Mollhiney — Action of Ferric Chloride on Metallic Gold. 293 



Art. XLIY. — The Action of Ferric Chloride on Metallic 

 Gold ; bj Parker C. McIlhi^tey, Ph.D. 



In the course of a number of experiments on the solubility 

 of gold the action of pure concentrated hydrochloric acid on 

 precipitated gold was tried bj placing the two together in 

 glass tubes, which were then sealed up and heated to about 

 150° C. for varying lengths of time. In one of the tubes con- 

 siderable gold was found to have been dissolved, while in others 

 none was dissolved, and investigation showed that the gold 

 which had gone into solution was contaminated with a trace of 

 iron. The experiment was repeated, using O'OiG gram' of the 

 same gold and lO*^' of hydrochloric acid. After heating, the 

 gold was found completely dissolved and on separating the gold 

 from the solution by H^S and determining the iron in the fil- 

 trate 0*0008 Fe^Og was, found, about -^ the amount of gold. 

 Schild" states that ferric chloride attacks gold with formation 

 of ferrous and auric chlorides. Xapierf and Comey:|: state that 

 ferric chloride dissolves gold, and Comey states that it is dis- 

 solved by hydrochloric acid containing ferric chloride. 



In view of the fact that ferrous salts precipitate gold from 

 solution very perfectly, it seems remarkable that the reaction 

 given by Schild conld take place to such an extent as to 

 dissolve a weighable amount of gold, and in any event 

 it would not account for the solution of fifty parts of 

 gold by one of iron. In the experiments cited the portion 

 of the sealed tubes not occupied by liquid was fall of 

 air, and on measuring its volume it was found that sufficient 

 oxygen was present in it to have reacted with the hydrochloric 

 acid and gold to produce water and gold chloride in such quan- 

 tities as were found in solution, providing that the small 

 amount of ferric chloride was assumed to act as a carrier of 

 chlorine from the hydrochloric acid to the gold. In order to 

 ascertain definitely that it was the iron and not some other 

 undiscovered impurity which had caused the gold to dissolve, a 

 quantity of gold was obtained which had been purified at the 

 j^Tew York Assay Office six times by solution, precipitation and 

 fusion. Some of this gold was dissolved in aqua regia, precipi- 

 tated with oxalic acid and washed for a long time by decanta- 

 tion with distilled water. 0*500 gram of this precipitated gold 

 was placed in a tube with 10"=° hydrochloric acid and 0*0002 

 gram ferric chloride and the tube sealed without removing 

 the air. Another tube was prepared containing the same 



*Berg. u. Hiittenm. Ztg., xlvii, 251. f Phil. Mag., 1844, iii, xxiv, 370. 



X Diet. Sol., 172. 



