9 8 CHEMICAL PROPERTIES AND COMPOSITION 



view. For this we choose the so-called positive or negative 

 character of the elements to start with, and define this as 

 tendency to combine with positive or negative electricity,. 

 The extreme positive and negative elements, such as sodium 

 and chlorine, then show the strongest indications of affinity, 

 which suggests the assumption that in the chemical com- 

 bination the opposite electrical charges can act on one 

 another. Then the intermediate elements, such as carbon, 

 which are neither decidedly positive nor negative, often show 

 a tendency to combine with themselves which is wanting 

 in the extreme members. The second consequence of the 

 tendency to combine with electricity is therefore the ap- 

 pearance of free atoms with electric charges, ions, in 

 solvents which e. g. weaken the electric attraction, and 

 show a high dielectric constant, such as water: this break- 

 ing up or loosening again produces a facility for reaction 

 which the compounds of the intermediate elements do not 

 possess, and in carbon compounds the opposite effect is seen 

 in their characteristic inertia in reaction. All these pheno- 

 mena of affinity are most marked when the atomic weight 

 is small and the atomic volume large, and consequently the 

 density small. 



B. Affinity of the Elements in more Complex 

 Compounds. 



After what has been given in the foregoing on the 

 characteristic effects of affinity in simple compounds, the 

 corresponding phenomena in more complex derivatives 

 must be studied. First the additive character of the heat 

 of formation is to be noted, and secondly, the composition 

 of explosive compounds. 



i. Additive Character of the Heat of Formation. 



It was Thomsen 1 in the first place who attempted to 

 reduce the thermal phenomena of organic chemistry to 

 their elements in the simple formation and destruction of 



1 Thermochemische Untersuchungen, iv. 237. 



