28 WILLIAM H. EMMONS 



added. The dissolved gold was determined at the end of i hour 

 and 3 hours. At the end of 3 hours the gold dissolved was 

 greater, probably because some ferrous sulphate had changed to 

 ferric sulphate. Even o . 01 gm. of the ferrous iron greatly decreases 

 the solubility of gold in the ferric sulphate and HO solution, and 

 o. 25 gm. of ferrous sulphate drives nearly all the gold out of solu- 

 tion. These experiments are illustrated by Fig. 3. The lower 

 curve represents conditions at the end of 1 hour, the upper curve 

 at the end of 3 hours, when some of the ferrous salt had oxidized 

 by contact with the air. 



20. To determine the rate at which ferrous sulphate, in the 

 presence of sulphuric acid and manganese dioxide, would be oxi- 

 dized to the ferric salt, Brokaw made the following experiment: 



One hundred c.c. of 1 . 6 normal FeSO was acidified with sulphuric 

 acid and shaken vigorously with 5 gm. of powdered Mn0 2 . After 

 5 minutes the solution was filtered. No ferrous iron was detected 

 by the ferricyanide test, showing that the irOn had been com- 

 pletely oxidized to the ferric state. 



IV. DISCUSSION OF EXPERIMENTS 



Nitrates. — Dilute acid nitrate-chloride waters readily dissolve 

 gold, since they are equivalent to weak aqua regia. The chlorine 

 set free by the reaction oxidizing HC1 is more active than a solu- 

 tion of chlorine in water, and converts gold into gold chloride. 



In the reaction by which gold is dissolved in chloride solution 

 its solvent power may be ascribed to its "nascent" state. In 

 such reactions the presence of an element with more than one 

 valence is a necessary condition and its valence is reduced as gold 

 passes into solution. 



The reaction of 3HCI+HNO3, giving nascent chlorine, may be 

 written as follows: 1 



o 



CI- H+H-O- N =0+2H Cl-*2H a O+Cl J +Cl-N = 



When nascent chlorine reacts with gold, it forms soluble gold 

 chloride. 



1 Alexander Smith, General Inorganic Chemistry, 449 (1907). 



