Vol. 6, 1920 PHYSICS: P. W. BRIDGMAN 507 
La, and Nd were considerably impure. The graphite was the best Acheson 
graphite, but the results were not reproducible. Similarly results with 
Si were not reproducible. All that can be expected of C and Si is the 
order of magnitude of the effect. 
Normal Solids. — The substances with negative pressure coefficients of " 
resistance are Na, K, Mg, Hg, Ga, Ti, Zr, As, W, La, Nd, Si, and black 
phosphorus. Mg and W were previously measured. It is now possible 
to give better values because of increased purity of the specimens avail- 
able. La and Nd are the first metals in the rare earth group whose pres- 
sure coefficients have been measured; they show no novel features. Ti 
and Zr are also from a new region of the periodic table. The interesting 
feature of their behavior is the extreme smallness of the coefficient. Hg 
has not been previously measured in the solid state; its coefficient is 
somewhat greater than that of the liquid. Abnormal results were ex- 
pected for gallium, because it expands when it freezes, but it was found 
instead to be quite normal. Arsenic might be anticipated to be abnormal 
because of its position in the periodic table relative to bismuth and 
antimony, but it turns out to be normal. Silicon, a non-metallic element, 
decreases in resistance, as is normal for metals, but the pressure coefficient 
becomes larger with increasing pressure and the temperature coefficient 
may reverse in sign at high pressures, both of which are abnormal features. 
Black phosphorus, also non-metallic, is remarkable for the very large 
size of the effect, the resistance decreasing under 12000 kg. to about 3% 
of its initial value. The relative coefficient, however, does not change so 
much as it does for some metals. Na and K are the first alkali metals 
whose pressure coefficients have been measured. They are remarkable 
for the largeness of the effect, which is larger than for any other metals 
as yet measured. Na decreases 40% and K 70% in resistance under 
12000 kg. The pressure coefficient of these metals decreases greatly with 
increasing pressure and increases with increasing temperature, and the 
temperature coefficient decreases with increasing pressure. The metals 
previously measured have shown relatively little change in these coeffi- 
cients. 
Abnormal Solids. — Three new elements have been found whose resist- 
ance increases under pressure; these are Li, Ca, and Sr. This was a great 
surprise because all of these metals are highly compressible. With the 
single exception of the variation with pressure of the pressure coefficient 
of strontium, the behavior of these three metals is like that of Bi and Sb 
in that the instantaneous pressure coefficient increases with increasing 
pressure and decreases with increasing temperature, and the temperature 
coefficient falls with rising pressure. 
Relative behavior of Resistance of Solid and Liquid. — The pressure co- 
efficient of liquid bismuth is found to be negative and normal, although 
that of the solid is positive and abnormal. This points to the importance 
