262 Wells S Foote — One Hundred Years of Chemistry. 



ical period begins, was engaged in the prodigious task of 

 accurately determining these constants for nearly all the 

 known elements. It is recorded that he analyzed quan- 

 titatively no less than two thousand compounds in 

 connection with this work during his career. His table 

 of 1818 has proved to be remarkably accurate for that 

 pioneer period, and it indicates his remarkable skill as an 

 analyst. 



It is to be observed that Berzelius in this early table 

 made use of Avogadro's principle in connection with 

 elements forming gaseous compound's, and thus obtained 

 correct formulas and atomic weights in such cases, but 

 that in many instances his atomic weights and those now 

 accepted bear the relation of simple multiples to one 

 another, because he had then no means of deciding upon 

 the formulas of many compounds except the rule of 

 assumed simplicity. For example, the two oxides of 

 iron now considered to be FeO and Fe 2 3 he regarded as 

 Fe0 2 and Fe0 3 , knowing as he did that the ratio of 

 oxygen in them was 2 to 3, and believing that a single 

 atom of iron in each was the simplest view of the case, 

 so that as the consequence of these formulas the atomic 

 weight of iron was then considered to be practically 

 twice as great in its relation to oxygen as at present. 



These old atomic weights of Berzelius, used with the 

 corresponding formulas, were just as serviceable for cal- 

 culating compositions and analytical factors as though 

 the correct multiples had been selected. As time went 

 on, the true multiples were gradually found from consid- 

 erations of atomic heats, isomorphism, vapor densities, 

 the periodic law, and so on, and suitable changes were 

 made in the chemical formulas. 



Berzelius used 100 parts of oxygen as the basis of his 

 atomic weights, a practice which was generally followed 

 for several decades. Dalton, however, had originally 

 used hydrogen as unity as the basis, and this plan finally 

 came into use everywhere, as it seemed to be more log- 

 ical and convenient, because hydrogen has the smallest 

 atomic weight, and also because the atomic weights of a 

 number of common elements appeared to be exact multi- 

 ples of that of hydrogen, thus giving simpler numbers for 

 use in calculations. 



Within a few years a slight change has been made by 



