PROCEEDINGS 
NATIONAL ACADEMY OF SCIENCES 
Volume 6 SEPTEMBER 15, 1920 Number 9 
FURTHER MEASUREMENTS OF THE EFFECT OF PRESSURE 
ON RESISTANCE 
By p. W. Bridgman 
Jki^ferson PhysicaIv Laboratory, Harvard University 
Communicated August 22, 1920 
In a previous paper ^ data for the effect of pressures up to 12000 kg/cm^ 
on the resistance of 22 metals were given. It has now been possible to 
extend the results to 18 more elements, and 6 alloys. The extension has 
been made possible by tv^o changes in the technique. In the first place, 
by a change in the method of leading electrical connections into the pres- 
sure chamber it has been possible to replace the previous method of 
measuring resistance with a Carey Foster bridge by a potentiometer 
method. This makes it possible to measure accurately specimens whose 
total resistance is very low, and removes the restriction that the specimen 
must be in the form of a fine wire. In the second place, by a modifica- 
tion in the design of the apparatus, it has been possible to considerably 
extend the temperature range. The results now cover a range from atmos- 
pheric to 12000 kg. pressure, and an extreme temperature range from 0° 
to 275° C. 
In selecting the substances to be measured over this increased range 
I have paid particular attention to the matter of liquid metals. Previous 
to this, the effect of pressure on both the liquid and solid state was not 
known for a single metal. The resistance of metals in the liquid state 
would seem to be particularly worthy of study, because here the crystal- 
line structure introduces no complications. Six elements have now been 
investigated in the liquid and the solid states. Furthermore, I have 
endeavored particularly to investigate some of the more unusual elements, 
in the expectation that elements from unusual parts of the periodic table 
might show new types of behavior. This attempt has been rewarded by 
the discovery of three more elements whose pressure coefficient of resistance 
is positive; bismuth and antimony were the only ones known previously. 
A number of commercial alloys have been included as being of some 
interest because of their wide use for scientific purposes. The measure - 
505 
