9. What are the inherent qualities of steam? Elasticity, Expansibility, and Latent or Concealed Heat.

10. What is meant by elasticity?

Elasticity of steam is the power which it has in itself of returning to its original form, after being made to deviate by some external force; the force which it exerts in endeavouring to recover its position being the measure of its elasticity.

11. How is the amount of elastic force of steam obtained by calculation?

Rule: To the indicated temperature of the steam in degrees of Fah. add 100, multiply the sum by .00564, and the sixth power of the product equal the force in inches of mercury; which, being multiplied by 491, equal pounds per square inch elastic force.

Suppose the temperature of steam 262° Fah. 262° + 100× ·00564=2.0416866 = 74 inches of mercury; and 74x-491-36.3 lbs. elastic force.

12. What is expansibility?

Expansibility is the amount of force that steam is capable of exerting, by the recession of its

particles from one another, so that it occupies a greater space, while its weight remains the same: commonly termed expansive force.

13. How are the properties of steam by expansion estimated?

Steam of any given density expanded to double its volume exerts then half its original force; if expanded to three volumes, it will then exert one-third its original force; if expanded to four volumes, is then capable of exerting one-fourth its original force, &c., in an inverse ratio with expansion; hence the following rule relative to the steam-engine:-As the whole distance passed through by the piston, both before and after expansion, is to that portion passed through previous to the steam being cut off, so is the pressure of the dense steam to the pressure after expansion.

Suppose steam at 20 pounds, or 5 pounds above the atmospheric pressure, and cut off at 15 inches of the stroke, what force will the steam exert when expanded to 60 inches?

60:15:20:5 lbs.; or

15x20

= 5 lbs.

60

14. What is latent heat?

Latent or concealed heat, occasionally designated "heat of fluidity," is an excess of caloric or heat in steam, that is not discoverable otherwise than by a measurable amount of practical effect; and by such means it has been satisfactorily proved that the total amount of latent and indicated caloric in steam of water at all temperatures is a constant sum, viz. 1212° Fah., the -latent heat at 212°, or boiling point, being 1000°, or very nearly so. Water at the boiling point, or 212° Fah., requires about 5 times the quantity of heat to convert it to a state of steam as it did to raise it from 32° to the boiling point; and then the temperature, as indicated by a thermometer, is not elevated by the excess of caloric, but remains an equal quantity, viz. 212°.

15. Are all waters equally efficacious to the production of steam?

No; from sea-water; or other waters holding salts similarly in solution, by which the gravity is increased, steam is not produced of an equal elasticity at an equal degree of temperature, because fresh water boils at 212° Fah., whereas

sea-water, equally circumstanced, does not boil. until raised to a temperature of 213.2°. From a saturated solution of sea-water at a temperature of 212° Fah., the force of vapour produced is only about 11.37 pounds per square inch elastic force; whereas the vapour from fresh water at an equal temperature is 14.7 pounds; and, under similar circumstances, sea-water at 220°, the force of vapour equal 13.25 pounds; whereas from fresh water at 220°, the force of vapour equal about 17.5 pounds per square inch.

16. How is the increased gravity or saltness of the water to be ascertained?

It may be ascertained by means of an hydrometer properly graduated into twelve divisions or degrees, the point of least buoyancy or greatest immersion being in that of fresh water, and the other point, or greatest buoyancy and least immersion, in that of water containing 3ds its weight of salt, the water then being in a state of saturated solution. All sea-waters do not hold in solution equal degrees of saline matter, the water as tested in one locality being in excess to that

of another, as the following-that of the British

17. What is the difference of the temperatures relative to the production of steam at equal densities, from those of fresh and sea-waters individually?

Sea-water naturally holds in solution 3d its weight of salt, which becomes gradually augmented by evaporation; each grade as approaching to saturation requiring a higher degree of temperature in attaining the boiling point;—thus, at 3ds of saturation, the boiling point is 214.4° Fah.; at ds it is 215.5°; and at 3ds, beyond which grade of saturation the water in a steam or marine boiler ought never be allowed to exceed, the