92 CHEMICAL PROPERTIES AND COMPOSITION 



that of hydrogen as zero, in ordinary calories per gram-ion 

 the results are : 



Na Mg Al Ma Zn Cd Fe" Tl Ni Co 



5 6 '5 53-6 39-4 2 4' 2 l6 ' 6 8 3 Io<1 - 1 1 T& 



Pb Sn" Cu" Ag Hg' 



0-7 0-7 89 26-4 20-7 



for formation of positive ions : and for negative 

 Cl 39-9 Br 28-9 I 13.7, 



from which it follows, e. g. that the formation of hydro- 

 chloric acid in aqueous solution is accompanied by an 

 evolution of 39-9 calories, sodium chloride by 



39.9 + 56-5 = 96-4. 



Since a volt per gram equivalent in the table p. 90 means 

 23-09 calories, we may compare the work and heat, and 

 arrive for sodium at 2-58 x 23-09 = 59-6 as work against 

 56-5 as heat ; for chlorine 30-2 against 39-9, and so on- 

 But in comparing these values it must be borne in mind 

 that at any temperature but the absolute zero, the work 

 depends greatly on concentration, since the work done on 

 dilution to n times normal solutions has to be subtracted, 

 and amounts to 0-002 x log/n calories per gram-ion, which 

 for a decinormal solution is 1-4 cal. 



Allowing for this, we may first note what is character- 

 istic of the metallic nature in these thermochemical data. 

 This is most marked for potassium, to which the following 

 numbers refer, giving the heat of formation of the equivalent 

 quantity, and subsequent solution in water : 



S. aq. 0. aq. F. aq. Cl. aq. Br. aq. I. aq. 

 55-6 82-3 113-1 101 2 90-2 75 



The relation expressed by the following formula is 

 characteristic, and recurs among the typical metals : 



(M. Si) < (M. Oi) < (M . F) > (M. Cf) > (M. Br} > (M.I), 



it holds even for metals of the smallest thermochemical 

 values such as silver : 



