Modern Thermodynamics
- Chapter 1
1.4 Temperature, Heat and Quantitative Laws of Gases
During the seventeenth and eighteenth centuries, a fundamental change occurred in our conception of
Nature. Nature slowly but surely ceased to be solely a vehicle of God's will, comprehensible only
through theology. The new "scientific" conception of Nature based on rationalism and experimentation
gave us a different world view, a view that liberated the human mind from the confines of religious
doctrine. In the new view, Nature obeyed simple and universal laws, laws that humans can know and
express in the precise language of mathematics. Right and wrong were decided through experiments and
observation. It was a new dialogue with nature. Our questions became experiments, and Nature's answers
were consistent and unambiguous.
It was during this time of great conceptual change that a scientific study of the nature of heat
began. This was primarily due to the development of the thermometer which was constructed and used in
scientific investigations since the time of Galileo Galilei (1564-1642)ii,iii. The impact of this simple
instrument was considerable. In the words of Sir Humphry Davy (1778-1829), "Nothing tends to the
advancement of knowledge as the application of a new instrument ".
The most insightful use of the thermometer was made by Joseph Black (1728-1799), a professor
of medicine and chemistry at Glasgow. Black drew a clear distinction between temperature or degree of
hotness, and the quantity of heat (in terms of current terminology, temperature is an intensive quantity
while heat is an extensive quantity). His experiments using the newly developed thermometers
established the fundamental fact that, the temperatures of all the substances contact with each other will
eventually reach the same value i.e. systems that can exchange heat will reach a state of thermal
equilibrium -- an idea that was not easily accepted by his contemporaries because it seems to contradict
the ordinary experience of touch to which a piece of metal felt colder than a piece of wood, even after
they had been in contact for a very long time. But the thermometer proved this point beyond doubt. With
the thermometer, Black discovered specific heat, laying to rest the general belief at his time that the
amount of heat required to increase the temperature of substance by a given amount depended solely on
its mass, not specific to its makeup. He also discovered latent heats of fusion and evaporation of water --
the later with the enthusiastic help from his pupil James Watt (1736-1819) iv .
Portrait of Joseph Black
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