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��4 OUTLINES OF PHYSICAL CHEMISTRY

others have devoted their wisdom and their patience, the reader is referred to the larger treatises on theoretical chemistry (such as that of Ostwald).

We may, therefore, pass on immediately to a systematic exposition of the fundamental theories. As these theories are now generally accepted, we' need not devote so many pages to their discussion as will be required for a critical examination of certain comparatively recent doctrines, which are not so universally admitted.

The Gaseous State

The Density of Gases and Vapowrs

The gaseous state is characterised by an extremely feeble intermolecular attraction. A gaseous mass has neither a definite form nor a definite volume, but expands uniformly through any space which is placed at its disposal.

The volume of a gaseous mass is a function of its temperature and pressure.

Boyle's Law. 1 At constant temperature, the volume occupied by a gaseous mass is inversely proportional to the pressure to which the gas is subjected :

p v = p l v l = constant.

Gay-Lussac's Law (Dalton's Lay). 9 ^ Under constant pressure, the same rise in temperature produces in all gases the same increase in volume. All gases have the same coefficient of expansion by heat :

a = JL = 0-00867 of the volume at 0°C.

��manner the following formulas were interpreted : HS0 4, NH„ CO„ Si0 2, CaO, NaO, FeO <ftc. We see that these expressed quite perfectly the composition of sulphuric acid, ammonia, carbonic anhydride, silicic anhydride, lime, sodium oxide, ferrous oxide, Ac. These formula had only the single purpose of showing as simply as possible the results furnished by analysis. They were to a great extent inde- pendent of all hypothesis and all theory.

1 Often known on the Continent as Mariotte's Law.

2 Known also as Charles's Law.

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