316 Conductivity of Aqueous Solutions. Part XI. 



113. DESCRIPTION OF THE EXPERIMENTS. 



The apparatus, consisting of two connecting U-tubes, was almost iden- 

 tical with that used by Noyes and Sammet, and the procedure followed in 

 the transference experiments was nearly the same. Referring the reader 

 therefore to their article* for the main features, we will here describe 

 only the modifications adopted in our work. In order to avoid all danger 

 from leakage, the two U-tubes were joined by drawing over their ends 

 two thicknesses of light black tubing, tightly wiring this on, and entirely 

 covering the joint with melted paraffin. The anode consisted of a circular 

 platinum plate, convex downward, soldered with gold to a platinum wire. 

 The cathode was a straight platinum wire which dipped into the solution 

 always less than 1 cm., so that by having the current dense the reduction 

 of the nitric acid was as far as possible prevented. Since the solution 

 weakened around the cathode and concentrated around the anode, to avoid 

 stirring, the cathode arm was filled with liquid nearly to the top, while the 

 anode arm was filled only a few centimeters above the bend and the elec- 

 trode was placed just below the surface. To keep the solution at this level 

 the anode arm was fitted with a rubber stopper carrying a delivery tube 

 which dipped into an outside vessel of water whose level could be varied. 



Given in outline, the method of carrying out the transference experi- 

 ments consisted in passing a suitable current for three hours and fifteen 

 minutes (except when otherwise noted in the table) through the stand- 

 ard nitric or hydrochloric acid solutions in the apparatus just described, 

 determining the quantity of electricity by means of two silver coulometers 

 placed in series with it, one on either side, dividing the electrolyzed solu- 

 tion into a cathode, an anode, and three middle portions, and titrating 

 each of these with barium hydroxide (or, in the case of the 0.002 normal 

 solutions, measuring the conductance at 20) to determine the concen- 

 tration-changes. From the analyses of the cathode and anode portions 

 two separate values of the transference-number were obtained, and by 

 the analysis of the middle portions it was made certain that no error arose 

 through convection. 



The method of procedure at the end of the electrolysis was to transfer 

 by means of a pipette the three middle portions to tared wide-mouth 

 Erlenmeyer flasks with rubber stoppers. Then the two U-tubes were 

 separated from each other, stoppered, well cleaned and dried outside, and 

 weighed. The solutions in them were then, after thorough mixing, poured 

 as completely as practicable into tared flasks, again weighed, and finally 

 titrated, allowance being made in the calculation for the small portion 

 that remained in the tubes, which were themselves cleaned, dried, and 



*J. Am. Chem. Soc, 24, 946 (1902) ; Ztschr. phys. Chem., 43, 51 (1903). 



