﻿394 Mr. W. C. D. Whetham on the Velocities of the 



when the potential gradient along the tube is unity. In the 

 case of the Cr 2 7 group travelling through an agar-jelly 

 solution of deeinormal strength v 1 = '00044 centhn.per second. 

 In the earlier investigation the same group travelled through 

 an aqueous solution of corresponding strength with a velocity 

 of -00047 centim. per second. The effect of the jelly is thus 

 to slightly retard the motion, but the alteration appears to be 

 not more than about 10 per cent. 



The use of jelly having been thus justified, a solution of 

 sodium acetate (whose strength was afterwards found to be 

 about 0*07 grm. equiv. per litre) in agar jelly was prepared 

 and coloured red with phenolphthalein, just enough caustic 

 soda being added to bring out the full colour. Half of this 

 was decolorized by means of a few drops of dilute acetic acid, 

 and placed in the longer limb of the tube. When it had 

 cooled and become solid, the alkaline red portion was poured 

 into the other limb and also allowed to solidify. A glass 

 scale was fixed behind the junction-tube, and the whole placed 

 in front of a window. The position of the boundary was then 

 read off on the scale by means of a telescope. An electro- 

 motive force of about 40 volts was applied, and the 

 velocity with which the boundary between the coloured and 

 colourless solutions travelled observed, readings being taken 

 at intervals of half an hour. The details of the first set of 

 observations are : — 



Time. 



Galvanometer- 



Position of 



Velocity in centim. 



h m 



reading. 



boundary. 





per hour. 



11 47 



41°'0 



21-97 







11 48 





21-96 







11 49 





21-95 







12 17 



41°'0 



21-71 



= •26") 





12 18 





21-71 



= •25 



- -505 



12 19 





21-70 



= -25J 





12 47 



41°-1 



21-51 



= •20} 





12 48 





21-51 



= •20 J 



- -40 



12 49 





21-50 



= •20 J 





Similar sets of observations were then made at intervals of 

 10 minutes, the following being the space traversed in centi- 

 metres during that time : — 



•10 -09 -09 -09 -09 -09 -08 

 •09 -09 -09 -09 -09 -08 -08 

 •07 



The final mean velocity deduced from these figures, by 



