V liter and Browning — Electrolysis, etc. 389 



Art. XL. — On the Electrolysis and Purification of Gal- 

 lium; by Horace S. Uhj/er and Philip E. Browning. 



[Contribution from the Sloane Physical and the Kent Chemical Labora- 

 tories of Yale University.] 



During the process of separating metallic gallium from an 

 alkaline solution by electrolysis it was noticed that black coral- 

 like deposits sometimes formed around the cathode instead of 

 the bright liquid globules which were expected. Since we 

 have not found any mention of "trees" in the literature of 

 gallium and since one of us has determined a sufficient condi- 

 tion for their production, it seems desirable to present a brief 

 account of these interesting structures.* 



The electrolyte used was obtained in the following manner. 

 The leady residuef was shaved into small pieces with an ordi- 

 nary iron ice-plane and dissolved in a solution made from equal 

 volumes of water and strong nitric acid. On cooling, most of 

 the lead crystallized out as the nitrate. Concentrated sul- 

 phuric acid was then added to the filtrate and the resulting 

 liquid was evaporated nearly to dryness. The insoluble lead 

 sulphate was removed by filtration after the addition of water. 

 Silver was next precipitated as the chloride by treating the 

 filtrate with hydrochloric acid. By adding an excess of 

 ammonia to the filtrate the hydroxides of gallium and indium 

 were thrown down while most of the copper and zinc com- 

 pounds were kept in solution. When working with large 

 masses of material it was found necessary to repeat the last 

 operation in order to effect a satisfactory purification of the 

 hydroxides of gallium and indium. Finally, these hydroxides 

 were separated from each other by taking advantage of the 

 facts that indium hydroxide is insoluble in a solution of sodium 

 hydroxide whereas gallium hydroxide is readily soluble in an 

 excess of caustic soda. The filtrate thus obtained constituted 

 the electrolyte used in the cells. With regard to the chemical 

 processes just outlined, it may be remarked that each step was 

 checked spectroscopically and found to produce satisfactory 

 and efficient separations. 



The electrolytic cells consisted of the following assemblage 

 of very simple parts. The vessel containing the liquid was an 

 ordinary glass crystallizing dish 10 cm3 in diameter and 6 - 3 om3 

 deep. The anode was a thin rectangular sheet of platinum 

 foil, the edges of the submerged portion being 5'5 cms horizon- 

 tally and Z-^ m% vertically. The cathode consisted of a plati- 

 num wire sealed into a glass tube with about 2 mms projecting 

 at the lower end. This design usually enabled the gallium to 



*The configuration of the gallium trees closely resembles that of certain 

 arborescent forms of native copper, the similarity being very striking in the 

 case of a specimen from Bisbee, Arizona. 



fThis Journal, vol. xli, p. 351, April, 1916. 



Am. Jour. Sci. — Fourth Series, Vol. XLII, No. 251.— November, 1916. 



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