CHEMISTRY: RICHARDS AND BOYER 
389 
and current density it was possible to deposit practically all of the indium 
with only a little gallium; and thereafter most of the gallium could be sepa- 
rated in a slightly acid solution without the appearance of an important 
amount of zinc. Gallium obtained in this way from material which had 
previously been purified by the hydroxide method, melted at a temperature 
as high as 30.8°, a higher melting point (indicating a purer substance) than is 
recorded anywhere in the literature. The metal obtained by the hydroxide 
process, without electrolysis, melted at a temperature as low as 26.9°. Time 
has as yet been lacking for making complete spectroscopic and other tests of 
this material in order to confirm its complete purity, but enough has been 
done to show that this method is a very satisfactory and convenient one. 
Because of its obvious advantages it must have been employed before by 
others, but no mention has as yet been found of it. 1 
Having thus prepared gallium of substantial purity, we proceeded to de- 
termine its compressibility, both in the solid and in the liquid condition. 
This was an interesting problem since comparatively few substances have 
been measured in both states. However, gallium has the remarkable and 
rare property of occupying more volume in the solid than in the liquid con- 
dition. The determination of the compressibility was desirable in order to 
add to the long list of elements already determined at Harvard. The apparatus 
and principle of the method was essentially similar to that ernployed 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 mer- 
cury in the piezometer, but on the other hand, it could not be conveniently 
solidified in any tube under such an inert liquid as toluene without bursting 
the tube. After many more or less satisfactory devices had been tried, the 
best results were obtained by solidifying gallium in the first place, 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 slightly larger test tube 
under the inert liquid. Twenty-three grams of pure gallium were used in 
this work, and the compressibility was found to be 2.09 X 10 -6 , placing gal- 
lium precisely on the curve joining the other compressibilities 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 somewhat less (1.97 X 10~ 6 ). 
Liquid gallium was determined not only in this apparatus but also in one simi- 
lar to that used for caesium (Publication of the Carnegie Institution of Wash- 
ington, No. 76, p. 20). The liquid was thus found to have a compressibility 
of 3.97 X 10 -6 , a value almost exactly identical with that for mercury, and 
nearly twice as great as that of solid gallium, although its volume is less. 
The determination was made at 30°. This confirms the universal experience 
that solids have compressibilities 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. 2 
