90 CHEMICAL PROPERTIES AND COMPOSITION 



itself in the opposite tendency to form negative ions. 

 Here we stand on purely experimental ground if, e. g. the 

 positive character is defined as leading to separation at the 

 negative pole during electrolysis. 



A direct measure of the facility of formation of positive 

 ions or of the fixation of positive electricity is given in the 

 electromotive force needed for the electrolysis of a binary 

 compound, assuming that this electrolysis consists in a simple 

 transformation of the ions into the ordinary state of matter, 

 the compound consequently being present in solution only 

 in the form of ions, as is the case with potassium chloride 

 on sufficient dilution. The electrolysis then means that the 

 chlorine and potassium ions, giving up their negative and 

 positive electricity respectively, form chlorine and potassium, 

 the first however in the state of diatomic molecules. 



Hence it follows immediately that the electromotive forces 

 applied to decompose binary compounds, as mentioned 

 above, must be of an additive character, obtainable by 

 addition of quantities referring to each ion, called by 

 Nernst l ' Zersetzungsspannungen.' Assuming arbitrarily 

 the value for hydrogen as zero, the values for normal 

 solutions according to Neumann - are the following in volts : 

 Affinity for positive electricity : 



Na Mg Al Mn Zn Cd Fe Tl Ni Co Pb Sn Sb 

 -f 2.58 1-47 1-28 1-06 0-74 0-38 0-33 0-30 022 0-22 0.17 0-16 0-13 



Bi As Cu Ag Hg Pel Pt Au 

 0-25 0-31 0-34 0-78 0'79 0-82 0-94 1. 10 



Affinity for negative electricity : 



01+1-31, Br 0-94, I 0-52, 



which is in accordance with the facts, for hydrochloric 

 acid, e. g. in normal solution, is decomposed by an electro- 

 motive force of i '3 1 volts, magnesium iodide by 



1-47 + 053 = 1.99. 



1 Berl Ber. 30. 1547. 



2 Zeitschr.f Phys. Chem. 14. 193 ; 27. 57. 



