154 Intel ligence and Miscellaneous Articles. 



in the physical laboratory of the Berlin University, whether the 

 hydrogen carried by electrolysis to one side of a thin plate of pla- 

 tinum would after a time make itself perceptible on the opposite 

 side, by producing galvanic polarization there also. These experi- 

 ments have in fact given the result expected. 



To the two opposite sides of a plate of platinum 0*02 millim. 

 thick, and placed vertical, the even edges of two glass vessels, the 

 form of which was that of tubulated receivers of a retort, were 

 cemented with sealing-wax. One of the openings of each 

 Mas cemented to the above-mentioned platinum plate ; the second 

 was directed upwards. The edges of the platinum plate projected 

 on all sides outward beyond the layer of the cement, so that cer- 

 tainly no conducting bridge of fluid existed between one side and 

 the other of the platinum. The glass vessels were filled with dis- 

 tilled water to which a few drops of pure sulphuric acid had been 

 added ; through the upper openings of the vessels two other pla- 

 tinum plates dipped into it. Previously to the putting-together of 

 the apparatus the three platinum plates were cleaned by heating 

 and washing. In order to prove whether the platinum was per- 

 fectly compact, a sample of the sheet platinum used was fused as a 

 closure to the extremity of one branch of a manometer exhausted of 

 air ; it was found that in the course of two months no perceptible 

 trace of air had penetrated. 



Since the travelling of gas in platinum can at any rate only take 

 place with extreme slowness, and the small quantity which has pe- 

 netrated to the further surface can be readily exhausted, the entire 

 apparatus was kept under the exhausted receiver of an air pump, 

 so that only the conducting- wires to the three platinum plates ex- 

 tended outside. Further, it was necessary to avoid permitting a 

 depolarizing current, even of short duration, to be generated. On 

 this account, instead of the galvanometer an instrument had to be 

 employed which could indicate the existing difference of potential 

 without a lasting current. For this purpose Lippmann's capillary 

 electrometer* proved very suitable. In the observations the mi- 

 croscope was kept directed to a definite place in the capillary glass 

 tube, and the difference of pressure was determined which was ne- 

 cessary in order, on alternating connexion of the two poles of the 

 electrometer with the two platinum plates, to carry tie mercury 

 thread in the capillary tube to the same division-stroke. In the 

 following a positive pressure-difference indicates a greater positive 

 potential in plate B than in plate C ; the difference 1 corresponds 

 to that of about ^^ of a Daniell element. 



The apparatus having been put together, the three platinum 

 plates were left for 18 hours in conducting connexion with each 

 other and with the earth, in order to get rid of the remains of older 

 polarizations. They were then insulated from each other and from 

 the earth ; and during 14 days the electromotive force between the 

 central one (B) and one of the outer ones (C) was investigated 

 daily, to ascertain if from other causes rapid variations of polari- 



* Poggendorff's Amialen, vol. cxlix. p. 551 . 



