140 BRIDGMAN. 



show any change in the usual types of behavior formerly found. 

 The principle facts found before for normal metals were: (1) The 

 pressure coefficient is little affected by temperature, (2) The tempera- 

 ture coefficient is little affected by pressure within the range, and (3) 

 the instantaneous pressure coefficient decreases with increasing pres- 

 sure (the maximum change in the instantaneous coefficient was that 

 of lead which changed about 30% under 12000 kg.). 



Sodium and potassium show no such constancy of behavior, as 

 might be expected from the high values of their compressibiUties and 

 pressure coefficients of resistance. Thus for sodium the values of 



the instantaneous pressure coefficients 



_w \dp/ T 



at 0° at 0, 6000, 



and 12000 kg. respectively are -O.O4663, 0.04435, and O.O4268, a total 

 decrease by a factor of 2.49. At 80° the corresponding coefficients 

 are — O.O4786, O.O4466, and O.O43O7, a total decrease by a factor 

 of 2.56. This is a httle larger than the factor of decrease at 0°, which 

 is what one would expect. A comparison of corresponding pressure 

 coefficients at 0° and 80° shows the pressure coefficient of sodium is 

 by no means independent of temperature, but the change in the 

 pressure coefficient with temperature is less than the change in resist- 

 ance itself. The mean temperature coefficient of resistance may 

 also be found from the table of resistance of sodium, and is 0.00475 

 at kg., and 0.00408 at 12000 kg. The relative change is much larger 

 than that found previously for any of the other metals, but still is not 

 large compared with the variations of the pressure coefficient over 

 the same range of pressure. 



The same sort of phenomena are seen to characterize potassium, 

 although the coefficients are not known over so wide a range as are 

 those of sodium. At 25° the instantaneous pressure coefficients of 

 resistance at 0, 6000, and 12000 kg. respectively are O.O3I86, 0.04955, 

 and O.O47I, a decrease by a factor of 2.62. At 95° the pressure coeffi- 

 cients at 6000 and 12000 kg. are O.O3IO24 and O.O4885, and at 165° 

 the coefficient at 12000 kg. is O.O3IO27. The pressure coefficient 

 therefore increases markedly with increasing temperature. The mean 

 temperature coefficients between 25° and 60° at 0, 6000, and 12000 kg. 

 respectively are 0.00454, 0.00341, and 0.00184. The decrease is 

 relatively much larger than for sodium, and is nearly as large as the 

 relative decrease in the pressure coefficient over the same range. 



The alkali metals sodium and potassium differ, therefore, in the 

 following particulars from the metals previously measured. The 



