Simple substances, Lavoisier

L. B. G. de Morveau made the first table of chemically simple" substances. A. L. Lavoisier used this in his Ttmti EUmentaire de Chinde published in 1789. 

To the question, what is the cause of a chemical reaction Lavoisier s answer was descriptive and concrete, not geometric and abstract. Lavoisier did not rule out the possibility of an abstract and geometric chemical philosophy in the future but thought it was premature at the time. An avid investigator of the chemistry of organisms as well as of mineral substances, Lavoisier for the present shared the view of his contemporary, the British natural philosopher John Robison, that the phenomena of fermentation, nutrition, secretion, and crystallization are not susceptible to simple mechanical reasoning. 

Chemists working on the same problems could only know they were studying the same substances if they spoke the same language. The chemical language, like chemical instruments, defined the discipline.46 The instruments and the nomenclature were illustrated in elaborate diagrams and "tableaus." Lavoisier s "Tableau des substances simples" is one of the most famous. (See fig. 1.) Here he organizes thirty-three simple substances into four categories ... 

Lavoisier delivered two shocks to the Aristotelian elements. His experiments on water led him to conclude in 1783 that it is not a simple substance at all, not properly called an element, as had always been thought . And, concerning that other fluid element of antiquity, he announced that atmospheric air is composed of two elastic fluids of different and opposite qualities , which he called mephitic air and highly respirable air . Neither water nor air, in other words, is an element. 

For a detailed analysis of this whole sequence of Lavoisier s struggle with simple bodies, see Robert Siegfried, Lavoisier s Table of Simple Substances, its Origin and Interpretation, Ambix 29 (1982) 29-48. 

Lavoisier s Table of Simple Substances Its Origin and Interpre-... 

In 1789, Antoine-Larrrent Lavoisier (1743-1794 CE) pubhshed a Table of Simple Substances (p. 175-176) in his book Traite Mementaire de Chimie, presente dans un ordre nouveau at d apres les decouvertes modernes, (55). The subtitle to the table was Simple substances belonging to all the kingdom of natrrre, which may be considered as the elements of bodies . None of the fom elements of Empedocles (earth, air, water, fire) or the three principles of Paracelsus (mercury,... 

The instrument that Lavoisier used with the greatest success to demonstrate the truth of his system was the balance, an instrument with a beam pivoting on a central knife-edge, with a scale pan at each end. Chemical substances are neither created nor destroyed during reactions, and this truth can be shown to hold for any substance that has weight. We shall see later that Lavoisier needed a different instrument to try to show that caloric, the matter of heat, behaved as a simple substance in chemical reactions. This was a problem precisely because caloric had no weight. 

Lavoisier s operational definition of a simple substance as one that had not yet been decomposed was an invitation to chemists to decompose whatever they could and to identify or discover as many undecomposed substances as possible. Heat was a powerful agent both for separating substances from one another and for decomposing a substance, either on its own or in combination with another substance. Furnaces of all kinds were traditional sources of heat for such purposes, as was the blowpipe, an instrument that Lavoisier took for granted, and so discussed only briefly in his writings. The blowpipe turned out to be one of the most powerful instruments for the identification of new simple substances. 

Once it entered chemistry, the blowpipe proved to be a most delicate instrument for the qualitative analysis of mineral ores, revealing the presence of minute quantities of metal in very small samples. Chemists typically worked with samples the size of a mustard seed, and in those samples could detect even half a percent of a particular metal. This was far more sensitive than analysis in solution, the wet way. The blowpipe led to the discovery of several metals during Lavoisier s lifetime, including nickel, manganese, molybdenum, and tungsten. Because these metals could not be decomposed, Lavoisier duly listed them in his table of simple substances. 

Lavoisier resolved materials into their ultimate constituents, that is, he decomposed them chemically until the last point that analysis is capable of reaching . By this means, he was able to draw up a table of simple substances that he claimed were elements. This table was published in his groundbreaking book Traite Elementaire de Chimie, which appeared in 1789. The reproduction of his table here in Figure 2 shows that it contained many substances that are now considered to be elements. The table also includes light and... 

Potassium and sodium.— A. L. Lavoisier regarded the alkalies and earths as simple substances which, with increasing knowledge, may prove to be complex. In the second part of his A New System, of Chemical Philosophy (London, 1810), J. Dalton considered the metallic oxides potash and soda to be simple elements, and the metals potassium and sodium to be compounds of potash or soda with hydrogen. H. Davy refuted J. Dalton s argument, and later remarked ... 

The second section of the Elements starts with what Lavoisier calls simple substances and provides a list of these elementary substances. Many of the 33 substances, ranging from antimony to zinc, would prove to be in their simplest form. These are materials that had not been broken down into simpler substances. He treated them as elements, although he was careful to leave open the possibility that chemicals on the list might be broken down in the future. In particular, he included several substances such as magnesia and alumina, which he suspected were oxides of unidentified metals. In addition to providing a working definition of elements and a list, he also attempted to clarify the names for the different substances, listing his new name and a variety of old names. 

Lavoisier s table of simple substances from Elements of... 

The crucial event in Lavoisier s career was his realization that air (which nearly everyone believed to be a simple substance defined by its physical, rather than by any chemical, properties) must play a part in chemical transformations - most dramatically those observed in ordinary combustion, the roasting (calcining) of metals, and the reduction of ores or cakes . ... 

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