PART IX.

HEAT AND THE STEAM ENGINE.

SECTION I.-RULES RELATING TO THE MECHANICAL ACTION OF HEAT, ESPECIALLY THROUGH STEAM.

1. Thermodynamics. As to measures of temperature, and of quantities of heat, see pages 105, 106.

RULE I. To find the quantity of heat required to produce a given rise of temperature in a given weight of a given substance; multiply together the rise of temperature, the weight, and the specific heat of the substance. (See Table, pages 278, 279.)

RULE II.-To convert quantities of heat into equivalent quantities of work:

British Fahrenheit-units into foot-lbs.,
British Centigrade-units into foot-lbs.,
French units into kilogrammetres,

British units of evaporation into foot-lbs.,

745,800;

French units of evaporation into kilogrammetres, 227,300. The first three numbers are values of the dynamical equivalent of heat, often called "Joule's Equivalent," and denoted by J. RULE III.-To convert temperatures on the ordinary scales into absolute temperatures. (See page 105):

In Fahrenheit's degrees,.........add 461°2
In Centigrade degrees,..

In Réaumur's degrees,.

29 274 0

Absolute temperature of melting ice,......493°2 274° 219°2 Atmospheric boiling point of water,......6732 374

(See Table, pages 280, 281, 282.)

299 2

RULE IV. To find the efficiency of a perfect heat engine, working between given limits of temperature; divide the difference or range between the limits of temperature, by the higher limit of absolute temperature.

REMARK. The efficiency thus found is never fully realized by any actual heat-engine, but is approximated to in the course of improvement.

TABLE OF WEIGHT, VOLUME, ELASTICITY, EXPANSION, AND SPECIFIC HEAT.

EXPLANATION OF SYMBOLS.

Po-Mean pressure of the atmosphere, in lbs. avoirdupois on the square foot, = 2116.3.

Do-Heaviness, or weight of one cubic foot of the substance, in lbs. avoirdupois, under the pressure of one atmosphere, and
at the temperature of melting ice, except for water, for which the temperature is 39°1 Fahrenheit.

Vo-Volume in cubic feet of one pound avoirdupois of the substance, at the before-mentioned pressure and temperature.
S.G.-Specific gravity, that of water being taken as unity.

E.-Expansion of unity of volume for fluids, or unity of length for solids, at the temperature of melting ice, in rising to the
temperature of water boiling under the pressure of one atmosphere.

C.-Specific heat, that of water being taken as unity.
K.-Specific heat in foot-pounds per degree of Fahrenheit.

are distinguished by the symbols Cu, Cp, or Kv, Kp, as the case may be.

For gases, specific heats at constant volume and constant pressure

C,

K,

Cp

K,

Air,.

0'080728

12.387

26214

*365

0169 130°3

0.238

183'45

Oxygen,..

0'089256

II.204

23710

*367

0*156 120*2

0.218

168.3

Hydrogen,.

Q'005592

178.83

378819

*366

2'410 1860.6

3*405 2628.7

Steam,

0*05022**

19'913**

42141*

*365* 0.37°

286.

0*480

371'

Ether Vapour,..............

0*2093

4'777**

ΙΟΙΙΟ*

...

...

...

0'481

3713

Bisulph. Carbon,...

0.2137*

4.679*

9902*

...

...

O'1575

121.6

Carb. Acid, ideal,...

0*12259*

8.157*

17264*

*365*

...

Do., actual,........

O'12344

Olefiant Gas,........

0'0795

12:58

...

...

...

...

...

0.217
0.309

167.
284'9

...

Coal Gas,...{to...

from

Do., Average,

Nitrogen,..

Vapour of Mercury,

* This mark is affixed to results computed for the ideal condition of perfect gas.

12.753 1*7762*

TABLE OF THE ELASTICITY OF A PERFECT GAS.

EXPLANATION OF SYMBOLS.

T.-Temperature, measured from the ordinary zero.

t.-Absolute temperature, measured from the absolute zero. P.-Pressure of a perfect gas in pounds avoirdupois on the square

foot.

V.-Volume of one pound avoirdupois in cubic feet.

PV.-Product of these quantities at any given temperature.
PV-Value of that product for the temperature of melting ice.