Climate Change
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Burning has been important to people ever since early humans learnt how to generate fire. Wood turns to ashes when it burns and some metals become soft powders when they are heated. To the 17th century scientists Johann Becher (1625-1682) and Georg Stahl (1660-1734) there was a clear explanation for observations like these. Burning could be explained by the removal of a substance – and that substance they called phlogiston. Therefore, materials lose mass when they burn because they lose phlogiston. Stahl developed this idea, which became known as the Phlogiston Theory.
Like many other scientists of the day Antoine Lavoisier (1743-1794), a French chemist, was working on combustion – but the great difference between his work and that of other scientists was that Lavoisier introduced quantitative chemistry (chemistry involving accurate measurements). To help his work, Lavoisier developed a balance that could weigh to 0.0005g.
While working on the combustion of phosphorous and sulphur he discovered that, contrary to expectations, after burning the mass of the material was greater than it had been at the start – yet if the elements had lost phlogiston, surely their mass should have decreased? Further experiments showed Lavoisier that air is absorbed as these elements burn. He began to wonder if maybe something was taken in during burning rather than given out.
Supporters of the phlogiston theory came up with an explanation to get over this problem. They said that metallic phlogiston has negative mass. This meant that metals lost negative mass when they burned, causing their mass to increase. The supporters of the theory even had an explanation for materials that did not appear to change mass when heated – they said that they contained phlogiston that weighed nothing!
By a series of careful experiments Lavoisier showed that air was actually made up of several different components. He found the proportion of oxygen in the air and showed that oxygen was removed from the air during the process of burning. As a result of this work, he developed the theory that when substances burn in air they combine with oxygen from the air and form an oxide (a compound containing oxygen). He recognised that respiration in living things, the rusting of iron and burning were all forms of the same type of reaction. His ideas were backed up with large amounts of experimental evidence including detailed observations and accurate