ONE HUNDRED YEARS OF CHEMISTRY 291 



he was the first in this country to prepare hydrofluoric 

 acid (6, 354, 1823), and he first detected bromine in one of 

 our natural brines (18, 142, 1830). 



Atomic Weights. 



As soon as the atomic theory was accepted, the relative 

 weights of the atoms became a matter of vital importance 

 in connection with formulas and chemical calculations. 

 In advancing his theory, Dalton had made some very 

 rough atomic weight determinations, and it has been men- 

 tioned already that Berzelius, at the time that our histor- 

 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 compounds, 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, 



