Rule of greatest simplicity

Dalton made a sixth assumption to resolve the dilemma of the absolute number of atoms present in a molecule he called it the rule of greatest simplicity. It states that if two elements form only a single compound, its molecules will have the simplest possible formula AB. Thus, he assumed that when hydrogen and oxygen combine to form water, the reaction is... 

FIGURE 230. Plate depicting atoms in Dalton s A New System of Chemical Philosophy (Manchester, 1808-1810). Dalton s rule of greatest simplicity (perhaps a Quaker style of science as well as lifestyle) has the formula of water as HO rather than H O (hydrogen peroxide, H2O2, would be discovered by Gay-Lussac and Thenard in 1815). 

Dalton resisted Gay-Lussac s findings. They caused problems for his rule of greatest simplicity. Since an equal volume of hydrogen reacts with an equal volume of chlorine, it is reasonable that those volumes contain equal numbers of elementary particles. However, if two volumes of hydrogen react with one volume of oxygen, as observed by Gay-Lussac, this would not be consistent with Dalton s formulation of water as HO. (Note that hydrogen peroxide, H2O2, was not discovered until 1815.)... 

The gaseous part of the reference environment described above behaves ideally, so that no corrections need to be made to the uj q. Therefore, only the h and s of the mixture as a whole need to be corrected viz. equation [1]. A convenient means for approximating these corrections is with generalized deviation charts or equations. In order to make their use possible, a mixture rule to obtain pseudo critical temperature and pressure is needed, and Kay s rule offers the greatest simplicity in its application. Thus,... 

Rule no. 3 the rule of the greatest simplicity of elementary reactions (bimolecular)... 

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