the Metals of the Alkalies and Alkaline Earths. 



87 



In the case of potassium, sodium and lithium, it was to be 

 feared that a conducting power a httle too small would be ob- 

 tained, on account of their unavoidably oxidizing a little before 

 the observations could be made. The oxidation of the wires took 

 place gradually, and had some influence on their resistances, as 

 some experiments on this poiut showed ; the I'esistance of a wire 

 immediately after being secured in the wire-holder was deter- 

 mined, and again after 5', 10', 15', &c. had elapsed. In the fol- 

 lowing Table the values of L, and the calculated values of A, are 

 given : — 



In the alteration of the resistance with the time, as is shown 

 by the Table, lies in all probability the chief reason why the ab-. 

 solute values of Lj and Lg in the former Table for potassium and 

 sodium vary more tliau in the case of the other metals. A cir- 

 cumstance, owing to which several experiments failed, may be 

 mentioned : sometimes a perfect metallic contact between the 

 wire and the wire-holder was not obtained, in which case the 

 resistance appeared too great, and always varying, so that the 

 needle of the galvanometer could not be brought to remain at 

 the zero-point ; its movements were rapid and violent, especially 

 when the trough was slightly shaken. 



The conducting power of potassium and sodium at diflferent 

 temperatures was next determined for the solid as well as for the 

 liquid state. For these experiments the metal was introduced 

 into a wide thermometer-tube, which was blown out at two 

 points, a and b (fig. 6), before the glassblower's lamp, and at 

 both of which places a short platinum wire was fused in ; a tube 

 of wider bore was joined on at one end. Through this tube 

 hydrogen was passed for a short time, and then a piece of metal 

 was pushed in at c ; the whole length of it was heated until the 

 metal was fused, when hydrogen was passed in at c, forcing the 

 metal to the other end of it, upon which both ends were sealed 

 by fusion ; over a and b two pieces of caoutchouc tubing were 

 fitted, one end of which was closed with pieces of glass rod, the 

 other containing glass tubing. These were filled with quick- 

 silver, and formed the quicksilver cups in which the connecting 



