MR. W. C. D. WHETHAM ON IONIC VELOCITIES, 
355 
available. In order to prevent the necessity of experimentally determining these 
constants, I thought it better to observe the velocities of both ions of a salt and 
compare their sum with the value deduced from the conductivity. The salts used 
were (i.) the chloride and nitrate of cobalt (the colours of which in alcoholic solutions 
are blue and red respectively) giving the velocity of the acid radicles, and (ii.) cobalt 
and calcium chlorides (blue and colourless) and cobalt and calcium nitrates (red and 
colourless), giving the velocity of the cobalt ion. 
It was found that the observed velocities were very small, and in order to increase 
them a shorter tube was used of rather greater cross-section. This enabled a greater 
potential gradient to be applied. The area of cross-section was determined as before 
and came out 0'746 sq. centim. 
A series of solutions of cobalt chloride and cobalt nitrate of different strengths 
was made up and the specific resistances determined. They were then placed in 
pairs of equivalent strength in the velocity apparatus, and a long investigation made 
on their behaviour. It was found that with weak solutions, wdiose strength was 
below 0’08 grm, equivalent per litre, the phenomena were quite regular. The junction 
travelled against the current, as it ought, since the change of colour depends on the 
acid radicles. As the strength of solution ino’eases new phenomena appear. When 
the concentration reaches O'l grm. equivalent per litre the junction sometimes 
divides into two parts, which often travel in opposite directions, producing a broad 
purple band between the red and the blue solutions. 
The junction sometimes seems to travel entirely the wrong way, but there is always 
either a fainter band which goes the right way, or, if this cannot be seen, the colour of 
the solution in that direction gradually changes. These pheiiomena more and more 
disturb the normal course of the experiment as the concentration of the solutions 
becomes greater, and with the strongest solutions which can conveniently be used 
(O'] 5 grm. equivalent) are very marked indeed. 
In order to examine the applicability of the theory to these cases, it is necessary to 
choose solutions so dilute that the motion of the ions is normal, but still strong 
enough to show their colours plainly, and give an appreciable difference of density. 
The best solutions to use were found to be those whose strength was about 0'05 grm. 
equivalent per litre. 
Solutions of cobalt nitrate and cobalt chloride in alcohol of '05 strength were, 
therefore, set up in the velocity tube, and the following results were obtained :— 
Current from red to blue. Temperature, 17°'8. 
V = '39 '35 '43 '43. Mean, '40 centim. per hour. 
G = 49'5 49-4 48-8 48-5. „ 49°'l 
Current from blue to red. 
V = '42 '41. Mean, '42 centim. per hour. 
G=49'1 48'G. „ 48°'9 
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