Pressure.*

Horse-power corresponding to piston-speed (in feet per minute) of

10

20

30

40

50

60

70

80

90

100

200

300

400

10 ....................

.0005

.0010

.0015

.0020

.0025

.0030

.0035

.0040

.0045

.0050

.0099

.0149

.0199

15

.001

.003

.004

.005

.007

.008

.010

.011

.012

.014

.027

.041

.055

20.......................

.002

.004

.007

.009

.011

.013

.016

.018

.020

.022

.045

.067

.089

25...............................................

.003

.006

.009

.012

.015

.019

.022

.025

.028

.031

.062

.093

.124

30..............................................

.004

.008

.012

.016

.020

.024

.028

.032

.036

.040

.079

.119

.158

35.......................

.005

.010

.015

.019

.024

.029

.034

.039

.044

.048

.097

.145

.194

40.......................

.006

.011

.017

.023

.029

.034

.040

.046

.051

.057

.114

.171

.228

45......................

.007

013

.020

.026

.033

.039

.046

.053

.059

.066

.131

.197

.263

50......................

.0074

.015

.022

.030

037

.045

.052

.059

.067

.074

.148

.223

.297

55.............................................

.008

.017

.025

.033

.042

.050

.058

.067

.075

.083

.166

.250

.333

60.......................

.009

.018

.028

.037

.046

.055

.064

.073

.083

.092

.184

.275

.367

65......................

.010

.020

.030

.040

.150

.060

.070

.080

.090

.100

.201

.301

.402

80......................

.011

.022

.033

.044

.055

.065

.076

.087

.098

.109

.218

.327

.436

75.......................

.012

.024

.035

.047

.059

.071

.083

.094

.106

.118

.236

.354

.472

80.......................

.013

.025

.038

.051

.063

.076

.089

.101

.114

.127

.253

.380

.506

85......................

.0135

.027

.041

.054

.068

.081

.095

.108

.122

.135

.270

.406

.541

90.....................

.014

.029

.043

.058

.072

.086

.101

.115

.129

.144

.288

.432

.575

95

.015

.031

.046

.061

.076

.092

.107

.122

.137

.153

.306

.458

.611

100.......................

.016

.032

.048

.065

.081

.098

.113

.129

.145

.161

.323

.484

.645

105............................................

.017

.031

.051

.068

.085

.102

.119

.136

.153

.170

.340

.510

.680

110.......................

.018

.036

.054

.071

.089

.107

.125

.143

.161

.179

.357

.536

.715

115............................................

.019

.038

.055

.074

.093

.112

.130

.149

.168

.187

.373

.560

.746

120.......................

.0196

.039

.059

.078

.098

.118

.137

.157

.177

.196

.392

.588

.785

125............................................

.020

.041

.061

.0S2

.102

.123

.143

.164

.184

.205

.410

.614

.819

130................................

.021

.043

.064

.085

.107

.128

.149

.171

.192

.213

.427

.640

.854

135............................................

.022

044

.067

.089

.111

.133

.156

.178

.200

.222

.445

.667

.889

140 ..........................................

.023

.046

.069

.092

.115

.139

.162

.185

.208

.231

.462

.693

.924

145.......................................

.024

.048

.072

.096

.120

.144

.168

.192

.216

.240

.479

.719

.958

150....

.025

.050

.074

.099

.124

.149

.174

.199

.223

.248

.496

.745

.993

*In boiler, by gauge.

II-Diameter in inches of cylinder required for a given horsepower, piston-speed, and boiler-pressure. (1) Find in the table the number nearest to the given piston-speed and steam-pressure. (2) Multiply the number obtained in (1) by 0.7854. (3) Divide the given horse-power by the quantity obtained in (2). (4) Take the square root of the quantity obtained in (3).

Example.-What should be the diameter of cylinder of an engine developing 2 horse-power, with a piston-speed of 150 feet a minute, and a boiler-pressure of 100 pounds per square inch? (1) The number from the table is the sum of 0.161 and 0.081, or 0.242. (2) The product of 0.242 and 0.7854 is 0.1900668. (3) The quotient of 2 divided by 0.1900668, is about 10.5226 (4) The square root of 10.5226 is 3.24+, or about 3 1/4 inches, the required diameter of cylinder.

III.-The number of pounds of water required to be evaporated per hour for each horse-power exerted, and for various boiler-pressures, map be approximately estimated from the accompanying table.

Pressure of steam in boiler by gauge.

Pounds of water per effective horse-power per hour.

10..........

..........118

15..........

..........111

20..........

..........105

25..........

.........100

30..........

.......... 93

40.........

.......... 84

50..........

.......... 79

Pressure of steam in boiler by gauge.

Pounds of water per effective horse-power per hour,

60.........

............75

70.........

............71

80.........

............68

90.........

............65

100.........

............68

120..........

...........61

150.........

............58

It is convenient, in calculations of the amount of water evaporated at various pressures and from various temperatures of feed, to reduce them to a common standard, namely, the equivalent amounts that would be changed into steam of atmospheric pressure, if the temperature of feed was 212 Fahrenheit ; or, as it is commonly called, to evaporation "from and at 212." Two tables are appended, for the purpose of facilitating t his red action,

The second table is taken from Professor Rankine's "Treatise on the Steam Engine."