scarcely more than a cen- tury since the principles of mechanics were first applied to the design of bridge structures in such a way as to determine even approximatel}^ the amount of stress produced in any member by the imposed load. Naturally the first efforts made toward a truly rational bridge design were in fact simple and crude and only loosely approximate in their results. Probably the first analytic treatment of bridges was gi\-en to the design of arches in masonry and then in cast iron. As the action of forces m structures became better known through the development of mechanical science, the applications of the latter became less crude and approximate and the approach to the refined accuracy of the present day was begun. 67. First Cast-iron Arch. — These older structures, nearlv all of them arches or more or less related to the arch, first appeared in cast iron in the latter part of the eighteenth century, when noth- ing like an accurate analysis of forces de^'eloped by the applica- 70 EARLY TIMBER BRIDGES L\ AMERICA. 71 tion of a given load was known. The first cast-iron arch was erected over the Severn in England near Coalbrookdale in tlie year lyjg. This bridge had a span of loo feet, and the under surface of the arch or so flit at the crown \\-as 45 feet abr)\-e the points at the abutment from which the arch sprang, or, as civil engineers put it, the arch had a span of 100 feet and a rise or versinc of 45 feet. Other east-iron arches were built in Ergland soon after. 68. Early Timber Bridges in America. — Timber bridges ha e been built since the earliest historic ]K'riods and e\'en earlier, but the widest and boldest applications of timber to bridge struc- tures have been made in this country, beginning near the end of the eighteenth century and running to the middle of the nine- teenth century, when timber began to be displaced liy iron. Timber bridges and those of combined iron and timber are built to some extent e\-en at the present day, but the most extended work of this class is to be found in the period just named. In 1660 what was called the ' ' Great Bridge " was built across the Charles Ri\-er near Boston, and was a structure on piles. Other similar structures followed, but the first long-span timber bridge, where genuine bridge trussing or framing was used, appears to have been completed in 17Q2, when Colonel William P. Riddle constructed the Amoskeag Bridge across the Alerrimac River at Alanchester, X. FT, in six spans of a little OA-er 92 feet from centre to centre ( >f piers. From that time timber bridges, mosth- on the combined arch and truss ]irinciple, were built, many of them examples of remarkably excehent engineering structures for their day. Among these tlie most prominent were the Bellows Falls Bridge, in two spans of 184 feet each from centre to centre of piers, over the Connecticut River, built in 1783-92 bv Colonel Enoch Hale: the Essex-^Merrimac Bridge over the ;\Ien-imac Ri\-cr, three miles ab(n-e Xewburyport, Mass , built by Timothy Palmer in 1792, consisting actually of two bridges with Deer Island between them, the principal feature of each being a kind of arched truss of 160 feet span on one side of the island and 113 feet span on the other; the Piscataqua Bridge, seven miles above Portsmouth, N. H., in which a "stu- pendous arch of 244 feet cord is allowed to be a masterly piece 72 BRIDGES. of architecture, planned and built by the ingenious Timothy Palmer of Newburyport, ^lass.," in 1794; the so-called "Per- manent Bridge" over the Schuylkill River at Philadelphia, built in 1804-06 in two arches of 150 feet and one of 195 feet, all in the clear, after the design of Timothy Palmer; the Waterford Bridge over the Hudson River, built in 1804 by Theodore Burr, in four combined arch and truss spans, one of 154 feet, one of 161 feet, one of 176 feet, and the fourth of 180 feet, all in the clear; the Trenton Bridge, built in 1804-06 over the Delaware River at Trenton, N. J., by Theodore Burr, in five arch spans of the bowstring type, ranging from 161 feet to 203 feet in the clear; a remarkable kind of wooden suspension bridge built by Theodore Burr in 1808 across the Mohawk RiA^er at Schnectady, N. Y., in spans ranging in length from 157 feet to 190 feet; the Susquehanna Bridge at Harrisburg, Pa., built by Theodore Burr in 181 2-16 in twelve spans of about 210 feet each; the so-called Colossus Bridge, built in 18 12 by Lewis Wemwag over the Schuyl- kill River at Fairmount, Pa., with a clear span of 340 feet 3^ inches; the New Hope Bridge, built in 18 14 over the Delaware River, in six 175 feet combined arch and truss spans, and a considerable number of others built by the same engineer. Some of these wooden bridges, like those at Easton, Pa., and at Waterford, X. Y., remained in use for over ninety years with only ordinary repairs and with nearly all of the timber in good condition. In such cases the arches and trusses have been housed and covered with boards, so as to make what has been commonly called a covered bridge. The curious timber sus- pension bridge built by Theodore Burr at Schenectady was used twenty years as originally built, but its excessive deflection under loads made it necessary to build up a pier under the middle of each span so as to support the bridge structure at those points. These bridges were all constructed to carr^^ highway traffic, but timber bridges to carry railroad traffic were subsequently built on similar plans, except that Burr's plan of wooden suspension bridge at Schenectady was never repeated. 69. Town Lattice Bridge.— A later tvpe of timber bridge which was most extensiA-ely used in this countrv was invented by Ithiel Town in January, 1820, which was known as the Town EARLY TIMBER BRIDGES IN AMERICA. m 73 i^ 74 BRIDGES. lattice bridge. This timber bridge Avas among those used for railroad structures. As shown by the plan it was composed of a close timber lattice, heavy plank being used as the lattice members, and they were all joined by wooden pins at their inter- 'Ay/k-yA'^AyAY AyAv ^A-^AYA- JyilY>;.^^^^Njj^^^^Yi^Y^Y'^Y'^li^ TDVN LATTICE TRUSS. = Fig. 3. sections. This type of timber structure was comparatively com- mon not longer ago than twenty-five years, and probably some structures of its kind are still in use. The close latticework with its many pinned intersections made a very safe and strong frame- work, and it enjoyed deserved popularity. It was the fore- runner in timber of the modern all-riveted iron and steel lattice truss. It is of sufficient significance to state, in connection with the Town lattice, that its inventor claimed that his trusses could be made of wrought or cast iron as well as timber. In many cases timber arches were combined with them. 70. Howe Truss. — The next distinct advance made in the development of bridge construction in the United States was made by brevet Lieutenant-Colonel Long of the Corps of Engi- neers, U.S.A., in 1830-39, and by AVilliam Howe, who patented the bridge known as the Howe truss, although the structure more lately known under that name is a modification of Howe's original truss. Long's truss was entirely of timber, including the keys, pins, or treenails required, and it was frequently built HOWE TRUSS. 75 V6 BRIDGES. in combination with the wooden arch. The truss was consider- ably used, but it was not sufficiently popular to remain in use. The Howe truss was not an all-wooden bridge. The top and bottom horizontal members, known as ''chords," the inclined braces between them and the vertical end braces, all connecting the two chords, were of timber, and they were bolted at all inter- sections; but the vertical braces were of round iron with screw ends. These rods extended through both chords and received nuts at both ends pressing on cast-iron washers through which the rods extended. These wrought-iron round rods were in groups at each panel-point, numbering as many as existing stresses required. The ends of the timber braces abutted against cast-iron joint-boxes. The railroad floor was carried on heavy timber ties running entirely across the bridge and resting upon the lower chord members. It was a structure simple in char- acter, easily framed, and of materials readily secured. It was also easily erected and could quickly be constructed for any reasonable length of span. It possessed so many merits that it became widely adopted and is used in modified form at the present day, particularly on lines where the first cost of con- struction must be kept as low as possible. The large amount of timber in it and the simple character of its wrought-iron or steel members greatly reduces its first cost. 71. Pratt Truss.— In 1844 the two Pratts, Thomas W. and Caleb, patented the truss, largely of timber, which has since been perpetuated in form by probably the largest number of iron and steel spans ever constructed on a single type. The original Pratt trusses had timber upper and lower chords, but the vertical braces were also made of timber instead of iron, while the inclined braces were of round wrought iron with screw ends, the reverse of the web arrangement in the Howe type. This truss had the great advantage of making the longest braces (of iron) resist tension only, while the shorter vertical braces resist compression. As a partially timber bridge it could not compete with the Howe truss, because it contained materially more iron and consequently was more costly. This structure practicaUy closed the period of development of timber bridges. SQU/IiE ]VI[IPPL1'"S WORK. 77 72. Squire Whipple's Work. — What amounted to a new epoch in the development of Ijridge constmction in this country prac- ticahy began in 1S40 when Scjuire \\'lup]de Vjuilt his first l)(:iw- string truss with wrought-iron tension and cast-iron eom]iression members. While the i^ratts and Howe had begun to empkn^ to some extent the analysis of stresses in the design of their bridge members, the era of exact firidge analysis began with Squire Whipple. He subjected his bridge designs to the exacting requirements of a rational analysis, and to him belongs the honijr of placing the tlesign of bridges upon the firm foundation of a systematic mathematical analysis. 73. Character of Work of Early Builders. — The names of Palmer, Burr, and AVernwag were connected with an era oi ad- mirable engineering works, but, with bridge analysis practically unknown, and with the simplest and crudest materials at their disposal, their resources were largely constituted of an intuitiA-e engineering judgment of high quality and remarkable force m the execution of their designs never excelled in American engi- neering. They occasionally made failures, it is true, but it is not recorded that they e^■er made the same error twice, and the works which they constructed form a series of precedents which have made themselves felt in the entire development of American bridge building. CHAPTER VII. 74. Modem Bridge Theory. — The evolution of bridge design having reached that point where necessity of accurate analysis began to make itself felt, it is necessary to recognize some of the fundamental theoretical considerations which lie at the base of modern bridge theory, and which in^'olve to a considerable extent that branch of engineering science known as the elasticity 01 strength of the materials used in engineering construction. The entire group of modern bridge structures may be divided into simple beams or girders, trusses, arches, suspension bridges, and arched ribs, each class being adapted to carry either highway or railway traffic. That class of structure known as beams or girders is characterized by A-ery few features. There are solid beams like those of timber, with square or rectangular cross- sections, and the so-called flanged girders which are constituted of two horizontal pieces, cme at the top and the other at the bottom, connected by a vertical plate running the entire length of the beam. The fundamental theon' is identically the same for both and is known as the "common theor}^ of flexure," i.e., the theory of beams carrying loads. If an ordinary scantling or piece of timber of square or rect- angular cross-section, like a plank or a timlier joist, so commonlv used f )r floors, be supported at each end, it is a matter of com- mon observation that it Avill sustain an amount of load depending upon the dimensions nf the stick and length of span. AVhen such a bar or piece is loaded certain f(irces or stresses, as they are called, are brought into action in its interior. The word ' ' .stress" is used simply to indicate a force that exists in the interior of any piece of material. It is a force and nothing else. It is treated and analyzed in CA'ery way prcciselv as a force. If the stresses or forces set up by the loading in the interior of the bar 78 THE STKEISSES IS BEAMS. 79 become greater than the material can resist, it begins to break, and the breaking (jf that portion of the timber in which the stresses or forces are greatest constitutes its failure. The load which produces this failure in a beam is called the breaking load of the beam. In engineering jjractice all beams are so designed or proportioned that the greatest load ]:)laced on them shall be only a safe percentage of the breaking load ; the safe load usually being found between -J and -J of the breaking load. In most buildings the safe or working load, as it is called, is probably about }- of the breaking L.iad. 75. The Stresses in Beams. — The proper design of beams or girders to carry prescribed loads is based upon the stresses which are developed or brought into action bv them. It can easily be observed that if a beam supported at each end be com- posed rif a number of thin planks or boards placed one upon the other, it will carry \-ery little load. Each plank or board acts independently of the others and a A-ery small load will cause a sag, as shown in Fig. 6. If there be taken, on the other hand, Fig. 5. Fig. 6. H Fig. 7. a beam made of a single stick of timber of the same width and depth as the number of planks shown in Fig. 6, so as to secure the solid beam shown in Fig. 7, it is a further common observa- tion that this latter beam may cany man)- times the load Avhich the laminated beam, shown in Fig. 6, sustains. The thin planks or boards readily slide over each other, so that the ends present 80 BRIDGES. the serrated form shown in Fig. 6. The preventing of this sHd- ing is the sole cause of the greatly increased stiffness of the solid beam shown in Fig. 7, for there is thus dcA-eloped along the imaginary horizontal sections in the solid beam of Fig. 7 what are called shearing forces or stresses ; and since they exist on horizontal sections or planes running throughout the entire length of the beam, they are called horizontal shears. At each end of the beam shown in Fig. 7 there will be an upward or supporting force exerted bjr the abutments on which the ends of the beam rest. Those upward or supporting forces are shown at R and R' and are called reactions, because the abutments, so to speak, react against the ends of the beam when the latter is loaded. These reactions depend for their value on the amount and the location of the loading which the beam carries. Obviously these upward forces or reactions tend to cut or shear off the ends of the beam immediately above them, and if the loads were sufficiently large and the beam kept from bending, the reactions would actually shear off those ends, just as punches or shears in a machine-shop actually shear off the metal when the rivet-hole is punched, or when a plate is cut by shearing into two parts. The beam, however, bends or sags before shearing apart actually takes place. 76. Vertical and Horizontal Shearing Stresses. — If it be sup- posed that the length of the beam is divided into a great number Wl w. W, W, Wj w, w, w, --, , 0.0 o^ n\ n ri F I rx -4--,-,-_l_4- -i-;-4- ??^i?^^^. Fig. 8. Fig. 9. of parts by imaginary vertical lines, like those shown in Fig. 8, then vertical shearing forces will be developed in those vertical planes and sometimes, though not often, they are enough to VERTICAL AXD IIOIUZnXTAL SIIEAIUXG STRESSES. 81 cause failure. It is not an uncommon tlnnc;, on the otlier hand, in timber to have actual shearing failure take place along a h( iri- zontal plane through tlie centre of the beam. Indeed this is recognizetl frec[uently as the principal method of failure in \-cry short spans. AVhen this horizijntal shearing failure takes ];ilace, the upper and k)\\'er parts of the beam slide OA'cr each other and act precisely like the group of ]danks shown in Fig. 6. If, then, the loaded beam be diA'ided by A-ertical and hori- zontal planes into the small rectangular portions shown in Figs. 8 and 9, on each such vertical and horizontal imaginary plane there will be respectively vertical and horizontal shearing forces, which are shown by aiTows in Fig. 9. It ^^■ill be noticed in that figure that in each comer of the rectangle the two shearing forces act either to\\'ard or from each other; in no case do the two adjacent shearing forces act around the rectangle in the same direction. This is a condition of shearing stresses peculiar to the bent beam. It can be demonstrated by theon,- and is confirmed by experiment. There is a further peculiarity about these shearing forces which act in pairs either toward or from the same angle in any rectangle, and it is that the two stresses adjacent to each other huve precisely the same value per square inch (or any square unit that may be used) of the surface on W'hich they act. These stresses per square inch var}^ howe^-er, either along the length of the beam or as the centre line of any normal cross-section is departed from. They are greatest along the centre line or central horizontal plane represented hy AB, and thev are zero at the top and bottom surfaces of the beam. Inasmuch as the h(irizontal shear along the plane A'B' is less than that along .4/-^ in Fig. 9, a part of the latter has been taken up hv the horizontal fibres of tl:e beam lying bet\\-een the two planes. In (>ther wt^rds, the horizontal layer of fibres at A'B' is subiected to a greater stress or force along its length than at AB. The same general obser^-ation can be made in reference to any horizontal laver of fibres that is farther away from the centre than another. Hence the farther any fibre is from the centre the greater will be the stress or force to A\-hich it is sub- jected in the direction of its length. It results, then, that the 82 BRIDGES. horizontal layers of fibres which are farthest from the centre line of the beam, i.e., those at the exterior surfaces, will be subjected to the greatest force or stress, and that is precisely what exists in a loaded beam whatever the material may be. 77. Law of Variation of Stresses of Tension and Compression. — Since a horizontal beam supported at each end is deflected or bent downward when loaded, it will take a curved form like that shown in either Fig. 7 or Fig. 10; but this deflection can only take place by the shortening of the top of the beam and the lengthening of its bottom. This shows that the upper part of the beam is compressed throughout its entire length, while the lower part is stretched. In engineering language, it is stated that the upper part of the beam is thus subjected to compression and the lower part to tension. The horizontal layers or fibres receive their tension and compression from the vertical and hori- zontal shearing forces in the manner already explained. If the conditions of loading of the bent beam should be subjected to mathematical analysis, it would be found that throughout the originally horizontal plane AB, Fig. 7, passing through the centre of each section there would be no stress of either tension or com- pression, although the horizontal shearing stress there would be a maximum. Further, as this central plane is departed from the stress of tension or compression per square inch m any vertical section would be found to increase directly as the distance from it. This is a very simple law, but one of the greatest importance in the design of all beams and girders, whatever may be the form or size of cross-section. It is a law, which appHes equally to the solid timber beam and to the flanged steel girder, whether that girder be rolled in the mill or built up of plates and angles or other sections in the shop. It is a fundamental law of what is called the common theor\' of flexure, and is the verv foundation of all beam and girder design. The horizontal plane represented by the line AFi in Fig. 8, along which there is neither tension nor compression, is called the "neutral plane," and its intersection with any normal cross-section of the beam is called the ' ' neutral axis" of that section. Mathematical analysis shows that the neutral plane passes tlirough the centres of gravity of all the normal sections of the beam and, hence, that the neutral axis FUNDAMENTAL FOIiMUL.E OF THEORY OF BEAMS. S3 passes through the centre of gravity of the section to wliicli it belongs. 78. Fundamental Formulae of Theory of Beams.— The funda- mental foi-mulae of the the.ny of loaded beams may be quite simply written. Fig. 10 exhibits in a much exaggerated manner a bent beam supporting any system of loads IF,, TF„ l\\, etc., Fig. 10. Fig. II. while Fig. 11 shows a normal cross-section of the same beam. In Fig. 10 .4 i? is the neutral line, and in Fig. 11 CD is the neutral axis passing through the centre of gravity, e.g., of the section. If a is the amount of force or stress on a square inch (or other square unit), i.e., the intensity of stress, at the distance of unity from the neutral axis CD of the section, then, by the fundamental law already stated, the amount acting on another square inch at any other distance r: from the neutral axis will be ac. This quan- tity is called the "intensit}' of stress" (tension or compression) at the distance z from the neutral axis. Evidentlv it has its 84 BRIDGES. greatest values in the extreme fibres of the section, i.e., ad and ad^. At the neutral axis az becomes equal to zero. FG in Fig. I T represents the same line as FG in Fig. i o. If the line FH in Fig. II be laid down equal to ad and at right angles to FG, and if represent the centre of gravity, e.g., of the section, then let the straight line LH be drawn. Any line drawn parallel to FH from FG to LH will represent the intensitj^ of stress in the corresponding part of the beam's cross-section. ObAdously, as these lines are drawn in opposite directions from FG, those above will indicate stress of one kind, and those below that point stress of another kind, i.e., if that above be tension, that below will be compression. It can be demonstrated by a simple process that the total tension on one side of the neutral axis is just equal to the total compression on the other side, and from that condition it follows that the neutral axis must pass through the centre of gravity or centroid of the section. Returning to the left-hand portion of Fig. 1 1 , let dA represent a very small portion of the cross-section ; then will az . dA be the amount of stress acting on it. The moment of this stress or force about the neutral axis will be azdA .z=az'.dA. If this expression be applied to every small portion of the entire section, the aggregate or total sum of the small moments so found will be the moment of all the stresses in the section about the neutral axis. That moment will have the value M = faz\dA=af2'd.A=aI (i) In equation (i) the symbol /'means that the sum of all the small quantities to the right of it is taken, and / stands for that sum which, in the science of mechanics, is called the moment of inertia of the cross-section about its neutral axis. The value of the quantity I may easily be computed for all forms of section. Numerical values belonging to all the usual fonns employed in engineering practice are found in extended tables in the hand- books of the large iron and steel companies of the countr)', so that its use ordinarily involves no computations of its value. Equation (i) may readily be changed into two other forms for convenient practical use. In Fig. lo iiiii is supposed to be PRACTICAL APPLICATIONS. 85 a very short portion of the centre Hne of the beam represented by dl. Before the beam is lient tlie section FG is supposed to have the position MA' parallel to /'(_). Also let // be the small amount of strctchini^; or ct)mpressiiin (shortening) of a unit's lengt.h of fibre at unit's distance from the centre line AJJ of the beam, then will luJl and ii::Jl be the short lines jiarallel to OA' in the triangle (jiiiN shown in the figure. The jxiint (" is the centre of curvature of the line niii, and Cii=Cni is the radius. The two triangles Ciiiii and iiiXU are therefore similar, hence iiJl mil dl I I fi f) p If the quantity called the coelhcient or modulus of elasticity be represented by E, then, by the fundamental law uf the theory of elasticity in solid bodies, a =Eu (3) As has already been shown, the greatest stresses (intensities) in. the section are -\-ad (tension) and —ad^ (compression). If A" represent that greatest intensity of stress, then K =ad, and "= , (4) d If the value of a from equation (4) be substituted in equation (i), mJ-^/ (5) 79. Practical Applications. — Equation (5) is a formula con- stantly used in engineering practice. All quantities in the second member are known in any given case. K is prescribed in the specifications, and is known as the ' Avorking resistance" in the design of beams and girders. For rolled steel beams in buildings it is frequentlv taken at 10,000 pormds, i.e., 16,000 pounds per square inch, about one fourth the breaking strength of the steel. In railroad-bridge work it maybe found between 10,000 and 1 2,000 pounds, or approximately one fifth of the breaking strength of the steel. The quantities / and d depend upon the form and dimensions of the cross-section, and are either known or ma}' be determined. The quotient l^d is now known as the "section modulus," and its numerical ^•alues for all forms of rolled beams 86 BRIDGES. can be found in published tables. The use of equation (5) is therefore in the highest degree convenient and practicable. 80. Deflection. — It is frequently necessary, both in the design of beams and framed bridges, to ascertain how much the given loading will cause the beam or truss to sag, or, in engineering language, to deflect below the position occupied when unloaded. The deflection is determined by the sagging in the vertical plane of the neutral line below its position when the structure carries no load. In Fig. 10 the curved line AB is the neutral line of the beam when supporting loads. If the loads should be removed, the line AB would return to a horizontal position. The line drawn horizontally through .4 and indicated by x is the position of the centre line of the beam before being bent. The vertical distance ?l' below this horizontal line shows the amount by which the point at the end of the line x is dropped in consequence of the flexure of the beam. The vertical distance w is therefore called the deflection. Evidently the deflection varies with the amount of loading and with the distance from the end of the beam. The curved line AB in one special case only is a circle. The general character of that curve is determined by the loading and the length of span. In order that the deflection may be properly considered it is necessary that the relation between x and zi' shall be estab- hshed for all conditions of loading and length of span. If the value of u from equation (2) be placed in equation (3), there will result E "=7 ^^) If the value of a from equation (6) be substituted in the last member of equation (i), there will at once result U ^^ It is established by a very simple process in differential cal- culus that ~P^1^ (8) BEXDLXG MOMEXrs AXD SHEARS WITH SIXCLE LOAD. 87 Hence, substituting from equation (8) in equation (7), AI=EI'^., (g) ax ' Equation (9) may be used by means of some A^ery sim]>le operations in integral ealculus to determine the A'alue (jf ic in terms of x and the loads on the beam Avhen the value of the bend- ing moment .1/ is known, and the procedures for determining that quantity will presently be gi\'en. Using the processes of the calculus, the two following equa- tions will immediately be found : t^kf"''^^ '"' As already explained, numerical values for both E and / may be taken at once from tables already prepared for all materials and for all shapes of beams ordinarily employed in structural work, so that equation (11) enables the deflection or sag of the bent beam to be computed in any case. The expression is the tangent of the angle made by the neutral line of a bent beam with a horizontal line at any gi\-en point, and it is a quantity that it is sometimes necessary to determine. di^< and dx are indefinitely short vertical and horizontal fines respectively, as shown immediately to the left of B in Fig. 10. Equation (11) is not used in structural work nearly as much as equation (5), but both of them are of practical value and in- volve onlv simple operations in their use. 81. Bending Moments and Shears with Single Load. — The second members of equations (5) and (9) exhibit values of the moments of the internal forces or stresses in any normal cross- section of a bent beam about the neutral axis of the section, while the values of M must be expressed m terms of the external forces or loading. Inasmuch as the latter moment develops just the internal moment, it is obvious that the two must be equal. In order to write the value of the external moment m terms of BRIDGES. any loading, it is probably the simplest proeedure t<:i consider a beam cam-ing a single load. In Fig. 12, AB is such a beam, and ir is a load which may be placed anywhere in the span, whose length is /. The distances of the load from the abutments are represented by .v^ and .v,. The reactions or supporting forces exerted under the ends of the beam at the abutments are shown by R and R' . The reactions, determined by the simple law of the lever, are i?=ir'^^- and R' =W-I^ (12) The greatest bending moment in the beam will occur at the point of application of the load, and its value will be M=Rx, ir / -R'.W (13) Fig. 12. The bending moments at the end of the beam are obviously zero, and the second and fourth members of ecjuation (13) show that the moment increases directly as the distance from either end. Hence in the lower portion of Fig. 12, at D, immediately under the load TF, the line DC is laid off at any convenient scale to represent the moment .1/^. The straight lines AC and CB are then drawn. Kny vertical intercept, as FH or KL. between AB and either AC or CB will represent the bending moment at the corresponding point in the beam. The simple triangular diagram ACB therefore represents the complete condition of bending of the beam under the single load IF placed at any point in the span. BEXDIXG MOMKXrS A.\D SHEARS WITH AXV LOADS. 89 The beam ,4/)' is supj.iosed for the moment to have no weight. Consequently the only force acting upon the portion of the beam AO is the reaction K, and, similarly, R' is the only force acting upon the portion OB. ()b^•iously so far as the simple action of these two forces or reactions is concerned, the tendency of each is to cause vertical slices of the beam, so to sj.ieak, to slide o\-er each other. In other Avords, in engineering language, the por- tion AO of the beam is subjected to the shear S=R, while OB is subjected to the shear 5'= —J". The cross-sectional area of the beam must be sufficient to resist the shear 5 or S'. The upper part of Fig. 13 shaded with broken A'ertical lines indicates this condition of shear. It is e\'iclent from this simple case that the total vertical shears at the ends of any beam will be the reactions or supporting forces exerted at those ends, and that each will remain constant for the adjoining portion of the beam. The third member of equation (13) shows that tlie greatest bending moment M^ in the beam varies as the product .\\x., of the segnients of the sjian. That product will have its greatest value when .\\=.v.,. Hence a simple beam loaded by a sini^le weiglit will be subjected to the i^reatcst possible bending iiioiiient wJien the weight is placed at the middle of the span, at ichieh point also thai moment icill be found. 82. Bending Moments and Shears with any System of Loads. — The general case of a simple beam loaded A\'ith any sj-stem of weights whatever may be represented in Fig. 13, in which the bcLmi of Fig. 12 is supposed to carry three loads, -d\, u\, ic^. The spacing of the loads is as shown. The reactions or supporting forces R' are determined precisely as in Fig. 12, each reaction in this case being the resultant of three loads instead of one. Apply- ing the law of the lever as before, the reaction R will have the value R^W:l + W,^Uu\'^ + )±^. . . . (14) A similar value may be written f(->r R', but it is probably simpler, after having found one reaction, to write 7?' = ir, + ir, + ir,-A^ (15) 90 BRIDGES. As the beam is supposed to have no Aveight, no load wiU act upon the beam between the given weights. The bending moments at the points of appHcation of the three weights or loads will be (i6) M,=R(a + b)-]\\b, ]■ ■ ■ M,=R{a + b + c)-W,{b + c)-\V,c. J After substituting the value of R from equation (14) in equa tions (16) the values of the latter are at once known. R c A ^ -^ '^ ^ r' / / N^ ^^^ \- p\ /^ ^ ^ '^^^^ =-=f ■Ljth( 1^\ B wy D " L ' 1 1 N ■ ' 1 1 i w, S=R I|ll4(t| 1 1 1 1 1 1 1 1 1 1 1 1 T ( 3 V Q ni|ii 1 11 Ml I i 1 1 i 1 II iiii ill! iJ W2- 1 1 1 1 1 1 1 ] 1 ji-j 1 l> 1 1 1 1 rl| til 1 1 M i s'=- w ■'■'q Fig. 13. The bending produced by each weight will also be represented precisely like that in Fig. 12. The triangle AXB represents the bending produced by W ^■, AOB the bending produced by IT'/- and APB the bending produced by 11 '3. The resultant bending effect produced by the three loads or weights acting simulta- neously is simply the summation of the three effects each due to a single load. Hence DC is erected vertically through the point of application of ]\\, so as to equal DN added to the two vertical intercepts between AB and AP, and AB and ,40. Similarly, HF is equal to HO added to the intercepts between AB and AP, and AB and BN. Finally, KL is equal to PL added to the other two intercepts, one between AB and BA', and the other between SHEAR IN TElUfS OF BkWDIXO MOMENT. ;il AB and BO. Straight linos then arc drawn through A, C, F, K, and B. Any \-crtical intercept between AB and ACFKB will represent the bending moment in the lieam at the corresponding point. Obviously any number of loads of any magnitude, or a uniform load, may be treated in precisel\' the same way. An important practical rule can readily be deduced from the equations (i6), each one of which may be regarded as a gen- eral equation of moments. If the s>-stem of three, or any other number of loads, be mox'cd a small distance J.v, while they all remain separated by the same distances as before, the bending moment M will be changed by the amount shown in equation (i6a): J.l/ = A'J.v-ir^J.v-n\,JA--etc. . . . (i6u) If the notation of the differential calculus be used by writing the letter d instead of J, and if both members of equation (i6a) be then divided by d.v, equation (i6b) will result: — 7T= J .-=•''- ^1' 1-11 2- etc. = shear. . (i66) The second member of this equation shows the sum of all the external forces acting on one portion of the beam, that por- tion being limited by the section about which the moment AI acts. That sum of all the external forces, as gi^'en by the second member of equation (ibb), is evidently the total transverse shear at the section considered. Equation (ibb) then shows, in the language of the differential calculus, that the first derivati\'e of M in respect to .v is equal to the total transverse shear. It is further estal)lished in the dift'erential calculus that whene^'er a function, such as M, the bending moment, is a maximum or a minimum, the first derivative is equal to zero. The application of this principle to equation {i6b) shows that the bending mo- ment in any beam or truss has its greatest value whercA'er the shear is zero. Hence, in order to determine at what section the bending moment has its greatest ^•alue in any loaded beam carrying a gi\'en system of loads, it is only necessary to sum up all the forces or loads, including the reaction R, on that beam from one end to the point where that sum or shear is zero ; at this latter point the greatest moment sought will be found. This '93 BRIDGES. is a very simple method of determining the section at which the greatest moment in the beam exists. The preceding formula; and diagrams may be extended to include any number of loads, and they are constantly used in engineering practice, not onlv for beams and girders in buildings, but also for bridges carrying railroad trains. Whatever may be the number of loads, the expressions for the bending moments at the various points of application of those loads are to be written precisely as indicated in equations (i6). When the number of loads becomes great the number of terms in the equa- tions correspondingly increase, but in reality they are just as simple as those for a smaller number of loads. The diagram for the vertical shear in this beam is the lower part of Fig. 13. As in the case of Fig. 12 the shear at A is the reaction R, as it is R' at the other end of the beam. The shear in the portion AD of the beam has the value R, but in passing the point D to the right the weight TFj represented by 07 must be subtracted from R, so that the shear over the section b of the span is R — W^ or QV in the diagram. Similarly, in passing the point H toward the right, both l-F^ and W^ must be subtracted from R, giving the negative shear (the previous shear being taken positiA-e) FIF. The negative shear FIF remains constant throughout the distance c, but is increased by W^ at the point L, so that throughout the distance d the shear S' = —R'. These shear values are all shown in the lower portion of Fig. 13 by the vertical shaded lines. Obviously it is a matter of indifference whether the shear abo\'e the straight line GJ is made positive or negative ; it is only necessary to recognize that the signs are different. In the case of heavy beams, either built or rolled, as in rail- road structures, it is of the greatest importance to determine both the bending moments and the shears, as represented in the preceding equations and diagrams, and to provide sufficient metal to resist them. The case of Fig. 13 is perfectly general for moments and shears, and the methods developed are applicable to any amount or any system of loading whatever. 83. Bending Moments and Shears with Uniform Loads. Fig. 14 represents what is really a special case of Fig. 13, in which BENDING MOMENTS AND SHEARS WITH UNIFORM EOADS- 00. the loading is uniform for each unit of length of the beam throuoh- out the whole span /. Inasmucli as the load is unifomhy dis- tributed, it is CA-idcnt that the reaction at each end of the beam will be one half the total k)ad, or Fig. 14. The general expression for the bending moment at any point G in the span, and located at the distance x from the end .4, will take the form I\I==Rx ■ ivx "'a-(/-t). (18) This equation, giving the A'alue of M, is the equation of a parabola with the A-ertex over the middle of the span. The bending moment at the latter point will be found by placing .v = - in 2 equation (iS), which will give M- (19) Hence, in Fig. 14, if the A^ertical line DC be erected at D. so as to represent the value of M in equation (19) to a conA'cnient scale, the parabola ACB may be at once drawn. Any vertical inter- cept, as GF between AB and the curve AFCB, -will represent by the same scale the bending moment in the beam at the point indicated b-s' the intercept. Equation (19), giA'ing the greatest external bending moment in a simple beam due to a uniform load, is constantly emploA'cd in structural work, and sliows that 94 BRIDGES. that moment is equal to the total load multiplied by one eighth of the span. It has already been shown, in connection with Fig. 12, that when a single centre weight rests on a beam the centre bending moment is equal to that weight multiplied by one fourth the span. If the total uniform load in the one case is equal to the single load in the other, these equations show that the single centre load will produce just double the bending moment due to the same load uniformly distributed over the span. Wherever it is feasible, therefore, the load should be distributed rather than concentrated at the centre of the span. That portion of Fig. 14 shaded with vertical lines shows the shear existing in the beam. Evidently the shear at each end is equal to the reaction, or one half the total load on the span. The expression for the shear at any point, as G, distant x from A will be S =R~wx =it'l- —x) (20) If x=- in equation (20), 5 becomes equal to zero. In other words, there is no shear at the centre of the span of a beam uni- formly loaded. Hence, if at each end of the span a vertical line AK or BL be laid off downward, and if straight hues KD and DL be drawn, any vertical intercept, as GH, between these lines and AB will represent the shear at the corresponding point. Equation (20) also shows that the shear 5 at any point is equal to the load resting on the beam between the centre D and that point. Although this case of uniform loading is a special one it finds wide application in practical operations. 84. Greatest Shear for Uniform Moving Load. — The preced- ing loads have been treated as if they were occupying fixed positions on the beams considered. This is not always the case. Many of the most important problems in connection with the loading of beams and bridges arise under the supposition that the load is movable, like that of a passing railroad train. One of the simplest of these problems, although of much importance, con- sists in finding the location of a unifomi moA-ing Liad, like that of a train of cars, which Avill produce the greatest shear at a given GREATEST SHEAR FOR UNIFORM MOVING LOAD. 95 point of a simple beam, such as that represented in Fig. 15, in winch a moving load is supposed to pass continuously over the span from the left-hand end .4 . It is required to determine uhat position of this uniform load will produce the greatest shear at the section C. -Al Fig. 15. Let the moving load extend from A to any point D to the right of C. The two reactions R and R' may be found by the methods alreatly indicated. Let TL represent the uniform load resting on the portion CD of the span. The shear 5' existing at C will be S'=R'-W (21) Let R'" be that part of R' which is due to IP, and A'" that part due to the load on AC. Evidently R'" is less than IP ; then S' =R" + R"'^]V (22) Since the negative quantity TT' is greater than the positive quan- tity R'", S' will have its greatest value when both IP and R'" are zero. Hence the greatest shear at the point C will exist when S'=R" (23) Obviously the loading must extend at least from A to C in order that R" may have its maximum A'alue. Hence the greatest shear at any section leill exist lelieii the iiiiifonu loael extends frojii tlie end of tJie span to that seetioii, lehate-eer may be the density of tJie h\}d. If the segment of the span covered by the moving load is greater than one half the span, the maximum shear is called the main shear; but if that segment is less than one half the span, the maximum shear is called the eoiinter-shear. The reason for these two names will be apparent later in the discussion of bridge- trusses. This rule for determining the maximum shear at any section of a beam is equallv applicable to bridge-trusses under certain conditions, and has an important bearing upon the determination 96 BRIDGES. of the greatest stresses in some of the members of bridge-frames, although it has less importance now than it had in the earlier days of bridge building. 85. Bending Moments and Shears for Cantilever Beams. — The case of a loaded overhanging beam or cantilever bracket, as shown in Fig. 16, is sometimes found. In that figure a single weight 11' is supposed to be applied at the end, while a uniform load tc per unit of length extends OA'cr its length /. The bending moment at any point C distant .v from the end will obviously be M=Wx+. (24) Fig. 16. The greatest value of the bending moment will be found by placing X equal to / in equation (24), and it wiU have the value ^A-n7+^ (,5) The shear at any point and at the end A respectively will be 5 = ll' + ua- and 5^=11'+ a'/ (26) The shear due to IT is equal to itself and is constant throughout the whole length of the beam. The second term of the second member of equation (24) is the equation of a parabola with its vertex at B, Fig. 16. Hence if AF be laid off equal to '-^, and if the parabola FHB be drawn, any vertical intercept, as HK, between that curve and AB will represent the bending moment at the corresponding point. (3n the other hand, the first term of the second member of equation (24) shows tliat the bending moment due to lb varies directly GREATEST BEXDfXG MOMEXT WITH AXY LOADIXG. OT as the distance from B. Hence if AG be laid oli A'crtieallv down- ward from ,4 equal to 117 to any convenient scale, then any inter- cept, as KL, between AB and BG will represent the bending moment due to 11' at the eoiTesponding point of the beam. 86. Greatest Bending Moment with any System of Loading. — One of the most important positions of loading to be established either for simple beams or for bridge -trusses is that at which any given system of loading whatever is to be placed on any span so as to produce the maximum bending moment at any prescribed point in that span. In order to make the case per- fectly general a sj'stem of arbitrary loads, like that shown in Fig. 17, is assumed and the system is supposed to be a moA'ing one. -,^-<,ri-T,- iWi jW- J"t I w, , Wi Ivv« , I w; 1 w„ IR' ■i- Fig. 17. The separate loads are placed at fixed distances apart, indi- cated by the letters a, b, c, d, etc., 11', being supposed to be at the head of the train, while 11',, is the last load having a variable distance .v between it and the end of the span. In Fig. 1 7 this system of moving loads or train is supposed to pass oaxt the span / from right to left. The problem is to deteiTnine the posi- tion of the loading, so that the bending moment at the section C of the beam or truss will be a maximum, the section C being at the distance /' from the left-hand end of the span. The com- plete analysis of this problem is comparatively simple and may readily be found, but it is iKit necessary for the accomplishment of tlie present purpose to give it here. In order to exhibit the formula which expresses the desired condition, let ll',,' be that weight whicl: is realh- placed at C, but which is assumed to be an indefinitelv short distance to the left of that point, for a reason which wili presently be explained. The equation of condition or criterion sought will then be the following: /'^ ir, + ir,+ ...+ir„. ^ ^ . / "ir, + ir, + ir,+ ... +ir„ If the loads are so iilaced as to fulfil the conditiosi expressed 98 BRIDGES. in equation (27), the bending moment at section C" will be a max- imum. If the variation in the train weights is very great, it is possible that there may be more than one position of the train which will satisfy that equation. It is necessary, therefore, frequently to try different positions of the loading by that cri- terion and then ascertain which of the resulting maximum moments is the greatest. It is not usually necessary to make more than one or two such trials. The application of the equa- tion is therefore simple and involves but httle labor. It will usually happen that Il'„' in equation (27) is not to be taken as the whole of that weight, but only so much of it as may be necessary to satisfy the equation. This is simply assuming that any weight, W, may be considered as made up of two sepa- rate weights placed indefinitely near to each other, which is permissible. iVfter having found the position of loading which satisfies equation (27), the resulting maximum bending moment will take the following form : lM^=^'^[n\a+i]\\ + W,)b+ . . . +{W, + W,+ . . . +W„)x] -W^a-{]l\ + VV,)b- . . . -{W, + W,+ . . . +W„,_,){1). (28) In this equation x corresponds to the position of loading for maximum bending, while the sign ('') represents the distance between the concentrations IF„'_j and Il'„'. This equation has a very formidable appearance, but its composition is simple and it is constantly used in making computations for the design of railroad bridges. The loads 11',, 11^, W^, etc., represent the actual weights on the driving-axles and other axles of locomo- tives, tenders, and cars, and the spacings a, b, c, etc., are the actual spacings found between those axles. In other words, these quantities are the actual weights and dimensions of the different portions of moving railroad trains. The computations indicated by equation (28) are not made anew in ever)^ instance. Concentrated weights of typical loco- motives, tenders, and cars are prescribed by different railroad companies for their diff'erent classes of trains, ranging from the heaviest freight trafhc to the lightest passenger train. A tabu- APPLICATIONS TO ROLLED BEAMS. 99 lation is then made from equation (28) for each such typical train, and it is used as frequently as is necessary to design a bridge to carry the prescribed traffic. The tabulations thus made are ne\-er changed for a gi\-en or prescribed loading. 87. Applications to Rolled Beams. — It is to be remembered that these last observations do not limit the use of equations (27) and (28) to railroad-bridge trusses only; they are equally appli- cable to solid and rolled beams and are frequently used in connec- tion with their design. Great quantities of these beams and various rolled steel shapes are used in the construction of large modem city buildings, as well as in railroad and highway bridge structures. The steel frames of the great office buildings, so many of which are seen in New York and Chicago as well as in other cities, which carry the entire weight of the building, are formed wholly of these steel shapes. The so-called handbooks published by steel-producing companies exhibit the various shapes rolled in each mill. These books also give in tabular statements many numerical values of the moment of inertia, the section modulus, and other elements of all these sections, so that the formulae which ha^'e been established in the pre- ceding pages may be applied in practical work with great con- ■\'enience and little labor. Tables are also gi\-en showing the sizes of rolled beams required to sustain the loads named in them. Such tables are formed for practical use, so that, know- ing the distance apart of the beams, their span, and the load per square foot which they carry, the required size of beam may be selected without CA'en computation. Such labor-saving tables are quite common at the present time, and they reduce greatly the labor of numerical computations. CHAPTER VIII. 88. The Truss Element or Triangle of Bracing. — A number of the preceding formulas find their appHcations to bridge -trusses, as well as to beams ; hence it is necessary to give attention at least to some simple forms of those trusses. The skeleton of everj^ bridge-truss properly designed to carry its load is an assemblage of triangles. In other words, the truss element, i.e., the simplest possible truss, is the triangular frame, such as is shown in skeleton in Figs. i8 and i8a. These simple triangular frames are sometimes called the King-post Truss. The action of such a triangular frame in carrying a vertical load is extremely simple. In Fig. i8 let the weight W be suspended Fig. i8. Fig. iSa. from the apex C of the triangle. The line CF represents that weight, and if the latter be resolved into its two C(imponents parallel to the two upper members of the triangular frame, the two component forces CG and CD will result. If from D and G the horizontal lines DH and (jO be dra^^•n, those two lines will represent the horizontal components of the forces or stresses in the two bars CA and CB. The force FID will act to the left at the point .4, and the force CG will act to the right at B, and as these two forces are ecjual and opposite to each other, equilibrium wih result. Either of the horizontal forces will represent the magnitude of the tension in AB. Both AC and CB will be in 100 SIMPLE TRUSSES. 101 compression, the former being compressed bv the forec Cf>, and the latter by the force CG . The manner of drawing a paralleb ogram of forces makes the triangle C(MJ similar tnCXlS, and(77Z) similar to CXA ; hence H\V divided by L'H will be ecjual to AX divided by A7>. I5ut H\V is the A'ertical component of the stress in CF>, while CH is the vertical component oi the stress in AC, the latter being represented by the reaction A' and the former by the reaction R' . It is seen, therefore, that the weight ir is carried b)' the frame to the two aljutment supports .4 and B, precisely as if it were a solid beam. In other words, the important iirinci])le is estalilished that \\'hen weights rest upon a simple truss supported at each end they Avill produce reactions at the ends in accordance with the principle of the lever, jireeisely as in the case of a solid beam. In engineering parlance it is stated that the weight lb is diAdded according to the principle of the lever, and that each portion travels to its proper abutment through the members of the triangular frame. If the two inclined members of the triangular frame are equally inclined to a vertical, the case of Fig. i8a results, in which one half of the weight goes to each abutment. The triangular frame, with ecjually inclined sides, shown in Fig. iS(!, is evitlentlv the simplest form of roof-truss, constituting two equallv inclined members with a horizontal tie. 89. Simple Trusses. — The simplest forms of trussing used for bridge purposes are those sh(;)wn in Figs. 19, 20, and 21. There are many other forms which are exhibited in complete treatises on bridge structures, but these three are as simple as any, and they haA-e been far more used than any other types. The hori- zontal members af and AB are called the "chords," the former being the upper chord and the latter the lower chord. The A-ertical and melined members connecting the two chords are called the web members or braces. AVhen a bridge is loaded, either bv its own Avcight only, or by its own weight added to that of a moving train of ears, the upper chord will evidently be in compression, while the lower ch<^rd is in tension. A por- tion, which may be called a half, of the web members will be in tension and the other portion, or half, will be m compression. The function of the upper and lower chords is t(j take up or 103 BRIDGES. resist the horizontal tension and compression which correspond to the direct stresses of tension and compression existing in the longitudinal fibres of a loaded solid or flanged beam. The metal designed to take these so-called direct stresses is concentrated in the chords of trusses, whereas it is distributed throughcedure is not quite accurate. The com- plete consideration of an exact method of computation would take the treatment into a region of rather compHcated anah'sis beyond the purposes of these lectures, but its outlines will be set forth on a later page. The exact method of treatment of two or more web systems invoh'es the elastic properties of the material of which the tnisses are composed. In the best mod- em bridge practice engineers prefer to design trusses of all lengths with single web systems, although the panels are fre- quently subdi\-idcd to a\-oi(.l stringers and floor-beams of too great weight. 95. Influence of Mill and Shop Capacity on Length of Span. — In the early years of iron and steel bridge building the sizes of indi^'idual members were limited bv the shop capacity for hand- ling and manufacturing, and bv the relati\-eh' small dimensions of bars of A-arious shapes, and of jilatcs which could be produced by rolling-mills. As both mill and shop processes haA'e advanced and their capacities increased, coiTcsponding progress has lieen made in bridge design, t'ivil engineers ha\"e a\'ailed themseb'cs of those ad^'ances, so that at the ]iresent time single-SA'stem tmsses A\"ith de]:iths as great lis 85 feet or more and spans of OA'er 550 feet are not considered s]ieeiallv remarkable. 96. Trusses with Broken or Inclined Chords. — ^\s the lengths of spans have increased certain suVistantial adA'antages ha\'e l;ieen gained in design b}' no longer making tlie upjier clujrds hori- 110 BRIDGES. zontal in the case of long through-spans, or indeed in the cases of through-spans of moderate length. The greatest bending moments and the greatest chord stresses have been shown to exist at the centre of the span, while the greatest web stresses are found near the ends. Trusses may be lightened in view of those considerations by making their depths less at the ends than at the centre. This not only decreases the sectional areas of the heaviest web members near the ends of the truss, but also shortens them. It adds somewhat to the sectional area of the end upper- chord members, but the resultant effect is a decrease in total weight of material and increased stability against wind pressure by the decreased height and less exposure near the ends. It has therefore come to be the ruling practice at the present time to make through -trusses with inclined upper chords for prac- tically all spans from about 200 feet upward. A skeleton dia- gram of such a truss is given in Fig. 24. Fig. 24. 97. Position of any Moving Load for Greatest Web Stress. — In the preceding treatment of bridge-trusses with parallel and horizontal chords a moving or live load has been taken as a series of uniform weights concentrated at the panel-points. This simple procedure was formerly generally used, and at the jjresent time it is occasionally employed, but it is now almost universal practice to assume for railroad bridges a movmg load consisting of a series of concentrations, which represent both in amount and distribution the weights on the axles of an actual railroad train. If a bridge is supposed to be traversed by such a train, it becomes necessary to determine a method for ascertaining the positions of the train causing the greatest stresses in the various members of the bridge-truss. The mathematical demonstration of the formula; determining CRITEIUOXS FOR BOTH CHORD AND WEB STRESSES. Ill those positions of loading need not be gi\-en here, but it can be found in almost any standard work on bridges. In order to show concisely the results of such a demonstration let It be desired to find the position of a mo\-ing Lxid whicli will give the greatest stress to any web member, as 5 in Fig. 24. Let the ponit of intersection of UK and DC be found in the point (J, then let C'A' be extended, and on its extension let the perpendic- ular /; be dropped from (). The distance of the point from A, the end of the span, is /, while 111 is the distance AD. Using the same notation which has been employed in the discussion of beams, together with that shown in Fig. 24, equation {^^t,) ex- presses the condition to be fulfilled by the train-loads in order that 5 shall ha\-e its greatest stress. Tlie first parenthesis in the second member of that equation represents the load between the panel p and the left end of the span, while the second parenthesis represents the load in panel p itself. n\ + ir,+ ... +ir„ = -- (n\ + ir,+ etc.) + (n-3 + n>etc.)^"i+':i. (,,) It will be noticed in equation (33) that the quantity iii shows in what panel the inclined web member whose greatest stress is desired is located, and it is important to obser\'e that panel carefully. If, for instance, the A'crtical member I\f> were in question, the point would be located at the intersection nf the panel XK and the lower chord of the bridge. In other words, the point must be at the intersection of the two chord mem- bers belonging to the same panel in which the web member is located. 98. Application of Criterions for both Chord and Web Stresses. — The criterion, equation (33), belongs to web members only. If it is desired to find the position of moving load which will give the greatest chord stresses in any panel, equatiiin (27), already established for beams, is to be used precisely as it stands, the quantity /' representing the distance from one end of the span to the panel-point about which moments are taken. 112 BRIDGES. If the desired positions of the mo^'ing load for greatest stresses have been found by equations (27) and {jT,), those stresses themseh'es are readily found by taking moments about panel-points for chord members and about the intersection- points 0, Fig. 24, for web members. These operations are simple in character and are performed with great facility. Tabulations and diagrams are made for given systems of loading by which these computations are much shortened and which enable the numerical work of anv special case to be performed quickly and with little liability to error. These tabulations and dia- grams and other shortening processes may be found set forth in detail in many pubHcations and works on bridge structures. They constitute a part of the office outfit of civil engineers en- gaged in structural work. The criterion, equation (27), for the greatest bending mo- ments in a bridge is applicable to any truss whatever, whether the chords are parallel or inclined, but it is not so with equation {t,t,). If the chords of the trusses are parallel, the quantity i in equation i:},^,) becomes infinitely great, and the equation takes the following form : TF, + IF,+ ... -MI'„ = i(lF3 + ir^ + etc.). . . (34) Ordinarily the span / divided by the panel length p is equal to the number of panels in the span. Hence equation (34) shows, in the case of parallel or horizontal chords, that when the moving load IS placed for the greatest web stress in any panel, the total load on the bridge is equal to the load in that panel multiplied by the total number of panels. 99. Influence Lines.— A graphical method, know as that of "influence lines," is used for determining the greatest shears and bending moments caused bv a train of concentrated weights passing along a beam or bridge-truss. Obviouslv it must express in essence that which has alreadv been shown bv the formula; which determine positions of moving loads for the greatest shears and bending moments. In realitv it is the appli- cation of graphical methods which have become so popular to the determination of the greatest stresses in beams and brido-es. INFLUENCE LINES FOR MOMENTS. 113 100. Influence Lines for Moments both for Beams and Trusses. — It is convenient to construct these influence lines for an arbi- trary load which may be considered a unit load ; the effect of any other load will then be in proportion to its magnitude. The results determined from intfucnce lines draAvn for a load Avhich may be considered a unit can, therefore, be made aA-ailable for other loads by multiplying the former by the ratio Ijetween any desired load and that for which tlie influence lines are found. Fig. 25. — Bending Moment in a Simple Beam. AB in I"ig. 25 represents a beam simply supported at each end, so that any load .c resting upon it will be divided between the points of support, according to the law of the lever. Let it be desired to determine the bending moment at the section A' produced by the load g in all of its pc)sitions as it passes across the span from .4 to B. Two expressions for the bending moment must be written, one for the load g at any point m.-lA', and the other for the load at any point in BX. The expression for the first bending moment is .V =.?■.' (7 -.v), and that for the latter ]\I' I- -x. (a) (b) As shoAvn in the figure, c and x. the latter locating the section at AA-hich the bending moments are to be found, are measured to the right from .4 . Equation (a) shows that if the quantity a(l- X-) be laid oft", bv anv convenient scale, as BK at right angles '^Q 4J5 XC will represent the moment .1/ by the same scale Avhcn x = r or'when z has anv value between o and x. Similarly will IIJ^ BRIDGES. AD be laid off at right angles to AB by the same scale as before, to represent gx. Then '\\'hen .v =;: the expression for ^1/' will have the same value XC as before. Hence if the lines AC and CB be drawn as parts of .4A' and DB, any vertical intercept between AB and ,4 CB will represent the bending at A' produced by the load ^ when placed at the point from which the intercept is drawn. The lines AC and CB are the influence lines for the bending moments produced by the load g in its passage across the span AB. It is to be observed that the influence lines are continuous only when the positions of the moving load are consecutive. In ■case those positions are not consecutive the influence lines are polygonal in form. If there are a number of loads g resting on the span at the same time, the total bending moments produced at X will be found by taking the sum of all the vertical intercepts between AB and ACB, drawn at the various points where those loads rest. The influence lines drawn ior a single load, therefore, may ■ be at once used for any number of loads. The load g is considered as a unit load. If the vertical inter- cepts representing the bending moments by the scale used are themselves represented by y, and if IT' represent any load what- ever, the general expression for the bending moment at A', pro- duced by any system of loads, will be 'g^^Vy (,) If this expression be written as a series, the general value of the bending moment will be the following: ^^^ = ^-^">i + n'>.+ 11^3 + etc.) (d) The effect of a moving train upon the bending moment at any given section is thus easilv made apparent bv means of influence lines. It is obvious that there will be as manv influence lines to be drawn as there are sections to be considered In the case of a tniss-bridge there will be such a section at eA-erv panel- point. ' A slight modification of the preceding results is to be made INFLUENCE LINES FOR SHEARS. 115 when the loads are apphed to the beam or truss at panel-points only. In Fig. 25 let I, 2, 3, 4, 5, 6, and 7 be panel-points at which loads are applied, and let the load g be located at the distance z' to the right of panel-ponit 5, also let the panel length be p. The reactions at 5 and will then be 7\, = f'^— ^ and R = ""- p " '^p' The reactions at .4 wih then be R=g~"\ Hence the moment at any section A' in the panel in question will be M=Kx-R^{z'-(z-x))=g I ~ ^^-^'+^--Vj (e) Remembering that c~::' is a constant quantitA^ it is at once clear that the preceding expression is the equation of a straight line, with .1/ and ;: or :;' the variables. If :;' = o, equation (e) becomes identical with equation (a), while if z' =p, it becomes identical with equation (b). Hence the influence line f(.>r the panel in which the Itiad is placed, as 5-6, is the straight line KL. It is manifest that when the load fj is in any other panel than that in which the section -Y is located, the effect of the t^^'o reac- tions at the extremities of that panel will be precisely the same at the section as the weight itself acting along its own line of action. Hence the two ]iortions AK and BL of the influence line are to be constructed as if the load were applied directly to the beam or truss, and in the manner already shown. The com- plete influence line will then be AKLB, and it shows that the existence of the panel slightly reduces the bending at any section within its limits. The panel 5-6, as treated, is that of a beam in which the bending moment will, in general, A-ary fmm ]ioint to point. If AB were a truss, however, -V avouIcI ahA'ays be taken at a panel-point, and no intercept between panel-points, as 5 and 6, would be considered. loi. Influence Lines for Shears both for Beams and Trusses. — The influence lines for shears in a simple beam, supported at each end, can be drawn in the manner shoAvn in Fig. 2^0. In that figure AB represents a non-continuous beam with span / sup- 116 BRIDGES. ported at each end and a conA^entional load tvom A. The reaction at .4 will be at the distance z Fig. 25a. — Shear in a Simple Beam. Let X be the section at which the shear for various positions of g is to be found. When g is placed at any point between A and A' the shear 5 at the latter point will be S = R=g=-g if) but when the load is placed between B and A' the shear becomes S'=R=g~g (h) Obviously these two values of the shear are equations of two parallel straight lines, that represented by equation (/) passing through ,4, and that represented by equation (Ii) passing through B, the constant A-ertical distance between them being ^p-. Hence let BF be laid off negatively doAvnward and .46" positively up- ward, each being equal to g by any convenient scale. The ordi- nates clraAvn from the A-arious positions i, 2, 3 ... 6 of ,£: on .47? to .4 D and BC will be the shears at X produced by the load g at any point of the span, and determined by equations (/) and (/;). The influence line, therefore, for the section A' will be the broken line ADCB. When ^ is at A' the sign of the shear changes, since the latter passes through a zero value. If a train of weights U\, IF,, 11',, etc., passes across the span, the total shear at A' will be found by taking the sum of the vertical INFLUENCE LINES FOR SHEARS. 117 intercepts between AB and ADCB, drawn at the positions occu- pied by the x-arious sinj^le weights of the train. Jf tliose single weights are expressed in terms of the unit load g, the shear 5 will have the \'alue g y being the general \'alue of the intercept between AB and the influence line. The latter shows that the greatest negati\-e shear at .V will exist when the greatest possible amount of loading is ]ilaeed on .4 A' only, while the greatest positix'C shear at the same section will exist when BX only is loaded. If BX is the smaller segment of span, the latter shear is called the ''counter- shear," and the former the ' 'main shear." If the loads are applied at panel-points of the span only, the treatment is the same in general character as that employed for bending moments. In Fig. 25a let 4 and 5 be the panel-points between which the load g is found, and let the panel length be p. Also, let z' be the distance of the weight g from panel-point 4. The reactions at ,4 and 4 will then be / - - p-:' R = - "a and R^ = '— - tj. The shear at the section X ior any position of the weight ,t: will then be 5.K-R.-4;-;) a. As this is the equation of a straight line, with 5 and c or z' for the coordinates, the infiuence line for the panel in which the section A is located will be the straight line represented b>- RL in Fig. 2^a. Ifc' is placed equal to o and p successively, then will equa- tion (k) become identical with equations (/) and ih) in succession. The shears at points 4 and 5 will therefore take the same A'alucs as if the loads were applied directly to the beam. For the reasons stated in connection with the consideration of bending moments, loads in other panels than that containing the section for which the influence line is drawn will have the same effect on that sec- 118 BRIDGES. tion as if they were applied directly to the beam or truss. Hence AKLB is the complete influence line for this case. It is evident that there must be as many influence lines drawn as there are sections to be discussed. Also, if ^^ is taken as some convenient unit, i.e., looo or 10,000 pounds, it is clear that the labors of computation will be much reduced. 102. Application of Influence-line Method to Trusses. — In con- sidering both the bending moments and shears when the loads are applied at panel-points, it has been assumed, as would be the case in an ordinary beam, that the bending moments as well as the shears may vary in the panel; but this latter condition does not hold in a bridge-truss. Neither bending moment nor shear varies in any one panel. Yet the influence lines for mo- ments and shears are to be drawn precisely as shown in Figs. 25 and 25a. The section A' will always be found at a panel-point, and no intercept drawn within the limits of the panel adjacent to that section carrying the load g is to be used. This method will be illustrated by the aid of Fig. 256. The employment of influence lines may be illustrated by determining the moment and shear in a single section of the truss shown in Fig. 24, which is reproduced in Fig. 25c, when carrying the moving load exhibited in Fig. 256, although its use may be much extended beyond this simple procedure. The moving load shown in Fig. 256 is that of a railroad train consisting of a uniform train-load of 4000 pounds per hnear foot drawn by two locomotives with the wheel concentrations sho^vn ; it is a train-load frequently used in the design of the heaviest class of railroad structures. If the criterion of equation (27) be applied to this moving load, passing along the truss shown in Fig. 25c, from left to right, it will be found that the greatest bending moment is produced at the section when the second driving-axle of the second locomotive is placed at the truss sec- tion in question, as shown in Fig. 2 5f. The unit load to be used in connection with the influence lines will be taken at 10,000 pounds. Remembering that the panel lengths are each 30 feet, it will be seen that the panel-point Q is 150 feet from A. Hence the product gx will be 1,500,000 foot-pounds. Similarly the product g{l-x) will be 900,000 foot- INFLUENCE-LINE METHOD FOR TRUSSES. 119 pounds. Laying off the first of these quantities, as AD, at a scale of 1,000,000 foot-pounds per linear inch, and the second cjuantity, as BK, by the same scale, the influence line ACB can at once be completed. \>rtical hues are next to be drawn through the positions of the A'"ari(jus weights, including one through the centre of the uniform train-Ljad no feet in length resting cm the truss. The vertical line through the centre of the uniform train-load is shown at 0. Bj' carefully scaling the vertical intercepts be- tween AB ,and ACB, and remembering that each of the loads on the truss must be divided by 10,000, the fullowing tabulated statement will be obtained, the sum of the intercepts for each set of equal weights being added into one item, and all the items of intercepts being multiplied by 1,000,000: •I95X] [lO X .4X1 000,000 = 8,580,000 :oot-pounds 1.78 X 2.6 X = 4,628,000 2.14 X 4 X = 8,560,000 .485 X 2 X = 970,000 1.525 X 2.6 X = 3,965,000 .9 X 4 X = 3,600,000 .12 X 2 X 1 r = 240,000 2)30,543,000 Moment for one truss = 1 5 , 2 7 1 , 500 The lever-arm of cf, i.e., the normal distance from to ef, is 39. 7 feet. Hence the stress in ef is 15il7M°° = 384, 700 pounds. 39-7 All the chord stresses can obviously be found in the same manner. In order to place the same moving load so as to produce the greatest shear at the same section 0, the criterion of equation (33) must be emploved. The dimensions of the truss shown in con- nection with Fig. 29 give the following data to be used in that :2io feet, ;;;=6o feet, and ^^ = 30 feet. Hence equation : I pi = iot. —'■ Introducing these quantities into equa- tion (33), and remembering that the train moves on to the bridge- 130 BRIDGES. from A, it would be fotind that the second axle of the first locomotive must be placed at the section 0, as shown m Fig. 2 5 J, which exhibits the lower-chord panel-points numbered from I to 7. The conventional unit load g will be taken in this case at 20,000 pounds. It is represented as AG and BF (Fig. Fig. 25ir. Fig. 25^. 2sd), laid off at a scale of 10,000 pounds per inch. K is imme- diately under panel-point 5 and L is immediately above panel- point 6, hence the broken line AKLB is the influence line desired The vertical lines are then drawn from each train concentration in its proper position, all as shown, including the vertical hne through the centre of the 54 feet of uniform train-load on the left. The .summation of all the vertical intercepts between AB and the influence line AKL, having regard to the scale and to INFLVENCE-LIKE METHOD FOR TRUSSES. Ul the ratio between the various loads and the unit load g, will give the following tabular statement: 22X54X .2 X 10,000 = 23,760 pounds 2 2 X 1.3X " = 28,600 '' 3 02 X 2 X " = 60,400 9 X I X " = q,ooo " 4 06 X I-3X " = 53.780 4 53 X 2 X " = 90,060 5 X I X " = 5,000 2)270,600 Shear for one titiss = 1 3 5 , 300 These simple operations illustrate the main principles of the method of influence lines from which numerous and useful exten- sions may be made. CHAPTER IX. 103. Lateral Wind Pressure on Trusses. — The duties of a bridge structure are not confined entirely to the supporting of vertical loads. There are some horizontal or lateral loads of considerable magnitude which must be resisted ; these are the wind loads resulting from wind pressure against both structure and moving train. In order to determine the magnitudes of these loads it is assumed in the first place that the direction of the wind is practically or exactly at right angles to the planes of the trusses and the sides of the cars. This assumption is essen- tially correct. There is probably nothing else so variable as both the direction and pressure of the wind. These variations are not so apparent in the exposure of our bodies to the wind, for the reason that we cannot readily appreciate even considerable changes either in direction or pressure. As a matter of fact suitable measuring apparatus shows that there is nothing steady or continued in connection with the wind unless it be its incessant variability. Its direction may be either horizontal or inclined, or even vertical, while within a few seconds its pressure may vary between wide limits. Under such circumstances the wind is as likely to blow directly against both bridge and train as in any other direction, and inasmuch as such a condition would subject the structure to its most severe duty against lateral forces, it is only safe and proper that the assumption should be made. The open work of bridge -trusses enables the wind to exert practically its full pressure against both trusses of a single-track bridge, or against even three trusses if they are used for a double-track structure. Hence it is customary to take the exposed surface of bridge-trusses as the total projected area on a plane through- out the bridge axis of both trusses if there are two, or of three 122 LATERAL M'lND PRESSURE ON TRUSSES. 123 trusses if there are three. Inasmuch as the floor of a bridge from its lowest point to the to]) of the rails or cither highest point of the floor is practically closed against the passage of the \\-ind, all that surface bet^^•een the lowest point and the top cif the rail or highest floor-member is considered area on which \\-ind pressure may act. I\Iany experimental observations show that on large surfaces, greater perhaps than 400 or 500 square feet in area, the pressure of the wind seldom exceeds 20 or 25 pounds per scjuare foot, while it may reach 80 or 90 jxmnds, or possibly more on small surfaces of from 2 to 40 or 50 square feet in area. This dis- tinction between small and large exposed areas in the treat- ment of wind pressures is fundamental and shpuld never be neglected. This whole subject of wind pressures has not yet been brought into a completely definite or well-defined condition through lack of suificient experimental observations, but in order to be at least reasonably safe civil engineers frequently, and perhaps usually, assume a wind pressure acting simultaneously on both bridge and train at 30 pounds per square foot of exposed surface and 50 pounds per square foot of the total exposed surface of a bridge structure which carries no moving load. This distinction arises chiefly from the fact that a wind pressure of 30 pounds per square foot on the side of many railroad trains, particularly light ones, will overturn them, and it would be useless to use a larger pressure for a loaded structure. There ha\-e been wind pre'ssures in this country so great as to blow unloaded bridges oft' their piers ; indeed in one case a locomotive was overturned which must have resisted a wind pressure on its exposed surface of not less than 90 pounds and possibly more than 100 pounds per square foot. The consideration of wind pressure is of the greatest impor- tance in connection with the high trusses of long spans, as well as in long suspension and cantilever bridges, and in the design of high viaducts, ah of which structures receive lateral wind pres- sures of great magnitude. Some^ engineers, instead of deducing the lateral wind loads from the area of the projected tniss surfaces, specify a certain 124 BRIDGES. amount for each linear foot of span, as in " The General Specifica- tions for Steel Railroad Bridges and Viaducts ' ' by J\Ir. Theodore Cooper it is prescribed that a lateral force of 150 pounds for each foot of span shall be taken along the upper chords of through- bridges and the lower chords of deck-bridges for all spans up to 300 feet in length; and that for the same spans a lateral force of 450 pounds for each foot of span shall be taken for the lower chords of through-spans and the upper chords of deck-spans, 300 pounds of this to be treated as a moving load and as acting on a train of cars at a line 8 /% feet above the base of rail. When the span exceeds 300 feet in length each of the above amounts of load per linear foot is to be increased by 10 pounds for each additional 30 feet of span. Special wind-loadings and conditions under w'hich they are to be used are also prescribed for viaducts. These wind loads are resisted in the bridges on which they act by a truss formed between each two upper chords for the upper portion of the bridge, and between each two lower chords for the lower portion of the structure. d- K< Fig. 26. 104. Upper and Lower Lateral Bracing. — Fig. 26 shows what are caUed the upper and lower lateral bracing for such trusses as are shown in the preceding figures. The wind is supposed to act in the direction shown by the arrow. DEKA and KLBC are the two portals at the ends of the structure, braced so as to resist the lateral wind pressures. It will be observed that the systems of bracing between the chords make an ordinary truss, but in a horizontal plane, except in the case of inclined chords like that of Fig. 24. In the latter case the lateral trusses are obviously not in horizontal planes, but they may be considered in computa- tions precisely as if they were. These lateral trusses are then treated with their horizontal panel wind loads just as the vertical trusses are treated for their corresponding vertical loads, and the resulting stresses are employed in designing web and chord BRirXIE PLANS AXD SIIOPWOh'K. 125 members precisely as in vertical trusses. The wind stresses in the chords, in S(jme cases, are to be added to those due to vertical loading, and in some cases subtracted. In other words, the resultant stresses are recognized and the chord members are so designed as proi)crly to resist them. At the present time it is the tendency in the best structural work to make all the web members of these lateral trusses of such section that they can resist both tension and compression, as this contributes to the general stiffness of the stiaicture. On account of the great variability of the wind pressures and the liability of the blows of greatest intensity to vary suddenly, some engineers regard all the wind load on structure or train as a moA'ing load and make their comjiutations accordingly. It is an excellent prac- tice and is probably at least as close an appn )ximation to actual wind effects as the assumption of a unifonn wind pressure on a structure. Both the lateral and transverse wind bracing of railroad bridges have other essential duties t(.» perf(jrm than the resistance of lateral wind pressures. Rapidly moving railroad trains pro- duce a swaying effect on a bridge, in consequence of unavoidable unevenness of tracks, lack of bakmce of locomotiA'c driving-wheels, and other similar influences. These must be resisted wholly by the lateral and trans\'erse bracing, and these results constitute an important part of the duties of that bracing. These peculiar demands, in connection with the lateral stal;)ility of bridges, make it the more desirable that the lateral and transA'crse bracing should be as stiff as jiracticable. 105. Bridge Plans and Shopwork. — After the computations for a bridge design are completed in a ci\-il engineer's oflice they are placed in the drawing-room, where the most detailed and exact plans of every piece which enters the bridge are made. The numerical computations connected A\-ith this i)art^ of bridge construction are of a laborious nature and must be made with absolute accuracy, othenvise it would he quite impossible to put the bridge together in the field. The A-anous quantities of bars, plates, angles, and other shapes required are then ordered from the rohing-mill by means of these plans or drawings. On receipt of the material at the shop the 126 BRIDGES. shopwork of manufacture is begun, and it involves a great variety of operations. The bridge-shop is filled with tools and engines of the heaviest description. Punches, lathes, planers, riveters, forges, boring and other machines of the largest dimensions are all brought to bear in the manufacture of the completed bridge. io6. Erection of Bridges. — When the shop operations are completed the bridge members are shipped to the site where the bridge is to be erected or put in place for final use. A timber staging, frequently of the heaviest timbers for large spans, called false works, is first erected in a temporary but very substantial manner. The top of this false work, or timber staging, is of such height that it will receive the steelwork of the bridge at exactly the right elevation. The bridge members are then brought onto the staging and each put in place and joined with pins and rivets. If the shopwork has not been done with mathematical accuracy, the bridge will not go together. On the accuracy of the shopwork, therefore, depends the possibility of properly fitting and joining the structure in its final position. The operations of the shop are so nicely disposed and so accu- rately performed that it is not an exaggeration to state that the serious misfit of a bridge member in American engineering prac- tice at the present time is practically impossible. This leads to rapid erection so that the steelwork of a pin-connected railroad bridge 500 feet long can be put in place on the timber staging, or false works, and made safe in less than four davs, although such a feat would have been considered impossible twenty years ago. 107. Statically Determinate Trusses. — The bridge structures which have been treated require but the simplest analvsis, based ^^-, r-l-">^ °"^-' °" statical equations of equilibrium of f\!''' ^'U^f''^ forces acting in one plane, i.e., the plane ^l „r\F of the truss. It is known from the science ^icil/ \ .'-|=-^-^ of mechanics that the number of those y ^'i a~i^ equations is at most but three for any '"hT system of forces or loads, viz., two equa- FiG. 27. tions of forces and one of moments. This may be simply illustrated by the system of forces F , STATICALLY DETERMIXATE TRUSSES. 127 F,, etc., In Fig. 27. Let each force be resolved into its vertical and horizontal components 1' and H . Also let l^, /,, etc. (not shown in the figure), be the normals or leA-er-amis dropped from any point A on the lines of action of the forces F , F,, etc., so that the moments of the forces ab(jut that point ^vili be F / , FJ.,, etc. The conditions of purely statical equilibrium are expressed by the three general ec^uations ^1 + H. , + etc. =F^ ens a^ + F.. cos a,_ + etc. =0; . (35) ]'i+ r, + etc. =F^ sin Cj + F, sin a, + ete. =0; . . (36) Fl = FJ^ + FJ., + etc.=o. . . ' (3-) If all the forces except three are known, obviouslv those three can be found by the three precedmg equations ; but if more than three are unknown, those three equations are not sufficient to find them. Other equations must be available or the unknown forces cannot be found. In modem methods of stress deter- minations those other needed equations express known elastic relations or values, such as defiections or the work performed in stressing the different members of structures under loads. A few fundamental equations of these methods will be giA-en. In Figs. 19, 20, and 21 let the truss be cut or divided by the imaginarv' sections OS. Each section cuts but three members, and as the loads and reactions are known, the stresses in the cut members \\-iU yield but three unknown forces, which may be found by the three equations of equilibrium (35), (36), (37). If more than three members are cut, however, as in the section T]' of Figs. 22 and 23, making more than three unknown equations to be found, other equations than the three of statical equilib- rium must be available. Hence the general principle that -if it is possible to cut not more than three members by a sceiion through the truss, it is statieally determinate, but // // is not possible to cut less than four or nu^rc. th.e stresses are statieally indcierminalc. At each joint in the truss the stresses in the members meeting there constitute, with the external forces or loads acting at the same point, a SA'stem in equilibrium represented by the two equa- tions (t,^) and (36). If there are ni such joints in the entire structure, there will be 2;;? such equations by which the same number of unknowm quantities may be found. Since equilibrium 128 BRIDGES. exists at every joint in the truss, the entire truss will be in equilib- rium, and that is equivalent to the equiHbrium of all the external forces acting on it. This latter condition is expressed by the three equations (35), (36), and (37), and they are essentially included in the number 2111. Hence there will remain but 2111—1, equations available for the determination of unknown stresses or external forces. If, therefore, all the external forces (loads and reactions) are known, tlie 2;» — 3 equations of static equilibrium can be applied to the determination of stresses in the bars of the truss or other structure. It follows, therefore, that the greatest num- ber of bars that a statical^ determinate truss can have is 11 = 2111-7, (38) In Fig. 19 there are tweh'e joints and twenty-one members, omitting counter web members and the \-erticals ab and //, which are, statically speaking, either superfluous or not really bars of the truss. Hence 111 = 12 and 2)» — 3=21 (39) Again, in Fig. 21 there are fifteen joints. Hence ;» = i5, 2111— T, = 2j, and there are twenty-seven bars or members of the truss. The number of joints and bars in actual, statically determinate trusses, therefore, confirm the results. 108. Continuous Beams and Trusses — Theorem of Three Mo- ments. — These considerations find direct application to what are known as " continuous beams," i.e., beams (or tioisses) which reach continuously over two or more spans, as shown in Fig. 28. w w "^v/z/^Q^ ■ Fig. 28. The beam shown is continuous over three spans, but a beam or truss may be continuous over any number of spans. In gen- eral the ends of the beam or girder may be fixed or held at the ends A and D, so that bending moments .1/ and AL at the CONTINUOUS BEAMS AND TRUSSES. 12'J same points may have value. The bending moments at the other points of support are represented by AJ ^, AI^, etc. The points of support may or may not be at the same elevation, but they are usually assumed to be so in engineering practice. Finally, it is ordinarily assumed that the continudus structure is straight before being loaded, and that in that condition it simply touches the points of support. Whether the preceding assumptions are made or not, a perfectly general equation can be written express- ing the relation between the bending moments o\'er each set of three consecuti\'e points of support, as Al , il/,, and iU,, or Af^, A I.., and .I/3. Such an equation expresses what is called the "Theorem of Three JMoments." It is not necessary to giA-e the most general form of this theorem, as that which is ordinarily used embodies the simjdifying assumptions already described. This simplified form of the "Theorem of Three Moments" applied to the case of Fig. 28 will yield the following two ec^ua- tions : AIl, + 2AI,{l, + l,)+AIJ,+ ^^-2W{l,'^z''): -^i]V{l,'-z')z=o. (40) AIJ, + 2AI,{l, + l,)+AIJ,+ y^\Vil,'-=') + 'iir(//-:-)::=o. (41) '3 The figure over the sign of summation shows the span to Avhich the'' summation belongs. If there is but one weight or load IF in each span, the sign of summation is to be omitted. In an ordinary bridge structure or beam the ends are simply supported and .1/= .1/3 = 0. In any case if the number of sup- ports be n, there will be » - 2 equations hke the preceding. If the end moments .1/ and AI, are not zero, they aviII be deter- minable by the local conditions in each instance. In any e^-ent, therefore, thev wih be known, and there will be but u - 2 unknown moments' to be found bv the same number of equations. AVhen the moments are known the reactions follow from simple formulae. 130 BRIDGES. 109. Application to Draw- or Swing-bridges. — In general the reactions or supporting forces of the beams and trusses of ordi- nary civil-engineering practice are vertical, and all their points of apphcation are known. Hence there are but two equations of equilibrium, equations (36) and (37 j, for external forces. These two equations for the external fijrces and the n—2 equa- tions derived from the theorem of three moments are therefore always sufficient to determine the n reactions. After the reac- tions are known all the stresses in the bars or members of the trusses can at once be found. The preceding equations and methods as described are constantly employed in the design and consti-uction of swing- or draw-bridges. no. Special Method for Deflection of Trusses. — The method of finding the elastic deflections produced by the bending of solid beams has already been shown, but it is frequently necessary to determine the elastic deflections of bridge-trusses or other jointed or so-called articulate frames or stiTictures. It is not practicable to use the same formulse for the latter class of struc- tures as for the former. The elastic deflection of a bridge- or roof-truss depends upon the stretching or compressions of its various members in consecjuence of the tensile or compressive forces to which they are subjected. An}' method by which the deflection is found, therefore, must invoh-e these elastic changes of length. There are a number of methods wliich give the desired expressions, but probably the simplest as weh as the most ele- gant procedure is that which reaches the desired expression through the consideration of the A^'ork performed in the truss members in producing their elastic lengthenings and shortenings. The general features of this method can readilv be shown by reference to Fig. 29, It may be supposed that it is desired to find the deflection of any point, as J, of the lower chord pro- duced both by the dead and live load which it carries. It is known from what has preceded that every member of the upper chord will be shortened and that exery member of the lower chord will be lengthened; and also that generally the vertical web members will be shortened and the inclined web members lengthened. If there can be obtained an expression giA'ing that part of the deflection of / which is due to the change of iength SPECIAL METHOD FOR DEFLECTION OF TRUSSES. 131 of an}' one member of the truss inde]x>ndentl\' of the others, then that expression may be apphed to e\'ery other member in the entire truss, and b>' taking the sum ui aU thuse efteets the desired deflection will at once result. While this ex])rcssi()n will he found for some one particular tiaiss member, it will be of such a general form that it may he used for an\' tiaiss member whatever; it Avill be written for the upper-chord member BC m Fig. 29. Us D u, E u,, 8 panels @ ;}0'=240' t. to c. end puis Fig. 29. The general problem is to determine the deflection of the point J when the bridge carries lioth dead and mo\-ing load o\-er tlie entire span, as shown in Fig. 29. The general plan of procedure is first to find the stresses due to this combined load in every member of the truss, so that the correspijnding lengthening or shortening is at once shown. The effect of this lengthening and shortening for any single meniber BC in producing deflection at / is then determined ; the sum of all such eft'ects for every mem1:)er of the truss is next taken, and that sum is the deflection sought. In this case the vertical deflection will be found, because that is the deflection generally desired in connection with bridge struc- tures, but precisely the same method and essentially the same fonnuhT? are used to find the deflection in any direction what- ever. The following notation will be employed : Let Tc ■= deflection in inches at any panebpoint or joint of the truss ; " P = any arbitrary load or weight supposed to be hung at the point where the deflection is desired and act- ing as if graduallv applied. This maybe taken as unity ; " Z = stress produced in any member of titiss by P ; " S = stress produced in any member of truss by the com- bined dead and moving loads ; 132 BRIDGES. Let / = length in inches of any member of the truss in which Z or 5 is found ; " A = area of cross-section of same member in square inches ; " E= coefficient of elasticity. 5 or Z may be either tension or compression, and the formula- will be so expressed that tension will be made positive and com- pression negative. The change of length of the chord member BC produced by a S stress gradually increasing from zero to 5 is — -/. If it be sup- posed that BC is a spring of such stiffness that it will be com- pressed by the gradual application of Z exactly as much as the shortening of the actual member by the stress S, the deflection of the point 4 with the weight P hung from it, and due to that compression alone, will be precisely the same as that due to the actual shortening of BC by the combined dead and moving loads. It is known by one of the elementary principles of mechanics that, since P acts along the direction of the vertical deflection ic, the work performed by the weight P over that deflection is equal to the work performed by Z over the change of length /. Hence 2 J-Z 2 SI la z p SI AE or (42) The quantity Z -^ P is the stress produced in the member by a unit load applied at the joint or point where the deflection is desired. Again, 5^.4 is the stress per unit of area, i.e., intensity of stress, in the member considered by the actual dead and mov- ing loads. For brevity let these be written then p=z and ~^=s\ zsl DEFLECTION METHOD APPLIED TO TRJANGULAR FRAME. 133 If the influence of every member of the truss is similarly ex- pressed, the value of the total deflection j^roduced by the dead and moving loads will be "^Z£ ^44) The sign of summation 2 indicates that the summation is to extend o\'er all the web and chord memVjers of the truss. III. Application of Method for Deflection to Triangular Frame. — Before applying those equations to the case of Fig. 29 it is best to consider a simpler case, i.e., that of the triangular frame shown in Fig. 18. The reactions are /^=yir and R' ^'W (45) The stresses in the various members are : In CB, S = -'^\V sec a. '■ CA, S = p]'secj3. " AB, 5 = ^-11' tan /9 = ^'11' tan a. Also : CB = /; sec a ; area ( )f sectirtening of pieces subjected either to tension or compres- sion, and for the work performed in the elastic bending of beams carrying loads at right angles tci their axes, l^oth of these ex- pressions can be \-ery simply found. Let it be supposed that a piece of material whose length is L and the area of whose cross-section is .4 is either stretched or compressed by the weight or load 5 applied so as to increase gradually from zero to its full value. The elastic change of length will be ^ -, E being the coefficient of elasticity. The AH average force acting will be A5, hence the work performed m producing the strain ^^•ill be Ir^'^ (48) 2AE It will generally be best, although not necessary, to take L in inches. >he expression (48) applies either to tension or com- pression precisely as it stands. To obtain the expression for the work performed by the stresses in a beam bent by loads acting at right angles to its axis, a differential length ( n^Lx = o■, } nI\Iy = o. . (57) The second and third of these equations express the condition that the vertical and horiz(jntal deflections respectiA'ch' of the two ends in reference to each other shall be zero. Tlie condi- tions expressed by equation (57) are constantly used in engi- neering practice to determine the bending moments and stresses Avhicli exist in the arched rib with flxed ends. The graphical method is ordinarily used for that purpose, as its employment is a comparatively simple procedure for a rib whose curvature is any whate\'er. If the rib has hinged joints at the ends, as in Fig. 34, obviously there can be no bending moment at either of those two points, and hence the two equations of condition which were required in connection with Fig, ^t, to determine them will not be needed. There is, therefore, no restriction as to the angle of inclination of the centre line of the rib at those two points. Again, it is obvious that either end .4 or B may have vertical movement, i.e., deflec- tion in reference to the other, without affecting the condition of stress in any member of the rib ; but it is equally obvious that neither A nor B can be moved horizontally, i.e., deflected in reference to the other, without producing bending in the rib and developing stresses in the various members. The unknown 148 BRIDGES. quantities in this case are, therefore, only the horizontal thrust H exerted at the two springing points A and B, and the two vertical reactions, making a total of three unknow^n quantities, equations for two of which will be given by equations (36) and (37). The other equation required is the third expression in equation (57), expressing the condition that the horizontal deflec- tion of either of the points .4 or B in respect to the other is zero, since the span AB is supposed to remain unchanged. By the application of the graphical method to this case, as to the pre- ceding, the employment of equations (36), (37), and (58) will afford an easy and quick determination of the three unknown quantities, whatever may be the cur\'ature of the rib. Z uMy=o (58) If the reactions and horizontal thrust H are found, stresses in every member may readily be computed and the complete design made. If the arch is three-hinged, as in Fig. 35, the condition that the bending moment must be zero at the crown C under all con- ditions of loading gives a third statical equation independent of the elastic properties of the structure which, in connection with equations (36) and (37), give three equations of condition suffi- cient to determine the two vertical reactions and the horizontal thrust H. In this case, as has already been stated, no elastic equations of condition are required. The determination of the end reactions, bending moments, and horizontal thrust H, in these various cases, is all that is necessarv in order to compute with ease and immediately the stresses in every member of the rib. These computations are obviously the final numerical work required for the complete design of the structure. These procedures are always followed, and in precisely the manner indicated, in the design of arched ribs by civil engineers, whether the rib be articulated, i.e., with open bracing, or with a solid plate web, like those of the Washington Bridge across the Harlem River. CHAPTER XI. 123. Beams of Combined Steel and Concrete.* — A reference has alreaeh- been made to a class of beams and arches recently c(.ime into use and nvw quite widel)- employed, composed of steel and concrete, the former being completely surrounded by and im- bedded in the latter. These composite beams are very exten- si\-ely used in the floors of fire-proof buildings as well as for other purposes. Arches of combined concrete and steel were probably first built in Gennany and but a comparatn-ely few years ago. During the past ten years they ha\-e been largely introduced into this country, and many such structures ha\'e not only been designed but built. The most prominent design of arches of combined concrete and steel are those of the proposed memorial bridge across the Potomac Ri\'er at Washington, for \\'hich a first prize was awarded as the result of a national competition in the early part of 1900. So far as the bending or flexure of these composite beams and arches is concerned, the theory is identically the same for both, the formula^ for each of which are gi^•en below. In order to express these formula the follo\^'ing notation will be needed : P is the thrust along the arch determined by the methods explained in the consideration of arched ribs. / is the distance of the line of the thrust P from the axis of the arched rib. E^ and E^ are coefficients of elasticity for the two materials. .4 J and .4., are areas of normal section of the two materials. /j and P are moments of inertia of .4, and .4., about the neutral axes of the composite beam or arch secti(^ns. * T'or a complete and detailed statement of this \\']i(ilc subject. includinL^ desiL^n \\i irk. reference shoidd be made to the authrir's •• Elasticity' and Resistance of Materials." 149 150 BIIIDCES. < c a d f- y ff C Q L < L L C D a a < C .^ < BEAMS OF COMinXEl) STEEL AXD COSCIIKTE 151 152 BRIDGES. A'j and fe^ are intensities of bending stress in the extreme fibres of tlie two materials. h^ and h^ are total depths of the two materials. c?j and d^ are distances from the neutral axes to farthest fibres of the two materials; distances to other extreme fibres would be (/jj — (ij and (li^ — d^). \\\ and n\ are loads, either distributed or concentrated, car- ried by the two portions. W = I'Fj + 11'^ is total load on the beam or arch. 11', , W, , £, li-yiF a"'^ ^= = #; ■■• '?i + '7. = i; ^ = ^'- The application of the theory of flexure to the case of a beam or arch of two difterent materials, steel and concrete in this case, will give the following results : M=Pl; hence ]\I^=q,Pl and RI,=q,Pl. . . (59) ^^-w-e:^^^ ^^°) "^^^W^ EJ. + EJ, ^''^ P . Md . ^^^^ P Md These formulae exhibit some of the main features of the analysis which must be used in designing either beams or arches of combined steel and concrete. In the use of these equations care must be taken to give the proper sign to the bending moment M. They obviouslj^ apply to the combination of any two mate- rials, although at the present time the only two used in such com- posite structures are steel and concrete. If the subscript i belongs to the concrete portion, and the subscript 2 to the steel portion, there may be taken £, = 1,500,000 to 3,000,000 and £2 = 30,000,000. Hence e = 20 to 10. The purpose of introducing the steel into the concrete is to make available in the composite structure the high tensile resist- BEAMS OF COMBINED STEEL AND CONCRETE. 153 ance of that metal. A very small steel cross-section is sufficient to satisfactoril)' accomplish that purpose. The percentage of the total composite section represented by the steel will vary some- what with the dimensions of the structure and the mode of using the material; it will usually range from 0.75 per cent to 1.5 per cent of the total section. The large mass of concrete in which the steel should be completely imbedded serves not only to afford a large portion of the compressive resistance required in both arches and beams, but also to preserve the steel effectively from corrosion. Many experiments ha\'e shown that it rcciuircs Vmt a small per cent of steel section to give great tensile resistance to the composite mass. CHAPTER XII. 124. The Masonry Arch. — The masonr}' arch is so old that its origin is lost in antiquity, but its complete theory has been developed with that of other bridge structures only within the latest period. It is only possible here to give some of the main features of that theor}' and a few of the fundamental ideas on which it is based. It is customary among engineers to regard the masonry arch as an assemblage of blocks finely cut to accu- rate dimensions, so that the assumption of either a unifomi or uniformly varying pressure in the surface of contact between any two ma}^ be at least sufficiently near the truth for all practical purposes. .Vlthough care is taken to make joints between ring- stones or voussoirs completely cemented or filled with a rich cement mortar, it is usually the implicit assumption that such joints do not resist tension. As a matter of fact many arch joints are capable of resisting considerable tension, but, in conse- quence of settlement or shrinkage, cracks in them that may be almost or quite imperceptible frequently prevent complete con- tinuity. It is, therefore, considered judicious to determine the stabiUty of the ordinary masonry arch on the assumption that the joints do not resist tension. In these observations it is not intended to con\-ev the impres- sion that no analysts treat the ordinary arch as a continuous elastic masonry mass, like the composite arches of steel and con- crete. Although much may be said in fa^-or of such treatment for all arches, it is believed that prolonged experience with arch structures makes it advisable to neglect any small capacity of resistance to tension which an ordinary cut-stone masonry joint may possess, in the interests of reasonable security. The ring-stones or voussoirs of an arch are usuallv cut to form circular or elliptic curves, or to lines which do not differ sensibly 15-1 OLD AXD NEW THEORIES OF THE ARCH. 155 from those curves. The arch-ring may make a complete semi- circle, as in the old Roman arches, or a segment of a semicircle ; or the stones may be arranged to make a pointed arch, like the Gothic ; or, again, a complete semiellipsc may be formed, or pos- sibly a segment of that curve. When a complete semiellipse or complete semicii-cle is formed, the arches arc said to be full- centred, and in those cases they spring from a horizontal joint at each end. On the other hand, segmental arches spring from inclined iofnts at each end called skew-backs. 125. Old and New Theories of the Arch. — In the older theories of the arch, considered as a series of blocks simply abutting against each other, the resultant loading on each block was assumed to be vertical. In the modern theories, on the other hand, the resultant loading on any block is taken precisely as it is, either vertical or inclined, as the case may be. Many arches are loaded with earth over then- arch-rings. This earth loading produces a horizontal pressure against each of the stones, as Avell as a vertical loading due to its own weight. In such cases it is neces- sary to recognize this horizontal or lateral pressure of the earth, as it is called, as a part of the arch loading. It is known from the theory of earth pressure that the amount of that pressure per square foot or any other square unit may vary between rather wide limits, the upper of A^'hich is called the abut- ting power of earth, and the latter the conjugate pressure due to its "own weight only. If w is the weight per cubic unit of earth and A- the depth considered, and if m Broadway in Brooklyn to Delancey Street, New York City, now being built, with a main span of 1600 feet between centres of towers. The entire length of the metal structure is 7200 feet, and the eleva- tion of the centres of cable at the tops of the towers is 333 feet aboA^e mean high Avater. Fig. 4^, shows a view of this bridge. Its three principal divi- sions are the cables, the stiffening tnisses, and the toAvers. The latter afford suitable points of support for the cables, Avhieh not only extend OA^er the river span, but are carried back to points iro BRIDGES. on the land where they are securely attached to a Heavy mass of anchorage masonry. These anchorages must be sufficiently heaA-y to prevent any load which may come upon the bridge from movmg them by the pull of the cables. It is usual to Fig. 43. — New cast River Bridge. make these masses so great that they are capable of resisting from two to two and a half times the pull of the cables. 134. The Stiffening Truss. — The function of the stiffening trusses is peculiar and imperatively essential to the proper action of the whole system. If they are absent and a weight should be placed upon the cable at any point, a deep sag at that point would result. If a moving load should attempt to pass along a roadway supported by a cable only, the latter would be greatly distorted, and it would be impossible to use such a structure for ordinary traffic. Some means must then be employed by which the cable shall maintain essentially the same shape and position, whatever may be the amount of loading. It can be readily shown that if any perfectly flexible suspension-bridge cable carries a load of uniform intensity over the span from one tower to the other, the curve of the cable will be a parabola, with its A'ertex at the lowest point. Furthermore, it can also be shown that if any portion of the span be subjected to a uniform load, the corre- sponding portion of the cable will also assume a parabolic LOCAriON A.YD ARRANGEMENT OF STIFFENING TRUSSES. 171 curve. It is assumed in all ordinary suspension-bridge design that the total weight of the structure, including the cables and the suspension-rods which connect the stilTening trusses to tlie cable, IS uniformly distributed over the ^xm, and that assum])- tion is essentially correct. So far as the weight of the structure is conecrneil, therefore, the curA-c ..f the calile will always be parabolic. It <.nly remains, therehjre, to de\'ise such stiifening trusses as will cause any moA-ing load passing on or .n-er the bridge to be carried uniformly to the cables throughout the entire span. This condition means that if any moving load whatever covers any portion of the span, the corresponding pull of the suspension-rods on the cables must be uniform from one tower to the other, and that result can be practically accom- pHshed by the proper design of stiffening trusses; it is the complete function of those trusses to perform just that duty. 135. Location and Arrangement of Stiffening Trusses. — It has been, and is at tlie present time to a considerable extent, an open question as to the best location and arrangement of the stiffening trusses. The more common method in structures built is that illustrated by the New York and Brooklyn and the new East River bridges. Those stiff'ening trusses are uniform in depth, extending from one tower to the other, or into the land spans, and connected with the cables by suspension-rods running from the latter down to the lower chords of the trusses. It is obA'ious that the floor along which the moving load is carried must have considerable transverse stiffness, and hence it may appear advis- able to place the stiffening trusses so that the floor may be carried by them. On the other hand, some civil engineers maintain that it is a better distribution of stiffening metal to place it where the cables themseh'cs may form members of the stiffening trusses, with a view to greater economy of material. Figs. 44, 45, and 46 illustrate some of the principal proposed methods of constructing stiffening trusses in direct connection with the cables. The structure shtwvn in Fig. 44 illustrates the skeleton design of the Point Bridge at Pittsburgh. The curved member is a parabolic cable composed of eye-bars. This jiara- bolic cal)le carries the entire weight of the structure and moving load when unifomilv distributed. If a single weight 173 BRIDGES. rests at the centre, the two straight members of the upper chord may be assumed to carry it. If a single weight rests at any other point of the span, it will be distributed by the bracing between the straight and curved members of the stiffening truss. Obviously the most unbalanced loading will occur when one half of the span is covered with moving load. In that case the bow- string stiffening truss in either half of Fig. 44 wih make the re- FlG. 46. quired distribution and prevent the parabolic tension member from changing its form. The type of bracing shown in Fig. 45 possesses some advan- tages of a peculiar nature. Each curved lower chord of the stiffening truss corresponds to the position of the perfectly flexi- ble cable with the moving load covering that half of the span which belongs to the greatest sag of the cable. The two para- bolic cables thus cross each other in a symmetrical manner at the centre of the span. If the moving load covers the entire span, the line of resistance or centre line of imaginary cable will be the parabola, shown by the broken line midway along each crescent stiffening truss. The diagonal bracing placed between the cables is so distributed and applied as to maintain the posi- tions of cables under all conditions of loading. The mode of constructing the stiffening truss between two DIVISION OF LOAD. 173 cables, shown in Fig. 46, is that adopted by Mr. G. Lindenthal in his design for a proposed stiffened suspension bridge across the Hudson Ri\'er with a si)an of about 3000 feet. The two cables are parabolic in curvature and may be either concentric or parallel. This system of stiffening bracing possesses some advantages of unifdrmity and is well placed to secure eflicicnt results. The same system has been used in suspension Ijridges of short span by ilr. Lindenthal at both St. Louis and Pittsljurgh. The stiffening bracing produces practieallv a continuous stiffening truss from one tower to the other, whereas the systems shown in Figs. 44 and 45 inA'oh-c practically a joint at the centre of the span. In all these three types of A-ertical stiffness the floor is designed to meet only the exigencies of local loading, being connected with the stift'ening truss above by suspension bars or rods, prefer- ably of stiff' section. When stiffening trusses are placed along the line of the floor, as in the case of the two East River bridges, to which reference has already been made, those trusses need not necessarily be of uniform depth, and they may be continuous from tower to tower or jointed at the centre, like those of the New York and Brooklyn suspension bridge. This centre joint detracts a little from the stiff'ness of the structure, but in a proper design this is not serious. 136. Division of Load between Cables and Stiffening Truss. — In a case where continuous stiffening trusses are employed it is obvious that they may carry some portion of the moving load as ordinary trusses. The portion so carried wih be that which is required to make the deflection of the stiffening truss equal to that of the cable added to the stretch of the suspension-rods. In the old thcorv of the stiffening truss constructed along the floor of the bridge this efl'eet was ignored, and the computations for the stresses in tliose trusses were made by the aid of equations of statical equilibrium only. That assumption, that the cable carried the entire load, was necessary to remove the ambiguity which would otherwise exist. In modern suspension-bridge design those trusses may be assumed continuous from toAver to tower with their ends anchored at the towers, or they may be 174 BRIDGES. designed to be carried continuously through portions of the land spans and held at their extremities by struts reaching down to anchorages, so that those ends may never rise nor fall, but move horizontally if required. If there are no pin-joints in the trusses at the centre and ends of the main span, equations of statical equilibrium are not sufficient to enable the reactions under the trusses and the horizontal component of cable tension to be found. One of the best methods of procedure for such cases is that of least work, in which the horizontal component of cable ten- sion is so found that the total work performed in the elastic deflection of the stiffening trusses, suspension-rods, cables, and towers is a minimum. After having found this horizontal com- ponent of the cable tension and the reactions under the stiffening trusses, the stresses in all the members of the entire structure can be at once determined. It is obvious that the stiffening truss and the cables must deilect together. It is equally CAddent that the deeper the stiffening trusses are the more load will be required to deflect them to any given amount, and hence that the deeper the}'' are the more load they will carry independently of the cable. It is desirable to throw as much of the duty of carrying loads upon the cables as possible. It therefore follows that the stiffening trusses should be made as shallow as the proper discharge of their stiffening duties will permit. 137. Stresses in Cables and Moments and Shears in Trusses. — The necessary limits of this discussion will not permit even the simplest analyses to be given. It is evident, however, that the greatest cable stresses will exist at the tops of the towers, and that if the horizontal component of cable tension be found by any proper method, the stress at any other point will be equal to that horizontal component multiplied by the secant of cable inclination to a horizontal line, it being supposed that the sus- penders are found in a A-ertical plane. If the stiffening trusses are jointed at the centre of the main span, as well as at the ends, the simple equations of statical equilibrium are sufficient in number to make all computations, for the reason that the centre pin-joint gives the additional con- dition that, whatever may be the amount or distribution of loading, the centre moment must be zero. If / is the length of STRESSES IX CABLES AXD MOMEXTS IX TRUSSES. 175 main or centre span and p the moving load per linear font of span, and if the stiffening trusses run from tower to tower, the follow- ing equations will give their greatest moments and shears both by the old and new theory of the stiffening truss. /=lo,icl per lin. ft., /=k-iii,'th of span in ft., Old Ihcory. New tlieory. Max. moment.. . . .1/ =0.01856/'/- .1/ =0.01652/^/- ) no centre Max. shear 5= Ipl S = lpl ) hmge. With centre hinge J/ =-0.01883/7/- and 5 = i/?/ The details of the theory of stift'ening trusses for suspension bridges have been well developed during the past few years and are fully exhibited in modern engineering literature. The long spans requiring stiff'ened suspension bridges are usually found over navigable streams, and hence those bridges must be placed at comparatively high elevations. This is illustrated by the clear height of 135 feet required under the East rii\'er suspension- bridge structures already completed and in progress. Further- more, the heights of towers above the lowest points of the cables usually run from one eighth to one twelfth of the span. These features expose the entire structure to comparati\-ely high wind pressures, which must be carefully provided against. This is done by the requisite lateral bracing between the stiffening trusses and bv Avhat is called the cradling of the cables. The latter expression simply means that the cables as they are built are swung out of a vertical plane and toward the axis of the structure, being held in that position by suitable details. The cables on opposite sides of the bridge are thus moved in toward each other so as to produce increased stability against lateral movement. Occasionally horizontal cables are stretched be- tween the tOAvers in parabolic curves in order to resist horizontal pressures, just as the main cables carry vertical loads. This matter of stabihty against lateral wind pressures requires and receives the same degree of careful consideration in design as that accorded to the eff'ects of vertical loading. The same gen- eral observation applies also to the design of the towers. 138. Thermal Stresses and Moments in Stiffened Suspension Bridges.— All material used in engineering structures expands 176 BRIDGES. and contracts with rising and falling temperatures to such an extent that the resulting motions must be provided for in struc- tures of considerable magnitude. In ordinary truss-bridges one end is supported upon roUers, so that as the span changes its length the truss ends move the required amount upon the rollers. In the case of stiffened suspension bridges, however, the ends of the cables at the anchorages are rigidly fixed, so that any adjust- ment required by change of temperature must be consistent with the change of length of cable between the anchorages. The backstays, Avhich are those portions of the cables extending from the anchorages to the tops of the towers, expand and contract precisely as do the portions of the cable between the tops of the towers. As the cables lengthen, therefore, the sag or rise at the centre of the main span will be due to the change in the entire length of cable from anchorage to anchorage. In order to meet this condition it is usual to support the cables at the tops of the towers on seats called saddles which rest upon rollers, so as to afford any motion that may be required. Designs have been made in which the cables are fixed to the tops of steel towers. In such cases changes of temperature would subject the towers to considerable bending which would be provided for in the design. The rise and fall at the centres of long spans of stift'ened sus- pension bridges is considerable; indeed, for a variation of 120° Fahr. the centre of the New York and Brooklyn Bridge changes its elevation by 4.6 feet if the saddles are free to move, as intended. In the case of a stiffened suspension bridge designed to cross the North River at New York City with a main span of 3200 feet a variation of 120° Fahr. in temperature would produce a change of elevation of the centre of the span of 6.36 feet. Such thermal motions in the structure obviously will produce stresses of con- siderable magnitude in various parts of the stiffening trusses, all of which are invariably recognized and provided for in good design. 139. Formation of the Cables. — \t the present time suspen- sion-bridge cables are made by grouping together in one cylindrical mass a large number oi so-called strands or individual small cables, each composed of a large number of parallel wires about one sixth of an inch in diameter. The four cables of the New York ECONOMICAL LIMIT.^ OF SPAXS. 177 and Br(_)(.klyn Bridge arc each composed of 19 strands, each of the latter containing 3,:;2 parallel wires, making a total of 6308 wires, the caldes themsel\x\s being 15 J- inches m diameter. The wire is No. 7 gauge, i.e., o.iS inch in diameter. In the new East River Bridge each of the four cables is iS} inches m diameter and contains 37 strands, each strand being composed of 208 wires all laid parallel to each other, t>r a total of 7696 wires. The size of the wire is No. 6 (Roebling) gauge, i.e., 0.192 inch in diam- eter. These strands are formed by laying wire by wire, each in its pro]ier place. The strands are then liound tr)gether into a single cable, around which is tiglitly wound a sheathing or casing of smaller wire, 0.134 inch in diameter for the New York and Brookhai Bridge. The tightness of this Ijinding \\'ire insures the unity of the wh< )le cable, each wire having been placed in its origi- nal position so as to take a tension equal to that of each of the other wires. The suspensi(in-rods are usually of ^^'ire cables and are attached by suitable details to the lower chords of the stiffen- ing truss, also by specially designed clamps to the cable. The stiffening trusses are usually built with all riveted joints, so as to secure the greatest possible stiffness from end to end. The stiffenetl suspension bridge has been sho\^'n by experience, as well as by theory, to be well adapted to carry railroad traffic over long spans. 140. Economical Limits of Spans. — In the past, suspension bridges have, in a number of cases, been built for comparatively short spans, but it is \\'ell recognized among engineers that their economical use must be found for spans of comparativeh' great lengtJi. While definite lower limits cannot now be assigned to such spans, it is probable that with present materials of con- struction and Avith aA'ailable shop and mill capacities the ordi- nary' truss-bridge may be economically used up to spans approxi- mateh' 700 to Soo feet, and that aboA'C that limit the cantilever system is economicallv applicable to lengths of span not yet determined but probabh' between 1600 and 2000 feet. The special field of economical employment of tlie long-span stiffened suspension bridge Avill be found at the upper limit of the canti- lever svstem. S(T far as present investigations indicate, the stiffened suspension type of stiaicture may be emploA'cd to 178 BRIDGES. advantage from about 1800 feet up to the maximum practicable length of span not yet assignable, but perhaps in the vicinity of 4000 feet. Obviously such limits are approximate only and may be pushed upward by further improvements in the produc- tion of material and in the enlargement of both shop and mill capacity. PART III. IVATER-IVORKS FOR CITIES AhlD TOWNS. CHAPTER XIV. 141. Introductory. — A preceding lecture in this course has shown to what an advanced state the pubhc supply of water to large cities was developed in ancient times. The old Romans, Greeks, Egyptians, and other ancient peoples evidently posesssed an adequate appreciation of the value of eflicient systems of public water-supply. Very curiously that appreciation dimin- ished so greatly as almost to disappear during the middle ages. The demoralization of public spirit and the decrease of national power which followed the fall of Rome induced, in their turn, among other things, a neglect of the works of the great water system of Rome, entailing their partial destruction. The same retrogression in civilization seemed to affect other ancient nations as well, until probably the lowest state of the use of public waters and the construction of public water systems was reached some- where between a.d. 1000 and a.d. 1300 or 1400. Without reasonable doubt the terrible epidemics or plagues of the middle ages can be charged to the absence of suitable water-supphes and affiliated consequences. During that middle period of the absence of scientific knowledge and any apparent desire to ac- quire it, sanitary works and consequently sanitary conditions of life were absolutely neglected. No progress whatever was made toward reaching those conditions so imperative in large centres of population for the well-being of the community. Grossly polluted waters were constantly used for public and private sup- plies, and no efforts whatever were made among the masses 179 180 WATEn-WORKS FOR CITIES AND TOWNS. toward the suitable disposition of refuse matters or, in a word, to attain to sanitary conditions of living. A few important works were completed, particularly in Spain, but nothing indicati^-e of general relief from the depths of igno- rance and sanitary demoralization to which the greater portion of the civilized world had sunk at that time. The city of Paris took all its water from the Seine, except that which was supplied by a small aqueduct built in 1183. So small was the supply, aside from the water obtained from the river, that in 1550 it is estimated that the former amounted to about one quart only per head of population per day. The situation in London was equally bad, for it was only in the first half of the thirteenth century that spring-water was brought to the city by means of lead pipes and masonry conduits. Public water-works began to be constructed in Germany on a small scale in the early part of the fifteenth centur3^ Obviously no pumps were available in those early days of water-supply, so that the small systems which have been mentioned were of the gravity class; that is, the water flowed naturally in open or closed channels from its sources to the points of consumption. Pumps of a simple and crude type first began to be used at a point on the old London Bridge in 1582, and in Hanover in 1527. Subsequently to those dates other pumps were set up on London Bridge, and installa- tions of the same class of machinery were made in Paris in 1608, usually operated by water-power in some simple manner, as by the force of the water-currents. In 1624 the Paris supply re- ceived a reinforcement of 200,000 gallons per day by the comple- tion of the aqueduct Arcueil. The New River Companv was incorporated in 16 iq for the partial supply of the city of I..ondon, and it began to lay its pipes at that time. As its name indicates, it took its supply fro'n New River, and the inception of its busi- ness is believed to mark the first application of the principle of supplying each house with water. This company is still in exist- ence and furnishes a considerable portion of the present London supply. 142. First Steam-pumps. — The application of steam to the creation or dc\-elopment of power by Watt, near the end of the eighteenth century, stimulated greatly the construction of water- ir.l TAVi'-.S rPPLF OF PARIS A XT) IJ).\'Dl)\'. 181 works, CIS it offered a very convenient and economical system of pumping. It seems probable that the first steam-pumps were used in London in 1761. Twenty years later a steam-pump was erected in Paris, while anotlier A\-as installed in 1 783. The second steam-pump in Lond(.)n was prijbably constructed in 1787. In all these earlier instances of the use of steam-pumps river supplies were naturally used. 143. Water-supply of Paris and London. — After the early employment nf steam ]5umping-machinerv demonstrated its great efficienc}- for public water-supplies, the extension of the latter became more rapid, and since 1800 the supplies of the two great cities of London and Paris ha\X' been greatly increased. As late as i8()o the Paris supplv amounted to about 65 gallons per head of population, one fourth of which was used as pr)table, being drawn from syirings, while three fourths, drawn from rivers, was used for street-cleaning or other pul)hc purposes. This sup- ply, howcA'cr, was found inadequate and was re-enforced in 1892 bv an addition of 30,000,000 gallons per (h\\ of ])otable water brought to the citv by an aqueduct 63 miles long. Another addition of about 15,000,000 gallons has been provided more recently. Rather curiouslv the water-supply of London is afforded by eight private companies, one of whicli is the old Ncav River Companv alreadv mentioned. These companies, with one excep- tion, draw their supply mainly from the rivers Thames and Lea, all such water being filtered. The remaining company draws its water from deep wells dri\-en into the chalk. The total popu- lation supplied amounts to about 5,500,000, the rate of supply being thus less than 45 gallons per head per dav. 144. Early Water-pipes. — Inasmuch as tlic use of east iron for pipes Avas onh' liegun about the year iSoo, other materials were used prior to that date. As is well kn(nvn, the pipes used in ancient water-works were either of lead or earthenware. In the eighteenth centurv wooden ]iipes made of logs Avith their cen- tres bored out Avere used, sometimes 6 or 7 inches m diameter. As many lines of these log pipes Avere used as needed to conduct a single' line of supplv. In the earlier portion of the nineteenth centtiry such log pipes, usually of pine or spruce, were used by 182 WATEIi-WORK,':S FOR CITIES AND TOWNS. the old Manhattan Company for the supply of New York City. A section of such a wooden pipe, with a bore of about 2 J inches is preserved in the museum of the Department of Ci^'il Engineer- ing of Columbia University. Large quantities of such pipes were formerly used. 145. Earliest Water-supplies in the United States. — The earli- est system of public water-supply in this country was completed for the citv of Boston m 1652. This was a gravity system. It is believed that the first pumping-machinery for such a supply was set up for the town of Bethlehem, Pa., and put in operation in 1754. Subsequently water-supplies were completed for Provi- dence, R. I., 1772, and for Morristown, N. J., in 1791 ; the latter has maintained a continuous existence since that date. The first use of steam pumping-machinery in this country was in Philadelphia in 1800. This machinery, curiously enough, was largely of wood, including some portions of the boiler; it was necessarily very crude and would perform with 100 pounds of coal only about one twenty-fifth or one thirtieth of what may be expected from first-class pumping-machinery at the present time. Other cities and towns soon began to follow the lead of these earlier municipalities in the construction of public water- supplies, but the principal development in this class of public works has taken place since about 1850. It is estimated that the total population supplied in 1880 was about 12,000,000, which rose to about 23,000,000 in 1890, and it is probably not less than 50,000,000 at the present time. 146. Quality and Uses of Public Water-supply. — Advances in the public supplies in this country have been made rather in the line of quantity than quality. Insufficient attention has been given both to the quality of the original supply and to the char- acter of the reservoirs in which it is gathered until within possibly the past decade. A few cities like Boston have scrutinized with care both the quality of the water and the character of the bot- tom and banks of reservoirs, and have spared neither means nor expense to acquire a high degree of excehence in their potable water. The same obserA-ations can be applied to a fcAV other large cities, but to a few only. The realization of the dependence of public health upon the character of water-supplv, however, AMOLWr OF PL BLIV ]VArKR-,SLPPLY. 183 has been rapidly extending, and it aa'iII doulitless be but a shurt time before the care exereisei.l in enlleeting and jireparing water for public use aviII lie as great in this cnuntrA'as in Europe, where few large cities rmnt the hltratii m i if ]3ul die ^\•aters. The distriljutiiin (^f water sup]:died fur public use is not limited ,to domestic purposes, althcmgh that class of consum])tion con- trols public health so far as it is affected by the consumptifjii t)f water. The a]:>plications r>f water to such public puiposes as street-cleaning and the extinguishing of fires are of the greatest importance and must receiA-e most careful consideration. Again, the so-called sA'stem of water-carriage in the disposal of domestic and manufacturing wastes, ci instituting the field of sewage-dis- posal, depends wholly u]ion the efficiency of the Wciter-supply. 147. Amount of Public Water-supply. — The first cjuestion confronting an engineer in the design of puljlic water-supply is the amount which should be jirovided, usually stated on the basis of an estimated quantity per head of population. This is not in all cases completely rational, but it is by far the best basis available. If the water-supply is designed for a small city or town previously supplied by wells or other individual sources, the first vear's consumption will be low per head of population for the reason that many people wih retain their own sources instead of taking a share of the public supply. As time elapses that portion of population decreases quite rapidly in numbers, and in a C(^mparativelv few years practically the \\-hole population will use the public supply. In communities, therefore, where public systems have long existed and it is desired either to add to the old su]-iplv or to install new ones, the only safe basis of estimate is the entire population. 148. Increase of Daily Consumption and the Division of that Consumption.— The amount of Avater required per liead of popu- lation might naturally be assumed identical with the past con- sumption, but that Avould frequently be incorrect. It is one of the most prominent features (^f the histrirA' of puldic Avater-sup- plies in this cixintrv that the consumpti. .n per head of i^opulation has increased Avith great rapiditv from the earlv years of the installation of the dift'ercnt sA'stems, for reasons bcth legitimate 184 WATER-WORKS FOR CITIES AXD TOWXS. and illegitimate. The daily aA'erage consumption of water from the Cochituate AVorks of the Boston supply increased from 42 gallons per head of population in 1850 to 107 gallons in 1893, and in the ilystic Works of the same supply the increase was from 27 gallons in 1865 to 89 gallons in 1894. Again, the daily average consumption in Chicago rose from 43 gallons per head per day in i860 to 147 gallons in 1893, while in Philadelphia during the same period the increase was from 36 gallons per head per day to 150 gallons. In Cambridge, ilass., the increase in daily average consumption per head of population was from 44 gallons in 1870 to 70 gallons in 1894. These instances are sufficient to show that, under existing conditions, the daily con- sumption Avas increased at a rapid rate in the cities named, and they have been selected as fairly representative of the whole field. Civil engineers have made extended studies in connec- tion with this question in a great number of cities, for it bears upon one of the most important lines of public works. It is absolutely essential to the health and business prosperity of every city that the water-supply should be abundant, safe, and adapted to the industrial and commercial pursuits of its popula- tion. It is imperative, therefore, that the division of the daily supply should be carefully analyzed. For this purpose the water-supply of a city may be, and frequently is, divided into four parts: (i) That used for domestic purposes; (2) That used for commercial and industrial purposes; (3) That used for public purposes ; (4) That part of the supply which is wasted. I. That portion of the supply consumed for domestic pur- poses includes not only the AA-ater used in priA'ate residences, but in those branches of consumption Avhich maA' be considered of a household character foimd in hotels, clubs, stores, markets, laundries, and stables, or for any other residential service. As might be expected, this branch of consumption A-aries largely from one city to another. The results of one of the most inter- esting and suggestiA-e studies CA-er made in connection Avith this subject are given by Mr. Dexter Brackett, M. Am. Soc. C. E., in IXCREASE OF DAILY COXSUMPTION. 185 the Transactions of the American Society of ViyH Engineers for i8()5. In Boston the purely domestic consumption A-aried in different houses and ajxirtmcnts from 59 gallons per head per day in costly a])artmcnts down to 16.6 gallons jier head per day in the poorest ekiss of ajx-irtment. In Brookline, one of the finest suburbs of Boston, the c^uantit)' Avas 44.3 gallons per day. In some other cities of Massachusetts, as Newton, Fall Ri\'er, and Worcester, tliis class of consumjjtion \-aried from 6.6 gallons to 26.5 gallons per day, the latter quantity being found at Newtr)n in some oi the best residences, and the former at houses alsci in Xewton ha\'ing but one faucet each. In ^'on- kers, N, Y., where the system was metered, the amount was 21.4 galk)ns per head of population per daA', while in portions of London, England, it varied from 18.6 to 25.5 gallons per head per da)'. The average of these figures gives a residt of 18.2 gallons per head jier day, which, in round numbers, maA' be put at 20 gallons. 2. It is obAaous that the rate of consumption for commercial and industrial purposes in any city must A'ary far more than that for domestic purpioses, for the reason that some cities may be essentialK' residential in character while others may be essen- tially manufacturing. At the same time, it is to be remembered that many manufacturing establishments may haA'c their own AA'ater-supph'. The city of I'all River, Mass., is eminently a manufacturing cit\-, A'ct Mr. Brackett found tlx-it the manufac- turinc^ demand on the jxiblic water-sup])ly amcumted to 2 gallons onlv per inhabitant per day, as the mamifaeturers draAv the most of their supply from the riA'cr, but that where the manufacturers depend upon the public supply for all their Avater the amount rises to a value betAveen 20 and 30 gallons per inhabitant. In B(^ston in 1892 the Avater consumed for all manufacturing and industrial purposes, including railroads, gas-Avorks, elcA-ators, brcAveries, etc., amounted to 9.24 gallons per head of popula- tion per day, Avhile in "i'onkers in 1897 the total consumption for commercial purposes was 27.4 gafions per head per day. In the city of Ncav York, as nearly as can be estimated, the consump- tion for commercial purposes is probably not far from 25 gallons 186 ^YATER-^YORKS FOR CITIES AND TOWNS. per inhabitant per day. Reviewing all these results, it may be stated that the water consumption for commercial and indus- trial purposes will generally range from lo to 30 gallons per inhabitant per day. 3. The consumption of water for public purposes is a smaller amount than either of the two preceding. It covers such uses as public buildings, schools, street-sprinkling, sewer-flushing, fountains, fires, and other miscellaneous objects, more or less similar to those just named. The total use of this character was 3.7s gallons per inhabitant per day for Boston -in 1892, and 5.57 gallons per inhabitant per day for Fall River in 1899. A few other cities give the following results: Minneapolis in 1897, 5 gallons; Indianapolis, 3 gallons; Rochester, N. Y., 3 gallons; Newton, Mass., 4 gallons; Madison, Wis., 10 gallons. In Paris it is estimated that not far from 2.5 gallons per head of population per day are used. It is probable, therefore, that an amount of 5 gallons per day per inhabitant will cover this partic- ular line of consumption. 4. K substantial portion of the water-supply of every city fails to serve any useful purpose, for the reason that it runs to waste either by intention or by neglect. The sources of this waste are defective plumbing, including leaky faucets and cocks ; deliberate omission to close faucets and cocks, constituting wilful waste; defective or broken mains, including leaky joints; and waste to prevent freezing. 149. Waste of Public Water. — All these wastes except the last are inexcusable. There is no difficulty in detecting defective plumbing, and its existence is generally known to the householder ; but if the wasted water is not measured and paid for, it is far too frequently considered more economical to continue the Avaste than to pay for the plumber's services. In a multitude of cases cocks are left open indefinitely for all sorts of insignificant reasons ; in closets, under the erroneous impression that the continuous running of the stream will materially aid in a more effective cleansmg of soil- and sewer-pipes, failing completely to appre- ciate that a far more powerful stream is required for that purpose ; sometimes in sinks, for refrigerating purposes, and in many other ]VASTE OF PriSLIC MATER. 187 inexcusably wrotig ways. These sources of wilful waste lead to large losses and constitute one of tlie most tmsatisfactorv phases of admmistration of a jmblie water SA'stem, Such Idsses result in a \-ieious waste of pulilic monev. The amount of Avater flow- ing iron\ leak)' joints and from leaks in ])ipes and mains is neces- sarily indeterminate because it escapes without eA-idenee at the stu-face except in rare cases. In every instance where exanhna- tions have licen made and a careful record kept of the amount of water supplied to a city, it lias been found that tlic aggregate of the measured amounts consumed fail nearly t" equal the ti ital supply. There are probable ermrs both in the measurement of the quantities supplied and in the quantities consumed, but the large discrepancy cannot be aecnunted fur in this manner. In many cases consumed water has excn been carefully measured by meters, as at Yonkers, New York, NcAvton, Milton, and Fall River, ilass., i\Iadison, Wis., and at other places, but yet the discrepancy appears to be nearly as wide as ever. Again, in 1893 observations were carefully made on the consumption of the water received by the I\Iystic supply of the Boston system at all hours of the twenty-four. t)bviously between i and 4 .a..m. the useful consumption should be nearly nothing, but, on the contrary, it was fotmd to be nearly 60 per cent of the average hourly consumption for the entire twenty -four hours. The waste at Buffalo, N. Y., in 1894 was estimated at 70 per cent of the total supply. Similar obserA'ations in other places have given practically the same results. It has also been found that, in a number of instances, where old watercourses have been completely obliterated by considerable depths of filling required by the adopted grades of city streets and lots, and excavations for buildings have subsequently been opened practically the full volume of the former streams are flowing along the original but filled channel. This result has been observed under a prac- tically impervious paved city surface. It is difticult to imagme the source of such a supply except from defective pipe systems or sewers. A flow of a least 100,000 gallons per day from a broken pipe Avhich found its Avay info a scAver has also been dis- coA-ered AA'ithout surface evidence. These and many other results of experience eonelusiA-ely demonstrate that much Avater 188 WATER-WOBKS FOR CITIES AXD TOWXS. flows to waste unobserved from leaky joints and defective or broken pipes. Inasmuch as cast-iron water-pipes are produced in lengths which net 12 feet as laid, there will be at least 440 joints per mile. Furthermore, as leaky joints and broken pipes are as likely to occur at one place as another, it seems reasonable to estimate leakage through them as proportionate to the length of the pipe- line in a system; and that conventional law is frequently as- sumed. New pipe-lines have sometimes shown a leakage of 500 t(i 1200 gallons per mile of line per day. Civil engineers have sometimes specified the maximum permissible leakage of a new pipe-line at 60 to 80 gallons per mile of line per day for each inch in diameter of pipe, thus permitting 600 to 800 gallons to escape from a lo-inch pipe. In 1888 the late ilr. Chas. B. Brush reported a leakage of about 6400 gaUons per mile per day from a practically new 24-inch cast-iron main, 11 miles long, of the Hackensack Water Company, the pressure being no pounds per square inch. Tests of water-pipes in German and Dutch cities have been reported as showing less waste than 300 gallons per mile per day, but such low results, unless for A-ery low pres- sures and short lines, ma)-' reasonably be doubted. Obviously losses of this character will probably increase with the age of the pipe. By a verv ingenious procedure based upon his own experience, ilr. Emil Kuichling of Rochester, N. Y,, reaches the conclusion that a reasonable allowance for the waste from leaky joints and defective pipes is 2500 to 3000 gallons per mile of cast-iron pipe-line per day. If, as is frequently the case, the population per mile of pipe ranges from 300 to 1000, the preced- ing allowance amounts to 3 to 10 gallons per head of population per day. The loss or waste due to running cocks or faucets to prevent freezing cannot be estimated with sufficient accuracv to receive a definite valuation, but it must be considered an ele- ment of the total item of waste. 150. Analysis of Reasonable Daily Supply per Head of Popula- tion. — It has repeatedly been found that the losses or wastes set forth in the preceding statements amount apparentlv to quanti- ties varying from 30 to 50 per cent of the total supplv; or, to put it a little differentlv, the water unaccounted for in even the best ACTUAL DAILY CONSUMPTION IN AMKUICAN CITIES. 189 systems now constructed a]-)parently may reach one third to one half of the total sujiply. This is an exceedingly wasteful and unbusinesslike showing. It is pr(ibal)le that tlie statement is, to some extent at least, an exaggeratii m. It is practically certain that cither the amount sup)plied or the amounts consumed, or both, are ne\-er measured witli the greatest accuracy, and that the errors are such as generally swell the ap]3arent quantity wasted. After making judicious use of the data thus alTorded by experience, it is probalde that tlie following tabular state- ment given liy Messrs. Turncaure and Russell represents limits within Avhich sin >uld be found the daily a\'erage su]iply of water in a well-C(.>nstructetl and well-administered system. Use. Gallnns pur Ika.l in - Day. Minimum. AveraRe. Maximum. 3 15 -S 20 4° 3 5 10 30 Industrial and oimmcrcial.. Pul ilic Waste Total 3S 7 5 J 15 The A'alues given in the preceding table are reasonable and sufficient to supply the legitimate needs of any community, but, as will be shown in the succeeding table, there are cities in this countr}' whose aA'erage consumption is more than twice the maximum rate given above. 151. Actual Daily Consumption in Cities of the United States. — The foUowing table exiiibits the average dail>- consumption of water throughout the entire year for the cities given, as deter- mined for the years indicated in the table. The city of Ikiffalo sh(-)ws a daily consumption of 271 gallons per inhabitant, and Alleglieny, Pa., 247 gahons per inhabitant. There are a considerable number showing an average daily con- sumption per inhabitant of 160 gallons (ir more. All such high aA-crages exhibit extravagant use of water, or otherwise ineffi- cient ''administration (-)f the water-supph-. The reduction of such high rates of consumi^tion is one r)f the most difficult prof)- lems confronting tlie administration of public W(-irks. The use 190 WATER-WOBKS FOR CITIES AND TOWXS. TABLE I. Popula- Population. tifjn per Tap. iRoo. Per Cent (jf Taps Metered 1890. New York i Chicago I Philadelphia Brooklyn St. Louis Boston Cincinnati San Francisco Cle\-eland Buffalo New Orleans Washington Montreal Detroit Milwaukee Toronto Minneapolis Louisville Rochester St. Paul Providence Indianapolis Allegheny Columbus Worcester Toledo Lowell Nashville Fall River Atlanta Memphis Quebec Dayton, O. . . Camden, N.J Des Moines, la Ottawa, Ont Yonkers, N. Y Newton, Mass Madison, Wis. . . Albany, N. Y New Bedford, Mass . Springfield, Mass. . . . Holjroke, Mass ; ,099,850 [ ,046,964 838.547 451.770 44S.477 305.891 298,997 270.055 255,664 242,039 230,392 216,000 205,876 204,468 iSi ,000 164.738 161 ,129 133.896 133.156 132,146 105,436 105.287 88.1 50 84.655 81,434 77,696 76,168 74.398 65.533 64.495 63,000 61,220 58.313 50.093 44,000 32.033 24.379 13.426 98. 000 55.000 49.299 40,000 13-9 20 2 7-1 2 5 6.1 3 8.7 2 5 II. 8 8 2 6.6 5 8.5 4 I 9-9 41 4 8.7 5 8 6.3 2 54-0 4 6-5 3 5-3 I 7 5-1 2 I II . I 31 9 4.0 4 I 16.5 6 3 II. 9 5 9 5-4 II 4 12.7 4 2 9.4 62 4 35-6 7 6 70 11-5 6 4 8.9 89 4 18.6 9 4 9.2 22 9 14.9 8 14.9 74 6 20 . 89 6 II. 9 3 7 10.4 20 .0 3 8 20 .0 60 4- 2 12.0 82 4 5 ■ 5 67 4 II . 31 4 79 140 132 72 72 80 112 61 103 186 37 158 67 161 no 100 75 74 66 60 48 71 238 78 59 72 66 146 29 36 124 160 47 131 55 130 68 40 40 162 99 87 77 c .t^ rt Per Cent ■.;:.^0 of Taps ? S Metered ' 5 ^ >" 27.0 100 2.8 139 0.74 162 1-9 89 7-4 98 5.2 100 6.5 35 28.0 63 4.5 142 . 85 271 35 I - 5 200 1.6 8^ 8.2 152 510 lOI 3-7 100 16.0 88 6.6 97 18.0 71 1-7 60 74.0 57 7-1 74 7.1 247 9-3 127 90.0 66 35-° 70 33.0 82 24.0 139 82.0 35 99 -o 42 4.6 100 170 24.0 50 200 42.6 43 200 99 • 8 100 77-3 65 6i . 52 12.3 15-4 319 5.82 1900. 115 190 229 III 143 12 1 73 175 262 48 174 156 84 93 83 51 54 79 183 67 59 83 140 35 61 98 62 185 48 76 62 44 192 lOI 88 103* ' Estimated. of the meter has proved most efficient in prcA'enting Avastes or other extravagant consumption, as in that case e\'ery consumer pays a prescribed rate for the amount which he takes.' ACTUAL DAILY COXSUMPTION IN FOREIGN CITIES. 191 152. Actual Daily Consumption in Foreign Cities. — It has been for a long time a well-rec(_)gnized fact that the daily use of water in American municipalities is far greater per inhabitant than in Etn-opean cities. It is difficult to explain the marked TABLE II. City. Estimated PMiiulati-.n. C' insumT'ti"r^ per Capita Dailv, Gallons. England, 1806-07:* Londini Manchester Liverpciol Birmingham Bradford Leeds Shettield Nottingham Brighton Plymouth Germanv, iSoo (Lueger) : Berlin. Breslau Cologne Dresden Diisseldorf Stuttgart Dortmund "Wiesbaden France, 1892 (Beehmann) : Paris Marseilles Lyons Bordeaux Toulouse Nantes Rouen Brest Grenoble Other countries, 1S92-96 (Beehmann): Naples Rome Florence Venice Zurich Geneva Amsterdam Rotterdam Brussels Vienna St. Petersburg Bombay Sidney Buenos Ayres .700,000 849,093 790,000 680, J 40 436,260 420,000 4 1 ^ ,000 272,781 i6q,ooo 98,575 [,427,200 330,000 2S1 ,700 276,500 144,600 139,800 89,700 62 ,000 2 ,500,000 406,0 10 401 ,930 252,654 148,220 125 ,000 107,000 70,778 60,855 48 1 ,500 437.410 I 02 ,000 I 30,000 80,000 70,000 :^ I 5,000 240.000 480,500 1 ,36 ^ ,000 960,000 SlO,000 423,600 680,000 42 40 ,i4 28 3' 4,? 2 L 24 4,1 5'» 18 25 26 58 26 264 264 2 I 1 1 60 61 20 5 3 20 20 40 61 38 34 * Compiled, excev cept the figures for London, by Hazen. Enginccrxni X-a'S. iSgo, xl.. p. 193 WATER-WORKS FOR CITIES AND TOWNS. difference, but it is probably due in large part to the more extrav- agant general habits of the American people. Examinations in a number of cases have shown that the actual domestic use of water, at least in some of the American cities, is not very- different from that found in corresponding foreign cities. Table II exhibits the consumption of water in European cities, as compiled from various sources and given liy Turneaure and Russell. These foreign averages, with three exceptions, represent reasonable quantities of water used, and they have been con- firmed as reasonable by many special investigations made in this country. 153. Variations in Rate of Daily Consumption. — The preced- ing observations are all based upon an average total consumption found by dividing the total annual consumption by the number of days in the year. This is obviously sufficient in a determination of the total supply needed, but it is not sufficient in those matters which involve a rate of supply during the different hours of the day, or the amount of the supply for the summer months as com- pared with those of the winter. As a general rule the greatest supply will be required during the hot summer months when lawn- and street-sprinkling is most active. It appears from observations made in a considerable number of the large cities of the United States that the maximum monthly average con- sumption may run from about no to nearly 140 per cent of the monthlv average throughout the year. As an approximate value only, it may be assumed for ordinary purposes that the maximum monthly demand will be 125 per cent of the average. The daily rate taken throughout the year is considerably more variable than the monthly. There are days in some por- tions of the year when consumption by hotels and industrial activities is at a minimum. On the other hand, there are other days when those activities are at a maximum and the total draft will be correspondingly high. Experience has shown that the maximum total draft may vary from about 115 to nearly 200 per cent of the average. It is permissible, therefore, to take approximately for general purposes the maximum total daily con- sumption as 150 per cent of the average. Manifestly any total SUPPLY OF FIHE-STREAMS. 11)3 consumption will have an hourly rate which may vary greatly from the early morning hours, when the draft should be almost nothing, to the forenoon hours on certain days of the week, when the dratt is a maximunv These \-ariations have frcrpentlv been investigated, and it has been shown that the maximum rate per hour of a maximum da>- ma\- sometimes rise higher than ^^oo per cent of the average himrly rate for the year. These consid- erations oln-iously attain their greatest imp(-)rtance m connection with the ca]Xicity of the ])lant, cither power or gravitv, from which the cit\' directly dra\\-s its supply. The hourh' ca])acity of the pumps rk, although instances of that kind nf waste have been found. It is an old wastage kni i-wn as far fjack in time as tlic ancient d-loman \\-ater-supid)'. Tlie second and third items ])rol:)al)ly constitute the f)ulk of tlie wastage in this eitv. 156. Division of Daily Consumption in the City of New York. — In tlie ceuirsc of his scarcli for tlic A'arious sources of consump- tion, Mr. I'Veeman concluded from liis examinations and from the use of the \'arious means placed at his command for measur- ing the daily consumjition between December 2d and December 5th, i8qq, and December 8th and December 15th, i8()q, that the average daily consumption could be divided as follows: Oallons per Inhabitant ])cr I)a\'. Probable average amount really used. ... 40 Assumed incurable waste "'° ' '-c Curable waste, probably 65 ^ ' Daily uniform rate oi deli\'ery by Croton Aqueduct 115 In his investigations Mr. Freeman had the elevation of water in the Central Park reserA'oir carefully observed every six min- utes throughout the twenty-four hours. At the same time the uniform flow through the new Croton Aqueduct was known as accuratelv as the flow through such a conduit can be gauged at the present time. Knowing, therefore, the concurrent variation 01 volume in the Central Park reservoir supplied by the new Croton Aqueduct and the rate of flow in that aqueduct, the con- sumption of water per twent\'-four hours would be known A\'ith the same degree of accuracy with which the flow m the aqueduct is measured^ It was found by these means that the actual con- sumption lietween the hours of 2 and 4 a.m. was at the rate of 04 gallons per inhabitant per day, although the actual use at that time was as near zero as it is possible to apiiroach during the Avh.-.le tAventy-four hours. Nearly all of that rate of con- sumpti(in represents waste. Summing up tlic whole matter in the light of his investiga- tions Mr. Freeman made the folk;wing as his nearest estimate 198 WATER-WORKS FOR CITIES AXD TOWXS. to the actual consumption of the dailj^ supply of water of New York City : Gallons per In- ACTUAL use: habitant per Day. Domestic (ax'erage) 12 -20 Manufacturing and commercial 20 -30 City buildings, etc 2 -4 Fires, street flushing and sprinkling 0,4- o . 7 Total 34 -55 I.N'CURAHLE WASTE (probabilities): Leaks in mains 1—2 Leaks in old and abandoned service-pipes 1-2 Poor plumbing, all taps metered and closely inspected 2-3 Careless and wilful wastes 1-2 Under-registry of meters i- i Total incurable waste and under-registry 6-10 Minimum use and waste 40-65 Needless waste: Leaks in street-mains (a guess) 15-10 Leaks in service-pipes between houses and street-mains (a guess) 15-10 Defective plumbing (a guess) 25-15 Careless and wilful opening of cocks (a guess) i 7-14 To prevent freezing in winter and for cooling in summer 3-1 Total needless waste 75-50 Total consumption 115-115 157. Daily Domestic Consumption. — The quantity assigned in the preceding statement to domestic use is confirmed by the abundant experience in other cities where services are carefully metered, as in Fall River, Lawrence, and Worcester, Mass., and in Woonsocket, R. I., where measurements by meters show that the domestic consumption has A-aried from 11 .2 to 16,3 gallons per inhabitant per day. Furthermore, annual reports of the former Department of Public A¥orks and the present Depart- ment of Water-supply for the City of New York show that during the years 1890 to i8g8 such meters as have been used in the territory sujiplied by the Croton and the Bronx aqueducts indicate a daily consumption varying from 13.8 to 24.2 gallons per inhabitant per day. The same character of confirmatory evidence can be applied to the quantities assigned to manufac- turing and commercial uses, city buildings and fires, street flushing and sprinkling. IXCURABLE AXD CURABLE WASTES. 199 158. Incurable and Curable "Wastes. — TIk- items cr>mposing incurable waste, unfortunately, cannot Ix- so definitely treated. It is perfectly well known, however, amont,^ ci\'il engineers, that a large amount of leakage takes place fmm curporation C(^cks, which are those inserted in the street-mains to form the connec- tion between the latter and the house scr\-ice-pipes. Again, many of these ser\'ice-pi]ies are abandoned and insufficiently closed, or not closed at all, leaving constantly lomning streams whose continuous subsurface discharges esca]ie detection and frequently find their Avay into sewers. AVater-]:npcs which have been laid many vears frccjucntlv become so deeplv corroded as to aft'rird man^• leaks and sometimes cracks. Doubtless there are nianv portions of a great distributing system, like that in Xew York Citv, which need replacing and afford many large leaks, V)ut uncliscoN'erable from the surface. Many lead ioints of street- mains also become leaky with age, while others are leaky when first laid in spite of insjiection during construction. Just how much these items of waste w(juld aggregate it is impossible accu- rately to state, but from careful observations made in other places 5 to 10 gallons per clav ]ier head of population seems reasonable. A three-vear-old east-iron fire-protection pipe 5.57 miles long and mainlv 16 inches in diameter, under an average pressure of 114 pounds per square inch, was tested in Providence in iqoo and showetl a leakage at lead joints eriod equal to a half-hour; usuallv it lasts but a few minutes onlv. In this country an a\'erage rate of i inch ]3er hour, extending throughout one hour, is phenomenal, althr)ugh that rare amount is sometimes exceeded. A maximum rate of about 4 inches per hour, lasting 15 to ^^o minutes, is, roughly speaking, about as high as any precipitation of which we have reliable records. The wasteways or other provisions for the discharge of surpilus or flood waters of the Metropolitan Water- supph' of Boston are designetl to aft'ord relief for a total ]ire- cipitation of 6 inches in twent>--four hours. It is safe to state that an excess of that accommodation will probably never be required. 165. Extent of Heavy Rain-storms.— In ah engineering ques- tions necessitating the consideration of these great rain-storms it is necessarv to remember that their extent is frequentlv much o-reater than' the areas of watersheds usuahy contemplated m connection with water-supplv work. The late Mr. James B. Francis f.nmd in the great storm of October, i86q, which had its maximum intensitv in Connecticut, that the area over which inches or more of rain fell exceeded 24.000 square nnles, and that the area over which a depth of 10 inches or more fell was ^ I Q miles. Again, in the Xew England storm of February, 208 WATER-WORKS FOR CITIES AND TOWNS. 1886, 6 inches or more of rain fell over an area of at least 3000 square miles. Storm records show that as much as 8 or 10 inches in depth have fallen oA'er areas ranging from 1800 to 500 square miles, respectively, in a single storm. 166. Provision for Low Rainfall Years. — The capacity of any public water-supply must evidently be sufficient to meet not only the general exigencies of the year of lowest rainfall, but also the conditions resulting from the driest periods of that year. It is customary among civil engineers to consider months as the smaller units of a dry year. It is necessary, there- fore, to examine not only the annual rainfalls but the monthly rates of precipitation during critical years, i.e., usually during dry years. It is impossible to determine absolutely the year of least rain- fall which may be expected, but evidently the longer the period over which observations have extended the nearer that end will be attained. It is sometimes assumed that the lowest annual rainfall likely to be expected in a long period of years is 80 per cent of the average annual rainfall for the same period. Or, it is sometimes assumed that the average rainfall for the lowest two or three consecutive years will be 80 per cent of the average for the entire period, and that the year of minimum rainfall may be expected to yield two thirds of the annual average precipi- tation. Such features will necessarily vary with the location TABLE VI. Mean Monthly Rainfall, Inches. Respective Ratios. Probable Depth in Inches of Actual Rainfall. Januar}' February March April 4 X 1.65 = 6.6 4 X I • 50 = 6.0 4 X 1.65 = 6.6 May lune July August September October November December 4 4 ) 4 ^ 4 ; 4 ) 4 ^ 4 / 4 ; < -85 < -75 = < -35 < .25 < .30 < -45 = < 1.20 < 1.60 3 4 3-° 1.4 I . 1.2 I .8 = 4.S = 6.4 AVAILABLE PORTION OF RAINFALL 209 of the district considered. Conclusions Avliich may be true for the New England or northern Atlantic States probabty will not hold for the south Atlantic and Gulf States. Data for such conclusions must be obtained from the rainfall cif the locality considered. Table A'l exhibits the comparative monthly rain- fall which J. T. Fanning suggests may be used approximately for the average Atlantic coast districts. If the average monthly rainfall throughout the year were one inch, the values of the ratios would show the actual monthly precipitation. In general the table would be used bv di\-iding the total yearty rainfall by 12, and then multiplying that monthly average by the proper ratio taken from the table opposite the month required. Such tables should only be used for approx- imate purposes and when actual rainfall records are not available for the district considered. 167. Available Portion of Rainfall or Run-off of Watersheds. — If the public Avater-supply is to be drawn from a stream where the desired rainfall records exist, it is necessary to knoAv what portion of the rainfall, either in the driest or in other years, may be available. This is one of the departments of the hydraulics of streams for which much data yet remain to be secured. The watersheds or areas drained by some streams, like the Sudbury River of the Boston, and the Croton of the New York water- supply, liaA^e, however, been studied with sufficient care to give reliable data. The amount of ^A-ater floAving in a stream from anv watershed for a given period, as a year, is called the annual "run-off" of the watershed, and it is usually expressed as a certain percentage of the total ramfall on the area drained. For certain purposes it is sometimes more conA-enient to express the run-off from the AA-atershed as the number of cubic feet of AA'ater per second per square mile of area. Table \ II, taken from Tumeaure and Russell, exhibits run-oft" data for a consider- able number of streams in connection AA'ith both average and minimum rainfalls. The information to be draAAm from this table is sufficient to giA-e clear and general relations betvA-een the recorded precipita- tion and run-oft". The percentage of run-oft" is seen to A-ary quite widely, but as a rule it is materialh' less for the year of minimum 210 WATER-WOEKS FOR CITIES AND TOWNS. TABLE VII, STATISTICS OF THE FLOW OF STREAMS, Stream. Area Drained, Si luare Miles. Average Yearl>', Year uf Minimum Fluw. Rain, Inches. Sudliur\' Cochituate Mystic Connecticut Croton Upper Hudson. . . Genesee Passaic Upper Mississijipi iS.Sy 26.9 4.5°o 1 ,060 S22 IS75-97 IS63-96 IS7S-96 1871-85 IS70-94 IS88-96 IS94— 96 IS77-93 I8S5-99 Flow, ' Per ■ Rain, Inches. Cent. Inches. 08I20 79! I 9 69125 3Si24 70 -3 36 82 12 9.S 08 2.1 44 5 7 4 90 1 22 48 96 45 25 56 6 32.78 2 31.20 6 31.22 5 40 . 02 8 38.52 o 33-49 5 31.00 ° 35-64|i5 4 22.86 Flow, Per Inches. Cent. I 19 9 76 9 32 8 25 4 .S4 7 46 6 67 .S 23 I 62 34.1 31 -3 29.8 45' 37 .6 .8 ^1-5 12.7 71 Stream. Area Drained, S'.iuare Miles, Yea Average for December ' Avera.i^e frir June to to May. ! NovemVjer. Rain, ' Flow, Per | Rain, Flow Inches. Inches. Cent, ilnches.llnche Per Cent. Sudbur)'. . . . Cochituatc. . . M>-stic Cotmecticitt. . Croton Upper Hudson Genesee Passaic iS. 26, 10,234 33^ 4.500 1 ,060 S22 1875-97 22.9S17.52 76.0 1S63-96 122.97 14.87 64. 7 1878— 96 22 . 1 1 15 . 12 68.4 1871-85 20.1317.95 89.1 1870-94 '23.39:17.81 76.1 1S88— 96 |i8 . 20 16 . 23 89.0 1S94— 96 19 . 58 10 . 20 52.2 ^'^77~93 |22.47 18.22; 81. I 22 . 61 1 24.10 21 .66: 56: 99 5°' 24 39 70 20 46 2 2 84 22 30 20 76 - 7 13 33 7 5 13 19 29 flow than for the aA'crage year. That feature of the table is an expression of tlie general law, other things being equal, that the smaller the precipitation the less will be the percentage of run-oft". A number of influences act to produce that result. During a year of great precipitation the earth is more nearly saturated the greater part of the time, and hence when rain falls less of it will |")crcolate into the ground and more of it will run off. Again, if the ground is absolutely dry, a certain amount of rain would ha\x' tn fall before any run-off Avould take place. The area and shape ()f a watershed Avill also aftect to some extent the fl(.)w of the stream which drains it, A larger mn-off would reasonably be expected from a long narrow Avatershed than from one more nearh' circular in outline. The greater the massing of the water- RUX-OFF OF SUDBURY WATJiRSIIKD. 211 shed, so to sjieak, tlic more opportunity there is for the water to be held by the ground and the less would be the run-(.)ff. TABLE vin. AVERAGE YIELD OF SUDBUR\- WATERSHED, 1.S75-LS99, IN'CLUSIVE, VARKJUSLY EXPRESSED. (Area <.>r watursin -Miiari; miles.) A Square Mil Cubie Feet. i>er Seeiind. Million Gallnns per Day. Cnllceteil, Inelies Per Cent Oilleete.l. J;inuar\' I i . 037 1,252 >\'bru;iry ' 2 . 004 , i . 87 7 March I 4 . 4S1) I 2.001 April I ,^.124 2 . o i() May 1 , OSo ■ 1 . 086 Ji->"c 7,:i5 I .475 .Uily 305 .107 iVugnst 47S I , 30C) September 37(1 I , 243 October iS2(; . 536 Nu\-einber I i .474 -9,^1 December I 1,612 i , 042 Year 1.055 1,070 ,■! .050 .S ■ ' 7 5 ,1 48,'; 1 ,930 ,821 ■ 5 5 i ,410 . (156 I .645 I .S50 .48 2 51,6 71 ,7 117,4 107 . 5 58.1 28,0 1 ,1 ■ o 21.0 ,1') -o 5 I - Total, Inehes, 4 . ,1 ?, 4.20 4 41 ,1- -4 ,V3,3 2.03 ,5-77 4,16 ,."1 - 3 4.37 4.22 168. Run-off of Sudbury Watershed. — Table \'III has lieen given h\ IMr, Charles \\\ Sherman, as representing the average 3-ield of the Sudbury watershed for the jieriod 1S75 to 1899, inelusive, ex]iressed in several different waA'S, The average rainfall was 45. 8^ inehes, and the percentage whieh represents the run-off is 49,1 per eent of the total. The average monthly run-off \-aries from .305 eubie foot (for Juh') tn 4.489 eubie feet (for March) ])er second jier square mile. As a general rule it may be stated that the a\'erage run-oif fr( >m the drainage areas of New England streams amounts A'ery closely to 1,000,000 gal- lons ]"ier square mile ]X'r (ka-. The area of the Sudl.iury water- shed IS 75.2 square miles, with 6.3 per cent of that total area i-iccu]iied h\ the surface of lakes or reservoirs. As will ]iresently be seen, the amcnint of expensed water surface m any watershed has an appreciable influence \\\vm its run-off, 169. Run-off of Croton Watershed. — The total area of the Croton watershed, from which Xew York City draAvs its supiTy, 213 WATER-WORKS FOR CITIES A\D TOWNS. i.e., the area up-stream from the new Croton Dam, is 360.4 square miles, of which 16,1 square miles, or 4.47 per cent, of its total area is water surface. Mr. John R. Freeman found in the investigations covered by his report to the comptroller of the city of New York in 1900 that the average annual rainfall on that area for the thirty-two years beginning 1868 and ending 1899 was 48.07 inches, and that the average run-off for the same period was 47.7 per cent of the total average rainfall, equivalent to a depth of inches. AqiiL-ducts near Jerome Park Reservnir, New York City. Table IX gives the main elements of the rainfall and run-off for the Croton watershed during the thirty-two year period, for the averages just given. The table shows that the least annual rainfall was 36.92 inches for 1880, and that the run-off represented a depth of 12.63 inches only, or 34.21 per cent of the total annual precipitation. EVAPORATIOX Fh'OM RESERVOIRS. 213 TABLE IX. RAINFALL ON CROTON WATERSHED IN TOTAL INCHES— 1.SH8-1898. NATURAL FLOW OF CROTON RIVER AT OLD CROTON DAM, IN EQUIVALENT INCHES, PERCENTAGE OF RUN-OFF TO RAINFALL FOR EACH YEAR. Year. Tutal Rainfall. Total Run-nff Per Cent. Year. Total Rainfall. Total Run-off. Per Cent. lS6S 5° 03 3 3 ■ 3 3 66.22 1885 43 67 17.71 40. 55 iStig 4S 3" 23.61 48. 8 2 1SS6 47 74 20 1 42 10 1870 44 63 19.20 4302 1887 57 29 26 61 46 4 5 I 87 I 48 1)4 I q . 46 39.76 1888 60 6() 35 27 58 12 1872 40 74 1 6 . Q 2 41 .53 1889 5 5 70 31 39 56 36 1S73 43 ^^7 25.02 57 03 1890 54 °5 2 5 1)5 48 1 1S74 4^ 37 25.10 59 -M 1891 47 20 23 4S 49 7 5 1S75 43 b6 24.77 56.73 1892 44 28 17 68 39 93 1S76 40 68 2 I . 09 5 I . S4 1893 54 «7 29 05 52 94 1877 48 23 20.22 41 .02 1S94 47 3 ^ 20 56 43 44 1S7S 5 5 70 27.17 48. 78 189s 40 58 15 95 39 3 I 1871; 47 04 19.65 41 .77 1S96 45 85 23 26 so 73 1S80 36 0- 12 .63 34.21 1S97 53 1 2 2 5 59 48 17 18S1 46 60 I Q . 2 5 41 .23 1898 5 7 40 29 7-' 51 77 1 88 2 52 35 24 . 28 46.38 1899 44 67 22 28 49 SS iS8,? 1884 42 51 70 28 13.3 3 24.08 31 .22 46 . 96 Average for ,ij years 4S 07 2 2 93 47 70 As a rule the same feature of a low percentage < )f run-off will be found belonging to the years of low rainfall, although there are many irregularities in the results. On the other hand, the high percentages of run-otf are for the years 1868, 1888, and 1889, and they will generally be found belonging to years of relatively great precipitation. A low percentage of run-off will also be Lnver if the year to ^^'hich it beL.mgs folk"n\'s a dry year or a dry cycle of two or three years. Similarly the high percentages of run-off win, as a rule, be higher if they follow years of high precipitation ; that is, if they belong to a cycle of relati^■el^' great rainfall. 170. Evaporation from Reservoirs. — If it is contemplated to build reservoirs on a watershed the cajxicity of which is being estimated on the basis of either the driest year or the driest two- or three-year cycle, it is necessary to make a deduction from the rainfall for the evaporation which will take place from the sur- face of the proposed reservoir. In order that that deduction may be made as a proper allowance for added water surface in a drain- age area, it is necessary that the amount of evaporation be deter- rnined for the district considered. The rate (.^f evaporation is dependent upon the area of water surface, upon the wind, and upon the temperature both of the water and air abo^•elt. Numerous 214 WATER-^yORKS FOR CITIES AND TOWNS. evaporation observations have been made both in this and other countries, and extensive evaporation tables have been prepared by the Weather Bureau, from which a reasonable estimate of the mtjnthh" evaporation for all months in the year may be made for almost any point in the United States. I-^articularly available Aqueduct Division Wall of Jerume Park Reservoir, New York City. observations have been made bv Mr. Desmond Fitzgerald of Boston on the Chestnut Hill reservoirs of the Boston AVater- supply, and by Mr. Emil Kuichling, engineer of the Rochester Water-works, on tlie Alount Hope reservoir of the Rochester supply. Table X exhibits the results of the observations of both these ci\'il engineers. As would be anticipated, the period from ]\Iay to September, both inclusive, shows by far the greatest evaporation of the whole year, while December, January, and Februarv arc the months of least evaporation. The total annual evaporation at Boston was 39.2 inches and 34.54 inches at I^ochester. EVAPORATION FROM THE EARTH'S SURFACE. 215 TABLE X^ MEAN MONiTHLY EVAPORATION'S. Chestnut Hill RcsLTVoir, B..stMn. Mass. Evapi itatii m, Iiuhcs. Per Cent of Yearly Eva]M iratiim Mdunt Hmik- R(.scT\'oir, Rnchustrr, N. V. Evarii iratiiin, Inches. Pur Cunt of Vuarlv EN-aiH .ration. JanuarN' Fcln-nar\- March .' AiM-il May Jxinc July Avtgiist Sejitcmbcr October N(i\-cnibcr December Tcital for year Mean temperature O . 1)6 54 Q.S .i6 7.6 II .4 14. J 15.2 14.0 10,4 S . I 0.52 ° ,^4 4 1)4 .S -47 .^ ■ .-io 415 .1 ■ I '-' 1.4,^ I ■ M 48°. 6 A reference to data of the AA'eather Bureau will sIkiw that annual ex'ajioration as high as 100 inches, or e\-en more, may be expected on the jdateaux of Arizona and Xew Mexico. ( )ther portions of the arid country in the Avestern part of the United States Avill intlicate annual CA'aporations rrnming anyA\-]iere from so to go inches ]ier A'car, Avhile on the north Pacific coast it will fall as low as iS to 40 inches. 171. Evaporation from the Earth's Surface. — Data are lack- ing for anything like a reasonably accurate estimate of evapiora- tion from the earth's surface. It is Avell known that the loss of water from tliat source is considerable in soils like those of swamps, ]iarticularlv when exposed to the warm sun, but no reliable estimate can be obtained for the exact amount. Xor is this necessarA- ior the usual AA-ater-supph- problems, since it is included in the dift'erence betAA-een the total rainfall of any district and the .ibseiwed rtm-off m the streams. Indeed evapo- rati(^n from reservoirs is similarly included for reserA-oirs existing when the run-off obserA'ations are made. CHAPTER XVI. 172. Application of Fitzgerald's Results to the Croton Water- shed. — The evaporation data determined by Messrs. Fitzgerald and Kuicliling are sufficient for all ordinary purposes in the North Atlantic States. In the discussion of the capacity of the Croton watershed Mr. Fitzgerald's results will be taken, as the conditions of the Croton watershed in respect to temperature and atmosphere are affected by the proximity to the ocean, and other features of the case make it more nearly like the Metropoli- tan drainage area near Boston than the more elevated inland district near Rochester. If the monthly amounts of evaporation be taken from the preceding table, and if it further be observed that a volume of water i square mile in area and i inch thick contains 17,377,536 gallons, the following table (Table XI) of amounts of evapora- tion from the reservoirs in the Croton watershed, including the new Croton Lake, will result, since the total area of water surface of all these reservoirs is 16. i square miles. FABLE XI Tan. 06 X 16 .1X1 7.377.S,36 = 268.600,000 gallons Feb. I 05 X X = 2Q3.,Soo,ooo Mar. I 70/ ■ ' X = 475,700,000 Apri 2 97 X ' ' X = 831 ,000,000 May 4 46 X ' ' X ^ T ,247 ,QOO.OOO Tunc s .';4X ' ' X ' = I .5 50,100,000 Tuly 5 <)S >- ' ' X = I ,675,200.000 Au?. 5 50 X ' ' X = T ,558.000.000 Sept. 4 r2X ' ' X = 1 .1 52 ,Soo,ooo Oct. 3 16 X ' X = 88.;, 200, 000 No^^ 2 25 X ' X = 620.600.000 Dec. T 51 ^ ' ' X = 42 2, ^00.000 ,39 20 Total = 10,968.300.000 216 THE CAPACITY OF THE CROTON WATERSHED. 217 It will be seen from this table that the total annual evaporation from all the reservoir surfaces of the Croton watershed, as it will exist when the new Croton Lake is completed, will be nearly 11,000,000,000 gallons, enough to supply the boroughs of Bronx and Manhattan at the present rate of consumption for about forty days. 173. The Capacity of the Croton Watershed. — The use of the preceding figures and numbers can be well illustrated by con- sidering the capacity of the Croton watershed in its relations to the present water needs of the boroughs of Bronx and Man- hattan which that watershed is designed to supply. The total area of the Croton watershed is 360.4 square miles, of which 16. i square miles, as has already been observed, is water surface. As a matter of fact the run-oft' observations from that watershed have been maintained or computed for the thirty-two-year period from 1868 to 1899, inclusi\'e, covering the evaporation from the reservoirs and lake surfaces as they have existed during that period. The later obserA-ations, therefore, include the eft'ects of evaporation from the more lately constructed reservoirs, but none of these data cover evaporation from the entire surface of the new Croton Lake, Avhose excess over that of the old reservoir is nearly one third of the total water surface of the entire shed. As a margin of safetA* and for the purpose of simplification, sepa- rate allowance will be made for the evaporation from all the reservoir and lake surfaces of the entire watershed as it will exist on the completion of the new Croton Lake, as a deduction from the run-oft'. The preceding table (Table XI) exhibits those deductions for evaporation as they will be made in the next table. In Table IX the year 1880 yields the lowest run-oft' of the entire thirtv-two-year period. The total precipitation was 36.92 inches, and onlv 34.21 per cent of it was available as run-oft'. The first column in Table XII gives the amount of monthly rain- fall for the entire year, the sum of which aggregates 36.92 inches. Each of these monthty quantities multiplied by .3421 will give the amount of rainfall aA'ailable for run-off, and the latter quan- titv multiplied by the number of square miles in the watershed (360.4) win show the total depth of available Avater concentrated 218 ^YATER^VORKS FOR CITIES AND TOWNS. Upon a single square mile. If the latter quantity- be multiplied bv 1 7, ^78,000, the tutal number of gallons available for the entire month will result, fnjm which must be subtracted the evaporation for the same m(_>nth. Carrying out these operations for each month in the year, the monthly available quantities for water- supply will be found, as shown in the last column. TABLE XII. t2 I =1.173) X 360.4"/ 17,378.000 (Tan. 3.43 (Feb. 3 (Mar. 3 (April 3 (May I (lune I (July 5 (Aug. 4 (Sept. 2 (Oct. 2 (Nov. 2 (Dec. 2 40 X 90 X 57 X 04 ,< .40 X S6 :< 16 X 42 X .S3X 52 X iQX = 1.163) X ' X = 1.334) X ■ X = 1.221) X ■ X = .3^6) X ' X = .479) X ' X = 2.005) X ■ X = 1.4^3) X ■ X = .828) X ■ X = .068) X ■ X = .794) X = .886) X X — 268,600,000= 7,077,700,000 — 293,800,000= 6,989,900,000 — 475,700,000= 7,879,000,000 — 831,000,000= 6,816,000,000 — 1,247,900.000= 982,000,000 — 1,550,100,000= 1,449,800.000 — 1,673,200.000 =10.890,000,000 — 1,3 38. () 00, 000 = 7, 3 7 3, 100, 000 — 1,152,800,000= 4,032,900,000 — 884,200.000= 5,178.500.000 — 629,600.000= 4,343,100.000 — 422,300.000= 5,126.300.000 .56.92 The sum of the twelve monthly available quantities will give the total number of gallons per year applicable to meeting the water demands of the boroughs of Bronx and Manhattan. 174. Necessary Storage for New York Supply to Compensate for Deficiency.— At the present time the average daily consump- tion per inhabitant of those two boroughs is 115 gallons, and if the total population be taken at 2,200,000, the total daily con- sumption will be 2,200 000X115=253,000,000 gallons. If the latter quantitv be multiplied by 30.5, the latter being taken as the average number of days in the month throughout the year, the average monthly draft of water for the two boroughs in ques- tion will be 7,716,500,000 gallons. The subtracticm of the latter quantity from the monthly results in the preceding table will exhibit a deficiency which must be met by storage or a surplus available for storage. Table XIII exhibits the twelve monthly differences of that character. It is seen from this table that the total monthly deficiencies aggregate 27,705,700,000 gallons and that there are onlv two months in Avhich the run-off exceeds the consumption, the sur- plus for those tAvo months being only 3,336,000,000 gallons. XECESSARY STORAGE EOR XEW YORK SUPPLY. .'lO TABLE XIII, 7,077.700,000 — 7,71(1,500,000= — 03,S,Soo,ooo 6,nSc).goo,000 — ■■ = — 720,000,000 7,870.000.000— " = + 162,500.000 6.S10.000.000 — ■' = — 000,500,000 982.000,000— " = — 6,754,500.000 1, 441). 800, 000 — " = — 0,200,700,000 10. 800. 000. 000 — " = +3,173.500.000 7 -."i 7,-i ,' 00,000 — " — — 34,3.400,000 4.032.1100.000- " = — 3,08,3,000,000 5,178.500.000- " = — 2 . 53.s,ooo.ooo 4.343,100,000— " = — 3,373,400,000 5 .1 20.300.000 — " = — 2. 5gO,200,000 — 2 7, 7 05, 700, 000 +3,,3,30,OOO.OOO + 3.3,^0.000.000 — 24,450 ,700,000 The total deficiency for the year is tlicrefore 24,439,700,000 gallons. l)i\-iding the latter t}uantit\- ]>y the aA'crage daily draft of 253.000,000 gallons, there A\ill result a periiod cif q-j days, (.ir more than one quarter cif a year, during whicli the minimum annual rainfall would fail t(T sujiply any water to the city at all. These results sho\\' that in case of a 1(ia\- rainfall A'car, like that of iSSo, the precipitation u]"iiin the t'ruton Avatcrshed wijuld supply sufficient water for the Imrnughs 1 if I'jronx and ]\lanhattan at the present rate of eonsumiitiim for tiiree fourths of the A'car only. .V (.listressingh- serious water famine would result unlcb"s the year A\'ere begun by sufficient ayailable storage in the rescr- A'oirs of the basin at least ecjual to 24,430,700,000 gallons. Should such a loAy rainfall year or one nearly approaching it be one of a two- or three-year low rainfall cycle, such a reser^-e storage would be impossible and the resulting conditions lyould be most serious for the citA'. If an a^-erage year, fur which the total rainfall would fie about 48 inches preceded such a year of low rainfall, the conditions would be less serious. The figures would stand as follows: Total itm-i ifi' = I 7.077.5:^6 X ,:;6o , 4 X 22 , 93 - 17,377,3,^6 X 16 I X 30 , 2 = 132,640,000,000 galli;ins. Total annual consumption = o:!.,i45.ooo,ooo Ayailable for storage = 40. -"Q5. 00°. 000 Deficiency '". = 24,439,700,000 Surplus = 13,833,300,000 2e0 WATEB-WORKS FOR. CITIES AND TOWNS. The average year would, therefore, yield enough run-off water if stored to more than make up the deficiency of the least rainfall year by nearly 16,000,000,000 gallons. In order to secure the desired volume it would therefore be necessary to have storage capacity at least equal to 24,459,700,000 gallons; indeed, in order to meet all the exigencies of a public water-supply it would be necessary to have far more than that amount. As a matter of fact there are in the Croton watershed seven artificial reser- voirs with a total storage capacity of nearly 41,000,000,000 gal- lons, besides a number of small ponds in addition to the new Croton Lake which with water surface at the masonry crest of the dam has a total additional storage capacity of 23,700,000,000 gallons. The storage capacity of the new Croton Lake may be increased by the use of flash-boards 4 feet high placed along its crest, so that with its water surface at grade 200 its total capacity will be increased to 26,500,000,000 gallons. After the new Croton reservoir is in use the total storage capacity of all the reservoirs and ponds in the Croton watershed will be raised to 70,245,000,000 gallons, which can be further augmented by the Jerome Park reservoir when completed by an amount equal to 1,900,000,000 gallons. This is equivalent, at the present rate of consumption, to a storage supply for 285 days for the boroughs of Manhattan and the Bronx. 175. No Exact Rule for Storage Capacity. — This question of the amount of storage capacity to be provided in connection with public water-supplies is one which cannot be reduced to an exact rule. Obviously if the continuous flow afforded from any source is always greater per day than any draft that can ever be made upon it, no storage -reservoirs at all would be needed, although they might be necessary for the purpose of sedimenta- tion. On the other hand, as in the case of New York City, if the demand upon the supply has reached its capacity or exceeded it for low rainfall years, it may be necessary to provide storage capacity sufficient to collect all the run -oft" of the watershed. The civil engineer must from his experience and from the data before him determine what capacity between those limits is to be secured. When the question of A'olume or capacity of storage is settled the mode of distribution of that volume or capacity THE COLOR OF WATER. 221 in reservoirs is to be determined, and tliat affects to some extent the potability of the water. If there is a large area of shallow storage, the vegetable matter of the soil may affect the water in a number of ways. Again, it is advisable in this connection to consider certain reservoir effects as to color and contained organic matter in general. 176. The Color of Water. — The potability* of water collected from any watershed is materially affected by its color. Although iron may produce a brownish tinge, by far the greater amount of color is produced by dissolved vegetable matter. Repeated examinations of colored water have shown that discoloration is in many cases at least a measure of the vegetable matter con- tained in it. AVhile this may not indicate that the water is materially unwholesome, it shows conclusive!}'' the existence of conditions which are usuall}.' producti\-e of minute lower forms of vegetation from which both bad taste and odors are likely to arise. There are two periods in the year of maximum intensity of * What is generalh' known as the "Michigan standard of tlie purity of drinking-^yater," as specified by the Micliigan State Laboratory of Hygiene, is here tjivcn: " I. The total residue should not exceed 500 parts per million. "2. The inorganic residue may constitute the total residue. "3, The smaller amount of organic residue the better the water, "4. The amount of earthy bases should not exceed 200 piarts per million. "5. The amount of sodium chloride should not exceed 20 piarts per million (i.e.. 'chlorine' 12.1 parts per million). "6. The amount of sulpihates should not exceed 100 parts per million. "7. The organic nratter in 1,000.000 parts of the water should not reduce more than S piarts of potassiimi permanganate (i.e., 'reijuired oxygen' 2,2 parts per million) . "S. The amount of free ammonia should not exceed 0,05 part per million, "g. The amount of albuminoid ammonia should not exceed 0.15 part per million. "10. The amount of nitric acid should not exceed 3,5 parts per million (i e,. 'N as nitrate' .9 p>art per million). "it. The best water contains no nitrous aeid. and any water which con- tains this substance in quantity suflicient to be estimated should not be re- garded as a safe drinking-water, "12. The water must contain no toxicogenic germs as demonstrated by tests upon animals, "The water must be clear and transparent, free from smell, and without either alkaline or acid taste, and not above 5 French standard of hardness." This standard is too high to be attained ordinarily in natural waters. 222 WATER-WORKS FOR CITIES AXD TOWNS. color, one occurring in June and the other in November. The former is due to the abundant drainage of peaty or other exces- sively vegetable soils from the spring rains. After June the sun bleaches the water to a material extent until the autumn, when the dying vegetation imparts more or less coloring to the water falling upon it. This last agency produces its maximum effect in the month of November. There are various arbitrary scales employed by which colors may be measured and discolored waters compared. Among others, dilute solutions of platinum and cobalt are used, in which the relative proportions of those substances are varied so as to resemble closely the colors of the water. The amount of plati- num used is a measure of the color, one unit of which corresponds to one part of the metal in 10,000 parts of water. Again, the depth at which a platinum wire i mm. (.039 inch) in diameter and I inch long can be seen in the water is also taken as a measure of the color, the amount of the latter being inversely as the depth. This method has found extended and satisfactory use in connec- tion with the Metropolitan Water-supply of Boston, the Cochi- tuate water having a degree of color represented by .25 to .30, while the Sudbury water has somewhat more than twice as much. The Cochituate water is practically colorless. The origin of the color of Avater is chiefly the swamps which drain into the water-supply, or the vegetation remaining upon a ncAv reservoir site when the surface soil has not been removed before the filling of the reservoir. The drainage of swamps should not, as a rule, be permitted to floAV into a public water- supply, as it is naturally heavily charged with vegetable matter and is correspondingly discolored. This matter, like many others connected with the sanitation of potable public waters, has been most carefully investigated by the State Board of Health of Massachusetts in connection with the Boston water-supply. Its work has shown the strong adA'isability of diverting the drainage of large swamps from a public supply as carrying too much vege- table matter e\'en when highly diluted by clear water conforming to desirable sanitary standards. 177. Stripping Reservoir Sites. — The question of stripping or cleaning reservoir sites of soil is also one which has been care- STRIPPIXG RESERVOIR SITES. 223 fully studied by the Alassachusctts State Board nf Health. As a consequence lar^-e amounts of monev ha\-c Ix-en expended by the city of B(jston in stripjiino- the soil from rescr\-oir sites to the average depth m some cases of g inches for wooded hind and 12.} inches for meadow land. This was done in the case of the Nashua River reservoir having a superficial area of 6.56 square miles at a cost of early $2,910,000, or about $700 per acre. It has been found that the beneficial eft'ect of this strijiiung is fullv secured if the black loLim in which vegetation flourishes is re- nio\-ed. W,ichu~etts Reservoir, showing Stripping of Soil. This stripping i^f soil is indicative of the great care taken to secure a high quality of water for the cit}' of B(^ston, fmt it is not done in the Crc;>t(^n watershed of the Xew Yi.irk su])ph'. It can- not be doubted tliat the cjualitv of the Croton su]ip]\- ^^•ould have been sensiblv enhanced b\' a similar treatment 1 if its reservoir sites. Mr. F. B. Stearns, chief engineer of the ]\Ietropolitan AVater-supplv of Boston, states that in some eases the eft'ects of filling reservoirs without remo\-ing the soil and \-egetable matter have ''continued for tA\'ent\' A'cars or more A\"ithout apparent diminution." On the other hand, water discolored bv vegetable 224 WATER-WORKS FOR CITIES AXD TOWNS. matter becomes bleached to some extent at least by standing in reservoirs whose sites have been stripped of soil. 178. Average Depth of Reservoirs should be as Great as Prac- ticable. — In the selection of reservoir locations those are prefer- able where the average depths will be greatest and where shallow margins are reduced to a minimum. It may sometimes be necessary to excaxate marginal portions which would otherwise be shallow Avith a full reservoir. There should be as little water as possible of a less low-water depth than 10 or 12 feet, otherwise there may be a tendency to aquatic vegetable growth. The following table exhibits the areas, average depths, capacity, and other features of a number of prominent storage -reservoirs. COMPARATIVE TABLE OF AREAS. DEPTHS, AND CAPACITIES OF STORAGE RESERVOIRS WITH HEIGHTS AND LENGTHS OF DAMS. Name and Location of Reservoir. Area. Average Square Depth, Miles. Feet. Ma.ximum Height .,f Dam. Above Ground. Abo^"e Rock, Length cif Dam, Feet. Capacity, Million Gallons. Swift River, Mass Nashua River, Mass Nira, near Poona, India Tansa, Bombay, India Khadakvasla, Poona, India . . New Croton. N. Y Elan and Claerwcn, Birming- ham, Eng., water-works (total for six reservoirs) . . . All Boston water-works reser- voirs combined Vyrnwy, Liverpool, Eng Ware River, Mass Sodom, N. Y Reservoir No. 5 , Boston water- works Titicus, N. Y Hobbs Brook, Cambridge water-works Cochituate, Boston water- works Reservoir No. 6, Boston water-works 36.96 6.56 7 ■ -5 5-5° 5-5° 2-, 34 5.S2 I -75 I .62 1.91 1 . GO 1-35 0.29 S3 46 27 33 32 43 14 8 25 144 129 100 127 100 i,S7 98-128 14-65 84 71 (>5 158 107 225 129 89 70 US 2,47° 1,250 3,000 8,770 5 ,080 .35° 7S5 500 ,865 1,500 406,000 63,068 41.143 37.5°'> 36,737 32,000 4,460 20,838 15,867 14,56a 1 1,190 9,500 7.43s 7,000 2.500 2,160 1,500 179. Overturn of Contents of Reservoirs Due to Seasonal Changes of Temperature. — It will be noticed that the average depth is less than about 20 feet in few cases only. If the water is OVERTURN OF CONTENTS OF RESERVOIRS. 225 deep, its mean temperature throughout the year will be lower than if shallow. During the warmer portion of the }'ear the upper layers of the water are ol)viously of a higher temperature than the lower portions, since the latter receive much less imme- diate effect from the sun's rays. ^Vs the upper portions of the water are of higher temjierature, they arc also lighter and hence remain at or near the to]i. Fur the same reason the water at the bottom oi the reser\-oir remains there throughout the warm season and until the coul weather of the autumn begins. The top layers < >f water then continue tc) fall in tem])craturc until it is lower than that of the ^A'ater at the bottom, ^^'hen the surface- water becomes the heaviest and sinks. It displaces subsurface- water lighter than itself, the latter coming to the surface to be cooled in turn. This operation produces a crunplete overturning of the entire reservoir A'olume as the late autumn or earh- winter approaches. It thus brings to the surface water which has lieen lying at the bottom of the reser\-oir all summer in contact Avith Avhat A'egetal )le matter ma\' ha\-c been there. The depleted oxvgen of the bottom water is thus rc])lenished Avith a corresponding better- ment of condition. It is the great sanitarv effort of nature to improA'C the qualitA' of stijred water entrusted to its care, and it continues until the surface is cooled to a temperature perh-aps loAver than that of the greatest density of Avater. Another great tum-OA'cr in the Avater of a lake (^ir reams in Crutrm Watershed, showing Slopes of Saturation. i8i. Gate-houses, and Pipe-lines in Embankments. — It is necessary to construct the requisite pipe-lines and conduits lead- ing from the storage -reserA'oirs to the points of consumption, and si.imetimes such lines bring the water to the reservoir. Wherever such pipes-line or conduits either enter or leave a reservoir gates and ^•alves must be proA'ided so as properly to control the ad- mission and outflow of the water. These gate-houses, as they are called, because they contain the gates or valves and such other appurtenances or details as are requisite for operation and maintenance, are usually built of substantial masonry. They are the special outward features of every reservoir construction, and their architecture should be characteristic and suitable to the functions which they perform. Where the pipes are carried through embankments it is necessary to use special precautions to prevent the water from flowing along their exterior surfaces. Many reservoirs haA'e been constructed under defective design in this respect, and their embankments have failed. Frequently 230 WATER-WORKS FOR CITIES AND TOWNS. small masonry walls are built around the pipes and imbedded in the bank, so as to form stops for any initial streams of water that might find their way along the pipe. In short, every care and resource known to the civil engineer must be employed in reservoir construction to make its bottom and its banks proof against leakage and to secure permanence and stability in every feature. 182. High Masonry Dams. — The greatest depths of water impounded in reserA'oirs are found usually where it is necessary to construct a high dam across the course of a river, as at the new Croton dam. In such cases it is not uncommon to require a dam over 75 to 100 feet high above the original bed of the river, which is usually constructed of masonry with foundations car- ried down to bed-rock in order to secure suitable stabilitv and prevent flow or leakage beneath the structure. It is necessary to secure that result not only along the foundation-bed of the dam, but around its ends, and special care is taken in those por- tions of the work. The new Croton dam is the highest masonry structure of its class yet built. The crest of its masonry oA'crflow-weir is 149 feet above the original riA'er-bed, with the extreme top of the masonry work of the remaining portion of the dam carried 14 feet higher. A depth of earth and rock excavation of 131 feet below the river-bed was necessary in order to secure a suitable foundation on bed-rock. The total maximum height, therefore, of the new Croton dam, from the lowest foundation-point to the extreme top, is 294 feet, and the depth of water at the up-stream face of the dam will be 136 feet when the overflow is just beginning, or 140 feet if 4 feet additional head be secured by the use of flash-boards. In the prosecution of this class of work it is necessary not only to reach bed-rock, but to remove all soft portions of it down to sound hard material, to clean out all crevices and fissures of sensible size, refillmg them with hydrauHc cement mortar or concrete, and to shape the exposed rock surfaces so as to make them at least approximately normal to the resultant loads upon them, to secure a complete and as nearly as possible water-tight bond with the superimposed masonry. If any streams or other small watercourses should HIGH MASONRY DAMS. 331 be encountered, they must either be stopped or led off where they will not affect the work, or, as is sometimes done, the water issuing from them may be carried safely through the masonry 9 £L£ 196 OV£HrLOW SECTION OF- AIEW CROTON DAM Cniss-sectiiiii ol New Ciotoii Dam. mass in small pipes. The object is to keep as much water out of the foundation-bed as possible, so as to eliminate upward pressure underneath the dam caused by the head of water m the subsequently full reservoir. It is a question how much dependence can be placed upon the exclusion of water from the foundation-bed. In the best class of work undoubtedly the bond can be good enough to exclude more or less water, but it is probably only safe and prudent so to design the dam as to be stable even though water be not fully excluded. The stability of the masonry dam must be secured both for the reservoir full and empt3^ 'With a full reservoir the hori- zontal pressure of water on the up-stream face tends to overturn 232 WATER-WORKS FOR CITIES AND TOWNS. the dam down-stream. When the water is entirely withdrawn the pressure under the up-stream edge of the foundation becomes much greater, so that safety and stabiHty under both extreme conditions must be assured. There are a number of systems of computation to which engineers resort in order to secure a design which shah certainly be stable under all conditions. That which is commonly emjjloyed in this country is based upon two funda- mental propositions, under one of which the pressure at any point in the entire masonry mass must not exceed a certain safe amount per square foot, while the other is of a more technical character, requiring that the centre of pressure shall, in every horizontal plane of the dam, approach nowhere nearer than one third the horizontal thickness of the masonry to one edge of it. A further condition is also prescribed which prevents any por- tion of the dam from slipping or sliding over that below it. As a matter of fact when the first two cijnditions are assured the third is usually fulfilled concurrently. Obviously there will be great advantage accruing to a dam if the entire mass of masonry is essentially monolithic. In order that that may be the case either concrete or rubble is usually employed for the great mass of the masonry structure, the exterior surfaces frequently being composed of a shell of cut stone, so as to provide a neat and taste- ful finish. This exterior skin or layer of cut masonry need not average more than i^ to 2-1- feet thick. The pressures prescribed fr)r safety in the construction of masonry dams vary from about 16,000 to 28,000 or 30,000 pounds per square foot. Sometimes, as in the masonry dams found in the Croton watershed, limits of 16,000 to 20,000 pounds per square foot are prescribed for the upper portions of the dams and a gradually increasing pressure up to 30,000 pounds per square foot in passing downward to the foundation-bed. There are reasons of a purety technical character why the prescribed safe working pressure must be taken less on the down-stream or front side of the dam than on the up-stream or rear face. The section of a masonry dam designed under the conditions outlined will secure stability through the weight of the structure alone, hence it is called a gravity section. In some cases the rock bed and sides of a raAdne in which the stream must be HIGH MASONRY DAMS. 233 dammed will permit a curved structure to be built, the curva- ture bemg so placed as to be convex up-stream or against the water pressure. In such a case the dam really becomes a hori- Foundation Masonry of New Croton Dam. zontal arch and, if the curvature is sufficiently sharp, it may be designed as an arch horizontally pressed. The cross-section then has much less thickness (and hence less area) than if de- signed on a straight line so as to produce a gravity section. A number of such dams have been built, and one ^'ery remarkable example of its kind is the Bear Valley dam in California ; it was built as a part of the irrigation system. CHAPTER XVII. 183. Gravity Supplies. — When investigation has shown that a sufficient quantity of water may be obtained for a required pubHc supply from any of the sources to which reference has been made, and that a sufficient storage capacity may be pro- vided to meet the exigencies of low rainfall years, it will be evi- dent if the water can be dehvered to the points of consumption by gravity, or whether pumping must be employed, or recourse be made to both agencies. If the elevation of the source of supply is sufficiently great to permit the water to flow by gravity either to storage -reser- voirs or to service-reservoirs and thence to the points of con- sumption, a proper pipe-line or conduit must be designed to afford a suitable channel. If the topography permits, a conduit may be laid which does not run fuh, but which has sufficient grade or slope to induce the water to flow in it as if it were an open channel. This is the character of such great closed masonry channels as the new and old Croton aqueducts of the New York water-supply and the Sudbury and Wachusetts aqueducts of the Boston supply. These conduits are of brick masonry backed with concrete carried sometimes on embankments and sometimes through rock tunnels. When they act like open chan- nels a very small slope is employed, 0.7 of a foot per mile being a ruling gradient for the new Croton aqueduct, and i foot per mile for the Sudbury. Where these conduits cross depressions and follow approximately the surface, or where they pass under rivers, their construction must be changed so that they will not only run full, but under greater or less pressure, as the case may be. 184. Masonry Conduits. — In general the conduits employed to bring water from the watersheds to reservoirs at or near places 234 MASONRY CONDUITS. 335 of consumption may be divided into two classes, masonry and metal, although timber-stave pipes of large diameter are much used in the western portion of the country. The masonry con- duits obviousty cannot be permitted to run full, meaning under pressure, for the reason that masonry is not adapted to resist the tension which would be created under the head or pressure of water induced in the full pipe. They must rather be so em- ployed as to permit the water to flow with its upper surface exposed to the atmosphere, although masonry conduits are always closed at the top. In other words, they must be per- mitted to rrni ]iartially full, the natural grade or slope of the water surface in them inducing the necessary velocity of flow or current. Evidently the velocity in such masonry conduits is comparatively small, seldom exceeding about 3 feet per second. The new and old Croton aqueducts, the Sudburv^ and Wachu- setts aqueducts of the Metropolitan Water-supply of Boston, are excellent types of such couA'cyors of water. They are some- times of circular shape, but more frequently of the horseshoe outline for the sides and top, with an inverted arch at the bottom for the purpose of some concentration of flow when a small amount of water is being discharged and for structural reasons. The interiors of these conduits are either constructed of brick or they may be of concrete or (ither masonry aft'ording smooth surfaces. In the latest construction Portland-cement concrete or that concrete reinforced with light rods of iron or steel is much used. Bricks, if employed, should be of good quality and laid accurately to the outline desired with about |-inch joints, so as to oft'er as smooth a surface as possible for the water to flow over. In special cases the interiors of these conduits may be finished with a smooth coating of Portland-cement mortar. If comluits are supported on embankments, great care must be exercised in constructing their foundation supports, since any sensible settlement would be likely to form cracks through which much water might easily escape. AA'hen carried through tunnels they are frequently made circular in outline. They must occasionahy be cleaned, especialh' in view of the fact that low orders of vege- table growths appear on their sides and so obstruct the free flow of water. 23d WATER-WORKS FOR CITIES AND TOWNS. 185. Metal Conduits. — Metal conduits have been much used within the past fifteen or twenty years. Among the most promi- nent of these are the Hemlock Lake aqueduct of the Rochester Water-works, and that of the East Jersey Water Company through which the water-supply of the city of Newark, N. J., flows. When these metal conduits or pipes equal 24 to 30 or more inches in diameter they are usually made of steel plates, the latter being of such thickness as is required to resist the pressure acting within them. The riveted sections of these pipes maj- be of cylindrical shape, each alternate section being sufficiently small in diameter just to enter the other alternate sections of little larger diameter, the interior diameter of the larger sections obviously being equal to the interior diameter of the smaller sections plus twice the thickness of the plate. Each section may also be slightly conical in shape, the larger ends having a diameter just large enough to pass sufficiently over the smaller end of the next section to form a joint. Large cast-iron pipes are also sometimes used to form these metal conduits up to an interior diameter of 48 inches. The selection of the type of con- duit within the limits of diameter adapted to both metals is usually made a matter of economy. The interior of the cast-iron pipe is smoother than that of the riveted steel, although this is not a serious matter in deciding upon the type of pipe to be used. Steel-plate conduits haA-e been manufactured and used up to a diameter of 9 feet. In this case the pipe was used in connection with water-power purposes and with a length of 153 feet only, the plates being + inch thick. The steel-plate conduits of the East Jersey Water Company's pipes are as follows : Length 21 miles. 5 " The diameters and lengths of the metal pipes or conduits of Diameter. Thickness. 48 inches 1 inch s J 1 ' ' 4 48 " 48 " 36 " GESERAL FORMULA FOR DISCHARdE OF COXDUITS. 237 the Hemlock Lake conduit of the Rochester Water-works are as follows : 36-inch wrought-inni pipe. . g.6o miles. -4 " " " .. 2.96 24 " cast-iron ])ipe 15. 82 " Total. 28.39 All metal conduits or pipes are carefully coated with a suit- able asphalt or tar preparation or A-armsh applied hot and sometimes baked before being put in place. This is hir the purpose of protecting the metal against corrosion. Cast-iron pipes have been used longer and much more extensively than wrought iron or steel, but an experience extending over thirty to forty years has shown that the latter class of pipes possesses satisfact■ V ^ Grade ^ ■^ ..c^ — ^ r^ O Cj -^ Discharge. Gallons per 24 Hours. i-974 2..1,1.S 3-5 4 2.338 2.338 2.3')8 I .yy^ 2.338 78r 114 404 661 S87 240,200,000 70,400,000 73,300,000 85,000,000 * From rcprirt by J. R. Freeman to B. S. Coler, 1 Soo- t From report of Xew York Aqueduct Commission. type, as thev carry water under pressure. Hence the slope or sine of inclination ^ l:)elr)ngs to the hydraulic gradient ratlier than to the grade of the pipe itself. W here the pipe-line is a long one its average grade frequently does not differ much from the hydraulic gradient, but tlie latter quantity must always be used. As in the case of the masonry conduits, the coefficient c in Chezv's formula Avill vary considerably AA'ith the degree of roughness of the interior surface of the pipe, with the slope 5, and with the mean radius r. An important distinction must be made between riveted steel pipes and those of cast iron, for the reason that the ri\-et-heads on the inside of the former exert an appreciable influence upon the coefficient c. The rivet-heads add to the roughness or unevenness of the interior of the pipe. Table XV gives the elements of the Aoav or discharge in the two pipe-lines which have been taken as types, as determined by actual meas- FLCnV OF WATER THROUGH LARGE CLOSED PIPES .'47 urements; it also exhibits similar elements for timber-stave pipes, to ^Yhlell reference will be made later. CKOTdN A(,il KIli:CT IX KARllI. As would be expected, the ^'elocitA' of floAV in these pipes ma^^ be and generally is consiclerabh" higher than the velocity of movement in masonry channels. Both Tables X\' and XA'I give considerable range of coefficients computed and firranged fr(im authoritative sources, and the coefficients c for Chezy's formula represent the best hydraulic practice in connection with such works at the present time. In using the formula for anv special case, great care must be taken to select a value for c AA'hich has been established for conditions as closely as possible to those in question. This is essential in order that the results of estimated discharges may not be disappointing, as thev sometimes have been where that condition so necessary to accuracA^ has not been fulfilled. 248 ir.iri!,7MroA'A',s for cities and nm'NS. TABLE XV. VALUES OF COEFFICIENT C. Pipe-line. Hydraulic Radius I Hydraulic Gradient. Mean Velocity. Hemlock Lake. Rush Lake to Mt. Hope . SudVjurj' aqueduct East Jersey Water Co Timber-stave pipe, Ogdcn, Utah 24 4« 4« 4«' 48' 4S' 4S wrought iron wr't and cast cast iron steel ri\"cted pipe 9" 6" 6" . 00041 1 .00239 .00255 ,// J ,» 1 •'" I 2" 12" . 002 44S 44« 7o« 965 195 73S 965 '95 62 Coefficient Discharge. Cubic Feet per Seccmd. Gallons IX-T :?4Hi.iurs- K em arks. Hemlock Lake 87. 3 99- 7 96 . 5 1 40 .14 . . 10,83124 I . ,S 3 1 2 4 I . S 3 I 2 4 1 7.000,000 Rush Lake to Mt. Hope Sudbury acjueduet 7 ,000,000 '_ Pipe new ,, 144.09 I iSSo. ti li After cleaning. " " 141 74* .1894-95. " 14^.16*. . i Before East Jersey Water Co Timber-stave pipe, Ogden, lUah 103-3 72 96 TOO "5 119 122 124 126 5S.O2 37,500,000 cleaning, c = loS 1S91. 1S97, ,1 .1 ,, << ,. If (( K « <. .. .. l( <[ (I - These values correspond to the formula c = FLO]]- OF ]]'ATEF rHROUUlI LARGE CLOSED PIPES. ^-'iO > w y-. y. W h --- rr H 1^ K-1 ^ 1 ,^ ^ j^ ry. 1-, , ct ct! ^^ 1 X ]- 1--^ " c> ! 1^, ^ X X 'A " „ r- - - „, ~ ri 1- _ r-i ^t -t 00 X -t -t 'r, ir, XT '/^ -t c. c 000 ^ u n :/r -'■. C r- .J. 1- r- 1- r- c/:' ^': -t ^ t 0' 0' "* X ^ - -r "-. r. --I -h l- - rt c- cC ? It ^ ^ I >- •t '"■ ■X X c C ^ -tX' n.-y -t Ti -t ■- C CO lyi ir.-j: z -t ■ ■x ■■- "- -t X fi -f- T. w r^ r-X XX X ^ -t 00 000 - ^^^ ,_ X X' C. "1 2 -t ^ 2 ^ ^ > 0, ^. ^ t^ ; ; - £ ^ L/:: : : - I .^ 0. rt >* ■^ ■c - -t ^■-. ■ ■ n -fc =: -o l^: :^ .'n. '. -f ■ r- - h- cr c z: " : ^ ; < >- ^,\ .^ = ,Z UT -' S^ ■J II ^ ^ -■ r' .t: ■- yr, -1- 1^ ^ XT: iN ^ "^ i; ' 'C' "■ "' ^' "■ ^' ■-".'■■na i K, " .^ H C, C ^ ^^. „ ro r. ■; r^ r^. f^j -t -t -t i^ i^. C :tEf >'t ,55" —1 ^ £ K ^' E » »; i ^ a _B -K Zi:x:Z2Z:Z22 350 WATER-WORKS FOR CITIES AND TOWNS. 191. Change of Hydraulic Gradient by Changing Diameter of Pipe. — It has already been seen, in the case of closed pipes or conduits, that the hydraulic gradient with slope jt governs the velocity of flow, and also that all parts of the pipe-Hne must be kept below that gradient. It is sometimes desirable, in order to CROTOX A'jUEDUCT IN ROCK. meet conditions either of topography or of flow, to raise or lower the hydraulic gradient over the Avhole or some portion of the pipe-line. This can easily be done to any needed extent by varying the diameter of the pipe. An increase in diameter will in general decrease the velocity of the water and increase its pressure, thus increasing correspondingly the height of the col- umns of water in the piezometer-tubes. As the top surface of the latter determines the hydraulic gradient, it is seen that in- creasing the diameter of a portion of the pipe-line will corre- spondingly raise the gradient over the same portion. Thus by CONTROL OF FLOW IN METAL CONDUFTS BY GATES. XiSl a proper relative variation of diameters the hydraulic gradient of a gn-en piiie-lme may readily be controlled withm sufficient limits t( > meet any ordinary requirements of this character. ig2. Control of Flow by Gates at Upper End of Pipe-line.— Ob\-iously, if the pressure m the pipe-line is diminished, less thick- ness of metal will be required to resist it, and a coiTcsponding degree of economy may be reached by a decrease in the quantity of metal. In the 21 miles of 48-inch steel-plate pipe of the liast Jersey Water Company there is a fall of 340 feet; if, therefore, the How through that pipe were regulated bv a gate or gates at its lower end, the lower porti(_-)n of the line \vould 1 >e sulijectcd to great intensity of pressure. If, howcA'cr, the flow through the pipe is controlled by a gate or gates at its upper end, enough water only may be admitted to enable it to fl()\\' full witli the velocity due to the hydrauhe gradient. By such a procedure the pressure upon the pipe over and aboA'c that whicli is necessary to produce the gradient is avoided. This condition is n(-)t only judicious in the reduction of the amount of metal required, but also in reducing both the leakage and the tendency to further leakage, which is largely increased by high pressures. This fea- ture of control of pressure in a long pipe-line Avith considerable fall is al^^'ays worthy of most careful C(^nsideratinn. 193. Flow in Old and New Cast-iron Pipes — Tubercles. — The velocity of flow through east-iron mains or conduits or through the cast-iron ]ii]ies of a distribution system of public water- sup]"ih' de]iends largely upon the condition of the interior surface of the pipes as affected by age. All cast-iron pipes before being shipped from the founclr}^ AA'here they are manuftictured are immersed in a hot bath of suitable coal-tar pitch composition in order to protect them from corrosion. After having been in use a few A'cars this coating on the interior of the pipes is worn off in spots and corrosion at once begins. The iron oxide pro- duced under these circumstances forms projections, or tubercles as they are called, of greath- exaggerated volume and out of all proportion to the actual weight of oxide of iron. AVhen the pipes are emptied these tubercles are readily remoA'cd In- scrap- ing, but before their removal they greatly obstruct the flow of water through the pipes. Indeed this obstruction is so great 252 WATER-WORKS FOR CITIES AND TOWNS. that the discharging capacity of cast-iron mains must be treated in view of its depreciation from this source. Table XA'II exhibits the value of the coefficient c to be used in Chezv's formula for all cast-iron pipes ha^-ing been in use for the periods shown. TABLE XVII. TABLE OF VALUES 0F_/" AND c. Hydraulic Velocity, Authority. Pipe-iine. Diameter, Inches. Radius Inches. Feet per Second. Coefficient Coefficient Darcy New pipe 3.22 .8 j 0.29 ( 10.71 78.5 100. .041S .0257 Darcy -| Old cast-iron pipe lined | with deposit ) 9.63 2.41 j 1. 00 "( 12.42 72.5 74.0 . 0489 . 0468 Darcy Pipe above cleaned 9-63 2.41 i 0.91 ( 14.75 90.0 98. .0316 .0269 Brush - Cast-iron pipe tar-coated j and in service 5 years, j' 20 5 j 2.00 1 3.00 114. IIO.O .0197 .0214 Karrach • Cast-iron pipe in service 1 II years \ 20 5 ( 2.71 \ 5-" 83.0 .056s .0376 Darrach \ Cast-iron pipe in service ) 7 years f 36 9 ( 1.58 ( 2.37 60.0 66.0 .0716 .0586 (Jbviously it is not possible to clean the smaller pipes of a distribution system, but large cast-iron conduits mav be emptied at suitable periods and have their interior surfaces cleaned of tubercles or other accumulations. At the same time, if necessary, a new coal-tar coating can be applied. Table XVIII exhibits the values of the coefficient c to be used in Chezy's formula for new and clean coated cast-iron pipes. It represents the results of actual hydraulic experience and is taken from Hamilton Smith's "HydrauHcs." A comparison between this table and that wdiich precedes \\'\S\, show how serious the effect of tubercles may be on the discharging capacitv of a cast-iron pipe. In using Chezy's formula, v^c\/rs, in connection with either Table XVII or XVIII, the slope or sine of inclination .? of the hydraulic gradient may be readily computed by equation do), which gives the head lost by friction in a closed circular pipe as TUlBER-SrA VE PIPES. 253 TABLE XVIII. VALUES OF c IN FORAIULA: VrizcVrs. , ^ D amctcrs in Fri. t ( o T'P^CO .05 . I I 1-5 2 2 ■ 5 3 3 ■ 5 4 - - 8 J So .0 06 . I 102.8 ]o8 .8 1 12.7 1 1 (j , 7 120.2 123.0 127.8 131 -S l^A-■>i 137-5 2 77'. H SS.o 104. 1 1 . g 1 1 . 2 I 20 3 123.S 127. T 2 g . g 1 ^4.3 138 141.0 14^-3 ,Sj .4 u,^ . 7 loS. 7 I 1 5 ■ *> 120.8 1 24 8 1 28 3 131-4 134-^ 138.0 142 3 J45-4 i47-'> 4 85-0 tJ7 . 1 1 2 . 1 1 S . 124. 128 I 131 5 134.0 137.4 141-9 145 5 [48. 1 5 [ .0 5 S7 . 00 . 3 114. 4 121.3 I2(). 5 130 f.) 134 1 137-1 140 . 144-7 148 I 151.2 153.0 80. I 101 .0 I lb. 3 123. :: 128.5 132 () 1 ^'.> 3 130.4 142.3 14O.Q 150 5 153-5 7 00 .0 10J.4 1 iS.o 125 .0 130.4 134 b 138 2 141 ■ 5 144.5 149.0 152 7 S go . lOJ ■ 3 110.3 I 2O . 4 132.0 13'' 3 140 14.^- 3 14(1.3 151.0 154 9 p go . 7 104 . 120.4 127.7 13.?. 3 137 7 141 145.0 148.1 152,8 150 lO uo . S 104-5 121 .4 128.8 134-5 130 142 g 140.4 1 40 . 7 154.0 1 I 00.1) 104. 7 122.0 129.7 135-^ 140 2 144 2 147 -7 151 .0 1 2 g I . 104.8 122.5 130.4 130.4 141 1 145 2 T48,,S 152. ; \.^ gi .0 105 . 122.0 1 .-; I . I 3 7 - I 141 •> 14O 1 .40-8 153. 2 14 QI . 105.0 123. 2 131-5 137-0 142 5 140 7 150, 3 1 54.0 I q gl . 105.0 123.0 131-8 138.0 142 g 147 151-1 154-0 JOl, f") 123.0 132. g It =f--f — . It is only necessary in a straiijht pipe or one nearly straight to compute the quantity / d 2g ' 194. Timber-Stave Pipes. —In the western part of the countrv^ long c(.")nduits or pipe-Hnes are frequently constructed of timber called redwood. Staves of suitable thickness, sometimes i-J inches, are accurately shaped and finished with smooth surfaces so as to form large pipes of any desired diameter. These staves are held rigidly in place with steel bands drawn tight with nuts on screw-ends, so as to close tightly the joints between them. Such AA-ooden conduits are rapidly and cheaply built and are A-ery durable. They have the further advantage of requiring no interior coating, as the timber surface remains indefinitely un- aft'ected by the water flowing over it. The latter part of Table X\' shows coefficients for Chezy's formula which may be used for such a class of timber conduits. As the interior surfaces of such closed conduits are always very smooth, the coefficients are seen to be relatively large, anil such pipes are, therefore, v-ell adapted t(-i maintain unimpaired discharging capacity for great lengths of time. CHAPTER XVIII. 195. Pumping and Pumps. — When it is impossible to secure water at sufficient elevation to be delivered to the points of con- sumption by gravity, it is necessary to resort to pumping in order to raise it to the desired level. Indeed it is sometimes necessary to resort to pumping in connection with a gravity supply in order to deliA'er water to the higher parts of the distri- bution system, the lower points being supplied by gravity. This combination of gravity supply with pumping is not unusual. That part of New York north of Thirty-fourth Street between Lexington and Fifth avenues, north of Thirty-fifth Street be- tween Fifth and Sixth avenues, north of Fifty-first Street be- tween Sixth and Xinth aA'cnues, north of Fifty-fifth Street between Ninth and Tenth a\'enues, north of Fifty-eighth Street between Tenth and Eleventh avenues, and north of Seventv- second Street between Eleventh Avenue and the North River, with elevation of 60 feet or more abo\-e mean high tide-water, is supplied from the high-service reservoir near High Bridge, the water being ele\'ated to it from the Crntnn supply liy the pump- ing-station at the westerly end of the bridge. The elevation of the water surface in the High Bridge reserA-(-)ir is 20S feet, and that of the large reservoir in Central Park 115 feet, above mean high tide-water. Some siiecially high points on the northern part of JIanliattan Island are supplied from the High Bridge tower, whose water surface is ,:;i6 feet aboA-e mean high tide. The pumps employed for the purpose of elevating water to distributing-reservoirs are among the finest pieces of machinery built by engineers at the present time. They are usually actuated by steam as a motive power, the steam being supplied from suit- able boilers or batteries of br^lers in which coal is generally used as fuel. The modern pumping-engine is in reality a combination 254 PUMPING AND PUMPS. 255 of three classes of machinery, the boilers, the steam-engines, and the pumps. There are various types of boilers as well as of engines and pumps, all, when judiciously designed and arranged, well adapted to the pumping-engine process. The pumps are n T r.. ^AC>=-1 rs'a^l. Skeleton Pumps. generally what are called displacement pumps; that is, tlie water in the ]iump-cvlinder is displaced bv the reciprricating motion of a ]iiston or ]ilunger. These pumps mav be either double- acting i^r single-acting ; in the former case, as the piston or plunger moA'cs in one direction it forces the water ahead of it into the 356 WATER-WORKS FOR CITIES AND TOWNS. main or pipe leading up to the reservoir into which the water is to be deh\-ered, whiile tlie water rising from the pump-well iVdlows back of the piston or plunger to the end of its stroke. AAdien the motion is reversed the latter water is forced on its way up- ward through the main, while the Avater rises from the pump-\A'ell into the other end of the water-cylinder. In the case of single- acting pumps water is drawn up into the water-cylinder from the pump-well during one stroke and forced up through the main during the next stroke, one operation only being performed at one time. The pump-well is a well or tank, usually of masonry, into which the water runs by gravity and from A\'hich the pump raises it to the reservoir. For the purposes of accessibility and convenience in repairing, the pump is always placed at an eleva- tion above the water in the pump-well, the pressure of the atmos- phere on the water in the well forcing the latter up into the pump-cylinder as the piston recedes in its stroke. The height of a column of water i square inch in section representing the pressure of the atmosphere per square inch is about 34 feet, but a pump-cylinder should not be placed more than about 18 feet above the surface of the water in the pump-well in order that the water may rise readily as it follows the stroke of the plunger. In the operation of the ordinary pump the direction of the water as it flows into and out of the pump-cylinder must neces- sarily be reversed, and this is true also with the type of pump called the differential plunger-pump, which is really a single-act- ing pump designed so as to act in driving the water into the main like a double-acting pump, i.e., both motions of the plunger force water through the main, but only one draws water from the pump-well into the pump-cylinder. A'alves mav be so arranged in the pump-piston as to make the progress of the water through the pump continuous in one direction and so avoid the irregu- larities and shocks which necessarily arise to some extent from a reversal of the motion of the water. The steam is used in the steam-cylinders of a pumping-engine precisely as in every other type of steam-engine. At the present time compound or triple-expansion engines are generallv used, among the Avell-known types being theAA'orthington duplex direct- acting pump Avithout crank or fly-wheel, the Gaskill crank and PUMPING AND PCMP.'i. 257 fly -wheel pumping-cngine, the Alhs and the Leavitt pumping- engines, both of the hitter employing the crank and fly-wheel and both may be used as single- i:>r doul)le-aeting pumps, usually as the latter. The characteristie feattu'c of the well-known Worthington pumping-engine is the movement of the valves of each of the two engines liy the other for the purpose of securing a c^uiet seating of the A'al\-cs and smooth working. One of the most imixirtant details of the pumping-engine is the system of valves in the water-cylinder, and much ingenuity has been successfully exjiended in the design id' proper valve systems. These pump-\-ah-es must, am(;)ng (.ither things, meet the following requirements as efficiently as possible : they must close promptly and tighth', so that no ^^■atcr may pass through them to create slip or leakage; they should have a small lift, so as to allow prompt closing, and large waterways, to permit a free flow thrciugh them with little resistance ; they must also be easily operated, so as to require little power, and, like all details of machinery, they should be simple and easily accessible for repairing when necessary. As steam is always used expansively, its force impelling the plunger will have a constant value during the early portion of the stroke onty, and a much less value, due to the expansion of the steam, at and near the end of the stroke, while the head of water against which the pump operates is practically constant. There is, therefore, an excess of eft'ort during the first part of the stroke and a deficiency during the latter part. Unless there should be some means of taking up or cushioning this dift'erence, the operation of the pump would be irregular during the stroke and productive of water-hammer or blows to the engine. Two means are employed to remove this undesirable effect, i.e., tlie fly-wheel and the air-chamber, or both. In the one case tlie excess of Avi.irk perfiirmed by the steam m the early part of the stroke is stored up as encrgv' in the accelerated motion of the fly-wheel and given out by the latter near the end of the stroke, thus producing the desired equalization. The air-chamber is a large reservoir containing air, attached to and freely communi- catino- with the force main or pipe near its connection Avith the pumps. In this case the excess of work performed at the begin- 258 WATER-WORKS FOR CITIES AND TOWNS. ning of the stroke is used in compressing the air in the air-cham- ber, sufficient water entering to accomphsh that purpose. This compressed air acts as a cushion, expanding again at the end of the stroke and reinforcing the decreasing effort of the steam. 196. Resistances of Pumps and Main — Dynamic Head. — Ob- viously the water flowing through the pipes, pump-cylinders, and pump-valves will experience some resistance, and it is one purpose in good pum ping-engine design to make the progress of the water through the pump so direct and free as to reduce these losses to a minimum. Similarly the large pipe or main, called the force-main, leading from the pump up to the reservoir into which the water is delivered, sometimes several thousand feet long, will afford a resistance of friction to the water flowing through it. The head which measures this frictional loss is given by equation (10) on page 239. All these resistances will increase Alli^ Pump. rapidly with the x-elocity with ^^•]uch the water flows through the pipes and other passages, as do all hvdraulic losses It^is obviously advisable, therefore, to make this velocity as "low as practicable without unduly increasing the diameter of the force mam. This velocity seldom exceeds about 3 feet per second RESISTANCES OF PUMPS AND MAIN. 259 mm'-"^^"' -'-"^ Section of Allis Pumping Engine. 260 WATER-WOBKS FOR CITIES AND TOWNS. The static head against which the pumping-engine operates is the A-ertical height or elevation between the water surfaces in the pump-weh and the reservoir. The head which represents the resistances of the passages through the pump and force-main, when added to the sum of the static head and the head due to the velocity in the force-main, gi^-es what is called the dynamic head ; it represents the total head against which the pump acts. If /; represents the static head, li' the head due to all the resist- ances, and' h" the head due to the A'elocity in the force-main, then the dynamic head will he H =h+h' + h" =]i+f^— + n— -{ , 'd2g 2g 2g in which / has a A'alue of about .015 and n is a coefficient which when multiplied by the velocity head will represent the loss of head incurred by the water in passing through the pump-cylinder and valves. The latter quantity is variable in value ; but it is seldom more than a few feet. igy. Duty of Pumping-engines. — It is thus seen that the col- lective machines and force-main forming the pumping system aflord opportunity for a number of serious losses of energ}^ found chiefly in the boiler, the engine, and the pump. The excellence of a pumping-plant, including the boilers, may obviously be measured by the amount of useful work performed by a standard quantity, as 100 pounds of coal. Sixty or more years ago, in the days of the old Cornish pumping-engine, the standard of excellence or "duty" was the number of foot-pounds of work, i.e., the number of pounds lifted one foot high, performed by one bushel of coal. As early as 1843 the Cornish pumping-engine reached a duty, per bushel of coal, of 107,500,000 foot-pounds. These pumping-engines were single-acting, the steam raising a weight the descent of which forced the water up the delivery- pipe. At a later date and until about ten years ago the usual stand- ard or criterion applied to pumping-engines for city \\-ater-works was the amount of work performed in lifting water for each 100 pounds of coal consumed; this result was also called the "duty" of the engine. In order to determine the dutv of a pumping- engine it was thus only necessary to r)bserve carefully for a gi\-en period of time, i.e., twenty-four hours or some other arbitrary DATA TU BE OBSERVED IN PUMPING-ENOINE TESTS, -llil period, the amount of coal consumed, the con(Hti( >n of the furnace- fires at the beginning and end of the test being as nearl\- the same as possible, and measure at the same time the total amount of water discharged into the reser\-ou-. The total weight of water raised multiplied by the total number of feet of elevation from the water surface in the ]iumi)-well to that in the reservoir would give the total number of foot-pounds of useful work ]jer- formed. This quantity di\'ided 1)y tlie number of hundred pounds of coal consumed would tlien gi\-e what is called the " dutv" of the pumping-engine. ig8. Data to be Observed in Pumping-engine Tests.— ()b- A'iously it is necessary to ofjserve a considerable number of data with care. No pum].i works with absolute perfection. A little water will run back through the \-alves before they are seated, and there will be a little leakage either through the \-al\es or through the packing ar(_)un(l the piston or plunger, or both sources of leakage may exist. Tliat leakage and back-flow represent the amount of slip or water which escapes to the back of the plunger after having been in front of it. In well-constructed machinery this slip or leakage is now very small and may be but a small fraction of one per cent. Inasmuch as the amount of work per- formed by the steam will be the same whether this slip or leakage exists or not, the latter is now frequently ignored in estimating the duty of pumping-engines, the displacement of the piston or plunger itself being taken as the volume of water pumped at each stroke. Again, in discussing the efficiency of the steam portion of the machinerv the amount of partial A-acuum maintained in the vacuum-pum]), which is used to move the water of the condensed steam, is affected by atmospheric j^ressure, as is the work which is performed. Hence in comjdete engine tests it is necessary to observe the height of the barometer during the test. It is also necessary to observe the tem]ierature of feed-water supplied to the boiler, and to use accurate appliances for ascertaining with the greatest exactness practicable the weight of dr>- steam used in the steam-cvlinders and the amount of ^^'ater which it carries. It is not necessary for the ]iresent purpose to discuss with minute- ness these details, but it is eA'ident from the preceding observa- 363 WATER-WORKS FOR CITIES AND TOWNS. tions that the complete test of a pumping-engine involves the accurate observation of many data and their careful use in com- putations. The determination of the duty alone is but a simple part of those computations, and the duty is all that is now in question. 199. Basis of Computations for Duty. — It was formerly neces- sary in giving the duty of a pumping-engine to state whether the 100 pounds of coal was actually coal as shovelled into the furnace, or whether it was that coal less the weight of ash remain- ing after combustion. It was also necessary to specify the quality of coal used, because the heating capacity of different coals may vary materially. For these different reasons the statement of the duty of a pumping-engine in terms of a gi\-en "\\'eight of coal consumed involved considerable uncertainty, hence in 1891 a committee of the American Society of Mechanical Engineers, appointed for the purpose, took into consideration the best method of determining and stating the duty of a pumpino-- engine. The report of that committee may be found in vol. xii of the Transactions of that Society. The committee recom- mended that in a duty test 1,000,000 heat-units (called British Thermal Units or, as abbreviated, frequently B.T.U.) should be substituted for 100 pounds of coal. In other words, that the following should be the expression for the duty : ■p. , _ foot-pounds of work done ^ ^ "total number of heat-units consumed^ ^'°°°'°°°- For some grades of coal in which 1,000,000 heat-units would be available for every 100 pounds the numerical value of the dutv expressed in the new terms would be unchanged, but for other grades of coal the new expression of the duty might be consid- erably different. 200. Heat-units and Ash in 100 Pounds of Coal, and Amount of Work Equivalent to a Heat-unit. — The following table exhibits results determined by Mr. George H. Barrus (Trans. A. S. M. E., vol. XIV. page 816), giving an approximate idea of the total num- ber of heat-units which are made available by the combustion of 100 pounds of coal of the kinds indicated: HEAT-UNirS AXD ASH. 2G3 Semibituminous : George's Creek Cumberland, rercentagr .,f A^-h. 1,287,400 to 1,421,700 . 1 ti ) 8 . 6 Pocahontas, 1,360,800 to 1,460,300 3 . 2 t( 1 6 . 2 Ne\Y RiA'er, 1,385,800 to 1,392,200 3,5 to 5 . 7 Bituminous ; Youghiogheny, Pa., lump, 1,294, 100 5.9 Youghiogheny, Pa., slack, 1,166,400 10.2 Frontenac, Kan., 1,050,600 177 Cape Breton Caledonia, 1,242,000 8.7 Anthracite : 1,152,100 to 1,318,900 9,1 to 10,5 \V. .rthiiiLjtiiii I'limp. 204 WATER-WORKS FOR CITIES AXD TOWNS. Each unit or B.T.U. represents the amount of heat required to raise one pound of water at 32° Fahr. 1° Fahr., and it is equal to 778 foot-pounds of work. In otlier words, 77S foot-pounds of work is said to l:)c the meclianical equivalent of one heat-unit. The amount of work, therefore, which one pound of dry steam is cap- able of performing at any given pressure and at the corresponding temperature mav readih' be found bv multiplving the number of available heat-units which it contains, and which may be readily Section of Worthington Pump. computed if not already known, by 778, or as in a pumping- engine duty trial, knowing by observation the number of poiinds of steam at a given pressure and temperature supplied through the steam-cylinders, the number of heat-units supplied in that steam is at once known or may easilv be computed. Then observing or computing the trjtal weight oi water raised bv the pumping-engine, as well as the total head (the dynamic head) agamst which the pumping-engine has worked, the total num- ber of foot-pounds of work performed can lie at once deduced. This latter quantity dixdded by the number of million heat-units will gi\-e the desired duty. THREE METHODS OF ESTIMATING DUTY. 265 201. Three Methods of Estimating Duty. — At the present time it is frequently, and jierhaps usually, eustomary to gi\-e the duty in terms of loo potmds of eual cinisumed, as well as in terms of 1,000,000 heat-units. I'requentlv, also, the dut\- is expressed in terms of 1000 pounds of dry steam containing about 1,000,000 heat-units. As has sometimes been written, tl:e dutv unit is 100 for coal, 1000 tor steam, and 1,000,000 for heat-units. 202. Trial Test and Duty of Allis Pumping-engine.— The fol- lowing data are taken from a duty test of an Allis pumping-engine at Hackensack, N. J., m 1899 by Prof. James E. Denton. This pumping-engine was bmlt to give a duty not less than 143,000,000 foot-pounds f(jr each " 1000 pounds of dry steam consumed by the engine, assuming the \\-eight of water delivered to be that of the number of cubic feet displaced by the plungers on their in- ward stroke, i.e., to be 145,000,000 foot-pounds at a steam pressure of 175 pounds gauge." The capacity of the engine was to be 12,000,000 gallons per twenty-four hours at a piston speed not exceeding 217 feet per minute. The engine was of the verti- cal triple-expansion tvpe with cylinders 25.5 inches, 47 inches, and 73 inches in diameter with a stroke of 42 ^^r inches, the single- acting plunger being 25.524 inches in diameter. The following data and figures illustrate the manner of computing the duty ; DUTY PER 10(11) POUXDS OF DRY STEAM BY PLUXGER DISPL.ACE.M EXT. 1. Circumference of plunger.s, C7 So. 1S75 ms. 2. Length of stroke. 7 4^ .0625 ins. 3. Number of plungers (single-acting") 3 4. Aggregate displacement of jilunger per re\'olution = ^^' =J 64,4^^7 . I cu. ins. 4T 5. Revolutions during 24 hours, .^ 4.3.,vi7 6. Weight of one cubic foot of water, le 6j .42 lbs. 7. Total head pumped against, // 266 .fit ft. 8. Total feed-water per 24 hours, '/' 160.354 lbs. s. of drv steam Allis at St. Paul. Minn 189 .0 144,46 vOOO Lake Erie Engine AVorks at Buffalo 207.7 135.403,745 Million B. T. U. These results show that material ad^-ances have been made in pumping-engine designs within a comparati\-ely few years. CHAPTER XIX. 205. Distributing-reservoirs and their Capacities. — The water of a public supply seldom runs ivom the sturage-reser\-oir directly into the distributing system or is pumped directly into it, al- though such practices may m some cases be ]iermissible for small towns or cities. Generally distributing-reservoirs are pro\-ided either in or immediately adjacent to the distributing system of pipes, meaning the water-pipes large and small which are laid through the streets of a city or town, and the service-pipes lead- nig from the latter directly to the consumers. The capacity ordinarily gi\-en to these distributing-reser\-oirs is not controlled by any rigid rule, luit depends upon the local circumstances of each case. If they are of masonry and covered with masonry arches, as required for the reception of some filtered waters, they are made as small as practicable on account of their costs. If, on the contrary, they are open and formed of suitablv constructed embankments, like the distributing-reservoirs of New York City in Central Park and at High Bridge, thev are and should be of much greater capacit\'. The storage A-olume of the High Bridge reservoir amounts to 11,000,000 galLnis, while that of the Central Park reservoir is 1,000,000,000 gallons. Again, the capacitA' of the old receiving-basin in Central Park is 200,000,000 gallons. These reserA'ou's act also as equalizers against the A'arA'ing draft on the system during the different por- tions of the dav and furnish all desired sti.^rage fcir the demands of fire-streams, which, while it lasts, mav lie a demand at a high rate. It may be approximately stated under ordinary circum- stances that the capaeitv of distributing-reservoirs for a gi\"en system should equal from t^^•o or three to eight or ten days' 267 268 WATER-WORKS FOR CITIES AND TOWNS. supply. It is advantageous to approach the upper of those hmits when practicable. The volume of water retained in these reservoirs acts in some cases as a needed storage, while repairs of pumping-machinery or other exigencies may temporarily stop the flow into them. The larger their capacity the more effec- tively will such exigencies be met. 206. System of Distributing Mains and Pipes. — Gate-houses must be placed at the distributing-reservoirs within which are found and operated the requisite gates controlling the supply into the reservoir and the outflow from it into the distributing system. The latter begins at the distributing-reservoir where there may be one or two or more large mains, usually of cast iron. These mains conduct the water into the branching system of pipes which forms a network over the entire city or town. A few lines of large pipes are laid so as to divide the total area to be supplied into convenient portions served by pipes of smaller diameter leading from the larger, so that practically every street shall carry its line or lines of piping from which every resident or user may draw the desired supply. Obviously, as a rule, the further the beginning of the distributing system is departed from in follow- ing out the ramifications of the various lines the smaller will the diameter of pipe become. The smallest cast-iron pipe of a dis- tributing system is seldom less than 3 inches, and sometimes not less than 4 or 6 inches. There should be no dead ends in any distributing system. By a dead end is meant the end of a line of pipes, which is closed so that no water circulates through it. Whenever a branch pipe ceases it should be extended so as to connect with some other pipe in the system in order to induce cir- culation. The entire distributing system should therefore, in its extreme as well as central portions, constitute an interlaced system and not a series of closed ends. This is essential for the purity and potability of the water-supply. A circulation in all parts of the entire system is essential and it should be everywhere secured. The diagram shows a portion of the distributing system of the city of New York. It will be noticed that there is a com- plete connection of the outlying portions, so as to make the inter- NO 119 DISTRIBUTION PIPES OF THf PUBLIC WATER. SUPPLY OF THE CITY OF NEW YORK BOROUGH OP MANHATTAN Campiltddom Piar.i if, CHdce OF the CHIEF ENGINEER or DEP T-OF WATER SXiPPLY B, E. D P..iEr,e.M. E, JJndei Svptr^uor ol John R.f roeman, C.E. Oclct«T. 16M 3c«l«. H-Kh J 956 Icrrt. :S»-H— ■ Fic. 4. — New York City Distributing Syste DISTlUHVriNG MAINS AND PIPES. 269 lacing and corresponding circulation as complete and acti\'e as possible. 207. Diameters of and Velocities in Distributing Mains and Pipes. — In laying out a distributing system it will not ]x' possible ■to base the diameters at different points on close computations for \-el(jcity or discharges based upon considerations of frictii m or other resistances, as the conditions under Avhich the jiipcs are found are too complicated to make such a method \Yorkal)le. Approximate estimates may be made as to the number ()f cnn- sumers to be supplied at a given section of a main ]ji]:ie, and con- sec[uently what the diameter should be to pass the required daily supply so that the velocity may not exceed certain maximum limits known to be advisable. Such estimates may be made at a considerable number of what may be termed critical points of the system, and the diameters may be ascertained in that man- ner with sufficient accuracy. In this field of hydraulics a sound engineering judgment, based upon experience, is a very important element, as it is in a great many other engineering operations. It will follow from these considerations that as a rule the larger diameters of pipe in a given distributing system will belong to the greater lengths, and it will be found that the velocities of water in the various parts of a system will seldom exceed the following limits, which, although stated with some precisir)n, are to be regarded only as approximate: For 4-inch pipe 23 feet per second. 6 1 1 12 16 20 24 30 36 48 60 17 I 2 12 9 8 7 7 •^'•J WATER-WORKS FOR CITIES AND TOWNS. 208. Required Pressures in Mains and Pipes. — In designing distributing systems it is very essential so to apportion the pipes as to seeure the requisite pressure at the various street services. Like many other features of a water-supply system no exact rules can be given, but it may be stated that at the street-level a pressure of at least 20 to 30 pounds should be found in resident districts, and from 30 to 35 or 40 pounds in business districts. The character and height of buildings affect these pressures to a large extent. Old pipe systems usually have many weak points, and while pressures requisite to carry water to the top of three- or four-story buildings are needed, any great excess above that would be apt to cause breaks and result in serious leakages. If the distributing system is one in which the pressure for fire- streams is to be found at the hydrants, then greater pressures than those named must be proA'ided. In such cases the pressures in pipes at the hydrants should range from 60 to 100 pounds. 209. Fire-hydrants. — Fire-hydrants must be placed usually at street a )rners, if the blocks are not too long, and so distributed as to control with facility the entire district in which they are found. Unless fire-engines are used to create their own pressure, the Lnver the pressure at the hydrant the nearer together the hydrants must be placed. It is obvious, however, that when the pressure of the system is depended upon for fire-streams it is desirable to have the pressure comparati\'ely high, so far as the hydrants arc concerned, as under those conditions they may be placed farther apart and a less number will be required. 210. Elements of Distributing Systems. — The following table gives a number of statistics, exhibiting the elements of the dis- tributing system of a considerable number of cities, including some pumping and meter data pertinent to the costs of pumping on the one hand and the extension of the use of meters on the other. It contains information of no little practical value in connec- tion with the administration of the distributing S3''stems and the cr>nsumption rif water in it. This table has been compiled by ]\Ir. Chas. W. Sherman of the New England A'\"ater- works As.so- ciation, and was published in the proceedings of that association for September, 1901. The service-pipes, varying from ^ to 10 ELEMENTS OF DISTRIBUTING SYSTEM. 271 inches in diameter, arc of cast iron, wrought iron, lead, gah-anized iron, tin-lined, rul)l)er-lined, cement-lined, enamelled and tarred, the practice varying widely not only from one city to another, but in the same city. 372 WATER-WORKS FOR CITIES AND TOWNS. TABLE Name t,f City or Town. Albany. N. Y Atlantic City, N. J. Boston, Mass Burlington, Vt . . . . Cambridge, Mass , Chelsea, Mass , . . C.I. C.I. IC.L. -CI. ( W.I. Concord, N. H . . . Fall River, Mass. . Fitchburg, Mass . . Holyoke, Mass . . . Lowell, Mass Lynn, Mass Madison, Wis Manchester, N. H. C.I. IC.I. "I C.L. C.I. C.I. (C.I. ■( W.I. Metropolitan Water-works ~| Owned by. . . . i Tot. Sup. by.. I W I. - C.L. (C.I. C.I. iC.L. 'I C.I. I C.I. 'IC L. ICI. J C.L. I I ( Kal. Minneapolis, Minn , ^ Steel New Bedford, Mass New London, Conn Newton, Mass Providence, R. I H.P Fire System .. Quincy, Mass Springfield, Mass . Woonsocket, R. I. Yonkers, N. Y . . . Worcester, Ma C.I. IW.I - C.L. (C.I. C.I. C.I C.I. I W.I. ■C.I. (C.L. (C.I. I Kal. C.I. 4-30 2-48 6-16 6-24 2-20 2-20 4-16 4-20 6-60 4-60 4' 36 4- 24 4- 20 6- .36 2- -24 1- -.56 713.4 38 . o 37.8 *iO . 2 87.3 66.6 Si .6 127. 8 129.4 34.3 5)6.0 69.8 1360-3 269 92 7 50 5 I 36 6 324 6 5 <> 144 7 84 t 4.i 8 74 I 173 5 27 . 09 4.61 24. 00 IS.7I 6.43 o. 56 808 SI9 7606 213 968 253 267 954 499 860 109S 952 169 743 3172 73S 25S 935 1886 92 539 54S ■ Public hydrants only. ELEMENTS OF DlSTRIBUriXG SYSTEM. 273 XIX. G i.£§ g « 3 H Pi X' H H 80 1 20 ^o i-4 4,240 ^20S 80 TO 40-90 *-s .7.525 45IO 018 70-S5 i-6 3,350 14,207 0,140 2 .U I 800 ,^00 4S-50 t-2 104 - -- 3,340 t.,043 4,432 1010 040 5 54 So '1 155 H S, i'2 i-s 6,544 2.427 7.U .So- 1 00 i-4 3,010 2TO 10,034 1 3,504 =;.s86 oOO 45-(,o i-4 2,571 ^.U 2,75s 2 586 4-0 5 , 5 r 3 I 34,400 3.667 2bS 10,585 ^105 1005 ^—10 20,004 0,2,S0 5.0:10 :,S-fi4 1.420 31 s 40-4S *-4 3,oSS 229 801 ."^4 *-o 7,087 6,001 3.1 00 14-73 A-TO 21 , 5 66 I 7, Si 3 1880 j 10-!, H S, I ioo-i:!0 L.S.* 1-6 0.764 3,122 lOOI 7S-S; e~3 4.33'^ 123 450 408 50-120 1-0 2 , T ^ 4,goS 1, 8 So 4,852 1 70 L S. ■,„oH.S* ;: ^ y"' ^ .. li'^ ■ M,£ ? ^ '^jz - t|^^ \ CI "l C.L. CI. C.I. IC.I. 1 W.I. 6-16 4-30 6-24 2-20 *-30 Fitchburg, Mass Lowell, Mass 1 6. ',.9 ( 167 1 167 242.4 1,480,048 Lynn, Mass Madison, Wis Manchester. N. H I W.I. Ic.i. C.I. (C.L. "l C.I. IC.I. "IC.L \ CI. - C.L. ( Kal. 3 CI. 1 Steel. C.I. I WI. ^C.L. C.I. C.I. CI. (CI. '1 Kal- l W.I. - C.I. / C.L. C.I. 2-20 4-16 4-20 6-60 4-60 14—50 4- .3'^ 4-24 4-20 6-36 12-24 2-20 1-36 4-20 88,780.036 87,265,319 47,5.30,830 ] Owned by Water-works f Tot. Sup. by... . J 96.5 ( 51 .8 ) 125.6 I 21 ,800,000 iO(;).38o,ooo 80,400,000 New Bedford, Mass New London, Conn Iy2 130,336,508 Newton, Mass Providence, R. I H.P Fire-system 254 (124.7 72,500,000 lor ,301 ,600 60,320.100 68,533,300 Quincy, Mass Springfield, Mass Woonsocket, R. I Yonkers N Y 239-5 51,024,641 2-40 ELEMENTS OF DISTRIBUTIXG SYSTEM. XlX.— C the water before ho\\-ing into the settling-basins a small auKjunt of alum or sulphate of alumina, depending upon the degree of turbidity, the average being about 1.6 grains per gallon, rising to perhaps 4 grains in floods. By these means a few hours of aided sedi- mentation would produce more subsidenee than could be ob- tained in several days without the chemicals. A similar recom- mendation has been made for the purpc ise > if improving the A\"ater- supply for the city of AVashington, I). C, from the Potomac River. In other eases between 5 and 6 grains C)f lime per gallon have produced effeeti\"e results. 214. Amount of Solid Matter Removed by Sedimentation. — Under adverse conditions, or with sediment which remains obsti- nately suspended, not more than 25 to 50 per cent of the solid material will be remoA-ed by sedimentation, Ijut Avhen the process is working satisfactorily, sometimes by the aid iif chemicals acting as coagulants, qo t(T qq per cent ca'Cii of the solid material mav be remo\-ed. The operation of sedimentation has another beneficial eftect in that the solid m;itter Avhen Ijeing deposited carries dciwn with it large numbers of bacteria, Avhich, in some cases, haA'c been (observed tn be So or qo per cent iif the total contents of the Avater. In other Avonls, the suljsidenee of the solid matter clears the water of a large porti(jn of the Ijacteria. 215. Two Methods of Operating Sedimentation-basins. — Sedi- mentation is carried on in tAA'o Avays, one being the "fill-and- draAv" method and the other the "continuous" method. In the former method a basin or reserA'oir is first filled with water 280 WATER-WORKS FOR CITIES AND TOWNS. and then allowed tc stand while the subsidence goes on for per- haps twenty-four hours. The clear water is then drawn off, after which the reservoir is again filled. In the continuous method, on the other hand, water is allowed to flow into a single reservoir or series of reservoirs through which it passes at an extremely low velocity, so that its contents will not entirely change within perhaps twenty-four hours or more. In this method the clear water is continuously discharging at a com- paratively low rate, the velocity in the reservoir being so small that the solid matter may be deposited as in the fiU-and-draw method. Both of these methods are used, and both are effective. The choice will be dependent upon local conditions. In the continuous method the sijlid matter is largely deposited nearer the point of entrance into the reservoir, but more generally over the bottom in the fiU-and-draw method. The velocity of flow in the reservoirs of the continuous method generally ranges between 0.5 inch and 2.5 inches per minute. Occasionally the velocity may be slightly less than the least of these values, and sometimes one or two inches more than the maximum A-alue. 216. Sizes and Construction of Settling-basins. — The sizes of the settling-basins will obviously depend to a considerable ex- tent upon the daily consumption of water. There is no general rule to be followed, but the capacity of storage volume of those actually in use run frc^m less than i to possibly 14 or 15 days' supply. Under ordinary circumstances their volumes may usually be taken from 5 to 6 or 8 days' supply. Their shape should be such as to allow the greatest economjr in the construc- tion of embankments and bottoms. They may generally be made rectangular. Their depths is also a matter, to some extent, of constructive economy. The depth r)f water will usually be found between about 10 and 16 feet, it being supposed that possibly 2 or 3 feet of depth will be required for the collection of sedi- ment. These basins must be water-tight. The bottom surfaces may be covered with concrete 6 to 9 inches thick, with water- tight firm puddle 12 to 18 inches thick underneath, resting on firm compacted eartli. The inner embankment surfaces or slopes may be paved with 10- or 12-inch riprap resting on about 18 inches of broken stone over a layer of puddle of equal thick- TWO METHODS OF FILTRATION. 281 ncss with the bottom and continuous with it. Occasionally the bottom and sides may be simph' puddled whh clav and lined with brick or ripra]) pavement, laid on gravel, or broken stone. It is only necessary that the sides and bottoms shall be tight and of such degree of hardness and continuity as to admit of thorough cleaning. The bottoms of sedimentation-basins may advantageously not be made level. In order to facilitate cleaning away the solid matter settling on them, a valley (jr depression may be formed along the centre line to which the two portions of the bottom slope. A grade in this channel or central \'alley of i in 500 with slopes on either side of i in 200 or i in 300 will be effective in the disposition of the solid matter. At the lowest end of the central valley there slnDuld be suitable gates through which the accumulated sedinient can be moA^ed out of the basin. This sedimentary matter will in many cases be soft mud, but its movement will alwavs be facilitated bv the use of suitable streams of water. The frequency of cleaning will depend upon the amount of sediment carried by the water and up( m its accumula- tion in the basin. AAdienever its depth ranges from i to 2 or 3 feet it is remoA-ed. Complete control of the entrance of the water to and its exit from the basin must CA'idently be secured by suitable gates or A-ah"es and other appliances required for the satisfactory ("iper- ation of the basin. In some cases the cost of sedimentation- reservoirs with concrete bottoms and sides has risen as high as Sqooo per million gallons of cajiacity ; but where the cheaper lining has been used, as in the case nf reser^'oirs at Philadelphia, the range has been from about S3300 to about S4300. 217. Two Methods of Filtration. — After the process of sedi- mentation is completed there will necessarily always be found the remains of organic matter and certain other polluting material which should be removed before the water is allowed to enter the distributing svstem. This removal is accomplished usually by filtration through clean sand, but occasionally through porous material, such as concrete slabs, porcelain, or other similar material. The latter processes are not much used at the present time, and thev will not be further considered. 282 WATER-WORKS FOR CITIES AND TOWNS. The filtration of water through sand is canned on by two distinct metliods, one called slow sand filtration and the other rapid sand filtration. In the first method the water is simply allowed to filter slowly through beds of sand from 2 to 3 or 5 feet thick and suitably arranged for the purpose. In the second method special appliances and conditions arc employed in such manner as to cause the water to flow through the sand at a much more rapid rate. The method of slow sand filtration will first receive attention. 218. Conditions Necessary for Reduction of Organic Matter. — ■ The most objectionable class of polluting materials includes organic matter which from one source or another finds its way into natural Avaters. Such material has originally constituted or formed a part of living organisms and chemically consists of varying proportions of carbon, oxygen, hydrogen, and nitrogen. As found in public Avater-supplies it is usually in some stage of decomposition. The chemical operations taking place in these decompositions are more or less complicated, but in a general way it may be said that the first step is the oxidizing of the car- bon which may produce either carbon monoxide or carbon dioxide and a combination of nitrogen with hydrogen as ammonia. When the conditions are favorable, i.e., when free oxygen is present, the ammonia may be oxidized by it, thus producing nitric acid and water. If, as is generally the case, suitable other substances, as alkalis, are present, the nitric acid combines with them, form- ing nitrates more or less soluble and essentially innocuous. It is therefore seen that the complete result is a chemical change from the original organic matter, oft'ensive and possibly dangerously polluting, to gaseous and soHd matter, the former escaping from the water and the latter either passing ofl" unobjectionably in a soluble state or precipitating to the bottom as inert mineral matter. In order that these processes may be completely eft'ec- tive, two or three conditions are necessary, i.e., sunlight, free oxygen, and certain species of that minute and low class of organ- isms known as bacteria, the nature and conditions of existence of which have been scientificahy knoAvn and studied within a period extending scarcely farther back than ten or fifteen years. The precise nature of their operations and their relations to the ,VLOir FILThWTlOX TIIROVGH SAXD. 2S3 presence of the necessary oxygen, cir just the ])arts which they play in the process (jf tlecomjjositicjn, are mjt ct dissolved oxygen in potable water may vary from 8.1 ])arts at 80° Fahr. to 14.7 parts bv weight at 32° Fahr. in 1,000,000 at atmospheric pressure. In some cases Avhere liability to dangerous contamination exists it mav be adA'isable to increase the aA-ailable supply of oxygen in the water Iiy using a slow sand filter intermittenth^ as has hicen done at Lawrence, ]\Iass. Instead of permitting a continuous flow of water through the sand, that fioAv is allowed 284 WATER-WORKS FOR CITIES AXD TOWXS. for a period of 6 to 12 hours only, after which the falter rests and is drained for perhaps an equal period. During this intermis- sion another filter-bed is brought into use in the same manner. Alternatino; thus between two or more filters, the fl(_nv in any SLOW FILTRATION THROUGH SAND. 285 one is intermittent. In this manner the oxygen of the air finds its way into the sand voids of eaeh dramed filter in turn and thus becomes available m the presence of suitable species of bacteria No,1. CROSS-SECTION AT NORTH END OF BED. NO, 2. CROSS-SECTION AT BEGINNING OF PIPE UNDERDRAIN. No. 3. CROSS-SECTION AT SOUTH END OF BED. SCALE IN FEET FOR NOS.I, 2, AND 3. ELEV.2S No. 4. CROSS-SECTION AT END OF LOWEST GRAVEL UNDERDRAIN. SCALE IN FEET 1 01 234S67 89 10 NORMAL HIGH WATER ON FILTER. ■^leV^T NO. 5. LONGITUDINAL SECTION OF A BEDj AT WESTERLY END OF FILTER. SCALE IN FEET 10 10 20 30 iO 60 TYPICAL SECTIONS OF UNIT BEDS IN LAWRENCE CITY FILTER. APRIL, 1901. COPIED FROM PLAN FURNISHED BY A. D. MARBLE, CITY ENGINEER. for reducing the organic matter in the water next passing through the filter. Intermittent fihers operated in this manner are not much used, but the most prominent instance is that at Lawrence, Mass. At that place the water after being filtered is pumped to a higher elevation for use in the distribution system. The 286 WATJ'J]i-\VOIiK.S FOR CITIES AXD TOWXS- pumps have been run nineteen hours out of the twenty-four, and the water is shut off from the filters five hours before the pumps stop. Tlie gate admitting water to the filter is open one hour before they start. Nine hours of eaeh day the filter does not receive water, and rests absolutely about four hours. 220. Removal of Bacteria in the Filter. — The grains of the sand at and near the surface of a slow sand filter, within a short time after its operation is begun, acquire a gelatinous coating, densest at the surface and decreasing rapidly as the mass of sand is entered. This gelatinous coating of the grains is organic in character and probably largely made up of numerous colonies of bacteria whose presence is necessary for the reduction of the organic matter. It is necessary to distinguish between these species of bacteria and those which are pathogenic and charac- teristic of such diseases as typhoid fever, cholera, and others that are water-borne. Every potable surface-water and possibly all rain-water carry bacteria which are not pathogenic and which apparently accumulate in dense masses at and near the surface of the slow sand filter. As the water finds its wav through the sand it loses its organic matter and its bacteria, both those of a pathogenic and non-pathogenic character. Potable water, there- fore, is purified and rendered innocuous by the removal in the filter of all its bacteria, including both the harmless and dan- gerous. 221. Preliminary Treatment — Sizes of Sand Grains. — In de- signing filtration-works consideration must be given to the charac- ter of water involved. There are waters which when standing in open reservoirs exposed to the sunlight will develop disagree- able tastes and odors, and it may be necessary to give them pre- liminary treatment especially for the removal of such objection- able constituents. The character and coarseness of the sand emploved are both elements affecting its efficiency as a filtering material. It should not be calcareous, for then masses of it may be cemented together and injure or partially destroy the working capacity. Again, if it is too coarse and approaches the size of gravel, water may run freely through it Avithout experiencing any purification. iVIuch labor has been expended, especially by tlie State Board PRliLIMIXAKY TREATMKM^SIZES OF SAND ORAIAS. 287 of Health of ilassachusetts, in in\-t'stigatmg the charaeteristics of sand and the sizes of grains best adapted to hher purjxjses. In that work it lias beeume neeessar^• to elassifv sands aeeording to degrees of hneness or eoarseness. The iliameter of a grain of sand in the system of elassification emjiloN-ed means the eube root of the product of the greatest and least diameters of a grain multiplied by a third diameter at right angles to the greatest and least. The " effecti\'e " size of an}- gi^-en mass of sand means the greatest diameter of the finest lo per cent of tlie total mass. There is also a term called the ' ' uniformitA' coefficient." The unifomiitA' coefficient is the quotient arising from diA'iding the greatest diameter of the finest 60 ]ier cent of the mass b\' the greatest diameter of the finest 10 per cent of the same mass. These are arbitrary terms which ha^-e been reached by experience as con\-enient for use in classifying sands. EAddently absolute uniformity in size will be indicated by a uniformity coefficient of I, and the greater the variety in size the greater will he the uniformity coefficient. Sands taken from different A'icinities and sometimes e\'en from the same bed will exhibit a great range in size of grain. 10; I 00 80 70 > i/Kl^_ .^--—^^^"''7''^^^ / / ( "^^ / ^ h.A- ^ 0/ 0/ / / ly oy^ / / / / ^ lo/ / T^^^ 0/ \ A / ~t/U / 1/ / 1/ L 1 /"J, j 0,/ V FINE / V ! / 0/ y gj /' COARSE — -7-" -^ _J Fig. .Vl .04 .40 .(» a.iO o.-'o DIAMETER IN MM. -Sizes of Grain or Fineness of Sand. Fig. 5 represents the actual variety of size of grain as found in eight lots of sand among others examined in the laboratory of the Massachusetts State Board of Health. The A-ertical scale 388 WATER-WORKS FOR CITIES AXD TOWNS. shows the per cent by weight of portions having the maximum grains less in diameter than sliown on tlie horizontal line. The more slope, like No. 5 or 6, the greater is the variety in size of grain. Those lines more nearly vertical belong to sands more nearly uniform in size of grain. 222. Most Effective Sizes of Sand Grains. — Investigations by the ^Massachusetts State Board of Health indicate that a sand whose effective diameter of grain is .2 mm. (,008 inch) is perhaps the most efficient in removing organic matter and bacteria from natural potable waters. .\t the same time wide experience with the operation of actual filters seems to indicate that no particular advantage attaches to any special size of grain, so long as it is not too fine to permit the desired rate of filtration or so coarse as to allow the water to flow through it too freely. Experiments have shown that effectiA^e sizes of sand from .14 to .38 mm. in diameter possess practically the same efficiency in a slow sand filter. The action of the filter is apparently a partial straining out of both organic material and bacteria, but chiefly the reduc- tion of organic matter in the manner already described and probably the destruction to a large extent of the bacteria, espe- cially those of a pathogenic nature, although at the present time it is impossible to state the precise extent of either mode of action. 223. Air and Water Capacities. — Another important physical feature of filter-sands, especially in connection with intermittent filtration, is the amount of A'oids between the grains. When the intermittent filter is allowed to drain, so that the only water remaining in it is that held between the grains by capillary attrac- tion, generally at the bottom of the filter unless the sand is very fine, the volume of the water which remains in the vr.ids is called the water capacity of the sand. The remaining volume between the grains is called the air capacity of the same sand. It is evi- dent that the air capacity added to the water capacity will make the total voids between the sand grains. Fig. 6 shows the amount of air and water capacities of the same sands whose sizes of grains are exhibited in Fig. 5. The depth r,f the sand is supposed to be 60 inches, as shown on the vertical line at the left of the diagram, while the percentages of the total volume representing the amounts of A-oids is shown on AIR AXD WATER CAPACITIES. ^S9 the horizontal hnc at the bottom of the diagram. Both air and water eapacities for eaeh sand are shown bA- the A-arious numbered Hnes partialh' \-ertieal and partiahA- inclined. It will be observed that the fine sands No. 2 and No. 4 have large water capacities, the water capacity being shown by 60 64 48 42 36 30 S4 IS « 0000 / / / \ j uT § 1 \ \ AIR \ ! \ \ 0-: (D i d z s ^ z d 'M Z . D Z < 0: \ ^ \ \ z Z < 5 '3 d \ \ d z \ \ \ S d s \ 1 \ \ s N \ \ ^ \ V \ ^ I i.j -JO j.-i 30 as 40 4.5 peb cent by volume Fig. 6. that part of the diagram Iving below and to the left of each line. It will be n(_"iticecl that No. 5 sand is made up nf ap- proximately equal portions of fine and coarse grains, the fomier largely filling the A'oids between the latter. This mixture, as shown by the Xo. 5 line, gives a very high water capacity and a correspondingly low air capacity. (lb\dously a sand with a high water capacity has a con-esponclingly low air capacit}', and in general would not be a very good sand for an intermittent filter, since it is the purpose of the latter to secure in the voids 390 WATER-WORKS FOR CITIES AND TOWNS. between the sand grains as much oxygen as practicable whenever the filter may be at rest. 224. Bacterial Efficiency and Purification — Hygienic Efficiency. ■ — As the function of a filter is to remove as far as possible the organic matter and bacteria of the applied water, there must be some criterion by Avhich its efficiency in the performance of those functions can be expressed. The bacterial efficiency is represented by the ratio found by dividing the number of bacteria after filtra- tion in a prescribed cubic unit, as a cubic centimeter, by the num- ber which the same \'olume of raw water held before being ap- plied to the filter. This is a rather misleading ratio, for the reason that the effluent water may contain bacteria of certain species which grow in the lower portions of a filter or in the drains '\\diieh conduct the effluent from it. It is possible, therefore, that bacteria may be found in a filter effluent Avhen all of the bactena originally held in the water have been removed. Hence the ratio expressing what is called the bacterial purification arises from dividing the number r)f bacteria aetuallv removed from a cubic centimeter of water by the filter by the number originally held by a cubic centimeter of raw water. The smaller the first of these ratios the higher the degree of efficiency. Extended expe- rience, both in the filters of such laboratories as that of the [Mas- sachusetts State Board of Health and with actual filters of public water-supplies, show that under attainable conditions of opera- tion 98 to 100 per cent of all the bacteria originally found in the water may be removed. There is also used the term hygieinc efficiency Avhich is used in connection with slow sand filters. This means simply the per cent of pathogenic bacteria removed by the filter, and there is good reason to believe that it is at least as high as the bacterial purification. 225. Bacterial Activity near Top of Filter. — The work of re- moval of bacteria and organic matter has been found by extended investigations to be performed almost entirely within 6 or 8 mches of the top surface of the sand; indeed' the most active part of that operation is probably concentrated within less than 3 inches of the surface. At any rate the retained bacteria and nitrogenous matter are found to decrease ven^ rapidly within a RATE OF FILTIIATIOX. 291 fnot from the upper surface, below which stratum the cjuantity is rekiti\-ely very small and its rate of decrease necessarily slow. ..\ little of this nitrogenous or gelatinous matter is found to sur- round to a slight extent the sand grains fi mnd at the bi >ttom of the filter. Some authdrities have considered that the more stead)' uniform efiiciency oi the deeper filters is due to this efl'cct. 226. Rate of Filtration. — The rate at wliich water can be made to How through a slow sand filter is of economical impor- tance,' for the reason that the higher tlie rate the less Avill be the area required to purify a given quantity per clav. I'oreign engineers and other sanitar}' authorities ad\-ocate generally slower rates of filtration than ^Vmerican engineers are inclined to faA'or. The usual rate in Europe is not far from 1.6 to 2.5 million gallons per acre per clav. There is also considerat)lc range in this countrA-, and tlie rate may reach 3 million gallons per acre per day. Indeed a considerable number of tests have shown that for shcirt periods of time, at least, some waters mav be efficiently filtered at rates as high as 7 to S million gallons per acre per day, but probably no American engineer is ready to introduce such high rates as yet. As a matter of fact the rate will depend con- siclerablv upon the character of water used. Clear water from mountain lakes and streams uncontaminated and carrjdng little solid material may be filtered safely and properly at much higher rates of filtration than riA'er or other waters carrying more sedi- ment and more organic matter. This jirinciple is recognized brith in Europe and in this countr}'. It ■\^'Ould appear from ex]ierience that slow sand filters at the present time Avith rates of 2.5 to 3 million gallons per acre per day ma}' be employed for practicallv anv water that mav be considered suitable for a public supplv, and that Avith these rates high degrees of both bacterial purification and liA'gienic efficiency may 1 )e reached. 227. Effective Head on Filter. — Inasmuch as the depth of sand ranges from perhaps 3 to 5 feet the Avater aviII experience considerable resistance in floAving through it. The distance in elcAvation between the AA-ater surface oA'cr the filter and that of the AA^ater as it leaA-es the filter measures the loss of head experienced in passing through the sand and the drainage- passages under it. It has been maintained by some foreign 392 WATER-WOIiKS FOR CITIES AND TO]VXS. authorities that this loss of head should be not more than 24 to 30 inches ; that a greater head would force the water through the sand at such a rate as to render desired purification impossible. Experience both in the laboratory and with public filters in. this country does not appear to sustain that view of the matter ; considerably greater heads than 30 inches have been used with entirely satisfactory results both as to the removal of organic matter and bacteria. It appears to be best so to arrange the Ifow of water through the sand and the underdrains as to avoid in either a pressure below the atmosphere, as in that case some of the dissoh-ed air in the water escapes and produces undesirable disturbances in the sand, resulting in reduced efficiency. Xo precise rule can be given in respect to this feature of filtration, but it seems probable that satisfactory results may be obtained under proper working of filters with a loss of head not greater than the depth of water on the filter added to the depth of sand in it, although that maximum limit would ordinarily not be reached. The depth of water on the filter may be taken from 3 to 5 feet. In this country it is seldom less than the least of these limits, and perhaps not often equal to the greater limit. 228. Constant Rate of Filtration Necessary. — Care should be taken in the operation of filters to avoid any sudden change in the texture or degree of compactness of the sand. At the t'imes when workmen must necessarily Avalk over the surface the^- should be provided with special broad-based footwear, so as to produce as little eftect of this kind as possible where they step. Sudden changes in the degree of compactness cause correspond- ingly sudden changes in the rate of fihration, and such changes produce a deterioration of efficiency. This may be due to two or three reasons. Possibly such changes may open small chan- nels through which water finds its way too freely; or the break- mg of the gelatinous bond between the grains of sand mav operate prejudicially. At any rate it is essential to avoid such sudden changes and maintain as nearly uniform a rate of filtration the entire filter as possible. Again, the age of a filter affect's t some extent its efficiency. A month or two of time is required when a new filter is started, to attain what mav be called its normal efficiency. Even after that length of timethe filter aains OA-er o SCRAPING OF FILTERS. 293 in its power to retain and destroy bacteria. This action is par- ticularly characteristic of filters formed of comparatively coarse sand. 229. Scraping of Filters. — More or less solid inert as well as organic matter accumulates on the surfaces (if the slow sand filters, so that at t. -xl of proper peril )ds of time, depending upon the character of the water filtered, this surface accumulation must be scraped oft' and remoA^ed together with the sand into which it has penetrated. In scraping the filter it is im])ossible to re- move less than .25 or .5 inch of sand, and at least .5 to .75 inch is removed whenc\'er a filter is scraped. Sometimes i or 2 inches may be remoA'ed. This sand may Ijc washed and again placed upon the filter for use. The operation of scraping exhiljits a fresh sand surface to the applied water. It has been held, par- ticularlv by foreign authorities, that this operation of scraping militates against the eft.ciency of the filter for the time Vicing. The investigations of the ^lassachusetts State Board of Health and other experiences in this countr)' do not confirm that vicAV wdiich is based on the assumption that the top nitrogenous film is essential to efticiency. These investigations have shown that this film is not necessary in intermittent filters; that in many instances no diminution of efficiency has resulted from a removal of the film to a depth of .3 inch; that e^-en the presence of that film has not given efficiency to coarse sand when the coating was thick enough to completely clog the filter; and, further, that the material of this nitrogenous film is found at a depth of sev- eral inches below the surface. It is practically certain that the scraping to depths not exceeding i inch have no sensible effect upon the efficiencv under proper management and operation of the filters. This is particularh' tnic if the thickness of sand is from T. to 5 feet. It is undoubtedh- true that with verv shallow sand filters from i to 2 feet in depth the scraping of the surface mav have some effect upon bacterial efliciency. It has been the custom in connection Avith some European filters to waste the water which first passes through after clean- ing, but the usual practice in this countrv is to fill slowlv the filter nth filtered AA-ater from beloAv and, after the sand is submerged, to permit it to stand a little Avhile before use. Care taken in w 294 WATEFi-WOUKS FOR CITIES AXD TOWXS. this manner Avill insure an efficiency to a freslily scraped filter sufficient to a^-oid any Avastage. 230. Introduction of Water to Intermittent Filters. — Where intermittent filters are used it is of the greatest importance to conduct the water to them so as not to disturb the sand on their surfaces. This can readily be done in a number of wa5's. If the shape of the filter is not oblong, it will be adA'isable to iVjrm a num- ber of main drains or passages in the sand from which smaller depressions or passages near together may lead the water to all parts of the surface. The fiowing of the first water through these depressions will permit the entire surface to be coA-ered so grad- ually as not to disturb the sand grains, and it is essential that such means or their equiA'alent be employed. If the filter is long and narrow in shape, the main ditch along one of the longer sides, with depressions at right angles to it or across the filter and near together, will be sufficient to accomplish the desired purpose. Obvioush' when filters are not intermittently used such precautions are not needed. 231. Effect of Low Temperature. — In the earlv davs ()f the use of sand filters in this country it was frequently supposed that the low temperature of the winter caused decreased bacterial purification and a decrease in poAver to reduce organic material. It now appears that such is not the case. The effects of low temperature, such as is experienced in Avinters of this climate, may be overcome by temporarily covering the filters so that heaAy ice cannot form and produce disturbances in one Avay or another prejudicial to efficiency of operation. The agencies which operate to reduce efficiency in cold Aveather are no" longer believed to be those due to Ioav temperature. They are rather indirect and mechanical, and may be readily oA-ercome by the prevention of the formation of ice. 232. Choice of Intermittent or Continuous Filtration. The process of sIoav sand filtration Avhen continuous has been shoAA-n by experience to be entirely eft'ectiA-e for ordinary potable Avaters, but in those cases Avhere the amount of dissolved oxygen may be loAv and Avhere the amount of organic matter is relatively high it may be advisable to resort to intermittent filtration. Neith'er method, hoAvever, can be depended upon to render potable a tilZE AXD ARRAXdEMEXT OF SLOW SAXD FILTERS. 2'.i5 water which has been robbed of its free oxygen by an excessive amount (.if contaminated organic matter. Nor can tliese processes be expected to remo\'e C(jl()ring matter prciduced ti\- peaty soils or other conditions in \\'hieh large amounts of \-egetable matter have been absorVied b}^ the Avater. The methods, therefore, have their Hmitations, although their held of application is sufhcicntly wide to coA'cr nearh' all classes of jk itablc water. 233. Size and Arrangement of Slow Sand Filters. — ^\mong the hrst questions to arise in the design of slow sand filters are their size and arrangement. The total area will Ijc determined by the total claih- draft and the rate of filtratii >n. Rates ( if filtra- tion running from 2.5 to ,3 million gallons per acre per dar, or even more, ha\"e been found satisfactory and are cusfomarv in this countrv. HaA'ing given, therefore, the total daih' quantifv required, it is onh' necessary to divide tliat by the rate of filtration per acre and the result will be the number of acres rec[uired for the total filter-bed surface. This net area, howe\'er, is not suffi- cient. Unless there is ref|uisite storage (.if filtered water to meet the \-ariation in the hourly draft for the day, the capacity of the filters must be sufticient to meet the greatest hourl}' rate, which must be taken at least i-;\- times the average hourly demand during the dav ; indeed this is only pi-udent in any ease. Again, it is nccessarv to di^'ide tlie total filter surface into small portions called beds, so that one or more of them may be withdrawn from use for cleaning or repairs, Avhile a sufficient filter-area remcdns in operation to supply the greatest hourly draft. This surplus area wiU usually run from 5 to 20 per cent of the total area ( if the filter-beds, although for small towns and cities it may be much more. The sizes of the filter-beds will depend upon the local circumstances of each case. It is evident that as each single bed must have its individual set of appliances and its separating walls, the purpose of economy will be best served by making the beds as large as practicable. At the .same time they must not be made too large, for in that case the portion out of use might form so large a percentage of the total area as to increase unduly the cost of the entire plant. A size of bed varsdng between .5 and 1.5 acres is frequently and perhaps gen- erally found in foreign filtering-plants. If filter-beds range in 296 WATER-WORKS FOR CITIES AXD TOWXS. area from .5 acre to 2 acres, the latter for large plants, the pur- poses of ecoiK.imv and convenience in administration will probably be well served. The grouping of the beds is an important con- sideration and will depend somewhat, at least, upon the shape of the plot of ground taken for the filters. It is advisable that the inlets to the different beds should, as far as possible, discharge from a single inlet-pipe or main. This will generally be most conveniently accomplished by making the beds rectangular in shape, grouped on each side of the supply-main, with their longest dimensions at right angles to it. This arrangement is illustrated bv the grouping of the filter-beds in the Albany plant, shown in Fig. 7. In the case of a single oblong bed, like that at Lawrence, Mass., shown in Fig. 4, page 284, its relatively great length and small width makes it possible to run the main supply along one side, from which branch depressions \\-ith concrete bottoms enable the water to be distributed uniformlv over its surface in the man- ner shown in the figure. It is further necessary to group the filter-beds, pumps, sand-cleaning appliances, and other portions of the plant, so that the ends of economy and efficient adminis- tration mav be served in the highest degree. It is alwavs neces- sary that tliese features of the whole filtration SA'stem should be carefully kept in vie\\' in laying out the entire plant. 234. Design of Filter-beds. — The preparation of the site for a group of filtration-beds also involves the consideration of a num- ber of principal questions. In the first place, the depth required for the sand and underdrains will not be far from 5 feet, and there must be a suitable bottom prepared below the collecting-drains. Again, the dc]-)th of water above the sand mav varv from 3 to 5 feet, making the total depth, including the bottom, of the'^ filter proper about 10 or 11 feet, and this may represent the depth of exca\-ation to be made. If the material on ^A-hich the filter to be built is soft, it may be necessary to driA^e piles to support the superincumbent Aveight. The bottom must be made water- tight. This can be done either by the use of a layer of well rammed or packed clay, i to 2 feet in thickness, carrying 6 or 8 inches of concrete, or by a surface of pa^-ed brick or stone. If the sides of the filter-beds are ..f embankments with surface slopes, the latter may be protected m the same manner. If the DESIGX OF FILTER-BEDS. 2r, sides are of walls of masonry, concrete is an excellent material to be used for the purpose. In designing the sides of filters or of the piers projecting up through the sand for the support of the roof, m case there is one, 208 WATER-WORKS FOR CITIES AXD TOWXS. it is imperative that care be taken to prevent water from flowing dcAvn through the joints between the sand and tlie sides of piers or tlie masonry sides of the filter-beds. There should be no vertical joint of that character, but the faces of masonry in con- COVERED FILTERS. 2 twice as much as open filters, fait the}- enhance the sanitary A'alue of the water. The heiglit of the masonrv roof must be abi_)ut 2 to 3 feet abfiA'c the upjier surface of tlie water and high enou.gh to offer C( mvenicnt access to the sand when it is to be cleaned and renewed. The length of span for the arches or domes is seldom more than 12 or 15 feet. 236. Clear-water Drain-pipes of Filters. — After the Avater has passed through the sand it must be withdra\\'n from the 1 lottom < )f the filter Avith as little resistance as practicable. This necessi- tates, in the first place, the liottom of the filter to be so shaj^ed as to induce the Plow of the filtered water toward the lines of drain-pipes which are laid t(T receive it. These pipes consist of the main members and the branches, the mam members being laid along the centres of the beds and the liranches running from them. The bottoms of the filters, therefore, should be formed with depressions in which the mam pipes are laid, and Avith sucli grades as to expedite the moA^ement of the AA-ater fioAving through the branches. If the bottoms are of concrete, they can adA-an- tageously be made of inA^erted arches or domes, the drain-pipes being laid along the lines of greatest depression. In such cases the loads produced by the Aveight of the roof are more nearly uifi- formly distributed over the bottom. The sizes of the drains aa-III 300 WATER-WORKS FOR CITIES AND TOWNS. be dependent upon the areas from which they withdraw water. It is advisable to make them rather large, in order that the water may flow through them more freely. They seldom need exceed 6 or S inches. They are preferably made of salt-glazed vitrified pipes laid with open joints, around and in the vicinity of which are placed gravel or broken stone, the largest pieces with a maximum diameter of i to 2 inches. The largest broken stone or coarsest gravel is near the pipe and should decrease in size as Interior of Covered Filter at Ashland, Wis. the drain -pipe is receded from, so that the final portions of the graA'el farthest remo\'ed from the drains will not permit the filter- sand to pass into it. When properly designed and arranged, the loss of head in passing from the farthest points of a filter-bed to the point of exit from the filter will not exceed about .01 to .02 of a foot. 237. Arrangement of the Sand at Lawrence and Albany. — AboA'e this gravel is placed the filtering-sand, about 4 feet thick in the Albany filter and 3 to 4 feet thick in the filter at Lawrence, Mass. The sand in the Albany filter was specified to have not ' ' more than 10 per cent less than .27 mm," in diameter and "at least 10 per ARRANGEMENT OF SAND AT LAWRENCE AND Aj^BANY. 301 cent by vreight shall be less than .36 mm." in diameter. Over the entire floor was spread not more than 1 2 inches of gravel or broken stone, the lower 7 inches consisting of broken stone or gravel with greatest diameter varying from i inch t(T 2 inches ; the remaining 5 inches of the lower i foot was composed of broken stone or gravel decreasing from i inch m greatest diam- eter to a grain a little coarser than that of the sand above it. In all cases, sand for the filter-bed should be free from everythino- that can be classed as dirt, including clav, loam, and vegetable matter. Furthermore, it should be free from any mineral "matter which might change the character of the water and render it less fit for use. This filtering-sand is usually placed in position with a hori- zontal surface. At Lawrence, ho\ve\-er, it \\-as placed with '"^Si^l MMMHMJJBl ■MWWWMWr* ^-'"^WP^JBHI f^^U IgiBHB WSSBSm *,;.'■; „.;' •■'■ •■^a*-? ^1 ^K ^ ^9b 9|^9B|k9H h^b^^^^^bb nUf: .'. ^'-JH ^^^^^^M 1 -^i^ "J! BEi"^*^ |[^K%^^^^H K| ''<'':;'^ f"* ' ^Vj[^cpHp■■ F .^-^ SrtiWIJiMBi ^HHHHB|^fl ^^^^T^ptvTjIjBl DH'^' !' . ^ -' >!^'^3^H -fi ^ fllHH ^^^^^^^^1 wf^'-- \^^^^'^f^L ^t' - ^ "''''^^^1 ■^■■■iMK-'i^^^H ^K-' ^^ -^^Ka ^^^^^H^H ^^' '"^^^Lt^H ^^^'^' 'i^l Bi^^^*'^H ^^^^■j WBmBMJ |K*4: ..-'V^B IE Si 11 L,> ■^■^P»"W^^ ■■■'^^ ffl jHHR!?!^^^^^^H ^HpHpHHRH ^^l^^^»~ jiaj^ '' ^P f fc ' ^-'ia I^By^^^^'^^^ hBI^^HH ■Bp T' <'i i^iH BK '"^ ^^^^^ SF- :■ 4^ ^I^BttiRlB^^^ Or I^HB^^^v- - -^-v M \^ sj^^l ^^R^^^'-.' m 'H P.irtiuUy Filk-d Cuvered S;tnd Filter shdwin^^ DrLiiii pipu. a waw surface, the horizontal distance between the crests of two consecutive waves being 30 feet, the concrete gutter for admitting the water being half-way between, all as shown in the illustrations. The sand of this filter was of two grades, the coarser sand having an eft'ective size of 0.3 mm. (.118 inch) and the finer an eft'ective size of 0.25 mm. (.098 inch). The two dif- 302 WATER-WORKS FOR CITIES AXD TOWXS. ferent sizes of sand are seen not to be arranged in horizontal layers, l")ut so that the finer is OA-er the drains and the coarser between. The Xo. 70 sand is capable of passing 70 million gal- lons per acre per day with a head on it equal to the depth of sand, while the No. 50 sand can pass 50 million gallons per acre per day with a head on it equal to its depth. There appears to be no special adA'antage in placing the sand in filters other than in horizontal layers with an effective size practically uniform. 238. Velocity of Flow through Sand. — The A'elocity with Avhich water will flow through a gi\-en depth r)f sand •with a kmjwn depth or head above the surface of the latter has been carefulh' iuA-estigated by the i\Iassachusetts State Board of Health with the following results : t'=the velocity at which a solid column of water, Avhose sec- tion equals in area that of the bed of sand, moves down- ward through the sand in meters per day; this is practi- cally the number of million gallons passing through the sand per acre per day. c = a constant, having the A-alue of 1000 for clean sand, and 800 for filter-sand after having been some time in use. (7 =the eft'ective size of the sand-grain in millimeters. Ji =the head lost by the water in passing through the sand at the rate v; this is the eft'ective head of water producing motion through the sand. /=the thickness of the sand bed. / = the temperature of the water in degrees Fahr. The velocity v, as determined by experiment, takes the fol- lowing form: Ji / 1+ 10 V = ca-- l \ 60 This formula cannot be used for the flow of water through all sands of all thicknesses and under aU circumstances. It is lim- ited to eft'ective diameters of sand between .1 and 3 mm., having a uniformity coefficient not greater than 5. /; and / mav be taken in any unit as long as both are expressed in the same unit, since the ratio of the two quantities will then not be aft'ected. FREQUEXCY OF SCHAFIXG. 303 If the effective head of water on the fihxr or the head lost is equal to the tliiekness of the bed of sand, tlie ratio of /; divided l:>v / will be I. In ease the formula is used to express the quanlit\' of water flowing thrrmgh the sand ])er acre per tkiy, it must Ije remembered that -c will be the numljer of million gallons and not the total number of gallons. The formula can onl}^ be used when the sand is Avell compacted and where the A'oids of the sand are entirely filled with water. 239. Frequency of Scraping and Amount Filtered between Scrap- ings. — The frequency of the scraping of filters will depend upon the amount of organic matter in the ^^•:lter and upon the rate of filtratii;>n. Bet\\-een the years 1S93 and iqoo the jieriods between scrapings of the Lawrence filter ranged generalh' frum 20 to 32 davs, although periods as small as 13 or 19 are found in the records. The quantity of water passed betAA-een scrapings varies generalh" from 67 million to 90 million gallons, although it fell as low as 49 millions and rose as high as 109 millions. In the case of the .VlfiauA- filter-]dant, up to the end of the year 1900 the shortest period betAveen scrapings AA-as about 15 days and the kmgest about 4.2 daA's, the smallest ciuantity of AA'ater passing through auA' filter betAveen scrapings being 26,735,000 gallons and the largest 76,982,000 gallons. The operation n{ the Albany filters for the A'car 1901 shows that the aA'crage nin of a tied AA-as 26 days betAA'een scrapings, Avith a total of 70,000,000 gallons per acre for that period. These figures represent aljout the usual Avorkings of sIoav sand filters at the jiresent time, the period betAveen scrapings rtmning usually Viefween 15 and 30 days, and the quantitA' from 30 nfillion galL.ins per acre to 100 million gallons per acre. 240. Cleaning the Clogged Sand. — The clogged sand scraped from the fi^p of the filters at the periods of cleaning is removed to a eoiiA-enient point AAdiere appliances and machinery are aA-ail- able for Avashing it. This is an item of some importance in the administration of filters, as the sand Avhieh is removed and washed is at a later period replaced upon the filter-bed. \^arious methods haA-e been tried for the purjiose of cleaning sand etti- cientlv and economically. The continuous ejector sand-AAasher, one set of AAdiieh is used at Albany, is probably as efficient as any 3U4: WATER-WORKS FOR CITIES AXD TOWNS. CONTROLLING OR REGULATL\G APPARATUS. 305 machine yet devised. It is shown in Fig. 8. It will be obsen^ed that the dirty sand is fed to the machine at one end into a hopper- shaped receptacle. In the bottom of this hopper is a n(jzzle through which water is discharged from a pipe running along the entire bottom of the machine. This jet of water forces the sand upward through a suitable pipe into a reservoir ^\•hich dis- charges the sand and water into another hopper, and so on through the series of five. Evidently there may be any number of hop- pers in the series, a jet of water being proA'ided at the bottom of each. In this manner the sand and water are thoroughly mixed together and compelled to flow upward from each hopper to the next, the dirty water overflowing also from each hopper into a tank underneath, whence it runs to waste. The clean sand and water flow out of the machine at the end opposite to that at which they entered. After the washed sand is dried it is ready to be replaced in the filter. 241. Controlling or Regulating Apparatus. — It is essential to the proper working of a slow sand filter that the amount of water admitted to and passing through it shall be as nearly uniform as practicable. This necessitates controlling or regulating ajipara- tus, of which there are two general classes, the one automatic and the other worked by hand. There are a considerable num- ber of appliances of both classes. The filtered water flows from the end of the drains to one or two small tanks formed by suit- able masonrs^ walls imniediately outside of the filter-beds and rises to a level determined by the loss of head in passing through the filter. The difference in elevation between the water surface over the sand and that in the filtered water-tanks shows the eftective head which causes the water to flow through the sand. The object of the controlling or regulating appliances is to keep that head as nearly constant as possible. Both the hand and automatic appliances preserve the value of that head by main- taining constant discharges through either vertical or horizontal orifices, the orifices themselves being movable. They may be rectangular or other orifices with horizontal lips or crests. If the control is automatic it is accomplished usually by a float which raises and lowers the orifice in such a way as to maintain a con- stant dift'erence of level between the filtered and the unfiltered 300 WATER-WORKS FOR CITIES AXD TOWXS. COST OF SLOW SAXD FILTERS. 307 AYc'iter. The figures illustrate lioth types of regulating appliances, the actions of which ^\■ill lie readily understood. 242. Cost of Slow Sand Filters.— The cost of bi .th the open and co\-ered slow sand filters \a-i11 oliA'iously \-ar\- according to the C( .St of lalior and materials at then- sites. The original cost of the Lawrence filter, about 2.44 acres in total areal' was nearly $25,000 per acre. The C( .st ( if co\-ered filters, S(.. far as constnicted ni this country, varies from about $44,000 to nearly $51,000 per Hi.'servoLr GRAi ^.... '/TO BESFBVOIR. 3- Fir.. 0. — Rail-float Regulator of Rate Fir,. lo. — Regulating Apparatu.s Designed of Filtration. by J. H. Fuertes for the Tome Institute Filters. acre excluding the pipe, pumping plants, and sedimentation- basins. The Albany covered filters cost about $38,000 per acre including filtering materials, but excluding excavation, pumps, buildings, sedimentation-basins, ]ii]iing, and sand-washing ma- chinerv, or nearly $46,000 per acre including those items except pumps and sedimentation-basins. The roof, included in the preceding estimate, cost about $14,000 per acre. The smaller the filters the greater the cost per acre, as a rule, as would be expected. A single open filter at Poughkeepsie and three open filter-beds at Berwvn, Pa., cost respectivelv >^42,ooo and $36,000 per acre, the former being little less than .7 acre in area and the 308 WATER-WORKS FOR CITIES AXD TOWNS. latter having an aggregate area of a little more than one-half acre. A covered filter at Ashland, Wis., consisting of three beds of one- sixth acre each, cost at the rate of about $70,000 per acre. 243. Cost of Operation of Albany Filter. — The cost of operat- ing the Albany filter, including only the costs of scraping, remov- Fig. II. — Regulator of Rate of Filtration. Fig. 12. — Regulator of Rate of Filtration, ing sand, refilling, incidentals, lost time, and washing the sand during seventeen months ending December 29, 1900, was $1.66 per milKon gallons filtered. The cost of removing the sand (ex- OPERATIOX AXD COST OF OPERATION OF LAWRENCE FILTER. 30': eluding scraping), washing, and refilling was $1.21 per eubic yard. The tutal eost of operating the entire filter-plant, includ- ing all items, for the year 1900 was $4.52 per million gallons filtered. This covers all expenses, including pumping, superin- tendence, and laboratory, which can be charged to the operation of the filter-plant. The aA'crage removal of albuminoid ammonia at Albany for the year 1900 was 49 per cent and of the free am- t 1 I • ^^^^^ fl-j i£zu J J ■■:■:■■■ Fig. 13. — Regulator Designed by W. H. Lindley for the Filters at Warsaw, Poland. monia 78 per cent of that in the raw water, while the average bacterial removal was over 99 per cent, running from 98.3 per cent to 99.6 per cent. The volume of water used in washing the sand was about tweh-e and a half times the volume of the sand. Each cubic yard oi sand washed, therefore, required twelve and a half cubic vards of water. 244. Operation and Cost of Operation of Lawrence Filter. — It Avas originally intended that the Lawrence filter should be worked intermittently. The I\ferrimac River water, which is used by the citv of Lawrence, was known to carry at certain periods of the year sufficient t}'phoid germs received from the city of Lowell to produce at least mild epidemics. The intermittent operation was considered necessary' to furnish the filter with the requisite oxygen to destroy beyond a doubt all pathogenic bacteria. The increasing demands of water consumption during the years that have elapsed since filtration began in 1804 have seriously modi- fied these conditions, so that the intermittent feature of operation of the filter is no longer vers^ prominent. During 1898, for instance, the filter was drained only four to thirteen times per 310 WATER-WORKS FOR CITIES AXD TOWXS. month, with an average of eight monthly drainings. In 1899 the drainings were more frequent, A'an,'ing from five to fourteen per month and averaging eleven times. Finally, in 1900, the monthh- drainings ranged from three to thirteen, with an average of eight. It may be considered, therefore, that the Lawrence filter occupies a kind of intermediate position between inter- mittent and continuous operation. The total cost of operating the filter at Lawrence, including scraping and washing of sand, refilling, removal of snow and ice, and general items in the period from 1895 to 1900, both inclusive, varied from a minimum of S7.70 per million gallons to $9.00 per million gallons. If the removal of snow and ice be omitted, these amounts Avill be reduced to $5.10 and S6.90 respectively. The cost of washing the sand only in the Lawrence filter during the same period varied horn 45 to 67 cents per cubic yard. The volume of water rec^uired for that washing varied from ten to fourteen times the A-(jlume of sand. 245. Saxiitary Results of Operation of Lawrence and Albany Filters. — The average number of bacteria in the ilerrimac River water applied to the filter during the period 1894 to 1899, both inclusive, A-aried from about 1900 per cubic centimeter to 34,900, and the percentage of reduction attained by passing the water through the filter \'aried in the same peri(^d generally from 9 7 to 99.8 per cent, with an aA'erage of about 99.1 per cent. In the city of Lawrence the a\'erage number of cases of typlK^id fever per 10,000 of population has been about one third, since the introduction of filtered water, of the number of cases which existed prior to the installation of the filters, and less than one fourth as many deaths. A large number of the cases of typhoid occurring after the installation of the filter have been traced to the use of unfiltered water, and it is probable that all or nearty all could be similarly accounted for. In the city of Albany the experience had been quite similar. The average number of deaths per year from tvphoid fever for ten years before the introduction of filtered water was 84, while in 1900, with the filter in operation, the total number of deaths was 39. These figures are sufficient to show the marked bene- ficial eft'ect of filtered water on the public health. RAPID FILTRATIOX WITH COAGULANTS. 311 246. Rapid Filtration with Coagulants.— It has been seen that the rate of filtration through open sand filters does not usually exceed 2 to 4 million gallons per acre per day under ordinary circumstances, iluch greater rates W(juld clog the sand and prixluce less efficient results. Experience has also shown that such methods cannot be depended up(jn to remove from water coloring matter of a vegetable urigin or very finch' divided sedi- ment. In order to accomplish these ends it is necessary to Jewell Filter. employ suitable chemicals which, acting as coagulants, may accomplish results impracticable in the open filter. Resort has therefore been made first to the adoption of suitable coagulants and then to such increased heads or pressures as to force the water through the sand at rates from 25 ti^ ,^0 or even 50 times as great as practicable in slow sand filtration. These rapid sand filters are called mechanical filters. If the water is forced through 313 'n'ArEK-]t'nRKS FOR CITIES AXD TOWNS. them under pressure, they consist of closed tanks in which sand is placed so as to leaA-e sufficient volume above it for the influent water and, supported upon a platform carrying perf(jrated pipes, strainers, or equivalent details through which the filtered water may flow into a suitable system of effluent pipes in the lower part of the filter. If water is forced through the sand by the required head, the upper part of the filter may be open, but of sufficient height to accommodate it. The same filtering material, clean sand, is used as in the slow filters; the only dift'erences, aside from the higher rate of filtration, are the greater head and the intro- duction of a coagulant to the water. The depth of sand used may vary from 2 to 4 feet. The thickness of a relatively fine sand may be less than that of a coarser sand. 247. Operation of Coagulants. — The coagulant which has been found to give the best results is ordinary alum or sulphate of aluminum. If sulphate of aluminum is dissolved in water con- taining a little lime or magnesia, aluminum hydrate and sulphuric acid are formed. The aluminum hydrate is a sticky gelatinous substance which gathers together in a flocculent mass the particles of suspended matter in the water, and it also adheres to the grains of sand when those masses have settled to the bottom. This flocculent, gelatinous mass covers the sand and passes into its voids. As the water is forced through it the bacteria and sus- pended matter are held, leaving a clear effluent to pass through. Other cdkgulants are used, such as the hydrate of iron, but it costs more than alum and is not so eft'ective in removing color, although it is an excehent coagulant for removing turbidity. Physicians have made objection to the use of alum for this purpose, on the ground that any excess might pass into distribution-pipes and so be consumed by the water-users to the detriment of health. While it is possible that further experience may show that there is material ground for this objection, it has thus far not been found to be so. It is, however, essential that only the necessary amount of alum should be used and that there may be a sufficient amount of alkali to combine with the sulphuric acid. (3therwise the acidulated water may attack the iron and lead pipes and so injure the water and produce serious trouble. It can only be stated that the method and operation of these mechanical filters PRIXCIPAL PARTS OF MECHANICAL FILTER-PLANT. 313 have thus far been sufficiently successful to avoid any of these difliculties. 248. Principal Parts of Mechanical Filter-plant — Coagulation and Subsidence. — The principal parts of a complete mechanical filter-plant in the order of their succession are a solution-tank, a measuring-tank, a sedimcntation-basm, and a filter. In case of great turbidit}' the sedimentation may be completed m two The JewL-11 Filter-plant at Xnrristuwii, reim. stages, the first in a settling-basin prior to receiving the coagulant, and the second in another basin subsequent to the coagulation. The tanks are usually of wood, although they may be of steel. The solution-tank is a comparatively small vessel in which the alum is dissolved. The solution is then run into the measuring- tank, from which it flows into the water at a constant rate main- tained by suitable regulating apparatus. It is imperative for the successful working of the mechanical filter- plant that the coagulant be introduced to the water at a uniform rate. This 314 WATER-WORKS FOR CITIES .LVD TOWNS. rate will obviously depend upon the character of the water. The coagulating solution runs from the measuring-tank into the pipe through which the water to be filtered flows and in which it first receives the alum. The water and the coagulating solution are thus thoroughly mixed and flow into the sedimentation-basin. The subsidence which is provided for in this basin may be omitted in very clear waters which carry little solid matter, but the operation of the filter itself will be more satisfactorily accom- plished if as much work as feasible is done before reaching it. The mixture must remain in this basin a sufficient length of time to allow such subsidence as can reasonably be attained. It appears from experience in this part of the work that it is not well to introduce the coagulant too long before the water enters the filter, especially if the water be fairly clear. In the case of the presence of finely divided solid matter, however, sufficient time must be permitted for the necessarv settlement. A period ranging in length from ^J hour to 6 or 8 hours may be advantageously assigned to this part of the operation, the shorter period for clear Avaters and the longer for very turbid waters. It has been suggested that two apphcations of the coagulant might be beneficial, the principal portion being given to the water before entering the sedimentation-basin and the other just before the waters enters the filter. The work of the filter, especially with turbid waters, may be much reduced by simple subsidence for a period of perhaps 24 hours before receiving the coagulant, the secondary subsidence taking place in the settling-basin in the manner already described. Duplicate solution- and measur- ing-tanks will be required in order that the process may be con- tinuous while one set is out of use. In this process it is absolutely essential also that the coagulant should be of the best quality, inferior grades haA'ing been found to be unsatisfactory in their operation. 24g. Amount of Coagulant — Advantageous Effect of Alum on Organic Matter. — The amount of sulphate of alumina will vary largely with the quahty of water. In the investigation made by Mr. Fuller in connection with the Ohio River supply for the city of Cincinnati, he found that with very slight turbidity only f grain was required per gaUon of water, but that a high degree of HIGH HEADS AND RATES FOR RAPID FILTRATloX. :51'^> turbidity required as much as 4.4 grains per gallon, witli inter- mediate amounts for intermediate degrees of turbidity. It was estimated that these quantities would correspond to an a^-erage annual amount of about 1.6 grains per gallon. In case there should be a period of three days of subsidence preliminarA' to filtration, he estimated that tVir the greater part of the time the amount of alum would vary from i to 3 grains Y>ev gallon. Occa- sionally more and sometimes less would be required. Alum has some specially A'aluable r[ualities in connection with this class of purification work. It coml lines with coloring matter, particularly that which has been acquired from contact of the water with vegetation, and precipitates it. It seems to combine also, to some extent, with the organic matter carried by the water and thus enhances the efficiency <^f filtration. 250. High Heads and Rates for Rapid Filtration. — The prin- cipal work of investigation of filtration in mechanical or pressure filters has been made for the cities of Pittsburg, Cincinnati, Lijuis- Adlle, and Providence, R. I. In the experimental work of those investigatirms rates oi filtration ranging from 46 million tci 170 million gallons per acre per day ha\'e lieen empL^yed with essen- tially the same efliciency. This is a practical result of great importance, ]iarticularlv if in the continued use of these filters on a large scale a satisfactorily high efficiency can be reached and maintained. It was observed that the number of bacteria in the effluent \-aricd A^'ith that in the vdw water. It was also noticed that similarh- to the operation of slow sand filters the rate of fil- tration should not be changed suddenly, as that is likely to cause breaks in the sand and militate against continued efficiency. In his experimental work at Cincinnati ^Ir. Fuller found that with fine sand an available head on the filter of 12 feet gaA-e economical results. He also states that ' ' high rates are more economical than low ones, and that the full head which can be economicallv used should be provided. Just where the econonfi- cal limit of the rate of filtration is can only be determined from practical experience with a wider range of conditions than exist here, but there seem to be no indications that the capacity of a plant originallv constructed on a medium rate basis (100 million to 12^ million gallons per acre daily) could not readily and eco- 316 WATER-WORK.S FOR CITIES AXD TOWXS. nomically be increased, as the consumption demanded, to rates at least as high as the highest tried here (170 million gallons per acre daily), provided the full economical increase in loss of head could be obtained." 251. Types and General Arrangement of Mechanical Filters. — These mechanical or pressure (by gravity) filters have until lately been constructed by companies owning patents either on the process or on the different parts of the filters. The fundamental patent, however, protecting rapid sand filters with the continu- ous apphcation of a coagulant has expired and the city of Louis- ville, Kv., is now constructing rapid sand filters different in design from those heretofore used. The types that have been most common heretofore are the Jewell subsidence gravity filter, the Continental gravity filter, the New York sectional-wash gravity filter, and others. They all possess the main feature of accelerating the rate of filtration by pressure, either in a closed tank (rarely) with comparati\'el3r small water volume above the sand or by an open filter with sufficient head of water above the sand to accomplish the high rate desired. This latter method is that now generally used, as by it the requisite steadiness of head or pressure can be secured. The closed type is subject to obi'ec- tionable sudden changes of pressure which prevent or break uniform rates of filtration. The sand is supported upon a plat- form with a suitable system of pipes fitted with valves or gates for the withdrawal of the filtered water, the space below the platform forming a small sedimentation-chamber. They are usually constructed in comparatively small circular units, so that one or more of a group may be withdrawn from operation for the purposes of cleaning or repairs without interfering with the operation of the others. This system of small units, gives some marked practical advantages, as housing is readilv accompUshed, and if necessary the plant may be easily removed from one point to another. It is obvious that with the large amount of water forced through a given area of filter-bed the sand ^\•ill become clogged within a comparatively short time, requiring washing and repfac- ing. Mr. Fuller found at Cincinnati that the periods between washmgs when fine sand was used in the filters ranged from 8 to TYPES AXD GEXERAL ARRAXGEMEXT. 317 24 hours, with an average of 15, but with coarse sand the average became 20, with a range of from 6 to 36 hours. The time required for washing the sand at Cincinnati was 20 minutes for coarse or 30 minutes for fine. At Providence Mr. Weston found that the average time of washing was about 11 minutes. The cleaning is accomplished partially by stirring the sand with revolving amis, as shown in the accompanying figures, but generalh- bv continental P'ilter. forcing the water in a re^•erse direction through the sand and allowing the wash-water either to run to waste or to be again purified. The filters are designed for the purpose of cleaning bv the reversal of the direction of the flow of water. Latterly the sand has been cleaned by forcing compressed air at a low pressure through it and the superimposed water. The passage of the air or water upward through the sand produces such a com- motion among the grains that they rub against each other and 318 WATER-WORKS FOR CITIES AXD TOWXS. clean themselves of the adhering material, allowing it to be car- ried off by the water above the sand. Both methods are much used and are satisfactorily effective for the purpose. It was found at Cincinnati that 4 to 9 per cent, with an average of 5 per cent, of filtered water was required for washing the fine sand, and onlv 2 to 6 per cent, with an average of 3 per cent, for the coarse sand of the mechanical filters used in Air. Fuller's experiments. ]\Ir. Weston has found about the same figures in his experimental work at Providence. The wash-water need not be wasted at all if it is pumped back into the subsidence-tanks. It has been found in some cases that the efficiency of the filters after washing is not quite normal, and that possibly 2 or 3 per cent of the water must be wasted unless it is allowed to run back into the subsidence-tanks and again pass through the filter. Under such circumstances it has required 20 to 30 minutes of operation of the filter after washing to regain its normal effi- ciency. 252. Cost of Mechanical Filters. — The cost of these mechani- cal filters has been found to range as high as a rate of $500,000 per acre, which is probabh' about ten times as much as the rate of cost for the slow sand filters. On the other hand, the efficiency of the mechanical filters may be as high as the other class, with a rate of filtration from thirty to fifty times as great, and with a cost of operation less than that of the slow sand filters. The cost of the filters per million gallons of filtered water may, there- fore, be reduced to perhaps one fourth of that of the slow sand type. 253. Relative Features of Slow and Rapid Filtration. — It is premature, even unnecessary, to make a comparison between the slow and rapid sand filters. The former are well adapted to a large class of potable waters in which there is not too much or too finely divided solid matter and in which the coloring from organic origin is not serious. They have the advantage of requir- ing no chemicals and are capable of attaining a high degree of efficiency. The average rate of filtration may be taken about 3,000,000 gallons per acre per day. The rapid sand filter, on the contrary, requires the appHcation of a coagulant, but has thirty to fifty times the capacity of the other class. It is better adaoted RELATIVE FEATURES OF SLOW AND RAPID FILTRATION. 319 to the remo\-al of turbidity and color, and when properly oper- ated it gives a high efficiency. A sufficiently extended experience has nut yet, ho\ve\-er, been attained to enable a complete state- ment to be made as to the entire field to which they may be adapted. They have certainly been shown to possess A-aluable qualities in a number of respects, and they are unclouljtedly destined to play an important part in the purification of waters. PART IV. SOME FEATURES OF RAILROAD ENGINEERING. CHAPTER XXI. 254. Introductory. — The first step toward the construction of a railroad is the location of the line, which requires as an initia- tive a careful ocular examination of the general vicinity of the proposed road, supplemented by simple and approximate instru- mental work rapidly performed. Following this reconnaissance, as it is called, more complete surveys and examinations are made both in the field and on the maps plotted from the data of the field-work. The prosecution of this series of operations produces the final location, together with the accumulation of such maps, profiles, and other data as may be required in the construction of the road-bed, bridges, and other structures constituting the complete railroad line with its ballast and track in place ready for traffic. The ultimate purpose of any railroad line is the transportation of passengers and freight under conditions, including those of a physical natu-e connected with the road as well as the rates received, leading to profitable returns. Competition or other circumstances attending the traffic of a given road will fix the maximum rates to be charged for transportation. It is the business, first, of the civil engineer so to locate and design the road and, second, of the manager so to conduct the transportation as to make the margin of profits the greatest possible. It will be the purpose of this lecture to consider in a general way only 320 Till': ROYAL (lOHGE. ni The K-v,lI Gor, 322 SOME FEATURES OF RAILROAD ENGINEERING. some of the features of a railroad and its operation which are related directly to civil engineering. 255. Train Resistances. — It is a fact confirmed by constant daily experience that, however nicely the machine impelling the railroad train or the tracks supporting the cars may be built, considerable frictional and other resistance is offered to the move- ment of the train when the latter passes over a perfectly level and straight track. A considerable portion of the cost of transportation is ex- pended in overcoming this resistance. When the line fails to be either level or straight other resistances of magnitude are devel- oped ; they are called the resistances of grades and curves : and it is the business of the civil engineer so to design the railroad as to reduce these two classes of resistance to an absolute minimum, in view of certain other conditions which must be cojicurrently maintained. 256. Grades. — The grade of a railroad is expressed usually in this country by the number of feet through which 100 feet of length of line rises or falls, or by some expression equivalent to that. If, for instance, the line rises 1.5 or 2 feet in 100, it is said to have an ascending grade of 1.5 or 2 per cent. Or if the line falls the same amount in the same length, it is said to have a descending grade of 1.5 or 2 per cent. It is evident that a grade which descends in one direction would be an ascend- ing grade for trains moving in the opposite direction, so that grades favoring traffic in one direction oppose it in the other. Hence, other things being equal, that road is the most advantageous for the movement of trains which has the least grade. The grades of railroads seldom exceed 2 or 2.5 per cent, although, as will presently be shown, there are some striking exceptions to that general obser^-ation. The actual angles of inclination of railroad tracks from a horizontal line are therefore as angles very small, but their disadvantages for traffic increase rapidly. A simple principle in mechanics shows that if the railroad train with a weight W moves up a 2 per cent grade, one com- ponent of the train weight acts directly against the tractive force of the locomotive or other motive power. If a is the angle of GHADES. o2:) inclination of tlie track to a horizontal line, this opposing com- ponent will have the value W sin a. When angles are small their sines are essentially equal to their tangents. Hence, in this case, sin a would have the value .02 or 1/50 of the train weight. If the weight of the train were 500 tons, which is a rather light train for the present time, this opposing force would be 10 tons, or 20,000 pounds, which, as we shall see later on, is more than one half of the total tractive force of any but the heaviest loco- motives built at the present clay. This simple instance shi iws the advantage of keeping railroad grades down to the lowest practicable values. One of the most economical freight-carrying roads in the United States is the Lake Shore and Michigan Southern of the New York Central system, running from Buffalo to Chicago. Its maximum grade is 0.4 of i per cent. The maximum grade of the N. Y. C. &' H. R. R. R. is 0.75 of i per cent between Xew York City and ^Albany and between Albany and Buffalo, 1.74 per cent at Albany, i . 1 2 per cent at Schenectady, and i per cent at Batavia. Pushers or assistant locomotives are used for heavy trains at the three latter points. The maximum grade of the Pennsylvania R. R. on the famous Horseshoe Curve between Altoona antl Crcsson is 1.8 per cent. It is advantageous, where- ever practicable, to concentrate heavy grades Avithin a short distance, as in the case of the New York Central at ^Ylbany, and use auxiliary engines, called pushers or assistants. Some of the heaviest grades used in this country are found on the trans-con- tinental lines where they pass the summits of the Rocky ^foun- tains or the Sierras. In one portion of its line over a stretch of 25.4 miles the Southern Pacific R. R. rises 2674 feet with a maximum grade of 2.2 per cent; also apprciaching the Tehacipi Pass in Cahfornia the maximum grade is about 2.4 per cent. At the Marshall Pass on the Denver &' Rio Grande R. R. there is a rise of 3675 feet in 25 miles with a maximum grade of 4 per cent. The Central Pacific R. R. (now a part of the Southern Pacific system) rises 992 feet in 13 miles with a maximum grade of 2 per cent. The Northern Pacific R. R. rises at one place 1668 feet in an air-line distance of 13 miles with a maximum grade of 2.2 per cent. Probably the heaviest grade in the world on an 324 ^OME FEATUIiES OF TiAILROAD EXGIXEERIXG. ordinan^ steam railroad is that of tlie Calumet Mine branch of the Den\-er & Rio Grande R. R., which makes an elcA'ation of 2 700 feet in 7 miles on an 8 per cent grade and with 25° curves as maximum curvature. These instances are sufficient to illustrate maximum railroad grades found in the United States. 257. Curves. — Civil engineers in different parts of the world have ratlier jieculiar classifications of cur^xs. In this country the railroad curve is indicated bv the number of degrees in it which subtend a chord 100 feet in length. Evidentb' the smaller the ra(]ius i">r the sharper the cur\-ature the greater will be the number of degrees between the radii drawn from the centre of a circle to the extremities of a loo-fect chord. ^Vmerican civil engineers use this system for the reason that the usual tape or chain used in railroad surveying is 100 feet long. ^V verv simple and elementary trigonometric analvsis shcnvs that under this svstem the radius of anv curve will be ec^ual to 50 divided by the sine of one half of the angle between the two radii clraAvn to the extremities of the loo-feet chord. In other words, it is ecjual to 50 divided by the sine of one half the degree of curva- ture. The application of this simple formula will give the fol- lowing tabular values of the radii for the curves indicated: Curve. 1°. . 3 ■ 4°. 5°. 6^ / ■ 8°. 9°- 10°. 12°. i5°- 20°. vadius in Feet 5729 65 2864 93 1910 08 1432 69 1 146 28 955 36 81Q 02 716 78 637 27 573 69 47S 74 3 S3 06 2S7 91 258. Resistance of Curves and Compensation in Grades. In- asmuch as file resistance offered ti 1 hauling the tram around a TBANSITIOX CURVES. ''^o curve increases quite rapidly as the radius of curvature decreases, it is obvious tliat in constructing a railroad the degree of each curA'e should be ke])t as low as practicable, and that there should be no more cur\'os than neeessar5^ While no definite rule can be given as to such matters, curves as sharp as io° (37,1.09 feet radius) should be avoided wherever practicable. It is not ad- A'isable to run trains at the highest attainalile speeds around such cur\-es, nor is it done. Inasmuch as curve resistance has cnnsid- eraV)le magnitude, as well as the resistance of grades, it is natural that whereA-er curves occur grades should be less than would be permissible on straight lines or, as they are called, tangents. If a maximum gradient is prescribed in the construction (jf a railroad, that gradient will determine the maximum weight of train which can l:ie hauled on the straight portions or tangents of the road. If one of these grades should occur on a curve, a less weight of train could be handled by the same engine than on a tangent. Hence it is customary to reduce grades by a small amount fi ir each degree of curvature of a curve. This operation of modi- fA'ing the grades on curves so as to enable a locc^motive to haul the same train around them as up the maximum grade on a tan- gent is called compensating the curves for grade. There is no regular rule prescribed for this purpose, because the combination maA' necessarily vary between rather wide limits in A'iew of speed, conditiiin oi track, and other influencing elements. The com- pensation, hiiwcA'er, has perhaps frequentlv been taken as lying between .03 and .05 per cent of grade for each degree of curva- ture. In other words, for a 5° curve the grade would be .15 to .25 per cent less than on a tangent. This compensation for grades is carefully considered in each ease by ei\"il engineers in view of experience and such data as special investigations and general railroad operation have shoAvn to be expedient. 259. Transition Curves. — High speeds for Avhich modem rail- roads are constructed haA'c made it necessary not ijnly to pnitect road-beds, but als(A to make the passage from tangents to curves as easy and smooth as possible. This is accomplished by intro- ducing between the curve and the tangent at each end what is called a "transition" curve. This is a compound curve, i.e., a curve AA'ith varying radius. At the point where the tangent or 326 SOME FEATURES OF RAILROAD ENGINEERING. 2 b ^'' ^ J t 1 ^ ■Si^ 1 1 ■V 1 \ W ^C 3 \ 1 U_c— ^>^ 2 b ROAD-BED, IXCLlDIxn TIES. 327 straight line ceases Uie radius nf the transition curve is infinitely great, and it is graducdly reduced to the radius of tlie actual curve at the jxiint wlicre it meets the latter. I3v means (">i sucli gradual change of eur\-ature the trucks of a rajjidh" mo\"ing train do not suddenly jxiss from the tangent to the eur\-e pmper, but the\' jiass gradually from nuition in a straight line to tlie sharjiest curwiturc o\-er the transition eur\'e. The rate of transi- tion is fixed by the character of the cur\'es, whicl: have lieen sul)- jected to carelul analysis bv civil engineers, and the\' can be found fulh' discussed in standard works on railroad Location. 260. Road-bed, including Ties.-- Xot onl\' the high rates of speed of modern railroad trains but the great weights of locomo- tives and cars ha\X' demanded a remarkLitde degree of perfectiini in the e<:instruetion of the road-bed and in the manufacture of rails. The fa\'orite ballast at the present time for the best ty]")es of road-beds is generalh' broken stone, although gra\'el is used. The first reriuisites are a solid foundation and jierfect drainage whether in cuts or fills. Figs, i , 2, 3, and 4 sliow two iir tliree types of road-bed used bA' the New York C'cntral and Hudson Riwr R. R., the Pennsvlvania R. R., and a si'iecial tyjK- adopted by the B. lV- ("). for the belt-line tunnel at Baltimore. These sections shijAv all main dimensions and the ])ro\'ision made for drainage. The general depth of ballast is at>out 18 inches, including the drainage laver at the bottom. The total width of road-bed for a double-track line A^aries frequently between 24 and 25 feet, while the width of a single-track line maybe found between 13 and 14 feet. In the cross-sections shown the requirements for drainage Stunt Lriua Erifk Pr;iii) Fig. 4.— Baltimore Belt-line Tunnel, B. & O. Ry. are found to be admirabh' met. Timlier ties are almost invaria- bb' used at the present time m this country, although some experi- mental steel ties have been laid at various points. Fig. 5 shows 328 SOME FEATURES OF RAILROAD E^G1^'EERJ^'G. the steel tie adopted for experiment on the X. Y. C. & H. R. R. R. witliin tile eitv limits of New York. The time will undoubtedly come when some substitute for timber must be found, but the ■'^ tdLfL Gage-i &y,- y 3 B . . jj^ — 3^ - A-A &: h A SECTION B ■= ^«"-i- ^ r — 10 ^ -" L B-B HALF PLAN Fig. 5. -additional cost of steel ties at the present time does not indicate tiieir early adoption. 261. Mountain Locations of Railroad Lines. — The skill of the civil engineer is sometimes seve ely taxed in making mountain locations of railroads. Probably no more skilful engineering SWITCHBACKS ON THE LINE OF THE LIMA AND OROYA RAILWAY IN PERU. Fig. 6. work of this kind has ever been done than in the crossings of the Rocky Alountains and the Sierras in this country by trans-con- tinental railroad lines, although more striking examples of railroad location for short distances may perhaps be found in Europe or other countries. The main jiroblem m such cases is the making MOUNTAIN LOCATIONS OF RAILROAD LINES. 3;i9 of distance in order to attain a desired elc\'ation without exceed- ing maximum grades, such as those which liave already been given. i\Iost interesting engineering expedients must sometimes be resortetl to. One of the oldest of these is the s\\-itchback plan shoAvn in Ing. 0. This is i~irobably the simplest procedure in order to make distance in attaining elc\-atir>n. The line is Canon of the Rio Las Animas, near Rockwnod. run Up the side of a mountain at its maximum grade as far in one direction as it may be desirable to go. It then runs back on itself a short distance before being diverted so as to pass up another grade in the re\'erse chrection. This zigzagging of alignment mav obviously be made to attain any desired elevation and so OA-ercome the summit of a mountain range. The old switchback coal road near ^Mauch Chunk, Pa., is one of the oldest and more famous instances of the method, which has many times been employed in other locations. 330 SOME FEATURES OF RAILROAD ENGINEERING. THE GEnRCETOWX LOOP—TUXXEL-LOOPS. 331 A more striking mctliod, perhaps, is tliat of lor)ps by which tlie direction of a line or mtition (jf a train on it is continuous. Dis- tance is made bv a judicious use of the te)pogra])liy of tlie locality S(.i as to run the line as far up the side i )f the valley as practicaljle and then turn as much as a semicircle or more, sometimes o\'er a bridge structure and sometimes in tunnel, sn as to give further ele\'ation 1 1\' running either on the ojiposite side of the valley or on the same. A succession of loops or other curA'cs suitalily located will gi\'e the distance desired in order to reach the sum- mit. 262. The Georgetown Loop. — Fig. 7 shows one of these spiral or loop loeatmns on the Georgetown V>raneh i;if the Union Pacific Raih^tad in d 'lorado. It is a well-known and jin miincnt instance of railroad loeation of this kind. On the higher portion of this loop svstem included in the figure there is a A'iaduet on a cur\-e which ertjsses the line 75 feet alcove the rail Ixdow it and go feet abo\-e the water. This location is a six-cimen ( if excellent railn lad engineering. The length of line shown in the figure, including the spiral, is S.\ miles, and it crist $265,000 per mile exclusive of the brielges. 263. Tunnel-loop Location, Rhsetian Railways, Switzerland. — In Figs. S and 9 are shown two portions of the Albula liraneh of the Rhirtian Raihvavs, Canton Graulxinden, southeastern Swit- zerland. The line connects the valleys of the Albula and the Inn, the former being (^ne (^f the branches of the Rhine and the latter of the Danube; it therefore cuts the dn'ide between the \\-atersheds of th(>se two rivers. It is a 3.2S-feet gauge single- track road, and is luiilt largeh' ior tourist traffic, as the scenic properties of the line are remarkable. The maximum grade on this hne is 3.5 per cent. Over one portion of the line 7.8 iniles long one third of that distance is in tunnel and 13 per cent of it on -daducts. The radii of the centre 1 ncs of the tunnels are 460 and 304 feet, while the lengths of the tunnels range from 1591 to 2250 feet, with a maximum grade in them of 3 per cent. The weight of rails used is 50 ]iounds per A^ird on grades of 2.5 per cent or less, but for heavier grades 55- pound rails are em]doved. The cross-ties are of mild steel and weigh 80 pounds each except in the long Albula tunnel, where 333 SOME FEATURES OF RAILROAD EXOINEERING. :^~.:^ ^ ^^- \ SI \ ~L ^-9 w '^X ^ * ■i-^^ I \ \ \ \ TUXXEL-LOOP LOCATIOX. 333 Jr 4 'fIf'lIM i ><'■ ;m-i^x;. ■?., v \ ^ \\ ^^ 334 SOME FEATURES OF RAILROAD EXGIXEERIXG. treated oak ties are used as being better adapted to the special conditions existing there. It will be observed that in each case the line rises from the left-hand portion of the figure toward the right. The tunnels are represented by broken lines, and thev are in every instance on circular curves. Fig. 9 represents the line running from a point on the east side of the Albula River through a heavy cut and then across the valley of the Albula into a tunnel 2250 feet lc)ng. The line then runs chiefly in cuts to a point where there are two tunnels, one over the 1 ither ; indeed the line o^•er- laps itself in Ljops and tunnels a number ol times in that vicinity. That portion of the road shown in Fig. 8 is less remarkable than the other, although it exhibits extraordinary alignment. This example of railroad location is one of the most striking among those yet completed. It would appear to indicate that no topo- graphical difficulties are too great to be overcome by the civil engineer in railroad location in a most rugged and precipitous country. Obviously such a line could not be economically operated flo3'ed in coiineetion with other fixed signals alongside the track. The main features of these various systems of blocking are, in respect to their signalling, the same, liut the means for actuat- ing or manipulating the signals and the ce illustrated in a typical way by the diagrams, Figs. 11, 12, and 13, which exhibit in a skeleton manner I^attenall's improA-ed S_\'kes system which belongs to the Auto-Controlled Manual class. In these figures the end of block i, the whole of blocks 2 and 3, and the beginning of block 4 are sh(.iwn. Stations A, B, and C indicate the ex- tremities of blocks. The signals 5, 5', and 5" are the home sig- nals, while I\ I)', and /"■'" indicate distant signals, and A, A', and A" advance signals. ^Vs the diagrams indicate, the stretch of double-track road is representetl with east- and west-bound tracks. In order to simjdify the diagrams, signals and stations are sluiwn for one track onh'; they would simjily be duplicated for the other track. The signal cabin is supposed to be located at each station, and at that cabin arc found the levers and other appliances for working the signals operated there, the signals themseh-es being exposed alongside the track. In each signal cabin there is an indicator, as shi;)wn at/, /', and /". < )n the face of each indicator there are tw<3 slots, shown opposite the lines E and F. In the ujiper of these slots appears either the word "Clear" or "Blocked." In the lower slot appears either the word "Passed" or "On." The significance of these words will appear presently. On this indicator face at P, P', and P" are located electric push-buttons called plungers. The operation of the levers indicated at L, the ci^unterweights d, and the locking detail / are e\'ident from an inspection of the figure, and need no si^ecial explanation. It is only necessary to state that the locking-device / liolds the bar be until it is released at the proper time, and that the counterweight may then return the lever from its extreme leftward position to that at the extreme right, ax the same time placing the semaphore ann 5 in the posi- tion of danger. It is particularly important to bear in mind 346 SOME FEATURES OF RAILROAD EXGINEERINO. •J! ■5£ pi -^^^ TYPICAL WOIiKIXG OF AUTO-COXTROLLED AfAXTAL SYSTEM. 3^7 this last obscr\-ation. The counterweight is the feature n[ the system which always holds tlie scma])hore arm in the position of danger, making that its normal ]")(isition, except when it is put to safety for the passing of a train. If a Avest\\'ard train is represented in Fig. 1 1 at T as approach- ing station ,-1 to enter the lilock 2, both the distant signal J > and the home signal 5 being at danger, flic svstem is so arranged that the signalman at station .1 cannot change tho.sc signals, i.e., to a position of safety, until the signalman at station B pemiits him to do so. If the signalman at station .1 desires to open lilock 2 for the entrance of the train T, he asks the signalman at station B by wire to release the lock / t(T enable him to do so. If there is no train in block 2, the signalman at station /)' ])ushes the button P' or "plunges" it. This raises the lock / at station .4 and the signalman immediately pulls the IcA'er L to its extreme leftward position, throwing both the signals 5 and IJ to the position of safety or clear, indicated by the dotted lines at 5". At the same time the indicator E at station ,-1 shows the W(")rds ' ' Clear to B,' ' while the slot B' at B sho-ws the words ' ' (.hi from .4," The signals at stations B anil C are suppc>scd to be in their normal position of danger, and the indicator E' at station B shi:nvs the words "Blocked to ("." The home and distant signals 5' and /)' are now at danger, but the train T may enter block 2 and pn^ceeds to do scT, it being remembered that the signalman at staticm .4 cannot moye the leyer B, as it has passed out of his control; not eyen the signalman at station B can giA-e him poAver to do so. The train T now passes station .4 into block 2. As the last car passes oyer the point G its wheels strike what is called a track- treadle, an appliance haA'ing electrical connecti(in with the lock /. The effect of the wheels of the last car of the train passing oyer the treadle at (J is to release lock /, enabling the signalman at statit.ni .4 immediately to raise the arms 5 and D to the position of danger. It is to be obseryed that he cannot do this until the entire train has passed into block 2 ; nor, since his plunger is locked by the same treadle at G, can he signal "Safety" or "Clear" to the entrance of block i. Hence n(.^ train can enter blcx-k i to collide with the rear end of the train just entering block 2 . AAdien the signalman at station .4 has raised his signal 5 to danger, it 348 SOME FEATURES OF RAILROAD ENGINEERING. again passes out of his control, indeed out of botli his control and that of the signalman at B, until the last car of the train passes over the treadle (7 at the entrance of block 3 . The train has now passed into block 2 and is approaching station B. The signalman at B asks C by wire to release the lever L', and if block 3 is clear, C plunges at P". C then throws his lever L' so as to place the home and distant signals S' and D' at safety. The condition of things will then be shown by Fig. 12. As soon as the last car of the train has passed over the treadle at G' his lever L' will be released and he can then throw the lever to the danger position, raising the home and distant signals S' and D' to the horizontal. After the danger position is assumed by the home signal S', as well as the distant signal D' , he has no power over them until the signal- man at station C confers it on him by plunging the button P". While the train has been in block 2, the indicator /' has shown ' ' Blocked to C" and ' ' Train on from .4 ," but as the train passes B the indicator reads "Blocked to C" and "Train passed from A" while the indicator /" at C reads "Blocked to D" and "Train on from B." This condition of the signals and trains is shown by Fig. 13. Also, when the last car passes over the treadle G"', but not till then, B ma}' permit A to admit a train to enter block 2 should .4 so desire. Finally, when the train approaches C, the signalman at that point asks D to enable him to permit the train to enter block 4, and C confers the power by plunging if that block is clear. Fig. 13 exhibits the corresponding signals at ( '. This sequence of operations is typical of what takes place in this particular block-signal system at the limits of e\-erv succes- sive block, and differs only m details characteristic of this sys- tem from thr)se \\-hich are perf(jrmed in any other block-signal systemi. 279. General Results. — It is seen first that no signalman can operate a signal until the condition in the block ahead of him is such as to make it proper for liim to do so, and then he can only indicate what is necessary for the safe entrance of the train into that block. Furthermore, immediatclv <")n the passage of the train past his home signal he must put the latter to dan<^er DISTAXT SIGXALS. 349 or the counterweight may do it for him, the train itself when in a safe position lia\-ing conferretl the requisite power upon him. The signalman at the ad\-anee end of the bloek alwa^'s knows when the train is about t(j enter it, for he is obliged to give his permission fnr that entrance. His indicator sin iws this result, and \^'ill cinitinuc to show it until the train passes out < if the block. It is to be i:)bser\-cd that the ujiper openings marked E on the indicator giA'c infi irmation o{ the condition (jf the block in ad- vance, A\'lnle the lower openings gi\'e information of tlie block in the rear. It is particularly important to notice that after the signal- man at the advance end of a block has ''plunged" his plunger remains Inekcd and it cannot be released until the train admitted to the blrick covered by the plunger has compkoely passed out of that block, pennitting the track-treadle at the entrance to the next block ti> unlnek the jilunger. This feature makes it im]i(issi- ble fur (Hie train to enter a tdock until the preceding train has passed out uf it. If the permissiA'C SA'stem of using a block lie cmploved, in which the train is jiemiitted to enter tliat lilc:ick before a pre- ceding train leax'cs it, the treadle gi\-es no jirotectinii against a rear-end collisn.in Avith the first train. In such an exigency other devices must he used or the following train must proceed cautioush', expecting to find the track oceupied. 280. Distant Signals. — Thus far the distant signals haA'C been treated incidentally only. They may be o]ierated concurrently with or indepemlentlv of the home signal in such a way that if danger is indicated, the distant signal gives its indicati(.")n prior to that of the home signal. In this manner protection is given to the rear of a train ap^proaching a block against the home signal set at "danger." After the obstruction is removed and the block cleared, the home signal is set at "safety" before tlie distant signal is cleared. 281. Function of Advance Sigrials. — The advance signals are used when for anv purpose it is desired to form a short block in a reo-ular block. If, iw instance, block 3 in Fig. 1 1 were obstructed by a train stopped bv some failure of a locomotive detail, a train approaching station B in section 2 against the home signal 5' 350 SOME FEATURES OF RAILROAD E.XGIXEERIXG. set at ' ' danger" would be obliged to stop before entering block 3. It might then be permitted to enter the latter block, to be stopped by the advance signal .1' set at ''danger" or under instructions to pass it cautiously, expecting to hnd the track obstructed. It is thus seen that the ach^ance signal creates wh^i t may be called an emergencv block, and in reality finally controls the movement of trains in the block in which it is located. It would never be cleared unless the home signal were first cleared, nor would it be set at ' ' danger" unless the home signal gave the same indication. The preceding operation of the block system' of signalling con- trols the movement of trains along a double-track line. 282. Signalling at a Single-track Crossing. — A somewhat simi- lar sequence of signal operations controls train mo^'cments at a crossing, whether single- or double-track. Fig. 14 illustrates the Fig. 14. use of signals required for the s£ife movement of trains at a single- track railroad crossing, which is supposed to be that of a north- and-south line crossing obhquely an east-and-west line. Precisely the same arrangement of signals operated in the same manner would be required if the crossing were at the angle of 90°. The signal cabin is placed, as shown, as near as practicable to the actual intersection of tracks. Trains may pass in either direction on either track, but. in every case they would f)e griverned bv the signals at the right-hand side of the track as seen by the engineman. There will therefore be a set of signals on' both sides of each track, each set governing the movement of trains SIGXALLIXO AT A SIXGLE-TRACK CROSSING. 351 in its own direction. Eacli home signiil may lie jiliiccd about ,^50 feet from tlie actual intersection, and each distant signal 1200 to 1500 feet from the home signal, or 1550 feet to 1800 feet from the intersection. Each adwince signal must be at least as far in advance of the home signal as the maxinnun length of train, since it ma)' l)e used to sto]i a train, the rear car of wliich should completeh' pass the home signal. In their normal prisitions everv hcimc signal should l:ie set at ''danger," earr^•ing with them the distant signals gi\'ing the same indication. Idie adx'ancc signals must also indicate ''clanger" with tlie home signal. No train can then pass flic crossing until the home and distant sig- nals indicate a clear line h ir it, the other signals at the crossing, except possiftlv the advance signal, being set at ' ' danger." If for anv reason it is desired to hold the train after it is entirely free of the crossing, the ad\'ance signal Avould a)s(j indicate ''danger." It is thus seen that if the signals are ]iri i]ierh' set and obeyed, it is impossibl for two trains to attempt a crossing at the same time. It is not an uncommon occurrence, ho\\'e\-er, for an engine- man to run his train against th danger signal, and in order to make it im]")ossible for the train to reach the crossing CA'cn under these circumstances a derailing deA'iee is used. This derailing' arrangement is sho\Mi in Fig. 14, about ,^00 feet from the cross- ing, although it mav be placed from 300 to 500 feet from that point. Its puqiosc is to derail any train attcm]:)ting to make the crossing against the danger signal. Tlie ojieration of the derail is eA'idcnt from the skeleton lines of the figure. When the home signal is at danger the moA'afde i)art of the derailing device is at tliis point turned so as to catch the flanges of the wheels as thev attempt t k3 ,10 Fig. 15. the line of single track is to take the place of each rail with its set of signals in that figure. There will be but four derails, one for each track onlv on the approach to the crossing. The working of the signals with the derails is precisely the same as has already been explained for the single-track crossing, 284. Signalling for Double-track Junction and Cross-over. — Fig. 16 represents a skeleton diagram of signals required for a junction of two double-track roads and a cross-over. This arrangement covers the use of switches. The location of signals Fig. 16. and signal cabin as shoAvn is self-explanatory, after ^vhat has already been stated in connection with single- and double-track crossings. It will be observed that the home signals for both the west-bound main and branch tracks are identical in loca- tion, and are shown by the solid double flag, the distant signal being shown by its notched end at a considerable distance back GENERAL UB6ERVATI0XS. 353 of the double home signal. It will, furthermore, be observed that at each home signal there is a derailing-switeh interljeked, in the lock-and-bluek system presently to be explamed, with the home signals operated simultaneously with them. If, therefore, an engmeman attempts tu run his train past a home signal set at danger, the result will be the derailment of his train, thus brought to rest before it ean make aiiA' eullision with aiiuther. It is obvious in this ease that if the switehes from the main to the braneh traeks vr at the extremities uf the eruss-o\'er are worked independently, the}' must be operated dircetly in eon- nection with the signals. Fur eomplete proteetiun they shuuld be interliicked with the signals sij that it wouLl 1je imin issil ile to elear an\' signal witlmut simultaneously setting tlie switehes ci^nsistenth' with tin >se signals. The ihagram exhilnts elearly the indieatii^ns whicli must Ije made in order to effeet any desired train mo\'ement at sueli a junetion of traeks. 285. General Observations. — Similar arrangements of signals, tlerails, or switehes must Ijc made wherever switehes, eross-rjvers, and junctions are founcl, the detailed variations of those signals and switehes being made to meet the imlixadual rer|uirements of each local case. The cijinbinaticiiis of switclics and switcli- signals frei;[uently Ijecome \'ery C':mi]:>licated in yards where tlie tracks are nuineri_"ius and the ccnnbinaticnis exceedingh' A'aried, in order to meet the ci;>nditions created by the niowment of trains inti."> and out 1 )f the yard. The preceding cxjdanatii^ns are intended onh- tc) gi\-e a clear idea of the main features of signalling, m order to secure the high- est degree of safety and facilitv in the mcn-ement 1 if trains r_)\-cr a mc>dern railroaif. While the}' exhibit the external or a]'i]iarent eoml^inaticms of signals ten" that purpijse, thev (lo ni it touch in detail and scared}' in general upon the mechanical a])]diaiices found in the signal cabin and along the tracks recjuired ti > acci nu- plish the necessarA' signal mo\'ements. The ciinsiderations in detail of those ajijiliances wcaild co\-er extended examinati< ms of purclv mechanical, electrical, pneumatic, and electro-pneu- matic combinaticuis too invoh'ed to Ije set forth in anv but the most extended and careful stud}'. The}' liaA'c at the present time been brought to a wonderful degree of mechanical perfection 354 SOME FEATURES OF RAILROAD EXGINEERING. and afford a field of most interesting and profitable study, into which, however, it is not possible in these general statements of the subject to enter. 286. Interlocking-machines. — The earliest machine perfected for use in this department of railroad signalling was the Saxby Fig. 17. and Farmer interlocking-machine, first brought out in England and subsequently introduced in this country between 1874 and 1876. This machine has been much improved since and has been widely used. Other interlocking-machines have also been devised and used in this country in connection with the most improved systems of signalHng, until at the present time a high degree of mechanical excellence has been reached. The interlocking-machine in what is called the lock-and-block system of signalling is designed to operate signals, or signals in connection with switches, derailing-points, or other dangerous INTERLOCKIXG-MACHIXES. 355 track features, so as to make it impossible for a signalman to make a wrong combination, that is, a combination in which the signals will induce the engincman to run his train into danger. The signals and switches or other track details are so connected and interlocked with each other as to form certain desired combina- tions by the movement of designated le\'ers in the signal cabin or tower. These combinations are predetermined in the design and connections of the appliances used, and they cannot be changed when once made except by design or by breakage of the parts ; they cannot be deranged by any action of the signal- man. He may delay trains by awkward or even wrong move- ment of levers, but he cannot actually clear his signals for the movement of a train without simultaneously giving that train a clear and safe track. As has been stated, he cannot organize an accident. Figs. 17 and iS show banks or series of levers belonging to interlocking-machincs. As is evident from these figures, the levers are numerous if the machine operates the switches and signals of a large yard, for the simple reason that a great manv combinations must be made in order to meet the requirements of train movements in such a yard. The signal- man, hoAvever, makes himself acquainted with the various com- binations requisite for outgoing and incoming trains and the possible movements required for the shifting or hauling out of emptv trains. He has before him diagrams showing in full the lever movements which must be made iov the accomplishment of any or of all these movements, and he simply follows the direc- tions of the diagrams and his instructiiins in the perfomiance of his duty. He cannot derange the combinatii^ns, although he mav be slow in reaching them. The locking-frame which com- pels him to make a clear track whenever his signals give a clear indication to the engineman lies below the lower end of the levers seen in the figures. The short arms of the levers carry tappets with notches in their edges into which fit pointed pieces of metal or dogs; the arrangement of these notches and dogs is such as to make the desired combinations and no others. It will be obser\'ed that a spring-latch handle projects from a point near the upper end of each lever where the latter is grasped in operat- ing the machine. This spring-latch handle must be pressed 35 356 SOME FEATURES OF RAILROAD EXGIXEERING. APPLYING POWER LV SYSTEMS OF SIGNALLING. 357 close to the lever before the latter can be moved. The pressing of the spring-latch handle against the lever effects a suitable train of unlocking before which the lever cannot be moved and after which it is thrown over to the full limit and locked there. The desired c<3mbination for the mo\'ement of the train through any number of switches may require a similar movement of a number of levers, but the entire moA'ement of that set, as required, must be completely effected before the signals are cleared, and when they are so cleared the right combination forming a clear track for the train, and that one only, is secured. These meagre and superficial statements indicate in a general wa^^ however imperfectly, the ends attained in a modern interlocking-machine. They secure for railroad traffic as nearly as possible an absolutely safe track. They eliminate, as far as it is possil:ile to do so, the inefficiency of human nature, the erratic, indifl'erent, or wil- fully negligent features of human agency, and substitute there- for the certainty of efficient mechanical appliances. In S(ime and perhaps many States grade crossings are required by statute to adopt measures that are equivalent to the most advanced lock-and-block system of signalling. So vast has become railroad traffic upon the great trunk lines of the country that it would be impossible to operate them at all without the perfected modem svstems of railroad signalling. Thev constitute the means bv which all train movements are controlled, and without such sj's- tems great modem railroads could not be operated. The swiftly mo\'ing ''limited" express passenger trains, equipped with practically every luxury of modem life, speed their wav so swiftly and smoothly over many hundreds of miles Avithout the incident of an interruption, and in such a regular and matter-of-fact wav, that the suggestion o( an intricate system of signalling governing its movements is ncA'cr tin aight of. Yet such a train mo\-es not a vard over its track without the saving authoritv of its block signals. If the engineman were to neglect even for a mile the indication of the semaphore, he would place in fatal peril the safety of his train and of every life in it. 287. Methods of Applying Power in Systems of Signalling. — The mechanical appliances used in accomplishing these ends are among the most efficient in character and delicate yet certain in 358 SOME FEATURES OF RAILROAD ENGINEERING. motive power which engineering science has yet produced. The electric circuit formed b}- the rails of the track plays a most im- portant part, particularly in securing the safety of the rear of the train in making it absolutely certain whether even rear cars that may have broken away have either passed out of the block or are still in it. The electric circuit in one applicatirjn or another was among the earliest means used in railroad signalling. Elec- tric power is also used in connection with compressed air for the working of signals. Among the latest and perhaps the most advanced types of lock-and-block signalling is that which is actuated by low-pressure compressed air, the maximum pressure being 15 pounds only per square inch. The compressed air is supplied b}' a simple compressor, and it is communicated from the signal cabin to the most remote signal or switch by pipes and suitable c^'linders fitted with pistijns controlled by valves, thus eft'ecting the final signal or switch movements. It has been successfully applied at the yard of the (J-rand Central Station in New York Citv and at manv other similar points. In this con- nection it is interesting t( > observe that while the original Saxljy and Farmer interlocking-machine Avas installed from England in this country, as has already been observed, about 1875, American engineers have within a year reciprocated the favor bv furnishing and putting in place most successfullv in one of the great railroad yards of London the first low-pressure pneumatic lock-and-block system * found in Great Britain. 288. Train-staff Signalling. — The lock-and-block svstem gives the highest degree of security attainable at the present time for double-track railroad traffic, Imt the simpler cliaracter of the single-track railroad busmess can be advantageoush' controlled by a somewhat simpler and less expensive system, which is a modi- fication of the old train-staft" methr)d. It is one of the ' ' machine " methods of signalhng. The type which has been used widely in England, Australia and India, and to some extent in this country is called the Webb and Thompson train-stall: machine, shown in Fig. 19. It will be observed tliat the machine contains ten staft's (18 to 20 inches long and i to 1} inches in diameter) but as many as fifteen are sometimes used. These staffs can be * By Standard Railroad Signal Compan)- of Tro)-, X. Y. TR. 1 /.V-,S' T. 1 FF SIGN. 1 LLING. 359 removed from the machine at one end of a section of the road at which a train is to enter, only by permission from the operator at the farther end of the section. If the station at tlie entrance to that section is caRcd ,1, and the station at tlic farther end .V, the following description of the operation of the instrument is given by Mr. Charles Hansel in a very concise and excellent man- ner: ' ' When a train is ready to move from ^4 to X the operator at .4 presses down the lever which is seen at the bottom of the right- hand dial, sounding one bell at A', which is for the purpose of cidling the attention of the ojierator at -V ti ) the fact that .4 desires to send a train forward. The o])erator at A' ackni )wlcdges the call 1 1)' ])ress- ing the IcA'cr i m his instrument, sounding a bell in the tower fit -4. The operator at A then asks per- mission from A" to Avithdraw staff by pressing doAvn the lc\'er licforc men- tioned three times, gi\'ing three rings on the ficll at A', and immediately turns his right-hand pointer to the left, leaving it m the horizontal position pointing to the words ' For staff,' indicating that he desires operator at A' to release his instil- ment so that he can take a staff" or train order from it. If there is no train or any p<3rtion of a train between .4 and A', the holding down of the lever at A" closes the circuit in the lock magnets at ,1, which enaliles the operator at .4 to with- draw a staff". As soon as this staff' is removed from .4, .4 turns the left-hand pointer to the words 'Staff" out,' and in removing this staff" from the instrument A the galvanometer needle which is seen in the centre of the instru- ment between the two dials vibrates, indicating to the operator Fig. ig. — Wehb and Thompson Train-staff Machine. 360 SOME FEATURES OF RAILROAD ENGIXEERING. at X that .4 has withdrawn his staff. A' then releases the lever which he has held down in order that A might withdraw a staff and turns his left-hand indicator to ' »Staft' out,' and with this position of the instrument a staff' cannot be withdrawn from either one. ' ' The first method of delivering this staff" to the engineer as a train order was to place it in a staff'-crane, which crane was located on the platform outside of the block station. A^^ith the staff in this position it has been found in actual practice that the engine- man can pick it up while his train is running at a speed of 30 miles per hour. A second staff' cannot be removed from A nor a staff removed from A' until this staff which was taken by the engine- man in going from .4 to X is placed in the staff' instrument at A'; consecjuently the delivering of a staff' from .4 to the engineman gives him absolute control of the section between .4 and A'. ' ' This train-order staff' also controls all switches leading from the main line between .4 and A', for with the style of switch-stand which we have designed for the purpose the trainman cannot open the sAvitch until he has secured the staff' from the engine- man and inserted it in the switch-stand, and as soon as he throws the switch-lever and opens the switch he fastens the train-staff' in the switch-stand, and it cannot be removed until the switchman has closed and locked the switch for the main line. 'When this is done he may remove the train-staff' and return it to the engine- man. It will thus be seen that this train order, in the shape of a staff', gives the engineman absolute control OA-er the section, and also insures that all switches from the main line are set properly befrire he can deliver the train-staff' to the instrument at A'. ' ' In order that the operator at X may be assured that the en- tire train has passed his station, we may divide the staff' in two and deliver one half to the engineman and the other half to the trainman on the caboose or rear end of the train, and it will be necessarsr for the operator at X to have the two halves so that he may complete the staff in order to insert it into the staff' instru- men at A', as it is impossible to insert a portion of the staff' ; it must be entirely complete before it can be returned to the staff" instrument." Instead of using the entire staff as a whole or in two parts, TRAIN-STAFF SIGNALLING. 361 Mr. Hansel suggests that one or more rings on the body of the staff he remo\-ed from the latter and given to the engineman or other trainman to be placed upon a corresponding staff at the extreme end of the section. This would answer the purpose, for no staff can be inserted in a machine unless all the rings are in their proper positions. These rings can be taken up by a train moving at any speed from a suitable crane at any point alongside the track. For a rapid movement of trains on a single-track railroad under this staff" system an engineman must know before he approaches the end of the section whether the staff' is ready for delivery to him. In order to accomplish that purpose the usual distant and home signals may readily be employed. The distant signal would show him what to expect, so that he would approach the entrance to the section either at full speed or with his train under control according to the indication. Similarlv, electric ■circuits may be employed in connection with the staff" or rings in the control of signals which it mav be desired to employ. The electric train-staff may also be used in a permissiA'e block system, the section of the track between stations A and A' con- stituting the block. In Fig. 19, showing the machine, a hori- zontal ami is seen to extend across its face and to the right. This is the permissiA^e attachment which must be operated by the special staff' shown on the left half of the machine about midway of its height. If it is desired to mn two or three trains or two or three sections of the same train frrmi A before admitting a train at A' in the opposite direction, the operator at .4 so advises the operator at A'. The latter then permits A to remove the special staff' with which the extreme right-hand end of the per- missi\'e attachment is unlocked and a tablet taken out. This tablet is equivalent to a train order and is given to the train immediatelv starting from .4. A second tablet is given in a similar manner to the second section or train, and a third to the third section. The last section of train or train itself starting from .4 takes all the remaining tablets and the special staff for insertion in the machine at A'. In this manner head-to-head collisions are prevented when a number of trains are passing through the block in the same direction before the entrance of a 362 SOME FEATURES OF RAILROAD ENGINEERING. train in the opposite direction. This system has been found to work satisfactorily wliere it has been used in this country, al- though its use has been quite limited. Evidently, in itself, it is not sufficient to prevent rear-end collisions in a block between trains moving in the same direction. In order to avoid such collisions where a train falls behind its schedule time or for any reason is stopped in a block, prompt use must be made of rear flagmen or other means to stop or to control the movement of the first following train. Fig. 20. The most improved form of high-speed train-staff machine is shown in Fig. 20, as made and installed by the Union Switch and Signal Company and used by a number of the largest railroad systems of the United States. In these machines the staffs are but a few ounces in weight. CHAPTER XXIII. 289. Evolution of the Locomotive. — The eA'olutmn of the steam loeomotive ma}- be called the most spectacular portion of the development of railroad engineering. The enormous engines used at the present time for hauling both heav\' freight and fast passenger trains possess little in common, in respect of their principal features, with the crude machines, awkward in ap)pearanee and of little hauling capacity, which were used in the early jaart of the nineteenth century 111 the lieginning of railroad operation. The primitive and ill-proportioned machine, ungainly in the highest degree, designed and built by Trevithick as far back as 1803, was a true progenitor of the modem locomoti\-e, although the family rcsemljlance is not at first very e\ddent. Several such locomotive machines were designed and operated between 1800 and 1829 when Stevenson's Rocket was brought out. The water Avas carried in a boiler mi a wagon immediately behind the engine, and the steam-cylinder in those early machines was placed almost anywhere but where it now seems to Ijclong. The Rocket has some general features of resemblance to the machines built seventy years later, but when placed side bv side it might easily be supposed that seven hundred years rather than se\Tnty had elapsed between the two productions of the shop. After the famous loeomotiA'e trial in which Riibert Stevenson distanced his competitors, the design of the locomoti\'e advanced rapidly, and it was but a few years later when the modern loctn- motive began to be accurately foreshadoAved in the machines then constructed. This was true both in England and the United States. The first steam locomotive in this country is believed to be the machine built by John Stevens at Hobiiken, X. J., in 1S25 and operated in 1 82 5-2 7. This locomotive has practically the 363 364 SOME FEATURES OF RAILROAD ENGIXEERIXG. arrangement of boiler and cylinder which is found upon the modem contractors' engines used for pile -driving, hoisting, and similar operations. It would certainly be difficult to imagine that it had any relation to the great express and freight locomo- tives of the present day. The rectilinear motions of the piston were transformed into the rotary motion of the wheels by means of gearing consisting of a simple arrangement of cog-wheels. About the same time a model of an English locomotive called the Stockton and Darlington No. i was brought to the United States by Mr. WiUiam Strickland of Philadelphia. The next important step in American locomotive development was the construction of the locomotive ' 'John Bull" for the Camden and Amboy Railroad Company in the English shops of SteA'enson & Company in the years 1830-31. This machine has the general features, although not the large dimensions, of many modem locomotives. The cow-catcher is a little more elaborate in design and far-reaching in its proportions than the similar ap- pendage of the present day, but the general arrangement of the fire-box and boiler, the steam-cylinders, the driving-wheels and smoke-stack is quite similar to a modem American locomotive. This machine, "John Bull," and train made the trip from New York City to Chicago and return under its own steam in 1893. It was one of the prominent features of the World's Columbian Ex- position. It rests in the National Museum at AVashington, where it is one of the most interesting early remains of mechanical engineering in this country. One of the cars used in this train was the original used on the Camden and Amboy Road about 1836. Its body was used as a chicken-coop at South Amboy, N. J., for many years, and was rescued from this condition of degrada- tion for the purpose of the Exposition trip in 1S93. The original dri\-ing-wheels had locust spokes and felloes, the hubs and tires being of iron. The locomotive "George Washington" was built, as a con- siderable number have been since, with one driving-axle, and was designed to be used on hcaAw grades. This machme was built by Wilham Norris & Sons of Philadelphia, who were th^s progenitors of the present great estabhshment of the Baldwin Locomotive Works. While the development of the locomotive was sub- IXCREASI- OF LOCOMOTIVE WEIGHT. 305 jectcd to many vicissitudes in princijjlcs, general arrangement, and size in order to meet the A'arying requirements of dilTerent roads as well as the faneies or more rational ideas of the designers, its advance was rapid. As early as 1S46 \\-e find praeticalh- the modern c«:>nsolidation ty]X', f(jllowed in 1851 by the ordinary eight-wheel engine of whicli thuusands ]ia\-e been constructed within flic pa t fifty years. The first Alngul lunlt l:)y the Baldwin Locomotive Works was almost if not (:|uite as early in the field. Both these types of maclfines carry the |)rinci])al portion (_if their weight upon the driving-wheels and Avere calculated to A'ield a high tracti\-e capacity, especially as the weights of the engines increased. The weight of the little ''Jolm Bull" was Ijut 22,425 pounds, while that of the great modern macliinc maA' be as mucli as 207,800 pounds, with 5,:;, 500 pouiiils on a single driving-axle. 290. Increase of Locomotive Weight and Rate of Combustion of Fuel. — The deAxlopment of railroad business in the United States has been so rapid as ti3 create rigorous exactions rjf c\'crv feature i">f a li.icomotiA'c calculated tci increase its tractiA'C fierce. Anv enhancement of train-Ljad without increasing the costs of the train force or other cost of movement Avill ob\'i(3ush' lead to econonn' in transportation. In i.irder tliat tlie locomotu'C mav A'icld the correspondmgh' augmented tractiA'e fierce the weight resting upon the dru'crs must he increased, Avhich means a greater machine and at the same time higher working pressures of steam. Idiis demands grea er boiler ca]xicitA' and strength and a propc^'tii^nateh' increased rate of coml")ustion, so as to move the locomotive and train l^v the storcd-up energy oi the fuel transformed in the engine through steam pressure Tlie higher that pressure the gr ater the amount of energy stored up in a unit of weiglit of the steam and the greater Avill fie the eapacit\" of a given amount of water to perfcjnn the W(:irk of hauling a train. The greater the Avcight of tram nn^ved and the greater its speed the more energv must Ijc supplied Ijy the steam, and, again, that can only be done Avitli a correspondingly greater consumption of fuel. In the early days of the small and crude machines to Avhich allusion has already been made the simplest fuel was sufticienth' eft'ective. As the duties pertVirmcd bv the locomotive became more intense a higher grade of fuel. 366 SOME FEATURES OF RAILROAD ENGINEERING. i.e., one in wliich a greater amount of heat energy is stored per vuiit of weight, Avas required. Both anthracite and bituminous coal haA-e admirably filled these requirements. The movement of a great modern locomotive and its train at an average rate of 30 to 60 miles per hour requires the combustion of fuel at a high rate and the rapid evapo ation of steam at pressures of 180 to 225 or more pounds per square inch. The consumption of coal by such a locomotive may reach 100 pounds per minute, and two barrels of water may be evaporated in the same time. This latter rate would require over a gallon of water per second to be ejected through the stack as exhaust steam. Some of the most marked improvements in locomotive practice have been made practically within the past six or seven years in order to meet these exacting requirements. While the operations of locomoti^'cs will obviously depend largely upon quality of fuel, speed, and other conditions, the investigations of Prof. W. F. M. Goss and others appear to indi- cate that 12 to 14 pounds of water per hour may be evaporated by a good locomotive boiler per square foot of heating surface, and that 25 to 30 pounds of steam will be required per indicated horse-power per hour. 291. Principal Parts of a Modem Locomotive. — The principal features of a modern locomoti^-e are the boiler with the smoke- stack placed on the front end and the fire-box or furnace at the rear, the tubes, about 2 inches in diameter, through which the hot gases of combustion pass from the furnace to the smoke- stack, the steam-cylinders with their fittings of A-alves and valve movements, and the driving-wheels. These features must all be designed more or less in reference to each other, and whatever improvements have been made are indicated almost entirely by the relative or absolute dimensions of those main fea- tures. The boiler must be of sufficient size so that the water contained in it may afford a free steam production, requiring in turn a corresponding furnace capacity with the resulting heating surface. The latter is that aggregate surface of the interior chambers of the boiler through which the heat pro- duced by combustion finds its way to the water evaporated in steam; it is composed aknost entirely of the surfaces of the THE WOOTTEN FIRE-BOX AND BOILER. 307 steel plates of the fire-box and of the numerous tubes running through the boiler and jiarahel to its centre, exposed to the hot gases of combustion and in contact with the water on the op- posite sides of those plates. Evidently an increase in size of the fire-box with the coiTespondingly increased combustion will furnish a proportionally larger amount of steam at the desired high ]5ressure, but an increase in the size of the fire-box is limited both in length and in ^^'idtll. It is found that it is essentially impracticable for a fireman to serve a fire-box more than about 10 feet in length. The maximum width of the locomotive limits the width of the fire-box. 292. The Wootten Fire-box and Boiler. — As the demand arose for an enlarged furnace the width of the latter was restricted b}'' the width between the d^i^'ing-wheel tires, less than 4 feet 6 inches. That difficult}' ^^'as OA^ercome by what is known as the Wootten fire-box, ^^dlicll was brought out by John E. AVootten of the Phila- FlG. 21. delphia and Reading Railroad about 1877, and has since been developed and greatly improved by others. The Wootten boiler with its sloping top) and great width extending out over the rear driving-wheels presented a rather curious appearance and was a distinct departure in locomotive -boiler design. Fig. 21 shows an ele^'ation and two sections of the original Wootten 368 SOME FEATURES OF RAILROAD ENGINEERING. type of boiler. It will be noticed that in front of the fire-box there is a combustion-chamber of considerable length, 2^ to 3 feet long. This boiler was first designed to burn the poorer grades of fuel, such as coal-slack, in which the combustion-chamber to complete the combustion of the fuel was thought essential. By AVootten's device, i.e., extending the boiler out over the driving- wheels, a much greater width of fire-box was secured, but the height of the locomotive was considerably increased. It cannot be definitely stated just how high the centre of the locomotive boiler may be placed above the track without prejudice to safety in running at high speeds, but it has not generally been thought best to lift that centre more than about 9A feet abtjA'e the tops of rails, and this matter has been held clear]}' in vieAv in the development of tlij wide fire-box t)'pe of lrci)moti\'e boilers. Like CA-erv other new form of machine, the AA'ootten boiler developed some Aveak features, although there was no disappoint- ment in its steaming capacity. It will be noticed in the figure that the plates forming that part of the boiler OA'er the fire-box show abrupt changes in cur\'aturc which induced ruptures of the stav-bolts and resulted in cither weaknesses. This boiler passed through various stages of development, till at the present time I'igs. 22 and 23 show its mrjst adA'anccd fonm, Avhich is satisfactory in almost or quite every detail. The sudden changes in direction of the plates in the first Woritten example ha\'e been displaced bv more gradual and easy shapes. Indeed there are few features other than those which characterize simple and easy boiler constructirin. The enormous grate area is evident from tlie horizontal dimensiitns of the fire-ljrix, which arc about 120 inches in length by aViout 106 inches in breadth. The boiler has OA''er 4000 square feet of heating surface and carries about 200 pounds per sr[uare inch pressure of steam. The combustion- chamber in front r)f the fire-box has been reduced to a length of about 6 inches, just enough for the prritection of the expanded ends of the tubes. The barrel of the boiler in front of the fire- box has a diameter of 80 inches and a length of about 15 feet. The grate area is not far fnim 100 square feet. The improve- ments AAdiich have culminated in the production of this boiler are due largely to Mr. Samuel Higgins of the Lehigh A^alley Road. THE WOUTTEN FIRE-BOX AND BOILER. 569 4Rlvi T2 Rivets H»'Dia. a Rivets l.m'Dla. 8,KlBo. _, , , ^ Plan of Dome Klnt 511 Tabes 1' DIa. 480 Screw Slaj» IV^'Di*. 1265 " " 1' 2^ Taper Tap 12 Tlids. Taper ^i-ln 7-L.S. onlj ">i'TBper Tap 12 Tbda. Roles drilled In Ercotlng S'lop •JLj_l_tJ« , B«IIStT>d> u • • * ■ ■ Ti'Dl*,"--, 2!^ Taper Tap 12 Thdi- . Taper 3^ "in 12° Fig. 22. Plan of LoQgltudJnal Stam New To rk Railroad Club ..'^^'^-^fH)^®/-*" o O o"o rr n >; ,k^ \. p ^ Tap ^ Tap l^ Tap g I p Taper ?i In 12 for R.S. X —- UbH' gJi Taper Tap 12 Thdl Taper ^j'tflis' 370 SOME FEATURES OF RAILROAD ENGINEERING. 293. Locomotives with Wootten Boilers. — Fig. 24 exhibits a consolidation freight locomotive of the Lehigh \"alley Railroad, having the boiler shown in Figs. 22 and 23. This machine is one of the most efficient and powerful locomotives produced at the present time. The locomotive shown in Fig. 25 has a record. It is one used on the fast Reading express serA'ice be- tween Philadelphia and Atlantic City during the season of the latter resort. It has run one of the fastest schedule trains in the world and has attracted attention in this country and abroad. Its type is called the Atlantic and, as the view shows, it is fitted with the Wootten impro^•ed type of boiler. It will be noticed that the wide fire-box does not reach out over the rear Fig. 24. drivers, but over the small trailing-wheels immediatelv behind them. This is a feature of wide locomotive fire-box practice at the present time to which recourse is frequentlv had. There is no special significance attached to the presence of the small trailing-wheels except as a support for the rear end of the boiler, their diameters being small enough to allow the extension of the fire-box over them without unduly elevating the centre of the briiler. The cylinders of these and many other locomotives are known as the A'auclain compound. In other words, it is a compound locomotive, there being two cylinders, one immediately over the other, on each side. The diameter of the upper cylinder is much less than that of the lower. The steam is first admitted int(T the small upper cylinder and after doing its work there passes into LOCOMOTIVES WITH WOOTTE.Y BOILERS. 371 the lower or larger cylinder, where it does its work a second time with greater expansion. By means of this compound or double- cylinder use of the steam a higher rate of expansion is secured and a more uniform pull is exerted upon the train, the first generally contributing to a more economical empli)\-ment of the steam, which in turn means a less amount of fuel burned for a given amount of tractive work performed. In the early part of November, 1901, an engine of this type hauling a train composed of five cars and weighing 235 tons made a run of 55.5 miles between Philadelphia and Atlantic City at Fig. 25. the rate of 71.6 miles per hour, the fastest single mile being made at a rate of a little less than So miles per hour. The power being developed by these engines runs as high as 1400 H.P. at high speeds and 2000 H.P. at the lower speeds of freight trains. The chief economic advantage of these wide fire-box machines lies in the fact that very indifferent grades of fuel mav be con- sumed. Indeed there are cases where fuel so poor as to be unmarketable has been used most satisfactorilv. "With a narrow and small fire-box a desired high rate of combustion sometimes demands a draft strong enough to raise the fuel 1 iver the grate- bars. This ditficultv is avoided in the large fire-box, where suffi- cient combustion for rapid steaming is pr(:iduced with less inten- sitv of blast. 372 SOME FEATURES OF RAILROAD EXGIXEERIXG. 294. Recent Improvements in Locomotive Design. — Concur- rently with the development of the Wootten type of boiler, other wide fire-box types have been brought to a high state of excel- lence. In reality general locomotive progress within the past few years has been summed up by J\Ir. F.J. Cole as follows : (a) The general introduction of the wide fire-box for burning bituminous coal. {b) The use of flues of largely increased length. (c) The improvements in the design of piston-valves and their introduction int<3 general use. (d) The recent progress made in the use of tandem compound cylinders. The piston-valve, to which reference is made, is a valve in the shape of two pistons connected by an enlarged stem or pipe he entire length of the double piston, the arrangement depend- ing upon the length of steam-cylinder or stroke ; it may be 3 1 or 32 inches. This piston-^-alve is placed between the steam- ss;^^5P^s^55^5^^?^ ^5^5W^'P^!!5^?':^^5^^55:^5!^« Fig. 26. cylinder and the boiler, and is so moved bv eccentrics attached to the driving-wheel axles through the medium of rocking levers and valve-stems as to admit steam to the cylinder at the beginning of the stroke and allow it to escape aiter the stroke is completed. Fig. 26 shows a section through the centre of one of these piston- valves. It will be noticed that the live steam is admitted around COMPOUND LOCOMOTIVES WITH TANDEM CYLINDERS. a central portion of the valve, and that the steam escapes through the exhaust-passages at each end of the piston-valve. This type of N'alve is ad\'antageous with high steam pressures for the reason that its ' ' blast," i.e., the steam pressure, de(>nloti^•e with this tandem arrangement of com])ound eylinders will be shown farther on. Figs. 27 antl 2S show two seetions, one transverse and one longitudinal, nf a type of large hre-b(jx bi iilcr built by the Ameri- ean Locomoti^'e AVorks at Seheneetady. Idie diameter of the barrel of the boiler in front ( )f the fire-1 >< ix is about 5 feet 8 inehes, while the elear greatest width of the tire-bdx is 5 feet 4^- inehes. The length of the latter is S feet 7 inehes, making a total grate area in this particular instance of o\"er 45 square feet. There are 33S 2-ineh tulies, each lO feet in length. The total length o\-er all of tlie bi liler is 3 1 feet \ inch. The result cif such a design is an aiTangcment by which a large grate area is secured and a corresponding high rate of combustion without a ti ») viijlent draft. In designing locomoti\'e boilers for liituminous eoal one square foot of grate area is sometimes proAdded for each 60 to 70 square feet of heating surface in the tubes. 296. Evaporative Efficiency of Different Rates of Combustion. — In the dcN'eliipment of this particular class of Ljcomotive Fii",. 2g. boilers it is to be remembered that as a rule the highest rates of combustion frequently mean a decreased evaporation of water at boiler pressure per pound of fuel. Modem locomotives may bum over 200 pounds of eoal per square foot of grate area per hour, and in doing so the evaporation may be less than 5 pounds 376 SOME FEATURES OF RAILROAD ESGINEERINO. of water per potind of fuel. On the other hand, when the coal burned does not exceed 50 pounds per square foot of grate area per hour, as much as 8 pounds of water may be evaporated for each puund C)f cual. It is judicious, therefore, to have large grate area, other things being equal, in order that the highest attainaljle efficiency in evaporation may be reached. 296a. Tractive Force of a Locomotive. — The tractive force of a locomotive arises from the fact that one solid body cannot be mo\'ed over another, however smooth the surface of contact may be, without deveLjping the force called resistance of friction. This resistance is measured Ijy what is called the coefficient of friction, determined only by experiment. The resistance of friction and this coefficient will depend both upon the degree of smoothness of the surface of contact and fni its character. If surfaces are lubricated, as in the moving pjarts of machiner}?, the force of friction is very much decreased, but in the absence of that lubricant it Avill have a much higher value. The coeffi- cient of friction is a ratio which denotes the part of the Aveight of the body mr)A-ed which must fie applied as a force to that body in order to put it in motion against the resistance of friction. In the case of lubricated surfaces this ratio may be as small as a few hundredths. In the case of Ic) omotixx- driving-wheels and the track on which they rest this value is usuall}-' taken at .2 to .25. There are times when it is desirable to increase the resistance of friction betAveen locomotiA'e drivers and the rails. For this purpose a simple device, called the sand-box, is frequentlv placed on the top of a locomotive boiler with pipes nmniiig down from it so as to discharge the sand on the rails immediatelj- in front of the drivers. The sand is crushed under the wheels and offers an increased resistance to their slipping. The tractive force of a locomotive may also be computed from the pressure of steam against the pistons in the sieam- cylinders. If the indicated horse-power in the cylinder be repre- sented by H.P., and if all frictional or other resistance between the cyhnder and the draw-bar be neglected, the following equality will hold : Draw-bar pull X speed of train in miles ) ^t -n 1. x^ o ," =H.P. X ^s.ooo X60. per hour X 5 280 ^ •- - TRACTIVE FORCE OF A LOCOMOTIVE. 377 If 5 = speed in miles per hour, and if T = draw-bar pull, then the preceding equality gi\'es 375XH.P. T S This value of the "pull" must be diminished by the friction of the locomotive as a machine, Ijy the rolling resistance of the trucks and tender, cuid by the atmos])heric resistLuice of the locomi:iti\X' as the head of the train. Pnjf. Goss proposes the following approximate A'alues for these resistances in a paper read before the Xew England Railroad Clul:i m December, igoi. A number of tests liaA'c slniwn that a steam pressure of ,^.8 pounds per square inch on the pistmi is required to OAXTCome the machine friction i if the loei miotixx'. Hence if d is the diam- eter of the pistmi in inches, L the ]nston-stroke in feet, and /-' the diameter of dri\'er in feet, while / is that part of the draw-bar pull required to o\-ereome machine friction, the following equation will hold : Again, if IT tie the rolling load in tons on tender and trucks (exluding that on drix'ers), and if r be that part of the draw-1iar pull required to overcome the rolling resistance due to lb, then experience indicates that approximately, in pounds, 5^ 6,)" As before, 5 is the speed in miles per hour. Finally, if /; be that part of the draw-bar pull in pounds required to overcome the head resistance (atmospheric) of the locomotive, there may be written approximately The actual draw-bar pull in pounds aA'ailable for mo\-ing the train will then be -,7qH.P. d'L .,,/ 5\ The maximum value of t should be taken as one fourth the great- est weight on drivers. 378 SOME FEATURES OF RAILROAD EXGIXEERIXG. If H is the total heating surface in square feet, and if 12 pounds <:.f water be evaporated per square foot per hour, while 28 pounds of steam are required per horse-power per hour, then i.H 375H.P. 161H Hence 161H d'L „./ , 5 The actual draw-bar pull in pounds may then be computed by this formula. Some recent tests of actual trains (both heavy and light) on the N. Y. C. & H. R. R. R. between Mott Haven Junction and the Grand Central Station, New York City, a distance of 5,3 miles, by JM . Bion J. Arnold, by means of a dynamometer- car, gave the actual average draw-bar pull per ton of 2000 pounds as ranging from 12 to 25 pounds going in one direction and 12. 1 to 24 pounds in the opposite direction. There were eight tests in each direction, and the greatest speed did not exceed 30 miles per hour. As the diameter of the driver appears in the preceding formu- la;, it may be well to state that an approximate rule for that diameter is to make it as many inches as the desired maximum speed in miles per hour, i.e., 70 inches for 70 miles, or 80 inches for 80 miles, per hour. 297. Central Atlantic Type of Locomotive. — Fig. 29 represents what is termed the Central Atlantic type (single cylinder) of engine, which is used for hauling most of the fast passenger trains on the New York Central and Hudson River Railroad. The characteristics of boiler and fire-box are such as are shown in Figs. 27 and 28. The cylinders are 21 inches internal diameter, and the stroke is 26 inches. The total grate area is 50 square feet, and the total heating surface 3500 square feet. The total weight of the loco- motive is 176,000 pounds, with 95,000 on the drivers. It will be obser\'ed that the total weight of locomotive per square foot of heating surface is scarcely more than 650 pounds, which is a low value. The boiler pressure carried may be 200 pounds per CONSOLIDATION ENGINE, N. Y. C. ct- //. R. R. R. oid square inch or more. The tractive force of this locomotive may be taken at 24,700 pounds. There is supphcd to these engines, among others, what is called a traction-increasing device. This traction-increaser is nothing more nor less than a compressed-air cylinder secured to the boiler, so that as its piston is pressed out- ward, i.e., downward, it carries with it a lever, the fulcrum of which is on the equalizing-lever of the locomotive frame, the other or short end of the lever being attached to the main bar of the frame itself. This operation redistributes the boiler-load on the frame, so as to increase that portion whicli is carried by the drivers. This has been found to be a convenient device in starting trains and on up grades. In the present instance the traction-increaser may be operated so as to increase the load on the drivers by about 12,000 pounds. It is not supposed to be used except when needed under the circumstances indicated. Fig. 30. A number of indicator-cards taken from the steam-cylinders of these engines hauling the Empire State Express and other fast passenger trains on the Hudson River Division of the X. Y. C. & H. R. R. R., show that with a train weighing about 20S tons while running at a speed of 75 miles per hour 1323 H.P. was developed. Fig. 30 shows these indicator diagrams. With a train weighing 685 tons 1452 H.P. was indicated at a speed of 63 miles per hour. 298. Consolidation Engine, N. Y. C. & H. R. R. R. — One of the heaviest wide fire-box compound consolidation engines re- cently built for the New York Central freight service is shown in Fig. 31. It will be noticed that there is but one cyUnder on each side of the locomotive, and that they are of different diam- 380 SOME FEATURES OF RAILROAD ENGINEERING. eters. One of these cylinders, 23 inches inside diameter, is a high-pressure cylinder, and the other, 35 inches inside diameter, is a low-pressure cylinder, the stroke in each case being 34 inches. The total grate area is 50.3 square feet, the fire-box being 8 feet long bjf 6 feet 3 inches wide. The total heating surface is 3480 square feet. The diameter of the barrel of the boiler at the front end is 72 inches, and the diameter of the drivers 63 inches. The Fig. 31. pressure of steam in the boiler is 210 pounds per square inch. The total weight of the locomotive is 194,000 pounds, of which 167,000 rests upon the drivers. These engines afford a maxi- mum tractive force of 37,900 pounds. This engine is tvpical of those used for the New York Central freight serA'ice. They haA^e hauled trains weighing nearly 2200 tons over the New York Central road. 299. P., B. & L. E. Consolidation. — The consolidation loco- motive shown in Fig. 32 is a remarkable one in that it was for a time the heaviest constructed, but its weight has since been exceeded by at least two of the Decapod type built for the Sante Fe company. It was built at the Pittsburg works of the Ameri- can Locomotive Company for the Pittsburg, Bessemer and Lake Erie Railroad to haul heavy trains of iron ore. The total weight is 250,300 pounds, of which the remarkable proportion of 225,200 is carried by the drivers. The tender carries 7500 gallons of L. S. i£- M. S. FAST PASSENGER ENGINE. 381 water, and the weight of it when loaded is 141,100 pounds, so that the total weight of engine and tender is 391,400 pounds. The average weight of engine and tender therefore approaches 7000 pounds per lineal foot. This is not a compound locomoti\'e, Fic. 32. but each cylinder has 24 inches inside diameter and 32 inches stroke, the diameter of the dri\'ing-wlicels being 54 inclies. The boiler carries a pressure of 220 pounds, and the tractive force of the locomotive is 63,000 p(3unds. A noticeable feature of this design, and one which does not agree with modern views prompting the design of wide fire-boxes, is its great length of 1 1 feet and its small width of 3 feet 4I inches. There are in the boiler 406 2 [-inch tubes, each 15 feet long, the total heating surface being 3805 square feet. 300. L. S. & M. S. Fast Passenger Engine. — The locomotive shown in Fig. ;^^ is also a remarkable one in some of its features, chief among which is the 19 feet length of tubes. It was built at the Brooks works of the American Locomotive Company for the Lake Shore and Jlichigan Southern Railroad. The total weight of engine is 174,500 pounds, of which 130,000 pounds rests upon the drivers. The rear truck canies 23,000 pounds and the front 382 SOME FEATURES OF RAILROAD EXGIXEERIXG. truck 21,500 pounds. This is not a compound engine. The cylinders have each an inside diameter of 20-^- inches, and 28 inches stroke. As this locomotive is for fast passenger traffic, the driv- ing-wheels are each 80 inches in diameter, and the driving-Avheel Fig. 33. base is 14 feet. The fire-box is 85X84 inches, gi^'ing a grate area of 48-;^ square feet and a total heating surface of 3343 scjuare feet. There are 283 2J|-mch flues, each 19 feet long. The tender carries 6000 gallons of water. Cast and compressed steel were used in this design to the greatest possible extent, and the result is shown in that the weight divided by the square feet of heating surface is 52.18 pounds. 301. Northern Pacific Tandem Compound Locomotive. — The diagram shoAvn in Fig. 34 exhibits the outlines and main features of a tandem compound locomoti\'e to which allusion has already been made. It was built at Schenectady, New York, in 1900, for the Northern Pacific Railroad, and was intended for heavy service on the mining portions of that line. The diameters of the high- and low^-pressure cylinders are respectively each 15 and 28 inches, with a stroke of 34 inches, while the boiler pressure is 225 pounds per square inch. The total weight of the machine is 195,000 pounds and the weight on the drivers 170,000 pounds, the diameter of the drivers being 55 inches. As the figure shows, it belongs to the consolidation type. The fire-box is 10 feet long by 3.5 feet wide, giving a kohtiiehk pacific tandem compound locomotive. 3b3 384 SOME FEATURES OF RAILROAD EXGIXEERIKG. grate area of 35 square feet, with which is found a total heating surface of 3080 square feet. There are 388 2 -inch tubes, each 14 feet 2 inches long. These engines are among the earliest com- pound-tandem type and have been very successful. Other locomotives of practically the same general type have been fitted with a wide fire-box, 8 feet 4 inches long by 6 feet 3 inches wide, with the grate area thus increased to 52.3 square feet. 302. Union Pacific Vauclain Compound Locomotive. — The next example of modem locomotive is the Wauclain compound type used on the Union Pacific Railroad. It is a ten-wheel pas- FiG. 35. sengcr engine and one of a large number in use. The weight on the driA'ers is 142,000 pounds, and the total weight of the locomotive is about 185,000 pounds. The high-pressure c^dinder has an inside diameter of 15-^- inches, while the low-pressure cvlin- der has a diameter of 26 inches. The stroke is 28 inches and the diameter of the driving-wheels 79 inches. On the Union Pacific Railroad the diameter of the driving-wheel varies some- what with the grades of the divisions on which the engines run. In some portions of the country, as in Southern California, oil has come into quite extended use for locomotive fuel. 303. Southern Pacific Mogul with Vanderbilt Boiler. — The locomotive shown in Fig. 36 belongs to the Mogul type, having three pairs of driving-wheels and one pair of pilots. It is fitted with the Vanderbilt boiler adapted to the use of oil fuel. The THE '■;:(:()•• DLCAPOD LOCOMOTIVE. 385 locomotives the burning d oil, Avhich rec^uircs praeticalh' nn lalnir in firing, although the services of a fireman must still tie retained. 304. The " Soo " Decapod Locomotive. It lias been seen that the results of Trevcthick's early eft'orts was a crude and simple machine, with what might be termed, m i'(iurtes\- tn that earlv attempt, a single ]"iair iif drivers. Subsc quenth", as Iricnmotive evolution took place, two pairs <:if dri\-ers c(iu]ded with the horizontal connecting-rcul were emplnved. Then the !Mogul with the three pairs of couj^led (:lri\"ers was used, and at or about the same time the conscilidation tA'i^e witli frair pairs of coupled drivers was f(;)und adapted in a high rlegree to the hauling of great freight trains. The last evoluti(^n in dri^dng- wheel arrangement is exhibited in Fig. 5;;. It belongs to what is called the Decapod t}'pe. As a matter of fact, fwe pairs of coupled driAdng-Avheels ha\'c been occasionallv used for a con- siderable number of years, l^ut this engine is the Decapod brought up to the highest point of modern excellence. As shown, it uses steam hx the A'auclain compound system, the small or high- pressure cvlincler being underneath the L^w-pressure cvlinder. They have been built by the Baldwin Locomoti^'e Works for 386 SOME FEATURES OF RAILROAD EXGF\EERL\G. the Minneapolis, St. Paul and Sault Ste. Marie Railroad Com- pany, on what is called the " Soo Lme." It has given so much satisfaction that more of this t\'pe but of greater weight are being built fur the same company. This engine was limited to Fig. 37. a total weight of 215,000 pounds, with 190,000 pounds on the drivers. 305. The A., T. & S. F. Decapod, the Heaviest Locomotive yet Built. — The heaviest locijmotive ^^et constructed, consequently occupving tlie primacy in weight, is that shown in Fig. 38. It is a Decapod operated with others of its type by the A., T. & S. F. ■-^ -■ 4,,^.^- A,- Yjg. s8. Company near Bakersfield, California. It is a tandem compotmd coahburner, as shown bv the illustration, the high-pressure cylin- der Vieing in front of the low-pressure. The dimensii ms oi cylin- ders are iq and 3? ^ ,i2 inches stroke, and the dri\dng-wheels are 57 inches in diameter. The total height from the top of stack THE HEAVIEST EOCUMUTIVE YET BUILT. ;ks7 /^-^i' 388 SOME FEATURES OF RAILROAD EXGIXEERIXG. down to the rail is 15 feet 6 inches, while the height of the centre of the boiler above the rails is 9 feet 10 inches. Figs. 39 and 40 show some of the main boiler and fire-box dimensions. There are 463 2} -inch tubes, each 19 feet long. The total heating sur- face is 5390 square feet, about one eighth of an acre, the length of the fire-box being 108 inches and the width 78 inches. The heating surface in the tubes is 5 1 5 6 square feet, and in the fire-box 210.3 square feet; the grate surface having an area of 58.5 square feet. The boiler is designed to carry a Avorking pressure of 225 pounds per square inch, the boiler-plates being -||- inch, -jV inch, and I inch thick, according to location. As shown by the illus- trations, the boiler is Avhat is termed an extended wagon-top with wide fire-box. The total weight of the locomotive itself is 267,800 pounds, while the weight on the driving-wheels is 237,800 pounds, making 47,560 pounds on each axle. The tractive force of this locomotive is estimated to be over 62,000 pounds. COMPAniSOX OF SOME OF THE HEAVIEST LOCOMOTIVES. '''SO 306. Comparison of Some of the Heaviest Locomotives in Use. — The lolliiwing table gi\"es a cumparisijii of the liea\'iest lueumii- thx's thus far buih., as taken from the Railroad (Jazettc fur Janu- ary 31, 1902, re\'ised ti > September i, 1902. ei l^^'ARlSl)^' of heaviest locumutives. AlchisLin, T. ii>, & Santu Ff. Name ^t builder Size i)t e\liuders Total weight Weight on dri\'ers . , . . Dri\'ing-\vheels, diam. . Heating surfaee Grate area Baldwin 207,800 Ills. -'J7,8oo lbs. ^7 in. ^.;lJO sq. ft. 5.S.5 511. ft. Pillsburg, Bessemer^ Lake Erie Pitt sburK -4 ■ ^tO,.? 1^ m. 00 lbs. --^:~ 00 ll;,s. i,8o^ ni. sq.ft. SM. ft. IlUn.. eentri Pittsburn ,i -.32 in . 2.iO,ooo lbs. o.S.ooo lbs. 54 in. ,.;22sq. ft. i..^ sq. ft. ■. ^o m . ,200 lbs Lehiuh Valley. Baldwin iS & ,^o ■ .^o in. 2 2 3,o.S2 lbs. 202,2,32 lbs. .S ,1 in . 4,104 sq . ft. 00 sq 1 1 . These instanees of modern locomotive construction are im- pressive, especiall_\' when considered in contrast with the tvpe of engine in use not mnre than iifty years ago. They indicate an almost incredible ach'fince inrailmad transpi^irtation, and the\' accciunt iov the fact that a fiushel 1 if wheat can be brought o\"cr- land at the present time from Chicago to Xew Y a residence within a nnle (.if it. PART V. THE NICARAGUA ROUTE FOR A SHIP-CANAL. 307. Feasibility of Nicaragua Route. — The feasibility of a ship-canal between the two oceans across Nicaragua has been recognized almost since the discovery of Lake Nicaragua in 1522 bv Gil Gonzales de Avila, who was sent out from Spain to succeed Balboa, after the execution of the latter by Pedro Arias de Avila at Ada on the Isthmus of Panama. 308. Discovery of Lake Nicaragua. — Gil Gonzales set sail from the Bay of Panama in January of that year northward along the I^acific coast as far as the Gulf of Fonseca. He landed there and proceeded to explore the countrj^ with one hundred men, and found what he considered a great inland sea, as aa'c now know, about 14 miles from the Pacific Gcean at the place of least separation. The country was inhabited, and he tVumd a native chief called Nicarao, who was settled with his people at or near the site of the present city of Ri^-as. As he found it a goodly country, fertile and abounding in precious metals, he immediately proceeded to take possession of it for his so^'ereign, but the Spanish ex])lorer was sufficiently gracious to the friendly chief to name Lake Nicaragua after him. From that time the part of Nicaragua in the A'icinity of the lake received much atten- tion, and the Spaniards made conquest of it without delay. Among those who were the earliest visitr)rs was a Captain Diego JMachuca, who, with two hundred men under his command, ex- plored Lake Nicaragua in 1529 and constructed boats on it, a brigantine among them. He seems to haA'e been the first one who entered and sailed down the Desaguadero Ri^-er, now called :!90 EATiLY MARITIME COMMERCE WITH LAKE NICARAd'A. 301 the San Jucm, and one of the rapids in the upper portion of the river now bears his name. He pursued his eourse into tlie Caribbean Sea and sailed eastward to the Isthmus of Panama. M.ip uf American Isthmus, showing Proposed Canal Routes. 309. Early Maritime Commerce with Lake Nicaragua. — Sub- sequently sea-going vessels passed through the San Juan River in both directions and maintained a maritime trade of some mag- nitude l")etween the shores of Lake Nicaragua and Sftain. (.)b- viously these vessels nnist ha\'e been rather small for ocean-going craft, unless there was nKire water in the San Juan River in those early days than at present. There are some obscure traditi(->ns of earthciuakes having disturbed the bed of the river and made its passage more dithcult by reducing the depth of water in some of the rapids'; but these reports are little more than tradi- tionary and lack authoritatiA-e confirmation. It is certain, how- ever, that the marine traffic, to which reference has been made, was maintained for a long period of years, its greatest activity 393 THE XrCArtACr'A ROUTE FOR A SUIP-CANAL. existin£^ at about the Vicginnint^ of the seA'ciiteciith century. It was in ci >nnectirin witli tins traffic probahjly that the city of Granada at the nnrth\A'estcrn extremity of the lake was estab- Hshed, ])erha]:)S before i5,iO. 310. Early Examination cf Nicaragua Route. — Although the apparently eas)' connectii m between tlie Caribljean Sea and Lake Nicaragua, together with tlie jircjximit}' of tlie latter to the Pacific coast, at once indicated the jiossibilitv of a feasible Avater com- munication between the two oceans, probabh' no systematic invcstigatirin to determine a definite canal line was made until that undertaken by .Manuel Galisteo in 1779 under the instruc- tion of Cdiailes III., who was tlien vn the throne of Spain. Galis- teo made a report in 17S1 that Lake Nicaragua was 134 feet higher than the Pacific ( )cean, and that high mountains inter- vened between the lake and the ticean, making it impracticable to establish a water cijmmuni ation l:)etween the two. In spite of the discouragement of this ri.port a company was subsequently formed under the patronag of the crown to construct a canal from Lake Nicaragua along the Sanoa PiA'cr to the Gulf of Nico^-a, but nothing ever came of the project. 311. English Invasion of Nicaragua. — The countrv Avas in- A'aded in 17 So Ijy an English expedition sent r)ut I'rom Jamaica und r Captain Horatio Nelson, Avho subsequenth- became the great admiral. He ])roce ckd up the San Juan RiA-er, and after some fighting captured l:)y assault Pert San Juan at Castillo \dcio. Nelson and his force, howcA'cr, Avere ill qualified to take care of themseh-es in that trojiical country Avhcrc drenching rains AA'cre constanth' falling, and he Avas tliercfore obliged to aban- don his jdan ( )f taking possessii m of Lake Nicaragua and returned instead to Jamaica. The trojdcal fcA'crs induced I^.a* exp(.isure reduced the crew of his oaaii shi]>, two hundred in number, to rinly ten after his return to Jamaica, and he liimself nearh' lost his life bA' sickness. 312. Atlantic and Pacific Ship-canal Company. — Subsequently to tins period the Nicaragua n mtc attracted more or less attention until ;\lr. E. Cr. Squicr, the first consul for the United States in Nicaragua, negotiated a treat)' between the two countries for facilitating the traflic from the Atlantic to the Pacific t.)ccan by Sl'IiVEY AXD PROJECT OF COL. 0. Tl'. CIIILDS. 303 means of a ship-canal (.r railmad in tlie interest \A-n, then trans- shipped them to ri\-er stcambi);its running u]! the San [nan Ri\-er and across the Sdulherly end of the lake t<> a small town called La Virgin, whence a ginid road fur 14 miles (jvcrland led to the Pacific port nf San Juan del Sur. Pacific coast steamshi].)s com- pileted the tri]) between the latter pi irt and San Pranciscn. 313. Survey and Project of Col. 0. W. Childs. — Idiis trafiic stimulated the ijld idea 1 >f a ship-canal across the Central Ameri- can isthmus on the Nicaragua route to such an extent that Col. ( ). W. Childs, an eminent ci\dl engineer, was instructed by the Aaieriean Atlantic and Pacific Shiji-canal Com])anA' to make sur\"e\-s and examinations for the project of a ship-canal on that route, l^he results of his surA'e\'s, made in 1S50-52, ha\X' become classic in interoceanic canal literature. fie eoncludei.l that the most feasible nDute lay u\j the San Juan River from Grcvtown to Lake Nicaragua, across that lake, and down the general course of the Rio Crrande on the west side of Nicaragua to Brito on the Pacific coast, d'his is practically identical with the route adopjteel bv the Isthmian Canal Commissii;>n now (iqoi) being discussed in Congress. 314. The Projsct of th3 Maritime Canal Company. — The project planned b\' CijI. tdiilds, like those Avhich preceded it, had no sufisfantial issue, but the general suliject of an isthmian canal aerijss Nicaragua was, from that time, under almo t constant agitati: >n and consideratii )n mijrc or le -s acti\"c until the ^Maritime Canal Com]Xinv of Nic:iragua was organized in Feliruary, i8Sg, under concessions secured fr( mi the goA'crnm^ents of Nicaragua and Costa Rica bv Mr. A. G. Alemocal. This company-made a careful examination i:>f all ]n"eceding proposed riuites, and finallv settled upon a ]ilan radicallv different in some res]iccts fmm anv before consideted. The Cariblx'an end of the canal was located on the Greyfi^iwii Lagoon west of GreA-ti"iwn. From that ]"iriinT the line followed up the valley of the Deseado I^iver and cut across the 394 THE NICARAGUA ROUTE FOR A SHIP-CANAL. hills into the valley of the San Juan above its junction with the San Carlos. A dam was to be constructed across the San Juan River at Ochoa, below the mouth of the San Carlos, so as to bring the surface of Lake Nicaragua down to that point. From its junction with the San Juan River the canal line followed that river to the lake, across the latter to Las Lajas, and thence down the Rio Grande to the Pacific coast at Brito. It was contem- plated under this plan to carry the lake level to a point called La Flor, 13.5 miles west of the lake, and drop down to the Pacific Breakwater of the ^^aritime Canal Cnmpaiiv. The closed former entrance to Gre}'to\vn harbor is sliown oii the left. from that point by locks suitably located. After partialh' ex- cavating the canal prism for about three quarters of a mile from the Grey town Lagoon, constructing a line of railroad up the Deseado valley, as well as a telegraph line, and doing certain other work preparatory to the actual wo k of construction, the Maritime Canal Company became involved in financial difliculties and suspended operations without again resuming them. 315. The Work of the Ludlow and Nicaragua Canal Commissions. — In i8q5 and again in 1897 two commissions were appointed by the President of the United States to consider the plans and esti- THE ROUTE OF THE ISTHMIAN CANAL COMMISSION. 395 mates of the ilaritime Canal Company in the one case, and the problem of a ship-canal on the Xicaragtia route in the latter. Neither of these commissions, ho\ve\-er, had the funds at its disposal requisite for a full and comjjlete consideration of the problem. In 1S99, therefore, the Isthmian Canal Commission was created b>' Act of Congress, and appointed by the Presi- dent of the United States, to determine the most feasible and practical route across the Central American isllimus fur a canal, together with the cost of constructing it and placing it under the control, management, and ownership of the United States. This commission consisted of nine memlicrs, and in- cluded ci\-il and militcu-y engineers, cm officer of the na\-y, an ex-senator of the Unitetl States, and a statistician. It was the pro\dnce and duty of this commission to make examinations of the entire isthmus from the Atrato RiA-er in the northwestern corner of South America to the western limits of Nicaragua for the purpose of determining the most feasible and practical route for a ship-canal between those territorial limits. This brings the general consideration of the isthmian canal question to the Nica- ragua route in jiarticular, to AA-hich alone attention will be directed in this part. 316. The Route of the Isthmian Canal Commission. — The Isthmian Canal Commission adopted a route jiractically folloAving the San juan Ri\'er from near Grey town to the lake, across the latter to Las Lajas on its westerly shore, and thence uji the c( mrse of the Las Lapis River, across the continental diA'ide into the Rio Grande valley, and down the latter to Brito at the nn luth of the Rio Grande on the Pacific coast. As has already lieen stated, this is practically the line adopted by Col. Cdnlds almost exactly fiftv vears ago. It is also essentialh' the route adopted by the Nicaragua Canal Commission appointed in 1897, and which completed its operations immediately prior to the creation of the Isthmian Canal Commission. The amount of Avork per- formed in the field under the direction of the commission can be realized from the statement that twenty working parties Avere organized in Nicaragua with one hundred and fifty-nine civil engineers and other assistants, and four hundred and fifty-fiA'e laborers. 396 THE MCARAGVA ROUTE FOR A SHIP-CANAL. 317. Standard Dimensions of Canal Prism. — By the Act of Congress creating it, the latter commission was instructed to consider plans and estimates fur a canal of sufficient capacity to accommodate the largest ships afloat. In order to meet the requirements of those statutory instructions the commission decided to adopt 35 feet as the minimum depth of water in the canal throughout its entire length from the deep water of one ocean to that of the other, wherever the most feasible and practi- cal route might be located, the investigations of the commission having shown that the final location to be selected must narrow down to a choice between the Panama and the Nicaragua routes. It Avas further decided by the commission that the standard width of excavation at the bottom of the canal should be 150 feet, with 500 feet for the ocean entrances to harbors, and Soo feet in those harbors. Greater widths than that of the bottom of stand- ard excavations were also adopted for river and lake portions. HARBOR SECTION LAKE BOHIO LAKE NICARAGUA Standard Sections adopted by the Isthmian Canal Commission. The slopes of tlie sides cd the excaA-ation Avere determined to be I vertical on i-t h()rizontal for firm earth, but tis flat as i A'crtical on 3 or even 6 h(.)nzontal for soft mud or silt in mtirshv locations. In rock cutting belcw water the sides of the excavation \\-ould be vertical, fiut as steep as 4 A'crtical on i horizontal above water. The longest ship afloat at the present time (1902) is the Oceanic of the White Star Line, and its length is about 704 feet. THE SAN JVAN DELTA. 31.17 The wiliest ships, i.e., the ships hu\'ing the greatest beam, are na\"al \'essels, and at the ])resent time nnne lias a greater Ijeani than aliout 77 feet. In order to alTi ird aeei immijckition fur furtlier de\-elu])ment in butl: lengtli and fieam uf ships witliuut leading tu extra \'agant dimensiems, the eummissiun ileeided lo pro\'ide loeks haA'ing a usafile length uf 740 feet \\\{\\ a elear width eif 84 feet. These general dimensiuns meet fully tlie re- quirements of the ka\', and were adupted fur jjlans anel estimates on both the I'anama and A'iearagua ruutes. 318. The San Juan Delta.- The entire Central .-Vmenean isthmus is \-oleanie in eharaeter, and this is jiartieularh' true uf the eountry along the Niearagua ruute with the exeejiliun i.if the luwlands immediateh' baek of the ueean shure-lme in the xaeimty of Grevtown. Frum the latter jioiiit to Fort San Carlos, where the San Juan River leax'es the lake, is ajiproximately 100 miles. With the exeeption of the 15 miles nearest to the seacoast the San Juan IviA'er runs mostly thruugh a rugged eountrA' witli high hills densely wooded on either side. The soil is mostly heavy clav, although the bottom of the valley immediately adjaeent to the rh'er is largely of sand}' silt with some mixture of elay. Be- tween the bids baek of Greyto\\'n and the seacoast the country is almost a continuous morass covered \N'ith coarse grasses and other dense tropical \-egetation, but with a number of small isolated hills projecting up like islands in the surrounding marsh, and interspersed with numerous lagoons. All this flat euuntry has the appearance of forming a delta through which a number of mouths of the San Juan River find their way. One of these, called the Lower San Juan, empties into the Grey town Lagoon, but the main mouth of the San Juan, called the Colorado, branches from the main ri\'er at the point where the Lower San Juan begins, about 13 or 14 miles from the ocean. The Colorado itself is composed of two branches, and at the place where it empties into the sea there are a number of long narrow lagoons parallel to the seashore, appearing to indicate comparatively recent shore formation. Again, a small river called the Rio San JuaniUo leaves the main riA'cr 3 or 4 miles above the junction of the lower San Juan and the Colorado, and pursues a meandering course through the low marshy grounds back of Grevtown, and finally again 398 THE NICARAGUA ROUTE FOR A SHIP-CAXAL. joins the Lower San Juan near the town. This marshy lowland is underlaid by and formed largely of dark-colored sand brought down mostly from the volcanic mountains of Costa Rica by two rivers, the San Carlos and the Serapiqui, the former joining the San Juan about 44 miles and the latter about 23 miles from the sea. f ^.... . -:'.v-TJS'^Z-'««358ti!aliitS*(..' III! liilMiillin ^ .. j^ ^MK jd^^^HL^iM Sfl^L^^^^i wi"' j'^r' ■■? '^ . ■ M'-'-^i ..W.T '^- i" ■" .;- .. ^s^mmi ^ LlMi^FL_^'"""" ^^^ 1^ Gre\"to\\"n Laguon (former!}' G^^,■^■tn^v]| Har]n>r). showincr Gre)'Lids, and from that p(jint to a distance of about 75 miles from the t)eean other rapids are found, the prin- cijxd of which are the L'aslillo and the Tor(j. The Castillo l^apids are at the point called Castillo \'iej(j, where there is located an old Spanish fort on the to]i of the high hill around the base of which the ri\'er llows. The town of Castillo \'ie)o has a small popiulation of perhaps 500 to 600 pe(_)ple. It is a place with his- torical associations, ft) which reference has already been made. It was here that Cajifain (afterwards Admiral) Nelson captured the Spanish fort in 17S0. It is a place of some importance in connection with the ri\'er traflic in consequence of necessary transhipment of freight and passengers to o\-crcome the rapids. 321. The Upper San Juan. — The u]i]ier reaches of the San luan within aljout 20 miles of the lake are bordered with con- siderable marsh\- ground. In the \-icinity of its exit from the lake there is a wide stri]) of soft marshy country around the entire southeastern shore. 322. The Rainfall from Greytown to the Lake. — The entire country between tireytown and the lake is intensch' tropical, and the A-egctati(.in is characteristically dense. It is particularly so at Grevtown, \\'here the total annual rainfall sometimes reaches as much as 300 inches. It rains many times in a da\', and nearly e\"er\' day in the A'car. The strong easterly and northeasterly trade winds, lu\n-\--laden with the ewapt.-iration from the tropiical sea, meet the high ground in the A'lcinity of Cireytown and pre- cipitate their water\' contents in frequent and hca\-y shoAvers. The general course of the San Juan valley is a little north of west or south of east, and the trade winds apjicar to fo low the course of the A-allev to the lake. The rainfall steadily decreases as the seashore is left lichind, so that at Fort San Carlos, the point of exit of the ri\-cr from the lake, the annual precipitation may vary from 73 t(3 100 inches. There is no so-called dry season between the lake and the Caribbean Sea, although at Fort San Carlos the rainfall is so small between the middle of December and the mid- dle of ^lav that that period may perhaps be considered, rela- ti\-eh- speaking, a dry season. It is CA-ident, thcref.-ire, that all the conditions are fa\-(^rable to luxuriant tropical growths over 400 THE XICAEAGVA ROUTE FUR A SHIP-CAXAL. this entire eastern portion of the canal route, and the coarse grasses, palms, and other tropical ^•egetation found in it are inde- scribably dense. The same general observation is applicable to the forest and undergrowth throughout the entire course of the riA'er from Greytown to Fort San Carlos. All of the high ground is heaA'ily timbered, ^Ylth undergro\\-th so dense that no survey line can be run until it is first completely cut out. That obser- vatii->n holds with added force throughout the swamp}- country TIk- Maritime Canal Company's Canal Cut leading rjut <.»f Gre\"t(iwn Lagnlv. This j^ool, with ]3ractieall\- no sensible current, is called Agua Muerte, or Dead \A'ater. The relatively great depth of this p(jol shows eonclusi\'ely that the upper San Juan, i.e., above the mouth of the San Carlos, carries no silt, otherwise the pool would be filleil; in other words, that part of the San Juan Ri\-er is not a scdiment-liearer. The slope of the river surface in the Toro Rajiids, about 27 miles from the lake, gives a fall of 7 i\r feet in 1 1\ miles. 324. Discharges of the San Juan, San Carlos, and Serapiqui. — In times of heavy floods the San Carlf the Colorado and Castillo, and on the other between Castillo aboA'e the rapids to Fort San Carlos. It is the custom, therefore, to 402 THE NICARAGUA ROUTE FOR A SHIP-CANAL. transfer passengers and freight from boats below the rapids at Castillo by a short tramway to other boats in waiting above the rapids at that point. Boats pass up Machuca and Toro rapids at practically all seasons, but sometimes with difficulty. In order to meet the exigencies of low water in the Lower San Juan a railroad called the Silico Lake Railroad, with 3 feet gauge, has been constructed from a point opposite the mouth of the Colorado, called Boca Colorado, to Lake Silico in the marshes back of Greytown, a distance of about 6 miles. Light-draft boats connect Lake Silico with Greytown for the transfer of passengers and freight. The type of light-draft steamboat used on the San Juan River is the stem-wheel pattern, so much used on the west- em rivers of this country, the lower deck carrying the engines and boilers as well as freight, while the upper deck, fitted with crude staterooms, furnishes a kind of accom^modation for pas- sengers. 326. The Canal Line through the Lake and Across the West Side. — The little town of Fort San Carlos on a point raised some- what above the lake where the San Juan I^iver leaA'cs the latter is the second place on the entire river from Grevtown where any population may said to be found, and probably not more than 400 or 500 people even there. Its position is on the north side of the river, at the extreme southeastern end of the lake, com- manding a fine view of the water and the countr)'- bordering it in that vicinity. To the westward lie the Solentiname Islands, a group a short distance to the north of Avhich the sailing line for the canal in the lake is located. After passing this group of islands that line deflects a little toward the south, so that its course westward is but a httle north of west, straight to a point near to and opposite Las Lajas on the westerly shore of the lake, southwest from the large island on Avhich Ometepe and lladeira are located; indeed those two A'olcanic cones, the former still active, constitute the entire island. The point cahed Las Lajas is at the mouth of a small river of that name which discharges any sensible amount of water only during the Avet season; it is located not more than 10 miles from Ometepe, and aff.^rds a most impressive view of that perfect volcanic cone rising almost an exact mile above the water. The general direction of the CHARACTER OF THE COUXTRY WEST OF THE LAKE. 403 ■canal route is a little west of snuth from Las Lajas on the lake to Brito on the oeean shore. The line follo\\-s the Las Lajas about a mile and a half only of the 5 miles from the lake in a southwesterly direction to the point A\'here tlie enntinental (li\-ide is crossed. The elevation of the divide at this place is about 145 feet only above sea-level. The line then descends immediately into the valle)' of the Rio Grande and follows that stream to its mouth at Brito. 327. Character of the Country West of the Lake. — The country on the west side of the lake exhiliits a character radically difterent from that on the easterly side, i.e., bet\\'een the lake and the Caribbean. It is a country in which much more poj)ulation is found. While there are no towns along the 1 7 miles of the The Maritime Canal Company's Railroad near Greyto^Yn. route from Las Lajas to Britix the old citv Rivas, containing perhaps 12,000 to 13,000 pei-^ple, is ab.iut o miles from Las Lajas, 1 the small t-wvns of San Jorge, Buenos Ayres, Pr^ticsi, as well ani 404 THE NICARAGUA ROUTE FOR A SHIP-CANAL. as others, are in the same general vicinity. Plantations of cacao and various tropical fruits abound, and there is a large amount of land under cultivation. It is largely a cleared country, so that far less dense forest areas are found. There are two distinct seasons in the year, the wet and the dry, the latter extending from about the middle of December to the middle of May. The annual rainfall is extremely A'ariable, but in the vicinity of Rivas it may run from 30 or 40 to nearly 100 inches. The country is of great natural beauty, and one which, under well-administered governmental control, would afford many places of delightful residence. The trade winds blow across the lake from east to west with considerable intensity and great regularity. The}- produce a beneficial effect upon the climate and render atmospheric conditions far more agreeable than in that part of Nicaragua in the vicinity of Grevtown. It will be remembered that Rivas is the city where the .Vmeri- can filibuster Walker was taken prisoner by the Costa Ricans and Nicaraguans and shot in 1857. 328. Granada to Managua, thence to Corinto. — At the north- western end of the lake is located the attractive city Granada, sometimes called the "Boston of Nicaragua." A reference to a map of Nicaragua will show that a short distance north of Granada is the river Tipitapa, which connects Lake Nicaragua with Lake Managua, the latter lying 18 miles to the northwest of the former. A railroad connects Granada with the city of Managua, which is the capital of Nicaragua, running on its way through the city of ]\Iasaya, chiefly noted for the volcano of the same name located near by, and which has been subiected to a most destructive eruption. The old lava-flow stiU shows its path of destruction by a broad black mark extending many miles across the country. A railroad connects Lake Managua at Momotombo with the Pacific port of Corinto. 329. General Features of the Route. — It is thus seen that the proposed route of the Nicaragua Canal lies first along the valley of the San Juan River, then across the lake, cutting the con- tinental divide west of the latter at the low elevation of 145 feet aboA-e the sea, thence following the valle\- of the Rio Grande to the Pacific Ocean at Brito. From Greytown to Castillo the San ARTIFICIAL HARBOR AT GREYTUWN. 405 Juan River is the boundary between Nicaragua and Costa Rica, and concessions from both go\x'rnnients would be necessary for that part of its construction. I'^rom Castillo to the I-'acific Ocean the route lies entirely in Xicaraguan territory, and the only crjn- cession necessiu")' fo thtit portion of the line would be from the government of Nicaragua. From Castillo to and around the southern end of the lake the boundary-line is located 3 miles easterly from the ri\'cr, fol owing its turns, and the same distance from the lake shore, all by an agreement recently reached between the two go\'ernments. The summit level of the canal would therefore be the surface of the water in Lake Nicaragua, which is carried down to Conchuda, 52 miles from the lake on the San Juan River toward the east, by a great dam located there, and to a lock between 4 and 5 miles from the lake toward the west. Hence the summit level would stretch throughout a distance of about 126 miles, leaving a little more than 46 miles on the Caribbean end and about 1 2 miles on the Pacific end of the regular canal section. The 50-mile stretch from the lake to the point where the canal cuts the San Juan River near Conchuda is a canalized portion of the San Juan River, as a large amount of excavation must be done there in order to gi\'e the minimum required depth of 35 feet. The points of river bends or curves are in some cases cut oft' by exca\'ated canal section in order to shorten the Hne and reduce the curvature. Considerable por- tions of the line in the lake, particularly near Fort San Carlos, would be excavated. For several miles in the latter vicinity large quantities of silt and mud must Ije remo\-ed, as the lake is siiallow and the bottom is A-ery soft. The entrance into the western portion of the canal at Las Lajas requi es a large amount of rock excavation, as the shore and bed of the lake there are almost entireh' of rock. 330. Artificial Harbor at Greytown. — The preceding obser- vations are mostly of a general character, and give but httle consideration to the engineering features of the canal construc- tion In considering the canal as a carrier of ocean traffic probably the first inquiry will be that relating to harbors. In reality there is no natural harbor at either end of the Nicaragua routed Fifty years ago there was an excellent harbor at Grey- 406 THE NICARAGUA ROUTE FOR A SHIP-CANAL. town into which ships drawing as much as 30 feet found ready entrance, and within which was afforded a Avell-protected an- chorage. As early as that date, however, a point of land or sand-pit was alread}^ pushing its way northward in consequence of the movement of the sand along the beach in that direction, and in 1865 it had nearly closed the entrance to the harbor. . .— ^t'.w^ I ■ ' ■ •'^"'..^ -'- M ■^^l^^^^^^ujj^imB^mm^am--l3£IM ^^j-Jif -^^thfeasJW^^^y^B^^^^^^M'B l^^'j'^^-'v'^; 1 ;''^;,\.. J* ii^_jijJ|Wr ''^fjlh; •^'^f^Wy^^f* C wWSf ^ * ^'■'"•"--.il ' A^iS^X,^ =«^^|p^|?frfiS^# ^^L^\ • \:'t^^'^'-'W' -^|::^ V- /--.v. Scene on tlie San Juan River. For many years that entrance has been entirely closed, and now what was once the protected harbor of Greytown is a shallow body of water, completely closed, and known as the Greytown Lagoon. There is a narrow, circuitous, and shallow channel leading from it out to an opening in the sand-bar, which may be navigated by boats drawing not more than 2 or 3 feet, and by means of which freight and passengers are taken from steamers, which are obliged to anchor in the offing. Occasionally heavy storms break through this strip of sand between Greytown Lagoon and the ocean, and for a short time form a shallow en- trance to the former. The sand movement in that vicinity northward or westward is so active that it is but a short time before such openings are again closed. The deepest water in the lagoon probably does not exceed 8 or 10 feet at the present ARTIFICIAL IIARBOIi AT BlUTO. 407 time, and the most of it is much shallower. The tidal action at Greytown is almost nothing, as the range of tide between high and low is less than i foot. The mean level of the Caribbean Sea is the same as that of the Pacific Ocean. Under these circumstances it is necessary to create what is practically a. new harbor at Greytown, and that work is con- templated m the pkms of the Isthmian Canal Commission, The canal line is found entering the lagoon about i mile northwest of Greytown, where a harbor is planned having a. length of 2500 feet and a width of 500 feet, increased at the inner end to Soo feet to proxdde a turning-basin. The entrance to this harbor from the ocean Avill be dredged to a width of 500 feet at the bottom, and it will be protected outside of the beach-line by two jetties, the easterly about 3000 feet long, and the westerly somewhat shorter. These jetties would ' ' be built of loose stone of irregular shape and size, resting on a suitable foundation," the largest, constituting the co\'cring, weighing not less than 10 to 15 tons each. These jetties would be carried 6 feet above high water and have a top width of 20 feet. The trade A\'inds, which blow from the easterly and northeasterly, would have a direction approximately at right angles to that of the easterly jettj^, and ships making the entrance of the canal Avould consequently be protected against them while between the jetties. The easterly of these jetties would act as an ijbstruction against the westerly movement of the sand, but it is practicalh.^ certain that a con- siderable amount of the latter avouIcI be swept into the channel, and possiblv to some extent into the harbor, necessitating dredg- ing a considerable porti(^n of the time. The commission estimates that the maintenance of the entrance and harbor would require an annual expenditure of $100,000. 331. Artificial Harbor at Brito. — The harbor at Brito presents a problem of a different kind. There is absolutely no semblance of a harbor there at the present time (1902 ) ; it is simply a location on the sandy beach of the ocean protected against swells from the west hx a projecting rock^' point called Britii Head, the Rio Grande Ri\'er emptying into the ocean just at the foot of Brito Head, between it and the canal terminus. The entire harbor and its entrance would be excavated in the Ioav ground of that 408 THE NICARAGUA ROUTE FOR A SHIP-CANAL. vicinity, composed mostly of sand and silt, although there would be a Httle rock excavation. The entrance to the harbor would be dredged 500 feet wide at the bottom, and be protected by a single jetty on the southeasterly side. The harbor itself would be excavated back of the present beach ; it would have a length of 2200 feet and a width of 800 feet. As the depth of water increases rather rapidly off shore, the lo-fathom curve is found at about 2200 feet from low-water mark, hence the jetty would not need to be more than probably 1800 to 2000 feet long. In this vicinity the water is usually smooth ; indeed but few storms annually visit this part of the coast. The conditions are quite similar to those found on the coast of Southern California. There is little sand movement in this vicinity, and the annual expen- ditures for maintenance of the harbor and entrance would be relatively small; the commission has estimated them at $50,000. 332. From Greytown Harbor to Lock No. 2. — The canal line, on leaving the harbor at Greytown, is found in low marshy ground for a distance of about 7 miles, the excavation being mainly through the sand, silt, mud, and vegetable matter characteristic of that location. Throughout almost this entire distance the natural surface is but little above sea-level. The first ground elevated much above this marshy country is known as the Mis- terioso Hills, in which Lock No. i is founded, having a lift of 36J feet and raising the water surface in the canal by that amount above sea-level. Another stretch of marshy country, but not quite so wet as the preceding, follows for a distance of about 1 1 miles, when the Rio Negro Hills rise abruptly to an elevation of a Httle over 150 feet above sea-level. At this point is located Lock No. 2, with a lift of 18 J- feet. This lock is about 21 miles from the 6-fathom hne oft" Greytown. The canal line here prac- tically reaches the San Juan River, the latter lying a considerable distance easterly of the canal, between this point and the ocean. Between Greytown and Lock No. 2 embankments, never reaching a greater height than 10 to 15 feet, are required to keep the water in the canal at A'arious locations along the low ground. These embankments do not necessarily folloAv parallel to the centre line of the canal route, but are planned to connect hills, or rather high ground, so as to reduce their length and give them a more Bc.d<- of MacM MiiMH^ 20 30 PLAN SECTION ON LINE A-A. -f-40 , Lock No. I, Nicaraj:;ua Route, about Seven Miles from Greytown. FROM LOCK NO. TO THE LAKE. 409 Stable character than if they were located close to the canal ex- ca\'ati()n. While some embankments will still be found abo\-e Lock Xtj. 2, they are few, and even lower than those already noticed. From Lock No. 2 to Lake Nicaragua the route of the canal lies practically along the San Juan River, the chief excep- Telegniph r)ftice at Oclma on tlu- San Juan River. tion to that statement being the cut-oft" in the vicinity of the Conchuda dam. 333. From Lock No. 2 to the Lake. — Inasmuch as both the Serapiqui and San Carlos rivers flow from Costa Rican territory into the San Juan, that is, from its right bank, the canal line neces- sarily is located along the northerly or left bank of that river. At a distance of 2 3 miles from the ocean the canal line cuts through what are called the Serapiqui Hills opposite the mouth of the river of that name, and at a distance of a little over 26 miles from the ocean it pierces the Tamborcito Ridge, where is found the deepest cutting on the entire route. The total length of 410 THE NICARAGUA ROUTE FOR A SHIP-CANAL. cut through this ridge is about 3000 feet, but its greatest depth is 297 feet, and it consists largely of hard, basaltic rock. The next lock, or Lock No. 3, is found about 17 miles from Lock No. 2, or 38 miles from the sea, and it has, like Lock No. 2, a lift of 18^ feet, raising the surface of the water in the canal to an elevation of 73-^- feet above the sea. Continuous heavy cutting through what are called the Machado Hills brings the line to Lock No. 4, at a distance of a little less than 41 miles from the ocean. This lock has a lift varying from 30.5 to 36.5 feet, inas- much as it raises the surface of the water in the canal to the sum- mit level in the lake. The maximum lift of 36.5 feet would be required when the lake level stands at an elevation of no feet above the sea, and 30.5 feet when the same surface stands at an elevation of 104 feet above the sea. Although the water surface in the canal level above this lock is identical with the summit level in the lake, the canal line again runs through continuous heavy cutting for a distance of 5 miles before it reaches the canal- ized San Juan. This portion of the line between Lock No. 4 and the San Juan River is called the Conchuda cut-off, for the reason that the point called Conchuda, where the great dam is located, is but 3 miles down the river from the point where the canal enters it. From Conchuda to the lake, as has already been stated, the canal line follows the course of the San Juan River, which must be canalized by considerable excavation of earth and rock, both along the bed and in cut-offs. The greater part of this cutting must obviously be on that portion of the river toward the lake, as that is the highest part of the river-bed in its natural condition. 334. Fort San Carlos to Brito. — The distance from the point of entrance of the canal into the San Juan River near Conchuda to Fort San Carlos on the shore of Lake Nicaragua is about 50 miles, while the distance across the lake on the canal line is 70.5 miles, which brings the line tD Las Lajas on the southwesterly shore of the lake. There is considerable heavy cutting through the continental divide between the lake and the first lock westerly of it, i.e.. Lock No. 5. The maximum cutting is but 76 feet in depth, and the average is but little less than that for nearly 3 miles. This lock EXAMIXATIOXS BY BORJNGS. 411 is located a little less than lo miles from the lake and nearly 176 miles from the 6-fathom line off Greytown. The place at which this lock is located is known as Buen Rctiro. The lift of Lock No. 5 A-aries from 28-i feet as a maxmium t(j the minimum of 22^ feet, bringing the water surface m the canal down to Si-^V feet above mean ocean le\-cl. Lock Xo. 6 is located but about 2 miles west of Lock No. 5, and also has a lift of 28.! feet. The hne now ft . i s ^^ Pt^O ^Pyg^Hpliy^jijy^^- ^^^P^^jf^K^jfr^S^BBr^ Bm^ ^^^^%1 ^S^^^^'^p!^^^ Surveying Party of the Isthmian Canal Commission on the San Juan River. runs along the course of the Rio Grande to the ocean, Lock No, 7 being also 2 miles west of Lock No. 6, again with a lift of 28.I feet. The last lock on the line, or Lock No. 8, but a mile from the Pacific Ocean, and about 182 miles from the Caribbean Sea, has a maxi- mum lift of 2^ feet, and a minimum lift of 20} feet, the range of tide in the Pacific Ocean being but 8 feet at Brito. There are thus four locks between the lake and the Pacific Ocean, each having a possible Hft of 28-.} feet. The entire distance between the 6-fathom lines in the tAvo oceans is 183.66 miles. 335. Examinations by Borings.— ObA'iously it is of the great- est importance that such structures as the locks and dams re- quired in connection with this canal route should be founded on 412 THE NICARAGUA ROUTE FOR A SHIP-CANAL. bed-rock. In order to determine not only such questions, but the character of ah materials to be excavated from one end of the route to the other, a great number of borings were made along the canal line, not only by the water-jet process, but also with the diamond drill. By means of the latter, whenever it was so desired, cores or circular pieces could be taken out of the bed-rock so as to show precisely its character at all depths. These borings, both through earthy material by the jet and into bed-rock by the diamond drill, were made at suitable distances apart along the centre line of the canal, and in considerable numbers, closer together at proposed lock and dam sites. By these means every lock on the line has certainly been located on bed-rock, as well as the great dam at Conchuda. In addition to this the commis- sion has been able to classify the material to be excavated, so that if the canal should be built every contractor would know precisely the character and quantity of the various materials which he would have to deal with. 336. Classification and Estimate of Quantities. — The following table is arranged to exhibit a few only of the principal items of excavation, so as to give an approximate idea at least of the magnitude of the work to be done : Dredging 130,920,005 cu. yds. Dry earth 47.440,316 Soft rock 14,029,170 Hard rock 24,131 ,214 Rock under water 2 ,780,040 Embankment and back-filling 8,389,960 Clearing 6,831 acres. Stone-pitching 250,089 sq. yds. Concrete, excluding retaining-walls 3,400,840 cu. yds. Concrete in retaining-walls 424,321 Cut stone 22,272 Steel and iron, excluding cast-iron culvert lining 61,735,230 lbs. Cast-iron culvert lining 19,286,000 Brick culvert lining ,34. 54= cu. 5'ds. Cost of lock machinery Si, 600, 000 Excavation in coffer-dam 9,907 cu. yds. Pneumatic work 145,557 Pilin,g 415,600 lin. ft. Rock fill in jetties 45 i ,500 cu. yds. Clay puddle, bottom and sides of canal 936,800 CLASSIFICATION AXD UXIT PRICES. 413 337. Classification and Unit Prices. — The classification of the material to be excavatetl, both on the Kicaragua and Panama routes, was one to which the commission ga\-c ver)- thoughtful study no less than to the prices to be used in making the esti- mates. The following table, taken from pages 67 and 68 of the commission's report, cxhiljits the classification and tlie prices adopted by the commission for ptu'] )oses ( )f its estimates ; Removal of hard reck, per cu. yd Si . 1 5 Removal of soft rock, per cu, yil .So Removal of earth, not handled liy dredge, per cu. \-d .45 Removal of drcdLiablc material, per cu. yd ,20 Remox'al of rock, under water, per cu, yd 4 75 Embankments anil back-hllm.;^, per cu. yd .00 Rock m jetty construction, per cu. yd -5° Stone-pitchmg, includin,i;" necessary hackin;,;-, per sip yd 2 .00 Clearing and grubbing in swamj.i seelinns id' Nicaragua. ]ier acre.. . . 200 00 Other clearin.g and .grubbing on both routes, per acre 100 .00 Concrete, in place, per ctr )-d S . 00 Finished .granite, jier cu. >'d 60 . 00 Brick in culvert linuig, per cu. yd i 5 . 00 All metal in locks, c.xclusn'e of machmery and ctd\-crt linings, per lb. .075 All metal in sluices, per lb .075 Cast iron in ctthert lining, per lb .04 Allowance for each lock-chamlier for operating machmery 50,000 00 Additional allowance for each group ( if locks for ] h .wer-j .lant 100,000.00 Price of timber in locks, per M B. il 100 00 Sheet-piling in spillways, per M B. M 7 5°° Bearing piles in spillways, per lin. ft .50 Average price of jmeumatic Avork for the Bohio dam, below elexa- tion — 30. per cu. yd ^9 5° Caisson work for the Conchuda dam, m place, per cu. >'d 20.00 Single-track railroad complete with switches, stations, and lulling stock, per mile of main hnc 75,000 . 00 There are evidently other more or less uncertain expenditures, depending upon all possil)le conditions affecting the cost of such work, including those of climate, police, and sanitation. In order to cover such expenditure the commission determined to add 20 per cent to ah its estimates of cost on both routes, and that percentage was so added in all cases. 338. Curvature of the Route.—Among the engineering fea- tures of a ship-canal fine it is evident that curA^ature is one of great importance. Small steam-vessels may easily navigate almost any tortuous channel, but it is not so with great ocean 414 THE NICARAGUA ROUTE FOR A SHIP-CANAL. steamships. On the other hand, it may require very deep and expensive cutting to reduce the curvature of the route, as curves are usually introduced to carry the line around some high ground. It is necessary, therefore, to make a careful and judicious balance between these opposing considerations. The commission wisely Boring Party of the Isthmian Canal Commission on a Raft in the San Juan River. decided to incur even heavy cutting at some points for the purpose of avoiding troublesome curvature on the Nicaragua route. The table on page 415, taken from page 1,^5 of the commission's report, gives all the elements of curvature for the entire line. From the description of the line as gi\'en, it is e\-ident that much curx'ature must be fe provided, \\diate\-er ma\'be the char- acter of the season, therefore, there must be at least sufficient water stored in the lake to pnjvidc for the wastage of evaporation from the lake and canal surfaces and for the proper o])eration of all the locks throughout the length of the canal. 'Die super- ficial area of Lake Nicaragua is but little less than 3000 sf|uare miles. The quantity "f water rec^uired for the operation of the canal, amounting to 1000 cubic feet per second, would, for the entire year, make a layer of water o\'er the lake surface of less than 5 inches in thickness. In other words, the (jperation of the canal, for a traffic of about 10,000,000 t(jns annually, requires an amount of water less than one twelfth of that which would be evaporated from the lake surface during the same period. 342. The Required Slope of the Canahzed River Surface. — The dam located at Conchuda and fitted with suitable mo\'af)le gates affords means of accomphshing the entire lake-surface control. That dam is Located, however, nearly 5;, miles from the lake, and in order that the requisite discharge may take ])lace over it during the rainy season there must be C(.)nsiderablc slope of the water surface in the canalized ru'cr from the lake down to the dam. It was necessary, therefore, to compute that slope, from data secured by the comnussii m, with the kike surface at various elevations between the minimum and maximum per- mitted. These slopes were found to be such that the difference in elcA-ations of the surface of the water at the dam and in the lake might varv from about 6 to q feet, those hgures representing the total faU for the distance of 5,^ miles. 343. All Surplus Water to be Discharged over the Conchuda Dam. The Nicaragua Commission contemplated the construc- tion of dams not only on the San Juan River at Boca San CarL -s, about 6 miles below Conchuda, but also another a few miles west of the lake at La Flor, so as to discharge the surplus waters at both points, but by far the largest part oA-er the dam at Boca San Carlos. The Isthmian Canal Commission, however, decided 420 THE NICARAGUA ROUTE FOR A SHIP-CANAL. to build no dam on the west side of the lake, but to discharge all the surplus waters over the dam at Conchuda. 344. Control of the Surface Elevation of the Lake. — The rain- fall records in the lake basin have shown that a dry season begin- ning as early as November may be followed by an extremely low rainfcdl period, Avhich in turn Avould be followed by a dry season in natural sequence, lasting as late as June. It may happen, therefore, that from November until a year from the succeeding June, constituting a period of nineteen months, there will be a The Active Volcano Ometepe in Lake Nicaragua, showing Clouds on I.eeward Side of the Summit. The crater is nearly eleven miles from the canal line. very meagre rainfall in the lake basin, during which the precipi- tation r.f tlie seven low rainfall wet months mav not be sufficient e\-en to make good the depletion of CA-aporation alone during the same period. It would be necessary, then, at the end of any wet season whatever, i.e., during the first half of any December, or in November, to make sure of sufficient storage in the lake to meet the requirements of the driest nineteen months that can be anticipated. That condition was assumed by the commission, and the elements of control of the lake surface, in its plans, are COXTRUL OF THE SURFACE ELEVATION OF THE LAKE «I 422 THI-J MCAHAdVA TiOUTE FOR A SI/IP-CA XAL. such as to allfjrd resources to meet precisely those low-A^'ater con- ditions. The commissiiin's study of these features of the Nicaragua Canal problem resulted in plans of works to prevent the surface of the lake e^-er falling below 104 feet above sea-level, or rarely if ever rising higher than the elevation of no feet aboA'e the same level, thus making the possible range of the lake surface about 6 feet between its lowest and its highest position. ObA'iously at the end of a dry season the gates at the dam will always be found closed, and there will be no water escaping from the lake except by e\'aporation and t(5 supply the needs of canal operation. It is ecjually evident that the gates Avill also remain closed so as to permit no wastage during the earh' part of the Avet season. As the wet season proceeds the surface of the lake will rise toward, and generally quite to its maximum eleva- tion ; the o] leratic m ( if wasting over the weirs will then commence. The time of beginning of this wastage will depend upon the amount and distrifjutii in of the rainfall during the wet period. Indeed no wastage whatever would be permitted during such a low-Avater wet seasim as that shr)wn by the records of iSgo, whicli was almost phenomenal in its Ioav precipitation. The rainfall for the entire drainage-basin would be impounded in the lake m that case, and it would then fall short of restoring the depletrni resulting from e\-aporation and requirements oi the canal. (Jn the other hand, during such a wet season as that of 1897 ^vastage would begin at an early date. In general it may be said that neither the rate nor the law of the rise rif water surface in the lake can be predicted. There will be years when no wastage will be permitted, but generally considerable wastage will be necessarv in order to prevent the lake rising above the permissible highest stage. Detailed cr)mputations based upon the statistics of actual rainfall records in the basin of Lake Nicaragua mav be found Ijv referring to pages 147 to 152 of the Report of the Isthmian Canal Commission, and they need not be repeated here. Th(^se com- putations show a.mi mg other things that October is often a month of excessive I'ainfall, and that the greatest elcA-ation of the lake surface is likely to follow the precipitation of that month. Hence CONTROL OF THE SCRFACE ELEVATION OF THE LAKE. ^'-^ the greatest discharge of surpkis waters over the Conchuihi dam may be expected in conseciucnce of the resulting run-off or inflow o C/2 n Q into the lake. Those computations also show that at long inter- ' als of tniae the lake surface might reach an elevation of nearly 424 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 112 feet above sea-level for short periods, causing the discharge in the canalized river or over the Conchuda dam to reach possibly 76,000 cubic feet per second, the elevation of the water at the dam being 104 feet above sea-level. Furthermore, the Sabalos River and one or two other small streams, emptying into the San Juan above the dam, might concurrently be in flood for at least a few hours and augment the discharge over the dam to 100,000 cubic feet per second. The regulating-works at the dam, con- sisting of the movable (Stoney) gates, were devised by the com- mission to afford that rate of discharge, an aggregate net or avail- able length of overflow crest at the dam and wasteway of 1590 feet being necessary for that purpose with a depth of water on the crest not exceeding 7 feet. +1H' -^110 High Water CONCHUDO DAM. SECTION SHOWING CAISSONS -'Ciilason N'j. V2. 70 Ft. No 11. 78 Ft. o Nodl--J-:M, S2 Ft,".^' -■ - No. 10. 8;'. Ft. CONCHUDO DAM DIAGRAM SHOWING ARRANGEMENT OF SLUICEGATE The commission states on page 156 of its report: While, therefore, no detailed instructions can be set forth regarding the condition of the sluices at the wasteway on specified dates, the general lines of their operation should be stated below, viz. : GREATEST VELOCITIES IN CANALIZED RIVER. 425 " I. A full lake with surface probably a little above no feet on December i. " 2 . Wasteway sluices closed at least from about December i to some date in the early portion of the succeeding rainy season, or throughout that season if it be one of unusually low precipi- tation. "3. A variable opening of wasteway sluices, if necessary, during the intermediate portion of the rainy season, so asto main- tain the lake surface elevation but Uttle, if any, below I'lo at the beginning of October. "4. The operation of wasteway sluices during October and November so as to reach the ist of December with a full lake, or lake elevation p obably a little above 1 10 feet." It is thus seen that while the measures for control and regula- tion are entirely feasible, they are not sharply defined, nor so sim- ple that some experience in their ope ation might not be needful for the most satisfactory re ults. 345. Greatest Velocities in Canalized River. — It is necessary to ascertain whether the velocitie; induced in the canalized por- tions of the San Juan Rive would not be too high for the con- venience of traffic during the highest 1 ainfall season. The following table. and the succeeding paragraph, taken from the commission's report, show that no sensible difficulty of this kind would exist. Elevation of Water at Dam. Elevation of Lake. 103 Feet. 104 Feet, Feet, I 10 III I 12 Feet per Seeond, 4-16 4.S5 Miles per Hour. 2 .8 3 ■ 1 3 ■ 3 Feet p-^r Second, 30 4 ■ 2 4-5 Miles per Hour. 2.9 3 ■ I ' ' The discharge of the river corresponding to the velocity of 2.7 miles per hour is 63,200 cubic feet per second; while that corresponding to ;i,.;i, miles per hour is 77,000 cubic eet per second. These estimated high velocities will occur but rarely, and they will not sensibly inconvenience navigation. In reality they are too high, for the reason that wliile the overflow at the minimum 4 420 THE MCAIiAGCW ROUTE FOR A SIIIP-CAXAL. WASTEWAYS OR OVEIiFLOWS. 437 river section materially increases the areas of those seetily two or three da}'s in eyer^^year during which northers blow into the harbor with such intensity that ships anchored there must put t..i.d l;.ii.-i;i„> 'i'.Ziiil^l^ id /[ Vi>ll..«Ul.i, Clu,- CI a I3lui-Cl,i SCALE OF FEET i Vdio" CUy aoJ S....a / f Yollow Cli.y nnd S.id fine Uravipl H,,ndor,J \\>llo« Ch I Bund iinJ CIuvUIbj J aond «ilh Litlk' Blu..Cl..y«ith kiUl,-tur,J ^^ Blu,.Clay«.. l^ Soft Rook it-_. EOHIO DAM Profile of Bohio Dam Site, selectuil for Plans anil Estimate, ^^'itll section of I )an"i. After the completion of all its examinations and after a care- ful study of the data disclosed by them, the commission deemed 448 THE PANAMA ROUTE FOR A SHIP-CANAL. it advisable to plan such a dam as would cut off absoluteh' all possible subsurface flow or seepage through the sand and gravel iDelow the river surface. It is to be observed tha such a subsurface flow might either disturb the stabiUty of an earth dam or endan- ger the water-supply of the summit level of the canal or both. The plan of dam finally adopted by the commission for the pur- poses of its estimates is shown by the accompanymg plans and sections. A heavy core-wall of concrete masonry extends from bed-rock across the entire geological valley to the top of the structure, or to an elevation of loo feet above sea-level, thus absolutely closing the entire valley against any possible flow. The thickness of this wall at the bottom is 30 feet, but at an ele- vation of 30 feet below sea-level its sides begin to batter at such a rate as to make the thickness of the wall 8 feet at its top. On either side of this wall are hea^'y masses of earth embankment of selected material properly deposited in layers with surface slopes of I on 3. As shown b}' the plans, the lower portions of the core-wall of tliis dam A^'ijukl be sunk to Ijed-rock by the pneu- matic process, the joints f)etwcen the caissrms being closed and sealed by cylinders sunk in recesses or wells, also as shown by the plans. 373. Variation in Surface Elevation of Lake. — The profile of this route shows that the summit level Avould have an ordinaiy elevation of 85 feet above the sea, but it may be drawn down for uses oi the canal to a minimum elevation of 82 feet above the same datum. On the other hand, under circumstances to be discussed later, it may rise during the floods of the Chagres to an elevation of 90 or possibly 91 or 92 feet above the level of the sea. The top of the dam therefore would be from 8 to 10 feet above the highest possible water surface in the lake, which is sufficient to guard against wash or overtopping of the dam by waves. The total width of the dam at its top would be 20 feet, and the entire inner slope would be paved with heavy riprap suitably placed and bedded. 374. Extent of Lake Bohio and the Canal Line in It. — This dam would create an artificial lake having a superficial area during high water of about 40 square miles. The water would be backed up to a point called Alhajuela, about 25 miles up the river THE FLOODS OF THE C II AG RES. 449 from Bohio. For a distance of nearly 14 miles, i.e., from Bohio to Obispo, the mute (jf the canal Avould lie in this lake. Although the water would be from 80 to qo feet decyi at the dam for several miles below Obispo, it would l:)e necessary to make some exca- vation along the general course of the Chagres in order to secure the minimum dej^th of 35 feet for the naAdgable channel. 375. The Floods of the Chagres. — The feature of Lake Bohio of the greatest importance to the safe and convenient operation of the canal is that by -which the floods of the river Chagres are controlled or regulated. That ri\'er is liut little less than 150 miles long, and its drainage area as nearlv as can be estimated, Lcrmitted tc) flcnv over its crest, or even in immediate proximit\- to the do\\-n-stream emliankment. Indeed it is not intended by the ci mimission that there shall Ije anv waste- way or discharge anywhere near the dam. At a ]>iiint about 3 miles southwest of the site of tlie dam at Bohio is a low saddle or notch in the hills near the head-wa.ters of a small stream called the (bgante Ki\er. The elevation of this saddle or notch is such that a solid masdurv weir with a crest 2000 feet Lmo- mav reatlilv STORAGE IX LAKE BOIIIO FOR DRIEST DRY SEASON. 451 be constructed with its foundations on bed-rock without deep excuN'ation. This stiticture is called the Gigante spdlway, and all surplus flood-waters fnjm the Chagres would flow over it. Tlie Avatcrs discharged would flow down to and through some large marshes, one called Pena Blanca and another Agua Clara, before rejoining the Chagres. Inasmuch as the canal line runs just easterly of thr)se marshes, it would be necessary to protect it with the lc\'ees or embankments to Avhicli allusion has already been made. These embankments are neither much extended nor very costly for such a project. Tlu protection of the canal would he further aided bv a short artificial channel between the two marshes, Pnea Blanca and .Vgua Clara, for whicli jn-ovisfm is made in the estimates of the commission. After the surplus waters from the Gigante s|)illway pass these marshes they again enter the Chagres lvi\-er or flow o\'er the l;:>w, half-submerged countrv along its borders, and tlience througli its mouth to tlie sea near the ti >wn of Chagres, aliout 6 miles northwest of Gatun. 377. Storage in Lake Bohio for Driest Dry Season. —The ma- sonry crest of the Gigante spillway would be placed at an ele\'a- tion of 85 feet above the sea, identicallv the same as that wliicli mav be called the normal summit level of the canal. It is esti- mated that the total uses of water in the canal added tc) the loss by evaporation, taken at six inches in de]5th per month, frrjm the surface of the lake will amount fri al)Out 1070 cufiic feet per second if the traffic through the canal should anKiunt to 10,000,000 tons per annum in ships of ordinary size. This draft per second is the sum of 406 cubic feet per second for L )ckuge, 207 for evap' >- ration, 250 for leakage cit lock-gates, and 200 for power and other purpiises, making a total of 106:;, wliich has been taken as ioto cubic feet per second. Tlie amount of storage in Lake B^ihio betAveen the elevations of 85 and 82 feet above sea-le\-el, as designed, is sufficient to su])]dy the needs of that traffic in excess of the smallest recorded low-water Row of the Chagres River during the drv seasr)n of a low-rainfall year. The lowest monthly a\'erage flow r)f the Chagres on recorrl at Bohi("i is 600 cubic feet per second for March, jSqt, and for the pui*poses of this compu- tation that minimum flow has lieen supposed to continue for three mimflis. This includes a sensible margin of safetv. In not 452 THE PANAMA ROUTE FOR A SHIP-CANAL. even the driest year, therefore, can it be reasonably expected that the summit level of the canal would fall below the elevation of 82 feet until the total traffic of the canal carried in ships of the present ordinary size shall exceed 10,000,000 tons. If the average size of ships continues to increase, as will probably be the case, less water in proportion to tonnage will be required for the purposes of lockage. This follows from the fact that with a given tonnage the greater the capacity of the ships the less the number required, and consequently the less will be the number of lockages made. 378. Lake Bohio as a Flood-controller. — On the other hand it can be shown that with a depth of 5 feet of water on the crest of the Gigante spillway the discharge of that weir 2000 feet long '*>. M^ i-^'^%*»>t^ .'*, Siwff *.S5W'rw'''VH*l5 *wr '■ . nil IMIluJIIIIiliOT f^l^ The Eastern Face of the Culebra Cut. will be at the rate of 78,260 cubic feet per second. If the flood- Abaters of the Chagres sliould Aoav into Lake Bohi(T until the head of water on the crest of the Gigante weir rises to yi feet, the rate EFFECT OF IlIOHEST FLOODS. 453 of discharge over that weir would be 140,000 cubic feet per second, which, as ah-eady shown, exceeds at least by a little the highest flood-rate on rec(_)rd. The ojxTation (jf Lake B(.)hii) as a flood controller or regulator is therefore exceedingly simple. The fl( lotl-watcrs of the Chagres would pour into the lake and immediately begin to flow over the (ligantc weir, and continue to do so at an increasing rate as the flood continues. The dis- charge of the weir is augmented by th^.- increasing flooil, and decreases only after the passage of the crest of the flood-wave. No flood e\'en as great as the greatest su])])osaV)le flood (jn record can increase the elevation of the lake more than 92 to 92', feet above sea-level, ami it will < >nly be at long intcr\-als r)f time A\'hen floods will raise that elevation mr)re tlian aV)out 90 feet above sea-level. The control is automatic and unfailingly certain. It prevents absolutely any damage from the highest suj.tposable floods ( )f the Chagres, and reserA'cs in Lake P» )hio all that is re- quired for the purposes of the canal and for wastage by evapora- tion through the lowest rain fall season. The floods of the Chagres, therefore, instead oi constituting the olistacle t(3 construction and convenient maintenance of the canal heretofore supposed, are deprived of all their prejudicial effects and transformed into beneficial agents for the o])eration of the waterway. 379. Effect of Highest Floods on Current in Channel in Lake Bohio. — The highest floods are of short duration, and it can lie stated as a general law that the higher the flood the shorter its duration. The great floods which it is necessary to consider in connection with the maintenance and operation of this canal would last but a comparatix'ely few hours only. The great flood- flow of 140,000 cubic feet per second would increase the current in the narrowest part of the canal below ( )bispo to possibly 5 feet per second for a few hours only, but that is the only incon- venience which would result from such a flood-discharge. That velocity could be reduced Viy additional excavation. 380. Alhajuela Reservoir not Needed at Opening of Canal. — Inas- much as this system of control, devised and adopted by the Isth- mian Canal Commission, is completely eft'ective in regulating the Chagres floods; the reservoir proposed to be constructed by the new Panama Canal Company at Alhajuela on the Chagres 454 THE PAXAMA ROUTE FOR A SHIP-CANAL. about 1 1 miles above Obispo is not required, and the cost of its C(jnstruction would be avoided. It could, however, as a project be held in rescr\-c. If the traffic of the canal should increase to such an extent that more water would be needed for feeding the summit level, the dam could be built at .Vlhajuela so as to impound enough additional water to accommodate, with that stored in Lake Bohio, at least fiA'C times the 10,000,000 annual traffic alread\' considered. Its existence would at the same time act with suV)Stantial eft^ect in controlling the Chagres floods and relieve the Gigante spillway of a corresponding amount of duty. 381. Locks on Panama Route. — The l:>cks on the Panama route are designed to have the same dimensions as those in Nica- ragua, as was stated in the lecture on that route. The usable length is 740 feet and the clear width 84 feet. They would be built chiefly of cijncrete masonry, while the gates would be of steel and of tlic mitre type. 382. The Bohio Locks. — The great dam at Bohio raises the water surface in the canal frc >m sea-level in the Atlantic maritime section to an ( )rdinarv maximum of 90 feet above sea-level ; in other words, the maximum ordinar}^ total lift would be 90 feet. This total lift is divided into two parts of 45 feet each. There is therefore a flight of two locks at B(jhio ; indeerl there are two flights side by side, as the twin arrangement is designed to be used at all lock sites on both routes. The typical dimensions and arrangements of these locks, with tlie requisite cuh-erts and r)ther features, are shown in the plans and sections between pages 396 and 397, Part \". They are not essentially dift'erent from other great modern ship-canal Ijcks. The excavatii.m tVir the Bohio locks is made in a rocky hill against Avhich the south- westerlv end < )f the proposed Bohio dam rests, and thcv are less than Tooo feet from it. 383. The Pedro Miguel and Miraflores Locks. — After leaA'ing Bohio Lake at t)bispo a flight of two locks is found at Pedro ^Miguel, a1>out 7.q miles from the fr)rmcr or 21^ miles from Bohio. These locks have a total ordinary maximum lift of 60 feet, divided into two lifts of 30 feet each. The fifth and last lock on the route is at Miraflores. The average elevation of water between Pedro Miguel and Aliraflores is 30 feet abo\-e mean sea-level. Inas- GUARD-GATES NEAR OBISPO. 455 much as the range of tide between high and low in Panama Bay IS about 20 feet, the maximum Hft at .Aliraflores is 40 feet and the minimum ab.jut 20. 'idie twin locks at Aliraflores bring the canal surface down to the Pacific (Jecan lc\-el, the distance from those locks to the 6-fathom cur\-e m Panama Bay l)eing 8. 54 miles. There arc therefore h\-e locks on the Panama route, all arranged on the twin plan, and, as cm the Nicaragua r(jute, all are founded on rock. 384. Guard-gates near Obispo. — Xear (Jbisi)o a pair of guard- gates are arranged "so that if it should become necessary to draw off the water from the summit cut the level (if Lake Bohio would not be aff'ected." 385. Character and Stability of the Culebra Cut. — An unpre- cedented concentration of heav}^ cutting is found Ijctween Obispo and Pedro Miguel. This is practically (jiie cut, alth(.)ugli the northwesterly end toward ( )lnspo is called the Em])erad()r, while the deepest part at the 1 >ther end, about ,^ miles from Pedn 1 Miguel, is the great Culebra cut with a maximum depth on the centre line of the canal of 286 ft. C)n page 93 of the Isthmian Canal Commissiiin's report is the following reference to the ma- terial in this cut: ' ' There is a little \"cry hard rock at the eastern end of this section, and the western 2 miles are in ordinar\- ma- terials. The remainder consists of a hard indurated clav, with some softer material at the top and some strata and dikes of hard rock. In fixing the price it has been rated as soft rock, but it must be given si jies equivalent to thiise in earth. This cut has been estimated on the basis of a bottom width of 150 feet, with side slopes of i on i.' When the old Panama Canal C(impany began its excavatii ni in this cut considerable difficulty was ex- perienced hy the slipping of the material outside of the limits of the cut into the exca\'ation, and the marks of that actic^n can be seen plainly at the present time. This experience has given an impression that much of the material in this cut is unstable, but that impression is erroneous. The clay which slipped in the earh' davs of the work was not drained, and like wet clay in numerous places in this country it slipped down int(^ the excava- tion. This material is now drained and is perfecth' stable. There is no reason to anticipate any future difficult}' if reasonable 456 THE PANAMA ROUTE FOR A SHIP-CANAL. conditions of drainage are maintained. The high faces of the cut will probably weather to some extent, although experience with such clay faces on the isthmus indicates that the amount of The Culebra Cut. such action will be small. As a matter of fact the material in which tlie Culebra cut is made is stable and will give no .sensible difficulty in maintenance. 386. Small Diversion-channels. — Throughout the most of the distance between Colon and Bohio on the easterly side of the canal the French plan contemplated an excavated channel to receive a portion of the waters of the Chagres as Avell as the flow of two smaller rivers, the Gatuncillo and the Mindi, so as to con- LE.XGTII AXD CURVATURE. 457 duct them into the Bay (.f Manzaniho, immediately to the east of Colon. That si )-callcd diversion-channel was nearly completed. Under the plan of the commission it would rccei\'e none of the Chagres flow, Ijut it would be a\-ailable for intercepting the drain- age of the high ground easterly of the canal line and the flow of the two small ri\-ers named, so that these waters would not find their way into the canal. There are a few other small works of similar character in dillerent pcjrtions of the line, all of which were recognized and iiro\-ided for Ijy the commission. 387. Length and Curvature. — The t(jtal length of the I^anama route from the O-fathom curve at CoLjn to tlie same curve in Panama Bay is 40. og miles. The generLil direction of the route in passing from Colon to Panama, is fr(jm northwest t(j southeast, the latter point being about 22 miles east of he Atlantic terminus. The depression through which the line is laid is one of easy topog- raphy except at the continental di\'ide in the Culcbra cut. As a consequence there is little hea\-y work of excavation, as such matters go except in that cut. .V further consequence of such topography is a comparati\x-ly easy alignment, that is, one in which the amount of curA'ature is not high. The smallest radius of curA'ature is 3281 feet at the entrace to the inner harbor at the Colon end of the route, and where the width is 800 feet. The radii of the remaining curves range from 6234 feet to 10,629 feet. The following table gives all the elements oi curvature on the route and indicates that it is not excessi\-e : XuiiihfcT i.r c nr\'cs. LcTi^lli Ra.lius. Tutal Cur\'ature . ss 13,1 23 11.483 0.84-' S.202 6,162 6.234 3 . 2 S I 14 17 I I 04 III 32 .i5 5 50 QO 2 77 00 .v5 45 7 5 5T , . . ■ ' ■ 4S 4 . . ■ . 4 ■ - ^ 1 1 '1 1 4 .... 2,44 .... I . '17 S ' i ...85 771 .1') 388. Principal Items of Work to be Performed. — The principal items of the total amount of A^•L^rk to be performed in completing 458 THE PANAMA ROUTE FOR A SHIP-CANAL. the Panama Canal, under the ])lan of the commission, can be classified as sliown in the following table : Dredging 27,659,540 cu. yds. Dry earth 14.386.054 Suft ruck 3(), 893, 235 Hard rock 8,806.340 Rock under water 4,891,667 Embankment and back-lilling 1,802.753 Total 97.440,4^9 Concrete 3,762,175 cu. yds. Granite 13,820 Iron and steel 65,248.f)Oo lbs. ExcaA-ation m coiTer-dani 7,260 cu. )'ds. Pneumatic work 108,410 " 389. Lengths of Sections and Elements of Total Cost. — The lengtlis of the various sections of this route and the costs of completing the work upon them are fully set forth in the following table, taken from the commission's report, as were the two pre- ceding : TOTAL ESTIMATED COST. Mili s C-.st. Colon entrance and h^irljrir .... 14 13 30 43 6 J 88,057,707 1 1 ,009,839 11,567,275 2,952.154 = 95.434 44.414,460 9.0S1 ,321 1,193.286 5.781,401 12.427.071 6.369.640 T .209,419 2 .44S 076 Bohio locks includin'"'' ex.ca\'atiun Lake Bohio . . Culebra section 7 I 8 91 33 20 Pedro Miguel locks, meludinjj,- excavation and dam. . . . Pedro Mio-nel level Miraflores locks, nicluding exca\-ation and spillway .■■ - Rohi<) dmn Pena Blanca iiutlet 1 ,<)20.982 ] 00,000 Gatun diversif")n Total 49 Ol) 120,1 04,465 En.gineering, police, sanitation, and .general contingen- 24,038,803 .S144, 233,35s The item in this table called Panama Railroad diA^ersion affords provision for the reconstruction of the railroad necessitated by THE TWENTY FE1{ CENT ALLOW AXCEX EOLt EXJCEXC/ES. 4.-)0 the fomiati.in of Lake B,,lnr engineering, police, sanitation, and general C( .ntmgeneies." For the purposes of eonijiarison the same ])ercentage to co\-er these items was used on b(jth routes. As a matter ui fact the large amount of \V( irk Avhich has already been performed on the I^anama route removes man}- uncertainties as to the character of material and other features of difficulty whicli wcmld \>c disclosed only after the beginning of the work in Nicaragua. It has therefore been contended Avith considerable basis of reason that a less percentage to cover these uncertainties should be employed in connection A\'ith the Panama estimates than in connection with those for the Nicaragua route. Indeed it might be maintained that the exigencies Avhich increase cost should fie made propor- tional to the length of route and the untrie(.l features. On the other hand, fioth I^anama and Colon are comparatively large centres of poinilation, and, furthermore, there is a considerable population stretched along the line ( if the Panama Railroad be- t.Aveen those points. The climate and the unsanitary condition of practicallv CA'ery centre of population in Central America and on the isthmus contribute to the continual presence (-if tropi- cal fcA-ers, and other diseases contingent upon the existing erm- ditions rif life. It is probable, among other things, tliat yellow fcA'cr IS alAA-aA's present on the isthmus. Inasmuch as tlie Nica- rao-ua route is practically without p(-)pulation, the amount of 4G0 THE PANAMA ROUTE FOR A SHIP-CANAL. disease existing along it is exceedingly small, there being practically no people to be sick. The initial expenditure for the sanitation of the cities at the extremities of the Panama route, as well as for the country between, W(juld be far greater for that route than on the Nicaragua. This fact compensates, to a substantial extent at least, for the physical uncertainties on the Nicaragua line. Indeed a careful examination of all the conditions existing on both routes indicates the reasonableness of applying the same 20 per cent to both total estimates of cost. 391. Value of Plant, Property, and Rights on the Isthmus. — The preceding estimated cost of $144,233,358 for completing the Panama Canal must be increased by the amount necessary to be paid for all the property and rights of the new Panama Canal Company on the isthmus. A large amount of excaA'ation has been performed, amounting to 77,000,000 cubic yards of all classes of materials, and nearly all the right of way has been purchased. The new l^anama Canal Company furnished the commission with a detailed inventory of its entire properties, which the latter ■ classified as follows : 1. Lands not liuilt on. 2. Buildings, 2431 in number, divided among 47 subclassifi- cations. 3. Furniture and stable outfit, with 17 subclassifications. 4. Floating plant and spare parts, with 24 subclassifications. 5. Trolling plant and spare parts, with 17 subclassifications. 6. Plant, stationary and semi-stationary, and spare parts, with 25 subclassifications. 7. Small material and spare parts, with 4 subclassifications. 8. Surgical and medical outfit. 9. Medical stores. 10. r)fiice supplies, stationery. 11. Miscellaneous supplies, with 740 subclassifications. The commission did not estimate any value for the vast amount of plant along the line of the canal, as its condition in relation to actual use is uncertain, and the most of it would not be aA^ailable for efficient and economical execution of the work by modem American methods. Again, a considerable amount NEW COMPAXYS OFFER TO SELL FOR FORTY MILLIOXS. J:'Jl of excavated material along some portions of the line has been deposited in spoil-banks immediately adjacent to the excavation from which it was taken, and W(juld ha\'e to he rehandled in fonning the increased size of prism contemplated in the com- mission's plan. In view of all the ciniditions affecting it, the commission made the following estimate of the value of the pro]3crty (jf the new Panama Canal Company, as it is now found on the Panama route : Canal excavation $21, 020,, ^86 Chagrcs diversion 178,186 Gatun diversion 1,396,456 Railroad diversion (4 miles) 300,000 22,895,028 Contingencies, 20 per cent 4,579,005 Aggregate 27,474,033 Panama Railroad stock at par 6,850,000 Maps, drawings, and records 2,000,000 $36,324,033 The commission added 10 per cent to this total "to cover omissions, making the total valuation of the" property and rights as now existing, $40,000,000. In computing the value of the channel excavation in the above tabulation it was estimated that " the total quantity of excava- tion which will be of value in the new plan is 39,586,332 cubic yards." 392. Offer of New Panama Canal Company to Sell for $40,000,000. In [anuary, 1902, the new Panama Canal Company oft'cred to sell and transfer to theUnited States Government all its property and rights on the isthmus of every description for the estimate of the commission, viz., $40,000,000. In order to make a proper comparison between the total costs of constructing the canal on the two routes it is necessary to add this $40,000,000 to the preceding aggregate of $144,233,358, making the total cost of the Panama Canal $184,233,358. It wih be remembered that 462 THE PANAMA ROUTE FOR A SHIP-CANAL. the corresponding total cost of the Nicaragua Canal would be $189,864,062. 393. Annual Costs of Operation and Maintenance. — It is ob- vious that the cost of operating and maintaining a ship-canal across the American isthmus would be an annual charge of large The Railroad Pier at La Boca, the Panama end of the Canah amount. A large organized force would be requisite, and no small amount of material and Avork of various kinds and grades would be needed to maintain the Avorks in suitaljle crmdition. The commission made very careful and thorough studies to ascertain as nearlv as practicable what these comparative costs would be. In doing this it gaA'e careful consideration to the annual expenditures made in maintaining the A'arious ship-canals of the world, including the Suez, Manchester, Kiel, and St. ilary's VOLCANOES AND EAIiTHQUAKES. 4'J3 Falls canals. The conclusion reached was that the estimated annual costs of maintenance and operation could reasonably be taken as follows: For the \iearagua Canal $3,300,000 For the Panama I'anal 2,000,000 Difference in fa\-or of i^anama $1,300,000 394. Volcanoes and Earthquakes. — Much has been written regarding the comparatn'e lialdlit}' to damage (jf canal Avorks along these two mutes by A'(jlcanic or seismic agencies. As is well kno\\'n, the entire Central American isthmus is a \'olcanic region, and in the past a consicleraljlc number (jf destructi\'e volcanic eruptions ha\-e taken place at a number of points. There is a line of live volancocs extending southcasterh- through Nicaragua and Costa kica. Alan)' earthquake shocks ha\'e occurred tlir(iughi mt Nicaragua, Cijsta Kica, and the State of Panama, some of which ]ia\-e done more or less damage in large portimis of those districts. At the same time many liuildings vdiich have l:)een injured have not been substantiullv built. In fact that has generally 1 )cen the case. Pdth r( mtes lie in dis- tricts that are dmibtless sulijcct to earthquake shocks, Imt there is little pridiability that the substantial structures of a canal along either line would be essentially injured b\- them. The conclu- sions of the commission as to this feature < )f the matter are con- cisely stated in three paragraphs at the top of page 170 of its report : ' ' It is possible and even probable that the more accurately fitting portions of the canal, such as the lock-gates, may at times be distorted by earthquakes, and some incouA'cnience mav result therefrom. That contingency may be classed with the accidental collision i^f ships with the gates, and is to be proA'ided for in the same way, by duplicate gates. "It is possil:>le also that a fissure might open which would drain the canal, and, if it remained o]")en, might destroy- it. Tliis possibilitv should not be erected by the fancy intri a threatening danger. If a timorous imagination is ti3 fie the guide, no great work can be undertaken anywhere. This risk may be classed 464 THE P-1.V.1.-1/--1 ROUTE FOR A SHIP-CANAL. with that of a great conflagration in a city like that of Chicago in 1871, or Boston in 1872. ' ' It is the opinion of the commission that such danger as exists from eartlicjualces is essentially the same for both the Nicaragua and Panama routes, and that in neither case is it sufficient to prevent the construction of the canal." The Nicaragua route crosses the line of live volcanoes run- ning from northwest to southeast through Central America, and the crater of Ometepe in Lake Nicaragua is about 11 miles only from the hne. The eruptions of Pelee and Soufriere show that such proximity of possible volcanic action may be a source of great danger, although even the destruction by them does not certainly indicate damage either to navigation or to canal structures at the distance of 1 1 miles. Whatever vol- canic danger may exist lies on the Nicaragua route, for there is no volcano nearer than 175 miles to the Panama route. 395. Hygienic Conditions on the Two Routes. — The relative healthfulness of the two routes has already been touched upon. There is undoubtedly at the present time a vast amount of un- healthfulness on the Panama route, and practically none on the Nicaragua route, but this is accounted for when it is remembered, as has also been stated, that there is practically no population on the Nicaragua route and a comparatively large population along the Panama line. There is a wide-spread, popular impres- sion that the Central American countries are necessarily intensely unhealthful. This is an error, in spite of the facts that the con- struction of the Panama Railroad was attended with an appalling amount of sickness and loss of life, and that records of many epidemics at other times and in other places exist in nearly all of these countries. There are the best of good reasons to believe that with the enforcement of sanitary regulations, Avhich are now well understood and completely aA-ailal:)le, the Central American countries would be as healthful as our Southern States. A proper recognition of hygienic conditions of life suitable to a tropical climate would work wonders in Central America in reducing the death-rate. At the present time the domestic administra- tion of most of the cities and towns of Nicaragua and Panama, as well as the generality of Central American cities, is characterized TIME (IF PASSAGE THIiOVGH THE CANAL. 4C5 b)- the absence (if practically everything Avhich makes fnr public wealth, and by the jiresence of nearly every agency working for the diseases which flourish in tropical climates. When the United otates Inivemment reaches the point of actual construction of an isthmian canal the sanitary features of that work should be administered and enforced in every detail with the rigng the two routes, as well also as the total amounts and radii of curvature. MICARAGUA ■■>■ ft-'^'."*".'* ■'?* 6.'''o' 6.* Concret« ; ; f ;i,702,175 *■/'. ■f .'■' '■-i\t--^-':j'r:'::l ■(_■';.''•,■., ■■!';:p;:;ij . fi, , ft/p Cubic Vur.lrt '■<''-- ■.V-ft '•^■;•;:>:^ NUMBER OF CURVES = 29 LENGTH OF CURVES = 2e. 35 MILES - TOTAL CURVATUR£^77l'-39' NUMBER OF CURVES = 56 LENGTH OF CURVBS = 49.29 MILES TOTAL CURVATURE ^^2339' 50 V' PANAMA = 49.09 MILES ■JICARAGUA — 133.66 MILES Diagrams comparing some of the main Elements of the two Routes. The commission has estimated ten years for the completion of the canal on the Panama route and eight years for the Nicaragua route, including in both cases the time required for preparation 468 THE PANAMA ROUTE FOR A SHIP-CANAL. and that consumed by unforeseen delays. The writer beHeves that the actual circumstances attending work on the two routes would justify an exchange of these time relations. There is great concentration of work in the Culebra-Emperador cut on the Panama route, covering about 45 per cent of the total ex- cavation of all grades (43,000,000 cubic yards), which is dis- tributed over a distance of about 7 miles, with the location of greatest intensity at Culebra. This demands efficient organi- zation and special plant so administered as to reduce the working force to an absolute minimum by the employment of machinery to the greatest possible extent. A judicious, effective organiza- tion and plant would transform the execution of this work into what may be called a manufactory of excavation with all the intensity of direction and efficiency of well designed and admin- istered machinery which characterizes the concentration of labor and mechanical appliances in great manufacturing establish- ments. Such a successful installation would involve scarcely more advance in contract operations than was exhibited, in its day, in the execution of the Avork on the Chicago Drainage-canal. By such means only can the peculiar difficulties attendant upon the execution of great works in the tropics be reduced to con- trollable dimensions. The same general observations may be applied to the construction of the Bohio dam, even should a no more favorable site be found. The greatest concentration of excavation on the Nicaragua route is between the lake and the Pacific, but it constitutes only 10 per cent of the total excavation of all grades, and it can be completed in far less time than the great cut on the Panama route. If this were the only great feature of work besides the dam, the time for completion of work on this route would be materially less than that required for the Panama crossing. As a matter r>f fact, there are a succession of features of equi\'alent magnitude, or very nearly so, from Greytown nearly to Brito, extending over a distance of at least 175 miles, requiring the construction of a substantial service railroad over a considerable portion of the distance prior to the beginning of work. This atten- uation of work requires the larger features to be executed in succession to a considerable extent, or much duplication of plant LMDUSTBIAL AND COMMERCIAL VALUE OF THE CANAL. 469 and the employment of a great foree of laborers, praetieally all of whom must be foreigners, housed, organized, and maintained in a praetieally uninhabited tropieal country where many serious difficulties reach a maximum. It is not within the experience of civil engineers to execute by any practicable means that kind of a pn igramme on schedule time. The weight of this obser\'ation is much increased when it is remembered that the total volume of work may be taken nearly twice as great in Nicaragua as at Panama, and that large portions between Lake Nicaragua and the Caribbean Sea must be executed in a region of continual and enormous rainfall. It would seem more reasonable to the writer to estimate eight years tVir the completion of the Panama Canal and ten years for the completion of the Nicaragua Canal. 398. Industrial and Commercial Value of the Canal. — The prospective industrial and commercial value of the canal also occupied the attention of the commission in a broad and careful study of the elements which enter that part of the problem. It is difficult if not impossible to predict just what the effect of a transisthmian canal would be either upon the ocean commerce of the United States or of other parts of the world, but it seems reasonable to suppose from the result of the commission's exam- inations that had the canal been in existence in 1899 'i-t least 5,000,000 tons of the actual traffic of that year would have been accommodated by it. The opening of such a Avatenvay, like the opening of all other traffic routes, induces the creation of new traffic to an extent that cannot be estimated, but it would appear to be reasonable to suppi.ise that within ten 3^ears from the date of its opening the vessel tonnage using it would not be l^ss than 10,000,000 tiins. The Nicaragua route would favor in distance the traffic be- tween our Atlantic (including Gulf) and Pacific ports. The dis- tances between our Atlantic ports and San Francisco would be about 378 nautical miles less than b)^ Panama. Between New Orleans and San Francisco this clift'erence in favor oi the route by Greytown and Brito Avould be 580 nautical miles. It must be remembered, hMI\lh-LS().\ OF ROLTES. 471 throw the advantage in fa\'i"ir o[ the Panama waterway. This last ()l)ser\-ati()n would Ik ild wath particular f( )ree if f( ir anv reasan a \'essel sliould not eontinue lier jjassage, or should ecjntinue it at a redueed speed during hours of darkness, whieli eould not be eseajied on the Xdearagua Canal, hut might be a\'(jided at Panama. For all trafhe between tlie Atlantic (including (_iulf) jxirts and the west coast of South America tlie Panama crossing wouLl be the most ad\'cuitagcous. As a matter of fact, while there may be some small adx'antage in miles Ijy (jne route or the otlier fur the trafhe between some i)articular ])oints, on the whole neitlier r mte Would liax'e an\' \'cr\' great ad\'anlage o\'er the otlier in ]iiiint (if distance or time; eitlier would ser\-e efhcienlh' tlic ]iur]i(ises rjf all ocean traffic in which tlie pjorts (jf the United States are directly interested. The effect of this slhp waterway upon the Avelbljeing of the United States is not altogether of a eommcrcial character. As indicated 1:)V tlic commission, this additional bond lietAveen the two portions of tlie country will haxx- a beneficial effect upon the unity of the ])olitical interests as well as upt.m tlie commercial welfare of tlie eountr\-. Indeed it is the judgment of many well-informed ])eople that the commercial adxantages resulting fr(.)m a closer touch between the Atlantic and Pacific coasts of the country are ( >f less consef[uence than tlie unifying of ]:)( ilitical interests. In a final comparison between tlie tAvo routes it is to be remembered that the concession under wliieli the new I'anama Company has been and is now ]irosL'euting its work is practically valueless for the purposes o( this enuntr}'. It will theref(.)re be necessary to secure from tlie rejjublic of Colombia, for the Pan- ama route, as well as fr> )m tlie repul dies of Nicaragua and Ci >sta Rica, for the .Xicaragua route, such new concessions as niav be adequate for all the ])urposes of the United States m the con- struction of this transisthmian canal. The cost of tlii ise eon- cessions in either ease must lie added to the estimated total cost of the work, as sst forth, in order to reach the total cost of the canal almig either route: 39Q. Comparison of Routes. — Conciseh' stating the situation, its main features may lie expressed somewhat as hjllows; 472 THE P.1.V.1.1/-1 ROUTE FOR A SHIP-CANAL. Both routes are entirely ' ' practicable and feasible." Neither route has any material commercial advantage over the other as to time, although the distance between our Atlantic (including Gulf) and Pacific ports is less by the Nicaragua route. The Panama route has about one fourth the length of that in Nicaragua; it has less locks, less elevation of summit level, and far less curvature, all contributing to correspondingly decreased risks peculiar to the passage through a canal. The estimated annual cost of operation and maintenance of the Panama route is but six tenths that for the Nicaragua route. The harbor features may be made adequate for all the needs of a canal by either route, with such little preponderance of advantage as may exist in favor of the Panama crossing. The commission estimated ten years for the completion of the Panama Canal and eight years for the Nicaragua waterway, but the writer believes that these relations should be exchanged, or at least that the time of completion for the Panama route should not be estimated greater than for the Nicaragua. The water-supply is practically unlimited on both routes, but the controlling or regulating works, being automatic, are much simpler and more easily operated and maintained on the Panama route. The Nicaragua route is practically uninhabited, and conse- quently practically no sickness exists there. On the Panama route, on the contrary, there is a considerable population extend- ing along the entire line, among which yellow fever and other tropical diseases are probably always found. Initial sanitary works of much larger magnitude would be required on the Pan- ama route than on the Nicaragua, although probably as rigorous sanitary measures would be required during the construction of the canal on one route as on the other. The railroad on the Panama route and other facilities offered by a considerable existing population render the beginning of work and the housing and organization of the requisite labor force less difficult and more prompt than on the Nicaragua route. The greater amount of Avork on the Nicaragua route, and its distribution over a far greater length of line, involve the employ- COMPARISOX OF ROUTES. 473 ment of a correspondingly greater force of laborers, with greater attendant difficulties, for an equally prompt completion of the work. The relative seismic conditions of the two routes cannot be quantitatively stated with accuracy, but in neither case are they of sufficient gravity' to cause anxiety as to the eft'ects upon com- pleted canal structures. Concessions and treaties require to be secured and negotiated for the construction of the canal on either route, and under the conditions created by the $40,000,000 oft'er of the new Panama Canal Company this feature of both routes appears to possess about the same characteristics, although the Nicaragua route is, perhaps, freer from the complicating shadows of prior rights and concessions. mm