I love science but never thought much about the history of science. It appeared boring to me – at least it did at first. Because some of the obsolete scientific theories are so much fun: in particular that of combustion. It is, indeed, incredible how 'stupid' this theory may appear to be – although the zeroth law of thermodynamics, which is not stupid but so obvious, wins by a mile or two – it has also played its part in the formulation of the modern combustion theory.

The Phlogiston theory was developed in the 17th Century by JJ Becher and popularised later on by Georg Stahl. The theory maintained that all flammable materials contain a colourless, odourless substance called phlogiston. In fact the theory declared that when a material was burning, phlogiston from that material was being released in the air. Charcoal, for instance, was thought to contain loads of phlogiston because combustion almost totally consumed it. Phlogiston theory, therefore, could account for the weight lost during combustion of any material because they were losing phlogiston.

However not all materials lose weight during combustion. Metals like magnesium, instead, gained weight. The Phlogiston theory, which seemed to be so perfect at first, was completely baffled by the combustion of those metals. How could it be? Fighting for survival, the Phlogiston theory speculated that phlogiston in metals like magnesium and other materials that gained weight during combustion, had a negative weight.

Negative weight! I ask you. When the metal was burned, it lost the negative weight as the phlogiston escaped resulting in a gain in weight of the burned metal.

Antoine Lavoisier, the French scientist who is widely regarded as the father of modern chemistry, finally killed the Phlogiston theory by showing that combustion required air, or rather oxygen gas and was independent of phlogiston or any other substance. Lavoisier consequently developed a new theory, called the caloric theory.

Lavoisier properly formulated that oxygen reacted with a material during combustion but, like Becher and Stahl, he confused heat with combustion. Lavoisier's caloric theory held that changes in temperature are due to the transfer of an imponderable fluid, invisible and weightless, called caloric. He was, of course, wrong. It is kind of hard to imagine that people like Lavoisier could get things wrong but wrong he was. In the early 19th Century, the caloric theory was challenged and slowly dismissed in nowhere's land.

The modern theory of heat transfer is the kinetic theory, which states that heat is transferred by vibrations of particles in a solid, liquid, gas and other states of matter.

It does seem unbelievable that scientific theories put forward things like negative weight, amongst others. Whats more, the theories that are currently accepted may be laughed at in a couple of decades or centuries. Let's say, for example, that Newton got the Gravitational law wrong! I'll let you reflect on that.

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