And yet Lavoisier did not completely discard the concept of a material associated with fire: we can see some of the evolution of the concept 'matter of fire' from phlogiston to caloric in this article. Thus, Lavoisier's work on combustion provided a better understanding of two of the elements of the ancients.

According to the phlogiston theory, earths were simple bodies, and metals were obtained from them by addition of phlogiston in fact, metals are the simple bodies, and earths are obtained from them by reaction with oxygen. It also explained the relationship between metals and earths (or oxides as we now call them). Lavoisier's explanation of combustion extended to respiration as well-a process no less important to humans if much less dramatic. Control of the various gases produced in combustion, major and minor, has become one of the important scientific, technological, environmental, and political issues of our own time. Nor has the role of combustion diminished since Lavoisier: first coal and then oil powered the waves of industrialization which began in Lavoisier's day. Fire and combustibility played a central role in chemical theories from the ancients up to the time of Lavoisier: it was an element of the ancients ( chapter 1) sulfur, or the principle of combustibility was an elementary principle of the alchemists (see chapter 2) and the phlogiston theory of combustion dominated chemistry for most of the 18 th century. Controlling fire allowed early humans to keep warm, alter their food, and transform other aspects of their material surroundings (by smelting and working metals, for example). It would be difficult to overestimate the consequence to chemistry of an understanding of fire, for fire represents one of the most dramatic as well as one of the earliest symbols of chemical change. The explanation of combustion and respiration in terms of oxygen is surely one of the most important of the many important contributions of Lavoisier to chemistry. These ratios by themselves may not seem particularly interesting or informative however, if we take a ratio of these ratios, we obtain a useful and possibly surprising result: a small, whole-number ratio.Fire and Earth: Lavoisier Elements and Atoms: Chapter 5

For example, copper and chlorine can form a green, crystalline solid with a mass ratio of 0.558 g chlorine to 1 g copper, as well as a brown crystalline solid with a mass ratio of 1.116 g chlorine to 1 g copper. The law of multiple proportions states that when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small, whole numbers. For example, there are many compounds other than isooctane that also have a carbon-to-hydrogen mass ratio of 5.33:1.00.ĭalton also used data from Proust, as well as results from his own experiments, to formulate another interesting law.

That is, samples that have the same mass ratio are not necessarily the same substance. It is worth noting that although all samples of a particular compound have the same mass ratio, the converse is not true in general.

Lavoisier atomic theory