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ROPER^S 
Practical  Hand -Books 

For  Engineers  and  Firemen. 


NEW  REVISED  AND  ENLARGED  EDITION. 

HANDY-BOOK  FOR  STEAM  ENGINEERS 
AND  ELECTRICIANS. 

PRICE,  $3.50. 

pRice. 
Roper^s  Catechism  for  Steam  Engineers  and  Electric- 
ians,      $2.00 

Roper's  Questions  and  Answers  for  Steam  Engineers 

and  Electricians, 2.00 

Roper's  Hand-Book  of  Land  and  Marine  Engines,  •  3.50 
Roper's  Care  and  Management  of  the  Steam  Boiler,  2.00 
Roper's  Use  and  Abuse  of  the  Steam  Boiler,  ....    2.00 

Roper's  Young  Engineers'  Own  Book, 2,50 

Roper's  Hand-Book  of  the  Locomotive, 2.50 

Roper's  Instructions    and   Suggestions  for    Engineers 

and  Firemen, 2.00 

Roper's  Hand-Book  of  Modern  Steam  Fire  Engines,  •    3.50 


DAVID  MCKAY,  Publisher, 

^  1022  Market  Street,  Piiiladelpiiia,  Pa. 


ROPER'S  CATECHISM 

FOR 

STEAM  ENGINEERS 

AND 

ELECTRICIANS 

INCLUDING  THE  CONSTEUCTION  AND  MANAGEMENT  OF 

STEAM  ENGINES,  STEAM  BOILERS  AND 
ELECTRICAL  PLANTS 

WITH     ILLUSTRATIONS 
EDWIN    R.    KELLER,   M.E. 

AND 

CLAYTON    W.    PIKE,    B.  S. 


PHILADELPHIA  : 

DAVID    McKAY,     Publisher, 

1022  Market  Street 


Offlcoofthe 

600  33 

Entered,  according  to  Act  of  Congress,  in  the  year  1873,  by 

STEPHEN  ROPER, 
in  the  Office  of  the  Librarian  of  Congress,  at  Washington. 


Entered,  according  to  Act  of  Congress,  in  the  year  1884,  by 

E.  CLAXTON  &  COMPANY, 
in  the  Office  of  the  Librarian  of  Congress,  at  Washington. 


Copyright  by  DAVID  McKAY,  1897. 


Copyright  by  DAVID  McKAY,  1899. 


SECOND  copy. 


^3 


PREFACE  TO  THE  TWENTY-FIRST  EDITION. 


The  great  value  of  a  catechism  lies  in  the  fact 
that  judicious  questioning  emphasizes  the  more 
important  points  of  a  subject  and  also  stimulates 
the  mind  of  the  student  to  think  more  definitely 
and  clearly  upon  the  subject  than  would  be  the 
case  in  merely  reading  about  it.  In  these  respects 
the  written  catechism  is  the  best  substitute  for 
oral  teaching,  and  the  authors  trust  that  this 
volume  will  be  found  of  value  for  this  purpose. 

The  enactment  of  State  laws  requiring  the 
licensing  of  engineers  has  imposed  upon  many 
the  necessity  of  passing  examinations  for  license. 
The  authors  likewise  hope  that  it  will  prove 
useful  to  engineers  in  preparing  for  such  exam- 
inations. . 

Edw^in  R.  Keller, 

Clayton  W.  Pike. 
Philadelphia,  September,  1899. 


CONTENTS. 


For  Alphabetical  Index  to  Subjects,  see  page  359. 


Mechanics.  p^^j. 

The  Six  Mechanical  Elements  of  Machinery,      .    .        1 

Force, 1 

Inertia, 2 

Motion, 3 

Velocity,      4 

Acceleration,   ...        4 

Falling  Bodies, 5 

Mass  and  its  Relation  to  Force  and  Acceleration,  .  6 

Momentum, 7 

Energy  or  Work, 8 

Power,      10 

Horse-power, 10 

Parallelogram  of  Forces,      11 

Moment  or  Statical  Moment, 11 

The  Lever, 13 

The  Wheel  and  Axle, 16 

The  Wedge, 16 

The  Pulley, 16 

The  Screw, 17 

Transmission  and  Measueement  of  Powee. 

Methods  of  Transmitting  Power, 18 

Shafting,      18 

Belting, 20 

vii 


Vlll  CONTENTS. 

PAGE 

Velocity  of  Belts, 20 

Power  Transmitted  by  Belts, 20 

Calculation  of  Width  of  Belt  for  a  Given  Horse- 
power,    20 

Calculation  of  Length  of  Belt  Needed, 21 

Rope  Driving, 22 

Gearing, 23 

Spur  Gears, 24 

Friction  Clutches, 25 

Pneumatic  Transmission  of  Power, 25 

Compound  Compressor, 26 

The  Intercooler, 27 

Reservoirs  or  Receivers, 27 

Flow  of  Compressed  Air  Through  Pipes,     ....  28 

Efliciency  of  Compressed  Air  Systems, 28 

Electric  Transmission  of  Power, 29 

Types  of  Motors, 30 

Calculation  of  Line, 31 

Lubricants, 32 

Best  Lubricants  for  Different  Purposes, 32 

Oil  Separators, 32 

Measurement  of  Power, 33 

Different  Methods  Available, 33 

Indicator  Method,      33 

Electrical  Method, 34 

Prony  Brake  Method, 35 

HEAT,  FUEL,  GASES,  WATER,  AND  STEAM. 
Heat. 

Nature  of  Heat, • 37 

Temperature,      37 

The  Thermometer, 38 


CONTENTS.  IX 

PAGE 

Thermometer  Scales, 39 

Diagram  for  Changing  from  Centigrade  to  Fahren- 
heit Degrees, 39 

Specific  Heat, 41 

Latent  Heat, 41 

Unit  of  Heat, 41 

Mechanical  Equivalent  of  Heat, 42 

Methods  of  Transferring  Heat — Radiation,      ...  42 

Conduction  of  Heat, .  42 

Conducting  Power  (for  heat)  of  Various  Substances,  42 

Combustion  and  Fuels. 

Nature  of  Combustion, 44 

Smoke, 44 

Fuel,  Nature  and  Constituents  of, 45 

Carbon, 45 

Air  Required  to  Burn  1  Pound, 47 

Value  of  Wood  as  Fuel  Compared  to  Coal,  ....  47 

Heat  Evolved  from  Various  Fuels, 48 

Hydrogen  in  Fuel, 49 

Liquid  Fuels — Petroleum, 49 

AlE. 

Oxygen,  Nitrogen,  and  Hydrogen, 51 

Air— the  Atmosphere, 52 

Atmospheric  Pressure, 52 

Volume  of  Air  at  Various  Temperatures,     ....  53 

The  Barometer, 54 

Measurement  of  Heights  by  the  Barometer,    ...  55 

Water. 

Composition  of  Water  and  Its  Properties,    ....  56 

Specific  Gravity  of  Water, 56 


X  CONTENTS. 

PAGE 

Physical  States, 67 

Weight  of  a  Cubic  Foot  of  Water, 57 

Boiling  Point, 58 

Specific  Heat,      59 

Flow  of  Water,  Head, 60 

Calculation  of  Pressures  Corresponding  to  Various 

Heads,      61 

Flow  from  an  Orifice  in  the  Bottom  of  a  Tank,  .    .  61 

Flow  of  Water  Through  Pipes, 62 

Loss  of  Head  by  Friction  in  Pipes, 63 

Steam. 

Steam  and  its  Properties, 64 

Volume  of  Steam , 64 

Saturated  Steam,    . 65 

Superheated  Steam, 65 

Latent  Heat  of  Steam, 66 

Total  Heat  of  Steam, 67 

What  the  Gauge  Indicates,      68 

Condensation  of  Steam, 68 


THE  STEAM  BOILER. 

Plain  Cylindrical  Boiler, 75-77 

Cornish  Boiler, 77 

Lancashire  Boiler,      .    .    .    .  \ 79 

Galloway  Boiler, 80 

Fire-tube  Boilers, 81 

Water-tube  Boilers, 84 

Advantages  of  Water- tube  Boilers, 84 

Marine  Boilers, 87 

Locomotive  Boilers, 89 

Horse-power  Rating  of  Boilers, 91 


CONTENTS.  XI 

PAGE 

Evaporative  Power, 92 

Grate  and  Heating  Surface, 95 

Boiler  Materials, 100 

Methods  of  Riveting, 100 

Strength  of  Boilers, 102 

Boiler  Setting, ,    .  109 

Caee  and  Management  of  Boilers. 

Water  Level, Ill 

Firing,      112 

Cleaning  and  Blowing  Off, 116 

Scale  Formation  and  Corrosion,      123 

Foaming, 125 

Priming,      127 

ADJUNCTS  OF  STEAM  BOILERS. 
The  Safety  Valve. 

Safety  Valves, 128 

Spring-pop  Valves, 130 

Rules  and  Formulae  for  Safety  Valves, 131 

Steam  Pressure  Gauges, 138 

Water  Columns  and  Gauge  Cocks, 138 

Vacuum  Gauges, 139 

Salinometer, 141 

The  Econometer, 141 

Importance  of  Correct  Supply  of  Air  to  the  Boiler 

Furnace, 142 

Pumps  and  Injectors. 

Classification  of  Pumps, 142 

Power  Required  to  Raise  Water, 145 

Capacity  of  a  Pump,  Calculation  of, 145 


L  CONTENTS. 

PAGE 

Boiler  Feed  Pumps, 145 

Pumps  for  Hot  Water,      146 

Injectors  and  Their  Action, ,  146 

Failure  of  Injectors  to  Work, 149 

Setting  up  Injectors,  General  Directions,     ....  150 

Inspirators,      151 

Ejector  or  Lifter, , 151 

Comparison  of  Pumps  with  Injectors, 152 

Advantages  of  Heating  Feed-water, 153 

Closed  Type  of  Feed-water  Heaters, 1 55 

Open  Feed- water  Heaters, 155 

Economizers, 159 

Furnaces  and  Flues,  Pressure  Eequired  to  Collapse,  1 60 

Methods  of  Strengthening, 162 

Grates, ...  163 

Shaking  Grates,      164 

Automatic  Firing, 165 

Chimneys  and  Stacks, 167 

Proportioning  Stacks, 168 

Table  of  Sizes  of  Chimneys  for  Various  Sizes  of 

Boilers, 170 

Steam  Separators,      171 

Steam  Traps, 173 


THE  STEAM  ENGINE. 
Classification  and  General  Description. 

Invention, 175 

Horse-power  of  Engines,      177 

Mean  Effective  Pressure,  Calculation  of,      ....  180 

Classification  of  Engines, 188 

Simple  and  Multiple  Expansion  Engines,    ....  191 


CONTENTS.  Xlll 

PAGE 

High-speed  Engines,     .    , 194 

Throttling  and  Automatic  Cut-off  Engines,    .    .    .  195 

Valves  and  Valve  Geaes. 

Various  Kinds  of  Valves  and  Valve  Gears,      ...  197 

The  Slide  Valve  and  Its  Action, 199 

The  Zeuner  Valve  Diagram, 202 

How  to  Set  Valves, 2U5 

Balanced  Valve, 207 

Corliss  Gear, 207 

Piston  Valve, 207 

Separate  Valves  for  Admission  and  Exhaust,  .    .    .  207 

Steam  Engine  Goveenoes, 

General  Principles  of  Operation, 209 

,  Throttling  Governors, 209 

Method  of  Action  of  Fly-wheel  Governors,     .    .    .  211 

Installation,  Caee,  and  Management. 

Foundations, 213 

How  to  Set  Up  an  Engine, 214 

Piping  Engines, 216 

Instructions  for  Care  of  Engines,  ........  217 

Piston-rod  and  Valve  Packing,  ........  218 

3  of  Knocking  and  Remedies, 221 


ADJUNCTS  OF  THE  STEAM  ENGINE. 
The  Steam  Engine  Indicatoe. 

Description  of, .    ,    o    .    .    ,    .    224 

Tabor's  Indicator,      .... 225 

How  to  Attach  the  Indicator,      .    , 226 


XIV  CONTENTS. 

PAGE 

Analysis  of  Indicator  Diagrams, 228 

Mean  Effective  Pressure,      229 

How  to  Calculate  the  Horse-power  from  a  Card,    .  231 

CONDENSEES. 

Object  of  a  Condenser, 233 

Surface  Condenser, 233 

Jet  Condensers^ 233 

The  Vacuum, 234 

Power  Gained  by  Using  Condenser, 234 

MATERIALS  AND  THEIR  PROPERTIES. 
Composition  and  General  Peoperties. 

Elements  of  Matter,      236 

Atoms  and  Molecules, 237 

Properties  of  Metals, 238 

Specific  Gravity, 239 

Iron — Wrought  and  Cast, 240 

Steel, 241 

Effect  of  Rise  of  Temperature  on  Tensile  Strength 

of  Iron, 242 

Copper, 242 

Variation  of  Strength  with  Rise  of  Temperature,  .  242 

Alloys, 243 

Strength  of  Mateeials. 

Tensile  and  Crushing  Strength,      244 

Wrought  Iron  ;  Tensile  and  Crushing  Strength,     .  245 

Strength  of  Woods, 245 

Factors  of  Safety, 245 

Beams, 246 

Columns,      247 


ELECTRICITY. 
Fundamental  Experiments,  Properties,  and  Units. 

PAGE 

Fundamental  Experiments, 248 

Ampere's  Rule, 252 

Resistance, 252 

Lines  of  Magnetic  Force, 254 

Magnetic  Lines  of  Force  Due  to  a  Current,     .    .    .  256 

Galvanometer, 258 

Electric  Pressure  Produced  by  Induction,   ....  259 

Fleming's  Rule  for  Direction  of  Induced  Currents,  260 

Electro-motive  Force, 266 

Units, 267 

The  Ampere,  Volt,  Ohm,  and  Watt, 268 

Resistance, 270 

Conductivity, , 270 

Resistances  in  Multiple, 271 

Resistances  in  Series, 271 

Specific  Resistance, 272 

Table  of  Relative  Resistances  of  Conductors,      .    .  273 

Practical  Use  of  Conductors  and  Insulators,    .    .    .  274 

Current  Effects  ;  Heating, 274 

Electrolytic  Effects, 277 

Electro-motive  Force,  Methods  of  Producing,     .    .  278 

Ohm's  Law  and  Its  Application, .    .  280 

Calculation  of  Current  in  Divided  Circuits,     .    .    .  282 

Electrical  Measurement. 

Quantities    to     be    Measured    and     Instruments 

Needed, 285 

Measurement  of  Current, 285 

Measurement  of  Electro-motive  Force, 287 


XVI  CONTENTS. 

PAGE 

Measurement  of  Resistance, 288 

Measurement  of  Power, 291 

Electric  Batteries. 

Chemical  Generators, 292 

Secondary  or  Storage  Batteries, 292 

Primary  Batteries, 293 

Open-circuit  Cells, 293 

Closed-circuit  Cells, 295 

DaniellCell, 295 

Bichromate  Cell, 296 

Dry  Cells 296 

Dynamos, 

Function  of  a  Dynamo, 297 

Ideal  Simple  Dynamo,      297 

The  Armature, 299 

Ring  Armatures, 299 

Drum  Armatures, 299 

Armature  Cores, 300 

The  Field, 300 

Classification    of   Dynamos— Series,    Shunt,    and 

Compound,      300 

Regulation  of  Shunt  Dynamos, 302 

Distribution  of  Electrical  Energy. 

Analogy  to  Water  System,       303 

The  Switchboard  and  Its  Uses, 304 

Circuit  Breakers, 304 

Ground  Detector,    .    ,    .    .    , »    .    .    .    .  306 

Running  Generators  in  Multiple, 307 

Systems  of  Distribution, 308 

Series  System, 308 


CONTENTS.  XVll 

PAGE 

Parallel  System, 309 

Modified  Systems,  Three-wire, 311 

Advantages  of  Using  High  Pressures, 312 

Size  of  Conductors  Needed, 312 

Safe  Carrying  Capacity  of  Wires, 313 

Table  of  Properties  of  Copper  Wire, 315 

Methods  of  Carrying  Conductors, 316 

Electric  Lighting. 

Arc  Lamps ;  Classification, 320 

Requirements  for  Successful  Operation, 320 

Constant  Potential  Arcs, 321 

Open  Arcs, 322 

Closed  Arcs, 322 

Incandescent  Lamps, 323 

The  Filament, 324 

Candle  Powers  in  Commercial  Use, 325 

Life  and  Efficiency  of  Lamps, 326 

Eecteic  Motors. 

The  Motor  a  Dynamo  Reversed, 327 

Uses  of  Series,  Shunt,  and  Compound  Motors,   .    .  328 

Regulation  of  Speed, , 328 

Protective  Devices, 330 

Size  and  Speed  of  Motors, 332 

Motor  Generators,      333 

The  Storage  Battery. 

The  Chloride  Battery, 334 

Phenomena  of  Charge  and  Discharge,  ......  335 

Principal  Sources  of  Trouble, 336 

Advantages  in  the  Use  of  Cells, 336 

Capacity  of  Storage  Cells, 337 


XVlll  CONTENTS. 

PAGE 

Efficiency, ,  337 

Method  of  Connecting  Batteries,    ,    .    , 338 

Electeic  Signals. 

Elements  of  all  Signal  Systems,     .       341 

Electric  Bells  ;  Single  Stroke, 342 

Vibrating  Bells, 342 

Common  Arrangements  of  Bells,   .....        .    .  343 

The  Annunciator, 344 

Fire  Alarm  Attachment, .345 

Burglar  Alarm  Systems, 346 

Watchmen's  Time  Systems, 347 

Batteries  Eequired  for  Signal  Systems,         ....  349 

The  Telephone. 

Properties  of  Sound, 350 

Telephonic  Transmission  of  Speech  ;  Receiver  and 

Transmitter, 35 1 

Magneto  Receiver, 352 

Battery  Transmitter, 353 

Improved  Forms  of  Transmitter, 354 

The  Induction  Coil, 354 

The  Magneto  Call, 355 

Telephone  Systems,  Intercommunicating,    ....  355 

Exchange  Systems, 35(3 


ROPER'S  CATECHISM 

FOR 

STEAM   ENGINEERS 

AND 

ELECTRICIANS. 


MECHANICS. 

Q.  Of  what  elements  are  all  machines  made  up? 

A.  Of  six,  known  as  the  six  mechanical  ele- 
ments. These  are  the  lever,  pidley,  wheel  and  axle, 
inclined  plane,  ivedge,  and  the  screw. 

Q.   For  w^hat  is  machinery  nsed  ? 

A.  To  make  force  available  for  practical  pur- 
poses. Machinery  does  not  create  force,  but  trans- 
mits it,  diffusing  it,  concentrating  it,  or  changing 
its  direction. 

Q.  What  is  force  ? 

A.  Force  is  that  which  produces  motion  or 
tends  to  produce  it.  If  a  force  acting  on  a  body 
meets  with  a  resistance  equal  and  opposite  to  it, 
no  motion  results,  but  pressure  is  exerted  on  the 
particles  of  the  body.  But  if  the  force  is  not 
balanced,  motion  will  take  place. 
1  1 


'A  roper's  catechism  for 

Q.  What  two  varieties  of  force  are  there? 

A.  External  and  internal.  External  forces  are 
those  exerted  by  bodies  on  other  bodies.  Internal 
forces  are  those  exerted  by  the  particles  of  a  body 
on  neighboring  particles.  The  force  of  steam 
against  the  walls  of  the  pipe  or  vessel  containing 
it,  is  external.  Each  particle  of  steam  exerts  an 
equal  amount  of  force  on  its  neighbor,  and  this  is 
an  example  of  internal  force. 

Q.  What  is  the  difference  betAveen  force  and 
pressure  ? 

A.  Pressure  is  a  particular  case  of  force.  An 
external  force  which,  on  account  of  a  balancing 
resistance  does  not  produce  motion,  is  generally 
referred  to  as  a  pressure. 

Q.  What  is  weight? 

A.  The  weight  of  a  body  is  the  force  exerted  by 
the  earth  on  it  (an  equal  amount  of  force  is 
exerted  by  it  on  the  earth).  When  a  body  rests 
on  another  body  the  upper  body  exerts  upon  the 
lower  body  a  pressure  or  foixe  equal  to  its  iveight. 
The  lower  body  exerts,  of  course,  an  equal  and 
opposite  force  on  the  upper. 

Q.   What  is  meant  by  inertia  ? 

A.  That  property  of  matter  by  virtue  of  which 
it  tends  to  resist  a  change  of  state.  Thus,  if  a 
body  is  at  rest  its  inertia  makes  it  offer  a  resist- 
ance to  any  attempt  to  put  it  in  motion.     If  a 


STEAM    ENGINEERS    AND    ELECTRICIANS.  6 

'body  is  in  motion  its  tendency  is  to  keep  moving, 
and  it  will  do  so  unless  some  force  is  applied  to  it 
to  bring  it  to  rest. 

Q.  What  is  motion  ?  , 

A.  Motion  is  that  property  which  matter  has 
while  it  is  changing  its  position. 

Q.  How  would  you  understand  the  term  abso- 
lute motion  f 

A.  As  a  change  of  position,  with  reference  to 
some  fixed  point  in  space. 

Q.   What  does  relative  motion  signify  ? 

A.  Change  of  position,  with  reference  to  some 
other  body  which  we  are  for  the  moment  consider- 
ing. Thus  two  cars  in  the  same  train  have  rela- 
tive motion  with  regard  to  the  station  which  they 
have  left.  They  have,  however,  no  motion  rela- 
tive to  each  other. 

Q.  What  is  uniform  motion  ? 

A.  Uniform  motion  is  that  in  which  equal 
spaces  are  always  passed  over  in  equal  amounts 
of  time. 

Q.  W^hat  is  variable  motion? 

A.  That  in  which  equal  spaces  are  passed  over 
in  unequal  amounts  of  time. 

Q.  What  is  accelerated  motion  ? 

A.  That  in  which  the  space  passed  over  in  one 
second  is  continually  increasing  or  diminishing. 

Q.  AVhat  are  Newton' s  laws  of  motion  ? 


4  ROPER'S    CATECHISM    FOR 

A.  First.  A  body  at  rest  will  remain  at  rest,  or 
if  in  motion  will  continue  to  move  uniformly  in 
a  straight  line  till  it  is  acted  upon  by  some  force. 

Second.  If  a  body  be  acted  upon  by  several 
forces  it  will  obey  each,  as  if  the  others  did  not 
exist,  and  this  will  be  the  case  whether  the  body 
be  at  rest  or  in  motion. 

Third.  If  a  force  act  to  change  the  state  of  a 
body  with  respect  to  rest  or  motion,  the  body  will 
offer  a  resistance  equal  to  and  directly  opposed  to 
the  force.  Or  to  every  action  there  is  opposed  an 
equal  and  opposite  reaction. 

Q.  What  is  perpetual  motion  and  why  is  it  im- 
possible ? 

A.  See  explanation  in  "Roper's  Engineers' 
Handy-Book,"  pages  6  and  7. 

Q.  What  is  velocity  ? 

A.  Velocity  is  the  rate  at  which  motion  takes 
place.  If  a  body  moves  over  a  distance  of  100 
feet  in  10  seconds,  its  velocity  is  10  feet  per  second. 

Q.  What  is  uniform  velocity  ? 

A.  Velocity  is  uniform  when  equal  spaces  are 
passed  over  in  equal  times.  If  this  is  not  the 
case  the  velocity  is  said  to  be  variable. 

Q.  What  is  acceleration  ? 

A.  Acceleration  is  the  rate  at  which  the  velocity 
changes,  that  is,  the  gain  (or  loss,  as  the  case  may 
be)  in  velocity  in  1  second. 


STEAM   ENGINEERS   AND    ELECTRICIANS.  5 

Q.  What  case  of  accelerated  motion  can  you 
mention? 

A.  That  of  a  freely  falling  body  which  starts 
from  rest,  falls  16.1  feet  the  first  second,  48.3  feet 
the  next  second,  and  so  on. 

Q.  What  are  the  simple  formulae  which  enable 
us  to  calculate  the  performance  of  falling  bodies, 
when  the  influence  of  the  friction  of  the  air  is 
considered  of  no  importance  ? 

A.  v  =  l/64.4  h  and  h  =  16.1  i\ 

Q.  What  is  the  meaning  of  the  letters  in  these 
formulae  ? 

A.  V  =  velocity  in  feet  per  second; 

h  =  height   through    which   the   body  has 

fallen,  in  feet; 
t  =  number   of    seconds    required    to   fall 
through  the  distance  h. 

Q.  If  a  body  falls  from  a  height  of  100  feet, 
what  velocity  will  it  have  when  it  reaches  the 
earth's  surface? 


A.  v  =  V  64.4  X  100  =  1/  6440  =  80.2  feet 
per  second. 

Q.  How  long  will  it  take  for  the  body  to  fall 
through  100  feet? 

A.  h=  16.1  t'  or  t'  =  ^  ;  therefore 
lb.  1 


t  =  \j^  =  2.49  seconds. 


100 
'16.1 


6  roper's  catechism  for 

Q.  What  is  the  acceleration  produced  by  gravity? 

A.  It  is  at  the  surface  of  the  earth,  about  32.2 
feet  per  second,  and  diminishes  as  we  go  up  from 
the  earth's  surface. 

Q.  What  is  the  mass  of  a  body  ?  ■ 

A.  It  is  the  quotient  of  the  weight  of  the  body 
divided  by  the  value  of  the  acceleration  due  to 
gravity. 

Q.  Is  the  weight  of  a  body  everywhere  the 
same? 

A.  No;  it  diminishes  as  we  rise  from  the  earth's 
surface. 

Q.   Is  the  mass  always  the  same  ? 

A.  Yes;  for  though  the  weight  changes,  the 
value  of  the  acceleration  due  to  gravity  changes 
to  the  same  extent;  therefore  the  quotient  of  the 
two  is  constant,  and  this  by  definition  is  the  mass. 

Q.  When  a  force  is  applied  to  a  body  at  rest 
what  is  the  effect  ? 

A.  The  body  is  put  in  motion  which  is  uni- 
formly accelerated.  The  acceleration  produced  is 
proportional  to  the  force,  as  double  the  force  act- 
ing on  the  same  body  will  produce  twice  as  much 
acceleration. 

Q.  If  the  same  force  is  applied  to  a  bod}'  weigh- 
ing 10  pounds  and  to  another  weighing  twice  as 
much,  on  which  will  it  produce  the  greater  acceler- 
ation ? 


STEAM    ENGINEERS    AND    ELECTRICIANS.  7 

A.  On  the  10-pound  body  it  will  produce 
double  the  acceleration  that  it  will  on  the  20- 
pound  body. 

Q.  What  general  rule  can  you  give  for  the  rela- 
tion between  force,  mass,  and  acceleration  ? 

A.  The  force  (in  pounds)  =  the  mass  X  accel- 
eration or  with  sufficient  accuracy  for  most  pur- 

,,      „              the  weisfht  in  pounds     ,   ^, 
poses,  the  lorce  = ^      — X  the 

acceleration  in  feet  per  second. 

Q.  What  acceleration  will  a  force  of  20  pounds 
produce  if  applied  to  a  body  weighing  20  pounds  ? 

A.  F  (force)  =  — v>    q — ^  X  A  (acceleration), 

,       32.2  X  F 
ox  A^ 


W 
32.2  X  20 


32.2  feet  per  second. 


20 

This  case  is  that  of  a  freely  falling  body  where 
the  force  due  to  its  weight  acts  upon  its  mass  tend- 
ing to  accelerate  it. 

Q.  What  is  the  momentum  of  a  moving  body  ? 

A.  It  is  the  force  which  acting  upon  it  for  1 
second  will  bring  it  to  rest.  It  is  equal  to  the 
product  of  the  mass  of  the  body  by  its  velocity. 

Q.   Has  a  body  at  rest  any  momentum  ? 

A.  No;  for  its  velocity  is  zero,  and  hence  the 
product  of  mass  times  velocity  is  zero  also. 


O  ROPER  S    CATECHISM    FOR 

Q.  What  is  work  in  the  science  of  Mechanics? 

A.  Work  involves  two  things,  force  and  space, 
and  the  amount  of  work  is  equal  to  the  product 
of  force  by  space.  If  either  is  absent  no  work  is 
done. 

Q.  What  is  the  unit  of  work  ? 

A.  The  foot-pound,  which  is  the  amount  of  work 
performed  in  raising  a  weight  of  1  pound  through 
a  height  of  1  foot. 

Q.  What  example  can  you  give  of  forces  acting 
without  work  being  done  ? 

A.  A  weight  resting  on  a  table  exerts  force,  but 
as  there  is  no  motion  no  work  is  being  done  by 
the  weight. 

Q.  Was  work  done  in  placing  the  weight  on  the 
table? 

A.  Yes;  if  the  height  of  table  is  4  feet  and  the 
weight  is  10  pounds,  the  amount  of  work  done 
was  40  foot-pounds. 

Q.  What  is  energy  ? 

A.  Energy  is  the  power  of  doing  work.  For 
example,  the  weight  on  the  table  has  the  power 
to  do  w^ork  if  it  is  allowed  to  fall  from  the  height 
of  the  table. 

Q.   How  many  forms  of  energy  are  there  ? 

A.  Two, — potential  energy  and  kinetic  energy. 
The  energy  in  the  weight  above  mentioned  is  a 
case  of  potenticd  energy.    A  body  in  motion  has  also 


STEAM    ENGINEERS   AND    ELECTRICIANS.  9 

the  capacity  for  doing  work  stored  up  in  it,  and  the 
energy  resident  in  moving  bodies  is  called  kinetic 
energ}^ 

Q.  Can  you  give  other  examples  of  potential 
energy  ? 

A.  A  spring  in  tension  or  compression,  a  tank 
of  water  at  a  height,  a  reservoir  of  compressed 
air,  a  piece  of  coal. 

Q.  Give  some  examples  of  kinetic  energy. 

A.  A  moving  train,  a  cannon  ball,  a  fly-wheel, 
a  stream  of  water,  the  waves  of  the  ocean,  heat, 
electric -current  flow. 

Q.  What   is   the   formula  for  the  energy  in  a 

moving  body? 

M  X  V'^ 
A.  E  (energy  in  foot-pounds)  = ^ ,  where 

M  is  the  mass  and  V  the  velocity  of  the  moving 

body  in  feet  per  second.    In  more  convenient  form, 

TT  X  F^ 
E  =        .   ■ — ,  where  W  is  the  weight  in  pounds., 

Q.   How  much  energy  is  stored  up  in  the  piston 

and  piston-rod  of   an  engine  if  the  speed  of  the 

piston  is  600  feet  per  minute,  and  their  weight  is 

100  pounds? 

.     ^       100  X  60  X  60       _„„  „    ^  , 

A.   E  =^ ^^^-j =  5590  foot-pounds. 

Q.  What  is  the  primary  source  of  energy  on  the 
earth  ? 


10  roper's  catechism  for 

A.  The  rays  of  the  sun  which  raise  water  from 
sea-level  to  the  clouds  from  which  it  falls  in  rain, 
and  which  causes  the  growth  of  plants  from  which 
has  come  our  coal. 

Q.  What   is   the   principle   of   conservation  of 


energy 


?* 


A.  That  the  amount  of  energy  in  the  universe 
is  fixed  and  cannot  be  changed  by  man.  He  can 
transmit  it  and  alter  the  form  in  which  it  appears, 
as  from  potential  to  kinetic,  but  can  in  no  wise 
create  or  destroy  it. 

Q.  What  is  power  ? 

A.  Power  is  the  rate  at  which  work  is  done,  or 
at  which  energy  is  changed  from  one  form  to 
another;  thus,  if  a  man  lifts  in  one  hour  100 
weights  of  100  pounds  each  to  a  height  of  4  feet, 
he  has  done  work  at  the  rate  of  100  X  100  X  4, 
or  40,000  foot-pounds  per  hour. 

Q.  What  is  meant  by  a  horse-power  ? 

A.  Doing  work  at  the  rate  of  33,000  foot- 
pounds per  minute. 

Q.  In  the  example  above,  what  horse-power  is 
the  man  doing? 

A.  40,000  foot-pounds  per  hour  =  —^ —  foot- 
pounds   per    minute,    or   666f   foot-pounds    per 

*See  also  "Roper's  Engineers'  Handy-Book,"  images  14 
and  15. 


STEAM    ENGINEERS   AND    ELECTRICIANS.  11 

2 
minute ;     666f   -v-   33,000  =    j^    horse-power 

very  nearly. 

Q.  What  is  the  rule  for  obtaining  the  horse- 
power ? 

A.  To  obtain  the  work  done  multiply  the  force 
in  pounds  by  the  distance  in  feet. 

To  obtain  the  power  divide  this  product  by  the 
time  required  to  do  the  work,  in  minutes. 

To  obtain  the  horse-power  divide  further  by 
33,000. 

Q.  How  can  forces  be  conveniently  represented 
so  as  to  calculate  the  effect  which  they  will  pro- 
duce on  a  body  ? 

A.  We  represent  each  force  by  a  line  whose 
direction  represents  the  direction  of  the  force,  and 
whose  length  is  proportional  to  the  amount  of  the 
force. 

Q.  What  is  the  principle  known  as  the  paral- 
lelogram, of  forces  f 

A.  If  two  forces  acting  on  a  body  be  represented 
by  two  lines  forming  two  adjacent  sides  of  a 
parallelogram  (their  lengths  being  proportional  to 
the  strength  of  the  forces  and  their  directions  the 
same  as  those  of  the  forces),  the  diagonal  of  the 
parallelogram  will  represent  what  is  called  the 
resultant  of  the  two  forces,  namely,  a  force  which 
acting  alone  would  produce  on  the  body  the  same 


12  roper's  catechism  for 

effect  as  would  the  two  forces.  The  direction  of 
the  diagonal  represents  the  direction  of  the  result- 
ant or  equivalent  force,  and  its  length  represents 
the  strength  of  that  force. 

Q.  What  is  the  resultant  force  which  will  equal 
two  forces  of  3  and  4  pounds,  acting  at  the  same , 
point  and  at  an  angle  of  90  degrees  ? 

A.  Lay  out  the  line  A  B  with  4  units  of  length 
to  represent  the  force  of  4  pounds,  and  A  C  with 
3  units  of  length  at  right  angles  to  A  B,  to  repre- 
sent the  other  force. 
Complete  the  parallelo- 
gram by  drawing  B  D 
and  C  D;  then  the  diag- 
onal A  D  will  represent 
the  resultant,  and  if 
measured  or  calculated 
its  length  will  be  found  to  be  5  units.  The  result- 
ant force  will  then  be  5  pounds  exerted  at  an 
angle  of  36°  53^  to  the  hne  A  B. 

Q.  What  will  be  the  resultant  of  a  force  of  10 
pounds  in  one  direction  and  a  force  of  5  pounds 
acting  in  the  same  line  but  in  the  opposite  direc- 
tion ? 

A.  10  less  5,  or  5  pounds.  When  the  forces  are 
parallel  or  in  the  same  line  no  parallelogram  can 
be  formed. 

Q.   What  is  the  moment  of  a  force  ? 


STEAM   ENGINEERS   AND    ELECTRICIANS.  13 

A.  It  is  the  number  which  represents  its  ten- 
dency to  cause  rotation  about  a  certain  point.  For 
example,  if  a  stick  5  feet  long  is  pivoted  at  one 
end  and  if  a  force  of  5  pounds  be  applied  at  the 
other  end,  the  force  would  tend  to  make  the  stick 
rotate  about  the  pivot  point.  This  tendency 
would  be  greater  if  the  force  were  greater  or  if  the 
length  of  the  stick  were  greater.  It  is,  in  fact, 
proportional  to  the  product  of  the  force  by  the 
perpendicular  distance  from  the  pivot  point  to 
the  line  of  direction  of  the  force,  and  this  product 
is  technically  known  as  the  moment  of  the  force 
about  the  pivot  point. 

Q.  What  is  the  particular  value  of  the  idea  of 
moments  ? 

A.  It  gives  a  simple  treatment  of  levers  and 
questions  governing  the  rotation  of  bodies. 

Q.  AVhat  is  the  general  principle  of  moments 
as  applied  to  levers  ? 

A.  When  two  forces  are  acting  at  different 
points  in  the  same  body,  if  the  moments,  taken 
about  a  given  point,  of  the  forces  are  equal  and 
opposed  in  direction,  the  body  will  be  at  rest, 
otherwise  the  body  will  be  set  in  motion.  When 
there  are  more  than  two  forces  they  may  be 
divided  into  two  sets, — one  set  tending  to  rotate 
the  body  in  one  direction  about  the  point,  and  the 
other  set  tending  to  rotate  the  body  in  the  other 


14  roper's  catechism  for 

direction.  If  the  sum  of  the  moments  of  the 
first  set  of  forces  is  equal  to  the  sum  of  the 
moments  of  the  second  set,  the  body  will  be  at 
rest;  but  if  the  sums  of  the  moments  of  the  two 
sets  of  forces  are  unequal,  the  body  will  be  set  in 
motion. 

Q.   How  does  this  principle  apply  to  levers  ? 

A.  In  the  use  of  levers,  as,  for  example,  the  case 
of  a  man  trjdng  to  raise  a  rock  by  means  of  a 
crowbar,  we  have  three  forces  applied  at  three 
different  points  of  the  crowbar, — one  force  the 
strength  of  the  man,  another  the  weight  of  the 
rock,  and  the  third  the  upward  thrust  of  the  point 
of  support.  By  taking  moments  about  the  point 
of  support,  the  moment  of  the  third  force  becomes 
zero,  since  its  lever  arm  is  zero,  and  the  bar  is  in 
equilibrium  under  the  action  of  two  equal  moments. 
If  one  force  is  known,  as,  for  example,  the  weight 
of  the  rock,  we  can  calculate  the  force  which  must 
be  applied  by  the  man.  If  the  moment  of  the 
force  used  by  the  man  is  the  greater,  he  will  move 
the  rock;  if  less,  he  cannot  do  so. 

Q.  What  three  classes  of  levers  are  there  ? 

A.  First  Those  in  which  the  fulcrum  or  point 
of  support  is  between  the  applied  force  and  the 
resisting  force. 

Second.  Those  in  which  the  resisting  force  is 
between  the  applied  force  and  the  fulcrum. 


STEAM    ENGINEERS    AND    ELECTRICIANS.  15 

Third.  Those  in  which  the  apphed  force  is 
between  the  fulcrum  and  the  resisting  force. 

Q.  With  a  lever  of  the  first  class,  10  feet  long, 
what  force  must  be  applied  at  the  end  to  lift  a 
weight  of  9000  pounds,  if  the  fulcrum  is  distant 
from  the  weight  1  foot? 

A.  Call  the  force  F.  Then  by  the  principle  of 
moments,  when  the  applied  force  is  just  sufficient 
to  balance  the  weight,  i^  X  9  =  9000  X  1,  or  i^  = 
9000  --  9  =  1000  pounds. 

Q.  Is  any  'power  gained  by  using  a  lever,  or, 
more  accurately  speaking,  is  any  energy  gained  ? 

A.  No;  the  same  expenditure  of  work  is  re- 
quired to  raise  a  weight  of  9000  pounds,  whatever 
may  be  the  machinery  used  to  perform  the  work. 
A  lever  merely  allows  a  person,  too  weak  to  lift  a 
certain  weight  with  the  hands,  to  do  so  by  taking 
a  longer  time  to  perform  the  act.  Looked  at  from 
the  standpoint  of  work,  if  the  9000  pounds  is 
lifted  1  foot  in  height,  9000  foot-pounds  of  work 
are  done.  The  end  of  the  lever  at  which  the 
force  of  1000  pounds  is  applied,  moves  through  a 
distance  of  9  feet  if  the  other  end  moves  through 
1  foot.  Therefore,  the  work  done,  which  is  always 
the  product  of  force  times  distance  through  which 
the  force  is  exerted,  is  1000  X  9,  or  9000  foot- 
pounds, the  same  as  if  the  stone  were  lifted 
directly. 


16 


ROPER  S    CATECHISM    FOR 


In  one  sense  it  may  be  said  that  we  gain  force 
by  the  use  of  the  lever,  in  that  we  can,  by  taking 
a  longer  time  to  do  the  work,  get  along  with  a 
smaller  force. 

Q.  How  does  the  wheel  and  axle  differ  from  a 
lever  ? 

A.  The  wheel  and  axle  may  be  considered  as  a 
lever  in  which  the  points  of  support  and  resist-" 
ance  are  continually  renewed.  The  center  of  the 
axis  is  the  fulcrum,  the  radius  of  the  wheel  is  the 
long  arm  and  the  radius  of  the  axle  the  short 
arm  of  the  lever. 

Q.  What  is  the  relation  between  the  applied 
force  and  the  resulting  force  in  the  case  of  a  wedge  ? 
A.  If  a  force  of  F  pounds  be  applied  at  the 
point  B  in  the  direc- 
tion B  A,  the  resulting 
force  W  (in  a  direction 
perpendicular  to  A  B) 
will  have  the  follow- 
ing relation : 

W_  _  length  A  B 
F    ~~  length  C  D* 
Q.  What  two  kinds  of  pulleys  are  there  ? 
A.  The  fixed,  which  only  turns  on  its  axis,  and 
the  movable,  which  moves  up  and  down  as  well  as 
turns  on  its  axis. 

Q.  What  is  the  use  of  a  fixed  pulley? 


STEAM    ENGINEERS   AND    ELECTRICIANS.  17 

A.  Merely  to  change  the  direction  of  force. 

Q.  What  advantage  is  gained  by  a  movable 
pulley  ? 

A.  It  enables  us  to  raise  a  weight  by  the  appli- 
cation of  a  force  half  as  great  as  the  weight, 
although  we  take  twice  as  long  to  do  the  work. 

Q.  With  two  movable  pulleys  what  would  be 
the  gain  ? 

A.  We  should  need  a  force  of  only  one-quarter 
the  weight. 

Q.  Does  it  make  any  difference  whether  the 
movable  pulleys  are  separate  or  consist  of  sheaves 
mounted  in  the  same  case  ? 

A.  No. 

Q.  Give  the  general  rule  for  finding  the  force 
necessary  to  lift  a  certain  weight  with  the  ordinary 
block  and  tackle. 

A,  Divide  the  weight  by  the  number  of  sheaves 
hi  the  movable  pulley. 

Q.  What  is  the  rule  for  finding  the  force  which 
must  be  applied  at  the  end  of  the  lever  of  a  jack- 
scrcAv  in  order  to  lift  a  certain  weight  ? 

A.  Multiply  the  weight  by  the  pitch  of  the 
screw,  in  inches,  and  divide  by  6.2832  times  the 
length  of  the  lever,  also  expressed  in  inches.* 

*For  complete  explanation,  see  "Eoper's  Engineers' 
Handy-Book,"  pages  23  and  24. 


18  roper's  catechism  for 

POWER  TRANSMISSION  AND 
MEASUREMENT* 

SHAFTING. 

Q.  What  are  the  principal  methods  of  trans- 
mitting power  ? 

A.   By  shafting  with  pulleys  and  belts. 
By  rope  driving. 
By  gear  wheels. 
Hydraulic. 

Pneumatic,  by  compressed  air. 
Electrical,  b}^  dynamos,  line,  and  motors. 
Q.  Why  is  shafting  now  made  of  steel  instead 
of  iron? 

A.  Because  a  steel  shaft  for  the  same  weight 
and  size  is  stronger  with  respect  to  the  twisting 
strain,  and  stiffer  as  regards  transverse  strains  due 
to  the  weight  of  pulleys  and  pull  of  belts. 

Q.  What  two  requirements  must  be  met  by 
shafting  ? 

A.  It  must  be  large  enough  to  transmit  the 
required  power  at  the  given  speed  without  being 
twisted  too  much.  It  must  also  have  sufficient 
size  to  stand  the  transverse  pull  due  to  its  own 
weight,  the  weight  of  the  pulleys,  and  the  weight 
and  pull  of  the  belts. 

Q.  What  general  rule  should  guide  the  location 
of  hangers? 


STEAM    ENGINEERS   AND    ELECTRICIANS.  19 

A.  They  should  be  as  near  as  possible  to  the 
pulleys,  and  should  not  be  over  8  feet  apart  for 
light  shafting. 

Q.  Give  the  rule  for  calculating  the  diameter  of 
a  shaft  to  transmit  a  certain  horse-power  at  a  cer- 
tain number  of  revolutions  per  minute. 

A.  Multiply  the  horse-power  by  70  and  divide 
by  the  number  of  revolutions  per  minute,  and 
extract  the  cube  root  of  the  quotient.  The  result 
will  be  the  diameter  of  the  shaft  in  inches. 

Q.  What  is  the  rule  for  obtaining  the  greatest 
allowable  distance  between  hangers  for  a  certain 
size  of  shaft? 

A.  Multiply  the  square  of  the  diameter  in 
inches  by  140  and  extract  the  cube  root.  The 
result  will  be  the  distance  in  feet. 

Q.  What  is  the  rule  for  finding  the  number  of 
horse-power  which  a  shaft  of  a  certain  diameter 
will  transmit  at  a  certain  speed? 

A.  Multiply  the  cube  of  the  diameter  in  inches 
by  the  number  of  revolutions  per  minute  and 
divide  the  product  by  70. 

Q.  Can  these  rules  be  depended  upon  for  all 
cases  ? 

A,  No;  only  for  ordinarily  heavy  pulleys.  For 
any  very  heavy  pulleys  the  diameters  given  by 
these  rules  would  be  too  small. 


20  roper's  catechism  for 


BELTING. 

Q.  What  are  the  advantages  of  leather  over 
rubber  belts  ? 

A.  Leather  belts  have  a  longer  life,  and  are  less 
affected  by  oil  and  by  heat  and  cold.  They  will 
stand  being  run  through  shifters  or  crossed. 
When  worn  they  can  be  cut  up  into  narrower 
belts,  whereas  rubber  belts  when  worn  are  of  no 
use. 

Q.  What  two  points  determine  the  width  of  a 
belt  for  transmitting  a  certain  horse-power  ? 

A.  The  speed  at  which  the  belt  runs  and  the  safe 
working-strain  of  the  belt,  which  may  be  taken 
as  45  pounds  per  inch  width  for  single  belting. 

Q.  How  much  more  power  will  a  belt  transmit 
when  running  at  6000  feet  per  minute  than  at  a 
speed  of  3000  feet  per  minute  ? 

A.   Twice  as  much. 

Q.  At  about  what  speed  is  it  best  to  run  belts  ? 

A.  Between  4000  and  5000  feet  per  minute. 

Q.  What  is  a  common  rule  for  determining  the 
width  of  belt  to  transmit  a  certain  horse-power  ? 

A.  That  a  belt  1  inch  wide,  at  a  speed  of  1000 
feet  per  minute,  will  transmit  1  horse-power;  a  2- 
inch  belt  will  transmit  2  horse-power,  and  so  on. 

Q.   Is  this  rule  a  safe  one  to  follow  ? 

A.  Yes;  for  the  most  favorable  cases,  where  the 


STEAM    ENGINEERS   AND    ELECTRICIANS.  21 

belts  are  open  and  horizontal,  with  a  long  distance 
between  centers,  a  narrower  belt  may  be  used. 

Q.  Will  a  belt  30  feet  long  transmit  more  power 
than  the  same  belt  20  feet  long  ? 

A.  Yes,  if  it  is  horizontal;  for  owing  to  the 
greater  weight  of  the  longer  belt  it  will  sag  down 
a  little  more  in  the  center  and  give  a  little  greater 
arc  of  contact  on  the  pulleys. 

Q.  What  is  the  objection  to  vertical  belts? 

A.  The  weight  of  the  belt  tends  to  pull  it  away 
from  contact  with  the  lower  pulley  and,  therefore, 
to  transmit  a  given  power  a  vertical  belt  must  be 
run  tighter  than  if  it  were  horizontal.  Moreover, 
with  a  horizontal  belt  the  upper  side  tends  to  sag 
down  owing  to  its  weight,  and  this  increases  the 
arc  of  contact  with  the  pulley. 

Q.  Why  do  the  formulae  of  different  authors 
for  finding  the  width  of  belts  differ  so  much  ? 

A.  Because  some  use  a  greater  permissible  ten- 
sion on  the  belt  than  others,  which  shortens  the 
life  of  the  belt  and  renders  repairs  more  frequent.* 

Q.  What  is  the  rule  for  obtaining  the  length  of 
an  open  belt? 

A.  Multiply  the  sum  of  the  diameters  of  the 
two  pulleys  by  3.1416  and  divide  by  2.  To  the 
quotient  add  twice  the  distance  between  centers. 

*See  Belting,  "Roper's  Engineers' Handy-Book,"  pages 
34-43. 


22  roper's  catechism  for 

Q.   Is  this  rule  strictly  accurate  ? 

A.  Yes,  if  the  diameters  of  the  pulleys  are  the 
same;  if  not,  the  result  is  slightly  too  small. 

Q.  How  would  you  measure  the  length  of  a  belt 
in  a  coil  ? 

A.  Add  the  outside  diameter  to  the  diameter  of 
the  hole  and  divide  by  2.  This  would  give  the 
mean  diameter  which  should  be  expressed  in  feet. 
Then  multiply  this  by  3.1416  and  the  product  by 
the  number  of  coils  in  the  roll. 

Q.  How  would  you  determine  the  proper  size  of 
a  driven  pulley  to  run  at  a  certain  number  of 
revolutions  per  minute,  having  given  the  diameter 
and  speed  of  the  driving  pulley  ? 

A.  Multiply  the  diameter  of  the  driver  by  the 
number  of  revolutions  which  it  makes  per  minute 
and  divide  the  product  by  the  number  of  revolu- 
tions which  the  driven  pulley  is  to  make. 

Q.  In  arranging  for  belting,  which  side  should 
be  the  loose  side,  the  upper  or  lower  ? 

A.  The  upper,  so  that  the  weight  of  the  belt 
may  make  it  sag  down  and  thus  make  a  longer  arc 
of  contact  between  belt  and  pulleys. 

Q.  What  advantages  does  rope  transmission 
have  over  belt  driving  ? 

A.  The  cost  of  rope  is  less  than  that  of  belting, 
and  the  pulleys  do  not  have  to  be  so  accurately 
lined  up. 


STEAM    ENGINEERS   AND    ELECTRICIANS.  23 

Q.  What  are  the  two  general  methods  of  using 
ropes  ? 

A.  First.  To  put  ropes  on  hke  so  many  parallel 
spliced  belts,  one  working  in  each  groove  of  the 
pulley. 

Secondly.  To  wrap  the  rope  around  the  pulleys 
as  many  times  as  there  are  grooves,  then  to  carry 
it  through  idlers  so  arranged  that  the  tension  can 
be  varied,  and  then  to  carry  the  rope  back  to  the 
starting-point  and  to  splice  it. 

Q.  What  is  the  objection  to  the  first  method? 

A.  The  separate  ropes  do  not  all  pull  equally. 

Q.  How  is  this  partially  overcome  ? 

A.  By  making  the  grooves  of  the  smaller  pulley 
with  a  sharper  angle. 

Q.  At  what  speeds  do  the  ropes  run  ? 

A.  At  speeds  varying  from  25  to  100  feet  per  sec- 
ond, the  most  common  practice  being  about  80  feet. 

Q.  Can  you  give  any  figures  showing  what 
horse-power  is  transmitted  by  a  certain  size  rope  ? 

A.  A  1-inch  rope 'at  a  velocity  of  5000  feet  per 
minute  will  transmit  about  13  horse-power. 

TOOTHED  AND  FRICTION  GEARING. 

Q.  What  is  the  pitch  of  a  gear  wheel  ? 

A.  The  distance  measured  along  the  pitch  circle 
from  a  point  on  one  tooth  to  the  corresponding 
point  on  the  next  tooth. 


24  eoper's  catechjsm  for 

Q.  What  is  the  thickness  of  a  gear  tooth  ? 

A.   Its  width  measured  along  the  pitch  circle. 

Q.  What  is  the  space  f 

A.  The  difference  between  its  pitch  and  its  thick- 
ness. 

Q.  What  is  backlash  f 

A.  The  amount  by  which  the  space  is  greater 
than  the  thickness. 

Q.  What  are  spur  gears  used  for  ? 

A.  To  connect  parallel  shafts. 

Q.  When  are  bevel  gears  used  ? 

A.  When  it  is  desired  to  connect  shafts  making 
an  angle  with  each  other. 

Q.  What  are  the  two  principal  forms  of  gear 
teeth  ? 

A.  The  cycloid  and  the  involute,  the  latter  being 
used  when  the  number  of  teeth  is  small. 

Q.  How  would  you  calculate  the  diameter  or 
number  of  teeth  in  a  driven  wheel  to  run  a  certain 
speed  having  given  the  diameter  or  number  of 
teeth  of  the  driver? 

A.  Just  as  the  diameter  of  a  driven  pulley  is 
calculated.  * 

Q.  For  what  are  friction-clutch  connections 
principally  used  ? 

A.  To  take  the  place  of  tight  and  loose  pulleys, 

*See  also  "Roper's  Engineers'  Handy-Book,"  pages 
50-52. 


STEAM    ENGINEERS   AND    ELECTRICIANS.  25 

and  to  connect  two  or  more  sections  of  a  line  of 
shafting  so  that  the  sections  may  be  disconnected 
or  thrown  together  without,  stopping  the  shaft. 

Q.  Describe  the  general  principle  on  which  most 
friction  clutches  are  constructed. 

A.  A  pulley  is  mounted  so  as  to  turn  freely  on 
a  sleeve  in  which  the  shaft  turns.  This  pulley 
has  either  a  special  rim  attached  to  the  arms  or 
else  a  disk  attached  to  the  hub,  which  is  gripped 
between  the  jaws  of  the  clutch  device.  The 
clutch  is  mounted  on  and  keyed  to  the  shaft.  The 
jaws  of  the  clutch  are  made  to  open  or  shut  by 
moving  the  clutch  collar  in  one  direction  or  another 
along  the  shaft  by  a  fork  handle.  The  motion  of 
the  clutch  collar  operates  some  kind  of  toggle  joint 
which  moves  the  jaws;  when  the  jaws  are  closed 
so  as  to  grip  the  rim  or  disk,  the  pulley  is  made 
to  turn  with  the  shaft. 

COMPRESSED  AIR. 

Q.  What  are  some  of  the  purposes  for  which 
compressed  air  is  used  as  a  means  of  transmitting 
power  ? 

A.  For  operating  cranes,  hoists,  drills,  rivet- 
ing-machines, coal-mining  machinery,  railroad 
signals,  shop  tools,  sand  blasts,  brakes,  etc. 

Q.  Describe  the  general  method  of  power  trans- 
mission by  compressed  air. 


26  roper's  catechism  for 

A.  Air  is  compressed  by  some  form  of  piston 
pump  driven  by  a  steam  engine,  water  wheel, 
electric  motor,  or  anj;^  convenient  source  of  power. 
Pipes  carry  the  compressed  air  to  the  point  where 
it  is  to  be  used,  where  it  is  led  into  the  air  motor 
or  other  machine  in  which  it  is  to  be  used. 

Q.  What  is  the  general  nature  of  the  air  motor  ? 

A.  An  ordinary  steam  engine  or  steam  pump 
may  be  used  as  a  compressed  air  motor,  according 
as  rotary  or  reciprocating  motion  is  desired.  Com- 
mercial motors  differ  from  these  only  in  form  and 
detail. 

Q.  Why  in  steam-driven  air  compressors  is  the 
duplex  or  compound  type  used  so  largely  ? 

A.  With  a  single  steam  and  single  air  cylinder 
the  maximum  steam  pressure  is  at  the  beginning 
of  the  stroke,  while  in  the  air  cylinder  the  great- 
est pressure  is  at  the  end  of  the  stroke.  This  is 
equalized  to  a  great  extent  by  having  two  cylinders 
of  different  sizes  and  performing  the  first  part  of 
the  compression  in  the  larger  and  finishing  it  in 
the  smaller  cylinder. 

Q.  Has  the  compound  compressor  any  other 
advantage  ? 

A.  Yes;  it  is  more  efficient,  i.  e.,  it  com^Dresses 
a  greater  quantity  of  air  with  a  given  amount  of 
steam  than  would  a  simple  compressor. 

Q.  What  is  the  intercooler  ? 


STEAM    ENGINEERS    AND    ELECTRICIANS.  27 

A.  A  tank  containing  coils  through  which  runs 
cold  water.  This  tank  is  so  connected  between 
the  large  and  small  air  cylinders  that  after  the 
air  has  received  the  first  part  of  its  compression  it 
is  led  through  the  intercooler  before  it  passes  into 
the  second  compressing  cylinder. 

Q.  What  is  the  advantage  of  the  intercooler  ? 

A.  The  air  being  cooled  after  the  first  com- 
pression it  does  not  reach  so  high  a  temperature 
in  the  second  cylinder,  so  that  lubrication  is  much 
easier ;  moreover,  it  is  found  that  by  using  the 
intercooler  a  given  quantity  of  air  can  be  com- 
pressed with  the  use  of  a  less  quantity  of  steam 
than  would  be  the  case  without  it. 

Q.  How  much  of  a  saving  in  steam  is  attained 
by  the  cooling  of  the  air? 

A.  About  10  per  cent,  by  the  intercooler  and  5 
per  cent,  by  the  water  jackets  around  the  air-com- 
pressing cylinders. 

Q.  How  is  the  regulation  of  air  pressure  main- 
tained ? 

A.  By  a  balanced  valve  operating  a  little  piston 
which  in  turn  operates  another  controlling  the 
steam  supply  for  the  steam  cylinder  of  the  com- 
pressor. 

Q.  What  are  receivers  and  why  are  they  used  ? 

A.  They  are  steel  tanks  of  suitable  size  and 
strength,  placed  one  near  the  compressor  and  one 


28  roper's  catechism  for 

near  the  point  where  the  air  is  to  be  used.  Their 
object  is  to  prevent  fluctuations  of  pressure  in  the 
system.  They  thus  preserve  a  steady  flow  of  air 
in  the  pipe  hne  and  keep  the  loss  of  pressure  by 
friction  down  to  a  minimum. 

Q.  AVhat  is  a  common  pressure  for  compressed- 
air  systems  ? 

A.  80  pounds. 

Q.  How  does  the  loss  of  pressure  due  to  fric- 
tion of  air  flowing  through  pipes  vary  ? 

A.  In  proportion  to  the  length  of  pipe  and  in 
proportion  to  the  square  of  the  velocity  or  quan- 
tity per  minute  which  goes  through  the  pipe. 

Q.  Can  you  give  any  figures  showing  the  num- 
ber of  cubic  feet  of  compressed  air  used  by  air 
motors  ? 

A.  In  small  motors  of,  say,  one  horse-power 
about  700  cubic  feet  per  horse-power  per  hour; 
with  large  motors  as  low  as  500  cubic  feet  per 
horse-power  per  hour. 

Q.  What  percentage  of  the  power  put  into  the 
air  compressor  would  j^ou  expect  to  get  out  of  the 
air  motors?  In  other  words,  what  would  be  the 
efficiency  of  a  complete  pneumatic  transmission 
system  ? 

A.   From  35  to  55  per  cent. 


STEAM   ENGINEERS   AND    ELECTRICIANS.  29 


ELECTRIC  TRANSMISSION  OF  POWER. 

Q.  Describe  the  general  method  of  transmitting 
power  electrically. 

A.  The  energy  of  a  steam  engine,  water  wheel, 
or  other  source  of  power  is  used  to  drive  an  elec- 
trical generator  or  dynamo,  which  changes  energy 
from  the  mechanical  form  into  the  electrical  form. 
This  electrical  energy  is  conveyed  from  the  gener- 
ator by  insulated  copper  wires  of  suitable  size  to 
the  point  where  it  is  desired  to  use  the  energy. 
At  that  point  electric  motors  or  other  electric 
devices  are  attached  to  the  wires  and  change  the 
energy  back  again  intf  the  mechanical  form. 

Q.  What  two  classel  of  transmission  are  there? 

A.  Transmission  by  direct  current  and  trans- 
mission by  alternating  current. 

Q.  In  the  electrical  transmission  of  power  when 
would  you,  generally  speaking,  use  an  alternating 
current  transmission,  and  why  ? 

A.  When  the  distance  is  over  1500  feet, — be- 
cause it  requires  a  smaller  conductor  to  transmit 
a  certain  power  if  the  pressure  used  be  high  than 
if  it  be  low,  and  alternating  currents  can  more 
readily  be  changed  from  high  to  low  pressure  than 
can  direct  currents,  and  are  therefore  more  con- 
venient to  use  when  high  pressures  are  employed.* 

*See  also  "Roper's  Engineers'  Handy-Book,"  page  65. 


30  roper's  catechism  for 

Q.  What  three  types  of  direct-current  motors 
are  there  ? 

A.  The  shunt  wound,  the  series  wound,  and 
the  compound  wound.* 

Q.  For  what  class  of  service  are  these  types 
used? 

A.  The  series  motor  is  used  on  hoists  and 
street-car  motors,  where  constancy  of  speed  is  not 
necessary,  but  where  a  strong  starting-torque  is 
desired.  The  shunt  motor  is  used  for  the  greater 
part  of  the  work  requiring  constant  speed,  the 
compound  motor  being  used  in  a  few  special 
cases. 

Q.  What  type  of  direct-current  motor  is  gener- 
ally used  for  driving  machine  tools  ? 

A.  The  shunt-wound  motor,  because  it  naturally 
runs  at  nearly  constant  speed  at  all  loads. 

Q.  Suppose,  as  with  a  lathe,  we  wish  to  get 
several  different  speeds,  how  is  this  accomplished  ? 

A.   By  a  regulating  rheostat  or  controller. 

Q.  What  is  the  gain,  in  size  of  wire  used  on 
the  line,  if  we  employ  a  220-volt  system  instead 
of  a  110-volt  system? 

A.  The  220-volt  system  requires  but  one-quarter 
the  weight  of  copper  in  the  line. 

Q.   Do  any  disadvantages  occur  to  you  ? 

A.  The  220-volt  line  and  motor  are  a  little 
*  For  a  description  of  these  types  see  page  300. 


STEAM    ENGINEERS   AND    ELECTRICIANS.  31 

more  difficult  to  insulate  from  the  earth,  and  they 
are  therefore  slightly  more  liable  to  cause  trouble 
from  leakage-currents  and  accidental  shocks. 

Q,  Is  the  shock  from  220  volts  dangerous  ? 

A.  Not  unless  taken  by  a  person  in  exceedingly 
delicate  health. 

Q,   Is  the  shock  from  550  volts  dangerous  ? 

A.  It  is  exceedingly  severe,  although  rarely,  if 
ever,  fatal. 

Q.  What  determines  the  size  of  wire  to  be  used 
for  connecting  a  generator  and  motor  ? 

A.  The  power  to  be  transmitted,  the  pressure 
used,  the  distance,  and  the  permissible  loss  in 
pressure. 

Q.  What  determines  the  allowable  loss? 

A.  The  variation  in  speed  of  the  motor,  between 
no  load  and  full  load,  which  you  are  willing  to 
allow. 

Q.  Even  with  no  loss  of  pressure  in  the  line, 
what  variation  of  speed  would  you  expect  with 
the  average  small  motor  ? 

A.  About  3  per  cent. 

Q.  How  would  you  calculate  the  size  of  wire, 
having  given  the  power,  pressure,  distance,  and 
permissible  loss  ?  . 

A.  See  "Roper's  Engineers'  Handy-Book," 
pages  67,  717,  718. 


32  eoper's  catechism  for 

LUBRICATION. 

Q.  What  is  the  object  of  a  lubricant? 

A.  To  diminish  friction  by  interposing  a  thin 
film  between  the  revolving  or  sliding  surfaces. 

Q.  Does  any  lubricant  have  any  tendency  to 
improve  a  bearing  ? 

A.  No;  it  simply  keeps  the  surfaces  apart, 
diminishes  friction  and  prevents  overheating. 

Q.  What  are  the  requirements  for  a  good  lubri- 
cant ? 

A.  It  must  have  sufficient  body  to  keep  the 
surfaces  apart,  but  must  be  as  fluid  as  possible 
consistent  with  this  requirement.  It  must  have 
the  smallest  possible  friction,  must  not  gum  or 
corrode;  it  must  have  a  high  flashing-point,  and 
must  remain  fluid  at  the  lowest  temperature  at 
which  it  will  be  used. 

Q.  W^hat  would  you  use  for  slow  speeds  and 
heavy  pressures  on  the  bearings  ? 

A.   Graphite,  soapstone,  tallow,  or  grease. 

Q.  What  is  an  oib  separator  and  on  w^hat  prin- 
ciple does  it  operate  ? 

A.  A  device  for  separating  the  oil  from  the 
steam  coming  from  the  exhaust  of  an  engine. 
The  principle  on  which  it  operates  is  to  destroy 
the  momentum  of  the  oil  which  is  carried  along 
with  the  steam.     This  is  accomplished  by  baffle 


STEAM    ENGINEERS   AND    ELECTRICIANS.  33 

plates  which  alter  or  reverse  the  direction  of  flow 
of  the  steam.  The  heavy  oil  particles  are  thus 
thrown  against  the  plates  and  are  given  time  to 
fall  under  the  action  of  gravity  into  a  chamber 
from  which  they  may  be  afterward  drawn  off. 

MEASUREMENT  OF  POWER. 

Q.  What  are  three  common  methods  of  measur- 
ing power  ? 

A.  By  means  of  the  steam-engine  indicator,  by 
electrical  methods,  and  by  the  Prony  brake  or 
some  other  form  of  dynamometer. 

Q.  Which  is  the  most  accurate  ? 

A.  Whenever  the  electrical  method  can  be  ap- 
plied it  is  the  quickest  and  most  accurate. 

Q.  How  would  you  determine  by  the  indicator 
method  the  power  used  by  a  certain  tool  ? 

A.  By  indicating  the  engine  with  the  tool  run- 
ning and  without  it.  The  difference  in  the  power 
shown  by  the  two  cards  gives  the  power  used  by 
the  tool. 

Q.  Is  this  method  accurate  ? 

A.  Not  if  the  power  used  by  the  tool  is  small 
compared  to  the  power  of  the  engine.  In  this 
case  it  is  like  trying  to  weigh  a  fly  on  a  platform 
scale,  by  weighing  a  man  on  the  scale  with  the  fly, 
and  then  weighing  the  man  without  the  fly  and 
subtracting  one  weight  from  the  other. 
3 


34  eoper's  catechism  for 

Q.  What  instruments  would  you  require  for  the 
electrical  method,  if  direct  currents  were  used  ? 

A.  An  amperemeter  and  voltmeter  of  proper 
range  or  a  wattmeter,  though  the  latter  is  much 
less  commonly  at  hand. 

Q.  How  Avould  you  measure  the  power  used  in 
operating  a  tool  driven  by  a  direct-current  electric 
motor  ? 

A.  I  would  measure  the  electrical  pressure 
betw^een  the  two  terminals  of  the  motor  by  con- 
necting to  the  terminals  a  voltmeter  of  suitable 
range;  I  would  at  the  same  time  find  what  current 
was  supplied  to  the  motor  by  connecting  an  am- 
meter in  the  circuit  suppling  the  motor;  I  would 
take  several  readings  of  both  instruments  and 
would  multiply  the  average  reading  of  the  volt- 
meter in  volts  by  the  average  reading  of  the  am- 
meter in  amperes;  this  product  I  would  divide 
by  746,  and  the  quotient  would  be  the  electrical 
horse-power  supplied  to  the  motor;  then  I  would 
throw  off  the  belt  betw^een  the  motor  and  tool  and 
repeat  the  measurement  above  so  as  to  get  the 
horse-power  used  by  the  motor  when  running 
idle;  subtracting  this  from  the  total  power  sup- 
plied to  the  motor  would  give  the  power  used  by 
the  tool. 

Q.  "Will  this  method  be  correct  if  the  motor  is 
of  the  alternating  current  type  ? 


STEAM    ENGINEERS    AND    ELECTRICIANS.  35 

A.  No;  for  the  product  of  volts  and  amperes 
does  not  give  the  power.  In  this  case  a  watt- 
meter must  be  used. 

Q.   Describe  the  Prony  brake. 

A.  The  Prony  brake  consists  of  two  or  more 
blocks    of    wood    at-     ^        » 

tached  to  a  lever  arm,    j* — ^™V 

and  so  arranged  that    3(^^31== © — = 

they  can  be  clamped   v — 9 

more  or  less  tightly  to 

a  pulley  or  shaft,  the 

power  transmitted  by  which  it  is  desired  to  measure. 

Q.   How  is  the  powder  measured  ? 

A.  When  the  blocks  are  clamped  to  the  pulley 

or  shaft  the  tendency  is  for  the  Prony  brake  to 

revolve  with  the  shaft,  but  weights  are  put  in  the 

pan   hanging  from   the   end    of    the   brake-arm, 

until  this  tendency  is  balanced  and  the  arm  stands 

horizontal.      The  number  of   revolutions,  R,  the 

weight,  W,  and  the  length,  L,  from  the  center  of 

the  shaft  to  the  point  of  the  lever  to  which  the 

weight  pan  hangs,  are  noted.     The  horse-power  is 

calculated  from  the  formula — 

^                          WXLXRXQ-28 
Horse-power  = ^^^ , 

or  if  the  distance  L  is  made  5'  3'',  the  formula 
WX  R 


becomes,  Horse-power  = 


1000 


36  roper's  catechism  for 

Q.  AVhat  may  be  substituted  for  the  pan  and 
weights  ? 

A.  A  spring  balance,  the  average  of  its  read- 
ings being  used. 

Q.   What  is  a  dynamometer  ? 

A.  Any  instrument  used  to  measure  power,  as, 
for  example,  the  Prony  brake. 

Q.  For  what  purpose  is  a  spring  dynamometer 
used  ? 

A.  For  measuring  the  power  required  to  propel 
vehicles,  such  as  carriages,  street-cars,  or  railway 
coaches. 


STEAM    ENGINEERS    AND    ELECTRICIANS.  37 

HEAT,  FUEL,  AIR,  W  ATER,  AND  STEAM. 

HEAT. 

Q.  What  is  heat? 

A.  Heat  is  a  form  of  energy.  In  any  body  its 
molecules  are  in  a  state  of  incessant  oscillating 
motion,  and  the  energy  of  these  moving  molecules 
or  particles  of  the  body  is  the  heat  of  that  body.* 

Q.  What  is  temperature,  and  how  does  it  differ 
from  heat  ? 

A.  Temperature  is  a  measure,  not  of  the  heat 
in  a  body,  but  of  the  tendency  of  that  body  to 
give  up  its  heat  to  other  bodies.  Two  bodies 
may  be  at  the  same  temperature  and  yet  possess 
very  different  quantities  of  heat.  For  example, 
a  cubic  inch  of  iron  and  a  cubic  foot  of  iron  may 
both  be  put  in  the  same  oven,  and  after  remaining 
there  for  a  considerable  time  they  would  be  at  the 
same  temperature  as  would  be  shown  by  a  ther- 
mometer. But  the  cubic  foot  of  iron  has  1728 
times  as  many  heat-units  in  it  as  the  cubic  inch,  as 
could  be  proved  by  putting  them  in  equal  quanti- 
ties of  water,  and  noting  to  what  temperature  the 
water  is  raised  in  each  case.  According  to  the 
molecular  theory  of  the  structure  of  matter  a 
higher  temperature  means  that  the  molecules  of 

*  For  the  explanation  of  the  molecular  theory  of  matter, 
see  "  Roper's  Engineers'  Handy-Book,"  page  611. 


38  roper's  catechism  for 

the  body  are  moving  more  rapidly.  They,  there- 
fore, will  communicate  motion  to  surrounding 
bodies  the  more  readil}^,  and  this  is  the  reason 
that  bodies  at  high  temperatures  give  up  heat  to 
those  at  the  lower  temperatures.  A  lower  tem- 
perature means  that  the  velocity  of  the  molecules 
is  less,  and  as  the  temjoerature  gets  lower  and 
lower  their  velocity  would  become  smaller  and 
smaller  until  a  temperature  is  reached  at  which 
their  velocity  is  zero,  that  is,  they  are  at  rest. 
This  temperature  is  known  as  the  absolute  zero  of 
temperatures. 

Q.  How  is  temperature  measured  ? 

A.   By  means  of  a  thermometer. 

Q.  How  is  a  thermometer  usually  made  ? 

A.  A  thermometer  consists  usually  of  a  small 
hollow  glass  tube  with  a  bulb  at  its  lower  end. 
The  air  having  been  exhausted  from  the  tube  it  is 
partially  filled  with  mercury  and  sealed.  The 
tube  is  placed  in  melting  ice  and  the  position  of 
the  top  of  the  mercury  column  marked  on  the 
glass.  The  same  thing  is  done  with  the  tube 
placed  in  boiling  water.  The  distance  between 
these  two  marks  is  divided  into  a  certain  number 
of  equal  parts,  according  to  which  scale  is  used. 

Q.  What  are  the  three  thermometer  scales  in 
common  use  ? 

A.  The  Fahrenheit,  Centigrade,  and  Reaumur. 


STEAM    ENGINEERS   AND    ELECTRICIANS. 


39 


COMPARISON  OF  FAHRENHEIT,  CENTIGRADE,  AND 
REAUMUR  SCALES. 


CENT. 

"Drill  {•r./Y-   t^,^i'ti+       4  AA    _^.^ 

FAHR. 
?1? 

REAU. 

xsoiiing-point   XvO  ^^^ 

"~~~  qQ  Jt>oiiing-point 

of  water. 

200 

of  water. 

90  — 

190 

180 

—  70 

80  — 

170- 

—  60 

70  — 

160 

150 

140 

60  — 

—  50 

150 

so- 

 180 

—  40 

lo — 

110 

-100 

—  zo 

50  — 

90 

80 

—  20 

20  — 

70 

60 

f  A  

—  10 

lu  — 

40 

Freezing-point.       0  ■ 

OX,  

^— —     Q  Freezing-point. 

-10  — 

to 

10 

0 

10 

—10 

-20  — 

20 

-30— 

20 

TVTpjTPnTTT  fTPPr^fia     —  M£^ 

° 

ATiOJL^Ul  J'    iiCC/iC&«    '^••li  ^^^^^ 

40  roper's  catechism  for 

Q.  Where  is  the  Fahrenheit  scale  used  ? 

A.  The  Fahrenheit  scale  is  used  in  England, 
Canada,  and  in  the  United  States. 

Q.  What  is  the  difference  between  Fahrenheit's, 
Centigrade,  and  Reaumur' s  scales  ? 

A.  Fahrenheit's  zero  is  32°  below  freezing,  Ijoil- 
ing-point  of  water,  212°;  Centigrade  zero  is  at 
freezing,  boiling-point,  100°;  Reaumur's  zero  is  at 
freezing,  boiling-point,  80°.  Hence,  180  Fahren- 
heit degrees  are  equal  to  100  Centigrade  degrees 
or  80  Reaumur  degrees,  or  9  Fahrenheit  degrees 
are  equal  to  5  Centigrade  or  4  Reaumur  degrees. 

Q.  What  are  fixed  temperatures  ? 

A.  One  the  melting-point  of  ice,  and  the  other 
the  boiling-point  of  pure  water. 

Q.   Why  do  you  call  these  fixed  temperatures  ? 

A.  Because  it  is  impossible  to  raise  the  tempera- 
ture of  ice  above  32°  Fahr.,  and  no  amount  of 
heat  will  raise  boiling  water  above  a  temperature 
of  212°  Fahr.,  if  contained  in  an  open  vessel. 

Q.  Does  the  thermometer  indicate  the  amount 
of  heat  in  any  body  ? 

A.   No;  only  the  changes  in  temperature. 

Q.  To  how  high  temperatures  can  the  mercurial 
thermometer  be  used  ? 

A.  To  about  600°  Fahr.  At  about  675°  mer- 
cury vaporizes. 

Q.  What  method  is  adopted  to  determine  tern- 


STEAM    ENGINEERS   AND    ELECTRICIANS.  41 

peratures  so  high  that  no  thermometer  can  give  a 
rehable  result,  as,  for  example,  the  temperature 
in  a  blast  furnace  ? 

A.  We  take  a  body,  such  as  platinum,  and 
place  a  mass  of  this  metal  in  the  blast  furnace, 
and  when  the  mass  has  acquired  the  temperature  of 
the  furnace  we  transfer  it  to  a  vessel  containing  a 
,,  known  weight  of  water.  We  can  then  observe 
the  rise  of  temperature  by  means  of  an  ordinary 
thermometer,  and  from  this  and  the  weight  of  the 
platinum  and  its  specific  heat  (.0324)  we  can 
calculate  the  temperature. 

Q.  What  is  specific  heat  ? 

A.  Specific  heat  of  a  substance  is  an  expression 
for  the  quantity  of  heat  in  any  given  weight  of  it 
at  certain  temperatures.  It  is  the  number  of 
heat-units  necessary  to  raise  the  temperature  of 
1  pound  of  the  substance  1  degree. 

Q.  What  is  sensible  heat  ? 

A.  That  which  is  sensible  to  the  touch. 

Q.  What  is  latent  heat  ? 

A.  It  is  that  which  a  body  absorbs  in  changing 
from  a  solid  to  a  fluid  state,  called  the  latent  heat 
of  liquefaction,  or  that  which  it  absorbs  in  chang- 
ing from  the  liquid  to  the  gaseous  state,  called  the 
latent  heat  of  vaporization. 

Q.  What  is  a  unit  of  heat  ? 

A.  The  unit  of   heat   is   the   amount  of   heat 


42  roper's  catechism  for 

required  to  raise  the  temperature  of  1  pound  of 
water  1°,  or  from  32°  to  33°  Fahr. 
'  Q.  What  is  the  mechanical  equivalent  of  heat  ? 

A.  The  energy  necessary  to  raise  1  pound  778 
feet  high  ;  that  is,  778  foot-pounds  of  mechanical 
energy,  if  used  to  produce  heat,  will  be  just  equal 
to  1  heat-unit,  being  just  able  to  raise  the  tem- 
perature of  1  pound  of  water  1°  Fahr. 

Q.  How  is  heat  transferred  from  one  body  to 
another  ? 

A.  In  three  ways, — by  radiation,  by  conductioHj] 
and  by  convection.* 

Q.  What  substances  radiate  heat  most  readily  1 

A.  Those  which  absorb  it  most  readily  and 
reflect  it  the  least. 

Q.  What  color  should  the  covering  of  steam 
pipes  be  painted  ? 

A.  White,  because  white  radiates  less  than 
dark  colors. 

Q.  If  the  pipe  is  bare,  as,  for  instance,  a  copper 
pipe,  should  it  be  kept  burnished  or  dull  ? 

A.   Burnished. 

Q.  What  are  some  of  the  best  conductors  of 
heat? 

A.  Generally  speaking,  the  metals,  of  which 
silver,  copper,  and  gold  are  the  best. 

*For  full  explanation,  see  "  Eoper's  Engineers'  Handy- 
Book,  ' '  page  94. 


STEAM   ENGINEERS   AND    ELECTRICIANS.  43 

Q.  Is  there  any  similarity  between  heat  conduc- 
tivity and  electrical  conductivity  ? 

A.  Generally  speaking,  good  conductors  for 
heat  are  also  good  conductors  electrically,  although 
the  metals  do  not  stand  in  the  same  relative  order 
for  both  cases. 

Q.  What  are  some  of  the  best  non-conductors  ? 

A.  Magnesia,  mineral  wool,  hair  felt,  cork,  air 
(not  in  motion). 

Q.  To  what  practical  use  are  non-conductors  of 
heat  put  ? 

A.  To  the  covering  of  steam  pipes. 

Q.  Apart  from  the  waste  of  fuel  clue  to  loss  of 
heat  by  radiation  from  steam  pipes,  is  there  any 
other  effect  ? 

A.  Yes;  there  is  a  lowering  of  pressure  and  a 
condensation  of  steam  into  water,  which,  if  exces- 
sive, would  cause  trouble  in  an  engine. 

Q.  How  much  heat  does  a  pound  of  water 
receive  in  passing  from  a  liquid  at  212°  Fahr.  to 
avapor  at  212°? 

A.  It  receives  as  much  heat  as  would  raise  it 
966°  if  the  heat  was  sensible  instead  of  latent. 

Q.  What  is  convection  of  heat  ? 

A.  It  is  the  transfer  or  diffusion  of  heat  in  a 
fluid  mass  by  means  of  its  particles. 

Q.  Will  water  boil  in  a  vacuum  with  less  heat 
than  under  the  pressure  of  the  atmosphere  ? 


44  roper's  catechism  for 

A.  Yes;  in  a  vacuum  of  1  pound  absolute  pres- 
sure water  boils  at  98°  to  100°. 

Q.   Does  water  give  out  heat  in  freezing  ? 

A.  Yes;  water  in  freezing  gives  142  heat- 
units. 

Q.  AVhat  is  a  thermal  unit? 

A.  It  is  the  quantity  of  heat  required  to  raise  1 
pound  of  water  1°,  the  water  being  at  its  maxi- 
mum density  (=39°  Fahr. ).  It  is  also  called  a 
British  thermal  unit,  and  is  abbreviated  B.  T.  U. 

COMBUSTION  AND  FUELS.  '       ■ 

Q.  What  is  combustion  ? 

A.  Combustion  is  a  chemical  process  which 
takes  place  rapidly,  in  which  the  one  or  more  of 
the  elements  which  make  up  the  combustible  body 
combines  with  the  oxygen  of  the  air.  Briefly, 
combustion  is  a  rapid  oxidation  accompanied  by 
flame  or  fire. 

Q.  What  is  smoke  ? 

A.  Smoke  is  the  result  of  imperfect  combustion, 
and  its  appearance  is  due  to  minute  unburned 
particles  in  the  air. 

Q.  What  is  necessar}^  to  produce  complete  com- 
bustion ? 

A.  We  must  have  sufficient  air,  must  mix  the 
combustible  thoroughly  with  the  air,  and  must 
maintain  the  combustible  and  air  mixed  with  it 


STEAM    ENGINEERS   AND    ELECTRICIANS.  45 

at  a  temperature  above  the  igniting-point  of  the 
combustible. 

Q.  What  is  the  meaning  of  the  term  fuel  ? 

A.  Fuel  is  used  to  denote  substances  that  may 
be  burned  with  air  rapidly  enough  to  produce 
sufficient  heat  for  commercial  purposes. 

Q.  What  sort  of  substances  does  fuel  consist  of  ? 

A.  Of  vegetable  substances  or  the  products  of 
their  decomposition. 

Q.  What  are  some  of  the  principal  fuels  used 
in  the  production  of  steam  ? 

A.  Coal,  coke,  wood,  petroleum,  natural  gas, 
peat,  and  vegetable  refuse  of  various  kinds. 

Q.  What  are  the  elementary  substances  which 
are  found  in  most  fuels  ? 

A.  Carbon,  hydrogen,  oxygen,  nitrogen,  and 
small  quantities  of  other  elements. 

Q.  What  is  the  chief  constituent  of  coal  ? 

A.  Carbon. 

Q.  How  much  carbon  does  good  coal  contain  ? 

A.  Anthracite  contains  about  90  per  cent. 

Q.  Are  there  any  other  elements  in  coal  except 
carbon  ? 

A.  Yes  ;  hydrogen,  nitrogen,  and  sulphur  in 
small  quantities. 

Q.  How  much  heat  does  1  pound  of  pure  car- 
bon yield  in  burning  ? 

A.   14,000  units,  approximately. 


46 


roper's  catechism  for 


TABLE 

OF     TEMPEEATUEES     EEQUIEED     FOE     THE     IGNITION     OF 
DIFFEEENT   COMBUSTIBLE   SUBSTANCES. 


Substances. 

Temperature 
of  Ignition. 

Remarks. 

Phosphorus,       

140° 

Melts  at  110°. 

Bisulphide  of  carbon  vapor, 

300° 

Melts  at  130°. 

Fuhuinatiijg  powder,     .   .    . 

374° 

Used  in  percussion  caps. 

Fuhuiiiate  of  mercury,  .   .   . 

392° 

According  to  Legue  and 
Champion. 

Equal  parts  of   chlorate  of 
potash  and  sulphur,        .    . 

395° 

Sulphur,       

400° 

Melts,  280° ;  boils,  850°. 

Gun-cotton, 

428° 

According  to  Legue  and 
Champion. 

Nitro-glycerine, 

494° 

"            "            " 

Eifle-powder,     

550° 

"            "            " 

Gunpowder,  coarse,     .... 

563° 

Picrate  of  mercury,  lead,  or 

iron,  

565° 

11           ti           <i 

Picrate  powder  for  torpedoes, 

570° 

«            «            (( 

Picrate  powder  for  muskets, 

576° 

«            <(            11 

Charcoal,   the  most  inflam- 

mable willow  used  for  gun- 

powder,     

580° 

According  to  Pelouse 
and  Fremy. 

Charcoal  made  by  distilling 

wood  at  500°, 

660° 

<(            i<            (< 

Charcoal  made  at  600°,  .   .   . 

700° 

11           It            (i 

Picrate  powder  for  cannon,  . 

716° 

Very  dry  wood,  pine,     .   .   . 

800° 

Very  dry  wood,  oak,   .... 

900° 

Charcoal  made  at  800°,   .   .   . 

900° 

It  will  be  seen  by  the  above  table  that  the  most  combust- 
ible substances,  generally  considered  very  dangerous,  will 
only  ignite  by  heat  alone  at  a  high  temperature,  so  that  for 
their  prompt  ignition  it  requires  the  actual  contact  of  a 
spark. 


STEAM    ENGINEERS    AND    ELECTRICIANS.  47 

Q.  How  many  heat-miits  does  1  pound  of  good 
coal,  containing  90  per  cent,  of  carbon,  produce  ? 

A.   It  produces  in  burning  about  13,000  units. 

Q.  What  is  the  mechanical  equivalent  of  13,000 
units  ? 

A.  10,114,000  foot-pounds, — that  is  to  say, 
10,114,000  pounds  raised  1  foot  high. 

Q.  How  much  air  does  it  require  to  burn  1 
pound  of  coal? 

A.  About  155  cubic  feet. 

Q.  How  much  air  does  it  require  to  burn  100 
pounds  of  coal  ? 

A.  About  15,500  cubic  feet  of  air. 

Q.  What  is  the  difference  between  anthracite 
and  bituminous  coal  ? 

A.  Anthracite  coal  is  nearly  all  carbon,  having 
only  about  10  per  cent,  of  other  matter,  while 
bituminous  coal  has  from  15  to  50  per  cent,  of 
other  materials  besides  pure  carbon. 

Q.  What  is  the  relative  fuel  value  of  anthracite 
coal  and  wood  ? 

A.  A  pound  of  coal  is  equal  to  about  2\  pounds 
of  wood. 

Q.  What  is  coke? 

A.  Coke  is  what  is  left  of  coal  after  the  volatile 
ingredients  have  been  driven  off  by  distillation, 
as  in  gasworks;  or  by  partial  combustion,  as  in 
coke-ovens. 


48 


ROPER  S    CATECHISM    FOR 


TABLE 

SHOWING  THE  TOTAL  HEAT  OF  COMBUSTION 

OF  VARIOUS   FUELS. 


Sort  of  Fuel. 


Equiva- 
lent in 
pure 
carbon. 


Evapora- 
tive power 
in  lbs.  water 
from  212° 
Fahr. 


Total  heat  of 

combustion 

in  lbs.  water 

heated  1° 

Fahr. 


Charcoal, 

Charred  peat, 

Coke— good, 

Coke — mean, 

Coke — bad, 

Coal: 
Anthracite,    ...,,... 
Hard  bituminous — hardest,   . 
Hard  bituminous — softest,     . 

Coking  coal, 

Cannel  coal, 

Long-flaming  splint  coal,    .    . 
Lignite,      

Peat: 

Perfectly  air-dry, 

Containing  25  per  cent,  water. 

Wood  : 

Perfectly  air-dry, 

Containing  25  per  cent,  water, 


0.93 
0.80 
0.94 

0.88 
0.82 


1.05 
1.06 
0.95 
1.07 
1.04 
0.91 
0.81 


0.66 


0.50 


14.00 
12.00 
14  00 
13.20 
12.30 


15.75 
15.90 
15.25 
16.00 
15.60 
13.65 
12.15 


10.00 
7.75 


7.50 

5.80 


13,500 
11,600 
13,620 
12,760 
11,890 


15,225 
15,370 
13,775 
15,837 
15,080 
13,195 
11,745 


9,660 
7,000 


7,245 
5,600 


I 


Remark. — In  a  boiler  of  fair  construction,  a  pound  of 
coal  will  convert  9  pounds  of  water  into  steam.  Each 
pound  of  this  steam  will  represent  an  amount  of  energy,  or 
capacity  for  performing  work,  equivalent  to  746,666  foot- 
pounds, or  for  the  whole  9  pounds,  6,720,000  foot-pounds. 
In  other  words,  1  pound  of  coal  has  done  as  much  work  in 
evaporating  9  pounds  of  water  into  9  pounds  of  steam  as 
would  lift  300  tons  10  feet  high. 


STEAM    ENGINEERS   AND    ELECTRICIANS.  49 

Q.  Next  to  carbon,  which  of  the  constituents  of 
coal  is  the  greatest  heat  producer  ? 

A.   Hydrogen. 

Q.  What  is  the  number  of  heat-units  produced 
by  burning  a  pound  of  hydrogen  ? 

A.   62,000  British  thermal  units. 

Q.  Why  do  some  coals  have  a  greater  heat-pro- 
ducing value  per  pound  than  does  pure  carbon  ? 

A.   Because  they  are  so  rich  in  hydrogen. 

Q.  What  is  meant  by  the  term  ' '  free  hydrogen ' ' 
in  connection  with  coal  ? 

A.  In  all  fuel  containing  carbon,  hydrogen,  and 
oxygen,  the  proportion  of  hydrogen  may  be  equal 
to  or  greater,  but  never  less,  than  that  required  to 
form  .water  with  the  oxj^gen.  It  is  only  the 
hydrogen  in  excess  of  this  which  is  available  as  a 
source  of  heat,  and  this  is  called  free  hydrogen. 
The  hydrogen  existing  in  combination  with  oxygen 
in  the  state  of  water,  so  far  from  contributing  to 
the  actual  amount  of  heat  produced,  must  be 
,  evaporated  at  the  expense  of  the  heat  developed 
by  the  combustion  of  the  carbon. 

Q.  How  does  the  heat-producing  value  of  petro- 
leum compare  with  that  of  coal  ? 

A.  It  is  about  ^  greater,  pound  for  pound. 

Q.  What  are  some  of  the  advantages  of  using 
petroleum  as  a  fuel  ? 

A.  It  gives  a  steadier  fire,  is  more  easily  hand- 
4 


50  roper's  catechism  for 

led,  makes  no  ashes  and  little  smoke,   and  does 
not  take  up  so  much  space. 

Q.  What  determines  the  advisability  of  using 
petroleum  rather  than  coal  at  a  certain  place  ? 

A.  The   most   important   point  is  the  relative  '. 
cost  of  the  two. 

Q.  How  many  pounds  of  water  can  be  evapo- 
rated by  a  pound  of  coal  ? 

A.  This  depends  upon  the  kind  of  boiler  used 
and  its  condition,  and  also  on  the  kind  of  coal, 
the  amount  varying  from  6  to  12  pounds.  Under 
most  favorable  conditions  an  evaporation  of  over 
13  pounds  of  water  per  pound  of  combustible 
has  been  secured. 

Q.  What  is  the  meaning  of  the  term  ' '  com- 
bustible ' '  used  in  connection  with  coal ;  for 
example,  in  the  expression,  ' '  pounds  of  water 
evaporated  per  pound  of  combustible  ?  ' ' 

A.  The  amount  of  ' '  combustible  "  in  a  quantity 
of  coal  is  found  by  subtracting  from  the  original 
weight  of  the  coal  the  weight  of  the  water  in  the 
coal  plus  the  weight  of  the  ash  produced  when 
it  is  burned. 

AIR  AND  OTHER  GASES. 

Q.  What  are  the  three  most  important  element- 
ary gases — that  is,  the  three  most  important 
elements  existing  naturally  in  the  gaseous  state  ? 


STEAM    ENGINEERS   AND    ELECTRICIANS.  51 

A.   Oxygen,  nitrogen,  and  hydrogen. 

Q.  What  are  some  of  the  most  important  char- 
acteristics of  oxygen? 

A.  It  is  colorless,  tasteless,  and  odorless.  It 
supports  combustion,  which  process  is  the  chemi- 
cal combination  of  the  oxygen  of  the  air  with  the 
burning  substance.  It  is  necessary  for  the  respi- 
ration of  animals  and  clearing  the  blood  of  im- 
purities. It  combines  readily  with  nearly  all  other 
chemical  elements. 

Q.  What  is  iron  rust  ? 

A.  A  combination  of  iron  with  oxygen,  known 
as  oxide  of  iron. 

Q.  What  relation  does  rusting  bear  to  com- 
bustion ? 

A.  Rusting  is  slow  oxidation;  combustion  is 
rapid  oxidation. 

Q.  What  are  some  of  the  characteristics  of 
nitrogen  ? 

A.  It  is  also  colorless,  tasteless,  and  odorless. 
Unlike  oxygen,  it  does  not  combine  readily  with 
other  elements;  it  will  not  burn  nor  support  com- 
bustion; mixed  with  oxygen  it  forms  atmospheric 
air,  its  function  being  to  dilute  the  oxygen. 

Q.  Give  some  of  the  qualities  of  hydrogen. 

A.  It  is  colorless  and  tasteless  and  odorless 
when  pure.  It  is  the  lightest  of  known  substances, 
being   only   one-sixteenth   as   heavy   as   air.     It 


52  roper's  catechism  for 

unites  most  readily  with  oxygen,  combining  with 
it  to  form  water  in  the  proportion  of  1  part  by 
weight  of  hydrogen  to  8  parts  of  oxygen.  It 
burns  in  air  with  a  bluish  flame. 

Q.  Of  what  does  the  atmosphere  consist  ? 

A.  Of  oxygen  and  nitrogen  mixed  together  (not 
chemically  combined),  in  the  ratio  of  about  1 
part  by  volume  of  oxygen  to  4  parts  of  nitrogen. 

Q.  How  far  from  the  earth's  surface  is  the 
atmosphere  supposed  to  extend  ? 

A.   At  least  45  miles. 

Q.  Is  its  density  uniform — that  is,  is  it  the 
same  at  different  heights  ? 

A.  No;  it  is  less  dense  as  we  go  farther  from 
the  earth's  surface. 

Q.   Does  air  have  any  weight  ? 

A.  Yes;  a  cubic  foot  at  the  level  of  the  sea 
weighs  about  yfo-  of  a  pound. 

Q.  What  is  atmospheric  pressure,  so-called  ? 

A.  It  is  the  pressure  exerted  on  all  bodies  by 
the  air,  owing  to  its  weight.  Since  all  gases  trans- 
mit a  pressure  equally  in  all  directions,  and  since 
air  has  weight,  it  follows  that  any  square  inch  of 
surface  has  a  pressure  exerted  on  it  equal  to  the 
weight  of  a  column  of  air  1  square  inch  in  cross- 
section  and  of  45  miles  or  more  in  length. 

Q.  How  much  is  this  weight,  or,  in  other  words, 
how  much  is  the  atmospheric  pressure? 


STEAM   ENGINEERS   AND    ELECTRICIANS. 


53 


TABLE 

SHOWING     APPROXIMATE     INCREASE     IN     BULK     OF 
DUE   TO  INCREASE   OF  TEMPERATURE,  AT 
ATMOSPHERIC  PRESSURE. 


Fahrenheit. 

Temp.  32  (Freezing-point) 

"   38 

"   34 

"35       .... 

Bulk    Fah 
.  1000   Tei 

1002 

1004 

1007 

1009 

1012 

1015 

1018 
.  1021 

1023 
.  1025 

1027 

1030 
.  1032     ' 

1034 

1036 

1038 

1040 

1043     ' 

1045 

1047 

1050 

1052 

1055      ' 

1057 

1059 

1062 
.  1064 

1066 
.  1069     ' 
.  1071 

1073 

1075 

1077 

1080 

1082 

1084 

1087 

1089 

1091 

1093 

1095 

1097 

renheit. 

up  75   ... 

Bulk 
1099 

76  (Summer  heat)  . 

'   77 

'   78   

1101 
1104 
1106 

"     36 ...  : 

"   37 

'   79  ...  . 

'   80  ...  . 

1108 
1110 

"   38     

'   81   .  .  . 

1112 

"   39 

'   82  ...  . 

1114 

"   40   

'83 

1116 

«'   41 

'   84  ...  . 

1118 

"   42 

'   85  ..."  . 

1121 

"43      

'   86 

1123 

"44         .... 

'   87 

ll'?5 

"   45   

'   88  .  .  . 

1128 

"46         ... 

'   89 

1130 

"   47   

'   90  ...  . 

1132 

"   48   

'   91 

1134 

"   49 

'   92  ...  . 
'   93   .  ,  . 

1136 

"   50   

1138 

"51       .... 

'   94 

1140 

"   52 

"   53 

"   54 

'   95 . 

'   96  (Blood  heat)  .  . 

'   97 

'   98   

1142 
1144 
1146 

"   55 

1148 

"   56  (Temperate)  .  . 

'   99  ...  . 

1150 

'100   ... 

1152 

"   58 

'  110   ... 

1173 

"   59           .  . 

120 

1194 

"   60 

'130   ... 

1215 

"   61 

'  140  ...  . 

1235 

"   62 

"   63 

"   64 

"   65 

"   66 

'  150.  ..  . 
'  160.  ..  . 
'  170  (Spirits 
'  180  ...  . 
'  190 

boil',  176) 

r55 
1275 
1295 
1315 
1334 

"   67 

'  200  ...  . 

1364 

"   68 

'  210 

1372 

'•   69 

"   70 

'  212  (Water 
'  302 

boils)  .  . 

1375 
1558 

"   71 

'392   ... 

1739 

"   72 

-  •'   73   

"   74 

'  482  ...  . 
'  572  ...  . 
'  680 

1919 

2098 
2312 

54  roper's  catechism  for 

A.  At  sea-level  and  at  32°  Fahr.  it  is  about  14.7 
pounds  per  square  inch,  or,  in  round  numbers, 
15  pounds. 

Q.  What  would  you  understand  b}^  a  pressure 
of  three  atmospheres  ? 

A.  A  pressure  of  45  pounds  per  square  inch. 

Q.  What  instrument  is  used  to  measure  atmos- 
pheric pressure  ? 

A.   The  barometer. 

Q.   How  is  it  made  ? 

A.  By  filling  a  glass  tube  about  3  feet  long  with 
mercury  and  then  inverting  the  tube,  letting  its 
open  end  rest  in  a  vessel  containing  mercury. 
The  height  of  the  top  of  the  mercury  column  in 
the  tube  is  read  by  a  graduated  scale. 

.  Q.  Why  does  the  mercury  not  run  entirely  out 
of  the  tube  into  the  vessel? 

A.  The  mercury  column  is  acted  upon  by  two 
forces;  its  weight  tends  to  make  it  run  out,  but  the 
atmosphere  pressing  on  the  surface  of  the  mercury 
in  the  vessel  resists  this  action.  The  mercury 
column  in  the  tube,  therefore,  falls  only  to  the 
point  where  the  pressure  per  square  inch  due  to 
the  weight  of  the  column  is  just  equal  to  the 
pressure  per  square  inch  exerted  by  the  atmos- 
phere. 

Q.  Will  the  reading  of  the  barometer  on  a 
mountain  be  higher  or  lower  than  at  sea-level  ? 


I 


STEAM    ENGINEEES    AND    ELECTRICIANS.  55 

A.  Lower;  for  the  atmospheric  pressure  being 
less,  it  cannot  balance  so  long  a  column  of  mer- 
cury. 

Q.  Why  does  the  mercury  column  of  the 
barometer  at  a  certain  place  stand  at  different 
heights  at  different  times  ? 

A.  Owing  to  the  presence  of  more  or  less  water, 
vapor  in  the  atmosphere  which  changes  the  weight 
per  cubic  foot  of  air,  and  consequently  alters  the 
atmospheric  pressure. 

Q.  How  can  the  height  of  a  place  above  sea- 
level  be  measured  by  the  barometer  ? 

A.  By  reading  the  barometer  at  the  given  place 
and  comparing  this  reading  with  that  taken  at 
some  known  altitude.  Roughly,  each  inch  of 
length  of  the  barometer  column  corresponds  to  a 
difference  in  level  of  1000  feet. 

Q.  Can  heights  also  be  measured  by  the  ther- 
mometer ? 

A.  Yes;  by  observing  at  what  temperature 
water  boils.  At  sea-level  it  boils  at  212°  Fahr. 
Roughly,  for  every  500  feet  rise  above  sea-level 
the  temperature  of  the  boiling-point  is  1  degree 
less.* 

Q.  What  is  the  effect  of  heat  on  air  ? 

A.  To  expand  it. 

*For  more  accurate  calculations  of  heights,  see  "Roper's 
Engineers'  Handy-Book,"  pages  121-134. 


66  roper's  catechism  for 

Q.   What  is  the  method  of  calculatmg  this  ex- 


pansion 


A.  Under  constant  ^  pressure,  for  each  degree 
Fahr.  rise  in  temperature  the  volume  of  air  ii 
increased  by  ^2"  ^^  i^^  volume  at  32°  Fahr. 


WATER. 

Q.   Of  what  is  water  composed  ? 

A.  Of  the  elementary  gases,  oxygen  and  hydro- 
gen, in  the  proportion  by  weight  of  89  parts  of 
oxygen  to  11  parts  of  hydrogen.  By  volume  the 
ratio  is  1  part  of  oxygen  to  2  parts  of  hydrogen. 

Q.   Is  pure  water  found  in  nature  ? 

A.  No;  water  has,  in  solution,  oxygen,  nitrogen, 
and  ammonia,  taken  up  from  the  air,  and  traces 
of  salts  of  many  minerals.  It  may  also  contain 
organic  impurities  resulting  from  the  decomposi- 
tion of  animal  or  vegetable  matter. 

Q.  Water  is  taken  as  the  standard  for  specific 
gravity  of  liquids,  but  is  its  specific  gravity 
always  uniform  ? 

A.  No;  the  weight  of  a  cubic  foot  of  water 
depends  upon  its  purity.  The  presence  of  any 
salts  in  solution  makes  it  heavier  as  in  the  case  of 
sea  water. 

Q.  Does  the  temperature  of  water  have  any 
effect  upon  its  specific  gravity  ? 

A.   Yes;  at  about  39.2°  Fahr.  pure  water  is  at 


I 


STEAM    ENGINEERS    AND    ELECTRICIANS.  57 

its  greatest  density,  that  is,  weighs  most  per  cubic 
foot.  Above  this  temperature  it  is  less  dense; 
below  this  point  it  also  becomes  less  dense  until 
at  32°  it  solidifies  into  ice. 

Q.  Under  what  conditions,  then,  is  water  taken 
as  the  standard  for  specific  gravities  ? 

A.  With  the  understanding  that  the  water  is 
pure  and  is  at  a  temperature  of  39.2°  Fahr. 

Q.  In  what  three  physical  states  or  forms  does 
water  exist  ? 

A.  As  ice,  water,  and  steam. 

Q.  How  do  the  weights  of  a  cubic  foot  of  ice, 
water,  and  steam  compare  ? 

A.  A  cubic  foot  of  ice  weighs  about  57  pounds; 
of  water,  about  62 J-  pounds;  and  of  steam,  at  5 
pounds  gauge  pressure,  yl-g-  pounds,  and  at  100 
pounds  gauge  pressure,  y^^-g-  pounds. 

Q.  What  is  necessary  to  change  from  one  of 
these  forms  to  the  other? 

A.  Merely  the  application  or  withdrawal  of  heat. 

Q.  Is  water  a  good  conductor  of  heat  ? 

A.  No. 

Q.  Is  it  a  good  conductor  of  electricity  ? 

A.   Not  if   reasonably  pure.     The  addition  of 
some  soluble  metallic  salt,  like  sodium  carbonate 
or  of  sulphuric  acid,  makes  it  a  good  electrical 
conductor. 
!l       Q.  What  are  some  of  its  other  properties  ? 


58  eoper's  catechism  for 

A.  It  is  tasteless,  odorless,  and  colorless,  and  a 
solvent  for  most  gases  and  a  vast  number  of 
liquids  and  solids. 

Q.   At  what  temperature  does  water  boil  ? 

A.  This  depends  upon  its  purity  and  upon  the 
atmospheric  pressure.  Reasonably  pure  water  at 
the  sea-level  boils  at  212°  Fahr. 

Q.  On  a  mountain  3000  feet  above  sea-level,  at 
about  what  temperature  would  you  expect  water 
to  boil? 

A.  At  about  206°  Fahr.,  as  for  every  500  feet 
above  sea-level  the  boiling-point  drops  approxi- 
mately 1  degree. 

Q.  How  does  the  boiling-point  of  salt  water 
compare  with  that  of  fresh  water  ? 

A.   It  is  higher. 

Q.  Which  will  hold  the  greater  quantity  of  a 
substance  in  solution,  hot  water  or  cold  water? 

A.  This  depends  on  the  nature  of  the  substance. 
Salts  of  lime  are  less  soluble  in  hot  water  and, 
therefore,  if  they  exist  in  a  natural  water  will  be 
deposited  when  the  water  is  heated  to  a  high 
temperature. 

Q.  How  does  the  specific  heat  of  water  com-- 
pare  with  that  of  other  substances  ?  flj 

A.  It  is  greater  than  that  of  nearly  all  other^ 
and  it  is  for  this  reason  that  it  is  chosen  as  tlie 
standard  for  specific  heats. 


STEAM    ENGINEERS   AND    ELECTRICIANS.  59 

Q.  What  is  the  specific  heat  of  ice  ? 

A.  About  .5,  or  half  that  of  water. 

Q.  How  many  units  of  heat  are  necessary  for 
melting  1  pound  of  ice  ? 

A.  About  142. 

Q.  How  can  water  be  decomposed  into  its  con- 
stituents— oxygen  and  hydrogen  ? 

A.  By  passing  an  electric  current  through  it.* 

Q.  Can  we  recombine  these  two  gases  to  form 
water  ? 

A.  Yes;  by  burning  the  hydrogen  in  a  jet  in  a 
vessel  containing  the  oxygen. 

Q.  What  is  the  specific  gravity  or  density  of  a 
body? 

A.  Its  weight  per  unit  volume;  and  since  the 
unit  volume  used  by  physicists  is  the  cubic  centi- 
meter the  specific  gravity  or  densitj^  is  the  weight 
(in  grams)  per  cubic  centimeter. 

Q.  What  would  be  the  specific  gravity  of  pure 
water  ? 

A.  1,  because  the  weight  of  a  cubic  centimeter 
of  pure  water  is  1  gram. 

Q.  What  is  taken  as  the  standard  of  specific 
gravities  ? 

A.  Water,  because  its  specific  gravity  is  1. 

Q.  How  could  you  obtain  the  specific  gravity 
of  any  liquid  ? 

*See  "Roper's  Engineers'  Handy-Book."  page  134. 


60  eoper's  catechism  for 

A.  By  weighing  equal  bulks  of  the. liquid  and' 
of  water  and  dividing  the  weight  of  the  liquid  by 
tlie  weight  of  the  water. 

Q.  How  could  you  obtain  the  specific  gravity 
of  a  solid  heavier  than  water  ? 

A.  Weigh  it  in  air;  place  it  in  a  jar  even  full 
of  water  and  catch  the  overflow  of  water  and 
weigh  it.  Divide  the  weight  of  the  body  in  air 
by  the  weight  of  the  water  it  displaces;  the  quo- 
tient will  be  the  specific  gravity. 

Q.  When  a  body  whose  specific  gravity  is 
greater  than  1,  that  is,  greater  than  that  of  water, 
is  placed  in  water,  what  occurs  ? 

A.   The  body  sinks. 

Q.   How  much  water  does  it  displace  ? 

A.  A  volume  in  cubic  feet  or  inches  equal  to 
the  volume  of  the  sinking  body. 

Q.  What  happens  if  the  specific  gravity  of  the 
bod}^  is  less  than  1  ? 

A.  The  body  floats,  sinking  only  to  a  certain 
depth  in  the  water. 

Q.   How  much  water  does  it  disi3lace  ? 

A.  Such  an  amount  as  will  weigh  the  same  as 
the  floating  body. 

Q.  What  is  meant  by  the  term  "head  "  ajoplied 
to  water? 

A.  It  means  a  difference  in  level ;  for  example, 
with  a  filled  tank  at  the  top  of  a  house,  the  upper 


STEAM    ENGINEERS   AND    ELECTRICIANS.  61 

level  of  the  water  in  the  tank  being,  say,  50  feet 
above  the  level  of  a  spigot  in  the  basement,  there 
would  be  exerted  at  the  spigot  a  pressure  equal 
in  pounds  to  the  weight  of  a  column  of  water  50 
feet  high  ;  we  should  say,  then,  that  there  was  at 
the  spigot  a  head  of  50  feet. 

Q.  With  a  head  of  100  feet,  how  would  the 
.pressure  compare  with  the  preceding  case  ? 

A.  It  would  be  double,  the  pressure  being 
strictly  proportional  to  the  head. 

Q.  What  pressure  corresponds  to  a  head  of  1 
foot? 

A.  Remembering  that  a  cubic  foot,  or  1728  cubic 
inches,  of  water  w^eighs  62.5  pounds,  it  is  easily 
calculated.  A  column  of  water  12  inches  high  by 
1  inch  square  would  contain  12  cubic  inches  and 
would  weigh  yyfg-  or  y^  of  62.5  pounds,  or  .43 
pound.  Therefore,  the  pressure  due  to  a  head  of 
1  foot  would  be  .43  pound  per  square  inch. 

Q.  When  water  flows  from  an  orifice  in  the 
bottom  of  a  tank  under  a  head,  how  can  its  velocity 
be  calculated  ? 

A.  Were  it  not  for  friction  of,  and  eddy  currents 
in,  the  water  at  the  orifice,  each  particle  of  water 
would  emerge  at  a  velocity  the  same  as  it  would 
have  if  it  were  allowed  to  drop  through  a  height 
equal  to  the  head  (the  head  in  this  case  is  the 
difference  in  level  between  the  upper  surface  of 


62  roper's  catechism  for 

the  water  and  the  orifice).  The  formula  is  v  = 
V  64. 4  h,  or  velocity  in  feet  per  second  equals  the 
square  root  of  64.4  X  the  head  in  feet.  Owing 
to  eddy  currents  set  up  at  the  orifice,  the  actual 
velocity  will  be  slightly  less  than  the  value  of  v 
obtained  from  the  formula. 

Q.  Suppose  that  you  desired  to  know  the  num- 
ber of  cubic  feet  of  water  flowing  from  an  orifice, 
how  would  you  obtain  it? 

A.  First  obtain,  as  above,  the  velocity  in  feet  per 
second,  multiply  this  by  the  area  of  the  orifice  in 
square  feet,  and  multiply  the  product  by  ■^.  The 
result  will  be  the  quantity  in  cubic  feet  per  second. 

Q.   Why  do  you  multiply  by  ^^  ? 

A.  Because  the  jet  of  water  issuing  from  the 
orifice  has  an  area  less  than  that  of  the  orifice, 
it  being  from  six-  to  eight-tenths  as  large,  accord- 
ing to  the  form  of  the  orifice. 

Q.  When  water  is  led  from  a  tank  through  a 
long  pipe  and  then  allowed  to  flow  from  the  mouth 
of  the  pipe  into  the  air,  will  the  velocity  be  the 
same  as  calculated  above  ? 

A.  No;  it  will  be  less,  owing  to  the  friction  of 
the  water  against  the  walls  of  the  pipe,  which 
causes  a  loss  of  pressure  or  loss  of  head. 

Q.   What  does  the  loss  of  pressure  depend  on  ? 

A.  The  length*of  pipe,  its  diameter,  and  the 
smoothness  of  the  interior. 


STEAM   ENGINEERS    AND    ELECTRICIANS.  63 

Q.  Is  the  loss  of  pressure  greater  as  the  pipe  is 
longer  ? 

A.  Yes;  the  loss  is  strictly  proportional  to  the 
length  of  pipe,  the  loss  for  a  length  of  200  feet 
being  double  that  for  100  feet. 

Q.  What  effect  does  increasing  the  size  of  pipe 
have  on  the  loss  of  pressure  ? 

A.  The  larger  the  pipe  the  less  the  lost  pressure. 
The  loss  of  pressure  is  proportional  to  the  length 
of  the  pipe  and  the  square  of  the  velocity,  and 
inversely  proportional  to  the  diameter  of  the 
pipe.^ 

Q.  Having  these  tables,  how  would  you  calcu- 
late the  velocity  at  which  water  escapes  from  a 
pipe  500  feet  long,  the  height  of  the  water  in  the 
tank  being  50  feet  above  the  mouth  of  the 
pipe  ? 

A.  Calculate  first  the  flow,  assuming  no  loss 
owing  to  friction;  then,  with  this  flow,  from  the 
tables  calculate  the  loss  of  head  ;  subtracting 
this  head  from  50  feet  gives  the  effective  head. 
Finally,  using  the  effective  head,  calculate  the 
velocity  of  flow. 

*  For  tables  of  the  loss  of  pressure,  see  "Eoper's  Engi- 
neers' Handy-Book,"  page  42. 


64  roper's  catechism  for 

STEAM. 

Q.  What  is  steam  ? 

A.  Steam  is  the  gaseous  form  of  water  produced 
by  the  application  of  heat  sufficient  to  raise  the 
temperature  of  the  water  to  212°  Fahr. 

Q.  What  are  the  most  prominent  properties* 
possessed  by  steam  ? 

A.  First,  its  high  expansive  force;  second,  its 
property  of  condensation;  third,  its  concealed  or 
latent  heat. 

Q.   Is  steam  in  itself  invisible  ? 

A.  Yes;  and  it  only  becomes  visible  by  loss  of 
temperature,  as  when  a  jet  is  discharged  into  the 
open  air,  and  is  then  seen  in  the  form  of  vapor. 

Q.  If  a  jet  of  steam  flowing  into  the  air  gave  a 
cloudy  appearance  close  to  the  opening,  what 
would  you  conclude? 

A.  That  the  steam  was  very  moist,  — that  is,  that 
it  was  carrying  along  with  it  a  large  quantity  of 
water  in  finely  divided  particles. 

Q.   How  is  the  condensation  of  steam  effected  ? 

A.   By  the  lowering  of  its  temperature. 

Q.  What  is  the  difference  in  volume  between 
water  and  steam  at  a  temperature  of  212° 
Fahr.  ? 

A.  1700;  that  is  to  say,  any  given  quantity  of 
water  converted  into  steam  at  the  pressure  of  the 


STEAM    ENGINEERS   AND    ELECTRICIANS.  65 

atmosphere  or  212°  Fahr.  will  present  a  volume 
1700  times  greater  than  its  original  bulk. 

Q.  What  is  dry- saturated  steam  ? 

A.  The  vapor  formed  from  water  at  a  certain 
temperature  and  pressure  and  either  remaining  in 
contact  with  the  water,  or,  if  withdrawn  from  con- 
tact with  the  water,  not  subjected  to  any  further 
heating. 

Q.  What  is  superheated  steam  ? 

A.  Dry-saturated  steam  not  in  contact  with 
water  and  raised  to  a  higher  temperature  than 
that  at  which  it  was  formed. 

Q.  How  does  ordinary  steam  differ  from  dry- 
saturated  steam  ? 

A.  It  has  minute  particles  of  water  suspended 
in  it. 

Q.  Can  steam  be  raised  to  a  very  high  tempera- 
ture? 

A,  Yes;  steam  can  be  heated  to  nearly  a  red 
heat,  but  not  while  it  is  held  in  contact  with 
water. 

Q.  Is  steam  at  ordinary  pressure  hot  enough  to 
ignite  wood  ? 

A.  Not  without  the  intervention  of  some  other 
substance,  such  as  linseed  oil,  greasy  rags,  or  iron 
turnings. 

Q.  What  do  you  understand  by  the  term  ' '  steam 
pressure  "  ? 
5 


66  roper's  catechism  for 

A.  The  elastic  force  which  steam  exerts  in  every 
direction. 

Q.  What  is  the  sensible  heat  of  steam? 

A.  The  heat  which  goes  to  raise  its  temperature, 
as,  for  example,  if  water  at  32°  Fahr.  has  heat 
applied  to  it,  its  temperature  will  rise  up  to,  but 
not  above,  212°  Fahr.  The  number  of  heat-units 
required  to  raise  1  pound  of  water  from  32°  Fahr. 
to  any  temperature  is  called  the  sensible  heat  cor- 
responding to  that  temperature. 

Q.  A¥hat  other  name  is  given  to  the  sensible 
heat  ? 

A.  The  heat  of  the  liquid  or  the  heat  in  water. 

Q.  What  is  latent  heat? 

A.  Heat  which  is  not  sensible  to  the  touch  nor 
indicated  by  the  thermometer. 

Q.   Is  there  more  than  one  latent  heat  ? 

A.  Yes;  the  latent  heat  of  liquefaction,  as,  fo] 
example,  the  heat  absorbed  when  ice  melts  into 
water;  and  the  late^it  heat  of  vaporization,  or  the 
heat  absorbed  when  water  is  changed  to  steam. 

Q.  How  may  the  existence  of  latent  heat  be 
shown  ? 

y1.  If  a  thermometer  be  placed  in  a  vessel  con- 
taining water  which  is  being  heated,  the  reading 
of  the  thermometer  increases  as  heat  is  applied 
till  it  reaches  212°,  at  which  point  the  water 
boils.     After   this,   although  heat  is  continually 


I 


STEAM   ENGINEERS    AND    ELECTEICIANS.  67 

applied,  the  thermometer  goes  no  higher.  This 
amount  of  heat  which  goes  to  change  the  physical 
state  of  water  without  changing  its  temperature 
is  called  latent  heat. 

Q.  What  is  the  latent  heat  of  vaporization  of 
water  ? 

A.  The  amount  of  heat  needed  to  change  a 
pound  of  water  into  steam. 

■  Q.  What  is  the  sum  of  the  latent  heat  of  vapor- 
ization and  the  heat  of  the  liquid,  at  any  tem- 
perature, called? 

A.  The  total  heat  corresponding  to  that  tem- 
perature. 

■  Q.   Is  the  total  heat  the  same  for  all  pressures  ? 
A.  At  atmospheric  pressure  it  is  1180,  at  100 

pounds  gauge  pressure  it  is  1217,  and  at  135 
pounds  it  is  1223.  ' 

Q.  Does  the  elasticity  of  steam  increase  with 
an  increase  of  temperature  ? 

A.  Yes,  but  not  in  the  same  ratio;  because  if 
steam  is  generated  from  water  at  a  temperature 
which  gives  it  the  pressure  of  the  atmosphere,  an 
additional  temperature  of  38°  will  give  it  a  pres- 
sure of  2  atmospheres,  and  a  still  further  addition 
of  42°  will  give  it  a  pressure  of  4  atmospheres. 

Q.  Do  you  know  any  simple  formula  connecting 
the  pressure  and  temperature  of  saturated  steam  ? 

A.  Experiments   have  been  made  from  which 


b<5  roper's  catechism  for 

tables  have  been  constructed,  known  as  tables  of 
the  properties  of  steam,  which  give  the  relation 
between  pressure  and  temperature.* 

Q.  What  is  indicated  by  the  ordinary  steam 
gauge  ? 

A.  The  pressure  of  the  steam  above  the  atmos- 
phere,— that  is,  the  number  of  pounds  by  which 
it  exceeds  atmospheric  pressure. 

Q.  How  would  you  get  the  total  pressure  of  the 
steam, — that  is,  the  number  of  pounds  pressure- 
above  zero  ? 

A.  By  reading  the  barometer,  calculating  the 
number  of  pounds  of  atmospheric  pressure  corre- 
sponding to  the  barometer  reading,  and  adding 
this  to  the  reading  of  the  steam  gauge. 

Q.  When  a  pound  of  steam  is  condensed  to 
water,  how  much  heat  is  given  up  to  the  surround- 
ing air? 

A.  An  amount  of  heat  equal  to  the  latent  heat 
of  steam  at  the  temperature  at  which  it  is. 

Q.  If  afterward  the  water  cools  to  a  still  lower 
temperature,  how  much  heat  is  given  off? 

A.  The  amount  can  be  found  by  subtracting  the 
heat  of  the  liquid  at  the  lower  temperature  from 
that  corresponding  to  the  upper  temperature;  the 
difference  will  be  the  number  of  units  of  heat 
given  out  per  pound  of  cooling  water. 

*See  "Roper's  Land  and  Marine  Engines." 


STEAM    ENGINEERS   AND    ELECTRICIANS.  69 

THE  STEAM  BOILER* 

Designing  steam  boilers  is  not  within  the 
province  of  the  stationary  engineer.  It  is  his 
duty  not  to  build  boilers,  but  to  operate  them  to 
the  best  advantage.  Frequently,  however,  he  is 
called  upon  to  assist  in  the  selection  of  the  type  of 
boiler  for  a  given  purpose,  and  in  this  he  should 
remember  that  the  three  most  important  objects 
to  be  attained  are  safety,  durability,  and  economy. 

To  secure  safety  it  is  necessary  that  the  boiler 
should  be  made  of  good  material,  with  good  work- 
manship. 

To  secure  durability  the  boiler  ought  to  be  con- 
structed so  as  to  give  the  greatest  facilities  and 
easiest  access  for  cleaning,  repairing,  and  renewal 
of  any  of  its  parts.  The  boiler  should  also  be  so 
designed  as  to  avoid  unequal  strains  by  expansion 
and  contraction,  as  far  as  possible. 

In  attempting  to  secure  economy  in  the  genera- 
tion of  steam,  it  is  necessary,  first^  to  secure  perfect 
combustion  of  the  fuel,  so  as  to  produce  the  great- 
est amount  of  heat;  secondly^  to  apply  the  heat  in 
the  very  best  manner  to  the  boiler,  so  as  to  heat 
the  water  in  the  most  rapid  manner  possible  ; 
thirdly,  to  be  very  careful  to  prevent  the  heat  from 
escaping  by  radiation  or  with  the  products  of 
combustion.     If  these  three  conditions  be  com- 


70  roper's  catechism  for 

plied  with,  our  arrangements  will  be  of  the  most 
economical  character.  The  evaporative  efficiency 
of  any  boiler  and  furnace  is  to  be  measured  by  the 
amount  of  water  evaporated  by  any  given  weight 
of  fuel  in  a  given  time.  Mere  waste  of  fuel,  how- 
ever, is  not  the  only  defect  attendant  upon  an 
inferior  construction  of  boiler  and  furnace.  Where 
these  are  not  of  the  best  kind,  they  must  be  of 
larger  size  in  order  to  do  the  required  amount  of 
work;  the  grate  surface  must  be  larger,  and  more 
air  must  be  needlessly  raised  to  a  higher  tempera- 
ture, thus  carrying  off  a  large  amount  of  heat  in 
the  waste  products  of  combustion;  all  of  which 
involves  increased  outlay  of  capital  and  larger 
running  expenses. 

Many  of  the  defects  of  modern  boilers  might 
be  attributed  to  the  fact  that  some  of  the  in- 
ventors or  designers  seem  to  be  partly,  if  not 
totally,  ignorant  of  the  first  principles  of  mechan- 
ical science,  and  to  competition  between  boiler 
makers  themselves,  in  their  efforts  to  undersell 
each  other;  consequently  they  have  to  deceive 
purchasers  and  steam  users  by  magnifying  small 
l)oilers  into  large  ones.  Therefore,  when  the  boiler 
comes  to  be  tested,  its  evaporative  powers  are 
found  to  be  lacking,  the  fuel  has  to  be  burned 
under  a  sharp  draught,  and  instead  of  the  best 
results  the  worst  are  obtained. 


STEAM   ENGINEERS   AND    ELECTRICIANS.  71 

In  regard  to  the  metal  of  the  boiler  itself,  it  is  a 
well-known  fact  that  the  thicker  the  iron  is,  and 
the  poorer  its  conducting  qualities,  the  greater  will 
be  the  amount  of  heat  that  will  be  lost  or  wasted; 
when,  by  using  a  superior  quality  of  iron,  one 
whose  tensile  strength  and  conducting  powers  are 
both  very  great,  we  lessen  the  resistance  to  the 
passage  of  the  heat  from  the  furnace  to  the  water 
and  greatly  increase  the  economy  of  the  boiler. 
It  is  well  known  to  engineers  that  there  is  a  wide 
difference  in  the  physical  properties  of  different 
grades  of  iron  and  steel  used  in  boiler  construction. 
Some  kinds  of  boiler  plate  have  nearly  double  the 
tensile  strength  of  others,  and,  consequently,  to 
secure  the  same  strength  the  latter  would  have  to 
be  made  twice  as  thick  as  the  former.  This  would 
involve  the  interposition  of  a  more  difficult  path 
between  the  fire  and  the  water,  reducing  the 
efficiency  and  producing  a  weaker  boiler,  because 
the  thicker  plate  has  been  subjected  to  greater 
strains  in  the  bending.  Consequent^  the  thinner 
plate,  is  by  far  the  more  advantageous.  On  the 
other  hand,  as  the  tensile  strength  of  boiler  plates 
increases,  its  ductility  decreases,  and,  therefore, 
great  care  must  be  taken  in  selecting  boiler  mate- 
rials, to  be  sure  that  they  possess  not  only  tensile 
strength,  but  also  ductility,  otherwise  the  plates 
will  be  subjected  to  initial  strains,  and,  further- 


72  roper's  catechism  for 

more,  the  boiler  will  not  be  sufficiently  flexible  to 
withstand  the  varying  strains  to  which  it  is  con- 
stantly subjected.  For  these  reasons  it  has  been 
fouiid  that  the  best  material  for  boilers  is  one  which 
has  a  moderate  tensile  strength,  50,000  to  60,000 
pounds  per  square  inch,  and  which  will  elongate 
20  to  25  per  cent,  before  breaking  and  contract  50 
per  cent,  in  cross-section  at  the  point  where  rup- 
ture takes  place. 

Every  attempt  to  lessen  the  first  cost  of  a 
boiler  by  diminishing  the  heating-  and  grate- 
surface  is,  to  a  certain  extent,  carrying  out  the 
principle  of  ''  penny  wise  and  pound  foolish." 

An  engine  extra  large  for  the  work  to  be  done 
causes  a  loss  of  fuel,  while  a  boiler  moderately 
larger  than  necessary  to  do  the  work  is  productive 
of  economy  in  the  use  of  fuel.  A  boiler  taxed  to 
its  utmost  capacity  will  evaporate,  say,  from  5  to 
6  pounds  of  water  per  pound  of  coal,  while  the 
same  boiler  might  evaporate  half  the  quantity  of 
water  at  the  rate  of  8  to  10  pounds  of  water  per 
pound  of  fuel.  This  is  due  partly  to  the  fact  that 
when  the  boiler  is  forced  the  heating  surface  is  not 
sufficient  to  utilize  all  of  the  heat  from  the  prod- 
ucts of  combustion,  and  partly  also  to  the  excess 
of  air  above  that  necessary  for  combustion  which 
passes  through  the  grate  and  which  is  heated  with- 
out producing  any  useful  effect. 


STEAM    ENGINEERS    AND    ELECTRICIANS.  73 

For  instance,  a  locomotive  boiler  burning  10 
pounds  of  coal  on  each  square  foot  of  grate  surface 
in  an  hour,  will  evaporate,  say,  8  pounds  of  water 
for  each  pound  of  coal.  The  same  boiler,  running 
at  a  high  speed,  and  burning  75  pounds  of  coal 
on  each  square  foot  of  grate  surface,  will  evaporate 
7  pounds  of  water  for  each  pound  of  coal  burned. 
Here  is  a  vast  difference  in  the  total  amount  of 
evaporation, — each  pound  of  coal  produces  less 
steam  in  the  proportion  of  9  to  7  pounds. 

On  the  other  hand,  increasing  the  size  of  boiler 
for  a  given  evaporation  must  not  be  carried  to 
excess,  because  beyond  a  certain  limit  there  is  no 
advantage  to  be  derived  and  the  increased  first 
cost  then  becomes  a  waste  in  the  other  direction. 
There  is  a  certain  fixed  relation  between  grate 
surface,  heating  surface,  and  quantity  of  water 
evaporated,  in  each  type  of  boiler,  which  has  been 
found  in  practice  to  be  the  most  advantageous, 
and  any  material  departure  from  this  in  either 
direction  will  impair  the  cost  of  operation.* 

A  boiler  may  generate  steam  with  great  economy, 
but,  owing  to  the  steam  being  wasted  by  improper 
application  to  the  engine,  the  result  is  unsatis- 
factory and  the  boiler  unjustly  blamed.  On  the 
other  hand,  a  boiler  that  carries  out  water  with  its 

*  For  proportions  of  grate  area,  heating  surface,  etc. ,  see 
page  95  e^  seg-.;  also,  "  Eoper's  Handy-Book, "  Chapter  X. 


74  roper's  catechism  for 

steam  may  show  a  large  evaporation,  but  the 
steam  being  wet,  is  almost  useless  in  the  engine; 
so  that  in  judging  the  results  of  a  steam-power 
plant,  great  care  must  be  taken  to  examine  closely 
into  all  of  the  conditions,  before  condemning  either 
the  boiler  or  the  engine. 

In  selecting  a  type  of  boiler  for  a  given  pur- 
pose, there  are  many  circumstances  to  be  taken 
into  account.  Generally  speaking,  the  most  im- 
portant considerations,  as  stated  above,  are  safety, 
economy,  and  durability;  of  these,  safety  should 
alwa^^s  be  first  considered,  because  there  are  no 
conditions  under  which  human  life  and  property 
are  not  at  stake.  Consequently,  if  a  boiler  is 
not  safe,  it  is  not  fit  for  use  under  any  circum- 
stances. The  question  of  economy  must  be  looked 
at  in  a  different  way.  Generally  speaking,  that 
boiler  is  the  most  economical  which  evaporates  the 
greatest  amount  of  water  with  the  least  consump- 
tion of  coal,  but  there  may  be  conditions  under 
which  this  is  not  the  case;  for  example,  in  the  coal- 
regions,  where  fuel  is  very  inexpensive,  a  highly 
efficient  boiler,  which  is  of  necessity  more  com- 
plex than  one  which  is  less  so,  might  cost  more  to 
operate  on  account  of  the  interest  on  the  greater 
first  cost  and  the  cost  of  attendance  than  a  simple 
fine  or  even  a  plain  cylinder  boiler;  and  it  is  a  fact 
that  the  most  efficient  and  therefore  most  expen- 


STEAM    ENGINEERS    AND    ELECTRICIANS.  75 

sive  boilers  are  not  commonly  nsecl  where  fuel  is 
cheap.  Similar  considerations  might  lead  to  the 
selection  of  a  less  durable  boiler.  Suppose,  for 
example,  the  case  of  a  bridge  to  be  built  in  some 
out-of-the-way  locality,  the  work  requiring  but  a 
short  time  and  the  cost  of  transportation  large 
compared  to  the  value  of  the  boiler.  Under  these 
circumstances  it  would  probably  not  pay  to  use  a 
boiler  of  the  highest  grade,  but  preferably  one 
which  was  merely  safe  and  cheap,  did  not  require 
much  attention,  cleaning,  etc. ,  and  need  not  neces- 
sarily be  durable.  Such  conditions,  however,  are 
very  uncommon  and,  generally  speaking,  the  most 
efficient  and  durable  boiler  is  the  safest  and  the 


DIFFERENT  TYPES— ADVANTAGES  AND 
DISADVANTAGES. 

Q.  How  would  you  classify  steam  boilers  ? 

A!  Into  cylindrical,  flue,  fire  tubular,  and  water 
tubular. 

Q.  What  advantages  does  the  plain  cylinder 
boiler  possess  over  other  types  ? 

A.  It  is  simple,  inexpensive,  easy  to  clean  and 
repair,  and  reasonably  safe. 

Q.  What  are  its  disadvantages  ? 

A.  Its  disadvantages  are  numerous  and  great. 
First,  on  account  of  its  relatively  small  heating 


ROPER  S    CATECHISM   FOR 


STEAM    ENGINEERS    AND    ELECTRICIANS.  il 

surface,  it  is  very  bulky,  and,  consequently,  for  a 
given  evaporative  capacity,  the  space  it  occupies 
lis  much  greater  than  in  more  modern  types. 
Secondly,  on  account  of  the  high  temperature  at 
Iwhich  the  gases  escape  from  the  stack,  it  wastes 
fuel,  and  for  this  reason  it  is  the  least  economical 
type  of  boiler  in  existence.  Thirdly^  it  takes  a 
very  long  time  to  raise  steam.  Fourthly,  the 
scale  formed  in  the  bottom,  where  the  heat  is 
imost  intense,  makes  a  non-conducting  stratum 
which  soon  renders  that  portion  of  the  heating 
surface  useless  and  causes  the  iron  to  burn  at  that 
oint. 

Q.  Are  plain  cylinder  boilers  much  used  at  the 
present  time  ? 

A.  No;  they  have  disappeared  almost  entirely, 
mainly  on  account  of  their  inefficiency.  They 
ire  found  occasionally  in  localities  where  the  cost 
3f  fuel  is  very  low. 

Q.  Name  the  principal  varieties  of  flue  boilers 
md  briefly  describe  their  characteristics. 

A.  The  Cornish,  Lancashire,  and  Galloway 
3oilers  are  the  principal  varieties  of  flue  boilers. 
[n  the  Cornish  type  an  internal  cylindrical  flue 
extends  the  whole  length  of  the  boiler  and  the 
urnace  is  usually  contained  in  the  flue.  ,  The 
l^ancashire  boiler  has  two  internal  flues  with  a 
urnace  in  each,  the  two  flues  uniting  into  one 


78 


roper's  catechism  for 


STEAM    ENGINEERS   AND    ELECTRICIANS.  i\) 

behind  the  bridge  wall.  The  Galloway  is  similar 
to  the  Lancashire,  but  has  a  number  of  conical 
tubes,  called  Galloway  tubes,  inside  and  across  the 
flues,  through  which  the  water  circulates.  The 
furnaces  are  either  within  the  flues  or  external.* 

Q.  What  are  the  relative  advantages  and  dis- 
advantages of  the  above-named  boilers  ? 

A.  The  Cornish  boiler  has  a  greater  heating 
surface  than  the  plain  cylindrical  boiler,  and  it 
has  the  further  advantage  that  that  portion  of  the 
shell  on  which  the  scale  is  deposited,  is  the  coolest 
instead  of  the  hottest  point.  It  has  the  disad- 
vantage that,  for  the  same  water  capacity,  it  must 
have  a  greater  diameter. 

The  Lancashire  boiler  has  the  same  advantages, 
and  additionally  the  combustion  is  more  complete 
than  in  the  Cornish  type,  because  the  furnaces 
may  be  fired  alternately  and  the  smoke  which 
would  issue  from  the  stack,  if  there  were  but  one 
furnace,  is  to  a  great  extent  consumed  by  coming 
in  contact  with  the  products  of  .combustion  from 
the  other  furnace.  It  also  has  the  disadvantages, 
in  common  with  the  Cornish  boiler,  that  its  diam"- 
eter  is  greater  and,  further,  the  liability  of  the 
internal  flue  to  collapse,  both  of  which  disadvan- 
tages it  possesses   to  an  even  greater  degree  than 

*  For  description  of  flue  boilers,  see  "  Roper's  Engineers' 
Handy-Book,"  pages  160-164. 


80  roper's  catechism  for 

the  Cornish  boiler.  The  liability  of  the  flue  to 
collapse,  however,  is  not  very  great  when  the 
flues  are  properly  stiffened  or  corrugated. 

The  Galloway  boiler,  being  virtually  a  modified 
Lancashire  boiler,  possesses  all  of  its  advantages; 
and,  additionally,  by  virtue  of  the  conical  tubes, 
which  are  placed  transversely  in  the  flues,  it  has 
a  greater  heating  surface  and  better  circulation. 
Furthermore,  the  flues  are  much  less  liable  to 
collapse.  All  of  this  is  accomplished  by  the 
Galloway  tubes.  Of  the  three  boilers  mentioned 
the  Galloway  type  is  the  safest  and  most  econom- 
ical in  the  use  of  fuel. 

Q.  What  methods  are  employed  to  stiffen  the 
flues  of  boilers  and  to  provide  for  linear  expan- 
sion and  contraction  ? 

A.  This  end  was  formerly  accomplished  by 
making  the  flues  in  short  lengths  and  connecting 
them  by  /\-shaped  rings,  riveted  on  each  section 
of  flue.  The  stiffening  of  the  flue  alone  is  also 
accomplished  by  placing  T-shaped  rings  within 
the  flues,  at  intervals,  and  by  the  use  of  Galloway 
tubes.  This,  however,  does  not  take  care  of  ex- 
pansion and  contraction.  The  best  way  of  ac- 
complishing both  ends  is  by  corrugating  the 
flue,  which  has  the  further  advantage  of  increas- 
ing the  heating  surface  without  taking  up  any 
more  space  in  the  boiler. 


STEAM    ENGINEERS   AND    ELECTRICIANS.  81 

Q.  What  is  meant  by  fire-tube  or  tubular  boil- 


ers 


? 


A.  Fire-tube  or  tubular  boilers  are  those  in 
which  the  combustion  gases  pass,  not  only  around 
the  outside  shell,  but  also  through  tubes  which  are 
surrounded  by  water. 

Q.  In  what  respect  do  they  differ  from  flue 
boilers  ? 

A.  In  no  essential  feature,  except  that  instead 
of  one  flue  of  large  diameter  there  are  a  number 
of  small  flues  or  tubes. 

Q.  What  is  the  difference  between  internally 
and  externally  fired  tubular  boilers  ? 

A.  The  internally  fired  type  consists  of  an  ex- 
ternal cylindrical  shell  containing  a  furnace  ex- 
tending from  the  front  of  the  boiler  to  a  point 
about  midway  in  the  length  of  the  boiler.  From 
this  point,  and  extending  to  the  rear  end  of  the 
boiler,  there  are  a  number  of  tubes  which  lead  the 
gases  of  combustion  to  the  back,  whence  they  pass 
under  the  outside  shell  to  the  front  and  into  the 
stack.  In  the  externally  fired  type  the  tubes 
extend  the  whole  length  of  the  boiler,  and  the 
furnace  is  outside  and  under  the  front  end  of  the' 
boiler.  The  products  of  combustion  pass  along 
the  bottom  of  the  shell  to  the  back  of  the  boiler, 
and  then  return  through  the  tubes  to  the  front 
where  they  enter  the  stack  connection.     From  the 


82 


ROPER  S    CATECHISM    FOR 


STEAM   ENGINEERS   AND    ELECTRICIANS.  83 

course  which  the  gases  take,  this  latter  type  is 
frequently  designated  as  ''Return  Tubular."^ 

Q.  What  ad\^antages  does  a  tubular  boiler  pos- 
sess over  the  cylinder  and  flue  boilers  ? 

A.  The  tubular  takes  up  less  room,  generates 
steam  more  rapidly,  and  requires  less  fuel;  more- 
over, tubes  are  less  dangerous  than  flues,  on  ac- 
count of  their  small  diameter  and  great  strength. 

Q.  Why  are  tubular  boilers  more  economical 
than  plain  cylinder  and  flue  boilers  ? 

A.  Because  their  heating  surface  is  much  greater, 
and  consequently  the  greater  portion  of  the  heat 
contained  in  the  combustion  gases  is  imparted  to 
the  water. 

Q.  What  are  their  disadvantages  as  compared 
to  the  above-mentioned  types  ?  Are  they  impor- 
tant? 

A.  The  disadvantages  are  that  the  first  cost'  is 
greater,  and  that  they  are  more  difficult  to  clean 
and  repair,  because  they  are  less  accessible.  These 
disadvantages  are  unimportant  compared  to  the 
great  gain  in  economy,  f 

Q.  What  may  be  said  about  the  tubular  boiler 
in  regard  to  safety  ? 

A.  The  tubular  boiler  is  just  as  safe  as  the 
cylindrical  boiler,  and  more  so  than  the  flue  boiler, 

*See  "Roper's  Engineers'  Handy-Book,"  pages  165-168. 
t  For  comparison  with  water-tube  boilers,  see  next  page. 


84  roper's  catechism  for 

because  the  parts  subjected  to  internal  pressure 
have  the  same  strength,  while  those  subjected  to 
external  pressure,  being  smaller  in  diameter,  are 
much  stronger. 

Q.  What  is  a  water- tube  boiler? 

A.  It  is  one  in  which  the  water  circulates 
through  a  series  of  tubes,  which  are  surrounded 
by  the  combustion  gases. 

Q.  What  is  the  position  of  the  tubes  in  this 
class  of  boilers  ? 

A.  Different  makers  place  the  tubes  in  different 
positions.  In  the  most  common  type,  such  as 
the  Babcock  and  Wilcox,  Heine,  Gill  and  Root,  the 
tubes  are  inclined;  in  others,  such  as  the  Cahall, 
they  are  vertical,  and  occasionally  the}^  may  even 
be  found  curved  spirally.* 

Q.  What  are  the  principal  advantages  of  the 
water-tube  boiler  as  compared  with  other  types  ? 

A.  Its  advantages  are  that  it  is  safer,  more  eco- 
nomical, steams  more  rapidly,  is  easily  repaired, 
more  durable;  its  form  may  be  adapted  to  almost 
any  existing  conditions,  and  it  may  be  easily  taken 
apart  and  transported.  Its  only  disadvantages 
are  that  it  is  heavy  and  expensive. 

Q.  Why  is  this  type  of  boiler  the  most  econom- 
ical in  the  use  of  fuel? 

*  Descriptions  of  the  different  types  in  a  comdeused  form 
can  be  found  in  Babcock  and  Wilcox's  "Steam." 


STEAM    ENGINEERS   AND    ELECTRICIANS.  85 

A.  Because  it  has  an  enormous  amount  of  heat- 
ing surface,  and  because  the  metal  which  con- 
stitutes the  heating  surface  is  comparatively  light; 
because  the  combustion  is  very  thorough,  and  com- 
paratively little  heat  is  contained  in  the  escaping 
gases. 

Q.   Why  is  it  the  safest? 

A.  Because  for  a  given  rating  the  parts  sub- 
jected to  strain  are  of  smaller  diameter  than  in 
any  other  type,  and,  moreover,  none  are  subjected 
to  external  pressure.  Further,  because  it  is  so 
flexible  that  the  whole  structure  accommodates 
itself  to  changes  in  temperature  without  causing 
undue  strains. 

Q.  AVhat  would  probably  be  the  difference  in 
an  explosion  of  a  water  -  tube  and  a  fire  -  tube 
boiler  ? 

A.  Explosions  occurring  in  fire -tube  boilers 
usually  wreck  the  entire  boiler,  and  in  some  cases 
whole  batteries  have  been  known  to  explode  as 
the  result  of  a  single  defect  in  one  of  the  shells, 
entailing  great  loss  of  life  and  property.  In  the 
water  -  tube  type,  while  more  or  less  serious 
explosions  have  occurred,  it  is  very  rare  for  any- 
thing more  than  a  single  tube  or  header  to  give 
way;  this  may  be  easily  repaired  and  does  not 
generally  entail  much  loss. 

Q.  Why  is  it  durable  ? 


ROPER'S    CATECHISM    FOR 


STEAM    ENGINEERS    AND    ELECTRICIANS.  87 

A.  Because  it  is  easily  accessible,  and  because, 
as  already  stated,  it  adapts  itself  to  the  varying 
expansion  and  contraction  without  producing 
undue  strains;  further,  the  circulation  is  good  and 
consequently  the  temperature  of  the  different 
parts  is  fairly  uniform. 

Q.  To  what  class  do  locomotive  and  marine 
boilers  belong? 

A.  They  may  be  said  to  belong  to  the  tubular 
type,  but  they  have  certain  characteristics  not 
embodied  in  the  ordinary  tubular  boiler,  Avhich 
really  place  them  in  separate  classes  by  them- 
selves. 

Q.  Give  a  brief  description  of  a  modern  marine 
boiler. 

A.  It  usually  consists  of  a  short,  circular  shell 
of  large  diameter  with  an  internal  corrugated  fur- 
nace. At  the  back  of  the  furnace  is  a-  chamber 
into  which  the  gases  pass  from  the  furnace.  This 
is  called  the  back  up-take.  A  similar  chamber  in 
the  front,  called  the  front  up-take,  connects  with 
the  stack.  The  tubes  are  placed  above  and  around 
the  furnace,  and  extend  from  the  front  to  the  back 
up-take. 

Q.  What,  then,  is  the  essential  difference  be- 
tween a  marine  boiler  and  an  internally  fired 
tubular  boiler? 

A.  The  principal  difference  is  that  while  in  the 


05  ROPER'S    CATECHISM    FOR 

ordinary  internally  fired  tubular  boiler  the  gases 
pass  from  the  furnaces  through  tubes  to  the  back 
and  then  along  the  outside  to  the  front;  in  the 
marine  boiler  the  gases  do  not  pass  around  the 
outside  at  all,  but  go  from  the  furnace  directly 
into  the  back  up-take,  thence  through  the  tubes 
to  the  front  up-take  and  into  the  stack. 

Q.  What  conditions  have  brought  about  this 
design  of  boiler  for  marine  purposes  ? 

A.  For  marine  purposes  a  boiler  must  be  short, 
as  otherwise  it  could  not  be  set  and  operated  in 
the  available  space;  and  it  must  be  self-contained, 
because  brick  setting,  on  account  of  its  great 
weight  and  the  motion  of  the  ship,  would  be  out 
of  the  question.  It  must  also  make  steam 
rapidly. 

Q.  What  pressure  may  be  carried  in  modern 
marine  boilers  ? 

A.  Upward  of  200  pounds  per  square  inch. 

Q.   How  many  furnaces  are  generally  used  ? 

A.  Boilers  less  than  9  feet  in  diameter  usually 
have  only  one;  those  from  9  to  13  feet,  two;  over 
13  feet,  three;  and  the  largest,  sometimes  exceed- 
ing 15  feet  in  diameter,  have  four  furnaces. 

Q.  What  is  meant  by  a  double-ended  boiler? 

A.  When  the  boilers  are  fired  from  the  sides  of 
the  ship  they  are  frequentl}^  placed  back  to  back 
or  are  made  double-ended — that  is,  they  have  fur- 


STEAM    ENGINEERS   AND    ELECTRICIANS.  89 

naces  at  both  ends,  with  a  common  or  separate 
back  up-takes.  The  latter  arrangement  is  prefer- 
able, because  if  anything  should  happen  to  a 
tube  in  one  end,  this  may  be  repaired  without 
affecting  the  other  half  of  the  boiler. 

Q.  What  are  the  advantages  and  disadvantages 
of  marine-type  boilers  ? 

A.  They  do  not  occupy  much  floor  space, 
require  no  brick  setting,  have  a  large  steaming 
capacity  for  a  given  size  and  weight,  but  they  are 
not  as  economical  in  the  use  of  fuel  or  as  safe  as 
the  best  types  of  land  boilers. 

Q.  Are  marine-type  boilers  ever  used  for  sta- 
tionary purposes  ? 

A.  The  marine  type  of  boiler  is  occasionally 
found  on  land.  It  is  well  adapted  for  use  where 
the  vibration  is  so  great  as  to  render  brick  setting 
impracticable,  and  where  floor  space  is  limited. 

Q.  Give  a  brief  description  of  a  locomotive 
boiler. 

A.  The  locomotive  boiler  consists  of  a  rectang- 
ular furnace  or  fire-box,  often  made  of  copper, 
which  contains  the  grate  bars.  The  fire-box  is 
inclosed  in  the  boiler  shell,  which  is  also  rec- 
tangular where  it  contains  the  fire-box,  but  the 
remainder  of  the  shell  consists  of  a  long  cylinder 
of  comparatively  small  diameter,  which  contains 
a  large  number  of  tubes.     The  products  of  com- 


90  roper's  catecpiism  for 

bustion  first  strike  a  fire-brick  arch  which  deflects 
them  into  the  tubes,  through  which  they  pass 
into  the  funnel  or  stack  placed  on  the  smoke-box 
at  the  front  end.  Locomotives  generally  use 
forced  draught,  which  is  obtained  by  allowing  the 
steam  from  the  engine  cylinders  to  exhaust  through 
the  funnel. 

Q.  What  conditions  have  led  to  the  design  now 
generally  used  for  locomotive  boilers  ? 

A.  A  boiler  suitable  for  use  on  locomotives 
must  be  light  and  of  small  diameter ;  light, 
because  it  is  carried  along  at  a  high  rate  of  speed, 
and  of  small  diameter  on  account  of  the  limited 
width  of  the  road  bed.  For  the  same  reasons, 
and  on  account  of  the  jarring  motion,  brick  set- 
ting is  out  of  the  question,  and  hence  it  must  be 
self-contained.  It  must  be  capable  of  making 
high-pressure  steam  quickly  rather  than  econom- 
ically. 

Q.  Is  the  locomotive  boiler  economical  in  the 
use  of  fuel  ? 

A.  Yes,  but  not  as  economical  as  the  better 
types  of  stationary  boilers. 

Q.  How  is  the  necessary  strength  of  the  flat 
surfaces  of  the  fire-boxes  obtained  in  locomotives? 

A.  By  short  stay-bolts  connected  to  the  outside 
shell  of  the  boiler.  The  top  of  the  fire-box  is 
sometimes   braced  by  girders  called  crown-bars, 


STEAM   ENGINEERS    AND    ELECTRICIANS.  91 

a;nd  sometimes  to  the  semi-circular  shell  of  the 
boiler  above  by  means  of  stay-bolts  placed  radially. 

Q.  What  are  the  advantages  and  disadvantages 
of  the  locomotive  type  of  boiler  ? 

A.  Its  advantages  are  that  it  is  compact,  steams 
quickly,  and  requires  no  brick  setting.  Its  dis- 
advantages are  that  it  is  expensive,  not  as  eco- 
nomical as  the  best  stationary  boilers,  and  is  inac- 
cessible for  cleaning  and  repairs. 

Q.  Are  locomotive-type  boilers  used  for  station- 
ary purposes  ? 

A.  Yes;  they  are  well  adapted  for  stationary 
boilers  where  head  room  is  limited,  where  it  is 
desired  to  make  steam  quickl}^  rather  than  eco- 
nomically, and  where  vibration  or  other  condi- 
tions would  make  brick  setting  undesirable. 

Q.   How  is  steam  taken  from  locomotive  boilers? 

A.  Usually  from  a  steam  dome  placed  on  the  top 
of  the  shell.  This  is  to  insure  dry-steam.  Dry- 
pipes  are  also  sometimes  used  instead  of  domes. 

HOESE-POWER  AND  EFFICIENCY. 

Q.  What  is  meant  by  the  term  horse-poiver  as 
applied  to  steam  boilers  ? 

A.  A  boiler  of  one  horse-power  capacity  is  one 
which,  under  ordinary  conditions,  supplies  as 
much  steam  as  is  consumed  in  the  average  steam 
engine  in  developing  one  horse-power. 


92  eoper's  catechism  for 

Q.  Is  there  nothing  more  definite  than  this  by 
which  the  horse-power  of  boilers  may  be  rated  ? 

A.  Yes;  the  horse-power  of  steam  boilers  is  now 
generally  based  on  an  evaporative  capacity  of  30 
pounds  of  water  per  hour  from  feed-water  at  a 
temperature  of  100°  Fahr.  to  steam  at  a  pressure 
of  70  pounds.  This  was  fixed  by  a  committee  of 
judges  at  the  Centennial  Exposition  in  1876,  and 
is  equivalent  to  33,305  heat-units  per  hour  im- 
parted to  the  water.  It  is  known  as  the  Centen- 
nial Rating. 

Q.  How  nearly  does  the  horse-power  of  steam 
boilers,  rated  according  to  this  rule,  come  to  the 
actual  consumption  of  steam  in  ordinary  steam 
engines  ? 

A.  For  an  automatic  cut-off,  high-speed,  non- 
condensing  steam  engine  it  is  just  about  right. 
For  plain  slide-valve  engines  with  throttling 
governors  the  Centennial  Rating  is  much  too  low, 
while  for  multiple  expansion  and  condensing 
engines  it  is  too  high. 

Q.  How,  then,  would  you  fix  the  size  of  boilers 
for  different  engines,  assuming  that  the  horse- 
power of  the  boilers  were  based  on  the  Centennial 
Rating? 

A.  It  is  always  well  to  have  the  boiler  capacity 
a  little  in  excess  of  that  of  the  engine,  because  its 
efficiency  is  not  impaired  by  operating  it  below 


STEAM    ENGINEERS   AND    ELECTRICIANS.  93 

its  rated  capacity.  If  the  engine  were  of  the  high- 
speed, automatic  cut-off,  single-expansion,  non- 
condensing  type,  I  should  rate  the  boiler  about 
10  per  cent,  higher  than  the  engine;  if  of  the 
same  type,  but  condensing,  about  equal;  if  plain 
slide  valve,  non-condensing,  with  throttling  gov- 
ernor, 40  to  50  per  cent,  higher;  the  same,  con- 
densing, 10  to  20  per  cent,  higher;  if  automatic  or 
four- valve  non-condensing,  about  equal;  the  same, 
condensing,  about  10  to  20  per  cent,  lower;  if  com- 
pound, high-speed,  non-condensing,  about  10  per 
cent,  lower;  the  same,  condensing,  15  to  25  per 
cent,  lower  ;  if  compound,  four- valve,  or  Corliss, 
non-condensing,  10  to  15  per  cent,  lower;  the  same, 
condensing,  25  to  35  per  cent,  lower;  if  triple  ex- 
pansion, non-condensing,  10  to  15  per  cent,  lower; 
the  same,  condensing,  35  to  45  per  cent,  lower. 

Q.  Why  are  the  above  rules  only  approximate  ? 

A.  Because  the  evaporative  capacity  of  a  boiler 
depends  on  the  temperature  of  the  feed-water  and 
also  on  the  pressure  of  the  steam.  A  boiler  of 
100 '  horse-power  can  evaporate  3000  pounds  of 
water  from  100°  to  steam  at  70  pounds  pressure; 
but  if  the  temperature  of  the  feed-water  is  less,  or 
if  the  pressure  greater,  it  will  not  evaporate  as 
much,  and  vice  versa. 

Q.  What,  then,  is  the  best  method  of  determin- 
ing the  size  of  a  steam  boiler  ? 


94  roper's  catechism  for 

A.  The  best  method  is  to  determme  what  amount 
of  steam  is  to  be  consumed  and  the  pressure  at 
which  it  is  to  be  dehvered  to  the  engine,  to  specify 
these  requirements  and  the  desired  evaporative 
efficiency  to  the  boiler-maker,  and  to  leave  the  de- 
tails of  construction  to  him,  binding  him  to  guar- 
antee the  boiler  to  furnish  the  requisite  amount  of 
steam  easily  and  under  all  conditions. 

Q.  Approximately,  what  horse-power  of  boiler 
(Centennial  Rating)  would  be  required  to  supply 
steam  to  a  100  horse-power,  four-valve,  non-con- 
densing engine,  consuming  26  pounds  of  steam 
at  70  pounds  pressure  per  horse-power  per  hour  ? 

A.  Weight  of  steam  required  =  100  X  26  ^ 
2600  pounds  per  hour;  H.  P.  (Centennial  Rating)  = 

-— —  :=  87,  but  it  would  probably  be  better  to  use 

a  boiler  rated  at  90  to  100  horse-power. 

Q.  What  is  meant  by  evaporative  efficiency  ? 

A.  The  number  of  pounds  of  steam  generated 
per  pound  of  fuel  consumed. 

Q.  What,  roughl}^,  are  the  results  that  may  be 
obtained  in  this  respect  ? 

A.  In  flue  boilers  of  the  best  types,  6  to  9  pounds; 
in  tubular  boilers,  8  to  10  pounds;  in  water- tube 
boilers,  10  to  12  pounds  of  water  per  pound  of  coal; 
the  average  results,  however,  are  from  10  to  25 
per  cent,  below  these  figures. 


STEAM    ENGINEERS    AND    ELECTRICIANS.  95 

GRATE  AREA  AND   HEATING  SURFACE. 

Q.  What  determines  the  grate  surface  m  boilers  ? 

A.  Principally  the  quality  of  coal  and  the 
draught.  In  general,  it  is  well  to  have  the  grate 
surface  large,  but  not  so  large  that  the  air  passing 
through  it  will  be  greatly  in  excess  of  the  amount 
required  for  combustion  of  the  fuel. 

Q.  What  amounts  of  coal  can  be  consumed  per 
square  foot  of  grate  surface  ? 

A.  Anywhere  from  4  to  120  pounds,  depending, 
as  already  stated,  upon  the  quality  of  the  coal  and 
the  draught. 

Q.  What  is  meant  by  heating  surface  ? 

A.  The  heating  surface  of  a  boiler  means  the 
aggregate  area  of  all  of  the  parts  of  the  boiler  which 
come  in  contact  with  the  flame  or  products  of 
combustion  on  the  one  side,  and  with  the  water 
or  steam  on  the  other.  In  other  words,  it  is  all 
that  part  of  the  surface  through  which  the  heat  of 
the  fire  is  transmitted  to  the  water  or  steam. 

Q.  How  would  you  calculate  the  heating  sur- 
face of  different  types  of  boilers  ? 

A.  Rule  for  Cylinder-Boilers. — Multiply  f 
of  the  circumference  of  the  shell  in  inches  by  its 
length  in  inches,  add  the  area  of  one  end  in  square 
inches,  and  divide  by  144.  The  quotient  will  be 
the  number  of  square  feet  of  heating  surface. 


96  roper's  catechism  for 

Rule  for  Flue-Boilers. — Multiply  f  of  the 
circumference  of  the  shell  in  inches  by  its  length 
in  inches;*  multiply  the  combined  circumference 
of  all  the  flues  in  inches  by  their  length  in  inches. 
Take  the  sum  of  these  two  products  and  add  the 
area  of  one  end  in  square  inches.  Deduct  the 
sum  of  the  areas  of  the  cross-sections  of  all  the 
flues  in  square  inches.  The  result  divided  by 
144  is  the  heating  surface  in  square  feet. 

Rule  for  Vertical  Tubular  Boilers  (such  as 
are  generally  used  for  fire-engines). — Multiply  the 
circumference  of  the  fire-box  in  inches  by  its 
height  above  the  grate  in  inches.  Multiply  the 
combined  circumference  of  all  the  tubes  in  inches 
by  their  length  in  inches,  and  to  these  two  prod- 
ucts add  the  area  of  the  lower  tube-  or  crown- 
sheet,  and  from  this  sum  subtract  the  area  of  all 
the  tubes,  and  divide  by  144.  The  quotient  will 
be  the  number  of  square  feet  of  heating  surface  in 
the  boiler. 

Rule  for  Horizontal  Tubular  Boilers. — 
Multiply  f  of  the  circumference  of  the  shell  in 
inches  by  its  length  in  inches;  multiply  the  com- 
bined circumference  of  all  the  tubes  in  inches  by 
their  length  in  inches.  To  the  sum  of  these  two 
products  add  f  the  area  of  both  tube-sheets;  from 
this  sum  subtract  the  combined  area  of  all  the 
tubes ;    divide   the   remainder   by    144,    and  the 


STEAM   ENGINEERS    AND    ELECTRICIANS.  97 

quotient  will  be   the   number  of   square  feet  of 
heating  surface. 

Rule  for  Locomotive  Boilers. — Multiply  the 
length  of  the  furnace-plates  in  inches  by  their 
height  above  the  grate  in  inches;  multiply  the 
width  of  the  ends  in  inches  by  their  height  in 
inches;  multiply  the  length  of  the  crown-sheet  in 
inches  by  its  width  in  inches;  also  the  combined 
circumference  of  all  the  tubes  in  inches  by  their 
length  in  inches;  from  the  sum  of  these  four 
products  substract  the  combined  area  of  all  the 
tubes  and  the  fire-door;  divide  the  remainder  by 
144,  and  the  quotient  will  be  the  number  of 
square  feet  of  heating  surface. 

Q.  How  much  heating  surface  per  horse-power 
should  be  provided  in  fire-  and  water- tube  boilers  ? 

A.  About  12  to  15  square  feet. 

Q.  How,  then,  can  you  approximate  the  horse- 
power of  a  given  boiler  ? 

A.  By  calculating  the  heating  surface  in  square 
feet  and  dividing  it  by  14. 

Q.  What  is  the  average  ratio  between  grate  and 
heating  surface  in  stationary  boilers  ? 

A.  The  average  is  about  35  feet  of  heating  sur- 
face to  1  square  foot  of  grate  surface.  This  is  for 
good  anthracite  coal,  but  for  poorer  grades  the 
proportionate  surface  of  the  grate  should  be 
larger. 
7 


98  roper's  catechism  for 

Q.   How  much  coal,  of  good  anthracite  quality, 
can  be  consumed  per  square  foot  of  grate  under 
ordinary  conditions? 
A.  About  11  pounds. 

Q.  According  to  these  figures,  how  much  coal, 
on  an  average,  would  be  consumed  per  horse-^DOwer 
per  hour  ? 

A.   Heating  surface  per  H.  P.,  =  12  sq.  ft. 

Grate  "  "  :=  |- 1.      " 

Coal  consumption  per  sq.  ft.  of 

grate  per  hour,  =11  lbs. 

Coal  consumption  per  H.  P.  per 

hour,  :^  ^  X  11  =  3f  lbs. 

Q.  If  all  the  heat  in  the  fuel  were  utilized  in 
making  steam,  what  would  be  the  smallest  theo- 
retical amount  of  good  anthracite  coal  consumed 
per  hour  ? 

A.   Heat-units  required  per 

H.  P.  (Cent'l  R'g),    =  33,305 
Heat-units  in  best  an- 
thracite coal,  =  14,000 
Minimum  consumption 

per  H.  P.  per  hour,   =  fll^l"  =  2.4  lbs. 

BOILER  SHELLS. 

Q.  What  materials  are  used  for  boiler  shells  ? 
A.  Wrought  iron  and  steel.     The  latter  is  rap- 
idly replacing  the  former  as  a  boiler  material. 


STEAM    ENGINEERS   AND    ELECTRICIANS.  99 

Q.  Why  is  steel  preferred  ? 

A.  Because  for  a  given  strength  it  is  hghter  ; 
and,  as  a  thinner  plate  may  be  used,  the  efficiency 
of  the  heating  surface  is  greater. 

Q.  What  thickness  of  boiler  plate  do  you  con- 
sider the  safest,  most  durable,  and  economical  for 
boilers  ? 

A.  First,  to  insure  safety  in  shells  and  flues  of 
boilers;  the  thickness  proper  to  use  depends  very 
much  on  the  quality  of  the  iron,  diameter  of 
boiler,  and  pressure  to  be  carried.  Secondly,  as  to 
durability,  the  thickest  iron  is  not  always  the 
best,  as  the  outside  of  the  sheet  becomes  burned 
and  crystallized,  and  in  most  cases  gives  less  wear 
and  satisfaction  than  a  thinner  gauge.  Thirdly, 
as  to  economy,  thin  boilers  are  more  economical 
with  fuel,  and  wear  longer,  provided  in  all  cases 
that  the  diameter  and  the  pressure  are  in  propor- 
tion. 

Q.  What  would  you  consider  the  proper  thick- 
ness for  boilers  ? 

A.  The  thickness  of  boiler  iron  or  steel  should 
range  between  f  and  y\-  of  an  inch,  for  the  rea- 
son that  plates  of  greater  thickness  than  f  of  an 
inch  are  liable  to  burn,  especially  if  the  circula- 
tion is  poor,  and  they  are  difficult  to  work  and 
rivet.  If  the  plates  are  less  than  y\  of  an  inch 
thick,  they  cannot  be  properly  caulked,  and  they 


100  roper's  catechjsm  for 

are  liable  to  waste  away  by  corrosion  so  as  to 
impair  the  safety  of  the  boiler. 

Q.  What  properties  should  be  possessed  by 
materials  used  for  boiler  plates  ? 

A.  Whether  iron  or  steel,  the  test-piece  should 
have  a  tensile  strength  of  not  less  than  50,000 
pounds  per  square  inch  ;  it  should  elongate  25 
per  cent,  in  8  inches  before  breaking,  and  should 
contract  50  per  cent,  in  cross-section  at  the  point 
where  rupture  takes  place.  It  should  stand  bend- 
ing without  injury  around  a  radius  equal  to  the 
thickness  of  the  23late. 

Q.  Is  the  pressure  the  same  on  all  riveted  seams 
in  boiler  shells  ? 

A.  No;  the  pressure  on  the  longitudinal  rivets 
is  nearly  double  that  on  the  curvilinear  rivets. 

Q.  What  do  you  mean  by  longitudinal  and  cur- 
vilinear rivets  ? 

A.  By  longitudinal  rivets  I  mean  those  that  run 
lengthwise  on  the  boiler;  the  curvilinear  are  those 
that  are  around  the  circumference  of  the  shell. 

Q.  If  the  pressure  on  the  longitudinal  seams  is 
double  that  on  the  curvilinear,  how  can  all  parts 
of  the  boiler  sustain  the  same  pressure? 

A.  By  making  the  longitudinal  seams  double 
riveted  and  the  curvilinear  single. 

Q.  What  is  the  difference  in  strength  between 
single-  and  double-riveted  seams? 


STEAM    ENGINEERS   AND    ELECTRICIANS.         lOl 

A.  Single-rivetecl  seams  are  equal  to  about  56 
per  cent,  of  the  material  used,  while  double  rivet- 
ing is  equal  to  about  70  per  cent. 

Q.  What  do  you  mean  by  ' '  equal  to  about 
56  per  cent,  of  material  used ' '  ? 

A.  I  mean  that  the  boiler  plates  lose  44  per 
cent,  of  their  strength  in  the  process  of  riveting. 

Q.  What  do  you  consider  the  proper  diameter 
for  rivets  of  boilers  ? 

A.  That  would  depend  very  much  on  the  diam- 
eter of  the  boiler,  thickness  of  iron,  and  pressure 
to  be  carried.  For  boilers  from  36  to  42  inches 
diameter,  and  f  iron,  if  single  riveted,  the  rivets 
ought  to  be  f  of  an  inch  for  curvilinear,  and  f  for 
the  longitudinal;  if  double  riveted,  f  will  answer 
for  both  longitudinal  and  •  curvilinear  seams. 
From  -f-Q  iron  down  to  y\  smaller  rivets  will 
answer. 

Q.  Which  do  you  consider  the  best  method  of 
riveting  boilers,'  by  hand  or  by  machine  ? 

A.  For  average  or  thin  boiler  plates,  hand 
riveting  does  very  well,  but  for  heavy  iron,  ^^g-  or 
J  inch  thick,  machine  work  is  far  superior;  the 
power  of  the  machine  brings  the  work  together 
better  and  with  less  injury  to  the  iron  than  can  be 
done  by  hand. 

Q.  How  should  the  fiber  of  the  iron  be  placed 
to  give  the  greatest  strength  ? 


102  roper's  catechism  for 

A.  The  direction  in  which  the  iron  is  rolled 
should  always  be  placed  around  the  boiler,  and 
not  lengthwise,  because  in  cylindrical  boilers  the 
strain  in  the  line  of  the  axis  is  much  less  than  the 
circumferential  bursting  strain. 

Q.  Do  you  consider  it  an  advantage  to  drill  the 
rivet-holes  in  boilers  instead  of  punching  ? 

A.  Yes;  for  all  first-class  work  there  can  be  no 
doubt  but  that  all  the  rivet-holes  ought  to  be 
drilled,  on  account  of  the  liability  of  the  plates 
to  become  fractured  by  the  process  of  punching, 
causing  a  great  reduction  in  the  strength  of  the 
boilers. 

Q.  Do  you  consider  the  use  of  the  drift-pin 
ought' to  be  dispensed  with  as  much  as  possible  in 
making  boilers  ? 

A.  Yes;  a  reckless  use  of  the  drift-pin  has  in 
many  cases  resulted  in  great  injury  to  the  boiler 
plates;  and  there  is  good  reason  to  believe  that 
such  injuries  as  are  caused  by  the  drift-pin  often 
hasten  the  destruction  of  the  boiler. 

Q.  What  is  a  drift-pin  ? 

A.  It  is  a  tapering  steel  pin  introduced  into  the 
holes  in  the  seams,  to  bring  them  into  line. 

Q.  How  do  you  propose  to  dispense  with  the 
use  of  the  drift-pin? 

A.  If  the  holes  are  laid  off  carefully  in  the 
sheet,  and  punched  with  judgment,  there  will  be 


STEAM    ENGINEERS    AND    ELECTRICIANS.         103 

very  little  need  for  the  clrift-pin,  as  the  holes  can 
be  straightened  by  a  flat  reamer.  Such  work  will 
be  greatly  superior  to  that  where  the  drift-pin  is 
used. 

Q.  Do  you  think  i^  would  be  of  any  benefit  to 
slightly  heat  the  boiler  plates  before  rolling  them 
to  form  the  shell  of  the  boiler? 

A.  Yes;  I  think  it  would  add  very  materially 
to  the  strength  and  durability  of  boilers  if  the 
sheets  were  rolled  while  warm,  as  the  fiber  of  the 
iron  would  be  drawn  out;  while,  in  the  common 
practice  of  cold  rolling,  the  fiber  is  crushed  and 
broken. 

Q.  Does  hammering  improve  the  quality  of 
iron  ? 

A.  No;  it  only  hardens  it,  but  at  the  same  time 
renders  it  more  brittle,  while  rolling  imparts 
toughness. 

Q.  What  fact  is  observable  when  boiler  iron  is 
broken  suddenly,  as  in  the  case  of  steam-boiler 
explosions  ? 

A.  It  generally  presents  a  crystalline  fractured 
appearance;  when,  if  broken  by  some  slow  pro- 
cess, it  presents  a  fibrous  or  silky  appearance, — 
in  the  first  case  the  fiber  is  fractured,  and  in  the 
other  it  is  drawn  out. 

Q.  What  does  the  crystalline  fracture  indicate  ? 

A.   It  indicates  hardness,  while  a  fibrous  fracture 


104  roper's  catechism  for 

is  a  mark  of  softness  and  ductility.  The  finer  and 
more  uniform  the  crystals,  the  higher  the  qualit}^ 
of  the  iron. 

Q.  Is  the  pressure  equal  on  all  sides  of  the  shell 
of  a  boiler  when  under  steam  ? 

A.  No;  there  is  more  pressure  on  the  lower  than 
on  the  upper  side  of  a  boiler;  as  the  steam  presses 
equally  on  the  surface  of  the  water  as  on  the  upper 
side  of  the  boiler,  the  weight  of  the  water  must 
be  added  to  the  pressure  on  the  lower  side. 

Q.  Are  the  shells  and  flues  of  boilers  sometimes 
injured  by  the  application  of  the  cold-water  or 
' '  hydrostatic ' '  test  ? 

A.  Yes;  the  shells  and  flues  of  boilers  are  some- 
times injured  by  a  reckless  use  of  the  test,  and  in 
many  cases  explosions  take  place  soon  after  the 
test  is  applied. 

Q.  Would  the  shell  and  flues  of  a  boiler  be 
stronger  under  a  cold-water  pressure  of  70  or  80 
pounds  to  the  square  inch  than  under  the  same 
steam  pressure  ? 

A.  No;  as  iron  increases  in  strength  by  the 
application  of  heat  up  to  550°  Fahr.,  the  boiler 
would  be  stronger  under  the  steam  pressure. 

Q.  How  do  you  calculate  the  bursting  pressure 
per  square  inch  of  a  C3dindrical  boiler? 

A.  The  rule  is  to  multiply  the  thickness  of  the 
shell   in   inches   by   the   tensile   strength   of   the 


STEAM    ENGINEERS    AND    ELECTRICIANS.         105 

material  in  pounds  per  square  inch,  and  divide 
the  product  by  one-half  the  diameter  of  the  boiler 
in  inches. 

Q.  How  do  you  calculate  the  safe  working 
pressure  ? 

A.  Multiply  the  thickness  of  the  shell  in  inches 
by  the  tensile  strength  in  pounds  per  square  inch. 
Multiply  one-half  the  diameter  by  the  factor  of 
safety.  Divide  the  first  product  by  the  second, 
and  the  quotient  will  be  the  safe  working  pressure. 

Q.  What  is  meant  by  the  factor  of  safety  ? 

A.  By  factor  of  safety  is  meant  the  ratio  of  the 
ultimate  breaking  strength  to  the  proper  allowable 
working  strength.  For  example,  if  a  boiler  shell 
is  made  of  steel  having  a  tensile  strength  of 
60,000  pounds  and  the  thickness  is  calculated  with 
a  factor  of  safety  of  4,  the  greatest  strain  which 
would  come  on  any  square  inch  of  cross-section 
is  15,000  pounds;  or,  in  other  words,  the  boiler 
could  carry  four  times  as  much  pressure  before 
bursting. 

Q.  What  is  the  factor  of  safety  usually  em- 
ployed in  designing  boiler  shells  ? 

A.  It  varies  from  3  to  5.  A  safe  average  for 
stationary  boilers  is  4. 

Q.  What  value  of  tensile  strength  must  be  used 
in  the  above  rules  for  working  and  bursting  pres- 
sure ? 


106 


ROPER  S    CATECHISM    FOR 


A.  That  depends  on  how  the  joints  are  riveted. 
The  value  of  tensile  strength  in  the  above  rules  is 
the  ultimate  breaking  strength  of  the  material 
multiplied  by  the  efficiency  of  the  joint. 

Q.  What  do  you  mean  by  the  efficiency  of  the 
joint  ? 

A.  I  mean  the  number  by  which  the  original 
strength  of  the  material  must  be  multiplied  to 
give  its  strength  after  riveting. 


t(S>  O   O  (9  Q  O  ID      , 


Q.  What  is  the  efficiency  of  single-  and  double- 
riveted  joints  ? 

A.  As  already  stated  above,  it  is  about  j^-^-q  for 
single-riveted  and  about  -^q-  for  double-riveted 
joints.  The  efficiencies  of  joints  depend,  how- 
ever, not  only  on  the  thickness  of  j^late,  but  also 
on  the  spacing  of  the  rivets  and  the  material  used. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         107 

Q.  How  would  you  express  by  formulae  the 
relations  existing  between  safe  working  pressure, 
bursting  pressure,  thickness  of  shell,  efficiency  of 
joint,  and  factor  of  safety  ? 

A.   If  p  is  the  safe  working  pressure  in  pounds 
per  square  inch, 
P      "      bursting  pressure  in  pounds  per 

square  inch, 
W     "      ultimate     tensile      strength     in 

pounds  per  square  inch, 
t      ' '      thickness  of  shell  in  inches, 
e      "      efficiency  of  the  joint, 
/     "      factor  of  safety, 
d      ' '      diameter  of  boiler  in  inches. 
To  find  the  bursting  pressure: 
j,_t  X  WX  e 
id        ' 
To  find  the  safe  working  pressure  : 
_tXWXe 
^~     idXf   ' 
To  find  the  thickness  of  shell  for  a  given  work- 
ing pressure  and  factor  of  safety: 
_  i^  XpXf 
WX  e      ' 
To  find  the  factor  of  safet}^  of  a  given  boiler: 
f  =,  WX  e  X  t 


108  eoper's  catechism  for 

Q.  As  an  example:  If  a  boiler  48  inches  in 
diameter  is  made  of  steel  having  an  ultimate  ten- 
sile strength  of  55,000  pounds  per  square  inch, 
thickness  of  shell  f  of  an  inch,  joints  double 
riveted,  what  is  the  bursting  pressure  ? 

,           r>       I  X  55,000  X  .70       ^„„^  , 

A.         P  = :r-^ — -i^ =  1000  pounds 

i  X  48  ^ 

per  square  inch. 

Q.  With  a  factor  of  safety  of  5,  what  would  be 
the  safe  working  pressure  ? 

,  f  X  55,000  X  .70         ^„„  , 

A.  p=   -r  x-4^^^    =  200  pounds 

per  square  inch. 

Q.  If  the  boiler  had  to  work  under  150  pounds 
pressure  with  a  factor  of  safety  of  4,  what  would 
be  the  proper  thickness  of  shell  ? 

.  ^       1  X  48  X  150  X  4       3    „       .     , 

A.  t  =       55^000  X. 70       ^  *  "^  ^"^  ^^^'^- 

Q.  If  a  boiler  of  the  same  diameter  were  made 
of  wrought,  iron  having  an  ultimate  tensile 
strength  of  50,000  pounds,  shell  \  inch  thick, 
joints  single  riveted,  what  would  be  the  factor  of 
safety  for  a  working  pressure  of  100  pounds  ? 

,  ^__  50,000  X  .56  X4_^^^ 

^'        ^-     iX48x  100    -^'^^^ 

which  is  somewhat  higher  than  is  usually  allowed 
by  boiler  makers. 


STEAM    E^-GINEERS    AND    ELECTRICIANS.  109 

BOILER   SETTING. 

Q.  What  materials  should  be  used  for  settmg 
boilers  ? 

A.  The  walls  should  be  of  hard  burned  brick 
laid  in  Portland  cement.  They  should  be  of 
ample  thickness  so  as  to  prevent  loss  by  radiation. 
All  surfaces  exposed  to  the  action  of  the  hot  gases 
should  be  lined  with  best  quality  fire-brick  laid  in 
a  thin  mortar  of  fire-clay. 

Q.  What  should  be  the  course  of  the  gases  in 
a  tubular  boiler  ? 

A.  It  should  be  set  in  such  a  way  that  the  gases 
do  not  pass  over  the  top  of  the  boiler,  unless  there 
is  ample  space  for  a  man  to  enter  and  clean  off 
soot. 

Q.  What  should  be  the  distance  between  the 
grate  bars  and  the  bottom  of  the  boiler  shell  ? 

A.  Not  less  than  24  inches.  In  large  boilers  it 
may  be  as  much  as  30  inches. 

Q.  What  should  be  the  distance  between  the 
back  tube  sheet  and  rear  wall  ? 

A.  From  18  inches  for  a  48-inch  shell  to  24 
inches  for  a  72-inch  shell. 

Q.  What  is  the  best  method  of  holding  boiler 
walls  in  place? 

A.  With  the  aid  of  buck-staves. 

Q.  What  are  buck-staves  ? 


110  roper's  catechism  for 

A.  Vertical  cast-  or  wrought-iron  braces  placed 
on  the  outside  of  the  boiler  walls,  held  together  at 
the  top  and  bottom  by  tie-rods.  Buck-staves  are 
often  made  of  rails,  flattened  at  the  end  to  take 
the  tie-rods. 

Q.   How  should  the  front  of  boilers  be  inclosed  ? 

A.  The  best  method  is  by  a  full  flush  front, 
which  consists  of  cast-iron  plates  covering  the 
entire  front  of  the  setting,  leaving  no  brickwork 
in  sight.  The  half-arch  front  which  covers  only 
the  furnace  is  cheaper  but  less  desirable. 

Q.  When  a  number  of  boilers  are  set  together, 
Avhat  plan  should  be  adopted  ? 

A.  Each  boiler  should  be  set  independently  of 
the  others,  and  each  should  have  a  separate  con- 
nection to  the  stack. 

Q.  Why  is  this  arrangement  better  than  the 
old  way  of  setting  them  in  batteries,  with  a  com- 
mon flue  connection  ? 

A.  Because  each  boiler  can  be  operated  and  shut 
down  independently  of  the  others;  because  the 
draught  of  one  is  not  affected  by  the  others;  and, 
finally,  because  with  the  old  method  of  setting,  it 
often  happened  that  when  one  shell  gave  out  the 
whole  battery  exploded. 

Q.  What  kind  of  boiler  should  be  used  where 
excessive  vibration  exists  or  where  brickwork 
would  be  too  heavy  ? 


STEAM   ENGINEERS   AND    ELECTRICIANS.         Ill 

A.  A  locomotive-  or  marine-type  boiler  is  fre- 
quently used  under  these  circumstances,  because 

they  require  no  brickwork  whatever. 

f 

CARE  AND  MANAGEMENT. 

Q.  What  is  the  first  duty  of  an  engineer  when 
he  takes  charge  of  an  engine  and  boiler  ? 

A.  It  is  his  duty  to  examine  his  boiler  and  see 
that  the  water  is  at  the  proper  level. 

Q.  How  much  water  should  the  boiler  contain 
when  in  use  ? 

A.  The  water  should  be  kept  up  to  the  second 
gauge  while  working,  and  up  to  the  third  at  night. 

Q.  Why  should  the  level  of  the  water  be  raised 
at  night  ? 

A.  As  a  precaution  against  the  water  becoming 
too  low  from  leakage  or  evaporation. 

Q.  In  case  the  water  should  become  dangerously 
low,  what  would  be  the  duty  of  the  engineer  ? 

A.  He  should  immediately  draw  the  fire  and 
allow  the  boiler  to  cool,  and  not  admit  any  cold 
water  to  the  boiler  or  attempt  to  raise  the  safety 
valve,  as  it  would  be  positively  dangerous. 

Q.  Why  would  it  be  dangerous  to  raise  the 
safety  valve  ? 

A.  Because  it  would  lessen  the  pressure  in 
allowing  the  steam  to  escape  from  the  boiler,  thus 
permitting  the  water  to  rise  up  and  come  in  con- 


112  roper's  catechism  for 

tact  with  the  overheated  iron,  and  probably  cause 
an  explosion. 

Q.  In  case  the  water-supply  should  be  cut  off 
from  the  boiler  for  a  short  time,  what  w^ould  be 
the  duty  of  the  engineer  ? 

A.  He  should  cover  his  fire  with  fresh  fuel,  stop 
his  engine,  and  keep  the  regular  quantity  of  w^ater 
in  the  boiler  until  the  accident  is  repaired  and  the 
water-supply  renewed. 

Q.  How  should  an  engineer  proceed  to  get  up 
steam  ? 

A.  He  should  first  see  that  the  water  is  at  the 
proper  level;  he  should  then  remove  all  ashes  and 
cinders  from  the  furnace,  and  cover  the  grate  with 
a  thin  layer  of  coal;  and  after  placing  wood  and 
shavings  on  the  coal,  he  will  be  ready  to  start  the 
fire. 

Q.  What  advantage  is  it  to  place  a  covering  of 
coal  on  the  grate  before  the  wood  or  shavings  ? 

A.  It  is  a  saving  of  fuel,  as  the  heat  that  would 
be  transmitted  to  the  bars  is  absorbed  by  the  coal, 
and  the  bars  are  also  protected  from  the  extreme 
heat  of  the  fresh  fire. 

Q,  Should  an  engineer  allow  his  fire  to  burn 
gradually  when  he  commences  to  get  up  steam 
from  cold  water  ? 

A.  Yes;  as  by  allowing  the  fuel  to  burn  very 
rapidly,  some  parts  of  the  boiler  become  expanded 


STEAM    ENGINEERS    AND    ELECTRICIANS.         113 

to  their  utmost  limits,  while  other  parts  are  nearl}^ 
cold.  Of  course,  a  great  deal  depends  upon  the 
time  in  which  he  has  to  raise  steam. 

Q.   How  should  an  engineer  regulate  his  fire  ? 

A.  He  should  always  keep  the  fire  at  a  uniform 
thickness,  and  not  allow  any  bare  places  or  accu- 
mulations of  ashes  or  dead  coals  in  the  corners  of 
the  furnace,  as  these  places  admit  great  qviantities 
of  cold  air  into  the  furnace  and  render  the  com- 
bustion very  imperfect. 

Q.  Should  an  engineer  avoid  excessive  firing  as 
much  as  possible? 

A.  Yes;  as  excessive  firing  is  always  attended 
with  more  or  less  danger,  because  the  intense  heat 
repels  the  water  from  the  surface  of  the  iron  and 
allows  the  boiler  to  be  burned. 

Q.   How  thick  should  an  engineer  keep  his  fires  ? 

A.  About  3  inches  for  anthracite  coal  and  about 
5  inches  for  soft  coal;  but  he  should  regulate  the 
thickness  of  the  fire  according  to  the  capacity  of 
the  boiler;  if  the  boiler  is  too  small  for  the  engine, 
the  fire  should  'be  kept  thin,  the  coal  supplied  in 
small  C[uantities  and  distributed  evenly  over  the 
grate,  and  the  grate  kept  as  free  as  possible  from 
ashes  and  cinders;  but  if  the  boiler  is  extra  large 
for  the  engine,  the  thickness  of  the  fire  makes  but 
little  difference. 

Q.  What  should  an  engineer  do  in  case,  from 


114  roper's  catechism  for 

neglect  or  any  other  cause,  his  fire  should  become 
very  low  ? 

A.  He  should  neither  poke  nor  disturb  it,  as 
that  would  have  a  tendency  to  put  it  entirely  out, 
but  he  should  place  shavings,  sawdust,  wood,  or 
greasy  waste  on  the  bare  places,  with  a  thin  cover- 
ing of  coal;  then  by  opening  the  draught  to  its 
full  extent  the  fire  will  soon  come  up.  If  it 
should  become  necessary  to  burn  wood  on  a  coal 
fire,  it  is  always  best  to  make  an  opening  through 
the  coal  to  the  grate-bars,  so  that  the  air  from  the 
bottom  of  the  furnace  can  act  directly  on  the  wood 
and  increase  the  combustion. 

Q.  Should  an  engineer  give  great  attention  to 
the  regulation  of  the  draught  in  the  furnace  ? 

A.  Yes;  the  regulation  of  draught  is  one  of  the 
most  important  of  an  engineer's  duties;  in  fact, 
it  is  next  in  importance  to  the  regulation  of  the 
water  in  the  boiler. 

Q.   How  do  you  explain  that  ? 

A.  Because  it  is  well  known  that  immense 
quantities  of  fuel  are  recklessly  wasted  by  igno- 
rance and  carelessness  in  the  management  of  the 
draught. 

Q.  How  should  an  engineer  regulate  his  draught 
to  obtain  the  best  results  from  the  fuel  ? 

A.  He  should  have  no  more  draught  at  any  time 
than  would  produce  a  sufficient  combustion  of  the 


STEAM    ENGINEERS   AND    ELECTRICIANS.         115 

fuel  to  keep  the  steam  at  the  working  pressure,  as 
by  opening  the  clamper  to  its  utmost  limits  great 
quantities  of  heat  are  carried  into  the  chimney 
and  lost. 

Q.  Can  an  engineer  carry  out  this  principle  of 
regulating  the  draught  in  all  cases  ? 

A,  No;  only  in  furnaces  and  boilers  that  are 
sufficiently  large  to  furnish  the  necessary  amount 
of  steam  without  forcing.  Of  course,  where  the 
boiler  is  too  small  for  the  engine,  or  has  not  suf- 
ficient heating  surface  it  is  impossible  to  economize 
fuel. 

Q.  Is  it  objectionable  to  throw  steam  or  water 
under  the  grate-bars  of  locomotive  boilers,  when 
such  boilers  are  used  for  stationary  engines  ? 

A.  Yes;  as  steam  or  water  in  the  ashpit  forms 
a  lye  with  the  ashes  and  corrodes  the  iron  and 
destroys  the  water-legs  of  the  boiler. 

Q.  Should  an  engineer  in  all  cases  keep  his  ash- 
pit clean  ? 

A.  Yes;  by  allowing  the  ashpit  to  become  filled 
with  ashes  and  cinders  the  air  becomes  heated  to 
a  high  temperature  before  entering  the  fire;  the 
grate-bars  also  become  overheated,  and  in  many 
cases  either  badly  warped  or  melted  down. 

Q.  How  should  an  engineer  keep  his  safety 
valve  ? 

A.  He  should  keep  it  at  all  times  in  good  work- 


116  roper's  catechism  for 

ing  order,  and  move  it  at  least  once  a  day,  partic- 
ularly in  the  morning, 

Q.  AVhy  should  he  move  the  safety-valve  every 
morning  ? 

A.  To  see  that  all  its  parts  are  in  good  working 
order  before  getting  up  steam. 

Q.  Would  you  consider  it  reprehensible  conduct 
on  the  part  of  an  engineer  who  would  weight  his 
safety-valve  in  order  to  carry  a  pressure  greater 
than  that  he  knew  to  be  safe  ? 

A.  Yes;  such  conduct,  if  proved,  ought  to  be 
sufficient  to  disqualify  any  engineer  from  ever 
taking  charge  of  an  engine  and  boiler  again. 

Q.  What  is  the  duty  of  an  engineer  in  regard  to 
blowing  out  his  boilers  ? 

A.  He  should  carefully  remove  all  the  fire  from 
the  furnace,  and  see  that  the  steam  is  at  the  proper 
pressure,  say  from  45  to  50  pounds.  He  should 
also  close  his  damper. 

Q.  Should  any  time  intervene  between  the 
drawing  of  the  fire  and  the  blowing  out  of  the 
boiler? 

A.   Yes;  at  least  one  hour. 

Q.  Why  should  the  blowing  out  of  the  boiler 
be  deferred  for  an  hour  after  the  fire  is  drawn  ? 

A.  To  allow  the  furnace  to  cool,  and  prevent 
the  boiler  from  being  injured  with  the  heat  after 
the  water  is  all  blown  out. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         117 

Q.  Why  not  blow  out  the  boiler  under  a  high 
pressure  of  steam,  say  70,  80,  or  even  90  pounds 
to  the  square  inch  ? 

A.  Because  the  higher  the  steam  pressure  the 
higher  the  temperature  of  the  iron,  so  that  by 
blowing  out  the  boiler  under  a  high  steam  pressure, 
the  change  is  so  sudden  that  it  has  a  tendency  to 
contract  the  iron  and  cause  the  boiler  to  leak. 

Q.  Should  the  engineer  fill  his  boiler  with  cold 
water  immediately  after  blowing  out  ? 

A.  No;  as  the  introduction  of  cold  water  into 
the  boiler  before  the  temperature  of  the  iron 
becomes  lower  would  in  all  probability  cause  the 
boiler  to  leak. 

,Q.  How  often  should  an  engineer  blow  out  his 
boiler  ? 

A.  Whenever  he  discovers  any  appearance  of 
mud  in  the  water. 

Q.  Is  it  not  customary  with  some  engineers  and 
owners  of  steam  boilers  to  blow^  out  their  boilers 
once  a  week  ? 

A.  Yes;  but  the  wisdom  of  this  practice  is 
doubtful.  When  fresh  water  is  boiled,  it  is  sup- 
posed to  deposit  its  minerals,  and  after  that  it  is 
not  advisable  to  blow  out  the  pure  water  and  fill 
the  boiler  with  water  holding  matter  in  solution 
and  suspension.  How  often  a  boiler  should  be 
blown  out  depends  on  the  nature  of  the  water  used. 


118  roper's  catechism  for 

Q.  Should  an  engineer,  when  filUng  his  boilers, 
open  some  cock  or  valve  in  the  steam  room  of  the 
boiler  and  allow  the  air  to  escape  ? 

A.  Yes;  otherwise  the  air  would  retard  the 
ingress  of  the  water,  and  also  collect  in  the  steam 
room  of  the  boiler  and  prevent  the  regular  expan- 
sion of  the  iron  when  the  fire  is  started. 

Q.  What  do  you  mean  by  the  steam  room  of  a 
boiler? 

A.  1  mean  that  portion  of  the  boiler  occupied 
by  steam  above  the  water. 

Q.  AVhat  is  meant  by  the  water  room  in  a  steam 
boiler  ? 

A.  That  portion  of  the  boiler  occupied  by  water. 

Q.  What  do  you  call  the  fire-line  of  the  boiler  ? 

A.   The  fire-line  of  the  boiler  is  a  longitudinal 
line  above  which  the  fire  cannot  rise  on  account  of 
the  masonry  by  which  the  boiler  is  surrounded. 
•  Q.   How  often  should  an  engineer  clean  the  tubes 
or  flues  of  his  boiler  ? 

A.  At  least  once  a  week;  he  should  also  remove 
all  ashes  and  soot  that  become  attached  to  the  out- 
side of  the  boiler. 

Q.  What  advantage  is  gained  by  cleaning  the 
flues  and  tubes  regularly,  and  also  removing  the 
soot  and  ashes  that  become  attached  to  the  boiler  ? 

A.  It  makes  a  great  saving  in  fuel,  as  it  allows 
the  fire  to  act  directly  upon  the  iron. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         119 

Q.  How  often  should  an  engineer  clean  his 
boilers  ? 

A.   Every  three  months,  if  possible. 

Q.  Should  an  engineer,  when  cleaning  his  boil- 
ers, examine  all  stays,  braces,  seams,  and  angles 
of  the  boiler  or  boilers  ? 

A.  Yes;  he  should  make  a  thorough  examina- 
tion of  all  parts  of  the  boiler,  seams,  rivets, 
crown-sheet,  crown-bars,  crow-feet,  cotters,  and 
braces;  he  should  also  sound  the  shell  of  the 
boiler  with  a  very  light  steel  hammer. 

Q,   Why  should  the  engineer  sound  the  boiler? 

A.  Because  it  is  the  only  way  in  which  he  can 
determine  the  condition  of  the  iron. 

Q.  How  often  should  an  engineer  test  his  steam- 
er pressure-gauge  ? 

A.  At  least  once  a  year. 

Q.   Can  an  engineer  test  a  steam-gauge  himself  ? 

A.  No;  unless  he  has  a  test-gauge,  which  is  not 
very  often  the  case.  The  gauge  ought  to  be  tested 
by  another  gauge  built  or  made  expressly  for  that 
purpose. 

Q.  How  should  an  engineer  keep  his  glass 
water-gauges  ? 

A.  He  should  keep  them  perfectly  clean  inside 
and  out. 

Q.  How  can  an  engineer  clean  his  glass  water- 
gaus'es  inside  ? 


120  roper's  catechism  for 

A.  By  opening  the  drip-cock  and  closing  the 
water- valve,  and  allowing  the  steam  to  rush  down 
the  glass  and  carry  out  the  mud  or  sediment. 
They  should  also  be  swabbed  out  with  a  piece  of 
'  cloth  or  waste  on  a  small  stick,  when  the  boiler  is 
cold;  but  care  should  be  taken  not  to  touch  the 
inside  of  the  glass  with  wire  or  iron,  as  an  abrasion 
Avill  immediately  take  place. 

Q.  In  case  an  engineer  has  a  glass  water-gauge, 
should  he  neglect  his  gauge-cocks  ? 

A.  No;  he  should  examine  them  several  times 
in  the  day,  see  that  they  are  in  good  working  order, 
and  grind  or  repair  them  if  necessary.  He  should 
always  be  sure  to  shut  them  tight,  as  by  leaving 
them  loose  the  steam  and  water  destroy  the  seat 
of  the  valve  and  render  them  useless. 

Q.  What  evidence  do  dirty  or  broken  glass 
gauges,  filthy  boiler-heads,  leaking  and  muddy 
gauge-cocks  give  of  a  man's  ability  as  an  en- 
gineer ? 

A.  They  furnish  strong  evidence  of  his  igno- 
rance or  neglect  of  duty. 

Q.  What  should  an  engineer  do  in  cold  weather, 
when  his  pumps,  boiler  connections,  steam  gauges, 
or  water-pipes  are  liable  to  be  frozen  ? 

A.  He  should  open  all  drip-  or  discharge-cocks 
and  allow  the  water  to  run  out  when  he  stops  work 
at  night,   and  in  the  morning  make  a  thorough 


STEAM    ENGINEERS    AND    ELECTRICIANS.         121 

examination  of  all  steam-  and  water-connections 
before  he  starts  his  fires. 

Q.  In  case  it  becomes  necessary  to  stop  the 
engine,  and  the  steam  commences  to  blow  off  at 
the  safety-valve,  what  is  the  duty  of  the  engineer  ? 

A.  He  should  immediately  start  his  pump  or 
injector,  and  also  cover  his  fire  with  fresh  coal,  so 
that  the  circulation  might  be  kept  up  by  the  feed- 
water,  and  the  extreme  heat  of  the  fire  absorbed 
by  the  fresh  coal,  instead  of  being  communicated 
to  the  iron  of  the  boiler;  and  he  should  not 
attempt,  under  any  circumstances,  to  interfere 
with  the  free  escape  of  the  steam  through  the 
safety-valve. 

Q.  Whenever  the  fire-door  of  the  furnace  is 
open,  should  the  damper  be  closed,  if  possible  ? 

A.  Yes;  the  door  and  the  damper  should  never 
be  open  at  the  same  time,  unless  it  is  absolutely 
necessary,  as  the  cold  air,  that  would  otherwise 
have  to  pass  through  the  fire  and  become  heated, 
rushes  in  through  the  open  door  above  the  fire  and 
impinges  on  the  tube  and  crown-sheets,  and  has  a 
tendency  to  contract  the  seams  and  cause  leakage. 

Q.  In  case  it  should  become  necessary  to  ex- 
amine the  check-valve  while  steam  is  on  the  boiler, 
how  should  it  be  done  ? 

A.  The  stop-cock  between  the  check-valve  and 
boiler  should  be  first  closed  before  any  attempt  is 


122  roper's  catechism  for 

made  to  unscrew  or  remove  the  check.  Any 
neglect  to  close  the  stop-cock  might  result  in  a 
serious  accident. 

Q.  How  should  an  engineer  proceed  to  make  a 
joint  on  the  man-hole  or  hand-holes  of  his  boiler  ? 

A.  He  should  first  carefully  remove  all  gum  or 
other  material  from  the  seat  or  flange  where  the 
joint  is  to  be  made,  so  that  the  gasket  may  have  a 
smooth  and  solid  bearing  before  he  commences  to 
tighten  the  nut. 

Q.  Do  you  know  any  other  important  duty  an 
engineer  should  consider  himself  bound  to  per- 
form ? 

A.  Yes;  he  should  daily  make  a  thorough  ex- 
amination of  all  safety-valves,  pumps,  injectors, 
and  all  steam-  and  water-connections. 

Q.  What  should  be  said  of  an  engineer  who 
would  allow  his  boiler  and  engine  to  run  jon  from 
bad  to  worse,  expecting  some  day  to  have  a  general 
overhauling,  instead  of  making  repairs  as  they 
were  needed  ? 

A.  He  should  be  considered  totally  unfit  for 
the  position  of  an  engineer. 

Q.  When  can  it  be  said  that  an  engineer  has 
done  his  duty  ? 

A.  When  he  shows  by  his  work  that  he  has 
cared  for  everything  connected  with  his  engine  and 
boiler  in  the  best  possible  manner. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         123 


SCALE-FORMATION,  CORROSION,  FOAMING, 
AND  PRIMING. 

Q.  What  are  the  results  of  scale  in  boilers,  and 
why? 

A.  Increased  coal  consumption  and  burning  of 
the  plates.  Because  the  scale  being  a  poor  con- 
ductor of  heat,  the  heat  of  the  fire  is  not  imparted 
to  the  water  as  completely  as  if  the  scale  were  not 
there.  For  the  same  reason  the  water  does  not 
protect  the  iron  against  crystallization  and  burning. 

Q.  What,  roughly,  is  the  conductivity  of  scale 
as  compared  to  iron  ? 

A.  About  1   :  35. 

Q.  What  are  the  principal  ingredients  contained 
in  water  which  cause  the  formation  of  scale  ? 

A.  Sulphate  of  lime,  phosphate  of  lime,  car- 
bonate of  lime,  magnesia,  silica,  and  alumina. 
In  sea-water  the  most  important  of  these  is  sul- 
phate of  lime. 

Q.   How  may  the  formation  of  scale  be  checked  ? 

A.   By  the  use  of  boiler  compounds. 

Q.  Is  there  any  boiler  compound  which  will  be 
effective  in  all  cases  ? 

A.  No;  the  composition  of  a  boiler  compound 
should  be  determined  by  the  nature  of  the  im- 
purities. Thus,  a  proper  amount  of  carbonate  of 
soda    introduced   regularly  with    the   feed- water 


124  roper's  catechism  for 

would  prevent  the  formation  of  scale  if  the  in- 
gredient in  the  water  which  tends  to  produce  it  is 
sulphate  of  lime;  but  this  would  be  of  no  value 
if  the  scale  -  producing  substance  is  silica  or 
alumina. 

Q.  What  are 'the  principal  substances  used  to 
check  the  formation  of  scale  ? 

A.  Carbonate  of  soda  if  the  scale-forming  in- 
gredient is  sulphate  of  lime;  phosphate  of  sodium 
for  the  sulphates  of  lime  and  magnesium;  milk 
of  lime  for  the  carbonates  of  lime  and  magnesium; 
caustic  soda  and  soda  ash  for  the  carbonate  and 
sulphate  of  calcium;  and  sulphate  of  magnesium 
and  tannate  of  soda  foT  the  sulphate  and  carbonate 
of  lime. 

Q.  How,  then,  should  we  proceed  if  it  is  found 
that  an  undue  amount  of  scale  forms  in  the 
boiler  ? 

A.  We  should  have  a  chemical  analysis  of  the 
feed-water  made  and  add  sufficient  quantities  of 
the  proper  kinds  of  salts  to  transform  the  scale- 
producing  ingredients  into  soluble  salts. 

Q.  In  what  other  ways  may  the  formation  of 
scale  be  prevented  ? 

A.  The  use  of  feed-w^ater  heaters  and  purifiers 
of  the  open  type  is  often  sufficient,  especially 
where  the  amount  of  impurity  is  not  very  great. 

Q.  In  what  way  does  this  remedy  the  difficulty? 


STEAM    ENGINEERS   AND    ELECTRICIANS.         125 

A.  By  causing  the  impurities  to  be  deposited 
in  the  heater  or  purifier,  where  they  can  do  no 
harm  and  whence  they  may  easily  be  removed 
without  interfering  with  the  operation  of  the  plant. 

Q.   What  is  meant  by  corrosion  ? 

A.  By  corrosion  is  meant  the  wasting,  pitting, 
or  grooving  of  the  iron  in  the  boiler. 

Q.   To  what  is  it  generally  due  ? 

A.  External  corrosion  is  due  to  the  chemical 
action  of  sulphur  or  other  products  contained  in 
the  fuel  and  in  the  atmosphere.  Internal  corro- 
sion is  caused  by  the  chemical  action  of  acid  and 
mineral  substances  contained  in  the  water. 

Q.   AVhat  are  the  remedies  ? 

A.  Numerous  remedies  are  employed  to  prevent 
internal  corrosion,  such  as  painting  the  interior  of 
the  boiler  with  Portland  cement,  allowing  a  thin 
layer  of  scale  to  form,  or  suspending  metallic  zinc 
in  the  water  and  steam  spaces,  all  of  which  are 
effective  in  some  cases.  There  seems  to  be  no 
effectual  remedy  against  external  corrosion  when 
produced  by  foreign  substances  contained  in  the 
fuel. 

Q.   What  is  meant  by  foaming  ? 

A.  By  foaming  is  meant  a  violent  agitation  of 
the  water  in  the  boiler.  It  can  be  detected  by  the 
rising  and  falling  of  the  level  of  the  water  in  the 
gauge  glass  and  by  its  disturbed  condition. 


126  roper's  catechism  for 

Q.  What  is  the  cause  of  foaming  in  steam 
boilers  ? 

A.  Foaming  in  steam  boilers  might  be  attributed 
to  different  causes.  First^  to  the  boiler  not  having 
a  sufficient  amount  of  steam-room,  so  that  when- 
ever the  valve  opens  to  admit  steam  to  the  cylinder, 
the  pressure  on  the  surface  of  the  water  is  less- 
ened, allowing  the  water  to  rise  up  from  the  bot- 
tom of  the  boiler.  Second^  foaming  is  sometimes 
caused  by  the  foul  condition  of  the  boiler;  but  in 
such  cases  it  will  be  easy  to  discover  the  cause,  as 
the  water  in  the  glass  gauge  will  appear  quite 
muddy.  Third,  foaming  is  caused  by  the  presence 
of  any  substance  of  a  soapy  or  greasy  nature  in 
the  water.  But  whatever  may  be  the  cause  of 
foaming,  it  is  always  attended  with  great  danger 
to  the  boiler  and  a  certain  amount  of  injury  to  the 
engine. 

In  all  cases  where  a  boiler  foams  badly,  the 
water  is  lifted  from  the  fire-surface  of  the  boiler, 
and  allows  the  iron  to  burn;  also,  the  mud  and 
water  from  the  boiler  are  carried  over  with  the 
steam  to  the  cylinder,  occupying  the  clearance 
between  the  piston  and  the  head  of  the  cylinder, 
not  only  destroying  the  surface  of  the  cylinder  by 
the  grit  and  dirt,  but  in  many  cases  causing  the 
fracture  of  the  cylinder-head. 

Q.  What  is  the  best  preventive  against  foaming  ? 


STEAM    ENGINEERS   AND    ELECTRICIANS.         127 

A.  The  best  preventives  against  foaming  are — 
First,  a  clean  boiler.  Second,  pure  water.  Third, 
a  sufficient  amount  of  steam-room.  Fourth,  a 
steam  pipe  well  proportioned  to  the  size  of  the 
engine. 

Q.   What  is  meant  by  priming  ? 

A.  The  passage  of  water  from  the  boiler  to  the 
cylinder  of  the  engine  in  the  shape  of  spray. 

Q.   How  may  it  be  detected  ? 

A.  By  the  appearance  of  the  exhaust  from  the 
engine,  which,  when  moist,  is  white  instead  of 
colorless,  as  is  the  case  when  dry,  and  by  a  click- 
ing noise  in  the  cylinder,  which  almost  invariably 
accompanies  the  presence  of  moisture. 

Q.  AVhat  causes  priming  ? 

A.  Usually  the  want  of  sufficient  steam  space 
in  the  boiler,  or  the  water  being  carried  at  too 
high  a  level. 


128       roper's  catechism  for 

ADJUNCTS  OF  STEAM  BOILERS. 

THE  SAFETY-VALVE. 

The  form  and  construction  of  this  indispensable 
adjunct  to  the  steam  boiler  are  of  the  highest 
importance,  not  only  for  the  preservation  of  life 
and  property,  which  would  in  the  absence  of  this 
means  of  safety  be  constantly  jeopardized,  but  also 
to  secure  the  durability  of  the  steam  boiler  itself. 

Increasing  the  pressure  to  a  dangerous  degree 
would  be  impossible  in  any  boiler  if  the  safety- 
valve  were  what  it  is  supposed  to  be, — a  perfect 
means  for  liberating  all  the  steam  which  a  boiler 
may  produce  with  the  fires  in  full  blast,  and  all 
other  means  for  the  escape  of  steam  closed.  Until 
such  a  safety-valve  shall  be  devised  and  adopted 
in  general  use,  safety  from  gradually  increasing 
pressure  must  depend  on  the  attention  and  watch- 
fulness of  the  engineer. 

Q.  AVhat  is  the  object  of  the  safety-valve? 

A.  It  is  a  valve  intended  to  relieve  the  boiler 
from  extra  pressure,  and  prevent  bursting,  col- 
lapse, or  explosion. 

Q.   How  is  this  accomplished  ? 

A.  By  balancing  the  steam  pressure  against  that 
of  a  spring  or  weight  in  such  a  way  that  when  the 
pressure  in  the  boiler  exceeds  the  limit  of  safety, 


STEAM    ENGINEERS   AND    ELECTRICIANS.         129 

it  overcomes  the  action  of  the  spring  or  weight 
and  opens  a  valve,  allowing  the  surplus  pressure 
to  be  relieved. 

Q.   How  often  should  the  safety-valve  be  moved  ? 

A.  At  least  once  a  day,  more  particularly  in  the 
morning. 

Q.  Why  should  the  safety-valve  be  moved  in 
the  morning? 

A.  So  as  to  be  sure  that  it  is  in  good  working 
order  before  starting  the  fire. 

Q.  What  are  the  most  important  principles  to  be 
adhered  to  in  the  construction  of  the  safety-valve  ? 

A.  Simplicity  of  construction,  directness,  and 
freedom  of  action. 

Q.  Does  the  safety-valve  become  worn  and 
leaky  by  the  continual  action  of  the  steam  ? 

A.  Yes;  all  safety-valves  become  leaky  and 
ought  to  be  ground  carefully  on  their  seats. 

Q.  What  is  the  best  material  to  use  for  grinding 
safety-valves  ? 

A.  Pulverized  glass,  grit  of  grinding-stones,  or 
fine  emery. 

Q.  Should  safety-valves  be  constructed  with 
loose  or  vibratory  stems  ? 

A.  Yes;  as  the  rigid  or  solid  stem  is  apt  to  be- 
come jammed  by  the  canting  of  the  lever  and 
weight,  and  in  such  cases  the  higher  the  pressure 
the  more  difficult  it  is  for  the  valve  to  open. 


130  roper's  catechism  for 

Q.  What  are  the  principal  kinds  of  safety- 
valves  ? 

A.   There  are  three  principal  classes,  namely: 

(a)  The  dead-weight  safety-valve,  in  which 

the  pressure  of  the  steam  is  balanced 
by  a  weight  placed  directly  on  the 
valve-spindle. 

(b)  The  spring  safety-valve,  which  is  similar 

to  the  above  except  that  the  weight 
is  replaced  by  a  spring. 

(c)  The  lever  safety-valve,  in  which  a  weight 

or  spring,  instead  of  acting  directly 
on  the  valve-spindle,  is  attached  at 
the  end  of  the  lever,  the  adjustments 
being  made  by  altering  its  position 
on  the  lever. 
Q.  What  are  the  relative  advantages  of  springs, 
as  compared  to  weights  in  safety-valves  ? 

A.  Weights  have  the  advantage  that  they  do 
not  change,  which  springs  are  liable  to  do  when 
in  tension.  On  the  other  hand,  weights  could  not 
be  used  on  vessels  or  locomotives  on  account  of 
the  motion;  the  momentum  which  the  weight 
would  acquire  would  constantly  alter  the  blowing- 
off  pressure.  For  these  reasons  weight  safety- 
valves  are  mostly  used  in  connection  with  station- 
ary boilers,  while  spring  safety-valves  are  used 
exclusively  for  marine  and  locomotive  boilers. 


STEAM   ENGINEERS   AND   ELECTRICIANS.         131 

Q.  How  are  safety-valves  set  for  a  given  blowing- 
oif  pressure  in  the  dead- weight  and  spring  type  ? 

A.  By  simply  adjusting  the  weight  or  the  ten- 
sion of  the  spring  until  it  is  equal  to  the  blowing- 
off  pressure  in  pounds  per  square  inch,  times  the 
area  of  the  valve  in  square  inches. 

Q.  How  do  you  calculate  what  weight  should 
be  placed  on  the  end  of  a  given  lever  safety-valve 
for  a  certain  blowing-off  pressure? 

A.  Multiply  the  area  of  the  valve  in  square 
inches  by  the  blowing-off  pressure  in  pounds  per 
square  inch  and  the  distance  of  the  valve  from 
the  fulcrum  in  inches;  multiply  the  weight  of  the 
lever  in  pounds  by  the  distance  of  its  center  of 
gravity  from  the  fulcrum  in  inches;  multiply  the 
weight  of  the  valve  and  steam  in  pounds  by  their 
distance  from  the  fulcrum  in  inches;  add  the  last 
two  products  together,  subtract  their  sum  from 
the  first  product  and  divide  the  remainder  by  the 
total  length  of  the  lever.  The  quotient  will  be 
the  required  weight  in  pounds. 

Q.  How  do  you  calculate  the  distance  of  the 
weight  from  the  fulcrum  for  a  given  blowing-off 


pressure 


? 


A.  Multiply  the  pressure  by  the  area  and  the 
distance  from  the  fulcrum  from  the  valve;  multi- 
ply the  weight  of  the  lever  by  the  distance  of  its 
center  of  gravity  from  the  fulcrum;  multiply  the 


132 


roper's  catechism  for 


weight  of  the  valve  and  stem  by  their  distance 
from  the  fulcrum;  add  the  last  two  products, 
deduct  them  from  the  first  product,  and  divide 
the  remainder  by  the  weight  of  the  ball.  The 
quantities  being  again  taken  in  pounds  and  inches, 
the  result  will  be  the  distance  of  the  weight  from 
the  fulcrum  in  inches. 

Q.   How  do  you  calculate  the  bloAving-off  pres- 
sure for  a  given  position  of  the  ball  ? 


A.  Multiply  the  weight  of  the  valve  and  stem 
in  pounds  by  their  distance  from  the  fulcrum. 
Multiply  the  weight  of  the  lever  by  the  distance 
of  its  center  of  gravity  from  the  fulcrum.  Multi- 
ply the  weight  of  the  ball  by  its  distance  from  the 
fulcrum.  Multiply  the  area  of  the  valve  by  its 
distance  from  the  fulcrum.  Divide  the  sum  of 
the  first  three  products  by  the  last  product.     The 


STEAM    ENGINEERS   AND   ELECTRICIANS.         133 

quantities  being  all  taken  in  pounds  and  inches, 
the  result  will  be  the  pressure  at  which  the  valve 
will  blow  off  in  pounds  per  square  inch. 

Q.   How  can  these  three  rules  be  expressed  by 
simple  formulse  ? 

A.   If  in  the  diagram  on  opposite  page  — 
W  =  weight  of  ball  in  pounds, 
w  =  weight  of  valve  and  stem  in  pounds, 
ii\  =  weight  of  lever  in  pounds, 
l^  =  distance   from   fulcrum   to  valve  in 

inches, 
Zj  =  distance  from  valve  to  ball  in  inches, 
I  =  distance  from    fulcrum   to  center  of 

gravity  of  lever  in  inches, 
p  z=  steam  pressure  in  pounds  per  square 

inch, 
a  =  area  of  valve  in  square  inches, — 
then : 

pal,  =  10  l^  +  u\  I  +  W  (/,  -f  g 
_  p  a  /,  —  [w  I,  +  IV,  q 

^  ~  a  I, 

pal,  —  IV  I,  — IV,  I 

Q.   How  would  you   find   the  distance  of   the 
center  of  gravity  of  a  lever  from  the  fulcrum  ? 


134  ropee's  catechism  for 

A.  If  the  lever  is  of  "aniform  cross-section,  as  in 
the  diagram  shown  on  page  132,  the  center  of 
gravity  would  be  at  its  middle  point;  but  if  the 
lever  is  taper,  proceed  according  to  the  following  — 
Rule  for  finding  the  distance  of  the  center  of 
gravity  of  taper  levers  from  the  fulcrum. — To  the 
width  of  the  small  end  of  the  lever  add  one-third 
of  the  difference,  in  width,  between  the  large  and 
the  small  end  of  the  lever.  Multiply  the  sum  by 
the  length  of  the  lever,  and  divide  the  product  by 
the  sum  of  the  large  and  the  small  end  of  the 
lever,  all  in  inches.  The  quotient  will  be  the  re- 
quired distance  in  inches. 

Q.  How  would  you  express  this  in  a  formula  ? 
A.  If  we  let — 

a  =  width  of  the  large  end  in  inches, 
b  =  width  of  the  small  end  in  inches, 
I  =  distance  of  center  of   gravity  from 

fulcrum  in  inches, 
L  =  total  length  of  lever  in  inches, — 
the  formula  is: 

_  g  4-  2  5     L 
~    a  +  6    •  3  * 

Q.  With  the  aid  of  this  rule  and  the  one  given 
on  page  133,  find  the  weight  to  be  placed  at  the 
end  of  the  lever  of  a  safety-valve  under  the  fol- 
lowing conditions : 


STEAM   ENGINEERS   AND    ELECTRICIANS.         135 

width  of  large  end  of  lever  =  3  inches, 

width  of  small  end  of  lever  =  2  inches, 

total  length  of  lever  =  30  inches, 

area  of  valve  =  7  sq.  inches, 

weight  of  lever  =  9  pounds, 

weight  of  valve  and  stem  -    =  6  inches, 

distance  of  valve  stem  from 

fulcrum  =  3  inches, 

blowing-off  pressure  =  60  pounds. 

A.   By  the  rule  for  finding  the  distance  of  center 

of  gravity,  we  have 

,       3  +  2x2^  30       ,,.. 
I  =  — g    I    2 —  X  -Q-  =  14  mches. 

By  the  rule  for  finding  the  weight  of  the  ball, 
we  have 

60  X  7  X  3  —  [6  X  3  +  9  X  14] 
^~  30 

=  37.2  pounds 
for  the  required  weight  to  be  placed  at  the  end  of 
the  lever. 

Q.  Suppose   this  weight  were   moved   back  so 
that  its  distance   from   the   fulcrum   became   26 
inches,  at  what  pressure  would  the  valve  blow  off  ? 
A.   By  the  second  formula, 

6X3  +  9X14  +  37.2  X  26       ^„  , 

p  =rz 1  x  Z ^       pounds. 

Q.   Where  should-  the  weight  be  placed,  so  that 
the  valve  would  blow  off  at  a  pressure  of  45  pounds  ? 


136  roper's  catechism  for 

A.  By  the  third  formula, 

45X7X3  —  6X3  —  9X14 
^i-f^2—  37  2 

=  21^  inches  from  fulcrum. 

Q.  How  large  should  the  area  of  safety-valves 
be  made  for  different  sizes  of  boilers  ? 

A.  There  are  a  great  many  rules  governing  the 
areas  of  safety-valves.  Some  rules  base  it  on  the 
heating  surface,  some  on  the  grate  surface,  some 
on  the  coal  consumption,  some  on  the  water 
evaporated,  and  some  on  the  heating  surface  and 
gauge  pressure.  The  rule  given  by  Professor 
Thurston  gives  average  values.     It  is  as  follows: 

Rule.  Multiply  the  heating  surface  in  sq.  feet 
by  5  and  divide  the  product  by  10  plus  the  gauge 
pressure  in  pounds  per  sq,  inch.  The  quotient 
divided  by  2  gives  the  proper  area  in  square  inches. 

Q.  How  much  steam  should  a  safety-valve  be 
capable  of  discharging? 

A.  About  twice  as  much  as  that  corresponding 
to  the  rated  capacity  of  the  boiler,  because  when 
the  boiler  is  forced  to  the  utmost  it  is  capable  of 
generating  a  much  greater  quantity  of  steam  than 
its  rating  calls  for. 

Q.  Should  a  boiler  have  only  one  safety-valve? 

A.  No;  it  should  have  at  least  two,  for  each 
boiler  fired  separately  or  for  each  set  of  boilers 
placed  over  one  fire. 


STEAM   ENGINEERS   AND    ELECTRICIANS. 


137 


A  TABLE  FOE  SAFETY-VALVES. 

Containing  the  Cikcumfeeences  and  Aeeas  of 

Circles  from  ^-^  of  an  inch  to  4  inches. 


Diameter. 

Circumfer- 
euce. 

Area. 

Diameter. 

Circiinifei- 
euce. 

Area. 

tV 

.1963 

.0030 

2  ins. 

6.2832 

3.1416 

i 

.3927 

.0122 

tV 

6.4795 

3.3411 

A 

.5890 

.0276 

i 

6.6759 

3.5465 

i 

.7854 

.0490 

A 

6.8722 

3.7582 

A 

.9817 

.0767 

i 

7.0686 

3.9760 

f 

1.1781 

.1104 

T% 

7.2649 

4.2001 

t\ 

1.3744 

.1503 

1 

7.4613 

4.4302 

^ 

1.5708 

.1963 

/f 

7.6576 

4.6664 

t\ 

1.7671 

.2485 

1 

7.8540 

4.9087 

1 

1.9635 

.3068 

fe 

8.0503 

5.1573 

H 

2.1598 

.3712 

8.2467 

5.4119 

f 

2.3562 

.4417 

H 

8.4430 

5.6727 

f 

2.5525 

.5185 

1 

8.6394 

5.9395 

2.7489 

.6013 

if 

8.8357 

6.2126 

if 

2.9452 

.6903 

i 

9.0321 

6.4918 

11 

9.2284 

6.7772 

lin. 

3.1416 

.7854 

t 

3.3379 

.8861 

3  ms. 

9.4248 

7.0686 

3.5343 

.9940 

tV 

9.6211 

7.3662 

tV 

3.7306 

1.1075 

? 

9.8175 

7.6699 

•i 

3.9270 

1.2271 

A 

10.0138 

7.9798 

tV 

4.1233 

1.3529 

I 

10.2102 

8.2957 

1 

4.3197 

1.4848 

T% 

10.4065 

8.6179 

tV 

4.5160 

1.6229 

f 

10.6029 

8.9462 

^ 

4.7124 

1.7671 

tV 

10.7992 

9.2806 

A 

4.9087 

1.9175 

i 

10.9956 

9.6211 

1 

5.1051 

2.0739 

A 

11.1919 

9.9678 

H 

5.3015 

2.2365 

1 

11.3883 

10.3206 

f 

5.4978 

2.4052 

il 

11.5846- 

10.6796 

f 

5.6941 

2.5801 

i 

11.7810 

11.0446 

5.8905 

2.7611 

f 

11.9773 

11.4159 

H 

6.0868 

2.9483 

12.1737 

11.7932 

if 

12.3700 

12.1768 

4  ins. 

12^.5664 

12.5654 

138       roper's  catechism  for 

GAUGES. 

Q.  What  is  meant  by  a  gauge  ? 

A,  A  gauge  is  any  instrument  or  device  used 
for  measuring. 

Q.  What  are  the  princijDal  gauges  used  in  con- 
nection with  steam  boilers  ? 

A,  The  steam  pressure  gauge,  vacuum  gauge^ 
water  gauge,  sahnometer,  and  econometer. 

Q.   Describe  the  steam  gauge. 

A.  There  are  two  kinds:  those  which  merely 
indicate  the  pressure  and  those  which  make  a 
permanent  record  of  it.  Both  are  usually  con- 
structed on  the  principle  invented  by  Bourdon, 
and  consist  of  a  thin  tube  of  elliptical  cross-sec- 
tion, bent  into  a  curved  shape.  The  steam  whose 
pressure  is  to  be  measured  is  admitted  into  the 
tube  and  tends  to  make  the  cross-section  circular. 
This  tendency  causes  the  tube  to  straighten  itself 
out  partially,  and  the  instrument  is  so  constructed 
with  a  pointer  and  gearing  that  the  straightening 
of  the  tube  moves  the  pointer  which  indicates  the 
pressure  within  on  a  suitable  dial.  The  recording 
gauge  has,  in  addition,  a  clock  which  moves  the 
dial,  giving  it  one  revolution  in  24  hours,  so  that 
by  the  aid  of  a  pen  or  stylus  filled  with  ink  a 
complete  record  of  the  pressure  carried  during  this 
time  can  be  had. 


STEAM    ENGINEERS    AND    ELECTRICIANS.         139 

Q.   Do  steam  gauges  register  absolute  pressure  ? 

A.  No;  they  are  usually  constructed  to  indicate 
pressure  above  the  atmosphere — that  is,  at  atmos- 
pheric pressure  (14.7  pounds  per  square  inch)  the 
pointer  stands  at  zero. 

Q.  What  precautions  should  be  taken  in  using 
pressure  gauges  ? 

A.  The  pointer  should  always  stand  at  zero 
when  there  is  no  pressure  in  the  boiler.  If  it 
does  not,  it  should  be  adjusted.  Even  after  this 
is  done,  the  readings  at  other  pressures  may  be 
incorrect  and  its  readings  should  be  checked  from 
time  to  time  by  comparing  with  a  standard  gauge 
which  is  known  to  be  correct. 

Q.  What  is  a  vacuum  gauge  ? 

A.  It  is  made  in  the  same  way  as  a  pressure 
gauge,  but  it  is  arranged  to  read  pressures  below 
the  atmosphere  instead  of  above. 

Q.   How  are  vacuum  gauges  calibrated  ? 

A.  They  are  usually  calibrated  in  inches  of 
mercury  instead  of  pounds, — that  is  to  say,  the 
readings  indicate  to  how  many  inches  the  vacuum 
would  allow  a  column  of  mercury  to  rise  under 
atmospheric  pressure.  Each  inch  of  mercury 
corresponds  roughly  to  a  vacuum  of  about  half  a 
pound,  so  that  a  reading  of  20"  on  a  vacuum 
gauge  would  mean  that  the  pressure  is  about  10 
pounds  below  that  of  the  atmosphere. 


140  roper's  catechism  for 

Q.  Why  are  they  calibrated  in  this  way  and  not 
in  absolute  pressures  ? 

A.  Because  the  mechanism  which  operates  the 
gauge  depends  for  its  action  upon  the  difference  in 
pressure  of  the  atmosphere  and  vacuum  chamber; 
hence,  as  the  pressure  of  the  atmosphere  varies, 
the  gauge  would  not  be  accurate  if  calibrated  in 
pounds  absolute  pressure. 

Q.  What  is  a  water  gauge  ? 

A.  It  is  a  device  for  indicating  the  level  of  the 
water  in  the  boiler.  It  usually  consists  of  a  plain 
glass  tube  placed  on  the  outside  of  the  boiler,  and 
connected  at  the  top  to  the  steam-  and  at  the  bot- 
tom to  the  water-space. 

Q.  What  is  a  safety  water  column  ? 

A.  It  is  a  modification  of  a  glass  water  gauge, 
with  floats  so  arranged  that  a  signal  is  given  both 
when  the  water  is  too  high  and  when  it  is  too  low. 

Q.  Do  you  consider  the  use  of  safety  water 
columns  advisable? 

A.  The}^  are  very  useful  where  an  engineer  or 
fireman  has  other  duties  to  perform  besides  attend-, 
ing  to  the  boiler;  but  it  is  a  mistake  for  engineers 
to  neglect  watching  the  water-level  on  account  of 
this  device  becau-se  it  may  get  out  of  order. 
There  can  be  nothing  so  dangerous  in  running 
boilers  as  neglecting  the  water.  In  some  instances 
where  these  safety  water  columns  were  used,  the 


STEAM    ENGINEERS   AND   ELECTRICIANS.         141 

firemen  have  been  known  to  systematically  fall 
asleep  and  depend  on  the  alarm  in  the  safety  water 
column  to  awaken  them  at  the  proper  time. 

Q.  Is  the  glass  gauge  the  only  device  used  for 
indicating  the  water-level  ? 

A.  No ;  every  boiler  should,  in  addition,  be 
fitted  with  gauge  cocks  placed  at  different  levels. 
These  are  partly  for  the  purpose  of  checking  up 
the  glass  gauge  and  partly  for  use  in  case  the 
gauge  glass  should  break,  which  is  not  an  infre- 
quent occurrence. 

Q.  What  is  the  salinometer  ? 

A.  It  is  an  instrument  or  gauge  used  for  indi- 
cating the  quantity  of  salt  contained  in  the  water 
of  marine  boilers. 

Q.  What  is  the  econometer  ? 

A.  It  is  an  instrument  or  gauge  used  for  indi- 
cating, continuously  and  automatically,  the  quan- 
tity of  carbonic  acid  contained  in  the  products  of 
combustion. 

Q.  How  much  carbonic  acid  should  they  con- 
tain? 

A.  As  much  as  possible. 

Q.   How  can  this  be  attained  ? 

A.  By  supplying  enough  air  to  the  furnace  for 
a  complete  combustion  of  the  fuel,  but  not  much 
in  excess  of  that  amount. 

Q.  What  is  the  result  if  too  much  air  is  supplied  ? 


142 


ROPER  S    CATECHISM   FOR 


A.  A  portion  of  the  heat  of  combustion  is  con- 
sumed in  raising  the  temperature  of  the  excess  of 
air  and  consequently  wasted.  The  following  table 
shows  the  amount  of  wasted  fuel  for  different  per- 
centages of  carbonic  acid  in  the  flue  gases: 


TABLE 

SHOWING    WASTE    OF    FUEL     DUE    TO    EXCESSIVE    SUPPLY 
OF   AIR. 

(coal  of  medium  quality.) 


Percentage  carbonic  acid 
in  flue  gases, 

2 

4 

6 

8 

10 

12 

14 

No.  of  times  the  quan- 
tity of  air  required  for 
complete  combustion, . 

9.5 

4.7 

3.2 

2.4 

1.9 

L6 

1.4 

Percentage  waste  of  fuel 
at420OFahr., 

90 

45 

30 

23 

18 

15 

13 

PUMPS  AND  INJECTORS. 

Q.   What  is  a  pump  ? 

A.   It  is  a  device  for  lifting,  forcing,  or  transfer- 
ring water  or  other  liquids. 

Q.   How  are  pumps  usually  operated  ? 
A.    (a)  By  belting  or  gearing  from  some  power 
shaft,  called  power  pumps. 
(6)  By   the   direct   connection   to   a  steam 
cylinder  equipped  with  suitable  valve 


STEAM   ENGINEERS   AND    ELECTRICIANS.         143 

gear  for  the  distribution!  of  the  steam, 
called  steam  pumps, 
(c)  By  direct  connection  or  gearing  to  an 
electric  motor ;  these  are  called  electric 
pumps. 
Q.  Which  of  the  above  types  is  usually  adopted 
for  feeding  boilers  ? 
A.   The  steam  pump. 

Q.  What  different  kinds  of  steam  pumps  are 
there  ? 

A.  (a)  Fly-wheel  pumps — those  in  which  the  re- 
ciprocating motion  of  the  steam  piston 
is  first  converted  into  rotary  motion 
by  means  of  a  crank  shaft,  with  a  fly- 
wheel to  help  it  over  the  dead  cen- 
ters, and  then  re-converted  by  another 
crank  and  rods  into  reciprocating  mo- 
tion for  the  water  cylinder. 
(6)  Direct-acting  pumps — those  in  which  the 
water  piston  or  plunger  is  mounted- 
on  the  same  rod  as  the  steam  piston 
and  the  power  transmitted  from  the 
latter  to  the  former,  direct  and  with- 
out the  intervention  of  a  crank  shaft 
and  fly-wheel.  In  this  type  an  auxil- 
iary valve  gear  is  required  in  addition 
to  the  main  valve  gear,  to  help  the 
machine  over  its  dead  points. 


144  roper's  catechism  for 

(c)  Duplex  pumps — consisting  of  a  combina- 
tion of  two  pumps  so  coupled  together 
that  the  steam-valve  of  the  one  is 
operated  by  the  piston  of  the  other, 
and  vice  versa. 

Q.  Which  of  these  is  most  commonly  used  as  a 
boiler-feed  pump  ?     Why  ? 

A.  The  duplex  pump,  because  it  is  the  simplest. 

Q.  W^hat  is  the  difference  between  a  force  pump 
and  a  suction  pump  ? 

A.  A  force  pump  is  one  in  which  the  energy  is 
expended  in  forcing  the  water  against  some  oppos- 
ing pressure,  such  as  that  in  the  boiler.  A  suction 
pump  is  one  which  takes  the  water  from  a  lower 
level  than  that  of  the  pump,  as,  for  example,  a 
pump  placed  at  the  top  of  a  well. 

Q.  Is  there  any  limit  beyond  which  water  can-, 
not  be  lifted  by  a  suction  pump  ?     Give  reasons. 

A.  Yes;  water  cannot  be  lifted  by  a  suction 
pump  over  33  feet  vertically,  and  it  will  deliver 
water  slowly  only,  at  this  height.  The  reason  for 
this  is  that  the  pump  does  not  actually  lift  the 
water,  but  merely  creates  a  vacuum  in  the  water 
cylinder,  and  the  water  is  lifted  by  the  atmospheric 
pressure  on  its  surface.  The  atmospheric  pressure 
will  support  a  column  of  water  about  33  feet  in 
height,  hence  this  is  the  limit  beyond  which  water 
cannot  be  raised  by  a  suction  pump.     If  the  pump 


STEAM    ENGINEERS   AND    ELECTRICIANS.         145 

and  the  piping  is  tight,  however,  it  will  draw 
water  horizontally  almost  any  distance. 

Q.  Is  there  any  limit  in  the  height  to  which  a 
piimp  will  force  water  ? 

A.   None;  except  the  power  of  the  pump. 

Q.  How  do  you  calculate  the  power  required  to 
pump  water  ? 

A.  Multiply  the  number  of  pounds  of  water  to 
be  pumped  per  minute  by  the  vertical  distance,  in 
feet,  between  the  levels  of  the  supply  and  dis- 
charge, and  divide  the  product  by  33,000;  the 
result  will  be  the  theoretical  horse-power.  To 
this  must  be  added  the  losses  in  friction  corre- 
sponding to  the  velocity  of  the  water  (see  page  63). 
If  instead  of  pumping  the  w^ater  to  a  higher  level 
it  is  required  to  force  it  against  a  pressure,  multi- 
ply by  2J  times  the  pressure  instead  of  the 
height,  making  the  same  correction  for  losses  as 
above. 

Q.  How  do  3^ou  determine  the  capacity  of  boiler- 
feed  pumps  ? 

A.  Calculate  the  amount  of  water  which  the 
boiler  is  capable  of  evaporating  under  normal 
conditions  by  multiplying  the  horse-power  of  the 
boiler  by  30.  This  will  give  the  number  of  pounds 
of  water  it  will  evaporate  per  hour.  Divide  this 
by  8.35,  which  will  give  the  number  of  gallons. 
The  pump  should  be  capable  of  supplying  about 
10 


146  roper's  catechism  for 

double  this  quantity,  so  that  it  will  be  adequate 
when  the  boiler  is  forced. 

Q.  When  the  water  is  hot,  what  precautions 
must  be  taken  with  the  pump  ? 

A.  It  should  be  brass-lined  so  that  it  will  not 
corrode,  and  it  must  be  placed  below  the  level  of 
the  water-supply,  as  otherwise  the  hot  water  will 
not  follow  the  plunger.  It  is  also  advisable  to 
place  a  valve  between  the  supply  and  the  pump, 
so  that  any  accumulated  vapor  may  be  liberated. 

Q.  What  is  an  injector? 

A.  It  is  an  apparatus  for  forcing  water  against 
a  pressure  by  the  direct  action  of  a  jet  of  steam 
upon  a  mass  of  water. 

Q.   Briefly  describe  the  injector  and  its  action. 

A.  It  consists  of  a  steam  nozzle  through  which 
enters  the  steam  used ;  a  water-supply  tube 
through  which  enters  the  water  to  be  forced  ;  a 
combining  tube  which  begins  at  the  end  of  the 
steam  nozzle,  being  that  part  of  the  apparatus 
where  the  steam  and  water  first  come  in  contact; 
and,  finally,  a  delivery  tube  from  which  the  mix- 
ture of  steam  and  water  enters  the  discharge  pipe. 
All  of  these  parts  have  peculiar  shapes,  which 
have  been  determined  by  years  of  experimenting; 
the  object  being  to  give  the  steam  and  water  the 
proper  velocities  at  different  stages  in  the  process. 
The  action  of  the  apparatus  may  be  explained  as 


1 


STEAM    ENGINEERS   AND    ELECTRICIANS.         147 


INJECTOR. 

S,  Steam  nozzle. 

B,  Spinale  for  adjusting  supply  of 

C,  Combining  tube. 
Z>,  Delivery  tube. 


148  roper's  catechism  for 

follows  :  The  steam  leaves  the  nozzle  and  enters 
the  combining  tube  at  a  high  velocity.  The 
friction  between  the  steam  jet  and  the  air  in  the 
water-supply  pipe  causes  the  latter  to  be  exhausted 
and  consequently  the  water  being  relieved  of  the 
pressure  upon  its  surface  soon  rises  and  enters  the 
combining  tube,  where  it  comes  in  contact  with 
the  steam  jet  and  condenses  it.  In  being  con- 
densed the  cross-section  of  the  steam  jet  is  greatly 
reduced,  and  the  entire  energy  of  its  velocity  is 
concentrated  upon  a  very  thin  jet.  This  energy 
being  more  than  sufficient  to  force  it  into  the 
boiler,  some  of  it  is  imparted  to  the  water  which 
it  meets  in  the  combining  tube,  and  the  entire 
mixture  of  steam  and  water  is  carried  into  the 
delivery  tube  and  thence  into  the  boiler  by  virtue 
of  the  momentum  which  it  has  acquired.  Of 
course,  the  apparatus  must  be  carefully  propor- 
tioned, since  if  there  is  too  much  water  the 
energy  of  the  condensed  steam  will  not  be  suf- 
ficient to  carry  it  into  the  boiler,  while  if  there 
is  too  little,  the  steam  will  not  be  condensed. 

Q.  What  are  the  advantages  of  injectors  over 
pumps  ? 

A.  The  principal  advantages  are  that  water 
enters  the  boiler  in  a  steady  stream;  practically 
none  of  the  energy  of  the  steam  used  to  operate 
it  is  wasted,   as  all  the  energy  in  excess  of  that 


STEAM    ENGINEERS   AND    ELECTRICIANS.         149 

necessary  to  force  the  water  into  the  boiler  is 
utilized  in  raising  its  temperature;  the  water  does 
not  enter  the  boiler  cold — it  is  more  compact  and 
has  no  moving  parts. 

Q.  What  is  the  commonest  cause  of  the  failure 
of  injectors  to  operate  ? 

A.  The  presence  of  air  in  the  suction  pipe. 
This  must  be  avoided  by  properly  packing  the 
valve  stem  and  by  entirely  submerging  the  end  of 
the  suction  pipe.  Sediment  or  dirt  in  the  nozzles 
will  also  interfere  with  the  proper  working  of  the 
apparatus.  They  should  be  carefully  cleaned  out 
if  this  occurs. 

Q.  If  the  injector  does  not  get  water,  where 
would  you  look  for  the  trouble  ? 

A.  It  would  probably  be  due  to  one  of  the  fol- 
lowing causes:  a  leak  in  the  supply  pipe,  clogging 
up  of  the  strainer,  too  hot  water,  too  low  a  steam 
pressure  for  the  required  lift,  or  the  water-supply 
may  be  cut  off.  I  should  examine  the  water  pipe 
first  to  see  that  it  was  intact. 

Q.  If  the  injector  starts,  but  afterward  the  jet 
breaks,  where  would  you  expect  to  find  the 
difficulty  ? 

A.  Any  of  the  causes  given  in  the  preceding 
answer  might  produce  this  result,  or  the  trouble 
might  be  caused  by  a  loose  disc  in  the  valve  in  the 
supply  pipe,   causing  it  to  partly  close.     In  the 


150  roper's  catechism  for 

■  latter  case,  the  trouble  could  be  remedied  by- 
reversing  the  valve. 

Q.  What  is  the  difference  between  lifting  and 
non-lifting  injectors? 

A.  In  the  former  there  is  a  partial  vacuum 
formed  in  the  feed  pipe  on  starting,  in  the  latter 
a  pressure  is  required  in  the  water-supply. 

Q.  What  are  the  principal  points  to  be  observed 
in  setting  up  injectors  ? 

A.  All  pipes,  whether  steam,  water-supply,  or 
delivery,  must  be  of  the  same  or  greater  internal 
diameter  than  the  hole  in  the  corresponding  branch 
of  each  injector,  and  as  short  and  straight  as 
practicable.  When  floating  particles  of  wood  or 
other  matter  are  liable  to  be  in  the  supply  water, 
a  strainer  must  be  placed  over  the  receiving  end  of 
the  water-supply  pipe.  The  holes  in  this  strainer 
must  be  as  small  as  the  smallest  opening  in  the 
delivery  tube,  and  the  total  area  of  all  the  holes 
must  be  much  greater  than  the  area  of  the  water- 
supply  pipe,  to  compensate  for  the  closing  of  some 
of  them  by  deposits.  The  steam  should  be  taken 
from  the  highest  part  of  the  boiler,  to  avoid  the 
carrying  over  of  water  with  the  steam.  ' '  Dry 
pipes ' '  should  always  be  used  on  locomotives  to 
insure  dry  steam;  wet  steam  cuts  and  grooves  the 
steam  spindle  and  steam  nozzle.  The  steam  should 
not  be  taken  from  the  steam  pipe  leading  to  an 


STEAM    ENGINEERS   AND    ELECTRICIANS.         151 

engine,  unless  such  pipe  is  large.  Sudden  varia- 
tions in  pressure  may  break  the  jet.  After  all  the 
pipes  are  properly  connected  to  the  injector  and  to 
the  boiler,  and  before  steam  and  water  are  admitted 
through  them  to  the  injector,  they  should  be  dis- 
connected and  well  washed  out  by  blowing  steam 
or  running  water  through  them,  to  wash  out  all 
red  lead,  scale,  or  other  solids  that  may  be  in  the 
pipes.  Finally,  in  setting  injectors  it  is  important 
to  place  them  as  low  as  possible,  since  their 
capacity  is  reduced  and  the  promptness  and  relia- 
bility of  their  action  diminished  as  the  height  of 
lift  is  increased. 

Q.  What  is  an  inspirator  ? 

A.  It  is  a  double-jet  injector — that  is,  one  con- 
taining two  sets  of  jets,  of  which  one  is  used  for 
lifting  the  water  from  the  source  of  supply  and 
the  other  for  forcing  it  into  the  boiler. 

Q.  What  is  an  ejector? 

A.  It  is  an  instrument  similar  to  the  injector, 
but  designed  for  lifting  water  only,  without  forcing 
it  against  a  pressure. 

Q,  Is  an  injector  more  economical  than  a  pump 
as  a  boiler  feeder  ? 

A.  Not  always;  the  injector  is  the  more  eco- 
nomical of  the  two  when  the  feed-water  is  cold, 
but  the  pump  is  the  more  economical  when  the 
feed-water  has  been  heated. 


152 


ROPER'S    CATECHISM   FOR 


TABLE* 

SHOWING  THE  EELATIVE   EFFICIENCIES  OF  PUMPS 
AND   INJECTORS. 


Method  of  Supplying  Feed- 
Water  TO  Boiler. 

Temperature  of  feed-water  as  deliT- 
ered  to  the  pump  or  to  the  injector, 
60°  Fahr.     Rate  of  evaporation  of 
boiler,  lOpounds  of  water  per  pound 
of  coal  from  and  at  212°  Fahr. 

Relative  amount 
•of  coal  required 
per  unit  of  time, 
the  amount  for  a 
direct-acting 
pump,  feeding 
water  at  60°,  with- 
out a  heater,  being 
taken  as  unity. 

Saving  of  fuel 
over  the  amount 
required  when 
the  boiler  is  fed 
by  a  direct- 
acting  pump 
without  heater. 

Direct-acting  pump,   feeding 
water    at   60°,    without    a 

heater,        

1.000 
.985 

.0 

Injector  feeding  water  at  150°, 
without  a  heater,    .... 

1.5  per  ct. 

Injector    feeding    through    a 
heater  in  which  the  water 

is  heated  from  150  to  200°, 

.938 

6.2      " 

Direct-acting    pump   feeding 
water  through  a  heater,  in 
which  it  is  heated  from  60 

to  200°, 

.879 

12.1      *• 

Geared  pump,  ran  from  the 

engine,    feeding  water 
through  a  heater,  in  which 
it  is  heated  from  60  to  200°, 

.868 

13.2      *' 

*  Computed  by  Professor  D.  S.  Jacobus. 


STEAM    ENGINEERS    AND    ELECTRICIANS.         153 

Q.  Should  a  boiler  plant  have  both  a  pump  and 
an  injector? 

A.  Yes,  whenever  possible;  because  either  the 
one  or  the  other  may  at  some  time  refuse  to 
operate.  In  some  cases  it  would  be  better  to  have 
two  pumps,  and  in  others  two  injectors.  (See 
table  on  opposite  page. ) 

Q.  With  what  kind  of  boilers  are  injectors  used 
the  most  ?     Why  ? 

A.  AVith  locomotives,  because  they  use  cold 
water,  and  therefore  an  injector  is  more  efficient; 
also  because  the  jarring  motion  of  the  engine  does 
not  affect  an  injector  in  the  least,  while  its  effect 
on  the  pump  would  be  detrimental.  An  injector 
is  also  much  lighter  than  a  pump. 

HEATING   FEED-WATER. 

Q.  Why  should  the  feed-water  be  heated  before 
it  enters  the  boiler? 

A.  Because  cold  water  fed  into  a  boiler  under 
steam  produces  strains  that  will  shorten  the  life  of 
the  boiler;  because  a  large  proportion  of  the  solid 
matter  frequently  contained  in  water  will  separate 
out  at  a  high  temperature,  and,  consequently,  if  , 
the  feed-water  is  heated  sufficiently  solids  will 
be  deposited  in  the  heater  that  would  otherwise 
produce  scale  in  the  boiler;  and  because  by  using 
exhaust  steam,  or  some  other  source  of  heat  which 


154 


roper's  catechism  for 


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STEAM    ENGINEERS   AND    ELECTRICIANS.         155 

would  otherwise  be  wasted,  a  very  material 
economy  is  effected  in  the  consumption  of  fuel. 

A  pound  of  feed  -  water  entering  a  steam 
boiler  at  a  temperature  of  50°  Fahr.,  and  evapo- 
rating into  steam  of  60  pounds  pressure,  requires 
as  much  heat  as  would  raise  1157  pounds  of  water 
1  degree.  A  pound  of  feed- water  raised  from  50° 
Fahr.  to  220°  Fahr.  requires  170  units  of  heat; 
which,  if  absorbed  from  exhaust- steam  passing 
through  a  heater,  would  be  a  saving  of  15  per 
cent,  in  fuel.  Feed-water  at  a  temperature  of 
200°  Fahr.,  entering  a  boiler,  as  compared  in 
point  of  econoni}^  with  feed-water  at  50°  Fahr., 
would  effect  a  saving  of  over  13  per  cent,  in  fuel; 
and  with  a  well-constructed  heater  there  ought  to 
be  no  trouble  in  raising  the  feed-water  to  a  tem- 
perature of  212°  Fahr. 

Q.  What  is  the  difference  between  open  and 
closed  feed-water  heaters  ? 

A.  In  closed  heaters  the  exhaust  steam  passes 
through  a  series  of  brass  tubes  and  the  water  is 
pumped  through  the  space  around  the  tubes  into 
the  boiler,  or  the  water  may  be  jjumped  through 
the  tubes  and  the  steam  pass  around  the  tubes. 
In  the  open  type,  the  steam  comes  in  actual 
contact  with  the  water,  the  latter  passing  over  a 
series  of  cast-iron  or  steel  pans  placed  in  a  chamber 
through  which  the  exhaust  steam  passes. 


156 


roper's  catechism  for 


g  M  .S  o 


S  =«  2 


STEAM    ENGINEERS    AND    ELECTRICIANS. 


157 


OPEN    HEATER,— PITTSBURGH    TYPE. 

(Steam  enters  below  the  pans  at  the  left  and  passes  out  at  the  top. 
Water  enters  through  the  pipe  at  the  top,  the  flow  being  regulated  by  a 
cock  which  is  controlled  by  the  float  and  rod.  The  small  cylinder  at  the 
right  separates  the  oil.  [See  also  page  172.]  The  connection  to  the  pump 
is  near  the  top  of  the  small  cylinder.  Through  an  opening  in  the  side 
of  the  shell  the  pans,  which  rotate  around  a  central  shaft,  may  be 
cleaned.    Shell  and  pans  of  steel.) 


158  ropek's  catechism  for 

Q.  What  is  the  difference  in  the  method  of 
installing  open  and  closed  heaters  ? 

A.  In  open  heaters  the  pump  is  placed  between 
the  heater  and  the  boiler,  hence  the  pump  takes 
hot  water  and  must  therefore  be  placed  below  the 
level  of  the  water  in  the  heater,  otherwise  the 
water  will  not  follow  the  plunger.  With  the  closed 
type  the  water  enters  the  pump  cold  and  is  forced 
through  the  heater  into  the  boiler. 

Q.  Why  can  open  heaters  not  be  used  with 
injectors  ? 

A.  Because  if  the  water  is  heated  to  a  high  tem- 
perature, as  it  should  be,  in  the  heater,  the  injec- 
tor will  not  work,  it  requiring  moderately  cold 
water  to  condense  the  steam  in  the  combining 
tube.  If  the  steam  in  an  injector  is  not  con- 
densed the  apparatus  will  refuse  to  force  the  water 
into  the  boiler. 

Q.  Which  type  is,  in  general,  preferable — the 
open  or  the  closed  ? 

A.  Each  has  its  advantages  and  disadvantages. 
The  closed  heater  may  be  located  in  any  conve- 
nient position  relative  to  the  pump,  while  the  open 
type  must  be  placed  at  a  higher  level  than  the 
pump,  which,  as  already  stated,  has  to  pump  hot 
water;  the  open  type  is  not  under  pressure  (except 
that  of  the  exhaust  steam),  hence  it  is  lighter  and 
cheaper.     It  is  more  easily  cleaned;  it  heats  the 


STEAM   ENGINEERS   AND    ELECTRICIANS.         159 

water  to  a  higher  temperature;  its  purifying  prop- 
erties are  better,  and  it  produces  no  back  pressure 
on  the  engine.  On  the  other  hand,  the  feed-water 
may  contain  grease  which  will  injure  the  boiler, 
although  it  is  claimed  that  by  a  suitable  oil 
separator  this  may  be  entirely  eliminated. 

Q.  What  is  an  economizer  ? 

A.  It  is  a  device  used  for  heating  the  feed-water 
by  means  of  the  products  of  combustion  of  the 
boiler  furnace  as  they  pass  into  the  stack. 

Q.  How  is  it  constructed  ? 

A.  The  economizer  usually  consists  of  a  series 
of  cast-iron  or  steel  tubes  connected  at  either  end 
by  headers  similar  to  those  used  in  water-tube 
boilers.  The  water  circulates  through  the  tubes, 
which  are  placed  in  the  flue  connection  just  at  the 
entrance  to  the  stack. 

Q.  What  fittings  should  an  economizer  have  ? 

A.  As  it  is  virtually  a  water-tube  boiler,  it 
should  have  a  blow-off  pipe  and  a  safety-valve, 
because  if  the  boiler  is  not  supplying  steam  as 
usual  the  water  in  the  economizer  tubes  will  be 
evaporated,  producing  an  excessive  pressure. 

Q.  For  what  purpose  are  economizers  generally 
used  ? 

A.  For  the  purpose  of  increasing  the  capacity 
or  efficiency  of  existing  boiler  plants. 

Q.  Why  are  they  generally  not  necessary  in  new 
installations  ? 


160  roper's  catechism  for 

A.  Because  if  the  boilers  are  properly  con- 
structed they  do  not  allow  much  heat  to  be  wasted 
through  the  chimney. 

Q.  What  other  method  of  heating  the  feed- 
water  is  sometimes  used  ? 

A.  It  is  heated  by  the  use  of  condensers  in 
connection  with  the  engines.  (See  "Condensers," 
page  233.) 

FURNACES  AND  FLUES. 

Q.  Can  you  calculate  the  strength  of  a  flue  by 
the  same  rules  that  apply  to  the  shells  of  boilers  ? 

A.  No;  because  the  same  rules  for  strength 
of  cylinders  under  pressure  from  within  do  not 
apply  to  those  which  are  subjected  to  a  pressure 
from  without. 

Q.  If  pressure  is  exerted  on  the  internal  or 
external  surface  of  the  cylinder,  is  the  effect  not 
the  same  in  both  cases  ? 

A.  No;  when  pressure  is  exerted  within  a  tube 
or  cylinder,  the  tendency  of  the  strain  is  to  cause 
the  tube  to  assume  the  true  cylindrical  form;  but 
when  pressure  is  exerted  on  the  outside  of  the 
tube,  the  tendency  of  that  pressure  is  to  crush  the 
tube  or  flatten  it;  as  it  is  a  well-known  fact  that 
iron  of  any  strength  when  formed  into  a  tube  will 
require  a  much  greater  strain  to  tear  it  asunder 
than  it  would  take  to  crush  it.     A  thin  hoop  of 


STEAM    ENGINEERS    AND    ELECTRICIANS.         161 

iron  will  resist  a  very  great  amount  of  tearing 
force,  but  if  that  same  hoop  or  circle  be  placed  as 
a  prop  under  half  the  weight  that  was  exerted  to 
tear  it  apart,  it  would  be  crushed  flat. 

Q,  What  is  the  difference  between  external  and 
internal  strain? 

A.  Internal  is  a  tearing  strain,  while  external 
is  a  crushing  strain;  and  flues  and  tubes  of  boilers 
are  nothing  but  a  series  of  props,  and  a  constant 
tendency  of  the  pressure  is  to  flatten  the  tube  or 
flue  and  cause  it  to  collapse. 

Q.  What  is  a  collapse  ? 

A.  It  is  the  crushing  or  flattening  of  a  flue  by 
overpressure,  and  is  often  attended  with  terrible 
results. 

Q.  How  do  you  calculate  the  strength  of  flues 
or  cylinders  subjected  to  external  pressure? 

A.  It  has  been  shown  by  experiment  that  the 
strength  of  such  cylinders  is  proportional  to  the 
square  of  the  thickness  of  the  cylinder  and  in-, 
versely  proportional  to  the  length  and  to  the 
diameter.     The  formula  for  collapsing  is: 

P=  806,000^, 
la 

where  P  is  the  collapsing  pressure  in  pounds  per 

square  inch, 

I  is  the  length  of  the  cylinder  in  feet, 

d  is  the  diameter  of  the  cylinder  in  inches. 

11 


162  roper's  catechism  for 

Rule  for  Finding  the  Collapsing  Pressure 
OF  A  Cylindrical  Flue.- — Multiply  the  square  of 
the  thickness  in  inches  by  the  number  80,600. 
Multiply  the  length  of  the  flue  in  feet  by  its 
diameter  in  inches.  Divide  the  first  product  by 
the  second,  and  the  quotient  will  be  the  collaps- 
ing pressure  in  pounds  per  square  inch. 

Q.  If  the  length  of  a  cylindrical  flue  is  10  feet, 
its  diameter  2  feet,  and  thickness  J  inch,  what 
will  be  the  collapsing  pressure  ? 

^      P  =  ^0^'7^X|X^  =  215  pounds. 

Q.   How  may  long  flues  be  strengthened  ? 

A.  This  may  be  done  in  various  ways.  The 
old  method  was  to  rivet  rings  of  angle-  or  tee-iron 
around  the  flue  at  fixed  intervals,  or  to  make  the 
flue  in  sections  and  to  join  them  together  b}^  rivet- 
ing on  _f\-shaped  rings.  The  modern  method  is 
to  make  the  entire  flue  of  corrugated  iron,  which 
not  only  adds  strength,  but  facilitates  expansion 
and  increases  the  heating  surface. 

Q.  When  the  flue  is  stiffened  by  rings,  as  de- 
scribed above,  how  do  you  calculate  its  strength  ? 

A.  By  the  same  rule  as  that  for  plain  flues, 
except  that  the  length  between  rings  is  taken  as 
the  length  of  the  flue. 

Q.  What  method  is  employed  in  the  Galloway 
boiler  for  strengthening  the  flues  ? 


STEAM    ENGINEERS   AND    ELECTRICIANS.         163 

A.  The  Galloway  tubes,  which  are  conical  in 
form  and  placed  within  and  across  the  flues,  being 
riveted  to  the  sides. 

GRATES. 

Q.  What  is  the  simplest  form  of  grate  ? 

A.  It  consists  of  a  series  of  cast-iron  bars 
shaped  like  beams,  supported  at  either  end,  and 
so  placed  as  to  allow  spaces  between  them  for  the 
passage  of  air. 

Q.  What  points  should,  in  general,  be  observed 
in  grates  ? 

A.  They  should  be  flat  on  top  and  supported, 
but  not  fixed  at  the  ends,  as  otherwise  the  expan- 
sion and  contraction  will  cause  them  to  get  out  of 
shape.  The  spaces  between  the  bars  should  be 
numerous  and  as  large  as  possible.  The  width  of 
the  spaces,  however,  depends  on  the  kind  of  coal 
to  be  used,  and  in  practice  varies  from  f  to  f  inch. 
The  height  of  the  grate  above  the  bottom  of  the 
ashpit  should  be  from  24  to  30  inches,  and  the 
bars  should,  in  general,  be  inclined  downward  to- 
ward the  bridge  wall,  as  the  fuel  may  then  be 
more  easily  distributed.  The  length  is  limited  by 
the  distance  to  which  a  fireman  can  throw  the 
coal,  which  is  about  6  feet. 

Q.  How  much  coal  is  generally  consumed  per 
square  foot  of  grate  surface  ? 


164  roper's  catechism  for 

A.  This  depends  on  the  nature  of  the  draught 
and  the  kind  of  coal.  For  land  boilers  fired  with 
a  good  quality  of  anthracite  coal,  9  pounds  per 
square  foot  is  a  fair  average.  In  some  boilers 
operating  under  a  light  draught  the  coal  con 
sumption  is  as  low  as  4  pounds,  while  in  locomo- 
tives using  a  blast  pipe  to  produce  a  stron^ 
draught  as  high  as  120  pounds  of  coal  may  be 
burned  per  square  foot  of  grate  surface  per  hour 

Q.  How  much  grate  surface  should  be  alloweu 
per  horse-power  ? 

A.  In  land  boilers  about  J  square  foot  of  grat^ 
surface  is  given  per  horse-power.  With  good  biti^ 
minous  coal,  better  results  are  obtained  by  usin 
a  smaller  grate  area  and  a  strong  draught.  Wit.^ 
coal  containing  a  high  percentage  of  ash  it  i-^ 
better  to  use  a  large  grate  surface  with  a  compara- 
tively slow  rate  of  combustion. 

Q.  What  is  a  shaking  grate  ? 

A.  It  is  a  grate  designed  for  cleaning  the  fire 
breaking  up  clinkers,  and  removing  them  withou': 
opening  the  fire  door. 

Q.  What  are  the  advantages  to  be  derived  from 
such  an  arrangemxcnt? 

A.  Whenever  the  fire  doors  are  opened  cold  air 
rushes  in,  tending  not  only  to  impair  the  efficiency 
of  the  boiler,  but  also  its  durability.  Moreover, 
it  is  impossible  for  a  fireman  to  thoroughly  stir 


STEAM    ENGINEERS   AND    ELECTRICIANS.         165 

out,  with  a  slicing-bar,  every  part  of  the  grate. 
Hence,  if  the  coal  has  a  tendency  to  form  cUnkers 
the  advantages  of  a  shaking  grate  would  be 
material. 

Q.  AVhat  is  meant  by  automatic  stoking  ? 

A.  A  system  by  Which  the  coal  is  fed  to,  and 
the  ashes  removed  from,  the  furnace  automatically 
without  opening  the  furnace  doors. 

Q.  How  long  have  automatic  or  mechanical 
stoking  devices  been  in  use  ? 

A.  A  device  similar  in  many  respects  to  the 
modern  mechanical  stokers  was  employed  by 
Watt  in  1785. 

Q.  Under  what  conditions  are  mechanical 
stokers  especially  desirable? 

A.  When  the  fuel  used  consists  of  mine  refuse, 
screenings,  or  other  materials  not  generally  used 
in  manual  firing. 

Q.  What  advantages  are  claimed  for  mechanical 
stokers  ? 

A.  Fuel  economy,  prevention  of  smoke,  saving 
*fin  labor,  and  cleanliness  in  the  boiler  room. 
^,      Q.  Why  is  mechanical  stoking  productive  of 
economy  in  the  use  of  fuel? 

A.  Because  the  coal  is  spread  upon  the  grate 
uniformly  and  at  the  time  when  it  is  needed. 
With  hand-firing  the  coal  is  fed  to  the  furnace  at 
irregular  intervals,  and  usually  more  coal  is  put 


166  koper's  catechism  for 

on  than  necessary.  Besides,  each  time  the  boiler 
is  fired  and  cleaned,  the  furnace  doors  are  opened 
and  cold  air  rushes  in.  All  of  these  features 
which  attend  hand-firing  are  injurious  to  the 
economy  of  operation.  With  a  system  of  mechan- 
ical stoking  they  are  not  inciirred,  and  hence  the 
efficiency  may  be  materially  increased. 

Q.  Why  do  mechanical  stokers  lessen  the  pro- 
duction of  smoke? 

A.  Because  the  fuel  is  fed  uniformly  in  small 
quantities  instead  of  intermittently  and  in  bulk, 
as  in  the  case  of  hand-firing.  A  uniform  tem- 
perature is  maintained  in  the  furnace,  and  the 
motion  of  the  grate  keeps  the  spaces  open  for  the 
continual  passage  of  the  air.  Hence  the  combus- 
tion is  at  all  times  complete,  which  means  absence 
of  smoke. 

Q.  Why  are  they  productive  of  saving  in  labor  ? 

A.  Because  there  is  no  cleaning  of  fires  or 
manual  labor  of  any  kind,  except,  perhaps,  the 
bringing  of  the  coal  to  the  hoppers;  and  even  this 
is  frequently  accomplished  by  machinery. 

Q.   Why  are  they  more  cleanly  ? 

A.  Because  the  usual  dirty  appearance  of  boiler 
plants  is  produced  by  the  dust  raised  in  shoveling 
the  coal,  cleaning  the  fires,  and  removing  the 
ashes,  all  of  which  operations  are  abolished  in 
mechanical  stoking. 


STEAM    ENGINEERS    AND    ELECTRICIANS.         167 

Q.   Do  mechanical  stokers  pay  in  small  plants  ? 

A.   No,  they  do  not;    because  the  cost  of  the 

plant  and  the  power  consumed  in  operating  would 

not   be  warranted   by   the   saving   which   w^ould 

accrue. 

CHIMNEYS  AND  STACKS. 

Q.  What  is  the  object  of  a  chimney  or  stack? 

A.  It  is  for  the  purpose  of  producing  a  draught, 
ejecting  the  products  of  combustion,  and  supply- 
ing fresh  air  for  the  combustion  of  the  fuel. 

Q.  How  does  a  chimney  produce  a  draught  ? 

A.  The  tendency  of  the  rarefied  gases  is  to  rise, 
producing  a  partial  vacuum  which  causes  a  rush 
of  air  through  the  furnace. 

Q.  Which  kinds  of  coal  require  the  tallest 
stacks  ? 

A.  Anthracites,  because  they  do  not  burn  as 
readily  as  bituminous  coals. 

Q.  On  what  does  the  draught  produced  by  a 
chimney  depend? 

A.  It  depends  on  two  factors:  on  the  height  of 
the  chimney  and  on  the  difference  in  weight  of 
the  gases  contained  in  the  chimney  and  the  atmos- 
phere. 

Q.  On  what  does  this  difference  in  weight 
largely  depend? 

A.  Upon  the  temperature  of  the  gases  leaving 
the  boiler. 


168  roper's  catechism  for 

Q.  At  what  temperature  do  the  gases  usually 
leave  in  well-designed  boilers  ? 

A.   500  to  600  degrees  Fahrenheit. 

Q.  At  what  temperature  of  the  escaping  gases 
is  the  best  draught  obtained  ? 

A.  At  about  580  degrees  Fahrenheit. 

Q.  On  what  does  the  area  of  the  chimney  for  a 
given  boiler  plant  depend  ? 

A.  It  depends  upon  the  quantity  of  coal  con- 
sumed. 

Q.  What  relation  is  there  between  the  quantity 
of  coal  consumed  and  the  area  of  the  chimney  ? 

A.  The  area  of  the  cross-section  in  square 
inches  should  be  from  1 J  to  2  times  the  number 
of  pounds  of  coal  consumed  per  hour. 

Q.  According  to  this  rule,  what  would  be  the 
proper  diameter  of  chimney  for  500  horse-power 
boilers  of  the  water-tube  type  ? 

A.  Assuming  an  evaporation  of  10  pounds  of 
water  under  normal  conditions  per  pound  of  coal, 
we  have: 

Pounds  of   water  evaporated   per   pound  of 

coal  =  10. 
Total  pounds  of  water  evaporated  per  hour 

=  30  X  500  =  15,000. 
Pounds  of  coal  consumed  per  hour 

=  '±'^  =  1500. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         169 

Area  of  chimney  =  1500  X  IJ  to  1500  X  2 

=  2250  to  3000  square  inches. 
Diameter   of   chimney  =  53J   to  61f  inches 
or,  say,  60  inches. 
Q.  What   is    the   relation    between   grate   and 
chimney  area? 

A.  A  fair  average  of  coal  consumed  per  square 
foot  of  grate  surface  for  anthracite  coal  is  12 
pounds.  Hence  the  chimney  area  being  about  If 
square  inches  per  pound  of  coal,  we  have: 

Chimney  area  per  pound  of  coal  =  If  square 

inches. 
Chimney  area  per  square  foot  of  grate  surface 
=  lfXl2  =  21  square  inches  =  -^-^^ 
=  I  square  foot ; 
or,  in  other  words,  the  chimney  area  should  be 
about  Y  of  the  grate  area. 

Q.  Is  there  any  relation  between  the  cross-sec- 
tion of  chimney  and  horse-power  ? 

A.  For  fire-tube  boilers  the  average  heating 
surface  is  12  square  feet  per  horse-power,  while  the 
ratio  of  grate  to  heating  surface  is  about  1  :  35. 
Hence  the  grate  surface  per  horse-power  may  be 
taken  roughly  as  -g-f ,  or  about  J.  If,  now,  we  take 
the  results  above,  we  have  for  the  chimney  area 
per  horse-power,  J  X  y  =  ar  ^^^  fire-tube  boilers, 
and  a  trifle  smaller,  say  ^V?  ^^i'  water-tube  boilers. 
Q.  What  determines  the  height  of  chimneys  ? 


170 


roper's  catechism  for 


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STEAM    ENGINEERS   AND    ELECTRICIANS. 


171 


A.  The  height  of  chmmeys  is  determined  by 
the  required  draught.  It  is  influenced  by  the 
kind  of  coal  to  be  burned  as  well  as  by  its  loca- 
tion, as  it  must,  in  general,  be  higher  than  hills 
or  buildings  in  the  immediate  vicinity. 


STEAM  SEPARATOES  AND  TRAPS. 

Q.   For  what  purpose  are  steam  separators  used  ? 

A.  For  removing  moisture  from  steam  before 
it  enters  the  engine  cylinder;  or  they  may  be  used 
for  extracting  other  liquids  from 
vapors,  as,  for  example,  the  oil 
contained  in  exhaust  steam. 
The  first  named  is  generally 
called  a  live  steam  separator. 

Q.  Why  should  it  be  advis- 
able to  extract  the  entrained 
water  from  steam  before  using 
it  in  the  engine? 

A.  Because  an  accumulation 
of  water  in  the  cjdinder  is  often 
the  cause  of  blowing  out  the  head 
of  the  cylinder  or  steam-chest 
cover;  and  also  because  the 
presence  of  moisture  in  steam  re- 
duces the  economy  of  the  engine. 

Q.  How  should  a  separator  be 
constructed  to  be  efficient  ? 


172  roper's  catechism  for 

A.  The  steam  entering  the  apparatus  at  a  high 
velocity  should  have  its  direction  of  flow  altered 
or  reversed,  so  as  to  destroy  the  momentum  of 
the  liquid  particles,  permitting  them  to  fall  by 
gravity  into  a  vessel  provided  for  that  purpose. 
This  being  accomplished,  the  steam  should  not 
again  come  in  contact  with  the  water,  as  it  is 
liable  to  pick  up  particles  of  an}^  liquid  with 
which  it  comes  in  contact.  Finally,  the  cross- 
section  for  the  passage  of  the  steam  should  be 
ample  in  all  parts  of  the  apparatus,  so  that  the 
losses  by  friction  will  be  reduced  to  a  minimum. 

Q.  For  what  other  purpose  are  separators  fre- 
quently used  ? 

A.  To  extract  the  oil  from  feed-water  in  open 
heaters. 

Q.   How  are  these  constructed  ? 

A.  In  various  ways.  In  the  Pittsburgh  heater, 
illustrated  on  page  157,  the  separation  of  oil  is 
accomplished  by  means  of  a  small  cylinder  placed 
on  the  side  of  the  apparatus  near  the  bottom. 
This  cylinder  is  connected  by  pipes  to  the  steam- 
and  water-spaces  of  the  heater,  as  shown  in  the 
cut;  the  feed  to  the  pump  is  at  the  top  of  the 
small  cylinder.  As  the  oil  floats  on  the  surface 
of  the  water  it  is  evident  that  none  will  find  its 
way  into  the  small  cylinder,  so  long  as  the  water 
is   maintained   at   its  proper  level,  while  if   the 


STEAM    ENGINEERS   AND    ELECTRICIANS.         173 

level  of  the  water  should  become  too  low  the 
pump  will  not  be  supplied  with  water. 

Q.   For  what  purpose  are  steam  traps  used  ? 

A.  For  the  purpose  of  removing  condensed 
steam  from  a  system  of  steam  piping,  without 
allowing  any  of  the  steam  itself  to  escape. 

Q.   How  is  this  accomplished  ? 

A.  The  trap  is  connected  to  the  piping  to  be 
drained  and  contains  an  outlet  controlled  by  a 
valve.  The  valve  in  some  traps  is  operated  by  a 
float,  and  in  others  by  means  of  a  bent  tube  of 
elliptical  cross-section.  In  the  former  the  opening 
and  closing  of  the  valve  is  determined  directly  by 
the  amount  of  water  in  the  trap.  In  the  curved- 
tube  system  the  opening  and  closing  of  the  valve 
depend  upon  the  temperature. 

Q.  Suppose  a  separator,  trap,  heater,  or  other 
appliance  should  require  cleaning  or  repairing, 
will  it  not  be  necessary  to  shut  down  the  plant  ? 

A.  No;  they  should  always  be  provided  with 
by-passes  for  both  steard  and  water,  that  is,  they 
should  be  connected  with  the  piping  in  such  a 
way  that  the  steam  or  water  may  be  made  to  pass 
temporarily  through  auxiliary  pipes  around  the 
heater  trap  or  other  appliance. 

Q.  Give  a  brief  description  of  the  manner  in 
which  a  by-pass  is  usually  constructed. 

A.  As  generally  constructed  a  by-pass  consists 


174 


ROPER'S    CATECHISM   FOR 


of  a  pipe  leading  around  the  appliance  and  fitted 
with  three  valves — V,  V„  and  V,„ — as  shown  in 
the  accompanying  cut,  the  trap  (in  this  case) 
being  connected  to  the  piping  by  pipe  unions  U, 
U.  Under  ordinary  conditions,  that  is,  when  the 
trap  is  in  operation,  the  valves  V,  and  V„  remain 
open  while  V,„  is  closed.  If,  however,  the  trap 
is  to  be  taken  out  for  any  reason,  it  is  only  neces- 


sary to  close  the  valves  V,  and  V„  and  to  open 
y ,,,.  The  steam,  instead  of  passing  through  the' 
trap,  will  then  pass  around  it  through  the  by-pass, 
and  the  trap  or  other  appliance  may  be  discon- 
nected by  means  of  the  two  unions  U,  U,  without 
in  any  way  interfering  with  the  operation  of  the 
plant.  For  feed- water  heaters,  etc.,  a  similar 
by-pass  should  be  provided  for  the  water. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         175 


THE  STEAM  ENGINE. 

The  steam  engine,  as  it  exists  to-day,  may  be  said 
to  be  the  invention  of  James  Watt.  While  he 
was  not  the  originator  of  the  idea  of  utilizing  the 
pressure  and  expansive  force  of  steam  for  the 
purpose  of  doing  mechanical  work,  Watt's  dis- 
coveries and  inventions,  in  this  connection,  were 
of  such  importance  that  he  is  generally  considered 
as  the  inventor  of  the  steam  engine. 

In  looking  over  the  models  of  engines  and 
accessories  of  James  Watt,  a  great  many  of  which 
are  exhibited  in  the  South  Kensington  Museum, 
London,  it  is  surprising  to  note  how  little  change 
the  steam  engine  has  undergone  during  the  past 
century.  It  is  to-day,  in  fact,  the  same  machine 
that  it  was  then;  and  while  the  results  which  have 
since  been  accomplished  in  the  way  of  economy, 
regulation,  speed,  and  power  doubtless  exceed  the 
most  sanguine  expectations  of  the  early  workers 
in  this  field,  the  modern  engine  is,  nevertheless, 
practically  the  same  machine  that  it  was  a  century 
ago. 

The  efforts  of  steam  engineers,  since  the  days  of 
James  Watt,  have  produced  not  only  vastly  more 
powerful  machines,  higher  and  more  uniform 
speed  and  what  now  seems  perfect  running,  but 


176  eoper's  catechism  for 

they  have  also  very  materially  increased  the  effi- 
ciency of  the  engine.  And  yet  the  results  which 
have  been  obtained  in  the  way  of  economy  still 
leave  much  to  be  desired.  The  steam  engine  and 
boiler,  considered  as  an  apparatus  for  converting 
the  potential  energy  contained  in  coal  or  other 
fuel  into  mechanical  work,  is  a  most  extravagant 
machine.  With  the  very  best  engines  and  boilers 
we  are  not  able  to  develop  a  horse-power  with  a 
consumption  of  much  less  than  3  pounds  of  coal 
per  hour,  while  if  all  of  the  energy  were  utilized 
we  should  obtain  from  that  amount  of  good  coal 
not  less  than  14  horse-power.  In  other  words, 
the  best  engines  and  boilers  utilize  only  about  7 
per  cent,  of  the  latent  energy  of  the  fuel.  As  far 
as  the  engine  itself  is  concerned,  the  mechanism 
leaves  but  little  to  be  desired.  In  such  engines  as 
are  generally  used  for  electric  lighting,  that  is,  the 
high-speed  automatic  cut-off  type,  the  regulation 
is  such  that  the  full  load  may  be  suddenly  thrown 
on  or  off  without  producing  a  variation  in  the 
speed  of  the  engine  greater  than  1  to  2  per  cent., 
and  at  all  loads  such  engines,  when  properly 
adjusted,  run  smoothly,  noiselessly,  and  without 
producing  vibration. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         177 

HORSE-POWER. 

Q.  What  is  meant  by  the  power  of  a  steam 
engine  ? 

A.  The  amount  of  work  it  will  do  in  a  given 
space  of  time. 

Q.   Define  the  unit  of  power. 

A.  The  unit  generally  adopted  for  the  power  of 
steam  engines  is  the  horse-poiver.  An  engine  of  1 
horse-power  means  one  which  will  raise  550 
pounds  1  foot  a  second  or  its  equivalent. 

Q.  What  would  be  equivalent  to  this  amount 
of  work? 

A.  As  work  is  the  product  of  force  times  space, 
a  weight  of  550  pounds  raised  1  foot  would  be 
equal  to  550  foot-pounds  of  work.  If  1  pound 
were  raised  550  feet' or  2  pounds  275  feet,  the 
amount  of  work  would  be  the  same.  Hence,  a 
horse-power  may  be  defined  as  550  foot-pounds 
per  second,  33,000  foot-pounds  per  minute,  1,980,- 
000  foot-pounds  per  hour,  and  so  on. 

Q.  Name  some  form  of  work  other  than  raising 
a  weight,  which  would  be  equivalent  to  1  horse- 
power. 

A.  An  electric  current  of  10  amperes  at  74.6 
volts. 

Q.  What  determines  the  horse-power  of  a  steam 
engine  ? 
12 


178  roper's  catechism  for 

A.  The  diameter  of  the  cylinder,  length  of 
stroke,  average  or  mean  effective  pressure  on  the 
piston,  and  the  speed. 

Q.   How  do  you  calculate  the  horse-power  of  an 


engme 


A.  By  multiplying  the  area  of  the  piston  in 
square  inches  by  the  mean  effective  pressure  acting 
upon  it;  multiplying  the  length  of  stroke  in  feet 
by  the  number  of  strokes  (twice  the  number  of 
revolutions)  per  minute;  multiplying  the  first 
product  by  the  second,  and  dividing  by  33,000. 

Q.  What  would  be  the  horse-power  of  an  18"  x 

18"  engine  at  200  revolutions  per  minute,  with  a 

mean  effective  pressure  of  45  pounds  per  sq.  inch  ? 

A.  Area  of  piston  =  18  X  18  X  .7854  =  254 

square  inches, 

Total  mean  pressure  on  piston  =  254  X  45 

=  11,430  pounds. 
Number  of   strokes  per  minute  =  2  X  200 

=  400, 
Length  of  stroke  =  18  -f-  12  ^  1.5  feet, 
Distance  traveled  by  piston  per  minute  = 

400  X  1.5  =  600  feet, 
Work  done  per  minute  =^  11,430  X  600  = 

6,858,000  foot-pounds, 
Horse-power  =  6,858,000  --  33,000  =  208. 
Q.   How  would  you  write  the  above  rule  in  the 
shape  of  a  formula  ? 


STEAM    ENGINEERS   AND    ELECTRICIANS.         179 

A.   Let  HP  =  horse-power, 

P  =  mean  effective  pressure  in  pounds 

per  square  inch, 
L  =  length  of  stroke  in  feet, 
A  =  area  of  piston  in  square  inches, 
N  =  number  of  strokes  per  minute, 
B  =  number  of  revolutions  per  min- 
ute, 
S  =  piston  speed  in  feet  per  minute, 
d  7=  diameter  of  cylinder  in  inches; 
the  formula  corresponding  to  the  above  rule  would 
be: 

(A  =  .7854cP) 

PLAN       APS 
33,000    ^^  33,000' 

Q.  Given  the  horse-power,  mean  effective  pres- 
sure, and  piston  speed,  how  would  you  find  the 
proper  diameter  of  cylinder?  Give  rule  and 
formula. 

A.  The  formula  would  be 


,          I  42,017  HP      ^„_     I 
d  =  ^J — '—~ or  205  ^'- 


HP 

PS         ^^  "^^  ^  PS 


and  the  rule  as  follows :  Multiply  the  horse-power 
by  42,017;  multiply  the  piston  speed  by  the 
mean  effective  pressure;  divide  the  first  product 
by  the  second  and  extract  the  square  root  of  the 
quotient. 


180       eoper's  catechism  for 

Q.  Write  formulse  for  length  of  stroke,  piston 

speed,  and  number  of  revolutions  when  the  other 

quantities  are  given. 

,    J       ,.       ,     ,    ,  r         ^3,000  HP 

A.   Length   ot   stroke  =  L  =  — '     ,    ,^       = 
^  FAN 

16,500  HP  _  21,010  HP 
PAR       ~      P  RcV    ' 
Piston  speed  =  S=NL  =  2RL  = 
33,000  HP 


PA       ' 

Number   of   revolutions   =   R   = 

16,500  HP  _  21,010  HP 
PAL       ~      PLd' 


S 
2L 


Q.  What  do  you  understand  by  the  mean  effec- 
tive pressure  ? 

A.  The  average  forward  pressure  on  the  piston 
less  the  back  pressure. 

Q.  What  is  the  average  forward  pressure  ? 

A.  It  is  a  pressure  depending  upon  the  initial 
pressure  in  the  cylinder  and  the  point  of  cut-off. 

Q.  How  do  you  find  the  average  (forward) 
pressure  in  a  given  case  ? 

A.  In  the  following  table  look  up  the  multiplier 
corresponding  to  the  cut-off.  To  the  initial  gauge 
pressure  in  the  cylinder  add  14.7  pounds  to  ob- 
tain the  initial  absolute  pressure.  Multiply  this 
by  the  number  corresponding  to  the  cut-off  in  the 


STEAM    ENGINEERS    AND    ELECTRICIANS. 


181 


table,  and  the  product  will  be  the  absolute  average 
forward  pressure. 

Q.  What  would  be  the  average  pressure  corre- 
sponding to  80  pounds  initial  by  the  gauge  and  J 
cut-off? 

A.  80  +  14.7  =  94.7  X  .5965  =  56.45  absolute 

14.7 


41.75  gauge. 


TABLE 

OF  MULTIPLIERS  FOR  MEAN  ABSOLUTE  PRESSURES. 


Cut-Off. 

Rate  of 
Expan- 
sion. 

Multi- 
plier. 

Cut-Off. 

Rate  of 
Expan- 
sion. 

Multi- 
plier. 

1 

4 
3 

2.66 
2 

.5965 
.6995 

.7428 
.8465 

1 

i 
f 

1.6 
1.5 
1.33 
1.14 

.9188 
.9370 
.9657 
9919 

Q,   How  do  you  find  the  mean  effective  pressure? 

A.  Find  the  absolute  mean  forward  pressure  as 
described  above  and  deduct  the  absolute  back 
pressure. 

Q.   What  is  the  back  pressure? 

A.  It  is  the  pressure  opposing  the  piston.  In 
engines   exhausting    into    the   atmosphere    it   is 


182  roper's  catechism  for 

usually  about  15  pounds  per  square  inch  (atmos- 
pheric pressure).  In  condensing  engines  it  varies 
from  two  (2)  pounds  per  square  inch  up  to  at- 
mospheric pressure,  depending  on  the  vacuum. 
Where  the  exhaust  is  used  in  a  heating  system,  it 
varies  from  16  to  25  pounds,  depending  on  the 
amount  of  friction  in  the  piping. 

Q.  What  horse-power  would  be  developed  by 
an  engine  under  the  following  conditions: 
Stroke,  12  inches; 
Diameter  of  cylinder,  12  inches; 
Initial  gauge  pressure,  80  pounds  per  square 

inch; 
Speed,  300  revolutions  per  minute; 
Back  pressure  (gauge),  5  pounds  per  square 

inch; 
Cut-off,  1. 
A.   The  absolute  initial  pressure  is  80  +  14.7  = 
94. 7  pounds,  and  the  multiplier  in  the  table  cor- 
responding to  \  cut-off  being  .5965,  the  average 
forward  pressure  is  94.7  X  .5965  =  56.45  pounds 
absolute.     The  back  pressure  being  5  -f-  14.7  = 
19.7  pounds  absolute,  the  mean  effective  pressure 
is  56.45  —  19.7  =  36.75  pounds  per  square  inch. 
Area  of  piston  =  12  X  12  X  .7854  =  113.1 

square  inches. 
Total  mean  pressure  on  piston  =  36.75  X 
113.1  =4153  pounds. 


STEAM   ENGINEERS   AND    ELECTRICIANS.         183 

Length  of  stroke  :=12-v-12  =  l  foot. 
Number  of  strokes  =  300   X   2  =  600  per 

minute. 
Distance  traveled  by  piston  =  600  X  1  ^= 

600  feet  per  minute. 
Work  done  per  minute  =  600  X  4153  == 

2,491,800. 
Horse-power  =  2,491,800  --  33,000  =  75 
horse-power. 
Q.   If  in  the  above  example,  instead  of  exhaust- 
ing against  a  back  pressure,  a  condenser  had  been 
used,  in  which  there  was  a  vacuum  of  22  inches, 
what  would  have  been  the  gain  in  power  ? 

A.  Since  each  inch  of  vacuum  corresponds  to 
about  |-  pound,  the  back  pressure  would  be  22  X 
^  ==  11  pounds  less  than  atmospheric,  or  14.7  — 
11  =  3.7  pounds  absolute.  Hence  the  mean 
effective  pressure  =  56.45  —  3.7  =  52.75  pounds, 

.,.     T                     52.75X113.1  X600       ,^^ 
and  the  horse-power ^ =  108. 

That  is,  the  gain  in  power  would  be  108  —  75  = 
33  horse-power,  or  over  40  per  cent. 

•  EXPLANATION  OF  TABLE. 

The  table  on  the  following  pages  is  calculated 
for  different  cylinder  diameters  from  4  inches  to  5 
feet  and  for  piston  speeds  of  300  to  600  feet  per 
minute.     To  find  the  horse-power  of  any  engine 


184 


roper's  catechism  for 


TABLE 

OF   HOESE  POWEE   FOR    DIFFERENT  CYLHSTDEE   DIAMETERS 
AND   PISTON   SPEEDS. 

Horse-Power  per  Pound  Mean  Effective  Pressure. 


2'«'^ 

Speed  of  Piston  in  Feet  per  Minute. 

s  5 

300 

350 

400 

450 

500 

550 

600 

Inches. 

4 

.114 

.133 

.152 

.171 

.19 

.209 

.228 

4>^ 

.144 

.168 

.192 

.216 

.24 

.264 

.288 

5 

.18 

.21 

.24 

.27 

.30 

.33 

.36 

5>^ 

.216 

.252 

.288 

.324 

.36 

.396 

.432 

6 

.256 

.299 

.342 

.385 

.428 

.471 

.513 

6K 

.807 

.391 

.409 

.461 

.512 

.563 

.614 

7 

.348 

.408 

.466 

.524 

.583 

.641 

.699 

"ly, 

.401 

.468 

.534 

.602 

.669 

.735 

.802 

8 

.456 

.532 

.608 

.685 

.761 

.837 

.912 

8>^ 

.516 

.602 

.688 

.774 

.86 

.946 

1.032 

9 

.577 

.674 

.770 

.866 

.963 

1.059 

1.154 

9J^ 

.644 

.751 

.859 

.966 

1.074 

1.181 

1.288 

10 

.714 

.833 

.952 

1.071 

1.390 

1.309 

1.428 

10^ 

.787 

.919 

1.050 

1.181 

1.313 

1.444 

1.575 

11 

.864 

1.008 

1.152 

1.296 

1.44 

1.584 

1.728 

113^ 

.943 

1.1 

1.257 

1.414 

1.572 

1.729 

1.886 

12  ^ 

1.025 

1.195 

1.366 

1.540 

1.708 

1.880 

2.050 

13 

1.206 

1.407 

1.608 

1.809 

2.01 

2.211 

2.412 

14 

1.398 

1.631 

1.864 

2.097 

2.331 

2.564 

2.797 

15 

1.606 

1.873 

2.131 

2.409 

2.677 

2.945 

3.212 

16 

1.827 

2.131 

2.436 

2.741 

3.045 

3.349 

3.654 

17 

2.054 

2.396 

2.739 

3.081 

3.424 

3.766 

4.108 

18 

2.312 

2.697 

3.083 

3.468 

3.854 

4.239 

4.624 

19 

2.577 

3.006 

3. 436 

3.865 

4.295 

4.724 

5.154 

20 

2.855 

3.331 

3.807 

4.265 

4.7r9 

5.234 

5.731 

21 

3.148 

3.672 

4.197 

4.722 

5.247 

5.771 

6.296 

22 

3.455 

4.031 

4.607 

5.183 

5.759 

6.334 

6.911 

23 

3.776 

4.405 

5.035 

5.664 

6.294 

6.923 

7.552 

24 

4.111 

4.797 

5.482 

6.167 

6.853 

7.538 

8.223 

25 

4.461 

5.105 

5.948 

6.692 

7.436 

8.179 

8.923 

26 

4.826 

5.630 

6.435 

7.2.39 

8.044 

8.848 

9.652 

27 

5.199 

6.066 

6.932 

7.799 

8.666 

9.532 

10.399 

28 

5.596 

6.529 

7.462 

8.395 

9.. 328 

10.261 

11.193 

29 

6.006 

7.007 

8.008 

9.009 

10.01 

11.011 

12.012 

STEAM    ENGINEERS    AND    ELECTRICIANS. 


185 


Horse-Power  per  Pound  Mean  Effective  Pressure. 


I..I 

Speed  of  Piston  in  Feet  per  Minute. 

2  o  = 

5    5 

300 

350 

400 

450 

500 

550 

600 

Inches. 

30 

6.426 

7.497 

8.568 

9.639 

10.71 

11.781 

12.852 

31 

6.865 

8.001 

9.144 

10.287 

11.43 

12.573 

13.716 

32 

7.308 

8.526 

9.744 

10.962 

12.18 

13.398 

14.616 

33 

7.770 

9.065 

10.360 

11.655 

12.959 

14.245 

15.54 

34 

8.238 

9.611 

10.984 

12.357 

13.73 

15.103 

16.476 

35 

8.742 

10.199 

11.656 

13.113 

14.57 

16.027 

17.484 

36 

9.252 

10.794 

12.336 

13.878 

15.42 

16.962 

18.504 

37 

9.774 

11.403 

13.032 

14.861 

16.29 

17.919 

19.548 

38 

10.308 

12.026 

13.744 

15.462 

17.18 

18.898 

20.616 

39 

10.86 

12.67 

14.48 

16.29 

18.1 

19.91 

21.62 

40 

11.424 

13.328 

15.232 

17.136 

19.04 

20.944 

22.848 

41 

12.006 

14.007 

16.008 

18.009 

20.00 

22.011 

24.012 

42 

12.594 

14.693 

16.792 

18.901 

20.99 

23.089 

25.188 

48 

13.20 

15.4 

17.6 

19.8 

22.0 

24.2 

26.4 

44 

13.818 

16.121 

18.424 

20.727 

23.03 

25.333 

27.636 

45 

14.454 

16.863 

19.272 

21.681 

24.09 

26.339 

28.908 

46 

15.128 

•17.626 

20.144 

22.662 

25.18 

27.698 

30.216 

47 

15.768 

18.396 

21.024 

23.652 

26.28 

28.908 

31.536 

48 

16.446 

19.187 

21.928 

24.669 

27.41 

30.151 

32.152 

49 

17.142 

19.999 

22.856 

25.713 

28.57 

31.427 

34.284 

50 

17.85 

20.825 

23.8 

26.775 

29.75 

32.725 

35.7 

51 

18.54 

21.665 

24.76 

27.855 

30.95 

34.045 

37.08 

52 

19.296 

22.512 

2.5.728 

28.944 

32.16 

35.376 

38.592 

53 

20.052 

23.394 

26.736 

30.078 

33.42 

36.762 

40.104 

54 

20.82 

24.29 

27.76 

31.23 

34.7 

38.17 

41.64 

■  55 

21.594 

25.193 

28.792 

32.391 

35.99 

39.589 

4.3.188 

56 

22.386 

26.117 

29.848 

33.579 

37  31 

41.041 

44.772 

57 

23.196 

27.062 

30.928 

34.794 

38.66 

42.526 

46.392 

58 

24.018 

28.021 

32.024 

36.027 

40.03 

44.033 

48.036 

59 

24.852 

28.994 

33.136 

37.278 

41.42 

45.562 

49.704 

60 

25.698 

29.981 

34.264 

38.547 

42.83 

47.113 

51.396 

by  means  of  this  table,  multipl}^  twice  the  number 
of  revolutions  per  minute  by  the  length  of  stroke 
in  feet.  This  will  give  the  piston  speed  in  feet 
per  minute.     Look  up  the  horse-power  from  the 


186  koper's  catechism  for 

table  for  this  piston  speed  and  the  proper  diameter 
of  cyHnder  and  multiply  it  by  the  mean  effective 
pressure.  Take  the  above  example  as  an  illustra- 
tion; the  piston  speed  was  found  to  be  600  feet 
per  minute,  and  hence  for  a  12-inch  cylinder  the 
horse-power  from  the  table  is  2.05  for  each  pound 
of  mean  effective  pressure.  Hence  multiplying 
this  by  the  mean  effective  pressure,  52.75,  we  have 
52.75  X  2.05  =  108  horse-power. 

Q.  Is  the  pressure  in  the  boiler  and  the  pressure 
in  the  cylinder  nearly  equal  in  all  cases  ? 

A.  No;  the  pressure  in  the  C3dinder  is  in  many 
cases  less  than  the  pressure  in  the  boiler. 

Q.  From  what  causes  does  the  difference  between 
the  pressure  in  the  boiler  and  the  pressure  in  the 
cylinder  arise  ? 

A.  Firsts  from  a  malconstruction  of  the  steam- 
pipe  and  steam-ports;  secondly^  from  loss  by  radi- 
ation and  condensation;  thirdly^  from  the  action  of 
the  governor;  and,  fourthly^  from  the  bad  condition 
of  the  piston. 

Q.  What  is  the  most  economical  steam  pressure 
to  use  in  the  cylinder  of  a  high-pressure  engine  ? 

A.   From  80  to  90  pounds  to  the  square  inch. 

Q.  Why  should  80  or  90  pounds  to  the  square 
inch  be  more  economical  than  lower  pressure,  say 
40  or  45  pounds  to  the  square  inch  ? 

A.   On   account   of   the   back   pressure   of   the 


STEAM    ENGINEERS   AND    ELECTRICIANS.         187 

atmosphere;  for  instance,  if  we  have  a  pressure 
of  45  pounds  to  the  square  inch  on  the  piston, 
the  loss  by  atmospheric  pressure  is  15  pounds  to 
the  square  inch,  which  is  about  J-  of  the  pressure 
on  the  piston,  leaving  only  30  pounds  for  useful 
effect  and  to  overcome  the  friction  of  the  engine; 
if  Ave  have  a  pressure  of  90  pounds  to  the  square 
inch,  the  loss  is  only  15  pounds  to  the  square  inch, 
or  about  ^. 

Q.  Is  it  economical  to  use  an  engine  that  is  too 
large  for  the  work  to  be  done  ? 

A.  No;  because  an  engine  running  below  its 
rated  load  wastes  steam.  If  it  is  a  throttling 
engine^  the  steam  is  throttled,  or  reduced  without 
doing  work,  which  means  a  loss.  If  it  is  an 
automatic  cut-off  engine  the  expansion  is  increased, 
which  also  impairs  the  economy  of  the  engine. 

Q.  Why  does  increasing  the  rate  of  expansion 
reduce  the  economy  ? 

A.  There  is  one  point  of  cut-off  which  is  more 
economical  than  any  other,  because  at  that  point 
the  steam  expands  to  atmospheric  pressure  and  is 
not  capable  of  doing  any  more  w^ork  when  ex- 
hausted. This  cut-off,  for  an  initial  pressure  of 
80  pounds,  is  J.  If  the  rate  of  expansion  is 
reduced,  the  steam  is  exhausted  before  it  has  done 
as  much  work  as  it  is  capable  of  doing,  while  if 
the  rate  of  expansion  is  increased,  the  terminal 


188  roper's  catechism  for 

pressure  is  liable  to  fall  below  that  of  the  atmos- 
phere, in  which  case  the  opposing  pressure  of 
the  atmosphere  will  retard  the  piston  during  the 
latter  part  of  its  stroke.  This  also  means  a  waste 
of  power. 

DIFFERENT  KINDS  OF  ENGINES. 

Q.  What  is  the  difference  between  condensing 
and  non-condensing  engines  ? 

A.  In  non-condensing  engines  the  steam,  after 
having  done  its  work  in  the  steam  cylinder,  escapes 
into  the  atmosphere,  or  sometimes  into  a  heating 
system  where  the  heat  still  contained  in  the  steam 
is  partially  utilized.  In  the  condensing  engine 
the  steam  exhausts  into  a  condenser,  where  it 
comes  in  contact  with  some  cooling  medium,  in 
consequence  of  which  it  is  condensed,  producing 
a  partial  vacuum  behind  the  piston. 

Q.  What  is  the  object  of  condensing? 

A.  To  increase  the  effective  pressure  on  the 
piston  and  consequently  the  power. 

Q.  By  how  much  is  the  power  of  a  non-con- 
densing engine  increased  when  a  condenser  is 
added? 

A.  The  power  is  increased  in  the  ratio  which 
the  vacuum  in  the  condenser  bears  to  the  mean 
effective  pressure. 

Q.  Suppose  an  engine  working  at  80  pounds 


STEAM    ENGINEERS   AND    ELECTRICIANS.         189 

initial  pressure  and  J  cut-off  exhausting  against 
the  atmosphere,  had  a  condenser  added.  If  there 
were  an  effective  vacuum  of  26  inches,  what  would 
be  the  percentage  increase  m  power  if  the  speed 
remained  the  same  ? 

A.  According  to  the  rules  given  above,  the  mean 
effective  pressure  was  originally 

(80  +  14.7)  X  .5965  —  14.7  =  41.75  pounds, 
which  was  increased  by  adding  a  condenser  whose 
vacuum  is  26  inches  by 

26  --  2  =  13  pounds. 
Hence  the  increase  in  power  is 

-— -—  =:  31  per  cent. 
41.75  ^ 

Q.  Does  it  not  require  power  to  operate  a  con- 
denser ? 

A.  Yes;  but  generally  not  so  much  as  is  gained 
by  its  use. 

,  Q.  What  percentage  is  gained  in  economy  by 
condensing? 

A.  From  20  to  35  per  cent.,  depending  on  the 
type  and  size  of  engine. 

Q.  Why,  then,  are  not  all  engines  built  for 
condensing  ? 

A.  Because  in  small  engines  the  saving  in  fuel 
would  not  be  enough  to  warrant  the  additional  first 
cost,  and  the  increased  labor  and  attention  which 
the  plant  would  require.     Further,  in  many  in- 


190  eoper's  catechism  for 

stallations  the  steam  leaving  at  atmospheric  pres- 
sure can  be  used  to  good  advantage  for  heating 
purposes  or  for  purifying  the  water  before  it  enters 
the  boiler.  Finally,  in  cities  the  cost  of  the  water 
is  frequently  in  excess  of  what  would  be  saved  in 
fuel. 

Q.   How  much  water  is  required  for  condensing  ? 

A.  About  25  times  as  much  as  passes  through 

the  engine. 

(See  also  ' '  Condensers, ' '  page  233. ) 

Q.  AVhat  do  you  mean  by  "simple"  or  single 
expansion  and  by  multiple  expansion  engines  ? 

A.  A  simple  or  single  expansion  engine  is  one 
in  which  the  steam  is  used  expansively  in  one 
cylinder  or  set  of  cjdinders  only,  and  after  ex- 
hausting is  not  used  again  for  doing  work  in  the 
engine.  In  multiple  expansion  engines  the  steam 
expands  successively,  doing  work,  in  two  or  more 
cylinders  or  sets  of  cylinders. 

Q.  What  are  the  names  given  respectively  to 
engines  in  which  the  steam  expands  two,  three, 
and  four  times  ? 

A.  Compound,  triple  expansion,  and  quadruple 
expansion  engines. 

Q.  What  is  meant  by  compounding  ? 

A.  By  the  term  "compounding"  is  meant 
expanding  the  steam  successively  in  two  or  more 
cylinders. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         191 

Q.  Why  are  engines  compounded  ? 

A.  To  secure  greater  economy  in  the  use  of 
steam. 

Q.  Is  not  the  friction  of  an  engine  greater  if  it 
uses  the  same  amount  of  steam  in  two  or  three 
cylinders  than  if  the  entire  work  is  performed  in 
a  single  cylinder  ? 

A.  Yes;  because  each  cylinder  (except  in  tan- 
dem compound  engines)  has  its  own  crank  and 
attending  mechanism. 

Q.  Why,  then,  is  expanding  successively  in 
several  cylinders  productive  of  economy  in  the 
use  of  fuel  ? 

A.  The  higher  the  initial  steam  pressure  used 
in  a  steam-power  plant,  and  the  lower  the  terminal 
pressure  (provided  it  is  not  less  than  the  back 
pressure),  the  greater  the  economy.  Hence,  in 
order  to  secure  the  greatest  fuel  economy,  there 
must  of  necessity  be  a  wide  range  of  temperature 
from  live  to  exhaust  steam.  If  the  expansion 
occurred  in  a  single  cylinder,  the  walls  of  the  latter 
and  a  portion  of  the  steam  passages  would  be 
subjected  to  this  variation  in  temperature  at  each 
stroke.  In  other  words,  the  cylinder  walls  and 
steam  passages  would  be  chilled  at  the  end  of  the 
stroke  and,  therefore,  the  live  steam  would  be 
partially  condensed,  as  it  enters  the  cylinder, 
without  doins:  work.     It  is  in  reducing  this  loss 


192  roper's  catechism  for 

of  steam  by  condensation,  called  initial  condensa- 
tion, that  compounding  effects  economy  in  fuel, 
because  if  the  expansion  occurs  successively  in 
two  cylinders,  instead  of  all  in  one,  the  range  of 
"•temperature  is  only  one-half  as  great  and  con- 
sequently the  condensation  is  reduced  proportion- 
ately. 

Q.  What  should  be  the  relative  sizes  of  cylinders 
in  multiple  expansion  engines  ? 

A.  They  should  be  so  proportioned  that  approx- 
imately the  same  amount  of  work  is  done  by  each 
cylinder.  The  first  cylinder  will  be  the  smallest 
in  diameter  and  the  last  the  largest. 

Q.  What  names  are  given  to  the  different 
cylinders  of  multiple  expansion  engines  ? 

A.  The  one  which  takes  the  steam  direct  from 
the  boiler  is  called  the  high-pressure  cylinder,  and 
the  one  in  which  it  expands  last  before  finally 
being  exhausted  to  the  atmosphere  or  condenser 
is  called  the  low-pressure;  the  others  are  called 
intermediate-pressure  cylinders. 

Q.  What  is  a  receiver  ? 

A.  It  is  a  chamber  in  which  the  steam  is  stored 
from  the  time  it  leaves  one  cylinder  until  it  is 
admitted  to  the  next. 

Q.  Why  is  a  receiver  necessary? 

A.  Because  the  cranks  of  the  different  cylinders 
are  usually  not  placed  in  the  same  position.     For 


STEAM    ENGINEERS   AND    ELECTRICIANS.         193 

example,  in  a  two-  or  four-cylinder  engine  they 
would  generally  be  placed  at  90°  and  in  a  three- 
cylinder  engine  at  120°.  Hence  the  cylinders  are 
not  taking  steam  during  the  time  it  is  exhausted 
in  the  preceding  cylinder  and,  therefore,  a  chamber 
must  be  provided  for  storing  the  steam  until  it  can 
be  used. 

Q.  Why  are  cranks  set  at  different  angles  ? 

A.  To  secure  a  more  uniform  turning  force  on 
the  crank  shaft. 

Q.  Does  not  the  fly-wheel  accomplish  the  same 
result  ? 

A.  Yes;  but  if  this  can  be  done  without  the  aid 
of  a  fly-wheel  it  is  much  better,  especially  since 
in  many  instances,  such  as  in  marine  engines,  a 
fly-wheel  cannot  be  conveniently  used. 

Q.  Why  are  compound  engines  operated  as  con- 
densing engines  wherever  possible  ? 

A.  Because  the  increase  in  the  mean  effective 
pressure  in  the  low-pressure  cylinder  is  a  large 
proportion  of  the  total.  Low-pressure  cylinders 
of  multiple  expansion  engines  frequently  have  a 
mean  forward  pressure  of  only  3  or  4  pounds,  and 
hence  by  the  use  of  a  condenser  this  may  be 
increased  very  materially. 

Q.  What  do  you  understand  by  a  high-speed 
engine  ? 

A.  Strictly  speaking,  a  high-speed  engine  is  one 
13 


194  roper's  catechism  for 

which  has  a  high  piston  velocity;  but  the  term  is 
now  generally  used  to  mean  engines  of  high  rota- 
tive speed. 

Q.  What  advantages  do  high  (piston)  speed 
engines  possess  as  compared  to  low-speed  engines  ? 

A.  Other  things  being  equal,  they  are  lower  in 
first  cost,  more  economical  to  operate,  and  run 
more  smoothly. 

Q.  What  additional  advantage  is  possessed  by 
high  (rotative)  speed  engines? 

A.  They  are  better  adapted  for  driving  electric 
machinery  and  other  shafting  which  requires  to  be 
run  at  a  high  speed  of  rotation. 

Q.  Why  are  high-speed  engines  lower  in  first 
cost? 

A.  The  power  of  an  engine  depends  on  the 
piston  area,  stroke,  mean  pressure,  and  speed, 
varying  directly  as  each  one  of  these  factors.  If 
the  speed  is  increased,  any  one  of  the  other  three 
factors  may  be  proportionately  decreased,  and, 
therefore,  it  follows,  that  a  high-speed  engine  may 
be  built  smaller  and  hence  more  cheaply  for  a 
given  horse-power  than  a  low-speed  engine. 

Q.  Why  are  they  more  economical  in  the  use  of 
fuel? 

A.  Because  one  of  the  principal  losses  in  steam 
engines  is  that  due  to  initial  condensation  and 
re-evaporation,  and  this  is  the  less  the  more  steam 


STEAM    ENGINEERS   AND    ELECTRICIANS.         195 

passes  through  a  given  cylinder  in  a  given  time. 
Hence  it  is  less  in  high-  than  in  low-speed  engines. 

Q.  Why  do  they  run  more  smoothly  ? 

A.  Principally  because  the  effect  of  the  recipro- 
cating parts  is  to  equalize  the  turning  force  on  the 
crank  pin,  so  that  it  is  nearly  the  same  at  every 
part  of  the  stroke. 

Q.  A¥hat  do  you  understand  by  automatic  cut- 
off and  throttling  engines  ? 

A.  Automatic  cut-off  engines  are  those  in  which 
the  speed  is  kept  constant  under  a  variable  load 
by  a  governor  acting  upon  the  cut-off — that  is,  one 
in  which  the  steam  is  admitted  longer,  for  heavy 
loads  than  for  light  loads,  the  exact  point  at 
which  it  is  cut  off  being  regulated  by  the  governor. 
In  the  throttling  engine,  the  period  of  admission 
remains  the  same  under  all  loads,  but  the  initial 
pressure  is  regulated  by  the  action  of  the  governor 
on  a  throttle  valve. 

Q.  Which  of  the  two  is  the  more  economical 
method  ? 

A.  The  automatic  cut-off;  because  when  the 
pressure  of  steam  is  reduced  by  a  throttle  valve,  it 
expands  without  doing  work  and  hence  an  amount 
of  energy  is  lost  equal  to  that  which  would  be 
necessary  to  raise  the  steam  from  the  pressure  at 
which  it  is  admitted  to  the  C3dinder  to  that  at 
which  it  is  delivered  by  the  boiler. 


196  roper's  catechism  for 

Q.  Under  what  conditions  could  throttling 
engines  be  used  ? 

A.  When  the  load  remains  uniform  or  nearly 
so,  because  throttling  engines  with  plain  slide 
valves  are  simpler  and  cheaper  to  build  than  auto- 
matic cut-off  engines. 

Q.  What  are  single-  and  double-acting  engines  ? 

A.  Single-acting  engines  are  those  in  which 
steam  is  admitted  on  one  side  of  the  piston  only. 
In  double-acting  engines  it  is  admitted  alternately 
on  either  side  of  the  piston. 

Q.  What  are  the  relative  advantages  of  these 
two  types  ? 

A.  For  the  same  diameter  of  cylinder,  length 
of  stroke,  steam  pressure,  and  speed,  the  double- 
acting  engine  develops  twice  as  much  power.  The 
single-acting  engine,  however,  has  no  piston  rod, 
cross-head,  or  guides,  the  connecting  rod  being 
attached  direct  to  the  piston.  Engines  of  this 
class  usually  run  faster,  however,  than  double- 
acting  engines,  and  they  are  so  arranged  that  the 
crank  dips  into  a  vessel  filled  with  oil,  every 
revolution,  all  of  the  moving  parts  being  encased 
in  an  iron  boxing.  They  are,  therefore,  well 
adapted  for  use  where  the  atmosphere  contains 
much  grit  and  dust. 

Q.   What  is  a  rotary  engine  ? 

A.   It  is  one  in  which  a  motion  of  rotation  is 


STEAM    ENGINEERS   AND   ELECTRICIANS.         197 

i  produced  directly  by  the  pressure  of  the  steam 
and  not  a  reciprocating  motion  first,  which  is 
afterward  converted  into  a  rotary  motion,  as  in 
the  ordinary  type. 

VALVES  AND  VALVE  GEAES. 

Q.  What  do  you  understand  by  the  valve  gear 
of  an  engine? 

A.  All  that  part  of  its  mechanism  which  is 
used  in  the  distribution  of  steam. 

Q.  Of  what  does  the  simplest  form  of  valve 
gear  consist  ? 

J..  Of  a  plain  slide  valve,  an  eccentric,  and  the 
rods  or  links  necessary  for  transmitting  the  motion 
of  the  latter  to  the  former. 

Q.   Describe  the  plain  slide  valve. 

A.  The  diagram  on  page  198  shows  the  simplest 
form  of  slide  valve  in  its  central  position,  that  is, 
in  the  position  where  steam  is  neither  admitted  to 
nor  exhausted  from  the  engine.  V  is  the  valve, 
S  S  are  the  steam  passages  through  which  steam  is 
admitted  to  the  cylinder  C  from  the  steam-chest 
X.  The  latter,  being  in  communication  with  the 
boiler,  is  always  filled  with  live  steam  when  the 
throttle  valve  is  open.  E  is  the  exhaust  passage 
which,  being  in  communication  with  the  exhaust 
pipe,  allows  the  steam  to  pass  into  the  atmosphere 
or   condenser  after   it   has  done  its  work   in  the 


198 


KOPER'S    CATECHISM    FOR 


STEAM    ENGINEERS   AND    ELECTRICIANS.         199 

cylinder.  R  is  the  valve  rod  which  receives  its 
motion  from  the  eccentric  and,  passing  through  a 
stuffing-box,  imparts  motion  to  the  valve. 

Q.  Explain  briefly  the  method  of  action  of  the 
valve. 

A.  As  already  stated,  the  valve  in  the  above 
diagram  is  shown  in  a  position  where  steam  is 
neither  admitted  to  nor  exhausted  from  the 
cylinder.  In  this  position  of  the  valve,  the  piston 
which  has  nearly  completed  its  stroke,  is  moving 
toward  the  left,  while  the  valve  is  moving  toward 
the  right,  as  indicated  by  the  arrows.  Presently 
the  valve  will  have  uncovered  the  left  steam  pas- 
sage and  steam  will  be  admitted  behind  the  piston. 
This  will  continue  until  the  steam  passage  is  again 
covered  by  the  valve  on  its  return  stroke.  In  the 
meantime  the  other  steam  passage  will  have  been 
uncovered  and  placed  in  communication  with  the 
exhaust  chamber  E,  and  exhaust  will  take  place 
until  this  passage  is  again  covered  by  the  valve. 
After  that  the  process  is  reversed,  steam  being 
admitted  to  the  right  hand  end  of  the  cylinder 
and  exhausted  from  the  left;  and  so  on,  continu- 
ously. 

Q.  What  are  the  four  important  events  in  the 
steam  distribution,  which  take  place  in  every 
double  stroke  of  the  engine  ? 

A.  Admission,  cut-off,  release,  and  compression. 


200  roper's  catechism  for 

Q.   Explain  what  you  mean  by  these  terms. 

A.  When  the  passage  is  first  uncovered  admis^ 
sion  takes  place  and  continues  until  the  point  of 
cut-off  is  reached,  which  is  when  the  passage  is 
again  covered.  Release  occurs  when  the  passage 
is  opened  to  the  exhaust,  and  compression  when 
the  latter  is  closed.  From  the  time  steam  is  cut 
off  until  it  is  released  expansion  takes  place. 

Q.  What  do  you  mean  by  the  terms  lap,  lead, 
eccentricity,  travel,  overtravel,  angular  advance  ? 

A.  Outside  or  steam  lap  is  the  distance  the  outer 
edge  of  the  valve  laps  over  the  outer  edge  of  the 
steam  passage,  in  the  central  position  of  the  valve, 
the  distance  a  h  in  the  cut. 

Inside  or  exhaust  lap  is  the  distance  the  inner 
edge  of  the  valve  laps  over  the  inner  edge  of  the 
steam  passage,  in  the  central  position  of  the  valve, 
the  distance  c  d  in  the  cut. 

Lead  is  the  amount  the  steam  port  is  open  when 
the  piston  is  beginning  its  stroke.  If  the  piston 
begins  its  stroke  before  the  steam  passage  is 
uncovered  the  lead  is  negative. 

Eccentricity,  or  throw  of  the  eccentric,  is  the 
distance  from  the  center  of  the  shaft  to  the  center 
of  the  eccentric. 

Travel  of  the  valve  is  the  total  distance  it  moves 
on  its  seat  between  extreme  positions.  This  travel 
is  equal  to  twice  the  throw  of  the  eccentric. 


STEAM    ENGINEERS   AND   ELECTRICIANS.         201 

Overtravel  is  the  distance  the  valve  travels  above 
what  is  necessary  to  fully  uncover  the  steam  pas- 
sage. 

Angle  of  advance  is  the  angle  by  which  the 
eccentric  is  in  advance  of  the  position  which 
would  bring  the  valve  in  its  central  position  when 
the  crank  is  on  a  dead  center. 

Q.  Having  given  the  various  dimensions  of  a 
valve  gear  of  this  kind,  how  do  you  determine 
when  the  events  described  above  will  take  place  ? 

A.  Graphically — that  is,  with  the  aid  of  some 
diagram  such  as  Zeuner's,  Sweet's,  or  Reuleaux's. 
Of  these,  Zeuner's  is  the  one  generally  used  in 
practice. 

Q.  Briefly  explain  the  Zeuner  diagram  and  its 
use. 

A.  *Draw  a  line  0  X  to  represent  the  crank  at 
the  beginning  of  the  stroke,  and  with  this  as  a 
radius  draw  the  crank  circle  ZX^,  Xj,  Xg,  X^. 
Suppose  the  crank  to  turn  in  the  direction  of  the 
arrow.  Through  the  point  0  draw  the  line  R  R^ 
making  the  angle  R  0  Y'  equal  to  the  angle  of 
advance,  and  lay  off  the  distances  OR  and  OR 
equal  to  the  eccentricity  or  throw  of  the  eccentric. 
On  the  lines  0  R  and  0  R  as  diameters  draw  the 
two  circles  0  C  i?  Z)  and  0  E  R  F.  With  0  as  a 
center  and  a  radius  0  A  equal  to  the  outside  or 

*From  "Eoper's  Engineers'  Handy-Book,"  pp.  391-393. 


202 


roper's  catechism  for 


steam  lap  draw  a  circle  A  C  D,  and  similarly  with 
a  radius  0  B  equal  to  the  inside  or  exhaust  lap, 
draw  a  circle  B  E  F.     Through  the  point  0  and 


J 


ZEUNER   DIAGRAM. 


the  intersections  (7,  D,  E,  and  F  draw  the  lines 
0  X,,  0  Zj,  0  Xg,  and  0  X,.  We  are  now  able 
to  take  from  the  diagram  all  of  the  data  necessary 


STEAM    ENGINEERS   AND   ELECTRICIANS.         203 

for  a  complete  understanding  of  the  distribution 

of  steam  in  the  cylinder: 

0  X^  is  the  position  of  the  crank  when  admission 

of  the  steam  begins. 
0  X^  is  the  position  of   the  crank  when  cut-off 

takes  place,  hence — 
X^  0  X^  is  the  angle  traversed  by  the  crank  during 

the  period  of  admission. 
0  -Xg  is  the  position  of  the  crank  when  the  exhaust 

opens. 
0  X^  is  the  position  of  the  crank  when  the  exhaust 

closes,  hence — 
Xg  0  X^  is  the  angle  traversed  by  the  crank  during 

the  period  of  exhaust,  and — 
X^  0  Xj  is  the  angle  traversed  by  the  crank  during 

the  period  of  compression. 
The  distances  from  the  intersection  of  the  circles 
R  and  R^  with  the  lines  0  X,  0  X^,  etc. ,  represent 
the  travel  of  the  valve  corresponding  to  the  posi- 
tions OX,  0 Xj ,  of  the  crank.  The  circle R repre- 
sents the  forward  and  the  circle  R'  the  return 
stroke,  hence — 
0  X  is  the  distance  the  valve  has  traveled  from  its 

central  position  at  the  beginning  of  the  stroke. 
0  X',  the  same  for  the  return  stroke. 
0  ^  is  the  outside  or  steam  lap,  hence— 
A  K  is  the  distance  the  steam  port  is  open  at  the 

beginning  of  the  stroke  or  the  steam  lead. 


204  roper's  catechism  for 

0  R  is  the  full  travel  of  the  valve. 
0  5  is  the  inside  or  exhaust  lap,  hence — 
B  Kis  the  distance  the  exhaust  port  is  open  at  the 
beginning  of  the  stroke  or  the  exhaust  lead. 

At  the  points  C  and  D  the  travel  of  the  valve  is 
just  equal  to  the  outside  lap;  hence  in  these  posi- 
tions of  the  crank  the  steam  port  opens  and  closes 
respectively;  similarly  at  the  points  E  and  F  the 
travel  is  just  equal  to  the  exhaust  lap;  hence,  in 
these  positions  of  the  crank  the  exhaust  port  opens 
and  closes  respectively.  If  we  lay  down  from  the 
point  A  a  distance  A  H,  equal  to  the  width  of  the 
port,  and  with  0  as  a  center  and  a  radius  0  H 
draw  an  arc,  cutting  the  line  0  i?  at  J, — 
J  R  is  the  distance  the  valve  travels  more  than 
enough  to  fully  open  the  port,  or  the  over- 
travel. 

Similarly,  if  we  lay  off  from  B  the  distance  B  L, 
equal  to  the  width  of  the  port,  and  from  the  center 
0  and  a  radius  equal  to  0  L  draw  an  arc,  cutting 
the  line  0  R  at  M, — 

31 R  is  the  distance  the  valve  travels  more  than 
enough  to  fully  open  the  port  to  the  exhaust. 

It  will  thus  be  seen  that  by  a  careful  study  of 
the  diagram  all  information  necessary  for  the 
proper  design  and  setting  of  the  valve  gear  may 
readily  be  had.  For  example,  in  the  above  dia- 
gram the  cut-off  takes  place  a  little  later  than  f 


STEAM    ENGINEERS   AND   ELECTRICIANS.         205 

stroke.  It  is  evident  that  if  it  is  desired  to  have 
the  cut-off  take  place  earUer,  say  at  J  stroke,  it 
will  be  necessary  for  the  outside  lap  circle,  A  C  D^ 
to  intersect  the  valve  circle  R  in  the  line  Y  Y. 
This  may  be  accomplished  by  increasing  the  out- 
side lap,  by  reducing  the  eccentricity,  or  by  chang- 
ing the  angle  of  advance.  However,  any  one  of 
these  changes  would  also  affect  the  entire  distribu- 
tion, and  it  would  probably  be  necessary  to  lay 
down  several  diagrams  before  the  most  advantage- 
ous dimensions  could  be  obtained. 

Q.  How  would  you  proceed  to  set  the  slide- 
valve  of  an  engine  ? 

A.  Place  the  crank  on  the  dead  center  and  give 
the  valve  the  necessary  amount  of  lead ;  then  turn 
the  engine  on  the  other  center,  and  if  the  valve 
has  the  same  amount  of  lead  it  is  properly  set. 
But  if  the  lead  on  one  end  is  more  or  less  than  on 
the  other,  the  difference  must  be  divided.  When 
the  valve  is  attached  to  the  rod  by  means  of  jam- 
nuts  great  care  must  be  taken  not  to  jam  the  nuts 
against  the  valve,  as  that  would  prevent  the  valve 
from  seating. 

Q.   What  is  a  link  motion  ? 

A.  It  is  a  mechanism  consisting  of  two  eccen- 
trics and  rods  and  a  slotted  link,  designed  for  the 
purpose  of  reversing  an  engine  and  varying  its 
point  of  cut-off. 


206  roper's  catechism  for 

Q.  How  is  this  accomplished  in  the  Stephenson 
Imk? 

A.  The  two  eccentrics,  called  respectively  the 
forward  and  back  eccentric,  are  placed  on  the  shaft 
in  different  relative  positions  in  such  a  way  that,  if 
the  valve  were  operated  by  the  one,  the  engine 
would  move  forward;  and  if  by  the  other,  it  would 
be  reversed.  The  link  is  attached  to  the  ends  of 
the  two  eccentric  rods  and  hence  receives  a  rocking 
motion.  It  is  slotted  and  carries  a  movable  block 
in  the  slot  to  which  the  valve  rod  is  attached.  If 
the  block  is  at  the  end  of  the  link  nearest  the  for- 
ward eccentric,  the  engine  will  move  forward, 
while  if  it  is  at  the  other  end,  it  will  be  reversed. 

Q.  What  happens  when  the  block  is  in  some 
intermediate  position? 

A.  The  travel  of  the  valve  becomes  less  as  the 
block  approaches  the  center,  and  hence  the  cut-off 
becomes  earlier.  In  the  central  position  of  the 
block,  the  travel  of  the  valve  is  not  sufficient  to 
uncover  the  ports,  and  hence  the  engine  remains  at 
rest. 

Q.  In  the  ordinary  form  of  D  slide  valve,  is 
there  not  a  good  deal  of  friction  between  the  valve 
and  its  seat  ? 

A.  Yes;  the  friction  in  the  old  forms  of  slide 
valve  is  very  great,  because  the  steam  pressure  on 
the  back  of  the  valve  forces  it  tightly  against  its  seat. 


STEAM   ENGINEERS   AND    ELECTRICIANS.         207 

Q.  How  can  this  be  avoided  to  a  great  extent  ? 

A.  By  the  use  of  pressure  plates,  which  relieve 
the  back  of  the  valve  of  its  pressure,  or  by  the  use 
of  the  piston  valve,  which,  being  of  circular  cross- 
section  instead  of  flat,  is  balanced  and  conse- 
quently the  only  pressure  tending  to  force  it 
against  the  seat  is  that  due  to  its  own  weight.* 

Q.  What  objection  is  there  to  piston  valves? 

A.  It  is  claimed  that  the  seat  wears  unevenly 
and  hence  they  cannot  be  kept  tight.  With  a 
suitable  construction,  however,  the  bushings  form- 
ing the  seat  can  be  taken  out  and  replaced  with 
very  little  trouble  and  expense. 

Q.  Next  to  the  slide-valve  gear,  as  described 
above,  what  is  the  most  common  valve  gear  used 
in  stationary  engines  ? 

A.   The  Corliss  gear. 

Q.  What  are  the  essential  differences  between 
the  Corliss  and  the  plain  slide-valve  gear  ? 

A.  Instead  of  a  single  valve  which  admits  and 
exhausts  the  steam,  the  Corliss  gear  has  four 
independent  valves  which  rotate  partially  about 
an  axis.  The  four  valves,  of  which  two  are  for 
the  admission  and  cut-off  and  the  other  two  for 
the  release  and  compression  of  the  steam  in  the 
cylinder,  are  operated  by  a  single  eccentric  and 
wrist  plate,  but  the  two  steam  valves  are  connected 

*See  "Roper's  Engineers'  Handy-Book,"  pp.  398-402. 


208  roper's  catechism  for 

to  the  wrist  plate  in  such  a  way  that  they  can  be 
detached  at  any  moment.  This  is  accompHshed 
by  a  tripping  or  releasing  mechanism  controlled 
by  a  ball  governor,  and  as  soon  as  the  steam  valves 
are  released,  they  are  closed  by  the  action  of  a 
dash  pot,  and  hence  the  cut-off  is  under  the  direct 
control  of  the  governor.  The  exhaust  valves  are 
not  released  from  the  wrist  plate,  and  hence  the 
release  and  compression  are  constant. 

Q.  What  do  you  understand  by  a  four-valve 
engine  ? 

A.  It  is  one  having  a  valve  gear  midway  between 
the  plain  slide  valve  and  the  Corliss  gears.  It  has 
four  independent  valves  like  the  Corliss,  but,  like 
the  plain  slide  valve,  their  motion  is  'positive  and 
they  have  no  releasing  mechanism.  The  cut-off 
is  varied  by  the  travel  of  the  valve. 

Q.  What  are  the  relative  advantages  and  dis- 
advantages of  the  Corliss  and  four- valve  types  of 
valve  gear  ? 

A.  The  Corliss  has  the  advantage  that  the  cut- 
off is  quick  and  sharp  and  that  there  is  very  little 
power  lost  in  friction.  The  valves  being,  however, 
under  the  control  of  a  spring  or  dash  pot,  they 
cannot  be  run  at  a  high  rotative  speed.  .  This 
constitutes  the  main  advantage  of  the  four-valve 
gear,  that  it  can  be  run  at  as  high  a  speed  as  a 
single-valve  engine,  and  it  is  almost,  but  not  quite, 


STEAM    ENGINEERS   AND    ELECTRICIANS.         209 

as  economical  as  the  Corliss.  Both  have  the  ad- 
vantage over  single-valve  engines  that  the  steam 
enters  and  leaves  the  cylinder  by  separate  passages, 
and  hence  there  is  less  loss  by  condensation. 
They  are,  therefore,  much  more  economical  in  the 
use  of  steam  than  single- valve  gears. 

GOVERNORS. 

Q.  What  are  the  principal  methods  in  use  for 
governing  the  speed  of  stationary  engines  ? 

A.  By  the  centrifugal  governor  acting  on  the 
throttle  valve — that  is,  by  varying  the  initial  pres- 
sure in  the  cylinder  to  suit  the  load  ;  and  by  a 
centrifugal  or  inertia  governor  acting  on  the  valve 
gear  in  such  a  way  as  to  vary  the  point  of  cut-off 
to  suit  the  load. 

Q.  Which  is  the  better  method,  and  why  ? 

A.  The  one  in  which  the  cut-off  is  varied  to 
suit  the  load,  because  it  is  much  more  economical 
in  the  use  of  steam,  and  the  regulation  is  far 
better.  Moreover,  engines  in  which  the  steam, 
pressure  is  throttled  to  suit  the  load  often  knock 
violently  under  light  loads. 

Q.  Why  should  the  steam  never  be  throttled  on 
engines  running  at  a  high  piston  velocity? 

A.  Because  the  force  necessary  to  accelerate  the 
reciprocating  parts  at  the  beginning  of  the  stroke 
is  so  great  in  high-speed  engines  that  if  the  steam 
14 


210  ROPER^S  CATECHISM  FOR 


CENTRIFUGAL  BALL  GOVERNOR. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         211 

.  were  throttled  the  fly-wheel  would  have  to  supply 
it,  and  hence  there  would  be  a  reversal  of  pressure 
on  the  crank  pin  each  stroke.  This  would  not 
only  cause  very  noisy  running,  but  it  would  soon 
wear  out  the  engine. 

Q.  How  is  the  governor  usually  made  to  vary 
the  cut-off? 

A.  By  a  releasing  mechanism,  as  already  ex- 
plained above  (Corliss  valve  gear);  by  the  action 
of  a  ball  governor  on  the  block  of  a  link,  as  in  the 
Porter- Allen  engine;  or  by  a  shaft  governor. 

Q.  What  is  a  shaft  governor  ? 

A.  It  is  one  in  which  the  centrifugal  action  of 
a  weight  or  weights,  placed  in  a  fly-wheel,  is 
balanced  against  a  spring  or  springs.  The  weights 
are  attached  to  pivoted  arms,  and  these  in  turn  to 
the  eccentric  of  the  valve  gear.  As  the  speed 
increases,  the  tendency  is  for  the  weights  to  move 
away  from  the  shaft  and  in  so  doing  to  alter  the 
position  of  th-e  eccentric,  varying  its  angular 
advance  or  its  throw,  or  both,  and  in  this  way 
altering  the  point  of  cut-off. 

Q.  What  is  the  difference  in  the  effect  on  the 
steam  distribution  when  the  cut-off  is  varied  by 
the  angular  advance  and  by  the  throw  of  the 
eccentric  ? 

A.  If  the  angle  of  advance  only  is  altered,  the 
lead  will  increase  as  the  cut-off  is  decreased.     If 


212 


ROPER'S    CATECHISM    FOR 


the  throw  of  the  eccentric  only  is  altered,  the 
reverse  takes  place.  Hence,  in  order  to  keep  the 
lead  constant  with  a  single  valve,  both  the  throw 


SHAFT  GOVERNOR,— BUCKEYE  TYPE. 

(A  A  are  the  weights  attached  to  the  ends  of  arms  a  a.  The  arms  are 
pivoted  to  the  fly-wheel  at  one  end' and  attached  to  the  loose  eccentric  C 
at  the  other.  FF  are  the  springs  which  resist  the  tendency  of  the  weights 
to  move  away  from  the  shaft.  In  this  type  of  governor  the  angular 
advance  only  is  varied.) 

of  the  eccentric  and  the  angular  advance  should 
be  varied.  In  the  governor  illustrated  above, 
this  is  not  necessar}^,  because  a  separate  valve  is 
used  to  cut  off  the  steam. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         213 

Q.  How  do  you  calculate  the  proper  diameter 
for  ball-governor  pulleys  ? 

A.  To  find  the  diameter  of  governor  shaft-pul- 
leys :  Multiply  number  of  revolutions  of  engine 
by  diameter  of  engine  shaft-pulley,  and  divide 
product  by  number  of  revolutions  of  governor. 

To  find  diameter  of  engine  shaft-pulley  :  Mul- 
tipl}^  number  of  revolutions  of  governor  by  diam- 
eter of  governor  shaft-pulley,  and  divide  product 
by  number  of  revolutions  of  engine. 

INSTALLATION,    CARE   AND   MANAGEMENT. 

Q.  What  is  the  best  material  for  engine  founda- 
tions ? 

A.  They  should  be  of  hard-burned  brick  laid 
in  Portland  cement  or  of  concrete. 

Q.  How  deep  should  they  be  carried  ? 

A.  The  proper  depth  depends  on  the  size  of  the 
engine.  The  builders  usually  furnish  a  founda- 
tion plan  showing  minimum  depth,  but  they 
should  always  rest  on  solid  ground. 

Q.  How  should  the  foundation  bolts  and  anchor 
plates  be  placed  in  the  foundation  ? 

A.  A  template  should  first  be  constructed  to 
hold  the  bolts  in  their  proper  positions  and  the 
bolts  suspended  from  the  template.  The  bolts 
should  be  threaded  at  both  ends  and  the  lower  nut 
held  in  a  suitable  pocket  in  the  anchor  plate.     In 


214 


ROPER'S    CATECHISM    FOR 


building  the  foundation  a  space  should  be  left 
around  each  bolt,  sufficient  to  allow  the  bolt  to  be 
moved  a  half  inch  in  any  direction. 

Q.   How  should  the  foundation  be  finished  ? 

A.  A  cap-stone  of  granite  makes  the  best  finish, 
but,  as  a  rule,  the  expense  is  too  great.  After  the 
engine  is  set  on  the  foundation  and  leveled  by 
means  of  iron  wedges,  the  space  between  the 
bottom  of  the  engine  and  the  top  of  the  founda- 
tion should  be  filled  with  grout  or,  preferably, 
molten  sulphur,  to  give  an  even  bearing. 

Q.  Should  foundations  be  built  the  same  width 
from  bottom  and  top  ? 

A.  No;  they  should  be  wider  at  the  bottom  and 
have  a  slope  or  batter  of  about  two  inches  to  every 
foot  of  height  up  to  the  floor-level.  The  top 
should  be  about  an  inch  wider  than  the  bed  plate 
of  the  engine. 

Q.   How  would  you  proceed  to  set  up  an  engine  ? 

A.  First.  Determine  the  position  or  location 
the  engine  is  to  occupy  in  the  shop  or  factory. 

Second.  Lay  out  the  line  of  the  main  shafting 
in  the  building,  if  there  be  any;  if  not,  the  line 
of  the  building  itself,  at,  at  least,  three  different 
points  in  the  direction  in  which  the  main  shafting 
is  to  run;  now  line  down  from  the  center  of  the 
main  shaft,  or  from  the  line  of  the  building,  at 
two  different  points,   to  the  floor  on  which  the 


STEAM    ENGINEERS   AND    ELECTRICIANS.         215 

engine  is  to  stand,  and  from  these  points  line  to 
the  engine-shaft.- 

Third.  Determine  the  height  the  bed-plate  is 
to  stand  above  the  floor;  also  the  depth  of  the 
foundation. 

Fourth.  Make  a  template  the  exact  counterpart 
of  the  bed-plate,  in  which  to  hang  the  foundation 
bolts,  and  set  this  upon  four  props  at  right  angles 
to  the  main  shaft  in  the  building. 

Fifth.  Lay  up  the  brick  foundation  to  the  level 
at  which  the  engine  is  intended  to  stand;  then 
remove  the  template,  and  lower  the  bed-plate  on 
to  the  foundation. 

Sixth.  Level  the  bed-plate  by  means  of  iron 
wedges  and  pour  in  sulphur  to  give  it  an  even 
bearing.  After  that  the  nuts  may  be  screwed 
down  on  the  foundation  bolts. 

Seventh.  A  line  should  now  be  drawn  exactly 
through  the  center  of  the  cylinder,  and  another 
line  through  the  center  of  the  main  bearing. 
This  line  will  give  the  location  of  the  pillow-block 
or  outboard  bearing. 

Eighth.  Place  a  straight  edge  across  the  bottom 
of  the  bearings  and  adjust  them  with  the  aid  of  a 
spirit  level  until  they  are  perfectly  level. 

Ninth..  Swing  the  fly-wheel  into  its  proper 
position,  slip  the  shaft  through  it  and  key  it  in 
place.    Screw  down  the  caps  of  the  pillow-blocks. 


216  roper's  catechism  for 

Tenth.  Place  the  cross-head,  connecting  rod, 
etc.,  in  position,  bolt  on  the  front  cylinder  head, 
and  adjust  the  valve  gear. 

Q.  AVhat  are  the  principal  points  which  should 
be  kept  in  mind  in  running  the  steam  and  exhaust 
pipes  for  an  engine  ? 

A.  They  should  be  run  in  such  a  way  that  the 
free  flow  of  steam  will  never  be  impeded.  The 
steam-  and  exhaust-pipes  should  never  be  smaller 
than  the  outlets  provided  on  the  engine.  The 
pipes  should  be  run  as  straight  as  possible. 
Horizontal  runs  should  be  slightly  inclined  to 
allow  the  condensation  to  drain  of!  in  the  same 
direction  as  the  flow  of  the  steam.  The  piping, 
if  long,  should  have  a  suitable  provision  for 
expansion,  and  all  steam-  and  exhaust-piping 
should  be  covered  with  some  non-conducting 
pipe-covering. 

Q.  What  is  the  first  duty  of  an  engineer  in 
regard  to  the  steam  engine  ? 

A.  He  should  always  keep  it  clean  and  free  from 
rust,  oil,  and  grit.  This  does  not  involve  a  great 
deal  of  labor,  and  adds  very  materially  to  the  life 
of  the  engine. 

Q.   How  should  an  engine  be  started  ? 

A.  First  see  that  the  drips  are  all  open.  The 
cylinder  should  then  be  warmed  by  slightly  open- 
ing the  throttle. 


STEAM    ENGINEERS   AND    ELECTRICIANS.        217 

Q.  How  should  the  clrij^s  be  left  when  the 
engine  is  not  running  ? 

A.  They  should  be  left  open  so  as  to  allow  the 
condensed  steam  to  escape. 

Q.   How  do  you  pack  stuffing-boxes  ? 

A.  Before  packing  the  piston-  and  valve-rods 
all  the  old  packing  should  be  carefully  removed. 
The  new  packing  should  be  cut  in  suitable  lengths, 
and  the  joints  placed  at  opposite  sides  of  the  box. 
The  stuffing-box  should  then  be  screwed  up  until 
the  leakage  around  the  rod  is  stopped,  and  no 
further,  as  any  unnecessary  tightening  of  the 
stuffing-box  will  greatly  diminish  the  power  of 
the  engine  and  soon  destroy  the  packing  by  the 
increased  friction.  Piston-rod  packing  should 
always  be  kept  in  a  clean  place,  as  any  dust  or 
grit  that  may  become  attached  to  it  has  a  tendency 
to  cut  or  flute  the  rod. 

Q.  What  precautions  should  be  taken  with  the 
piston  ? 

A.  The  spring  packing  in  the  cylinder  should 
always  be  kept  up  to  its  proper  place,  because  if 
allowed  to  become  loose,  the  leakage  materially 
reduces  the  power  of  the  engine.  Setting  out 
packing- rings  requires  the  exercise  of  great  care, 
because,  if  set  too  tightly,  the  friction  produced 
will  not  only  have  a  tendency  to  cut  the  cylin- 
der,  but  will   also   perceptibly   lessen  the  power 


218  roper's  catechism  for 

of  the  engine.  The  piston  should  be  removed 
from  the  cylinder  at  least  twice  a  year,  and  the 
joints  formed  by  the  rings  on  the  flange  of  the 
head  and  the  follower-plate  carefully  ground  with 
emery  and  oil.  If  badly  corroded,  they  should 
be  faced  up  in  a  lathe  and  made  perfectly  steam- 
tight. 

Q.  How  should  the  spindle  of  a  ball  governor 
be  packed  ? 

A.  Great  care  should  be  taken,  when  packing 
the  spindle  of  a  governor,  not  to  screw  the  pack- 
ing down  too  tightly,  as  that  would  interfere  with 
the  free  movement  of  the  governor.  All  the  parts 
of  the  governor  should  be  kept  perfectly  clean  and 
free  from  the  gum  formed  by  the  use  of  inferior 
qualities  of  lubricating  oils. 

Q.   How  should  the  engine  be  lubricated  ? 

A.  All  the  surfaces  subjected  to  friction  should 
be  provided  with  sight-feed  oil-cups.  These 
should  be  turned  on  as  soon  as  the  engine  is 
started  and  examined  at  frequent  intervals,  to  see 
that  the  supply  is  not  exhausted  and  to  make  sure 
that  every  cup  is  feeding  correctly. 

Q.  Is  it  advisable  to  use  as  much  oil  as  possible 
on  an  engine? 

A.  No  more  oil  should  be  used  on  an  engine 
than  is  absolutely  necessary,  as  it  is  not  only  a 
loss,  but  often  detracts  from  the  appearance  of  the 


STEAM   ENGINEERS   AND    ELECTRICIANS.         219 

engine,  and  greatly  interferes  with  its  free  and  eas}" 
movement,  from  the  accumulation  of  gum  and 
dirt  on  its  working  parts. 

Q.  Suppose  any  part  of  the  engine  should  heat, 
what  would  be  the  proper  thing  to  do  ? 

A.  First  examine  the  lubricator,  and  if  it  is 
found  that  the  heated  part  has  not  been  receiving 
the  proper  amount  of  oil,  the  trouble  can  usually 
be  remedied  by  giving  it  a  liberal  supply.  Some- 
times it  is  necessary  in  a  new  engine  to  keep  the 
bearings  cool,  temporarily,  with  ice,  although  if 
they  run  very  hot  it  is  generally  better  to  stop 
the  engine  if  possible  and  determine  the  cause. 
In  case  the  crank-pin  should  heat — which  is  a 
common  occurrence  with  engines  having  a  narrow 
bearing  on  the  pin,  but  more  particularly  with 
engines  that  are  slightly  out  of  line — remove  the 
key  and  slacken  the  strap  and  box;  then  pour  in 
some  flour  of  sulphur  with  a  liberal  supply  of 
oil;  then  adjust  the  key,  and  the  trouble  will 
generally  disappear.  If  the  pillow-blocks  of  an 
engine  should  heat  badly,  remove  the  cap  and 
pour  in  a  good  supply  of  pulverized  bath-brick 
and  water  while  the  engine  is  in  motion;  after 
doing  this  for  some  time,  wash  out  with  oil,  and 
wipe  the  bearing  clean  with  waste.  In  case  any 
of  the  bearings  of  an  engine  should  heat  through 
the  accumulation  of  matter  deposited  from  the  oil 


220  roper's  catechism  for 

used,  or  sand,  grit,  or  whitewash  being  dropped 
into  the  bearings,  use  a  strong  solution  of  concen- 
trated lye  with  oil  when  the  engine  is  in  motion. 

Q.  Where  should  the  tools  and  materials  used 
about  an  engine  be  kept  ? 

A,  They  should  be  kept  in  a  clean  place. 
Never  set  steam-packing,  cotton-waste,  tops  of 
oil-cups,  or  anything  that  is  to  be  used  around  the 
cylinder,  valves,  piston-rod,  or  bearings  of  steam 
engines,  on  the  floor,  as  they  will  invariably  pick 
up  sand  or  grit,  which  injure  the  rubbing  and 
revolving  surfaces  with  which  they  come  in  con- 
tact. 

Q.   How  should  gum- joints  be  made? 

A.  If  they  frequently  need  to  be  taken  apart, 
the  gum  should  be  well  coated  with  pulverized 
chalk  or  soapstone  before  being  placed  between 
the  flanges.  This  prevents  it  from  adhering  to 
the  metal  and  being  destroyed  when  the  joint  is 
broken. 

Q.  What  does  a  clicking  noise  in  the  cylinder 
indicate  ? 

A,  It  frequently  indicates  the  pressure  of  moist- 
ure, and  it  can  generally  be  stopped  b}^  opening 
the  drip-cocks. 

Q.  What  are  some  of  the  principal  causes  of 
knocking  in  steam  engines  and  the  appropriate 
remedies  ? 


STEAM    ENGINEERS    AND    ELECTRICIANS.        221 

A.  Knocking  in  engines  generally  arises  from 
the  following  causes: 

First.  Lost  motion  in  the  boxes  on  the  cross- 
head,  crank-pin,  and  the  pillow-blocks,  and  in 
the  key  of  the  piston-rod  in  the  cross-head.  To 
stop  it,  take  up  lost  motion  by  means  of  the  key, 
or  file  off  the  edges  of  the  boxes,  if  brass-bound. 

Second.  It  is  sometimes  caused  by  the  crank 
being  ahead  of  the  steam,  which  in  most  cases  can 
be  relieved  by  moving  the  eccentric  forward  in 
order  to  give  more  lead  an  the  valve. 

Third.  Knocking  is  caused  in  many  cases  by 
too  much  lead  on  the  valve.  The  simplest  remedy 
for  this  is  to  move  the  eccentric  back  so  as  to  give 
less  lead. 

Fourth.  Frequently  it  is  caused  by  the  exhaust 
closing  too  soon.  The  best  remedy  for  this  would 
be  to  enlarge  the  exhaust-chamber  in  the  valve. 

Fifth.  Insufficient  clearance  between  the  piston 
and  the  cylinder-head  at  the  end  of  the  stroke. 
The  remedy  for  this  kind  of  knocking  would  be 
to  turn  off  the  heads  of  the  cylinder  on  the  inside, 
so  as  to  give  more  clearance. 

Sixth.  Knocking  sometimes  arises  from  the 
wrist  of  the  cross-head  and  the  crank-pin  becom- 
ing worn  out  of  round.  The  most  effective  remedy 
for  this  cause  is  to  turn  up  the  crank-  and  wrist- 
pin. 


222  roper's  catechism  for 

Seventh.  Insufficient  counter-bore  in  cylinder. 
In  such  cases  the  piston-rings  wear  a  shoulder  at 
each  end  of  the  cylinder,  and  whenever  the  keys 
are  driven  or  the  packing-rings  set  out,  the  edges 
strike  these  shoulders  and  cause  the  engine  to 
knock.  The  most  practical  remedy  for  knocking 
arising  from  this  cause  is  to  recoimter-hore  the 
cylinder. 

Eighth.  Knocking  is  sometimes  caused  by  the 
engine  being  out  of  line.  The  surest  remedy  for 
this  kind  of  knocking  would  be  to  put  the  engine 
exactly  in  line. 

Ninth.  Sometimes  it  arises  from  shoulders  be- 
coming worn  on  the  ends  of  the  guides  in  cases 
where  the  gibs  on  the  cross-head  do  not  run  over. 
The  most  reliable  remedy  for  such  knocking  would 
be  to  replane  the  guides. 

Tenth.  Knocking  is  sometimes  caused  by  the 
follower-plate  being  loose.  The  best  preventive 
for  such  knocking  is  to  bring  the  bolts  up  tight. 
To  do  so,  it  is  sometimes  necessary  to  remove  the 
deposit  of  rust  or  grease  in  the  bottom  of  the  holes. 

Eleventh.  Very  often  it  is  caused  by  the  pack- 
ing around  the  piston-rod  being  too  hard  and 
tight.  The  most  effectual  remedy  for  that  is  to 
remove  all  the  old  packing  from  the  box  and 
replace  it  with  new,  and  only  screw  the  box  up 
sufficiently  to  prevent  the  escape  of  steam.     Too 


STEAM    ENGINEERS   AND    ELECTRICIANS.         223 

much  friction  on  the  rod  is  a  great  loss  of  power, 
and  has  a  tendency  to  destroy  the  packing. 

Twelfth.  The  knocking  heard  in  the  steam-chest 
is  sometimes  caused  by  lost  motion  in  the  jam- 
nuts  or  yoke  that  forms  the  attachment  between 
the  valve  and  rod.  The  remedy  for  this  would 
be  to  remove  the  cover  of  the  steam-chest  and  re- 
adjust the  jam-nuts  on  the  valve-rod. 


224       roper's  catechism  for 


ADJUNCTS  OF  THE  STEAM  ENGINE. 

THE  INDICATOR. 

Q.  What  do  you  understand  by  the  steam  engine 
indicator  ? 

A.  An  instrument  which  records  the  pressure 
in  the  steam  cylinder  at  every  point  of  the  stroke. 

Q.  Give  a  brief  description  of  the  instrument 
and  explain  how  this  record  is  made. 

A.  The  indicator  consists  essentially  of  a  small 
hollow  cylinder  which  communicates  with  the 
engine  cylinder.  A  rod  attached  to  the  piston  is 
enclosed  in  a  spiral  spring  which  presses  against 
the  piston  and  opposes  its  motion.  The  end  of 
the  rod  extends  through  the  cover  at  the  top  of 
the  cylinder,  and  is  attached  to  a  series  of  levers, 
called  a  parallel  motion^  in  such  a  way  that  a 
pencil  attached  to  the  end  of  the  long  lever  will 
move  in  a  vertical  straight  line  when  the  piston 
ascends.  A  second  hollow  cylinder,  carried  on 
the  same  frame  as  the  first,  and  called  the  paper 
drum,  is  mounted  on  a  vertical  spindle,  about 
which  it  is  free  to  rotate,  but  by  the  action  of  a 
spring  contained  in  it  the  drum  tends  to  remain 
in  a  fixed  position.  A  groove,  shown  at  the  bot- 
tom of  the  drum,  carries  a  cord  which  is  attached 


STEAM    ENGINEERS    AND    ELECTRICIANS.. 


225 


by  means  of  a  reducing  motion  to  some  of  the 
reciprocating  parts  of  the  engine,  so  that  the 
pencil,  when  the  engine  is  moving,  would  trace  a 
horizontal  line  on  the  surface  of  the  drum,  which 
would  represent  the  stroke  of  the  engine.     As  the 


SECTION   OF  TABOR'S   INDICATOR. 


pencil,  however,  is  moved  up  and  down  by  the 
pressure  of  the  steam  in  the  cylinder,  it  follows 
that,  if  a  paper  is  placed  around  the  drum,  a 
diagram  will  be  traced,  representing  the  pressure 

15 


226     ^  roper's  catechism  for 

in  the  cylinder  at  every  point  in  the  stroke.  The 
vertical  height  of  any  point  in  the  diagram,  from 
the  bottom  or  atmospheric  line,  will  represent  the 
pressure,  and  the  horizontal  distances  will  repre- 
sent the  position  of  the  piston. 

Q.  How  would  you  proceed  to  take  an  indicator 
diagram  ? 

A.  It  is  impossible  to  give  directions  which 
would  apply  to  all  makes  of  indicators.  I  should 
carefully  read  the  directions  given  by  the  makers 
of  the  particular  type  of  instrument  in  my  pos- 
session, and  proceed  accordingly. 

Q.  Sketch  an  indicator  diagram  and  explain 
what  it  means. 

A.  In  the  accompanying  diagram  the  line  A  A 
is  the  atmospheric  line — that  is,  it  is  the  line 
traced  by  the  pencil  on  the  paper  when  the  engine 
is  in  motion  before  the  indicator  cylinder  is  placed 
in  communication  with  the  engine  cylinder. 
Hence  its  position  represents  the  pressure  of  the 
atmosphere.  The  point  B  represents  the  position 
of  the  pencil  at  the  beginning  of  the  stroke,  and 
hence  the  vertical  height  B  A  of  this  point  above 
the  atmospheric  line  A  A  represents  the  initial 
steam  pressure  in  the  cjdinder.  The  line  B  C 
represents  the  distance  traveled  by  the  piston 
during  the  period  of  admission,  and  the  point  C, 
where  the  first  change  in  direction  occurs,  is  the 


STEAM   ENGINEERS   AND    ELECTRICIANS. 


227 


point  of  cut-off.  Expansion  now  takes  place  in 
the  cylinder  and  continues  until  the  next  change 
in  direction  occurs  at  D,  which  is  the  point  at 
which  the  exhaust  port  begins  to  open.  The 
steam  is  released  from  the  cylinder,  and  the  pres- 
sure falls  more  rapidly  until  the  end  of  the  stroke 
E,  when  it  is  about  equal  to  that  of  the  atmos- 


HHhI 


EXPLANATORY   DIAGRAM. 


phere.  The  piston  then  begins  its  return  stroke 
against  the  back  pressure  represented  by  the  ver- 
tical height  of  the  line  E  F  above  the  atmospheric 
line  A  A.  If  the  engine  exhausts  into  the  atmos- 
phere, this  height  is  generally  very  small,  while 
if  it  is  a  condensing  engine,  the  back  pressure 
line  E  F  will  be  below  the  atmospheric  line  A  A, 


228  roper's  catechism  for 

indicating  a  negative  back  pressure.  At  F  the 
exhaust  closes  and  compression  begins,  which 
continues  until  the  end  of  the  stroke  G.  The 
same  cycle  is  then  repeated,  and  so  long  as  the 
load,  the  initial  pressure  and  the  back  pressure 
remain  the  same,  the  diagram  traced  by  each 
successive  stroke  will  be  practically  the  same. 
For  the  other  end  of  the  cylinder  the  diagram 
will  be  similar  but  reversed. 

Q.  What  are  the  principal  things  that  may  be 
ascertained  about  an  engine  with  the  aid  of  the 
indicator  diagram  ? 

A.  The  information  furnished  by  the  indicator 
diagram  is  of  the  most  important  kind.  It  en- 
ables us  to  determine: 

First.  The  power  of  the  steam  engine  under  all 
conditions,  or  the  power  consumed  by  any  one 
machine  driven  by  the  engine  or  by  the  engine 
itself  in  overcoming  the  friction  of  its  parts. 

Secondly.  The  forward  and  back  pressure  on 
the  piston  at  any  point  in  the  stroke. 

Thirdly.  The  average  forward  and  back  pres- 
sure and  the  mean  effective  pressure  on  the  piston. 

Fourthly.  The  positions  of  the  piston  when 
steam  is  admitted  and  cut  off;  the  period  of  ex- 
pansion, exhaust,  and  compression;  the  action  of 
the  valves;  and,  in  fact,  all  questions  relating  to 
the  steam  distribution. 


STEAM   ENGINEERS   AND    ELECTRICIANS.         229 

Q.  How  is  the  power  developed  by  the  engine, 
or  the  indicated  horse-power  calculated  from  the 
diagram  ? 

A.  The  indicated  horse-power  of  the  engine  is 
fomid  by  determining  the  mean  effective  pressure 
from  the  diagram  and  using  it  in  the  rules  and 
formulae  for  horse-power  given  on  pages  177-180. 

Q.  Explain  how  to  find  the  mean  effective 
pressure. 

A.  There  are  two  methods  in  common  use, — 
one  by  the  use  of  ordinates  and  the  other  by  the 
planimeter.  The  latter  method  is  more  exact  and 
less  laborious  than  the  former,  but  as  a  plan- 
imeter  is  not  always  available,  the  former  method 
is  much  used,  especially  for  rough  calculations. 

TO  DETERMINE  THE  MEAN  EFFECTIVE 
PRESSURE. 

First  Method. — Draw  vertical  lines  A  B  and  A  I 
touching  the  ends  of  the  diagram  (see  page  227), 
and  apply  a  rule  across  them  obliquely  as  shown 
by  the  dotted  line  in  the  diagram  in  such  a  way 
that  some  division  on  the  rule,  as  y^g-,  ^,  ^,  or  ^, 
will  divide  the  distance  between  the  verticals  just 
drawn  an  even  number  of  times,  preferably  20 
times.  Mark  off  points  on  this  line,  dividing  it 
into  equal  parts  excepting  the  first  and  last,  which 
are   only  one-half   as   large  as   the   intermediate 


230  roper's  catechism  for 

spaces,  and  draw  vertical  lines  or  ordinates 
through  these  points,  dividing  the  area  enclosed 
by  the  diagram  as  shown.  Next  take  a  long  strip 
of  paper  and  apply  its  edge  successively  to  each  of 
the  ordinates  and  mark  their  combined  length  on 
it.  This  length  multiplied  by  the  scale  of  the 
spring  used  and  divided  by  the  total  number  of 
ordinates  will  give  the  mean  effective  pressure. 
The  length  of  the  ordinates  is  measured  between 
the  forward-  and  back-pressure  lines. 

Second  Method. — If  a  planimeter  is  used,  it  is 
only  necessary  to  multiply  the  area  enclosed  by 
the  diagram  in  square  inches  by  the  scale  of  the 
spring,  and  divide  the  product  by  the  length  of 
the  diagram  in  inches.  The  quotient  will  be  the 
mean  effective  pressure. 

Q.  What  precautions  must  be  taken  if  the  indi- 
cated horse-power  is  to  be  calculated  very  accu- 
rately ? 

A.  The  mean  effective  pressure  must  be  calcu- 
lated separately  from  the  diagrams  of  the  head- 
and  crank-ends  of  the  cylinder.  In  doing  this  it 
must  be  remembered  that  the  back-pressure  line 
of  one  diagram  belongs  to  the  forward-pressure 
line  of  the  other,  and  vice  versa.  While  in  most 
engines  in  which  the  valves  are  properly  adjusted 
the  two  back-pressure  lines  are  identical,  yet  if 
the  greatest  accuracy  is  desired  the  mean  effective 


STEAM    ENGINEERS   AND    ELECTRICIANS.         231 

pressure  should  be  calculated  by  deducting  from 
the  mean  forward  pressure  as  obtained  from  the 
head-end  diagram,  the  mean  back  pressure  as 
obtained  from  the  crank-end  diagram,  and  vice 
versa.  It  must  further  be  borne  in  mind  that  the 
effective  area  of  the  piston  at  the  crank  end  is  less 
than  that  at  the  head  end  by  the  area  of  the  piston 
rod.  Hence  the  horse-power  is  different  for  the 
two  ends  and  should  be  calculated  independently; 
the  total  horse-power  of  the  engine  being  equal  to 
the  sum  of  the  two. 

Q.  Suppose  it  is  desired  to  find  the  horse-power 
of  an  engine  where  the  following  dimensions  and 
data  are  known: 

Stroke  =  36  inches. 
Diameter  of  cylinder  =  24  inches, 
Speed  =  150  revolutions  per  minute, 
Diameter  of  piston  rod  =  4  inches. 

The  engine  having  been  indicated  with  a  spring 
whose  scale  was  60  pounds  per  square  inch,  it  was 
found  with  the  aid  of  a  planimeter  that  the  areas 
of  the  diagrams  w^ere  as  follow^s: 

Head  end  =  3. 54  square  inches, 
Crank  end  =  3.42  square  inches, 
Length  of  diagrams  =  3.27  inches. 

Calculate  the  mean  effective  pressures  and  the 
horse-power  of  the  engine. 


232  roper's  catechism  for 

A.   The  mean  effective  pressure,  according  to  the 
above  (second)  method,  is — 

Head  end,        ^  ^„ —  ^  64.95  pomids, 

Crank  end,        ^    „        =  62. 32  pomids. 

The  area  of  the  piston  is — 

.7854  X  24  X  24  =  452.39  square  inches, 
and  the  area  of  the  piston  rod  is — 

.7854  X  4  X  4  =  12.57  square  inches. 
Hence  the  effective  areas  of  the  piston  are — 
Head  end,    452.39  square  inches. 
12.57      " 


Crank  end,  439.82       " 

The  total  mean  pressures  on  the  piston  are — 

Head  end,   452.39  X  64.95  =  29385  pounds, 

Crank  end,  439.82  X  62.32  =  27409  pounds. 

The  piston  speed  is — 

36 

12 

and  therefore  the  horse-power — 

jr    A      A     29385  X  900        „^,    . 
Headend.— 33^^^— ^801.4 

^      ,       T    27409  X  900 
Crank  end, 33000 ^ 


Total,     1548.9 


STEAM   ENGINEERS   AND   ELECTRICIANS.         233 

CONDENSERS. 

Q.  What  do  you  understand  by  a  condenser  ? 

A.  An  apparatus  for  condensing  the  exhaust 
-steam  of  an  engine,  thereby  reducing  the  back 
pressure  and  therefore  increasing  the  power. 

Q.  How  is  this  done  ? 

A.  By  bringing  the  steam  under  the  influence 
of  cold  water,  either  by  bringing  the  two  in  direct 
contact  or  by  allowing  the  steam  to  pass  around  a 
series  of  tubes  through  which  the  w^ater  flows. 
Condensers  constructed  on  the  first-named  plan 
are  called  jet  condensers^  while  the  latter  are  termed 
surface  condensers. 

Q.  What  are  the  principal  advantages  and  dis- 
advantages of  the  two  types  ? 

A.  Surface  condensers  have  the  advantage  that 
the  condensed  steam  is  not  mixed  with  the  con- 
densing water.  Hence  they  are  generally  used  on 
shipboard  so  that  the  condensed  steam  may  again 
be  used  in  the  boilers.  The  vacuum  is  also 
generally  higher  in  surface  than  in  jet  condensers, 
but  they  have  the  disadvantage  of  being  heavier 
and  much  more  expensive  to  construct  than  jet 
condensers.  The  tubes  are  also  liable  to  become 
leaky  and  impair  the  vacuum. 

Q.  At  what  temperature  should  jet  condensers 
be  kept? 


234  roper's  catechism  for 

A.  About  100°  Fahr.,  at  which  temperature 
they  have  been  found  to  operate  most  efficiently. 

Q.  What  degree  of  vacuum  should  exist  in  a 
good  condenser  ? 

A.   From  20  to  26  inches. 

Q.  What  do  you  mean  by  26  inches  of  vacuum  ? 

A.  As  the  atmospheric  pressure  will  support  a 
column  of  mercury  about  30  inches  in  height, 
each  inch  of  the  mercury  column  would  be  equiv- 
alent to  a  pressure  of  about  ^  pound.  A  complete 
vacuum  (which  can  never  exist)  would  be  a 
vacuum  of  30  inches,  corresponding  to  a  pressure 
of  0  pound  per  square  inch;  20  inches  of  vacuum 
would  be  one-third  less  vacuum  or  one-third  of 
the  atmospheric  pressure — that  is,  5  pounds  per 
square  inch  absolute  pressure.  Hence  to  find  the 
absolute  pressure  in  pounds  per  square  inch, 
deduct  one-half  of  the  vacuum  in  inches  from  the 
pressure  of  the  atmosphere.  Thus  15  inches  of 
vacuum  would  be,  15  —  15  X  i  =  7J-  pounds 
per  square  inch  absolutely. 

Q.  How  much  power  is  gained  by  the  use  of 
the  condenser? 

A.  From  20  to  30  per  cent.,  depending  on  the 
type  and  size  of  the  engine. 

Q.   How  much  water  is  required  for  condensers  ? 

A.  About  25  times  the  quantity  evaporated  in 
the  boiler. 


STEAM    ENGINEERS   AND    ELECTRICIANS. 


235 


TABLE 

SHOWING  VACUUM   IN   INCHES   OF  MERCURY  AND   POUNDS 
PRESSURE   PER   SQUARE   INCH. 


Mercury. 

Founds, 

Mercury. 

Pounds. 

2.037 

1 

16.300 

8 

4.074 

2 

18.337 

9 

6.111 

3 

20.374 

10 

8.148 

4 

22.411 

11 

10.189 

5 

24.448 

12 

12  226 

6 

26.485 

13 

14.263 

7 

28.552 

14 

236       eoper's  catechism  for 


MATERIALS  AND  THEIR  PROPERTIES. 

Q.  Of  what  is  all  matter  made  up  ? 

A.   Of  chemical  elements. 

Q.  What  are  chemical  elements  ? 

A.  Substances  having  certain  definite  and  pecu- 
liar properties  which,  so  far,  chemists  have  not 
been  able  to  split  up  into  simpler  substances,  and 
which  it  is  presumed  cannot  be  further  split  up. 

Q.  What  are  some  of  the  elements  ? 

A.  Among  the  metals :  Iron,  Copper,  Lead,  Tin, 
Zinc,  Silver,  Gold,  and  Platinum.  Among  the 
non-metals  are:  Antimony,  Bismuth,  Silicon,  Sul- 
phur, and  Carbon.  Among  those  which  exist  nor- 
mally in  the  gaseous  condition  are:  Hydrogen, 
Oxygen,  Nitrogen,  and  Chlorine. 

Q.  What  are  the  substances  called  which  are 
made  up  by  the  chemical  combination  of  two  or 
more  elements? 

A.  Compounds,  as,  for  example,  Water,  which 
is  a  compound  of  Oxygen  and  Hydrogen;  Ammo- 
nia, which  is  a  compound  of  Nitrogen  and  Hydro- 
gen; Carbonic  Acid,  which  is  a  compound  of  Car- 
bon and  Oxygen;  Zinc  Oxide,  which  is  a  compound 
of  Zinc  and  Oxygen;  and  common  Salt,  which  is 
a  compound  of  Sodium  and  Chlorine. 


STEAM    ENGINEERS    AND   ELECTRICIANS.        237 

Q.  What  are  the  molecules  of  a  substance  ? 

A.  The  smallest  particles  mto  which  a  substance 
can  be  divided  without  these  particles  losing  any 
of  the  distinctive  properties  of  the  substance. 

Q.  Have  you  any  idea  as  to  whether  molecules 
are  visible  under  the  microscope  ? 

A.  They  are  not.  Were  the  magnifying  power 
in  any  way  much  increased,  they  would  still  be 
too  small  to  be  seen.  Our  ideas  as  to  their  exist- 
ence are  derived  not  from  sight,  but  from  a  variety 
of  chemical  phenomena. 

Q.  Is  it  conceived  that  there  are  particles  even 
smaller  than  molecules  ? 

A.  Yes,  the  so-called  atoms.  It  is  believed  that 
each  molecule  of  a  compound  substance  is  made 
up  of  the  atoms  of  the  elements  contained  in  the 
compound.  For  example,  the  molecule  of  salt  is 
supposed  to  be  made  up  of  an  atom  of  sodium 
joined  to  an  atom  of  chlorine,  and  the  water  mol- 
ecule is  supposed  to  be  made  up  of  two  hydrogen 
atoms  joined  to  one  oxygen  atom.  The  molecules 
of  the  elements  are  supposed  to  be  made  up  of 
two  or  more  atoms  of  that  element. 

Q.  What  is  meant  by  the  term  ' '  atomic  weight ' ' 
of  a  substance  ? 

A.  It  is  found  experimentally  that  the  elements 
combine  with  each  other  in  certain  fixed  propor- 
tions or  in  multiples  of  them.     The  figures  which 


238  roper's  catechism  for 

represent  these  proportions  (hydrogen  bemg  used 
as  the  standard  and  its  combining  weight  called 
"one")  are  called  the  atomic  weights.  For  ex- 
ample: Experiment  shows  that  hydrochloric  acid 
is  made  up  of  35.4  parts  b}^  weight  of  chlorine  to 
1  part  by  weight  of  hydrogen;  and  that  in  other 
chlorine  compounds  the  proportion  of  chlorine  is 
represented  either  by  35.4  or  by  some  multiple  of 
it,  as  35.4  X  2,  35.4  X  3,  etc.  Thus,  salt  is  made 
up  of  35.4  parts  by  weight  of  chlorine  to  23  parts 
by  weight  of  sodium. 

Q.  What  is  supposed  as  to  the  construction  of 
substances  according  to  the  molecular  theory  ? 

A.  Every  substance  is  supposed  to  be  made  up 
of  an  immense  number  of  molecules,  which,  even 
in  the  solid  state,  are  never  entirely  at  rest,  and 
in  the  gaseous  state  are  in  perpetual  violent  com- 
motion, rushing  about  in  straight  lines  in  all  di- 
rections with  enormous  rapidity. 

Q.  What  are  the  principal  properties  of  metals  ? 

A.  Their  malleability,  or  capability  to  stand  ham- 
mering; their  ductility,  or  power  of  being  drawn 
out  into  wire;  their  tenacity,  or  strength;  their 
hardness ;  their  fusibility,  or  ease  of  melting;  and 
their  relative  weight,  or  specific  gravity. 

Q.  Name  some  of  the  most  malleable  of  the 
common  metals. 

A.   Gold,  Silver,  Aluminum,  Copper,  Tin,  Lead. 


STEAM   ENGINEERS   AND    ELECTRICIANS.        239 

Q.  Name  the  most  ductile. 

A.  Platinum,  Silver,  Iron,  Copper,  Gold. 

Q.  What  are  some  of  the  strongest  ? 

A.   Iron,  Copper,  Aluminum,  Platinum,  Silver. 

Q.  What  are  some  of  the  least  fusible  ? 

A.   Platinum,  Iron,  Copper. 

Q.  AVhat  are  some  of  the  heaviest,  or  which 
have  the  greatest  specific  gravity  ? 

A.  Platinum,  Gold,  Lead,  Copper,  Iron. 

Q.  How  would  you  define  the  specific  gravity 
of  a  substance  ? 

A,  The  ratio  of  its  weight  to  the  weight  of  an 
equal  bulk  of  water. 

Q.  How  would  you  find  the  specific  gravity  of 
a  solid  body  ? 

A.  If  it  is  heavier  than  water,  weigh  it  in  air 
and  then  weigh  it  suspended  in  water.  The  dif- 
ference in  weight  is  the  weight  of  an  equal  bulk 
of  water.  Divide  the  weight  in  air  by  the  weight 
of  the  equal  bulk  of  water  and  the  quotient  is  the 
specific  gravity. 

If  the  body  floats  put  just  the  weight  oil  it  that 
is  necessary  to  make  it  sink  even  with  the  surface 
of  the  water.  Then  from  the  sum  of  this  weight 
and  the  weight  in  air  subtract  the  weight  in  water. 
The  difference  is  the  weight  of  an  equal  bulk  of 
water.  Divide  the  weight  in  air  by  this  and  the 
quotient  will  be  the  specific  gravity. 


240  eoper's  catechism  for 

Q.  How  would  you  measure  the  specific  gravity 
of  a  liquid  ? 

A.  Take  a  vessel  filled  with  it  and  weigh  it. 
Then  weigh  the  same  vessel  filled  with  water. 
Divide  the  weight  of  the  substance  by  the  weight 
of  the  water  and  the  quotient  will  be  the  specific 
gravity. 

Q.  Is  there  any  simple  instrument  for  testing 
the  specific  gravity  of  liquids  ? 

A.  Yes;  the  hydrometer,  which  consists  of  a 
graduated  tube  of  small  diameter  attached  to  a 
bulb  containing  air  enough  to  make  it  float.  Just 
below  this  air  chamber  is  a  small  bulb  containing 
enough  mercury  to  keep  the  apparatus  upright. 
The  graduations  on  the  tube  give  the  specific  grav- 
ity of  the  liquid  in  which  the  hydrometer  is  placed. 

Q.  Is  water  used  as  the  standard  of  specific 
gravity  for  gases  ? 

A.  No;  air  at  a  standard  temperature  of  32° 
Fahr.  and  at  a  pressure  corresponding  to  the  at- 
mosphere at  sea  level. 

COMMON  METALS.  \ 

Q.  What  are  the  varieties  of  iron  ? 
A.  Wrought  iron,  cast  iron,  and  malleable  iron. 
Q.  What  is  steel? 

A.  A  modification  of  iron,  it  being  a  combina- 
tion of  iron  with  varying  percentages  of  carbon. 


STEAM    ENGINEERS    AND    ELECTRICIANS.         241 

Q.  What  are  some  of  the  properties  of  wrought 
iron? 

A.  It  is  tough,  malleable,  ductile,  fibrous,  and 
can  be  welded. 

Q.  How  does  cast  iron  differ  from  wrought 
iron  ? 

A.  It  contains  carbon,  sulphur,  silicon,  phos- 
phorous and  other  impurities.  It  is  crystalline 
in  structure,  is  neither  malleable,  ductile,  nor 
tenacious,  but  has  the  very  important  property  of 
allowing  itself  to  be  cast. 

Q.   What  is  malleable  iron  ? 

A.   Cast  iron  annealed  amid  iron  oxides. 

Q.  What  are  its  properties  ? 

A.  It  is  much  more  ductile  than  cast  iron  and 
has  a  higher  tensile  strength,  though  far  inferior 
in  both  respects  to  wrought  iron  and  steel. 

Q.  What  are  the  properties  of  steel  ? 

A.  Steel  partakes  of  the  properties  of  both 
wrought  and  cast  iron,  as  some  steels  can  be  cast 
and  others  welded.  By  varying  the  percentage  of 
carbon  in  its  composition  its  characteristics  can  be 
widely  changed.  It  can  be  made  soft  and  ductile 
or  hard  and  brittle.  Steel  also  has  the  important 
property  of  teinpermg,  or  being  artificially  hard- 
ened by  sudden  changes  of  temperature. 

Q.  What  effect  on  the  strength  of  steel  does  an 
increase  of  the  percentage  of  carbon  have  ? 
16 


242  roper's  catechism  for 

A.   It  increases  the  strength  of  steel. 

Q.  What  effect  does  it  have  on  the  ductihty  of 
steel? 

A.  The  ductility  is  diminished. 

Q.  At  about  what  temperature  is  iron  red  hot  ? 

A.  At  about  1000°  Fahr. 

Q.   At  about  what  temperature  does  iron  melt  ? 

A.  At  about  3000°  Fahr. 

Q.  How  much  is  iron  expanded  when  its  tem- 
perature is  raised  from  freezing  point  to  boiling 
point  ? 

A.   About  -glo  of  its  length. 

Q.  AVhat  is  the  effect  of  a  rise  of  temperature 
on  the  strength  of  iron  ? 

A.  It  increases  nearly  -^  to  about  600°  Fahr., 
after  which  it  falls.  At  1000°  Fahr.  its  strength 
is  about  half  the  maximum. 

Q.  How  does  copper  compare  with  iron  in  its 
principal  qualities? 

A.  It  is  more  malleable  and  more  ductile.  Its 
tensile  strength  is  a  little  less  than  one-half.  Its 
specific  gravity  is  a  little  greater.  It  is  a  much 
better  conductor  for  heat  and  electricity,  its  elec-  ^ 
trical  conductivity  being  about  six  times  that  of 
iron. 

Q.   How  is  the  tensile  strength  affected  by  heat  ? 

A.  It  is  diminished,  disappearing  entirely  at 
about  1300°  Fahr. 


STEAM   ENGINEERS    AND    ELECTRICIANS.         243 

Q.  What  is  the  temperature  at  which  copper 
melts? 

A.  At  about  2000°  Fahr. 

Q.   In  what  form  is  copper  mostly  used  ? 

A.   In  the  form  of  sheets  and  wires. 

Q.   In  what  other  ways  is  it  largely  used  ? 

A.  In  combination  with  other  metals  forming 
alloys. 

Q.  What  are  some  of  the  principal  alloys  ? 

A.   Brass,  Bronze,  and  German  Silver. 

Q.  What  is  the  composition  of  brass  ? 

A.  It  varies  with  the  purpose  for  which  it  is  to 
be  used.  Ordinary  brass  in  foundries  consists  of 
2  parts  copper  to  1  part  zinc.  A  little  tin  or  lead 
is  sometimes  added,  but  essentially  brass  is  an 
alloy  of  copper  and  zinc. 

Q.  What  is  bronze  ? 

A.  Bronze  is  essentially  an  alloy  of  copper  and 
tin,  consisting  of  about  8  parts  copper  to  1  part 
tin. 

Q.  What  is  German  Silver  ? 

A.  An  alloy  of  copper  and  zinc,  having  a  com- 
position of  about  3  parts  copper  to  1  part  zinc. 

Q.  What  are  some  of  the  striking  properties  of 
lead? 

A.  Its  softness  and  malleability  and  its  lack  of 
elasticity.  A  very  valuable  property  is  that  it  is 
not  readily  oxidized  nor  attacked  by  acids. 


244  roper's  catechism  for 

Q.   For  what  purposes  is  it  largely  used  ? 

A.  In  sheets,  pans,  and  pipes  and  as  a  constit- 
uent of  paints. 

Q.  How  does  it  compare,  in  tensile  strength, 
with  iron  ? 

A.  Its  tensile  strength  is  very  small  indeed  in 
comparison  with  that  of  iron. 

Q.  What  is  its  melting  point? 

A.  About  600°  Fahr. 

Q.  What  is  its  specific  gravity  ? 

A.  About  11,  nearly  double  that  of  iron. 

STRENGTH  OF  MATERIALS. 

Q.  What  do  you  understand  by  the  breaking 
strength  of  a  substance  ? 

A.  The  force,  in  pounds  per  square  inch,  that 
must  be  exerted  to  break  a  specimen  of  that  sub- 
stance when  it  is  placed  in  a  suitable  testing 
machine.  The  breaking  strength  may  be  either 
tensile  or  compressive. 

Q.  What  is  the  tensile  strength  ? 

A.  The  number  of  pounds  necessary  to  pull 
asunder  the  test  piece  of  1  square  inch  cross-sec- 
tion, the  force  being  applied  in  a  line  perpendicu- 
lar to  the  plane  of  the  section. 

Q.   What  is  the  compressive  strength  ? 

A.  The  number  of  pounds  that  must  be  applied 
to  crush  the  test  piece. 


STEAM   ENGINEERS   AND    ELECTRICIANS.         245 

Q.   What  is  the  tensile  strength  of  cast  iron  ? 

A.  About  16,000  pounds  per  square  inch. 

Q.  What  is  the  compressive  or  crushing 
strength  ? 

A.  About  100,000  pounds. 

Q.  What  are  the  tensile  and  compressive 
strengths  of  wrought  iron  ? 

A.  They  are  about  the  same,  viz. ,  50, 000  pounds. 

Q.  What  can  you  say  of  the  strength  of  steel  ? 

A.  It  may  be  made  to  have  almost  any  value,  by 
varying  the  composition,  from  50,000  to  200,000 
pounds  per  square  inch.  The  great  increase  in 
strength  is  accompanied  by  brittleness. 

Q.  What  are  the  strengths  of  oak  and  pine  ? 

A.  Tensile  about  7000  pounds  and  compressive 
about  3500  pounds  per  square  inch. 

Q.  In  calculating  the  sizes  of  pieces,  either 
metal  or  wood,  are  the  above  figures  used  without 
any  allowance  for  uncertainties? 

A.  No;  we  make  use  of  what  is  termed  a  Factor 
of  Safety.  We  assume  that  the  load  coming  on 
the  piece  is  a  certain  number  of  times  greater 
than  it  really  is  and  calculate  the  size  of  the  piece 
accordingly.  The  ratio  between  the  assumed  load 
and  the  real  load  is  the  Factor  of  Safety. 

Q.  What  values  are  used  for  the  factor  of 
safety  ? 

A.  This  depends  entirely  upon  the  nature  of 


246  roper's  catechism  for 

the  load.  If  it  is  steady,  with  no  vibration  as  in 
the  roofs  of  houses,  the  factor  is  taken  as  three. 
When  the  load  is  fairly  nniform,  but  with  vibration, 
as  in  the  case  of  shafting  hung  from  the  roof  trusses, 
the  factor  should  he  four.  If  the  direction  of  the 
load  is  reversed,  putting  the  piece  in  alternate  ten- 
sion and  compression,  the  factor  should  be  six. 

Q.  Suppose  it  were  desired  to  hang  a  weight  of 
50,000  pounds  on  the  lower  end  of  a  wrought-iron 
rod.  What  should  be  the  area  of  the  cross-section 
of  the  rod  ? 

A.  This  is  a  case  of  a  steady  load  where  the 
factor  of  safety  to  be  used  is  three.  Multiplying 
the  actual  load  by  3  we  obtain  150,000  pounds  as 
the  load  to  be  assumed.  The  tensile  strength  of 
wrought  iron  being  about  50,000  pounds  per 
square  inch,  it  is  evident  that  we  must  have  a 
section  of  150,000  ^-  50,000,  or  3  square  inches. 

Q.  On  what  does  the  weight  that  a  beam  will 
support,  depend? 

A.  On  the  length  of  the  beam  between  the 
points  of  support,  on  its  width  and  depth,  and 
on  the  manner  of  application  of  the  load. 

Q.  What  difference  does  it  make  as  to  the 
manner  of  loading  the  beam  ? 

A.  It  will  support  a  much  greater  load  if  it  is 
uniformly  loaded  than  if  the  load  is  applied  at 
one  point. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         247 

Q.  What  do  you  mean  by  a  uniformly  loaded 
beam  ? 

A.  A  beam  is  uniformly  loaded  when  the  weight 
per  square  inch  resting  on  it  is  the  same  at  all 
parts  of  its  length. 

Q.  When  a  beam  is  supported  at  both  ends,  at 
what  point  will  a  given  load  break  the  beam  most 
readily  ? 

A.  At  the  middle  of  the  beam. 

Q.  What  is  the  difference  between  the  load 
which  if  applied  in  the  middle  will  break  a  beam, 
and  the  load  needed  to  break  it  if  it  is  uniformly 
distributed  ? 

A.  A  given  beam  will  support  a  uniformly 
distributed  load  twice  as  great  as  that  which  will 
break  it  if  it  is  applied  at  the  middle. 

Q.  Can  the  values  for  crushing  strength  be  safely 
used  in  all  cases  ? 

A.  Not  when  the  length  of  the  piece  in  com- 
pression has  a  length  greater  than  four  times  a 
diameter.  When  this  is  the  case  the  piece 
becomes  a  column,  and  a  bending  action  comes 
into  play,  causing  the  piece  to  break  long  before 
the  load  corresponding  to  the  compressive  strength 
has  been  reached. 


248       roper's  catechism  for 


ELECTRICITY* 

Seven  simple  experiments  contain  the  funda- 
mental principles  on  which  nearly  all  electrical 
apparatus  depends. 

Experiment  1. — Place  in  a  jar  containing  a  solu- 
tion of  chromic  acid  a  plate  of  zinc  and  a  plate 
of  carbon.  The  plates  should  be  near  each  other 
without  actually  touching,  and  each  should  have 
fastened  securely  to  it  a  short  piece  of  small 
copper  wire.  Place  in  another  glass  jar  a  solution 
of  copper  sulphate  and  let  the  ends  of  the  copper 
wires  dip  into  the  copper  sulphate  solution  with- 
out touching  each  other. 

Q.  AVhat  will  happen  to  that  part  of  the  copper 
wires  dipping  into  the  solution  ? 

A.  The  wire  attached  to  the  carbon  plate  will 
be  gradually  eaten  away,  while  the  wire  attached 
to  the  zinc  plate  will  increase  in  size  by  an  equal 
amount. 

Q.  AVhat  is  deposited  on  this  wire  to  increase 
its  size  ? 

A.   Pure  copper. 

Q.  Suppose  this  wire  were  made  of  some  other 
material  than  copper,  would  copper  be  deposited 
on  it? 

A.   Yes;  if  made  of  iron,  zinc,  lead,  or  carbon. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         249 

Q.  What  does  this  experiment  seem  to  show  ? 

A.  That  there  has  been  set  up  a  current  of 
something  which  apparently  carries  copper  along 
with  it. 

Q.  What  name  has  been  given  to  this  current  ? 

A.  The  electric  current. 

Q.  Could  other  plates  than  zinc  and  carbon  be 
used  to  jjroduce  it  ? 

A.  Yes;  though  zinc  is  generally  used  for  one 
of  the  plates. 

Q.  Could  another  solution  than  chromic  acid 
be  used  ? 

A.  Yes;  the  solution  must  be  one  which  readily 
attacks  one  of  the  plates,  and  it  is  usually  some 
strong  acid. 

Q.  What  is  the  apparatus  called  in  which  an 
electric  current  is  produced  by  chemical  action  ? 

A.  A  battery  cell,  or,  simply,  a  cell. 

Q.  What  is  a  battery  ? 

A.  Properly  speaking,  a  battery  means  several 
cells,  but  it  is  often  used  to  mean  simply  one 
cell. 

Q.  What  is  the  wire  called  to  which  copper  is 
carried  ? 

A.  The  kathode. 

Q.  What  is  the  wire  called  from  which  copper 
is  taken  ? 

A.  The  anode. 


250  eoper's  catechism  for 

Q.   In  which  direction  does  the  current  flow  in  ; 
the  copper  sulphate  solution  ?  ; 

A.   From  the  anode  to  the  kathode. 

Q.  Is  there  a  current  flow  through  the  cell  con- 
taining chromic  acid  ? 

A.  Yes;  resulting  in  taking  zinc  from  the  zinc 
plate  and  carrying  it  into  solution. 

Q.  Suppose  one  of  the  copper  wires  were  cut, 
what  effect  would  this  have  on  the  flow  of  current  ? 

A.  It  would  stop  completely  the  action  described 
above. 

Q.  What  does  this  show  ? 

A.  That  what  is  called  the  electric  current  was 
flowing  around  through  a  path  or  circuit,  starting, 
say,  at  the  carbon  plate,  thence  through  the  copper 
Avire  attached  to  that  plate  to  and  through  the 
solution  of  copper  sulphate,  then  through  the 
other  wire  to  the  zinc  plate,  and  finally  through 
the  chromic  acid  solution  back  to  the  carbon 
plate.  Any  interruption  of  this  circuit  stops  the 
flow  of  current. 

Q.  Would  pulling  one  of  the  wires  out  of  the 
copper  sulphate  solution  have  the  same  effect  as 
cutting  the  wire  ? 

A.  Yes. 

Q.  Of  what  electrical  industry  is  this  experi- 
ment the  basis  ? 

A.   Electro-plating. 


STEAM    ENGINEERS   AND    ELECTRICIANS.        251 

Experiment  2. — Pull  the  copper  wires  out  of  the 
copper  sulphate  solution  and  touch  them  together. 

Q.  What  will  be  observed  ? 

A.  The  wires  become  heated. 

Q.   Equally  all  along  their  length  ? 

A.   Apparently  so. 

Q.  Is  the  zinc  plate  being  dissolved  as  in  Ex- 
periment 1  ? 

A.  Yes. 

Q.  What  does  this  experiment  show  ? 

A.  That  the  electric  current  heats  bodies  through 
which  it  passes. 

Q.  Suppose  the  wire  connecting  the  zinc  and 
carbon  plates  is  made  longer,  what  will  occur  ? 

A.  The  heating  will  be  less. 

Q.  And  if  the  wire  is  made  shorter  ? 

A.  The  heating  effect  is  much  greater. 

Q.  What  would  you  infer  from  this  ? 

A.  Since  a  decrease  in  the  heating  means  a 
decrease  in  the  current,  and  since  this  was  caused 
by  lengthening  the  wire,  it  would  seem  that  the 
wire  opposes  a  resistance  to  the  flow  of  the  elec- 
tric current,  and  that  the  longer  the  wire  the 
greater  the  resistance  which  it  offers. 

Q.  Can  you  think  of  any  electrical  apparatus 
working  on  the  principle  shown  in  this  experiment  ? 

A.  Electric  heaters  and  certain  electric  measur- 
ing-instruments. 


252  roper's  catechism  for 

Experiment  3. — Bring  a  compass  needle  or  a 
freely  suspended  bar  magnet  near  the  wire  in  Ex- 
periment 2. 

Q.  What  will  be  observed  ? 

A.  The  magnet  is  evidently  acted  upon  by  some 
force  due  to  the  current  flowing  through  the  wire. 
After  oscillating  it  comes  to  rest,  pointing  cross- 
ways  to  the  wire  and  nearly  perpendicular  to  it. 

Q.   Is  this  the  case  all  along  the  wire  ? 

A.   Yes. 

Q.  Why  does  the  needle  not  stand  exactly  per- 
pendicular to  the  wire  ? 

A.  Because  normally  it  tends  to  point  north. 
The  current  through  the  wire  tends  to  make  it 
stand  perpendicular  to  the  wire.  It  actually  takes 
a  direction  between  these  two. 

Q.  Notice  which  way  the  north-seeking  pole  of 
the  magnet  points.  Now,  if  the  magnet  is  held 
first  above  the  wire  and  then  below,  what  occurs  ? 

A.  Although  the  needle  tends  to  stand  in  a 
direction  cross- ways  to  the  length  of  the  wire,  yet 
when  above  the  wire  the  north-seeking  pole  points 
in  one  direction,  and  when  below  the  wire  in  the 
opposite  direction. 

Q.  Is  there  any  rule  for  telling  in  what  direction 
it  will  point? 

A.  Yes,  one  known  as  Ampere's  rule,  which  is: 
^'Imagine  yourself  swimming  with  the  current  and 


STEAM   ENGINEERS   AND    ELECTRICIANS.         Zo6 

turned  either  on  your  side,  face,  or  hack,  so  as  to  look 
at  the  magnet.  Then  the  north-seeking  pole  of  the 
magnet  luill  point  toivard  your  left. ' ' 

Q.  In  the  above  experiment,  suppose  that  the 
wire  carrying  the  current  is  free  to  move  while 
the  magnet  is  fixed,  what  will  occur  ? 

A.  The  Avire  will  move  either  toward  or  away 
from  the  magnet,  according  as  one  pole  or  the 
other  of  the  magnet  is  presented  to  it. 

Q.   What  does  this  show? 

A.  That  there  is  a  force  existing  between  a 
magnet  and  a  wire  carrying  a  current,  similar  to 
the  force  existing  between  two  magnets.  Further 
experiment  shows  that  the  strength  of  this  force 
depends  on  the  nearness  of  the  magnet  to  the  wire 
carrying  current,  and  that  the  direction  of  the  force 
depends  on  the  position  of  the  wire  with  respect 
to  the  two  poles  of  the  magnet. 

Q.  Can  this  magnetic  force  be  represented  con- 
veniently by  lines  as  in  the  case  of  other  forces  ? 

A.  Yes.  We  conceive  that  around  every  mag- 
net or  wire  carrying  current  lines  could  be  drawn 
either  straight  or  curved,  which  at  any  point  of 
their  length  should  represent  the  direction  of  the 
resultant  magnetic  force  at  that  point. 

Q.  How  could  you  actually  lay  out  the  lines  of 
force  due  to  any  magnet,  say  a  bar  magnet  ? 

A.   If  we  could  obtain  a  north-seeking  pole  of  a 


254  roper's  catechism  for 

magnet  without  its  accompanying  south-seeking 
pole,  we  could  place  it  near  the  north-seeking  pole 
of  the  bar  magnet  and  observe  the  path  which  it 
pursued  from  the  north  pole  to  the  south  pole  and 
plot  this  path  on  paper.  We  would  then  place 
the  test  pole  at  another  point  of  the  north  pole  of 
the  bar  magnet,  and  again  observe  the  path  and 
plot  it,  and  so  on.  In  this  way  the  space  around 
the  magnet  could  be  mapped  out. 

Q.  What  is  the  space  around  a  magnet,  in 
which  magnetic  force  exists,  called? 

A.  The  field  of  that  magnet. 

Q.   Does  every  magnet  have  a  field  ? 

A.  Yes;  and  since  lines  of  force  could  be  drawn 
in  this  field  which  would  represent  the  direction 
of  magnetic  force,  we  say  that  every  magnet  pro- 
duces lines  of  force. 

Q.  What,  then,  is  a  line  of  force  ? 

A.  It  is  a  line  which  represents  the  direction  of 
magnetic  force  in  the  region  where  the  line  is 
drawn  or  may  be  supposed  to  be  drawn. 

Q.  What  is  the  positive  direction  of  the  line  of 
force  ? 

A.  That  direction  in  which  a  free  north-seeking 
magnetic  pole  would  move.  A  free  south  pole 
would  move  in  the  opposite  direction. 

Q.  Since  we  cannot  obtain  a  free  north  pole  for 
testing  the  direction  of  magnetic  force,  how  can 


STEAM    ENGINEERS   AND    ELECTRICIANS.         255 

we  explore  and  map  out  the  magnetic  field  due  to 
any  magnet  or  wire  carrying  current  ? 

A.  By  taking  advantage  of  the  fact  that  a  short 
magnet  will,  if  free  to  move,  place  itself  length- 
wise along  the  lines  of  force. 

Q.   Explain  how  the  experiment  is  performed. 

A.  Place  under  a  piece  of  window-glass  a  bar 
magnet,  and  dust  on  the 
upper  side  of  the  glass 
some  iron  filings.  These 
filings  become  magnets 
which  are  exceedingly 
short,  and  when  they  are 
jarred  by  tapping  the  glass 
they  are  free  to  move 
and  set  themselves  into 
lines  corresponding  to  the 
lines  of  magnetic  force  as  shown  in  the  cut. 

Q.  Why  are  the  lines  of  filings  more  dense  at 
some  points  of  the  field  than  at  others  ? 

A.  Because  the  strength  of  the  magnetic  force 
is  greater  at  those  portions  of  the  field. 

Q.  How  would  you  describe  the  lines  of  force 
due  to  a  bar  magnet  ? 

A.  As  curved  lines  running  from  the  north  pole 
to  the  south  pole. 

Q.  What  are  the  lines  of  force  due  to  a  horse- 
shoe magnet  ? 


256 


roper's  catechism  for 


A.  Principally  straight  lines  from  the  north  to 
the  south  pole. 

Q.  How  can  you  obtain  the  field  due  to  a  cur- 
rent in  a  straight  wire  ? 

A.  By  drilling  a  hole  in  the  piece  of  glass  and 
passing  the  wire  vertically  through  this  hole  and 
then  dusting  on  iron  filings. 

Q.  AVhat  are  the  lines  of  force  due  to  a  current 
in  a  wire  ? 

A.  Circles  concentric  with  the  axis  of  the  wire, 
the  positive  direction  be- 
ing in  the  direction  in 
which  the  hands  of  a 
watch  move. 

Q.  Where  is   the  mag- 
netic force  greatest  ? 

A.  Next  to  the  wire,  as 
shown  by  the  greater  den- 
sity of  the  lines  of  force. 
Q.  Suppose  the  current 
through  the  wire  were  greatly  increased,  how 
would  the  density  of  the  lines  be  affected  ? 

A.  It  would  be  increased  in  the  same  proportion 
as  the  magnetic  effect  of  the  current  is  strictly 
proportional  to  the  strength  of  the  current. 

Q.  When  a  coil  of  wire  carrying  a  current  is 
brought  near  a  magnet,  can  the  direction  of 
motion  of  the  coil  or  magnet  be  told  in  advance  ? 


STEAM    ENGINEERS   AND    ELECTRICIANS.         257 

A.  Yes;  they  will  move  in  such  a  way  that  the 
greatest  possible  number  of  lines  of  force  due  to 
the  magnet  will  pass  through  the  coil. 

Q.  For  what  practical  purpose  can  this  principle 
of  the  effect  of  an  electric  current  on  a  magnet  be 
used  ? 

A.  AYe  can  detect  currents  in  wires  by  bringing 
a  magnet  near. the  wires,  and  can  also,  by  applying 
Ampere's  rule,  determine  in  which  direction  the 
current  flows. 

Q.  Is  there  any  other  method  of  determining 
the  direction  of  flow  of  a  current. 

A.  Yes;  by  making  use  of  the  principle  illus- 
trated in  Experiment  1.  The  current  can  be  led 
into  a  solution  of  copper  sulphate  (or  nearly  any 
solution  of  a  metallic  salt),  and  by  noting  which 
of  the  wires  increases  in  size  we  can  tell  in  which 
direction  the  current  flows,  as  it  flows  toivard  the 
wire  which  has  copper  deposited  on  it. 

Q.  Can  we  increase  the  effect  of  the  current  on 
the  magnet  ? 

A.  Yes,  in  three  ways  :  By  increasing  the 
strength  of  current,  by  bringing  the  wire  and  the 
magnet  nearer  together,  and  by  winding  the  wire 
which  carries  the  current  in  a  coil  and  placing  the 
magnet  in  the  axis  of  the  coil. 

Q.  When  this  is  done,  what  direction  will  the  cur- 
rent in  the  coil  tend  to  make  the  magnet  assume  ? 
17 


258  roper's  catechism  for 

A,  A  direction  parallel  to  the  axis  of  the  coil. 
Since  the  magnet  is  also  acted  on  by  the  earth's 
magnetism  tending  to  make  it  point  north,  it  will 
actually  assume  a  position  between  these  two 
directions.  The  angle  which  it  makes  with  north 
depends  on  the  relative  strength  of  the  earth's 
magnetic  force  and  the  magnetic  force  due  to  the 
coil.  AVith  no  current  passing  through  the  coil 
the  magnet  points  due  north.  When  a  small  cur- 
rent passes  through  the  coil  the  magnet  is  slightly 
deflected.  A  larger  current  deflects  it  more,  and 
so  on. 

Q.  What  is  the  apparatus  called  which  consists 
of  the  coil  of  wire  and  pivoted  magnet  described 
above? 

A.  A  galvanometer. 

Q.  For  what  purposes  should  you  say  that  the 
galvanometer  would  be  useful  ? 

A.  For  detecting  the  presence  of  electric  cur- 
rents, determining  in  which  direction  they  flow 
and  also  to  nxeasure  their  strength. 

Experiment  4- — Connect  to  a  galvanometer,  as 
described  above,  the  terminals  of  an  auxiliary 
coil  of  wire  placed  a  few  feet  distant,  the  connec- 
tion being  made  by  leading  a  wire  from  one  end 
of  the  auxiliary  coil  to  one  end  of  the  galvanom- 
eter coil,  and  another  wire  from  the  other  end  of 
the  auxiliary  coil  to  the  other  end  of  the  galvanom- 


STEAM    ENGINEERS   AND    ELECTRICIANS.         259 

eter  coil.  Bring  a  strong  magnet  near  the  auxil- 
iary coil,  watching  at  the  same  time  the  magnet 
needle  of  the  galvanometer. 

Q.  What  occurs? 

A.  The  magnet  needle  gives  a  sudden  jump 
and  continues  to  oscillate  to  and  fro,  coming  to 
rest  a  little  while  after  the  motion  of  the  strong 
magnet  has  stopped. 

Q.  What  does  this  show  ? 

A.  The  jump  of  the  galvanometer  needle  shows 
that  an  electric  current  has  been  produced  by 
moving  the  magnet  near  the  auxiliary  coil.  The 
fact  that  after  the  magnet  stops  the  needle  comes 
to  rest  in  its  original  position,  shows  that  the  cur- 
rent is  produced  only  while  the  magnet  is  moving. 

Q.  Suppose  that  instead  of  moving  the  magnet 
toward  the  auxiliary  coil,  the  coil  is  moved 
toward  the  magnet  ? 

A.  The  galvanometer  needle  jumps  in  the  same 
direction  as  before,  showing  that  current  is  pro- 
duced in  the  same  way  and  in  the  same  direction. 

Q.  Suppose  that  the  magnet  and  coil  are  moved 
away  from  each  other? 

A.  The  needle  jumps  as  before,  but  in  the 
opposite  direction. 

Q.  What  do  you  conclude  from  all  this  ? 

A.  That  moving  a  wire  and  a  magnet  relatively 
to  each  other  produces  an  electric  current,   and 


260 


ROPER'S    CATECHISM   FOR 


that  the  direction  of  the  current  depends  on  the  . 
direction  of  the  motion.  ; 

Q.   Has    the    current    so   produced   the    same  ' 
properties  as  the  current  produced  by  a  battery  ? 
A.   Absolutely  the  same;  the  two  are  identical. 
Q.  What  piece  of  electric  apparatus  is  based  on 
the  principles  illustrated  by  this  experiment  ? 
A.   The  dynamo. 

Q.  Making  use  of  the  idea  of  lines  of  force  in 
the  above  experiment,  what  result  do  you  arrive  at  ? 
A.  Moving  the  magnet  nearer  the  coil  causes 
the  coil  to  cut  across  lines  of  force  due  to  the 
magnet,  and  since  a  current  is  produced  by  the 
motion  we  may  conclude  that  ivhenever  an  electric 
conductor  cuts  across  lines  of  force  an  electric  current 
is  produced. 

Q.  When  the  magnet  was  moved  away  there 
was  a  current  produced  in  the  opposite  direction 
by  the  cutting  of  lines  of  force.     Is  there  any 
convenient   rule   for   de- 
termining   the    direction 
of  the  induced  current  ? 
A.  Yes;    a  rule  known 
ion  of     as  Fleming's. 
'"■  Point  the  forefinger  along 

the  positive  direction  of  the 
magnetic  lines  and  point 
the  thumb  stretched  at  right 


STEAM    ENGINEERS    AND    ELECTRICIANS.         261 

angles  in  the  direction  in  ichich  the  conductor  moves. 
If  now  the  second  finger  he  stretched  at  right  angles 
to  both  thumb  and  forefinger,  it  will  point  in  the  direc- 
tion of  the  induced  current. 

Q,  When  the  magnet  is  moved  nearer  the  coil, 
the  number  of  Hnes  of  force  due  to  the  magnet, 
which  is  enclosed  by,  or  which  passes  through,  the 
coil,  is  increased,  might  we  not  say  that  a  cur- 
rent is  produced  w^henever  the  number  of  lines 
enclosed  by  a  coil  is  changed  ? 

A.  Yes;  and  when  the  conductor  is  in  the  form 
of  a  coil  this  idea  is  of  great  value.  Looking  along 
the  positive  direction  of  the  lines  of  force,  when  the 
number  enclosed  by  the  coil  is  increased,  the  cur- 
rent around  the  coil  is  left-handed  as  we  look  at  it. 
If  the  number  enclosed  by  the  coil  is  diminished, 
the  current  will  be  right-handed  as  we  look  at  it. 

Q.  What  do  you  mean  by  right-handed  ? 

A.  In  the  direction  in  which  the  hands  of  a 
watch  move. 

Experiment  5. — If  the  current  from  a  battery  or 
other  current  generator  be  led  through  a  wire 
Avhich  is  coiled  around  a  rod  of  iron,  the  iron 
becomes  strongly  magnetized,  as  we  say  ;  that  is,  it 
exhibits  all  the  properties  of  a  magnet.  It  at- 
tracts other  pieces  of  iron,  and  it  has  polarity, 
one  end  attracting  the  north-seeking  pole  of  a  bar 
magnet  and  the  other  end  repelling  it. 


262  roper's  catechism  for 

Q.  What  is  the  combination  of  a  piece  of  iron 
with  a  coil  of  wire  around  it  called  ? 

A.  An  electro-magnet. 

Q.  After  current  is  cut  off  from  the  coil,  does 
the  iron  still  exhibit  magnetic  qualities  ? 

A.  Only  feebly.  The  magnetism  still  remain- 
ing is  called  permanent  or  residual  magnetism. 

Q.  What  is  the  advantage  of  an  electro-magnet 
over  a  permanent  magnet  ? 

A.  For  the  same  size  the  electro-magnet  is 
much  more  powerful. 

Experiment  6. — Suspend  a  coil  of  wire  so  that 
it  can  turn  freely  and  lead  a  current  through  the 
wire.     Then  bring  a  magnet  near  it. 

Q.  Will  the  coil  be  affected  by  the  magnet  ? 

A.  Yes,  the  coil  will  turn  so  as  to  enclose  as 
many  as  possible  of  the  lines  of  force  due  to  the 
magnet  and  will  finally  come  to  rest  in  that  position. 

Q.  Suppose  the  other  pole  of  the  magnet  be 
presented  toward  the  coil  ? 

A.  The  coil  will  turn  in  the  opposite  direction 
and  come  to  rest  in  such  a  position  that  it  encloses 
the  greatest  possible  number  of  lines  of  force  due 
to  the  magnet. 

Q.  Suppose  just  at  the  moment  the  coil  gets 
into  the  position  of  enclosing  the  maximum  num- 
ber of  lines  the  current  is  reversed  in  direction, 
what  will  be  the  effect  ? 


STEAM    ENGINEERS   AND    ELECTRICIANS.         263 

A.  The  coil  will  continue  to  turn  in  the  same 
direction  and  will  make  a  half  turn,  after  Avhich 
it  will  stop. 

Q.  Can  you  determine  in  which  direction  the 
coil  will  turn  ? 

A.  Yes,  by  applying  Fleming's  rule  previously 
mentioned,  using  the  left  hand.  Point  the  fore- 
finger along  the  positive 
direction  of  the  lines  of  force 
due  to  the  magnet  at  any 
part  of  the  coil.  Point  the 
second  finger,  held  at  right  <.- 
angles  to  the  forefinger,  in 
the  direction  of  the  current 
in  that  part  of  the  coil. 
Finally,  extend  the  thumb 
at  right  angles  to  both  of  the  fingers.  The  direc- 
tion in  which  the  thumb  points  will  be  the  direc- 
tion in  which  that  part  of  the  coil  will  move. 

Q.  And  if  at  this  point  the  direction  of  current 
is  again  reversed  ? 

A.  The  coil  will  rotate  in  the  same  direction  one 
half-turn  further. 

Q.  What  piece  of  well-known  electrical  appa- 
ratus operates  in  this  manner  ? 

A.   The  electric  motor. 

Q.  Does  it  make  any  difference  whether  the 
magnet  is  a  permanent  or  electro-magnet  ? 


264  roper's  catechism  for 

A.  None  at  ail,  except  that  greater  strength  can 
be  secured  by  usmg  an  electro-magnet. 

Experiment  7. — Suppose  we  have  the  same  coil 
of  wire  as  in  Experiment  6,  which  we  will  call 
^coil  No.  1,  connected  to  a  galvanometer,  and  near 
it  a  second  coil  attached  to  a  battery.  A  current 
is  flowing  through  coil  No.  2,  but  not  through  coil 
No.  1,  of  course. 

Q.  What  occurs  if  we  suddenly  disconnect  the 
battery  from  coil  No.  2,  and  what  does  it  show  ? 

A.  The  needle  of  the  galvanometer  will  give  a 
sudden  jump,  showing  that  by  stopping  the  cur- 
rent through  coil  No.  2  a  current  has  been  pro- 
duced, or  induced,  as  we  say,  in  coil  No.  1, 
although  coil  No.  1  is  not  connected  to  coil  No.  2 
in  any  way.  In  a  moment  or  two  the  needle  of 
the  galvanometer  will  come  to  rest  at  its  original 
position,  showing  that  the  current  has  ceased. 

Q.  What  will  occur  if  the  battery  be  again  con- 
nected to  coil  No.  2  ? 

A.  The  needle  will  again  jump,  but  this  time 
in  the  opposite  direction,  showing  that  the  induced 
current  is  in  the  opposite  direction. 

Q.  Suppose  that  the  current  instead  of  being 
entirely  stopped  were  diminished  and  then  in- 
creased, what  would  happen  ? 

A.  We  should  see  the  needle  go  first  one  way 
and  then  the  other,  as  before,  showing  that  any 


STEAM    ENGINEERS   AND    ELECTRICIANS.         265 

change  in  the  strength  of   current  hi  coil  No.   2 
tends  to  induce  a  current  in  No.  1. 

Q.  Looked  at  from  the  standpoint  of  Hnes  of 
force,  what  has  occurred  in  this  experiment  ? 

A.  From  the  standpoint  of  Hnes  of  force,  when 
the  current  in  coil  No.  2  is  increased  more  lines 
of  magnetic  force  are  enclosed  by  No.  1,  and  a 
current  is  produced.  When  the  current  is  dimin- 
ished less  lines  pass  through  No.  1,  and  a  current 
is  induced  in  the  opposite  direction.  The  nearer 
the  two  coils  are  to  each  other  the  greater  the 
effect,  and  if  a  soft  iron  core  be  introduced  into 
the  axis  of  the  coils,  the  induced  current  becomes 
enormously  greater  than  before. 

Q.  What  electrical  apparatus  is  illustrated  by 
tiiis  experiment? 

A.   The  transformer. 
.    Experiment  8. — Connect  a  battery  to  a  galvanom- 
eter and  notice  the  reading  of  the  needle  which 
shows  what  current  is  flowing  through  the  circuit. 
Connect  in  tandem  another  cell  of  battery. 

Q.  What  will  occur  ? 

A.  The  reading  of  the  galvanometer  needle  will 
be  increased,  being  about  double  what  it  was 
before. 

Q.  What  does  this  show  ? 

A.  That  the  current  through  the  circuit  is 
double. 


266  roper's  catechism  for 

Q.  Has  the  resistance  of  the  circuit  been  appre- 
ciably changed? 

A.  No. 

Q.  What  could  have  caused  double  flow  through 
the  same  resistance  ? 

A.  Reasoning  from  analogy  to  the  flow  of  water, 
the  pressure  tending  to  cause  flow  must  have  been 
doubled. 

Q.  Would  you  then  conclude  that  there  is  such 
a  thing  as  electrical  pressure  ? 

A.  Yes,  and  that  each  generator,  as,  for  instance, 
a  battery,  furnishes  a  definite  pressure,  and  that 
when  two  are  connected  in  tandem  the  two 
together  furnish  a  pressure  which  is  the  sum  of 
the  pressures  furnished  by  each. 

Q.  What  other  names  are  there  for  electric  pres- 
sure? 

A.  Difference  of  potential  (P.  D.),  electro- 
motive force  (e.  m.  f. ),  and  voltage.  ■ 

Q.  The  battery  produces  electric  pressure  by 
means  of  chemical  action;  is  there  any  other 
method  ? 

A.  Yes;  an  electric  pressure  is  produced  wher- 
ever a  conductor  cuts  across  lines  of  force;  or  if  the 
conductor  is  in  a  coil  a  pressure  is  produced  when- 
ever the  number  of  lines  of  magnetic  force 
enclosed  by  the  coil  is  in  any  way  changed. 
The    pressure    continues    only    so    long    as   the 


STEAM    ENGINEERS    AND    ELECTRICIANS.         267 

cutting  or  change  of  number  of  lines  of  force 
continues. 

Q.  Upon  what  does  the  amount  of  electric  pres- 
sure depend  ? 

A.  On  the  rate  of  cutting  the  lines  of  force — 
that  is,  the  number  cut  per  second  or  the  change 
per  second  in  the  number  enclosed  by  a  coil. 

Q.  Suppose  a  coil  has  10,000  lines  of  force 
passing  through  it,  its  plane  being  perpendicular 
to  the  lines  of  force,  which  lines  are  in  this  case 
supposed  to  be  parallel  and  straight.  Now  let 
the  coil  be  rotated  one  quarter- turn,  how  many 
lines  will  it  enclose  ? 

A.   Zero. 

Q.  Suppose  it  took  one-quarter  of  a  second  to 
make  the  quarter-turn,  what  would  be  the  rate  of 
change  of  lines  of  force  enclosed  by  the  coil  ? 

A.   10,000  ^i  =  40,000  per  second. 

ELECTRICAL   UNITS. 

Q.  What  is  the  unit  of  electrical  pressure  or 
electro-motive  force  ? 

A.  The  volt,  which  is  the  pressure  furnished  by 
a  certain  standard  cell. 

Q.   What  is  the  unit  of  resistance  ? 

A.  The  resistance  of  a  column  of  mercury  41.85 
inches  long  and  w^eighing  223  grains  at  32°  Fahr. 
It  is  called  the  ohm. 


268  roper's  catechism  for 

Q.  Are  the  standard  ohms  and  multiples  of  the 
ohm  used  in  practice  made  of  mercury  ? 

A.  No;  they  are  made  of  German-silver  wire,  or 
an  alloy  of  copper,  nickel,  and  one  or  more  metals. 

Q.  What  is  the  unit  of  current  ? 

A.  It  is  the  current  which  will  deposit,  in  one 
second,  on  the  kathode  plate,  from  a  standard 
solution  of  silver  nitrate,  .001118  gram  (.017 
grain)  of  silver.  It  is  called  the  ampere^  and  is 
in  its  nature  a  unit  of  rate  of  flow  and  analogous 
to  a  flow  of  a  certain  quantity  per  second. 

Q.  What  other  common  unit  is  employed  ? 

A.  The  watt,  which  is  the  unit  of  power.  It  is 
equal  to  a  volt-ampere  ;  that  is,  the  power  in  watts 
is  equal  to  the  product  of  the  number  of  amperes 
flowing  multiplied  by  the  number  of  volts  pressure 
causing  the  flow. 

Q.  What  relation  does  the  watt  bear  to  a  horse- 
power ? 

A.  One  horse-power  equals  746  watts  exactly, 
or,  in  round  numbers,  750. 

Q.  AVhat  multiple  of  the  watt  is  found  con- 
venient ? 

A.  The  kilowatt,  written  K.W.,  which  is  1000 
watts  and  nearly  equal  to  -|  horse-power. 

Q.  In  measuring  electrical  properties,  such  as 
current,  pressure,  resistance,  or  power,  what  is  the 
general  method  of  going  about  the  work  ? 


STEAM    ENGINEERS    AND    ELECTRICIANS.         269 

A.  Take  current  as  an  example.  We  find  some 
effect  of  current  easy  to  observe,  and  we  agree  to 
call  a  current  which  produces  this  effect  to  a  certain 
extent  unit  current,  as,  for  example,  the  current 
which  in  one  second  will  deposit  from  a  nitrate  of 
silver  solution  .017  grain  of  silver  is  called  unit 
current.  Having  an  unknown  current  which  it  is 
desired  to  measure,  we  observe  how  many  grains 
of  silver  it  will  deposit  in  one  second,  and  if  it 
deposits  .  17  grain  we  call  it  a  current  of  10  units 
or  10  amperes.  Of  course,  no  one  in  actually 
measuring  a  current  now  goes  through  the  long 
process  of  measurement  by  means  of  depositing  a 
metal  any  more  than  in  order  to  measure  a  length 
he  makes  a  journey  to  the  British  Museum  to  get 
the  standard  yard-stick.  Convenient  instruments 
working  on  the  principle  of  a  galvanometer  are 
made  so  that  when  a  current  of  1  ampere  flows 
through  their  coils  their  needle  points  to  1;  with 
a  current  of  2  amperes,  points  to  2,  and  so  on. 

Q.  What  multiples  of  the  units  given  above  are 
in  common  use? 

A.   The  megohm  =  1  million  ohms. 

The  microhm  =  1  millionth  part  of  1  ohm. 
The  kilowatt  =  1  thousand  watts. 

Q.  Can  these  prefixes,  meg,  micro,  and  kilo,  be 
used  with  the  other  electrical  units  ? 

A.  Yes;  although  such  use  is  not  very  common. 


270  roper's  catecpiism  for 

RESISTANCE. 

Q.  How  is  the  resistance  of  a  conductor  affected 
by  increasing  its  length  ? 

A.  The  resistance  is  increased  proportionately 
to  the  increase  in  length. 

Q.  What  is  the  effect  of  increasing  the  area  of 
cross-section  ? 

A.  The  resistance  is  lessened  proportionately;  in 
other  words,  the  resistance  is  inversely  pro23ortional 
to  the  area  of  the  cross-section. 

Q.  A  certain  size  wire,  100  feet  long,  has  a 
resistance  of  2  ohms, — what  will  be  the  resistance 
of  200  feet  of  the  same  wire  ? 

A.  2  X  2,  or  4  ohms. 

Q.  Suppose  that  100  feet  of  wire  -^  inch  diam- 
eter has  a  resistance  of  1  ohm, — what  would  be  its 
resistance  if  the  diameter  were  ^V  inch  ? 

A.  Since  the  new  diameter  is  one-half  the  old, 
the  area  of  cross-section  of  the  new  wire  is  J  X  J, 
or  one-quarter  that  of  the  old  wire.  The  resistance 
therefore  would  be  four  times  greater,  or  4  ohms. 

Q.  What  is  meant  by  the  conductivity  of  a  wire 
or  other  conductor  ? 

A.  The  opposite  of  resistance.  It  is  numeri- 
cally e(^ual  to  1  divided  by  the  resistance. 

Q.  A  wire  has  a  resistance  of  100  ohms, — what 
is  its  conductivity  ? 


STEAM    ENGINEERS   AND    ELECTRICIANS.         271 

A.    1-^0  5  01'  -Ol- 

Q.  When  two  re- 
sistances, as  Fand  R, 
are  joined  as  shown 
in  the  figure,  how  are 
the}^  said  to  be  connected  ? 

A.   In  parallel  or  multiple. 

Q.  When  so  connected,  what  is  their  joint 
resistance,  that  is,  the  resistance  from  A  to  B? 

A.   It  is  found  by  the  formula,  joint  resistance 

~  E-i-  Y' 

Q.  Two  resistances  of  10  and  20  ohms  respect- 
ively are  joined  in  multiple, — what  is  their  joint 
resistance  ? 

,    10  X  20       200       .2    I. 

^-   I0-+20^W==^^^^^^- 

Q.  When  the  resistances  are  equal,  what  is  the 
joint  resistance  ? 

A.  One-half  the  resistance  of  one. 

Q.  When  several  equal  resistances  are  connected 
in  multiple,  what  is  their  joint  resistance  equal  to  ? 

A.  To  the  resistance  of  one  divided  by  the 
number  of  them.  „  , 

Q.  When  are  two  conductors  said  to  be  con- 
nected in  series  f 

*For  complete  explanation,  see  "Eoper's  Engineers' 
Handy-Book,"  page  665. 


272  koper's  catechism  for 

A.  When  they  are  jomed  tandem,  or  end  on. 

Q.  When  two  resistances  are  connected  hi  series, 
what  is  their  Joint  resistance  equal  to  ? 

A.  To  the  sum  of  the  separate  resistances. 

Q.  What  is  specific  resistance  ? 

A.  It  has  the  same  relation  to  resistance  that 
specific  gravit}^  has  to  weight.  It  is  the  resistance 
of  a  cubic  inch,  or  it  may  be  expressed  in  cubic 
centimeters. 

Q.  What  are  some  of  the  substances  having 
large  specific  resistance  ? 

A.  Of  the  metals — lead,  mercury,  and  alloys. 
The  non-metals  have  a  much  higher  specific  resist- 
ance. 

Q.  What  are  some  substances  having  a  low 
specific  resistance  ? 

A.   Copper,  silver,  and  gold. 

Q.  What  are  non-conductors  ? 

A.  Substances  having  a  high  specific  resistance. 

Q.  What  are  conductors  ? 

A.  Substances  having  a  low  specific  resistance. 
The  metals  are  classed  as  conductors  and  the  non- 
metals  as  non-conductors. 

Q.  What  are  insulators  ? 

A.  "  Insulators  "  is  another  name  for  non-con- 
ductors or  poor  conductors. 

Q.  What  effect  does  a  change  of  temperature 
have  on  the  resistance  of  substances  ? 


STEAM    ENGINEERS   AND    ELECTRICIANS. 


273 


TABLE  OF  RELATIVE  RESISTANCES. 

(Substances  Arranged  in  Order  of  Increasing  .Resistance  for 
SAME  Length  and  Sectional  Area.) 


Name  of  Metal. 


Silver,  annealed,  .    . 

Copper,  annealed,     . 

Silver,  hard  dravrn. 

Copper,  hard  drawn, 

Gold,  annealed,    ,    . 

Gold,  hard  drav^'n,   . 

Aluminum,  annealed, 

Zinc,  pressed,    .    .    . 

Platinum,  annealed, 

Iron,  annealed,     .    . 

Gold-silver  alloy  (2  ozs.  gold, 
1  oz.  silver),  hard  or  an- 
nealed,     

Nickel,  annealed, 

Tin,  pressed, 

Lead,  pressed,  . 

German  silver,  hard  or  an- 
nealed,     

Platinum-silver  alloy  (1  oz. 
platinum,  2  ozs.  silver), 
hard  or  annealed,     .    .    .    . 

Antimony,  pressed,     .    .    .    . 

Mercury, 

Bismuth,  pressed, 

Carbon,  


Resistance  in  Microhm 

at  0°  Centigrade. 

32°  Fabr. 


Cubic 
Centi- 
meter. 


1.504 
1.598 
1.634 
1.634 
2.058 
2.094 
2.912 
5.626 
9.057 
9.716 


10.87 
12.47 
13.21 
19.63 

20.93 


24.39 
35.50 
94.32 
131.2 


Cubic 
inch. 


0.5921 

0.6292 

0.6433 

0.6433 

0.8102 

0.8247 

1.147 

2.215 

3.565 

3.825 


4.281 
4.907 
5.202 

7.728 

8.240 


9  603 
13.98 
37.15 
51.65 


Relative 
Resist- 
ance. 


1. 

1.063 

1.086 

1.086 

1.369 

1.393 

1.935 

3.741 

6.022 


7.228 
8.285 
8.784 
13.05 

13  92 


16.21 
23.60 
62.73 

87.23 
14. 


18 


274  EOPER's  CATECHISM  FOR 

A.  It  increases  the  resistance  of  metals  and 
diminishes  the  resistance  of  non-conductors. 

Q.  Can  you  remember  about  how  much  a 
change  of  temperature  of  one  degree  Fahrenheit 
affects  the  resistance  of  metals  ? 

A.  It  increases  the  resistance  of  the  common 
metals  roughly  about  2  parts  in  1000. 

Practical  Use  of  Conductors  and  Insulators. 
— For  carrying  electrical  energy  from  the  point 
where  it  is  generated  to  the  point  where  it  is  to  be 
used  we  want  to  use  such  material  and  of  such 
size  that  the  resistance  of  the  circuit  does  not 
exceed  reasonable  limits,  although  we  must  be 
guided  by  consideration  of  the  first  cost.  Copper 
has  the  lowest  specific  resistance  of  the  common 
metals  and  is  generally  employed,  although  if 
aluminum  gets  much  lower  in  price  than  now 
(30  cts.  per  pound),  it  will  be  a  serious  competi- 
tor to  copper.  Iron  is  used  only  on  short  tele- 
graph and  telephone  lines.  It  is  evident  that  the 
circuit  should  be  as  direct  as  possible,  as  the 
greater  its  length  the  greater  its  resistance,  and 
therefore  the  greater  is  the  amount  of  energy  lost 
on  the  line. 

Insulators  are  used  to  prevent  current  from 
being  led  off  the  conductors.  For  all  work  ex- 
cept outdoor  work,  and,  indeed,  for  a  large  part 
of  that,  the  conducting  wire  is  covered  with  one 


STEAM    ENGINEERS   AND    ELECTRICIANS.         275 

or  more  layers  of  some  compomid  of  rubber 
which  is  a  good  insulator.  The  thicker  this 
rubber  covering  the  better  its  insulating  proper- 
ties, for  we  have  made  the  path  of  leakage  of 
current  longer  by  thickening  the  rubber  coating. 
A  further  protection  is  given  by  suspending  the 
wires  at  intervals  on  porcelain  or  glass  or  other 
insulators,  so  that  the  wire  only  comes  in  contact 
with  its  coating,  porcelain,  or  the  air,  which  is 
also  an  exceedingly  good  insulator.  To  sum  up 
briefly,  make  the  path  through  which  you  want 
the  current  to  flow  as  short  and  easy  as  possible. 
Make  all  possible  leakage  paths  as  long  and  nar- 
row as  possible. 

CUEEENT. 

Q.  What  are  some  of  the  most  notable  effects 
of  electric  current  ? 

A.  It  heats  the  conductors  which  carry  it;  it 
produces  around  the  wire  a  magnetic  field  which 
exerts  a  force  on  all  magnetic  substances  placed 
within  the  field;  it  has  the  power  to  decompose 
or  electrolyze  solutions  of  many  chemical  com- 
pounds. To  these  three  effects  are  given  the 
names  heating  effect,  magnetic  effect,  and  electro- 
lytic effect. 

Q,  Is  the  heating  effect  proportional  to  the 
strength  of  current  or  number  of  amperes  ? 


276  roper's  catechism  for 

A.  No;  if  the  amperes  are  doubled  the  heating 
effect  is  four  times  as  great  instead  of  twice  as 
great.  With  three  times  as  many  amperes  the 
heating  effect  is  nine  times  as  great. 

Q.  What  is  the  law,  then,  which  connects  the 
heating  effect  with  the  strength  of  current  ? 

A.  The  heating  effect  is  proportional  to  the 
square  of  the  current  strength. 

Q.  How  is  the  heating  effect  of  a  certain  cur- 
rent affected  if  the  resistance  through  which  it 
flows  is  doubled  ? 

A.  The  heating  effect  is  doubled,  it  being 
strictly  proportional  to  the  resistance. 

Q.  Is  there  any  formula  which  gives  the  num- 
ber of  heat  units  produced  by  a  certain  current 
through  a  certain  resistance  ? 

A.  Yes;  in  " Roper' s  Engineers'  Handy-Book," 
page  670. 

Q.  Is  the  heating  effect  of  a  current  a  source  of 
danger  ? 

A.  It  may  be;  if  wires  which  carry  currents 
are  too  small  they  may  be  so  heated  as  to  set  fire 
to  neighboring  woodwork.  On  this  account  the 
insurance  underwriters  have  found  it  necessary  to 
prescribe  the  minimum  sizes  which  shall  be  used 
for  various  currents.  These  are  published  in 
tables  called  ' '  Tables  of  Safe  Carrying  Capacity 
of  Wires." 


STEAM   ENGINEERS   AND    ELECTRICIANS.         277 

Q.  Is  any  practical  use  made  of  the  heating 
effect  of  the  electric  current  ? 

A.  Yes;  in  electric  heaters  and  cooking  devices, 
and  also  in  the  incandescent  lamp,  where  the  fila- 
ment is  heated  white  hot. 

Q.  Is  the  magnetic  effect  of  a  current  propor- 
tional to  the  current  strength  ? 

A.  Strictly. 

Q.  Is  the  electrolytic  effect  also  proportional  to 
the  current  strength  ? 

A.  Yes;  doubling  the  number  of  amperes  will 
always  double  the  electrolytic  effect,  tripling  the 
amperes  will  triple  it,  and  so  on. 

Q.  When,  as  in  Experiment  No.  1,  a  metallic 
salt  is  electrolyzed,  does  the  amount  of  copper 
deposited  bear  any  definite  relation  to  the  current 
strength  ? 

A.  Yes;  one  ampere  will  always  deposit  a 
definite  amount  of  copper  per  second. 

Q.  Does  it  make  any  difference  what  salt  of 
copper  is  used  ? 

A.  Generally  speaking,  no;  but  with  one  or 
two  salts  the  number  of  grains  of  copper  deposited 
per  second  by  one  ampere  is  double  what  it  is 
with  the  ordinary  salts. 

Q.  Will  one  ampere  deposit  from  a  silver  salt 
solution  the  same  number  of  grains  per  second  as 
with  copper? 


278  roper's  catechism  for 

A.  No;  one  ampere  deposits  different  weights 
of  the  various  metals  per  second,  the  amounts 
being  proportional  to  the  atomic  weights  of  the 
elements  *  or  to  multiples  of  them. 

ELECTRO-MOTIVE   FORCE   OR   ELECTRIC 
PRESSURE. 

Q.  In  what  ways  may  electric  pressure  be  pro- 
duced ? 

A.  There  are  many  ways  of  which  these  four 
are  the  most  common: 

1.  By  rubbing  together  two  dissimilar  sub- 
stances, as  silk  and  glass. 

2.  By  heating  the  point  at  which  two  dissimilar 
metals  are  joined  together. 

3.  By  chemical  action,  as  in  Experiment  No.  1 
with  the  chemical  battery. 

4.  By  moving  a  magnet  relatively  to  a  coil  of 
wire,  as  in  the  dynamo,  the  principle  being  illus- 
trated in  Experiment  No.  4. 

Q.   Which  method  is  the  most  important? 

A.  The  last;  the  first  two  are  scarcely  used  at 
all  in  practice.  The  third  is  used  only  where 
small  amounts  of  power  are  required. 

Q.   If  there  is  a  difference  of  electrical  pressure 
existing  between  two  points  and  these  two  points 
be  joined  by  a  conductor,  what  will  occur  ? 
*See  " Roper's  Engineers'  Handy-Book,"  p.  612. 


STEAM    ENGINEERS    AND    ELECTRICIANS.         279 

A.  An  electric  current  will  flow  from  the  point 
of  higher  pressure  to  the  other  point. 

Q.   How  long  will  this  current  continue? 

A.  As  long  as  there  is  any  difference  of  pressure 
between  the  two  points.  If  the  two  points  are,  for 
example,  the  terminals  of  a  battery,  which  by 
chemical  action  keeps  up  a  difference  of  pressure 
between  its  terminals,  the  current  would  continue 
until  one  of  the  chemicals  of  the  battery,  the  zinc 
or  solution,  is  exhausted. 

Q.  How  could  you  determine  if  two  points 
were  at  the  same  pressure  ? 

A.  By  connecting  a  galvanometer  between  the 
points.  If  the  needle  of  the  galvanometer  was 
not  deflected  this  would  show  that  no  current 
flowed  through  it  and,  therefore,  that  no  difference 
in  electrical  pressure  existed  between  the  two 
points  to  which  it  was  connected. 

Q.  When  an  electric  pressure  exists  between  two 
points,  is  there  also  any  mechanical  pressure. 

A.  Yes;  the  medium  or  substance  separating 
the  two  points  is  under  a  mechanical  strain  which 
is  proportional  to  the  number  of  volts  electrical 
pressure  existing  between  the  two  points.  If  this 
voltage  is  very  great  the  substance,  be  it  air,  glass, 
porcelain,  or  otherwise,  is  actually  cracked  and  an 
electric  spark  passes  which  tends  to  relieve  the 
difference  of  pressure. 


280       roper's  catechism  for 


OHM'S   LAW. 

This  law,  which  is  the  relation  existing 
between  current,  pressure,  and  resistance  of  a 
circuit,  is  the  most  important  law  in  electrical 
science,  and  an  intelligent  application  of  it  will 
solve  most  problems  which  the  ordinary  engineer " 
will  meet.  This  law  is  as  follows:  In  an  electric 
circuit  the  total  current  (amperes)  is  equal  to  the 
total  electric  pressure  (in  volts)  divided  by  the 
total  resistance  (in  ohms).     In  shorter  form  it  is 

E 

expressed  by  the  formula  O  =  75-,  where  C  =  cur- 

rent  in  amperes,  E  =  pressure  in  volts,  and  E  = 
resistance  in  ohms.  Several  examples  will  illus- 
trate its  use. 

Q.  In  a  certain  electrical  circuit  there  is  an 
electro-motive  force  or  electrical  pressure  of  4  volts. 
The  total  resistance  of  the  circuit  is  2  ohms. 
How  much  will  be  the  current  ? 

E 

A.   (7  =  -^  =  f  =  2  amperes. 

Q.  What  electro-motive  force  or  electrical  pres- 
sure must  be  used  to  force  a  current  of  10  amperes 
through  a  circuit  whose  resistance  is  10  ohms  ? 

A.   C=~otE=CR  =  10x10  =  100  volts. 
K 

Q.   If  under  a  pressure  or  electro-motive  force 


STEAM    ENGINEERS   AND    ELECTRICIANS.         281 

of  100  volts  we  get  a  current  flow  of  20  amperes, 
what  is  the  resistance  of  the  circuit  ? 

A.    C=^OYR  =  ^  =  ^'-  =  5ohms. 

When  there  is  more  than  one  electro-motive 
force  acting  in  a  circuit,  we  must  use  for  the  value 
of  E  in  the  above  formula  the  resultant  of  all  the 
separate  electro-motive  forces  acting.  When  there 
are  several  resistances  in  a  circuit  their  joint 
resistance  must  be  used. 

Q.  Suppose  we  have  two  batteries,  one  giving 
2  volts  and  the  other  1  volt,  their  plates  being  zinc 
and  carbon,  but  different  solutions  being  used  in 
each.  Connect  the  zinc  of  one  to  the  carbon  of 
the  other,  and  then  connect  from  A  to  B  a  piece 
of  wire  having  a  resistance 
of,  say,  10  ohms,  as  shown 
in  the  sketch.  When  con- 
nected in  this  way  the  elec- 
tro-motive forces  are  added,    c^JuuumMJiuum} 

and  the  total  electro-motive      1^^ — /oohms ji 

force  is  2  -f-  1,  or  3  volts.  The  batteries  themselves 
have  some  resistance,  and  also  the  lead  wires  A  C 
and  B  D.  Suppose  that  the  resistance  of  one  bat- 
tery is  4  ohms  and  the  other  2  ohms,  the  resist- 
ance of  A  0  and  B  D  each  1  ohm.  Then  the 
total  resistance  of  the  circuit  is  10  +  1  +  2  -(-  4 
+  1  =  18  ohms.    What  will  be  the  current? 


^b 


282 

A.   The  current  will  be 


roper's  catechism  for 

resultant  E 


Totalis        18  —  6 


tt 


[XWUULUSJLSiWiSJUUU 


ampere. 

Q.  Suppose  that  one  of  the  batteries  was  re- 
versed so  that  the  two  zincs  are 
connected  together  as  in  the 
sketch  ? 

A.  The  batteries  now  oppose 
each  other  and  the  resultant  or 
effective  electro-motive  force  is 
2  —  1,  or  1  volt.  The  resistance  of  the  circuit  is, 
as  before,  18  ohms,  and  the  current  will  be  -^ 
ampere. 

Calculation  of  Current  in  Divided  Circuits. 

— Suppose  that  the  battery  has  an  electro-motive 

force  of  2  volts,   that  its 

resistance  is  J-  ohm,  that 

the  resistance  of  the  lead 

wire  A  B  is  S  ohms,  and 

that  between  C  and  B  we 

have  two  paths  of  resistance  10  and  20  ohms  each. 

Q.  What   will    be    the   total    current   flowing 

through  the  batter}^  and  through  A  Bf 

A.  First  find  the  total  resistance  of  the  circuit. 
The  joint  resistance  between  the  points  B  and  E 
is,  as  previously  shown  under  ' '  Resistance, ' ' 
10  X  20 


equal  to 


10  +  20 


:   ^0    ^    g|   ol^j^g^         rpj^g     ^(j^al 


STEAM    ENGINEERS   AND    ELECTRICIANS.         283 

resistance  of  the  circuit  is  therefore  6f  +  J  +  3, 

E 

or  10  ohms.     The  current  is  equal  to  p  =  ^^  ^  .2 

ampere. 

Q.  What  part  of  the  current  flows  through 
each  branch  ? 

A.  Obviously  the  greater  part  of  the  current 
will  flow  through  the  branch  having  the  smaller 
resistance.  ^^  or  J-  ampere  will  flow  through  the 
20  ohms  branch,  and  f-J  or  f  ampere  will  flow 
through  the  other  branch. 

Practical  Approximation. — If  the  resistance 
of  batteries  or  generator  and  the  leads  is  small 
compared  to  that  of  the  main  resistance  in  circuit, 
we  may  neglect  them,  using  for  R  in  the  formula 
the  resistance  of  the  external  circuit.  This  is 
generally  the  case  in  electric  lighting  circuits, 
where  the  resistance  of  the  generator  will  rarely 
exceed  one-hundredth  of  an  ohm,  and  where  the 
resistance  of  the  line  wires  will  usually  be  less  than 
one-twentieth  of  the  joint  resistance  of  the  lamps. 

Example. — Q.  On  a  110- volt  circuit,  what  is  the 
current  (total)  when  one  sixteen-candle-power 
lamp  of  220  ohms'  resistance  is  turned  on  ? 

A.  E=  110,  R  is  practically  220  ohms.  The 
current  =  ^^  =  ^  ampere. 

Q.  What  is  the  current  (total)  when  two  lamps 
are  turned  on  ? 


284  roper's  catechism  for 

A.  The  joint  resistance  of  two  similar  lamps  is 
220  X  220         220  X  220         .,r.     .  .    w 

2-20T220  =  TT220-  =  ^^^  ^^^^^^'  ''  '"^^ 
that  of  one  lamp.  The  total  current  =  {{%  =  1 
ampere.  The  current  through  each  lamp  is  the 
same,  and  is  ^  ampere  as  before. 

With  three  lamps  turned  on  the  joint  resistance 
is  one-third  of  220,  or  73J,  and  the  total  current 

^______  ^^  ^^^  ""   ^^  ^^^~ 

r~       r~~       1.^^     peres,  and  the  cur- 

r^       r^       r^    ^^^^  through  each 

lamp  is  still  ^  am- 
pere. Turning  on  one  lamp  then  adds  J  ampere 
to  the  total  current.  The  lamps  are  connected  in 
multiple  as  shown  in  the  figure. 

The  Use  of  Alternating  Currents  complicates 
the  calculation  of  current,  pressure,  and  resist- 
ance by  Ohm's  laAv,  and  the  method  of  making 
such  calculations  is  outside  of  the  scope  of  this 
book,  inasmuch  as  the  ordinary  engineer  would 
rarely  be  called  upon  to  do  so. 


STEAM    ENGINEERS    AND    ELECTRICIANS.         285 


ELECTRICAL  MEASUREMENT. 

Q.  What  are  the  electrical  quantities  which  the 
engineer  is  called  upon  to  measure  ? 

A.  Current,  electro-motive  force,  resistance,  and 
power. 

Q.  What  instruments  are  necessary  ? 

A.  For  direct-current  circuits,  an  ammeter  and 
voltmeter  of  proper  range. 

Q.  How  are  the  Weston  ammeters  constructed  ? 

A.  They  consist  of  a  fixed  permanent  magnet 
of  horse-shoe  form,  between  the  poles  of  which  is 
pivoted  a  coil  of  fine  wire  which  carries  the  needle. 
When  the  coil  is  connected  so  that  a  current  flows 
through  the  coil,  it  tends  to  turn  so  as  to  include 
the  maximum  number  of  lines  of  force  due  to  the 
magnet.  This  motion  is  resisted  by  a  pair  of 
springs  resembling  the  hair  spring  of  a  watch. 

In  the  instruments  for  measuring  currents  of 
mdre  than  an  ampere,  only  a  known  fraction  of 
the  current  passes  through  the  coil,  the  balance 
passing  through  a  conductor  placed  in  parallel 
with  the  coil. 

Q.  Suppose  we  have  a  circuit  similar  to  that  in 
the  sketch  and  we  desire  to  measure  the  current 
taken  by  four  lamps.     How  would  you  proceed  ? 

A.   If   these   are   16   candle-power    (16   c.   p.) 


286 


ROPER'S    CATECHISM   FOR 


lamps  on  a  110-volt  circuit,  we  know  that  they 
will  take,  roughly,  J  ampere  each.  Therefore  to 
measure  accurately  their  current  we  need  an 
ammeter  intended  to  measure  small  currents. 
Connect  its  terminals  to  two  points  on  the  circuit 
as  C  and  D  by  wires,  as  shown  by  dotted  lines. 
Then  cut  the  circuit  between  C  and  D.  The  total 
current  will  now  flow  around  through  the  am- 
meter and  the  reading  of  the  needles  will,  if  the 
instrument  is  correct,  give 


the  current  in  amperes. 
Notice  that  one  termi- 
(^5*25  ^^^  ^^  marked  +  and  the 
other  — .  If  the  instru- 
ment is  not  connected 
properly,  the  needle  will 
move,  or  try  to  move,  to 
the  left  of  the  scale.  In 
this  event  reverse  the  wire  connections  from  the 
points  C  and  D  to  the  instrument.  Such  an 
instrument  tells  the  polarity  of  the  circuit — that 
is,  which  is  the  higher  pressure  and  which  the 
lower  pressure  side.  When  the  +  binding-post 
is  connected  to  the  higher  pressure  side  of  the 
circuit  the  needle  deflects  in  the  proper  direc- 
tion. 

Q.   Suppose   we   have   no   ammeter   of   proper 
range  available,  but  we  have  a  resistance  whose 


STEAM   ENGINEERS   AND    ELECTRICIANS.         287 

value  we  know  and  which  will  carry  the  current 
to  be  measured  without  much  heating  ? 

A.  In  this  case  with  the  aid  of  the  voltmeter 
we  can  measure  current.  Suppose  we  have  a 
resistance  which  we  know  is  1  ohm  and  a  portable 
voltmeter  with  an  additional  scale  reading  from  0 
to  15  volts,  and  we  want  to  make  the  current- 
measurement  just  described.  Put  the  resistance 
in  between  C  and  D  and  connect  the  voltmeter 
terminals  to  the  ends  of  the  resistance.  Suppose 
the  reading  of  the  voltmeter  was  2.3  volts.  The 
current  through  the  resistance  is  by  Ohm's  law 
equal  to  the  electrical  pressure  or  electro-motive 
force  between  its  terminals  divided  by  the  resist- 
ance, or  2. 3  ^-  1,  which  is  2. 3  amperes.  This  is  the 
method  used  in  the  Weston  switchboard  instru- 
ments, a  resistance  of  known  value  being  placed 
in  the  main  circuit  of  the  dynamo  and  two  leads 
taken  off  from  its  terminals  and  run  to  a  volt- 
meter. 

Q.  How  would  you  measure  the  electrical  pres- 
sure between  two  points  ? 

A.  I  would  connect  the  terminals  of  a  voltmeter, 
one  to  each  of  the  points. 

Q.  Suppose  the  voltage  between  the  points  is 
greater  than  the  range  of  the  voltmeter.  For 
example,  suppose  you  wish  to  measure  a  voltage 
which  you  know  is  about  220,  but  have  an  instru- 


T-/ 


V* 


288  roper's  catechism  for 

ment  which  reads  only  to  150  volts,  what  is  the 
inethod  ? 

A.  Connect  between  the  two  points  A  and  B, 
whose  voltage  is  wanted, 
two  110- volt  lamps  in  se- 
ries. Then  make  the  con- 
nections shown  by  the  solid 
lines  and  read.  Change 
"  the  connections  to  the  dot- 

ted positions  and  read  again.  The  sum  of  the  two 
readings  will  be  the  voltage  between  A  and  B. 
Q.  Is  there  any  other  method  ? 
A.  Yes;  in  the  other  method  it  is  necessary  to 
have  a  known  resistance,  to  place  it  in  series  with 
the  voltmeter,  and  also  to  know  the  resistance  of 
the  voltmeter.  This  last  is  usually  given  on  the 
box  containing  the  instrument.  A  resistance  just 
equal  to  that  of  the  instrument  doubles  its  range. 
In  general,  to  get  the  value  of  the  reading  of  a 
voltmeter  when  a  resistance  has  been  put  in  series 
with  it,  multiply  its  reading  by  the  sum  of  the 
resistance  of  the  instrument  and  the  auxiliary 
resistance,  and  divide  the  product  by  the  resistance 
of  the  instrument. 

Q.   How  would  you  measure  a  resistance  ;   for 
instance,  the  resistance  of  a  coil  of  wire  ? 

A.   li    I   had   an   ammeter   and   voltmeter    of 
proper  range  I  would  put  the  ammeter  in  series 


STEAM    ENGINEERS    AND    ELECTEICIANS.         289 

with  the  coil  and  would  connect  the  voltmeter  to 
its  terminals.  Then  I  would  send  a  current  from 
a  battery  or  dynamo  through  the  coil  and  take  the 
readings   of    the   ammeter   and    voltmeter.      By 

Ohm's  law  current  =  — ^-—^ —  or  resistance  = 
resistance 

voltage 

current' 

Q.  What  do  you  mean  by  instruments  of  proper 
range  in  this  case  ? 

A.  The  ammeter  must  be  suitable  for  measur- 
ing the  largest  current  which  the  coil  can  carry 
without  overheating,  and  the  voltmeter  must  be 
such  that  the  voltage  at  the  terminals  of  the  coil 
will  give  a  deflection  of  the  need  large  enough  to 
be  readable  with  accuracy. 

Q.  Is  there  any  other  method  of  measuring 
resistance  ? 

A.  Several.  One  of  the  most  valuable,  since  it 
needs  only  a  voltmeter  of  known  resistance  and 
some  form  of  current 


X 


,.^y^^"^^^ 


generator,  is  known  as 
the  Voltmeter  Method. 
This  method  requires 
two  readings  of  the 
instrument.  For  the 
first  reading  the  in- 
strument is  connected  to  the  terminals  of  the 
19    • 


290  roper's  catechism  for 

current-generator.  For  the  second  reading  the 
unknown  resistance  is  put  in  series  with  the  volt- 
meter and  then  the  two  connected  to  the  generator. 
In  the  figure  X  is  the  unknown  resistance,  and  for 
the  first  reading  the  connection  shown  by  the 
dotted  hne  is  made.  For  the  second  reading  the 
connection  is  as  shown  by  the  solid  lines.  To  cal- 
culate the  resistance  from  the  readings  divide  the 
first  reading  by  the  second,  then  multiply  the 
quotient  by  the  resistance  of  the  voltmeter,  and 
from  the  product  subtract  the  resistance  of  the 
voltmeter. 

Q.  Which  of  these  methods  would  you  use  for 
low  resistances  of,  say,  less  than  100  ohms  ? 

A.   The  first  method. 

Q.  Which  for  high  resistances,  such  as  insula- 
tion tests  ? 

A.   The  voltmeter  method. 

Q.  How  would  you  connect  for  a  test  of  the 
insulation  of  the  armature 
coils   of   a  dynamo,    from 


''' '      the  frame  ? 


A.  As  in  the  figure,  the 
heavy  black  line  represent- 
ing a  commutator  seg- 
ment, and  the  cross-hatched 
portion  representing  the  frame.  The  white  space  be- 
tween, of  course,  represents  the  insulating  material. 


STEAM    ENGINEERS   AND   ELECTRICIANS.         291 

Q.  How  would  you  measure  the  power  used  in 
any  part  of  a  circuit,  as,  for  example,  in  a  lamp  ? 

A.  Power  being  the  product  of  volts  by  amperes 
(in  direct-current  circuits),  I  would  connect  an 
ammeter  in  series  with  the  lamp  and  a  voltmeter  to 
its  terminals,  and  would  multiply  their  readings 
together,  thus  obtaining  the  number  of  watts. 

Q.  Suppose  you  wished  to  get  the  horse-power  ? 

A.  I  would  divide  the  number  of  watts  by 
746. 


292       roper's  catechism  for 


ELECTRIC  BATTERIES. 

Q.  What  two  kinds  of  electric  generators  are 
in  most  common  use  ? 

A.  The  chemical  generators,  or  batteries,  and 
the  magneto- electric  generators,  or  dynamos. 

Q.   In  what  cases  are  batteries  used? 

A.  When  the  amount  of  power  to  be  supplied 
is  small,  as  for  bells,  time  clocks,  telegraphs,  tele- 
phones, surgical  lamps,  dental  engines,  etc.,  and 
in  some  cases  in  which  the  introduction  of  the 
engine  which  would  be  needed  to  drive  a  dynamo 
would  be  objectionable. 

Q.  Why  are  batteries  not  used  when  large 
amounts  of  power  are  required  ? 

A.  On  account  of  the  expense  of  the  chemicals 
used.  Zinc  is  in  nearly  all  batteries  the  fuel,  and 
since  the  energy  produced  by  burning  one  pound 
of  it  is  only  one-sixth  that  produced  by  one  pound 
of  coal,  and,  moreover,  since  the  cost  of  zinc  is 
about  sixty  times  that  of  coal,  it  is  much  cheaper 
to  generate  electric  power  by  means  of  coal  rather 
than  by  means  of  zinc. 

Q.  What  are  secondary  or  storage  batteries  ? 

A.  Those  whose  chemical  actions  may  be  re- 
versed by  sending  an  electric  current  (from  some 
outside   source)    through   them   in   the   opposite 


STEAM    ENGINEERS    AND    ELECTRICIANS.         293 

direction  to  the  current  which  they  have  produced. 
Thereby  they  are  restored  to  the  original  condition 
which  existed  before  they  were  used  to  produce 
electric  current. 

Q.   Do  they  store  electricity  ? 

A.  Not  at  all.  They  store  up  energy  in  the 
form  of  chemical  energy,  which  at  any  time  may 
be  changed  into  electrical  energy  by  connecting  the 
terminals  of  the  battery  together  by  some  con- 
ductor. 

Q.  What  are  primary  batteries  ? 

A.  Those  whose  chemical  actions  cannot  be 
reversed  by  passing  an  electric  current  through 
them  in  the  reverse  direction. 

Q.  Give  an  example  of  a  reversible  cell. 

A.  The  Daniell  cell. 

Q.   Is  it  used  as  a  storage  or  as  a  primary  battery  ? 

A.  As  a  primary;  others  being  better  adapted 
for  use  as  secondaries. 

Q.  Into  what  two  classes  may  primary  cells  be 
divided  ? 

A.   OiDcn-circuit  cells  and  closed-circuit  cells. 

Q.  What  is  an  open-circuit  cell  ? 

A.  A  cell  suitable  for  use  on  circuits  that  are 
normally  open,  being  closed  only  at  the  moment 
when  work  is  to  be  done;  as,  for  example,  bell 
circuits,  gas-lighting  circuits,  time  systems,  watch- 
clock  systems,  etc. 


294  roper's  catechism  for 

Q.  What  kind  of  a  cell  is  generally  employed 
for  such  work  ? 

A.  A  cell  known  as  the  Leclanche,  having  a 
zinc  plate  for  one  pole,  a  carbon  plate  for  the 
other  pole,  and  the  two  immersed  in  a  solution  of 
sal-ammoniac. 

Q.  What  is  the  voltage  furnished  by  such  a  cell 
and  what  is  the  resistance  of  the  ordinary  size 
cell? 

A.  About  IJ-  volts  and  from  -^-^  to  -f^  ohm 
resistance. 

Q.  Why  is  not  this  cell  suitable  for  closed  cir- 
cuit work  ? 

A.  Because  when  a  circuit  is  closed  hydrogen 
particles  begin  to  collect  on  the  carbon  plate,  and 
these  cut  down  the  voltage  and  at  the  same  time 
increase  the  resistance  of  the  cell. 

Q.  If  the  circuit  of  the  cell  is  opened  do  these 
disappear  ? 

A.    Yes;  in  a  few  minutes. 

Q.  Is  there  any  way  of  lessening  the  trouble 
caused  by  the  collection  of  hydrogen  particles  ? 

A.  Yes;  by  using  a  porous  carbon  and  by  put- 
ting next  to  the  carbon  a  slab  of  some  strong 
oxidizing  agent  like  manganese  binoxide.  In  the 
best  forms  of  cell  the  carbon  is  made  in  the  form 
of  a  thin,  hollow  cylinder,  and  the  manganese  in 
powdered  form  is  placed  inside. 


STEAM    ENGINEERS    AND    ELECTRICIANS.         295 

Q.  What  is  the  effect  of  the  manganese  bin- 
oxide  ? 

A.  It  gives  up  a  part  of  its  oxygen,  which 
attacks  the  hydrogen  particles  and  forms,  with 
them,  water. 

Q.  Why  are  some  zincs  made  in  the  form  of  a 
hollow  cylinder  extending  around  the  carbon  ? 

A.  To  diminish  the  resistance  of  the  cell.  The 
greater  the  surface  of  the  plates  and  the  nearer 
they  are  together,  the  less  is  the  resistance  of  the 
cell. 

Q.  What  cell  is  largely  used  for  closed  circuit 
work? 

A.  Some  form  of  the  Daniell  cell.  In  its  orig- 
inal form  it  consisted  of  a  zinc  plate  in  sulphuric 
acid  on  one  side  of  a  porous  wall  and  a  copper 
plate  in  a  solution  of  copper  sulphate  on  the 
other  side. 

Q.  What  is  the  gravity  cell  ? 

A.  A  form  of  Daniell  in  which  the  different 
specific  gravities  of  the  liquids  are  used  to  keep 
the  liquids  from  mixing  without  the  use  of  a 
porous  cup. 

Q.  What  is  the  voltage  and  resistance  of  a 
Daniell  cell  ? 

A.  The  voltage  is  about  1  volt.  The  resistance 
of  the  ordinary  size  gravity  is  in  the  vicinity  of  4 
ohms. 


296  roper's  catechism  for 

Q.  What  other  cell  is  largely  used  and  for  what 
class  of  work? 

A.  The  bichromate  cell;  for  small  motors  and 
cautery  work,  where  a  strong  current  is  needed  for 
a  few  minutes.  It  consists  of  zinc  and  carbon 
plates  immersed  in  chromic  acid. 

Q.  What  is  the  voltage  of  these  cells  and  their 
resistance  ? 

A.  About  2  volts.  Their  resistance  varies,  of 
course,  with  their  size,  that  of  the  smaller  sizes 
being  only  a  fraction  of  an  ohm. 

Q.  What  are  the  two  chief  objections  to  this  cell  ? 

A.  The  fumes  produced  and  the  eating,  of  zinc 
even  when  the  circuit  is  open. 

Q.   What  is  done  to  lessen  the  latter  objection  ? 

A.  The  cell  is  arranged  so  that  the  zinc  ■  plate 
can  be  easily  raised  out  of  the  solution  when  the 
circuit  is  open. 

Q.  What  are  dry  cells  ? 

A.  Cells  in  which  the  solution  has  been  reduced 
to  a  pasty  condition. 

Q.   What  are  their  advantages  ? 

A.  Their  greater  portability;  on  the  other  hand, 
their  resistance  is  higher,  and  they  polarize  more 
readily. 

Q.  What  do  you  mean  by  polarization? 

A.  The  collecting  of  hydrogen  particles  previ- 
ouslv  mentioned. 


STEAM   ENGINEERS   AND    ELECTRICIANS.        297 

DYNAMOS* 

Q.   For  what  is  a  dynamo  used  ? 

A.  To  change  mechanical  energy  into  electrical 
energy. 

Q.  The  dynamo  as  well  as  the  battery  are 
sometimes  likened  to  an  electrical  pump.  In 
what  respect  do  they  resemble  a  pump  ? 

A.  They  may  be  considered  as  raising  electricity 
from  a  low  level  to  a  high  level,  just  as  a  pump 
raises  water. 

Q.   Of  what  does  a  dynamo  consist  ? 

^.  Of  a  magnet  and  a  coil  of  wire  moving 
relatively  to  each  other.  Generally,  the  magnet 
is  fixed  and  the  coil  rotates  between  its  poles.  A 
difference  of  electric  pressure  is  set  up  between  the 
two  ends  of  the  coil,  and  if  these  ends  are  connected 
together  a  current  will  flow. 

Q.  Upon  what  does  the  amount  of  electrical 
pressure  depend? 

A.  It  is  proportional  to  the  rate  of  change  in 
the  number  of  lines  of  force  enclosed  by  the  coil. 
It  is,  therefore,  increased  by  increasing  the  strength 
of  the  magnet,  the  speed  of  revolution,  or  the 
number  of  turns  of  wire  in  the  coil. 

Q.  With  such  a  simple  dynamo,  is  the  direction 
and  strength  of  current  uniform  ? 


298  eoper's  catechism  for 

A.  No;  the  current  can  best  be  represented  by 
plotting  its  values  at  different  moments,  as  in  the 
figure.  Here  distances  to  the  right  along  the 
horizontal  line  represent  time.  Distances  above 
or  below  the  line  represent  the  strength  of  current 
at  different  times.  The  curve  shows  the  variation 
of  current  during  three  complete  revolutions  of 
the  coil.  It  is  evident  from  this  curve  that  the 
strength  of  current  is  alwaj^s  changing  and  that  it 
changes  direction  twice  in  each  revolution.  * 


Q.  What  is  such  a  current  called  ? 

A.   An  alternating  current. 

Q.   Can  it  be  used  for  practical  purposes  ? 

A.  Yes;  for  lighting  and  for  small  motors. 

Q.  How  is  the  current  rectified  or  made  contin- 
uous in  direction  in  the  circuit  where  it  is  to  be 
used? 

A.  By  the  commutator,  a  purely  mechanical 
device  which  changes  the  connection  between  the 
ends  of  the  coil  and  the  external  circuit  just  at  the 
moment  that  the  direction  of  the  current  in  the 
coil  is  reversed. 

*  See  also  ' '  Roper's  Engineers'  Handy-Book, ' '  page  689. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         299 

Q.  What  is  a  rectified  current  called  ? 

A.  A  direct  current. 

Q.   For  what  purposes  is  it  employed  ? 

A.  For  nearly  all  isolated  lighting  plants,  for 
operating  most  arc  lights,  for  driving  motors,  and 
for  charging  storage  batteries. 

Q.  What  is  the  moving  coil  called  ? 

A.  The  armature. 

Q.  How  does  it  differ  in  practice  from  the  ideal 
simple  dynamo  ? 

A.  The  armature  is  made  up  of  a  large  number 
of  coils  wound  on  an  iron  core.  The  larger  num- 
ber of  coils  give  greater  uniformity  to  the  strength 
of  current  and  diminishes  the  sparking  at  the 
commutator.  The  iron  core  is  used  to  keep  as 
many  as  possible  of  the  lines  of  force  produced 
by  the  magnet  in  the  space  in  which  the  armature 
is  moving,  thus  making  the  electrical  pressure 
higher  than  would  be  the  case  without  the  iron  core. 

Q.   How  is  the  iron  core  made  ? 

A.  Of  thin  circular  disks  held  together  by  bolts 
and  attached  to  the  armature  shaft  by  a  sort  of 
spider. 

Q.  What  two  classes  of  armatures  are  there  ? 

A.  The  Gramme  ring  and  the  drum-wound.^ 

Q.  What  is  the  reason  of  making  the  core  out 
of  disks  instead  of  solid  metal  ? 

*See  "  Roper's  Engineers'  Handy-Book,"  page  691. 


•300 


ROPER'S    CATECHISM   FOR 


A.  To  diminish  the  heating  of  the  core  by  use- 
less currents  set  up  in  the  core. 

Q.  Are  the  disks  separated  from  each  other  in 
any  way  ? 

'     A.   They   are    insulated    from    each    other   by 
enamel  or  by  thin  sheets  of  varnished  paper. 

Q.  Is  the  field  magnet  of  the  dynamo  a  perma- 
nent or  electro-magnet  ? 

A.  An  electro-magnet  excited  by  coils  carrying 
either  a  part  or  all  of  the  current  supplied  by  the 
dynamo. 

Q.  What  is  a  series  machine  ? 


SERIES   MACHINE. 


1 
I 

SI 

;o)^ 

eui 

^ 

SHUNT    MACHINE. 


A.  A  dynamo  in  which  the  field-magnet  coils 
carry  all  the  current  produced  by  the  machine — 
that  is,  the  current  flows  around  the  field-magnet 
coils  before  going  to  the  external  circuit. 

Q.  What  is  a  shunt  dynamo  ? 


STEAM    ENGINEERS    AND    ELECTRICIANS. 


301 


COMPOUND   MACHINE. 


A.  One  in  which  only  a  fraction  of  the  current 
is  had  around  the  field-magnet  coils. 

Q.  What  is  a  compound 
dynamo  ? 

A.  A  combination  of  shunt 
and  series. 

Q.  What  are  the  purposes 
for  which  a  series  dynamo  is 
used? 

A.  A  series  dynamo  tends 
to  produce  a  current  of  con- 
stant strength  whatever  load 
may  be  thrown  on  it.     It  is  therefore  used  for 
constant-current  circuits  such  as  street  arc  lighting. 

Q.  When  is  the  shunt  machine  used  ? 

A.  When  a  machine  is  desired  which  will  supply 
constant  pressure  at  all  loads. 

Q.   Does  a  shunt  machine  do  this  ? 

A.  Quite  well,  but  if  the  closest  regulation  for 
constant  pressure  is  desired  a  compound  machine 
is  used. 

Q.  What  is  an  over-compounded  machine  ? 

A.  One  which,  instead  of  maintaining  the  pres- 
sure constant  as  the  load  increases,  will  raise  the 
pressure  a  few  volts  proportionally  to  the  amount 
of  load. 

Q.  What  is  the  advantage  of  this  ? 

A.   There  are  two  advantages.     One  is  to  make 


302  roper's  catechism  for 

up  for  a  slight  lowering  of  speed  in  the  engine, 
which  takes  place  as  the  load  increases.  The  other 
is  to  make  up  for  the  loss  in  pressure  owing  to  the 
resistance  of  the  external  circuit  wires,  which  loss 
is  proportional  to  the  load  which  they  carry. 

Q.  How  can  the  pressure  furnished  by  a  shunt 
or  compound  dynamo  be  varied  ? 

A.  An  adjustable  resistance  called  a  rheostat  is 
connected  in  series  with  the  shunt-field  coils;  by 
turning  the  arm  of  the  rheostat  in  one  direction 
more  resistance  is  thrown  into  this  circuit  and  the 
current  flowing  around  the  coils  is  diminished. 
This  cuts  down  the  number  of  lines  of  force  pro- 
duced by  the  field  magnet,  and  therefore  the  pres- 
sure furnished  by  the  machine  is  lowered.  Mov- 
ing the  rheostat  arm  in  the  other  direction  raises 
the  pressure  by  cutting  out  resistance. 

Q.  AVhat  are  the  brushes  ? 

A.  The  brushes  are  pieces  of  copper  or  carbon 
resting  on  the  commutator  and  serving  to  take 
current  from  the  commutator  to  the  external 
circuit. 

Q.  In  order  to  secure  freedom  from  sparking 
what  care  must  be  exercised  in  setting  the  brushes  ? 

A.  The  brushes  must  be  opposite  each  other, 
and  must  fit  the  surface  of  the  commutator  prop- 
erly. The  rocker  arm  carrying  them  must  be 
turned  into  the  position  of  least  sparking. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         303 


DISTRIBUTION  OF  ELECTRICAL 
ENERGY. 

The  production  and  distribution  of  electrical 
energy  are  very  much  like  a  small  water-system, 
where  water  is  pumped  from  a  tank  to  a  high 
reservoir,  taken  from  the  reservoir  through  pipes 
to  the  place  where  it  is  to  be  used,  and  after  use 
led  back  to  the  tank  to  be  again  pumped  up  and 
again  used.  The  generator,  or  dynamo,  driven  by 
a  steam  engine,  gas  engine,  or  water-wheel,  corre- 
sponds to  the  pump.  The  distributing-pipes  in 
the  water-system  are  replaced  by  copper  wires  for 
the  electrical  system.  The  high-pressure  reservoir 
and  low-pressure  tank  are  replaced  by  the  switch- 
board bus  bars,  one  of  which  is  a  high-pressure 
and  the  other  a  low-pressure  bar.  The  high-pres- 
sure^ bar  is  also  called  the  positive  or  plus  (  +  ) 
bar,  and  the  other  the  negative  or  minus  ( — )  bar. 
They  are  each  copper  bars  mounted  on  the  marble 
or  slate  of  which  the  switchboard  is  made,  and 
are  called  bus  bars,  or  omnibus  bars,  from  the  fact 
that  all  the  current  is  carried  by  them.  The 
valves  of  the  water-system  are  replaced  by  switches, 
the  water-meters  by  ammeters,  and  pressure- 
gauges  by  voltmeters.  Some  devices  which  are 
used  in  electrical  distribution  have  nothing  similar 


304  roper's  catechism  for 

to  them  in  Avater- systems,  but  the  general  shni- 
larity  is  of  great  assistance  in  understanding 
electrical  distribution. 

Q.  What  is  a  switchboard  ? 

A.  One  or  more  slate  or  marble  slabs  mounted 
on  an  iron  or  wooden  framework  and  containing 
the  various  devices  for  controlling  the  electric  dis- 
tribution system. 

Q.  What  are  the  principal  devices  to  be  found 
on  the  switchboard  ? 

A.  1.  A  voltmeter  to  measure  electric  pressure. 
This  is  generally  furnished  with  a  switch  by  which 
it  may  be  connected  to  the  terminals  of  any  gene- 
rator or  to  the  bus  bars. 

2.  An  ammeter  for  each  generator  to  measure 
the  current  which  it  furnishes. 

3.  A  rheostat  for  each  generator  placed  in  series 
with  its  shunt-field  coils  and  controlling  the  pres- 
sure furnished  by  it. 

4.  A  device  for  each  machine,  such  that  if 
owing  to  any  trouble  a  current  greater  than  the 
maximum  for  which  the  machine  is  designed 
flows  through  the  machine,  it  is  automatically 
disconnected  from  the  circuit.  This  device  may 
be  a  fuse  or  a  circuit  breaker. 

5.  A  device  called  a  ground  detector^  for  showing 
when  the  conductors  in  the  system  are  by  accident 
brought  into  electrical  connection  with  the  earth; 


STEAM    ENGINEERS    AND    ELECTRICIANS.         305 

that  is  to  say,  with  gas-  or  steam-  or  water-pipes 
which  are  imbedded  in  the  earth. 

6.  Switches  for  disconnecting  the  generators 
from  the  bus  bars. 

7.  Switches  for  disconnecting  from  the  bus  bars 
the  distribution  circuits. 

8.  A  device  (either  fuse  or  circuit  breaker)  for 
protecting  each  distribution  circuit  from  having 
too  much  current  flow  over  it. 

Q.  What  are  fuses  ? 

A.  Strips  of  an  alloy,  generally  of  tin  and  lead, 
of  such  size  that  they  will  melt  and  interrupt  the 
circuit  when  a  current  in  excess  of  a  certain  amount 
flows  through  them. 

Q.  What  are  circuit  breakers  ? 

A.  Switches  so  arranged  that  they  open  auto- 
matically when  the  current  flowing  through  them 
exceeds  a  certain  value.* 

Q.  Why  are  circuit  breakers  used  in  preference 
to  the  much  cheaper  fuses  ? 

A.  Because  in  large  sizes  fuses  are  very  uncertain 
in  their  action  ;  a  fuse  designed  to  melt  at  500 
amperes,  for  example,  being  liable  to  melt  with  a 
current  of  400  or  600  amperes. 

Q.  How  is  a  simple  form  of  ground  detector 
made,  and  how  does  it  operate  on  a  circuit,  say, 
whose  pressure  is  about  110  volts? 

*See  "Roper's  Engineers'  Handy-Book,"  page  705. 
20 


306 


ROPER  S    CATECHISM    FOR 


Uu^ 


A.  The  ground  detector  consists  of  two  110-volt 
lamps  connected  in  series  with  each  other  and  across 
or  between  the  bus  bars.  The  junction  between  the 
two  lamps  is  connected  to  a  convenient  water-pipe. 
So  long  as  the  insulation  of  the  circuit  is  all  right 
the  two  lights  burn  alike  equally  dim,  since  they 
are  designed  for  110  volts  at  their  terminals  and 
they  have  only  55  volts  under  the  circumstances. 
But  suppose  any  point  on  the  circuit,  as  P,  is 
purposely  or  accidentall}^  connected 
to  earth,  then  the  left-hand  light 
will  burn  bright  while  the  right- 
hand  one  will  burn  exceedingly 
dim,  or  perhaps  not  at  all.  The 
reason  is  that  the  grounding  of  the 
point  P  has  put  it  in  electrical 
connection  with  the  point  A 
through  a  very  low  resistance. 
The  current  through  the  right-hand 
lamp  is,  therefore,  diminished,  its  terminals  being 
short-circuited.  The  left-hand  lamp  will  have 
practically  110  volts  between  its  terminals,  since 
the  joint-resistance  of  the  right-hand  lamp  and  the 
other  path  from  A  to  P  is  exceedingly  small,  and 
hence  the  pressure  used  up  being  also  exceedingly 
small.  If  the  point  P  were  on  the  other  side  of  the 
circuit,  the  right-hand  lamp  would  burn  brightly 
and  the  left-hand  one  ver}^  dimly. 


STEAM   ENGINEERS   AND    ELECTRICIANS. 


307 


Q.  How  would  you  find  the  location  of  the 
ground  ? 

A.  By  opemng  the  switches  one  by  one  till  one  is 
found  which  on  being  opened  relieves  the  ground. 
This  tells  on  which  feeder  the  ground  exists.  Then 
the  circuit  is  examined  in  detail  by  means  of  a 
magneto- bell,  it  being  split  up  into  sections  by 
throwing  open  local  switches,  taking  fuses  out  of 
local  distribution  boards,  and  disconnecting  at  fix- 
tures. 

Q.  May  any  number  of  dynamos  be  connected 
in  multiple  so  as  to  feed  on  the  same  pair  of 
bus  bars  ? 

A.  Any  number  of  shunt  machines  of  the  same 
voltage  may  be  so  used. 

Q.   Cannot  compound  machines  be  so  connected? 


A.   Not  without  a  connection  called  the  equalizer 
shown  by  the  dotted  line  in  the  cut. 


308  eoper's  catechism  for 

Q.  Suppose  you  have  one  machine  feeding  the 
bus  bars  and  desire  to  connect  up  with  it  machine 
No.  2,  how  would  you  proceed  ? 

A.  First  start  up  the  engine  Of  No.  2  and  turn  . 
its  rheostat  till  its  pressure  is  the  same  as  that  of 
the  bus  bars  or  perhaps  one-half  volt  higher. 
Then  close  the  single-pole  switch  in  the  equalizer 
circuit,  shown  dotted,  and  finally  close  the  ma- 
chine's double-pole  switch  which  connects  it  to 
the  bus  bars.  Its  ammeter  reading  will  then  in- 
crease, and  the  rheostat  handles  of  the  two  ma- 
chines are  moved  till  the  ammeters  read  alike  (if 
the  machines  are  the  same  size)  and  the  voltage 
of  the  bus  bars  is  correct. 

Q.  Is  any  different  arrangement  of  switches  ever 
employed  ? 

A.  Yes;  instead  of  a  two-pole  switch  in  the 
dynamo  leads  and  a  single-pole  switch  in  the 
equalizer  lead,  a  three-pole  switch  is  frequently 
employed.  In  this  case  the  middle  blade  is  used 
for  the  equalizer  wire,  and  is  so  adjusted  that  it 
closes  the  equalizer  circuit  just  before  the  other 
two  blades  close  their  circuits. 

SYSTEMS   OF   DISTRIBUTION. 

Q.   What  are  the  two  principal  systems  of  elec-  j 

trical  distribution  ?  I 

A.   The  series  system  and  the  parallel  system. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         309 

Q.  What  is  the  difference  between  the  two  sys- 
tems ? 


A.   In  the  series  system  the  entire  current  flows 
successively  through  each  lamp.     In  the  parallel 


system  the  current  from  the  dynamo  is  divided,  a 
part  flowing  through  each  lamp.  Afterward  these 
separate  currents  unite  and  flow  back  to  the  dy- 
namo. 

Q.  What  is  necessary,  on  a  series  system,  to 
make  the  lighting  successful  ? 

A.  It  must  be  a  constant-current  system — that 
is,  cutting  out  lamps  or  throwing  more  on  must 
not  change  the  value  of  the  current. 

Q.   How  is  this  accomplished  ? 

A.  By  an  automatic  regulator  on  the  machine 
which  increases  its  voltage  if  lamps  are  thrown  on, 
and  diminishes  it  if  lamps  are  cut  out. 

Q.  How  are  lamps  cut  out  on  this  system  ? 


310  roper's  catechism  for 

A.  By  short-circuiting  them — that  is,  by  provid- 
ing another  path  for  the  current  to  flow  other  than 
the  path  through  the  lamp  mechanism  and 
carbons. 

Q.  What  is  necessary  in  a  parallel  system  ? 
A.   It  must  be  a  constant-potential  or  constant- 
pressure  system. 

Q.   How  are  lamps  cut  out  on  this  system  ? 
A.   By  interrupting  the  branch  circuit  in  which 
the  lamp  is  connected. 

Q.  In  the  parallel  system,  why  does  cutting  out 
one  lamp  not  affect  others  ? 

A.  Because  it  does  not  change  the  current  flowing 
through  each  of  the  others.  The  current  through 
any  lamp  depends  on  two  things  only,  — the  pres- 
sure and  the  resistance  of  the  lamp.  Turning  out 
a  lamp  in  nowise  affects  the  resistance  of  other 
lamps  and  only  affects  the  pressure  at  the  terminals 
to  a  very  slight   de- 

^ jg         1^       y      gree ;  therefore  the  cur- 

Cj  i  <}>  i  4  a  i  a       rent  flowing  through 

.*^1 — o ^  1-8       J^     the    lamp    is   practi- 

j-j       •?....  ^  cally  the  same  as  it 

()    •  ?  T  Y  Y  Y  H*  ^^^  before  the  other 

^— — CD I'll' — I  lamp  was  turned  off. 

Q.   In  the  cut,  what 
are  the  wires  C  A  and  D  B  called  ? 
A.   The  feeders. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         311 

Q.  And  the  wires  E  F  smd  G  H  f 

A.  The  mains. 

Q.  And  from  F  to  the  lamp  and  H  to  the  lamp  ? 

A.  Branches. 

Q.  What  is  the  Edison  three- wire  system  ? 

A.  Two  110-volt  machines  are  connected  in 
series  and  the  middle  or  neutral  wire  is  connected 
to  their  junction.  When  the  same  number  of 
lamps  are  burning  on  each  side  of  the  neutral  wire 
there  is  no  current  flowing  through  the  neutral 
and  the  same  current  flows  through  each  machine. 
When  No.  4  is  turned  out,  for  example,  the  lower 


machine  supplies  only  the  current  necessary  for 
lamps  5  and  6,  while  the  upper  continues  to 
supply  the  same  as  before,  the  current  for  one 
lamp  returning  to  the  upper  machine  over  the 
neutral.  If  all  lamps  on  one  side  were  turned  out, 
the  machine  on  that  side  would  furnish  no  current, 
-  and  the  other  machine  would  continue  to  work  as 
before. 

Q.  What  is  the  advantage  of  this  system  ? 

A.   It  is  a  220-volt  system  and  therefore  requires 


312 


roper's  catechism  for 


much  smaller  wires  to  transmit  a  given  amount 
of  energy  with  a  given  loss,  wdthout  increasing  the 
voltage  of  the  lamps. 

Q.   How  much  is  the  gain  in  size  of  wire  used  ? 

A.  The  two  outside  wires  are  just  one-quarter 
as  large  as  they  would  be  with  a  110- volt  two-wire 
system.  If  the  neutral  is  made  of  the  same  size, 
the  three-wire  system  requires  %  as  much  copper 
as  the  two-wire  system,  using  the  same  voltage 
lamps  in  both  cases. 

TABLE 

SHOWING    GAIN    BY    USING    HIGH    PEESSURES,    THE   SAME 
SIZE   WIRES   BEING   USED   FOR   EACH   CASE. 


Power 
trans- 
mitted 
in  watts. 

Volts  at 
which 
trans- 
mitted. 

Corre- 
sponding 
number  of 
amperes. 

Power 

lost 

in 

watts. 

Volts 

drop 

in  line. 

Per  cent, 
power 
lost. 

Per  cent, 
volts 

lost. 

CXE 

E 

C 

C^  R 

C  R 

c^R^um 

CR-^E 

1100 

110 

10 

100 

10 

11. 

9.9 

1100 

220 

5 

25 

5 

2.75 

2.27 

1100 

550 

2 

4 

2 

.0227 

.363 

1100 

1100 

1 

1 

1 

.0009 

.091 

Q.  If  in  one  case,  to  transmit  a  certain  power, 
we  use  110  volts'  pressure  and  in  another  case 
1100  volts,  what  will  be  the  relative  amount  of 
copper  used  on  the  line  ? 

A.  With  1100  volts'  pressure  we  shall  need  only 
Yj-g-th  as  much  copper  as  with  110  volts. 


STEAM    ENGINEERS    AND    ELECTRICIANS. 


313 


Q.   What  disadvantages  have  high  jDressiires  ? 

A.  Greater  difficulty  in  insulating  the  lines  and 
danger  to  human  life. 

Q.  In  proportioning  the  size  of  electrical  con- 
ductors, what  two  requirements  must  be  met? 

A.  The  wire  must  be  large  enough  to  transmit 
the  energy  without  losing  more  than  a  prescribed 
per  cent.,  and  the  wire  must  further  be  large 
enough  so  that  the  current  will  not  heat  it  more 
than  is  allowed  by  the  insurance  regulations. 

INSURAI^CE  EULES   FOR  CARRYING-CAPACITY  OF  WIRES. 


National 

National  Board  of 

Assoc. 

English 
Board  of 
Trade. 

B.  &S. 

Electric 

Fire  Underwriters. 

Factory 

gauge. 

Light 

Mutual 

Association. 

Concealed. 

Open  work. 

Ins.  Co. 

0000 

175 

218 

312 

175 

000 

145 

181 

262 

145 

00 

120 

150 

220 

120 

105 

0 

100 

125 

185 

100 

83 

1 

95 

105 

156 

85 

66 

2 

70 

88 

131 

70 

52 

3 

60 

75 

no 

60 

41 

4 

50 

63 

92 

50 

33 

5 

45 

53 

77 

45 

26 

6 

35 

45 

65 

35 

21 

7 

30 

30 

16 

8 

25 

33 

46 

25 

13 

10 

20 

25 

32 

20 

8 

12 

15 

17 

23 

15 

5 

14 

10 

12 

16 

10 

3 

16 

5 

6 

8 

5 

2 

18 

3 

5 

3 

1 

314  roper's  catechism  for 

Q.  What  is  the  loss  of  pressure  allowable  on 
conductors  ? 

A.   See  ''  Roper's  Engineers'  Handy-Book,"  pp.  ^ 
714-717.  ^ 

Q.  The  distance  between  the  switchboard  and 
a  group  of  ten  16  c.  p.  lamps  is  100  feet.  What 
size  wire  must  be  used  so  that  the  loss  of  pressure 
on  the  wire  between  switchboard  and  lamp  is 
only  one-half  of  one  per  cent.,  the  voltage  of  the 
dynamo  being  110? 

A.  1.  One-half  of  one  per  cent,  of  110  is  .55 
volt,  the  allowable  loss  of  pressure. 

2.  The  current  for  ten  lamps  is  5  amperes. 

3.  By  Ohm's  law  C  =  f  or  i?  =  ^.     R  = '-^ 

=  .11  ohm — that  is,  the  wire  must  be  of  such 
size  that  the  total  length  of  it,  200  feet,  has  a 
resistance   not   exceeding  .11  ohm;    1000  feet  of 

this  size  wire  would  have  a  resistance ^r^ 

=  .55. 

4.  Looking  in  the  wire  tables  we  see  that  No.  7 
wire,  having  a  resistance  of  .491  ohm  at  60° 
Fahr.  fulfils  the  requirement. 

5.  Looking  in  the  table  of  safe  carrying  capaci- 
ties on  the  preceding  page,  we  find  that  according 
to  the  National  Board  of  Fire  Underwriters'  rules 
a  No.  7  wire  will  carry  a  much  greater  current 


STEAM    ENGINEERS   AND    ELECTRICIANS. 


315 


PROPERTIES  OF  COPPER  WIRE. 

ENGLISH   SYSTEM — BROWN    &   SHAEPE  GAUGE. 


2 

i'a 

Weights. 

Resistances  per  1000  feet 
in  International  ohms. 

3 

s- 

'|2 

1000 
feet. 

Mile. 

At  60°  F. 

At  75°' F. 

0000 

460. 

211600. 

641. 

3382. 

.04811 

.04966 

000 

410. 

"168100. 

509. 

2687. 

.06056 

.06251 

00 

365.  • 

133225. 

403. 

2129. 

.07642 

.07887 

0 

325. 

105625. 

320. 

1688. 

.09639 

.09948 

1 

289. 

83521. 

253. 

1335. 

.1219 

.1258 

2 

258. 

66564. 

202. 

1064. 

.1529 

.1579 

3 

229. 

52441. 

159. 

838. 

.1941 

.2004 

4 

204. 

41616. 

126. 

665. 

.2446 

.2525 

5 

182. 

33124. 

100. 

529. 

.3074 

.3172 

6 

162. 

26244. 

79. 

419. 

.3879 

.4004 

7 

144. 

20736. 

63. 

331. 

.491 

.5067 

8 

128. 

16384. 

50. 

262. 

.6214 

.6413 

9 

114. 

12996. 

39. 

208. 

.7834 

.8085 

10 

102. 

10404. 

32. 

166. 

.9785 

1.01 

11 

91. 

8281. 

25. 
20. 

132. 
105. 

1.229 

1.269 

12 

81. 

6561. 

1.552 

1.601 

13 

72. 

5184. 

15.7 

83. 

1.964 

2.027 

14 

64. 

4096. 

12.4 

65. 

2.485 

2.565 

15 

57. 

3249. 

9.8 

52. 

3.133 

3.234 

16 

51. 
45. 

2601. 
2025. 

7.9 

42. 

3.914 

4.04 

17 

6.1 

32. 

5.028 

5.189 

18 

40. 

1600. 

4.8 

25.6 

6.363 

6.567 

19 

36. 

1296. 

3.9 

20.7 

7.855 

8.108 

20 

32. 

1024. 

3.1 

16.4 

9.942 

10.26 

21 

28.5 
25.3 

812.3 

2.5 

13. 

12.53 

12.94 

22 

640.1 

1.9 

10.2 

15.9 

16.41 

23 

22.6 

510.8 

1.5 

8.2 

19.93 

20.57 

24 

20.1 

404. 

1.2 

6.5 

25.2 

26.01 

25 

17.9 

320.4 

.97 

5.1 

31.77 

32.79 

26 

1.5.9 

252.8 

.77 

4. 

40.27 

41.56 

27 

14.2 

201.6 

.61 

3.2 

50.49 

52.11 

28 

12.6 

158.8 

.48 

2.5 

64.13 

66.18 

29 

11.3 

127.7 

.39 

2. 

79.73 

82.29 

30 

10. 

100. 

.31 

1.6 

101.8 

105.1 

31 

8.9 

79.2 

.24 

1.27 

128.5 

132.7 

There  are  two  points  in  this  table  which  will  be  found  easy  to  remem- 
ber and  very  convenient  in  practice— namely,  that  the  resistance  of  1000 
feet  of  No.  10  is  almost  exactly  1  ohm  at  75°  F.,  and  that  a  change  of 
t       three  sizes  either  halves  or  doubles  the  resistance,  according  as  we  go  up 
or  down  the  table. 


316  roper's  catechism  for 

than  5  amperes,  so  that  a  No.  7  wire  is  suitable 
for  the  requirements. 

Q.  What  is  a  mil? 

A.   One-thousandth  of  an  inch. 

Q.  What  are  the  circular  mils  in  a  wire  ? 

A.  The  square  of  the  diameter  in  mils. 

Q.  What  relation  do  the  circular  mileages  of 
two  wires  bear  to  their  resistances  ? 

A.  Their  resistances  are  inversely  proportional 
to  their  circular  mileages. 

Q.  A  No.  2  wire,  No.  4  wire,  and  No.  6  wire 
are  connected  in  multiple  ;  to  what  size  wire  will 
their  joint  resistance  be  equal? 

A.  The  sum  of  their  circular  mileages  is, — 
66,564  +  41,616  -f  26,244  =  134,424,  and  this 
is  nearly  the  circular  mileage  of  a  No.  2/0  wire  to 
which  the  three  wires  will  be  practically  equivalent. 

WIRING  AND  APPLIANCES. 

Q.  What  two  classes  of  wiring  are  there  ? 

A.   Open  or  exposed  work  and  concealed  work. 

Q.  In  open  work,  what  varieties  are  there  ? 

A.  Porcelain  work,  where  the  wires  are  carried 
on  porcelain  knobs,  and  molding  work,  where  the 
wires  are  carried  in  a  grooved  molding  provided 
with  a  cap  to  hide  them  from  view. 

Q.  What  are  the  varieties  of  concealed  work  ? 

A.  Porcelain  work  and  conduit  work. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         317 

Q.  What  is  the  nature  of  conduit  work? 

A.  A  system  of  tubes  or  pipes  is  first  installed 
into  which  the  wires  are  afterward  drawn  in. 

Q.  What  are  the  fundamental  requisites  for  a 
conduit  ? 

A.  It  should  be  strong  enough  to  protect  the 
wires  from  all  accidents  such  as  hammering,  jar- 
ring, nails,  etc. ,  and  it  should  not  be  attacked  by 
cement,  plaster,  or  moisture.  Moreover,  it  should 
have  a  smooth  inside  surface,  so  that  the  insulation 
of  the  wires  may  not  be  injured  by  the  process  of 
drawing  them  in. 

Q.  What  kind  of  conduits  meet  these  require- 
ments ? 

A.  An  iron  or  steel  tube  like  a  gas-pipe  has  suf- 
ficient strength.  If  properly  painted  or  enameled 
it  is  not  affected  by  cement,  plaster,  or  moisture. 
To  secure  smoothness  a  special  pipe  must  be  made, 
with  this  end  in  view  ;  or,  as  in  some  conduits,  a 
lining  of  wood  or  some  compound  of  a  bituminous 
nature  may  be  employed. 

Q.  How  many  wires  are  placed  in  one  tube? 

A.  Two  in  the  two-wire  system  or  three  in  the 
three-wire  system,  except  sometimes  in  the  case 
of  large-sized  feeders  where  it  is  not  possible  to 
draw  two  in.  Where  alternating  currents  are  to 
be  used  both  the  wires  of  a  circuit  must  be  in  the 
same  tube  to  avoid  an  excessive  loss  of  pressure. 


318 


roper's  catechism  for 


Q.  What  is  a  cut-put,  and  when  is  it  used  ? 

A.  A  cut-out  is  the  name  given  to  a  combination 
of  fuse  blocks,  studs,  and  screws  and  convenient 
terminals  for  fastening  wires.  These  parts  are 
mounted  on  some  insulator,  as  slate,  marble,  or 
porcelain.  A  cut-out  with  fuse  is  used  at  every 
point  in  a  circuit  where  the  size  of  wire  is  changed. 

Q.   Why  is  this  ? 

A.  So  that  the  fuse  may  protect  the  smaller 
wire  from  an  excess  of  current. 

Q.  What  is  a  switch  ? 

A.  A  convenient  device  for  opening  or  closing 
an  electric  current.  It  performs  a  similar  service 
to  that  of  a  valve  in  a  water  system,  except  that  it 
has  no  positions  corresponding  to  partly  open.  It 
must  be  completely  open  or  completely  shut. 

Q.  What  is  a  single-pole  switch  ? 

A.   One  which  opens  one  wire  of  a  circuit. 

Q.  What  kre  double- 
pole 


-O 


and    triple  • 
switches  ? 

A.  Those  which  open 
two  or  three  wires  of 
the  circuit. 

Q.  When  are  three- 
way  switches  used  ? 
A.   When  it   is  de- 
sired to  control  lamps  from  either  of  two  points. 


3-w^y 


3 -way 


CIRCUIT  WITH   3-WAY  SWITCHES. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         319 

Q.  In  calculating  the  carrying  capacity  of 
switches,  what  general  rules  are  employed  ? 

A.  Where  current  goes  through  solid  metal 
allow  one  square  inch  per  1000  amperes,  and  w^here 
it  goes  through  the  joint  between  two  pieces  allow 
one  square  inch  of  contact  surfaces  to  each  75 
amperes. 


320       roper's  catechism  for 


ELECTRIC  LIGHTING. 

Q.   In  what  ways  may  arc  lamps  be  classified? 

A.  (1)  According  to  the  kind  of  distribution- 
system  for  which  they  are  intended,  as  constant 
potential  arc  lamps  and  series  arc  lamps;  the  latter 
are  in  general  used  now  only  by  central  stations. 
(2)  According  as  they  are  to  be  supplied  by  direct 
or  alternating  current,  into  direct-current  arcs  and 
alternating  arcs.  (3)  According  to  the  degree  of 
enclosure  of  the  arc,  into  open  arcs  and  closed  arcs. 

Q.  What  are  the  requirements  of  all  arc  lamps  ? 

A.  All  lamps  to  be  commercially  satisfactory 
must  do  two  things:  They  must  strike  the  arc — 
that  is,  after  current  has  commenced  to  flow  they 
must  automatically  draw  the  carbons  apart  so  as 
to  start  the  arc.  They  must  also  regulate — that  is, 
as  the  carbons  burn  away  they  must  be  automat- 
ically fed  together,  and  the  feeding  of  one  must 
not  appreciably  affect  the  brilliancy  of  others. 

Q.  How  are  these  accomplished  in  an  arc  lamp 
burning  on  a  parallel  or  constant  potential  system 
of  distribution? 

A.  The  current  coming  from  the  line  to  the 
positive  lamp-terminal  passes  through  a  coarse 
wire  coil  and  then  through  a  chain  or  brush  con- 
tact to  the  upper  carbon,  through  the  upper  and 


STEAM    ENGINEERS   AND    ELECTRICIANS.         321 

lower  carbons,  and  back  through  a  wire  resistance, 
which  can  be  varied,  to  the  other  terminal  of  the 
lamp  and  thence  to  line.  The  passage  of  current 
through  the  coil  lifts  an  iron  armature  or  core,  as 
the  case  may  be,  to  a  certain  distance  depending 
on  the  strength  of  the  current.  This  armature 
lifts  a  clutch-device  which  raises  the  upper  carbon. 
The  arc  is  thus  struck  and  the  lamp  continues  to 
burn,  the  two  carbons  being  gradually  consumed 
and  the  arc  becoming  longer.  As  the  arc  lengthens 
its  resistance  becomes  greater  and  the  current  less. 
This  allows  the  armature  to  drop  down  a  little, 
and  the  clutch  tripping  against  a  stop  lets  the 
upper  carbon  slide  through  a  little,  thus  shorten- 
ing the  arc.  The  moment  the  arc  has  been 
shortened  sufficiently  to  increase  the  current  enough 
to  lift  the  clutch  off  the  tripping-stop  the  feeding 
of  the  carbon  cCases '  and  the  lamp  continues  to 
burn  till  the  arc  again  becomes  too  long. 

Q.  Can  two  or  more  of  these  lamps  be  placed 
in  series  ? 

A.  No;  when  several  lamps  are  to  be  operated 
in  series  they  will  not  all  feed  at  the  same  time,  so 
that  the  action  of  one  would  interfere  with  the 
others  unless  some  different  arrangements  were 
introduced. 

Q.  What  modification   of    the    mechanism   is 
made  when  lamps  are  to  be  run  in  series  ? 
21 


322  roper's  catechism  for 

A.  An  additional  magnet  with  fine  wire  coil  is 
connected  as  a  shunt  around  the  arc,  and  its  arma- 
ture arranged  so  that  when  lifted  to  a  certain  point 
it  makes  the  clutch  feed.  As  the  arc  lengthens  its 
resistance  increases,  and  also  the  pressure  between 
its  terminals.  Hence  more  current  is  sent  around 
the  fine  wire  coils,  raising  their  armature  and 
starting  the  feeding  mechanism. 

Q.  What  is  the  difference  between  open  and 
closed  arc  lamps  ? 

A.  An  open  arc  lamp  is  one  in  which  the  air 
has  free  access  to  the  arc.  A  closed  arc  lamp  is 
one  in  which  a  small  inner  globe  placed  around  the 
arc  prevents,  to  a  great  extent,  the  access  of  air.. 

Q.  What  is  the  object  of  enclosing  the  arc? 

A.  The  consumption  of  carbon  is  diminished 
and  the  light  is  steadier. 

Q.  How  long  do  carbons  last  in  the  two  types 
of  lamp? 

A.  About  7  hours  in  the  open  arc  and  about 
100  hours  in  the  closed  arc. 

Q.   How  are  lamps  rated  commercially  ? 

A.  Lamps  are  rated  in  candle-power  according 
to  their  brilliancy  in  the  angle  of  greatest  bril- 
liancy. Thus  the  ordinary  street  lamp  rated  at 
2000  candle-power  gives  that  brilliancy  only  at  an 
angle  from  the  horizontal  of  about  45  degrees. 
At  any  other  angle  its  brilliancy  is  less,  and  the 


STEAM    ENGINEERS   AND   ELECTRICIANS.         323 

average  candle-power  below  the  horizontal  will  not 
be  much  over  800  candle-power.  Such  a  lamp 
requires  a  current  of  9. 6  amperes  and  about  45  or 
50  volts,  and  a  lamp  using  such  current  and  pres- 
sure that  their  product  is  450  watts  may  be  con- 
sidered commercially  a  2000  candle-power  lamp. 

Q.  What  current  does  a  nominal  2000  candle- 
power  closed  arc  take  ? 

A.  About  5  amperes  on  steady  burning,  though 
nearly  double  this  on  first  starting. 

Q.  What  is  the  voltage  between  the  carbons  ? 
•     A.  About  80  to  90  volts. 

Q.  What  effect  does  the  use  of  two  globes  have 
on  the  distribution  of  light  ? 

A.  It  is  more  even  with  the  closed  arc  on 
account  of  the  two  globes,  but  for  the  same  reason 
a  larger  percentage  of  light  is  absorbed. 

Q.  What  are  the  essential  features  of  the  incan- 
descent lamp  ? 

A.  Incandescent  lamps  consist  of  a  carbon 
filament  attached  to  platinum  wires,  which  is 
mounted  in  a  glass  globe  from  which  the  air  has 
been  exhausted  and  which  is  sealed  up  so  as  to  ex- 
clude air.  The  platinum  wires  serve  to  connect 
the  filament  to  the  terminals  of  the  lamp  base. 
The  vacuum  is  made  as  perfect  as  possible,  so  that 
there  may  remain  no  air  inside  the  globe  in  which 
the  highly  heated  filament  would  burn  aw^ay. 


324  roper's  catechism  for 

Q.   How  is  the  filament  made  ? 

A.  By  taking  a  slender  piece  of  some  material 
consisting  largely  of  carbon,  such  as  bamboo,  silk, 
paper,  or  cellulose,  and  heating  it  intensely  in  a 
furnace  so  as  to  drive  out  all  the  other  material, 
leaving  a  very  nearly  pure  carbon  thread.  In 
order  to  smooth  out  the  roughness  and  make  its 
section  uniform  at  all  points,  a  current  is  passed 
through  it  large  enough  to  heat  it  to  nearly  a  white 
heat  in  an  atmosphere  of  some  hydrocarbon,  like 
coal  gas.  This  causes  carbon  to  be  deposited  most 
largely  at  the  hottest  points,  which  are  those  of 
the  smallest  cross-section.  The  filament  is  then 
attached  to  the  platinum  leading-in  wires  and 
placed  in  the  globe. 

Q.  What  is  the  remainder  of  the  process  of 
making  the  lamp  ? 

A.  A  mechanical  air-pump  exhausts  the  air 
from  the  globe,  and,  finally,  by  passing  a  strong 
current  through  the  filament,  the  latter,  heated  to 
incandescence,  burns  away  the  remnant  of  oxygen 
remaining.  The  bulb  is  then  sealed  up  and  the 
platinum  wires  connected  to  the  lamp-base  ter- 
minals. Finally,  the  lamps  are  tested  to  see  at 
what  voltage  they  will  give  the  candle-power  for 
which  they  are  intended. 

Q.  What  is  the  effect  of  use  on  the  lamp  ? 

A.   Its  candle-power  graduall}^  diminishes  owing 


STEAM    ENGINEERS   AND    ELECTRICIANS.         325 

to  the  deposition  of  carbon  from  the  filament  on  the 
walls  of  the  globe,  the  layer  of  carbon  absorbing 
the  light-rays,  so  that  after  a  few  hmidred  hours' 
burning  the  lamp  must  be  replaced  by  a  new  one. 

Q.   What  candle-powers  are  ordinarily  made  ? 

A.  8,  10,  12,  16,  20,  24,  32,  50,  100,  150, 
though  the  last  two  sizes  are  rarely  used,  arc  lamps 
being  employed  instead. 

Q.  What  are  the  voltages  commonly  made  ? 

A.  From  50  to  60,  70  to  80,  100  to  120,  and 
200  to  250  lamps  of  110  and  thereabouts  being 
the  most  common. 

Q.  Why  are  220-volt  lamps  employed  ? 

A.  To  secure  economy  in  the  size  of  the  dis- 
tributing wires. 

Q.  Why  are  they  not  more  extensively  used  ? 

A.  Because  they  are  inferior  in  quality  to  the 
lower  voltage  lamps. 

Q.  What  are  the  two  important  qualities  of  an 
incandescent  lamp  ? 

A.   Its  length  of  life  and  its  efficiency. 

Q.  What  is  meant  by  efficiency  ? 

A.  The  number  of  watts  power  which  must  be 
supplied  to  the  filament  to  produce  1  candle-power. 
The  most  efficient  lamp  is  that  one  which  produces 
1  candle-power  with  the  least  number  of  watts. 

Q.  Is  there  any  relation  between  life  and  effi- 
ciency ? 


326 


roper's  catechism  for 


A.  Yes;  a  somewhat  unfortunate  one,  since  we 
cannot  improve  one  without  injuring  the  other. 
The  efficiency  increases  with  the  temperature  of 
the  filament,  while  the  life  is  correspondingly 
diminished. 

TABLE 

OF   EFFICIENCIES   AND   LIFE   OF   INCANDESCENT   LAMPS. 


Efficiency. 
Watts  per  can- 
dle. 

Life-hours. 

Watts  per  16 
c.  p.  lamp. 

Amperes  for  16 

c.  p.  110-volt 

lamp. 

2.6 
3.1 
3.6 
4.0 

400 

600 

800 

1000 

41.8 
49  6 
57.6 
64.0 

.38 
.45 
.52 
.60 

Q.  When  is  it  desirable  to  use  a  low  and  when 
a  high  efficiency  lamp  ? 

A.  It  depends  upon  the  cost  of  power.  If  coal 
is  cheap,  it  pays  to  use  a  low  efficiency  and  long 
life.  If  coal  is  dear,  the  high  efficiency  lamp 
should  be  used,  provided  the  speed  regulation  of 
the  engine  is  good  enough  to  prevent  fluctuations 
in  the  voltage  of  the  dynamo,  it  being  understood 
that  any  rise  in  voltage  above  that  for  which  the 
lamp  is  intended  shortens  its  life  very  seriously. 
Of  course,  where  all  the  exhaust  steam  of  the 
generator  engine  is  used  in  steam  heating  it  is  de- 
sirable to  use  the  low  efficiency  and  long-life  lamps. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         327 


ELECTRIC  MOTORS* 

Q.  How  does  a  motor  differ  from  a  dynamo,  as 
regards  the  purpose  for  which  it  is  used  ? 

A.  A  dynamo  transforms  mechanical  energy 
into  electrical  energy.  A  motor  transforms  elec- 
trical energy  into  mechanical  energy. 

Q.  How  do  direct-current  motors  differ  from 
dynamos,  as  regards  construction  ? 

A.  Practically  any  direct-current  dynamo,  if 
current  be  supplied  to  it,  will  operate  as  a  motor, 
and  a  well-designed  dynamo  will  make  a  good 
motor.  Certain  alterations  in  winding  and  in 
other  details  are  made  in  motors  to  improve  cer- 
tain qualities  that  may  be  specially  desired. 

Q.  Will  a  dynamo  used  as  a  motor  run  in  the 
same  direction  that  it  had  as  dynamo  ? 

A.  A  series  dynamo,  when  used  as  a  motor,  will 
run  in  the  opposite  direction,  and  a  shunt  motor 
will  run  in  the  same  direction. 

Q,  What  must  be  done  to  reverse  the  direction 
in  which  a  motor  will  run  ? 

A.  Change  the  connections  so  as  to  reverse  the 
direction  of  current  through  either  (but  not  both) 
field  or  armature.  It  may  further  be  necessary 
to  shift  the  brushes  to  prevent  sparking. 

Q.  When  are  series  motors  employed? 


328  ROPER'S  CATECHISM  FOR 

A.  The  series  motor  is  used  where  it  is  necessary 
to  start  with  full  load  and  where  automatic  regu- 
lation for  constant  speed  is  not  necessary,  a  hand 
regulation  being  used,  as,  for  example,  in  hoists, 
cranes,  street  railways,  etc. 

Q.  When  are  shunt  motors  used  ? 

A.  A  shunt  motor  is  used  where  automatic 
regulation  for  constant  speed  is  desired.  A  good 
shunt  motor  will  not  change  its  speed  more  than 
5  per  cent,  when  the  load  is  varied  from  zero  to  a 
maximum. 

Q.  Under  what  circumstances  would  compound 
motors  be  desirable  ? 

A.  Compound  motors  are  used  where  closer 
speed  regulation  than  that  given  by  shunt  motors 
is  desired,  and  in  special  cases,  such  as  on  planers 
where  it  is  desired  to  check  the  sudden  large  flow 
of  current  during  reversal. 

Q.  With  a  series  motor,  whose  use  is  almost 
entirely  on  constant  pressure  circuits,  how  is 
regulation  of  speed  accomplished  ? 

A.   There  are  two  common  methods: 

1.  To  change  the  pressure  supplied  to  it,  by 
putting  in  series  with  the  motor  a  rheostat  in 
which  more  or  less  pressure  is  used  up  according 
to  the  position  of  the  rheostat-handle.  Lowering 
the  pressure  will,  of  course,  lower  the  speed. 

2.  To  change  the  strength  of  the  field  of  the 


STEAM    ENGINEERS    AND    ELECTRICIANS.         329 

motor.  This  is  done  by  winding  the  field  coils  in 
sections  and  bringing  out  the  ends  to  a  sort  of 
commutating  device  called  a  controller.  In  one 
position  of  the  controller  handle  the  sections  will 
all  be  in  series,  cutting  down  the  current  and 
making  the  ampere  turns  of  the  field,  and  hence 
its  strength,  low.  In  the  next  position,  for  ex- 
ample, three  sections  will  be  in  series  and  three 
others  in  series,  and  the  two  sets  of  three  in 
multiple,  which  will  diminish  the  resistance,  let 
more  current  through,  and  increase  the  ampere 
turns.  Another  position  will  put  more  in  multiple 
and  less  in  series,  and  so  on  till  the  final  step  puts 
all  the  sections  in  multiple,  giving  the  lowest 
possible  resistance,  highest  number  of  amperes, 
greatest  number  of  ampere  turns,  and  strongest 
field.  With  the  series  motor  on  constant  potential 
circuits  the  speed  is  increased  in  proportion  as  we 
increase  the  field  strength.  A  combination  of  the 
two  methods  is  frequently  used,  the  resistance 
being  used  during  the  first  positions  in  order  to 
cut  down  the  excessive  flow  of  current  on  starting. 

Q.  How  are  shunt  motors,  on  constant  pressure 
circuits,  regulated  for  changes  in  speed  ? 

A.  By  putting  resistance  coils  in  series  wdth  the 
armature  and  throwing  more  or  less  of  them  in 
according  as  we  want  lower  or  higher  speed. 
Another  method  is  to  put  a  rheostat  in  the  field 


330  roper's  catechism  for 

circuit  and  vary  the  current  flowing  around  the 
field  coils  by  means  of  it. 

Q.  What  effect  does  weakening  the  field  have 
on  the  speed  of  the  series  motor  on  constant  pres- 
sure circuits  ? 

A.   It  lowers  the  speed. 

Q.  What  is  the  effect  with  a  shunt  machine  ? 

A.  Weakening  the  field  increases  the  speed. 

Q.   How  are  compound  motors  regulated  ? 

A.  Generally  like  shunt  motors;  but  in  some 
special  cases  the  series  coils  are  wound  in  sections 
and  thrown  in  series,  and  finally  in  multiple,  as 
is  the  case  with  series  motors. 

Q.  In  starting  shunt  or  compound  motors  what 
precaution  is  necessary  ? 

A.  It  is  necessary  to  put  a  considerable  resist- 
ance in  series  with  the  armature,  on  account  of  its 
very  low  resistance,  which  will  vary  from  y^Q-  to 
YQ^o-g-  of  an  ohm  or  less,  according  to  its  size. 
Such  a  low  resistance  thrown  across  110  volts 
would  cause  an  enormous  current,  which  would 
injure  the  commutator  and  brushes  by  sparking 
and  the  armature  coils  by  heating.  As  the 
machine  speeds  up  the  resistance  may  be  cut  down, 
because  the  armature,  which  is  turning  in  a  mag- 
netic field,  produces  an  electro-motive  force  oppo- 
site to  that  of  the  circuit,  which  tends  to  cut  the 
current  down. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         331 

Q.  What  further  protective  devices  are  needed 
with  motors  ? 

A.  All  motors  need  to  be  protected  from  the 
danger  of  being  overloaded.  An  overload,  by 
slowing  down  the  motor,  diminishes  the  back 
electro-motive  force  and  therefore  allows  an  excess- 
ive current  to  flow,  which,  if  long  continued, 
would  burn  out  the  armature.  The  protection 
formerly  used  was  a  pair  of  fuses,  one  in  each  of  the 
circuit  wires,  which  were  of  such  a  size  that  they 
were  expected  to  blow  at  any  current  exceeding 
that  corresponding  to  the  maximum  load  for  which 
the  motor  was  designed.  Owing  to  the  uncertain 
action  of  fuses,  a  circ ait-breaker  is  now  almost 
universally  used,  mounted  on  the  starting-box. 
Another  thing  which  must  be  guarded  against  is 
this:  Suppose  that'  the  circuit  to  which  the  motor 
is  connected  is  overloaded,  perhaps  by  some 
accident,  and  the  circuit-breaker  of  that  circuit 
on  the  switchboard  should  open.  This  would 
cut  off  current  from  the  motor  and  it  would 
stop.  Now  if  nothing  were  done  except  at  the 
switchboard  to  throw  in  the  circuit-breaker 
again,  we  should  throw  the  full  voltage  on  the 
motor  armature,  none  of  the  rheostat  being  in 
series  with  it,  as  it  had  been  previously  cut  out  of 
the  circuit  when  the  motor  was  first  brought  up  to 
The   result,  of   course,   Avould    be  a   tre- 


332  roper's  catechism  for 

mendous  flow  of  current  and  injury  to  commu- 
tator, brushes,  and  perhaps  the  armature,  depend- 
ing upon  how  quickly  some  one  opened  the  switch 
which  connected  the  motor  to  the  circuit.  To 
obviate  this  difficulty,  the  rheostat  arm  has 
attached  to  it  a  spring  which  tends  to  pull  it  back 
to  the  position  in  which  all  of  its  coils  are  in 
series  with  the  armature.  At  the  other  limit  of 
its  motion,  where  it  would  stand  when  all  the 
coils  had  been  cut  out  of  the  circuit,  is  a  magnet 
wound  with  fine  wire  and  supplied  from  the 
circuit  wires.  When  the  rheostat  arm  gets  to  this 
position  the  magnet  holds  it  there  by  its  attraction 
for  a  piece  of  iron  mounted  on  the  arm,  as  long 
as  the  current  flows  through  the  coil;  but  if  the 
circuit-breaker  goes  off  or  the  voltage  disappears 
for  any  reason,  the  magnet  lets  go  and  the  spring 
pulls  the  rheostat  arm  back  to  the  position  of  safety. 

Q.  What  are  the  commercial  sizes  in  which 
motors  are  built? 

^.  A,  *,  i,  h  1,  2,  3,  5,  71  10,  15,  20,  25,  50, 
75,  100,  and  upward. 

Q.  What  are  the  standard  voltages  ? 

A.   110  to  125,  220  to  250,  and  500  to  550. 

Q.  What  is  a  motor- generator  ? 

A.  A  combination  of  motor  and  generator  on 
the  same  shaft.  The  most  easily  understood  form 
would  be  a  motor  which  might  be  designed  for  any 


STEAM    ENGINEERS   AND    ELECTRICIANS.         333 

voltage,  speed,  and  power,  coupled  directly  to  the 
shaft  of  a  dynamo  designed  for  the  same  speed, 
but  for  any  voltage  and  the  same  output  as  the 
motor.  Such  a  machine  has  two  distinct  com- 
mutators, brushes,  armatures,  and  fields. 

Q.  How  is  this  arrangement  modified  in  prac- 
tice? 

A.  By  using  a  common  armature  core  and  field, 
and  putting  the  two  sets  of  armature  windings  on 
the  same  core,  insulated,  of  course,  carefully  from 
each  other. 

Q.  What  are  some  of  its  principal  uses  ? 

A.  1.  To  change  from  a  high  pressure  and  small 
current  to  a  lower  pressure  and  correspondingly 
greater  current. 

2.  With  its  generator  armature  in  series  with 
some  circuit  to  raise  the  pressure  of  that  particular 
circuit  higher  than  that  of  the  other  circuits  sup- 
plied from  the  principal  generator.  In  such  uses 
it  is  called  a  booster. 

3.  In  connection  with  storage  batteries,  it  being 
used  in  series  with  the  charging  mains  to  increase 
the  pressure  in  proportion  as  the  batteries  become 
more  fully  charged. 

It  is  also  used  to  a  considerable  extent  in  tele- 
phone exchanges  for  operating  the  calling  circuits, 
the  generator  end  being  arranged  to  give  an  alter- 
nating current. 


334       roper's  catechism  for 


STORAGE  OR  SECONDARY  BATTERIES. 

Q.  Of  what  does  the  storage  battery,  as  com- 
mercially sold,  consist? 

A.  Of  two  lead  plates,  or  sets  of  plates,  im- 
mersed in  a  jar  containing  dilute  sulphuric  acid, 
the  plates  having  the  form  of  grids,  the  holes  in 
which  are  filled  with  active  material. 

Q.   Of  what  does  this  active  material  consist  ? 

A.  On  the  positive  plate,  of  peroxide  of  lead. 
On  the  negative  plate,  of  metallic  lead  in  finely 
divided,  spongy  condition. 

Q.  What  do  you  mean  by  the  positive  plate  ? 

A.  Just  as  with  any  battery,  the  plate  from 
which  current  will  flow  through  a  conductor  con- 
necting it  to  the  other  plate. 

Q.  How  can  you  tell  by  the  eye  which  is  the 
positive  plate  of  a  storage  cell  ? 

A.   By  its  reddish  color. 

Q.   Is  there  any  other  way  ? 

A.  Yes;  there  is  always  one  more  negative  plate 
in  a  cell  than  there  are  positive  plates. 

Q.  Are  the  positive  and  negative  plates  in  con- 
tact? 

A.  The  positives  are  all  joined  to  each  other, 
likewise  the  negatives;  but  the  positives  are 
separated  from  the  negatives  by  about  ^  of  an 


STEAM    ENGINEERS   AND    ELECTRICIANS.         335 

inch,  the  space  between  bemg  filled  with  sulphuric 
acid. 

Q.  What  do  you  mean  by  the  discharge  of  a 
cell? 

A.  Allowing  it  to  furnish  current,  as  it  will  do 
if  the  positive  and  negative  terminals  are  con- 
nected by  a  conductor. 

Q.  What  are,  roughly,  the  chemical  changes  that 
take  place  during  discharge  ? 

A.  The  peroxide  on  the  positive  is  changed  to 
lead  sulphate.  The  spongy  lead  on  the  negative 
is  likewise  changed  to  lead  sulphate. 

Q.  What  do  you  mean  by  charging  a  cell  ? 

A:  Running  a  current  from  some  generator 
through  the  cell  in  the  opposite  direction  to  that 
of  the  current  which  it  furnished  during  dis- 
charge. 

Q.  What  chemical  action  takes  place  ? 

A.  The  reverse  of  what  occurred  during  dis- 
charge. On  the  positive  plates  lead  sulphate  is 
changed  to  lead  peroxide  and  on  the  negatives  to 
metallic  lead. 

Q.  What  pressure  is  furnished  by  such  a  storage 
cell? 

A.  When  fulty  charged,  about  2.2  volts.  This 
gradually  diminishes  during  discharge  to  1.<S  volts 
beyond  which  point  further  discharge  would  injure 
the  cell. 


336  roper's  catechism  for 

Q.  What  are  the  principal  sources  of  trouble, 
and  how  are  they  remedied? 

A.  The  principal  troubles  of  storage  cells  are 
short-circuiting,  buckling,  and  sulphating.  The  first 
is  caused  by  buckling  of  plates  or  by  the  dropping 
out  of  portions  of  the  pencils  of  active  material, 
which  in  time  form  between  the  positive  and 
negative  plates  a  connection  which  causes  loss  of 
charge  and  destruction  of  the  plates  if  not  noticed 
and  remedied  by  taking  out  the  material.  Buck- 
ling is  due  to  an  excessive  rate  of  discharge  or  an 
unequal  discharge  at  different  parts  of  the  plate. 
To  assist  in  preventing  it  the  plates  are  separated 
by  glass  or  rubber  distance-pieces.  Sulphating, 
or  the  production  of  a  complex,  hard,  white  lead 
sulphate,  is  caused  by  carrying  the  discharge  of 
the  battery  too  far  or  by  letting  it  stand  too  long 
without  recharging.  It  is  remedied  by  persistent 
charging. 

Q.  What  are  the  principal  advantages  of  using 
storage  cells  ? 

A.  To  take  care  of  light  loads,  thus  permitting 
dynamos,  engines,  and  perhaps  a  boiler  to  be  shut 
down;  to  maintain  a  steady  pressure;  and  to  take 
care  of  the  ' '  peak  of  the  load, ' '  *  thus  enabling 
the  machinery  to  work  at  a  more  even  load  and 
securing  greater  economy. 

*See  "Roper's  Engineers'  Handy-Book,"  page  755. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         66  i 

Q.   How  are  storage  cells  rated  ? 

A.  By  their  capacity  in  ampere-hours.  Thus,  a 
cell  of  50  ampere-hours  is  one  which  when  dis- 
charged at  its  normal  rate  gives  out  such  a  number 
of  amperes  for  such  a  number  of  hours  that  the 
product  of  the  number  of  amperes  by  the  number 
of  hours  equals  50.  The  capacity  of  a  cell,  or  the 
number  of  ampere-hours  which  can  be  taken  from 
it  without  carrying  the  voltage  lower  than  1.8  volts, 
is  very  much  affected  by  the  rate  of  discharge, 
being  much  less  at  a  rapid  than  at  a  slow  rate  of 
discharge. 

Q.  What  is  the  efficiency  of  a  storage  cell,  and 
how  is  it  measured  ? 

A.  The  efficiency  of  a  cell  is  the  ratio  between 
the  amount  of  power  which  can  be  taken  out  of 
it  and  that  which  is  put  into  it.  It,  like  capacity, 
varies  with  the  rate  of  discharge,  and  may  be 
anywhere  from  50  to  95  per  cent.,  according  to 
the  charge  and  discharge  rates  used.  Eighty  per 
cent,  for  the  normal  discharge-rate  of  a  cell  is  a 
good  value  except  for  the  very  largest  cells.  To 
measure  the  efficiency  the  watt-hours  put  in  dur- 
ing charge  are  measured  by  an  ammeter  and  volt- 
meter, and,  similarly,  the  watt-hours  taken  out  in 
discharge.  The  quotient  of  the  latter  by  the 
former  is  the  efficiency. 


22 


338       roper's  catechism  for 

METHOD  OF  CONNECTING  STORAGE  BATTERIES. 

Owing  to  the  fact  that  the  electro-motive  force 
of  a  cell  increases  with  charge  and  diminishes  with 
discharge,  it  is  necessary  to  have  special  arrange- 
ments by  which  a  dynamo  while  supplying  hghts 
may  charge  a  battery  of  cells,  and  by  which  the 
electro-motive  force  of  a  set  of  cells  may  be  kept 
constant  while  they  are  supplying  lamps.  The 
arrangement  for  discharge  will  be  first  described. 
Supposing  a  110-volt  system,  we  must  have  a 
number  of  cells  in  series  equal  to  \-^^  volts,  or 
about  60  cells.  When  fully  charged,  as  each  cell 
has  an  electro-motive  force  of  2.2  volts,  the  total 
electro-motive  force  of  the  60  cells  would  be  132 
volts,  a  pressure  which  would  seriously  injure  the 
lamps.  When  the  cells  are  fully  charged,  there- 
fore, a  sufficient  number  are  switched  out  of  cir- 
cuit to  bring  the  pressure  down  to  110  volts.  As 
the  cells  discharge  and  their  electro-motive  force 
falls,  these  cells  are  switched  back  into  the  circuit 
one  at  a  time,  till  at  the  end  of  the  discharge  they 
are  all  in  circuit. 

In  charging,  the  electro-motive  force  rises.  As 
it  is  desired  to  run  110-volt  lamps  and  charge  the 
cells  at  the  same  time,  we  cannot  raise  the  pres- 
sure of  the  lighting  dynamo;  so  an  auxiliary 
dynamo  or  booster  is  employed,  its  armature  being 


STEAM    ENGINEERS   AND   ELECTRICIANS. 


339 


put  in  series  with  the  cells  and  its  field  varied  by 
its  rheostat  so  as  to  give  enough  additional  volts 
for  charging  at  the  proper  rate.     The  accompany- 


ing diagram  of  connections  shows  the  arrange- 
ment. B  is  the  booster  and  R  its  rheostat.  V  is 
a  voltmeter  and  A  an  ammeter,  so  arranged  that 


340  roper's  catechism  for  i 

■i 
its  needle  stands  in  the  center  of  the  scale  when  no  '■ 
current  is  flowing  through  it,  moving  to  one  side 
for  a  charging  current  and  to  the  opposite  side  for  a 
discharge  current.  K  represents  the  main  battery 
and  H  the  switch  which  throws  the  reserve  cells 
in  and  out.  >S  is  a  double-throw  switch,  which  in 
one  position  connects  the  batteries  to  the  lamp  to 
be  supplied  with  current,  and  in  the  other  position 
connects  it  to  the  dynamo  for  charging.  E  is  sl 
switch  for  connecting  the  voltmeter,  so  as  to  give 
the  voltage  of  the  battery,  the  line,  and  the  charg- 
ing dynamo  and  booster  respectively.  0  is  an 
automatic  circuit-breaker,  which  will  operate  if 
too  great  current  is  taken  out  of  the  batteries,  and 
C  is  a  circuit-breaker  which  will  open  the  circuit 
if  the  charging  current  becomes  less  than  a  certain 
value.  This  last  is  necessary  if  a  compound- 
wound  dynamo  is  used  in  order  to  protect  the 
dynamo  from  having  a  reverse  current  sent  through 
it  from  the  battery  if  by  accident  it  was  slowed 
down  or  stopped  before  the  charging  switch  had 
been  opened. 

Several  other  arrangements  are  employed ;  but 
a  proper  understanding  of  the  one  described  above 
will  be  sufficient  to  enable  the  engineer  to  com- 
prehend the  others  without  difficulty. 


STEAM    ENGINEERS   AND    ELECTRICIANS.         341 


ELECTRIC  SIGNALS. 

Q.  Of  what  four  elements  are  most  signal 
systems  made  up  ? 

A.  Of  the  battery,  line,  the  operating  station, 
and  the  receiving  mechanism. 

Q.  What  is  the  function  of  each  element  ? 

A.  The  battery  furnishes  the  electrical  energy 
for  operating  the  signals,  and  the  line  serves  to 
transmit  this  energy.  The  operating  station,  which 
generally  consists  of  a  key,  a  switch,  or  a  push- 
button, closes  the  electrical  circuit  and  permits 
the  operating  current  to  flow.  The  receiving  sta- 
tions are  somewhat  varied  in  design.  They  may 
consist  of  a  bell  or  telegraph  sounder,  giving  the 
signals  by  sound,  or  of  a  galvanometer  or  a  shutter- 
drop,  which  conveys  the  signals  by  means  of 
sight.  Frequently  the  two  methods  of  sound  and 
sight  are  combined. 

Q.   Of  what  does  an  electric  bell  consist  ? 

A.  Of  an  electro-magnet,  to  the  armature  of 
which  is  connected  a  hammer  arranged  to  strike  a 
gong  when  the  armature  is  pulled  up  to  the  core 
of  the  magnet  by  the  passage  of  an  electric  cur- 
rent. When  current  ceases  the  magnet  loses  its 
strength  and  a  spring  pulls  the  armature  away 
from  the  core  and  also  the  hammer  from  the  gong. 


342 


roper's  catechism  for 


Q.  Into  what  classes  are  bells  divided  ? 
A.   Into  single-stroke  bells,  which  make  but  one 
stroke  each  time  that  circuit  is  closed,  and  vibrat- 
ing bells,  whose  hammer  continues  to  vibrate  as 
long  as  circuit  is  closed. 

Q.  How  is  a  single-stroke  bell 
connected  ? 

A.  As  shown  by  the  solid 
lines  in  the  cut. 

Q.  How  is  a  vibrating  bell 
connected  ? 

A.  As  shown  in  the  cut,  the 
connection  F-D  being  considered 
as  removed. 

Q.  Explain  the  complete  ac- 
tion of  the  vibrating  bell. 
A.  When  the  button  is  pressed  down,  the  cir- 
cuit being  closed,  current  will  flow  from  F  to  B, 
B  to  the  contact  point  C,  through  the  armature 
E  to  D,  from  D  through  the  magnet  coil  to  A, 
and  from  A  back  through  the  closed  push  and 
battery  to  F.  Owing  to  the  current,  the  electro- 
magnet pulls  the  armature  E  toward  itself  and 
the  hammer  strikes  the  gong  G;  but  as  soon  as 
the  armature  moves  toward  the  magnet  the  circuit 
is  opened,  because  C  no  longer  touches  E.  The 
current  therefore  stops,  and  as  the  electro- magnet 
no  longer  has  any  strength  the  armature  is  pulled 


STEAM    ENGINEERS   AND    ELECTRICIANS.         343 

away  from  it  by  the  spring  S.  This  movement, 
however,  brings  E  and  C  into  contact  again,  caus- 
ing the  whole  action  to  be  repeated,  and  this  con- 
tinues as  long  as  the  push-button  is  held  down, 
provided  the  battery  keeps  up  its  strength. 

Q.   What  three  styles  of  bells  are  there  ? 

A.  Wooden  box,  the  working  parts  of  which  are 
covered  with  wood  ;  iron  box,  when  they  are  cov- 
ered with  iron,  and  skeleton  frame,  w^hen  they  are 
not  covered  at  all. 

Q.  Show  how  you  would  connect  three  bells  to 
ring  by  one  push-button. 
t      A. 

[T  o[::jio[:{iO[] 


Q.  Show  how  to  connect  two  bells  to  be  rung 
by  either  of  two  pushes. 
'  A. 


41' 


d  od 


Q.  Show  how  you  would  connect  a  return  call 
between  two  points. 


844  roper's  catechism  for 

A. 


□O 


ill- 


d 


Q.  What  is  an  annunciator  ? 

A.  The  annunciator  in  principle  consists  of  a 
number  of  bells  mounted  together  in  a  case,  each 
operated  by  its  own  push  located  in  some  distant 
place.  In  practice,  however,  it  would  be  difficult 
to  tell  from  the  sound  of  the  bells  which  station 
was  calling,  so  the  hammers  and  gongs  are 
omitted,  and  instead  we  have  a  simple  mechanism 
operated  by  the  armature,  called  the  drop. 

Q.   Explain  the  details  of  one  form  of  drop. 

A.  It  consists  of  a  coil  whose  armature  is  an 
iron  rod  which  is  sucked  up  into  the  coil  when 
current  passes  through  it.  This  releases  a  pivoted 
needle,  which  is  hung  eccentrically  so  that  it  turns 
from  the  horizontal  to  the  vertical  position.  Each 
needle  being  numbered  or  otherwise  marked  the 
point  from  which  the  signal  was  sent  is,  of  course, 
known. 

Q.   How  are  the  needles  restored  ? 

A.  By  a  rod  carrying  little  stops,  which  when 
pushed  up  force  the  needles  back  to  their  original 
position. 


STEAM    ENGINEERS   AND    ELECTRICIANS. 


345 


Q.   What  is  an  automatic  set-back  annunciator  ? 

A.  One  in  which  this  rod  is  lifted  by  an  electro- 
magnet so  connected  that  current  flows  through  it 
when  any  push-button  is  pressed.  All  the  needles 
are  pushed  back  to  their  horizontal  position,  after 
which  the  needle  corresponding  to  the  push-button 
last  pressed  turns  to  the  vertical  position. 

Q.  Show  by  a  diagram  the  connections  for  an 
automatic  set-back  annunciator  system. 

A. 


Signal  Bell. 


Q.  How  does  the  return-call  annunciator  system 
differ  from  this  ? 

A.  By  the  addition  of  another  wire  between 
each  push-button  and  the  annunciator. 

Q.  What  is  a  fire-alarm  attachment  ? 

A.  A  device,  frequently  added  to  annunciators 
for  use  in  hotels,  which  closes  the  circuit  of  the 


346  roper's  catechism  for 

bells  in  the  rooms,  the  effect  being  the  same  as  if 
all  the  return- call  pushes  on  the  instrument  were 
pressed  simultaneously. 

Q.  How  does  a  burglar-alarm  system  differ 
from  the  ordinary  annunciator  system  ? 

A.  Burglar- alarm  systems  are  similar  to  simple 
annunciator  systems,  with  the  addition  of  a  bell 
in  an  auxiliary  circuit  which  is  closed  when  any 
of  the  drops  operate.  This  auxiliary  bell  will 
therefore  continue  to  ring  till  some  one  comes 
along  and  restores  the  drops  to  their  usual  posi- 
tion with  the  needles  horizontal.  The  push- 
buttons are  of  a  somewhat  modified  pattern  and 
are  placed  in  doors  and  window-casings,  so  that 
if  either  a  door  or  window  is  opened  the  contacts 
of  the  button  touch  each  other  and  close  the 
circuit,  causing  the  corresponding  drop  on  the 
instrument  to  operate.  Frequently  the  pushes  of 
all  the  windows  and  outside  doors  of  any  one 
room  are  connected  in  multiple  on  one  circuit,  so 
that  any  one  of  them  when  closed  operates  the 
drop  corresponding,  it  not  being  necessary  to 
have  a  drop  for  each  window  and  door,  but  only 
for  each  room. 

Q.  Why  are  watchmen's  clock  systems  used? 

A.  To  insure  that  watchmen  make  their  rounds 
at  the  time  and  in  the  order  that  they  are  expected 
to  do  so. 


STEAM    ENGINEERS    AND    ELECTRICIANS.         347 

Q.   Into  what  classes  may  they  be  divided  ? 

A.  Into  the  battery  and  magneto  systems,  ac- 
cording as  the  energy  for  actuating  the  recording 
device  is  obtained  from  a  battery  or  from  a  small 
dynamo. 

Q.  Explain  the  arrangement  and  operation  of  a 
battery  system. 

A.  This  system  is  wired  like  a  simple  annun- 
ciator system.  Its  push-buttons  are  of  such 
pattern  that  circuit  will  be  closed  in  them  only 
by  pushing  into  them  a  special  key  carried  by 
the  watchman.  The  annunciator  of  the  ordinary 
system,  with  slight  modification,  becomes  the 
watchman' s  clock,  the  signal  bell  and  self-restoring 
magnet  of  the  annunciator  being  omitted.  The 
armature  of  each  drop  is  made  to  actuate  a  little 
needle  which  punctures  a  hole  in  a  paper  recording 
dial.  This  dial  being  divided  in  spaces  corre- 
sponding to  the  hours  from  12  o'clock  to  12  o'clock, 
and  being  further  subdivided  into  spaces  corre- 
sponding to  five  minutes,  and  rotating  so  as  to  make 
one  complete  turn  in  the  12  hours,  the  position  of 
the  punctured  holes  on  the  paper  tells  at  what  time 
they  were  made  by  the  watchman.  The  dial  has 
also  a  number  of  circles  marked  on  it  correspond- 
ing to  the  number  of  stations,  and  each  needle 
pricks  its  holes  in  one  of  the  circular  spaces 
formed  by  these  rings,  so  that  a  hole  in  a  certain 


848  roper's  catechism  for 

ring  means  that  the  ke}^  has  been  put  in  the  cor- 
responding station  push-button. 

Q.  What  is  the  weak  point  of  this  system  ? 

A.  That  if  the  watchman  can  get  at  the  two 
wires  leading  to  any  station  and  can  connect  them 
together,  he  can  make  the  clock  register  as  if  he 
had  actually  gone  to  that  station. 

Q.   How  does  the  magneto  system  differ  from  it  ? 

A.  The  wiring,  and  clock  are  the  same;  but 
instead  of  the  special  push-button  to  be  operated 
by  a  key,  a  little  dynamo,  called  a  magneto,  is 
placed  at  each  station.  The  watchman  carries  a 
handle  which  he  puts  on  a  stud  connected  with 
the  shaft  of  the  dynamo  armature.  Turning  the 
handle  sends  a  current  through  the  coil  corres- 
ponding at  the  clock  and  causes  the  needle  to 
make  a  record. 

Q.  What  are  the  advantages  of  the  magneto 
system  ? 

A.  There  are  no  batteries  to  be  taken  care  of 
and  the  watchman  practically  cannot  make  a 
proper  record  without  going  to  the  station. 

Q.  What  kind  of  batteries  are  used  for  operating 
the  above  systems  ? 

A.  Some  form  of  the  zinc-carbon  sal-ammoniac 
cell. 

Q.  How  many  are  required  for  the  different 
systems  ? 


STEAM    ENGINEERS    AND    ELECTRICIANS.         349 

A.  For  single  bells  or  annunciators  with  short 
circuits,  as  in  a  dwelling-house,  three  cells  are 
usually  sufficient.  For  larger  buildings  five  or 
six  will  be  needed.  For  automatic  fire-alarms  a 
much  larger  number  is  needed,  the  exact  number 
being  stated  by  the  manufacturer,  as  a  rule.  For 
burglar- alarm  and  watch -clock  systems  six  are,  as 
a  rule,  sufficient,  and  sometimes  a  less  number 
may  be  used. 


350 


ROPER'S    CATECHISM    FOR 


THE  TELEPHONE. 

The  phenomenon  of  sound  is  caused  by  vibra- 
tions of  the  particles  of  air;  its  pitch  is  dependent 
upon  the  number  of  vibrations  per  second,  its 
loudness  on  the  wideness  of  those  vibrations,  and 
its  quality,  that  property  by  which  we  distinguish 
tones  of  the  same  pitch  and  loudness,  upon  the 
form  of  the  vibrations.     This  last  point  is  some- 


what difficult  to  understand.  Suppose  that  a 
mass  of  air  is  set  in  vibration  by  a  tuning-fork, 
and  that  we  study  the  motion  of  a  single  particle 
of  air  by  plotting  on  a  flat  surface.  Let  distances 
to  the  right  of  the  vertical  represent  time,  and 
vertical  distances  represent  the  distance  which  the 
particle  has  moved  through  at  any  time.  The 
motion  of  the  particle  would  be  represented  by  the 
wavy   line   in   the   figure.     Distances   above  the 


STEAM    ENGJNEERS   AND    ELECTRICIANS.         351 

horizontal  correspond  to  motion  in  one  direction 
from  its  position  of  rest,  and  distances  below  the* 
horizontal  represent,  similarly,  motion  in  the  oppo- 
site direction.  If  we  set  the  air  into  vibration  by 
means  of  a  bowed  violin- string,  the  shape  of  the 
wavy  line  would  be  very  much  altered,  as  in  the 
second  figure.  To  perfectl}^  reproduce  sounds  it  is 
necessary  to  reproduce  the  pitch  or  number  of 
waves  per  second  and  the  quahty  or  form  of  these 
waves,  and  sufficient  wideness  of  vibration  to 
affect  the  Hstening  ear. 

The  telephonic  transmission  of  speech  between 
two  points  may  be  best  considered  in  two  parts: 
(1)  The  transmitter,  which  produces  in  the  wires 
connecting  the  two  points  a  varying  current 
whose  curve  of  variation,  if  plotted,  has  the  same 
number  of  vibrations  per  second,  and  whose  form 
is  the  same  as  that  of  the  sound-waves  which 
strike  upon  the  diaphragm  of  the  transmitter 
mouthpiece.  (2)  The  receiver,  into  which  comes 
this  varying  current,  which  is  made  to  set  a  dia- 
phragm into  vibrations  exactly  similar  to  those  of 
the  transmitter  diaphragm.  The  receiver  dia- 
phragm, of  course,  sets  the  air  surrounding  it  into 
vibrations  similar  to  those  caused  by  the  voice 
speaking,  and  the  ear  of  the  listener  is  affected  in 
the  same  way,  though  not  so  strongly  as  if  the 
speaker  were  talking  directly  to  him. 


352  roper's  catechism  for 

Q.   Describe  the  magneto  receiver. 

A.  The  magneto  receiver  consists  of  a  bar  mag- 
net with  a  short  cylindrical  pole-piece  of  soft  iron 
on  one  end.  Mounted  on  this  pole-piece  as  an 
axis  is  a  little  wooden  spool  wound  with  fine  wire. 
In  front  of  the  spool  is  a  thin  circular  disk  of  soft 
iron. 

Q.  What  improvements  have  been  made  in  the 
receiver  ? 

A.  It  is  now  made  with  a  magnet  of  horse-shoe 
pattern,  each  pole  having  a  spool  of  wire  on  it. 

Q.  What  was  the  original  form  of  the  trans- 
mitter ? 

A.  Originally  the  same  instrument  was  used 
alternately  as  transmitter  and  receiver. 

Q.  Explain  the  operation  when  two  of  these 
receivers  are  connected  together  by  two  wires,  one 
being  spoken  into  and  the  other  serving  as  a 
receiver. 

A.  The  voice  of  the  speaker  sets  the  diaphragm 
of  the  transmitter  into  vibration.  The  motion  of 
the  iron  near  the  magnet-pole  alters  the  position 
and  density  of  the  magnetic  lines  of  force  enclosed 
by  the  coil  and  sets  up  a  varying  electro-motive 
force  in  the  coil.  This  produces  a  current  in  the 
line  with  a  variation  or  wave-form  similar  to  the 
original  sound-wave.  This  varying  current  flow- 
ing  around   the   coil   of   the   receiver  causes   the 


STEAM    ENGINEERS    AND    ELECTRICIANS.         353 

strength  of  its  pull  on  the  receiver  diaphragm  to 
vary  in  a  similar  way,  and  therefore  to  set  up  in 
the  receiver  diaphragm  vibrations  similar  to  those 
of  the  transmitter  diaphragm.  This  sets  the 
surrounding  air  into  similar  vibration.  This 
causes  the  listener's  ear  to  be  affected  just  as  if 
the  speaker  were  talking  directly  in  his  ear, 
although  not  so  loudly. 

Q.  What  form  of  transmitter  is  now  used  ? 

A.  That  which  is  known  as  the  battery  or  car- 
bon transmitter. 

Q.  Explain  how  it  differs  from  the  magneto 
transmitter. 

A.  In  the  magneto  transmitter  just  described 
the  varying  current  is  produced  by  setting  up  an 
electro-motive  force  whose  wave-form  of  variation 
is  similar  to  that  of   the  sound-wave   producing 


^ 


H' 


y^ 


CARBON   TRANSMITTER   AND  CIRCUIT. 

it.  Another  way  to  produce  the  varying  current 
is  to  use  a  constant  electro-motive  force^-  but 
employing  a  resistance  varied  by  the  sound-wave 
and  having  the  same  wave-form  of  variation.  A 
current  is  sent  through  the  circuit  consisting  of 
23 


354  roper's  catechism  for 

the  receiver,  line,  and  carbon  contact,  as  shown 
in  the  diagram.  One  of  the  carbon  pieces  is  fixed 
and  the  other  moves  with  the  diaphragm.  When 
the  latter  is  spoken  against,  its  vibrations  cause 
the  varying  pressures  on  the  contact  between  the 
two  carbon  pieces.  This  causes  the  varying  resist- 
ance, which  produces  the  varying  current  neces- 
sary to  transmit  speech. 

Q.  Do  the  present  forms  of  transmitter  consist 
of  a  single  carbon  contact  ? 

A.  No;  in  order  to  make  the  variation  of  resist- 
ance as  great  as  possible  the  number  of  contacts 
is  increased  by  having  the  circuit  pass  through  a 
number  of  small  carbon  particles  against  which 
the  diaphragm  presses. 

Q.  What  is  the  induction  coil,  and  why  is  it 
used  ? 

A.  On  long  lines  the  resistance  of  the  lines, 
which  is  fixed  in  value,  is  so  much  greater  than 
that  of  the  variable  carbon  contacts  that  the  effect 
of  the  latter  in  varying  the  total  resistance  in  cir- 
cuit is  practically  zero.  To  overcome  this  diffi- 
culty the  induction-coil  is  used.  Jt  consists  of  a 
bundle  of  fine  iron  wires  about  three  inches  long, 
and  wound  around  these  as  an  axis  is  a  coarse 
wire  coil  of  about  No.  16  wire  and  a  fine  wire 
coil  of  No.  24  or  smaller,  according  to  the  length 
of  line. 


STEAM    ENGINEEES   AND    ELECTRICIANS.         355 

Q,   How  is  the  coil  connected  ? 
I       A.  As  shown  in  the  diagram. 

11=3=^ pC=B 

IaaaaAa4  /^AA/^AAJ 


CONNECTIONS  USING   INDUCTION   COILS. 

Q.  What  are  the  methods  used  in  calUng  up  ? 

A.  By  a  battery  and  ordinary  vibrating  bell, 
called  the  battery  call,  and  by  a  magneto  and  special 
bell,  called  the  magneto  call. 

Q.  When  is  the  former  used  ? 

A.  Generally  for  distances  not  exceeding  a  few 
hundred  feet. 

Q.  On  what  two  systems  are  telephones  oper- 
ated? 

A.  On  the  intercommunicating  system  and  on 
the  exchange  system. 

Q.  What  is  the  intercommunicating  system  ? 

A.  The  intercommunicating  system  consists  of 
instruments  as  above  described,  combined  with  a 
suitable  number  of  wires  running  to  all  instru- 
ments, and  at  each  instrument  such  a  form  of 
mechanical-contact  changing  switch  as  to  enable 
each  telephone  station  to  call  up  any  particular 


356  eoper's  catechism  for 

station  without  interfering  with  any  others  who 
may  be  talking. 

Q.  What  is  the  general  scheme  of  wiring  for 
this  system? 

A.  To  each  instrument  as  many  wires  are  run 
as  there  are  telephones  in  the  system,  plus  two 
(three  in  some  systems).  These  wires  are  prefer- 
ably of  different  colors,  to  facilitate  making  proper 
connection. 

Q.  What  kind  of  a  call  is  used  ? 

A.  Either  may  be  employed,  but  the  battery 
call  is  more  common. 

Q.  What  requirement  must  a  successful  inter- 
communicating system  fulfil  ? 

A.  That  no  other  act  is  necessary  after  finishing 
conversation  than  to  hang  up  the  receiver  on  the 
hook.  Some  systems  require  that  a  lever  shall  be 
returned  to  a  certain  point  or  that  a  plug  shall  be 
put  in  a  certain  hole  in  addition  to  hanging  up 
the  receiver.     Such  systems  are  faulty. 

Q.  How  many  instruments  are  used  on  such 
systems  ? 

A.  Any  number  may  be  used,  but  it  is  rarely 
advisable  to  go  above  twelve  or  fifteen,  the 
exchange  system  being  preferable  when  a  greater 
number  is  required. 

Q.  What  is  the  general  nature  of  exchange 
systems  ? 


STEAM    ENGINEERS    AND    ELECTRICIANS.         357 

A.  In  such  systems  two  (or  sometimes  three) 
wires  run  from  each  telephone  to  a  central  point, 
at  which  an  operator  sits,  whose  duty  it  is  to  con- 
nect the  lines  of  any  two  telephones  by  means  of 
a  convenient  switchboard  and  to  disconnect  them 
when  they  have  finished  talking.  The  connections 
are  made  through  a  pair  of  flexible  cords,  called 
talking-cords,  which  are  attached  to  plug-shaped 
pieces. 

Q.   How  are  the  subscribers  called  up  ? 

A.   By  either  battery  or  magneto  call. 

Q.  What  is  the  general  method  of  operation  in 
an  exchange  system  when  one  party  wishes  to  talk 
to  another  ? 

A.  See  ''Roper's  Engineers'  Handy-Book," 
pages  771-773. 

Q.  May  any  number  of  instruments  be  con- 
nected on  an  exchange  system  ? 

A.  Yes;  the  switchboard  is  increased  as  fast  as 
the  addition  of  instruments  renders  it  necessary. 


J 


INDEX. 


Absolute  zero  of  temperature,  38 
Acceleration,  definition  of,  4 

relation    between    mass,  force, 
and,  7 
Accumulators,  electric  {see  Storage 

Batteries) . 
Air,  50 

compressors,  26 

flow  of,  27 

motors,  28 

volume  of,  at  various  tempera- 
tures, 53 
Alloys,  243 

Alternating  currents,  298 
Altitude  measured  by  barometer,  55 

by  thermometer,  55 
Ampere,  268 

Angle  of  advance  or  angular  ad- 
vance, 201 
Annunciator,  electric,  344 
Anode.  249 
Arc  lamps,  320 
Armatures  of  dynamos,  299 
Atmosphere,  52 
Atmospheric  pressure,  52 
Atomic  weights,  237 
Atoms  and  molecules,  237 
Automatic   cut-otf  and    throttling 
engines,  comparison  of,  195 

engines  {see  Engines). 

stoking  of  boilers,  165 
Axle,  the  wheel  and,  16    . 


Babcock  &  Wilcox  boilers,  84 
Barometer,  54 
Beams,  246 

uniformly  loaded,  247 
Bearings  {see  Journals). 
Bells,  electric,  341 
Belting,  20 

Belts,  calculation  of  width,  20 
Boiler  chimneys  and  stacks,  167 

compounds,  123 

flues,  160 


Boiler  furnaces,  160 

grates,  163 

materials,  98 

thickness  of,  99 

setting,  109 
Boilers,  69 

automatic  stoking  of,  165 

Babcock  &  Wilcox,  84 

care  and  management  of.  111 

Cornish,  77 

cylindrical,  75 

tire-tube,  80 

firing  of.  111 

Galloway,  80 

grate   surface  per  horse-power 
of,  95 

importance  of  correct  supply 
of  air  to,  141 

Lancashire,  79 

locomotive,  89 

marine,  87 

priming  of,  125 

rating  of,  91 

return  tubular,  83 

riveted  joints  of,  100 

scale  and  corrosion  in,  123 

tubular,  81 

water-tube,  84 
Boiling-point  of  water,  58 
Bourdon  steam  gauge,  138 
Brass,  243 
Bronze,  243 
Burglar  alarm,  346 
Bus-bars  on  electric  switchboards, 


Calorific  value  of  coals,  48 
Carbon  effect  on  strength  of  steel, 

241 
Cards,  indicator  {see  Indicators). 
Cast-iron  (see  Iron). 
Cathode,  249 

Centennial  rating  of  boilers,  92 
Centigrade  thermometer  scale,  38 
Chemical  elements,  236 


359 


360 


Chimneys.  167 

Circuit  breakers,  305 

Clutches,  friction,  24 

Coal,  45,  47 

Coke,  47 

Collapsing  pressure  of  boiler  flues, 

rule  for,  161 
Columns,  247 
Combustibles,    relative    value    of, 

48 
Combustion,  44 

heat  of,  48 
Commutators  of  dynamos,  298 
Composition  of  forces,  11 
Compound  dynamos,  30 

engines,  191,  192 
Compressed   air,   flow  of,  through 

pipes,  28 
Compression  in  engines,  225 
Compressors,  air,  26 
Condensers,  233 

injection  water  required,  234 

vacuum  of,  234 
Condensing  engines,   economy  of, 

188 
Conducting  power  of  substances  for 

heat,  42 
Conduction  of  heat,  42 
Conductivity,  electrical,  270 
Conductors,  electrical,  272,  274 
Conservation  of  energy,  10 
Convection  of  heat,  42 
Copper,  242 

alloys,  243 

wire,  electrical  table,  313,  315 
Corliss  engines,  207 
Corrosion  of  boilers,  123 
Corrugated  furnaces  and  flues,  162 
Coverings  for  steam-pipe,  42 
Current,  electric,  250,  251,  260,  275 

unit  of,  268 
Curvilinear  seams  of  boilers,  100 
Cut-off",  227 

automatic,  195,  207 

valves,  207 
Cycloid  gears,  24 

Daniell  battery,  295 
Dead  center  of  engines,  143 
Dead-weight  safety  valve,  130 
Diagrams, indicator  {see  Indicator) 
Draught  of  chimneys,  167,  171 
Ductility  of  metals,  238 
Dynamometers,  33,  36 
Dynamo  regulation,  302 


Dynamos,  297 

compound,  302 
operated  in  parallel,  307 
series,  300 
shunt,  301 


Eccentric,  steam  engine,  199 

Eccentricity,  200 

Econouieter,  141 

Economizers,  159 

Edison  3-wire  system  of  electrical 

distribution,  311 
Efficiency  of  injectors  and  pumps, 
relative,  152 
of  pneumatic  power  transmis- 
sion, 28 
Ejector,  151 

Electric  accumulator  {see   Storage 
Batteries) . 
arc  lamps,  320 
batteries,  292 
bells,  341 

circuit  breakers,  305 
conductivity,  270 
conductors,  calculation  of  sizes, 
313 
insulation  of,  274 
materials     used     {see    also 
Conductors),  274 
current,  heating  effects,  251 
distribution  of  energy,  308 
parallel  system,  309 
series  system,  309 
3-wire  system,  311 
sizes  of  conductors,  313 
dynamos,  297 
fuses,  305 

generators,  292,  297 
ground  detectors,  305 
heating,  251 
incandescent  lamps,  323 
Electric  induction  coil,  354 
lighting,  320 
motor  generators,  332 
motors,  327 

protective  devices  for,  331 
pressures  used  in  practice,  332 
resistance  (see  Eesistance). 
signals,  341 

storage  batteries,  292,  334 
switches,  303,  305,  319 
telephones,  350 
transformer,  265 
units,  267 


361 


Electric  wires,  tables  of  weights  and 
diameters,  315 

wiring,  316 
Electrical  experiments,  fundamen- 
tal, 248 

measurement,  285 

method  of  power  measurement, 
34 

transmission  of  power,  29 
Electrolysis,  248 
Electro-magnet,  262 
Electro-motive  force,  266,  267,  278 
Electro-plating,  250 
Elements,  the  six  mechanical,  1 
Energy,  conservation  of,  10 

definition  of,  8 

forms  of,  8 

sources  of,  10 
Engine,  steam  (see  Steam  engine),  175 
Exhaust,  steam  engine,  227 
Expansion  curve,  227 

Factors  of  safety,  105,  245 
Fahrenheit  thermometer  scale,  38 
Falling  bodies,  motion  of,  7,  8 
Feed-pumps  (see  Pumps). 
Feed-water,  advantages  of  heating, 
153 
heaters,  154 

advantages  of  each  type,  158 
closed  type,  155,  156 
open  type,  155,  157 
Berryman,  156 
Pittsburgh,  157 
relative  advantages  of  pumps 
and  injectors  for  supplying, 
152 
Field,  magnetic,  254 
Firing  of  boilers,  163 

automatic,  165 
Fittings,  boiler,  128 
Fleming's  rule  for  direction  of  in- 
duced electrical  currents,  260 
Flow  of  air,  28 
of  Avater,  61 
Flues  of  boilers,  160 
Foaming  of  boilers,  123 
Force,  definition  of,  1 
magnetic  lines  of,  254 
relation  between  mass,  accelera- 
tion, and,  10 
Forced  draught,  210 

representation     by    lines,    or 

graphically,  11 
resultant  of  two  or  more,  11 


Forces,  parallelogram  of,  11 

Foundations  of  engines,  213 

Fuels,  4 

Fulcrum,  14 

Furnaces  of  boilers,  160 

Fuses,  305 

Fusibility  of  metals,  238 

Galvanometer,  258 
Gauge  cocks,  141 
Gauges,  138 

vacuum,  139 

steam  pressure,  138 

water,  140 
Gearing,  23 
German  silver,  243 
Governors  for  steam  engines,  209 
Grates  for  boilers,  163 
Grate  surface  of  boilers,  95,  164 
Gravity,  specific,  239 
Ground  detectors,  305 

Hancock  inspirator,  151 
Heat,  conduction  of,  42 
definition  of,  37 
latent,  41 

mechanical  equivalent  of,  42 
of  combustion,  48 
radiation  of,  42 
specific,  4 

transference  of  methods,  42 
unit  of,  41 
Heaters,  feed-water  (see  Feed-water 

Heaters). 
Heating  due   to  electric  currents, 
251 
surface  of  boilers,  95 
Horse-power,  indicated,  229 

of  boilers  {.lee  Centennial  Rat- 
ing). 
of   steam    engines,  calculation 
of,  by  indicators,  229 
rules  for  calculating,  177 
tables  for  different  speeds 
and  pressures,  184 
Hydrogen,  51 
in  fuel,  45 
Hydrometer,  240 

Ice,  weight  of  cubic  foot,  57 
Incandescent  lamps,  323 

life  and  efficiency  of,  325 
Incrustation    and    scale   {see    Cor- 
rosion of  Boilers). 


362 


Indicated  horse-power  (see  Horse- 
power). 
Indicator  cards  or  diagrams,  226 
function  of,  225 
method  of  power  measurement, 

of  using,  226 

steam  engine,  224 

Tabor,  225 
Induction  coil,  electric,  354 

currents  of  electricity,  264 
Inertia,  2 
Injectors,  146 

action  of,  146 

failure  of,  149 

starting,  149,  150 

setting  up  of,  150 

vs.  pumps,  152 
Insulation  of  electric  wires,  274 
Insulators,  274 
Intercooler,  26 
Involute  gears,  24 
Iron,  240 

expansion  of,  due  to  heat,  242 

strength  of,  245 

variation  of   strength    due   to 
heating,  242 

wire  {see  Wire). 

electrical  tables,  315 

Jet  condensers,  233 
Joints,  riveted,  106 

Kinetic  energy,  8 

Lamps,  arc,  320 

incandescent,  323 
Lap  of  a  slide  valve,  200 
Latent  heat,  41 
Laws  of  motion,  Newton's,  3 
Lead,  243 

of  slide  valve,  200 
Leather  belts,  20 
Leclanche  battery,  294 
Lever,  safety  valve,  130 
Levers,  14 

rules  for  calculation,  15 
Lifters  or  ejectors,  151 
Lifting  ejectors  {see  Injectors). 
Lines  of  force,  254 

used  to  represent  forces ^  11 
Link  motion,  206 
Liquid  fuels,  49 
Locomotive  boilers,  87 


Longitudinal  seams,  100 
Loss  of  head  of  water  in  pipes,  62 
Low-pressure  cylinders  {see   Com- 
pound Engine). 
Lubrication,  32 

Machines,  elenients  of,  1 

purpose  of,  1 
Magnets,  electro-,  262 
Magnetic  field,  254 

lines  of  force,  254 
Malleability  of  nieials,  232 
Marine  boilers,  87 
Mass,  definition  of,  6 

relation  between  force,  accelera- 
tion, and,  7 
relation  of  weight  to,  6 
Materials  and  their  properties,  236 

strength  of,  244 
Mean    eflTective   pressure    obtained 
from    the    indicator, 
card,  229 
of  steam  engines,  181, 
229 
Measurement  of  heights  by  barom- 
eter, 55 
by  thermometer,  55 
Mechanical  elements,  1 
equivalent  of  heat,  42 
firing  of  boilers,  165 
Mechanics,  1 
Metals,  240 

principal  properties  of,  238 
Methods  of  transmitting  power,  18 
Mil,  circular,  316 
Moisture  in  steam,  64,  65 
Molecules  and  molecular  construc- 
tion of  matter,  23 
Moment,  13 

Momentum,  definition  of,  7 
Motion,  3 

Newton's  laws  of,  3 
of  falling  bodies,  5 
perpetual,  4 
Motors,     electric    {see    Electric 
Motors). 

Newton's  laws  of  motion,  3 
Nitrogen,  45,  51,  236 
Non-condensing  engine,  188 
Non-conducting  covering  for  steam- 
pipes,  43 
Non-conductors,  274 

Ohm's  law  and  its  applications,  280 


363 


Oil  separators,  32 

used  as  a  fuel,  49 
Oils  aud  lubrication,  32 
Ordiuates,  230 

Over-compounded  dynamos,  301 
Over-travel  of  a  valve,  200 
Oxygen,  45,  51,  236 

Packing  for  steam  engines,  217 
Parallel   system  of  electrical   dis- 

tributiou,  308 
Parallelogram  of  forces,  11 
Perpetual  motion,  4 
Petroleum  as  a  fuel,  49 
Pipe  coverings,  materials  for,  43 
Pipes,  flow  of  air  in,  28 
of  water  in ,  62 
Piping  of  engines,  216 
Piston  valves,  207 
Pitch  of  gears,  23 
Planimeter  and  its  use,  229 
Pneumatic  transmission  of  power, 

25 
Ports  or  passages,  steam,  197 
Potential  energy,  8 
Power,  definition  of,  10 

horse-power    {see    also   Horse- 
power), 10 
measurement,  33 
of  steam  engines,    calculation 
of,  177 
tables  of,  184 
transmission  by  gearing,  23 
by  ropes,  22 
by  shafting,  18 
electrical,  29 
methods  of,  18 
pneumatic,  25 
Pressure,  electric,  266,  267,  278 

mean  effective,  181,  229 
Priming  of  boilers,  123 
Prony  brake,  35 

PuUev,   as  a  mechanical  element, 
'16 
rule    for   calculating    gain    in 
force,  17 
Pumps,  142 

boiler- feed,  143 
capacity  of,  145 
classification  of,  142 
direct-acting,  143 
duplex,  144 
electric,  143 
fly-wheel,  143 
for  hot  water,  146 


Pumps,  lift  of,  144 

power,  142 

power  required  by,  145 

vs.  injectoi's,  152 
Purifying  feed-water,  153 

Kadiation  of  heat,  42 
Reaumur  thermometer  scale,  38 
Keceivers,  compressed  air,  27 

electric  telephone,  352 
Reciprocating  parts  of  steam  en- 
gines, 195 
Release,  200 

Releasing  valve  gear,  207 
Reservoirs  for  compressed  air,  27 
Resistance,  change  with  change  of 
temperature,  270 

electric,  251,  270 

specific,  272 
Resistances  in  multiple,  271 
Reversing  valve-gears,  206 
Riveted  joints  of  boilers,  106 
Rope-driving,  22 
Rubber  belting,  20 
Rust,  51 

Safe  current-carrying  capacity  of 

copper  wires,  318 
Safety,  factors  of,  105,  245 

valves,  128 
Salinometer,  141 
Scale  in  boilers,  123 
Screw  as  a  mechanical  element,  1 
Seams,  curvilinear,  100 

longitudinal,  100 
Separators,  171 
Series  dynamos,  300 

system   of   electrical  distribu- 
tion, 308 
Setting  boilers,  109 
Shaft-governors,  211 
Shafting  calculation  of  sizes,  19 
Shunt  dynamos,  300 
Slide  valves,  197 

Smoke-stack  {see  Stacks  and  Chim- 
neys). 
Specific  gravity,  60,  239 

heat,  4 

resistance,  272 
Stacks  for  boilers,  167 

proportioning  of,  168 

table  of  sizes  for  various  sizes 
of  boiler,  170 
Steam,  64 


364 


steam  boilers  {see  Boilers), 
dry  {see  also  Separators),  65 
engine,  175 

advantages  of  high  speed, 

194 
brake,  horse-power  of,  177 
care  and  management  of, 

217 
classification  of,  188 
compound,  191 
condensing    and   non-con- 
densing, 188 
Corliss,  207 
cut-offs,  207 
foundations,  213 
governors,  209 
high-  and  low-speed,  194 
indicated    horse-power  of, 
177,  229 
tables  of,  at   different 
piston  speeds,  184 
indicator    {see    also    Indi- 
cator), 224 
invention  of,  175 
knocking  in,  221 
lining  up,  214 
location  of,  214 
mean  effective  pressure  of, 

181,  229 
piping  for,  216 
reciprocating  parts  of,  195 
rotary,  196 
setting  valves  of,  205 
single-acting,  196 

and  double-acting,  196 
and     multiple    expan- 
sion, 192 
throttling    and    automatic 

cut-off,  195 
valves  and  valve-gears,  197 
latent  heat  of,  66 
moisture  in,  64 
pipe-covering,  43 
piping  for  engines,  216 
saturated,  45 
separators,  171 
superheated,  45 
total  heat  of,  67 
traps,  171 
Steel,  241 

Stoking,  automatic,  166 
Storage  batteries,  292,  334 
Strength  of  materials,  244 
String  of  indicator  diagram,  230 
Surface  condensers,  233 


Switchboards,  electric,  304 
Switches,  electric,  303 

Tabor  indicator,  225 

Teeth,  gear  teeth  forms,  23 

Telephone,  350 

Temperature,  definition  of,  38 

Tenacity  of  metals,  238 

Tensile  strength,  244 

Theoretical  indicator  diagram,  227 

Thermal  unit,  44 

Thermometers,  38 

Three-wire  system  of  electric  dis- 
tribution, 311 

Throttling  and  automatic  cut-off 
engines,  195 

Throw  of  eccentrics,  200 

Timber,  strength  of,  245 

Time  systems,  watchmen's,  346 

Total  heat,  67 

Transference  of  heat,  42 

Transformers,  265 

Transmitter,  electric  telephone,  353 

Transmission  of  power  {see  Power). 

Travel,  200 

Traps,  steam,  171 

Tubular  boilers  {see  Boilers). 

Unit  of  heat,  41 

of  work,  8 
Units,  electric,  267 

Vacuum  of  condensers,  234 

gauges,  139 
Valve  circle,  202 

gears  {see  also  Cut-off),  197 
releasing,  207 
reversing,  205 
the  link  motion,  205 
variable  cut-off  and  revers- 
ing, 205 
Zeuner's  diagram  for,  202 
Valves  and  valve-gears,  197 
balanced,  207 
different  varieties  of,  207 
friction  of,  206 
how  to  set,  205 
lap  and  lead  of,  200 
piston,  207 
plain  slide,  197 
safety,  128 
semi-rotary,  207 
separate,  for  admission  and  ex- 
haust, 207 
setting  of,  205 


365 


Velocity,  4 
Volt,  the,  267 

Watchmen's  time  systems,  34 
Water,  boiling  point  of,  58 
columns,  140 
composition     and     properties, 

56 
decomposition  of,  59 
flow  of,  61 
specific  gravity  of,  59 

heat  of,  58 
weight  of,  at  diflferent  tempera- 
tures, 56 
Wedge,  the,  16 
Weights,  atomic,  237 


Wheel  and  axle,  the,  16 
Wire  calculation  of  sizes  for  electric 
distribution,  313 
electric,  tables  of  weights  and 

diameters,  315 
properties  of  copper,  315 
safe-current  carrying  capacity 
of,  313 
Wiring,  electric,  316 
Work,  definition  of,  8 

unit  of,  8 
Wrought-iron  {see  Iron). 

Zero,  absolute,  38 

Zeuner's  diagram  for  valves,  202 


Ll.Ai'St?