More on Daltons Elementary Molecules, by Avogadro

Avogadro (1811) further developed the (atomic) proportion theory into molecules (so anticipating a kind of atoms-in-molecules theory) by the following considerations. 

Dalton had supposed that the water is formed by the union of hydrogen and oxygen, molecule to molecule. From this and from the mass ratio of the two components resulted in the oxygen one concluded that the molecule mass will be the same as the hydrogen as 7 to 1 (or, after the evaluation of Dalton, as 6 to 1). 

Quantum Nanochemistty— Volume II Quantum Atoms and Periodicity 

In the ammonia case, Dalton supposition on the relative number of molecules in mixture was totally wrong. He assumed that the nitrogen and the hydrogen were united molecule to molecule, whereas it was observed that a nitrogen molecule unite three hydrogen molecules instead. Molecule division (which do not enter in Dalton calculations) partially correlate, in this case, the error which could result from (his) other suppositions. 

Once it appears the consideration for weight instead of the first guessing the sulfurous gas density, as it was confirmed or rectified by new experiments, meaning, it must have been an error in sulfurous acid composition determination, which made increasing the quantity of radical, or, which is the same thing, the diminution of the oxygen quantity. The determination was made from the dry sulfuric acid produced. Therefore, one can assume that the sulfurous acid should be composed by 95.02 parts oxygen to 100 parts sulfur (or, more likely, sulfuric radical) instead of 92. 

---