KOLLOCK-SMITH — ELECTRO-ANALYSIS 



147 



much chromium, if any, was deposited when the acid was present 

 in large quantity. Thus, with a current of 4 amperes and 7 volts, 

 solution containing 1 c.c. of acid, 0.05 gram of metal was precipi- 

 tated in forty-five minutes ; while with two cubic centimeters of 

 acid and a current of 1 ampere and 4 volts the mercury showed no 

 increase in weight after thirty minutes. The following results, 

 obtained in the use of smaller amounts of acid, confirm this. By 

 adding 10 drops of acid (= .25 c.c.) and employing a current of 

 4 amperes and 7 volts, the liquid became colorless in thirty minutes, 

 but forty minutes were necessary for the complete removal of the 

 metal. With the same quantity of acid, and a current of 5 amperes 

 and 8 volts, the chromium was completely precipitated in thirty 

 minutes. With five drops of acid and a current of 3 to 4.5 am- 

 peres and 8 volts, the solution became colorless in eleven minutes. 

 It, therefore, seems that more than three drops of acid are sufficient 

 to materially affect the rate of precipitation. More than two drops 

 of acid must be present to prevent the separation of chromic oxide 



Curve 8. Chromium — 3.5 Amperes, 11-10 volts. 



which always took place with less than that amount of acid. The 

 following conditions gave the most rapid determination : A volume 

 of the solution, containing 0.1180 gram of chromium and three 

 drops of sulphuric acid (40 drops = 1 c.c), was electrolyzed with 

 a current of 4 to 5 amperes and six volts, the speed of the anode 

 being 400 revolutions per minute. In four minutes the solution 

 was colorless and in six minutes the chromium was found to be 

 completely deposited. The solution was siphoned off in the man- 



