

470 It. N. Maxson — Small Amounts of Gold. 



A N/10 arsenic solution was prepared as usual with the aid 

 of 20 grams of potassium acid carbonate to the liter. Twenty- 

 two cubic centimeters of this solution were drawn off and 

 titrated with an approximately N/10 iodine solution in the 

 usual manner. Four lots of this arsenic solution of 22 cm3 each 

 were then carefully drawn off and heated upon the steam bath 

 for thirty minutes, and when cool were titrated against the 

 above mentioned iodine solution. The volume of the solutions 

 used in these experiments was in all cases approximately 75 cc . 

 The results obtained are given in the accompanying table. 







Iod 



ine used to 



Standard As 2 3 



Iodine used to 



titrate after heating 



taken. 



titrate at once. 



■J hour 



on the water bath. 



cm 3 . 



cm 3 . 





cm 3 . 



22'0 



22-08 





22*10 



22*0 



22-07 





22-08 



22-0 



22-08 





22-09 



22-0 



22-07 





22-08 



These figures show conclusively that acid potassium carbon- 

 ate in solution of the concentration used in these experiments, 

 0'44 grms. in a volume of 75 cc , does not in thirty minutes heat- 

 ing upon the water bath undergo such change as to cause it to 

 absorb an appreciable amount of iodine in the following titra- 

 tion. Just what the eifect may have been in Rupp's experiments 

 cannot of course be determined in the absence of knowledge 

 in regard to the acidity of his gold solution, and the alkalinity 

 of his arsenic solution. 



In conclusion it is obvious that the criticisms made by Rupp 

 are not warranted by the facts. While, as its author now con- 

 cedes, the method proposed by Rupp is not to be considered of 

 value for the determination of small amounts of gold, all the 

 evidence goes to show that the process of Grooch and Morley 

 is accurate, and in the hands of a skillful analyst, adapted to 

 the estimation of minute quantities of gold. 



