No. 



1 .. 

 2.. 

 3.. 

 4.. 

 5.. 

 6.. 



72 Dr. H.J. S. Sand on the Concentration 



Table VI. 

 Determination of Diffusion-coefficient K of copper sulphate. 

 Solution E. Experiments 1-3 in apparatus 2 ; surface 

 of cathode 0*6i>9. Experiments 4-6 in apparatus 3 ; 

 surface of cathode 3' 782 sq. cm. 



Current 



in 

 milli- 

 amps. 



•675 

 1-004 

 1-038 

 668 

 641 

 6-37 



Current- 

 density in 

 milliavnps. 



0-966 

 1-436 

 1-485 

 1-766 

 1-694 

 1-683 



Time ob- 

 served in 

 seconds. 



3390 

 1530 

 1515 

 1095 

 1285 

 1275 



Temp. ( 

 in °C. 



144 

 14-2 

 13-8 

 15-4 

 150 

 14-4 



Ke by formula 

 (Table I.) 

 K=10-9 



X l-195^o 

 in cm. 2 /sec. 



379x10-6 

 3-79x10-6 

 3-99x10-6 

 4-08x10-6 

 4-41x10-6 

 4-31x10-6 



lormula 

 K0 



Mean 

 value 



ofK )8 . 



1+0026(0-18)' 



4-16x10-6 





4-21 x 10-6 





4-48x10-6 



4-46x10-6 



4-38x10-6 





4-78x10-6 





4-76x10-6 





According to Wiedeburg the diffusion-coefficient of copper 



sulphate at 18° is 4'479 x 10" 



and 4-220x10- 



cm.' 

 sec. 



cm/ 

 sec. 



at the concentration 0, 



at the concentration of solution E 



(see p. 63 & p. 57). Although the mean value for K l8 in the 

 above table is about what should be expected from Wiede- 

 burg's determinations, yet the differences between the single 

 experiments, none of which were known to have gone wrong 

 in any respect, is too great to justify the recommendation of 

 the method in its present form for more than a rough deter- 

 mination of diffusion-coefficients. 



Experiments on the Effect of Convection- currents on the Re- 

 lative Quantity of Hydrogen given off in the Electrolysis 

 of an Acid Solution of Copper Sulphate. 

 The following experiments deal with the relative quantity 

 of hydrogen produced by electrolysis of an acid copper- 

 sulphate solution when considerably greater current-densities 

 are employed than those used in the preceding experiments. 

 This subject has been experimentally treated by Schrader in 

 the paper already quoted, and by Houllevigne*. 



Both investigators employed vertical electrodes and neither 

 promoted nor hindered the natural convection-currents of 

 their electrolyte. The}' found that their results were roughly 

 expressed bv hyperbolical functions. 



* Ann. Chim. et Phys. [7] ii. p. 351 (1894). 



