MR. W. C. D. WHETHAM ON IONIC VELOCITIES. 
339 
between the molecules) as abscissa, and Z:/N as ordinates, he is able to obtain the 
specific molecular conductivity for infinite dilution. When the values for u and v are 
worked out for these ideal solutions, it is found that the velocity of any given ion is 
independent of the nature of the salt of which it forms part, and hence Kohlkausch 
assigns numbers to various ions which represent their specific ionic velocity. 
From a table of these numbers we can at once deduce the conductivity of any 
given salt solution, and the agreement of the values so obtained with those experi¬ 
mentally observed, furnishes the first confirmation of Kohlrausch’s theory. He 
calculates the conductivity of various salt solutions of strength O'l gramme equiva¬ 
lent per litre, and then experimentally determines it for solutions of that strength. 
Some of his results are as follows :— 
Name of salt. 
Alolecnlar conductivity 
calculated from tlie 
ionic velocities. 
Molecular conductivity 
observed. 
KCl 
1060 . 
1047 
NH^Cl 
1040 
1035 , 
NaCl 
860 
865 
4BaCl., 
840 
861 
iZnCl., 
780 
768 1 
KI 
1070 
1069 1 
KNO.3 
AgNO., 
1000 
983 
900 
886 
kc.,h.,6 ,. 
780 
784 ! 
HCi 
3260 
3244 
KOH 
1950 
1986 
NaOH 
1750 
1700 
The tabulated numbers are hjm X where h is the conductivity in terms of that 
of mercury, and m is the number of gramme equivalents of salt per litre. The general 
agreement is very remarkable, though several exceptions show that the law is not of 
universal application ; for instance, acetic acid should give 2980, while the observed 
number is 43. 
The next confirmation of the theory was given by Dr. Oliver Lodge (‘ B. A. 
Report,’ 1886), who actually observed the velocity of the hydrogen ion as it travelled 
along a glass tube and discolourized a solution of phenol-phthallein as it went. The 
tube contained a jelly in which was dissolved a little phenol-phthallein and common 
salt, with just enough soda to bring out the colour. The tube joined two vessels 
filled with sulphuric acid, and when a current was passed between them the hydrogen 
travelled with it, and liberated HCl as it went along the tube. This decolourized 
the phenol-phthallein, and could thus be traced. The velocity per unit potential 
gradient came out as '0029, ‘0026, and ’0024 centim. per second, while Kohlrausch’s 
theoretical number was •0030. 
This agreement is striking evidence in favour of Kohlrausch’s theory and leads us 
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