the Metals of the Alkalies and Alkaline Earths, 89 



following Table gives the differences of the observed values of A, 

 and those calculated from the above formulas : — 



The contraction of the metals on solidifying in the tube caused 

 the conducting powers to appear too small, the diameter being 

 considerably more reduced in some places than in others on 

 account of small vacuums forming. With sodium this inequality 

 was so great that the continuity of the wire was completely 

 broken ; in these cases the tube was heated in a bath above the 

 fusing-point and then rapidly cooled, in order to make the 

 vacuums as small as possible. With tubes of smaller bore the 

 vacuums caused by the contraction were smaller, as the adhesion 

 of the metal to the glass counteracted this tendency in some 

 degree. The diameter of the tubes used for the experiments was 

 0'446 millirn, for potassium, and 0'368 for sodium. The va- 

 cuums were here small, but still visible to the naked eye. The 

 influence they had on the determination of the conducting 

 power may be estimated by the comparison of the results ob- 

 tained with the pressed wires with those found by this method 

 for the same temperature. By the first we found for potassium, 



\=20-85if ^=20-4; 

 for sodium, X= 37-43 if / = 21-7. 



By the second for the same temperatures, 



X=1856 for potassium, 



\= 30*06 for sodium. 

 If the vacuums be considered constant for potassium at all 

 temperatures under 46°*8, and for sodium at all under 95°"4, the 



