652 TRANS. ST. LOUIS ACAD, SCIENCE. 



These values are not in all cases the most characteristic, though 

 they are in many cases, as will be seen in Part II. 



In compounds of two metals or two non-metals which cannot 

 be electrolyzed it is difficult to determine which is -f- and which 

 is — , though it is generally safe to say that the more basic element 

 is -\- and the more acidic — , For example, it is probably safe to 

 assume that in KgH, Na.H, CS,, PC/, and PC/3, K, Na C and P 

 are -f- and H, S and C/ are — . 



An isolated atom cannot be considered to have any valence ; the 

 polarity of such an atom is therefore zero. (Hypoth. II.) 



If 'the foregoing hypotheses are true, the decomposition of a 

 molecule must require an amount of energy proportional to the 

 total change of valence produced, less the total energy evolved by 

 the closing of atomic poles. In many cases the quantity of energy 

 required to decompose a molecule is really negative, Nitro-gly- 

 cerine is an example. 



In all such cases the sum of the polarities of the individual at- 

 oms tending to close upon themselves or upon neighboring atoms 

 is greater than the sum of the polarities tending to produce or 

 hold together the molecule. 



In Part II. are given the atomic weights and observed valences 

 of the elements, and the principal compounds in which those va- 

 lences occur. In compounds which cannot be electrolyzed the 

 more basic elements are considered electro-positive, and the more 

 acidic electro-negative. A summary is given in tabular form at 

 the end, showing the maximum, minimum and characteristic 

 valences. The characteristic valence is given only when it is dif- 

 ferent from the maximum and minimum. 



PART II. 



Valence and Atomic Weights of the Elements, 



HYDROGEN. 



H.jN and all ammonium compounds 



