Gases

Gases were the first phase of matter that people learned to understand. And the theory was delightfully simple: that gases are made up out tiny, ceaselessly-moving molecules.

By the time one comes to reading a book such as Understanding the Properties of Matter a reader may well be familiar with this idea. But I would urge the reader not to let that sense of familiarity distract from how radical the idea was when it was introduced. This could not be better illustrated than with the story of John James Waterston, a man whose name does not feature in this book. 

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He described these ideas with exceptional clarity in a paper submitted to Royal Society in 1845. He wrote:

…we must imagine a vast multitude of small particles of matter, perfectly alike in every respect 

…The quality of perfect elasticity being common to all the particles, the original amount of vis viva [what we call kinetic energy]…of the whole multitude must forever remain the same… as unchanged as the matter that is associated with it.

The medium must in this way become endowed with a permanent state of elastic energy, or disposition to expand, uniformly sustained in every part and communicating to it the physical character of an elastic fluid.

The referee at the Royal Society responded:

the paper is nothing but nonsense

It was not until 1896 that Lord Rayleigh discovered the existence of the paper and had it published. He wrote:

The omission to publish it at the time was a misfortune which probably retarded the subject by 10 to 15 years.

I urge you to try to retain your sense of wonder at the astonishing fact that the air in front of you is filled with molecules moving at hundreds of metres per second!  

  • Chapter 4 contains a description of the theory of an ideal gas and so-called the ‘kinetic’ theory of gases.
  • Chapter 5 contains data on the properties of real gases and discusses how we can understand the data using the ideas described Chapter 4.