The common gauge expresses a pressure in pounds per square inch called gauge pressure. When the gauge is open to the atmosphere, it reads zero. The gauge pressure plus atmospheric pressure is known as absolute pressure. Atmospheric pressure is 14.7 psi at sea level; it varies with location and atmospheric conditions. It is accurately indicated by a barometer.

The temperature as read on the Fahrenheit scale plus 460 is the absolute temperature.

The starting point of the absolute-pressure scale is absolute zero. It is lower than a zero gauge by an amount equal to the atmospheric pressure.

The temperature 460 below zero Fahrenheit is absolute zero. At absolute zero there is a complete absence of heat. Absolute zero has never been attained, but it has been approached within a few degrees.

Water is a chemical combination of hydrogen (H) and oxygen (O) that is represented by the formula H ₂O. It may also be treated as a chemical combination of hydrogen ions (H ⁺) and hydroxyl ions (OH ^?). If there is a greater number of hydrogen ions than hydroxyl ions as a result of the chemical action of impurities or solutes, the solution is acidic. A greater number of hydroxyl ions results in an alkaline solution. The degree of acidity or alkalinity of a substance is known as the hydrogen-ion concentration and is...