Page:Outlines of Physical Chemistry - 1899.djvu/62

 42 OUTLINES OF PHYSICAL CHEMISTRY

��The Tbansition from the Gaseous to the

Liquid State

Compression of Gases

We have already remarked that gases do not obey Boyle's Law exactly. In Fig. 8 the pressures are marked as abscissae (from to 820 atmospheres), and the products of pressures into their corresponding volumes, p v f %& ordinates.

At constant temperature, the line joining the ends of the ordinates ought to be straight and parallel to the axis of abscissae. This would be the case for a perfect gas, if Boyle's law were absolutely true.

But, in reality, the isothermal line representing the product pv is a curve similar to the one shown in the atmospheres, the gaseous mass is generally more com- pressible than Boyle's law requires; the product pv diminishes as the pressure increases. At a certain point the gas behaves according to the law, but when the pressure is still further increased the compression again becomes abnormal, but in the opposite sense ; the volume does not diminish as rapidly as the pressure increases, and the product p v rises very quickly. This phenomenon has been observed for a large number of gases at pressures

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