Intelligence and Miscellaneous Articles. 365 



In conclusion, the serpentine in the Warren County Ophiohte, 

 Ophicalcite, or Verdautique, as it has been variously called, is an 

 alteration or metasomatic product after a mineral of the pyroxene 

 group. The original rock would appear to have been simply a 

 pyroxenic limestone, the pyroxene occurring either in scattering 

 granules, or in granular aggregates of considerable size. An ex- 

 amination of the Essex County Ophiolite reveals a somewhat 

 similar though more complicated condition of affairs. A portion 

 of the serpentine here is also derived from a pyroxene ; but another, 

 and in cases a very large portion, is apparently after a mineral 

 which I have not as yet found sufficiently unchanged to be able to 

 identify. The rock is as yet insufficiently studied, and must be 

 made the subject of another paper. I am indebted to Mr. Greorge 

 F. Kunz for the Warren County material. — American Journal of 

 Science, March 1889. 



ON ELECTRODES WITH DEOPPING MEKCUKY. 

 BY PEOF. W. OSTWALD. 



In the Philosophical Magazine, 1886, vol. xxii. p. 70, 1 published a 

 preliminary notice on the use of electrodes with dropping mercury, 

 for measuring directly the potential of electrolytes. Some time 

 afterwards Dr. James Moser employed the same method, but, in 

 my opinion, he did not succeed in properly preparing the surface 

 of his electrodes ; an operation by no means easy. Dr. Moser * 

 obtained numbers differing from mine, and ascribes the fault to my 

 having erroneously interpreted a formula of Lippmann. 



If, in this formula, 



x'^e-\-oo^, 



X is the difference of potential with the small surface of mercury, 

 x^ the same with the large surface of the capillary electrometer, 

 and e the compensating force. Dr. Moser takes exception to my 

 having neglected x^ in my determinations. 



The experiment which I have made consists in varying the 

 external force e until the surface-tension of the small surface of 

 mercury attains its maximum value. In this case, according to a 

 theorem of von Helmholtz, the value of x becomes null, and we 

 have 



The compensating force is then, the sign excepted, equal to the 

 difference of potential between the mercury and the sulphuric acid 

 in the large surface ; that is to say, equal to the difference which 



* Cotnptes Rendus, cviii. p. 231 (1889), 



