CHARACTERISTICS OF CHEMICAL COMPOUNDS 89 



determination of constitution in this department, and was 

 discussed in that bearing in Part II. 



In the next place must be considered the magnitude 

 of the affinity which governs the sense of reaction and the 

 phenomenon of chemical equilibrium : its measure is often 

 simply found in the electromotive force, whilst the evolu- 

 tion of heat at the absolute zero depends on it, but suffers 

 a modification with temperature that causes a displacement 

 of equilibrium. 



Characteristic, thirdly, is the velocity of reaction, but in 

 accordance with the introduction of a new factor, time, it 

 offers more difficulty towards simple treatment from the 

 theoretical standpoint, so that here we are reduced to 

 a considerable accumulation of empirical material. 



We shall endeavour in the following to describe the 

 chemical character of the best investigated elements in 

 simple compounds according to the above principles, and 

 then trace out how far it reappears in more complex 

 derivatives. 



A. Chemical Character of the most important Elements 

 in their Simple Compounds. 



i. Positive or Metallic and Negative or Metalloid 

 Character. 



It is well known that in judging the chemical behaviour 

 of an element its so-called positive or negative character 

 forms an important guide. Starting from Berzelius' electro- 

 chemical concepts as an essentially qualitative notion, it 

 has begun in recent times to appear capable of quantitative 

 treatment. 



The theory of electrolytic dissociation affords the easiest 

 insight into these phenomena, and the positive elements, 

 such as potassium, are distinguished by it as possessing 

 a strong tendency to the formation of positive ions, which 

 is most marked in aqueous solution ; the negative or 

 metalloid character, e. g. of chlorine, accordingly shows 



