Gases_1

Gases vary in their degree of solubility in liquids; 1,050 litres of ammonia are soluble in 1 litre of water at 0° C. ; while only 02 litre of hydrogen can be dissolved in the same amount of water. A liquid at its boiling-point may be regarded as being saturated with its own gas, any addition of heat causing the evolution of vapour. The power of conduction of heat for gases is very slight, and is difficult to measure, for true conduction is prevented by the convection which goes on. The specific heat of gases is small as a rule, that of air at constant pressure being -2375, at constant volume -1684; that is to say, a gramme of air raised in temperature 1° C. requires -2375 calories if its pressure remain constant, its volume therefore increeising by Gay-Lussac's law. If its volume be kept constant it requires only -1684 calories to raise its temperature 1° C, the difference being due to the work done in the former instance by expansion of the air against the external pressure. The specific heat of hydrogen at constant pressure is 3049, this substance being the unique exception to the rule that the specific heats of all substances are less than that of water. Air at ordinary temperatures and pressures is an insulator of electricity, but at high temperatures and at low pressures it becomes a conductor. Oxygen is strongly magnetic; hydrogen and nitrogen are diamagnetic. [Diamagnetism.]