In engines which work without condensation, and therefore with high pressure steam, we shall have

= 618 c = 0.05

e + 0.05

To facilitate computation, the values of e' corresponding to all values of e, from e10 to e='90, are given in the following

:

In engines which work without expansion we have

a

e = 1 + c

For condensing engines without expansion, we shall then have

As the diameters of the cylinders of engines are generally expressed in inches, the corresponding areas of the pistons expressed in square feet are given in the following table, so that the values of A may be readily found:

The practical application of the preceding formula will be shown by the following examples.

EXAMPLES.

1. A 36-inch cylinder with 5 feet stroke is supplied by a boiler evaporating effectively 60 cubic feet of water per hour, and the piston makes 20 strokes per minute without expansion; — what is the power of the engine and the pressure of steam in the cylinder?

Let it be assumed that r = 6 × 144 = 864 and m = 0·1. Since the engine is a condensing engine, we have b=164 and e'=3691399. By the formulæ (25.) and (26.) we have

We'-VA (b + r)
H = 33000 (1 + m)

and since by the data we have

W = 1 A = 7.069 V= 2n L = 40 × 5·5 = 220,

the formula, by these substitutions, becomes

Since e = 1, the pressure P of steam in the cylinder, by (18.), is

which being the pressure in pounds per square foot, the pressure per square inch will be 15 lbs.

2. To find the effective evaporation necessary to produce a power of 80 horses with the same engine. Also, find the pressure of steam in the cylinder, the speed of the piston being the same.

By the formula (32.), with the above substitutions, we have
33000 × 80 × 1·1 + 220 × 7·069 × 1028
3691399

W=

= 1.22.

The evaporating power would therefore be only increased 22 per cent., while the working power of the engine would be increased nearly 40 per cent.

The pressure P in the cylinder will be given, by (18.), as before. 1.22 3691399 2732;

P

=

1555.18

· 164 =

inch.

which is equivalent to 19 lbs. per square

3. What must be the diameter of a cylinder to work with a power of a hundred horses, supplied by a boiler evaporating effectively 70 cubic feet of water per hour, the mean speed of the piston being 240 feet per minute, and the steam being cut off at half stroke? Also, what will be the full pressure of steam on the piston?

Taking, as in the former examples, m = 0·1, b = 164, and r=864, we shall have

W=11 V=240,

and by the column for condensing engines, in table, p. 519, we have e' = = 6029916, where e = 0.50. Making these substitutions in

We': =

we shall have

33000 H (1 + m) + VA (b + r),

1 × 60299163300000 × 1·1 + 240 × 1028 × A. Whence we find

A = 13.8;

and by the table, p. 520, the corresponding diameter of the cylinder will be 50 inches.

If P' be the full pressure of the steam, we shall have, by (18.),

which being in pounds per square foot, the pressure per square inch will be 161% lbs.

INDEX.

Air, elasticity of, 28. May be partially expelled from a vessel by the
application of heat, 44.
America, steam navigation first established in, 487. Circumstances
which led to it, 488. Fitch and Rumsey, their attempts to apply
the single-acting engine to the propulsion of vessels, 489. Stevens
of Hoboken commences experiments on steam navigation, 489.
Experiments of Livingstone and Fulton, 489. Fulton's first boat,
490. The Hudson navigated by steam, 491. Extension and im-
provement of river navigation, 492. American steamers, 494. Dif-
ference between them and European steamers, 494. Steamers on
the Hudson, 494. American paddle-wheels, 495. Sea-going Ame-
rican steamers, 496. Speed attained by American steamers, 497.
Lake steamers, 499. The Mississippi and its tributaries, 499.
Steam-boats navigating it, 500. Their structure and machinery,
500. New Orleans Harbour, 503. Steam tugs, 503.
Atmosphere, 38. Weight of, 39.

Atmospheric air, mechanical properties of, 38. Composition of, 253.
Atmospheric engine, Thomas Newcomen the reputed inventor of, 62.
Description of, as first constructed by Newcomen, 67. The opera-
tion of considered, 69. Not unfrequently used in preference to the
modern steam engine, 72. Advantages which it possessed over Sa-
very's, 73. Considerably improved by Beighton, 75. John Smeaton
investigates this machine, 76. Brindley obtains a patent for im-
provements in, 76. Applied by Champion of Bristol to raise water,
181. Possessed but limited power of adaptation to a varying load,
151. Expedient to remedy this, 151. Working-beam, cylinder, and
piston applied to by Newcomen, 322.
Atmospheric pressure rendered available as a mechanic agent by Denis
Papin, 38. Means of measuring the force of, 39. The idea of
using against a vacuum or partial vacuum to work a piston in a cylin-
der, suggested by Otto Guericke, 73.

Barometer gauge, 272.

Barton's piston, 248.

Beighton, his improvement of the atmospheric engine, 75.

Black, Dr., his doctrine of latent heat, 93.

Blasco de Garay, his contrivance to propel vessels, 16. The contrivance

of, probably identical with that of Hero, 17.

Blinkensop, his locomotive engine, 337.

Blowing-box, 429.

Blowing out, Seaward's method of, 454.
Blow-off cocks, 452.