Thus, when we warm or cool dry air, we add or remove sensible heat only, and are not concerned with latent heat. In our atmosphere it is superheated three or four hundred degrees, or far above its condensing or boiling temperature. It can be liquefied, but at very low temperatures, about 300☏ below zero. Dry air is itself a mixture of several gases, mainly nitrogen and oxygen, but these do not change in their proportions, and they behave so much the same, that we can consider dry air as if it were a single gas. In this chapter, when dry air is referred to, it will mean the air part when water vapor or moisture is referred to, it will mean the water part and when referring to just air, it will mean the mixture of dry air and water vapor. It is best to think of dry air and water vapor separately, for they behave independently of one another. First, atmospheric air is a mixture consisting of dry air and water vapor in varying relative amounts. Before we start to explain the psychrometric chart, let us review a few of the principles on which it is based. The tables are somewhat more accurate, but the chart is accurate enough for all practical purposes and is much easier to use. This can be accomplished through use of psychrometric tables or a psychrometric chart. In broader terms it is the science and practices associated with atmospheric air mixtures, their control, and the effect on materials and human comfort. Psychrometry is an impressive word which is defined as the measurement of the moisture content of air.
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