Page:Text-book of Electrochemistry.djvu/157

 ��CONDUCTIVITY OF ELECTROLYTES. chap.

��It has been found that at higher temperatures the trans- port numbers approach the value 0*5, which indicates that with rising temperature the mobilities of the ions tend to become the same. This rule applies to all combinations of a positive and a negative ion. If we compare the salts of different positive ions with the same negative ion, the conductivities of these (provided that the degree of dis- sociation remains constant) must tend to a common value as the temperature rises. From this it follows that the worse the electrolyte conducts the greater is the percentage increase of conductivity with the temperature. This rule ought to apply only to the values of X„, but it has been found to be true for moderate dilutions of highly dissociated bodies.

In the following table are given the mobilities l^ at extreme dilution of the more important ions; the positive ions are given first, then the negative ions. The temperature coeflRcient for the ions K, CI, Br, I, NH4. Ag, and JSO4 is about 2'2 per cent, of the value at 18°. For the sodium ion and the ions of the organic acids the coefficient is about 2'7 per cent, per degree ; for Li, 2*9 per cent. ; for OH, 1*8 per cent. ; and for H only 1*5 per cent.

The increase for the divalent ions Ca, Sr, Zn, Mg, and Cu is about 2'6 per cent., and for Ba, 2*5 per cent. From these numbers the temperature coefficients of the conductivities of most electrolytes — ^in dilute solution — can be calculated.

��Cations.

�ioo

�Anions.

Hydroxy], OH

�Hydrogen, H

�Potassium, K

�Chlorine, CI

�Sodium, Na

�Bromine, Br

�Lithium, Li

�Iodine, I

�Ammonium, NH^

�Silver, Ag

�Chloric acid, ClOj

�Barium, JBa

�Iodic acid, 10,

�Strontium, ^Sr

�Acetic acid, C^HjO^j

�Calcium, |C!a

�Sulphuric acid, SO^

�Magnesium, ^Mg

� � �Zinc, JZn

� � �Copper, JCu

� � �� �