180 ELECTROCHEMISTRY 



Assuming the rate of resolution to be constant, since the con- 

 tents of the anodic arm are not appreciably altered in reaction 

 in the electrolysis, it is possible to calculate from the above data 

 for each of the solutions and periods employed the loss due to 

 resolution. In the column headed ''Loss due to resolution" in 

 the accompanying tables these quantities are given. On adding 

 them to the amounts of casein lost from the solution from which 

 the "apparent" values of the electrochemical equivalent are 

 estimated one obtains the "corrected" values corresponding to 

 the total precipitation actually induced by the passage of the 

 current. 



The possible error in the refractometer reading is 1' of the 

 angle of total reflection, this corresponds to an error of, ±0.00010 in 

 the refractive index, that is, to an error of ±0.07 in the estimated 

 decrease in the percentage of casein due to electrolysis of the 

 solution, and to an error of ±0.0175 in the estimate of the amount 

 of casein deposited by the current. The possible error in each 

 estimate of the electrochemical equivalent, arising from this source, 

 is indicated in the tabulated results. 



The average values for the electrochemical equivalent in the 

 different solutions are obviously, within the experimental error, 

 identical. Now in solutions containing 50 X 10~^ equivalents 

 of base per gram, the combining capacity of casein is 50 X 10~^ 

 equivalents per gram, in solutions containing 80 X 10~^ equiva- 

 lents per gram, it" is 80 X 10~^ equivalents per gram, and in solu- 

 tions containing 100 X 10~^ equivalents per gram it is between 



99 and 100 X 10~^ equivalents per gram.* In the solutions 

 investigated, therefore, the combining weight of the casein varies 



100 per cent, yet the electrochemical equivalent, measured in this 

 way, remains the same. 



These facts are to be interpreted as follows: We have seen that 

 the casein anion, which is free from base, must migrate to the 

 anode. There it may be presumed to react with water, liber- 

 ating oxygen and free casein, which combines with the excess 



not upon the wire. Under these conditions, resolution is apparently more 

 rapid and even if the flocculent deposit be filtered off from the anodal fluid 

 before the alkaline cathodal fluid is mixed with it, the values of the electro- 

 chemical equivalent are low. No such phenomenon was observed when the 

 anode was of sufficient length. 



* Cf. Chap. IX. Also T. Brailsford Robertson (27). 



