Note 34: conductances of other solutions 431 



The conductivity as determined by Cavendish agrees much better with 

 potassic carbonate than with potassic hydrate, the conductivity of which is 

 much greater. 



It seems likely that calc. S. S. was sodic carbonate, and the conductivity 

 would agree very well with this explanation, only it is difficult to find among 

 the names in use at the time any which could be written in this form. Mr [P. T.] 

 Main has suggested Calcined Salsola Soda. The burnt seaweed from the shores 

 of the Mediterranean, from which soda was often extracted, was, I believe, 

 called salsola, but I doubt whether the word soda was then in use. 



The weights of the other substances are, when reduced to pennyweights, not 

 very far from the equivalent numbers now received, hydrogen being taken as 

 the unit. 



The most remarkable exception is common salt itself, the solution of which 

 was one in 29, and therefore in 1116 there were 37-2 parts of salt. Now the 

 equivalent of NaCl is 58-5, which is very much greater. 



Besides this the conductivity of a solution of salt in 29 of water would be 

 much less in comparison with that of the other solutions than would appear 

 from Cavendish's results, whereas if we assume that the molecular strength 

 of the salt solution was really the same as that of the other solutions, the numbers 

 do not differ much from those given by Kohlrausch. 



The following table shows the results obtained by Cavendish and by 

 Kohlrausch. 



Name given by 

 Cavendish 



Sea Salt 

 Sal Sylvii 

 Sal Ammoniac 

 Calcined Glauber's 



Salt 



Quadrangular Nitre 

 Calc. S. S. 

 f. alk. 



Oil of Vitriol 

 Spirit of Salt 



Modern 

 symbol 



Nad 



KC1 



NH 4 C1 



Na 2 SO 4 

 NaNO 3 



!Na 2 CO 3 ? + *H 2 

 iK 2 CO 3 + *H 2 O 



AHC1 + arHjjO 



The theory of the electric resistance of electrolytes has been put on an 

 entirely new footing by F. Kohlrausch, who has not only measured the re- 

 sistance of a large number of solutions of different strengths and at different 

 temperatures, but has discovered that the conductivity of a dilute solution of 

 any electrolyte in water is the sum of two quantities, which we may call the 

 specific conductivities of the components of the electrolyte, multiplied by the 

 number of electro-chemical equivalents of the electrolyte in unit of volume of 

 the solution. (Since the components of an electrolyte are not themselves 

 electrolytes, it is manifest that they can have no actual conductivity, but the 



