i9°5-] KOLLOCK-SMITH — ELECTRO-ANALYSIS. 139 



current invariably dropped sometimes as much as one ampere. But 

 upon washing down the cover glasses with cold water it rose to its 

 former strength. The dropping of the current is probably due to 

 the accumulation of steam bubbles upon the electrodes. During 

 the electrolysis some of the solution will of course be carried to the 

 sides of the containing vessel and to the cover glasses by the escap- 

 ing gases or by the agitation of the liquid. After many trials it 

 was found that it is unnecessary to wash down this portion when 

 the higher currents are used. The condensed steam continually 

 frees the sides from the solution. The cover glasses may now and 

 then be tilted against the sides of the tube in order to run off the 

 water which collects in large drops. 



It has been repeatedly observed in the present work that the 

 greater the concentration of the electrolyte, the greater the rapidity 

 of deposition, but the last traces of metal were always difficult 

 to remove. For this reason, after a solution had become colorless, 

 the electrolytic action was continued several minutes in order to 

 precipitate the minute amount remaining unprecipitated. It is, 

 therefore, also important to have the volume small toward the end 

 of the decomposition. 



When the metal has been completely deposited, the anode 

 should be stopped, the cover glasses removed and the decomposi- 

 tion cell filled with distilled water. This should then be siphoned 

 off to the level of the spiral and the liquid replaced by distilled water 

 until the current drops to zero. This wash water should always be 

 put aside and tested in order to ascertain that the metal has been 

 completely deposited. The current should next be interrupted and 

 the tube removed and washed again with distilled water, inclining 

 and twirling the cell in order to more completely wash the amalgam. 

 As much of the water as possible should be poured from the cell 

 and the amalgam then be washed twice with absolute alcohol and 

 twice with ether. It should be wiped dry on the outside and after 

 the volatilization of the ether be placed in the desiccator and 

 weighed as previously described. 



Experimental Part. 

 Zinc. 

 The first experiments made after those described in the Jour. 

 Amer. Chem. Society 26, 16 14, were upon zinc sulphate. They 



PROC. AMER. PHILOS. SOC. XLIV. l8o. J. PRINTED JULY 31, I905. 



