174 Prof. H. "W. Beetz on Normal Elements 



a convenient standard cell. Using concentrated copper- 

 sulphate solution and dilute sulphuric acid of specific gravity 

 1*075, Kittler found the electromotive force, of such an ele- 

 ment to be 1*195 volt, which decreased to 1*059 volt when 

 the dilute sulphuric acid was replaced by concentrated zinc- 

 sulphate solution. 



Of the Daniell elements hitherto employed for measurement 

 of difference of potential, that of Raoult* best fulfils the con- 

 ditions here laid down • that of Lodgef, employing dilute 

 zinc-sulphate solution, less satisfactorily; whilst combinations 

 containing porous cells, such as that proposed by Buff J, are 

 still less suited to serve as normal elements. 



But none of these are able to maintain a constant electro- 

 motive force, as is now desirable for electrometric measure- 

 ments, since in all gradual diffusion of the liquids takes place. 

 I myself § have formerly made use of similarly arranged 

 normal elements, for measurements made according to the 

 compensation-method ; but they do not answer for electro- 

 metric measurements, and I have therefore been obliged con- 

 tinually to renew the element. For the length of time during 

 which unbroken observation with the electrometer is usual, 

 we may rely upon the constancy of the element. 



The frequent putting together and taking apart of an 

 element is a labour always willingly avoided. Hence the 

 permanently-connected zinc and mercury element of Latimer 

 Clark || was gladly welcomed. Its electromotive force (1*457 

 volt) was found nearly constant in different preparations of 

 the element according to the method described. But it has 

 two undesirable properties : the one is the great variation of 

 electromotive force with change of temperature, which, how- 

 ever, is easily allowed for in calculation, but which does not 

 exists in the case of the Daniell elements ; the other is the 

 great decrease which the electromotive force suffers if the cir- 

 cuit is closed even for a very short time. This may easily occur. 

 An unintentional contact in some of the auxiliary apparatus 

 employed in the measurements, for example in the key which 

 I have described**, is sufficient to render the element useless 

 for one or several days. I obtained a diminution of electro- 

 motive force, amounting to 2 per cent., in a Latimer-Clark 



* Ann. de Chim. et de Phys. [4] ii. p. 345 (1864). 

 t Phil. Mag. [5] v. p. 1 ("1878). 

 % Lieb. Ann. lxxxv. p. 4 (1853). 

 § Wied. Ann. iv. p. 5 (1878). 



|| Proc. Roy. Soc. xx. p. 444 (1878) ; Beihl. ii. p. 565 (1878). 

 ^] Kittler, toe. cit. p. 371. 

 ** Wied. Ami. x. p. 371 (1880)., 



