RESISTANCES. 751 



(998), is given by the following expressions, in which R represents 

 the resistance at the temperature of centigrade, 



Platinum R = R [o'i63i5VT +0-0089681 - i], 



Copper R = R [o-ii682VT + o-oi382iT-i], 



Iron R = R [0*05852 VT + 0-0030767 -i]. 



LIQUIDS. 



The conductivity of a solution increases at first with its strength, 

 and passes generally through a maximum, especially in the case of 

 very soluble bodies. The conductivity, moreover, increases with the 

 temperature. 



In tables for liquids, the specific resistances are estimated in 

 ohms. 



By the method indicated (990), M. Paalzow has obtained the 

 following numbers for different solutions : 



Aqueous Solutions. 



SulphuncAcid 



HydrochloncAad . . 



By means of sinusoidal currents (992) MM. Kohlrausch and 

 Nippoldt* have investigated a great number of solutions, and have 

 expressed their results in reference to percentages of solution. 



* KOHLRAUSCH. Leitfaden dcr Praktisehen Physik, p. 298. 



