586 Mr. E. F. Burton on the Action of 



Table II. 

 Pure Copper Colloidal Solutions. 



No. 



Date of 

 preparation. 



Date of 

 measurement 



of velocity. 



Specific Con- 

 ductivity at 



18° C. 



Velocity 

 at 18° C. 



1. 



2. 

 3. 

 4. 

 5. 

 6. 



June 19, 1907 

 „ 20, 1907 

 „ 5, 1908 

 ,, 16, 1908 

 „ 23, 1908 

 „ 27, 1908 



June 20, 1907 

 „ 26,1907 

 „ 5, 1908 

 „ 17, 1908 

 „ 24, 1908 

 „ 29, 1908 



7-7x10-6 

 6-5x10-6 

 8-2X10- 6 

 5-8x10-6 

 4-3x10-6 

 3-lXlO" 6 



+23-4x10-5 

 +25-4x10-5 

 +24-9x10-5 

 +25-4x10-5 

 +30-4X10-5 

 +33-0X10" 5 



For solutions Nos. 5 and 6 it will be noticed that the 

 velocities are rather larger than for the others, but it will be 

 seen that the specific conductivities o£ these solutions are also 

 much lower than those of the others; that is to say, these latter 

 two solutions were freer from electrolytes than'the others, and, 

 as we shall see, the general effect of added electrolytes is to 

 reduce the velocity of the particle. 



Although the velocities are all given at 18° C, the experi- 

 ments were not performed at precisely that temperature, but 

 corrections have been introduced to bring each reading to 

 that standard temperature. In the paper * referred to above 

 the following relation has been deduced as holding between 

 the velocity (v) and the coefficient of viscosity of the liquid 



medium (a) : , 



v y fi . v = a constant, 



as long as one deals with the same material in the particle 

 and the same liquid medium. That this is in accord with the 

 actual facts is confirmed by the following series of velocity 

 determinations carried out with a silver colloidal solution at 

 the temperatures indicated in Table III. The whole velocity 

 tube was lowered into a glass thermostat which could be kept 

 at the required temperature. 



A fundamental necessity for the validity of velocity results 

 obtained in this way, is that the specific conductivity of the 

 superincumbent layers of water should be the same as that of 

 the colloidal solution at the bottom of the tube. As these con- 

 ductivities in each case were made equal at the ordinary tempe- 

 rature of the room before the liquids were introduced into the 



* Phil. Mag. ser. 6, vol. xi., April 1906. 



