396 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



tions " 1819. Speaking in terms of Dalton's Atomic Theory 

 he suggests that 



" When atoms of two different substances combine, a 

 compound atom is produced, in which we suppose the force 

 producing combination to be infinitely stronger than all the 

 conditions which might tend to separate the united atoms. 

 This compound atom must be considered to be as indivisible 

 by mechanical means as an elementary atom." 



" These compound atoms combine with other compound 

 atoms, giving rise to atoms still more compound in their 

 nature. When these in their turn combine with others, 

 they produce atoms of still more complex composition. 

 These different atoms must be distinguished. We will 

 divide them into atoms of the first, second, third order, etc." 

 (Chemical Proportions, 1819, p. 26). As an example he 

 quotes the case of alum : 



Fourth Order. 



VAlum crystals 



Ox yg en \ Water 



Hydrogen / J 



The chief feature of Berzelius's theory of the structure of 

 salts is the combination of elements and compounds in 

 pairs ; it is therefore frequently described as the DUALISTIC 

 THEORY. Although it was applied in the first place only 

 to the combination of elements with oxygen, and^of basic 

 with acidic oxides, it was easily extended to include the 

 combination of metals with chlorine, even when the chlorides 

 were proved to be binary compounds, analogous with the 

 oxides, instead of ternary compounds analogous with the 

 sulphates. Further, in his " Memoir on the Sulpho-salts," 

 (Ann. Chim. Phys. 1826, 32, 60) Berzelius had no difficulty 

 in showing that these salts, formed by the combination of 



