CHAPTER I.

PROPERTIES OF STEAM.

First Cause.-Heat.-Effects.-Solids.-Liquids.—Gases.— Thermometer-Table of Properties of Bodies.-Table of Expansion of Water by Heat.-Barometer.-Steam Guage. -Tables of Elastic Force of Steam.-Rules for Calculating the same. Salt, or Sea Water.-Analysis.-Salinometer. -Motion of Steam.-Table of Motion.-Expressions of Force of Steam.-Rules for Calculating.-Velocity of Steam.--Bent Pipes.-Table of Properties of Steam.Loss by Cooling.

1. THE first subject of inquiry is that of heat, the agent used in the production of steam.

2. The natural and perceptible effect of heat when applied to different substances tends, in some, to expand and dilate their bulk to the altering their form and appearance; in others, entirely to dissolve and separate their component parts or atoms. Its action on metals is evidence of the former, and its operation on liquids an example of the latter process.

3. Of the actual nature of heat we may be said to know nothing, further than what is evident to the senses, by its action on the body, or its visible effects on matter: it would be vain, therefore, to waste time in wild conjecture or idle speculation, when it is in our power to note its action upon substances presented to its operation, and by this means establish such rules as may be useful in the following inquiries.

4. On the application of heat, the expansion and contraction of solids are various as their respective nature or qualities; but

the same material will expand and contract in all cases alike; regard being had that the bulk and temperature are the same.

5. The case, however, with liquids is widely different, hardly any two expanding alike, or even expanding in any equal degree, for an equal increase of heat at different temperatures. The expansion is less rapid, the nearer it approaches the point at which it congeals, and more rapid as it nears its boiling point.

6. In elastic fluids the case is again different; whether gases or vapours are subject to its action, a change of temperature causing an equal and uniform expansion, which expansion is the same in all.

7. To the study and knowledge of the above well-established facts, does that beautiful and useful little instrument the thermometer, or heat measure, owe its existence; but as its construction and use are now so generally understood, we may be spared the repetition of its description.

8. To assist us further in our subject, we will here subjoin the result of many experiments made by those who have devoted much time and ability towards their compilation, and on whose accuracy we may rely.

TABLE I.-Containing some of the Properties of various

10. Thus having some certain data with regard to solids, we here insert a table of the expansion of water by heat.

TABLE II.-Showing the Expansion of Water by Heat.

12. Before taking into consideration the elastic force of steam and the rules for calculating the same, it will be well to explain the means used for practically measuring it, and the reason for using such means.

13. If a glass tube closed at one end, and rather more than 30 inches long be filled with mercury, and then inverted into a vessel containing mercury, so that only about 28 inches of the tube may be above the surface of the mercury in the vessel, the mercury in the tube will remain suspended; if the tube, however, be gradually raised in a vertical direction until more than 30 inches are above the level of the surface in the vessel, the mercury will descend in the tube until it shall be just 30

inches above the level in the vessel.

14. The mercury will not always, however, remain stationary at 30 inches, but will vary its height according as the atmosphere is lighter or heavier; or according to the relative position the surface of the mercury in the vessel bears to the level of the sea, where the mean pressure of the atmosphere will support a column of mercury of 30 inches in height. The pressure of this column on a base of one square inch, will equal the

weight of 30 cubic inches of mercury, which weigh just 15 lbs.; which is the pressure of the atmosphere upon a square inch of surface.

15. This fact being established, it remains to show how it is to be applied to measuring the elastic force of steam.

16. A tube is provided, which is bent up like an inverted syphon, or in the shape of the letter U, and the bent part filled up to a certain level with mercury; if one end of this be attached to the vessel in which the steam is generated, and the other end open to the atmosphere, when the steam exerts a pressure on the surface of the mercury (in the leg of the syphon to which it has access) greater than the atmospheric pressure, the surface in the other leg will rise in proportion, and the difference of level between the two will be the measure of the excess of steam over the atmospheric pressure.

17. The following table will show the elastic force of steam at various degrees of temperature-the result of minute and careful inquiry. The names of the experimentors and the re sults obtained being placed in juxta-position, for the purpose of comparison.