﻿Intelligence and Miscellaneous Articles. 475 



in a short time goes so far that the plates come into contact, by which 

 the electrolytic process, of course, is stopped. 



These curvatures are obviously due to the fact that the sides of 

 the palladium plate are successively saturated with hydrogen, and 

 therefore expand, just as does a Breguet's spiral by an alteration in 

 temperature. 



Just as the expansion of palladium by absorbing hydrogen may be 

 rendered obvious by this experiment, so the contraction of the metal 

 by the escape of the gas may be shown even more strikingly. 



For this purpose the palladium plate, after having attained the 

 maximum of its first curvature, is removed from the liquid, washed, 

 dried, and brought into a spirit-lamp flame. As soon as it is suffi- 

 ciently hot, it curves in the opposite direction with extreme rapi- 

 dity, and so much that it seems to be regularly rolled up. 



In these contractions and expansions of the plate its other dimen- 

 sions also undergo change. When the process of charging a plate 

 with hydrogen, and afterwards expelling it by heat, has been fre- 

 quently repeated on the same plate, it can be distinctly seen that 

 it has not only become shorter, but also narrower and thicker. 

 After the process had been repeated six times my plate was 8 ir.il- 

 lims. shorter and 1'5 millim. narrower, but at the same time was 

 quite - l millim. thicker. That dimension, therefore, which is com- 

 pressed by rolling expands, and the two others, by which the metal 

 is stretched, crumple up when the hydrogen is expelled. Graham 

 has already shown, by the decrease of its specific gravity, that a 

 palladium wire is thicker when it becomes shorter. 



It may, in conclusion, be remarked that, although Graham and 

 Wurtz have not succeeded in preparing a hydride of palladium by 

 purely chemical processes, such a compound appears to be formed 

 by the electrolytic process ; for the dilute sulphuric acid in which 

 this process is performed becomes of a brown colour, without be- 

 coming turbid or depositing anything. A solution of caustic pot- 

 ash or ammonia in which, according to an old observation of mine, 

 tellurium used as negative pole produces a beautiful and deep wine co- 

 loration, remains quite clear with palladium.- — Voggendoiff' sAnnalen, 

 March 1869. 



ELECTRICAL POLARITY AND INEQUALITY OE THE AMALGAMATED 

 ZINC ELECTRODES IN SULPHATE OF ZINC. BY E. PATRY. 



In a series of experiments on the galvanic resistance of liquids, 

 in which I assisted Dr. Paalzow, polarization and galvanic ine- 

 quality of the so-called unpolarizable electrodes were met with as 

 sources of error. I was thereby led to examine this subject speci- 

 ally, in which I had the advantage of his counsel. 



Unpolarizable electrodes are obtained by using amalgamated zinc 

 and sulphate of zinc. When I used zinc and commercial zinc 

 vitriol, I found that the polarization and inequality were very di- 

 stinct as soon as the resistance of the circuit was not very great. I 

 observed that a number of gas-bubbles were liberated at the surface 



