A. E. Kennelly — Alternating Currents. 453 



Ag 

 Pb 



Fe 



Sb 



(calculated) S, 



trace 

 55-52 

 trace 



25-99 

 18-98 



Atomic ratios. 



-^207 = *268 



-M20 = '217 

 -=- 32 = *593 





100-49 





e atomic ratios 



by -217 we get : 



Pb, = 



Sb, 



s, 



1-24 

 1 



2-74 



= 4-96 

 4 

 10-96 



Giving the formula :— Pb 5 Sb 4 S n or 5PbS, 2Sb 2 S 3 . 



We have here, in formula, a freieslebenite in which instead 

 of lead and silver, the silver has been completely replaced by 

 lead, and although the crystallographic agreement of this min- 

 eral with freieslebenite has not been established, there seems 

 to be no good reason for not referring it to that species. 



Laboratory, U. S. G-eological Survey, "Washington, D. C. 



Art. XLYI. — On the Yoltametric Measurement of Alternating 

 Currents ; by A. E. Kennelly. 



It has until quite recently been generally supposed that an 

 electric current reversing its direction with the frequency that 

 characterizes what is commonly called an alternating current, 

 would not decompose water visibly, or in fact that if any 

 decomposition did take place at the electrodes, the recombina- 

 tion at the reversal was so speedy and complete that no free 

 gas was developed. It has been shown, however, lately, in 

 a paper by MM. Maneuvrier and Chappuis, read before the 

 Academie des Sciences, that when the electrodes are small, 

 free decomposition does take place, mixed gas being liber- 

 ated at each. Since that time Professors Ayrton and Perry 

 have contributed to the data on the subject, in an article ap- 

 pearing in "The Electrician" of London, July 13, 1888, and 

 in which some very interesting phenomena observed with 

 polarized electrodes are described, while it is mentioned that 

 the quantity of gas liberated under given conditions is a func- 

 tion not only of the current density per unit surface of elec- 

 trode but also of the rate of alternation. 



No statement of the connection that exists between these 

 variables seems to have yet been published. The following 

 experiments made recently at Mr. T. A. Edison's laboratory 



