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But the foregoing is all experimental results. What was the prevailing theory at the time? John Dalton was sufficiently skilled to determine the combining weights of elements and thus formulate the relative amount, or percentage, of various elements in a compound. This bulk property of matter he applied to the very atoms that combined to form atoms (molecules) of compounds. Combustion was accomplished by burning weighed amounts of a compound and determining the amount of carbon dioxide or water formed. Oxygen content was, and still is, determined by difference provided no other elements are present. However, this knowledge does not permit one to assign an empirical, no less a molecular formula to the substance. By 1810, Dalton had assigned the relative combining weights of H:C:O as 1:5.4:7, or closer to 1:6:8 by more modern standards. One of the failed rules of his atomic theory was the "rule of greatest simplicity", which stated that the simplest body formed by two elements should be binary, i.e., water is OH. The formation of both carbon monoxide and carbon dioxide fit his Law of Multiple Proportions. The last permutation of these three elements taken two at a time would dictate that marsh gas (fire-damp, methane), which has a C:H weight ratio of 3:1, should have the formula CH₂.

[Dalton did not write formulas as they are presented here. He employed differently designated circles for different atoms. It was Berzelius who introduced the modern symbols of the elements.]

In 1808, the French chemist Gay-Lussac demonstrated that two volumes of hydrogen combined with one volume of oxygen to produce two volumes of water vapor, much as Dalton had done with the Law of Multiple Proportions. Dalton was not enthralled with Gay-Lussac's results because they contradicted his Atomic Theory, which held that: 1) all atoms of a given element are the same size, 2) the greater the combining weight of an atom, the greater its size, and 3) if atoms are the fundamental building blocks of elements, then they should not combine with one another. Thus, in Dalton's view, equal volumes of gases under the same conditions could not contain the same number of atoms. By 1811, Avogadro and Ampere, had resolved this dilemma by proposing that hydrogen and oxygen, as well as other reactive gases are, in fact, diatomic and that equal volumes of gas under the same conditions do contain equal numbers of atoms (molecules). Unfortunately, this idea was not widely known nor accepted until 1860, when Cannizzaro, a #### of Avogadro, promoted his ideas at a meeting in Karlsruhe. Given the influence of Dalton's Theory in the first half of the 19th century, the structure water was often written as OH while others utlilized H20 after Gay-Lussac.

Concurrent with the

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The practitioners of organic chemistry of the late 18th and early 19th centuries were masterful at chemical analysis. This expertise began with Priestley's, who along with Scheele had discovered oxygen, observation that red mercuric oxide (cinnabar) when heated in a sealed vessel to produce quicksilver (mercury), did not lose mass (weight, if you wish). The vessel was shown to contain an "air" that made a candle burn brighter than in air and that could sustain a mouse. This air was called dephlogisticated air by Priestley. Informed of these developments, Lavoisier was able to provide a correct explanation of the process of combustion as an oxidation of a substance such as carbon or hydrogen to form carbon dioxide and water, respectively, rather than the substance losing "phlogiston" as had been proposed by Stahl and supported by Priestley. Lavoiser named this gas oxygen (oxy - sharp, gen - born) because the products of its reactions with non-metallic elements -- carbon, sulfur, phosphorous -- produced acidic solutions when dissolved in water. For these reasons, Lavoisier was led to believe erroneously that muriatic acid (aqueous hydrochloric acid) also contained oxygen.

An organic substance containing carbon and hydrogen could undergo complete combustion to provide carbon dioxide and water. The CO2 was absorbed in a wei