ONE HUNDRED YEARS OF CHEMISTRY 289 



which he had previously discovered, and he had begun 

 to express the formulas for compounds in terms of 

 atomic symbols. 



In 1808 Gay-Lussac had discovered his law of gas com- 

 bination in simple proportions, 1 a law of supreme import- 

 ance in connection with the atomic theory, but neither he 

 nor Dalton had seen this theoretical connection. Avo- 

 gadro had understood it, however, and in 1811 had 

 reached the momentous conclusion that all gases and 

 vapors have equal numbers of molecules in equal volumes 

 at the same temperature and pressure. 



Davy in 1807 had isolated the alkali-metals, sodium 

 and potassium, by means of electrolysis, thus practically 

 dispelling the view that certain earthy substances might 

 be elementary; and about four year plater he had demon- 

 strated that chlorine was an element, "not an oxide as had 

 been supposed previously, thus overthrowing Lavoisier 's 

 view that oxygen was the characteristic constituent of all 

 acids. 



At the time that our period of history begins, the 

 atomic theory had been accepted generally, but in a some- 

 what indefinite form, since little attention had been paid 

 to Avogadro's principle, and since Dalton had used only 

 the principle of greatest simplicity in writing the formu- 

 las of compounds, considering water as HO and ammonia 

 NH, for example. At this time, however, Berzelius for 

 ten or fifteen years had been devoting tremendous energy 

 to the task of determining the atomic weights of nearly 

 all of the elements then known by analyzing their 

 compounds. He had confirmed the law of multiple pro- 

 portions, accepted the atomic theory, and utilized Avo- 

 gadro's principle, and it is an interesting coincidence 

 that his first table of atomic weights was published in the 

 year 1818. 



An interesting account of the views on chemistry held 

 at about that time was published in the Journal by Deni- 

 son Olms ted (11, 349, 1826; 12, 1, 1827), who had 

 recently become professor of natural philosophy in Yale 

 College. 



The most ^illustrious European chemists of that time 

 were Berzelius of Sweden, Davy of England, and Gay- 

 Lussac of France, and the curious circumstance may be 



