In 1776 he performed another experiment in which he put a...

In 1776 he performed another experiment in which he put a crucible of mercury over a heater and left it for 12 days. It was not long before a light red film was observed on the surface of the mercury. He found that the air in contact with the mercury could not support life. He deduced that a part of the air inside the crucible had reacted with the mercury, forming a light red film. In order to confirm this, he separated the light red film and heated it.

He observed that a gas was released from it. This gas supported life. He came to the conclusion that there is nothing, which is given off from mercury when it is heated. But rather that there is a gas in the air which combines with the mercury to form mercurous oxide (HgO). Lavoisier then asserted that there was no evidence for the existence of phlogiston.

In chemical reactions the total weight of all substances entering into the reaction equals the total weight of all the substances resulting from that reaction. In other words, 'Rien ne se pera, et rien ne se crea.' (Nothing perishes, and nothing is created). In this way the theory of phlogiston lost its supporters.

We know today that when something catches fire it is because it enters into combination with oxygen, and not because an invisible substance comes out of the combustion in the form of flames.

The history of phlogiston and the theory of Lavoisier show us clearly that when Lavoisier said 'Nothing perishes and nothing is created.' By this he meant that in a chemical reaction nothing disappears and nothing is added, and he was not referring to the origin of the creation of the world, which is a philosophical issue.

Unfortunately, some people, imagining that Lavoisier had wanted to answer a philosophical question, asserted that the event of creation was not compatible with Lavoisier's theory, because he has said that nothing is created and nothing is lost. How, they asked, could something be created from nothing?

However, by referring to the history of the two theories, it becomes clear that Lavoisier was referring only to chemical reactions, which take place in the present world, and he meant that this world is such that within its bounds nothing extra can be added and nothing can disappear. And the problem of whether the world was created or whether it is eternal is a philosophical matter about which Lavoisier's theory remains totally silent.