SPECIAL TYPES OF ENGINES
In describing various special types of motors, attention is first directed to that class which depend on the development of heat in various gases, and this also necessitates some explanation of ice-making machinery, and the principles underlying refrigeration.
It is not an anomaly to say that to make ice requires heat. Ice and boiling water represent merely the opposites of a certain scale in the condition of matter, just as we speak of light and darkness, up and down, and like expressions.
We are apt to think zero weather is very cold. Freezing weather is a temperature of 32 degrees. At the poles 70 degrees below have been recorded. In interstellar space,—that is, the region between the planets, it is assumed that the temperature is about 513 degrees Fahrenheit, below zero, called absolute zero.
The highest heat which we are able to produce artificially, is about 10,000 degrees by means of the electric arc. We thus have a range of over 10,500 degrees of heat, but it is well known that heat extends over a much higher range.
Assuming, however, that the figures given represent the limit, it will be seen that the difference between ice and boiling water, namely, 180 degrees, is a very small range compared with the temperatures referred to.
In order to effect this change power is necessary, and power requires a motor of some kind. Hence it is, that to make a lower temperature, a higher degree of heat is necessary, and in the transit between a high and a low temperature, there is considerable loss in this respect, as in every other phase of power mechanism, as has been pointed out in a previous chapter.
In order that we may clearly understand the phenomena of heat and cold, let us take a receiver which holds a cubic foot of gas or liquid, and exhaust all the air from it so the vacuum will be equivalent to the atmospheric pressure, namely, 14.7 pounds per square inch.