P of water

Table II. Vapour Pressure (p) of Water at Various Temperatures (t). ...

When the partial pressure p of water vapor in the air at a given temperature equals the vapor pressure of water p, at the same temperature, the air is saturated and the absolute humidity is designated the saturation humidity H,. 

The s.v.p. is not an applied pressure, so its magnitude is generally quite low. The s.v.p. of water will certainly be lower than atmospheric pressure. The s.v.p. increases with temperature until, at the boiling temperature, it equals the atmospheric pressure. One definition of boiling says that the s.v.p. equals the applied pressure. 

For liquid water and for aqueous solutions we wiU assume Cp = 1 cal/g K, and, since the density p of water is -1 g/cm, we have pCp = 1 cal/cm K or pCp =1000 cal/Uter K. To estimate the heat capacity of gases, we will usually assume that the molar heat capacity Cp is j R cal/mole K. There are thus three types of heat capacity, the heat capacity per unit mass Cp, the heat capacity per unit volume pCp, and the heat capacity per mole Cp. However, we will use heat capacity per unit volume for much of the next two chapters, and we use the symbol pCp for most of the equations. 

Fig. 2.16 Partial pressure p of water vapor that can be pumped with the gas ballast valve open without condensation in the pump, as a function of the pump temperature for various partial pressures Pi of air. The lowest curve corresponds to the water vapor...

G. Gore, in his early work, showed that the presence of hydrogen fluoride in water lowered its f.p. E. Paterno and A. Peratoner11 measured the depression of the f.p. of water by soln. containing from 0057 to 2"80 mol. per litre and W. Ostwald showed that the results corresponded with the presence of molecules of HF, partially ionized, in the soln. 

Boiling points.—The effect of hydrogen chloride on the b.p. of water is illustrated by the curve, Fig. 

The equilibrium conditions with soln. of magnesium and potassium sulphates, at different temp., are illustrated by the diagram, Fig. 5. The point A represents the f.p. of water, 0° B, the cryohydric temp., —2 9° for magnesium sulphate C, the cryohydric temp., —L50, for potassium sulphate D, the cryohydric temp., —4 5°, for the mixed potassium sulphate and schonite E, the cryohydric temp., —5°, for the mixture of schonite and MgS04.12H20 F, the transition point, 0 7°, for the... 

It was recognized by physicists a century ago that the concept tiuit wc call temperature is just the conmolecular motion. The idea suggested itself of a temperature so low that molecules < ease to move. This temperature was named the absolute zero. We usually measure temperature by the Fahrenheit scale (f.p. of water F, b,p. 212° F), or, in scientific work, by tlie Centigrade or Celsius scale (f.p. of air-saturated water at 1 atm pressure 0° C, boiling point of water... 

A. Rosenheim and E. Lowenthal measured the effect of periodic acid on the b.p. and f.p. of water. They found ... 

Using this formula we can calculate, for example, the vapour pressure p of water at 0° and a pressure of 1 atmosphere. Here the vapour pressure p2 = 4=-b79 mm. (liquid under pressiure pg) ... 

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