ONE HUNDRED YEAES OF CHEMISTRY 299 



This form of notation was quite extensively employed 

 for a time, especially by mineralogists, but it was entirely 

 abandoned later. 



It is interesting to notice that Dalton, who lived until 

 1844, to reach the age of 78, differed from other chemists 

 in refusing to accept the letter-symbols of Berzelius. 

 In a letter written to Graham in 1837 he said: " Ber- 

 zelius 's symbols are horrifying. A young student in 

 chemistry might as soon learn Hebrew as to make him- 

 self acquainted with them. They appear like a chaos of 

 atoms . . . and to equally perplex the adepts of science, 

 to discourage the learner, as well as to cloud the beauty 

 and simplicity of the atomic theory. ' ' 



This forcibly expressed opinion was apparently tinged 

 with self-esteem, but there is no doubt that Dalton was 

 sincere in believing that the atoms were best represented 

 by his circular symbols, because, as is well known, he 

 thought that all the atoms were spherical in form, and it 

 is evident that circles give the proper picture of spherical 

 objects. At the present time some insight as to the 

 structure of atoms is being gained, and it appears possi- 

 ble that the time may come when pictures of their 

 external appearance that are not wholly imaginary may 

 be made. 



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 



