270 Wells & Foote — One Hundred Years of Chemistry. 



Changes in Formulas. — Even before the year 1826, 

 Berzelius displayed great skill in arriving at many for- 

 mulas that agree with our present ones, for example, H 2 

 for water, ZnCl 2 for zinc chloride, N 2 5 for nitric acid 

 (anhydride), CaO for calcium oxide, CO and C0 2 for the 

 oxides of carbon, and many others. But at the same 

 period other authorities, especially Gay-Lussac in France 

 and Gmelin in Germany, on account of a lack of appreci- 

 ation for Avogadro's principle and for other reasons, 

 such as the use of symbols to represent combining 

 weights rather than atoms, were using different formulas 

 for some of these compounds, such as HO, ZnCl and N0 5 , 

 so that their formulas for many of the compounds of 

 hydrogen, chlorine, nitrogen and several other elements 

 differed from those of Berzelius. The employment of 

 different formulas involved the use of different atomic 

 or combining weights. For example, with the formula 

 H 2 for water the composition by weight requires the 

 ratio 1 to 16 for the weights of the hydrogen and oxy- 

 gen atoms, while with HO the ratio is 1 to 8. 



Berzelius attempted to bring about greater uniformity 

 in formulas and atomic weights by making* changes in his 

 table of atomic weights published in 1826. He prac- 

 tically doubled the relative atomic weights of hydrogen, 

 chlorine, nitrogen, and of the other elements that gave 

 twice as many atoms in his formulas as in those of others, 

 and at the same time he wrote the symbols of these 

 elements with a bar across them to indicate that they 

 represented double atoms. For example, he wrote : 



HO Zn€l M) 5 

 instead of 



H 2 0, ZnCl 2 N,0 6 



This appears to have been an unfortunate concession 

 to the views of others on the part of Berzelius, for the 

 barred symbols were not generally adopted, partly on 

 account of difficulties in printing, and the great achieve- 

 ment in theory made by him was lost sight of for a long- 

 period of time. , 



The Law of Atomic Heats. — In 1819, Dulong and Petit 

 of France, from experiments upon the specific heats of a 

 number of solid elementary substances, came to the con- 

 clusion that the atoms of simple substances have equal 

 capacities for heat, or in other words, that the specific 



