. The Locomotive . surethat can be exerted on the water willbe lbs. per square inch. By thenature of the arrangement the pressurewill always be constant at lbs. persquare inch and cannot change as longas the piston is within the cylinder will assume further that we havesome means of supplying heat to thewater as indicated in the sketch. If westart with the water at the tempera-ture of 32° Fahrenheit and add heat to it the water will increasevery slightly in volume but will still remain a liquid until the tempera-ture of 212° is reached. At this point, if we continue to supply he
. The Locomotive . surethat can be exerted on the water willbe lbs. per square inch. By thenature of the arrangement the pressurewill always be constant at lbs. persquare inch and cannot change as longas the piston is within the cylinder will assume further that we havesome means of supplying heat to thewater as indicated in the sketch. If westart with the water at the tempera-ture of 32° Fahrenheit and add heat to it the water will increasevery slightly in volume but will still remain a liquid until the tempera-ture of 212° is reached. At this point, if we continue to supply heat,the temperature will remain constant at 212° and the water will beginto change from a liquid to a vapor. It will continue to follow thischange with a very rapid increase of volume at a constant temperatureuntil the water is all vaporized. When and just when the vaporizationis complete the volume occupied by the vapor will be cubic course, to do this, our apparatus would necessarily have to be of. F[(_ 112 THE LOCOMOTIVE. [October, somewhat different proportions than indicated in the sketch. Wewill now have in our cyHnder one pound of dry saturated vapor. Wewill have in that space occupied by the vapor a definite number ofmolecules or particles of extremely minute size although we shall notattempt to state the number. If we continue to add heat to the vapor it will continue to in-crease in volume and it now also will undergo a temperature is no longer dry saturated steam but superheated steam andif we raise the temperature of it to 262° F. it will be 50° higher thanwhen it was dry saturated and we would speak of it as being steam at lbs. and 50° superheat. Since the total number ofmolecules has not changed but the volume has increased it neces-sarily must be each cubic inch of the superheated vapor con-tains a smaller number of molecules than did a cubic inch of thesaturated steam. If now we cool the steam it will return to th
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