CHEMISTRY. 283 



6. Compressibility of Gallium in Solid and Liquid Condition. 



Having thus prepared gallium of substantial purity, Mr. Boyer pro- 

 ceeded to determine its compressibility, both in the solid and in the 

 liquid condition. This was an interesting problem, since compara- 

 tively few substances have been measured in both states. Moreover, 

 gallium has the remarkable and rare property of occupying more vol- 

 ume in the solid than in the liquid condition. The determination of the 

 compressibiUty was desirable in order to add to the long list of elements 

 already determined at Harvard under the auspices of the Institution. 

 The apparatus and principle of the method was essentially similar to 

 that employed in other cases, but a new difficulty was encountered. 

 As in the case of other metals, the gallium could not, of course, be 

 allowed to come in contact with the mercury in the piezometer, but, 

 on the other hand, it could not be conveniently solidified in any tube 

 under such an inert hquid as toluene without bursting the tube. After 

 many more or less satisfactory devices had been tried, the best results 

 were obtained by first sohdifying gallium and then placing a cylinder 

 of the solidified metal in a slightly larger short test-tube, just fitting 

 it, and capping this with another similar sHghtly larger test-tube 

 under the inert Hquid. Twenty-three grams of gallium were used in 

 this work and the compressibiUty was found to be 2.09 X 10"^, placing 

 gallium precisely on the curve joining the other compressibiUties in the 

 graph representing the periodic relation of this property to atomic 

 weight. The compressibility of gallium containing several per cent of 

 indium as obtained by the hydroxide method was found to be some- 

 what less (1.97 X10~®). Liquid gallium was determined not only in 

 this apparatus, but also in one similar to that used for caesium (Car- 

 negie Inst. Wash. Pub. No. 76, p. 20). The Uquid was thus found to 

 have a compressibiUty of 3.97X10"^, a value almost exactly identical 

 with that for mercury and nearly twice as great as that of solid gal- 

 hum, although its volume is less. The determination was made at 30°. 

 This confirms the universal experience that solids have compressi- 

 bilities distinctly less than the same substances as liquids, entirely 

 irrespective of the volumes which they occupy. The most marked 

 case of this kind thus far observed is that of ice.* 



7. Density of Solid and Liquid Gallium. 



With the assistance of Mr. Boyer, the densities also of solid and 

 liquid gallium were determined. These data have especial interest 

 because the expansion of gallium on freezing has been attributed by 

 some investigators to impurity. In the first place, careful determina- 

 tions were made by means of a pycnometer for solids (Richards and 

 Wadsworth, Jour. Amer. Chem. Soc, 38, 222, 1916) of the density of 

 the impure material containing some indium, in the solid and liquid 

 condition, the values being found respectively 5.975 and 6.166. Sub- 



*Richards and Speyers, Jour. Amer. Chem. Soc, vol. 36, 491, 1914; Carnegie Inst., Wash.J 

 Year Book No. 8, p. 221, 1909. 



