CHEMISTRY. 327 



(3) Purification of Gallium by Electrolysis. 



Further work with this method, concerning which a hasty preHmi- 

 nary announcement was made in the last report, confirmed the con- 

 clusion that gallium may be conveniently purified by careful elec- 

 trolysis. Nevertheless, unexpected complications arose. The earUer 

 experience, when pure gallium was obtained by the electrolytic process, 

 seems to be possible only when a very small amount of zinc is present 

 (as was the case with the specimen then used). Evidently distilling 

 at a high temperature, mentioned in the preceding section, is more 

 convenient than electrolysis for the elimination of zinc. Indium is 

 eliminated electrolytically without great difficulty. The melting-point 

 of this purest specimen was found to be 29.8° instead of 30.8°, as given 

 by mistake in the last report. Spectroscopic study of these precipi- 

 tates has been made, but further investigation is still needed for final 

 statement. In particular, the electrode potential of gallium, which we 

 have begun to study, needs careful determination. 



(4) The Surface Tension of Liquid Gallium. 



The peculiar nature of this element makes all its physical properties 

 of especial interest. Accordingly, with the help of Mr. Sylvester Boyer, 

 the surface tension was studied according to the flat-drop method. The 

 determinations were carried out in an atmosphere of carbon dioxid 

 contained within a glass box immersed in a thermostat at 30°, the 

 liquid flat drops of gallium about 2 cm. in diameter resting on a flat 

 dry-wood surface. Great care was taken to have the optical-glass 

 walls of thermostat and box parallel and vertical. Similar drops of 

 mercury studied in precisely the same way gave a satisfactory standard 

 of comparison. The only doubt as to finality in these results lies in the 

 possibility that in spite of much care to prevent oxidation, the gallium 

 might nevertheless be covered by a film of oxide. The results gave for 

 mercury a surface tension of 44.0 and for gallium 37.2 mg/mm. In the 

 course of this work the densities of the solid and liquid gallium w^ere 

 again measured, confirming essentially the values reported in the last 

 report, only slight deviations being indicated. 



(5) The Compressibility of Indium. 



In order to fill one of the gaps in the interesting periodic curve 

 relating the compressibilities of the elements to their atomic weights, 

 the compressibility of indium was carefully determined with the help 

 of Dr. J. Sameshima. The method was in principle similar to that 

 used in the earlier researches in this laboratory, but an improvement 

 was introduced which increased considerably the accuracy of deter- 

 mination when working with very small quantities, as in the present 

 case. The density of indium was found to be 7.31, its compressibility 

 2.7(10"^), not far from two-thirds that of mercury. This is nearly the 

 value which had been predicted from the general tendency of the curve. 



