90 On the Electric Conducting Power of the Metals of the Alkalies. 



error introduced into these results by these vacuums may be rec- 

 tified by multiplying the expressions before given by the factors 



^^■^^ =1-1233, 



18-56 

 and 



37-43 



= 1-2451; 



30-06 



by which we obtain for potassium, 



\=22-62-0-0920/ + 0000263^2. 



and for sodium, 



X= 40-52 -0-1459/ + 0-000158/^ 



We may take it for granted that above the point of fusion 

 these vacuums entirely disappear, and hence that from this point 

 upwards the given expressions are correct. "With potassium, 

 between the temperatures 46°-8 and 56°-8, there is certainly 

 some change in the nature of them ; but as we know no law 

 according to which this takes place, we are not in a position to 

 estimate their influence for this interval of temperature. 



Matteucci* has found, that with bismuth the conducting 

 power increases at the point of fusion, and I am able to corro- 

 borate his results by experiments performed in a similar way to 

 those just described : there is probably some connexion between 

 this and the contraction of this metal at the same point. 



For the sake of another example, Rose's metal was experi- 

 mented with ; the curve obtained was similar to that for potas- 

 sium. An interesting fact was observed with the pressed wires 

 which was not found with those cast in tubes ; namely, if a 

 pressed wire of Rose's metal be gradually heated and then cooled 

 and the resistances at certain temperatures noted, these are found 

 the same either with increase or decrease of temperature if the 

 wire has not been heated above 40° C. ; if, however, it has been 

 heated above 40° and cooled, greater values are found than 

 before, which become gradually smaller, at first quickly, and 

 afterwards slowly, till they attain their original magnitude. A 

 wire which had been heated to 80° showed a change in its resist- 

 ance even after an intei-val of six weeks. 



The possibility of obtaining wires of the metals of the alkalies 

 and alkaline earths, aflfords the means of ascertaining their order 

 in the thermo-electric series, on which subject I am at present 

 occupied, and shall shortly, if possible, make my results known. 



The foregoing experiments were performed in the Heidelberg 

 Physical Laboratory, under the direction of Professor Kirchhoff, 

 to whom I may be allowed in this place to express my sincere 

 thanks for the valuable aid and advice I received from him. 



* Ann. de Chim. et de Phys, 3rd series, vol. xliii. p. 472. 



