Intelligence and Miscellaneous Articles. 495 



that the energy proceeding from the sun is retained as vibrations 

 in the molecules of the calcic carbonate. 



I presuppose in this that in calcic carbonate we are dealing with 

 photo-luminescence. If it were a chemical luminescence, we might 

 take uranium, nitrate or any other body as the basis of our con- 

 siderations. In chemical luminescence the potential energy stored 

 up in the impact of the molecules is transformed into kinetic energy, 

 which also corresponds to a very high temperature. — Wiedemann's 

 Annalen, xxxviii. p. 485, 1889. 



ON THE MAXIMUM GALVANIC POLARIZATION OF PLATINUM 

 ELECTRODES IN SULPHURIC ACID. BY CARL FROMME. 



In a former communication I made experiments on the de- 

 termination of the maximum galvanic polarization of platinum 

 electrodes in sulphuric acid of varying strengths. The electrodes 

 had a surface either of 1 square centiin. (large electrodes) or of 

 0*008 square centim. (small electrodes). If the kathode was small 

 it always blackened, in consequence of the formation of platinum 

 black, but if it was large no change in the colour of the surface 

 was observed. 



The following experiments on platinized platinum electrodes 

 show the influence exerted by an initial strong platinization of 

 the anode or the kathode on the maximum value of the galvanic 

 polarization in sulphuric acid of varying strengths. 



The following are the principal results of the author's researches: — 



(1) A bright platinum foil when used as a kathode in dilute sul- 

 phuric acid becomes coated with platinum black, which with 

 sulphuric acid of less than 3 per cent, can depress the polarization 

 0'9 volt. Strictly speaking, therefore, it is impossible to determine 

 the maximum polarization in very dilute acid for a bright kathode. 



(2) A copious electrolytic deposit of platinum black on the kath- 

 ode from chloride of platinum does not diminish the polarization 

 more strongly, so long as the concentration of the sulphuric acid 

 is small. But in more concentrated acid (more than 3 per cent.) 

 it is of greater action than the feeble spontaneous platinization. 



(3) The decrease which the polarization experiences in consequence 

 of covering the kathode with a thick layer of platinum black is 

 greatest, as much as 0*9 volt, in the most dilute acids, and in the 

 most concentrated (of 50 to 65 per cent.) it is only 0*1 volt. 



(4) The platinization of the anodes, on the other hand, dimi- 

 nishes the polarization in the more concentrated acids more strongly 

 than in the dilute, in such a way that while in the latter the polar- 

 ization of bright electrodes decreases somewhat more in consequence 

 of platinizing the kathode, in acid of about 60 per cent, the plat- 

 inization of the anode has a very considerably greater influence 

 (as much as seven times as great). 



(5) The polarization of a voltameter with bright electrodes varies 

 with the concentration in a very complicated manner. Maxima 

 and minima are often very near each other. High values near or 

 even more than 3 volts are found with a small as well as with a great 

 degree of concentration. 



