Conducting -power of the Chlorides of the Alkalies, &;c. 423 



no means so high a place belongs to the acids as is generally 

 assumed for them. In galvanic piles, for example, a nearly 

 saturated solution of sal ammoniac can with advantage be em- 

 ployed in preference to the strongest acids that can be used for 

 this purpose. 



In another salt of ammonium, also, namely the nitrate, Wiede- 

 mann found a high conducting-power*. 



The behaviour of MgCl 2 is remarkable. When the conduct- 

 ing-powers of its solutions are compared with those of the other 

 chlorides of equal concentration, the former take the second place 

 when very dilute, at ] per cent, the fifth, and from 22 onward 

 the last. 



Nitiic acid shows a maximum of conducting-power, namely 

 for 18° when it contains 29*7 per cent. HN0 3 . It was already 

 found previously that a maximum belongs also to sulphuric and 

 hydrochloric acids f. It appears remarkable that these maximal 

 conducting -powers of all three acids have nearly the same mag- 

 nitude. Attention has already been called to this by Quincke J. 



If we try to express the conducting-power k as a function of 

 the salt-content p, we find that for the chlorides the form 

 k — ap -f- bp 2 -f- cp 3 renders the observations with tolerable com- 

 pleteness ; but the conducting-power of nitric acid is not even 

 approximately represented by this expression. As, moreover, 

 empirical laws in which the number of terms is considerable 

 present for calculation no advantage over a Table with an equi- 

 distant argument, nor exhibit in their coefficients a recognizable 

 physical meaning, it would be superfluous to go further into this 

 subject. 



On the contrary, it is evidently important to compare quanti- 

 tatively the different substances in those solutions in which they 

 are at once comparable — that is, in but slight concentration. 

 For the conducting-power of pure water is, in comparison with 

 the above numbers, to be put sensibly equal to zero; and the 

 course of the curves (p. 422) shows that the conducting-power 

 constantly increases ; consequently dilute solutions have a limit 

 which the ratio of the conducting-power to the salt-content ap- 

 proaches : it may be named the specific conducting-power of the 

 substance in aqueous solution. If the observations for the con- 

 tents 0*05 and 0*1 (i. e, 5 and 10 per cent.) be expressed in the 

 form 



k=ap + bp 2 , 



a will represent very nearly the specific conducting-power just 



* Pogg. Ann. vol. xcix. p. 228. 



+ Compare Pogg. Ann. vol. cxxxviii. p. 385, and vol. cli. p. 390. 



+ Pogg. Ann. vol. cxliv. p. 178. 



